STUDIES IN THE RESEARCH PROFILE BUILT ENVIRONMENT

DOCTORAL THESIS NO. 3

Experimental study of an intermittent ventilation system

in high occupancy spaces

Alan Kabanshi

FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT

Department of Bui lding, Energy and Environmental Engineering

STUDIES IN THE RESEARCH PROFILE BUILT ENVIRONMENT

DOCTORAL THESIS NO. 3

Experimental study of an intermittent ventilation system

in high occupancy spaces

Alan Kabanshi

Gävle University Press

© Alan Kabanshi 2017

Gävle University PressISBN 978-91-88145-11-6ISBN 978-91-88145-12-3 (pdf)urn:nbn:se:hig:diva-23754

Distribution:University of GävleFaculty of Engineering and Sustainable DevelopmentSE-801 76 Gävle, Sweden+46 26 64 85 00www.hig.se

Print: Ineko AB, Kållered 2017 Tryckt på FSC-märkt papper.

“…a rational calculation of heating and air-conditioning systems

must begin with the conditions for comfort…”

PROF. P. O. FANGER (1934 – 2006)

6

Abstract

Spaces with high occupancy density like classrooms are challenging to ven-

tilate and require a lot of energy to maintain comfort. Usually, a compromise

is made between low energy use and good Indoor Environmental Quality

(IEQ), of which poor IEQ has consequences for occupants’ health, produc-

tivity and comfort. Alternative strategies that incorporate elevated air speeds

can reduce cooling energy demand and provide occupant’s comfort and

productivity at higher operative temperatures. A ventilation strategy, Inter-

mittent Air Jet Strategy (IAJS), which optimizes controlled intermittent air-

flow and creates non-uniform airflow and non-isothermal conditions, critical

for sedentary operations at elevated temperatures, is proposed herein.

The primary aim of the work was to investigate the potential of IAJS as a

ventilation system in high occupancy spaces. Ventilation parameters such as

air distribution, thermal comfort and indoor air quality were evaluated and

the system was compared with a traditional system, specifically, mixing ven-

tilation (MV). A 3-part research process was used: (1) Technical (objective)

evalua-tion of IAJS in-comparison to MV and displacement ventilation (DV)

systems. (2) An occupant response study to IAJS. (3) Estimation of the cool-

ing effect under IAJS and its implications on energy use. All studies were

conducted in controlled chambers.

The results show that while MV and DV creates steady airflow condi-

tions, IAJS has cyclic airflow profiles which results in a sinusoidal tempera-

ture profile around occupants. Air distribution capability of IAJS is similar to

MV, both having a generic local air quality index in the occupied zone.

On the other hand, the systems overall air change rate is higher than a MV.

Thermal comfort results suggest that IAJS generates comfortable thermal

climate at higher operative temperatures compared to MV. Occupant re-

sponses to IAJS show an improved thermal sensation, air quality perception

and acceptability of indoor environment at higher temperatures as compared

to MV. A comparative study to estimate the cooling effect of IAJS shows that

upper HVAC setpoint can be increased up to 2.3 – 4.5 oC for a neutral thermal

sensation compared to a MV. This implies a substantial energy saving poten-

tial on the ventilation system. In general, IAJS has a potential to be used as

an energy-efficient ventilation system in high occupancy spaces.

Keywords: Intermittent airflow, Indoor air quality, Perceived air quality,

Thermal sensation, thermal comfort, Air movement acceptability, Convec-

tive cooling, Cooling effect

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iv

Sammanfattning

Lokaler där många människor vistas, som t.ex. klassrum, är ofta svåra att

ventilera. Att upprätthålla en bra termisk komfort kräver en hög energian-

vändning. Vanligtvis blir det en kompromiss mellan låg energianvändning

och bra kvalitet på inomhusmiljön (IEQ). Dålig IEQ får konsekvenser för

människors hälsa, produktivitet och komfort. Alternativa ventilationsstrategier,

som använder förhöjda lufthastigheter, kan minska kylbehovet och därmed

energianvändningen. I denna avhandling utvärderas en ny ventilations-

strategi, Intermittenta luftstrålar (IAJS), där korta perioder med hög lufthas-

tighet genererar en svalkande effekt, när rummets temperatur upplevs som

för hög.

Det primära syftet med arbetet var att undersöka potentialen hos IAJS

som ett ventilationssystem för klassrum, där den termiska lasten ofta är hög.

Strategin jämförs mot traditionella ventilationsprinciper som omblandande

ventilation (MV) och deplacerande ventilation (DV). Parametrar som luftdis-

tributionsindex, termisk komfort, luftkvalitet och energibesparing har utvär-

derats. Alla studier utfördes i klimatkammare.

Resultaten visar att medan MV och DV skapar konstanta luftflödesför-

hållanden genererar IAJS cykliska hastighetsprofiler samt en sinusformad

temperaturvariation i vistelsezonen. IAJS klarar att bibehålla ett bra termiskt

klimat vid högre operativa temperaturer jämfört med MV. I en jämförelse

med ett traditionellt HVAC-system visar beräkningar att dess börvärde kan

höjas från 2.3 till 4.5 °C med bibehållen termisk komfort. Detta indikerar en

avsevärd energibesparingspotential vid användande av IAJS.

Nyckelord: Intermittent luftflöde, Luftstrålar, Upplevd luftkvalitet, Termisk

komfort, Acceptans av luftrörelser, Konvektiv kylning, Kyleffekt

Acknowledgements

I am thankful for the opportunity to do my doctoral studies at the University

of Gavle. I owe my deepest gratitude to numerous people who provided sup-

port and encouragement that contributed significantly to the completion of

my studies.

I express my sincere gratitude to my supervisors: Professor Patrik

Sörqvist, Dr. Hans Wigö and Dr. Robert Ljung for their unwavering support,

positive attitude, enthusiasm, guidance and advice on my research and on

matters beyond research that has contributed tremendously to my professional

and personal development.

I am grateful to Professor Mats Sandberg (my secret supervisor), for his

comments, suggestions and discussions that inspired many research ideas for

this and other projects. On this note, I owe a debt of gratitude to Dr. Bin Yang

for his contribution through discussions, suggestions and comments. Professor

Edward Arens and Dr. Stefano Schiavon, for inviting me to work at CBE as

a visiting research student and providing comments on my research. Dr.

Dusan Licina for being a brother, for dreaming with me (Kudos to dreams

deferred) and for the support and advice during my studies. Dr. Despoina Teli

for reviewing and commenting on my thesis.

I would like to thank colleagues and friends at the University of Gävle,

whose names are too numerous to mention lest I forget some, your support,

companionship and the wonderful discussions during lunch and Fika made

Gävle a homely environment. This also extends to friends and colleagues at

UC-Berkeley (Veronika, Soazig and Caroline), I am grateful for the reception

my family received during our stay. To friends across the world, I am grateful

for your support, tolerance and the welcome social distraction during this pe-

riod. Indeed, it has been a journey worth a tale.

I am thankful to the staff at the University of Gävle for the help and sup-

port that I received during my studies. Much gratitude is owed to all the re-

search engineers at the University lab who helped during my experimental

studies.

Finally, to my wife Mpanga and my son Mp’Ala, all that should be said

is that you two are the spark that makes my life bright. Thank you.

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vi

List of Appended Papers

This thesis is based on the following papers, which are referred to in the text

by Roman numerals:

Paper I

Kabanshi, A., Wigö, H., & Sandberg, M. (2016). Experimental evaluation

of an intermittent air supply system–Part 1: Thermal comfort and ventilation

efficiency measurements. Building and Environment 95, 240-250.

Paper II

Kabanshi, A., Wigö, H., Ljung, R., & Sörqvist, P. (2016). Experimental

evaluation of an intermittent air supply system–Part 2: Occupant perception

of thermal climate. Building and Environment 108, 99-109.

Paper III

Kabanshi, A., Yang, B., Sörqvist, P., & Sandberg, M. (Accepted).

Occupant perception of air movements and air quality in a classroom with an

intermittent air supply system. Indoor and Built Environment.

Paper IV

Kabanshi, A., Wigö, H., Ljung, R., & Sörqvist, P. (2016). Human perception

of room temperature and intermittent air jet cooling in a classroom.

Indoor and Built Environment. Prepublished January, 28,

DOI: 10.1177/1420326X16628931

Paper V

Kabanshi, A., & Wigö, H. (2016). Experimental Evaluation of Intermittent

Air Jet Ventilation Strategy: Cooling effect and the associated energy savings.

The 14th International Conference on Indoor Air Quality and Climate,

Ghent, Belgium, July 2-9, 2016.

Reprints were made with permission from the publishers.

Nomenclature

Symbols Description Unit

do Nozzle diameter mm

S Spacing between nozzle centerline mm

M Metabolic rate met or W/m2

W Effective mechanical power W/m2

Icl Clothing insulation clo or m2 ⋅ K/W

fcl Clothing surface area factor -

ta Room air temperature °C

ťr or tr Mean radiant temperature °C

var Relative air velocity m/s

pa Water vapor partial pressure Pa;

hc Convective heat transfer coefficient W/(m2 ⋅ °C)

tcl Clothing surface temperature °C

T Temperature °C

V Mean air velocity m/s

V Room volume m3

TI Turbulence intensity %

ts Supply temperature °C

tex Exhaust temperature °C

tg Vertical temperature gradient °C

𝑇𝑒𝑞 Manikin equivalent temperature °C

𝜀𝑝𝑎 Local air change index -

𝜏𝑛 Nominal time constant h

𝜏𝑝 Local mean age of air h

𝑞𝑣 Volumetric airflow rate m3/s

𝜀𝑎 Air change efficiency %

𝜏 Room mean age of air h

Abbreviations

IAJS Intermittent air jet strategy

MV Mixing ventilation

DV Displacement ventilation

PAQ Perceived air quality

IAQ Indoor air quality

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viii

ADI Air distribution index

PMV Predicted mean vote

MTV Mean thermal vote

OTS Overall thermal sensation

PSAM Percentage satisfied with air movements

PPD Predicted percentage dissatisfied

PD Percentage dissatisfied

SET Standard effective temperature

IEQ Indoor environmental quality

HVAC Heating, ventilation and air conditioning

AHU Air handling unit

AJD Air jet diffuser

MD mixing diffuser

D Diffuser

C Column

CO2 Carbon dioxide

PCS Personal comfort systems

EU European Union

IPCC Intergovernmental panel on climate change

CBE Center for the built environment

CTA Constant-temperature anemometers

ANOVA Analysis of variance

EAC Environmental advisory council

HRE Heat removal effectiveness

CP Cooling power

CFD Computational fluid dynamics

P Measurement point

PLC Programmable logic controller

PID Proportional–integral–derivative

Table of Contents

Abstract iii

Sammanfattning iv

Acknowledgements v

List of Appended Papers vi

Nomenclature vii

1 Introduction 1

2 Literature review 3 2.1 Indoor Environment 3 2.2 Ventilation 3 2.2.1 Local air change index 4 2.2.2Airchangeefficiency 4 2.2.3IndoorairQuality(IAQ) 5 2.2.4 Thermal Comfort 6 2.3 Elevated air movements and indoor climate 8 2.3.1 Characteristics of air movements and human comfort 10 2.3.2Airmovementsandperceivedairquality. 11 2.4 Ventilation Strategies 12 2.4.1Mixingventilationstrategy 12 2.4.2Displacementventilationstrategy 12 2.4.3Alternativeventilationstrategy 13 2.5 ConfluentJets 14 2.6 Knowledge gap 14 2.7 Motivationofthestudy 14 2.8 Aimandresearchprocess 15 2.9 Outlineoftheappendedpapers 15

3 Methods 18 3.1 Research methods 18 3.2 IAJS:Systemdescription 18 3.3 Experimental facilities 19 3.4 Measurements 20 3.4.1 Objective measurements 20 3.4.2 Subjective measurements 23

3.5 EstimationofthecoolingeffectofIAJS 25 3.5.1Manikin-basedcoolingeffect 25 3.5.2Coolingpoweranalysis 25 3.6 LimitationsandValidityaspects 26

4 Results and discussion 28 4.1 Objectivestudy 28 4.1.1 Air speed and temperature characteristics in the occupied zone 28 4.1.2Ventilationperformance:Airdistributionindices 31 4.1.3Ventilationperformance:Thermalcomfort 32 4.2 Subjectivestudy 34 4.2.1Casestudy1 34 4.2.2Casestudy2 40 4.3 CoolingeffectofIAJS 42 4.3.1Manikin-BasedCoolingEffect 42 4.3.2Coolingpoweranalysis 43

5 General discussion 45 5.1 Implicationsonoccupantcomfortandbuildingenergyuse 45 5.2 Systemapplicability 46 5.3 Limitationsandfuturework 47

6 Conclusion 49

7 Miscellaneous publications 51 7.1 Journalarticles 51 7.2 Conferencearticles 51

References 52

Appendix A 63 1:MTVscale 63 2:Casestudy1questionnaire 63

Appendix B 72

Appendix C 73

1

1 Introduction

Energy has become an international political issue that threatens global wel-fare and regional security. The concerns over exhaustion of energy resources and environmental impacts are ever becoming serious and disquieting. The rapid growth in energy demand is apparent in the building sector, which has become the largest energy-demanding sector. Taking the European Union (EU) as an example, the built environment uses about 40% of the total re-gional energy and accounts for about 36% of the regions total CO2 emissions (Burman et al., 2014; European Commission, 2008). There are calls to reduce energy demand and improve energy efficiency in the built environment. This is reflected in the European Union (EU) energy and climate change strategy (da Graça Carvalho, 2012). The EU has given directives (2010/31/EU and 2012/27/EU) to its member states to improve on building energy performance and energy efficiency (European parliament council, 2010, 2012). In Sweden, the national board of housing, building and planning (Boverket) regulated the energy use in buildings with regard to location and type of heating (Boverket, 2008). Earlier, the Envi-ronmental Advisory Council (EAC) had set a target of 30% reduction on purchased energy by 2025 compared to that of 2000 in the building sector. This was also highlighted in Boverkets (2007) goals for 2020 on indoor environment, energy use and sustainability in the built environment. From a global perspective, reducing the energy demand in the building sector is challenging due to various reasons. First, the population is expected to grow to about 9 billion by 2050 (Cohen, 2001). Thus, to provide building services to the increased population means an increase in building energy demand. Second, infrastructure development and urbanization in developing countries is increasing which gradually adds to the current building energy demand (Cohen, 2006). Third, people in developed countries spend about 80-90% of their time in the built environment (Hoppe and Martinac, 1998), and as such, a good heating, ventilation and air conditioning (HVAC) system is needed for people’s health, comfort, productivity and quality of life. Therefore, it is very important to have an HVAC system that secures a high quality indoor environment, and at the same time has a low energy use/demand. At present, conventional systems such as mixing ventilation, which has the largest market share, produce homogeneous conditions at a high energy input in order to provide and maintain satisfactory habitable indoor condi-tions. This entails a trade-off between meeting the directive of low-energy requirements in buildings and occupant satisfaction with indoor climate.

