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SIMULATION ON EFFECTIVE

DYNAMIC SKYLIGHT

STRATEGIES

Chen Hu Master of Science in Building Performance and Diagnostics

05/11/2015

Advisors Erica Cochran, Flore Marion, Azizan Aziz, Vivian Loftness

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Contents

1. Abstract ............................................................................................................................. 3

2. Introduction ...................................................................................................................... 4

2.1 Objectives ................................................................................................................................4

2.2 Hypothesis ...............................................................................................................................4

2.3 Deliverables .............................................................................................................................4

2.4 Methodology ............................................................................................................................5

3. Background of U.S. Energy Consumption ............................................................................ 8

4. Literature Reviews of Skylight Benefits ............................................................................ 11

5. Introduction of Daylighting Simulation Software .............................................................. 28

6. Dynamic Skylight Strategy Simulation and Energy Analysis ............................................... 30

6.1 Pittsburgh Climate .................................................................................................................. 30

6.2 Autodesk Ecotect Model of Intelligent Workplace (IW) ............................................................ 35

6.3 Dynamic Skylight Shading Device ............................................................................................ 41

6.4 Skylight Material Hypothesis ................................................................................................... 42

6.5 Simulation Process .................................................................................................................. 43

6.5 Lighting Analysis of Dynamic Skylight System .......................................................................... 47

6.5.1 Standards and Regulations ........................................................................................................ 47

6.5.2 Illuminance Level Analysis.......................................................................................................... 48

6.5.3 Glare Analysis ............................................................................................................................. 68

6.6 Recommendation on Dynamic Skylight Strategies.................................................................... 84

6.6.1 Dynamic Skylight Strategies Evaluation ..................................................................................... 84

6.6.2 Dynamic Skylight Strategies Schedule ....................................................................................... 94

8. Energy Benefit of Proposed Skylight Strategies ................................................................. 98

9. Limitations .................................................................................................................... 101

10. Conclusion ................................................................................................................... 102

11. Future Work ................................................................................................................ 103

12. Acknowledgement ....................................................................................................... 104

13. Bibliography ................................................................................................................ 105

References ........................................................................................................................ 105

Appendix ........................................................................................................................... 108

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1. Abstract

Currently, 73% of U.S. commercial buildings are under 10,000 square feet, which is considered as small (less than 5,000 sf) or medium size (between 5,000 and 50,000 sf) buildings (EIA, Commercial Building Energy Consumption Survey, 2014). The commercial building sector in the northeast region of the U.S. accounts to 19.5% total commercial floor space and 21.4% total energy consumption. (Pei, 2013) It has been estimated that buildings with no more than two floors take up to 64% of total building number and 60% of commercial floor space is directly under roof space. However, currently only 2% - 5% of the total commercial building floor space has skylight installed. (Pei, 2013) This is a good opportunity for skylights applications since skylight system is more efficient in these kind of buildings due to their high roof-wall ratio. Properly designed and placed skylights can supply enough lighting for commercial buildings during clear weathers without using additional artificial lights. For cloudy weather, skylights can still reduce artificial lighting energy usage by supplying supplementary lighting. Researches also shows that skylight systems can increase occupants’ productivity (Bristolite, 2013). Thus, increasing the number of studies has been focused on efficient skylight system. This research is mainly concentrated on energy conservation part of dynamic skylight strategies. The dynamic strategies in this thesis project refers to the shading device type on skylight as not fixed, but adjustable in different times or under different weather conditions. For example, the blinds panel position can be changed at different time during a day (hourly schedule) or in different season (seasonal schedule). Venetian blinds are also replaced by tensioned shades during summer (seasonal schedule). Many studies have been conducted on influence of skylight on indoor environment analysis, however, there is few studies working on economic benefits aspect of skylight system currently. The analysis of related return of investment (ROI) of different skylight system is insufficient. This thesis project focuses on software simulation of dynamic skylight strategies. Using Autodesk Ecotect

and Radiance, the daylighting condition of Intelligent Workplace (IW) of Carnegie Mellon University is

simulated. Three skylight strategy experiment groups are analyzed through simulation: controlled group

(no shading device), Retrosolar venetian blinds group, and Lutron tensioned shade group. Four different

blinds panel position is analyzed in this project as well, fully closed, fully opened, positive 45 degree, and

negative 45 degree. Glare analysis is also conducted. Cases related to daylighting simulation for heating

dominated areas similar to Pittsburgh are studied to provide methodology for energy conservation

analysis.

The comparison between venetian blinds and tensioned shades is conducted to give advice on skylight

shading device selection. The recommendation on dynamic skylight strategies is provided in both

seasonal schedule and hourly schedule.

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2. Introduction

2.1 Objectives

The objective of this study is to quantify skylight dynamic shading device system’s visual benefit in

humid continental climate (northeast U.S. region) through software simulation. The simulation results

are mainly for open plan office and climate similar to Pittsburgh, PA which is located in the IECC Climate

Zone 5. Besides, the methodology of the simulation can be replicated and used in other region for

further study. An literature review was also conducted to summarize the benefits of successful building

skylight cases and simulation methods for skylight evaluation. A filed experiment was conducted in

Intelligent Workplace of Carnegie Mellon University in 2014. This study can be considered as a following

and supplementary study of the previous study. The previous field only provide venetian blinds

schedule at one position. Since the previous field experiment on skylight shading device is still static

(one blinds panel position), this simulation can make skylight strategy dynamic. It can provide more

detailed skylight strategy schedule.

2.2 Hypothesis

The goal of this research is to identify if dynamic skylight can achieve the following benefits (or

improvements) utilizing computer software to simulate different shading configurations and weather

conditions:

1. The dynamic skylight system can improve indoor visual environment.

a. The dynamic skylight system can help reduce glare issue from daylight.

b. Different blinds panel positions have different ability on preventing glare.

c. Tensioned shades can help prevent from the most glare compared with other groups.

2. Different skylight strategies have different visual performance at different times of a day,

under different weather conditions, and in different seasons.

a. Dynamic skylights can allow maximum sunlight while maintain occupant visual comfort

within related standards.

b. Tensioned shades provide the best indoor visual performance in summer.

c. Different angles of blinds panel have totally different effect on indoor visual

performance.

d. Venetian blinds can fulfill most of visual requirement and are more convenient

compared with tensioned shades.

3. Dynamic skylight strategies can reduce energy consumption compared with normal skylight.

2.3 Deliverables

This thesis project will provide the following items as outcome deliverables

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1. Detailed analysis of skylight strategies used in Intelligent Workplace of Carnegie Mellon University.

Including product information, explanation of its benefits, and related case study on each type of

skylight strategies.

2. Detailed Ecotect simulation model of Intelligent Workplace (IW) of Carnegie Mellon University

3. Simulation results on light level and glare. This thesis project emphasizes on visual benefits of

dynamic skylight strategies since the previous study focuses on thermal comfort.

4. Seasonal and daily skylight strategy using schedule based on simulation result. The schedule is

provided as a combination of considering light level and glare analysis.

5. Energy simulation on simplified skylight model and daily energy consumption calculation.

2.4 Methodology

In this thesis project, literature review and simulation studies are two methods to evaluate skylight

system benefits.

Literature Review

The literature review focuses on current studies of indoor visual performance of different skylight

applications through different software simulation, the energy benefit of skylight system, and the

economic benefit from energy saving of skylight system.

Simulation Study

The daylight condition of Intelligent Workplace (IW) of Carnegie Mellon University (Pittsburgh, PA

campus) is also simulated using Radiance based on Autodesk Ecotect platform. Three different skylight

strategies, control group with no shading device, Lutron tensioned shades covered ground, and

Retrosolar Venetian blind covered ground, are simulated and compared. For venetian blinds, 4 different

blinds panel positions, fully closed, fully opened, positive 45 degree, and negative 45 degree are

simulated. The simulation is under instruction of Bertrand Lasternas and Chao Ding from School of

Architecture, Carnegie Mellon University, Pittsburgh.

The parameters used to evaluate indoor visual environment in this thesis research are, illuminance, and

daylight glare index (DGI), and unified glare rating (UGR). Illuminance (lux) is the total luminous flux

incident on a surface, per unit area. It measures how much the incident light illuminates the surface.

Daylight glare index is developed by Hopkinson at Cornell in 1972 and it’s the first metric which

considered sky as the large glare sources. Unified glare rating (UGR) is also a measure of the glare in a

given environment. The different between UGR and DGI is that it takes artificial lighting into account.

Autodesk Ecotect Analysis software is a comprehensive concept-to-detail sustainable building design

tool. In this thesis research, it is used to simulate three different skylight systems for lighting analysis in

Radiance. Radiance software is a suite of programs for the analysis and visualization of lighting in design.

Using scene geometry, materials, luminaires, time, date, and sky conditions as inputs, the software

outputs visualized images for indoor visual quality evaluation.

For light level on desk (paper-based work) and vertical screen (computer-based work), the simulation is

set under clear weather and overcast weather. Each group is simulated on spring equinox (03/21),

summer solstice (06/21), and winter solstice (12/21), respectively under these two weather conditions.

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For glare analysis, only clear weather is considered since there is no glare problem under overcast

weather. For both light level analysis and glare analysis, each group is simulated at 5 time points on each

day, 9AM, 11AM, 1PM, 3PM, and 5PM except for winter solstice day under overcast weather condition

since artificial lighting is necessary for all groups on that day. Thus, only four time points is simulated on

that day.

Due to the fact that there is inadequate information on product brochure of the glazing material and

shading device used in IW, the material simulated in Ecotect is not exactly the same. The data collected

in field test is used to calibrate the simulation.

A simplified skylight model is made in this thesis project to quantify energy benefit of dynamic skylight.

The model is made in Design Builder and then exported into Energy Plus. The energy use intensity (EUI)

is calculated by Energy Plus for each six skylight strategy. The energy consumption for two proposed

skylight schedule is then calculated.

In this project, the thesis process flow chart is shown in Figure 1.2.1. The model is built in Autodesk

Ecotect based on original IW model in Autodesk Revit. Then models are exported into RADIANCE for

parameter calculation. Based on the analysis of calculation results, the recommendation of skylight

strategies schedule is provided.

Figure 1.2.1 Simulation Software Diagram

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3. Background of U.S. Energy Consumption

According to data published by U.S. Energy Information Administration (EIA), commercial and residential

building energy make 39% of total energy consumption in U.S. in 2012 (EIA, U.S. Energy Information

Administration, 2012). If skylight systems can be applied into most of commercial and residential

buildings, there could be a huge energy saving.

Figure 1.3.1 Major Energy Usage Breakdown in U.S. 2012 (EIA, U.S. Energy Information Administration, 2012)

From the commercial sector energy consumption survey conducted by EIA (EIA, U.S. Energy Information

Administration, 2014) (Figure 1.3.2), it is shown that from 2000 to 2014, the electricity retail sales to

commercial building sector almost remains steady. However, the average retail price of electricity for

both residential and commercial sector shows an increasing tendency (Figure 1.3.3). Thus, it is a huge

opportunity for skylight applications in commercial buildings since daylight can reduce electricity

consumption in artificial lighting and heating/cooling sectors. The saved electricity energy from skylight

systems can bring economic benefits as a result.

Figure 1.3.2 Average Retail Price of Electricity (EIA, U.S.

Energy Information Administration, 2014)

Figure 1.3.3 Commercial Sector Energy Consumption (EIA,

U.S. Energy Information Administration, 2014)

Commercial 18%

Residential 21%

Transportation 28%

Industrial 33%

U.S. Energy Consumption, 2012

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From residential building energy usage breakdown in 2005 (Figure 1.3.5), it is shown that space heating

and cooling are still the major energy consumption sectors. Lighting makes 11% in total energy

consumption. And for commercial buildings (Figure 1.3.4), lighting energy consumption takes 26% of

total energy use. Space heating and cooling take 14% and 13%, respectively. Since these parts make 53%

of primary energy use, skylight system is more beneficial for commercial buildings compared with

residential buildings.

Figure 1.3.4 Commercial Primary Energy End-Use Splits, 2005 (Energy, 2008)

Figure 1.3.5 Residential Primary Energy End-Use Splits, 2005 (Energy, 2008)

Figure 1.3.6 shows the total floorspace distribution of buildings in northeast region. Office buildings take

the largest part of total building floorspace in northeast U.S. Office buildings also have the largest

energy consumption in northeast region (Figure 1.3.7). Besides, according to Rocky Mountain Institute,

73% of commercial buildings (by number) are under 10,000 square feet in size (Institute, 2014). These

three facts indicate that skylight system can bring large energy saving benefit for commercial office

buildings in northeast U.S. compared with other kinds of buildings.

Lighting 26%

Space Heating

14% Space Cooling

13%

Ventilation 6%

Water Heating 7%

Electronics 6%

Refrigeration 4%

Computers 3%

Cookings 2% Other

19%

Commercial Primary Energy End-Use Splits

Lighting 11%

Space Heating

31%

Space Cooling 12%

Wet Clean 5%

Water Heating 12%

Electronics 7%

Refrigeration 7%

Computers 1%

Cookings 5%

Other 9%

Residential Primary Energy End-Use Splits

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Figure 1.3.6 Total Floorspace of Building in Northeast Region

(Pei, 2013)

Figure 1.3.7 Major Fuel Consumption in Northeast Region

(Pei, 2013)

Comparing renewable energy consumption between residential and commercial use (Figure 1.3.8),

residential renewable energy shows a much more oblivious increase than commercial use. Renewable

energy use in commercial sector does not show much fluctuation during recent 10 years. This shows a

great potential for renewable energy use in commercial building sector. Specifically, for skylight systems

design, solar panel can be integrated into design. One example is the combination of skylight and semi-

transparent photovoltaic. This kind of system can generate electricity through solar energy, which

increase energy performance of the skylight.

