Modeling Energy Consumption Effects of Glazing

Modeling Energy Consumption Effects of Glazing Daniel Lu 12/7/2012

Table of Contents Introduction... 3 Design Options... 5 Option 1... 5 Option 2... 5 Preliminary Energy Simulation... 7 Objectives... 7 OpenStudio Model... 7 Assumptions... 8 Simulation Results... 10 Detailed Analysis... 11 Transmitted Solar Energy... 11 Conduction Heat Loss... 13 Simulation with Artificial Lighting Control... 15 Baseline Adjustment... 15 Design Options with Lighting... 15 Adjusting for Lights Turned Off... 16 Glazing Cost... 18 Overall Results... 18 Discussion... 18 Conclusions... 19 Works Cited... 20 Appendix... 21 Open Studio Assumptions... 21 Floor Construction... 21 Wood Frame Wall Construction... 21 Medium Office Occupancy Schedule... 22 Infiltration... 23 Medium Office Temperature Setpoints... 23 Medium Office Lighting Schedule... 24 Preliminary Daylighting Analysis... 24 1

Interior Lighting Adjustments... 25 Procedure... 25 Example Screenshots... 25 Resulting savings... 27 2

Introduction For the Kawneer Enlightening Library competition, students must redesign an existing library with consideration for sustainable practices. My team submitted an entry to the competition to redesign the Terrazas Branch of Austin Public Libraries.The primary feature of our redesign is an interior seating space, where people sit on raised stairs that double as bookshelves. Plan Normally, the stairs would be used as a casual place for reading and conversation. The seating space would also be used for numerous events, utilizing the stage space to the south. 3

Section Our primary focus during the design was to ensure that the space would have enough ambient daylight for people to read during the regular library hours. DIVA, a daylighting analysis program, was used to compare two primary design options. Based solely on the architectural aesthetic and daylighting performance of the two design options, one design was ultimately chosen. The purpose of this study is to more holistically evaluate the effects of each option, particularly consequent HVAC energy consumption. Quantities of interest include the total site, primary, heating, cooling, and fan energy use. A preliminary analysis only accounted for outdoor, infiltration, and occupancy loads, predicting that both options have greater energy consumption. A second study added lighting loads to the models as well, while accounting for the effects of turning off artificial lights when sufficient daylight was in the stage space. Finally, a rough estimate of the capital cost was done by considering the cost of glass. Ultimately, the matrix below will be used to compare the two options based on both the competition phase criteria as well as the additional criteria considered from this study. From the matrix, a preferred option will be proposed. Architectural Aesthetic Daylight Performance Lighting Energy Heating Energy Cooling Energy Site Energy Primary Energy Cost of Glass Option 1 Option 2 4

Design Options All options have a 6.46 ft overhang and 10.5 ft tall by 17ft wide window on the north façade. The two design options considered had the same window to wall ratio relative to the total glazable surface area of each option. Total glazable surface area is defined as the area of exterior walls and roof for the stage area. This glazing percentage is kept constant to make comparable estimates between the two options. A higher window to wall ratio for one option could lead to greater transmitted solar radiation, convection, and conduction, making the two options incomparable. Option 1 One option was to raise the stage room roof to form a clerestory facing south, shown below in 3D and in section. 3.87 24.5 21.2 Option 2 A second option is to glaze the top southern corner of the stage area. One window and one skylight will span the entire 41 ft width of the space. A light shelf will be placed under the window to diffuse light further into the space. 5

30 30 30 1. Clerestory 2. Corner Glazing East Wall Area 53.2 m^2 48.7 m^2 West Wall Area 53.2 m^2 48.7 m^2 South Wall Area 96.8 m^2 81.8 m^2 Roof Area 94.8 m^2 93.7 m^2 Total Glazable Area 298 m^2 272 m^2 Glazing Area 19.72 m^2 18.05 m^2 % Glazing 6.62% 6.62% As calculated, the total glazing in each area is the same relative to the area of the walls and roof that could have been glazed. The clerestory s angled roof gives it a greater wall area, resulting in a higher amount of glazing. 6