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Compromising on the latter is shown to have consequences for occupants’ health, performance and learning abilities (crucial in classrooms), increased costs on healthcare and loss of productivity in organizations (Bakó-Biró et al., 2007; Fisk et al., 2011; Gaihre et al., 2014; Jones, 1999; Milton et al., 2000; Seppänen and Fisk, 2002; Wyon and Wargocki, 2013). The work presented in this thesis explores an alternative ventilation and climate control strategy called Intermittent Air Jet Strategy (IAJS). The strategy shows promising application in high occupancy spaces, specifically considered in this study are classrooms.

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2 Literature review

2.1 Indoor Environment

The indoor environment is an enclosed space, within the built environment, meant for human occupancy and activity. Indoor environments can be de-scribed by physical conditions, simply parameters such as acoustic, lighting, thermal climate and indoor air quality (IAQ; Clausen et al., 2012). The quality of the indoor environment, commonly referred to as Indoor Environmental Quality (IEQ), has a significant impact on occupants’ health, comfort and productivity (Olesen, 2008). For the works presented herein, the indoor environment is limited to buildings and attention is on two indoor environ-mental parameters: thermal climate and indoor air quality.

2.2 Ventilation

To generate and control the desired indoor environment, ventilation systems are widely used, particularly to enhance indoor thermal comfort and air qual-ity. The primary purpose of a ventilation system is to provide an adequate ventilating airflow. The airflow introduces fresh air into a defined space and removes used up air out of it (Etheridge and Sandberg, 1996). Traditionally, old room air in occupied spaces is diluted with fresh cool air, which addi-tionally, removes internal generated excess heat. In buildings, ventilation can be explained as a two systems process working simultaneously. The first process is the exchange of air in and out through the external building enve-lope and between internal partitions. This is done through unintended (cracks and holes) and intended openings (windows, doors and mechanical ventila-tion systems). The second process is the movement of air inside the room, this process is dependent on the first process but in many cases the depend-ence is mostly neglected both theoretically and experimentally (Etheridge and Sandberg, 1996). The performance of a ventilation system is determined using the concept of ventilation effectiveness introduced by Scandinavian researchers in the early 1980s (Mundt et al., 2004). The concept uses two separate groups of indices: First group involves two indices, the air change efficiency and local air change index, which determine the system ability to exchange room air. The second group also involves two indices, contaminant removal effective-ness and local air quality index, which determine the system ability to re-move air-borne contaminants from the room. In this thesis, the first group of

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indices were considered as they give insight on the degree to which the ven-tilation system distributes fresh air in the room, while no such information is obtained from the second group of indices (Mundt et al., 2004).

2.2.1 Air change index

Local air change index (𝜀𝑝𝑎) is the measure of how fast supplied air reaches

a specified point in a room. It is based on the statistical age of air concept, introduced by Sandberg (1981), and since the age is counted from the time the air enters the room, the quality of air at a given point will depend on its age, that is, the longer it stays in the room the more contaminants it accumu-lates. The age of air concept has proven useful in determining the air quality at a given point and it is defined by the ratio:

𝜀𝑝𝑎 =

𝜏𝑛

𝜏𝑝 (1)

In Equation 1, 𝜏𝑛 (= 𝑉/𝑞𝑣) is the nominal time constant (h) which can be calculated in a space with volume, V, and airflow rate, 𝑞𝑣. 𝜏𝑝 is the local mean age of air (h). The local air quality at a given point can physically be interpreted by the value of the local air change index in the following way: In a perfectly mixed case 𝜀𝑝

𝑎 = 1; 𝜏𝑛 = 𝜏𝑝, whereas a value less than one (𝜀𝑝𝑎 < 1) will indicate

relatively old air (poor air quality) and that greater than one (𝜀𝑝𝑎 > 1) indi-

cates fresh air or good air quality. The lower the local mean age of air, the higher the local air change index and consequently the better the air quality (Mattsson, 2011).

2.2.2 Air change efficiency

Air change efficiency (𝜀𝑎) is the measure of how efficiently the supplied air is distributed in the room. Simply, it is a measure of how fast the ventila-tion system replaces the old air in the room with new air. In pedagogical terms, it is a ratio between the lowest possible mean age of air (𝜏𝑛/2) and the room mean age of air (Mundt et al., 2004). This definition is shown in the following expression: 𝜀𝑎 =

𝜏𝑛

2∙<𝜏>∙ 100 [%] (2)

In Equation 2, 𝜏𝑛 is the nominal time constant (h) and 𝜏 is the room mean age of air (h), which is an average of all the local mean age of air (𝜏

𝑝). The

lower the room mean age of air, the higher the air change efficiency and consequently better air quality in the room. A perfectly mixed case, air change efficiency will be equal to 50%, whereas values less than 50% will indicate short circuit flow or short cut ventilation (poor air distribution) and

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values above 50% are common in stratified system (Mattsson, 2011; Mundt et al., 2004). If the air change efficiency is less than 40%, it is recommended to rearrange the ventilation installation or change the system. The indices presented above do not give an overall performance of the ventilation system as they do not account for the systems performance on thermal comfort. Awbi (2003) introduced an air distribution index (ADI) as a method to assess the ventilation performance in providing both thermal comfort and air quality. Almesri et al., (2012) improved the index to account for both homogeneous and nonhomogeneous environments. ADI has been shown to be effective not only on evaluating ventilation (air quality and ther-mal comfort) but also energy performance of an air distribution system (Karimipanah et al., 2008). In the works herein, ADI method was not con-sidered but rather air quality and thermal comfort were evaluated inde-pendently to get a comprehensive analysis of each variable on the resulting indoor climate due to IAJS.

2.2.3 Indoor air Quality (IAQ)

IAQ is a concept used to describe the state or cleanness of air in the room with regard to human comfort and health. The quality of indoor air may refer to an extent to which pollutants are removed and human requirements are met (Nilsson, 2003). Common indoor air pollutants are particles, volatile or-ganic compounds, inorganic gases (CO2, CO, etc.), tobacco smoke and other biological agents. A substantial amount of pollutants present indoors are in-ternally generated e.g., emissions from occupants, cooking, building materi-als and microbial growth (Brohus, 1997). Other pollutants like pollen and industrial/traffic smoke are outdoor generated. Despite the considerable amount of research on indoor air quality, the topic remains complex as much information on pollutants and their sources is incomprehensive. In addition, there is little understanding about the behavior of aerosols and the dynamic relationship between levels of exposure and occupant health (Jones, 1999; Owen et al., 1992; Wolkoff and Nielsen, 2001). In ventilation, two factors guide determination of IAQ: The chemical composition and the concentration of its components; and human judgement of IAQ. CO2 is commonly used as an indicator for evaluating and controlling indoor air quality with a maximum allowable concentration of about 1000 parts per million (ppm) by volume (Awbi, 2003; Persily, 1997). Spaces with concentration above 1000 ppm are considered polluted and consequently are deemed to have bad air quality. Additionally, standards (ASHRAE 62.1, 2013) provide guidelines to calculate the minimal airflow rates required in defined spaces. Although chemical composition of air is important, espe-cially in view of the health risks of breathing it, occupant perception of in-door air quality is an important aspect in assessing indoor environments as stipulated in the current guidelines/standards for ventilation (ASHRAE 62.1, 2013; CEC Report 11, 1992; CEN/EN 15251, 2007; CEN CR 1752, 1998).

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Occupants use their perception to determine or assess IAQ by means of air acceptability, irritation, air freshness and odor intensity (Melikov and Kaczmarczyk, 2012).

2.2.4 Thermal Comfort

One of the main functions of a ventilation system is to generate conditions necessary for maintaining occupant thermal neutrality or thermal comfort. This is achieved when there is a thermal energy balance between the sur-roundings and the heat dissipated by the human body (Clark and Edholm, 1985). A seated person doing light work in a comfortable environment has the following mechanisms of heat dissipation: thermal radiation 37%, con-vection from outer surfaces 32%, diffusion of water through the skin 21% and finally evaporation and convection in airways 10% (Nilsson, 2003; Wigö, 2005). Thermal comfort is influenced by six factors that determine heat gain and heat loss (Fanger, 1970; Parsons, 2014). Of these four are environmental factors: air temperature, mean radiant temperature, air speed and relative hu-midity. The other two are personal factors: metabolic rate and clothing insu-lation. Psychological factors such as individual expectations also play a role (de Dear and Braga, 1998). Taken together, ASHRAE Standard 55 (2013) defines thermal comfort as “that condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation.” The subjective evaluation is based on occupant responses on a psycho-physical scale which is a 7-point ASHRAE thermal sensation scale: -3 cold, -2 cool, -1 slightly cool, 0 neutral, +1 slightly warm, +2 warm, and +3 hot (ASHRAE standard 55, 2013).

2.2.4.1 The predicted mean vote (PMV)

The PMV model developed by Fanger (1970), is widely accepted and used in standards (ASHRAE 55, 2013; ISO 7730, 2005) and by practitioners to assess thermal comfort. PMV is defined as an index that represents the mean thermal sensation vote for a large group of people for any given combina-tions of thermal environmental conditions, activity and clothing levels (Van Hoof, 2008). Fanger (1970) developed the following equations to determine PMV:

𝑃𝑀𝑉 = [0.303𝑒(−0.036𝑀) + 0.028] × {(𝑀 − 𝑊) − 3.05 × 10−3 ×[5733 − 6.99 × (𝑀 − 𝑀) − 𝑝𝑎] − 0.42 × [(𝑀 − 𝑊) − 58.15] − 1.7 ×10−5 × 𝑀 × (5867 − 𝑝𝑎) − 0.0014 × 𝑀 × (34 − 𝑡𝑎) − 3.96 ×10−8 × 𝑓𝑐𝑙 × [(𝑡𝑐𝑙 + 273)4 − (ť𝑟 + 273)4] − 𝑓𝑐𝑙 × ℎ𝑐 × (𝑡𝑐𝑙 − 𝑡𝑎)} (3)

where, 𝑡𝑐𝑙 = 35.7 − 0.028(𝑀 − 𝑊) − 𝐼𝑐𝑙 × {3.96 × 10−8 × 𝑓𝑐𝑙 × [(𝑡𝑐𝑙 +273)4 − (ť𝑟 + 273)4] + 𝑓𝑐𝑙 × ℎ𝑐 × (𝑡𝑐𝑙 − 𝑡𝑎)} (4)

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(5)

(6) and, M is the metabolic rate (W/m2), 1 metabolic unit = 1 met = 58,2 W/m2; W is the effective mechanical power (W/m2); Icl is the clothing insulation (m2 ⋅ K /W),1 clothing unit = 1 clo = 0,155 m2 ⋅ K/W; fcl is the clothing surface area factor; ta is the air temperature (°C); ťr is the mean radiant temperature (°C); var is the relative air velocity (m/s); pa is the water vapour partial pressure (Pa); hc is the convective heat transfer coefficient [W/(m2 ⋅ °C)]; tcl is the clothing surface temperature (°C). As earlier stated, PMV predicts the mean thermal votes of a large group of people with identical comfort conditions i.e., same environmental condi-tions, clothes having the same thermal insulation and all having the same metabolic and physical activity level. Realistically, it is rare if not impossible to have the same conditions. Thus, individual votes are scattered around the mean value and, likely so, that some votes will fall further away from it. It is therefore meaningful to predict the number of people likely to feel ther-mally uncomfortable. Following the recommendation in ISO 7730 (2005), thermally dissatisfied people are identified as those who will vote hot, warm, cool or cold on the 7-point thermal sensation scale.

2.2.4.2 Predicted Percentage of Dissatisfied

Predicted percentage of dissatisfied (PPD) is an index which predicts the percentage of people in a group that will likely be dissatisfied with the ther-mal conditions (ISO 7730, 2005). It is based on PMV and is defined by the following equation.

𝑃𝑃𝐷 = 100 − 95 𝑒(−0.03353 𝑃𝑀𝑉4 − 0.2179𝑃𝑀𝑉2) (7) In Equation 7, PPD correlates with PMV in a way that when PMV deviates further from neutral (0), PPD increases. The standards combine PMV and PPD to recommend environmental conditions in which people can operate.

2.38 |tcl – ta|0.25 for 2.38 |tcl – ta|0.25 > 12.1ඥ𝑣𝑎𝑟

12.1ඥ𝑣𝑎𝑟 for 2.38 |tcl – ta|0.25 < 12.1ඥ𝑣𝑎𝑟

hc

1.00 + 1.290Icl for Icl ≤ 0.078 m2. K/W 1.50 + 0.645Icl for Icl > 0.078 m2. K/W

fcl

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For example, for sedentary activity ASHRAE standard 55 gives a PMV range of -0.5 to +0.5 and PPD < 10%, as a comfortable range. On the other hand, ISO 7730 gives three categories of thermal climate: class A: -0.2 < PMV < 0.2, PPD < 6%; class B: -0.5 < PMV < 0.5, PPD < 10%; and class C: -0.7 < PMV < 0.7, PPD < 15%. Fanger and colleagues developed the PMV-PPD model based on college-aged students and in laboratory homogeneous air-conditioned spaces with moderate climate. Since its introduction, numerous studies have been per-formed, with some giving support to the model while others have criticized the model and showed discrepancies (Charles, 2003; Van Hoof, 2008). The discrepancies are mostly around aspects such as geographic application range, types of buildings, and the models input parameters (Van Hoof, 2008). de Dear and Brager (1998) showed that PMV predicted without bias, the preferred operative temperature, in air-conditioned buildings, however, it overestimated thermal sensations in naturally ventilated buildings. PMV model is shown to also underestimate the cooling effect in conditions with elevated air movements above 0.2 m/s (Humphreys and Nicol, 2002). Researchers have proposed other models, especially applicable in condi-tions where the PMV model has more bias. de Dear and Brager (1998) de-veloped an adaptive thermal comfort model that accounts for occupants behavioral efforts to attain comfort. The model is especially useful in natu-rally ventilated buildings where the occupants have a greater degree of con-trol over their thermal environment (Nicol and Humphreys, 2002). Zhang (2003) introduced a model for transient conditions since the PMV model is applicable only in steady state thermal conditions, and ASHRAE standard 55 has adopted the Standard Effective Temperature (SET*) model to esti-mate thermal sensations in spaces with elevated air movements above 0.2 m/s. Nonetheless, PMV remains the widely used thermal comfort assessment tool.

