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Ben-Gurion University of the Negev The Jacob Blaustein Institutes for Desert Research
The Albert Katz International School for Desert Studies
Assessing the thermal behaviour of straw bale and mud geodesic domes in the southern Arava:
A hot arid zone case study
Thesis submitted in partial fulfilment of the requirements for the degree of
“Master of Science”
By: Jennifer Y Golding
Date: March, 2010
Ben-Gurion University of the Negev
The Jacob Blaustein Institutes for Desert Research The Albert Katz International School for Desert Studies
Assessing the thermal behaviour of straw bale and mud geodesic domes in the southern Arava:
A hot arid zone case study
Thesis submitted in partial fulfilment of the requirements for the degree of
"Master of Science”
By Jennifer Y Golding
Under the Supervision of Prof. Isaac A Meir
Department of Man in Drylands
Author's Signature …………….……………………… Date …………….
Approved by the Supervisor…………….…………….. Date …………….
Approved by the Director of the School …………… Date ………….…
בס"ד
This work is dedicated with love
To
Maayan Frieda Doron
Uriel Yaakov Buchner
Yonatan Simcha Doron
Noam Sara Buchner
And their future cousins
That their generation will represent a return to
A wiser use of resources
And a greater respect for health
Of our and all species
Acknowledgements בס"ד I am full of gratitude to the powers that be that I was blessed with these experiences. Professor Isaac A. Meir , thank you for agreeing to have me as your student, for the continued guidance, wisdom and importantly humour. I intend to put into practice the pearls gained here. I feel fortunate for the tuition in a subject so close to my heart and I thank my teachers, Prof. David Pearlmutter, Dr Evyatar Erell, Dr Yaakov Garb for the crucial and fascinating lessons. Dear Albert Fox and Lord Norman Foster for their joint project of keeping me afloat and educated for two years, I thank you deeply for this kindness. Dorit Levin & Avigad Vonshak I thank you for being supportive and flexible during my changing circumstances. My grandfather Pappa Michael (Myer) Golding whose generosity touches me, and whose company I shared for so many years. Thank you. To the Arava Institute, a stepping stone to Sde Boqer and much more. Noam Ilan, whose dome I first monitored and whose hospitality allowed me my first experience of sleeping in dome no.1 helping me develop fondness for them. All the Lotan crew, you are amazing. Mike Kaplin, the spiritual and practical father of the EcoCampus, son of the dudes who were doing this 50 years ago, you are an inspiration of action with humanity, you make me a proud Brit. Alex Cicelsky who has exercised such patient help when I needed… everything… during this experiment over the last two years, you eased my way, thank you and thank you. Wolfgang Vielen Dank for your help and candor. Dr. Michael Livni, much appreciation for your support and enthusiasm in having the scientific slant on your worthy and good work in the Amuta Tsel Hatamar. Mark Naveh with encouragement right from the beginning and always a warm welcome, you and your families and other kibbutz members made me feel in my second home in that beautiful setting. Stephanie, for letting me use your air-conditioned dome in the height of summer thank you!! Eviatar Etiel, Effi Tripler, Nehemia Stone & Sylvie Judeinstein merci for scientific and data support! Shachar Cicelsky your room is in my graphs, Nir, Israel, Ya’ara, Chen, you made the work fun. My study buddy Gabush, your company, advice and hot milk made all the difference! My SB family, Yonat, Nurit, Nadav, Salvatore, Chencha Noam n babe, Li, Eitan, Nata, Sarah, Elli, Alexandra, Ranit, Tanya, Rebecca, you are light and support. My parents Judith and Harold R. Golding, thank you for teaching me what is important in life and for giving me diverse backgrounds with two extraordinary sisters for life, Lisa and Nicole, you often amaze me with your wisdom and beauty. And of course Maayan, Uriel, Yonatan and Noam, you remind us what it’s all for.
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בס"ד
Table of contents
Table of contents ......................................................................................................... 1 1. General introduction .............................................................................................. 3
1.1 Energy, the environment and public health ........................................................ 3 1.1.1 Fossil fuel energy ......................................................................................... 3 1.1.2 Living Earth ................................................................................................. 4 1.1.3 Greenhouse gases, climate change and ecosystems ..................................... 5 1.1.4 Pollution and public health .......................................................................... 6
1.2. Building industry’s contribution to environmental degradation ........................ 7 1.2.1 Detachment of building envelope from climate ........................................... 7 1.2.2 A brief word about building materials: environmental impact, embodied
energy, embodied emissions & life cycle analysis ..................................... 8 1.2.3 Environment inside buildings ...................................................................... 9
2. Scientific background ........................................................................................... 10 2.1 Thermal comfort ............................................................................................... 10
2.1.1 The adaptive approach ............................................................................... 10 2.2 Building envelope ............................................................................................. 12
2.2.1 Thermal mass, insulation and their order in wall systems ......................... 12 2.3 Building in hot arid environments .................................................................... 16
2.3.1 Introduction ................................................................................................ 16 2.3.2 Solar radiation and buildings ..................................................................... 18 2.3.3 SOL-AIR approach .................................................................................... 19 2.3.4 Building structure and form ....................................................................... 20
2.5 Domes ............................................................................................................... 26 2.6 Straw building ................................................................................................... 32
2.6.1 Introduction ................................................................................................ 32 2.6.2 General perceptions of straw bale as a building material. ......................... 34 2.6.3 Straw bale building in earthquake zones ................................................... 35 2.6.4 Straw bale insulation properties ................................................................. 35
3. Research question ................................................................................................. 41 3.1 Framing the problem and relevance of this study ......................................... 41 3.2 Question ........................................................................................................ 42 3.3 Relevance and potential benefits of this study .............................................. 42
4. Case study .............................................................................................................. 44 4.1 Southern Arava ................................................................................................. 44
4.1.1 Climate & Geography ................................................................................ 44 4.2 Kibbutz Lotan ................................................................................................... 45
4.2.1 Ecological projects ..................................................................................... 45 4.2.2 Mud & straw bale building ........................................................................ 46 4.2.3 Electricity use ............................................................................................. 46
5. Experiment ............................................................................................................ 48 5.1 Project description overview ............................................................................. 48
5.1.1 Building survey .......................................................................................... 48 5.1.2 Temperature monitoring of buildings ........................................................ 48 5.1.3 Temperature monitoring of irrigated garden soil ....................................... 48
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5.2 Building survey description .............................................................................. 49
5.2.1 Three typologies: Heavy, insulated, lightweight ....................................... 49 5.2.2 Window proportion and orientation ........................................................... 59
5.3 Monitoring ........................................................................................................ 60 6 Monitoring .............................................................................................................. 61
6.1 Brief overview .................................................................................................. 61 Set 1: Comparison of domes, concrete and lightweight structures ..................... 61 Set 2: Optimisation of domes (comparing new and improved domes) ............... 61 Set 3: Energy consumption comparison of dome & concrete ............................ 62
6.2 Description of modes of operation .................................................................... 62 Set 1: Comparison of domes, concrete and lightweight structures ..................... 62 Set 2: Optimisation of domes - comparison of improved and original domes .. 64 Set 3: Energy consumption comparison of dome & concrete ............................ 65
7 Results ..................................................................................................................... 67 7.1 Summer results.................................................................................................. 67
Set 1: Comparison of domes, concrete and lightweight structures ..................... 67 7.2 Transition season (spring) results ..................................................................... 91
7.2.1 Spring, all closed ........................................................................................ 91 7.2.2 Apex and vents open in dome, N&S windows open in concrete and
lightweight. ............................................................................................... 93 7.2.3 Four windows, apex and vents open in dome. ........................................... 94
7.3 Winter results .................................................................................................... 95 7.3.1 Closed mode............................................................................................... 95 7.3.2 Comparison of shaded and less shaded concrete units .............................. 97 7.3.3 Optimal window operation ........................................................................ 99
7.4 Temperature monitoring of irrigated garden soil ............................................ 102 8 Discussion.............................................................................................................. 106
Significant findings ............................................................................................... 106 8.1 Summer ........................................................................................................... 106
8.1.1 Electricity use comparison of air conditioned dome and concrete units: reduction of cooling load ........................................................................ 106
8.1.2 Internal conditions in domes .................................................................... 112 8.1.3 Optimising domes with built-in & added features ................................... 113 8.1.4 Surface temperatures comparison of three building types ....................... 115 8.1.5 Irrigated soil temperatures ....................................................................... 116
8.2 Winter ............................................................................................................. 117 8.2.1 Effect of dome’s insulation to mass ratio and window positioning ......... 117 8.2.2 Comparison of exposed and largely shaded concrete units. .................... 118
9 Future research .................................................................................................... 119 9.1 Domes ............................................................................................................. 119 9.2 Straw bale building ......................................................................................... 120 9.3 Insulation thickness variations ........................................................................ 120 9.4 Recommendations for future domes ............................................................... 120 9.5 Implications for building in the Arava ............................................................ 121
Bibliography ............................................................................................................ 123
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1. General introduction
This research work is an attempt to discover the possible savings in energy
expenditure that can be achieved by the use of a particular experimental building
system. The investigated structures are galvanised steel geodesic frames, covered
with straw bales and coated with mud plaster.
Their location is an extreme, hyper-arid desert in southern Israel where summers are
now survived in air-conditioned interior spaces, representing very high electricity use.
The connection between contemporary building use and the natural world is not
immediately obvious. However the vast fossil fuel use in this industry (and others)
indeed affects many aspects of global health as we keep discovering the
interconnections in a holistic, global view. These adverse health effects are the
motivations behind the will to minimise fossil-fuel energy use with relation to
buildings, some of which are presented in the following general introduction.
1.1 Energy, the environment and public health
1.1.1 Fossil fuel energy
Availability of energy is an escalating global problem; fossil fuel prices are unstable,
sometimes erratic hitting a record high of $140 per barrel of crude oil in July 2008. Energy in
the form of fossil fuels used in industry, transport, food and electricity production and the
military has created dependency on supplying countries, complicated geopolitical connections
and disturbing international relations. Within this scenario Israel and the Middle East are
prominent.
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Graphs show a marked upshot in the 1950s of atmospheric carbon dioxide, methane, nitrous
oxide and CFC11, corresponding with the increased purchases of private cars and heating and
cooling devices for buildings1. In fact, at least 50% of energy used and greenhouse gas
emissions produced result from the construction and upkeep of buildings in ‘developed’
economies when accounting for materials production, transport and building demolition2,3.
One third of all global non-renewable energy is used in heating, refrigeration and air-
conditioning technologies4.
1.1.2 Living Earth
Planet Earth’s thin crust of land, water and atmosphere is constantly interacting with the living
organisms on it (accepted in the scientific community to have been doing so for over 3 billion
years) and they affect each other in many ways. The term ‘Gaia’ was coined by renowned
environmentalist James Lovelock in the sixties to describe this ‘living earth’ as a self-
regulating system. This is not a new concept, Earth having been described as alive in Greek
philosophy, Leonardo da Vinci seeing Earth and the human body as microcosms of each other
and the self-regulating system was suggested by geologist James Hutton in 1785 and T. H.
Huxley in 18775.
1 IPCC Scientific Assessment. 2001. Available from: http://www.grida.no/climate/ipcc_tar/wg1/fig4-1.htm 2 Roaf, S., Crichton, D., Nicol, F., Adapting Buildings and Cities to Climate change. 2005, Oxford: Architectural Press, Elsevier. 3 Charter for Solar Energy in Architecture and Urban Planning. 2nd ed, ed. T. Hertzog. 2007: Prestel Publishing 4 ASHRAE Green Guide, 2006. Burlington MA: Butterworth-Heinemann/Elsevier 5 Lovelock, J., The revenge of Gaia. 2006: Allen Lane Santa Barbara, CA.
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1.1.3 Greenhouse gases, climate change and ecosystems
Population growth is limited and stabilised on Earth by constraints set due to properties such as
atmospheric and oceanic composition and climate. Apart from some highly adaptable
extremophiles – such as organisms living on hot springs or very salty lakes - life forms operate
within particular environmental boundaries. Small changes in mineral content or temperature
can disturb cell activity. Larger animals can maintain internal conditions up to a point,
whereas single-celled organisms like algae and bacteria are directly affected by their
immediate environment. The relationship between increasing carbon content in the
atmosphere in the form of greenhouse gases and the increasing temperature of the Earth’s
atmosphere is generally accepted in the scientific community today. Varying effects on
ecosystems and weather systems are noted already and predicted to occur if the trend
increases. Many of these have devastating, destructive consequences.
One highly significant example is the life of algae in oceans. In a paper exploring algae
population changes, James Lovelock and geochemist Lee Kump (1994) describe a computer
model exploring changes in populations while increasing atmospheric carbon dioxide content.
As CO2 approached 500ppm, the algae population regulation that was maintained until then
began failing and the temperature increased. Algal populations soon became extinct. This is
due to a physical property of water: the surface layer of water that is heated by the sun’s rays
warms and expands, at 10°C becoming a separated layer (30m–100m deep) above the cooler
organic-rich layer below and does not mix. This layer contains little nutrients since dead
bodies sink to the bottom and no mixing from below occurs leaving only a few starving algae,
an oceanic desert. As the algae-rich water layer became smaller, so did their cooling effect,
causing the temperature to further increase and suddenly jump following algal extinction.
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In the real world, the currently increasing carbon content in the atmosphere is clearly measured
and so are the declining algal populations of the Pacific and Atlantic oceans as they warm6.
Another major influence of global heating is the melting of large glaciers, causing the sea
levels to rise significantly enough that every coastal residence on Earth will be at risk of
flooding. The island of Tuvalu in the south Pacific has already experienced significant
flooding due to the 1-2mm increase per year and their low-lying island shores7. A prediction
of “Intolerable and lethal heat waves” sweeping the earth is a further alarming prospect.
August of 2003 gave rise to a heat wave in Europe, initially thought to have been the direct
cause for over 35,000 deaths. In light of updated information the figure now seems to be
52,000 European fatalities, France alone suffering over 14,000 deaths while remaining over
40°C for two weeks8. In short, the global community is increasingly concerned and some
(albeit quite late) are mobilising towards lessening the effects and lowering the causes of
anthropogenic climate change. En large this means lowering fossil fuel combustion.
1.1.4 Pollution and public health
As a by-product of burning fossil fuels, in addition to greenhouse gases, various toxic
chemicals are released into the atmosphere. Even if one wishes to argue the point of
anthropogenic climate change, the local effects of polluting particles are proven in various
studies. Coal is one of the more ‘dirty’ forms of fossil energy and is on the increase worldwide
as demand for electrical power grows. When burned in power stations which produce
electricity, various toxic substances are released into the atmosphere (nitrous oxides and
sulphur oxides) forming acid rain and releasing particulates which cause respiratory problems
6 Lovelock, 2006. pp.31-33 7 Patel S., S., A Sinking Feeling. Nature, 2006. 440. 8 Larsen, J., Setting the record straight. 2006, Earth Policy Institute.
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such as asthma, chronic bronchitis, cardiac mortality and more. In central Israel, a study was
carried out following the pulmonary function and respiratory health of schoolchildren between
the ages of 13 and 14 in the vicinity of a new coal-fired power plant in Hadera. Asthma
prevalence, wheezing and shortness of breath increased from 5.6% in 1980 to 11.2% by 19899.
Another study in the same area - Hadera, testing childrens’ lung function development in 1996
and 1999 showed a strong negative association between development of pulmonary function
and the pollution levels at the child’s place of residence. It is clear from many studies the
world over that pollution and health are inversely proportional and symptoms suffered are
exacerbated by increasing demand for electricity from fossil fuels.
1.2. Building industry’s contribution to environmental degradation
1.2.1 Detachment of building envelope from climate
In the 19th century, as technologies became more complicated and scientific method
developed, the “master builders” profession of old began splintering into sub-jobs, including
engineering specialists, architectural designers and more. Today, architects as lead designers
create the general design - shell and interiors - to which other consultants contribute; structural,
HVAC&R (heating, ventilation, air-conditioning & refrigeration) and electrical engineers. In
the majority of buildings, to maintain acceptable internal conditions HVAC&R systems are
relied upon. The deeper plans often need larger systems which require resource-intensive
building and maintenance costs and fuel-intensive operation.
In fashionable, architect-designed buildings often large surfaces of the envelope are made of
glass. This exposure, either to direct sunlight or to cold external conditions, can cause
9 Goren, A. and S. Hellmann, Changing prevalence of asthma among schoolchildren in Israel. European Respiratory Journal, 1997. 10(10): p. 2279.
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overheating or heavy heat-losses thus require powerful air conditioning to keep comfortable
internal conditions. Some engineers even insist on having fixed windows that cannot open in
order to prevent disturbing the system or complicating calculations. This requires buildings to
be air conditioned all year round even if only a few of the months have uncomfortable weather.
Unless the engineering features are considered at the earliest conception of design, they cannot
be adequately integrated and therefore efficiency in terms of energy consumption is forfeited.
As well as the technologies now available, cheap energy from fossil fuels has also allowed
designers to become increasingly disinterested in energy conservation as an integral part of the
building form. The oil embargo of 1973 forced the industry to improve systems’ efficiency
and gave rise to the solar house movement. Yet the subsequent decades left this largely
ignored until the recent growth in awareness of environmental degradation, health problems,
fuel costs and wavering supplies. In light of the consequences, these issues are returning to
design consciousness.
1.2.2 A brief word about building materials: environmental impact,
embodied energy, embodied emissions & life cycle analysis
There are various ways to assess the environmental impact of materials. Among the main
considerations are the energetic aspects, called ‘embodied energy’ or ‘emergy’. This
considers energy expended from non-renewable sources during manufacture. Measuring
this can vary depending on the method used, the scope of the investigation and the
distance one travels back in the production line such as considering transportation and
raw material extraction.
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‘Embodied emissions’ calculates the GHG emissions and other toxic emissions resulting
from an object’s production. Again the calculations must be accurate and the method
clear to gain a real understanding of the product’s impact.
Affecting the environment are such processes as mining and quarrying, deforestation, oil
spills and if materials can be reused, recycled or disposed of.
Finally, ‘life cycle analysis’ considers the above as well as the maintenance required and
the expected lifespan of a building.
All these have important implications regarding the sustainability of a building. They
should be looked at in depth when considering materials and building methods yet are, of
course, out of the scope of this study.
1.2.3 Environment inside buildings
The lack of outdoor air has had adverse effects on building occupants’ health. If, as happens
often, ducts and tubes are not maintained, debris from dust, insects, mould or bacteria that
grow in the humidity which is taken out of the air is poured over occupants causing diseases
and even death. The bacteria Legionella is a famous example that occurred a few times in
Britain, once killing 7 guests who stayed in a building with a neglected system in Cumbria in
200210. Many such cases with various pollutants are recorded in indoor air quality studies.
Other off-gassing substances from glues, detergents, polishes, heavy metals, carpet fibres,
cosmetics (such as hair-dressers), pigments and naturally occurring argon released from the
Earth’s crust can build up to harmful levels when a flow of air is denied.
‘Sick Building Syndrome’ is a term well known, especially in large office buildings, reflecting the
myriad of complaints from suffering interns.
