Zero Energy Housing Retrofit Pittsburgh Theological Seminary Anderson Building 48-752 Zero Energy Housing Phillip Kuehne, Xinxin Hu 05/11/18
Table of Contents 1. Project Overview ............................................................................................................... 2 A. Project Background ....................................................................................................................2 B. Identifying Best and Worst Case Units ........................................................................................2 C. Project Assumptions ..................................................................................................................5 D. Baseline Consumption ...............................................................................................................5
2. Building Envelope .............................................................................................................. 7 2.A Building Envelope ....................................................................................................................7 2.B Roof.........................................................................................................................................9 2.C Window ................................................................................................................................. 11 2.D Air Leakage ............................................................................................................................ 12
3. Mechanical Equipment .................................................................................................... 13 3.A Water Heater ......................................................................................................................... 13 3.B Hydronic System Boiler .......................................................................................................... 14 3.C Window Air Conditioner ......................................................................................................... 15 3.D Energy Recovery Ventilator .................................................................................................... 15
4. Lighting and Appliances ................................................................................................... 18 4.A Lighting.................................................................................................................................. 18 4.B Refrigerator ........................................................................................................................... 18 4.C Clothes Washer and Dryer ...................................................................................................... 18 4.D Dishwasher ............................................................................................................................ 18
5. Renewables and Beyond Code Compliance ...................................................................... 20 5.A Solar PV Arrays ...................................................................................................................... 20 5.B Code Exceeding Envelope Retrofit .......................................................................................... 21
6. Energy Reduction Summary ............................................................................................. 22 6.A Overall Energy Performance Retrofit Measures ....................................................................... 22 6.B Energy Performance Retrofit Measures for Worst Unit ............................................................ 24 6.C Utility Metering...................................................................................................................... 24 6.D Energy Balance Summary ....................................................................................................... 26
5. Conclusion and Benefits ................................................................................................... 27
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1. Project Overview 1.A Project Background The Anderson apartment building located at 6020 Stanton Ave was the focus of this report. Anderson is a three-story, largely uninsulated 1960s masonry multifamily housing building with 12 two-bedroom dwelling units. The building uses the dwelling unit module to characteristically shift in plan which creates balconies and shadowing that helps create a rhythm to the façade. Anderson is a well-maintained building like the adjacent McMillan and Highlander apartment buildings to the east and south respectively. To provide some context, residential and commercial buildings account approximately 39% of the total energy consumption in the U.S.1 Improving existing building stock energy efficiency is a critical part of the country’s energy future as a large majority of buildings that will be consuming energy in the next twenty years have long been built. Pennsylvania is on the cusp of adopting International Building Code (IBC) 2015 and along with it, the corresponding International Energy Conservation Code (IECC) 2015 which will require new projects to meet stricter energy requirements. This is an especially important step forward for Pennsylvania considering its housing stock is among the oldest in the country at a median age of 50-61 years.2 A multifamily housing energy retrofit can have many benefits including social, ecological and financial (Triple Bottom Line).3 Finally, Pittsburgh Theological Seminary’s interest in retrofitting their buildings will also be an important demonstration of the benefits of energy conservation for future projects in the city, not to mention the climate.