Preliminary Energy Simulation Objectives Preliminary energy analysis examined the heating and cooling loads of the two design options with a third baseline case. Energy models made in OpenStudio and analyzed with EnergyPlus engine were used to evaluate the passive performance of the envelope options. To measure the performance, however, a standard DX fan coil and gas heating system was added in the models and monitored for heating, cooling, fan coil energy consumption. From these key parameters, the total site and source energy consumption can also be measured for each option. These measurements were then compared across the three cases. While the absolute values generated from the energy analysis may not be very true to the actual building, this will not interfere with the purpose of this study to examine the relative differences in energy consumption between the various building envelope modifications. OpenStudio Model The OpenStudio model focuses on the theater section, highlighted in blue below: The resulting baseline model has no glazing on the southern stage wall surfaces, as seen in the following screenshots. 7

Baseline Model Front, Looking South Baseline Model Back, Looking North The model consists of two spaces: the stage, and the rest of the highlighted region. Modifications are made to the envelope only, as shown before. Assumptions While the actual design separates the zone into two floors, current analysis will assume that the design s floor large opening make the two spaces effectively one zone. Continuous space No lightshelf will be placed in the corner glazing option s energy model. At only 30 inches depth it will likely contribute little to the heating and cooling of the space. The thermal mass of the wooden stairs are ignored to isolate the effects of glazing on heating and cooling loads. Results will still be comparable The only energy loads are infiltration, outdoor air, and occupancy. No consideration for lighting and electrical equipment is given to isolate the passive performance of the envelopes. The exclusion of artificial lights will be discussed later in this report, in 8

Simulation with Artificial Lighting. Infiltration and occupancy schedules are given in the Appendix. Surfaces highlighted in pink below are adiabatic, meaning heat transfer does not occur through those surfaces. In reality, those walls are interior partitions All floors are ASHRAE 189.1-2009 Floor Construction for Climate Zone 1-4. Details are in the Appendix. All wall constructions are ASHRAE 189.1-2009 Wood Frame Walls for Climate Zone 1-4. Details are in the Appendix. All windows are Openstudio s default Fixed Window Construction: U Value = 6.92 W/m^2 K =1.218 BTU / ft^2 F SHGC =.25 VT =.11 The exact construction is not given. However, referring to the DOE2 Glass Library found in equest, an approximate construction can be found: Single Reflective Pane with Aluminum Frame w/ No Breaks (DOE Library) U Value = 1.01 BTU / ft^2 F SHGC =.29 VT =.1 Standard DX Coil Heating and Cooling System Fans are always on at 390 cfm. Thermostate Setpoints for Heating and Cooling are set to default Medium Office Setpoints. Details are in the Appendix. Primary energy factors for electricity and natural gas are 3.167 and 1.084 respectively. 9

Energy (GJ) Daniel Lu Simulation Results A preliminary simulation, under the prior listed assumptions, produced the following results. No glazing 1- Clerestory Option 2- Corner Glazing Option Total Site Energy 76.6 84.47 84.51 Total Source Energy 123.4 143.57 143.53 Cooling Electricity End Use 5.73 9.32 9.70 Fan Electricity End Use 13.65 15.65 15.23 Heating Natural Gas End Use 57.22 59.51 59.58 Clerestory Option [% increase] Corner Glazing Option [% increase] Total Site Energy 10% 10% Total Source Energy 16% 16% Cooling Electricity End Use 63% 69% Fan Electricity End Use 15% 12% Heating Natural Gas End Use 4% 4% 160 140 120 Energy Comparison (No Lights) No glazing Clerestory Option Corner Glazing Option 100 80 60 40 20 0 Total Site Energy Total Source Energy Cooling Electricity End Use Fan Electricity End Use Heating Natural Gas End Use 10

kbtu - hr Temperature (F) Daniel Lu Neither option produced energy savings compared to an unglazed stage area. Despite increasing the total volume of the space, the clerestory has comparable energy consumption to the corner glazing option across all measurements. Detailed Analysis Evidently, the increased glazing led to higher heating and cooling loads because of higher transmitted solar energy and conduction through the windows. These two specific phenomena were also examined in greater detail. Transmitted Solar Energy The following graphs show hourly transmitted solar energy for a June 21 st and December 21st. Transmitted solar energy was recorded to be highest for the corner glazing option during the summer because solar radiation can enter the skylight as well as the vertical window. During the winter, clerestory and corner glazing options have around the same solar energy transmitted. As a result, the floor surface temperatures follow the same trends, exhibiting higher heat gains in both seasons. This increase in transmitted solar radiation significantly increases the cooling loads. Transmitted Solar Energy, 6/21 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 Floor Surface Temperature, 6/21 75 74 73 72 71 70 69 68 67 66 Time (hours) 11

