Why choose a heat pump?

The running cost of an air source heat pump is much lower than a conventional electrical heating system as the householder only pays for running the compressor and fan, therefore the majority of the energy supplied to the house is renewable and free. Also heat pumps give a long trouble free life with very low maintenance costs. The expected life of a  heat pump is 20 years – much higher than an oil or gas boiler.

Air source heat pump

The advantage of an air source heat pump over a ground source heat pump is that an air source heat pump requires far less space to install, and no excavations. This makes air source heat pumps far more suitable for the average urban home.

How Does an Air Source Heat Pump Work?

An air source heat pump is made up of three main components - an evaporator coil, a compressor, and a heat exchanger.

The evaporator coil is fitted to the outside of an external wall. Here it absorbs heat from the outside air. The compressor pushes the refridgerant gas through the system compressing it until it is at the desired temperature (typically up to 35-40 degrees Celcius). The hot refridgerant then passes through the heat exchanger where the heat from the refridgerant is transferred to water or air.

In the schematic above the evaporator coil is labelled as outdoor coil, and the heat exchanger is the indoor coil since the system illustrated is an air-air heating system.

How Does a Ground Source Heat Pump Work?

Lengths of pipe are buried in the ground, either in a borehole or a horizontal trench. The pipe is usually a closed circuit and is filled with a mixture of water and antifreeze, which is pumped round the pipe absorbing heat from the ground.

The Idiots Guide to Heat Pumps.

A heat pump. This has three main parts:

• the evaporator - (e.g. the squiggly thing in the cold part of your fridge) takes the heat from the water in the ground loop;
• the compressor - (this is what makes the noise in a fridge) moves the refrigerant round the heat pump and compresses the gaseous refrigerant to the temperature needed for the heat distribution circuit;
• the condenser - (the hot part at the back of your fridge) gives up heat to a hot water tank which feeds the distribution system.