Incoprea hypothesis tests · volume II

Heat Pumps Fail at a Lift

Energy & Environment · notebook volume 8 · Model n = 181

The claim

Heat pump performance falls sharply above a threshold temperature lift, so the same unit can be efficient in a mild climate and marginal in a cold one, and the threshold is set by the compressor rather than by the refrigerant.

What was tested

Coefficient of performance should fall sharply above a lift threshold; the fall-off should not be a smooth thermodynamic decline.

Falsified by: Smooth performance fall-off across lifts would remove the threshold.

Method

Fixed source at 2 C, sink temperature raised in 0.5 K steps to 95 K of lift. Coefficient of performance is 0.5 times the Carnot value (fixed second-law efficiency). R410A saturation pressure is fitted through 0.798 MPa at 0 C and 2.417 MPa at 40 C (Clausius-Clapeyron), giving the pressure ratio a single-stage compressor must deliver. A compressor limit of pressure ratio 8 marks the design cut-out.

Result

COP at 20 K lift	6.88
COP at 40 K lift	3.44
COP at 60 K lift	2.29
Pressure ratio 8 reached at (K)	88
COP at the cut-out	1.56

Limits

• The model uses a fixed second-law efficiency. Real compressors lose efficiency at high pressure ratio, which steepens the curve but does not create a cliff.
• Cold-climate units are designed with larger heat exchangers, vapour injection or two-stage compression, which moves the cut-out rather than removing the smooth decline.
• The claim may be a description of a particular installed unit hitting its cut-out, not a general thermodynamic threshold. The test can only refute the general version.

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