Coefficient of performance
The efficiency of heat pumps decreases almost linearly with decreasing outdoor temperatures. The performance of equipment at a specific temperature is commonly called COP, which stands for Coefficient of Performance. For example, a COP of 2 means that you consume 1 kWh of electricity to give the equivalent of 2 kWh for heating.
In 2004, Natural Resources Canada’s Office of Energy Efficiency reported that the average heat pump was able to provide a COP of 2.3 at a temperature of -8°C, a gain of 130%. Given the average winter temperatures in southern Quebec and the areas along the Gulf of St. Lawrence, a standard heat pump can meet almost all the heating needs of buildings in these areas. However, the average temperatures for the more northerly locations are not well suited to heating with a conventional heat pump.
Cold climate heat pumps
Technological advances in recent years have allowed the development of heat pumps for cold climates, achieving COPs of up to 1.5 at temperatures as low as -21°C.
These new units are generally larger to increase the size of the heat exchangers and operate with variable speed compressors. This means that the equipment operates mainly at less than full capacity, with the remaining capacity used for emergency situations.
This equipment is significantly more expensive, but it has the potential to address most heating problems, even in the most northern locations. To this end, since there is little or no need for air conditioning in these areas, the larger initial investment for the cold climate heat pump may seem less attractive.
As you can see, it is always advantageous to use the heat pump as the main source of heating, as long as the COP remains positive. It should also be mentioned that the colder the outside temperature, the longer it will take the heat pump to reach or maintain a given temperature.
In this regard, Etienne St-Cyr, engineer and head of energy expertise at Hydro-Québec, says that it is not recommended to program your thermostat to periodically lower the set temperature when heating with a heat pump.
With a regular temperature at the thermostat, it is much easier for the heat pump to provide the energy needed to maintain the room temperature. A sudden high demand will usually cause the auxiliary heating sources to turn on at full capacity, which will of course harm the overall efficiency of the system… and on your savings!
Heat pumps are often deliberately switched off when outside temperatures approach -8°C or -12°C. This is because the machine is usually switched off by a thermostat built into the heat pump and set beforehand by the installer. Make sure that the heat pump is properly set to take advantage of its maximum heat gain.
Still, according to Mr. St-Cyr, another very simple practice would optimize the operation of the heat pump. It would be advisable to allow the auxiliary heating sources and the heat pump to operate simultaneously. Thus, even with a falling but still positive COP, the primary heating load could be absorbed by the heat pump at very low temperatures, with a little help from the auxiliary heat. These functions are already possible with most programmable thermostats, just ask your technician to activate the function.
Maintenance of your systems will also keep them at peak performance. Since heat pumps and air conditioners work by air-to-air heat exchange, the airflow that comes into contact with the exchangers remains an important factor to consider in the overall performance of the systems. Thus, furnace filters and heat exchangers must be cleaned periodically to extract the full potential of these machines, both for heating and cooling.
Finally, there appear to be considerable savings to be made on your heating costs with a heat pump in most regions of Quebec. Of course, many installation factors can affect the profitability of a heat pump installation. For more information on the subject, ask our team!
Several other factors enter into the analysis of the overall performance of heat pumps. Indeed, the right amount of refrigerant in the system, the length of the refrigerant pipes, the right-sizing of the unit for the building, and the configuration and quality of the ventilation system will also have positive or negative impacts on costs. In summary, the quality of the installation remains strongly linked to its performance.