Figure 1.3.8 Renewable Energy Consumption: Residential and Commercial Sectors (EIA, U.S. Energy Information Administration, 2014)

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4. Literature Reviews of Skylight Benefits

This section provides literature reviews of daylighting simulation and field test research relating with

skylight energy and economic benefits. The research includes different climate zones, mainly climate

zones similar to Pittsburgh, which is the research zone in this thesis project. Different skylight systems

are studied and summarized in this literature review as well. Suitable skylight systems for different

building types, including classrooms, gymnastics, museums, and office buildings, are studied in these

researches. Some researches include simulation using computer software, which provide guideline for

daylight analysis in this thesis.

This literature review summarizes different skylight systems for different building types, the related

benefits, and research method for doing skylight simulation. It helps finding useful information used in

this thesis project. Some of researches studied in this thesis project analyze economic benefits of

skylight systems (li, Lam & Chang, Chel, Tiwari, & Chandra), the research methods provided in these

researches largely supplements the missing economic analysis missing in previous research. The

research conducted by Tagliabue et al in 2012 provided the overall concept and process for computer

simulation on daylighting system, and daylight benefits as well. One interesting point in these

researches studied in the combination of lighting dimming control and daylighting (Athienitis &

Tzempelikos, 2012). This research provides a more energy efficient way for daylighting system design,

which could be analyzed further. Table 4.1 summarizes benefits of skylight strategies, and Table 4.2

summarizes research methodology on skylight computer simulation.

4.1 Daylight utilization in perimeter office rooms at high latitudes: Investigation by computer

simulation (Dubois & Flodberg, 2011)

In 2011, M-C Dubois, K. Flodberg from University of Lund conducted simulation study of daylight

autonomy in perimeter office rooms at high latitudes. Using RADIANCE based simulation program

DAYSIM, following variables are studies: Glazing-to-wall ratios, climate, orientation, inner surface

reflectance, glazing visual transmittance. For each simulation model, continuous daylight autonomy

(DAcon) and daylight autonomy max (DAmax) were analyzed.

Research Method

The parametric study was achieved using DAYSIM program. Office models with different GWR were

used for calculations and data analysis. And for each case, continuous daylight autonomy and daylight

autonomy max were calculated for comparison.

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Results

This paper shows that the north orientation presents good DAcon potential and no direct sunlight risk

even with large GWR. It also shows that inner wall reflectance has significant effect on GWR as

orientation. Simulations with low-transmittance glazing (Tvis = 36%) showed that larger GWR (60%) are

needed to obtain the same DAcon as ‘small’ GWR (20%) with relatively little reduction in direct sunlight

risk [1]. It is also shown in this study that DAcon is slightly reduced with the use of a Venetian blind in the

case of an active user who manages the blinds coherently [1]. The study of different electric lighting

dimming and switching strategies showed that the choice of electric lighting system generally has more

effect on energy use than the GWR. Part of the research results is shown in Figure 10 and table below.

Figure 4.1.1 DAcon (%, top) and DAmax (%) as a function of GWR (%) in relation to distance from glazing for single-cell, south-oriented office in Stockholm

Glazing-to-wall ratio (GWR) DAcon DAmax

Effect of GWR for South-oriented office in Stockholm

Stockholm 10% 62% 2%

30% 78% 7%

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40% 80% 10%

60% 83% 22%

Effect of GWR relative to climate for a South-oriented office

Montreal 10% 63% 3%

30% 82% 10%

40% 90% 14%

60% 92% 23%

4.2 A model for estimation of daylight factor for skylight: An experimental validation using pyramid

shape skylight over vault roof mud-house in New Delhi, India (Chel, Tiwari, & Chandra, 2009)

In 2009, Arvind Chel et al used experimental hourly inside and outside data of an existing skylight

integrated vault roof mud-house to investigate and validate daylight factor in composite climate of New

Delhi. Three different practical horizontal surface levels ground, 75cm above ground, and 150cm above

ground) were modeled inside the big and small dome rooms.

Research Method

Illuminance level inside the room at the working surface as compared to the diffuse illuminance

available outside the building is used for determining daylight performance of building. The energy

saving potential of daylighting was evaluated based on the inside illuminance flux and efficacy of lamp to

be operated for getting same illuminance flux as that of natural daylight using roof integrated skylight.

The experimental value of daylight factor for the room was determined based on the percentage ratio of

inside illuminance on the working area to outside diffuse illuminance.

Results

The illuminance level inside mud-house in this research was found sufficient for office work inside the

room and the illuminance level was found 100 lux (minimum) inside both small dome and big dome

rooms from 10AM to 3PM in all months of the year. The experimental daylight factor over the year for

big and small dome rooms are found in the range of 1.5-3.5% and 2.5-7%, respectively, based on skylight

performance in both winter and summer. The total annual average artificial lighting energy saving

potential corresponding to the skylight illuminance in the existing building was estimated as

973kWh/year corresponds to mitigation of CO2 emissions 1526 kg/year. And the vertical distance above

floor surface for the skylight plays important role towards the amount of light output reaching on the

surface [2].

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The research also points that total lighting energy saving potential and annual mitigation of CO2

emission will be around 146 million kWh/year and 0.23 million metric tons per year if 5% of the total

households in Delhi state are built with mud-house like mentioned in the paper. Also, if 5% of the total

households in India are made of mud-house integrated with skylight in rural areas or semi-urban areas,

the annual lighting energy saving and annual CO2 emission mitigation will be about 6811 million

kWh/year and 10.7 million metric tons per year. Some detailed results are shown in Figure 11 - 14.

Figure 4.2.1 Hourly Energy Saving Potential of Skylight in Big Dome Building in January

Figure 4.2.2 Hourly Energy Saving Potential of Skylight in Small Dome Building in January

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Figure 4.2.3 Hourly Energy Saving Potential of Skylight in Big Dome Building in June

Figure 2 Hourly Energy Saving Potential of Skylight in Small Dome Building in June

Benefits

For skylight of small and big dome:

Average annual energy saving: 204 kWh/year and 564.5 kWh/year

Mitigation of CO2 emissions: 265-375 kg/year and 732-1038 kg/year

Carbon credit potential: $2.7-$3.8 per year and $7.3-$10.4 per year

For mud-house with skylight integrated two small and one big dome shape rooms:

Total artificial lighting energy saving: 973 kWh/year

Mitigation of CO2 emissions: 1526 kg/year

Carbon credit potential: $15.3/year

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4.3 Dynamic simulation and analysis of daylighting factors for gymnasiums in mid-latitude China (Zhao

& Mei, 2013)

In 2013, Yang Zhao and Hongyuan Mei from China divided 22 different design factors on interior

daylighting effects into three categories according to its relative impact, very high impact: latitude, date,

window position, glazing transmittance, building height, building depth and window area; general high

impact: reflectance of glazing, wall, ceiling and floor, building length, light attenuation of window

structure and light attenuation factor of indoor structure; little impact: time of day, orientation

coefficient, light reduction factor of outdoor obstruction, light reduction factor of wind deflector block,

cleanliness of window, and the surface area of wall, ceiling and floor.

Research Method

Using DIALux, a computer package for simulating and visualizing lighting in and around architectural

environments using backward radiosity calculation, mathematical model is used for daylighting factors

analyzing and classifying. Gymnasiums were modeled according to relative Chinese design code. The

year is divided into 24 time periods as calculation time. And three different locations located between

30 and 60 north were chosen for simulation.

Results

The research found out following point: 1. the required window area is smallest at the summer solstice

irrespective of the type of gymnasium. 2. The window area required when using a skylight is much

smaller than that of each side window design. 3. The required window area increases with reduced

glazing transmittance. 4. Irrespective of the type of gymnasium, the required skylight area shows a linear

increase with an increase in building height. 5. Greater building depth requires larger window area,

irrespective of the window position.

Integrated daylighting simulation into the architectural design process for museums (Kim & Seo, 2012)

In 2012, South Korea researcher Chang-Sung Kim and Kyung-Wook Seo found that a lighting design

method for exhibition spaces in museums is suggested. Researchers used both scale models tests and

simulations using RADIANCE to validate this method. The corrected results of simulation were applied to

existing museum to confirm the performance of the method in modeling an actual environment. By

modulating and controlling the parameters, the appropriate dimensions of the monitor-shaped toplight

for the museum were determined.

Research Method

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Architectural characteristics of the existing museum- Seoul Museum of Art were analyzed for

determining a new daylighting system. The illumination levels for the target area were defined

according to IESNA. A scaled model was measured and compared with simulation study using

RADIANCE. And integrated daylighting simulation was conducted based on the correction of simulation

results. The Figure 15 shows the simulation model in this study.

Figure 4.3.1 Picture of MT Model Simulations

Results

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The existing pyramid-shaped skylight provides a 54260lux illuminance level for direct sunlight into the

space on the summer solstice and 43720lux on the autumnal equinox, which is damaging in summer.

The relative errors between scaled model and Radiance simulation in this study were 35% to 45% on

average, however, the corrected simulations greatly reduced the differences to the range of 3% to 9%.

The study also proposed monitor-shaped toplight (MT) design models for the museum – 60MT23,

70MT23, 80MT23, 90MT23, 80MT14, and 90MT14. (The two digits after MT indicate the window height

and light well depth, and the number before MT indicates transmittance value.)

4.4 Energy saving through the sun: Analysis of visual comfort and energy consumption in office space

(Tagliabue, Buzzetti, & Arosio, 2012)

In 2012, Lavinia Chiara Tagliabue et al from Milan, Italy conducted a study to simulate energy saving

impact of daylighting system in office buildings. Optimization of daylighting, electrical consumption and

visual comfort are studied. A single office space with three different configuration of the openings

located in different orientation and position (south exposed window, north exposed window and

skylight) were simulated as three cases. Six simulation softwares, Autodesk Ecotect, Radiance, Evalglare,

Daysim, Dialux, and Energy Plus were used in this study.

Research Method

In this research, Ecotect was used to model three different daylight settings. Radiance, Evalglare, and

Daysim were used to calculate visual comfort parameters (luminance, illuminance, daylight factor,

daylight glare probability, daylight glare index, unified glare rating, daylight autonomy, and useful

daylight index). Energy Plus did calculation of heating and cooling demands. And Dialux calculated

electrical consumption for lighting. The office space was set to be a single unit which can be occupied by

two or three people located in Milan, northern Italy.

Results

The detailed calculation result is shown below.

Case NW Case SW Case SL

Energy Simulation (kWh/m3/year)

Heating Consumption 5.49 3.31 6.04

Cooling consumption 6.64 12 5.93

Electric equipment 21.9 21.9 19.71

Illumination without control 20.97 20.97 27

Illumination with control 11.52 11.52 27

Lighting simulation

Daylight Factor (%) 11.31 11.31 4.18

UDI (%): <100, 100-20000, >2000 8, 14, 78 8, 11, 81 17, 50, 33

DA (%) 73-93 76-93 42-67

The study shows that skylight system can provide a more homogeneous daylighting distribution for

indoor space, although the level of illuminance level cannot reach the comfort levels for visual tasks. If

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considering the whole energy consumption, north window would be optimal daylighting system. And it

can ensure visual comfort parameters without strong negative effects on energy consumption.

Benefit

A reduction of almost 30% on thermal consumption compared with south window case and 1% with

north window case.

4.5 Towards an analysis of the performance of lightwell skylights under overcast sky conditions

(Acosta, Navarro, & Sendra, 2013)

In 2013, Ignacio Acosta et al from Spain studied one of skylight systems-lightwell skylight (Figure 16)

under overcast sky condition. Daylight factors and luminous distribution produced inside a room were

studied. Several parameters of were analyzed: size and height/width ratio of the skylight, reflection

index of lightwell, different room proportions, and suitable spacing between skylights.

Research Methods

The simulation software used in this study is Lightscape 3.2. The initial simulated room was a

9m9m4.5m room and with a lightwell skylight placed in the center of the roof. The work plane on

which daylight factors are studied was located 1m above the floor. 4 trials regarding skylight size and

ration, reflection index of the skylight, room size and skylight spacing were simulated respectively.

Results

Trial 1- size and ratio of the lightwell skylight shows that the illuminance generated by it is almost

directly proportional its size. Trial 2- reflection index of the lightwell skylight proves that it is a

determining factor for illuminance. It is also deduced from this trial that in cases where the reflection

index of the skylight is between 0.5 and 0.7, considering a height/width ratio of the lightwell greater

than 2, the daylight factors are almost proportional to the reflection index. Trail 3- room ratio shows

that different room heights have little impact on daylight factors. And trial 4-lightwell spacing shows

that the uniformity of illuminance is proportional to the width/height ratio of the lightwell in the

absence of a reflected component.

Figure 4.5.1 Lightwell Skylight

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Benefits

The skylight with a reflection index of 0.7 produces an increase in illuminance of over 30% compared to

the skylight with an index of 0.5 which produces a similar increase compared to skylight with an index of

0.3.

4.6 Energy and cost studies of semi-transparent photovoltaic skylight (Li, Lam, & Cheung, 2009)

In 2009, Danny H. W. Li et al from City University of Hong Kong analyzed the thermal and visual

properties, energy performance, and environmental and financial issues of semi-transparent

photovoltaic skylight. Researchers measured solar irradiance and daylight illuminance of the skylight.

