I have a reconditioned beer cooler in my garage. No beer, just a cooler. It’s about the size of a microwave and I bought it on eBay after seeing one on Beechgrove Garden (BBC Scotland). They had it connected up as a heat pump to help prevent freezing in one of their greenhouses – the facts sheet is here. The principle is that you bury pipes in the garden and extract heat from the ground (I haven’t got round to that bit yet). The heat you get from a small unit like that is no big deal, but it should use less energy to run than the energy I would use heating the greenhouse to the same temperature… if you see what I mean. Just a couple of degrees would help, as we get frosts in early June and they can flatten seedlings.
Whitmuir Organics has a REAL ground source heatpump. The pipes are buried deep beneath large earth embankments, and from them they heat most of their new building. I can only bury my pipes a maximum of 18″ (45cm) beneath the surface because at that depth I reach solid rock – and I’m not sure I would be popular if I started blasting it out.
In the 1980s I was on the UK Department of Energy’s Geothermal Energy Steering Committee, and in those days heat pumps were hardly worth considering (not that ground source heat pumps use geothermal energy – they use heat from the sun that has warmed the Earth, not heat generated deep down, that’s quite different).
Things have changed a lot since the 1980s. The cost of fossil fuel has rocketed and heat pump technology has improved. I have yet to see if my little experiment will work. Trouble is, a lot of digging is involved. At present the ground is rock hard and covered by an ice sheet, like Greenland.
[Many false claims are made about heat pumps. If you are seriously thinking about installing one (not a toytown one like mine) then download the Energy Saving Trust’s .pdf file from here]