Energy (kbtu) Temperature (F) Daniel Lu Transmitted Solar Energy, 12/21 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 Floor Surface Temperature, 12/21 70 68 66 64 62 60 58 56 Moreover, both transmitted energy have increased to a maximum of 4.5 kbtu, as compared to 4 Btu for the summer case. Both phenomena occur because the sun is lower during winter months. Clerestory Option [% increase] Corner Glazing Option [% increase] Total Site Energy 10% 10% Total Source Energy 16% 16% Cooling Electricity End Use 63% 69% Fan Electricity End Use 15% 12% Heating Natural Gas End Use 4% 4% 12

Temperature (F) Temperature (F) Daniel Lu Conduction Heat Loss Below are graphs of the internal glass temperature in the clerestory window, in red, and the vertical window portion of corner glazing, in dotted green. For comparison, the blue line measures the baseline south wall s internal surface temperature. 100 Interior Glass Surface Temperature, 6/21 80 60 40 20 0 South Wall Clerestory Glass Glazing Internal Glass Surface Temperature, 12/21 120 100 80 60 40 20 0 South Wall Clerestory Glass Glazing During the summer, the vertical glass surfaces in both options have the same internal surface temperatures. These temperatures become higher than south wall temperatures during the day, resulting in greater cooling loads. During the winter, the vertical glass surfaces exhibit lower temperatures at night and early morning, compared to wall temperatures. This contributes to the slightly higher heating loads. 13

Clerestory Option [% increase] Corner Glazing Option [% increase] Total Site Energy 10% 10% Total Source Energy 16% 16% Cooling Electricity End Use 63% 69% Fan Electricity End Use 15% 12% Heating Natural Gas End Use 4% 4% 14

Simulation with Artificial Lighting Control Despite increasing heating and cooling energy consumption, designers often glaze buildings to provide more daylight into the space. This daylight can potentially supplant artificial lighting, reducing a building s overall electricity consumption. The previous three energy simulations, however, assumed the lights were always off. Subsequent analysis examined the impact of how much less artificial lighting each option would require. Both options would also require more heating and less cooling, because lights contribute a significant amount of heat. Baseline Adjustment First, the baseline model had to be adjusted to account for artificial lighting. Adding the default medium office building lighting schedule (See Appendix for details) to the baseline model produced notable increases in energy consumption as seen below. No glazing No Glazing w/ Lights No Glazing w/ Lights [% increase] Total Site Energy 76.6 110.67 44% Total Source Energy 123.4 263.7 114% Lighting End Use 0 40.98 4098% Cooling Electricity End Use 5.73 14.27 149% Fan Electricity End Use 13.65 13.65 0% Heating Natural Gas End Use 57.22 41.78-27% What s most striking from this comparison is the increase in cooling and decrease in heating resulting from adding lights. Cooling energy consumption has more than doubled. In fact, the building consumed 0.208 GJ additional cooling load and.376 GJ less heating load per GJ of lighting energy consumed. These two ratios will be used later to calculate cooling load decreases and heating load increases as a result of lights turned off. Design Options with Lighting Next, typical office lighting was added to both design options as well, producing the following results. No Glazing w/ Lights Clerestory Option w/ Lights Total Site Energy 110.67 119.04 120.6 Total Source Energy 263.7 283.18 287.25 Lighting End Use 40.98 40.98 40.98 Cooling Electricity End Use 14.27 17.71 18.93 Fan Electricity End Use 13.65 15.31 15.23 Heating Natural Gas End Use 41.78 45.04 45.46 Corner Glazing Option w/ Lights 15

