Nameplate performance is one point
Production rate, source temperature and sink demand change. At part load a compressor may slow, unload, stage off or cycle. Each method changes efficiency and minimum stable output differently.
Build a load-duration view
Bin annual hours by required heat output and representative temperatures. Apply verified machine performance in each bin, then include standby, crankcase heating, pumps and cycling losses. This is more credible than multiplying design COP by annual hours.
- Minimum continuous load
- Number and size of compressor stages
- Variable-speed limits
- Minimum on and off times
- Buffer volume
- Behaviour when source and sink diverge
Control the system, not only the compressor
Poor pump control, high return temperature or an always-open boiler bypass can erase expected savings. Commissioning should test several loads and seasons rather than accepting a single full-load point.
Sources
Primary and authoritative sources used for the material claims on this page.