Air source heat pumps are becoming increasingly popular but what benefits can they bring and are they a viable means of heating a home?
Classified as either air-to-air or air-to-water depending on whether the heat distribution system in the building uses air or water, air source heat pumps can have a number of environmental and operation advantages. For a start, more heat is supplied to the building than energy is consumed by the heat pump. An air-source heat pump with a COP of three will supply three kilowatts of heat energy for the consumption of one kilowatt of electricity. If the heat pump is replacing (or being used as an alternative to) electric space heating, the use of the heat pump will offer significant carbon savings.
Other benefits of air-source heat pumps over conventional boilers include no combustion or explosive gases within the building, no need for flues or ventilation, no local pollution (although noise from the external unit fan may be a problem), long life expectancy, and low maintenance costs.
However, there are significant issues that can reduce effectiveness as a means of providing an efficient domestic heating and hot water system as Fergal Rogers from Tuffin Ferraby Taylor LLP (TFT) building and property consultancy explains:
“Air source heat pumps (ASHP) are an effective means of providing heating to properties and while they rely on using electricity in order to operate they are, in most cases, still more efficient than using oil-fuelled or condensing gas boilers. Research by the Energy Savings Trust shows that there can also be a major saving in terms of reducing carbon emissions.
“The biggest problem for ASHP is that during the winter months when demand for heat is at its highest and the outside air temperatures are at their lowest, performance of the units drop off dramatically, in some cases delivering 1kW of heat for each 1kW of electricity consumed (co-efficient of performance = 1). As a result the performance of any system should be looked at over the entire period of operation, known as the seasonal performance factor (SPF), and consider the ratio of energy output to the system’s energy use annually.
“Another important consideration is how hot water is generated, as most common ASHPs do not operate at temperatures that satisfy hot water storage requirements. Two years ago the Energy Saving Trust reported a poor seasonal performance for those systems that were installed into older buildings. Performance levels in other markets, particularly on the continent, are often higher than in the UK, which may suggest a quality issue for UK installers.
“To conclude, ASHPs have their part to play in reducing carbon consumption, however they need to be aligned to the customer’s requirements and are most likely to become part of an integrated package, whereby a supplementary heat source, such as electricity, will be required to satisfy top-up loads for domestic hot water requirements.”