The absolute increase in energy consumption from the baseline with lighting is the same as before, because the model assumes a constant lighting consumption regardless of the month or season, as seen below in the breakdown for the clerestory. Lighting energy consumption is in yellow. Adjusting for Lights Turned Off Yet people can turn off electrical lights if there s enough daylight. The lighting energy consumption can then vary over the year, as the amount of daylight that enters the space depends on the ever changing path of the sun. A basic procedure for determining when the lights are turned off is given in the Appendix. Energy consumption values were adjusted to account for lights being turned off when enough daylight was in the space. According to the procedure, the clerestory design option will save 951.6 kw-hr of lighting electricity consumption per year or 3.42 GJ per year. The corner glazing option saved 2846 kw-hr per year or 8.95 GJ per year. As evidenced earlier, the corner glazing option has higher transmitted solar radiation, implying more transmitted daylight. Example DIVA output and detailed results are given in the Appendix. However, each option will require additional heating and less cooling because the lights are not emitting heat. Using the previous energy ratios, these offsets can also be calculated. An example calculation is shown below. 16

Energy (GJ) Daniel Lu Accounting for all offsets, each option has the following energy consumption distribution. No Glazing w/ Lights Clerestory Adjusted Clerestory Adjusted [% increase] Corner Glazing Adjusted Total Site Energy 110.67 116.19 5% 113.16 2% Total Source Energy 263.7 271.47 3% 256.65-3% Lighting End Use 40.98 37.55-8% 32.03-22% Cooling Electricity End Use 14.27 17.00 19% 17.06 20% Fan Electricity End Use 13.65 15.31 12% 15.23 12% Heating Natural Gas End Use 41.78 46.33 11% 48.83 17% Corner Glazing Adjusted [%increase] Even accounting for turning off lights, the total site consumption of both options is higher than that of the baseline. The increased daylight and assumed lighting control procedure were not enough to overcome the HVAC site energy use. However, the corner glazing does seem to have lower primary energy consumption, due to a significant decrease in lighting electricity consumption. 300 250 Energy Comparison (w/ Lights) No glazing No Glazing w/ Lights Clerestory Option w/ Lights Corner Glazing Option w/ Lights 200 150 100 50 0 Total Site Energy Total Source Energy Lighting End Use Cooling Fan Electricity Electricity End End Use Use Heating Natural Gas End Use 17

Glazing Cost As an additional factor to consider, the two options have different capital costs, which can be roughly estimated by accounting for the area of glass required. Tinted glass costs range from around $2 to $20 per square meter (Alibaba Group, 2012). Assuming a middle value of $10 per square meters, the clerestory will cost $2980.56 and the corner glazing will cost $2728.43. Obviously there are additional fabrication costs with framing and overall construction. However, these values will be used for a more qualitative yet holistic evaluation of the two designs. Overall Results Overall, the tradeoffs between each option can be evaluated in the following matrix. The matrix includes both qualitative and quantitative measures of performance. Designations of good and better for the architectural aesthetics come from the original architectural design team, which deemed both options equally preferable to an unglazed stage area. Designations of None, More, and Most come from the initial daylighting analysis, which determined that the corner glazing option could allow greater amounts of daylight to penetrate deeper into the space. Results are shown in the Appendix. Architectural Aesthetic Daylight Levels Lighting Energy Heating Energy Cooling Energy Site Energy Primary Energy Cost of Glass ($10/sq ft) Baseline Good None 40.98 41.78 14.27 110.67 263.7 $0 Clerestory Better More 37.55 46.33 17.00 116.19 271.47 $2980.56 Corner Better Most 32.03 48.83 17.06 113.16 256.65 $2728.43 From analyzing only heating, cooling, and site energy, it would appear that no glazing at all would be the best option. Results do suggest that the corner glazing design is the preferred option compared to the clerestory. Despite having higher heating and cooling loads compared to the clerestory, the corner glazing provides more daylight to offset artificial lighting. These relative benefits are highlighted in blue above. Discussion There are numerous ways to improve the accuracy of the model. Perhaps the biggest assumption made by the model is that the wooden stairs do not constitute any thermal mass. Yet the total volume of wood needed to construct the stairs could become significant. While this may improve accuracy of the absolute values, it may not significantly change the relative values 18

the three cases. Alternative procedures for controlling the lights could also be analyzed, especially ones that better follow the occupancy schedules of the library, and account for user behavior. Conclusions The challenge of increasing the amount of glazing for daylight without increasing heating and cooling loads is difficult to resolve. Both design options considered increased total site energy consumption, even with lighting savings included. However, the results indicate there is potential for energy savings due to increased glazing, as the corner glazing did consume less primary energy than the control case. Ultimately the corner glazing design is the better compared the clerestory option. Other daylighting strategies, such as light tubes, could be analyzed; such strategies may be better at channeling daylight into the space without increasing the HVAC energy load, which could beat the baseline design in site energy. Yet those same strategies may be less preferred by the architects, as they lend a different aesthetic. Or, more likely, such strategies may become costly to implement. In the end, options must be compared as holistically as possible to generate sustainable designs. 19