2.3 Elevated air movements and indoor climate

Room air velocity is one of the main factors that influence occupants’ expe-rience and perception of indoor climate and, as such, it is a prerequisite for thermal comfort. In traditional HVAC systems, there is a recommendation to limit air movements in the occupied zone, less than 0.2 m/s, to reduce the risk of draft (ASHRAE 55, 2013; CEN/EN 15251, 2007; ISO 7730, 2005). Draft, defined as “unwanted local cooling caused by air movements” (Fanger and Pedersen, 1977) causes thermal dissatisfaction in indoor spaces. Stand-ards, CEN/EN 15251 (2007) and ISO 7730 (2005), use the draft risk model developed by Fanger and colleagues (Fanger et al., 1988; Fanger and Christensen, 1986) to estimate the percentage dissatisfied (PD) due to draft based on the following environmental parameters: Mean air speed (V; m/s), Turbulence intensity (TI; % from 0 to 100) and room air temperature (ta; °C). The percentage dissatisfied can be estimated by the following expression (draft risk model):

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𝑃𝐷 = (3.143 + 0.3695 𝑉 ∙ 𝑇𝐼)(34 − 𝑡𝑎)(𝑉 − 0.05)0.6223 (8)

The draft risk model has been shown to overestimate the percentage of dis-satisfied, as such it has been removed from recent versions of ASHRAE standard 55 since 2010 (Schiavon et al., 2016). In addition, literature shows that there are number of factors that influence draft perception. These include metabolic rate, period of exposure (Griefahn et al., 2001; Toftum and Nielsen, 1996b), exposed body parts, their clothing insulation level, and overall thermal comfort/sensation (Mayer, 1987; McIntyre, 1978; Todde, 2000; Toftum et al., 2003; Toftum and Nielsen, 1996a). Other factors are, airflow direction (Toftum, Zhou, et al., 2000) and its characteristic e.g., flow and spectral frequency (Ring et al., 1993; Zhou et al., 2006), and occupant control of the environment (Toftum, Melikov, et al., 2000). The results in literature do not agree and not all factors are accounted for in the draft risk model. Review studies by Fountain (1991), and Fountain and Arens (1993) briefly describe how the research on air movements developed and how they were later used to guide the earlier version of ASHRAE Standard 55. The demand for research on indoor air movements increased due to draft related complaints in air-conditioned spaces. Rohles et al., (1974) published works on the effects of air movements and temperature on thermal sensation of a sedentary person. The findings showed a strong correlation between air speed, air temperature and thermal sensation. McIntyre (1978, 1979) inves-tigated occupants acceptability of air movements in relation to elevated tem-peratures. In one of the studies (McIntyre, 1978), he found that occupants’ choice of acceptable air speeds were lower than what was recommended (Fountain and Arens, 1993). In another study (McIntyre, 1979), he found that occupants with cool thermal states deemed the air movements drafty, while those who were warm deemed them pleasant. Based on these and other studies, standards have evolved regarding guidelines on acceptable air speed limits for thermal comfort. The standards (ASHRAE 55, 2013; CEN/EN 15251, 2007; ISO 7730, 2005), provide guidelines on use of elevated air movements to avoid occu-pant discomfort. ASHRAE standard 55 (2013) summarizes the guidelines in a Figure (Figure 5.3.3A in the standard but reproduced here as Figure 1) that clearly show acceptable range of air speeds as a function of operative temperature with specified conditions of when personal control of air speeds should be provided. The same standard also recommends using the SET* method to estimate the cooling effect when air speeds exceed 0.2 m/s, oth-erwise the PMV method is applicable. Details about the SET* method are found in ASHRAE Standard 55 (2013) and Schiavon et al., (2014).

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Fig. 1: Range of proposed air speed as a function of operative temperature and occupant

control requirements (Fig. 5.3.3A from ASHRAE Standard 55, 2013).

The relationships in Figure 1 are based on an equal mean radiant temperature (tr) and room air temperature (ta). If differences occur such that the tr < ta, the cooling effect of air movements is less effective, and if tr > ta the cooling effect of air movements is more effective (Schiavon and Melikov, 2008). It is for this reason that elevated air movements are more effective in warm indoor climates.

2.3.1 Characteristics of air movements and human comfort

A common agreement in literature is that airflow characteristics influence occupants’ acceptability of elevated air movements (Aynsley, 2007; Cui et al., 2013; Fanger et al., 1988; Hara et al., 1997; Huang et al., 2012; Konz et al., 1983; Melikov et al., 1994; Rohles et al., 1974, 1983; Yang et al., 2002). One theme that stand out is that fluctuating airflow has a higher cooling ef-fect than constant airflow (Tanabe and Kimura, 1994). These fluctuations are frequent in spaces with elevated air movements created with a diffuser or a fan. Thus, airflow in such spaces is typically turbulent. A number of studies (Fanger et al., 1988; Fanger and Christensen, 1986; Griefahn et al., 2000; Konz et al., 1983; Rohles et al., 1983; Tanabe and Kimura, 1994; Xia, Niu, et al., 2000; Xia, Zhao, et al., 2000) have studied the effect of turbulence intensity on people’s thermal sensation and comfort. Rohles (Rohles et al., 1983) reported that turbulent airflow offered occupants better thermal com-fort. This was supported by Tanabe and Kimura (1989a) who found that oc-cupants perceived fluctuating airflow with frequencies between 0.016 Hz and 0.1 Hz to have a higher cooling effect. Xia, Zhao, et al., (2000) expanded the comfortable frequency to include the range 0.3 Hz to 0.5 Hz for a thermal sensation range of neutral-to-warm. On the other hand, Fanger and Pedersen

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(1977) found that airflow with frequencies of 0.3 Hz to 0.5 Hz had the most negative effects of draft on occupants in cool-to-neutral thermal states. This was supported by findings by Zhou and Melikov, (2002). In summary, the studies confirm McIntyres (1979) conclusion and suggests that occupants’ perception or acceptability of fluctuating air movements equally depends on occupants’ thermal state. Although a lot of work has been done on the influence of airflow fluctu-ations, specifically turbulence intensity, limited studies have been done on intermittent or cyclic airflow. Konz et al (1983) compared airflow fluctua-tions generated by a fixed fan to that generated by an oscillatory (cyclic) fan. The results show that occupants favored airflow fluctuations generated by oscillating fans as opposed to fixed fans for the same mean air speed. On the contrary, Pasut et al (Pasut et al., 2014) found that oscillatory fans did not have any significant effect on occupants overall thermal sensation and com-fort. This is because of the oscillatory period (15 seconds with no air move-ments and 10 seconds with air movements) as occupants had a shorter exposure time to air movements and hence experienced no effective cooling. In a field study performed in a high school in Stockholm, Wigö (2013) found that occupants who were exposed to constant airflow wanted more air move-ments while those exposed to controlled short pulses of airflow fluctuations were satisfied with the thermal climate for the same mean air speed (p < 0.05). Similarly, Yang et al. (Yang et al., 2002) found that occupants ex-posed to controlled fluctuating airflow under a personalized ventilation sys-tem were satisfied with air movements with a mean air speed of 0.82 m/s while satisfaction was attained at 1 m/s when exposed to a constant airflow. Clearly, these studies show that, although rarely used, controlled fluctuating or intermittent air movements has both thermal comfort and energy saving benefits.

2.3.2 Air movements and perceived air quality.

There is evidence in literature that shows that elevated air movements im-prove perception of IAQ (Arens et al., 2008; Bedford, 1964; Melikov and Kaczmarczyk, 2008, 2012). The positive effect on perceived air quality can be attributed to the airflow interactions between the human convective boundary layer and elevated airflow. The convective boundary layer is in-strumental for convective heat loss on the human body and transport of pol-lutants around the human body (Licina et al., 2015a; Licina et al., 2015b). Elevated air movements distorts the convective boundary layer, conse-quently reducing personal exposure to pollution originating from occupants' feet/floor (Licina et al., 2015b), and also improves thermal perception. Berglund and Cain (1989) reported that occupant perception of indoor air quality improved with better perception of thermal climate. Other studies have also shown that elevated air movements diminished the negative effects of temperature, pollution and relative humidity on perceived air quality

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(Melikov, 2008; Melikov and Kaczmarczyk, 2008). Comparatively, fluctu-ating airflow has a similar effect on perceived air quality. For example, Yang et al., (2002) found that fluctuating airflow had the same effect as constant-elevated airflow on perceived air quality.

2.4 Ventilation Strategies

The main goal of a ventilation strategy is to provide acceptable indoor envi-ronment. However, additional aspects’ involving energy use and environ-mental sustainability have proven equally important. Thus, today energy use is an important aspect of a ventilation strategy. To this end, the strategy used to ventilate a defined space determines the IEQ and the energy needed to achieve ventilation. Traditionally, two fundamental ventilation strategies are commonly used in buildings/classrooms: Mixing ventilation (MV) and dis-placement ventilation (DV). This section gives a brief overview of the two systems and alternative ventilation systems.

2.4.1 Mixing ventilation strategy

Mixing ventilation strategy is the most widely used air distribution system in buildings. Under mixing ventilation, air is blown into the room, often in the ceiling level, at a relatively high velocity to obtain fully mixed ambient conditions and dilution of contaminant concentration (Awbi, 2003). Air ve-locities in the occupied zone are maintained below 0.2 m/s to avoid draft. The strategy has strengths on low installation costs, versatile in both cooling and heating mode and the technology is well developed (Hamilton et al., 2004; Hu et al., 1999). However, studies in classrooms show that the strategy has drawbacks on air distribution (Daisey et al., 2003; Lin et al., 2005), and it is limited in meeting high cooling demands, common in classrooms, as such it requires a high energy input and air flowrate (Cao et al., 2014; Hu et al., 1999; Smedje et al., 2011).

2.4.2 Displacement ventilation strategy

In displacement ventilation strategy, air with low velocity streams (0.15 to 0.2 m/s), usually cooled 2-3 degrees lower than ambient room air tempera-ture, is introduced into the room through diffusers located near the floor or a raised floor and is eventually exhausted at ceiling level (Etheridge and Sandberg, 1996; Hamilton et al., 2004). The cool air spreads across the floor and buoyantly rises when it interacts with heat sources (humans, computers and other heated fixtures) displacing the warmer and stale air toward the ceiling, where it is taken out of the room. DV has a moderately high cooling capacity, making it favorable in spaces with a high cooling demand like classrooms (Hamilton et al., 2004). On the other hand, with DV the flow in the occupied zone gets distorted as the distance from the supply diffuser in-creases due to the low supply velocity (Cao et al., 2014). Another disad-vantage is that the strategy is limited to cooling mode, i.e., may not be useful in heating mode, as it depends on buoyance forces, it would consequently

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have a poor air distribution in the occupied zone. There are also, frequent draft complaints associated with displacement ventilation (Melikov et al., 2005).

2.4.3 Alternative ventilation strategy

Traditional ventilation strategies generate steady state indoor conditions and they are associated with occupant complaints (Bluyssen et al., 1996; Melikov et al., 2005; Seppänen and Fisk, 2002). Other studies, have shown no differ-ences between common traditional ventilation strategies (MV and DV) on perceived indoor environment in classrooms (Smedje et al., 2011). Today, research suggests a paradigm shift in indoor science towards alternative ven-tilation strategies (Fanger, 2006). Alternative ventilation strategies may in-clude but not limited to personalized ventilation systems (Melikov, 2004, 2011), hybrid systems (based on confluent jets or impinging jets) that return properties of both MV and DV (Awbi, 2003), and MV or DV complementing systems such as task ambient air conditioning systems (Zhang et al., 2010). Adding to alternative ventilation strategies is the recently proposed intermit-tent air jet strategy covered in this thesis.

2.4.3.1 Intermittent air velocity system

Wigö (2005) in his doctoral thesis explored the possibilities of creating a controlled velocity field using an array of jets in the occupied zone in a class-room. As part of the work, Wigö and Sandberg (2001) evaluated ways of generating short pulses for convective heat loss on the upper body parts of a seated person by exploring setups in which an alternating velocity system was interchangeably operated with either a mixing or a displacement system. They faced challenges in stabilizing velocities as development of the jet in the room was too dependent on buoyancy forces, they eventually proposed an internal recirculating system which produced uniform velocity fields, without any temperature fluctuations, and the air speeds could easily be con-trolled (Wigö and Sandberg, 2002). Further investigations were done on the psychological and physiological effect on how occupants experienced the resulting indoor climate (Wigö, 2013; Wigö and Knez, 2005). The current body of work builds on the works of Wigö (2005) and pro-poses an intermittent air jet strategy (IAJS) as an alternate energy-efficient method of controlling indoor environmental conditions in spaces with high occupancy. In the current work, we explore IAJS both as an independent system that works as a primary ventilation system and as a room induction system working in conjunction with a mixing ventilation system. The strat-egy utilizes properties of single row of confluent jets to optimize elevated intermittent air movements in a ventilated space, consequently influencing convective and evaporative heat losses from a human body.

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2.5 Confluent Jets

Confluent jets are multiple circular jets issued from different apertures, but in the same plane, that interact downstream and coalesce (merge) as a single jet (Cao et al., 2014). Ghahremanian (2015) investigated near field charac-teristics of different configurations of confluent jets. One of the main find-ings (Ghahremanian et al., 2014) is that a row of free confluent jets on a pipe produce a higher center line velocity with low turbulence compared to a sin-gle jet or an array of jets. These characteristics are positive in ventilation applications, and they would have implications on air distribution, thermal climate and energy efficiency of a ventilation strategy.

2.6 Knowledge gap

The concept of confluent jets in ventilation systems is new and few studies have explored ventilation based on confluent jets (Cao et al., 2014). The first works of confluent jets appeared in a study by Cho et al., (2004) which analyzed the properties and possibilities of wall confluent jets as a ventila-tion system. Karimipanah et al., (2007) evaluated experimental and com- putational fluid dynamic (CFD) studies in a classroom and found that wall confluent jets in most cases performed better than the displacement system. Cho et al., (2008) followed up on the earlier works with a theoretical and experimental investigation and found that a confluent jet system produces a greater horizontal spread over the floor than a displacement ventilation sys-tem. Janbakhsh (2015) based the doctoral thesis on confluent jets, and ex-plored a range of cases from office setup to industrial applications. The findings show that a confluent jet supply system offers better mixing due to the interactions between the multiple jets and the room ambient air (Janbakhsh and Moshfegh, 2014a, 2014b). The works on confluent jets done so far involve wall confluent jets. To the best of the author’s knowledge, the only studies in literature related that to unconstrained confluent jets were done by Wigö (2005) who investigated the impact of a controlled intermittent velocity field on human’s psychology and physiology. He did not explore the system as a ventilation strategy. This thesis contributes knowledge and understanding of possible ventilation strat-egies based on unconstrained confluent jets. The work herein, focuses on overhead-generated intermittent single row of confluent jets.

2.7 Motivation of the study

Today, the built environment is ever growing and buildings are becoming more complex and big. Equally, delivering quality ventilation with homoge-neous indoor environmental conditions is becoming more expensive and complex. Particularly, the commonly used ventilation strategies are energy intensive and sensitive to deviations from optimal operational conditions re-sulting in adverse implications on the occupants’ experience of the indoor

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environment (Schiller et al., 1988). Interestingly, the report by the intergov-ernmental panel on climate change (IPCC) identify the building sector as having a high potential for energy and emissions reduction amongst the en-ergy sectors (IPCC, 2007). This potential is especially high with regard to building services such as HVAC, which accounts for 50% of the building energy use, of which, climate control is the most energy intensive part. Implementing energy saving strategies is challenging, especially in spaces with high occupant density like classrooms. High occupancy spaces demand a high-energy input to control climate due to high thermal loads. These thermal loads result in quick temperature build up and consequently occupant thermal discomfort. It is therefore very important to explore and develop alternative ventilation strategies that have a potential to provide good indoor environment at a low energy use. This was the main motivation for the current study.

