1、M.Thomas is a Project Engineer, and A.Parekh is a Senior Researcher, at CanmetENERGY, Natural Resources Canada, Ottawa, Ontario, Canada. M.Armstrong is a Research Council Officer at the National Research Council of Canada and the Canadian Centre for Housing Technology, Ottawa, Ontario, Canada. The I
2、mpact of a Heat Pump Water Heater on the Energy Consumption of a Single Detached House Marianne Armstrong, PEng Martin Thomas, CEng, PEng Member ASHRAE Anil Parekh Member ASHRAE ABSTRACT Heat pump water heaters (HPWHs) are one of the most energy efficient water heating options currently available in
3、 the Canadian market. These HPWHs operate by using electricity to circulate refrigerant in a loop to move heat from the surrounding room air into the water within the storage tank. Because the Coefficient Of Performance (COP) of a heat pump is much greater than 1.0, i.e. over 100%, the water heater
4、Energy Factor greatly exceeds that of conventional water heaters. HPWHs use the indoor space as source for energy, so during the winter months, it increases the space heating load; and during the summer months, can reduce the space cooling loads. The purpose of our testing was to study the whole hou
5、se energy impact of operating a HPWH in a typical Canadian house compared to conventional water heating systems. We performed these tests at a twin house test facility located in Ottawa (Canada). The field study focussed on four key questions: (1) Did the operation of the HPWH have any adverse impac
6、ts on the basement air temperature? (2) Was the HPWH operating more efficiently than the baseline water heaters? (3) What if any were the impacts on energy consumption during the heating and cooling seasons? and (4) Were there energy cost savings during the Heating and Cooling Seasons? From the resu
7、lts of our work we concluded that: The Heat Pump Water Heaters used less energy than a conventional resistance water heater or a gas-fired storage water heater. The space heating energy use was increased and the space cooling energy use was decreased. There was no detectable change in overall house
8、energy use during the heating season, but a 20% decrease in the overall house energy use during the cooling season was seen. Using local utility pricing, energy cost savings were seen in both summer (reduction in energy) and winter (transfer of electricity to natural gas fuel). There were no energy
9、cost savings seen in comparison to a natural gas water heater. The space temperature effects were temporary and did not affect the building structure. INTRODUCTION In Canada, approximately 294 PJ (about 0.28 quads) of energy, or 7.96 billion cubic metres (278 billion cubic feet) of natural gas equiv
10、alent, are used to heat water for residential use on an annual basis and this leads to approximately 14 mega-Tonnes (14 Mega-Tons) of carbon dioxide equivalent GHG Emissions. The current energy use to provide hot water is significant, being about 20 % of secondary residential energy use NRCan 2013.
11、On a household basis, a typical electrically heated home consumes about 4,300 kWh (146.7 Therms) of electricity for heating domestic hot water at an annual cost of about $430 CAD per household (using an assumed average electricity cost of 10 cents per kWh). For a near- or net-zero energy (NZE) home,
12、 this energy use could represent in the order of 60% of the homes annual energy consumption. To reduce the energy used to heat water and help meet the NZE target for housing, vast improvements in the performance of hot water systems are essential. One technology that looks promising, as an energy ef
13、ficient alternative to a conventional resistance element storage water heater, is the heat pump water heater (HPWH). Heat pump water heaters are one of the most energy efficient water heating options currently available on the North American market (This does not include the energy and the efficienc
14、y of central electricity generation and transmission which could be anywhere from between 25% and 60%, for a fossil fuel source). They operate by using electricity to compress, circulate and expand a refrigerant in a loop, where it changes state in order to move heat from the surrounding air into th
15、e water within a well-insulated storage tank. The heat taken from the surrounding air is regarded as free energy and thus the water heating Energy Factor (EF) can be over 2.0 (Note: with the exception of solar assisted water heaters, all other water heaters have an EF 1.0, and are normally in the ra
16、nge 0.85 to 0.95 for electric resistance storage water heaters or 0.55 to 0.67 for non-condensing gas-fired storage water heaters). Researchers have hypothesized that because the heat pump operation depends on moving heat from one space to another, heat pump water heaters could potentially impact th
17、eir surrounding environment, affecting room temperatures and the house space cooling / heating loads. For example, in winter, the heat that is removed from the basement in order to heat water could cool the basement air temperature and require additional heating from the furnace, and in summer, the
