Cheat sheet: Ground source heat pumps

What have you been up to?
I've been busy having one of those ground loops and a heat pump put in.

A what now? Heat pumps and ground loops? They sound like something the kids might be doing at their discos and youth clubs. Or round the back of them.
To you maybe. In the real world, they are a system of coiled or curved loops that transfer heat from the ground to buildings. It's a cleantech thing, but hardly a new or particularly cutting-edge one. In fact, they've been around for 50-odd years, and there are already a lot of them out there.

How much are they then?
Not cheap, in fact it costs a lot more than a standard boiler. Your entry point is about £6,000, but that's for a house and if you're looking for something for work they are likely to be a lot more expensive. But although they are pretty pricy to set up, in the long run they should save you plenty of cash. Some estimates suggest that when installed in an electrically heated home, a ground source heat pump could save almost a grand a year on heating bills alone. What's more, they are reckoned to be four times more efficient than oil and gas boilers and six times more efficient than air conditioning units.

And it saves you carbon too?
Yes, indeed. Almost seven tonnes of carbon dioxide a year for that average electrically heated home.

What's the deal then? How does it work?
Basically, a mixture of water and antifreeze is pumped around an underground pipe, absorbing heat from the ground as it goes.

Wuh?
Think of it as a refrigerator in reverse. While the loop in the white box in the kitchen draws the cold through it, the one under the ground draws in heat, flushing it through a pipe. A compressor is then typically used to save or boost the heat.

What's a compressor?
It's like those humming pipes on the back of the fridge. It takes the warmed liquid and, um, compresses it as and when it needs to, making it warmer still.

Doesn't that require energy though?
Yes. It's not a zero-carbon technology, but the amount of power required is small change in comparison to that used by a conventional boiler. The Energy Saving Trust says: " The efficiency of a ground source heat pump system is measured by the co-efficient of performance (CoP). This is the ratio of units of heat output for each unit of electricity used to drive the compressor and pump for the ground loop. Average CoP over the year, known as seasonal efficiency, is about 3-4, although some systems may produce a greater rate of efficiency."

Again, wuh?
In English, that means that for every unit of electricity used to pump or compress the heat, three to four more units of heat are produced. Add in the lower maintenance bills and you have one extremely cost- and carbon-efficient means of heating a building.

How do you get the heat into the building?
In much the same way as a conventional boiler system. You can use the heated pipes for underfloor heating or use it to power your radiators. Although in the case of the latter you may need a slightly larger radiator than you are used to, but if you're talking about offices, that's not really a problem. The fact that most of the heat can be conducted under the floor also means that trendy, open-plan, cubicle hellholes can be heated really efficiently.

So it's good for homes and businesses then?
Indeed it is. The US Environmental Protection Agency (EPA) called geothermal heat pumps, as the technology is also known, one of the most energy-efficient, clean and cost-effective solutions available – which isn't a bad endorsement. It's an increasingly mature technology too, with a million installations in the US. Any specialist engineer should be able to install one, and they last for years with next to no maintenance.

Underground pipes, though? You'd have to have your garden dug up then?
You can either have trenches dug or bore holes drilled. If you don't want to upset the begonias the bore holes are probably the best option.

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