Refrigeration COP and Carnot Limit
The fundamental cycle efficiency seer-eer never reads: COP = (h1 - h4)/(h2 - h1), the refrigeration effect over the compressor work, against its Carnot ceiling T_evap/(T_cond - T_evap) in absolute temperature. A cycle with 60 Btu/lb effect and 25 Btu/lb work runs COP 2.40 (EER 8.19); against a Carnot 6.25 for a 40/120 F lift it is 38% of ideal. A smaller lift - a higher evaporator, a cooler condenser - raises the ceiling, the lever for efficiency. Enter the P-h enthalpies; no parasitic loads. An engineering aid; the property data and state points govern.
Formula and source
COP = (h1 - h4)/(h2 - h1); COP_Carnot = (Tevap + 459.67)/((Tcond + 459.67) - (Tevap + 459.67)); eta_2nd = COP/COP_Carnot; EER = 3.412 COP.
The cooling coefficient of performance, its Carnot ceiling, the second-law efficiency, and the EER relation, standard refrigeration-cycle definitions, by name.
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