Cooling and Heating Season Performance Assessment of a mini-split cold climate air source heat pump at the Canadian Centre for Housing Technology

Publication date: September 18, 2014

Cold climate air source heat pumps (CC-ASHPs) are high efficiency heating and cooling systems that have recently become available in North America. They include centrally ducted systems, and ductless split systems (mini-splits) like the ones tested in this project. Existing test standards for air source heat pumps (CSA C656-05) do not include coefficient of performance (COP) results at cold temperatures suitable to Canadian climates, leaving the market unsure of their performance at low temperatures. It has also been suggested, that by taking a zoned heating approach using the ductless mini-splits, i.e. ensuring that the primary areas of occupancy are well conditioned and allowing other unoccupied areas of the house to drift away from the temperature set point (within reason), there will be energy savings that go beyond the straight-forward efficiency difference between the two technologies. This project attempts to close this knowledge gap by providing insights into system performance results at cold temperatures while also comparing the performance of the mini-splits to a standard high efficiency furnace and central air conditioning equipment.

In the fall of 2011, the Canadian Centre for Housing Technology (CCHT) installed two ductless split systems for testing against the standard equipment for both cooling and heating. The standard gas furnace system they were compared against was fully ducted, with at least one supply register in every room. The mini-split system consisted of two indoor units, one in the first floor family room, and one in the second floor master bedroom.

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 summary of key findings, the project demonstrated that the mini-splits, with a natural gas fireplace backup, had the capacity to maintain comfort in the house at the coldest outdoor temperatures encountered (below -15°C) with a COP greater than 2, and with some backup heat required. The system as installed included a 10kW (34,000 Btu/h) natural gas free standing fireplace, located in the first floor family room, intended to supply supplemental heat when required.

The mini-splits used significantly less energy than the standard system in both heating and cooling. In heating, the apparent COP ranged from approximately 2.3 at -15°C outdoor temperature to 3.1 at +9°C outdoor temperature. Results indicate a COP of close to 2.0 at -25˚C.
From a comfort perspective, during cooling the mini-splits produced cooler temperatures and more variation directly in front of the units, but in other locations temperatures were very similar to those produced by the standard system. During heating, the temperatures produced by the mini-splits and the standard system were similar except during the coldest times, when the mini-split temperatures dropped significantly below the set-point. The low mini-split temperatures were due to the failure of the backup fireplace to come on. Had the fireplace thermostat been properly adjusted (it was set to operate at too low a temperature), the mini-split system would almost certainly have maintained temperatures as well as the standard system.

Mini-splits such as the ones tested in this project will save homeowners on their heating and cooling bills compared with electric baseboard, fuel oil or propane heating. In regions with access to low cost natural gas supply for heating, mini-splits, 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.