10 'Errors' led to Legionella deaths. BBC News. http://news.bbc.co.uk/2/hi/uk_news/6520535.stm
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2. Scientific background
2.1 Thermal comfort
Conventional standards for thermal comfort operate within a narrow boundary,
rendering non-mechanical assistance in non-residential buildings difficult even when
the climate is mild. Current shortfalls in standards which are regularly contested are
said to be caused to a large extent by a disregard for factors such as culture,
expectations, local climate, activity levels (11,12) and differing personal motivations13.
Numerous surveys have been conducted questioning thermal comfort and searching
for new industry standards since the PMV – predicted mean vote was researched and
proposed by Fanger. Large scale surveys were conducted across regions like
Pakistan, Bangladesh, Australia and Norway, both in specific buildings such as
offices and throughout whole days of usual activity to gauge comfort levels in
different climates. The ‘adaptive’ nature of people to thermal discomfort has been
observed and documented.
2.1.1 The adaptive approach
The idea behind this approach is that, if the conditions inside a building are such to
cause any of its occupants discomfort, that occupant will “reach in ways which tend
to restore their comfort”. This was originally proposed by Nicol and Humphries.
11 Nicol, F., Roaf, S. Pioneering new indoor temperature standards - the Pakistan project. Architecture of the extremes. 1994. Y. Etzion, Erell, E., Meir I.A., Pearlmutter D. Dead Sea, Israel, The Desert Architecure Unit, J.Blaustein Institute for Desert Research, Ben Gurion Universtity of the Negev: 41-46. 12 Forwood. What is thermal comfort in a naturally ventilated building? Standards for thermal comfort, Windsor, 1994.E&F Spon. 13 Williamson, T. J., Coldicutt, S. & Riordan, P. . Comfort, Preferences, or design data? Standards for Thermal Comfort. 1994. Windsor, UK, E & FN Spon: 50-57.
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Since this approach also takes into consideration the local climate and seasonal
conditions, which seem to affect peoples’ comfort standards, buildings do not need to
stay in the same temperatures throughout the year, shown by numerous studies(14, 15).
The adaptive comfort standard (ACS) proposed to ASHRAE Standard 55 has great
energy saving potential according to Brager & De Deer16.
The range of conditions found comfortable in field surveys is much wider than
rational indices predict. Furthermore striving for neutrality, which is the aim of
thermal comfort standards, is not necessarily what people always want year round.
An example of this is from Sydney, Australia is where 16% voted feeling ‘warm’ in
summer and nearly 6% feeling cool in winter yet had no desire to change it . It has
also been found that there is a correlation between the mean temperatures measured
and the comfort vote; therefore in hotter climates people will be comfortable at higher
temperatures than cooler climates, which also alters with the same people and
locations in different seasons17. After plotting a graph of mean temperatures against
comfort votes from surveys worldwide, it was found that the relationship between
mean outdoor temperatures with free-running buildings is quite linear and clear, as
opposed to heated and cooled buildings18.
It is suggested by ASHRAE Standard 55 that naturally ventilated buildings are to use
an alternative to the PMV based method for establishing comfort zones.
14 Nicol, F., Roaf, S (1994). 15 Karyono, T. H. (1994). Higher PMV causes higher energy consumption in air-conditioned buildings: a case study in Jakarta, Indonesia. Standards for thermal Comfort. Windsor, E & FN Spon. P. 219-226. 16 Climate, comfort & natural ventilation: a new adaptive comfort standard for ASHRAE Standard 55: In proceedings of the moving thermal comfort standards into the 21st century, Windsor, UK, April 2001 17 J. Fergus Nicola, I.A.R., Arif Allaudinb and Gul Najam Jamy, Climatic variations in comfortable temperatures: the Pakistan projects Science Direct, 1999. 3(3): p. 261-279. 18 Nicol, J., F., Humphreys, M., A., Adaptive thermal comfort and sustainable thermal standards in buildings. Energy and Buildings, 2002: p. 563-572.
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Optimum comfort temperature is calculated based on the mean monthly ambient
temperature Ta,out
Tcomf = 0.31Ta,out + 17.8
2.2 Building envelope
2.2.1 Thermal mass, insulation and their order in wall systems
2.2.1.1 Thermal mass Thermal mass refers to the use of materials with high thermal capacity, such as mud,
brick and stone, in a building as a means to control internal conditions. Thermal
capacity or heat capacity quantitatively describes the amount of heat required to
elevate the temperature of a unit volume of the wall or roof (volumetric heat
capacity), or unit area of a wall.
The heat capacity per unit surface area is determined by the density of the material,
its thickness and specific heat. Under changing ambient temperatures and solar
radiation exposure, as the heat capacity of a material increases, heat flow into or out
of a building decreases19. The heat capacity is also significant when using
intermittent heating or cooling, but loses its significance in steady-state conditions.
Orientation and colour are the major determinants affecting external surfaces’
temperature range. Heat is conducted through the solid material, raising its
temperature and if there is enough heat, the remainder enters the interior space. The
rate of heat conduction through a solid is determined by the material’s conductivity
19 Givoni, B., Man, Climate & Architecture. Second ed. 1981: Applied Science Publishers. Pp.111-2, 132-3
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(W/m/K), its thickness (m) and the temperature difference between indoors and
outdoors.
When such materials are used as part of the envelope, they will reduce the peaks and
dampen the curve of a daily ambient temperature swing. This is called the decrement
factor. As the layer thickness and heat capacity of a material increases, the curve
straightens. This has the effect of keeping internal temperatures close to the daily
ambient average. The second effect is a time lag – a delay in the internal temperature
response to the outdoor air temperature changes, also called thermal time constant
(TTC). Thus ‘thermal mass’ has the dual effect of delaying and dampening the
ambient curve20.
Both as part of the envelope and as other internal elements such as heavy internal
walls or floors, thermal mass can store heat, for example in a passive solar home in a
cold climate, slowly absorbing direct solar radiation through glazing during daylight
hours, then slowly releasing it to the surrounding internal space once temperatures
drop. During warm weather, heat is absorbed slowly into the envelope mass and is
thus delayed entry into the building through its envelope. By the time of sundown,
when outdoor temperatures drop, ambient air acts as a heat sink carrying heat away
from the outer walls, sometimes aided by a breeze. However the interiors also
receive emitted heat making them warm in evening and night time. Relief from this
can be found if the building is opened up in the evening, heat is carried away from the
internal surfaces by the cooler air and thus the building is cooled for use the next day
as shelter from intense daytime heat. This is advised as a way to keep comfortable
conditions within a building especially in hot arid climates. Another common
20 Meir, I.,Y. Etzion and D. Faiman, Energy Aspects of Design in Arid Zones, J.Blaustein Institute for Desert Research at Ben-Gurion University of the Negev and State of Israel – Ministry of Infrastructure, 1998, p.46.
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traditional method in desert settlements like the Middle East and North Africa is to
spend evenings and sleep at night outdoors, sometimes on open rooftops, like the
desert city of Yazd in central Iran21.
The appropriate extent of time-lag in buildings is dependent on their use. Daytime
occupancy, such as in schools, will benefit from an 8-10 hour time lag so warmer
interiors at night will not be felt. Night time occupancy would require structures to
lose their heat more quickly22 either from the materials themselves or by appropriate
building operation. According to Olgyay (1963), generally speaking a half-day time
lag is appropriate in areas of high diurnal swings for a daily thermal balance, yet the
details need to be looked at according to the sun’s impact on various surfaces of a
building throughout the day and year in order to create the most appropriately
designed envelope23.
Achieving the average daily temperature using thermal mass is favourable when the
average is somewhere in or near the thermal comfort zone, such as in the Negev
Highlands where summer days are hot, but nights are cool enough to bring the mean
ambient temperature into comfort range. However in climates where discomfort is
experienced at night like humid coastal areas, the long cooling time needed for high
capacity envelopes can be a hindrance. When the mean daily temperature is mostly
above the comfort zone such as summer in the Southern Arava, mass alone will not
suffice to provide thermally comfortable indoor temperatures.
21 Roaf, S., Crichton, D. & Nicol, F. Adapting Buildings and Cities to Climate Change, 2005, Oxford: Architectural Press, Elsevier, p.39. 22 Saini B.S., Building in Hot Dry Climates. , Wiley, New York (1980).p.34 23 Olygay, Victor, and Olygay, Aladar, Design with Climate. Princeton, N.J.: Princeton University Press, 1963, pp.117-118.
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2.2.1.2 Insulation When the components of a material are finely divided, the presence of air, which is a
poor conductor of heat, severely impedes its passage. Density is lessened and the low
conductivity makes the substance an insulator.
One way of assigning a quantitative value to the insulation properties of a material is
the U-value. This describes numerically the overall thermal conductance (U) of a
material, using the conductivity (λ) - which is a property of the material, also called
thermal transmittance or air-to-air heat transmission coefficient, and its thickness.
The lower the U-value, the better the insulation effect. U-value, being a measure of
conductance, is the reciprocal of resistance (R), called R-value. It follows then that
R-value describes how effectively a material resists the flow of heat through it. The
performance of an insulation layer depends on its resistivity (r) (or conductivity), its
thickness, the difference between indoor and outdoor temperatures (temperature
gradient) and its order within the building element, like a wall or ceiling.
2.2.1.3 Order of envelope elements The thermal resistance of a wall is a simple sum of all the thermal resistances of each
layer. However, the thermal capacity of a wall system in a building will depend as
well on the degree of contact the thermal mass of the wall has with the interior air12.
Therefore, if a layer of insulation is placed on the internal surface and the high
thermal capacity material is on the outer surface, contact between interior air and the
storage mass of the wall is diminished. This greatly reduces the effect of the mass in
mediating internal temperatures by reducing peaks and creating thermal time constant
(TTC).
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2.2.1.4 U-values’ limited description Simply ascribing a numerical U-value of a wall however does not fully describe its
thermal behaviour concerning time lag or radiative emission and its effect on comfort
indoors.
Olgyay & Olgyay (1963) described a lightweight wooden wall and a 22.9cm thick
brick wall of the same U-value – 1.5 W/m2 °C - in the Iraqi summer climate showing
a time lag of 2 and 10 hours respectively24. Although the overall heat transmission
for both wall types was the same, between the hours of 7am and 7pm, 475 kJ were
transmitted through the wooden wall and 350 kJ through the brick wall. This makes
the day-time heat balance of the heavy wall advantageous, when it is needed most.
The U-value of a wall system in situ will be altered if there is ‘thermal-bridging’ such
as a metal frame or structural concrete allowing rapid passage of heat by conduction
between indoors and outdoors, moisture penetration allowing convective transfer or
air infiltration exacerbated by wind speed acceleration. Thus the whole assembly
must be considered in calculating total transmittance, which is a very complicated
process. In situ measurement lends a way to experimentally verify the thermal
performance of the whole system25.
2.3 Building in hot arid environments
2.3.1 Introduction
More than 1/3 of the Earth’s surface is now considered to be ‘arid’, semi-arid or
hyper-arid. 36%, 4.7 million km2, half of all states have part or all of their territory in
24 Saini B.S., Building in Hot Dry Climates. Wiley, New York (1980).p.34 25 Saini B.S., Building in Hot Dry Climates. , Wiley, New York (1980).p.35
17
deserts. Temperate regions comprise only 1.5million km2 (26). 15% of the world’s
population lives in deserts, which is around a billion people.
The major environmental issues to contend with when building in hot dry
environments are high temperatures, solar radiation and its subsequent re-radiation
from walls, floors, ceilings and surrounding surfaces as well as dust storms. These all
affect human comfort and determine the performance of a building.
There are of course many environmental factors affecting building design, each
climate and site with their own set of conditions such as prevailing wind velocity and
direction, precipitation, topography, cloud cover, soil type, geological activity such as
earth quakes, surrounding vegetation and buildings, potential inhabitants and more.
An adequate design response must consider its site carefully in order to result in a
building that is responsive to varying conditions especially if energy-efficiency is
desired.
However there are tried and tested means to work with the natural forces in creating
passively cooled and heated buildings.
A number of investigations has been carried out in recent decades indicating that the
problem of summer daytime overheating and cold winter nights in deserts can be
addressed in multiple ways.
This research focuses on an inland, hot and hyper-arid desert setting. Summer air
temperatures are high with a wide diurnal range. Winters have reduced temperatures
and solar radiation although skies are largely clear and bright, while the diurnal range
is larger than in summers. Low night time temperatures coupled with strong winds
create an environment requiring protection from cold.
26 Al-Temeemi, A. and D. Harris, A guideline for assessing the suitability of earth-sheltered mass-housing in hot-arid climates. Energy & Buildings, 2004. 36(3): pp. 251-260.
18
2.3.2 Solar radiation and buildings
Direct and diffuse solar radiation is one of the chief causes of heat gain in dwellings.
Unlike conduction and convection, which occur relatively slowly and need a liquid or
solid medium to pass through, radiative transfer travels at the speed of light, needing
no intermediate matter between radiator and receptor. As the sun’s rays pass through
the atmosphere, they are scattered and diffused by atmospheric contents such as
ozone, particles like dust, water vapour and pollutants and are partially reflected back
out to space by clouds. Along with this, the angle of incidence, local weather and the
number of daylight hours determine the local climate and heat gain from solar
radiation. These conditions change with geographic location. Generally, the band of
Earth between latitudes 15° and 35° north and south receives the highest amount of
solar radiation, second to that is the tropical equatorial belt between 15° north and 15°
south, where high atmospheric humidity diffuses, and increased cloud coverage
reflects some radiation back to space27. Kibbutz Lotan, at latitude 29.59° north is
within the hottest belt.
Electromagnetic short-wave radiation from the sun travels (an average of 93 million
miles, 150 million kilometres) through space until it hits the Earth’s surface. At the
building, it may be transmitted through glass, reflected from neighbouring surfaces or
absorbed into a solid.
One of the chief causes of discomfort in buildings in hot, dry climates is solar
radiation which is absorbed through envelope materials and is then emitted as infra-
red long-wave radiation - sensible heat, into the interior.
27 Konya, A. and Swanepoel C., Design primer for hot climates, Architectural Press, 1980, pp.9-10.
19
Solar radiation alone can increase the temperatures of surfaces by as much as 16°-
44.4°C and accelerates the rate of heat flow into a structure28.
2.3.3 SOL-AIR approach
The recognition that a feeling of heat in the body is a combination of the effects of
solar radiation and air temperature has given rise to the “Sol-Air” approach. This
considers the joint thermal impacts on buildings’ external surfaces of the sun’s rays in
tandem with ambient convective heat, noting the varying effects of solar rays
according to regions and seasons. This can be an informative tool in deciding
optimum orientation. In this equation, the absorptivity of the external building
material is considered, ambient temperatures and radiative impact. Thus a (fictitious)
air-temperature value is achieved, that would have the same effect in pushing heat
through a material as actually occurs with the radiation and air temperature combined.
The direction from which radiation is received during the over and under-heated
seasons can be mapped out. Optimum orientation would be found when radiation is
at a maximum during the under-heated period (derived from the psychometric chart)
and at a minimum during the overheated period of the year, i.e. summer.29 The times
and seasons of rooms and buildings use are important considerations which are
informed by the sol-air approach in optimising orientation for climatically suitable
habitats. However guides are alterable depending on the building shape and the
treatment of external surfaces among other environmental factors.
28 Saini, 1980, p.29 29 Olgyay 1962, pp.54-62
20
2.3.4 Building structure and form
2.3.4.1 Ratio of surface area to volume Since the hot arid climate is typified by relatively cold winters - the clear sky dome
being an effective heat sink for infra-red radiation from Earth’s surface - solar
exposure is desired during winter months to warm buildings. To gain direct solar
exposure in winter yet minimise it in summer, a compromise is sought between larger
and smaller external surface areas of a building (as well as glazing positioning,
discussed below). Another compromise is between the need to expose winter sun to
buildings’ surfaces yet minimise winter heat loss in the absence of radiation, therefore
minimising surface area to volume ratio (SA/V).
A square building is often seen to combine the largest ‘practical’ volume with the
smallest outside volume. With very small window openings and extremely effective
insulation this can be true, however as soon as large glazed openings are considered
as in contemporary buildings, this presents problems of excess loss and gain of heat.
The principle of SA/V ratio is that the larger the surface area is compared to the
internal volume; i.e. the less compact a shape, the larger the heat exchange between
exterior and interior, for there is more surface through which exchange can take place
while the volume remains the same. SA/V ratio adaptations as means of water and
heat saving can be found in nature, like the thicker sections of succulent plants in very
dry or cold areas compared to those in temperate zones30.
With the intense solar radiation of hot and arid environments, shade in summer is
paramount while restricting air movement and thus convective gain (as opposed to
hot and humid locations where cross ventilation is necessary to cool resulting in
30 Olgyay, V. and A. Olgyay, Design with climate: bioclimatic approach to architectural regionalism. 1963: Princeton University Press Princeton, New Jersey, USA. p.85
21
higher, more open larger surface areas). In the same vein, winter sun is usually strong
due to clear skies, thus in many hot, arid regions including the Arava, relatively little
direct solar glazing is necessary for capturing adequate heating in winter compared to
temperate regions. In cooler arid regions a larger surface for solar gain will be
necessary. Using the sol-air temperature Olgyay computed hourly gains and losses in
four climatic regions with differing ratios and orientations. He concluded that in a
hot arid zone, (in this case Phoenix, Arizona) the optimum basic form is a slightly
elongated rectangle at 1:3, longer faces to the north and south, shorter sides to east
and west. Using figures of radiation striking walls, Meir et al found the optimum
proportions for a rectangular building in the Negev Highlands area to be 3:2, longer
side facing north and south31. However, upon turning the building (i.e. changing to
2:3) there is less than 10% increase in the walls’ solar exposure, this shape is not very
long and therefore flexible as a ratio. The effect on indoor conditions depends on the
success of the wall insulation.
Figure 2.1 From the diagram above, the SA:V and SA:floor area ratios (FAR) of various basic shapes can be compared. Reproduced courtesy of Prof. D. Pearlmutter.
31 Meir, Etzion and Faiman, 1998, p.33
0.25 0.5 0.6 0.65 0.7
2.0 1.25 1.5 1.625 1.775
Surface/ Volume Ratio
Surface/ Floor area
Ratio
SA V SA FAR
22
As the size of any object grows, so its surface area is decreased compared to its
volume. However the same floor area with different envelope shapes will also
change SA/V and SA/floor area ratios (FAR).
The sphere has the lowest possible surface area to its enclosed volume. A
hemispherical dome with 20m2 floor area has a total SA of 60m2 and volume 33.6m3,
therefore its SA:V = 60/33.6 = 1.78
while a cube of the same 20m2 floor area has a total SA of 120 m2 and volume 90m3
therefore its SA:V = 120/90 = 1.3
If one considers only the external SA, not including the floor which has a different
means of heat exchange with the ground;
• Dome: 20m2 floor area : 40m2 external envelope surface area
• Cube: 20m2 floor area : 100m2 external envelope surface area
This will obviously affect heat exchange with the surrounding ambient air and
therefore internal conditions. Minimum energy transfer between the interior and
exterior of a building will occur when there is minimum envelope surface relative to
floor space32.
Figure 2.2, 2.3 A hemispherical dome and cube of 20m2 floor area each, yet dome’s external surface area (excluding floor) is 40 m2 and cube is 100 m2 (not to scale, viewed from side and above).
