FEASIBILITY OF LOW-RISE NET-ZERO ENERGY HOUSES FOR TORONTO

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1 FEASIBILITY OF LOW-RISE NET-ZERO ENERGY HOUSES FOR TORONTO Humphrey Tse 1 and Alan S. Fung 2 1,2 Department of Mechanical and Industrial Engineering, Ryerson University Canada 350 Victoria St., Toronto, Ontario, M5B 2K3, Canada Tel: Fax: htse@ryerson.ca, alanfung@ryerson.ca Type of Paper: Refereed ABSTRACT Net-zero energy homes are highly energy efficient homes that produce as much energy as it consumes annually. Using concepts of energy efficiency and renewable energy technologies, it is possible for homeowners to lower their energy requirements and costs. A base home was redesigned to become a Net- Zero energy home. This base home s energy consumption was found to be 3860 m 3 of natural gas and kwh of electricity annually. Using the program HOT2000, the details of the home were modified into an upgraded home. Implementing a ground source heat pump, solar DHW system, additional insulation, high performance windows, high efficiency HRV, energy efficient appliances, and CFL bulbs reduced the annual energy consumption. The upgrades decreased the energy usage to only 6960 kwh/year of electricity with no usage of natural gas. The increase in efficiency allowed for implementation of a PV system that could produce enough energy for the upgraded home. With the implementation of the PV system, the Net-Zero energy home is complete. RETScreen, an economic analysis program, was used to analyze the payback period of the ground source heat pump alone to be 3.4 years and the PV system alone to be 22.1 years. An estimation of the payback period for the upgrades of the entire home, all systems included, was found to be 31 years. And in Ontario with the standard offer of $0.42/kWh buyback of energy generated by PV cells it is much more feasible in Ontario. The payback reduces to 19 years, which is a 40% reduction in the payback period. If more offers like this were created the idea of a NZE home is much more feasible and will bring us closer to the idea of NZE. INTRODUCTION Since the oil crises in the 1970 s a major move towards promoting energy conservation was upheld. Governments mainly targeted the automotive industry as well as the residential energy sector. A growing concern for global warming has been the major focus of many environmental groups. A major factor to global warming is the increased greenhouse gas (GHG) emissions. Today, each Canadian home is responsible for producing an estimated five to seven tones of GHGs annually (Natural Resources Canada, 2005). In 2002, Canada made a commitment to reduce the amount of harmful greenhouse gases emitted to the environment by accepting the Kyoto Protocol. The reduction of GHGs represents a tremendous opportunity for Canadians to enjoy numerous environmental benefits. To meet the Kyoto Protocol, energy consumptions by the Canadian residential sector should be closely examined and improved since there is such a large output of GHG from the residential sector. Therefore, the idea of a self sustaining energy home would be appealing in helping to meet the Kyoto target and providing independency of rising energy costs, however, it must also be economically feasible. Net-Zero Energy (NZE) Homes combine efficient construction design, energy efficient appliances, and passive solar energy, integrated with commercially available renewable energy systems to achieve NZE consumption on an annual basis. NZE homes significantly reduce the production of greenhouse gases. Essentially, a NZE home is a highly energy efficient, grid-tied home that produces as much energy as it uses on an annual basis (Industry Canada, 2005). Housing accounts for 17 percent of secondary energy use in Canada and 16 percent of the GHG emissions (Natural Resources Canada, 2005). Converting to renewable energy sources, such as solar energy, can minimize or even eliminate the harmful outputs of GHG released by residential homes. When energy efficiency is combined with commercially available renewable energy technologies, it offers enormous potential for today s homeowner to lower their electricity requirements and costs, while at the same time delivering a long term sustainable solution to growth of GHG and other emissions. 1