The electricity generated by the skylight was also measured. The thermal and visual performance of PV

skylight with lighting control was evaluated as well.

Research Method

Data was collected from a transparent glazing and multi-crystalline silicon solar cells installed in a

primary school in Hong Kong. Researchers used pyranometers, illuminance meters and power analyzer

to measure solar irradiance, daylight illuminance and electricity generated by the skylight for both

summer and winter conditions. Case studies on a circulating atrium were also conducted to evaluate the

energy use, cooling requirements and monetary implications when the PV skylights together with the

daylight-linked lighting controls were applied. Four case were analyzed, tinted glass for the skylight

without dimming controls (base case); tinted glass for the skylight with dimming controls (case 2);

installing the semi-transparent solar modules to replace tinted glass for the skylight without dimming

controls (case 3); and installing the semi-transparent solar modules to replace tinted glass for the

skylight and with dimming controls (case 4).

Results

Field measurements of the skylight shows that transmittances for diffuse daylight and irrandiance can

be described by constant values of 20.1% and 21.5%, respectively. When direct beam components were

included, both the visible transmittance and solar transmittance could be described by 3rd order

polynomial functions. The daily mean energy conversion efficiency was found to be 10.83%. The Figure

17 and 18 show electricity benefits and peak load reduction between case 2 and 4.

Benefits

The major benefits in this study are shown in Table 1.

Table 4.6.1 Case Benefit

Cases 2 3 4

Emissions reductions (kg)

CO2 12400 27950 40300

SO2 38 86 123.8

NOX 21 47 68.3

Particulates 2 4 5.3

Monetary payback years

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Payback (considering electric tariff only) 1.1 38.6 27

Payback (considering electric tariff, chiller plant, cost and

CO2 trading) 0.8 32.8 23

Figure 4.6.1 The Electricity Benefits (Electricity Generated Plus Electricity Saved) for Case 2-4

Figure 4.6.2 The Peak Load Reduction for Case 2-4

4.7 A methodology for simulation of daylight room illuminance distribution and light dimming for a

room with a controlled shading device (Athienitis & Tzempelikos, 2002)

In 2002, A. K. Athienitis and A. Tzempelikos from Concordia University, Canada simulated an office room

with an advanced window system and calculated minimized electric due to the installation of dimming

controls. The particular system considered in this study is a double-glazed window with motorized highly

reflective blinds between the two glazings installed in an outdoor test-room and operated by a custom-

built computerized building automation system. [] The incidence angle, shading device position, and sky

conditions were analyzed. Both clear sky and overcast sky conditions were simulated. Daylight

22

illuminance on the work plane is analyzed in this study. And the result of field experiment and

simulation was compared.

Research Methods

The study determines the optimal shading device angle to get maximum daylight without causing glare

issues. A field experiment was conducted outdoor in Montreal. Test-room is 2.32.72.4 m with double-

glazed low-e coating and highly reflective louvers integrated between the two panes window. Using

solar radiation and daylight sensors, solar radiation and its visible portion were measured. For

simulation part, illuminance due to daylight at several points on the work plane for representative days

in each month, once every hour, from 9 AM to 5 PM was calculated. Researchers computed the energy

savings from the blinds and dimming control. The 553m simulated office locates in Montreal. Based

on the simulation, suggestions have been made.

Results

The comparison between field experiment and simulation is shown in figure 19.

Figure 4.7.1 Comparison of Measured and Predicted Illuminance Level due to Daylight

Benefits

The energy saving for the particular window in this study system with integrated blinds can exceed 75%

for overcast days and 90% for clear days, comparing with the case of no daylighting/dimming control.

23

The Table 4.1 summarizes case studies of benefits of different types of skylight strategies. Table 4.2

summarizes simulation studies. Some of these studies in Table 4.2 are in climate zones different from

Pittsburgh, some of them simulated other building types other than office building, and some of them

study other daylight applications other than skylight. However, all these studies provide detailed

information on how to use different software to conduct computer simulation. Thus, all these studies

are important guideline for this thesis project.

4.8 Lockheed 157 (Thayer, 1995)

The office building built in 1983 in Sunnyvale, California is a 5-story building with daylight applications.

The west and east façade of the building minimized the glazing area. An atrium with 18,000 sf area

locates between office spaces from the ground floor to the roof. On each floor, there are two separate

office area facing south and north. The daylight is provided through glazing on north and south façade

and through skylight of the atrium. There are also light shelves installed on both exterior and interior

facades assisting daylight to reach deeper into office area.

Skylight Type

4 rows of sawtooth shaped skylight with vertical north-facing clear glass and sloped south-facing

diffusing glass.

Benefits

Reduced 15% of absenteeism compared with originally 7%.

The energy saving per year leads to a $500,000 reduction on energy bill.

4.9 Simulation study on Los Angeles, Atlanta, and New York (Fontoynot M., 1984)

A simulation study was conducted based on a single-story office building in Los Angeles, Atlanta, and

New York respectively. The energy performance of the simulation model in each city is compared under

condition with and without daylighting application using the BLAST program. Daylighting dimming

control and roof monitors are simulated as daylight strategies in this study. Two lighting power density

are tested in this study, 2.5W/sf and 1.5 W/sf.

Skylight Type

Roof monitors with dimmable light control system.

Benefits

In 1.5 W/sf lighting power density model, the reduction on annual lighting energy is 48%.

In 2.5 W/sf lighting power density model, the reduction on annual lighting energy is 49% and on

cooling energy is 13%.

4.10 Simulation study on prototypical federal government building (U.S. DOW & FEMP, 2002)

24

Based on the federal building in Baltimore, Maryland, a simulation study is conducted. The building has

a floor area of 20,000 sf and it is a two-story building. This simulation focuses on equipment

improvement. The software used in this study to calculate energy consumption and cost is DOE.2e.

Skylight Type

General skylight with dimmable light control system

Benefits

The electricity consumption reduction is 3.8%.

4.11 California State Automobile Association (Daylighting Initiative, Pacific Gas and Electric Company,

1997)

The office building of California State Automobile Association in Antioch, California was studied in a

research conducted by Daylighting Initiative. The building has a floor area of 15,000 sf. Daylight is

gained through perimeter windows and skylights in this building. The skylight wells locate 5 feet higher

than the perimeter ceiling and are located every 20 feet in the office. The skylight is also operable for

natural ventilation. The building also has dimmable lighting system to reduce light power output from

100% to 20% and light input from 100% to 40%. Of all the interior lighting, 68% of them are under

dimmable control system.

Skylight Type

Triple-pane, acrylic, low-glare operable skylight wells, light sensors installed on louvers, dimmable

lighting control system, and fixed-pitch perforated window blinds

Benefits

A reduction of 32% of electrical lighting energy consumption

4.12 ACE Hardware store (Daylighting Initiative, Pacific Gas and Electric Company, 1999)

Daylighting Initiative conducted a study on the ACE Hardware store in El Cerrito. The building has a floor

area of 14,400 sf. The skylight in this building is produced by So-luminaire Daylighting System

Corporation and is integrated with movable mirror and infrared sensor. The sun can be tracked from

sunrise to sunset by the system.

Skylight Type

Active skylight integrated with movable mirror and infrared sensor, sun-tracking system

Benefits

A reduction of 65% on annual lighting energy consumption

25

4.13 A-1 Cold Storage Warehouse (Ciralight)

A-1 cold storage warehouse is built in 2003 with a floor area of 12,000 sf in Inglewood, California. There

is no window on exterior 8-inch thick concreate wall. The building is used as office area and warehouse.

The renovation project is done by Ciralight. The renovation includes adding daylighting with illumination

equivalent to 19,200 watts of fluorescent lights. The cost of vertical fenestration is saved since the

building’s skylight strategy focuses on ceiling skylight.

Skylight Type

The three mirror skylight system is integrated with GPS device which will track the path of the sun and

harvest the maximum sunlight to illuminate indoor spaces. The skylight system has a U-value of 0.35 and

SHGC 0.3196.

Benefits

Monthly saving on utility bills is $1000. The total electricity energy consumption reduction is equivalent

to 1.2 million ft3 of CO2 emission annually.

4.14 PetSmart Stores (Southern California Edison, 2008)

Skylights and energy management system were installed into PetSmart store in Modesto, California, in

2008. The dimmable control system connects to 52 of 77 fluorescent lighting fixtures. The illuminance

level is measured by hand held light meter from August 22nd to September 10th in 2008. The standards

used for evaluation is IESNA for open plan office. The result shows only 2 out of 9 measurements in the

electric light off case is lower than the recommendation.

Table 4.1 Skylight Strategy Benefit

Location HDD CDD Floor

area (sf) Story Skylight Type

Dimmable System

Energy Saving

Total Heating Cooling Lighting

Sunnyvale, CA 2210 475 585000 5 Static Sawtooth

skylights Yes 50%

New York, NY 4669 1272 10000 1 Static Roof Monitors

Yes 10% -4% 9% 43%

Atlanta, GA 2689 1763 10000 1 Static Roof Monitors

Yes 15%

14% 49%

Los Angeles, CA

893 1218 10000 1 Static Skylight Yes 18%

17% 55%

Baltimore, MD

3536 2026 20000 2 Static Skylight Yes 4%

Antioch, CA 2543 826 15000 1 Skylights with

louver shadings Yes 9%

32%

El Cerrito, CA 2376 193 14400 1 Skylight with sun

trackers Yes 28%

65%

Inglewood, CA

1066 717 12000 1 Skylight with sun

trackers Yes 52%

58%

Modesto, CA 2311 1673 23500 1 Static Skylight Yes 9%

20%

26

Table 4.2 Simulation Literature Review Matrix

Case Name Year Building

Type Location

Daylight Strategy

Study Object Benefits Simulation

Program Quantitative Qualitative

Daylight utilization in perimeter office

rooms at high latitudes: computer simulation (Dubois & Flodberg, 2011)

2011 Office

Building

Multiple locations

(Stockholm, Ostersund,

Malmo, Gothenburg,

Montreal, Quebec)

Single window

located on the 2.4m

wide facade

Glazing-to-wall ratios, climate, orientation, inner surface reflectance, glazing

visual transmittance, venetian blind management, electric lighting dimming and

switching systems

For high altitude area office rooms: an optimal glazing-to-wall (GWR) ratio ranging between 20% and 40%, with a north orientation requiring a larger GWR (40%), a south orientation a smaller GWR (30%).

The reflectance of inner surfaces has a significant effect on daylight autonomy and the use of low transmittance glazing demand a large GWR (60%) to achieve the same daylight autonomy as 20% GWR with high transmittance glazing.

Radiance, Daysim

Simulation and experimental

validation using pyramid shape

skylight over vault roof mud-house in New Delhi (Chel,

Tiwari, & Chandra, 2009)

2009 Classroom New Delhi

Skylight integrated vault roof

mud-house

Illuminous flux, lighting power, daylight factor,

mitigation of CO2 emission related to skylight

For skylight of small and big dome: o Average annual energy saving: 204 kWh/year and 564.5

kWh/year o Mitigation of CO2 emissions: 265-375 kg/year and 732-1038

kg/year o Carbon credit potential: $2.7-$3.8 per year and $7.3-$10.4 per

year

For mud-house with skylight integrated two small and one big dome shape rooms: o Total artificial lighting energy saving: 973 kWh/year o Mitigation of CO2 emissions: 1526 kg/year o Carbon credit potential: $15.3/year

NA

Dynamic simulation and analysis of

daylighting factors for gymnasiums in mid-latitude China (Zhao & Mei, 2013)

2013 Stadium Harbin Windows on

side wall and skylight

Correlation between 22 daylight design parameters

and interior daylighting effects

The required window area is smallest at the summer solstice irrespective of the type of gymnasium.

The window area required when using a skylight is much smaller than that of each side window design.

The required window area increases with reduced glazing transmittance.

Irrespective of the type of gymnasium, the required skylight area shows a linear increase with an increase in building height.

Greater building depth requires larger window area, irrespective of the window position.

DIAlux

Dalighting Design for Museums (Kim

& Seo, 2012) 2012 Museum Seoul

Monitor-shaped toplight

Visual impact of skylight in real building comparison

Daylighting simulation method can become an integral part of the architectural design that can produce a

60MT23, 70MT23, 80MT23, 90MT23, 80MT14, and 90MT14

Radiance

27

skylight predictable lighting environment for a museum.

are proposed as alternative designs for the museum.

Lightwell skylights under overcast sky conditions (Acosta, Navarro, & Sendra,

2013)

2013 Office

Building Seville

Lightwell skylight

Daylighting factors according to skylight ration and

illuminance depending on the reflection index of the

skylight

Reflection index is a determining factor for illuminance.

Daylight factors are proportional to the reflection index (skylight height/width ratio > 2).

Room heights have little impact on daylight factors.

Uniformity of illuminance is proportional to the width/height ratio of the skylight.

From reflection index 0.5 to 0.7, illuminance is increased by 30%.

From reflection index 0.3 to 0.5, illuminance is increased by 30%.

Lightscape

Energy and cost studies of semi-

transparent photovoltaic

skylight (Li, Lam, & Cheung, 2009)

2009 Office

Building Hong Kong

Semi-transparent photovoltaic

skylight

Thermal and visual properties, energy

performance, environmental and financial issues of

skylight

The semi-transparent PV skylight with dimming control has an annual electricity saving of 56.9 MW and peak cooling load reduction of 29.3kW.

The skylight system has an annual emissions of CO2, SO2, NOx and particulates reduction of 40300, 124, 8.5, and 5.3 kg respectively.

The simple monetary payback is 23 years.