1.B Identifying Best and Worst Case Units For this analysis, we used the REMRate software which is commonly used for conducting professional residential energy ratings. The guidelines for modeling multifamily residential housing state the analysis is to be performed at the dwelling unit scale, not the building scale because residential energy use patterns can vary substantially between residents. Two dwelling units were selected to represent the best and worst performing dwelling units in the Anderson apartment building. Given that all units have two bedrooms, our criteria for selecting the best and worst-case units were exterior wall area, solar exposure and adjacencies. Heat moves from warm to cold and so in Pittsburgh’s heating dominated climate, a large fraction of overall energy consumption can be lost in the form of heat energy moving from inside to outside in the cooler months. For this reason, an end unit made sense for the worst-case unit because of its larger exterior wall area. The winter sun can help heat the building passively in the winter and so the worst performing unit might also have poor solar exposure. Lastly, units adjacent to conditioned spaces have much less tendency to transfer heat across their boundaries and so a middle unit with conditioned space above and below was suspected to perform well. The following illustrations summarize properties of the best and worst-case units. 1
https://www.eia.gov/tools/faqs/faq.php?id=86&t=1%27 http://eyeonhousing.org/2014/02/the-age-of-the-housing-stock-by-state/ 3 https://rmi.org/news/social-equity-affordable-housing-and-the-net-zero-energy-opportunity/ 2
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Figure 1.1 Best Case Dwelling Unit
Figure 1.2 Best Case Unit Floor Plan
Table 1.1
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Figure 1.3 Worst Case Dwelling Unit
Figure 1.4 Worst Case Unit Floor Plan
Table 1.2
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1.C Project Assumptions 1. For water heater, the recovery efficiency input is based on the thermal efficiency of the water heater plate. The energy factor is calculated from the supplemental modeling tools of REM/Rate using thermal efficiency, tank size and standby loss. 2. For the water heater storage tank capacity, 30 gallons is chosen based on residential hot water sizing sheet. 3. 15 ACH@50Pa is assumed as the infiltration rate for the best and worst units. 4. The best and worst units don’t have recirculation for hot water supply. 5. The domestic hot water distribution pipes are not insulated. 6. The shelter class is 4 since we have the highlander building as a shading building. 7. For the clothes washer, the Resnet Default input is used due to limited information. 8. It is assumed both the best and worst units have window A/C for cooling.
1.D Baseline Consumption From the tables below, the best unit has lower HERS Score, lower energy consumption and site EUI comparing to worst unit. And it is reasonable because the North, South and East façade and the ceiling of the worst unit are contacting with outdoor environment. For the best unit, only the North and South Façade are contacting with outdoor environment. Less annual total energy consumption means less energy cost and leads to less Site Energy Use Intensity. Table 1.3 Existing Best Unit Energy Performance
Energy Performance
Site EUI HERS Score (KBtu/ft2)
Annual Total Annual Consumption Energy Cost (MMBtu/yr) ($/yr)
Best Unit
78.3
72.7
134
2943
Table 1.4 Existing Worst Unit Energy Performance
Energy Performance
Site EUI HERS Score (KBtu/ft2)
Annual Total Annual Energy Consumption Cost ($/yr) (MMBtu/yr)
Worst Unit
92.7
104.8
161
3049
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Table 1.5 Site Energy Use Intensity Comparison
Site EUI (KBTU/ft2)
No-Change
Retrofit
Retrofit + PV
Existing Best Unit
78.3
22.6
10.2
Existing Worst Unit
92.7
24.3
12.2
Average US Multi-Family (Fannie Mae Industry Survey, 2012)
59.6
Zero Energy Single Family
5-20
Table 3 shows the site EUI comparison between the worst unit, best unit and average US multifamily average site EUI and Zero Energy Single Family site EUI. Both the existing best unit and worst unit do not perform well since they have 31% and 56% more energy consumption comparing to the average US multi-family site EUI accordingly.
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2. Building Envelope 2.A Building Envelope When approaching building envelope retrofit strategies for masonry buildings in cold climates, there are to main strategies. The first and more complicated would be to add insulation to the interior. We chose not to pursue this approach for several reasons. Literature suggests that insulating to the interior and cutting off the heat flow from inside-out can create risks of freeze/thaw damage to the existing façade because the outer layer of brick that was previously warmed from the interior now gets much colder in the winter. Without going into too much detail, the risks lie in the brick’s material properties and quality of the drainage layer behind the brick (if it exists). For further reading on this topic, refer to Deep Dish Retrofits as cited below. 4,5 Furthermore, recognizing the building is currently occupied, we decided to present a strategy that would allow for tenants to remain in-situ throughout the retrofit as a revenue source for PTS. Exterior insulation retrofits are also typically perform better than interior insulation strategies. The typical existing exterior wall assembly was field measured to be approx. 12½” from inside plaster finish to exterior face of brick and is understood to be uninsulated based on owner feedback. The masonry exterior wall assembly is a “mass” wall meaning it’s monolithic as opposed to stick-built in the case of wood-framed construction. For mass wall construction, IECC 2015 requires a minimum continuous insulation value of R13 if less than half of the insulation is on the inside of the wall and R17 if more than half is on the inside. Table 2.1
4 5
Lstiburek, J. W. (2014). Deep-dish retrofits. Ashrae Journal, 56(8), 38. https://buildingscience.com/documents/insights/bsi-047-thick-as-brick
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Table 2.2 (retrofit layers highlighted)
Exterior
Interior
Figure 2.1 Proposed Wall Assembly A spray or roll-applied vapor and moisture control layer would be applied to the existing brick surface to seal the building and is indicated by the heavy dashed line in Figure X.X above. The proposed insulation type is a mineral wool semi-rigid insulation board which can allow drying to both sides and has exceptional fire resistance. Mineral wool also has a much lower carbon footprint than rigid extruded polystyrene type insulation (XPS).6 This factor could come in handy if pursuing a green building certification such as LEED.
