2610 -- A Note on the Transient Performance and Degradation Coefficient of a Field Tested Heat Pump--Cooling and Heating Mode PDF

The cyclic efficiency of compressor driven heat pumps and air conditioners is slightly less than the steady state efficiency at the same operating conditions.

In most cases the average electrical power consumed during the compressor on-time is approximated by the steady state value. (Further work may be needed to determine the extent of applicability of this assumption. It depends on the actual on-time and most likely depends on type of unit and throttling device. The approximation was found to be valid for both the heat pump and air conditioner now reported on.) As the blowers respond rather rapidly upon start-up the difference between cyclic and steady state efficiencies may be estimated simply by the average cyclic and steady state capacities. These two differ because the capacity upon start-up doesn't reach the steady state values right away. This is due to the refrigerant dynamics and in part to the thermal mass of the heat exchangers.