2.8 Aim and research process

The overarching aim of the study was to investigate and evaluate experimen-tally the potential of IAJS as a ventilation system in high occupancy spaces. Central to this was to gain a thorough understanding of the air distribution characteristics of IAJS. One of the objectives of the study was to evaluate ventilation performance of IAJS in comparison with mixing and displace-ment systems. The system was evaluated with respect to thermal comfort, ventilation efficiency indices, occupant perception and energy-saving poten-tial, using a classroom as a case study of high occupancy spaces. The aim of the study was attained through experimental studies consist-ing of a 3-part research process, namely:

i. Objective study: Investigated ventilation performance with regard to the resulting airflow and temperature characteristics in the occupied zone. The study evaluated ventilation capabilities through investiga-tion of air distribution, local air quality, room air change rate and thermal comfort.

ii. Subjective study: Explored the influence of IAJS on occupant expe-rience of indoor environment with regard to thermal climate, indoor air quality (IAQ) perception and air movement acceptability.

iii. Comparative study to estimate the cooling effect: Evaluated the cooling effect of IAJS and the practical implications of implement-ing the system on building energy use.

2.9 Outline of the appended papers

The first study (Paper I; Kabanshi, et al., 2016a) introduces the concept of IAJS and explores characteristics of the generated indoor environment. The study explains the operational and system construct of the air distribution

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system and evaluates the influence of the resulting intermittent jet on condi-tions both inside and outside the jet plane. Using a classroom mockup as a case study, characteristics of room air speeds and temperatures, air quality and thermal comfort measurements were investigated. The study also in-cluded performance evaluation of conventional systems i.e., mixing and dis-placement ventilation. The performance of MV was a benchmark for performance comparison with IAJS. As presented in Paper I, the strategy shows promise as a primary ventilation system in classrooms. The second study (Paper II; Kabanshi et al., 2016b) explored occupant response to thermal climate with IAJS as a primary and sole ventilation sys-tem. Specifically, the participants’ estimated overall thermal sensation, local thermal sensation, thermal comfort and thermal preference/ acceptability in different temperatures and air speeds. The participants found air speeds to be undesirable at lower temperatures, but reported an improved thermal sensation, comfort and acceptability at higher temperatures. The general findings in Paper II support the energy saving potential of IAJS in view of the human perception of indoor thermal climate. The third study (Paper III; Kabanshi et al., nd) assessed occupant re-sponse to intermittent air movements by evaluating air movement accepta-bility and the influence of intermittent airflow on the perception of indoor air quality. The third paper is an independent analysis of data collected dur-ing the second study and as such, experimental arrangement, setup and con-ditions were the same. The participants found air speeds unacceptable at lower temperatures and high air speeds acceptable at higher temperatures. IAJS also improved participants’ perception of air quality in conditions deemed poor under MV. The findings of Paper III add on to support the po-tential of IAJS as concluded in Paper II. The fourth study (Paper IV; Kabanshi et al., 2016c) evaluates human re-sponse to intermittent air jets as a ceiling mounted induction unit. In this paper, the system setup had a mixing system as primary ventilation deliver-ing outdoor conditioned air into the room, while IAJS ran as a secondary system enhancing air speeds and circulation of room air in the occupied zone. The aim was to investigate occupants’ response to room air re-circulation at elevated air speeds in classrooms. Similar to the second and third papers, occupants’ perception of indoor air quality and the thermal climate was as-sessed. The paper suggests a practical way of implementing IAJS in class-rooms with existing mixing ventilation systems. The fifth study (Paper V; Kabanshi and Wigö, 2016) estimates the cool-ing effect under IAJS in relation to MV. The study uses a comparative method to evaluate a temperature offset due to convective cooling under IAJS in comparison to MV for the same thermal sensation. Included in the study are thermal manikin measurements, which give insight on the influ-ence of IAJS on the human body, and the cooling effect on local body parts. Additionally, measurements of predicted mean vote (PMV) from the objec-tive study were used to estimate the overall cooling effect under IAJS. In this

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thesis, the cooling effect analysis is done with thermal sensation based on human responses (not included in Paper V). As shown in this study, IAJS has a potential to significantly reduce energy use in high occupancy spaces if well implemented.

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3 Methods

3.1 Research methods

IAJS was evaluated through a series of experimental climate chamber stud-ies. First, technical (objective) measurements were done to determine the indoor environment generated under IAJS. The systems air distribution and climate control capabilities were evaluated. This included evaluation of air-flow and temperature characteristics in the occupied zone and around occu-pants (human heat simulator). Second, two human response studies (questionnaire survey) were performed to evaluate occupant response to IAJS, as a primary system and one human response study as a secondary system. Lastly, a comparative study was performed to estimate the cooling effect and its implications on building energy use. In most cases, a classroom setup was used and the system performance was compared with a MV sys-tem.

3.2 IAJS: System description

IAJS provides overhead-generated intermittent airflow through ceiling mounted air jet diffusers (AJD). In this study, the AJD is a 160 mm diameter ventilation duct (Figure 2), fitted with plastic batches (Figure 2A) having single row specially designed circular nozzles: 9 nozzles, each with a diam-eter, d0 = 10 mm, arranged in a horizontal row with equidistant spacing (S= 1.4d0). The nozzle batches are fitted 4.5d0 apart from one end of the pipe to the other covering a column of the occupied zone.

The diffusers are mounted on the ceiling and they generate confluent jets that merge to form a long-horizontal two-dimensional single jet (the jets merge at 4d0 within the batch and 10d0 between the batches). Figure 2B shows the smoke visualization of the merging jets. The resulting jet has a sweep of about 75 cm from the centerline in the jet plane, at a distance of 150 cm away from the nozzle outlet.

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Figure 2: (A) Air jet diffuser and confluent nozzles; (b) smoke visualization of the system in operation.

In operation, the system is proposed to run with a minimal velocity of 0.4 m/s and maximum velocity of 0.8 m/s measured at breathing height (1.1 m from the floor). The operational velocities are chosen based on recommen-dation in literature: 0.4 m/s is the minimal velocity recommended for down-ward airflow to effectively blow away the thermal plume (Wigö, 2005; Licina et al. 2015b), and at this velocity personal exposure to room contam-inants transported within the human convective boundary layer is reduced (Licina et al., 2015a). 0.8 m/s is the recommended maximum velocity with no requirements for personal control (ASHRAE standard 55, 2013).

In this study, the intermittency was obtained by cutting on and off the air supply of AJDs, resulting in variable-periodic mean air speeds in the occupied zone. The air speeds were supplied for 3 minutes (ON), and cut off (OFF) for 3 min, 2 min, 1.5 min or 1 min depending on experimental design and temperature conditions. The cut off variations were based on the hypothesis that a longer time from air velocity exposure in a low temperature condition would reduce the risk of draft while the shorter period for higher temperature conditions would maintain the cooling effect while reducing discomfort due to elevated temperatures. All objective measurements were done with a 6 min cycle, 3 min ON and 3 min OFF, while for subjective measurements the 3 min supply was maintained but the cutoff time varied with increase in operative temperature.

3.3 Experimental facilities

All measurements were conducted in climate controlled environmental chambers: 4 studies (Papers: I, II, III and IV) in a classroom setup, room dimensions of 7.2 m x 8.4 m and a ceiling height of 2.5 m, at the University of Gävle (Figure 3A). The chamber was setup with possibilities to supply air independently through three air distribution strategies: three Air jet diffus-ers, two displacement diffusers and four ceiling mounted mixing diffusers.

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The classroom had windows located on the wall facing the outdoor simulat-ing chamber. The outdoor simulating chamber is designed to simulate dif-ferent thermal outdoor conditions from winter to summer with temperature possibilities of -20 oC to 35 oC. In all studies, the outdoor simulating chamber was set at the same temperature as the classroom air temperature. Thus, the differences between the mean radiant temperature (tr) and room air temper-ature (ta) was negligible.

Figure 3: (A) Classroom setup (B) Thermal manikin measurements and respective sitting positions.

One study involving a thermal manikin (part of Paper V) was done in a cli-mate chamber, 5.5 m x 5.5 m and ceiling height of 2.54 m, at the Center for Built Environment (CBE), University of California- Berkeley (Figure 3B). Details about control and capabilities of the climate chamber are discussed by Arens et al., (1991).

3.4 Measurements

3.4.1 Objective measurements

Measurements were conducted in the controlled environmental chamber (Figure 3A) with 18 cylindrical human heat simulators to represent human occupancy. The heat simulators were developed to produce heat corresponding to human occupants doing sedentary work (Mattsson, 1999). The room was designed as a classroom with three independent air supply systems: IAJS, DV and MV. All systems had a common exhaust. MV and DV ran with an airflow rate of 180 l/s. Airflow rate settings were maintained under IAJS but the supply fan was intermittently operated with a cycle of 6 min: 3minutes on and 3 minutes off. The systems were evaluated and compared with regard to air speeds and temperature characteristics in the room, thermal comfort for a sitting occupant and ventilation efficiency.

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A point-wise measurement technique was used for all objective measure-ments. Point-wise measurement techniques involve local measurements on a specified point using one sensor e.g., anemometers, thermistors, laser Dop-pler velocimetry and tracer gas measurements (Sandberg, 2007; Sun and Zhang, 2007). To get conditions across the room, an array of sensors are simultaneously used at different positions. This is disadvantageous as it “may either disturb the flow field, such as with intrusive methods (e.g., ther-mal anemometers) or excessively increase the complexity and cost of meas-urement settings/equipment for nonintrusive or partially intrusive methods, such as laser Doppler” (Sun and Zhang, 2007). However, the method is in-expensive and is user friendly, thus it is widely used by many researchers and engineers. Detailed discussions on measurement methods are presented by Sandberg (2007) and Sun and Zhang (2007).

3.4.1.1 Air speed and temperature

All temperature and air speed measurements were done with low velocity omnidirectional thermistor anemometers, type CTA88 (constant-tempera-ture anemometers). The thermistor anemometer is integrated with an air speed sensor having an accuracy of ±0.05 m/s and a temperature sensor with accuracy of ±0.2 oC (Lundström et al., 1990). One main source of measure-ment errors is the difference between measurement and calibration condi-tions (Sun and Zhang, 2007). Thus calibration of the sensors should be done with care and within conditions to be investigated. In addition, each sensor is calibrated individually due to difficulties in maintaining sensor reproduc-ibility during manufacturing. The sensor is sensitive to disturbances espe-cially in low velocity flow fields were thermal buoyancy generated by the sensing elements itself can become a source of inaccuracy. The sensors are controlled through a multichannel logger connected to a computer; in this study, a LabVIEW program (2009 version) was used. All thermistor ane-mometers measured with a sampling frequency of 1 Hz, and were calibrated prior to measurements.

Measurements were performed in accordance to ASHRAE standard 55 (2013): 1 minute interval, sample rate of 1 second and at the height of 1.1 m, 0.6 m and 0.1 m from the floor. Under IAJS, measurements were done both inside and outside the jet. Other temperature measurements were done with thermocouples, type T (copper-constant). Measurements were done in the supply, exhaust and at 6 equally spaced vertical points from the floor (0.1 m from floor) to the ceiling (0.1 m below ceiling) in the center of the room. In addition, surface room temperatures were measured with thermocouples taped with ventilation tape on the wall surfaces to avoid the influence of room air temperature. The ceiling and the floor were not measured.

3.4.1.2 System performance on thermal comfort

Measurements to predict thermal comfort (Paper I) were done with the ther-mal comfort data logger INNOVA 1221(INNOVA 1221, 2007). The logger

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was managed on a computer through a software-INNOVA 7701 running on a thermal comfort code based on ISO 7730. The software enables coordina-tion of the inbuilt modules and connected transducers to derive information and estimate PMV and PPD. The equipment has four transducers that measure the shielded room air temperature, air velocity, humidity and dry heat loss. The temperature transducer measures with an accuracy ±0.2 oC and the ve-locity transducers with an accuracy of ±0.05 m/s.

Thermal comfort measurements were done as stipulated in the standards (ASHRAE Standard 55, 2013; ISO 7730, 2005): at the height of 0.6 m from the floor for a sitting person and with a measurement interval of 3 minutes in steady state conditions. 1.2 met and 0.7 clo were used as personal input values for metabolic rate and clothing insulation, respectively. Under IAJS, measurements were divided into two: 1) the measurements were done under steady airflow conditions both inside and outside the jet. This was achieved by first taking measurements while the jets ran continuously. Then the meas-urements were repeated without the jets running. 2) Measurements were taken under transient conditions with intermittent operation of air speeds both inside and outside the jet. This gave insight on how the system would influence thermal sensation fluctuations of occupants exposed to IAJS. Torepresent human occupants, human heat simulators were used.

3.4.1.3 System performance on supply air distribution

The system’s ability to distribute supplied air in the room was measured with a tracer gas decay (Step-down) method using ventilation efficiency indices discussed in section 2.2.1 and 2.2.2. The tracer gas used was Sulphur hexafluoride (SF6). The classroom was dosed with about 400 ppm and thoroughly mixed with circulating movable fans for about 3 min. This was to thoroughly mix the room air and try to ensure that the room concentration was the same as the exhaust. All the measurement points were the same for all ventilation systems for comparison purposes.

3.4.1.4 Carbon dioxide measurements

As earlier stated, CO2 is commonly used as an indicator for evaluating and controlling indoor air quality (Persily, 1997). In the current study, CO2 measurements were done in human response studies (Paper I and II) but are presented here as they are objective measurements. Measurements were done during occupancy with Rotronic CL11 datalogger (Bassersdorf, Switzerland) at the height of 1.1 m from the floor in each sitting column. Measurements were logged at an interval of 10s and the accuracy of the instrument was ± (30 ppm + 5 % of the reading) between 0 and 5000 ppm. The instrument was newly purchased and was calibrated by the manufacturer.

3.4.1.5 Manikin measurements

A thermal manikin study was done to estimate the cooling influence of IAJS on occupants’ body parts. A female thermal manikin having 16 individually controlled body segments and a total surface area of about 1.5

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m2 was used to represent a human body and the associated thermal plume.The manikin had a clothing insulation level of 0.7 clo and was controlled using comfort mode, i.e., the heat loss and skin temperature in each individual segment was the same as an average person in a state of comfort under the environmental conditions (Tanabe et al., 1994). Two sitting positions were investigated as shown in Fig. 3B, based on assumed typical sitting postures in classrooms: sitting upright and inclined forward (30 degrees to the vertical). Since thermal manikin’s need steady state conditions for reliable measurements, the measurements under IAJS were done under constant airflow supply with the jet running for an hour and respectively without a jet, as previously done by Wigö and Nilsson (2004).

3.4.2 Subjective measurements

Subjective measurements quantify human responses to indoor environment through use of subjective scales. The scales are designed based on the psy-chological continua, relevant to the psychological phenomenon of interest or what is being inquired (ISO 28802, 2012). CEN/EN 15251 (2007) states that direct subjective responses to the tested system can be used as an overall evaluation of the generated indoor environment. Subjective measurements are advantageous as they help obtain a better understanding of the systems actual influence on occupants’ experience of the generated indoor environ-ment. However, they are disadvantageous in that they may interfere with what is being measured if the survey is not well designed, and there is little or no explanations to why participants provide certain responses. Addition-ally, the method may not be appropriate for certain groups of people e.g., babies, children and people with disabilities (ISO 28802, 2012).

