Coefficient of Performance - COP ! By Imran

Coefficient of Performance - COP The Coefficient of Performance - COP - is the basic parameter used to report efficiency of refrigerant based systems. COP is the ratio between useful cooling or heating output and power input and can be expressed as COP = Pc / P where COP = Coefficient of Performance Pc = useful cooling or heating power output (Btu/h, W) P = power input (Btu/h, W) The COP is an instantaneous measurement in that the units are power which can be measured at one point in time. COP can be used to define the cooling efficiency for a cooling system - or the heating efficiency for a heat pump system. Cooling - COP is defined as the ratio of of the heat removal to the power input to the compressor Heating - COP is defined as the ratio of the heat delivered to the power input to the compressor higher COP - more efficient system COP can be treated as an efficiency where COP of 2.0 = 200% efficiency. For unitary heat pumps, ratings at two standard outdoor temperatures of 47oF and 17oF (8.3oC and -8.3oC) are typically used. Example - COP for an Air Conditioner Unit At an instantaneous moment an air conditioner units cools air from 30 oC and 70% moisture to 20 oC and 100% moisture. The air flow through the unit is 0.1 m3/s and the electrical power consumption of the unit is 600 W. From the Mollier diagram we can see that the enthalpy of the input air is aprox. 78 kJ/kg and the enthalpy of the output air is aprox. 57 kJ/kg. The heat removed from the air can be calculated as Pc = ((78 kJ/kg) - (57 kJ/kg)) (0.1 m3/s) (1.2 kg/m3) = 2.5 kW COP for the unit can be calculated as COP = (2.5 kW) / (0.6 kW) = 4.2 Example - COP for a Heat Pump A heat pump delivers 4.8 kW (16378 Btu/h) of heat with electric power consumption 1.2 kW (4094 Btu/h). COP for the heat pump at the actual conditions can be calculated as COP = (4.8 kW) / (1.2 kW) = 4