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The Carnot COP (symbol ε) describes the theoretically maximum coefficient of performance of a heat pump based on the ideal Carnot cycle. It is calculated purely from the temperatures at the evaporator (TE) and the condenser (TC).
Formula: ε = TC / (TC – TE), both temperatures in Kelvin
Sample calculation: With a flow temperature of 35 °C (308.15 K) and a source temperature of 0 °C (273.15 K), the Carnot COP is 8.8.
- Evaporator temperature: TE = 273.15 K + 0 °C = 273.15 K
- Condenser temperature: TC = 273.15 K + 35 °C = 308.15 K
-  ε = 308.15 K / (308.15 K − 273.15 K) ≈ 8.8
Example: At a flow temperature of 35 °C (308.15 K) and a source temperature of 0 °C (273.15 K), the Carnot COP is 8.8. Real heat pumps only achieve 40 – 65 % of this value, as compressor losses, heat transfer and friction all reduce efficiency.
