Performance
COP or EER from capacity and power input
- where
- coefficient of performance (kW/kW)
- cooling or heating capacity (kW)
- electrical power input (kW)
- EER in Btu/h per W
Explain this equation
Works out how efficient a heat pump or air conditioner is: useful heat moved per unit of electricity. Use it to compare units or check one against its data sheet.
Q is the heating or cooling delivered and P is the electricity drawn, both in kW, so their ratio has no units. In cooling it is often called EER, in heating COP. American data quotes EER in Btu/h per watt; one watt is 3.412 Btu/h, so the US figure is the plain ratio times 3.412.
Efficiency is output over input. It can exceed 1 because the machine moves heat rather than making it.
Sense check: 7.1 kW of cooling for 2.2 kW in gives about 3.2, or about 11 in US units.
Watch out: make sure both figures are at the same rating conditions; COP falls as the temperature lift grows.
Works out the coefficient of performance (heating) or energy efficiency ratio (cooling) from measured or rated capacity and power input.
Enter your values to see the result.
Good to know
In UK and EU data (EN 14511) both COP and EER are kW out per kW in. US EER is in Btu/h per watt, 3.412 times larger. Use matching conditions: capacity and power at the same operating point. Seasonal figures (SCOP, SEER) are different and come from the manufacturer.
Common mistake
Comparing a UK EER with a US EER, or using compressor power only when the rating includes fans and controls.
Limits
Instantaneous ratio only.
Sources
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the equipment manufacturer’s data, CIBSE guidance, BS EN 378, the F-gas Regulations and your company procedures. Refrigerant work needs the correct F-gas certification.