Refrigeration COP and Carnot Limit
The fundamental cycle efficiency a SEER or EER rating never reads.
Example
You enter
- Suction enthalpy h1 (Btu/lb) 180
- Discharge enthalpy h2 (Btu/lb) 205
- Evaporator-inlet enthalpy h4 (Btu/lb) 120
- Evaporator saturation temp (°F) 40
- Condenser saturation temp (°F) 120
You get
- Cycle COP (EER) 2.4
- EER (BTU/hr per watt) 8.19
- COP carnot 6.25
- Eta 2nd 0.384
Details, formula, and sources
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.
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.
The COP, Carnot-limit, and EER relations are public thermodynamic results; the ASHRAE Handbook covers the cycle.
Estimate. AHJ and licensed professional govern.
Field names used by the API: h1_btulb, h2_btulb, h4_btulb, tevap_f, tcond_f, cop, eer, cop_carnot, eta_2nd
- Cycle COP the refrigeration effect over the compressor work, from the P-h enthalpiesvapor-compression cycle
- Carnot ceiling T_evap/(T_cond - T_evap) in Rankine; the ratio is the second-law efficiencythermodynamics
- EER EER = 3.412 x COP (Btu/Wh per unit COP)unit conversion