How low outdoor temperatures affect the COP and power of a heat pump

As the outdoor temperature drops, the heat pump has to work harder to transfer heat to the building.

Reduction in COP

The temperature difference between the external source and the supply increases, thus requiring more electrical energy for the same thermal output.

Reduction in available power

In many models, the maximum thermal power decreases as the outdoor temperature falls.

Defrost effect

Defrost cycles temporarily remove available heat from the building and reduce the average seasonal efficiency.

Proper selection

Sizing must be based on the power output of the unit at the design temperature of the area and not solely on the nominal catalog power.