LabVIEW

Skylight and light dimming for a room with a

controlled shading device (Athienitis & Tzempelikos, 2002)

2002 Office

Building Montreal

Window with

dimming control

Combined daylighting-lighting system numerical

simulation and visual performance evaluation

Daylight transmittance is a function of sky condition, blind tilt angle and angle of incidence.

The energy savings using light dimming control window system with integrated blinds can exceed 75% for overcast days and 90% for clear days.

NA

Energy saving through the sun: Analysis of visual

comfort and energy

consumption in office space (Tagliabue,

Buzzetti, & Arosio, 2012)

2012 Office

Building Milan

Daylight on north side wall, south side wall,

and skylight

Daylight energy conservation and visual

comfort

Skylight system can provide a more homogeneous daylighting distribution for indoor space

If considering the whole energy consumption, north window would be optimal daylighting system.

Skylight can ensure visual comfort parameters without strong negative effects on energy consumption.

A reduction of almost 30% on thermal consumption compared with south window case and 1% with north window case.

Ecotect, Radiance, Evalglare, Daysim,

Energy Plus, Dialux

28

5. Introduction of Daylighting Simulation Software

Table 5.1 Introduction of Daylighting Simulation Software

Tool Input Output Strengths Keywords Latest

Version

Energy Plus

Energy Plus uses a simple ASCII input file.

Private interface developers are already

developing more targeted / domain

specific user-friendly interfaces.

Energy Plus has a number of ASCII output files - readily adapted into spreadsheet form

for further analysis including building

annual heating and cooling consumption.

Accurate, detailed simulation capabilities

through complex modeling capabilities. Input is geared to the 'object' model way of thinking. Successful interfacing using IFC

standard architectural model available for

obtaining geometry from CAD programs. Extensive

testing (comparing to available test suites) is

completed for each version and results are available on the web

site. Weather data for more than 1250

locations worldwide available on the web

site.

Energy simulation,

load calculation,

building performance,

simulation, energy

performance, heat balance, mass balance

V8.2 (2014)

Adeline

Geometry and surface characteristic codes input using 3-D CAD (SCRIBE Modeler);

simple geometry can also be entered via

dialog boxes; analysis runtime parameters

(e.g., geographic location, time of year,

sky conditions) entered via graphic user

interface dialog boxes.

Various graphic displays of interior illuminance levels, including 3-D

renderings; also preformatted text files

containing detailed analysis results that can be passed on to dynamic

building simulation programs such as tsbi5, SUNCODE, DOE-2 and

TRNSYS.

3-D CAD input; complex geometry allowed;

accurate daylighting and electric lighting

calculations; graphic display of analysis

results.

Daylighting, lighting,

commercial buildings

V3.0 (2002)

29

Evalglare

Image to be evaluated

(smaller than 800800 pixels)

Daylight glare probability (DGP) and

image given in the RADIANCE image format

(.pic or .hdr)

The program calculates the daylight glare

probability (DGP) as well as other glare indexes (dgi,ugr,vcp,cgi) to the

standard output.

180° fish-eye-image, glare

source evaluation

and simulation

Ecotect

From simplest sketch design to highly

complex 3D models, 3DS and DXF files

Specific analysis/validation:

RADIANCE, POV Ray, VRML, AutoCAD DXF, EnergyPlus, AIOLOS,

HTB2, CheNATH, ESP-r, ASCII Mod files, and XML

Essential analysis feedback provided, daylight factors and illuminance levels

calculated at any point in the model, sun’s position and path

displayed relative to the model at any date, time,

and location

Environmental design and

analysis, solar control,

overshadowing, natural and

artificial lighting, life

cycle assessment and costing

Ecotect 2012 (2012)

Daysim

RADIANCE building scene files, a RADIANCE

sensor point grid file, EnergyPlus weather

data

Annual illuminance/luminance

profile, daylight autonomy/factor

distribution, annual electric lighting energy

use

Field study data based user behavior model,

energy saving potential estimation

Annual daylight

simulations, electric lighting

energy use, lighting controls

Daysim 4.0 （2013）

Radiance

Geometry and materials of design

space, DXF, Architrion, and IESNA standard

luminaire files, ArchiCAD, Vision3D

Luminance and illuminance values, plots

and contours, visual comfort levels,

photograph-quality images and video

animations

Physical accuracy in a graphics rendering

package, reliability and source code availability,

arbitrary surface geometry and

reflectance properties

Lighting, daylighting, rendering

Radiance 4.2

（2014）

DIALux

Self-created file, DWG or DXF file,

photometric files like IES, EULUMDAT, CIBSE

TM14, or LTLI

Pictures (JPG, BMP), movies (AVI), electronic

printouts (DXF, DWG, PDF)

Useful for for doing both the architectural and the technical lighting design

Lighting design,

daylight and artificial lighting,

emergency lighting, road

lighting

DIALux evo 3.3

30

AGI32

Project dimensions, luminaire photometry

(light fitting data) in IES standard format, surface color and

reflectance, texture, 3D models

Numeric results of Illuminance, luminance, exitance, BMP or VRML

file, luminance or illuminance patterns on

all surfaces image, radiosity based

rendered ouputor radiosity

Numerical analysis and fast high quality

rendering for exterior and interior lighting and

daylighting

Lighting, daylighting, rendering, roadway

AGI v15 (2014)

In this research, Ecotect will be used for Intelligent Workplace modeling since it can be used as platform

simulation software for Radiance lighting analysis. Radiance will be used for both light level and glare

analysis. The reason for choosing this software is that: Radiance has no limitation on geometry or the

materials that may be simulated and all the metrics used in this thesis project can be calculated by it.

Besides, simulation model can be exported into Radiance easily.

6. Dynamic Skylight Strategy Simulation and Energy Analysis

6.1 Pittsburgh Climate

For skylight system design, climate should be considered as an important factor in order to reach best

visual and energy performance of skylight. For example, the selection of glazing material can affect

insulation of the building, which can result in change of energy consumption. The weather condition

affects visual performance of skylight system. The skylight works better in clear day than cloudy and

rainy days. It also has effect on building’s solar energy gain from skylight. This section provides a basic

climate introduction of Pittsburgh.

Pittsburgh’s location is in the humid continental climate zone (Koppen Dfa/Cfa), and according to

ASHRAE, it belongs to climate 5A. Pittsburgh weather can vary dramatically from day to day; one day it

can be snowing and the next day can be hot and sunny. Seasons can be divided into 4 distinct seasons,

which are hot and humid summer, mild fall and spring, cold, cloudy, and moderately snowy winter.

From Figure 6.1.1 and 6.1.2, it is shown that the warmest month of the year in Pittsburgh is July, with an

average temperature of 72.6°F, and the coldest month of the year is January. Pittsburgh has a heating

dominated climate, which means the selection of building construction materials should put insulation

property as priority. Specifically, for skylight, the selection of glazing material should consider larger

thermal resistance. Besides, the use of skylight can help gain more solar energy, so that the heating

energy can be reduced.

31

Figure 6.1.1 Average Temperature in Each Month in Pittsburgh, Pennsylvania (WeatherSpark, 2014)

Pittsburgh temperature typically varies from 20°F to 83°F and is rarely below 5°F or higher than 90°F. In

warm season, average daily temperature is higher above 73°F, while it is only around 44°F in cold

season.

Figure 6.1.2 Average High Temperature, Average Low Temperature, and Precipitation of Pittsburgh from 1981 to 2010 (Data, 2014)

32

Skylight systems work most efficient during clear weathers. For rainy days, daylight provided by skylight

can be supplementary lighting for artificial lighting. The average total amount of annual rainfall of

Pittsburgh is 38.2 inch, with around average of 3 inch per month, and the total precipitation is greatest

in May while least in October. December and January have the most precipitation days during the year

on average, with an average 41.4 inch snowfall per season.

Figure 6.1.3 Average Humidity in Pittsburgh Each Month (WeatherSpark, 2014)

Figure 6.1.4 Average Dew Point in Pittsburgh Each Month (WeatherSpark, 2014)

According to Figure 6.1.3 and 6.1.4, the relative humidity typically ranges from 39% (comfortable)

to 92% (high humidity). The dew point typically varies from 12°F (dry) to 66°F (muggy) and is rarely

below -4°F (dry) or above 72°F (very muggy).

33

Figure 6.1.5 Monthly History – 2014 Degree Days of Pittsburgh (WeatherSpark, 2014)

Wind speed and wind direction (Figure 6.1.6 and 6.1.7) are necessary information needed for building

design. It is used for calculation of air ventilation in the building. During summer, wind flow help reduce

cooling load required for building and reduce air pollution in the building, while in winter wind flow

make the building require more energy for space heating.

Figure 6.1.6 The Average Daily Minimum (red), Maximum (black) Wind Speed with Percentile Bands (Inner Band from 25

th to

75th

Percentile, Outer Band from 10th

to 90th

Percentile) (WeatherSpark, 2014)

34

Figure 6.1.7 Wind Directions over the Entire Year (WeatherSpark, 2014)

The direction and strength of sunlight (Figure 6.1.8) and clouds (Figure 6.1.8) are directly related to

building design. It is also very important for skylight design. It affects amount of energy required for

space heating and amount of lighting required in the building. Putting windows of façade in the

appropriate location and direction will reduce building energy consumption.

Figure 6.1.8 Sun Path Diagram of Pittsburgh (2014) (WeatherSpark, 2014)

35

Figure 6.1.9 The Median Daily Cloud Cover (Black Line) with Percentile Bands (Inner Band from 40th

to 60th

Percentile, Outer Band from 25

th to 75

th Percentile) (WeatherSpark, 2014)

From the statistic above, there is an average of 59 clear days and 103 partly cloudy days per year, and

the median cloud cover ranges from 65% to 99%. The sky is cloudiest on January 2 and clearest

on August 12. The clearer part of the year begins around May 10. The cloudier part of the year begins

around October 29. The annual percent-average possible sunshine received value is 45% in Pittsburgh.

6.2 Autodesk Ecotect Model of Intelligent Workplace (IW)

The Robert L. Preger Intelligent Workplace is located inside Margaret Morrison Carnegie Hall, Pittsburgh,

Pennsylvania, and was completed in 1997. It is on the top of the building as an addition rooftop

construction. It integrates envelope, lighting, and mechanical systems to reach the optimal thermal,

visual, acoustic, and spatial comfort. This lab hosts faculty and graduate student offices, classrooms,

conference room, and research laboratories. In this research, the lighting analysis of dynamic skylight is

conducted in the middle part of IW. The Ecotect model is built based on Autodesk Revit model (Figure

6.2.1 and 6.2.2). The dynamic skylight field experiment area has been marked within blue area below

(Figure 6.2.3).

36

Figure 6.2.1 Plan View of IW

Figure 6.2.2 3D View of IW

In order to simulate the field experiment as accurate as possible, the windows on the side walls are

modeled in Ecotect. Modeled area is colored in purple. Figure 6.2.4 and 6.2.5 show the different

perspective of Ecotect model.

37

Figure 6.2.3 Simulated Area of IW in Ecotect

Figure 6.2.4 Perspective 1 of Simulation Area

Figure 6.2.5 Perspective 2 of Simulation Area

The experiment area in IW sets up three different skylight strategies, skylight without shading device,

skylight with Retro Solar venetian blinds, and skylight with Lutron tensioned shades. This setting

increases the uncertainty of the experiment result since each experiment bay can affect each other.

Besides, windows on side walls can also affect the result of the experiment. Thus, in computer

simulation, each simulation model has the same shading device put on each skylight bay, and side

window has the same shading device with the skylight. For example, control group has no shading

device on its 5 skylight bays and side windows. Tensioned shades group has shades installed on both its

all 5 skylight bays and side windows. In order to simulate dynamic skylight strategies, four different

blinds panel positions are simulated (Figure 6.2.6). Since the simulation is aiming at an office area. Three

desks are put in the center of the indoor area to make a simulation closer to real office environment.

Since the real experiment area in IW has a complex layout including partition walls, stairways, and desks

which is difficult to build in Ecotect model, the model in Ecotect simplified all these features and it is not

an exact representation of the IW furniture layout. The rendering effect in Ecotect of four different

blinds panel is shown in Figure 6.2.7 – 6.2.22.

38

Figure 6.2.6 Blinds Panel Position

Figure 6.2.7 Blinds Panel Position - Closed

Figure 6.2.8 Blinds Panel Position - Opened

Figure 6.2.9 Blinds Panel Position - Positive 45

Figure 6.2.10 Blinds Panel Position - Negative 45

39

Figure 6.2.11 Control Group

Figure 6.2.12 Inside View of Control Group

Figure 6.2.13 Shades Group

Figure 6.2.14 Inside View of Shades Group

Figure 6.2.15 Blinds Group (Closed)

Figure 6.2.16 Inside View of Blinds Group (Closed)

40

Figure 6.2.17 Blinds Group (positive 45)

Figure 6.2.18 Inside View of Blinds Group (Positive 45)

Figure 6.2.19 Blinds Group (Negative 45)

Figure 6.2.20 Inside View of Blinds Group (Negative 45)

Figure 6.2.21 Blinds Group (Open)

Figure 6.2.22 Inside View of Blinds Group (Open)

41

In Ecotect, two different camera perspectives are set for lighting analysis, a horizontal perspective

(Figure 6.2.25) at a height of 78.7 inch is set to simulate the visual performance of monitor surface at

sitting level, and a vertical perspective from the roof center pointing at the center of table (Figure

6.2.24) to simulate the visual performance at desk surface. The level selection is based on field

experiment conducted by Hau-Wen Wu in 2013 in IW. These two camera perspectives in Ecotect are

shown in the picture below (Figure 6.2.23). The indoor environment visual parameters are analyzed

through these two perspectives.