18、additional cooling of air by the heat pump water heater may contribute to the overall cooling of the house and thus offset some of air conditioning system operation. The project was conducted at a twin house test facility and focused mainly on the comparison of two different non-ducted, air-source h
19、eat pump water heaters, against a conventional storage-type electric hot water heater. Some limited testing was also done to compare one make of heat pump water heater against a gas-fired water heater, during the heating season. The operation of the two heat pump water heaters was evaluated at the t
20、est facility in typical Ottawa summer and winter conditions. The purpose of this set of experiments was to: (1) assess the potential for domestic water heating energy and cost savings, (2) determine the whole house energy and cost impact of operating a heat pump water heater in the basement of a com
21、mon Canadian house construction type, during both the heating and cooling seasons, and (3) identify potential comfort or condensation problems, that may result from changes in basement air temperature. APPROACH / EXPERIMENTAL METHOD Test Facility The twin house test facility, located in Ottawa, Onta
22、rio, features two highly instrumented, identical test homes, with simulated occupancy, to evaluate the whole-house performance of new technologies in side-by-side testing (see Figure 1). Each house is two storeys with 223 m2 (2,400 ft2) of floor area, not counting the full basements. Each house has
23、a design heating load of 12.1 kW (41,433 Btu/h) and a design cooling load of 7.2 kW (24,442 Btu/h or 2 ton) in accordance with the CSA F280-12 load calculation standard. House occupancy is simulated by computer controlled operation of lights and appliances, draws of hot water, and generation of heat
24、 in different rooms (to simulate the presence of occupants). Repeated testing under identical conditions (benchmarking) has shown that the two houses use nearly the same amounts of energy for space heating, air conditioning, hot water and utilities. All experimental results are adjusted for any slig
25、ht differences between the houses determined during the benchmarking process. The test houses are an ideal set-up for testing and comparing different technologies, because having two identical houses at the same location allows the effects of a relatively small change in one of them to be clearly sh
26、own in the collected data, rather than having to be based on an analysis of heating and cooling loads derived from outdoor temperatures, wind speeds and solar radiation. The house in which the equipment to be tested is installed, is called the experimental house, and the house with the standard equi
27、pment, is called the control house. The accuracy of this energy comparison method is about 2%. Figure 1 The test houses in (a) Winter and (b) Summer. Table 1. Experimental Set-up During Cooling circulation fan “on” at standby. High efficiency single-stage condensing gas furnace with split capacitor
28、motor; circulation fan “on” at standby. Cooling Cooling provided by a 13 SEER, 2 ton compressor unit Cooling provided by a 13 SEER, 2 ton compressor unit Ventilation HRV low speed continuous (65 cfm) HRV low speed continuous (65 cfm) Shading Venetian blinds closed with slats horizontal Venetian blin
29、ds closed with slats horizontal Thermostat-Cooling Single central thermostat, set to 24C (maintains house at 23.5C) Single central thermostat, set to 24C (maintains house at 23.5C) Thermostat-Heating Single central thermostat, set to 22C (maintains house at 21C) Single central thermostat, set to 22C
30、 (maintains house at 21C) Water Heater * Electric resistance water heater (60 Imp Gal, 270 L) Heat pump water heater A (80 US Gal, 303 L) or Heat pump water heater B ( 50 US Gal, 189 L) Doors All interior doors open All interior doors open Attic Insulation 10 inches of blown-in cellulose (R-37) 10 i
31、nches of blown-in cellulose (R-37) Simulated Occupancy Standard schedule Standard schedule Basement supply and return vents All 3 basement supply vents closed, return vent open. All 3 basement supply vents closed, return vent open. Test Set-Up Table 1 provides information about the test set-up durin
32、g the comparative energy monitoring in the control and experimental house. In benchmarking, each house had the baseline electric resistance water heater in it. During testing, the Experimental House either had heat pump water heater A or heat pump water heater B in it, while the control house always
33、 had the baseline electric resistance water heater in it. The hot water was drawn throughout the day according to the draw schedule which is illustrated in Figure 2 (both houses used the same pattern). Both heat pump water heaters were set to a set-point of 57C (135 F), and ran in hybrid mode (this
