A heat pump works by circulating a refrigerant through a closed loop that includes four main components: the evaporator, compressor, condenser, and expansion valve (see below). The process begins in the evaporator, where the refrigerant absorbs heat from an external source such as air, ground, or water, causing it to evaporate into a gas. This gas is then compressed by the compressor, which increases its temperature and pressure. The hot, high-pressure gas flows into the condenser, where it releases its heat to the building’s heating system (air or water), and condenses back into a liquid. Finally, the refrigerant passes through the expansion valve, which reduces its pressure and temperature, preparing it to absorb heat again in the evaporator. This cycle repeats continuously, efficiently transferring heat from one place to another.
Evaporator
The evaporator is a low-temperature heat exchanger where the refrigerant enters as a low-temperature liquid, absorbs heat from the heat source by evaporation at a low pressure and leaves as a low-temperature vapour.
Compressor
n the compressor the low pressure of the low-temperature refrigerant from the evaporator is raised to a pressure that is sufficiently high to match the desired condensing temperature in the condenser. During compression not only the pressure but also the temperature of the refrigerant will increase.
Condenser
The condenser is a high-temperature heat exchanger where the refrigerant enters as a high-temperature vapour, rejects heat to the heat sink by condensation at a high pressure and leaves as a high-temperature liquid.
Expansion valve
On its return to the evaporator from the condenser the high-temperature, high-pressure liquid refrigerant must be changed to the low-temperature, low-pressure liquid that enters the evaporator. This is usually achieved by a throttling device known as the expansion valve. When the hot liquid passes through this valve, not only will its pressure be reduced but at the same time its temperature will drop. As the pressure drops, refrigerant starts to evaporate in the valve and the heat of evaporation is taken from the refrigerant itself which causes its temperature to drop and the result is a low-temperature, low-pressure mix of liquid and vapour, which then enters the evaporator.
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