Figure 6.2.23 Camera Perspectives in Ecotect

Figure 6.2.24 Vertical Perspective

Figure 6.2.25 Horizontal Perspective

6.3 Dynamic Skylight Shading Device

One of the main purposes in this research is to compare influence of different shading devices on the

indoor environment. In this research, two shading devices, roller shades and venetian blinds are

compared with a skylight with no shading. Four different blinds positions are also compared. The

simulation model is based on field test conducted in 2013 by Hau-Wen Wu from Carnegie Mellon

42

University. The simulated shading device in this project comes from Retrosolar and Lutron (Figure 6.3.2

and 6.3.3).

The Retrosolar venetian blinds can reflect the unwanted high-angled sunlight in summer, and redirect

the low-angle sunlight in winter into the space for daylighting and solar heat gain. The Lutron tensioned

shades is a roller shade is a roller shade specifically designed for skylights and tilted windows. (Wu, 2014)

Figure 6.3.1 Control

Figure 6.3.2 Venetian Blinds

Figure 6.3.3 Roller Shades

The shading device simulation in Ecotect is a similar simulation. The key parameter is simulated according to information product brochure. The value showed in Table 6.3.1 is the combined effect of the skylight glazing and the blinds. Since some other parameters in Ecotect are not provided by the manufacture, the default value in Ecotect is used and then calibrated by previous data collected in field test.

Table 6.3.1 Shading Device Specs

Product Name SHGC (Glass 0.52) SHGC (Glass 0.32) VT

RETROSolar RETROLux O

Venetian Blinds 0.13 0.1 73%

Product Name SHGC (Single Glazed) SHGC (Double Glazed) VT

Lutron Tensioned Shades 0.27 0.32 4%

6.4 Skylight Material Hypothesis

Since the specific skylight glass product is missing, a hypothesis is necessary. Six kinds of glass products

from PPG industries are selected and compared. Since the simulation location is Pittsburgh (heating

dominated), the principle for selection is to consider the insulation property of the glass. Besides, the

SHGC is very important since the main purpose for skylight is to provide daylight.

In this thesis project, following skylight material parameters are considered as important (Collaborative,

2014):

U-Value: coefficient of measuring thermal resistance of material

43

Solar Heat Gain Coefficient: measure of the solar energy transmittance of a window

Light to Solar Gain: measure of material’s glazing ability to provide light without excess solar

heat gain

Visual Transmittance: the amount of light in the visible portion of the spectrum that passes

through a glazing material.

Table 6.4.1 Comparison of PPG glass product

U-Value Solar Heat Gain

Coefficient Light to

Solar Gain Visual

Transmittance Winter

Night Time Summer Day Time

Solarban 60 Coating on

Starphire Ultra-Clear Glass

0.29 0.27 0.41 1.8 74%

Solarban 60 0.29 0.27 0.39 1.79 70%

Sungate 400 0.32 0.31 0.6 1.27 76%

Sungate 500 0.35 0.35 0.62 1.19 74%

Sungate 600 0.23 0.21 0.36 1.77 63%

Starphire Ultra-Clear Glass

1.02 0.93 0.9 1.01 91%

Based on the product sheet provided by PPG Industries, the simulation glazing material in this thesis

project is Solarban 60 (Table 6.4.1). Although Solarban 60 coating on Starphire Ultra-Clear Glass has the

best visual and thermal performance, however, due to its high price, it is not practical to use for most of

office buildings. Generally, Solarban 60 provides good insulation with relatively clearance. Thus,

Solarban 60 is chosen to be simulated in this thesis project.

For light level analysis, totally 6 × 3 × 2 × 5 = 180 simulations were made. For glare analysis, since

simulations were only made under clear weather. Thus, totally 6 × 3 × 5 = 90 simulations were made.

6.5 Simulation Process

After finishing experiment model set up in Ecotect, next step is to export the model data into RADIANCE.

The following steps show how to simulate the visual performance of control group under

1. Select the ‘RADIANCE / DAYSIM’ under ‘Export Manage’ menu and then click ‘Export Model

Data’.

2. Select ‘Illuminance Image (Lux)’ since in this case the simulation goal is to model the interior

light level of control group. (Figure 6.5.2)

44

Figure 6.5.1 Light Level Simulation Step 1

3. Select ‘Final Render’ and check ‘Display image on completion’. (Figure 6.5.3)

Figure 6.5.2 Light Level Simulation Step 2

4. Select ‘Cloudy Sky (summer)’. In this simulation project, two weather condition, ‘Sunny Sky’ and

‘Cloudy Sky’, are used in three different seasons. (Figure 6.5.4)

45

Figure 6.5.4 Light Level Simulation Step 3

5. Select ‘At Specified Date and Time’ and set the time to ‘December 21th at 3PM ‘. Five time

points, 9AM, 11AM, 1PM, 3PM, and 5PM, in are used spring equinox, summer solstice, and

winter solstice in this simulation project. (Figure 6.5.5)

Figure 6.5.5 Light Level Simulation Step

6. Select ‘Interior View’ and then hit ‘Next’ two times. (Figure 6.5.6)

46

Figure 6.5.6 Light Level Simulation Step 5

7. Select the folder saving all the files under ‘Output Options’ and click OK to begin render. (Figure

6.5.7)

Figure 6.5.7 Light Level Simulation Step 6

47

6.5 Lighting Analysis of Dynamic Skylight System

6.5.1 Standards and Regulations

From Illuminating Engineering Society of North America (IESNA), the Table 6.5.1.1 and 6.5.1.4 show the

current luminance recommendations (lux) for lighting levels in different building types. (Richman, 2014)

This standard provides comparison baseline for the simulation. And Table 6.5.1.2 provides the

illumination requirement of different activities (Richman, 2014). The values in table 5 are maintained

average illuminance value and values in table 6 is the minimum value of illuminance for different

activities.

Table 6.5.1.1 Office Building Lighting Standard (Richman, 2014)

Building Type Space Type Maintained Average

Illuminance at Working Level (lux)

Measurement (Working) Height (1

meter = 3.3 feet)

Office Buildings

Single offices 400 At 0.8m

Open plan offices 400 At 0.8m

Conference rooms 300 At 0.8m

Table 6.5.1.2 Illumination Requirement of Different Activities (Richman, 2014)

Activity Illumination (lux)

Public areas with dark surroundings 20-50

Simple orientation for short visits 50-100

Working areas where visual tasks are only occasionally performed

100-150

Warehouse, homes, theaters, archives

150

Easy office work, classes 250

Normal office work, PC work, study library, show rooms,

500

Supermarkets, mechanical workshops, office landscapes

750

Normal drawing work, detailed mechanical workshops, operation

theaters 1,000

48

Detailed drawing work, very detailed mechanical works

1500 - 2000

Performance of visual tasks of low contrast and very small size for

prolonged periods of time 2000 -5000

Performance of very prolonged and exacting visual tasks

5000 - 10000

Performance of very special visual tasks of extremely low contrast and

small size 10000 - 20000

The standards and regulations on monitor screen are shown in Table 6.5.1.3.

Table 6.5.1.3 Work on Display Screen Equipment (DSE) or otherwise

Screen classes in accordance with ISO

9241-7 I II III

Screen Quality good medium weak

Average luminances of luminaires which are

reflected in the screen ≤ 1000 cd/m2 ≤ 250 cd/m2

Table 6.5.1.4 Illuminating Engineering Society of North America (IESNA) Standard

Illuminance 500 lux (Horizontal) IESNA (2011)

Unified Glare Ratio ≤ 19 IESNA (2011)

Luminance Ratio

Task to immediate background surface 3:1 (1:3)

IESNA (2011) Task to dimmer(bright) distance

background 10:1 (1:10)

Paper task to negative (positive) polarity VDT screen 3:1 (1:3)

Glare Ratio

Task to delight media 1:40, Task to luminaires 1:40

IESNA (2011) Light-source-adjacent-surfaces

to light source 1:20

6.5.2 Illuminance Level Analysis

49

Illuminance level is total luminous flux incident on a surface, per unit area. In this project, indoor

illuminance level of type 2 model on winter solstice, summer solstice, and spring equinox are simulated

to represent heating, cooling, and transition season. On each day, 5 time points are simulated, which are

at 9AM, 11AM, 1PM, 3PM, and 5PM. The reason for choosing these 5 time points is in order to keep

consistency with the field experiment. The simulation results of Radiance are shown below. The

different between illuminance and luminance is shown in Figure 6.5.2.1.

Figure 6.5.2.1 Illuminance and Luminance (Ransen, 2014)

The light level images rendered by RADIANCE are shown in the following sections. In these images, the

pictures with red frame mean the recommended performance, which means a light level between 500 –

1000 lux based on Richman’s study. The numbers in orange font means the light level in this situation is

too high (over 1000 lux). The numbers in red font means the light level in this situation is good (500-

1000 lux). The numbers in dark red font means the light level in this situation is medium (250 – 500 lux).

The numbers in black font means the light level in this situation is low (less than 250 lux).

For each condition analyzed below, an interim recommendation is proposed based only on light level

consideration. For those recommendations, the meaning of different color is shown in the following

table 6.5.2.1.

Table 6.5.2.1 Description on Color Representing Light Level

fulfill both requirement on desk and

monitor

need tasklight on desk

need tasklight on monitor

need additional shading device

50

need tasklight on both desk and monitor

Spring Illuminance Level Analysis under Clear Weather Condition

The figure 6.5.2.2 show the illuminance level on spring equinox day under sunny (clear) weather.

According to the standard referenced in table 6.5.1.1- 6.5.1.4, a light level lower than 200 lux is

considered too weak and between 500 lux and 1000 lux is considered comfortable. On monitor screen

(computer-based work), at 9AM, only blinds at positive 45 degree has a light level lower than

recommendation value of 500 lux. Control group at 9AM has an illuminance value over 1000 lux, which

is too bright for PC work. From 9AM to 11AM, all groups have a decrease on illuminance value except for

blinds at positive 45 degree. However, it still cannot reach the 500 lux line for the comfort level. Blinds

at closed position, at negative 45 degree positon, and tensioned shades also have a lower-than-500

illuminance value. At 11AM, fully opened blinds provide the best Illuminance value for visual comfort

among all groups. The light level of all groups keep decreasing after 11AM. Control group and blinds at

opened position have the best visual performance at 1PM. Other groups block too much sunlight and

artificial lighting is needed. At 3PM, only control group keeps light level over 500 lux. From 3PM to 5PM,

light level of all groups keeps decreasing and artificial lighting is needed even for control group.

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Figure 6.5.2.2 Light Level on Monitor, sunny, 03/21

For light level on desk (paper-based work), 500 lux is required according to IESNA. The simulation is

shown in Figure 6.5.2.3. At 9AM, blinds at opened / -45 degree position and tensioned shades provide

good visual environment. Indoor area becomes brighter from 9AM to 11AM. At 11AM, there is too much

light on desk of control group (over 1000 lux). Blinds at negative 45 degree provide daylight condition

for paper work at this time. The brightness on desk does not change much from 11AM to 1PM. Blinds at

negative 45 degree still works best on indoor visual environment during this time period. At 3PM, blinds

at opened position are the best skylight group among others. Light level of all groups decreases after

3PM. At 5PM, only control group can fulfill the minimum line of 500 lux although it is still a bit lower

than this value. Tensioned shades, blinds at closed position, and blinds at positive 45 degree is not

recommended to use on this day under clear weather condition since they block too much sunlight so

that additional artificial lighting is needed to maintain the 250 lux minimum requirement. When the

light level is under 250 lux, additional lighting is needed, and when the light level is between 250 and

500 lux, it is recommended for doing easy office works.

52

Figure 6.5.2.3 Light Level on Desk, Sunny, 03/21

The figure shows the light level changes on monitor and desk from 9AM to 5PM under sunny weather in

spring. The light orange area means good for light level (500 – 1000 lux) and light red area means

medium for light level (250 to 500 lux).

Figure 6.5.2.4 Light Level Change, sunny, 03/21

53

Interim Recommendation under sunny weather in spring

Spring, Sunny 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Close Open

Blinds -45 Open

54

Spring Illuminance Level under Overcast Weather Condition

The following picture (Figure 6.5.2.5) shows the illuminance level on monitor screen on spring

equinox day under cloudy (overcast) weather. For light level analysis on monitor screen, at 9AM,

illuminance value of all groups is too low to conduct computer-based work. Among all these groups,

control group has the highest illuminance value and blinds at negative 45 degree have the lowest.

Light level of all groups increases from 9AM to 11AM. At 11AM, only control group can provide a

light level reaching the medium quality of brightness. Indoor visual performance at 1PM is generally

the same as at 11AM. Control group still is the only group can reach the medium lighting quality

among other groups although illuminance value of blinds at opened position, at positive/negative 45

degree, and tensioned shades both increased. From 1PM o 3PM, all groups have a decrease of light

level on monitor screen. Except for control group, additional artificial lighting is needed. Light level

on desk of all groups continues decreasing from 3PM to 5PM. At 5PM, additional lighting is

necessary for all groups since every group has an illuminance value lower than 200 lux.

Figure 6.5.2.5 Light Level on Monitor, Overcast, 03/21

55

The following picture (Figure 6.5.2.6) shows the illuminance level on desk on spring equinox day

under cloudy (overcast) weather. At 9AM, both control group and blinds at opened position can

fulfill the requirement line of 500 lux for paper-based work. Light level on desk of all groups

increases from 9AM to 11AM. At 11AM, light level of control group is too bright (over 1000 lux).

