How Heat Pumps Work

Here’s a simple four-step summary which may not equip you to build your own heat pump, but which explains the fundamental principles.

There are three types of heat pump: air source, ground source, or water source (for more detail see Types of Heat Pump). For each type of heat pump, the basic technology is the same. The only difference is where the initial heat comes from.

What’s sometimes difficult to grasp about heat pumps is that the initial heat (taken from the air, from the ground, or from water) is not as hot as what comes out at the other end. So why’s it called a heat source? Read on.

• Evaporation

  "Refrigerant" liquids boil at very low temperatures, typically minus ten degrees. A heat pump system contains refrigerant in pipes. When water or air is passed over the pipes, the refrigerant boils and turns into vapour.

• Compression

  Next, the vapour is compressed. It’s a basic law of physics that when a vapour is forced to occupy a smaller space its temperature increases. In this case, the vapour will reach a temperature of between 75 and 125 degrees.

• Condensing

  Now the pressurised hot vapour is passed to a condenser or heat exchanger. It’s like steam escaping out of a kettle and hitting a metal plate. The plate heats up. This is the heat that is used to heat your home and hot water system.

• Expansion

  Finally, the cooled vapour is passed through an expansion valve (a valve which allows the pressure to decrease). As the pressure decreases, the vapour reverts to its liquid state, ready to start the whole process again.

If you've further questions about how heat pumps work, or want to talk it through with one of our experts, get in touch.