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- Start from the peak heating or cooling load in kW. For recovery duties, size to the steady process load rather than the rare peak. Cross-check against AHU selection calculation when the pump serves an air-handling unit.
- Heat pump capacity drops as the sink (heating) temperature rises or the source temperature falls. Always read capacity from the manufacturer's performance map at your design source and sink temperatures, not at the rating point. Input Effect on capacity Higher supply water temperature Capacity down, COP down Lower source temperature Capacity down, COP down Defrost cycles (air source, cold) Effective capacity down 5–15%
- Compare seasonal COP (SCOP), not just nominal COP. Factor defrost losses for air-source units and part-load performance. A high-temperature heat pump trades some COP for a higher deliverable temperature.
- For waste-heat sources, confirm the flow and temperature lift are sufficient. See heat pump waste heat recovery and wastewater source heat recovery for source-side design.
- Combine incremental capital against annual energy savings using the same framework applied in our industrial waste heat recovery case. Right-size the pump to the steady load to keep the payback realistic.
A correct heat pump selection calculation prevents both undersizing (poor performance) and oversizing (short cycling and wasted capital). The method below applies to space heating, domestic hot water, and process heat recovery alike.
Start from the peak heating or cooling load in kW. For recovery duties, size to the steady process load rather than the rare peak. Cross-check against AHU selection calculation when the pump serves an air-handling unit.
Heat pump capacity drops as the sink (heating) temperature rises or the source temperature falls. Always read capacity from the manufacturer's performance map at your design source and sink temperatures, not at the rating point.
| Input | Effect on capacity |
|---|---|
| Higher supply water temperature | Capacity down, COP down |
| Lower source temperature | Capacity down, COP down |
| Defrost cycles (air source, cold) | Effective capacity down 5–15% |
Compare seasonal COP (SCOP), not just nominal COP. Factor defrost losses for air-source units and part-load performance. A high-temperature heat pump trades some COP for a higher deliverable temperature.
For waste-heat sources, confirm the flow and temperature lift are sufficient. See heat pump waste heat recovery and wastewater source heat recovery for source-side design.
Combine incremental capital against annual energy savings using the same framework applied in our industrial waste heat recovery case. Right-size the pump to the steady load to keep the payback realistic.