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https://www.buildinggreen.com/news-article/avoiding-global-warming-impact-insulation
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The proposed fiber reinforced concrete panel cladding is proposed in a rain-screen application meaning that the cladding panels serve the purpose of keeping bulk water from entering the assembly. However, any little amount of water that does get past the cladding is able to easily drain away through the air gap behind the panels. The cladding panels can be specified in a variety of appearances and are prefabricated for expedited installation. Figure X.X below illustrates what Anderson might look like with this type of cladding.
2.B Roof The section is only for the worst unit since the ceiling of the best unit is not contacting with outdoor environment. Thus, there is no need to insulate the ceiling of the best unit. For the existing roof, blown cavity insulation is between ½’’ plaster and concrete roof deck as shown in Table 2.3. The insulation does not comply with the IECC 2015 requirement of 49 R-value shown in Table 2.4. Pittsburgh is in 5A climate zone and it is a cold climate dominated city. High thermal performance is a must to reduce heat loss from roof and reduces heating load in winter. And the air leakage through roof assembly is high due to poor air barrier.
Figure 1.2 Existing Roof Section
Table 2.3 Existing Roof Assembly
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Table 2.4 IECC 2015 Insulation and Fenestration Requirement
The proposed roof added 3 layers of Rockwool Multifix Flat roof insulation on existing roof assembly as shown in Figure 2.3 with water proof layer on the outside of the insulation panels.7 The water proof layer could prevent bulk water leakage.
Figure 2.3 Proposed Roof Assembly
The total R-Value of the proposed Roof value complies with the IECC 2015 code. The detailed roof assembly schedules are shown in the following table. Three layers of depth of 3’’, 3’’ and 3.5’’ with R value of 3.8 per inch were added to the existing roof. The total depth of the insulation layers is 9.5’’ with U-value of 36. Table 2.5 Proposed Roof Assembly for Worst Unit (retrofit layers highlighted)
1.
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Rockwool Multifix Flat Roof Insulation. https://cdn01.rockwool.com/siteassets/o2rockwool/documentation/product-documentation/technical-data-sheets/commercialroofing/multifix_techdatasheet_en.pdf?f=20180215083338
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2.C Window The original window is single pane glazing, Vertical Slider - Single Hung with wood frame. The Uvalue is 0.833 with Solar Heat Gain Coefficient of 0.8 shown in Table 2.6. And the proposed window assembly is double pane low E glazing with U-value of 0.30 and Solar Heat Gain Coefficient of 0.52 shown in Table 2.7. According to IECC 2015 Residential code shown in Table 5, the U-value of window assembly should be less than 0.32. Thus, we chose the proposed window assembly with U-value of 0.3 and a relatively higher solar heat gain coefficient of 0.52 comparing to other products in searching results on National Fenestration Rating Council website. This window is also a vertical slider – Single Hung type window. Table 2.6 Existing Window Assembly
Table 2.7 Proposed Window Assembly
Figure 2.4 Propose Window Assembly
Figure 2.8 Proposed Window Assembly Brand, Model
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2.D Air Leakage A building’s air tightness has a significant impact to its energy performance and while it is difficult to pinpoint the most accurate air leakage estimate for existing buildings, literature suggests that older multifamily buildings tend to be leakier than single family homes and a reasonable estimate is on the order of 20 ACH50.8 We also looked at the Lawrence Berkeley Laboratory Residential Diagnostics Database for insight and found 15 ACH50 to be a reasonable estimate. The database query inputs are shown below in Figure X.X. Our proposed simulation results use the more conservative of the two, 15 ACH50, as the baseline infiltration rate.