32 Meir, Etzion and Faiman, 1998, p.34
23
Consequential too is the amount of building material needed to construct the envelope
enclosing the same floor area.
2.3.4.2 Building orientation In summer time, the intense solar radiation is received mainly from above, the high
sun striking the roof as described graphically in figure 2.4 below.
After the roof, the highest radiation is from directions east and west33. This drives
heat inwards, even if windows and shutters are closed. Ventilation options on east
and west are limited during the day due to large heat gains by convection which
reduce effective internal climate control options and negate coolth stored in mass or
gained using insulation. In hot arid conditions ventilation during the day must be
well planned in order not to counter other means of keeping heat out. This is
different from hot humid locations where cross ventilation is essential for comfort.
The subjects of orientation and proportions of buildings have received a lot of
attention in literature. However it must be noted that, once glazing and other
openings have been properly designed and located, the poorer the insulation in a
building the greater the effect its orientation and configuration have on internal
comfort conditions34.
Walls may be positioned to minimise direct radiation upon them. If a building has
one axis longer than the other, it is advised to position it along the average track of
the sun. In the northern hemisphere for example, the summer sun rises in the north
east and sets in the north west, travelling through a high southern position at midday.
33 Etzion, Y., et al., Adaptive architecture: integrating low-energy technologies for climate control in the desert. Automation in Construction, 1997. 6(5-6): pp. 417-425 34 Yair, Etzion and Faiman, 1998, p.33.
24
By orienting the building east-west, with the longer sides facing north and south,
summer sun can be avoided on the northern façade to a great extent. Adding wide
enough eaves can provide complete shading from direct summer radiation on the
southern façade while decreasing eastern and western exposure. Thus larger control
can be exerted upon interior conditions by opening and closing windows and shutters
according to need. East and west openings should remain as small as possible to
avoid overheating as the sun rises and sets in those directions, which can exacerbate
summer conditions indoors. This effect is even stronger in the west as high ambient
temperatures are augmented by high radiation (see Sol-Air approach).
In winter, east and westerly exposure are also less desirable since maximum solar
gains come from the low southern sun with little on the other two and less yet on the
north side. (Of course the southern and northern effects are opposite in buildings in
the southern hemisphere.) Maximum temperature control therefore, is achieved by
allowing low southern solar radiation to enter through south facing glazing during
daytime for winter heating, then closing up to minimise heat loss after sundown,
having trapped the sun’s heat in some of the building’s mass.
25
35
2.3.4.3 Natural ventilation To achieve cross ventilation in hot arid areas, it is important to have openings on both
sides of the building. Meir et al (1998) recommend that even more important than
orienting a building façade windward is having correctly placed openings, which may
be optimal up to 45° from the direction of the wind (for example, west wind can be
well captured by a north-west or south-west window opening)36.
2.3.4.4 Shading Shading the outer surfaces of a structure is important for a number of reasons.
On a psychological level, intense glare can create discomfort, protection from it is
paramount to soothe and comfort in daytime heat37. Shading outer sunlit surfaces can
bring them closer to the temperature of shaded air, causing the reduced temperature
35 Etzion Y., Experimental projects in desert architecture - Israel, Journal of Arid Lands Studies, Vol. 5S, 1995. p. 81-84. 36 Meir, Etzion and Faiman, 1998, p.35 37 Saini, 1980, p.24-25.
Figure 2.4 Diagram showing
proportion of total
insolation radiation on each
of the ‘true’ directions,
north, east, west & south on
a perfect cube in the Negev,
in winter and summer.
(Courtesy of Prof. D Faiman)
26
gradient to drive less heat indoors. Solar radiation through windows can significantly
increase the cooling load. Understanding the types and importance of radiation;
direct, sky-diffuse and reflected, can aid the design of effective shading mechanisms.
Much experimentation has taken place to understand and increase thermal and visual
comfort indoors
2.5 Domes
Vaults and domes appear frequently in arid zones. In many desert urban settings,
notably in the Middle East, domes and vaulted roofs are part of the vernacular. Many
reasons have been given for their proliferation, some cultural, necessities due to
material availability, inherited craftsmanship and ancient philosophical motives (38,39).
Commonly supposed is that in arid zones stone was abundant and the dome shape
made construction of roofs without using wood possible40. Several thousands of
years ago in Upper Egypt, a response to the shortage of wood was the Nubian dome,
able to be built without shuttering as concentric rings of earth bricks were leaned on
each other forming vaulted enclosures, shelters from sun and heat41. This is a
building tradition described by Hassan Fathi with great pride as a climatically suitable
and beautiful alternative to rectilinear, concrete mass-housing provided to rural
communities by the Egyptian authorities and external architects “no more inspiring
architecturally than a row of air-raid shelters” 42 Recently, ecological degradation
causing a lack of timber prompted Nubian domes to be taken up as a building method
in the sub-Saharan belt of West Africa, as have shuttering-free (originally from
38 Fathi, H. Architecture for the Poor, University of Chicago Press, Chicago and London, 1973, pp.5-8. 39 Olygay, Victor, and Olgyay, Aladar, Design with Climate. Princeton, N.J.: Princeton University Press, 1963, p.7 40 Runsheng, T., I. Meir, and Y. Etzion, An analysis of absorbed radiation by domed and vaulted roofs as compared with flat roofs. Energy & Buildings, 2003. 35(6): p. 539-548. 41 Oliver, P., Encyclopedia of vernacular architecture of the world, P. Oliver, Editor. 1997, Cambridge University Press, p.354 42 Fathi,1976, p.14
27
southern France) corbelled domes in Senegal and Angola. Domes and vaults built
without shuttering are also found all over Iran, mostly in desert communities, made of
fired bricks and gypsum, sometimes ingeniously put together to span bazaar routes
and other large widths, while smaller rural structures are made of stone43. Their
popularity is thought to have remained due to their low cost and good thermal
performance44.
45.
Suggestions of climatological suitability relating mostly to the relief of summer heat
are prominent yet until recently were by nature qualitative descriptions rather than
derivations of measured or calculated data46.
High solar radiation was said by Olgyay to be ‘diluted’ on a round surface in the
1970s, he and Fathi (1986) suggested that this reduced local radiant flux kept surface
temperatures lower and therefore the heat flowing into the building is reduced. Yet
this does not fully explain curved roofs’ advantage in hot arid climates, since less
convective and radiant heat dispersion occurs if the roof surface temperature is lower,
for the temperature gradient between surface and ambient air is lower, and net solar
43 Oliver, P., 1997, pp.353-356 44 Hadavand, M., Yaghoubi, M. and H. Emdad, Thermal analysis of vaulted roofs. Energy and Buildings, 2008. 40(3): p. 265-275. 45 Woodless Construction: Using unstabilised earth bricks and vault and dome roofing in West Africa 46 Pearlmutter, D., Roof geometry as a determinant of thermal behaviour: A comparative study of vaulted and flat surfaces in a hot-arid zone. Architectural Science Review, 1993. 36(2): p. 75–86.
Figure 2.5 Yazd city with vault and domes roofs in Iran
Figure 2.6 The house of Hamad Said, designed by Hassan Fathi
28
heat flow into the building is not proven to be reduced. In 1978, Bahadori reported,
in his account of passive cooling strategies in Iranian architecture, how stratification
of air allowed the warm to rise to below the high curved roof and kept the lower
living area cooler and more comfortable47. However the idea that more heat is
dissipated by the large curved roof is not substantiated since higher daytime ambient
temperatures would convectively push heat into rather than out through the roof48.
Various experiments have taken place to determine the thermal behaviour of vaulted
and domed roofs.
In reality, daily conditions are in flux, solar radiation alters in intensity and direction
throughout daylight hours, winds and temperatures change, making heat transfer
between a building and its surroundings unsteady. While modelling can show the
tendencies of certain forces and their effects, it is difficult to show changing
conditions and complicated interactions between varying forces. However models
keep improving.
The first attempt to quantitatively assess and compare curved and flat roofs’ thermal
behaviour was carried out in an experiment by Pearlmutter (1993) combining
physical monitoring and mathematical solar computation. Physical models were
built, all with identical 50cm x 50cm plan, 50cm high plywood walls insulated with
5cm expanded polystyrene (EPS) and 1mm thick galvanised sheet metal flat and
semi-cylindrical roofs, one pair painted matte black the other white. (All models
were placed outdoors, leeward of a structure thus shielded from direct strong wind.)
Thermal stratification of vaulted roof (VR) was higher than in the flat roof (FR). VR
also maintained lower internal temperatures than FR throughout most of the day and
47 Hadavand, Yaghoubi, and Emdad, 2008. 48 Tang et al, 2003, p.275.
29
were even lower for the black-painted VR. Interesting to note is that Pearlmutter did
not find significant differences in internal temperatures between vaults oriented along
the sun’s path (with central axial line stretching from north to south and longer
façades facing north and south) or when oriented facing east and west49.
Other mathematical models have been carried out to estimate the behaviour of vaulted
roofs in differing orientations and wind directions. Hadavand and Yaghoubi (2008) 50
made a series of calculations on long slim buildings with VR in the hot arid climate of
Yazd, Iran, a climate very similar to the hot, arid Arava. Ambient temperatures were
set to 1st September with a maximum of 34°C and min 17°C. Their calculations
showed that due to self shading of the vault shape, surface temperature variations
were higher on the vaults, increasing as rim angle increased, while nearly uniform on
flat roofs. Increasing the rim angle was especially significant in reducing heat flow
into the room when the vault was oriented along the sun’s path, east-west (longer
façades facing north and south). This is due to the fact that if the sun radiates slightly
to one side of the vaulted roof, like on the southern part of the east-to-west path (in
the northern hemisphere), the steeper the arch (rim angle), the more (self) shaded the
northern part of it will be. Whereas a roof oriented along the north-to-south path will
have a fully irradiated eastern side in the first part of the day and a fully irradiated
western side on the latter part of the day.
49 Pearlmutter, 1993. 50 Hadavand, M. and M. Yaghoubi, Thermal behavior of curved roof buildings exposed to solar radiation and wind flow for various orientations. Applied Energy, 2008. 85(8): p. 663-679.
30
(Half-rim 25°) (Half-rim 45°) (Half-rim 60°) (Half-rim 90°)
Figure 2.7. Domes or vault sections with various rim angles. Below half-rim angle of 50° (that is 100° full rim angle) the roof was found to have little thermal advantage over a flat roof.
The convective coefficient over the windward side of the vaulted roof increased
(relative to a flat roof) thereby increasing convective heat transfer and lowering the
temperature of the roof surface. The surface temperature of the side receiving solar
radiation was cooled by up to 23°C when it was windward (to 35°C) than in the same
orientation when leeward (58°C).
Increased convective heat exchange will also occur through the roof of a dome due to
its large surface area in comparison with flat roofs. In hot summer weather, an
exposed dome’s surface temperature will inevitably be higher than the air’s
temperature, even during the day. The increased surface area enables increased heat
exchange via convection and thus more efficient cooling. As long as most of the
radiation is direct and not diffused, the larger surface will not cause an appreciable
increase of solar absorption overall, as long as effective angles of incidence are high.
31
Tang et al’s (2006) calculations51 showed that vaulted roofs had lower indoor air
temperatures compared to flat roofs which ever building type was used. Dissipation
of heat by convection and radiation at night occurred to a larger extent from curved
roofs due to the enlarged surface area compared to the flat roof. The advantage of the
curved roof in creating favourable indoor conditions in hot dry climates decreased
with decreasing half-rim angle. It was found that the rim angle needs to be ideally
around 100° (half-rim 50°), and at least that to be effective, below which there is
negligible difference between curved and flat roofs (see figure 2.7 above) and may
even cause higher internal temperatures.
However in contrast to passively run buildings, air conditioned buildings with curved
roofs displayed, in previous mathematical models, increased heat exchange compared
to flat roofs. In typical hot, dry conditions with a 90° half-rim angle, (180° full rim
angle) Tang et al (2003) calculated 40% more daily heat flow through the domed roof
than a flat roof.
When the same conditions are applied to vaulted roofs, a building positioned with its
longer sides facing north and south allows 20% more heat flow while an east-west
facing building 27% more heat flow than a flat roof, while heat flow is close to that
through a flat roof when the half-rim angle is below 50° 52. The increased heat flow
is mainly due to increased convective heat exchange between the enlarged domed and
vaulted roof surface area and ambient air, with additional effect due to the orientation.
Thus a curved roof building that is operating air conditioning (AC) will be more
effective when the rim angle is not above 100° (half rim 50°) since this increases heat
exchange and decreases the effect of the AC. Tang et al found that the factors greatly
affecting heat flow through the roof were the rim angle and the ambient temperatures, 51 Tang, R., Meir, I.A., Wu, T., Thermal performance of non air-conditioned buildings with vaulted roofs in comparison with flat roofs. Building and Environment, 2006. 41: p. 268-276. 52 Tang, R., Meir, I.A., Etzion, Y., Thermal behaviour of buildings with curved roofs as compared with flat roofs. Solar Energy, 2003. 74: p. 273-286.
32
while radius of roof, thickness and the materials it was made from interestingly did
not.
One of the most important advantages of the curved roof type is the amelioration of
heat flow into the buildings during the day by the higher internal volume below the
roof which does not exist in flat roofed buildings. Stratification of internal air means
the less dense, lighter-weight hot air gathers at the top, allowing cooler air to settle at
the lower part of the building. A simple opening at the apex will allow hotter air to
escape, which can act as a cooling mechanism for internal air.
However when high temperatures and high diffuse radiation prevail, curved roofs no
longer provide an advantage. They absorb almost the same amount of direct beam
radiation as flat roofs but more diffused sky radiation. Coupled with high ambient
temperatures, curved roofs in humid areas with typically high diffused radiation
absorb more heat and do not provide benefit as well as in arid regions. Internal
temperatures of curved-roof buildings benefit arid regions due to the clear skies; little
diffuse yet strong direct radiation, as well as the important and effective night cooling
by radiation from and through the larger roof surface area toward a clear sky dome.
Lastly
2.6 Straw building
2.6.1 Introduction
Straw in unbaled form has been used in buildings since humans began creating
shelter, and still is in roof, wall and flooring systems. Straw bale building has grown
in the last two decades a great deal.
It began when the horse-driven baling machine was invented by European settlers in
Nebraska’s grain-growing Sand Hills, who out of necessity, due to a lack of other
building materials like cement, wood or stone, used the bales as building blocks.
33
They stacked them to form walls and plastered interiors and exteriors with mud.
Some of these buildings are standing and occupied today, over a century old still
enduring and effective.
Figure 2.8. The Pilgrim Holiness Church, Nebraska, one of the oldest historical straw bale buildings.
In North America alone, straw bale production from grain farming is very large,
enough to meet all residential building requirements. Since grain farming is common
in many cultures and regions of the world, this renewable resource is abundant53.
Interest in straw bale building seems to be fuelled entirely by a grassroots desire to
increase efficiency and decrease waste in building, since the bales are insulating
elements and a ‘waste’ product of the grain farming industry. It does not come from
within the construction industry; there is no standardisation, central planning or
53 Mackwood, C., Mack, P., Thierrien, T., More Straw Bale Building. 2005, Gabriola Island, Canada: New Society Publishers, p.6.
34
industry-wide testing. Many independent builders and organisations running
workshops have been the cause of its proliferation and it is still gaining interest
worldwide. Straw bale buildings have in the last decades been built in Alaska,
Australia, Chile and China, Iraq and Israel, South Africa and the UK amongst other
countries. Due to the non-industrial, non-proprietary nature of this building type,
builders continually keep important lessons and experiences shared through networks
via the internet to become collective knowledge. To date though, there has been a
small number of quantitative research regarding things such as thermal properties of
straw bales in buildings.
2.6.2 General perceptions of straw bale as a building material.
There is a general opinion that straw bales as building blocks lighten the load our
buildings place on the planet. This is due to the insulation properties of the bales seen
to increase energy efficiency of buildings as well as the fact that they are a by-product
from farming, giving bales very low embodied energy. Embodied energy, also
referred to as emergy, is an accounting methodology aiming to find the sum of total
energy used in the production and life-cycle of a product (see 1.2.2 for context). The
fact that the carbon is locked into the plant structure (via photosynthesis) means bales
are carbon negative therefore do not contribute to climate change through greenhouse
gas emissions compared to other manufactured building materials54. Bales, if not
used in buildings or other ways, are often burned, releasing the carbon back into the
atmosphere and increasing pollution. For all these reasons and more, straw bale
buildings are generally perceived to be favourable to the environment, increasing
their popularity.
54 Assuming of course that the fossil fuel the baling machine uses and the transportation of the bales to their destination do not release more carbon into the atmosphere than is locked into the straw. If the bales are few and the distance travelled is far, or the bales are so large that machinery must be used to handle and move them, there may be a marginal carbon-sequestration effect.
35
2.6.3 Straw bale building in earthquake zones
Due to the lightweight properties of straw bales compared to many other building
materials, areas that are prone to seismic activity can benefit greatly. The collapse of
a building with components weighing 200kg/m3 will cause far less damage to
property and to living creatures than 1850-2400kg/m3 as in typical concrete, or clay
bricks whose range is 1600-2500 kg/m3(55). This is one reason it is gaining popularity
in earthquake-prone areas such as Turkey56.
The southern Arava as mentioned below in more detail is part of the Syrio-African
rift, where tectonic plates slide against each other at an average distance of 5mm per
year, causing tremors and occasional earthquakes felt throughout the country.
Earthquakes are thus another design consideration.
2.6.4 Straw bale insulation properties
2.6.4.1 Comparative monitoring of straw bale buildings Previous experimentation to find quantitative insulation values and to compare straw
bale buildings with similarly sized conventional buildings is still sparse. However
some testing has occurred.
The Canada Mortgage and Housing Corporation (CMHC) carried out energy
consumption monitoring on eleven straw bale homes built between 1996 and 2001
and compared them to predicted energy consumption by ‘standard’ housing. The
straw bale homes were selected due to their measurable fuel consumption, thus no
55 Harmathy, T.Z., Properties of Building Materials, in The SFPE Handbook fo Fire Protection Engineering 1988. 1988, Institute for Research in Construction: Ontario, Canada. p. 1-378-1-391. 56 Elias-Ozkan, S., Summers, F., Surmeli N., Yannas, S., A Comparative Study of the Thermal Performance of Building Materials, 2006.
36
wood-burners were used. ‘Conventional’ homes with the same dimensions were
modelled in HOT2000 software applying any floor and attic insulation present in the
straw bale homes, same window and floor dimensions and British Columbia 2001
standard building practice (2x6 walls, typical 4.5 leakage air changes per hour
(ACPH) + 0.2 ACPH reflecting mechanical ventilation that may be used57and
minimum 12.5mm reinforced double glazing – even if straw bale home had lesser
quality windows). The data are said to be too incomplete to directly determine an R-
value from these experiments but an average of 21% less heating energy was found to
be used in the straw bale homes (maximum savings at nearly 40% and worst
performance 12.7% higher).58
In Ankara, Turkey in 2006, a climate of relative extremes of long, cold winters and
hot, dry summers, the thermal performance of four building types was compared.