2 The following concept further discussed later, draws on commercially available renewable energy technologies, such as geothermal energy, solar thermal energy, and photovoltaic (PV) power along with increased insulation to the walls and windows, strategic orientation of the house, proper window sizing and highly efficient appliances to create a NZE home. Using HOT2000 software to model our home s efficiencies and RETScreen software to make an economical assessment of the implementation of a geothermal heat pump and the installation of a PV system. NZE home concept has been reviewed in previous papers. For example, Biaou, Bernier and Ferron (2004) did a simulation on a R2000 type home in Montreal. This home had 85.4m 2 of PV and a 2.5 ton GSHP. They found with this setup NZE was possible, the PV needed to produce 13550kWh annually to make NZE possible. In Tennessee, a near NZE home was built in It was part of the U.S. Department of Energy s Building Technoliges Program (Christian, 2005). Electricity consumptions were reduced due to implementation of a heat pump water heater and PV cells. The PV cells provided only 2000 kwh/year while the home consumed over kwh/year. That is why it was only a near NZE home. In our case the energy provided by the PV cells were sufficient for the home s energy usage. SIMULATION The analysis composed of three phases: Phase 1: A brand new typical residential home was chosen within suburban Greater Toronto Area. A model of this home was created using HOT2000. From the HOT2000 model we analyzed the energy consumption and energy required by the space heating and cooling, water heating, and lighting and appliances of the home on an annual basis. Phase 2: In this phase of the project, reduction of the energy consumption of the base home will be made possible by implementing upgrades. These upgrades include the usage of triple glazed low-e argon filled windows, energy conserving appliances and lighting, improved insulation, GSHP (Ground Source Heat Pump), and solar DHW (Domestic Hot Water) system. The upgraded home will also be analyzed using HOT2000. This will prepare for the third and final phase of the project. Phase 3: This is the final phase of the project, where the devices, such as PV cells, are implemented to supply all of the energy requirements and demands of the upgraded home and economic analyses, such as lifecycle cost and payback periods, on the PV module system and GSHP system will be completed using RETScreen. In these financial analyses, results from Phase 2 will be used, as well as economic factors, such as interest rate and fuel costs, would be taken into consideration. After all three phases are completed; the result will be a full cost and energy analysis comparison of the base home and the NZE energy home. Estimated payback periods for the PV module and GSHP will be found using RETScreen, and a rough payback period for the entire NZE home will be produced by dividing the total cost of the upgrades by the annual savings generated by the upgrades. RESULTS Base Home Analysis The base house selected for modeling in HOT2000 is a 2105 ft 2, 4 bedrooms, and 2-storey home with a single garage. The home will accommodate two adults and two children who occupy the house 50% of the time. The house is actually long in length, which is ideal for PV upgrades. Figure 1 shows the floor plan of the modeled home. Figure 1: Floor plan of the chosen home The model of the home was built in HOT2000 using the dimensions given by the floor plans. Using HOT2000 s built in weather library the weather patterns for Toronto, Ontario was chosen. The fuel prices were found to be $0.12 for electricity (Toronto 2

3 Hydro, 2006) and $0.57 for natural gas (Enbridge, 2006) for Toronto, Ontario. Further parameters are listed in Table 1 below. Table 1: Base House Parameters used in HOT2000 Base House Parameters 2105 ft 2 4 bedroom Size 1 garage 2 x6" frame, 16in spacing, R20 fibre batt Wall construction insulation, gypsum board interior, brick exterior 2 x10 frame, 24in Roof Construction spacing, R40 Batt, gypsum board interior 20x20"(2), 60x60"(2), Size (number) of windows 78X78", 42X42"(4) Standard double glazed Window type windows Appliances Conventional appliances Avg. appliance load 14 kwh/day Lighting 60 W incandescent bulbs Avg. lighting load 3 kwh/day Natural gas furnace: Heating unit 11.5kW capacity, 78% efficiency Standalone electric A/C Cooling unit unit: 5 kw capacity, 3 COP Heating set point 21 C Cooling set point 25 C Ventilation Fan w/o HRV 105 cfm exhaust Air change rate 50 Pa. Domestic hot water heater Natural gas Conventional tank, 0.55 energy factor Avg. hot water load 225 L/day After completing the HOT2000 simulation, the total annual energy consumptions were obtained. Table 2: Annual Energy Consumption/Cost Summary for the Base House Total Annual Natural Gas 3860 Consumption (m 3 ) Total Annual Electricity Consumption (kwh) Total Estimated Annual Energy Cost ($) Figure 2 is a pie graph that shows the percent break down of the annual energy consumption in the base home. Figure 2: Break down of annual energy consumption in the base house. The heat losses can be seen as well from the HOT2000 simulation. By increasing the insulation the consumptions will decrease for both heating and cooling. Table 3: Analysis of annual heat loss for Base House Annual Heat Annual Heat Loss Loss (MJ) (%) Ceiling Main Walls Doors Windows Basement Ventilation Below is a pie graph of the annual heat loss components in the base home to give a visual on where heat loss is most significant. Figure 3: Break down of annual heat loss in the base house. Energy Saving Devices For a NZE home, it is ideal to not only use renewable energy sources and a good building envelope, but to 3