Figure 2.5 LBL Residential Diagnostics Database Search Results
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http://www.energy.ca.gov/2006publications/CEC-500-2006-111/CEC-500-2006-111.PDF
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3. Mechanical Equipment 3.A Integrated Systems Diagram
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5
6 4 3
2
1
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Figure 3.1 Integrated Systems Diagram 1. Heat pump hot water heater in Anderson basement 2. Drain water heat recovery 3. Dedicated condensing boiler for Anderson, located in existing mechanical room or relocated to Anderson basement 4. Energy recovery ventilator. 2 per floor, each serving two units 5. Existing hot water radiators to remain 6. High efficiency window air conditioner if requested by tenants
3.B Water Heater Service hot water is provided to Anderson by a 100 gallon natural gas hot water heater located in the basement of the adjacent McMillan building. The energy factor was calculated using the link to the energy factor calculation spreadsheet in the REMRate help text. At an EF of 0.74, the existing natural gas hot water heater is 74% efficient at producing hot water per unit of natural gas. By comparison, Energy Star requires a minimum EF of 0.77 for gas storage water heaters
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larger than 55 gallons.9 For modeling purposes, the hot water storage capacity was sized at 30 gallons for both best and worst-case units using the A.O. Smith Residential Sizing guide.10 The distance from the existing water heater to the farthest plumbing fixture in the building can be approx. 200 ft. There appear to be opportunities to relocate the hot water storage tanks to the basement in the Anderson building which would reduce the distribution losses. This strategy could also save insulation cost as IECC 2015 requires a minimum of R3 insulation on hot water piping. Furthermore, to increase the overall service hot water system efficiency, we propose to install a drain water heat recovery coil which would recapture otherwise wasted heat from shower drains to preheat water coming into the water heater. Locating the water heaters in the basement of Anderson would bring the hot water equipment close to the drain piping to facilitate the integration of these two components.
Figure 3.2 Hot Water Heater Energy Factor (EF) Calculator
We propose (2) 50 gallon heat pump water heaters in series to be located in the basement of Anderson and connected to a drain water heat recovery coil. This capacity is equivalent to the existing system and sized to serve the Anderson building. Heat pump water heaters use electricity to move heat from the surrounding air to water and produce cooled, dehumidified air as a byproduct. The selected model heat pump is an A.O. Smith commercial grade Voltex hybrid heat pump water heater, model number HPTU-50N. This water heater has a Uniform Efficiency Rating (UEF) of 3.42, meaning it produces 3.42 units of hot water for every unit of electricity.
3.C Hydronic System Boiler The existing Peerless natural gas boiler located in the McMillan basement has a rated heating capacity of 1,344,000 BTU/hr (or nearly 48 kBTU/hr per Anderson dwelling unit) and serves both McMillan and Anderson. According to the Air Conditioning, Heating and Refrigeration Institute (AHRI), the recommended Annual Fuel Utilization Efficiency (AFUE) rating for a 198487 gas boiler is 70. This means the boiler produces an estimated 70 BTUs of useful heat for every 100 BTUs of natural gas fuel energy supplied. We conservatively assumed the boiler had 9
https://www.energystar.gov/products/water_heaters/residential_water_heaters_key_product_criteria https://www.jupiterheating.com/pdfs/ao-smith-water-heater-sizing-misc.pdf
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been replaced once based on information regarding commercial gas boiler life expectancies, hence 1984-87. With an AFUE rating of 70, there is plenty opportunity of increased efficiency. Anderson floor area factor = 0.404 Conditioned floor area factor = 0.922 Number of dwelling units = 12 1,344,000 BTU/hr x 0.404 = 542,976 BTU/hr 542,976 BTU/hr x 0.922 = 500,624 BTU/hr 500,624 BTU/hr / 12 = 41,718 BTU/hr << heating capacity per dwelling unit For this retrofit, we propose that Anderson and McMillan transition to separate hydronic system boiler to provide operational flexibility. Additionally, building envelope improvements will drastically reduce the heating demand load on the building and so a much smaller capacity, high efficiency boiler can serve Anderson alone. The proposed natural gas boiler is sized for an average peak heating design load of 6.7 kBTU/hr per Anderson dwelling unit, or 76.8 kBTU/hr for the entire building. A Peerless Combi PBC-52 natural gas condensing boiler with a heating capacity of 95.1 kBTU/hr and an AFUE rating of 95.3. In other words, the new boiler for the entire building is sized for roughly twice the capacity allocated to a single dwelling unit with the existing boiler.
