Heat pump COP: how efficiency is measured
COP, the coefficient of performance, is the heat a heat pump delivers divided by the electrical energy it uses at a given moment. A COP of 3 means each kilowatt-hour of electricity brings about 3 kilowatt-hours of heat into the house, because most of the heat is moved from outdoors or the ground rather than made.
What does a COP number mean?
COP is a ratio with no units. Heat output goes on top, electrical input on the bottom, both measured in the same unit over the same short test period. Electric baseboards and electric furnaces convert electricity to heat at close to a ratio of 1, so a COP of 1. A heat pump can top that because it works like a refrigerator in reverse, pumping heat from a cold place to a warm one.
A higher COP means a lower electricity use for the same heat. The heat pump basics are covered in how ground-source heat pumps work and in air-source versus ground-source heat pumps.
How do you work out running costs from COP?
Divide the heat you need by the COP to get the electricity required. Suppose a house needs 12,000 kWh of heat in a heating season, a made-up figure for illustration. At an average COP of 3, the heat pump uses 4,000 kWh of electricity. At an average of 2, it uses 6,000 kWh. Electric resistance heating would use the full 12,000 kWh.
To turn that into dollars, multiply by your electricity rate, which varies by province, utility and rate plan. Then compare with the cost of the same heat from gas or another fuel, a comparison laid out in natural gas versus electric heating and in heat pump versus furnace. The COP shows the electricity side only, and the fuel price decides the result.
Why does COP change with the weather?
The rated COP on a spec sheet describes particular test conditions, and your house will not match them all winter. The colder it is outside, the more work the heat pump does for each unit of heat, so air-source models see their COP fall as the temperature drops. Ground-source heat pumps start from steadier ground temperatures and lose less, a contrast described in ground temperature by depth in Canada.
The temperature of the heat you deliver matters too. Warming a floor loop to 35 degrees C takes less effort than heating water to 60 degrees C for older radiators, and COP is higher for the first. This is one reason low-temperature distribution suits heat pumps, as described in low-temperature hydronic heating.
What are SCOP, HSPF and other seasonal measures?
A single COP is a snapshot. Seasonal ratings average performance across a typical heating season to reflect changing conditions. Europe uses SCOP, and North American ratings such as HSPF play a similar role, although they are expressed in different units and test methods, so the numbers are not interchangeable. Compare ratings from the same standard only.
For cold climates, ask for performance data at low outdoor temperatures, not only the headline figure. The cold-climate heat pump guide explains what to look for, and heat pump sizing for cold climates covers how capacity falls with temperature.
What does COP have to do with Drake Landing?
Drake Landing Solar Community in Okotoks, Alberta did not use heat pumps. It stored solar heat in the ground and delivered it at roughly 40 to 50 degrees C, which allowed the homes' air handlers to heat directly. The same lesson applies to heat pumps. Lower supply temperatures and tight, well-insulated houses make any heat source work better, a point made in what Drake Landing teaches about net-zero heating.
When you compare quotes, ask the installer for the expected seasonal performance in your climate and for the load calculation behind the sizing. Rebate programs often set minimum efficiency ratings, so check current terms with the Government of Canada energy-efficiency pages, your provincial energy ministry and your utility.
Quick answers
What is a good COP for a heat pump?
Higher is better, and values around 3 or more are common in mild conditions for modern units. The useful figure for Canada is performance at your winter temperatures, so ask for low-temperature data.
Can COP be below 1?
A heat pump itself should not fall below about 1, since even electric resistance heating gives 1. Defrost cycles and backup heat in extreme cold lower the average across a system.
Is COP the same as efficiency percent?
A COP of 3 is sometimes called 300 percent efficient, but that is shorthand. The pump moves heat rather than burning fuel, so the ratio can exceed 1.
Why is a ground-source heat pump's COP more stable?
Ground temperatures change little through the year, so the unit does not face the sharp winter drop that outdoor air produces.