Three were monitored and the unfinished aerated concrete building was only
simulated. It is important to note that these buildings were part of an existing Eco-
Centre, not built specifically for this comparative thermal study and therefore very
different in shape and size to each other as well as in building materials. Also, when
heated, the amount of fuel burnt was not in direct proportion to the buildings’ volume,
creating discrepancies in the comparison of heating fuel. For the unconditioned
session in August, the small traditional mud brick and nearly twice as large plastered
straw bale buildings showed much smaller temperature and humidity fluctuations.
Even though the diurnal ambient temperature range was around 13°C, 18-32°C, theirs
was about 5°C between 23 and 28°C. While ambient humidity moved between 22%
57 Air changes per hour are not exactly known in the straw bale homes, some may use natural and/or mechanical ventilation and some may not. Air tightness tests were not carried out although 40mm thick plaster stucco skins on inside and outside wall surfaces are generally good air barriers. 58 Energy use in straw bale houses, in Technical Series 02-115. 2001, Canada Mortgage & Housing Corporation: Ottawa, Ontario. pp. 1-4.
37
and 78%, they remained within around 7% averaging about 45% for the mud brick
and 53% for the straw building. The onsite large prefabricated building (thin concrete
panel sandwich with EPS insulation boards) was measured for comparison and
showed very large fluctuations with temperature and humidity changes of the
ambient, rising a degree or two above maxima which were already 28 - 31°C, and
dropping humidity to within 3-5% of ambient minima at around 20%.
In the winter, the same amount of coal was used for all three buildings burning for
two days and then remained in between heating periods. Mud brick remained at a
higher temperature initially, reradiating stored heat into the building, although after a
number of days, as the heat leaked out of the mud building the straw bale building
more effectively kept it in with its insulation. The prefabricated building cooled
down faster than the others, while hollow brick performed very similarly to mud brick
except in its ability to store the initially injected heat. Humidity levels were again
kept most constant with the mud brick and straw bale buildings while being lower and
more erratic in both the prefabricated and hollow brick buildings59.
2.6.4.2 Monitoring straw bale buildings Another monitoring project took place in 1996 by Gail Brager of UC Berkley in
Hopland, California. The Real Goods Solar Living Centre showroom is a large
plastered straw bale building with passive solar heating, evaporative cooling and
other energy-conserving strategies. Shortly after its opening before its first full
winter-time operation, it was monitored indoors and out for air temperatures and
surface temperatures during 10 days. Supplementary simulations, telephone
interviews and surveys were also conducted. A time lag of 12 hours was found in the 59 Elias-Ozkan, Summers, Surmeli and Yannas, 2006
38
straw inside the wall. The smaller temperature variations of the interior straw
compared to the plastered sides suggests the working of highly isolative material.
The plastered interior surface of the straw bale wall was 2-4°C lower than internal air
temperatures, thus providing cooling throughout the day by the thermal mass
(unsolicited comments confirming ‘pleasant cooling’ felt from the walls). Late
afternoon when ambient was at a maximum of 36°C internal air was around 28°C
(with a little hike of about an hour to 34°C), while nights reached ambient lows of
9°C, interior space was above 18°C. Thus diurnal temperature changes were
substantially mitigated by the insulation of the straw and the mass of the earth to
improve comfort. (Other methods of passive control were also employed, natural
ventilation being key to comfort conditions achieved using operable windows and
doors, clerestory windows and stack effect).
Most recently in 2008 a house in Ottawa, Canada was monitored for electricity usage
in space heating (hot water in radiant floor slab). Space and water heating energy use
was found to be just over half the 24kWh/day considered as standard for a four
person family, while the house was occupied by five. This in the face of a slightly
larger air leakage than usual average Ontario houses built in 1990s and winter
temperatures often reaching minima of -20°C and lower. The R-value for the walls
was concluded to be close to the higher estimations in the literature thus far and to be
much better and sometimes twice as effective insulators as walls in most R-2000 and
EnergyStar® houses (partnerships of Canadian business/government and US
government department of energy/ EPA energy efficient technologies and standards
for buildings which exceed regulations)60.
60 Gusdorf, G., The Hirondelle House: Monitoring & modelling a straw bale house in Ottawa, in Sustainable Buildings & Communities. 2008, Natural Resources Canada: Ottawa.
39
2.6.4.3 R-values of straw bale So far, the most reliable results regarded for R-value determination of a straw bale
and mud-plastered wall is widely agreed to be that which occurred at the Oak Ridge
National Laboratories (ORNL), 1998, where some experienced straw bale builders
from California along with an authority figure on the subject, built a wall section for
testing. Unlike previous attempts, suspected to be unreliable (due to mud plaster that
did not have enough time to cure properly and sections of bale-wall that were
compressed resulting in gaps in the guarded hot-box frame which then had to be filled
with stuffed straw, and other such problems) this time the wall section was built as
closely as possible to the way it is done in home construction. The mud cured
properly for two months. The resulting R-value was determined to be R- 27.5
ft²·°F·h/Btu for the 19 inch wheat straw bale, which is R- 1.45 per inch, (metric = R-
0.255 m²·K/W) equivalent to R- 33 for a 23 inch bale. This figure was found to be
almost identical in an experiment conducted in 1995 in Nova Scotia, on behalf of the
Canadian Society of Agricultural Engineering. Watts et al performed three in situ
tests in an existing straw bale house using a hot plate and thermocouples. They found
the 18.4 inch thick wall to have a value of R- 28.4, resulting around R- 34 for a 23
inch bale wall.61
Table 1 Typical resistivity values for common materials Material Value per inch (metric)
Poured concrete R- 0.08 (0.014)
Brick R- 0.2 (0.35)
Glass R- 0.24 (0.04)
Most hardwoods R- 0.71 (0.13)
Most softwoods R- 1.41 (0.25)
Straw bale wall with plaster R- 1.45 (0.25)
61 Stone, N., Thermal Performance of Straw Bale Wall Systems, in Ecological Building Network (EBNet). pp. 4-6
40
Table 2 Typical modern insulation materials (ASHRAE website)
Mineral fibre, loose fill (rock slag or glass) R- 2.2 (0.39)
Vermiculite, exfoliated R- 2.13 (0.37)
Perlite, expanded R- 2.7 (0.47)
Mineral fibre blanket (rock, slag or glass) R- 3.25 (0.57)
Cellulose (milled paper and wood pulp) R- 3.4 (0.60)
Rigid Board and Slab expanded polystyrene, depending on type R- 4.0 (0.70)
to R- 6.25 to (1.10)
Polyisocyanurate R- 7.04 (1.24)
As Nehemia Stone mentions in his summary of the various attempts to assign
resistance values to straw bales, it is indeed interesting to note the difference in
resistance according to straw direction. With the general straw direction placed
parallel to the heat flow direction - that is the bale laid down ‘flat’, resistance was
diminished. In fact a 23” bale laid flat was found to perform with the same thermal
resistance as a 16” bale that was placed ‘on edge’, with the general direction of the
straw being perpendicular to the direction of heat flow62. The effect of straw
direction is confirmed in tests by the Austrian Straw-Bale Network 200063.
62 King, B. and M. Aschheim, Design of straw bale buildings: the state of the art. 1st ed. 2006, San Rafael, CA: Green Building Press, p.187. 63 Danish Building and Urban Research, Straw Bale overview, presentation.
41
3. Research question
3.1 Framing the problem and relevance of this study
The use of air conditioning globally is a growing phenomenon. Even in Europe which is
cooler than Israel, AC use has increased, in the USA 40-50% of electricity is used in AC(64,65)
(50-70% in households)66 operation and in the Middle East where this has occurred at a rapid
pace in the last decades, representing improvements in economic conditions and
increased electricity usage. In Kuwait for example, a dry desert climate similar to the
Arava with mean daily maxima of around 45°C, domestic AC use accounts for 75%
of electrical power consumption67. With increasing worldwide populations and
economic growth and the desire for thermal comfort, pollution is exacerbated as well
as fuel consumption and all the related political issues. In Israel there are of yet no
exact figures of consumption due to AC use, however it is very likely to represent a
large and growing percentage.
In the Arava the plans are to increase the population by attracting more people to the
desert. This is in order to justify cultural life as well as spending on local facilities.
There are currently just over 3,300 residents in the area, a population growing by
4.3%. At the southern end of the Arava is the city of Eilat, with a population of
46,500. A port and tourism spot with many hotels, some offering highly luxurious
accommodation, many residential homes, very hot weather and an increasing
64 Roaf, S., Fuentes, F., Thomas, S., Ecohouse 2, A Design Guide. 2nd ed. 2006, Oxford: Elsevier Ltd. p.8 65 Energy, U.D.o. Electricity Consumption by End Use in U.S. Households, 2001. 2001; Available from: http://www.eia.doe.gov/emeu/reps/enduse/er01_us_tab1.html. 66 Al-Homoud, D., Performance characteristics and practical applications of common building thermal insulation materials. Building and Environment, 2005. 40(3): p. 353. 67 Al-ajmi, F. and D. Loveday, Indoor thermal conditions and thermal comfort in air-conditioned domestic buildings in the dry-desert climate of Kuwait. Building and Environment, 2009. p.704
42
population all serve to increase AC use in buildings. Unless buildings themselves
help to alleviate the intense heat of the Arava summers and contribute to thermal
comfort.
A growing number of people is taking responsibility and attempting to create homes
and buildings that are more climatically suitable. Kibbutz Lotan’s Bustan
neighbourhood is a prime example; geodesic domes built using insulation in the form
of straw bales which are plastered with earth/clay.
3.2 Question
The question is if these efforts are more than just ideological. Do they represent real
or potential energy-saving with regard heating and cooling buildings’ interiors?
How do these domes behave in the harsh Arava climate? How does the specific
building system’s thermal behaviour compare to those of the conventional typologies
(i.e., heavyweight prefabricated concrete, lightweight mobile or just cheap)?
Can we understand something about the contribution of the dome shape and massive
insulation combined with the mass of earth plaster regarding their contribution to
thermal conditions?
3.3 Relevance and potential benefits of this study
While straw bales have been monitored around the world, to a small but growing
extent as they gain in popularity, little if any quantitative information is available
about the combination of straw bale and earth plaster in hot arid regions in the shape
of geodesic domes. They have certainly not existed in the Arava (in recorded history)
before being built on Kibbutz Lotan. Therefore their performance in this climatic
region is first monitored in this research study.
43
Assessing the behaviour of this building typology will present a number of
benefits, namely;
• understanding this system’s thermal behaviour compared to conventional
heavyweight and lightweight building types
• the people who spend time and energy building and modifying the
EcoCampus on the Bustan neighbourhood will get an idea of what works (if
anything) and what does not in the current forms
• recommendations for improvement of the domes based on scientific data may
be incorporated into future modifications which occur regularly
• electricity savings in the kibbutz may occur and with that economic benefits
• since the Bustan neighbourhood hosts an educational course with students
worldwide, lessons learnt may be proliferated to people from varying
backgrounds and professions
• the subject of the ratio of thermal mass to insulation is a longstanding debate;
yet the settling authorities have been erecting concrete slab units since the
1950s with a lot of thermal mass and little (probably with negligible effect)
insulation which absorb heat and represent uncomfortably hot interiors in
summer evenings. Getting some clarity about the effects of these ratios can
benefit Kibbutz Lotan in particular if lessons learnt are applied to existing
buildings. Improvements based on data also represent great potential regional
electricity savings if applied to other buildings in the region, or indeed are
incorporated into recommendations for regional building regulations. As
mentioned, with a growing population this is a very large amount of electrical
energy with all the attached problems mentioned in the general introduction.
44
4. Case study
4.1 Southern Arava
4.1.1 Climate & Geography
Figure 4.1 Map of solar radiation levels around the land of the globe & map of Israel showing position of the southern Arava.
Generally, solar radiation is highest on earth in the band between the latitude lines of
15° and 35° north and south. This research examined the thermal behaviour of three
building systems in the Southern Arava desert of Israel. The Arava Valley is part of
the Syrio-African rift , where seismic activity is regular. Kibbutz Lotan lies at
latitude 29,59° and longitude 35,05. This makes it one of the most highly irradiated
areas on earth. Its position in the Arava is 166m above mean sea level.
Average annual rainfall is 25mm, however until this last summer of 2009/2010 there
was no rain at all for three consecutive years.
Average daily summer temperatures are around 31.5°C while regularly soaring above
40°C in afternoons, with minima of around 26°C low humidity, high heat stress is
45
experienced here. Winters may reach occasionally below freezing point yet usually
range between 20.1 and 9.8°C at night68.
The low moisture in the air extends comfort range of high summer temperatures.
4.2 Kibbutz Lotan
Kibbutz Lotan was founded in 1983 on what was then the Jordanian side of the Arava
Valley. It is a community based on Reform Judaism with an emphasis on communal
living and ecology. A “progressive expression of Jewish religion and culture” is
sought in daily life, to fulfil the biblical ideal "to till the earth and preserve it” with
ideas reflecting Reform Zionism and equality69.
4.2.1 Ecological projects
There is a number of ecologically oriented projects in Lotan including organic food
gardens, grey water treatment, waste reuse and recycling, bird watching and the
EcoCampus where the domes were built.
68 Meir et al, 1998. 69 Kibbutz Lotan official website, 3/2010 http://www.kibbutzlotan.com/community/values/vision.htm.
Figure 4.2 Thermal comfort table shown in relation to Arava maxima and minima – contained within the marked square. It is visible that for the majority of the year comfort range is exceeded by Arava climatic conditions. (comfort table from Meir et al, 1998, modified)
46
The EcoCampus Neighbourhood is an integral part of the Green Apprenticeship
program of the Centre for Creative Ecology where permaculture is taught. The
neighbourhood integrates a wide variety of low-tech, hand made structures and
systems with modern engineering attempting to create a sustainable, carbon neutral
and healthy environment for education and student life.
The neighbourhood includes 10 domes (for up to 20 occupants), composting urine
diversion toilets, passive solar hot water showers, grey water treatment, solar ovens
and off-grid solar PV sidewalk lighting. A 10KW tracking PV system to supply
renewable energy is planned.
4.2.2 Mud & straw bale building
A number of building projects has taken place in Lotan using straw bales and earth
plaster including home extensions, the domes, office walls and now the largest straw
bale building in Israel is near completion. Domes are described in detail in section
5.2.1.2
4.2.3 Electricity use
The majority of buildings are however the predominant concrete slab type
proliferated by the settling authorities as in most of the Arava. Between 1995 and
2005 Lotan’s electricity use nearly doubled. A study about energy consumption of
kibbutzim in the Arava, among other issues looked at electricity consumption,
discovering an upward trend in its use. The major use of electricity was found to be
due to the use of air conditioning. An upward trend in the hottest month of August
between 1995 and 2005 was the driving force of the general annual upward trends in
annual consumption of the four kibbutzim studied. Confirming this was a reduction
47
in electricity levels occurring as members left daily to work outside the kibbutz
reflecting less space-cooling in buildings.70
צריכת חשמל חודשי מ 1995
100
150
200
250
300 ממוצע95-98ממוצע99-04ממוצע04-072008
ממוצע 95-98 183,505 170,748 117,487 125,745 187,175 261,870 309,815 304,020 280,008 189,868 130,202 149,303
ממוצע 99-04 145,598 120,836 127,720 102,940 180,450 218,706 259,744 263,398 216,610 156,438 110,544 130,990
ממוצע 04-07 157,737 130,298 125,148 124,853 200,679 239,348 272,955 274,005 224,809 172,205 123,592 148,200
2008 184,868 142,816 130,338 139,226 173,775 229,728 262,975 263,207 227,687 155,481 115,102 120,160
ינואר פברואר מרץ אפריל מאי יוני יולי אוגוסט ספטמבר אוקטובר נובמבר דצמבר
שו" קפיאל
Figure 4.3 Electricity usage by month for years 1995-1998, 1999-2004, 2004-2007 and 2007 on Kibbutz Grofit, a neighbouring kibbutz just south of Lotan in the Arava. The peaks are between June and the end of August.
Yotvata Meterological Station Temperature Measurements 1995-2004
0
10
20
30
40
50
Janu
ary
Februa
ryMarc
hApri
lMay
June Ju
ly
Augus
t
Septem
ber
Octobe
r
Novem
ber
Decem
ber
Deg
ree
C
-
10
20
30
40
50kW
h/da
y
Avg. HighAvg. LowkWh/day
70 Cohen, J., Lifestyle and Energy Consumption in Arava Valley Kibbutzim, in Department Man in Drylands. 2008, Ben Gurion University of the Negev. p. 64-75.
Figure 4.4 Electricity usage by month and monthly average maximum & minimum temperatures in Grofit, courtesy of Grofit management.
48
5. Experiment
5.1 Project description overview
5.1.1 Building survey
A physical survey was carried out including dimensions, ratios of surface areas,
volumes, floor areas, construction materials and their properties. Gathered
information is displayed below 5.2.1.
5.1.2 Temperature monitoring of buildings
HOBO H8 Pro Series microloggers with temperature sensors on all, humidity and
luminosity on some, were placed in various locations in and out of the buildings
depending on the monitoring regimes which are described in detail in section 6.
5.1.3 Temperature monitoring of irrigated garden soil
Ground temperature is monitored by the Yotvata Research & Development
Agriculture Information Centre71 meteorological station 10km south of Kibbutz
Lotan. Ground temperatures are measured at the surface and at depths 10cm, 30cm
and 50cm below the surface. These are taken of the local loess soil while dry.
Measurements of irrigated soil are not taken by them. Irrigated soil measurements
have been taken by agricultural soil scientists in the Arava but not during the summer,
only during periods of the year when crops are grown which is until May.
In order to get an idea of the potential of irrigated soil as a heat sink, which exists
already as herb and vegetable gardens in the Bustan neighbourhood, temperatures of
71 http://yair.arava.co.il/climatic/makl.htm for current and weekly summaries throughout the Arava. Annual reports are also available.
49
wet soil were taken at the same 10, 30 and 50cm depths. The garden soil is not local
loess alone but a mixture of compost from local food waste with local soil.
This soil from the Bustan neighbourhood garden was monitored. A hole was dug,
into which a metal reinforcement bar was placed. On the bar three HOBO sensors,
wrapped in plastic clingfilm and cellotape to protect from moisture, were fixed at the
assigned heights with metal wire. Once in the ground at the correct heights, the soil
was replaced to cover the bar and sensors and was irrigated with a litre of water. This
is the way irrigated soil is monitored by local soil scientists72.
The sensors were in place in mid August for four days.
5.2 Building survey description
5.2.1 Three typologies: Heavy, insulated, lightweight
5.2.1.1 Heavy: Concrete
Figure 5.11a, b South-eastern corner (left) and western façade (right) of less shaded concrete unit. North is completely shaded by thick vegetation, eastern façade partially shaded as is the roof. The mud is a cosmetic coating for aesthetic purposes, a few millimetres thick. The western wall of the envelope can be seen to butt up against the envelope of the neighbouring concrete unit.
72 Evyatar Etiel, PhD, Arava R&D, personal communication, August 2008
50
Figure 5.12 View of the roof of less shaded concrete unit, the roof is mostly exposed to direct solar radiation from above.
Figure 5.13 Plan of monitored concrete unit, with envelope walls and dimensions. Shading indicated refers to the less shaded unit tested subsequently. Dimensions in metres.