3.D Window Air Conditioner For cooling in summer, window air conditioners are found in existing building and they are assumed to be window air conditioner with 1.5-ton capacity for worst unit and 1-ton capacity for best unit. Each unit has only one window air conditioner with sensible heat fraction of 0.75 and Energy Efficiency Ratio of 12. The proposed window air conditioner for worst unit has capacity of 0.7-ton, rated output of 5.2 kBtu/hr and sensible heat fraction of 0.7 as well as Energy Efficiency Ratio of 12. The proposed window air conditioner for best unit has capacity of 0.4-ton, rated output of 8 kBtu/hr and sensible heat fraction of 0.7 as well as energy efficiency ratio of 12. They are from the same brand but with different capacity. The cooling demand is reduced due to tight and insulated envelope retrofit in stage one. They are from General Electric Energy Star shown in the following figure.
3.E Energy Recovery Ventilator There is no ventilation system in existing building. But ventilation system is required according to IECC 2015 Residential code. Thus, an Energy Recovery Ventilator(ERV) is proposed to provide sufficient fresh air. ERV is a better choice comparing to HRV since ERV could help supply air capturing moisture in exhaust air shown in the following figure.
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Figure 3.3 Summeraire SERV110 ERV for Worst Case Unit
For the best unit, the proposed ERV is a balanced ventilation system with supply rate of 110 cfm under static pressure of 50Pa shown in Figure 3. The ERV system is proposed to supply fresh air to on terminal unit and one middle unit on same floor. The ventilation rate required by ASHRAE 2016 62.2 for each unit is 51 cfm fresh air. Two units need 102 cfm fresh air. The total recovery efficiency is 52% and the sensible recovery efficiency is 70%. ERV system is operating for 24 hours, 7 days a week with fan usage of 11 watts.
Figure 3.4 vanEE 70EECM ERV - Best Case Unit Proposed ERV
https://hvi-1491.quickbase.com/db/bh6688vwb?a=dr&ifv=1&rid=9862&dfid=12 For the worst unit, the ventilation rate required by ASHRAE 2013 62.2 is 57 cfm per unit. One ERV would need to supply two units per floor with minimum 114 cfm supply air rate. The Summeraire SERV110 ERV is chosen with sensible recovery efficiency of 68%, total recovery efficiency of 45% and supply air rate of 135 cfm consuming 34 watts for fan operation.
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Figure 3.5 Summeraire SERV110 ERV for Worst Unit
https://hvi-1491.quickbase.com/db/bh6688vwb?a=dr&ifv=1&rid=6299&dfid=12
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4. Lighting and Appliances 4.A Lighting Our baseline model assumption, based on conversations with PTS personnel, is that 80% of the lighting has been upgraded to CFL. Operations indicated they have been replacing old incandescent lamps as they burn out. The design model assumed that the retrofit project would include upgrading 100% of the lighting to CFL.
4.B Refrigerator The existing Top-Freezer refrigerator is from General Electric with a high energy consumption of 642 kWh/yr shown in Figure 9. The proposed refrigerator is Energy Star Certified Residential Refrigerator (GE-GTE16DTHWW), Top-Freezer and with 468 Kwh/yr. The refrigerator has 27% less energy consumption annually. And it costs $533 to buy one. (https://marketplace.duquesnelight.com/refrigerators/130659544)
4.C Clothes Washer and Dryer An existing Speed Queen clothes washer and dryer were observed in the basement of the McMillan building. The dryer was assumed to be a natural gas type REMRate default inputs were used for washer and dryer due to lack of available manufacturer data. Energy Star rated models were chosen as replacement options: Dryer â&#x20AC;&#x201C; Whirlpool WED9290FW, 7.4 cu. ft., Washer â&#x20AC;&#x201C; Whirlpool WFW75HEF, 4.5 cu. ft. The proposed dryer is a ventless hybrid heat pump model which transfers heat from the ambient air to heat the clothes. The dryer is about $1,500 and the washer $800 at Home Depot.
