How do heat pumps work?
Air source heat pump
The main internal constitution of a heat pump is its compressor. Along with the compressor there are two heat exchangers, one called the evaporator and the other called the condenser. These are filled with refrigerant gas which constantly changes state from liquid to gas.
The purpose of the evaporator is to haul heat energy from the surrounding air on the outside, this causes the refrigerant to evaporate it into gas as it is warmed up. The warmer now gaseous refrigerant then passes through the compressor which increases the pressure and therefore the temperature of the gas. The hot gas then passes through the condenser which transfers the heat into the water of the heating system, this causes the gas to condense back into liquid form. The pressure in the gas is then released through the expansion valve and the process starts again.
Air source heat pumps have to periodically ‘defrost’ because ice can form on the evaporator coil in cold weather.
Air source heat pumps can as much as 400% efficient. This means for every 1kW of electricity used by the heat pump it can produce 4kW of usable heat.
Ground source heat pump
Ground source heat pumps work in exactly the same way as air source heat pumps. Instead of air passing through the evaporator, the heat is extracted from a liquid known as brine. This is pumped through coils in the ground to collect heat.
Ground source heat pumps are not susceptible to changes in external temperatures because ground temperature remain stable all year round.