Air Source Heat Pumps in Simple Terms

A Simple Explanation of Air Source Heat Pumps (ASHP) and How They Work

The technology inside an air source heat pump is very similar to any domestic refrigerator, which uses a vapour compression cycle. The main components in the heat pump are the compressor, the expansion valve and two heat exchangers. Refrigeration is not a new technology; it has been around for 100’s of years and is well proven. When was the last time you had your Fridge serviced?

Heat pumps move heat in the air into the home to provide a total solution for Domestic Hot Water (DHW) and all heating needs. Because heat pumps simply move energy, rather than creating it by burning fossil fuels, they are very efficient. For every 3KW of heat moved into the house only 1KW of electricity is consumed. This gives a perceived efficiency of 300% sometimes stated as a Co-efficient Of Performance (COP) of 3:1. The COP of our ASHP can be as high as 400%, comparable with the sort of efficiency you would get from a Ground Source heat pump but without the upheaval of installation.

How do they collect the heat?

Heat is collected by using a fan to force air, over a heat exchanger (simply a copper coil filled with refrigerant) to extract heat from the air.

How do they extract heat from cold air?

The best explanation I can give for this is as follows:- If you imagine that absolute zero is something like -275 degrees (these are not exact figures but you should get the idea!) Then any temperature above absolute zero (-275 degrees) you can extract energy from. So you have a massive range (from -275 to + 100) from which you can extract energy and convert to usable heat.

The Evaporator

The purpose of the Evaporator is to take heat obtained by the heat exchanger and boil a refrigerant (which boils at approximately -10°C) the act of boiling turns the refrigerant into a vapour which is then moved into the Compressor.

The Compressor

The Compressor does exactly what its name suggests; the vapour is compressed in volume and as its volume reduces its temperature increases. Temperatures of between 75°C and 125°C are achievable and the gas is then fed through a heat exchanger.

Condenser/heat exchanger

Forcing the hot gas across the cold water from the central heating system condenses the refrigerant turning it back into a liquid. As it condenses its heat is passed into the heat exchanger which supplies the DHW and central heating system.

The Expansion Valve

To complete the closed circuit of the heat pump the only thing which needs to be done is reduce the pressure of the condensed liquid and this is done via an Expansion Valve. When you expand a substance, it cools. Thus completing the cycle