4.D Dishwasher In baseline models, the dish washer is from REM/Rate default input. The WhirlpoolWDF518SAHB, Compact Tall Tub dish washer is proposed and saved 23% annual energy consumption comparing to code compliant Envelope and Mechanical Equipment model. The annual energy cost and electricity usage is shown in the following figure.
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Figure 4.1 Energy Guide for proposed dish washer
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5. Renewables and Beyond Code Compliance 5.A Solar PV Arrays Focusing first on building envelope to reduce heating and cooling demand loads and then upgrading to downsized high efficiency mechanical systems positions the building to be within reach of achieving net zero or nearly net zero energy consumption by introducing renewable technologies. Perhaps the most cost effective renewable technology is solar photovoltaic panels which are now cost competitive with grid energy in some locations. Electricity in Pennsylvania is still relatively inexpensive, but the state has generous net metering laws which support solar PV installations. The proposed solar PV arrays were conservatively sized to cover only 30% of the roof area recognizing existing rooftop vents would need to be avoided and nearby trees shade portions of the roof at different times of day.
Figure 5.1 Rooftop Solar PV Arrays (view looking northeast)
The proposed rooftop solar panel layout is arranged in two arrays of 35 panels each. Each panel has a nameplate capacity of 300 W and a panel efficiency of ~91% accounting for efficiency losses as the panel heats up. The selected Canadian Solar Polycrystalline panels have a rated efficiency of 17.5%, which is standard for most cost-effective panels on the market. Table 5.1
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5.B Code Exceeding Envelope Retrofit Depending on PTSâ&#x20AC;&#x2122;s project goals, considering additional insulation beyond IECC 2015 code requirements may be of interest. For example, if the project is trying to achieve net-zero energy consumption then exceeding code required building envelope thermal resistance (R-values) is probably a good idea. However, if the main project is not aiming for net-zero then the costbenefit of additional insulation may not make sense because at a certain point, providing more insulation yields diminishing energy savings. We looked at several scenarios with insulation values exceeding the energy code to understand the impact on heating and cooling design loads (kBTU/hr). The best-case dwelling unit most clearly shows the diminishing returns of adding more insulation to the building envelope. In Table 5.2 below, the worst case unit does not clearly indicate diminishing returns yet because the exterior wall has a proportionally higher impact on design loads as compared to the best case. Both units illustrate the overall impact of upgrading the building envelope to meet IECC 2015. Table 5.2
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6. Energy Reduction Summary 6.A Overall Energy Performance Retrofit Measures The energy performance comparisons are conducted by comparing the energy performance of each strategy with the baseline of the current stage as shown in the following two tables. Each subsequent row compares the stage performance to the previous row. Envelope row is compared with the existing best and worst unit case energy performance. Table 6.1
BestCase CodeCompliant Retrofit Envelope* Env+ME Env+ME+App Env+ME+App+PV
Energy Cost Percent Energy HERS Score Savings ($) Savings (%) 75 130 40 1676
31% 52% 39% 65%
98 69 42 12
Table 6.2
WorstCase CodeCompliant Retrofit Envelope* Env+ME Env+ME+App Env+ME+App+PV
Energy Cost Percent Energy HERS Score Savings ($) Savings (%) 111 123 22 1438
32% 50% 23% 42%
110 63 45 19
From the tables, Mechanical Equipment Upgrade and rooftop solar PV system saves more Energy, Energy Cost and achieves lower HERS score. However, Envelope Retrofit is the cornerstone of the retrofit. Tight and well insulated envelope reduces cooling and heating load and correct equipment sizing could be achieved. Appliances have less impact on percent energy savings and energy cost savings since their total energy consumption accounts for less percentage out of the total energy consumption. Solar PV system generates electricity to meet the demand of the electricity and shave the peak hour demand of the community electricity consumption. Notes: • * Envelope retrofit option is compared to the baseline models. Subsequent iterations are compared to the previous row • Env: Envelope • ME: Mechanical Equipment • App: Appliances • PV: Rooftop Solar Photovoltaic system