Three papers based on two case studies were investigated and are in-cluded in this thesis. The first case study (Paper II and III) evaluated occu-pant response to IAJS as a primary ventilation system. Here, the subjective questionnaire design was based on a combination of standards (ASHRAE 55, 2013; ISO 10551, 1995; ISO 28802, 2012; ISO 7730, 2005) and inquired on the overall body and local parts (head, neck, back, chest, arms, hands and legs). The second case study (Paper IV) evaluated occupant response to IAJS running as secondary system, ceiling mounted induction unit, in conjunction with a primary MV system. The questionnaire was designed in accordance with ISO 28802 (2012) but was modified, instead of using the thermal sen-sation vote (TSV), the mean thermal vote (MTV) was used. The MTV was suggested by Nilsson and Holmér (2003) and was also used by Wigö (2013). The MTV scale has 7 points, same as the TSV, but it also determines whether the condition is comfortable or not within the same scale (See Appendix A1). The scale clearly classify the scores between slightly warm (+1) and slightly cool (-1) as comfortable, and anything falling outside is classified as uncom-fortable (Wigö, 2013). One issue with the MTV scale is that it is not gener-ally accepted/known among researchers in the field as compared to the TSV.

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3.4.2.1 Questionnaire design

ISO 10551 (1995) and ISO 28802 (2012) emphasize the importance of sub-jective questionnaire design as occupant responses are influenced by how questions are presented. To this end, ISO 10551 has given guidelines on con-struction of subjective scales and identified five basic scales with a respec-tive layout as shown below:

‒ Perceptual (How do you feel now? e.g. hot) ‒ Affective (How do you find it? e.g. comfortable); ‒ Preference (How would you prefer to be? e.g. cooler); ‒ Acceptance (acceptable/unacceptable); ‒ Tolerance (Is the environment tolerable?).

In the studies herein, all questionnaires were designed with the layout given above and inquired on participants’ thermal and IAQ perception; of most interest was occupants’ acceptability of intermittent airflow. Perceptual as-sessment was applied to evaluate participants’ thermal sensations and overall air quality. Thermal sensations were reported on the ASHRAE 7-point scale (ASHRAE 55, 2013). This is a visual analogue scale ranging from cold to hot: cold (-3), cool (-2), slightly cool (-1), neutral (0), slightly warm (+1), warm (+2), hot (+3). Perceived air quality was assessed through five air qual-ity variables: Dry, humid, fresh, stuffy and smelly. In each condition, partic-ipants were asked to rate how they judged the air quality variables on a scale of 1 to 4 (1 – ‘not at all’, and 4 – ‘very much’).

A visual analogue affective scale was used to assess occupant thermal comfort. Likewise, the acceptance scale inquired on occupants’ acceptability of thermal climate, air movements and air quality. The acceptance scale was the same as the affective scale. The scales were split in the middle giving a clear distinction of the comfortable or acceptable scale: +0.1 “just comfort-able/acceptable” to +1 “very comfortable/acceptable”, and the uncomforta-ble/unacceptable scale: -0.1 “just uncomfortable/unacceptable” to -1 “very uncomfortable/unacceptable” (Schiavon et al., 2016; Zhang and Zhao, 2009).

The preference scale was used to evaluate preferred conditions in refer-ence to the exposure. For example, under thermal climate assessment, par-ticipants were considered satisfied with the thermal climate if their thermal comfort vote was on the positive side of the thermal comfort scale and indi-cated no change on the preference scale. Otherwise they were considered to be dissatisfied. Appendix A2 shows the questionnaire used in Paper I and II.

3.4.2.2 Analysis

All subjective responses were analyzed with SPSS software version 2014 (Wagner III, 2014). The paired t-test and repeated measures analysis of var-iance (ANOVA) was applied on normally distributed data, while for not nor-mally distributed data, analysis was done with Friedman ANOVA test and

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Wilcoxon signed-rank tests. Normality was tested with Shapiro-Wilk test. Correlations between variables for normally distributed data were estimated with Pearson correlation coefficient and Spearman's rank coefficient for non-normally distributed data.

3.5 Estimation of the cooling effect of IAJS

The cooling capacity of elevated air movements determines the energy sav-ing potential of a system. In practice, estimation of the cooling effect is important for the application of elevated air movements as it serves as a basis of system performance in comparison to energy use of other systems. In this study, two comparative methods were used to determine the cooling effect of IAJS and the implications on the building energy use.

3.5.1 Manikin–based cooling effect

To measure the physiological effect of IAJS on the human heat loss on indi-vidual body parts, a female thermal manikin was used. Measurements with a thermal manikin is the most accurate measuring method for human dry heat loss (Nilsson and Holmér, 2003). In this study, the manikin-based equivalent temperature was used to investigate the cooling effect under IAJS in com-parison to MV in isothermal conditions. The manikin-based equivalent tem-perature is the realistic skin surface temperature a manikin at comfort has in a uniform enclosure, which represents conditions of heat loss that the thermal manikin would have in the actual environment (Yang et al., 2009). The dif-ference in the manikin-based equivalent temperature (∆Teq) was used as a representation of the cooling effect. The manikin based cooling effect (∆Teq) is therefore the difference of manikin-based equivalent temperature with and without air jets and is defined by the following expression:

∆𝑇𝑒𝑞 = 𝑇𝑒𝑞1 − 𝑇𝑒𝑞2 (9)

Where, Teq1 is the manikin equivalent temperature under conditions with air jets and Teq2 is the manikin equivalent temperature under conditions without air jets.

3.5.2 Cooling power analysis

Zhang et al., (2015) introduced the concept of corrective power analysis to assess and compare personal comfort systems (PCS). They defined correc-tive power as the difference in room ambient temperature at which the same thermal sensation is achieved by introducing a comfort strategy i.e., cooling systems or heating systems. In this study, the term has been changed to cool-ing power (CP) as it well reflects the intention of using air jets in a classroom. The analysis compares the cooling power of IAJS to that of MV and DV for

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the same thermal sensation values. This also provides a basis for investigat-ing the performance of the system with regard to energy savings. Thus, the cooling power is defined by the expression:

𝐶𝑃 = 𝑇1 − 𝑇2 (10)

In Equation 10, T2 is the room ambient temperature under mixing and T1 is the room ambient temperature under IAJS for the same thermal sensation.

3.6 Limitations and Validity aspects

The experimental investigation herein is limited to climate chamber studies involving objective measurements on ventilation, air speed, temperature and thermal comfort in a classroom mock up and within an operative temperature range of 22 oC – 28.5 oC, air speed range of 0.4 m/s – 0.8 m/s under IAJS and relative humidity of range of 15 – 40%. Objective measurements are limited to a single-point measurement method, done in the occupied zone. Subjective measurements are limited to indoor thermal climate, perceived air quality and air movement acceptability.

Validity aspects considered are, internal and external validity. Internal validity concerns whether the observations are caused by the independent variables only, while the external validity involves the degree to which the findings can be generalized to a different population and circumstances (Liebert, 1995).

In the current study, the threat to internal validity was reduced by use of climate chambers which allowed control of individual variables such as room air temperature, air speed and radiant temperature. Thus, participants were exposed to the same environmental conditions, and personal factors such as clothing and activity level were also controlled, and all participants were acclimatized to the tested conditions. Participants were randomly se-lected and during the experimental sessions, participants were encouraged to do their best and answer all questions as honestly as possible.

External validity questions whether the results obtained in a study can be generalized to other persons and places. First, the participants, aged between 17 and 48 years, were recruited from a local University, as such one could assume that the results could be generalized to the age group used in the study. Second, thermal experience and acclimatization to climate zone is shown to influence occupants’ judgement and acceptability of indoor ther-mal climate, with occupants in hot and humid climates having a higher com-fortable temperature range than those in arid climates like Scandinavia (Charles, 2003; Humphreys, 1994; Oseland and Humphreys, 1994). In the works herein, the studies were performed in classroom mockup in a climate chamber with Scandinavian participants, therefore occupant perception of comfortable conditions would not necessarily be judged comfortable or ac-ceptable in other climatic regions. Most importantly, the results presented

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herein are not exempted from uncertainties associated with human laboratory studies.

Measurement instruments and characteristics of the measurement proce-dure may also affect validity of the results. To reduce measurement uncer-tainties, instrument calibration should be done before starting measurements and consistent measurement procedures are recommended. In the current study, measurements were done under the following uncertainties: Velocity and temperature instrument uncertainty of ±0.05 m/s and ±0.2 oC and the overall uncertainty of 9.1% and 10.3%, respectively. PMV-random uncer-tainty of 1.3% (the instrument overall accuracy was not given in the specifi-cations).

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4 Results and discussion This section presents a general overview of some results and discussions re-ported in the appended papers. Here, the results are presented in accordance with the research process.

4.1 Objective study

The aim of the objective study (Paper I) was to explore ventilation perfor-mance of IAJS in comparison to MV and DV. Using a classroom mockup as a case study, evaluation of characteristics of room air speed and temperature, air distribution and thermal comfort was done.

4.1.1 Air speed and temperature characteristics in the occupied zone

4.1.1.1 Air speed

Under IAJS, the resulting airflow in the room and around the human heat simulator was sinusoidal having two components: the low frequency com-ponent which defined the period of intermittency (0.003 Hz) and the high frequency which were wavelets (0.1 Hz) present on both low and high pulses (Fig. 4A). The high pulses had a mean air speed of 0.43 m/s and low pulses had air speed < 0.2 m/s (measured in the sitting positions under the AJD); the airflow during the whole cycle had a turbulence intensity of about 28% (Fig. 4B). An important observation to emphasize here is that the employed intermittent supply created very different velocity conditions between peri-ods of intermittence (low and high pulses). This airflow characteristic is crit-ical for practical implementation of the strategy as it enhances convective cooling and consequently allowing increase on the cooling temperature set-ting on the HVAC system. A similar observation was made outside the jet; the mean air velocity measured was about 0.36 m/s when jets were running and < 0.2 m/s when jets were off. The cycle had a turbulence intensity of about 22%. The absence of human heat simulators in the room gave a reduction ratio of about 83% on the measured velocities outside the jet. Thus, occupancy had an influence on the velocity characteristics outside the jet. We can thus deduce, airflow fluctuation benefits also extend outside the jet ,that is, enhanced convective cooling will to an extent be experienced outside the jet. Under DV and MV, the average velocity measured at the breathing height was <0.2 m/s. No effect due to human heat simulators was noticed on the velocity characteristics in the MV but in DV, the airflow distribution in the

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occupied zone was influenced by the presence of simulators. Air speed meas-urements in the middle of the room, at 0.1 m from the floor, differed depend-ing on whether human simulators were present (0.13 m/s) or not (0.23 m/s), resulting in a reduction ratio of 54%. This verifies that in high occupancy spaces DV limits the penetration distance of airflow along the room; a simi-lar observation was made by other researchers (Cao et al., 2014). Thus, occupants furthest from displacement diffusers are likely to complain of air quality but will also have a reduced risk of draft.

Figure 4: Air velocity characteristics under IAJS: (A) mean velocity profile in the occupied zone (B) Characteristics around the human simulator.

4.1.1.2 Temperature

Room temperature condition under IAJS and MV were similar, with both systems having a mean temperature distribution very close to the exhaust temperature. The only difference was noticed around the human heat simu-lator, while no fluctuations were observed under MV, measurements under IAJS was dependent on the status of the jets. Because of the intermittent airflow, the temperature had a sine wave like profile around the human sim-ulator, with frequency of about 0.003 Hz and temperature deviations of ± 0.5 oC about the mean (Figure 5). The fluctuations were more profound on

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measurements made on top of the human heat simulator, which was an indi-cation of a cyclic distortion and reformation of the free convective boundary layer around the simulator. This characteristic is beneficial at elevated tem-peratures, as it would induce thermal relief. Also the measurements confirm that air speeds at about 0.4 m/s distorts the human convective boundary layer as recommended by other researchers (Licina et al., 2015a; Wigö, 2005).

Figure 5: Temperature fluctuations around the human simulator under IAJS.

Table 1 shows temperature measurements in the room. DV gave a lower mean temperature in the occupied zone compared to IAJS and MV for the same supply temperature. This shows that DV had a better cooling capacity (as seen from the heat removal effectiveness), confirming the general con-sensus in literature (Awbi, 2003; Etheridge and Sandberg, 1996; Hamilton et al., 2004). In any case, the air temperature distribution under DV was char-acterized by thermal stratification and were all below the limit (< 3 oC/m) stipulated in ASHRAE (2013).

Table 1: Temperature measurements in the room

ts = supply temperature, ta = room ambient temperature, tex = exhaust, tg = vertical temperature gradient, and HRE = heat removal effectiveness.

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4.1.2 Ventilation performance: Air distribution indices

Table 2 shows results on air distribution indices: local air change index and air change efficiency. Measurements were done in four positions in the oc-cupied zone at 1.1 m from the floor. As shown, MV and IAJS had little dif-ferences between measurements for local air change index, although measurements outside the jet, under IAJS, had slightly lower values with 𝜀𝑝

𝑎 < 1. DV gave the best measurements in all measurement positions and conditions.

Table 2: Local air change index and Air change efficiency

Note: P (measurement point); * measurement points outside the jet

DV provided the highest air change rate of 3.99 h-1. Interestingly, despite the intermittency in supply, IAJS had a higher air change rate 3.74 h-1 compared to a MV with 2.90 h-1. This is attributed to the high momentum supply into the sitting zone, thus a large portion of the supply air reaches the breathing zone. Although the air change rate may not necessary mean good indoor air quality, it can be used as an indication of a well ventilated space (Cao et al., 2014; Pereira et al., 2009). Further evaluation of the air change rate under IAJS shows that conditions were equivalent to a system that was running continuously at a flowrate of 8.1 l/s. On a note of caution, this result should be interpreted with caution, as the influence of room infiltration during in-termittent supply was not accounted for or verified. The objective measurements on air distribution were limited by the re-sponse time of the tracer gas machine, hence it was difficult to perform de-tailed analysis of air distribution or the effect of intermittence on contaminant concentration in the sitting zone. The values shown in table 2 represent the mean values for the overall measurement period. Thus, the lo-cal ventilation capabilities of the system could be underestimated or overes-timated. For this reason, carbon dioxide measurements were done in the sitting zone during the human response studies (refer to section 3.3.1.4). Fig-ure 6 shows the results under full occupancy in the room with IAJS and MV, independently operated.

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Figure 6: CO2 measurements in each sitting column during one of the experimental ses-

sions.

The concentration profile suggests that the intermittence in supply had lit-tle/no effect on the air distribution in the room. Thus, IAJS was running just like a mixing ventilation system and as shown in Figure 6, the concentration profile between periods with MV and IAJS is very similar with a mean cen-tered around 800 ppm.