51
.
Figure 5.15 Detail of roof and parapet showing 22cm wide wall, prefabricated concrete slabs and rubble on roof, above insulation layer. Courtesy of Alex Cicelsky, CCE, Kibbutz Lotan.
Figure 5.16 Photograph of roof and parapet
Figure 5.14 North-eastern view of the first monitored concrete unit, with extensive shading on east & south façades and on roof
52
Dimensions - Concrete Floor area 40 m2
Roof area 48.5 m2
SA: Total external envelope (walls, roof, openings, parapet) 138.2 m2
SA: Total external envelope (walls, roof, openings, no parapet) 126.5 m2
Total glazing (with frames) 6.8 m2
Total openings (windows, doors) 10.5 m2
Total internal volume 97.3 m3
Ratios
Surface area: volume with parapet 1.4 : 1
without parapet 1.3 : 1
Surface area: floor with parapet 3.5 : 1
without parapet 3.1 : 1
SA total : SA glazing with parapet 20 : 1
without parapet 18.6 : 1
SA total : openings (glazing, doors) with parapet 13 : 1
without parapet 12 : 1
53
5.2.1.2 Insulated: Dome
Figure 5.21 Air conditioned dome with north-facing door
Figure 5.22 Section of dome with door south-facing. Dimensions for the air-conditioned dome and the other monitored domes are identical (allowing for hand-applied earth plaster)
54
Figure 5.26 Plan of Bustan neighbourhood. Top square showing 4 identical domes monitored, bottom square the air-conditioned dome, also identically built but facing opposite di i
Figure 5.23 Apex opening from below, inside dome.
Figure 5.25 HOBO micrologger on interior of an open vent.
Figure 5.24 Air-flow detector smoke highlighting the escape of air through the open apex while selected vents and apex were open
55
Figure 5.28 Interior of corridor, south-facing door, eastern wall.
Figure 5.27 Exploded 3D dome with components, courtesy of Lotan CCE office.
56
Dimensions - Dome (Only dome)
Floor area 19 m2 (15m2)
SA: Total external envelope (including, openings) 99 m2 (72m2)
Total glazing (with frames) 3.4 m2
Total openings (windows, doors) 5.74 m2
Total internal volume 50 m3 (40m2)
Ratios (Only dome)
Surface area: volume 2 : 1 1.8 : 1
Surface area: floor 5.2 : 1 4.8 : 1
SA total : SA glazing 29 : 1 21 : 1
SA total : openings (glazing, doors) 17 : 1 12.5 : 1
Layer Overall resistance
External walls and roof (from inside to outside)
5-9cm mud plaster R - 19 sq.ft.*°F*h/Btu 73
Or
R - 3.35 m2*K /W
(U=0.3 W/m2*K)
55cm wheat straw bale
5-9cm mud plaster74
73 Taken from the most reliable values to date, monitoring to estimate R value for bale and plaster wall, ORNL Laboratories, see section 2.6.4.3. Values were determined for a 19 inch bale, where Lotan’s domes are made with 55cm which is a little larger at 21 inches.
57
Domes
The units monitored in this research have gravel filled concrete block
footings capped with a galvanized sheet metal termite pan running from the
exterior to interior. The geodesic frames sit upon the footing along with the
bales. The exterior and interior finishes are earth and clay plastered to
varying recipes depending on the layer order. The layer plastered straight
onto the bales is higher in clay, the outer layers are higher in sand content.
They were applied by hand and trowels by eco-volunteers and students of
the Green Apprenticeship (GA) course taught at Lotan. Some external
pinning of the bales was applied. The 2-string wheat bales measuring 400
mm x 500 mm x 900 mm are not pre-compressed. Bales were laid flat, that
is strings up. 60 bales were used per dome.
10 domes were constructed, the first is a full dome, the subsequent domes
have elongated side walls to add headroom indoors.
The domes are earthquake safe structures hand engineered by students using
small amounts of readily available, low cost galvanized steel pipe.
Straw bales are a renewable, natural material, a waste product of agriculture.
They are comparatively local, coming from farms in the north of the Negev
desert, just a few hundred kilometres north of the Arava. They have 3 hour
flammability rating. The attempt was to keep all the materials of the domes
as renewable and local as possible, however due to the seismic activity in
this area the engineer required steel piping to achieve building permission.
58
5.2.1.3 Lightweight
Figure 5.31 North-eastern view of lightweight building. Materials The lightweight building is a prefabricated package – a steel frame, the walls made of
12mm gypsum wallboard sandwich with a 5cm cavity, no insulation and negligible
mass. The roof is polystyrene filled 5cm SIP – structural insulated panel. A door on
the north and one on the south made of plastic sandwich and double-glazed windows
- a small part of which is openable, are the only openings. Two non-openable
windows for light are small and high up on the western façade, visible in the
photograph above.
Dimensions - Lightweight
Floor area 40 m2 (15m2)
SA: Total external envelope (including openings) 113.5 m2 (72m2)
Total glazing (with frames) 2.3 m2
Total openings (windows, doors) 5.1 m2
Total internal volume 116 m3 (40m2)
59
Ratios
Surface area: volume 0.98 : 1
Surface area: floor 2.8 : 1
SA total : SA glazing 49.0 : 1
SA total : openings (glazing, doors) 22.0 : 1
Layer Overall resistance
Roof
Polystyrene filled 5cm SIP (structural insulated panel)
R – 8 - 10 sq.ft.*°F*h/Btu or R – 1.4 – 1.7 m2*K /W
External walls and roof (from inside to outside)
12mm gypsum wall board R – 0.45 sq.ft.*°F*h/Btu or R - 0.079 m2*K /W Approx. R - 1 sq.ft.*°F*h/Btu or R - 0.176 m2*K /W 75
as above
5cm air gap
12mm gypsum wall board
5.2.2 Window proportion and orientation
In both the concrete and lightweight buildings the windows are oriented to north and
south. The domes’ windows are however oriented northeast, northwest, southeast and
southwest. As mentioned above (2.2.1), this is against advice when building,
especially in the desert, since maximum control over interior climate is achieved
through manipulating northern and southern openings rather than east and west
openings.
75 http://www.allwallsystem.com/design/RValueTable.html ORNL Laboratories, and a number of different sources which all agree on this value.
60
5.3 Monitoring
5.3.1 Electrical meters Digital meters were compared to each other by operating a simple, 75W desk lamp
for 14hours, once attached to one meter and again to the other. One of the meters has
readings displaying two places after the decimal point, meaning its resolution is lower
than the other. With this in mind, the readings still reflected comparability, albeit
within error margin of the second decimal point showing a 100th of a kilowatt hour
(kWh).
After 14 hours attached to the light bulb, one meter showed the use of 1 kWh while
the other showed 1.3 kWh. Figures are shown in table below.
Start Finish Electricity used
Meter A. (later in
conc) 270.3 kWh 271.3 kWh 1 kWh
Meter B. (later in
dome) 468.63 kWh 469.66 kWh 1.3 kWh
Table 5.31 Calibration of both electricity meters used in the experiment to compare electrical energy of AC in dome and concrete unit. Within the resolution of meter A, comparability is satisfactory.
61
6 Monitoring
6.1 Brief overview
Set 1: Comparison of domes, concrete and lightweight structures
The first set of experiments aimed to compare the thermal performance of existing
buildings as is, with their inherent properties and ability to be used with regards
thermal comfort. Thus one concrete single-room dwelling, one existing lightweight
building and one dome were compared in closed and other modes of operation. One
dome was kept as a closed control throughout the experiment.
Set 2: Optimisation of domes (comparing new and improved domes)
The second set of summer monitoring aimed to compare an original dome with a
dome that has been refined with elements to further reduce summer heat gains and
increase comfort. These domes are in constant evolution, being repaired and
improved by the building team at Lotan. After comparing these domes, optimal
operation was attempted and monitored.
62
Set 3: Energy consumption comparison of dome & concrete
The third section aims to compare the predominant structure type in the Arava –
concrete units, to a dome in terms of the electrical energy required by an AC unit to
maintain a set, comfortable temperature and their warming up time once the air
conditioning units are turned off.
6.2 Description of modes of operation
Set 1: Comparison of domes, concrete and lightweight structures
Series A: Closed mode.
Closed mode allows a level starting point, by which to gage how the inherent
properties of the building materials and forms contribute to thermal performance, i.e.
how much radiation is absorbed by the envelope and conducted indoors, how much
heat is stored and for how long.
Two domes (as identical as possible considering the hand-made buildings) with
identical geodesic structures and orientation, one concrete building and one
lightweight building were closed up, with all windows and doors shut for 4 days in
order to allow them to stabilise.
HOBO H8 Pro Series microloggers with temperature sensors on all, humidity and
luminosity on some, were placed near the apex in the domes and at heights 1.5m and
0.5m in the centre of all the rooms. This is to detect conditions at standing and sitting
63
heights. The lower sensors were placed on plastic chairs, those at 1.5m were hung by
string.
Series B: Dome’s apex open, southern windows of lightweight and concrete open.
This operation mode compared the lightweight and concrete structures with their
southern windows open and northern windows closed to the experimental dome with
its apex open only, while windows and vents were closed.
Opening the apex of the experimental dome may allow heat to exit through the apex
but no forced incoming air. It was decided this is the closest comparative
configuration in the concrete and lightweight buildings, passively allowing air to exit
through the southern window but not the forced entry of northerly winds – which is
the prevailing wind direction in the southern Arava.
Series C: Lightweight & concrete buildings: north and south windows open; (but not
operated) experiment dome: open apex and vents; and window operation: closed
during day, open at night.
This mode of operation uses all current passive in-built features of the domes to
alleviate the heat of summer, namely preventing hot air penetration during the day
and allowing free cross ventilation through windows as well, at night. After two days
of this the ceiling fan was turned on.
In the dome, readings were taken with one HOBO micrologger placed on the internal
side of a north-eastern vent opening, the prevailing wind direction, while the other
was hung by the outlet of the open apex.
64
The concrete and lightweight buildings had their northern and southern windows
open. Both were monitored at 1.5m height.
Testing of later additions to the domes is described in the next section, Set 2
optimisation.
Set 2: Optimisation of domes - comparison of improved and original domes
Two domes were closed, all windows, vents and doors except for their apex. They
remained closed for nearly three days to ‘acclimate’ to present conditions so that a
fair starting point and subsequent comparison is achieved. On the third evening they
began to be operated in the optimal way - that is blocking daytime heat and solar
radiation through windows from around 8:30/9am and opening them up at
21:00/22:00 at night to allow the breeze to cool the building as much as possible.
While one dome was the original as built two years before this experiment, the other
dome had a few changes applied to it:
1. The apex was covered by a small mud-coated domelike structure that blocks
direct radiation from the sun yet is open on the sides below to allow
ventilation.
2. Reflective covers made from bubble-wrap with a metallic coating, mounted
onto cardboard the size of the window openings were prepared in order to aid
blocking direct solar radiation and heat entering through the windows.
3. A coil of 16mm plastic tubing was placed just under the mud floor for passing
water to cool or heat the dome but was not ready to be used yet. Actually
during this part of the experiment it was exiting through a plastic sleeve which
was passing through one of the built-in vents through the wall of the dome
65
close to the ground on the west. The rest of the tubing just lay on the ground
idle.
HOBO microloggers were placed at 1.5m height hanging from a string and at 0.5m
resting on a plastic chair in the centre of the dome. They were programmed to take
measurements and log them once every 10 minutes.
Set 3: Energy consumption comparison of dome & concrete
The electrical energy needed to keep a dome and a typical concrete unit cool for two
days in high summer was compared followed by their subsequent warming up after
auxiliary cooling was switched off. Both buildings were first allowed to remain open
for 2 days in order to stabilise them according to ambient conditions. This was
confirmed by measuring the internal surface temperatures of walls and floors to
observe that no ‘coolth’ has been stored in the mass of the structures. All surfaces
had the same initial temperatures, the dome, concrete and another unconditioned
dome for comparison, around 33°C.
The two buildings were then closed up, having been sealed as far as possible: all
windows and blinds shut and, fixed on their outside, reflective coverings made of
cardboard covered in bubble-wrap – the outer side of which is a metallic reflective
surface. All vents and the apex of the dome were sealed with mud on the outside and
stuffed tightly with fabric bundles (old clothing) for insulation from the inner side of
the dome envelope. In fact the dome used in this part of the experiment was the only
dome with an AC unit. It had been used previously with the AC on during the
summer whilst the dome was already sealed. This is why reheating it by opening the
66
windows was critical in making a fair comparison. It was compared in internal air
and surface temperatures to another non-air-conditioned dome to make sure of equal
starting conditions before the AC was switched on.
An AC unit in each of these buildings was turned on and the thermostat set to 26°C.
They both have the same ‘Freon’ – the coolant liquid. This is important in rendering
the two units comparable in terms of electricity used in the processes that allow the
Freon liquid to extract heat from the air in order to cool it. A hand-held thermometer
was used to confirm that, after two hours internal temperatures were comparable.
Attached between the air conditioning units and the electricity outlets of the walls
were electricity metres, to monitor the amount of electrical energy expended in
maintaining the stable thermostat-set temperatures.
The air-conditioning units were turned on and left on at the set temperature of 26°C
for 46 hours. The only time the buildings were opened was after two hours of
operation to check internal temperatures and when they were both turned off after 2
days of operation. Entry and exit from both buildings in order to turn off the units
were performed as swiftly as possible, opening and closing the doors immediately
and exiting immediately from the buildings, closing and locking the door. Thermo-
hygrometer was used to take temperatures and relative humidity measurements before
the air conditioners were turned off, so as to have as little impact on internal gains by
being there as possible. They were then turned off and the units were left closed and
locked. They both remained sealed for the next 24 hours while HOBO data loggers
recorded the temperatures and other internal conditions.
67
7 Results
7.1 Summer results
Set 1: Comparison of domes, concrete and lightweight structures
Series A: Closed mode.
Summer, Closed mode
20
25
30
35
40
45
9:00 21:00 9:00
Time
Tem
pera
ture
Deg
C
Ambient (Yotvata)Lightweight 1.5mDome: control 1.5mDome: experiment 1.5mConcrete (shaded) 1.5m
Figure 7.11 Typical 24 hours closed mode comparison of three building types; heavyweight
(concrete), lightweight (plasterboard) and domes (two of them for comparison). All values are
hourly averages. August 19th – 20th.
While ambient temperatures were swinging between 26°C and 39°C (measured two
metres above ground level in Yotvata meteorological station 10km south of Lotan),
68
the lightweight building (at 1.5 metres above the floor) reached maximum of over
38°C about one hour after ambient maximum, and minimum of nearly 31°C, 5°C
higher than the lowest ambient.
Both domes exhibited comparable, similar behaviour to each other, both reaching
temperatures between nearly 35°C and nearly 34°C – a fluctuation of less than 1°C
throughout the day, yet consistently ‘hot’ for thermal comfort. The concrete building
also exhibited stable temperatures in closed mode yet at 2 degrees lower than the
domes, between nearly 33°C and nearly 32°C.
The explanation for the lower temperatures inside the concrete unit was clarified in
later seasons to be the result of extensive shading from planted and dried vegetation
just outside the southern and eastern facades as well as on the roof. This was verified
by comparing another, much less shaded but otherwise identically built concrete unit
to assess the thermal impact of direct solar gain and solar shading. Results are
described in winter results, fig 7.32.
(A completely unshaded concrete unit was sought but not available in the kibbutz at
the time of testing).
Range Maximum Minimum
Ambient, 2m (Yotvata met. station) 12.8 38.9 26.1
Lightweight 1.5m 8.1 38.8 30.7
Concrete 1.5m 0.4 32.3 31.9
Dome - closed control, 1.5m 0.84 34.85 34.01
Dome - experiment, 1.5m 0.02 34.03 34.01
Ground surface (Yotvata met. station) 21.8 46.1 24.3
Table 7.11. Summer: Averages of maxima, minima and range during closed operation mode A. All
buildings with windows and vents were closed.
69
Surface temperatures : general patterns of behaviour
Surface temperatures: dome, concrete & lightweight
20
25
30
35
40
45
50
55
0:00 6:00 12:00 18:00 0:00
Time of day
Tem
pera
ture
Deg
CDome N, IN, 0.54mDome E, IN, 0.54mDome N, OUT, 054mDome E, OUT, 0.54mDome W, IN, 0.54mDome W, OUT, 0.54mHall E, OUT, 0.70mHall W, IN, 0.70mHall W, OUT, 0.70mDoor S, IN, 1.5mDoor S, OUT, 0.70mDome N, IN, Dome N, OUT, 1.1mDome E, IN, 1.1mDome E, OUT, 1.1mDome W, IN, 1.1mDome, W, OUT, 1.1mHall E, IN, Hall E, OUT, 1.1mHall W, IN, 1.1mHall W, OUT, 1.1mDoor S, IN, 1.8mDoor S, OUT, 1.8mDome E, IN, 1.6mDome E, OUT, 1.6mDome N, IN, 1.6mDome N, OUT, 1.6mDome W, IN, 1.6mDome W, OUT, 1.6mHall E, IN, 1.5mHall E, OUT, 1.5mHall W, IN, 1.5mHall W, OUT, 1.5mDome N, IN, arch 2.2mDome E, IN arch 2.2mDome W, IN arch 2.2mHall E, IN arch 2.2mHall W, IN arch 2.2mConc N, IN, 2cmConc N, OUT, 2cmConc E, IN, 2cmConc E, OUT, 2cmConc S, IN, 2cmConc N, IN, 0.54mConc N, OUT, 0.54mConc E, IN, 0.54mConc E, OUT, 0.54mConc S, IN, 0.54mConc N, IN, 1.6m
Figure 7.12 graph of surface temperatures showing three clear types of thermal patterns: little to no temperature change {a}, a definite rise in temperature between morning and evening {b} and that of a sharp rise and subsequent fall by the evening {c}.
a c
b
c
70
Three general patterns of thermal behaviour can be seen from the graph of surface
temperatures. That of little to no temperature change, a definite rise in temperature
between morning and evening and that of a sharp rise and subsequent fall by the
evening.
Little or no change (a)
The no to little change is shared by the interiors of the dome and hall in all
orientations, rising slightly as the height of the wall increases. Concrete’s interior
walls remain stable and little if any warming. The north, east and south walls of the
concrete are slightly lower that the dome’s internal but it must be reminded that these
are the very shaded walls. The first, shaded concrete unit had an internal party wall
on the west thus not an external envelope to its west.
Rise and fall (b)
Temperatures begin to rise and fall in the ‘hall’ or corridor attached to the south of the
domes (north on the opposite side of the neighbourhood, where the AC was
operated). This happens sharply at noon time with the interior surface of the south-
facing door of the dome. Sharper rises and subsequent falls are exhibited by the
external surfaces of east and west dome walls, sharper rises for the southern door’s
exterior and even sharper rises for the hall wall’s outer surfaces especially on the
west, which reaches over 50°C at later afternoon (49°C shown by this graph). The
exterior walls later lose their heat by 18:00 which is shown in this graph.
Constant increase (c)
The third trend of increasing and increasing temperatures is shared by: sharpest
increases (24-37°C ) – the lightweight building – both interior and exterior surfaces,
the outer surface of the hall’s wall, (reflecting morning rising sun), outer north-facing
dome wall, (which later does cool).