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Figure 6.1 Annual Energy Consumption Savings for each strategy for Best Unit
Figure 9 shows annual energy consumption savings for each code compliant strategy in four stages for best unit. For the Envelope stage, seal the envelope from 15 to 3 ACH at 50 Pa air leakage could reduce 18% of energy consumption. Decreasing U-value from 0.98 to 0.3 of the window only reduces 6% energy consumption since the window to wall ratio for best unit is only 9.4%. Increasing exterior wall insulation with R-13 Rockwool and Fiber Reinforcement Concrete Panel only achieved 10% energy saving since only the North and South wall are contacting with outdoor environment. For mechanical equipment upgrade, upgrading water heater from 0.74-energy factor to 3.53energy factor reduces 32% of annual energy consumption comparing to upgraded envelope case. The strategy is highly recommended since we also relocated the water heater to Anderson Basement floor to reduce the heat loss of water distribution. ERV increases the energy consumption since there is no ventilation system in the existing apartment. But ventilation is required in IECC 2015 code considering human health and indoor air quality. Thus ERV is definitely needed to supply enough fresh air. For the appliances upgrade, the default dishwasher energy consumption is too high so that proposed dish washer reduces 23% annual energy consumption. However, there is no dishwasher in Anderson Apartment which is good since occupants wash the dishes with zero energy consumption. Clothes Washer upgrade helps a bit and it is worth to replace the current one with the Whirlpool-WED92920FW clothes washer with higher energy efficiency. 23
To summarize, the recommended strategies are prioritized as follows: 1. Seal the Envelope • 15 → 3 (unit: ACH@50Pa) 2. Exterior Wall Insulation • R13 Rockwool and Fiber Reinf Conc Panel 3. Window U value • Double Pane LowE, U=0.3, SHGC=0.52 4. Water Heater EF • (2) AO Smith - HPTU-50N, Voltex Hybrid HP, 50 gal • Drain Water Heat Recovery • 0.74 EF to 3.53 EF 5. ERV • vanEE 70EECM ERV-11 watts 6. Clothes Washer Efficiency • Whirlpool - WED9290FW, 7.4 cu. ft., CEF=4.5, Hybrid HP 7. Rooftop Solar PV • (70) Canadian Solar - CS6U, 300W, Hi efficiency Polycrystaline
6.B Energy Performance Retrofit Measures for Worst Unit
Figure 6.2 Annual Energy Consumption Savings for each strategy for Worst Unit
Figure 6.2 shows annual energy consumption savings for each code compliant strategy in four stages for worst unit. For the Envelope stage, seal the envelope from 15 to 3 ACH at 50 Pa air
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leakage could reduce 14% of energy consumption. Insulating roof with R-36 Rockwool material saves 13% annual energy consumption. Increasing exterior wall insulation with R-13 Rockwool and Fiber Reinforcement Concrete Panel achieved 10% energy saving since the North, East and South wall are contacting with outdoor environment. Decreasing U-value from 0.98 to 0.3 of the window only reduces 5% energy consumption since the window to wall ratio for best unit is only 9.4%. For mechanical equipment upgrade, upgrading water heater from 0.74-energy factor to 3.53energy factor reduces 51% of annual energy consumption comparing to upgraded envelope case. The strategy is highly recommended since we also relocated the water heater to Anderson Basement floor to reduce the heat loss of water distribution. ERV decreases the energy consumption by 19% and ventilation is required in IECC 2015 code considering human health and indoor air quality. Thus, ERV is definitely needed to supply enough fresh air. The hydronic heating boiler and window air conditioner upgrade are very effective for worst unit and reduces 24% and 19% of energy consumption accordingly. For the appliances upgrade, the default dishwasher energy consumption is too high so that proposed dish washer reduces 22% annual energy consumption. However, there is no dishwasher in Anderson Apartment which is good since occupants wash the dishes with zero energy consumption. Clothes Washer and refrigerator upgrade helps a bit