Graham Rix

Ground Source and Air Source Heat Pumps

In most houses heat pumps are even more pointless than photovoltaic cells. The main advantage of ground-source and air-source heat pumps is as a way of getting your 10% or 20% ‘renewable energy’ box ticked when submitting a planning submission. If gas is available, there is no other sensible use of heat pumps.

Ground source heat pumps are powered by electricity, and work on the principle that you receive, in theory, around 3.2 units of electricity for every unit you put in.. Trouble is that gas costs around 3p per kWh, and electricity costs 13p. So, clearly, a conventional gas-fired system provides cheaper energy than a ground source heat pump. And you don’t even get to enjoy a smug feeling that you’re saving CO2: the government sponsored ‘Energy Saving Trust’ admits that no CO2 is saved. This is, of course, due to the way that grid-energy is generated in this country.

Furthermore many consultants admit that in reality the coefficient of performance is not 3.2, it’s often a good deal less, with a real world CoP of only around 2.

A ground source heat pump involves digging up much of your garden to a depth of 1.5m, and coughing up perhaps an extra £12,000 for your heating system, and you get nothing in return. But at least you can’t see ground source heat pumps, and so unlike most other renewable energy systems they’re won’t form a local eyesore.

Why do Local Planning Authorities like these systems? Answers by email please.

Are air source heat pumps better? The simple answer is no. Companies that sell both systems tend to suggest that an air-source system is what you use when ground-source is impractical. On average air-source pumps give you 2.5 times the electricity you put in (if used with underfloor heating, and rather less with radiators). So, they’re less efficient than ground source pumps; won’t last as long, and you need somewhere to put the rather ugly, and noisy, units. But at least they don’t involve digging up the garden, and so are cheaper to install. Again, their main use is as a box-ticking exercise for Planning applications.

A new worrying development is the Renewable Heat Incentive scheme, due to be introduced in April 2011. This will pay people (with their own money, of course) to adopt heat pumps. All bill-payers will be forced to subsidise the minority of confused householders who’ve installed heat pumps. Everyone’s electricity bill will rise. If the new scheme is anything like Feed in Tariff it could be very expensive for us all.