What COP measures
Heating COP is useful heat delivered divided by electrical input at a stated operating point. A COP of 3 means three units of heat are delivered for one unit of electricity under those conditions. It does not mean the plant will achieve that value throughout the year.
A worked operating point
If a system delivers 1,500 kW of useful heat while the compressor and agreed auxiliaries draw 500 kW, the COP at that boundary is 3.0. At that COP, 6,000 MWh of useful heat requires 2,000 MWh of electricity. At COP 4.0, the same heat duty requires 1,500 MWh.
The 500 MWh difference is large enough to change the economic result, which is why a rounded catalogue COP should never be applied to a full year without an operating profile.
State the boundary
Published figures may include only compressor power while a project meter includes source pumps, sink pumps, fans, crankcase heaters and controls. Heat-exchanger fouling, defrost, part-load cycling and standby periods can also reduce seasonal performance. Comparable figures need the same boundary and measurement period.
Record whether cooling is a useful co-product. A combined heating and cooling efficiency can be informative, but it cannot be compared directly with a heating-only COP unless the boundary and useful outputs are stated.
The lift matters more than the headline
Lowering the process supply temperature, increasing heat-exchanger area or selecting a warmer source can reduce compressor work. The most valuable efficiency improvement may therefore sit in the process integration rather than inside the heat pump package.
The compressor sees refrigerant evaporating and condensing temperatures, not merely the process inlet and outlet temperatures. Heat-exchanger approach temperatures widen the real lift and should be included in screening calculations.
From design COP to seasonal performance
An annual model should divide operation into representative bins for heat duty, source temperature, sink temperature and part load. Apply verified performance data in each bin and include shutdown, standby, backup heat and auxiliary electricity.
Metered seasonal performance is useful heat delivered over the agreed period divided by electricity over the same timestamps and boundary. Averaging a series of instantaneous COP readings gives the wrong answer when the operating intervals carry different heat loads.
What to request from a supplier
Ask for capacity, electrical input and COP across the expected operating envelope, including minimum source temperature, maximum sink temperature and minimum stable load. The selection should identify refrigerant, compressor configuration, flow rates, approach temperatures, included auxiliaries and software version.
A maximum leaving-water temperature is an equipment limit, not evidence of acceptable capacity or COP at that point. The model index therefore keeps missing operating data blank rather than filling it with an estimate.
Sources
Primary and authoritative sources used for the material claims on this page.