02.How heat pumps work
Air conditioners work on the heat pump principle. As the name suggests, they pump heat from one place to another. Appliances like fridges and heat pump water heaters use a similar system.
This is how the heat pump cycle works in an air conditioner:
- A fan draws hot air from your home over a cold liquid, called a refrigerant.
- Heat is absorbed from the air, cooling it, then it flows back into your home.
- The warmed refrigerant evaporates and flows into a compressor, which creates a high-pressure, high temperature gas.
- The gas is pumped through a heat exchanger outside your home, which allows heat to escape and the refrigerant to cool and liquefy again.
- The refrigerant flows through an expansion device that lowers its pressure, cooling it further to increase its potential to absorb heat again.
Reverse-cycle air conditioners can reverse this process and be used for cooling and heating.
Air conditioners are very efficient. For every kW of electricity consumed, two or more kW of heating or cooling capacity can be produced. Window and split-system models must carry an energy rating label — the more stars a model has, the more efficient it is, and the lower its running costs. Ducted systems have to meet minimum energy performance requirements, but don't carry the energy rating label. See the government's energy rating website for more info.
The efficiency of larger models (most ducted systems) is expressed as the cooling or heating co-efficient of performance (COP) — the ratio between the cooling or heating capacity (in kW) and the amount of electricity used in the cooling or heating process (in kW).