4 use energy efficient devices as well. This allows for minimal spending in renewable energy systems, since the size of the equipment would be smaller. Using listings of different appliances on Natural Resources Canada s website (Natural Resources Canada, 2006) energy efficient appliances were easily found. Table 4: Specific energy consumption of major appliances Specific Type of Energy Appliance Model Appliance Consumption (kwh/year) Refrigerator Kenmore *40* 391 Stove Thermador DP304CC 344 Clothes Washer Whirlpool WFW8500SR 152 Clothes Dryer GE PWSR363ED 898 Dishwasher Asko D Total 1979 (Natural Resources Canada, 2005) The total of appliance energy consumption of 1979 kwh/year is much lower than the 2003 average appliance consumption in homes, which was 3324 kwh/year (Natural Resources Canada, 2005). In HOT2000 the dryer consumption is considered in the other appliances option, therefore for the HOT2000 simulation 1081kWh/year or 2.97kWh/day is used. Lighting in homes has a factor of energy consumption as well. The old incandescent light bulbs are inefficient and break down fast. The newer CFL (compact fluorescent light) bulbs are much more efficient and even better than the past fluorescent light bulbs. The previous light bulbs flicker, yet the new compact bulbs have fixed that problem and also do not make a humming noise. They provide the same natural white light as incandescent lights. An average Canadian home has around 30 light fixtures, which has about an average cost of $200 annually for electricity (Natural Resources Canada, 2006). But by replacing just 5 of the incandescent light bulbs with the CFL bulbs, you can reduce $30 from the annual consumption cost. Key factor is to choose CFL bulbs that are Energy Star approved. Energy star approved CFLs have to meet minimum light outputs and meet strict efficacy or lumen-per-watt requirements (Natural Resources Canada, 2006). Table 5 is a guide the general wattage replacement for incandescent to CFL bulbs. The assumption of the base home using 60W incandescent light bulbs was used. Therefore, in the upgraded home 15W CFL bulbs will replace the previous light bulbs. Therefore there is a 75% reduction in the amount of energy used for lighting. Table 5: General wattage equivalency guide Standard incandescent bulb (watts) ENERGY STAR qualified CFL (suggested watts) (Natural Resources Canada, 2006) Windows There are windows located around the home and they are a major contributor to heat loss, thereby a main source of heating cost. Factors for choosing windows include, if the windows are Energy Star approved windows, and their window properties on the NFRC (National Fenestration Rating Council). Having Energy Star approval means that the window meets and performs to Energy Star standards. The NFRC shows different performance ratings that go more in-depth to assist in window selection. The label shows four different factors: U-factor, SHGC (Solar heat Gain Coefficient), VT (Visible Transmittance), and AL (Air Leakage). The U-factor describes the rate of heat loss. The lower the U- factor, the better the window s resistance towards heat flow and the better its insulating value. The SHGC is the amount of incident solar radiation that goes through a window. The lower the window s SHGC the lower the amount of solar heat it transmits. VT indicates the amount of visible light that is transmitted through the window. It is the fraction of incident visible radiation. VT considers the entire window and not just the glass portion. A higher VT means that the window transmits more light, which is desirable if you want to maximize daylight. For the Toronto region Table 6 shows the recommended properties that would be desired in a window. 4

5 Table 6: Recommended Window Properties (University of Minnesota, 2004) The windows that are modelled have triple glazed low-e coating, argon gas filled, and insulated vinyl frame. This type of window will usually have U = 0.18, SHGC = 0.40, and VT = 0.49 (University of Minnesota, 2004). A case study was done by University of Minnesota using RESFEN software, to compare different types of windows. In their case, a typical new 2000 ft 2 house with 300 ft 2 of window area, where all the windows are equally distributed on all four sides of the house and include typical shading. (University of Minnesota, 2004). Figure 4: Window Case Study (University of Minnesota, 2004) Showerheads Low flow showerheads are great for both energy and water consumption reduction. By reducing the amount of hot water used, the showerhead decreases water usage as well as the energy required to produce hot water. In an average 10-minute shower, 190 litres of hot water is used if a standard showerhead is used. (BC Hydro, 