What is Coefficient of performance (COP)?
Coefficient of performance (COP) is the ratio of useful heating or cooling delivered by a heat pump, chiller or refrigeration system to the energy input that drives it, in the same units.
Where COP is used
Engineers use COP to rate chillers, heat pumps and refrigeration plants, and to check how a running plant compares with its design. Product ratings are measured at fixed test conditions, while operating COP moves with load, condensing temperature and the temperature the process needs.
How it is calculated
COP is cooling or heating output in kW divided by electrical input in kW. Because NIST defines one ton of refrigeration as 3,516.853 watts, kW per TR equals 3.517 divided by COP, and energy efficiency ratio in Btu per watt-hour equals COP times 3.412. A plant at COP 4 therefore uses about 0.88 kW per ton.
Lower evaporating temperatures and higher condensing temperatures both reduce COP, which is why freezer duty costs more per unit of heat removed than chilled water.
Operating COP in Aqueduct
Aqueduct computes operating COP from delivered cooling, measured as flow and temperature difference, and the compressor, pump and fan power on each plant's electricity meters. Read against outdoor temperature, the trend separates a hot week from a real loss of efficiency, so a falling COP turns into a maintenance ticket instead of a surprise in next month's bill.