Blinds at opened position and at negative 45 degree position provide a comfort visual

environment for paper-based work. From 11AM to 1PM, except for blinds at closed position and

at positive 45 degree position, illuminance value of other groups continues increasing. Control

group still has too much sunlight on desk at this time. Blinds at opened position and at negative

45 degree position keep providing a comfortable visual environment. Light level on desk

decreases from 1PM to 3PM for all groups except for blinds at closed position. However, its light

level is still too low for paper-based work at this time. Indoor visual performance of blinds at

opened position and negative 45 degree position remain the best among all group. From 3PM to

5PM, light level of all groups decreases. At 5PM, only control group and blinds at opened

position can provide enough light for easy office work.

Figure 3.5.2.6 Light Level on Desk, Overcast, 03/21

56

Figure 6.5.2.7 Light Level Change, Overcast, 03/21

Interim Recommendation

Spring, Overcast 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Open Open Open

Blinds Open Open Open

57

Summer Illuminance Level under Clear Weather Condition

The following picture (Figure 6.5.2.8) shows the illuminance level on monitor screen summer solstice

day under sunny (clear) weather. At 9AM, every group except for blinds at negative 45 degree position

fulfill visual requirement. At this time, control group has the highest light level on monitor screen. From

9AM to 11AM, blinds at closed position and tensioned shades have a decrease on light level, and other

groups have increase. Control group even has an illuminance value of 5841 lux, which is too bright for

computer-based work. At 11AM, light level of blinds at closed position and tensioned shades group is

still low. Blinds at positive and negative 45 degree groups provide the most comfortable visual

environment at 11AM. At 1PM, light level of control, blinds at opened position, at positive and negative

45 degree all reaches their peak value. Performance of blinds at negative 45 degree is the best for

computer work at this time point. From 1PM to 3PM, light level of all groups decreases. Only blinds at

negative 45 degree position can fulfill the requirement (with an illuminance value of 201 lux) at this

time. At 5PM, only control groups can meet the requirement.

Figure 6.5.2.8 Light Level on Monitor, Sunny, 06/21

58

Figure 6.5.2.9. shows the illuminance level on desk on summer solstice day under sunny (clear) weather.

At 9AM, only blinds at negative 45 degree position and tensioned shades cannot meet the minimum

requirement of 500 lux. However, illuminance value of other groups is too high which can cause visual

discomfort. Besides, light level of tensioned shades is only slightly lower than 500 lux. Thus, tensioned

shades have the best visual performance at this time. At 11AM, control group, blinds at opened position,

and at negative 45 degree has extremely high light level on desk. Thus, shading device is needed at this

time. However, light levels of other groups are all lower than 500 lux. Additional task light is needed for

these three groups. At 1PM, light level of all groups is lower compared with at 11AM. The condition is

similar at 1PM and 3PM for all groups as at 11AM. Control group, blinds at opened and negative 45

degree position still have extremely high illuminance level and they all reach their peak light level at

1PM, and then start to decrease. Task light is recommended at this time period as well. At 5PM, control

group has an illuminance value of 670 lux, which can fulfill the visual comfort requirement for paper-

based work on horizontal level. At this time, no shading device is recommended.

Figure 6.5.2.9 Light Level on Monitor, Sunny, 06/21

59

Figure 6.5.2.10 Light Level Change, Sunny, 06/21

Interim Recommendation

Summer, Sunny 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Close Close Close Open

Blinds Closed 45 Closed Open

60

Summer Illuminance Level under Overcast Weather Condition

Figure 6.5.2.11 shows the illuminance level on monitor screen on summer solstice day under cloudy

(overcast) weather. At 9AM, only control group and blinds at opened position can meet the

requirement for computer-based work. Light level on monitor screen of all groups increases after

9AM. At 11AM, besides control group and blinds at opened position, blinds at negative 45 degree

position also meet the requirement although all these groups only have a medium quality of

brightness. Condition at 1PM and 3PM is not much different compared with at 11AM. However,

since the illuminance value of blinds at negative 45 degree decrease a little. The light on screen of

this groups is a little weak for computer-based work. At 1PM, light level on monitor screen of

control group, blinds at opened position, and tensioned shades all reaches their peak value, and

then starts to decrease. At 5PM, only control group can meet the requirement.

Figure 6.5.2.11 Light Level on Desk, Overcast, 06/21

For paper-based work (on desk), Figure 6.5.2.12 shows the daylight condition on summer solstice day

under overcast weather. At 9AM, three groups exceed the minimum value of 500 lux, control group,

61

blinds at opened position, and blinds at negative 45 degree position. The light level on desk of control

group is too bright at 9AM. Except for blinds at closed position, every other group has an increase on

illuminance value from9AM to 11AM. At 11AM, both light level on desk of control group and blinds at

opened position is too high. Blinds at negative 45 degree position have the best visual performance at

this time point. At 1PM, control group, blinds at closed position, and blinds at negative 45 degree all

reach their highest illuminance value. Blinds at negative 45 degree position still perform best on desk

light level. After 1PM, illuminance value of all groups shows a decrease. The overall condition is similar

to 1PM at 3PM. At 3PM, both blinds at opened position and at negative 45 degree position is

recommended. At 5PM, due to the decrease of illuminance, control group now provides an acceptable

light level. Blinds at negative 45 degree cannot provide enough light at this time. Blinds at opened

position have the most comfortable visual environment at this time.

Figure 6.5.2.12 Light Level on Desk, Overcast, 06/21

62

Figure 6.5.2.13 Light Level Change, Overcast, 06/21

Interim Recommendation

Summer, Overcast 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Open

Blinds Open

63

Winter Illuminance Level under Clear Weather Condition

Figure 6.5.2.14 shows the illuminance level on monitor screen on winter solstice day under sunny

(clear) weather. At 9AM, all groups can fulfill the visual requirement on light level for computer-

based work. Illuminance value of control group is little high compared with the standard value. At

11PM, all groups have the highest illuminance value on monitor screen during the day. Blinds at

positive 45 degree position have the largest increase compared to its value at 9AM. At this time,

light on monitor of control group is still too high to create comfortable visual environment for

occupant. At 1PM, light level of control group remains too high. Blinds at closed and negative 45

degree position, and tensioned shades cannot provide enough light on screen for computer-based

work. Blinds at opened position provide a relatively better visual environment compared with blinds

at positive 45 degree, though they both meet the requirement. At 3PM, only control group can meet

the requirement. Decrease on illuminance value continues after 3PM. At 5PM, additional lighting is

needed since no group has an illuminance value exceeding 100 lux.

Figure 6.5.2.14 Light Level on Monitor, Sunny, 12/21

64

For paper-based work, Figure 6.5.2.15shows light level change on a sunny (clear) winter solstice day of

six groups. At 9AM, only control group has an illuminance value over 500 lux (850 lux). At 11AM, light

level of control group on horizontal level is too bright for paper-based work. Illuminance value of all the

other groups does not exceed 500 lux at this time. However, Blinds at closed and opened position both

have an illuminance value closed to 500 lux, which can be considered as providing a comfortable visual

environment. At 1PM, light level of all groups shows decrease compared with at 11AM. Only control

group can meet the standard. At 3PM, control group has a lower but closed to 500 lux illuminance value,

thus, no additional light is needed. After 3PM, additional artificial light is necessary.

Figure 6.5.2.15 Light Level on Desk, Sunny, 12/21

65

Figure 6.5.2.16 Light Level Change, Sunny, 12/21

Interim Recommendation

Winter, Sunny 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Open Close Open Open

Blinds Closed 45 Open Open

66

Winter Illuminance Level under Overcast Weather Condition

Light level on monitor screen on winter solstice day under overcast weather is shown in figure

6.5.2.17. For the whole day, additional artificial lighting is needed. The control group has the highest

illuminance value among all 6 groups at every time point. Even the highest illuminance value of

control group at 1PM (188 lux) is still lower than 200 lux. Thus, no shading device is recommended

on winter solstice day under overcast weather condition and additional artificial light is needed for

all day.

Figure 6.5.2.17 Light Level on Monitor, Overcast, 12/21

Figure 6.5.2.18shows the illuminance level on desk on winter solstice day under overcast weather. At

9AM, both control group and blinds at opened position and negative 45 degree position have an

67

illuminance value exceeding 500 lux. Since illuminance value of control group (1128 lux) is a little bright

for paper-based work, blinds at opened or negative 45 degree position are preferred at this time. From

11AM till 3PM, blinds at negative 45 degree performances best among all groups. The general indoor

daylight condition is similar during this time period. At 5PM, control group and blinds at negative 45

degree position is recommended.

Figure 6.5.2.18 Light Level on Desk, 0vercast, 12/21

68

Figure 6.5.2.19 Light Level Change, Overcast, 12/21

Interim Recommendation

Winter, Overcast 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Open Open

Blinds Open Open

6.5.3 Glare Analysis

6.5.3.1 Glare Analysis in Ecotect

Glare issue is that difficulty in seeing under direct or reflected bright light. A significant ratio between

task luminance and background luminance level will cause glare inside the room (Figure 6.5.3.1). This is

a main problem in skylight application since there will be more sunlight inside room through skylight.

Figure shows the cause of glare problem. Unified Glare Rating (UGR) and Daylight Glare Index (DGI) is

used to measure the level of glare. The following table shows maximum UGR value in different

environment.

Table 6.5.3.1 UGR Standard on Different Activities

Office interior type, task or activity UGR

Performance of work, copying, etc. 19

Writing, typing, and reading, data processing on a PC

19

Technical drawing 16

CAD workstations 19

Conference and meeting rooms 19

Reception desks 22

Archives 25

69

Figure 6.5.3.1 Cause of Glare (Ransen, 2014)

In order to do the glare analysis in RADIANCE, a fisheye camera is needed in Ecotect model.

The detailed process of creating fisheye camera is showed below (Figure 6.5.3.2):

Under ‘Elements in Current Model’, create a new camera called ‘Camera_Fisheye’.

Choose ‘Hemispherical’ as lens type.

Change ‘Horizontal View Angel’ to 180 and ‘Vertical View Angel’ to 180.

Finish creating by clicking ‘Add New Element’.

Figure 6.5.3.2 Fisheye Setting in Ecotect

The rendering process is basically the same as light level simulation described before. The difference is

to choose ‘Luminance Image’ instead of ‘Illuminance Image’. For glare analysis, only situation under

sunny weather on spring equinox day, summer and winter solstice day is considered.

After finish the rendering, UGI is calculated in RADIANCE. Following command is used for calculation.

Use command ‘cd Desktop’ to access Desktop

Use command ‘cd Glare’ to access Glare folder

70

Use command ‘dir/w’ to see the list of filed in this folder

Use command ‘findglare –p fisheye_c1.pic > glare.glr’ to make a glr.file to be able to calculate

UGR value

Use command ‘glarendx –t dgi glare.glr’ to do the calculation

The same method is used for daylight glare index (DGI) calculation.

In this section, all the images with yellow boarding means there is glare issue under this condition, the

UGR or DGI value is over 19.

Glare Analysis (UGR) on Spring Equinox Day

Figure 6.5.3.3 shows fisheye image of indoor visual performance on monitor on spring equinox day. At

9AM, control group, shades group, and blinds at negative 45 degree position group show no glare

problems. At this time, shading device is not needed. At 11AM, UGR of control group increase to 21. It is

recommended to set blinds panel position to negative 45 degree since it is the only group without glare

at this time. At 1PM, the recommendation is the same as at 11AM. At 3PM, blinds is recommended to

be fully closed or remain negative 45 degree position as earlier. At 5PM, no shading device is needed

since control group now has a UGR lower than 19.

71

Figure 6.5.3.3 Glare Analysis on Monitor, 03/21

Simulation result on desk level is shown in Figure 6.5.3.4. On the desk, at 9AM, no shading device is

needed since even control group has a UGR value of 4. At 11PM, the UGR value of control groups

increases significantly to 24. At this time, no group can efficiently prevent glare. The lowest UGR value at

this time is still 21, of blinds at negative 45 degree position. Thus, additional shading device is suggested.

At 1PM, only tensioned shades can fulfill the requirement. The condition at 3PM is basically the same as

at 1PM. Tensioned shades and blinds at negative 45 degree position are two groups can prevent glare.

At 5PM, no group has a UGR value larger than 12, thus, no shading device is needed at this time.

72

Figure 6.5.3.4 Glare Analysis on Desk, 03/21

Interim Recommendation:

Spring 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Close Close Close

Blinds -45 -45 -45

73

Glare Analysis (UGR) on Summer Solstice Day

Figure 6.5.3.5 shows fisheye image of indoor visual performance on monitor on summer solstice day. At

9AM, except for blinds at fully opened position and positive 45 degree position, UGR value of all the

other groups does not exceed the maximum value of 19. From 11AM to 3PM, only blinds at fully closed

position and shades fulfill the standards. At 5PM, only UGR value of blinds at positive 45 degree exceeds

the maximum value. Generally, blinds at fully closed position and tensioned shades have the best ability

to prevent glare on monitor screen compared with other groups.

74

Figure 6.5.3.5 Glare Analysis on Monitor, 06/21

Simulation result on desk level is shown in Figure 6.5.3.6. On desk, the UGR values of all groups are

much higher than on monitor. At 9AM, control group, blinds at negative 45 degree position group, and

shades group all have a UGR value less than 19. At 11AM, all the groups can’t meet the requirement. At

1PM, only tensioned shades have a UGR value fulfilling the standards. The UGR values of all the groups

decrease after 1PM, however, at 3PM, still only tensioned shades has a value less than 19. At 5PM, all

groups can meet the standards requirement. At this time, no shading is needed for preventing glare. In

general, tensioned shades have the best performance on preventing glare on desk in summer.