2004). Low-flow showerheads can reduce the water consumption by half, without compromising the water pressure. The low-flow showerheads restrict the flow of water through small apertures, thereby increasing the speed of the water. This will use less water to provide the same type of feel that a conventional showerhead will provide. Conventional showerheads have an output of 15-19L/min, while low-flow showerheads use around 8-9L/min. A NZE home should not only save energy with an improved building envelope and structure design, but should also have energy saving appliances and devices to reduce the energy consumption. These additions help to make the ideal goal of a NZE home possible. Upgraded Home Analysis In Table 7, parameters used in the HOT2000 upgraded home scenario are shown. Table 7: Upgraded House Building Parameters used in HOT2000 Upgraded House Parameters Size 2105 ft 2 4 bedroom 1 garage 2x8" frame, 24 spacing, Wall Construction R28 fibre batt insulation and 2.5" XTPS foam board Roof Construction 2 x4, 2 layers of R28, Gypsum board interior Size (number) of windows 20x20"(2), 60x60"(2), 78X78", 42X42"(4) Window type Triple glaze low-e argon filled windows Appliances Energy saving Avg. appliance load 2.97 kwh/day Lighting 15 W compact fluorescent light bulbs Avg. lighting load 0.75 kwh/day Ground source heat pump Heating/Cooling unit 4.7 COP (H) and 15.2 SEER Heat Pump Annual COP 3.5 Heat Pump Annual Energy Consumption 3134 MJ Heating set point 19 C Cooling set point 25 C Ventilation Air change rate Domestic hot water heater Avg. hot water load HRV 80% efficiency 50 Pa. Primary: solar hot water heater Secondary: instantaneous electric water heater 98 L/day 5

6 Heating and cooling set points are derived from using a programmable thermostat. A 24-hour day is split into three 8-hour portions. Each portion will have its own set temperature. For a heating scenario; when the home is not occupied the thermostat is set to 17 C. When occupants of the house return home the thermostat is set to 21 C. When the occupants are asleep the thermostat is set to 19 C. The air change rate or infiltration rate has been lowered to 0.5@50Pa, which is lower than the R2000 standard of 1.5@50Pa. This is achievable with a very well built airtight house. Also majority of the window positions have been relocated to the south-facing wall to increase passive solar collection, thereby alleviating some of the space heating loads. It should be noted that no structural shape changes was made to the original house to reflect current mass-market appeal of the selected model house. Further increase in passive solar gain could be possible if optimal architectural form of current mass-market housing is adopted in the industry. Table 8 compares results of passive solar utilization between the base and upgraded houses. Table 8: Comparison of Solar Gains between Base House and Upgraded House Base House Upgraded House Usable Solar Gains (MJ) Figure 5: Break down of the annual energy consumption in the upgraded house. Heat losses found in the upgraded home are tabulated below. Table 10: Detailed analysis of annual heat loss for Upgraded House Annual Heat Loss (MJ) Annual Heat Loss (%) Ceiling Main Walls Doors Windows Basement Ventilation Figure 6 is a pie graph of the percent heat loss in different areas of the home. Usable Solar Gains Fraction (%) Space Heating System Load (MJ) From the HOT2000 simulation the results of the upgraded house are shown as follows: Table 9: Annual Energy Consumption/Cost Summary for the Upgraded Home Total Annual Electricity Consumption (kwh) Total Annual Natural 0 Gas Consumption (m3) Estimated Annual $ Energy Cost The cost of electricity, $0.12, is the same cost used previously for the base home case. Figure 5 shows the components of energy consumption for the upgraded house. Figure 6: Break down of annual heat loss in the upgraded house. When comparing Fig. 2 & 3, with Fig. 5 & 6, you can see that Fig. 5 & 6 have much more even shares in energy consumption and heat loss. This is because the more extreme portions, such as windows, in the base were improved to reduce the consumption and heat loss. 6

7 GSHP Feasibility Analysis Using heating and cooling demands calculated from HOT2000, we were able to find a heatpump that would be able to satisfy the needs of the upgraded home. We looked at the list of ECONAR GSHP. ECONAR s hydronic heat pump was chosen because of its ability to supply heated or chilled water for use in a wide range of heating and cooling applications. (Radiant Max, 2005) This was favorable for our model since, in-floor radiant heating was used in our simulation. The GSHP system that was chosen to be modelled was ECONAR s GW/290/291 system. With RETScreen the feasibility of the GSHP was found to be 3.4 years. Figure 7 is the feasibility graph obtained from the RETScreen analysis. Figure 7: GSHP System Financial Analysis Graph PV Feasibility Analysis