The Workflow StackHVAC modeling / Field guide 03
Build a useful heat pump performance map
A single rated COP cannot describe a heat pump across winter conditions. A useful map ties heating capacity and electrical input to outdoor temperature, indoor condition, and the machine’s operating state.
1. Define the system boundary
Decide whether the map includes the compressor alone, the outdoor and indoor fans, controls, defrost, and supplemental heat. Label gross coil heat, delivered heat, and total electrical input separately. Heating COP at one point is delivered heat rate ÷ electrical input when both use the same energy units.
2. Build a table of operating points
Record outdoor dry-bulb temperature, indoor entering condition, compressor speed or capacity stage, delivered heating capacity, total power, and test mode. Include low-temperature points near the intended design condition, not just the mild-weather rating point. For variable-speed equipment, minimum and maximum speed may tell different stories about cycling and backup heat.
For example, an illustrative map row with 8.0 kW delivered and 2.0 kW input has COP 4.0. A second row at a colder condition with 5.5 kW delivered and 2.5 kW input has COP 2.2. These numbers are teaching examples, not measured product performance.
3. Use the map with a load curve
Plot maximum available capacity and building heat loss against outdoor temperature under compatible indoor assumptions. Where load exceeds available heat pump capacity, quantify the gap and the backup strategy. Interpolate only within measured or validated points; avoid extending a mild-temperature fit into untested cold conditions.
4. Audit transient behavior
A steady-state point can miss defrost energy and lost heat delivery. Keep defrost and auxiliary heat identifiable in the data so the chosen system boundary is reproducible. Note operating limits, capacity turn-down, fan power, and whether the power measurement includes crankcase or standby loads.
Download the mapping worksheet
Use the heat pump map tool to interpolate consistent operating points within a measured range.
Further reading
The U.S. DOE Cold-Climate Heat Pump Technology Challenge specification identifies low-temperature capacity, efficiency, turn-down, and defrost as distinct evaluation items. Its qualification procedure is specific to eligible equipment; use the ideas here for an engineering map, not as a certification claim.