Heat Pump
Definition
A heat pump is a heat engine operating in reverse. Common air conditioners and refrigerators are well-known examples of heat pumps.
The heat pump can be used to heat or cool a space. Also, it can be used to extract or pump heat either into or out of a space. For home heating, a heat pump extracts heat from outside air (even at temperatures below freezing), or from the ground through liquid circulated through subsoil pipes, and transfers it indoors. During hot weather, the cycle is reversed; heat is extracted from the indoor air and expelled to the outside as in an air conditioner or refrigerator.
Basic Components
- Heating Mode
During the heating mode, the outdoor coil is the evaporator and the indoor coil is the condenser.
1) The refrigerant absorbs heat in the evaporator from the outdoor air, turning into gas
2) The compressor raises the pressure of the gas, increasing its temperature
3) The hot gas then flows through the condenser coils that are inside the heated space
4) The liquid then flows back through a pressure-reducing valve to the outdoor evaporator coils, being cooled through expansion
- Cooling Cycle
During the cooling cycle the evaporator and condenser coils exchange roles. The direction of flow of the refrigerant is reversed with a special valve.
Efficiency
The efficiency used for heat pumps is not expressed in terms of the ratio of energy output to energy input, but expressed in terms of the ratio of energy output to work input. In other words known as the, Coefficient of performance or COP.