To compare the effectiveness of several heat pump systems, we should rely on the so called COP value. The COP number defines, how much heat could be produced with a given amount of electricity, at a given temperature.
The following numbers are typical COP values for various heat pump systems. These values may vary depending on several factor, but these values could give a good approximation of what efficiency could be expected.
For example, on a mild winter day (10 ° C outdoor temperature) the air to water heat pump’s COP value is between 3.0 and 4.0 (with 1W of electricity the heat pump could produce 3 – 4W of heating energy). In this case, the conventional electric heating system’s COP value is 1.0. To put it simply, to produce 1 Joule of heating, the system should use 1 Joule of electrical performance.
As the temperature decreasing, the air source heat pump’s COP values is getting closer to 1. At the temperature of -18°, the heat pump is no longer capable of producing additional energy, so suddenly the system’s efficiency is reduced as well.
In contrast to this, the geothermal heat pump operates with almost constant efficiency in the whole year. It is possible, because the soil has a constant temperature, and the probes could absorb the same amount of energy constantly.
Geothermal heat pumps could operate with a COP of 4.0 – 5.0.
To determine a similar value to cooling – as the COP – we should use the EER (energy efficiency ratio), or SEER (seasonal energy efficiency ratio). These values are usually characterized by the values and units (kWh) / (kWh).