75

Figure 6.5.3.6 Glare Analysis on Desk, 06/21

Interim Recommendation:

Summer 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Close

Blinds Closed Closed

76

Glare Analysis (UGR) on Winter Solstice Day

In winter, performance at 5PM is not considered since at that time artificial lighting is needed and no

glare issue is found at that time either. Besides, glare issue is much more serious in winter compared

with summer since sun angle in winter is lower than in summer. With lower sun angle, more sun light is

reflected off the earth also at a lower angle, which causes more glare visible from the surface. When

sun angle is higher, the light has a more vertical angle and less glare is created.

Simulation result on monitor level is shown in Figure 6.5.3.7. From 9AM to 1PM, UGR values of all

groups exceed maximum value of 19 except for blinds at positive/negative 45 degree position. At 11AM

and 1PM, UGR values of control group, blinds at fully opened position, and blinds at positive position

even reach about 60. At 3PM, except for tensioned shades and blinds at positive 45 degree, other

groups can fulfill the standard. Compared among different groups, fully opened blinds can cause the

most serious glare problem even compared with no shading group. Blinds at negative 45 degree and

tensioned shades generally can prevent most of the glare during the day. Additional shading device is

needed from 11AM to 1PM as a combination with tensioned shades or venetian blinds.

77

Figure 6.5.3.7 Glare Analysis on Monitor, 12/21

Simulation result on desk level is shown in Figure 6.5.3.8. Glare problem on desk (horizontal level) is

much less serious than on monitor screen (vertical level). For the whole day, there is no glare problem

for all groups.

78

Figure 6.5.3.8 Glare Analysis on Desk, 12/21

79

Interim Recommendation

Winter 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Close

Blinds Closed

Glare Analysis (DGI) on Spring Equinox Day

Daylight glare index (DGI) analysis on spring equinox day is shown in figure 6.5.3.9. From 9AM to 11AM,

no shading device is needed since DGI value of control group does not exceed the maximum value of 19.

It is noticed that due to the reflection of blinds panel, blinds at positive 45 degree position keeps having

the highest DGI value among all 6 groups. Thus, this panel angle should be avoided on this day under

clear weather. From 1PM to 3PM, blinds at open position, blinds at negative 45 degree position, and

tensioned shades is recommended. After 3PM, since DGI value is no longer larger than 19, no shading

device is needed.

80

Figure 6.5.3.9 DGI on Monitor, 03/21

Glare Analysis (DGI) on Summer Solstice Day

Figure 6.5.3.10 shows the DGI analysis on summer solstice day. The glare issue is less serious in summer

than in winter. From 9AM to 5PM, control group remains a DGI value lower than 19 all the time. For all

groups during the whole, there is no group having a DGI value higher than 19.

81

Figure 6.5.3.10 DGI on Monitor, 06/21

Glare Analysis (DGI) on Winter Solstice Day

Simulation result on monitor level is shown in Figure 6.5.3.11. Glare problems is much more serious in

winter compared with in spring and summer due to the higher sun angle as mentioned before. For

control group, at 11AM, the DGI value even reaches 37. Thus, shading device is necessary on this day. At

9AM, blinds at opened, positive 45 degree, and negative 45 degree all can efficiently prevent glare. Due

to sun angle and panel reflection, from 11AM to 3PM, blinds at opened position and positive 45 degree

position both have a very high DGI value around 35. During this time period, only tensioned shades can

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keep a DGI value lower than 19. Thus, it is suggested to use tensioned shades from 11AM to 3PM. There

is no need for shading device after 3PM since the highest DGI value at 3PM is 19 of blinds at positive 45

degree position.

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Figure 6.5.3.11 DGI on Monitor, 12/21

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6.6 Recommendation on Dynamic Skylight Strategies

The goal of this thesis project is to provide dynamic strategies on skylight shading device setting. The

simulation results on light level (illuminance) and glare (UGR and DGI) are two factors used to make the

recommendations. The priority of recommendation is on visual performance since this thesis project

emphasizes on lighting condition evaluation. Besides, glare is the main reason causing visual discomfort

and light level is the main factor when designing skylight.

Since there is no glare issue under overcast weather condition, it is only considered under clear weather

condition. The light level under each group is firstly considered, and then glare is analyzed.

The following parts include performance evaluation for each simulation group under different weather

condition in different season, and the follow chart showing the detailed schedule for Lutron tensioned

shades and RETRO Solar venetian blinds.

6.6.1 Dynamic Skylight Strategies Evaluation

In this section, each simulation group is evaluated its visual performance under clear and overcast

weather condition in transition season (spring/autumn), summer, and winter. Control group is used as

base group for comparison. Recommendation given for each group is provided based on its performance

and comparison with base case. For light level analysis, ‘Strong’ means light level at that time point is

too high (over 1000 lux). ‘Good’ means comfortable visual condition (500 – 1000 lux). ‘Medium’ means

acceptable light level (250 – 500 lux). ‘Weak’ means that light is not enough for office working (lower

than 250 lux). ‘Over 19’ means there is glare issue in this condition. When light level is evaluated as

‘Strong’, glare is taken into consideration. It should be noticed that the recommendation made in this

part is considered ‘separate’ for each group itself, which means the recommendation is made merely

based on each group’s performance on light level and glare without comparing with each other.

Transition Season (Spring/Autumn), Clear Weather

Control (No Shading) Group (Base Case)

Figure 6.6.1.1 Evaluation on Control Group, sunny, 0321

Lutron Tensioned Shades Group

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Since the priority of recommendation is light level, it is advised that shades be closed from 9AM to

10AM. However, additional shading is needed for preventing glare.

Figure 6.6.1.2 Evaluation on Tensioned Shades Group, sunny, 0321

RETRO Solar Venetian Blinds at Opened Position

Glare problem is serious from 9AM to 3PM when blinds are on opened position. Besides, light level on

desk from 9AM to 12PM is too high. Thus, it is not advised to put blinds at this position from 9AM to

3PM. From 4PM to 5PM, blinds should be put at opened position.

Figure 4.6.1.3 Evaluation on Opened Blinds Group, sunny, 0321

RETRO Solar Venetian Blinds at Positive 45 Degree Position

For this group, glare happens during the whole day. Thus, it is not advised to put blinds at positive 45

degree position.

Figure 6.6.1.4 Evaluation on +45 Blinds Group, sunny, 0321

RETRO Solar Venetian Blinds at Negative 45 Degree Position

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The visual performance of blinds at negative 45 degree position from 9AM to 10AM is good, both for

light level and glare. Thus, this position for 9AM to 10AM is supported.

Figure 6.6.1.5 Evaluation on -45 Blinds Group, sunny, 0321

RETRO Solar Venetian Blinds at Closed Position

Before 3PM, there is glare problems. After 3PM, daylight is not enough. Thus, blinds at closed position

are not advised.

Figure 6.6.1.6 Evaluation on Closed Blinds Group, sunny, 0321

Transition Season (Spring/Autumn), Overcast Weather

Control (No Shading) Group (Base Case)

Since there is no glare issue under overcast weather, light level from 11AM to 1PM on desk is still

acceptable. Before 11AM and after 4PM, due to the low light level, additional lighting is needed.

Figure 6.6.1.7 Evaluation on Control Group, Overcast, 0321

Lutron Tensioned Shades Group

The light level on both desk and monitor is too low. Thus, shades should not be closed on transitional

day under overcast weather. Other shading device should be considered.

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Figure 6.6.1.8 Evaluation on Tensioned Shades Group, Overcast, 0321

RETRO Solar Venetian Blinds at Opened Position

As shown below, only at 1PM, the light level fulfills the working requirement. Hence, it is advised to put

blinds at opened position at this time.

Figure 6.6.1.9 Evaluation on Opened Blinds Group, Overcast, 0321

RETRO Solar Venetian Blinds at Positive 45 Degree Position

The light level on both desk and monitor is too low. Thus, blinds should not be put at positive 45 degree

position on transitional day under overcast weather.

Figure 6.6.1.10 Evaluation on +45 Blinds Group, Overcast, 0321

RETRO Solar Venetian Blinds at Negative 45 Degree Position

Although light level on desk fulfills requirement from 9AM to 4PM, the light on monitor is not enough

for the whole day. Hence, this position is not advised on this day.

Figure 6.6.1.11 Evaluation on -45 Blinds Group, Overcast, 0321

RETRO Solar Venetian Blinds at Closed Position

The light level on both desk and monitor is too low. Thus, blinds should not be put at fully closed

position on transitional day under overcast weather.

Figure 6.6.1.12 Evaluation on Closed Blinds Group, Overcast, 0321

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Summer, Sunny Weather

Control (No Shading) Group (Base Case)

The glare on monitor is serious during the whole day. Besides, light level is too high from 11AM to 3PM

on monitor, and from 9AM to 3PM on desk.

Figure 6.6.1.13 Evaluation on Control Group, sunny, 0621

Lutron Tensioned Shades Group

Shades can prevent glare on monitor efficiently for the whole day and on desk except from 11AM to

1PM. Thus, excluding this time period, shades are advised to use although additional lighting is needed

after 1PM.

Figure 6.6.1.14 Evaluation on Tensioned Shades Group, sunny, 0621

RETRO Solar Venetian Blinds at Opened Position

Blinds at positive opened position are not advised since there is too much glare before 3PM, and not

enough light on monitor after 3PM.

Figure 6.6.1.15 Evaluation on Opened Blinds Group, sunny, 0621

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RETRO Solar Venetian Blinds at Positive 45 Degree Position

Blinds at positive 45 degree position are not advised since there is too much glare before 5PM, and not

enough light on monitor after 5PM.

Figure 6.6.1.16 Evaluation on +45 Blinds Group, sunny, 0621

RETRO Solar Venetian Blinds at Negative 45 Degree Position

Blinds at positive 45 degree position is advised to use at 4PM, since there is no glare issue and light level

on desk is medium. Although light level on monitor is strong at this time, it is still acceptable since there

is no glare.

Figure 6.6.1.17 Evaluation on-45 Blinds Group, sunny, 0621

RETRO Solar Venetian Blinds at Closed Position

Although there is glare from 9AM to 3PM, the light level fulfills the requirement for most of time. With

proper partial shading device, it is advised to put blinds panel at closed position from 9AM to 3PM.

Figure 6.6.1.18 Evaluation on Closed Blinds Group, sunny, 0621

Summer, Overcast Weather

Control (No Shading) Group (Base Case)

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Although light level on desk from 9AM to 4PM is very high (over 1000 lux), there is no glare issue under

overcast weather. Therefore, it is still acceptable without any shading device on skylight from 9AM to

4PM. After 4PM, additional light is necessary.

Figure 6.6.1.19 Evaluation on Control Group, Overcast, 0621

Lutron Tensioned Shades Group

Since light level on both monitor and desk is too low, shades is not advised to use.

Figure 6.6.1.20 Evaluation on Tensioned Shades Group, Overcast, 0621

RETRO Solar Venetian Blinds at Opened Position

Before 10AM and after 2PM, the light on monitor is not enough. At 1PM, the light level on desk is too

high. Hence, it is advised to put blinds at opened position from 11AM to 12PM on summer day under

overcast weather condition.

Figure 6.6.1.21 Evaluation on Opened Blinds Group, Overcast, 0621

RETRO Solar Venetian Blinds at Positive 45 Degree Position

The light level on both desk and monitor is too low. Thus, blinds should not be put at positive 45 degree

position on a summer day under overcast weather.

Figure 6.6.1.22 Evaluation on +45 Blinds Group, Overcast, 0621

RETRO Solar Venetian Blinds at Negative 45 Degree Position

The light level on both desk and monitor is too low. Thus, blinds should not be put at closed position on

a summer day under overcast weather.

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Figure 6.6.1.23 Evaluation on -45 Blinds Group, Overcast, 0621

RETRO Solar Venetian Blinds at Closed Position

The light level on both desk and monitor is too low. Thus, blinds should not be put at closed position on

a summer day under overcast weather.

Figure 6.6.1.24 Evaluation on Closed Blinds Group, Overcast, 0621

Winter, Sunny Weather

Control (No Shading) Group (Base Case)

Shading device is needed since high light level and glare problem from 9AM to 3PM. Additional light is

needed after 5PM due to the scarce light on both desk and monitor.

Figure 6.6.1.25 Evaluation on Control Group, sunny, 1221

Lutron Tensioned Shades Group

After 1PM, light level on both desk and monitor is too low for work. Thus, shades is advised to use

before 1PM. Because of glare on monitor during the whole time period, additional shading for monitor

is advised.

Figure 6.6.1.26 Evaluation on Tensioned Shades Group, sunny, 1221

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RETRO Solar Venetian Blinds at Opened Position

From 11AM to 3PM, glare problem is serious, and after 3PM, light level on monitor is too low, thus, it is

not advised to put blinds panel at positive 45 degree positon in winter under clear weather condition

after 11AM.

Figure 6.6.1.27 Evaluation on Opened Blinds Group, sunny, 1221

RETRO Solar Venetian Blinds at Positive 45 Degree Position

After 11AM, glare problem is serious, thus, it is not advised to put blinds panel at positive 45 degree

positon in winter under clear weather condition after 11AM.

