Can renewable energy sources power the world?
Can renewable energy sources power the world?

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

8 Heat pumps

Another way of harnessing the Sun’s warmth is to use a heat pump. This works like a refrigerator, except that in countries such as the UK it is likely to be primarily used for heating rather than cooling.

Have a look at Figure 18, which shows the main elements within the most common type of heat pump.

Schematic diagram of a heat pump (source: EST, 2010)
Figure 18 Schematic diagram of a heat pump (source: EST, 2010)

Essentially, electricity is used to ‘pump’ heat from a low temperature in the evaporator to a higher temperature in the condenser. Here’s a more detailed description:

  • a.The heat pumping process is made possible by the use of a special refrigerant liquid that boils at low temperature (about –15 °C). At point 1 in Figure 18 it starts as a cool liquid at a low pressure.
  • b.In order to convert this cool liquid to a vapour, it must be given energy – the so-called latent heat of evaporation.
  • c.The refrigerant absorbs heat from the heat source in a heat exchanger, called the evaporator, and it vaporizes (point 2).
  • d.The vapour then enters an electrically driven compressor that raises both its pressure and temperature (point 3).
  • e.The hot vapour then enters another heat exchanger, the condenser, where it condenses to a warm liquid and gives up its latent heat of evaporation (point 4).
  • f.Finally the liquid is forced through a fine expansion valve where it loses pressure, vaporising and dropping in temperature.
  • g.The cycle is then repeated

There are two main types of heat pump and we’ll look at these next.

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371