Intuitively we can understand how a log fire works, electric radiator or an oil fired boiler but heat from the air seems counter intuitive so how does it actually work and is it reliable?
Well you already own a heat pump. Your fridge is a heat pump. Heat is extracted from the fridge and expelled as a waste product through a radiator grill at the back. An air source heat pump works in exactly the same way only the heat is captured to heat your home. It’s just as reliable as your fridge.
Heat isn’t generated. Its “pumped” from one place to another rather than sourced by burning fuel. The key material is a refrigerant which is evaporates and condenses easily. The refrigerant is compressed and as the pressure increases it condenses. As it condenses it releases heat. Conversely as the refrigerant is decompressed it evaporates and cools.
The best technical explanation of how this works in on wikipedia here: http://en.wikipedia.org/wiki/Air_source_heat_pumps
Heat pumps use electricity to power the compressor. So they do not produce free energy. However they are very efficient exploiting the physical properties of the refrigerant and the heat available in the air (even cool air). They are about 4 or 5 times more efficient than if the source were entirely electric such as with and electric radiator. The efficiency will vary with the ambient temperature of the air.
As well as air source heat pumps there are ground source heat pumps (sometimes called geo thermal) and water source heat pumps. The Royal festival Hall in London was heated by the water of the river Thames using a heat pump for many years when it was built in the 1950s.
Author: John Wolfendale
Bio: John is a founder of Eco Vida and is passionate about bringing modern design and construction practices to Spain. He believes a home which is warm in winter and cool in summer is largely a matter of design and selective use of materials. He is British and a Chartered Surveyor with 18 years experience living and working in Spain.