Typical Air to Water Heat Pump Cycle

The heat pump operates on the basis of a working fluid (refrigerant/coolant) which changes state (liquid/gas) in a continuous cycle and absorbs and releases heat.

The heat pump cycle is essentially based on the Carnot cycle. (Theoretical thermodynamic cycle proposed by French Physicist & Engineer Nicolas Léonard Sadi Carnot in 1824)

Heat pump heating/cooling circuit is shown below:

 

The diagram illustrates the operation of the heat pump cycle:

1. Evaporator
In a heat exchanger the liquid refrigerant absorbs energy from the heat source (water, soil or air) and evaporates as the temperature rises.

2. Compressor
In the compressor the introduction of electrical energy causes the vaporised refrigerant to compress and increase in temperature. The refrigerant (coolant) leaves the compressor as a super-heated gas/vapor.

3. Condenser
Super-heated gas/vapor flows into the condenser, releasing energy to the heating system, then condenses (exchanges heat) and leaves the condenser as warm, liquid refrigerant. The released energy heats the water for either space heating or domestic hot water use at the desired thermostat set temperature.

4. Expansion Valve
The warm, liquid refrigerant is transferred to the expansion valve. In the expansion valve the pressure is reduced very rapidly. The temperature of the coolant also drops very quickly without releasing energy. The cold, liquid refrigerant is then transferred to the evaporator and the cycle begins again.

By Mel Peatey