Figure 6.6.1.28 Evaluation on +45 Blinds Group, sunny, 1221

RETRO Solar Venetian Blinds at Negative 45 Degree Position

Since after 1PM, light level on both monitor and desk is too low, blinds should be put at negative 45

degree before 1PM. In order to prevent glare, additional shading for monitor is advised.

Figure 6.6.1.29 Evaluation on -45 Blinds Group, sunny, 1221

RETRO Solar Venetian Blinds at Closed Position

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Since blinds at closed position cannot prevent glare efficiently, it is not to put blinds panel at this

position in winter under clear weather.

Figure 6.6.1.30 Evaluation on Closed Blinds Group, sunny, 1221

Winter, Overcast Weather

Control (No Shading) Group (Base Case)

Additional light is needed due to lack of enough light on monitor during the whole day, and no shading

device is advised.

Figure 6.6.1.31 Evaluation on Control Group, Overcast, 1221

Lutron Tensioned Shades Group

The light level on both desk and monitor is too low. Thus, shades is not advised on a winter day under

overcast weather.

Figure 6.6.1.32 Evaluation on Tensioned Shades Group, Overcast, 1221

RETRO Solar Venetian Blinds at Opened Position

The light level on monitor is too low. Thus, blinds should not be put at opened position on a winter day

under overcast weather.

Figure 6.6.1.33 Evaluation on Opened Blinds Group, Overcast, 1221

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RETRO Solar Venetian Blinds at Positive 45 Degree Position

The light level on both desk and monitor is too low. Thus, blinds should not be put at positive 45 degree

position on a winter day under overcast weather.

Figure 6.6.1.34 Evaluation on +45 Blinds Group, Overcast, 1221

RETRO Solar Venetian Blinds at Negative 45 Degree Position

The light level on monitor is too low. Thus, blinds should not be put at negative 45 position on a winter

day under overcast weather.

Figure 6.6.1.35 Evaluation on -45 Blinds Group, Overcast, 1221

RETRO Solar Venetian Blinds at Closed Position

The light level on both desk and monitor is too low. Thus, blinds should not be put at closed position on

a winter day under overcast weather.

Figure 6.6.1.36 Evaluation on Closed Blinds Group, Overcast, 1221

6.6.2 Dynamic Skylight Strategies Schedule

This section gives the recommendation combing each group’s performance on both light level and glare.

When considering these two factors, since it’s usually to two layers of shading device, adding task light is

considered prior to adding additional shading device. The hour of satisfaction means at this time,

skylight strategy can fulfill both light level requirement and prevent glare efficiently.

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Recommendation in a sunny day in spring

In a sunny day in spring, tensioned shades are advised to be closed from 9AM to 4PM, and then opened

from 5PM. After 1PM, it is also recommended to have extra light. Venetian blinds are recommended to

put at negative 45 degree from 9AM to 4PM, and then open the blinds after 5PM. From 1PM to 4PM,

extra light on monitor screen is recommended.

According to this schedule, in a sunny day in spring, the total hours of satisfaction during the whole

simulation time are:

No shading device: 1 hour

Tensioned shades: 4 hours

Venetian blinds: 5 hours

Table 6.6.2.1 Recommendation in a sunny day in spring

Spring, Sunny 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Close Close Open

Blinds -45 -45 Open

Recommendation in an overcast day in spring

In an overcast day in spring, tensioned shades are advised to be opened for the whole day. At 9AM and

after 5PM, extra light on monitor screen is recommended. For venetian blinds, blinds panel is advised to

be kept at opened position from 9AM to 2PM. After 2PM, it is recommended to pull up the blinds.

According to this schedule, in an overcast day in spring, the total hours of satisfaction during the whole

simulation time are:

No shading device: 0 hours

Tensioned shades: 7 hours

Venetian blinds: 2 hours

Table 6.6.2.2 Recommendation in an overcast day in spring

Spring, Overcast 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Open Open Open

Blinds Opened Open Open

Recommendation in a sunny day in summer

In a sunny day in summer, tensioned shades should be kept closing from 9AM to 4PM in order to

prevent glare. After 5PM, shades should be opened. From 1PM to 4PM, additional lighting is

recommended for both monitor and desk. For venetian blinds, it is recommended to keep panels at

closed position for the whole day. After 11AM, additional lighting on monitor is recommended.

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According to this schedule, in a sunny day in summer, the total hours of satisfaction during the whole

simulation time are:

No shading device: 1 hour

Tensioned shades: 3 hours

Venetian blinds: 2 hours

Table 6.6.2.3 Recommendation in a sunny day in summer

Summer, Sunny 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Close Close Close Open

Blinds Closed Closed Closed

Recommendation in an overcast day in summer

In an overcast day in summer, tensioned shades are recommended to remain opened for the whole day.

After 5PM, additional lighting on monitor is needed. For venetian blinds, from 9AM to 11AM, it is

advised to keep blinds panels at negative 45 degree position. From 11AM to 2pm, blinds panel at

positive 45 degree is recommended. From 3PM to 4PM, panel should be put at closed position. After

5PM, blinds should be open.

According to this schedule, in an overcast day in summer, the total hours of satisfaction during the

whole simulation time are:

No shading device: 1 hour

Tensioned shades: 8 hours

Venetian blinds: 7 hours

Table 6.6.2.4 Recommendation in an overcast day in summer

Summer, Overcast 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Open Open

Blinds -45 45 Closed Open

Recommendation in a sunny day in winter

In a sunny day in winter, it is recommended to close tensioned shades from 9AM to 4PM. For venetian

blinds, blinds panel should be put at negative 45 degree from 9AM to 4PM. From 1PM to 4PM, extra

lighting is needed. Both blinds and shades should be opened after 5PM.

According to this schedule, in a sunny day in spring, the total hours of satisfaction during the whole

simulation time are:

No shading device: 0 hours

Tensioned shades: 0 hours

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Venetian blinds: 4 hours

Table 6.6.2.5 Recommendation in a sunny day in winter

Winter, Sunny 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Close Close Close Open

Blinds -45 -45 Open

Recommendation in an overcast day in winter

In an overcast day in winter, both shades and blinds should be opened for the whole day in order to

keep enough light level. Besides, additional lighting is needed.

According to this schedule, in an overcast day in winter, the total hours of satisfaction during the whole

simulation time are:

No shading device: 0 hours

Tensioned shades: 0 hours

Venetian blinds: 0 hours

The satisfaction hour is zero because even without any shading device, the skylight cannot meet the

light level requirement. Under this condition, additional lighting is needed.

Table 6.6.2.6 Recommendation in an overcast day in winter

Winter, Overcast 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM 5PM

Shades Open Open

Blinds Open Open

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8. Energy Benefit of Proposed Skylight Strategies

A brief energy analysis is conducted in this thesis project. An office building is built in Design Builder and

then exported into Energy Plus for energy calculation based on Department of Energy reference model.

The building has a floor area of 15000 sf. The energy consumption is then calculated for the proposed

skylight strategies in each analyzed condition. The model is shown in Figure 8.1.

Figure 8.1 Design Builder Model for Simulation

Energy use intensity of each simulation group is calculated and shown in the figure 8.2. From the figure,

it is shown that blinds at closed and positive 45 degree position are the most energy efficient shading

group. Control group has the highest EUI since it has no shading device.

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Figure 8.2 Energy Use Intensity of 6 Simulation Groups

The energy consumption of proposed skylight schedule is calculated on three simulation days, spring

equinox, summer solstice, and winter solstice. The calculation results are compared with control group.

The energy consumption is only calculated from 9AM to 5PM in each day since the proposed schedule is

only from 9AM to 5PM. The results are shown in figure 8.3 and figure 8.4.

Under sunny weather, control group has the highest energy consumption in all three seasons. In spring

and winter, proposed tensioned shades schedule has the same energy consumption as the proposed

blinds schedule. In summer, the proposed blinds schedule is more energy efficient than proposed

shades schedule.

Figure 8.3 Daily Energy Consumption under Sunny Weather

34.5

35

35.5

36

36.5

37

37.5

Control Shades Closed Opened -45 +45

Energy Use Intensity (kBtu/ft2)

EUI

0

100

200

300

400

500

Spring Summer Winter

Daily Energy Consumption under Sunny Weather (kBtu)

Control

Shades

Blinds

100

Under overcast weather, control group has the highest energy consumption in all three seasons. In

winter, proposed tensioned shades schedule has the same energy consumption as the proposed blinds

schedule. In spring and summer, the proposed blinds schedule is more energy efficient than proposed

shades schedule.

Figure 8.4 Daily Energy Consumption under Overcast Weather

The energy simulation shows that the proposed skylight strategies can reduce the energy consumption.

The proposed blinds schedule is more energy efficient than shades schedule.

0

100

200

300

400

500

Spring Summer Winter

Daily Energy Consumption under Overcast Weather (kBtu)

Control

Shades

Blinds

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9. Limitations

The limitations of this thesis project are listed below.

Simulation Process

Since the lack of detailed specifications of both glazing materials and shading device, the simulation in

Ecotect is not as same as real product. The product information of skylight glazing material is missing,

thus, the glazing material used in this thesis project is chosen from real market based on the evaluation

on its performance. However, some specification is still unknown since the product brochure only

provides parts of information. The calibration of the material specification is based on the field

experiment conducted by Hau-Wen Wu.

The experiment area in IW has two shading devices installed on skylight bay, thus, the results of the

experiment on each kind of shading device is affected by each other. Besides, the experiment was also

influenced by outdoor weather condition and indoor occupants’ activities. The simulation in Ecotect is

assumed to be under ideal condition, which excludes interference from occupants. The weather

condition in Ecotect is more stable compared with the experiment. Therefore, the calibration based on

the experiment is not 100 percent accurate.

The simulation model in Ecotect is not exact same as experiment area. The furniture, shading device

outside the side windows can affect the data collected in the experiment. In simulation, only three desks

are put indoor, and shading device on side windows is kept to be same as on skylight. These differences

make the simulation results and experiment results incomparable.

Recommendation based on Simulation Results

In this thesis project, simulation is only conducted at five different time points during a day. Thus, this is

not a continuous simulation. However, the recommendation provided in this thesis project is given in

continuous time period.

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10. Conclusion

Based on the results from the simulation, the main conclusions and findings are listed below.

Dynamic skylight strategies can efficiently help prevent glare problems.

Tensioned shades are not an optimal option as skylight shading device except for clear weather

in summer.

o Under clear weather condition in transition season, tensioned shades cannot efficiently

prevent glare, and additional lighting is needed in the afternoon. Under overcast

weather condition in transition season, Lutron tensioned shades is not advised since it

blocks too much daylight so that the light level on both monitor screen and desk.

o Under clear weather condition in summer, tensioned shades can efficiently prevent

glare but it can also block a large amount of sunlight. Thus, task light is needed. Under

overcast weather condition in summer, tensioned shades cannot provide enough

daylight for office working.

o Under both clear and overcast weather condition in winter, tensioned shades cannot

provide enough daylight for office working. Its ability on preventing glare is not good as

venetian blinds.

Venetian blinds have the best performance when the blinds panels are put at opened position

(vertical to the skylight plane) and negative 45 degree position.

o Under both clear and overcast weather condition in transition season, blinds panel at

opened and negative 45 degree position can prevent most glare and remain a

comfortable light level for office working at the same time. However, task light is

necessary at some time in the afternoon.

o Under clear weather condition in summer, blinds panel at closed position (horizontal to

the skylight plane) provides best visual performance. Under overcast weather condition

in summer, blinds panel at negative 45 degree and opened position works better than

other simulated positions although additional lighting is still needed.

o Under clear weather condition in winter, blinds panel at opened and negative 45 degree

position can prevent most glare. However, additional shading for monitor is needed.

Under overcast weather condition in winter, no shading device is advised and additional

lighting is needed.

Dynamic skylight strategies can help reduce energy consumption under both sunny and overcast

weather. Venetian blinds schedule is more energy efficient than tensioned shades schedule.

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11. Future Work

Future work includes:

Simulation on a More Continuous Time Period

Add more time points and days in each season to get a more general conclusion. Separate transition

season into spring and autumn. Consider more combined weather condition other than clear and

overcast. Combine outside temperature into consideration on analysis.

Energy Saving Calculation of Dynamic Skylight System

Use simulation tool like EnergyPlus or eQUEST to calculate energy saving of dynamic skylight system.

The calculation includes energy saving through heating and cooling season and artificial lighting.

Compare energy benefit of different shading devices based on seasonal schedule made in this thesis

project.

Economic Benefit Analysis of Dynamic Skylight Strategies

Calculate the return of investment (ROI) of dynamic skylight system application. The investment of

dynamic skylight system includes the cost of purchasing skylight material, the cost of skylight

manufacture, the cost of installing skylight, the cost of purchasing shading device, and the cost of

skylight and shading device maintenance. The potential economic return of dynamic skylight system

includes energy saving from artificial and heating/cooling energy. The productivity increase of building

occupants should also be considered.

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12. Acknowledgement

I would like mention special thanks to my advisor Erica Cochran, Flore Marion, Azizan Aziz, and Vivian

Loftness for all guidance they have provided throughout the whole project.

I would like to thank to Chao Ding and Bertrand Lasternas on Ecotect and RADIANCE simulation

instruction and following lighting analysis.

I would like to thank to previous skylight team member Hau-Wen Wu and Zhengzhao Pei for providing

me valuable advice on instruction and results analysis.

I would like to thank to Jihyun Park on providing me related lighting standards.

I would like to thank to my friends in our WII group, I-Ting Wang, Kai-Wei Hsu, and Hau-Wen Wu, for

supporting and encouraging me all the way through the thesis project.

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Appendix