4.1.3 Ventilation performance: Thermal comfort

The intermittence generates periodic air movements which were hypothe-sized to enhance convective cooling both inside and outside the jet. Objec-tive measurements of thermal comfort under IAJS showed that in indoor climate with air temperature of about 28 oC, PMV was between neutral (0) and slightly warm (+0.5). Measured under steady state with jets running, PMV = +0.23, PPD = 7.2% inside the jet, and PMV = +0.33, PPD = 9.4% outside the jet. While measurements in conditions without jets were similar to MV, the measurements under transient airflow resulted in PMV fluctua-tions as shown in Figure 7. In MV, the overall PMV = +1.31, PPD = 45%, While DV with a room temperature of about 26 oC had a PMV = +0.59, PPD = 12%. For detailed measurement results, refer to appendix B.

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Figure 7: PMV measurements inside and outside the jet with the intermittent operation of

the jets at supply temperature (ts) of about 22 oC or room temperature (tr) of about 28 oC.

In room air temperature of about 24 oC, the PMV measurement under MV was about +0.05, PPD = 5.9%. In IAJS and under steady state conditions with jets running, PMV = -0.62, PPD = 13.6% inside the jet, and PMV = -0.45, PPD = 9.3% outside the jet. Likewise, measurements without jets were similar to MV. Measurements under transient conditions showed improve overall thermal climate: mean PMV = -0.27, PPD = 7.3 measured inside the jet, and PMV = -0.18, PPD = 6.9% measured outside the jet. Figure 8 shows the resulting fluctuations in PMV measurements. As shown, PMV has a fluc-tuating profile following the profile of air speed. Since the thermal comfort machine is a tool for steady state conditions the reported results under tran-sient conditions may underestimate or overestimate the results. For this rea-son, it is only used to give insight on the physiological manipulation of the expected human heat loss or thermal sensations under IAJS. Thus, a human study was recommended.

Figure 8: PMV measurements inside and outside the jet with the intermittent operation of

the jets at supply temperature (ts) of about 14 oC or room temperature (tr) of about 24 oC.

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4.2 Subjective study

Investigating the occupants’ perception of the resulting indoor environment due to IAJS is an important aspect of evaluating a ventilation strategy. Espe-cially, that fluctuating air movements have a psychological influence on oc-cupants thermal comfort. Thus, human response to intermittent airflow characteristics is critical for this evaluation. In this thesis, two case studies were investigated: Case study one evaluated occupant response to IAJS as a primary ventilation system, while case study two evaluated occupant re-sponse to IAJS as secondary system (ceiling mounted induction unit) in con-junction with MV system.

4.2.1 Case study 1

In this study (Paper II and III), the goal was to explore human response to IAJS as a primary ventilation system (See Figure 9), as well as human esti-mates of the applicable air speeds and operative temperatures at sedentary function. 36 participants were recruited and they sat in a classroom mockup for 120 min. The participants (having a clothing insulation of 0.51 clo.) were exposed to twelve conditions: three room air temperatures (nominal: 22.5, 25.5 and 28.5 oC), each with varied air speeds (nominal: <0.15 m/s under MV, and 0.4, 0.6 and 0.8 m/s under IAJS) measured at breathing height. Each velocity condition lasted for about 30 min under IAJS and 40 min under MV.

Figure 9: (A) System setup1 and (B) experimental procedure.*- short questionnaire and

Adaptive questionnaire; the questionnaires were the same). Q1, Q2, Q3 and Q4 are

the main or exposure questionnaires.

1 IAJS and MV were independently operated but were connected to the same air handling unit (AHU) and supply fan. Inversely controlling two dampers (D1 and D2) to either supply through mixing diffusers (MD) or air jet diffusers (AJD) achieved this. Intermittency during IAJS was attained by inverse cyclic operation of the dampers, D2 and D3.

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4.2.1.1 Thermal sensation

Figure 10 shows boxplots of overall thermal sensation (OTS) across condi-tions. At 22.5 oC, MV was the most desirable condition, with a Friedman test giving a statistical significance, χ2 (3) = 49.683, p < 0.001. Wilcoxon signed-rank test showed that changing exposure from MV to IAJS worsened overall thermal sensations (p < 0.001). This makes sense because conditions under MV were already skewed towards slightly cool (-0.5), thus introducing air movements had a negative influence on occupants’ thermal sensation. No statistical differences were found between velocity conditions under IAJS. All conditions at 25.5 oC were perceived to be neutral (median = 0) but the distribution was skewed towards slightly warm under MV and towards slightly cool under IAJS. Statistical analysis across conditions was signifi-cant, χ2 (3) = 41.790, p < 0.001, which is attributed to the differences in distribution between MV and IAJS (p < 0.001). At 28.5 oC, conditions with IAJS were desirable, specifically 0.6 and 0.8 m/s. Votes under MV were out-side the comfort range based on recommendations given in ASHRAE stand-ard 55 (2013), and the difference between MV and IAJS was statically significant (p < 0.001). This suggests that introducing intermittent air veloc-ities in a range of 0.6 – 0.8 m/s would necessitate comfortable sedentary operation in operative temperature of about 28.5 oC.

Figure 10: Overall thermal sensation votes across test conditions; Slg (Slightly) and Vel (Velocity).

A thermal sensation model was developed using a multiple regression to pre-dict OTS given air velocity (V) and operative temperature (𝑡𝑜). The findings show that the variables predicted OTS with a statistical significance, F (2, 445) = 231.722, p < .0005, R2 = 0.510. Air velocity had a negative correlation (-0.373) while temperature had a positive correlation (0.608) with overall thermal sensation. The resulting general multiple regression model proposed here is:

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𝑂𝑇𝑆 = 0.31𝑡𝑜 − 1.72𝑉 − 7.15 (11)

This model can be useful in predict thermal sensation under defined opera-tional conditions of IAJS. Here, V is measured at 1.1m from the floor and 𝑡0 is the average room operative temperature. For example, applying the pro-posed air speed limits herein (0.4 – 0.8 m/s), the model predicts a tempera-ture range of 23.7 oC – 29.1 oC within which IAJS can operate in accordance with the comfortable range, slightly cool (-0.5) to slightly warm (+0.5), stip-ulated in ASHRAE standard 55. It is worth noting that in this study the room air temperature was equal to mean radiant temperature ( 𝑡𝑎 = 𝑡𝑜). In the ap-pended papers 𝑡𝑜 is sometimes replaced with 𝑡𝑎 (room ambient temperature). Evaluation of overall thermal sensation and local thermal sensation showed that under uniform/homogenous environments (MV), overall ther-mal sensations may be highly influenced by all the body parts. However, under transient conditions (IAJS) the major contributing factors maybe body parts with a higher heat-loss, in this case, highly exposed body parts to air movements like the head, neck, arms and hands. The results here are in agreement with findings by Yang et al., (2010a) on local thermal sensation due to ceiling-mounted personalized ventilation system. Another interesting observation was that, other studies (Arens et al., 2006; Schiavon et al., 2016) show that body parts with thermal sensations far from neutral have a stronger effect on overall thermal sensations than those whose sensation is near neu-tral. This was confirmed under MV and only in a low temperature condition (22.5 oC) under IAJS. However, in warm conditions (28.5 oC) under IAJS, overall thermal sensation was strongly correlated with body parts having thermal sensations close to neutral as opposed to those far from it. This leads to a conclusion that in undesirable warm thermal conditions and under tran-sient air speeds, overall thermal sensation will highly be influenced by body parts with high convective heat loss.

4.2.1.2 Thermal acceptability

Figure 11 shows the overall thermal acceptability across test conditions. 25.5 oC was the most thermally acceptable condition with 3 - 12 % of the subjects being dissatisfied. At 22.5 oC all conditions were below 80% satisfied, with more dissatisfaction reported under IAJS as compared to MV (p < 0.001). A relationship between thermal acceptability and air velocity had a medium negative correlation, Pearson correlation coefficient = -3.48, p < 0.001. Clearly, an increase in velocity reduced thermal acceptance and conse-quently increased percentage dissatisfied with the thermal climate. At 28.5 oC, MV was the least acceptable condition compared to conditions under IAJS (p < 0.003). As shown, use of intermittent air movements even as low as 0.4 m/s improved occupant’s thermal acceptability tremendously.

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Figure 11: Thermal acceptability of the environment for each respective test condition.

4.2.1.3 Air movement acceptability and preference

The overall air movement acceptability was highly correlated to the opera-tive temperature. Descriptively, air speeds under MV were most acceptable at 25.5 oC, 0.75(0.39, 0.96), and least acceptable at 28.5 oC, 0.1(-0.24, 0.58) and slightly above just acceptable at 22.5 oC, 0.25(0.1, 0.75). A Wilcoxon signed-rank test showed that occupants favored IAJS at 28.5 oC compared to 25.5 oC (Z = -3.933, p < 0.001) and 22.5 oC (Z = -2.950, p = 0.003). There was no statistical difference between 22.5 oC and 25.5 oC (Z = -1.606, p = 0.018) although the tendency showed that 25.5 oC was more acceptable (For detailed results refer to Appendix C). The findings here suggest that, at moderate temperatures (25.5 oC), both MV or IAJS will generate acceptable air movements. However, at elevated temperatures (28.5 oC) IAJS will be suitable, as it seems to offer favorable air movements. Similarly, at 22.5 oC, the subjects were between slightly cool and neutral (without intermittent air movement), when intermittent air move-ment were introduced, the conditions were perceived as drafty. This is also supported by the responses on occupant preference of air movements (Figure 12). Comparing with Figure 10, it shows that air movement preference cor-relates with the overall thermal sensation. A demand for less or more air movements is greater in conditions with thermal sensation votes further away from neutral, while no change is requested in conditions with thermal sensation votes (median) around neutral (0). These results confirm that occupants’ acceptability of intermittent air movements will depend on their thermal state (McIntyre, 1979; Tanabe and Kimura, 1989b; Xia, Zhao, et al., 2000; Zhou et al., 2006).

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Figure 12: Air movement preferences across test conditions; Slg (Slightly) and Vel (Velocity).

A logistic regression was applied to develop a model to predict percentage satisfied with air movements (PSAM) based on overall thermal sensation. Development of the model is discussed extensively in Paper III. The devel-oped model (Equation 12) was tested against the constant model and it reli-ably distinguished between unacceptable and acceptable conditions based on overall thermal sensation (chi square = 85.355, p < 0.001 with df = 1). Nagelkerke’s R2 of 0.256 and the overall prediction success was 79.7% (97.1% for acceptable and 19.5% for unacceptable). The full model im-proved the constant model by 7%.

𝑃𝑆𝐴𝑀 =𝑒𝑥𝑝(2.07 − 0.42𝑂𝑇𝑆² )

1 + 𝑒𝑥𝑝(2.07 − 0.42𝑂𝑇𝑆² ) (12)

Given room environmental conditions i.e., air velocity and temperature, Equation 11 can be used to determine overall thermal sensation and conse-quently, using Equation 12, percentage of occupants who will find air move-ments acceptable can be determined. These two models are limited to conditions used in this study: 36 participants, air speed range of 0.4 to 0.8 m/s, operative temperature range of 22.5 to 28.5 oC, activity level of 1.2 met, Icl at 0.51 clo and a low relative humidity (18-30%). The models may relia-bly apply to the environmental conditions herein; therefore, a recommenda-tion given is to perform more studies with a larger sample size across different conditions to improve the models.

4.2.1.4 Air quality perception

Occupants’ responses to air quality acceptability is shown in Figure 13. As shown, whereas occupants’ acceptability of air quality decreased with in-crease in temperature in conditions with MV, (χ2 (2) = 26.097, p < 0.001),

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no effect was observed in conditions with IAJS. Suggesting that intermittent air movements (even as low as 0.4 m/s) were offsetting the negative effect of increased temperature on overall air quality acceptability. Comparing be-tween systems in each temperature condition, no statistical differences were observed in 22.5 oC and 25.5 oC, however, at 28.5 oC air quality was more acceptable under IAJS as compared to MV χ2(3) = 44.491, p < 0.001.

Figure 13: Overall air quality acceptability; J. Accept (just acceptable.), V. Accept (very accepta-

ble), J. Unaccept. (just unacceptable) and V. Unaccept (very unacceptable).

Further analysis was done on air quality variables in order to isolate specific components that affected air quality acceptability under MV. The effect was found on air quality variables such as fresh and stuffy (see Figure 14). Under MV, occupants’ tendency to perceive the air as stuffy worsened with in-crease in room temperature (χ2(2) = 22.202, p < 0.001). IAJS registered bet-ter results than those reported in MV both at 25.5 oC (χ2(3) = 8.549, p = 0.036) and at 28.5 oC (χ2(3) = 33.995, p < 0.001). No statistical differences were found at 22.5 oC. Similarly, under MV, occupants’ perception of air to be fresh worsened with increase in temperature (χ2(2) = 24.789, p < 0.001). Air was judged to be fresher under IAJS than under MV in both 25.5 oC (χ2(3) = 22.500, p < 0.001) and 28.5 oC (χ2(3) = 38.442, p < 0.001). No differences were found at 22.5 oC.

Figure 14: Differences in judgment of air at different room air temperature and air speed;

1 represents ‘not at all’ and 4 represents ‘very much’.

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The results confirm that intermittent airflow will have a positive influence on air quality perception as also reported by Yang et al., (2002). They also show that perceived air quality is dependent on thermal state as conditions with increased air movements offsets the effect of increased temperature on PAQ (Melikov, 2008; Melikov and Kaczmarczyk, 2008). Generally, partici-pants found air speeds to be undesirable at lower temperatures, but reported an improved thermal sensation, comfort and acceptability at higher temperatures.

4.2.2 Case study 2

This study (Paper IV) investigated occupants’ perception of convective cool-ing with recirculated room air. The air was directed on the head of a sitting person from a ceiling mounted induction air jet diffuser, outdoor air was delivered with a MV system as shown in see Figure 15A. 41 students from the University of Gävle were recruited to participate in the study and were exposed to two velocity conditions: (1) with velocity fluctuations having high pulses (0.4 m/s) and low pulses (< 0.2 m/s); and (2) without velocity fluctuations (steady state with air speed < 0.2 m/s). Participants performed sedentary work and had a clothing insulation level of 0.7 clo. They were divided into two groups defined by the velocity exposure sequence i.e., With-Without group (N=19) started with airflow fluctuations (MV + fluctuating air jets) and ended without airflow fluctuations (only MV), and vice versa for the second group (Without-With group, N= 22). The supply airflow rate was 260 l/s and the room temperature was 25 oC. Each velocity condition lasted for about 30 min. The results show that just recirculating room air with intermittent air velocities can improve occupant perception of the indoor environment.

Figure 15: (A) system setup (B) experimental procedure (Q1, Q2, Q3 and Q4 are exposure

questionnaires).

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4.2.2.1 Thermal comfort perception

Figure 16 shows the trend on the overall perception of thermal climate across the experimental session. The exposure sequence shows that the group (Without-With) that started without velocity fluctuations reported 25 ºC to be warm and uncomfortable with an average sensation score of +2.2, but when the velocity fluctuations were introduced the sensation dropped to an average of +0.76 (p < 0.02). Similarly, the group (With-Without) that started with velocity fluctuations, reported an average score of +0.67 and when the ve-locity fluctuations were switched off, the score rose to +1.86 (p < 0.03). This shows that intermittent air jets significantly improved occupants’ thermal comfort.

Figure 16: The participants’ thermal response to velocity conditions across time.