71
Constantly increasing at higher temperatures (35-44°C) are the exterior surface of
north and east facing concrete walls. If northern and eastern walls are increasing in
temperature, probably the western façade would top the whole graph considering the
join effects of later afternoon ambient temperatures and direct solar radiation of the
setting sun.
Interior versus exterior temperatures
If we isolate the eastern sides of the building to compare thermal resistance of interior
and exterior surface, we can see that the lightweight walls offer very little resistance
or time lag and the temperatures of both sides are very similar, shooting upwards
sharply beside each other on the graph. The dome’s eastern external surface rises
sharply too with the morning sun yet loses heat by the late afternoon, while its interior
surface catches up around 4 hours later, yet remains stable, at 34.2°Cm .07°C higher
than its starting point 12 hours earlier at 6am, while the external surface reaches 39-
40°C by late morning. At 13:00 they measured 33.6°C internal and 39.4°C – this is a
6°C difference. Even more extreme are the differences between the hall’s surfaces,
being flat and directly facing the dun, externally reaching 45°C by late morning while
remaining the same as the dome’s wall at 34.2°C – this is a difference of over 11°C.
This is the insulation at work. Concrete, which like the hall is also flat and facing
morning sun – again it is reminded that this first unit is shaded almost completely, at
1.6m measured externally 35.6°C and 43.6°C by the evening and internally 32.5 and
33.7°C, thus the difference is 10°C.
72
Surface temperatures: dome, concrete & lightweightEAST only
20
25
30
35
40
45
50
0:00 6:00 12:00 18:00 0:00
Time of day
Tem
pera
ture
Deg
C
Hall E, OUT, 0.70mHall E, IN, Dome E, IN, 1.6mDome E, OUT, 1.6mHall E, IN, 1.5mHall E, OUT, 1.5mConc E, IN, 2cmConc E, IN, 1.6mConc E, OUT, 1.6mLight E, IN, 1.6mLight E, OUT, 1.6m
Figure 7.13 graph of surface temperatures showing three clear types of thermal patterns comparing the east side of each building.
73
Series B: Dome: apex open
Lightweight & concrete: southern windows open.
Summer: Dome's apex open only, concrete's & lightweight's south windows open, 1.5m
20
25
30
35
40
45
12:00 0:00 12:00 0:00 12:00 0:00 12:00
Time
Tem
pera
ture
Deg
C
Ambient (Yotvata)Dome: Experiment 1.5mDome: Control 1.5mConcrete 1.5mLightweight 1.5m
Figure 7.14 Experimental dome: apex open, windows vents and door closed. Concrete and lightweight buildings: southern window open, northern windows & doors shut. This is to allow passive air flow but not forced northerly (prevailing) winds in – the closest comparison to an open apex. All values are hourly averages. August 23rd – 26th.
Again, as expected, the lightweight building fluctuated with the ambient reaching
maxima within 1°C lower or higher than the highest ambient - around 40°C and
minima of 30°C which is around 5-6°C higher than ambient lows as in Series A.
The concrete unit again was stable, fluctuating less than 1°C at around 2°C cooler
than both domes. The lower temperatures of the concrete are later explained to be a
result of heavy shading (see fig 7.32). All values are hourly averages.
74
Summer: Dome's apex open only, 0.5m
20
25
30
35
40
45
12:00 0:00 12:00 0:00 12:00 0:00 12:00
Time
Tem
pera
ture
Deg
C
Ambient (YotvataDome: Experiment, 0.5mDome: Control 0.5m
Figure 7.15 Experimental dome with open apex only and control dome all closed, measured at
0.5m. All values are hourly averages. The dome with the open apex allows hot air to exit
thereby air stratified below is cooler by at least 1°C. August 23rd – 26th.
0.5m from floor: The experimental dome with its open apex was, as measured at
0.5m from the floor, consistently around 1°C cooler than the closed dome at the
coolest hours of early morning - about 32.5°C and 33.5°C respectively, and mostly
the same at the highest temperatures of late afternoon at around 34°C (Fig 7.15
above). This is a 6°C reduction from ambient at the hottest hours by both domes and
8°C and 9°C warmer against the coolest ambient hours, by the experiment and control
respectively. There is therefore, according to this evidence, an escape route through
the open apex for warmer air to exit the dome, thus cooling the lower part of the
dome at the cooler hours of the late night/early morning.
1.5m from floor: However, when measured at a height of 1.5m, the experiment with
the open apex is consistently higher at the hottest hours by 0.5-1°C as well as cooler
at the cooler hours by about 0.5°C (Fig 7.16). This seems to suggest the entry of heat
by solar radiation through the apex, displaying a weak-spot in the dome design vis-à-
75
vis keeping cool from direct sunlight during hot weather, yet only at increased
heights. The heat seems to rise; even though air is warmed during the day at the 1.5m
level, at 0.5m the domes with closed and open apex are nearly the same temperatures,
therefore stratification is effective even with the extra heating through apex by
radiation. This may be explained by the dome’s shape, typically allowing hotter air to
rise to the elevated sub-roof space leaving cooled spaces below.
Summer: Dome's apex open only, 1.5m
20
25
30
35
40
45
12:00 0:00 12:00 0:00 12:00 0:00 12:00
Time
Tem
pera
ture
Deg
C
Ambient (Yotvata)Dome: Exp 1.5mDome: Control 1.5m
Figure 7.16 Closed control dome and experimental dome with open apex only, both monitored at 1.5m height. All values are hourly averages. Temperatures of the experimental dome go both slightly above and below the closed dome, showing heat loss at cooler hours by convection through the apex and gain at hotter hours of the day, most probably from direct solar radiation through the open apex. August 23rd – 26th.
76
Range Maximum Minimum
Ambient, 2m 14.6 40 25.4
Lightweight 1.5m 9.5 39.9 30.4
Concrete 1.5m 1 32.9 31.93
Dome 4 – closed control, 1.5m 0.7 34.4 33.7
Dome 7 – experiment, 1.5m 1.2 35 33.8
Dome 7 – experiment, 0.5m 1.2 35 32.5
Ground surface 25 48.9 23.9
Table 7.16. Summer: Averages of maxima, minima and range of operation mode B: Dome’s apex
only open, southern windows of lightweight and concrete open.
77
Series C: Dome: apex & vents open
Lightweight & concrete: southern & northern windows open.
Summer: Experimental dome, apex & vents open & windows operated(T-in, T-out) before & after fan operation
20
25
30
35
40
45
50
6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00
Time
Tem
p D
eg C
Ambient
Tin
Tout
Ground
20:00 windows opened
08:00 windows closed
20:00 windows opened
20:00 windows opened
08:00 windows closed
08:00 windows closed& fan
operated
Figure 7.17 Tin = temperature monitored at north-eastern internal edge of vent in experimental dome. Tout = temperature monitored near the outlet apex of the experimental dome. Temperatures here are recorded during operation of the windows i.e. they are shut during the heat of the day and open at night, without and then with operating a ceiling fan. Hourly averages. August 29th – September 1st.
78
Summer: Experimental dome, apex & vents (T-out, T-in) open& window operation
20
25
30
35
40
45
50
6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00 6:00 12:00
Time
Tem
p D
eg C
Ambient
Tin
Tout
Ground
20:00 windows opened
08:00 windows closed
20:00 windows opened
Figure 7.18 Experimental dome, vents and apex open and operated windows; closed during the hot day, open during cooler night. No fan operated. All values are hourly averages. August 29th – 31st.
79
Summer: Experimental dome, apex & vents (T-out, T-in) open& window operation
20
25
30
35
40
45
50
6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00 6:00 12:00
Time
Tem
p D
eg C
Ambient
Average Tin & Tout
Ground
20:00 windows opened
08:00 windows closed
20:00 windows opened
Figure 7.19 Average of Tin and Tout, taken from hourly averages. August 29th – 31st.
The apex is around 3m high, the vents are just above the ground therefore the average
of these temperatures is taken to represent the mid-height values at 1.5m.
Operating in cooling mode without auxiliary cooling, yet with vents constantly open,
the experimental dome exhibited the ability to be, in the averaged temperature,
around three degrees warmer than the coolest ambient temperatures at early morning.
This is a marked improvement. The hottest hours of the day measured on average
(between Tin and Tout) 2°C lower than ambient maximum. However the inlet, Tin,
measured only 1.5°C higher than the ambient at the coolest; lowest Tin 28.5°C, lowest
ambient 27°C. This is cooler than temperatures in the centre of the dome. Opening
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the dome has the effect of mitigating the thermal time lag that existed when it was
closed, and even when partially opened. The curve is still significantly dampened but
not much delayed, in the averaged temperatures the delay is only about an hour.
Range Maximum MinimumAmbient, 2m 12.5 39.6 27.1 Dome 4 – closed control, 1.5m 0.7 35.3 34.6 Dome 7 – exp., avg. Tin & Tout 7 37.7 30.7 Ground surface 17.5 43.5 26
Table 7.19 Range maxima and minima average Tin & Tout, vents, apex open & window operation.
Summer: Experimental dome, apex & vents (T-out, T-in) open & fan operation
20
25
30
35
40
45
50
6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00
Time
Tem
p D
eg C
Ambient
Tin
Tout
Ground
Figure 7.191 Experimental dome with vents (Tin) and apex (Tout) open, while the fan was operated. No significant temperature difference seems to be made by the fan. August 31st – September 1st.
81
Summer: Experimental dome, apex & vents open (T-in, T-out) - no fan. 24 hours - 11am-11am.
20
25
30
35
40
45
50
6:00 12:00 18:00 0:00 6:00 12:00 18:00
Time
Tem
p D
eg C
Ambient
Tin
Tout
Ground
Summer: Experimental dome, apex & vents open (T-in, T-out) & fan operation. 24 hours - 11am-
11am
20
25
30
35
40
45
50
6:00 12:00 18:00 0:00 6:00 12:00 18:00
Time
Tem
p D
eg C
Ambient
Tin
Tout
Ground
Figure 7.192a,b As above with and without fan operation, added trendlines. Ambient and Tin trends are nearly identical. As ambient temperatures decrease, Tout remains relatively high, that is, absorbing heat from within dome, then as air is released out through the apex, the dome cools.
As can be seen from the comparison of trendlines with and without fan operation, the
actual temperatures seem to change very little, as do the relations between ambient,
Tin and Tout. It may be however an improvement on comfort conditions as
perceived by humans inside the domes due to sweat evaporation enhanced by air
movement.
Both graphs show 25 hours, from 11am to 11am the next day. During this period
there was a cooling of ambient temperatures as the end of August was approaching.
Set 2: Optimisation of domes - comparison of improved and original domes
Monitoring took place, comparing the improved and original domes with no
obstructions except that the HOBO micrologger in the original dome at 0.5m was
mistakenly programmed to be taken at far larger time intervals. The general pattern
82
of temperature change is visible but at a lower resolution, which slightly impedes
detailed comparison.
As mentioned above, after three days of both original and improved domes being
closed except for their apex, they were monitored while being operated optimally;
meaning windows were closed during the day and opened at night for ventilation.
The adjustments on the improved dome are listed above in Monitoring description of
Set 2.
0.5m height monitoring (Fig 7.194)
At 0.5m height, the improved dome shows a few differences to the original.
1. There is an increased time lag approaching peak temperatures in the improved
dome, peak occurring in the original dome at around 18:00-19:00 in the
evening rising and falling EVENLY at i.e. a bell curve (as is visible from
limited points). The improved dome’s temperatures rise more slowly, its
curve skewed, peaking at around ten at night, or between seven and midnight.
2. Peaks in improved dome are 1 to 2°C lower than the original, at nearly 31°C
and nearly 32°C respectively. When viewed against ambient peaks, the
improved dome offers a reduction of 8.8°C in late afternoon with no auxiliary
cooling, example: August 20th, 16:20: ambient = 39.5°C, original dome =
31.8°C, improved dome = 30.7°C.
3. Minima are lower in the improved dome by between 1°C to 3.2°C, although
one early morning shows no difference.
4. As an example, at 15:40 on August 19th (a time of measurement on the less
frequent 0.5cm original dome) the original shows 31.52°C whilst the
improved dome measured 29.9°C. This makes the improved dome at 15:40
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and 0.5m height, 1.6°C cooler than the original dome and 8.4°C less than
ambient.
Dome & Improved dome (apex cover and reflective window covers)
0.5m
20
25
30
35
40
18:00 6:00 18:00 6:00 18:00 6:00 18:00
Time
Tem
pera
ture
Deg
C
AmbientDome 0.5mImproved Dome, 0.5m
Figure 7.194. New & improved dome, optimal operation measured at 50cm. Improved dome shows reduced peaks, increased time lag and mostly lower minima. (Note: original dome’s data logger recorded at far larger intervals by erroneous programming. Differences are however decipherable.) Ambient and improved dome values are hourly averages, control dome values are actual measured values.
1.5m height monitoring (Fig 7.195)
1. Similarly to the temperatures at 0.5m height, the improved dome at 1.5m
shows more staggered temperature climbs, peaking at around ten at night.
2. At the daily maxima, the improved dome measured approximately 1.5°C to
2°C lower than the original dome.
15:40, Aug 19th 16:00, Aug 20th
84
3. Ambient maxima are over 39°C at late afternoons, meaning the domes at 1.5m
are lower by around 6°C for the original dome and around 8°C for the
improved dome at the hottest times of the day.
4. Since the domes were both operated ‘optimally’ excluding auxiliary cooling -
meaning the windows were open at night until morning, the minima for both
domes are nearly the same, although the improved dome is a fraction of a
degree cooler on most mornings. This may be the result of some heat stored
in the mass of the mud plaster, having entered through the apex as radiation or
through the windows, emitted or conducted or both.
5. The moment the windows were opened represents a temperature hike in both
domes. Even though ambient and indoor temperatures were nearly the same,
they were slightly higher outdoors and affected the indoor temperature.
However within an hour or so all temperatures continued descending until the
early morning.
85
Dome & Improved dome (apex cover & reflective window covers) 1.5m.
20
25
30
35
40
18:00 6:00 18:00 6:00 18:00 6:00 18:00
Time
Tem
pera
ture
Deg
C
AmbientDome 1.5mImproved Dome, 1.5m
Figure 7.195. Improved and original domes measured at 1.5m with optimal operation: open apex (added hood on improved dome), windows of both closed from morning until night, open for cooling at night until morning - with reflective covers on improved dome. Time lag increased and peaks further decreased by up to 2°C in improved dome. All values are hourly averages. August 18th – 21st.
86
Original dome 1.5m & 0.5m (no apex cover nor reflective window covers)
20
25
30
35
40
18:00 6:00 18:00 6:00 18:00 6:00 18:00
Time
Tem
pera
ture
Deg
CAmbientDome 1.5mDome 0.5mLinear (Dome 1.5m)Linear (Dome 0.5m)
Improved dome (apex cover & reflective window covers) 1.5m & 0.5m
20
25
30
35
40
18:00 6:00 18:00 6:00 18:00 6:00 18:00
Time
Tem
pera
ture
Deg
C
AmbientImproved Dome, 1.5mImproved Dome 0.5mLinear (Improved Dome, 1.5m)Linear (Improved Dome 0.5m)
Figure 7.196a,b Original & improved domes monitored at 0.5m and 1.5m concurrently. It can be seen from the trendlines that the improved dome has overall lower temperatures, averaging between around 30 - 31°C while the original 30.7 - 31.5°C. All values are hourly averages. August 18th – 21st.
87
Set 3: Energy consumption comparison of dome & concrete
After two hours of having the AC on set to 26°C in the dome and the concrete unit,
temperatures measured with the thermo-hygrometer showed the dome’s internal air to
be 27.9°C at the height of 1.5m in the centre of the dome and at 27.6°C at 0.5cm with
relative humidity (RH) at 45%. The concrete measured 28.5°C at 1.5cm and 28.8°C
at 0.5m with RH at 41%. It was decided this is acceptable and the units were closed
up again until the end of the experiment.
After 46 hours of air conditioning set to 26°C, the following measurements were
taken by the handheld thermo-hygrometer while the conditioning units were still on
(after which they were turned off the and units promptly exited to cause minimal
internal gains by human presence).
Dome, 0.5m Ambient 27.8°C All walls 26 – 27.2°C RH 47%
Concrete, 1.5m Ambient 27.0°C
11am after 46 hours of active air conditioning units, thermostats set at 26°C in dome and concrete units, taken with thermo-hygrometer
88
15
20
25
30
35
40
45
0:00:00 12:00:00 0:00:00 12:00:00 0:00:00 12:00:00 0:00:00 12:00:00
Time
Tem
pera
ture
Deg
C
AmbientDomeConcrete
Figure 7.197 Indoor temperatures for dome and concrete units that were fully sealed while AC
units were operated for 46 hours, their thermostats set to 26°C. After being switched off the
buildings were monitored for another 24 hours. All values are hourly averages. August 24th –
27th.
(See discussion for graph with original data collected every 10 minutes)
Cooling stage, air conditioners switched on.
The initial internal temperature measured by the HOBO micrologger inside the dome
at 1.5m shows 29.9°C. From the moment the air conditioner was switched on, the
dome took just over 6 hours to stabilise its temperature (13:20 – 19:40) at around
Air conditioners switched on Air conditioners switched off
Summer: Comparison of temperatures of dome & concrete with AC operation
89
25°C, with fluctuations of less than half a degree until the air conditioner was
switched off. The temperature decline is a definite and steep one until it evens off.
Concrete’s initial temperature is shown as between 33.59°C and 34.01°C. Its
temperature also drops sharply, initially, within just one hour a 4.5°C decrease
occurred to 29.9°C. After that there is relative stability around 29°C with a gentle
decline which lasts for over 7½ hours. Only then, at 22:40, the temperature drops
below the 29 mark into 28, declining for a further one degree in 6 hours. The next
degree mark takes 22 hours to be passed, from 27.9°C to 26.7°C at 01:50, exactly 1½
days (36 hours) since the air conditioner was turned on. Finally temperatures remain
at 26°C until the air conditioner is switched off. It should be mentioned that for just
one hour, after more than 42 hours 25.95°C was the coolest the concrete unit gets.
In the concrete unit a slight rise in temperatures, although less than one degree, can be
seen on the second day seeming to follow the rise and fall in ambient temperatures,
while in the dome the temperature is undisturbed.
Thus, total eventual reduction from pre to post air-conditioned space in the dome was
5°C and in the concrete unit was 8°C, yet at a much slower pace. Eventual
temperatures reached were slightly higher in concrete by nearly a degree than in the
dome. Certainly, the massive insulation existing in the dome’s walls prevents a lot of
the outdoor heat from entering therefore its starting temperature was lower and its
overall reduction less.
90
Warming stage, after air conditioners were switched off.
The air conditioners were switched off at midday, when the sun is high and outdoor
temperatures were around 33.4°C, buildings remaining sealed.
Dome’s temperatures began reacting within 15 minutes of AC going off. From
25.17°C it took an hour to rise one degree, over 2 hours to rise another and another 6
hours to rise the third degree to cross 28°C.
After 24 hours of no AC, internal temperatures moved from 25.16 to 28.32°C. That
is a 3°C hike.