Works Cited Alibaba Group. "Tinted Glass Search Results." Search Results. Alibaba Group, 2012. Web. 07 Dec. 2012. The Engineering Toolbox. "Illuminance - Recommended Light Levels." The Engineering Toolbox. The Engineering Toolbox, 2012. Web. 07 Dec. 2012. <http://www.engineeringtoolbox.com/light-level-rooms-d_708.html>. 20

Appendix Open Studio Assumptions Floor Construction Top Carpet: Roughness: Very Rough R Value=2.17 W /m^2-k Bottom Concrete: Roughness: Rough Thcickness=.1016 m Conductivity = 1.311 W/m-K Density= 2240 kg/ m^2 Specific Heat = 836.8 J/kg-K Wood Frame Wall Construction Wood Siding: Thickness =.01 m Conductivity =.11 W/m-K Density = 544.62 kg/m^3 Specific Heat = 1210 J/kg K Thermal Absorbance =.9 Solar Absorbance =.78 Insulation: Thickness =.1104 m Conductivity =.045 W/m-K Density = 265 kg/m^3 Specific Heat = 836.8 Thermal Absorbance =.9 Inside Carpet Concrete Outside Inside Gypsum Insulation Wood Siding Outside ½ Gypsum: Roughness: Smooth Thickness =.0127 m Conductivity =.16 W/m-K Density = 784.9 kg/m^3 Specific Heat = 830 J/kg K Thermal Absorbance =.9 21

1:00 AM 2:00 AM 3:00 AM 4:00 AM 5:00 AM 6:00 AM 7:00 AM 8:00 AM 9:00 AM 10:00 AM 11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM 4:00 PM 5:00 PM 6:00 PM 7:00 PM 8:00 PM 9:00 PM 10:00 PM 11:00 PM 12:00 AM Number of People 1:00 AM 2:00 AM 3:00 AM 4:00 AM 5:00 AM 6:00 AM 7:00 AM 8:00 AM 9:00 AM 10:00 AM 11:00 AM 12:00 PM 1:00 PM 2:00 PM 3:00 PM 4:00 PM 5:00 PM 6:00 PM 7:00 PM 8:00 PM 9:00 PM 10:00 PM 11:00 PM 12:00 AM Number of People Daniel Lu Medium Office Occupancy Schedule 20 18 16 14 12 10 8 6 4 2 0 Occupancy, Weekday 12 Occupancy, Weekend 10 8 6 4 2 0 22

Temperature (F) ACH Daniel Lu Infiltration 0.35 Daily Infiltration 0.3 0.25 0.2 0.15 0.1 0.05 0 1:00 AM 3:00 AM 5:00 AM 7:00 AM 9:00 11:00 1:00 AM AM PM 3:00 PM 5:00 PM 7:00 PM 9:00 PM 11:00 PM Medium Office Temperature Setpoints 90 80 70 60 50 40 30 20 10 0 Setpoints Heating Setpoint Cooling Setpoint 23

Electricity Consumption (kw-hr) Daniel Lu Medium Office Lighting Schedule 3.5 Lighting Electricity Consumption 3 2.5 2 1.5 1 0.5 0 Preliminary Daylighting Analysis DIVA Daylighting Analysis of Both Designs for 6/21 24