“With”-condition with MV + airflow fluctuations and “Without”-condition with only MV.

Another factor of interest under thermal comfort and indoor air speeds is draft, which is a concern common in many spaces with air speeds over 0.2 m/s at standard room temperature (25 ºC). To understand sensitivity of the occupants to intermittent air movements, participants rated their percep-tion of draft on a normalized scale 0 – 3, with 3 meaning very much. The reported mean difference on the draft rating between the conditions with air jets and that without them was 0.8. The difference was statistically insignif-icant. Thus, at 25 ºC the intermittent air jets had a low draft risk. Interest-ingly, when participants were asked about their preference to air movements, under exposure to air jets, about 42% wanted slightly more air movements and 48% were satisfied. On the other hand, in the condition without air movements, 14% indicated satisfaction while 80% wanted more air move-ments in the room.

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4.2.2.2 Perceived air quality

The exposure to air jets influenced occupants’ perception of air quality, spe-cifically, perception of air to be dry and perception of air to be fresh. Figure 17 shows participants mean scores on scale of 1 (not at all) to 5 (very much). The room air was considered dry in the condition without intermittent air jets (M = 3.74, SD = 2.95) compared to the one with intermittent air jets (M = 2.51; SD = 1.38). Similarly, room air was judged to be fresher under inter-mittent air jets (M = 3.44; SD = 0.4) than without them (M = 2.70; SD = 0.87).

Figure 17: Participants rating on Fresh and Dry perception of room air.

On average, the air quality in intermittent air velocity conditions was de-scriptively better than in conditions with only MV. An interesting observa-tion was that participants’ perception of indoor air quality was directly related to their thermal state. Comparing results on PAQ and MTV, led to a conclusion that air quality perception is independent of temperature but de-pendent on thermal state. The result here is in agreement with findings in case study 1 and also findings from other studies (Sekhar et al., 2003; Zhang et al., 2011).

4.3 Cooling effect of IAJS

Use of elevated air movements enhances convective cooling that gives com-fort at higher operative temperatures. The study herein (Paper V) explored two comparative methods to estimate the cooling effect of IAJS. The results are discussed in the subsequent sections.

4.3.1 Manikin–Based Cooling Effect

Figure 18 shows the manikin-based cooling effect (∆Teq) in both upright and inclined sitting postures. Here, only the upper body part is considered: left hand (L. Hand), left forearm (L.F arm), left upper arm (L.U arm), chest, head

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back, right hand (R. Hand), right forearm (R.F arm) and right upper arm (R.U arm); the lower body parts had no, if any negligible, differences between conditions with and without air jets. As shown, almost in all cases, ∆Teq was higher at the hands, followed by the head while on other body segments the cooling effect was similar. The sitting position also affected ∆Teq as lower values were obtained mostly in the upright sitting position than the inclined. This was also reflected in the whole body cooling effect; ∆Teq: 22 oC (up-right = -0.95, inclined = -0.5); 26 oC (upright = -0.89, inclined = -0.41) and 28 oC (upright = -0.62, inclined = -0.30). The lower values of ∆Teq indicate that there is a higher cooling effect due to the air jets compared to the re-ference value under MV.

Figure 18: Cooling effect analysis at 0.4 m/s for different room temperature and sitting postures

The manikin measurements show a higher local body part cooling effect (2 oC) as compared to the overall body cooling effect (1 oC). Zhang et al., (2015), stated that thermal manikins under-predict the actual whole body cooling effect to less than 1 oC compared to the cooling effect obtained with human subjects under exposure to air velocity < 1 m/s. This could explain why in the current study the highest whole body cooling effect was 0.95 oC with mean air speed of 0.4 m/s.

4.3.2 Cooling power analysis

Figure 19 shows a general overview of the shift in operative temperatures after introducing velocity fluctuations with an operational velocity of 0.4 m/s. As earlier stated, the difference between operative temperatures is de-fined as the cooling power (CP), which in this case is representative of the cooling effect of IAJS. Figure 19A shows results based on objective meas-urements with thermal comfort machine (Paper I). As shown, under the measurement conditions with MV and DV, 24 oC was the neutral tempera-ture, however in conditions with IAJS, the neutral temperature shifted to about 25.5 oC. By definition, air velocity fluctuations gave a CP = 1.5 oC.

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Figure 19B shows thermal sensation estimates based on the overall thermal sensation model (Equation 11) for 0.4 m/s under IAJS (solid blue line) and extrapolated responses under MV (solid green line). Under MV, 23 oC was found to be the neutral temperature, while with IAJS (0.4 m/s) the neutral temperature was 25.3 oC. Therefore, the resulting CP = 2.3 oC. In view of the human perception of the thermal environment, IAJS operating at a proposed minimal velocity (0.4 m/s) has the ability to correct the ambient environment by providing a cooling effect of about 2.3 oC. For the upper velocity limit (0.8 m/s), the estimated neutral temperature with the thermal sensation model (Equation 11) is 27.5 oC. By applying the same logic of cooling effect analysis, this translates to an offset of about 4.5 oC. Basing on earlier studies that addressed energy saving possibilities by utilizing strategies that use el-evated air movements (James et al., 1996; Schiavon and Melikov, 2008; Bin Yang et al., 2010b; Zhang et al., 2015) we can deduce that IAJS holds a high potential for energy saving in spaces with high occupancy.

Figure 19: Influence of IAJS on thermal sensation and operative temperature. (A) PMV measure-

ments with thermal comfort datalogger. (B) Comparison of human responses and thermal sensa-

tion estimate with a comfort tool2.

2) A comparative analysis of thermal sensation estimate with CBE-thermal comfort tool (Hoyt et al., 2013), for the same indoor conditions for a human response and velocity of 0.4 m/s, shows a close prediction between the SET method (dotted grey line) and the proposed thermal sensation model (Equation 11). The PMV model (not included in the figure) overestimated the neutral sensation (28 oC) agreeing with the findings of another comparative study (Kabanshi, 2016).

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5 General discussion

The current study evaluated an intermittent ventilation system in high occu-pancy spaces specifically in classrooms. The general overview of the results reveal that IAJS has a high potential as an energy-efficient ventilation strat-egy in high occupancy spaces. In report I, objective measurement results show that IAJS has a local air distribution capability equivalent to a MV but gives a higher room air exchange rate. In report II and III with IAJS as a primary system, the human response results indicate that the system is favor-able at moderate and higher operative temperatures, and it offsets the nega-tive influence of high temperatures on occupant perception and acceptability of indoor environmental conditions otherwise deemed poor under MV. In Report IV with IAJS as a secondary system, the results confirm and show that introducing elevated air movements offsets the negative influence of temperature on human perception of indoor environment. In view of the find-ings reported in these studies, report V evaluated the cooling effect of IAJS and the findings show promising energy saving possibilities. Thus, if this system were to be implemented, it would have implications on occupant comfort and consequently on the HAVC energy use.

5.1 Implications on occupant comfort and building energy use

We established herein that IAJS creates nonhomogeneous conditions around the occupants. This complicates the relationship between thermal sensation and thermal comfort. Whereas in homogeneous conditions thermal comfort is a physiological phenomenon dependent entirely on thermal sensation (steady-state heat balance), in nonhomogeneous conditions (fluctuating air-flow) it is a two-step process involving physiological and psychological fac-tors (Parkinson and de Dear, 2015; Zhang and Zhao, 2008, 2009). First, intermittent airflow increases convective cooling thereby improving thermal sensation (physiological process). Second, the airflow confers sensory pleas-ure or a “cool breeze feeling” otherwise known as “thermal alliethesia”, (psychological process). This thermal pleasure induced by intermittent air-flow is transient whereas comfort is stable, refer to (Hellwig, 2015) and (Cabanac, 1971). Cabanac (1971) describes the experience as an exciting feeling of pleasure due to a useful stimulus that should not last once the trouble is corrected. For this reason, the psychological factor increases occupants perceived cooling capacity of intermittent/fluctuating airflow as compared to what would have been experienced under continuous or steady

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airflow of the same magnitude. Therefore IAJS will induce an increased per-ception of convective cooling and satisfaction with air movements in warm indoor climates, consequently increasing thermal comfort.

In building HVAC systems, the deadband (thermostat setpoint range) is critical for occupant satisfaction with the thermal climate and the building energy use. Widening the deadband creates opportunities for energy savings as it reduces the cooling/heating demand and the terminal unit airflow vol-ume rate (Hoyt et al., 2015). As discussed in the section 4.3., basing on the setup and human response results herein, IAJS has the capabilities to offset the upper operative temperature by 2.3 – 4.5 oC. In this regard, implementa-tion of IAJS would have practical implications because the operable condi-tions are shifted and extended over an elevated and wider room temperature range, consequently the upper thermostat setting of the HVAC system can be increased accordingly. Adjusting the upper thermostat setting has been shown to extensively reduce building energy use; even raising the thermostat by only 1 oC can result in 10 – 14% annual energy saving on the cooling requirements (Aynsley, 2008). In a simulation study, Hoyt et al., (2015) showed that increasing the upper setpoint from 22.2 to 25 oC for San Fran-cisco would result in 29% of cooling energy saving and 27% on total HVAC energy savings.

5.2 System applicability

In paper II, a thermal sensation model was developed which predicts an op-erable temperature range of 23.7 oC – 29.1 oC within which IAJS generates comfortable thermal conditions, slightly cool (-0.5) to slightly warm (+0.5) as stipulated in ASHRAE Standard 55 (2013). The predicted range is limited to experimental conditions of: operative temperature range 22.5 to 28.5 oC, activity level of 1.2 met, Icl at 0.51 clo and a low relative humidity. Im-portant about the predicted temperature range, it gives insight on applicable climatic conditions suitable for implementation of IAJS as a primary venti-lation system or as a secondary system. From this, we see that IAJS as a primary system would be suitable for hot climates like the tropics where cooling is needed for most parts of the year (Schiavon et al., 2010). Thus, giving opportunities to reduce HVAC cooling energy by using intermittent airflow in operative temperatures between 23.7 oC and 29.1 oC. IAJS as a secondary system can work in almost all climates, especially in buildings with existing HVAC systems due to the ease in installing and implement the system. In here, I deliberately apply its use in climates with relatively shorter cooling periods. For example in subarctic climates, outdoor temperatures in summer (Yang et al., 2017) suggest that comfort can be maintained adap-tively by window opening, but in cases were opening windows may not be optional (polluted outdoor conditions), comfort maybe attained with IAJS as an induction unit recirculating and increasing room air speeds to offset in-creased room temperature.

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The type of high occupancy spaces is another aspect of applicability. In the current study, we considered classrooms due to their high occupancy density per floor area (high human thermal loads). Additionally, the evaluated mockups had fixed sitting arrangements. In view of current educational prac-tices, especially in grade schools where flexible room arrangements and al-ternative layouts are required, system flexibility would be a barrier in implementing the system in such spaces. Thus, practical application can exist in classrooms with fixed sitting arrangements like high schools, college or university classes. Additionally, the system can be applied in open-plan of-fices (contribution of equipment heat loads i.e., computers, printers etc., con-tributes to temperature increase) and in cafeterias.

5.3 Limitations and future work

The current study involved a mix of methods to evaluate IAJS. One of the methodological challenges especially under objective measurements was on appropriate instrumentation and tools for elevated and fluctuating air supply. The measurement instruments available at the time of the study, e.g., thermal comfort machine, tracer gas machine and the thermal manikin are designed with tools (i.e., PMV model) for steady state conditions. While transient models have been proposed (Guan, 2003; Lomas et al., 2003; Wan and Fan, 2008; Wang, 1994; Zhang, 2003), to the authors knowledge there are no measurement instruments that are integrated with these models to help meas-ure thermal sensation. Additionally, most of the models concern thermal transients as opposed to transient airflow. Thus, estimating thermal sensation and comfort would have still required airflow to be steady and continuous as applied in the current method.

Further studies are recommended to get a complete understanding of IAJS. To begin with, detailed objective studies, experimental and numerical, should be done to capture the transient behavior of the airflow and the inter-action with the room ambient conditions. In this regard, understanding near exit fields would help gain and refine knowledge on the characteristics of the ensuing single row confluent jets. Additionally, future studies can investi-gate the distance at which the concentration in the supply jet equals room ambient concentration. This investigation can be generalized to also include application on individual personalized ventilation systems. This may be use-ful in optimizing system design, validation and application. Due to limita-tions on response time of the concentration measurement equipment (tracer gas machine), the air distribution results herein should be interpreted with caution. Thus, detailed analysis on the influence of an intermittent supply is needed on fresh air distribution and contaminant dilution capacity in the sitting zone. Additionally, the influence of supply air temperature on IEQ, and computational studies of IAJS with CFD are possible areas of further research.

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The subjective studies herein were limited to a relatively small number of participants and a slightly unbalanced gender distribution, clothing insula-tion of 0.51 and 0.7 clo., low relative humidity, metabolic rate of 1.2 met, air speeds between 0.4 and 0.8 m/s and operative temperature range of 22.5 – 28.5 oC. This may limit the generalizability of the results. Further human studies are needed to gain more understanding on the influence of controlled cyclic airflow fluctuations and to improve the proposed thermal sensation and air movement acceptability models.

In the current study, occupant exposure to fluctuating airflow was limited to laboratory conditions and about 30 minutes per condition, as such under-standing the influence of the system in real work or school environments that may demand long exposure is critical in implementing the system. Areas of interest may involve answering questions such as: What implications would prolonged exposure have on occupants and to what extent does periodic physiological manipulation of the body heat loss (convective cooling) have on human fatigue process? Would application of air movement fluctuations in classrooms disrupt student concentration or impair learning? Do the psy-chological benefits reported on perceived air quality extend to SBS symp-toms? What intermittence timing do humans prefer and to what extent would it affect IEQ? Additionally, the influence of noise (due to airspeeds through nozzles) on agitation, learning and productivity should be investigated.

Lastly, although the results clearly indicate the potential energy saving benefits of IAJS, a comprehensive comparison of energy performance be-tween IAJS and other ventilation strategies is needed. This can extend to include investigations on opportunities and challenges of implementing IAJS in both existing buildings and future buildings.

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6 Conclusion

This thesis presents an experimental evaluation of a novel ventilation strat-egy proposed for high occupancy spaces. The strategy uses ceiling mounted high momentum air jet diffusers that generate confluent jets that coalesce into a single two-dimensional jet. Generally, the system creates good indoor climate while promising a substantial energy saving potential, as compared to mixing ventilation. The strategy can be used to provide both local air movements and fresh air in the sitting zone. Alternatively, it can also be used as a secondary system to increase air speeds and to improve mixing or de-stratify room air. The aim of this thesis was achieved through a 3-part re-search process; the conclusions from each part are presented below.

The results on the objective study showed that despite the intermittence in supply, IAJS creates satisfactory indoor environmental conditions as a pri-mary ventilation system in spaces with high occupancy like classrooms. The evaluation of air distribution shows identical conditions in the sitting zone, suggesting good local air quality with highly mixed conditions in the jet, competing fairly with MV system, but the strategy offers a better air change rate than a MV system. The high intermitent airflow supply creates non-uni-form airflow and non-isothermal characteristics around the occupant that fa-vors thermal comfort in higher operative temperatures. Due to limitations with equipment and tools that favor non-transient conditions, more studies with appropriate instrumentation are needed to derive general conclusions.

