J. Sager (NRCan)
M. Armstrong (NRC)
F. Szadkowski (NRCan)
Publication date: September 2013
Cold climate air source heat pumps (CC-ASHPs) are high efficiency heating and cooling systems that have recently become available in North America. Existing test standards for air source heat pumps (CSA C656-05) do not include coefficient of performance (COP) and capacity results at cold temperatures suitable to Canadian climates, leaving the market unsure of their performance at low temperatures. This project brings clarity to this knowledge gap by providing insights into system performance results at cold temperatures while also comparing the performance of CC-ASHPs to standard high efficiency furnace and central air conditioning equipment.
In the spring of 2012, the Canadian Centre for Housing Technology (CCHT) installed a CCASHP for testing against the standard equipment for both cooling and heating. The CCHT is a facility located in Ottawa, Ontario, designed for evaluating whole-house performance of residential technologies. It includes two highly instrumented, identical, unoccupied houses. Occupancy is simulated by computer controlled operation of lights and appliances, use of hot water, and generation of heat to simulate the presence of occupants. The CCHT was built to the previous R2000 program performance standard (EnerGuide Rating System 80). Design loads for the CCHT are heating 12.14 kW (41,433 Btu/h) at -25°C and cooling 7.16 kW (24,442 Btu/h) at 30°C.
As a general summary of key findings, the project demonstrated that the CC-ASHP, with an appropriately sized electric resistance backup, had the capacity to maintain comfort in the home at the coldest outdoor temperatures encountered (below -21°C) with a COP greater than 1.5 (indicating the system did not rely only on electric resistance at these temperatures). The system, as installed included a 10 kW (34,000 Btu/h) backup electric resistance heater, which served to temper the cooler supply air during system defrost cycles.
COP and capacity results for the CC-ASHP operation at the CCHT were as follows: In cooling, the COP ranged from an average of 2.4 at 20.4°C outdoor temperature to 3.7 at 28.3°C outdoor temperature during cooling season operation. Capacities ranged on average from 1.69 kW (5,766 Btu/h) to 6.11 kW (20,848 Btu/h) at these outdoor temperatures respectively. In heating, the COP ranged from an average of 1.5 at -21.1°C outdoor temperature to 3.0 at +4.9°C outdoor temperature during heating season operation. Capacities were, on average, 6.55 kW (22,350 Btu/h) and 2.47 kW (8,428 Btu/h) at these outdoor temperatures respectively.
From a comfort perspective, during cooling the CC-ASHP resulted in acceptable comfort and indoor temperature fluctuations as could be expected with any properly sized, effective, central air conditioning system. During heating, the CC-ASHP resulted in acceptable overall comfort although with larger indoor temperature fluctuations than would be expected with a standard system. During defrost cycles, the indoor supply air temperature dropped in order to defrost the outdoor unit until the electric resistance coil was able to temper this drop.
CC-ASHPs such as the one tested in this project will save homeowners on their heating and cooling bills in areas with low cost electricity supply (as an alternative to electric baseboards) or in areas without access to natural gas (as an alternative to fuel oil). In regions with access to low cost natural gas supply for heating, CC-ASHPs, despite being much more energy efficient than gas-fired equipment, will result in higher operating costs.
For access to the full publication, please contact the CanmetENERGY-Ottawa Business Office.
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