The world of renewable and alternative energy is cluttered with competing technologies, complicated terminology and jargon. Some of the alternatives – for heating your home, running your car, washing your clothes – are tried and tested while some are so new that their practical application to our ordinary lives is still a matter of theory and conjecture.
The Encyclopaedia of Alternatives, an occasional series starting this week, could help you find your way among the choices. From time to time, we’ll consult the experts to:
- explain how some of the more esoteric technologies work
- describe what they’re used for
- present the pros and cons
- and direct you to valuable sources of further information.
We’re starting with ground source heat pumps, but we’d love to hear from you about alternative energy options you’d like us to look into. Just add your comment below and we’ll see what we can find out.
About Ground Source Heat Pumps
Ground source heat pumps (GSHP) take advantage of the fact that, no matter how cold the temperature is outdoors, in most climates there’s always some residual heat below the surface of the soil. In the UK, that has been variously estimated at between 9 and 14 degrees. Of the various alternative technologies, GSHP is relatively well established outside the UK. According to the website Downsizer.net , more heating energy is produced this way than by solar PV and wind power together. The website suggests that 90% of new homes in Sweden are GSHP heated. Thousands have been installed across Europe but only a small number of those are in the UK.
How Does It Work?
GSHP uses the principal that as a substance is compressed, it loses its ability to hold heat. Heated-up molecules bounce around. When they are forced together, they stop moving and become cool. But all that kinetic energy has to go somewhere. It radiates away as heat.
That’s how your refrigerator works. A fluid that circulates around your fridge is compressed by pumps. The heat it contains is dissipated from the grille behind the fridge and the fluid, now chilled, continues on its journey around your fridge.
A ground source heat pump takes heat out of the ground in much the same way as a the heat exchanger takes it out of the air in your fridge. Except, the compressor is much bigger than the one in your fridge and instead of a grille, you have a central heating system. The system consists of a length of looped pipe – either coiled like a flattened Slinky toy or dropped down a bore hole – filled with a mixture of water and antifreeze. The fluid circulates through the system, giving up its heat through a heat exchanger and pump.
What are the Pros?
- Potentially lower fuel bills than conventional electric heating
- Possible income when the government’s Renewable Heat Incentive goes into effect.
- Could lower your home’s carbon emissions – depending upon what fuel you are replacing
- Can provide heat and hot water
- Needs little maintenance.
And the Cons?
- You need garden big enough for a trench or for a digger to make a bore hole.
- Produces a low level of heat compared to more conventional sources. Instead of small radiators, GSHP works best with underfloor heating or large radiant areas in a well insulated house.
- You still need electricity to operate the pump – though not as much as for heating with electricity – so you’ll still receive utility bills.
- Costs are high and payback varies depending upon the fuel you are replacing. Payback is faster if you are replacing electric heating or coal-fired heating. Savings are negligible if replacing gas central heating.
Costs and Savings
The Energy Saving Trust estimates the cost of a typical installation at between £9,000 and £17,000. How much you can save depends on what you are replacing and how you control your system. It’s a complicated matrix, best explained by this chart from the Energy Saving Trust. By the way, you may be wondering about operating efficiencies of 250 to 300% included in the chart. Because GSHP generates more heat energy than the electricity it uses, systems will always operate at more than 100% efficiency.
| Existing system | | Ground source heat pump performing at 250% | Ground source heat pump performing at 300% |
| Gas | £/year Carbon dioxide/year | £0 350kg | £130 800kg |
| Electric | £/year Carbon dioxide/year | £480 4,820kg | £610 5,270kg |
| Oil | £/year Carbon dioxide/year | £180 1,180kg | £310 1,640kg |
| Solid | £/year Carbon dioxide/year | £200 4,950kg | £330 5,410kg |
So is it for me?
Retrofitting GSHP systems can be expensive and disruptive so most experts suggest that it is most effectively used in new builds, particularly where gas for heat and hot water is not available.
To Find Out More
Read about the EST’s GSHP Trials
Download the EST Buyers’ Guide
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