The findings of the subjective study support the conclusions derived in the objective study, showing that IAJS is undesirable at lowers temperatures due to draft risk. However, the strategy improves thermal sensation, air qual-ity perception and acceptability of indoor environment at higher tempera-tures. A thermal sensation model and a model to predict percentage of occupants who will be satisfied with air movements were developed. The models can be used to determine design conditions in which IAJS complies with guidelines in the standards. In view of the human perception of the indoor environment, IAJS holds a potential as an energy efficient primary ventilation system, or as a secondary system augmenting reduction in cool-ing demand through controlled intermittent air movements. These conclu-sions are limited to the setup and experimental conditions herein, thus further human response studies, preferably field studies, are recommended to im-prove the proposed models and to build more understanding on the influence of IAJS on occupants.

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The study on cooling effect revealed the implications of implementing IAJS. Cooling effect analysis on the thermal manikin showed that under exposure to IAJS, the resulting airflow influences the upper body parts of a sitting person, with the highest effect experienced on the hands and the head. A comparative analysis of cooling effect based on human responses revealed that IAJS has a potential to offset the upper operative temperature by a min-imum of 2.3 oC, This creates opportunities to widen the deadband and in-crease the upper setpoint of the HVAC system, consequently offering opportunities to save building energy use.

Summing up the findings of this thesis, the overall conclusion of this ex-perimental study is that the system has a potential for use as a ventilation strategy in high occupancy spaces like classrooms. The use of air speeds can be categorized as a group personalized system with a single control.

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7 Miscellaneous publications

During the period of my PhD studies, I worked on other projects which are not part of this thesis. The following publications were in international jour-nals and conferences:

7.1 Journal articles

Kabanshi, A., Wigö, H., Poll, M. K. V. D., Ljung, R., & Sörqvist, P. (2015). The Influence of Heat, Air Jet Cooling and Noise on Performance in Classrooms. International Journal of Ventilation, 14(3), 321-332.

Holmgren, M., Kabanshi, A., Sörqvist, P. (2017). Occupant perception of ‘Green’ buildings: Distinguishing physical and psychological factors. Building and Environment, 114, 140-147.

Yang, B., Olofsson, T., Nair, G., Kabanshi, A. (2017). Outdoor thermal comfort under subarctic climate of north Sweden− a pilot study in Umeå. Sustainable Cities and Society, 28, 387 – 397.

Lui, S., Schiavon, S., Kabanshi, A., Nazaroff, W. (2017). Predicted Percentage Dissatisfied with Ankle Draft. Indoor air, (accepted December 2016. DOI: 10.1111/ina.12364 ).

7.2 Conference articles

Kabanshi, A., Liu, S., & Schiavon, S. (2016). Potential adaptive behaviour to counteract thermal discomfort in spaces with displacement ventilation or underfloor air distribution systems. Proceedings of the 14th international conference of Indoor Air Quality and Climate, July 3-8 2016, Ghent, Belgium.

Kabanshi, A. (2016). Experimental Evaluation of Intermittent Air Jet Ventilation Strategy: Cooling Effect Analysis. Proceedings of the 9th International Conference on Indoor Air Quality Ventilation & Energy Conservation in Building, IAQVEC 2016, 23-27 October 2016, Songdo, South Korean.

Kabanshi, A., Wigö, H., Ljung, R., & Sörqvist, P. (2014). Perception of intermittent air velocities in classrooms. Proceedings of the 13th International Conference on Indoor Air Quality and Climate, Indoor Air 2014, 7-12 July 2014, Hong Kong.

Kabanshi, A., Keus van de Poll, M., Ljung, R., & Sörqvist, P. (2014). Disruption of writing by background speech: a classroom experiment. Proceedings of the 11th International Congress on Noise as a Public Health Problem, Nara, Japan, June 1-5, 2014.

Kabanshi, A., Keus van de Poll, M., Wigö, H., Ljung, R., & Sörqvist, P. (2014). The Effect of Heat Stress on Writing Performance in a Classroom. Proceedings of the 13th International Conference on Indoor Air Quality and Climate, Indoor Air 2014, 7-12 July 2014, Hong Kong.

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Appendix A:

1: MTV scale:

2: Case study 1 questionnaire.

Enter ID: ………………….. Column: ........

Date: …………………………………… Time:…………………………………..

1. Onascaleof1to5,howwouldyourateyourconcentrationrightnow?1meanslowconcentrationand5meanshighconcentration(På en skala från 1 till 5, hur koncentrerad är du just nu? 1 betyder litekoncentrerad och 5 betyder mycket koncentrerad)Low High

1 2 3 4 5 2. Rightnow,towhatextentdoyoufeelheavyheaded.

1meansnotatalland5meansverymuch(Just nu, i vilken utsträckning känner du dig slö. 1 betyder inte alls och 5 betydermycket)Notatall verymuch

1 2 3 4 5

PartI:Mentalstatus ____________________________________________________________________

63

____________________________________________________________________ 3. How do youfindthetemperatureintheroomrightnow?

(Vad tycker du om temperaturen i rummet just nu?)

4. Rateyourcurrentthermalcomfort.(Bedöm den aktuella termiska komforten)

5. Rightnow,howacceptabledoyoufindthetemperatureintheroom?(Just nu, hur acceptabel tycker du temperaturen i rummet är?)

Please, statehowyouwouldprefertobenow: (Vänligenangehurduföredrarattvaranu)

Part II:Indoor climate

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6. Rightnow,howacceptablearetheairmovementsaroundyou?(Just nu, hur acceptabla är luftrörelserna runt omkring dig?)

7. Foreachtermbelow,circlethenumberthatbestrepresentshowyoufeelabout

theairqualityatyourdeskrightnow.Thenumbersrangefrom1(notatall)to4(verymuch).(För varje term nedan, ringa in det nummer som bäst representerar vad du tyckerom luftkvaliteten vid skrivbordet just nu. Siffrorna varierar från 1 (inte alls) till 4(mycket))

Notat all

Verymuch

1 2 3 4 Dry(Torr) 1 2 3 4 Fresh(Frisk) 1 2 3 4

Youwouldprefertohave:(Duskulleföredraattha:)

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Stuffy(Unken) 1 2 3 4 Humid(Fuktig) 1 2 3 4 Smelly(Luktar illa) 1 2 3 4 Other

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8. Rightnow,howacceptableistheairqualityatyourdesk?(Just nu, hur acceptabel är luftkvaliteten vid skrivbordet?)

9. Foreachtermbelow,howwouldyouprefertheairqualityintheroomtobe?(För varje term nedan, hur skulle du vilja att ha luftkvaliteten i rummet?)

Less No Change More

Dry (Torr) Fresh (Frisk) Stuffy (Unken) Humid (Fuktig) Smelly (Luktar illa)

Other (Specify) ……………..

10. Howareyouthermallyfeelingatthisprecisemomentonyour:(Hur känner du dig termiskt i detta ögonblick på:)

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Head Neck Back Chest Arms Hands Legs

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11. Rateyourcurrentthermalcomfortonyour:(Skatta din nuvarande termiska komfort på:)

Head NeckBackChestArmsHands

Legs

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12. Rightnow,howacceptabledoyoufindthethermalenvironmentonyour: (Justnu, hur acceptabel finner du den termiska miljön på:)

Head Neck Back Chest Arms Hands

Legs

Youwouldpreferthetemperaturetobe:(Du skulle föredra temperaturen att vara:)

Head Neck Back Chest Arms Hands Legs

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13. Rightnow,howacceptablearetheairmovementsaroundyour: (Just nu, huracceptabla är luftrörelserna runt din/ditt:)

Head NeckBackChestArmsHands

Legs

Howwouldyouliketheairmovementstobe?(Hur skulle du vilja att luftrörelserna var?)

Head Neck Back Chest

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14. Howwouldyoudescribeyourexperienceundertheventilationsystemrunningnow? Please explain!(Hur skulle du beskriva din upplevelse med ventilationssystemet som körs nu?Vänligen förklara!)______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

15. Wouldyousaythatyouarecomfortableinthisclimate right now?(Skulle du säga att du är bekväm i detta klimat just nu?)

16. Ifnot,whatwouldyoumostlikelydotofeelbetter?Selectthreechoicesbyindicating1,2and3inthatrespectiveorder.1meansthefirstoptionyouwouldtake,2isthesecondoptionassumingthat1isnotavailableand 3 if 1 and 2 are not available.(Om inte, vad skulle du göra för att trivas bättre?Välj tre val genom att skriva 1, 2 och 3 i den respektive ordningen. 1 betyder detförsta alternativet du skulle välja, 2 är det andra alternativet under förutsättningatt 1 inte är tillgänglig, och 3 om 1 och 2 saknas.)

Part III:Adaptive option ____________________________________________________________________

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Armsms Handsnd Legs

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17. Whatwouldyousuggestusdotoincreaseyourchancesofadjustingsothatyoueasilybecomethermallycomfortable?(Vad skulle du föreslå att vi gör för att öka dina chanser att anpassa dig så att dulätt blir termiskt bekväm?)-__________________________________________________________________________________________________________________________________________________________________________________________________________________________

STOPP!

Wait for new instructions.

Vänta på nya instruktioner.

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Appendix B: Thermal comfort measurements Table B1: PMV and PPD measurements at a supply temperature of 14 oC

System Measurements

Points Ta To U PMV PPD (%)

1 23.9 24.4 <0.20 -0.08 5.9

2 23.5 24.3 <0.20 -0.06 5.4

Mixing 3 23.8 24.4 <0.20 -0.07 5.8 4 24.1 24.9 <0.20 0.19 6.9 5 24 24.9 <0.20 0.18 6.8 6 23.5 24.6 <0.20 0.14 6

1 21.9 22.6 <0.20 -0.41 7.2

2 21.4 22.3 <0.20 -0.47 7

Displacement 3 19.9 20.7 <0.20 -0.91 22.3 4 22.1 22.9 <0.20 -0.31 6.5 5 19.8 20.5 <0.20 -0.93 24 6 19.5 20.5 0.21 -0.94 24.7

Inside Jet* 23.2 23.4 0.42 -0.52 10.6

AJD Inside Jet** 24.3 24.5 <0.20 -0.06 6.8 Outside Jet* 24.1 24.6 0.35 -0.45 9.3 Outside Jet** 24.2 24.7 <0.20 -0.07 5.8

Steady-stateAJSmeasurements:*jetsrunningcontinuously,**jetsareoff

Table B2: PMV and PPD measurements at a supply temperature of 22 oC

System Measurements

Point of Measure Ta To U PMV PPD (%)

1 27.8 28.6 <0.2 1.2 33.5

2 28.2 29.3 <0.2 1.41 44.6

Mixing 3 28.9 29.6 <0.2 1.41 46.8 4 28.8 29.2 <0.2 1.53 45.3 5 28.7 29.3 <0.2 1.58 48.4

6 28.1 28.6 <0.2 1.13 32.2

1 25.8 26.9 <0.2 0.73 18.8 2 26.3 26.6 <0.2 0.69 15.7

Displacement 3 26.1 26.3 <0.2 0.67 15.3

4 26 26.9 <0.2 0.7 18.4 5 25.2 25.9 0.21 0.39 8.4 6 24.7 25.7 0.23 0.36 7.8

Inside Jet* 27.2 27.7 0.42 0.23 7.2

AJD Inside Jet** 28.8 29.3 <0.20 1.1 31.51

Outside Jet* 28.4 28.8 0.35 0.33 9.48

Outside Jet** 28.7 28.9 <0.20 1.4 81.53

Steady-stateAJSmeasurements:*jetsrunningcontinuously,**jetsareoff

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Appendix C: Comparing between overall air movement acceptability and local air movementacceptability,nodifferencesexistedinallconditionsbothdescriptively(Fig.C1)andstatistically at 25.5 oC and28.5 oC.However, differenceswere found at22.5 oC in both MV (χ2(7) = 50.692, p < 0.001) and IAJS (0.4 m/s (χ2(7) = 58.838, p <0.001),0.6 m/s (χ2(7) = 58.972, p < 0.001) and 0.8 m/s (χ2(7) = 76.903, p <0.001)).Descriptively,asseen(Fig.1:D,GandJ),localairmovementacceptability(median)on neck, arms, hands and back are highly correlated to the overall airmovementacceptability. Statistical test with a Spearman rank order correlation(Table C1) confirms a strong relationship between overall air movementacceptability and local air movement acceptability (neck, arms, hands and back).Interestingly, it also shows that acceptability at the head correlates strongly withoverallairmovements.

Table C1: Spearman correlation test between overall and local air movement acceptability at 22.5 oC

MV-<0.15 m/s IAJS-0.4 m/s IAJS-0.6 m/s IAJS-0.8 m/s

rho p rho p rho p rho p Head 0.583 0.001 0.63 0.001 0.684 0.001 0.675 0.001

Neck 0.566 0.001 0.589 0.001 0.739 0.002 0.692 0.001

Back 0.49 0.002 0.608 0.001 0.663 0.003 0.686 0.001

Chest 0.634 0.001 0.443 0.006 0.423 0.009 0.464 0.004

Arms 0.632 0.001 0.582 0.001 0.735 0.001 0.801 0.001

Hands 0.486 0.002 0.546 0.001 0.792 0.002 0.713 0.002

Legs 0.469 0.003 0.347 0.034 0.296 0.075 0.415 0.011

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Fig C1: Overall and local air movement acceptability; J. Accept (just acceptable.), V. Accept (very

acceptable), J. Unaccept. (just unacceptable) and V. Unaccept (very unacceptable).

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Associated papers have been removed in the electronic version of this thesis. For more details about the papers see: http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-23754

Gävle University Press

ISBN 978-91-88145-11-6

ISBN 978-91-88145-12-3 (pdf)

University of Gävle

Faculty of Engineering

and Sustainable Development

SE-801 76 Gävle, Sweden

+46 26 64 85 00

www.hig.se

Experimental study of an intermittent ventilation system in high occupancy spaces

Spaces with high occupancy density like class-

rooms are usually challenging to ventilate with

traditional systems, as it is hard to meet comfort

requirements at a low energy use. Alternative

strategies with high air speeds show promise as

they deliver good IEQ at a low energy use.

A novel ventilation system called Intermittent Air

Jet Strategy (IAJS) is proposed, evaluated and

discussed herein. The strategy creates non-uniform

airflow and non-isothermal conditions around the

occupants. Objective measurement results show

that IAJS has an equivalent local air distribution

capability and a higher room air exchange rate

compared to a mixing ventilation system. Human

response results indicate that IAJS is favorable at

moderate and higher operative temperatures as it

offsets the negative influence of high temperatures

on occupant perception and acceptability of indoor

environment experienced under mixing ventilation.

IAJS is shown to influence the upper body parts of

sitting occupants and can extend neutral operative

temperature by a minimum of 2.3 oC compared

to a mixing system. This promises a substantial

energy saving potential if the system is well

implemented. Generally, the results indicate that

IAJS has a potential use in high occupant spaces.

Alan Kabanshi