The PV system that needs to be implemented to create a NZE home will have to produce 6960 kwh to meet the annual energy consumption of the upgraded home. The area that is available on the roof for a PV system is 70.3m 2. Canadian Solar s CS6A- 190P model fit the criteria required for our NZE home. The system would only need to occupy 33.5m 2 of the roof. This system has a module efficiency of 17.6% The simple payback period found using RETScreen was 22.1 years. Figure 8 is the a diagram that shows the year to positive cash flow of the selected PV system This system has a 5.89kWp. Figure 8: Photovoltaic Project Cumulative Cash Flows Payback of the NZE home With the implementation of PV panels, the amount of money that would be saved per year would be equal to the energy consumption cost per year of the base home. That means there would be an annual saving of $ per year. To get the simple payback period of the overall cost to upgrade the base home would be divided by the annual savings per year. The total cost was found to be $ This value considers the insulation upgrade costs, window upgrade costs, Solar DHW upgrade costs, heating system upgrade costs and the PV system cost. The break down is as shown in Table 11 below. Table 26: Summary of Costs for the Base Home and Upgraded Home Upgrade Costs ($) Insulation* Window 4403 Upgrade** Heating System and A/C 3589 Costs*** DHW 2884 Upgrade**** Solar Photovoltaic Cells*** Total Upgrade Cost (*RSMeans Construction Data, 2005 **Guler, 2000 ***RETScreen, **** Thermo Dynamics Ltd., 2004) The estimated simple payback period of the NZE is approximately 31 years. 7

8 CONCLUSION Recent improvements in renewable energy technology such as more efficient photovoltaic cells have made NZE homes a reality. However many upgrades/conservation measures are required to lower the energy consumption of the house. Upgrades in areas such as, insulation, windows, energy saving appliances, energy saving lighting, ventilation, heating, cooling etc. are required to achieve the lowest possible energy consumption within the house. Through this research it was found that the cost of upgrading to a net-zero energy house would cost approximately $108,000 and having a payback period of approximately 31 years. The payback period might seem excessively high but considering the fact that a well made house can last up wards of up to 60 plus years, the payback period seems acceptable. The payback period can be significantly reduced due to the fact that the Ontario government has announced to buy back excess energy generated from solar photovoltaic cells at a price of $0.42/ kwh (Broehl, 2006). If the $0.42 were to be factored in, the payback would be roughly 19 years. This would decrease the payback period by almost 40%. If the home were to be just the upgraded house, the payback period of the home would be about 10 years. Excess energy generated from wind, biomass and small hydro energy would also be purchased back by the government at $ 0.11/kWh (Broehl, 2006). The government also offers tax rebates for purchasing renewable energy equipment (Ministry of Energy, 2006). No grants are currently available from the government as an incentive for upgrading to a NZE home; however the Ontario incentive for buying back renewable energy is a very important step in the progression of utilizing renewable energy. If more benefits like this can be found it would make the idea of a NZE home much more feasible. REFERENCES Broehl, Jesse. Ontario Renewable Energy Policy Breakthrough Hailed. 21 March April < ory?id=44408> Christian, Jeff. Ultra-Low Energy Residences. ASHRAE Journal (January, 2005): Enbridge, Residential Natural Gas Pricing April 5, 2006 < ommunitypage&control=setcommunity&communit yid=327 > Guler, Burak. Impact of Energy Efficiency Retrofits on Residential Energy Consumption and Associated Greenhouse Gas Emissions. Daltech, Industry Canada, Net Zero Energy Homes, December Natural Resources Canada. Energy Consumption of Major Household Appliances Shipped in Canada. Gatineau: Her Majesty the Queen in Right of Canada, Natural Resources Canada. EnerGuide Appliance Directory, April 25, November 5, < ppliances/index.cfm> Natural Resources Canada. Basic Facts About Residential Lighting, April 28, November 5, < light_basic_facts.cfm> Natural Resources Canada, Energy Use and Green House Gas Emissions, November 21,2005. < ent04-05/chapter3.cfm?attr=0> Radiant Max, Hydronic Heat Pumps, 2005, < Thermo Dynamics Ltd. Solar Boiler: Solar Domestic Water Heating System., Thermo Dynamics Ltd. Solar Heating < Toronto Hydro-Electric System. Residential Rates April 3, 2006 < ntial/rates/index.cfm>. University of Minnesota, Fact Sheet: Selecting Energy Efficient Windows in Canada., Efficient Windows Collaborative Alliance to Save Energy, and Lawrence Berkeley National Laboratory. 25 Mar < > Biaou, A., Bernier, M, and Ferron, Y. Simulation of Zero Net Energy Homes < > 8