How does a heat pump work?
Air source heat pumps use the same type of technology that keeps your fridge cold, but in reverse. A liquid refrigerant that has an extremely low boiling point is pumped on a loop between two heat exchangers. This refrigerant takes on heat energy from the outside ambient air temperature and turns into a gas as it warms up. This gas is then compressed back into a liquid, which increases its temperature further. The warm refrigerant then goes through a heat exchanger, which transfers the warmth to a separate body of water for circulating round the central heating system. During the final stage, the liquid refrigerant goes through an expansion valve reducing the pressure and temperature and the cycle repeats.
Co-efficient of Performance (CoP) is why heat pumps are a useful technology. If you put 1kWh of energy into a system you will get more than 1kWh of heat energy out. Typically, a heat pump has a maximum CoP of 2 or 3, meaning for 1kWh of electricity you will get 2 or 3 kWh’s of heat. The actual ratio of ‘electricity in’ to ‘heat out’ will change over the course of the year.
Is my property suitable?
Heat pumps make most financial sense in properties which are off the gas grid and which therefore use expensive fuels like electricity, oil, LPG or coal for space heating. If you are connected to mains gas, then economically you will probably be better off with gas central heating.
A well-insulated home with high standards of airtightness is also preferable, although improving the general energy efficiency of your home will help – as reducing your heating needs will enable you to run a smaller and cheaper heat pump. This is because heat pumps are most effective in homes which warm up quickly, keep the heat in and so require little energy to maintain a temperature once it has been reached.
Heat pumps operate more efficiently when the temperature difference between the heat pump unit and the heat distribution system is smaller. Consequently, they produce heat at a lower temperature than a conventional central heating system and so a larger area is required for the heat distribution. Underfloor heating is ideal, but large heat-pump specific radiators can also be used. Heat pumps also work more efficiently when there are gradual rather than sudden temperature demands on the system and so need to be controlled differently to traditional central heating systems.
Finally, bear in mind that whilst the unit itself does not take up a lot of space, they need to be positioned somewhere outside with adequate air flow.