34、would allow the backup resistance heating elements to operate, if the heat pump was unable to meet the hot water demand). After leaving the water heater the hot water was blended with cold water in a mixing valve to provide hot water at a temperature of 52 C (126 F) Figure 2 The hot water draw patte
35、rn used. Equipment Tested The baseline 270 Litre (60 Imp. gallon) electric resistance storage water heaters operated with 240 V and had an upper and a lower heating element of 4,500 Watts each. They were located in the basements of the houses. The rated standby heat loss for this water Heater is 72
36、Watts. The rated energy factor, EF = 0.86 (From an online directory of water heater ratings). Two different heat pump water heaters were tested. The larger of the two heat pump water heaters had a capacity of 303 Litres (80 US Gallons), an upper element of 4.5 kW, a lower element of 2 kW, and a 700
37、W compressor. The smaller of the two heat pump water heaters had a capacity of 189 litres (50 US Gallons), an upper and a lower element of 4.5 kW and a 700 W compressor. Both heat pump water heaters used R-134a refrigerant. Both of the heat pump water heaters were non-ducted, i.e. they took air from
38、 the room that they were located in and delivered that air, after heat had been extracted from it, back into the same room. Both heat pump water heaters and the baseline water heater were located in the unfinished basement of the experimental house. Figure 3 Daily electrical energy comparison for wa
39、ter heating. RESULTS & DISCUSSION Energy Use Comparisons in Heating Season The data showed a significant decrease in water heating energy consumption, see Figure 3, where the heat pump water heaters used about 5 kWh (20.5 MBtu) of energy per day in comparison to the resistance water heaters which us
40、ed about 13 kWh (44.4 MBtu) of energy per day. Both heat pump water heaters performed similarly. These tests were conducted in the heating season and the impact of the water heater on the the heating system, i.e. a 6% (20 MJ or 19 MBtu) increase in energy consumed, can be seen in Figure 4. The effec
41、t of the heat pump water heater on the whole house energy use, shown in Figure 5, was not significant (differences were well within the 2% margins of error). Figure 4 Furnace only daily energy consumption. Figure 5 Whole house daily energy consumption. The cost of the energy used in the control and
42、experimental houses was calculated and compared, using local gas and electricity prices and it was found that the house with the heat pump water heater cost about $0.80 CAD less per day to run than the house with the electric resistance water heater. This cost difference was due to some of the energ
43、y load of the water heater being transferred to the space heating system, which in this case was natural gas. The cost of the natural gas was much lower than that of electricity. Energy Use Comparisons in Cooling Season In the cooling season the furnace fan is operated to circulate air and air-condi
44、tion the houses. In this case heat pump water heater B was compared to the electric resistance water heater and again the benchmark compared the two electric resistance water heaters, see Figure 6. Figure 6 Electrical energy comparison for water heating. Figure 7 Whole house daily energy consumption
45、. It can be seen that the water heating energy use is slightly lower in both cases when compared to the winter testing, this was probably due to a higher summer supply water temperature and generally warmer ambient air temperatures within the house. The electrical energy consumption of the furnace a
46、nd air-conditioning unit was the same for both the control and the experimental houses, however, when the electrical load of the water heaters is also added to the total, it can be seen that there is a significant reduction of about 7.0 kWh (23.9 MBtu) per day or 18% to 25% for the experimental hous
47、e containing the heat pump water heater, see Figure 7. In this case energy cost savings of about $1.00 CAD per day were seen in the house with the heat pump water heater, due to a direct reduction of the house electricity consumption, presumeably because of the cold air generated contributing to the
48、 house air conditioning. Heat Pump Energy Use Comparison to a Gas-Fired Water Heater in Heating Season A few days of testing were conducted where the basline electric resistance water heater was replaced with a 0.57 energy factor, gas-fired water heater. Tests were run with different hot water loads
49、 (i.e. the standard draw pattern was varied) and both houses were given the same variations. In this case the house with the heat pump water heater saw an 18% reduction in energy use, see Figure 8. Although the energy use reduction was significant, because of the relative price difference between electricity and natural gas, the natural gas water heater still costs less to operate, whether it be winter ($0.40 CAD less per day) or summer ($0.05 CAD less per day). Figure 8 Whole house daily energy comparison, Figure 9 A whole house energy analysis with with nat
