EER (Energy Efficiency Ratio)
The cooling efficiency measurement for heat pumps is the Energy Efficiency Ratio or EER. This is the same rating system used for air conditioners.
EER is the number of BTUs of cooling provided per watt of electrical energy consumed. The energy includes electricity used for indoor and outdoor fans and the compressor.
Although similar to COP, EER is calculated using different units of measure.
Cooling systems with EER ratings higher than 13 are the most desirable.
COP and EER measurements are based on laboratory tests and do not necessarily measure how the heat pump performs in real life. A heat pump's performance will vary depending on the weather and how much supplementary heat is actually required. Therefore, a more realistic measurement, especially for air-to-air heat pumps, is calculated on a seasonal basis that would include cooling and heating.
This efficiency measure is the Heating Season Performance Factor (HSPF).