Air Source Heat Pump Performance Curves

A heating process with a lower temperature (such as a piped floor system) will have an increased efficiency compared to a higher temperature system (such as a heated panel system). The opposite is true for a cooling process, where a lower cold temperature will increase efficiency.

Example - Maximum heat pump efficiency

An air source heat pump operates between a cold side temperature of -5oC and a hot side temperature of 40oC. The maximum theoretical efficiency can be calculated using (1b) as follows

Heating COP = (40 + 273) / ((40 + 273) - (-5 + 273))

= 6.95

Typical practical values for heat pumps are in the range of 2 - 4.

EER - Energy Efficiency Ratio

The Energy Efficiency Ratio (EER) is a measure of the cooling efficiency of a heat pump.

EER can be expressed as

Energy Efficiency Ratio = hc / pw (2)

Where

EER = Energy Efficiency Class

hc = Cooling Heat (Btu/h)

Pw = Electrical Power (W)

Example - EER

An air conditioner or heat pump in cooling mode consumes 1000 W of electricity and produces 10,000 Btu/h of cooling capacity. EER is calculated as follows

Energy Efficiency Ratio = (10000 Btu/hour) / (1000 Watts)

= 10

HSPF – Heating Season Performance Factor

The Heating Season Performance Factor (HSPF) is a measure of the overall heating efficiency of a heat pump during the heating season.

HSPF=hs / 1000Pws (3)

Where

hs = Heat generated during the season (Btu)

Pws = Electrical energy consumed during the season (kWh)

The HSPF can be thought of as the “average” COP for the entire heating season. The BTUs of heat output are usually compared to the Watts of electrical energy input. A HSPF of 6.8 can be compared to an average COP of 2. HSPFs in the 5-7 range are acceptable.

Example - Heat Pump Heating Seasonal Performance Factor

For a heat pump that delivers 120,000,000 Btu during the season, when consuming 15,000 kWh, the HSPF can be calculated as

HSPF = (120000000 Btu) / (1000 (15000 kWh))

= 8

SEER - Seasonal Energy Efficiency Ratio

The Seasonal Energy Efficiency Ratio is a measure of the seasonal cooling efficiency of a heat pump or consumer central air conditioning system.

A SEER of at least 13 is required to be sold in the United States. A SEER above 20 is a very efficient system.