Final temperature: 28.32°C
Concrete’s temperatures began to rise within 10 minutes. After one hour 26.34°C
became 29.1°C – nearly 3°C higher. At 16:50, after exactly 5 hours, temperatures
crossed 30°C, reaching 31.12°C by the time the 24 hours were up. That is a 4.78°C
hike.
Final temperature: 30.71°C
Electricity use To keep the concrete unit cool to the set thermostat temperature of 26°C, 24.6 kWh
were expended. To keep the domes at 26°C according the AC’s thermostat setting,
13.54 kWh were used.
Thus, keeping the dome cool took half the electrical power than did the concrete.
Electrical energy measured to keep
AC set to 26°C for 2 days in:
Concrete unit (meter A) 24.6 kWh
Dome (meter B) 13.5 kWh
91
It is important to mention at this stage that the overall internal of volume of the dome
is 50m3 and of the concrete is 97.3m3 which is nearly twice as big, while the SA/V
ratios are 1.3:1 and 2:1 for the concrete and dome respectively. The effects of these
dimensions and volumes of envelope-mass on AC energy use in cooling are discussed
further in section 8.
7.2 Transition season (spring) results
7.2.1 Spring, all closed
Range Maximum Minimum
Ambient, 2m 25.9 37.6 11.7
Lightweight 1.5m 12.6 33.2 20.6
Concrete 1.5m 3.1 28.7 25.6
Dome – closed control, 1.5m 1.6 26 24.4
Dome - experiment, 1.5m 1.9 26.7 24.8
Table 7.21 Transition season (spring), closed: Maxima, minima and range during closed operation mode A. All buildings with windows and vents closed.
Spring’s ambient range is larger than summer’s as can be seen from the following two
graphs of 6 days in the same period (figs 7.21 and 7.22), where daily maxima are
between 37.5 and 26.5°C. Even with these daily fluctuations, minima reaching 12°C,
the closed dome displays thermal stability with a diurnal range of 2°C. The
lightweight building’s range increased accordingly although its maxima were 5°C
92
lower than ambient maxima, further away from the closeness observed in the higher
temperatures during summer.
When ambient maximum dropped to 28.5°C lightweight’s remained 1.5°C above,
storing some gained heat within it. Both closed domes remained within less than 2°C
diurnal range at 24-26°C during the same ambient fluctuations, slightly affected by
the temperature hike on the second day yet less so than the concrete unit. Air
temperatures inside the closed concrete building, which was a largely exposed one (as
opposed to the building monitored in summer 2008 which was largely obscured from
direct radiation by foliage), rose more and stayed higher than the domes. With a 3°C
range between 25.6 and 28.7°C closed concrete’s interior was around 2/3°C warmer
than both closed domes.
SpringAll closed
10
15
20
25
30
35
40
12:00:00 0:00:00 12:00:00 0:00:00 12:00:00 0:00:00 12:00:00
Time
Tem
pera
ture
Deg
C
AmbientLightweight 1.5mConcrete 1.5m (exposed)Dome, experiment, 1.5mDome, control, 1.5m
Figure 7.21 Spring monitoring of concrete, lightweight and both domes in closed mode.
93
SpringApex & vents open, windows
10
15
20
25
30
35
40
12:00 0:00 12:00 0:00 12:00 0:00 12:00
Time
Tem
p. D
eg C
AmbientLightweightConcrete (exposed)Dome, exp. 1.5mDome, control, 1.5m
Apex, vents & all 4 windows exp.dome open/ S&N windows of concrete & lightweight open
Apex & vents of exp.dome open / S&N windows of concrete & lightweight open
Figure 7.22 Temperatures measured in concrete and lightweight buildings having north and south windows open while the experimental dome’s apex and vents were opened. Subsequently the dome’s 4 windows were also opened while concrete and lightweight’s remained open. (All hourly averages)
7.2.2 Apex and vents open in dome, N&S windows open in concrete and
lightweight.
In fig 7.21 above are displayed the temperatures of the same period as fig7.22 with
open windows. The difference between open and shut windows in the lightweight
building is small. This indicates that the thermal ‘work’ done by the envelope is
small too. Once the apex and vents of the experiment dome were opened, heat was
lost so that, instead of a 2° range it became a 4° range. The concrete dipped at the
same places following ambient flux nearly 2° above the dome.
94
Range Maximum Minimum
Ambient, 2m 12.8 26.5 13.7
Lightweight 1.5m 7.7 27.1 19.4
Concrete 1.5m 5.4 19.8 25.2
Dome - experiment, 1.5m 3.1 24.4 21.3
Table 7.22 Transition season (spring), apex & vents open in dome, north & south windows open
in concrete and lightweight buildings.
7.2.3 Four windows, apex and vents open in dome.
Once all of the windows were opened, the dome’s temperatures dropped to less than
3°C above ambient minimum which was 12.5°C, the dome’s diurnal range being
nearly 11°C. Concrete, having only 2 windows, remained with them open and a
range of 5-6°C. This may be related to the smaller number of windows and therefore
less heat being carried away. It is also likely to be a longer thermal ‘memory’ since
the concrete is 22cm thick and its mass acts as heat storage, whereas the insulation in
the dome is so great that less of the heat makes its way into the dome through the
straw walls - at least not at the springtime, when the previous weather and ground
temperatures are relatively low.
Range Maximum Minimum
Ambient, 2m 15.5 28 12.5
Lightweight 1.5m 7.7 27.1 19.4
Concrete 1.5m 5.4 19.8 25.2
Dome - experiment, 1.5m 10.8 26 15.2
Table 7.23 Transition season (spring), apex & vents & 4 windows open in dome, north & south
windows open in concrete and lightweight buildings.
95
7.3 Winter results
7.3.1 Closed mode
In the closed mode the domes were more stable in temperature with a range of 1°C or
less while concrete fluctuated diurnally a little over 2°C following ambient
temperatures. However the dome’s temperatures were consistently warmer at 20°C
and more comfortable than the cool 17°C of concrete.
Meteorological data for the month of February recorded by Yotvata meteorological
station for 3 days are missing. Excluding the days between the 3rd and 5th inclusive,
making sure that 24 hours from 00:00 to 00:00 were not counted, the monthly average
temperature was calculated and used in the adaptive model to find optimum comfort
temperature. Average was found to be 15.62°C. Within the adaptive approach
comfort for 90% of people will be between 17.6°C and 27.6°C and for 80% between
15.6°C and 29.6°C. Accordingly then, the concrete is just under calculated comfort
levels for 90% of people. If we include the radiative effect of the walls, this may very
well feel uncomfortable cool.
96
Winter, all closed
5
10
15
20
25
30
12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00
Time
Tem
pera
ture
Deg
C
AmbientLightweightConcreteExperiment DomeControl Dome
Exp. dome accidental open door
Figure 7.31 Winter: Concrete reacts more to ambient changes, domes are more stable and
warmer at 20°C.
The door of the experimental dome remained open for an hour or two not by plan. It
is clear from the graph above that this caused a loss of internal warmth, nearly 2°C
until the door was shut again. This decrease was at a time when ambient is increasing
– 12:30pm and previous days show the dome increasing slightly too around this time.
97
7.3.2 Comparison of shaded and less shaded concrete units
Fortunately, the possibility arose to compare a shaded with a far less shaded concrete
building. (Initially only the shaded one was available with somewhat surprisingly
low summer temperatures.) The shaded building has thick vegetation in front of the
eastern and southern facades as well as – most importantly on the roof, in the form of
constructed date-palm shading and furniture used as a gathering place in warmer
weather. While the other unit is also shaded, the roof is mostly clear with a tree
partially covering it and extensive vegetation to the north (less significant) and east
facades. (See images 5.12 & 5.14) Fig 7.32 show temperatures for the shaded
building are over 3°C cooler even in mid winter, February, when temperatures are
relatively low. This further illustrates the effect of direct solar radiation on the
envelope and how the concrete buildings most probably benefit in their comparison to
the domes, which are as yet completely unshaded. This should be taken into
consideration especially when viewing the first set of summer comparisons.
98
Winter, shaded concrete & exposed concrete,1.5m, window operation
6
8
10
12
14
16
18
20
22
24
26
12:00:00 0:00:00 12:00:00 0:00:00 12:00:00 0:00:00
Time
Tem
pera
ture
Deg
C Ambient
Concrete, Exposed
Concrete, Shaded
Figure 7.32 Comparison of shaded (by thick foliage and trees over roof) and less shaded
concrete buildings. The general difference is 3°C higher when less shaded. All are hourly
averages. February 11th-13th.
Apart from the higher temperatures of the more exposed concrete building, it displays
a slightly quicker ascent in temperatures as its envelope is heated by the direct solar
radiation and remains at its peak for longer. The exposed building begins to drop in
internal air temperature at 01:40, nearly 8 hours after the ambient dipped below its
indoor temperature of 23.8°C at 1800. That was after remaining at the exact same
temperature - 20.2°C - for 13 hours. Whereas the extensively shaded unit, having the
exact same range, took nearly 10 hours to reach it’s peak only to remain there for 4
hours at 17.5°C before beginning to cool. That decent was 4 hours after ambient
dipped below its internal temperatures and 7 hours after ambient’s peak. When
cooling, the difference between the two is less pronounced although the shaded unit
reacts sooner to the ambient drop, as mentioned above 4 hours after the crossover of
99
ambient and indoor temperatures and nearly 3 hours before the exposed unit. In a
manner of speaking one could say the thermal time constant (TTC) or thermal lag is
slightly larger in the shaded building because its maxima and minima are slightly
after the exposed unit’s. Although the speed of its reaction to ambient temperatures is
the major difference between the two, the other is of course, the overall higher
temperatures.
7.3.3 Optimal window operation
Winter, windows operated
5
10
15
20
25
30
12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00
Time
Tem
pera
ture
Deg
C
AmbientLightweight 1.5mConcrete, unshaded 1.5mDome exp. 0.5mDome exp. 1.5mDome control 1.5m
Figure 7.33 Comparison of dome, lightweight and less shaded concrete buildings with windows
operated, open during the pleasant daytime conditions and closed at night to preserve warmth
indoors. Close up below. All are hourly averages. February 11th-15th.
100
Winter, windows operated
17
18
19
20
21
22
23
12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00
Time
Tem
pera
ture
Deg
C
AmbientLightweight 1.5mConcrete, unshaded 1.5Dome exp. 0.5mDome exp. 1.5mDome control 1.5m
Figure 7.34 Close up of dome, lightweight and less shaded concrete buildings with windows
operated, open during the pleasant winter daytime conditions and closed at night to preserve
warmth indoors. All are hourly averages. February 11th-15th.
The two figures above show temperatures in the Arava winter while all the buildings
(except the control dome) were operated by having all their windows open during the
day which is very agreeable weather, and shut at night to preserve warmth during
chilly nights which are sometimes below 5°C. The dome’s apex and vents remained
sealed. As usual, the lightweight building closely followed ambient flux, retaining
some heat gained during the day with minima around 6°C above ambient minima and
a time lag of around 3 hours.
The concrete was the more exposed one in this monitoring session. It is described in
detail in the section above 5.2.1.1 as it was monitored concurrently and the data
extracted for comparing shaded and less shaded units.
101
In the experimental dome, only once did the lower position exceed the 1.5m
temperature, which may be the result of a door opening since it was daytime. (There
were mostly no disruptions yet on occasion the domes needed to be entered by a staff
member of the Bustan neighbourhood which is in constant evolution. If this did
happen it was made sure that the door was opened and closed promptly.) Otherwise,
0.5m was mostly just cooler than 1.5m by half a degree or less which is not within the
resolution of the HOBO microloggers of the type used in this experiment. The dome
displays a time lag of 3-5 hours, yet the range is not greater than in the same season in
closed mode. This will probably be due to the storage of the warmer air within the
dome and the 5-7cm of mud plaster mass of interior walls.
102
7.4 Temperature monitoring of irrigated garden soil
Irrigated garden soil already exists in the Bustan neighbourhood where herbs and
other edible plants grow. To evaluate any potential of this soil to act as a heat sink
for prepping incoming air into the domes, it was monitored at 10, 30 and 50cm below
ground level.
Summer, irrigated ground temperatures
15
20
25
30
35
40
45
50
12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00
Time
Tem
pera
ture
Deg
C
Ambient (Yotvata)
Surface, dry (Yotvata)
10cm below ground surface
30cm below ground surface
50cm below ground surface
Figure 7.41 Temperatures of irrigated garden soil monitored in the Bustan neighbourhood, ambient and ground surface temperatures from Yotvata met. station.
103
Summer, irrigated & dry ground temperatures at -10cm
20
25
30
35
40
45
12:00 12:00 12:00 12:00 12:00
Time
Tem
pera
ture
Deg
CAmbient (Yotvata)
-10cm, dry loess, Yotvata
-10cm, irrigated, Lotan
Figure 7.42 Temperatures at 10cm below ground level of irrigated garden soil monitored in the Bustan neighbourhood, dry loess measured at Yotvata met. station and ambient.
Summer, irrigated & dry ground temperatures at -30cm
20
25
30
35
40
45
12:00 12:00 12:00 12:00 12:00
Time & Date
Tem
pera
ture
Deg
C
Ambient
-30cm dry loess, Yotvata
-30cm irrigated, Lotan
Figure 7.43 Temperatures at 30cm below ground level of irrigated garden soil monitored in the Bustan neighbourhood, dry loess measured at Yotvata met. station and ambient.
104
Summer, irrigated & dry ground temperatures at -50cm
20
25
30
35
40
45
12:00 12:00 12:00 12:00 12:00
Time
Tem
pera
ture
Deg
C
Ambient (Yotvata)
-50cm, dry loess, Yotvata
-50cm, irrigated, Lotan
Figure 7.44 Temperatures at 50cm below ground level of irrigated garden soil monitored in the Bustan neighbourhood, dry loess measured at Yotvata met. station and ambient. The graphs above show that the irrigated soil of the Bustan Neighbourhood’s herb
gardens is consistently at lower temperatures in the heat of mid August than dry local
loess as measured by Arava R&D in Yotvata.
At -10cm, irrigated soil is on average 2.5°C lower than dry loess. Differences in
these measurements range between 0.67°C and 4°C at the maxima and between 3°C
and 4.53°C at minima. At maximum temperatures, dry loess soil is nearly the same
as ambient highs remaining within half a degree above or below, while wet garden
soil is between 0.68°C and 3.67°C below ambient.
At 30cm below surface level, irrigated garden soil again was consistently cooler than
dry loess by an average of 2°C at peaks and nearly 3°C at the lowest temperatures.
105
Both the curves are dampened with increased depth, staying within a 2 degree range
for irrigated soil and less than a degree range for dry loess at around 35°C.
Interestingly, while the local loess has a time lag of around 12 hours, irrigated soil’s
time lag is shorter, 4 to 5 hours. This may be due to the increased conductivity of the
wet soil, probably also the reason it is able to lose heat more effectively than the dry
soil.
The temperatures at 50cm depth were also lower with irrigated soil, remaining stable
for a day at 32.3°C (sensor stopped working after that but displayed same pattern as
dry loess) while dry loess was at 34.8°C, moving down less than 0.2°C over 4 days.
avg maxima peak time avg minima peak time
5am37.9 25.31600pm
Ambient
Soil type avg maxima peak time avg minima peak time time lag avg maxima peak time avg minima peak time time lag avg maxima avg minima time lagDry Loess 38.2 19-20pm 33.3 8-9am 3-4 hours 35.6 3-7am 35 15-1700pm 12 hours noneIrrigated 35.9 1730-20pm 29.35 8-9.30am 2-4 hours 33.7 10am-1600pm 32.34 10am-14.30pm 4-5 hours none
34.732.3
Depth-30cm-10cm -50cm
Table 7.44 Summary of ground temperature patterns for irrigated garden soil on Bustan neighbourhood and dry local loess measured in Yotvata.
106
8 Discussion
Significant findings
8.1 Summer
8.1.1 Electricity use comparison of air conditioned dome and concrete units:
reduction of cooling load
Even though a growing number of people realise the fuel-consumption problems and
health issues related to air conditioning use and strive to be comfortable in passive
buildings, this is not the majority. Nor is it what is practiced in most shops, offices,
hotels and indeed most residential buildings these days in ‘developed’ hot arid
regions. Therefore, until electrical prices rise dramatically again or until we run out
of fuel, savings due to AC efficiency will be significant on regional levels.
With relevance to fuel usage efficiency in mechanical space cooling, the greatest
source of climate change gases of any single technology76, findings of great interest
occurred in the experiment comparing electrical use by AC units and thermal
behaviour in the concrete and dome buildings.
Two buildings were closed completely, as far as their building types allowed, during
which time an AC unit in each was operating, set to 26°C while electrical expenditure
was measured by digital electrical meters. After two days the AC units were
switched off and the buildings were left closed, their reactions monitored.
76 Roaf et al, 2003, p.8.
107
10
15
20
25
30
35
40
45
6:00 AM 6:00 PM 6:00 AM 6:00 PM 6:00 AM 6:00 PM 6:00 AM 6:00 PM
Time
Tem
pera
ture
Deg
C
AmbientDomeConcrete
Figure 8.11 Comparison of temperature fluctuations in concrete and dome units with AC
operation. Both were sealed for 2 days while the AC units were on then left sealed for a further
day with AC units off. Values taken every 10 minutes. Hourly averages are displayed in the
summer results section & fig. 7.197.
As can be seen from the graph, the starting point of the dome’s interior temperatures
is around 4°C lower than those of the concrete unit, this was after both buildings were
left open until all wall temperatures equalized, to 33°C – ensuring a fair comparison.
The measurements were taken at 1.5m height. Within 6 hours of AC operation the
dome stabilised its temperature at 25°C where it remained, with fluctuations of less
than half a degree, until the AC was switched off. This reflects the thermal insulation
at work, even with a gap under the door and air infiltration, the large thickness of
insulation manages to keep internal temperatures stable relatively quickly and to
remain there. It is possible that the dome’s geometry and height provided the space
AC on
AC off
Summer: Comparison of temperatures of dome & concrete with AC operation
108
for hotter air to rise, allowing the measured stratum to remain at a cooler and stable
level of 25°C, but this has not been substantiated by measurements at varying heights
during AC operation.
Whereas the concrete unit’s temperatures dipped immediately in reaction to the AC
operation from 34°C to 29°C within an hour, it took another 6 hours for the 1.5m
position to cool by a further 2°C. This unit is the more exposed one (not the highly
shaded unit monitored earlier in the experiment), albeit even this unit is shaded, the
pattern and proportions of shading are shown in figure 5.12-4 in the buildings survey
chapter. The time taken for the temperatures inside to decrease is probably an
indication of stored heat in the concrete walls and roof, being conducted inside the
building and countering the effects of the cooled air from the AC. By 10am the next
day temperatures began to rise half a degree following ambient increases. It seems
there is an approximate 4 hour time lag following ambient minima and maxima even
with the AC on. As mentioned above, the system of prefabricated concrete walls of
this type incorporates polystyrene insulation sheets which were placed on un-
solidified concrete upon which more concrete was poured to finish the walls. This
system is reported to allow insulation sheets to float around and move in the liquid
concrete, resulting in some areas having double insulation and in others none. The
fact that temperatures rise again after a day of an operating AC shows that heat
manages to enter through the envelope, most likely through the thermal bridges of un-
insulated concrete which conduct heat to the interior (or exterior depending on
temperature gradient). This is doubtless intensified by direct solar radiation hitting
the walls and, mostly, the roof. The roof is insulated, however also has a layer of
gravel above increasing thermal mass, as well as having the parapet which will act as
thermal storage and probably conducting heat to thermal bridging.