Interior Lighting Adjustments Procedure Additional modeling in DIVA was used to determine when lights would be turned off. The basic geometry of the model was the same, as well as the weather file used. The following procedure for determining when lights are turned off was used. 1. For the 15 th day of each month: a. At 10AM, 12PM, 2PM, 4PM, perform DIVA analysis of daylight distribution on the staircase seats. i. If at least 75% of points in the stair area have 500 lux or greater, turn off the lights for the staircase. 500 lux is the baseline lighting level recommended for reading (Engineering Toolbox, 2012) ii. Assume the lights are on or off for the hour before and after as well. Savings will thus be roughly accounted for the library s regular hours of operation 9AM 5PM. b. Calculate total hours lights are off. c. Assume lighting of 9.69 W/m 2 over area of 108 m 2. Therefore, 1050 W will be reduced from the total lighting energy consumption per hour per day when the lights are off. 2. Apply savings per day to entire month. 3. Calculate total lighting saved per year. 4. Calculate additional heating and unrequired cooling per year. 5. Calculate the total site and source energy consumption. Example Screenshots Below are two example test runs in DIVA, which modeled how much daylight is received on the stairway area. DIVA provides both visualization and a quantitative distribution of lighting. For visualizations, pure white grid boxes are 2000 lux or greater, while black boxes are 500 lux or lower. 25

Test Case Example 1: Lights On As shown in the first highlighted values, this test simulated the stairway on Feburary 15 th at 10AM. DIVA also outputs that 96.1% of the area is below 500 lux, which means that lights will be turned on at this time. Test Case Example 2: Lights Off 26

Another test simulated the building on February 15h at 2PM. Results show that 19% of the stairway area is below 500 lux, which means that lights will be turned off. Resulting savings Based on the above procedure, data was collected for each design over the course of the year. Clerestory Option % of Stairs Area Below 500 lux on 15 th Day of Each Month 10:00 AM 12:00 PM 2:00 PM 4:00 PM January 92.7% 45.8% 5.0% 5.3% February 96.6% 63.0% 19.3% 12.4% March 99.9% 76.6% 39.3% 30.2% April 100.0% 90.8% 66.4% 58.4% May 100.0% 93.6% 89.5% 90.1% June 100.0% 90.2% 92.9% 94.8% July 100.0% 94.7% 91.0% 92.9% August 100.0% 94.4% 79.7% 73.8% September 99.7% 83.1% 48.7% 44.9% October 92.3% 60.4% 22.2% 21.6% November 85.2% 39.0% 5.3% 8.9% December 87.3% 35.9% 1.6% 6.2% 9AM - 11AM Hours Lights are On/Off and Resulting Savings 11AM - 1PM 1PM - 3PM 27 3PM - 5PM Total Hours Lights are Off Total Hours Per Month kw-hr Saved Per Month January Off On Off Off 6 186 195.37 February Off On Off Off 6 168 176.47 March Off On On On 0 0 0 April Off On On On 0 0 0

May Off On On On 0 0 0 June Off On On On 0 0 0 July Off On On On 0 0 0 August Off On On On 0 0 0 Septembe Off On On On 0 0 0 r October Off On Off Off 6 186 195.38 November Off On Off Off 6 180 189.07 December Off On Off Off 6 186 195.38 Total 951.68 Corner Glazing Option % of Stairs Area Below 500 lux on 15 th Day of Each Month 10:00 AM 12:00 PM 2:00 PM 4:00 PM January 48.4% 3.9% 0.0% 0.9% February 44.9% 10.4% 0.3% 1.2% March 47.4% 18.2% 4.9% 5.5% April 52.6% 26.8% 15.0% 18.7% May 58.8% 30.1% 25.0% 28.1% June 47.7% 29.2% 28.4% 34.8% July 50.1% 31.9% 26.1% 31.0% August 57.2% 29.9% 20.3% 23.4% September 47.6% 21.0% 8.4% 12.4% October 34.2% 10.5% 0.6% 4.0% November 35.1% 2.8% 0.0% 1.9% December 44.6% 1.5% 0.0% 1.6% 9AM - 11AM Hours Lights are On/Off and Resulting Savings 11AM - 1PM 1PM - 3PM 3PM - 5PM Total Hours Lights are Off Total Hours Per Month kw-hr Saved January On Off Off Off 9 279 293.07 February On Off Off Off 9 252 264.70 March On Off Off Off 9 279 293.07 April On On Off Off 6 180 189.07 May On On Off On 3 93 97.69 June On On On On 0 0 0 July On On On On 0 0 0 28

August On On Off Off 6 186 195.38 September On Off Off Off 9 270 283.61 October On Off Off Off 9 279 293.07 November On Off Off Off 9 270 283.61 December On Off Off Off 9 279 293.07 Total 2486.33 29