and it is worth to replace the current one with the Whirlpool-WED92920FW clothes washer with higher energy efficiency. The recommended strategies are: 1. Seal the Envelope • 15 → 3 (unit: ACH@50Pa) 2. Roof Insulation • R36 Rockwool and WP on Existing 3. Exterior Wall Insulation • R13 Rockwool and Fiber Reinf Conc Panel 4. Window U value • Dbl Pane LoE, U=0.3, SHGC=0.52 5. Water Heater EF • (2) AO Smith - HPTU-50N, Voltex Hybrid HP, 50 gal • Drain Water Heat Recovery • 0.74 EF → 3.53 EF 6. Heating Boiler AFUE • Peerless - 52 PBC, NG, AFUE=95.3%, MBH=114 • 70 AFUE → 95 AFUE 7. Window A/C unit Eff • 8.5 EER → 12 EER • high performance Env → Demand decreased 8. ERV • vanEE 70EECM ERV-11 watts 25
9. Rooftop Solar PV â&#x20AC;˘ (70) Canadian Solar - CS6U, 300W, Hi Eff Polycrystaline
6.C Utility Metering Sub-metering could be proposed for each unit to monitor their own use of natural gas and electricity. But service fees for installing sub meters would be expensive if PTS is going to pay for the service fees. Achieving net zero in multifamily housing can be a challenge in part because the plug and miscellaneous electrical loads become a higher percent of the overall consumption. The challenge lies in managing tenantsâ&#x20AC;&#x2122; behavior as many people are accustomed to particular patterns of energy consumption and it could be very difficult to manage without submetering. Furthermore, submetering would create an opportunity to provide feedback to tenants about their consumption â&#x20AC;&#x201C; a necessary measure if PTS were ever to consider having tenants pay utilities directly. Connecting the rooftop PV system to grid would be necessary since the generated electricity is assumed to be fully exported for commercial building use.
6.D Energy Balance Summary The mechanical equipment upgrade has significant impact on annual energy reduction after investigation of the energy performance of retrofit strategies for both best unit and worst unit. Increasing the energy utilization efficiency is a good strategy for multi-family apartment to reduce site Energy Use Intensity and achieve Zero Energy consumption. Then installing rooftop solar PV system and connect to the grid with net metering policy could help to achieve 2015 Common Definition of Zero Energy Housing. As shown in Table 3, the final retrofit case for best unit and worst unit have site EUI of 22.6 kBtu/ft2 and 24.3 kBtu/ft2 respectively which is much lower than the average multi-family site EUI of 59.6 kBtu/ft2. Tight and well-insulated envelope is the cornerstone of achieving Zero Energy consumption since it reduces cooling and heating load which led to smaller mechanical equipment size.
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5. Conclusion and Benefits The final HERS score is 19 for worst unit and 12 for best unit. This complies with IECC 2015 residential code. The final Site EUI for worst unit and best unit is 12.2 kBtu/ft2 and 10.2 kBtu/ft2 shown in Table 3. Although both best unit and worst unit retrofit models do not achieve zero energy, the site EUI is good enough for a multi-family apartment. They could install more rooftop solar photovoltaic panels to achieve zero energy consumption. After investigation of the energy performance of best and worst units, the recommended retrofit strategies are ranked as follows: 1. Seal the envelope: 3 ACH @ 50Pa according to IECC 2015 2. Insulate Roof • R36 Rockwool and Waterproof on Existing roof 3. Insulate Exterior Wall • R13 Rockwool and Fiber Reinf Conc Panel 4. Increase U-value of Window • Double Pane LowE, U=0.3, SHGC=0.52 5. Increase Water Heater Energy Efficiency (EF) • (2) AO Smith - HPTU-50N, Voltex Hybrid HP, 50 gal • Drain Water Heat Recovery • 0.74 EF → 3.53 EF 6. Heating Boiler AFUE • Peerless - 52 PBC, NG, AFUE=95.3%, MBH=114 • 70 AFUE → 95 AFUE 7. Install Energy Recovery Ventilator • vanEE 70EECM ERV-11 watts 8. Rooftop Solar PV Tight and well insulated envelope retrofit is the cornerstone for achieving zero energy multifamily apartment. The benefit for tight and insulated envelope is that it reduces cooling and heating load of the building. It leads to smaller size of mechanical equipment. Mechanical equipment upgrade has higher impact on annual energy consumption and HERS score rating. Rooftop solar photovoltaic system is a must to offset the imported energy from the grid.
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