Air source heat pumps

Heat pumps do exactly what the name suggests.  They convert low grade heat from outside the building, in the case of air source heat pumps from the outside ambient air, into useable grade heat inside the building. 

Most peoples’ concern with air source heat pumps is that they will fail to operate at low temperatures.  The efficiency of an air source heat pump is affected by the outside air temperature, generally, the colder the air, the less efficient the heat pump.  However, the air source units we fit, are able to operate down to approximately   -20 Celsius, at which point it is more viable to heat with another or alternate heat source.

In many situations the system can be set up to operate in a way that allows use of the heat pump for most of the heating requirements, then the alternate heat source, which may be some form of electrical immersion heater, but could be a gas boiler, oil boiler, solar panels, solid fuel burner etc.  One of the common problems with air source heat pumps is that people think that they could be fitted like a gas boiler, simply connected up to a heating system, and away you go.  Sadly this is not the case,  heat pumps, whether air source, or ground source work best with low temperature heating.  By this we mean primarily under- floor heating or fan coil heaters. This is because the most efficiency is obtained form the heat pump when it is generating low temperature output, ideally between 40 and 50 degrees Celsius.

There are models of both air source and ground source heat pumps coming on to the market which can generate higher temperatures more like a traditional gas or oil boiler.  The key to successful operation of an air source heat pump is to design the system it works with correctly.  The efficiency of a heat pump is called its coefficient of performance generally shortened to COP.  The way this is measured is how much heat a heat pump generates for each kilowatt of electricity it uses. An average air source heat pump, connected to a heating system which has a mix of under-floor heating and traditional radiators will operate at an average COP over the year of 2.5 to 2.8.  This means for every kilowatt of electricity it uses, it gives out 2.5 to 2.8 kilowatts of heat.  This is why heat pumps are considered a form of micro-generation because they effectively generate heat for use at the site they are fitted.

For a case study on an air source heat pump installation click on Roundcroft - Air source heat pump installation