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How a heat pump works?

Author:Beijing JRG ElectorMechanical Technology Developme Click: Time:2023-02-20 14:13:19

How a heat pump works – the ‘refrigerant cycle’

The ‘refrigerant cycle’ has four phases:

evaporation; compression; condensation; expansion.


A heat pump takes in heat or cold in from the air, water or underground and transforms it into heating or cooling for your building or water.

Sources include ambient air, exhaust air, underground heat, groundwater and water.

The energy from these sources is infinite, meaning it is renewable.

This energy makes up about 80% of the energy needed.

The heat pump captures the heat from the ground, or the air or water. This heat is then used by the heat exchanger, known as the evaporator, to turn the refrigerant in the heat pump into gas.

Image: Revolve / EHPA
Photo: Ecoforest


The refrigerant gas then reaches the heart of the heat pump: the compressor. The compressor compresses the refrigerant gas to a high pressure, which leads to a rise in temperature.

Why this works: High pressure heats up gas, just like a bicycle pump that heats up when you are using it.

To drive the compressor, additional energy is needed. This can come from electricity, gas or thermal energy. This makes up about 20% of the total energy needed to run the heat pump. If green electricity is used, for example from solar or wind energy – then the heat pump uses 100% renewables and is carbon neutral.


On the discharge side of the compressor, vapour which is now hot and highly pressurised passes through the second heat exchanger, called the condenser. This heat exchanger allows the refrigerant to release the heat into the heating system for the house. As a result, the refrigerant then turns back from a gas into a liquid state.

The heat coming into the house can do so through an air system, like an air conditioning unit, or a water-based system like floor heating or radiators, known as ‘hydronic’. The indoor unit can also contain a hot water storage tank.


The condensed refrigerant then passes through a pressure-lowering device, known as the expansion valve. The now low-pressure liquid refrigerant can then begin the cycle again.

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