The coefficient of performance, also called as the COP, of the heat pump is defined as the ratio of the desired effect from the heat pump to the power consumed by the heat pump. The desired effect from the heat pump is producing the heat inside the room and the power consumed by the heat pump is the power consumed by the compressor, hence COP is also defined as the ratio of heat produced inside the room to the power consumed by the compressor.
Let us suppose:
H1 – enthalpy of the refrigerant leaving the evaporator and entering the compressor
H2- Enthalpy of refrigerant leaving the compressor and entering the condenser
H3- Enthalpy of refrigerant leaving the condenser and entering the expansion valve
H4 – Enthalpy of the refrigerant leaving the expansion valve and entering the evaporator
During the expansion of the refrigerant in the expansion valve, its enthalpy remains constant, hence H3 = H4.
Coefficient of Performance or COP = Heat produced inside the room / Power consumed by the compressor
Heat produced inside the room is the heat absorbed from the condenser = H2 – H3, since the enthalpy of the refrigerant entering the condenser is more than the enthalpy of refrigerant leaving the condenser.
The power consumed by the compressor = H2 – H1
Hence COP of the Heat Pump = H2 – H3 / H2 – H1
Relation between COP of Heat Pump and Refrigerator
The main purpose of the refrigerator is to produce the cooling effect and it consumes power for this. The main purpose of the heat pump is to cool the room and it consumes power for it. From the above formula of the COP you will find that:
COP of Heat Pump = 1 + COP of the Refrigerator
The COP of the refrigerator and air-conditioner can be less than one or greater than one. The above formula also shows that the COP of the heat pump can never be less than one; it is always more than one.
It is worth mentioning here that efficiency of the engine can never be more than one, but the COP of the heat pump is always more than one. You should know that the terms efficiency and the COP are entirely different terms. The efficiency describes the capacity of the engine to produce power from the fuel, while the COP indicates how effectively the energy is used to produce the desired effect which is producing heat in case of the heat pump and coolness in case of the refrigerator.
This post is part of the series: Heat Pumps
Heat pumps are the devices that are used for heating the room. The heat pump consumes less power than the electric room heater, however their initial cost is high. This series of article describes the various parts of heat pump, its working and comparison to refrigerator and air conditioner.
- What is Heat Pump?
- Difference between Heat Pumps and Refrigerators
- Various Components of the Heat Pump - Part 1
- Various Components of the Heat Pump - Part 2
- Various Components of the Heat Pump - Part 3
- Various Components of the Heat Pump: Part 4
- Coefficient of Performance of the Heat Pumps
- Difference between the Heat Pump and the Air-Conditioner