109
The concrete unit subsequently continues decreasing in temperature as it begins to
approach the dome’s temperatures. Within 2 days of AC operation both set to 26°C
the concrete reached 26.34°C, more than a degree higher than the dome’s 25.17°C. It
would be interesting to observe the behaviour of the concrete unit during the course
of a further few days and see if temperatures continue to decrease with its mass acting
as coolth storage. This was not possible in the timeframe of this experiment. It may
be safe to assume that the dome would remain stable as it did since a few hours after
AC operation.
Electrical consumption by AC
The thermal behaviour of these two envelope types is also articulated by the
electricity consumption of the AC units as measured by two electricity metres. The
concrete unit should have a number of advantages over the dome in minimising heat
absorption and thereby increasing electricity efficiency with AC use, due to the
following physical attributes: a lower surface area to volume ratio (SA:V) due to the
larger, curved roof in the dome, (dome SA:V = 2:1, concrete SA:V = 1.4:1),
concrete’s shading on part of the roof and the whole of the east wall by vegetation
thereby receiving no direct radiation and a neighbouring concrete unit on its west side
significantly lowering direct solar radiation and the sol-air temperature during late
afternoon on most of the western façade. Yet the dome used just over half of the
electricity consumed in the concrete unit.
The clearest advantage of the dome is its thick insulation layer – 55cm of tightly
packed straw bale. Another very possible advantage is a more easily-controlled,
thinner interior thermal mass layer – 5-10cm of earth plaster representing less thermal
storage and ‘work’ for the AC. Although the exterior plaster layer is also thinner than
the 22cm of concrete, the external temperatures are similar to those of the concrete, so
110
while storage may be usually significant in altering internal conditions, it seems that
most of the mitigation in the dome is due to the insulation. Due to the massive
insulation, the normal advantages of heat-loss through the envelope of the dome’s
geometry in hot arid weather - known to enhance convective and radiative cooling
both at night and with increased wind-speed during the day, is not so clear. The
advantages are well known and documented, described in detail in section 2.5, yet
increase in significance as the insulation is less significant. Once the insulation is so
effective, the heat loss through the envelope affects internal thermal conditions far
less and could make an interesting possible further study for quantitative values.
What does however seem to be of benefit due to the geometry, is the possibility of
stratification of internal air, warmer air rising to the dome-space. Once the AC’s
thermostat is at a level which is below warmer air that has risen, the cooler air will
demand less work of the AC, minimising its use.
Volume differences of concrete and dome units
Another point that is important to consider is the volume of the dome which is half
that of the concrete unit. This is likely to be significant to a point, demanding higher
energy expenditure to cool the concrete volume initially. Yet, when viewing the
temperature patterns along with the electrical energy values, it seems that a clear
‘battle’ of heat movement is occurring between ambient temperatures and the AC unit
through the concrete envelope. It is fair to say that the smaller volume of the dome
will lessen electricity used, but the constant incoming heat as indicated by rising
temperatures inside the concrete unit some hours after ambient rises, may be the
reason for the great difference and continued electricity use during the two days of
operation. Once the space is cooled, which is the initial boost needed and electricity
used, the job of the AC is simply to maintain the temperature set on the thermostat.
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The more effective the insulation, the less the AC has to work to maintain internal
conditions. It can also be observed in the temperature graph that the initial boost
seems to be quite similar as the temperatures of both units dip and in fact the larger
faster dip occurs in the concrete unit, with a 4.5°C decrease within just one hour,
whereas dome’s drop is a mere 3.17°C in the first hour, thus even initial cooling
seems to be as efficient if not more in the concrete unit. Since the dome’s
temperatures stabilised after just a few hours of operation and remained there until the
end of the experiment, it shows the effective insulation at work, thereby indicating
less work necessitated by the AC. In a follow-up experiment it would be of great
interest to compare similar volumes with different materials to quantitatively
determine the separate effects of volume sizes.
Another heat-burden is the sheer volume of building mass enclosing the concrete unit.
This added mass that needs initial cooling surely caused increases in electricity use,
and even more clearly as displayed by the small rises during the day indicating heat
leakage and added burden on the AC. Maybe with more efficient insulation this
diurnal rise and fall with the ambient would be largely eliminated, however still the
sheer mass would take a long while to cool when the AC is turned on in the first days.
Finally, evidence that the insulation is the energy-saving element of significance may
be concluded by the temperature-rise differences after the ACs were shut down. The
dome, having a smaller volume and a larger proportion of external surface would
normally be expected to heat up more quickly than the larger concrete unit with a
comparatively smaller surface area. Yet after turning off the ACs and the buildings
remaining sealed, it was indeed the concrete that heated up at a faster rate and to a
higher temperature; the dome heated up by 3°C within 9 hours reaching a total
increase of 3.15°C after 24 hours. Concrete was hotter by 3°C within one hour
reaching an increase of 4.78°C after 24 hours. This displays a less effective
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performance in mitigation of ambient conditions by the envelope of the concrete unit,
despite its other geometrical advantages.
Savings of half of the electricity consumption of building operation, considering the
Arava climate, the large hospitality industry of this area where ACs remain on even in
the absence of human presence, and human behaviour which is so reliant and quick to
turn on these machines, proposes immense easing of today’s and future energy
problems. Furthermore, for each unit of energy conserved, or more precisely not
expended, resources are saved and the annual operating costs associated with
producing that energy unit will be reduced or eliminated77.
It is important to note though, that this comparison between the concrete and dome
involves more than one changing factor, the materials and the shapes and size are
different. A comparison involving identical geometry and different materials, or the
opposite, would give results isolating the effect of these properties. However in this
study existing systems in place in the Arava were compared to each other as systems.
8.1.2 Internal conditions in domes
The thermal treatment of the exterior envelope has an especially pronounced effect on
cooling and heating loads of buildings which are envelope-dominated - that is the
larger proportion of building structure consists of the external envelope. Possibly in
less envelope-dominated structures, like a large hotel with many interior walls,
energy use in cooling and heating will be affected less by the envelope’s thermal
properties, or in particular areas of the building which are closer to the exterior.
Certainly with the increase of surface area to volume ratio thermal treatment of the
envelope is more significant to internal conditions. Therefore the smaller the
77 Al-Homoud, D., Performance characteristics and practical applications of common building thermal insulation materials. Building and Environment, 2005. 40(3): p. 353.
113
structure, the more significant its envelope‘s thermal properties. As discussed in
section 2.3.4.1, a larger SA:V ratio serves to decrease thermal stability since there is
more surface for thermal exchange to take place. In the lightweight building the
ratios alone are more conducive to thermal stability than the other two buildings –
SA:V = 0.98:1. Yet its lack of thermal capacity means that thermal stability is not
attained.
8.1.3 Optimising domes with built-in & added features
When the apex of the dome was opened in the original dome, small temperature
differences were achieved at the lower stratified air levels, yet the uncovered apex
probably heated the air above due to incoming radiation. However, when the
improved dome was monitored, with the covered apex and reflective window covers,
a further 2°C reduction was achieved. Reflective covers, with bubble wrap on
cardboard and reflective metallic layer seemed to be of significance. This is not
surprising considering the windows are not due north, south, east and west, but are
positioned at north-east, north-west, south-east and south-west. This makes them
constantly exposed to incoming solar radiation, be it before or after noon, unless the
sun is very high up. The bright desert sun and light-coloured sandy loess adds to
reflected incoming radiation through the windows. It is thus advisable to position
windows north and south in order to better control both ventilation and radiation entry
to the building. It is likely that the increased thermal resistance of the covered
windows contributed to less convective gain and lower indoor temperatures as well.
Such simple window fixtures could be produced to fix onto and remove from
windows, thereby further reducing indoor temperatures and cooling load.
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In series C, when Tin and Tout are measured, albeit before the improvements were
made to the domes, there seem to be indications of the heating and cooling processes
and therefore of how to operate the done to gain summer cooling passively as far as
possible.
Summer: Experimental dome, apex & vents (T-out, T-in) open& window operation
20
25
30
35
40
45
50
6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00 6:00 12:00
Time
Tem
p D
eg C
Ambient
Tin
Tout
Ground
dome interior gaining heat: warm incoming air (Tin) loses
heat to interior space and leaves cooler (Tout)
dome interior losing heat: cooler incoming air (Tin) picks up heat
and leaves warmer (Tout)
Figure 8.2 Experimental dome, vents and apex open and operated windows; closed during the hot day, open during cooler night. No fan operated. All values are hourly averages. August 29th – 31st.
As the warm incoming air (Tin) enters during the warmer daytime hours, it loses heat
to interior space and leaves cooler (Tout). The opposite occurs in the cooler night and
morning hours; cooler incoming air (Tin) leaves warmer (Tout) therefore absorbing
heat and cooling the dome’s interior. This might indicate that, in order to still lose
heat in the daytime yet minimise gain, vents should be closed while the apex is open.
In the improved dome (monitored the year after) the covered apex allowed hot air to
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escape without gains due to direct solar radiation. Then night time cooling via vents
may be achieved since the ambient is cooler than interior even in the improved domes
by around 4°C.
The lowest temperatures achieved inside the improved domes with optimal operation
including reflective window covers and window operation were 30-31°C in the
hottest hours of the day, that is a reduction from ambient by 9-10°C.
Taking the average of August 2009, 31.68°C, and deriving the adaptive thermal
comfort from it (Ta,out x 0.31 + 17.8) we get 27.5°C. Thus, within 90% acceptability
lie 22.5°C and 32.5°C. Within 80% acceptability are 20.5°C and 35.5°C. The domes
with all current improvements just make it into the 90% acceptability range. Yet, to
this may be added the evaporative cooling effect of turning on a fan, as well as an
evaporative cooler.
Like most passive cooling or heating techniques, each of these alone will probably
not suffice to produce comfortable conditions to most modern western people. Yet in
combination, cooling loads can be greatly reduced and passively conditions are
greatly improved. This is most pronounced with the electrical usage in the dome
being just over half that of the concrete with both ACs set to 26°C.
8.1.4 Surface temperatures comparison of three building types
When comparing surface temperatures of the three building types, it is immediately
clear that the lightweight offers negligible thermal attenuation. The lines are nearly
the same and that means little if any heat is stopped from entering. The hall of the
dome, being a flat surface, has its exterior temperatures rising well above the curved
dome walls, on the east reaching by 13:00 nearly 45°C and 39.4°C respectively. Yet
116
impressively, the interior surface is still the same as the curved interior at 34.2°C.
This allows us to see the thermal attenuation of the straw bale and mud wall system
excluding the effect of a reduced angle of incidence known to be beneficial to domes
and reducing their radiative absorption up to 35%78. In the hall’s eastern wall
differences between internal and external wall surfaces are 11°C, this is even higher
on the western side, with temperatures over 50°C. Concrete also has the effect of
blocking a lot of the heat entering from one side to the other, at least concurrently. Its
internal and external difference is 10°C on the east. Measurements on the west were
not possible at that time due to availability, but will surely be higher on the external
surface due to the combined effect of high afternoon air temperatures and insolation
pushing heat through and intensifying the thermal increase (see sol-air section 2.3.3
for more detailed explanation). Thus a large massive wall is effective in dampening
the curve and delaying it, as is well known to be the effect of thermal mass, yet it is
the constant absorption and release of heat that is its weakness vis-à-vis thermal
performance, of special note when auxiliary cooling is used.
8.1.5 Irrigated soil temperatures
Decreasing albedo and increasing conductivity of soil when irrigated are opposing
influences with regard to thermal gain. Irrigated soil temperatures were monitored to
decipher which of the effects is dominant. It was found that the irrigated soil was
consistently cooler for depths of 10, 30 and 50cm below the ground (figures 7.41 –
7.44). While the temperatures were cooler than dry local loess, they are not much
cooler than the coolest passively cooled dome. It was a matter of interest to discover
78 Gomez-Munoz, V., M. Porta-Gándara, and C. Heard, Solar performance of hemispherical vault roofs. Building and Environment, 2003. 38(12): p. 1431-1438.
117
if irrigated soil, which already exists in the Bustan neighbourhood as herb and
vegetable gardens, could serve as a heat sink for warmer air before entering the
domes. It seems that allowing this slightly warmer air into the dome will counter the
insulation effects of the dome, which block daytime hot air from entering while
allowing hotter air to rise and exit through the apex. However, the idea of cooler wet
soil might be incorporated into other passive cooling strategies, such as an earth-
bermed section of a building, maybe with a layer of gravel allowing easier and faster
escape of heat, or an air-to-ground heat exchanger for cooling incoming air.
8.2 Winter
8.2.1 Effect of dome’s insulation to mass ratio and window positioning
Winter temperatures inside the concrete were cooler than the dome’s, in fact just
outside the calculated adaptive comfort conditions (average for February 2009
15.6°C, 90% acceptability 17.6 – 27.6°C).
The dome indicates, by having its door open and decreasing in warmth, that heat is
stored in the mass of the interior earth plaster – which at less than 10cm is small
relative to the 22cm of concrete. This means that infiltration of air manages to carry
away with it heat from the interior walls. A larger, denser mass with much higher
thermal capacity exemplified here by the concrete unit, takes longer to lose and gain
heat, therefore allows a different type of control over internal conditions. It follows
then that the appropriate amount and type of thermal mass is crucial for comfort
conditions depending on the climate and way a building is to be used.
The warmer temperatures achieved in the dome are despite thermal stratification due
to the curved roof. Windows positioned due south would serve to effectively allow
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direct solar radiation to enter and be stored in the mud walls and floor. This indicates
that the heating load for winter can also be greatly reduced inside the dome by the
large insulation values, and since the dome shape works against warm temperatures
below, it is a result of the insulation, not the dome shape.
8.2.2 Comparison of exposed and largely shaded concrete units.
The more shaded building is consistently 3°C cooler than the more exposed concrete
unit, which itself is not completely exposed as can be seen in the diagram in the
building survey section fig 5.13. This monitoring session took place in February,
winter in the Arava. This reinforces the vulnerability of internal conditions with mass
without adequate insulation, especially if there is a large mass, such as this 22cm
concrete slab. The difference is sharper in direct solar radiation and if the more
exposed building was not 2/3 blocked from radiation by a neighbouring building, the
difference would doubtless be even greater. This reduces user’s control over interior
conditions, be it by taking passive cooling measures or by operating mechanical
space-cooling or heating, since the walls’ ‘thermal memory’ is long.
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9 Future research
9.1 Domes
As mentioned above, it may be interesting to keep the AC on for longer in the
concrete unit to observe the indoor temperatures and see if they continue to decline as
they did slowly in the experiment that took place to compare electricity usage of
dome and concrete. Maybe absorption of ‘coolth’ will show some benefit to the
concrete structure, although apparent from the evidence thus far, unless there is
adequate insulation, mass will be absorbing direct solar radiation daily which will
serve to raise the envelope temperature. Winter space-heating may also serve to
inform the differences in behaviour of the two typologies. Another tool that can be
very informative and alas was not carried out in this research is thermal imaging.
Thermal imaging, to show heat-leakage in or out of the envelope, can help to
recognise weak spots in the domes and offer a visual comparison to the thermal
performance of the concrete envelope.
Air infiltration levels could be assessed with their effects on indoor conditions since
insulation becomes less effective with reduction in airtightness.
Monitoring temperatures within the walls to show heat flux at various points through
mud and bale can give a more detailed understanding of thermal machinations
through the dome’s envelope.
It could also be of interest to have the domes painted white and observe any thermal
effects. Since the insulation is so large, it is doubtful the increased albedo will have a
great effect, but even a small effect could contribute to comfort.
120
9.2 Straw bale building
Another building is nearly complete in Lotan, again a straw bale building with mud
plaster, yet it is rectangular, with very high walls, the largest straw bale building in
Israel to date. If monitored and compared to the straw bale domes, maybe additional
insight could be gained into the behaviour of these materials versus the behaviour of
the dome building forms.
9.3 Insulation thickness variations
Smaller bales - if not too expensive to produce (sometimes a simple adjustment to the
baling machine requested of the farmers is all that is needed79), can result in more
buildings for less material. The law of diminishing returns states that as more
resistance is achieved by a material, since the conductivity is inversely proportional to
resistance, the effectiveness is reduced. Therefore the increasing resistance that is
offered by a material does not proportionally reduce energy use or temperature
differences. It may be that 55cm of bale has already passed an effective insulation
value in relation to the material used, and reducing the thickness may offer additional
energy savings.
9.4 Recommendations for future domes
• Orienting windows north and south will serve to exert more control over
incoming direct solar radiation. In the same vein, east and west facing
windows should either not exist or have very effective coverings to block
summer radiation.
79 Mackwood, et al, 2005, p.29.
121
• All windows should have reflective covers available to block daytime
radiative and convective heat transfer into the building, or to make sure that
external shutters are adequately insulated to prevent convective transfer.
• Covering the apex works in alleviating incoming heat and should be applied to
all domes.
9.5 Implications for building in the Arava
From the results of monitoring three building types; lightweight insulated, heavy
mass and combined highly insulated with mass, it is clear a suitable combination of
mass and insulation contributes to thermal stability, passive control and internal
comfort conditions. The lightweight building consisting of little insulation alone,
while shading from direct radiation and defining a space, does little else to contribute
to thermal comfort. Temperatures get as high as the ambient maxima if not higher
and do not cool to summer minima, thereby internal conditions are highly
uncomfortable. It is shown in this research that a large amount of thermal mass in a
building envelope, especially when the envelope is the dominating structure, can be a
hindrance to thermal comfort if not coupled with adequate insulation. (This may
change with some metres of mass like a cave, but not on the building scale). While
temperatures are certainly stabilised by mass, they will absorb direct solar radiation,
eventually emitting sensible heat into building interiors creating uncomfortable
temperatures. Moreover, when attempted to be cooled by auxiliary cooling such as
AC machines, mass-heavy envelopes will challenge this effect by continually re-
emitting into and heating the interiors, further exacerbated by the increase in
temperature gradient caused by the operating AC. This cycle will continue as long as
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direct solar radiation falls upon a mass-heavy surface with thermal bridges. To
alleviate this, a significant and continuous layer of insulation should be applied.
Insulation coupled with mass is shown from the results obtained in this study, even in
envelopes with a larger surface area to volume ratio, to use far less electrical energy
in maintaining cool temperatures.
The simple act of opening the envelope at the top of a room can allow the escape of
warm air. When buildings are single storey or top storey, this may be incorporated
into their design which can add to passively cooling interior spaces. They should
however be covered to protect from solar gain.
When care and much documented, available knowledge of climatologically aware
building is applied, passively comfortable buildings can be achieved and vast
improvements in energy efficiency may be had. The Arava, an example of an
extreme desert climate of which there are many worldwide, is a region where, with
intelligent construction and operation of buildings, the energy efficiency
improvements are potentially large and can have a significant effect on current public
health as well as the health of the following generations.
123
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