Thermal Heat Pumps for the Home
What are they?
Heat pumps are electrically-powered devices that provide central heating and hot water, using much less energy than conventional boilers or room heaters.
How do they work?
Heat pumps use the same mechanism as a refigerator – just as the fridge takes heat out of the food
inside and warms up the room it's in, a heat pump extracts heat from the ground or the outside air
and warms the house. A pump connected to the ground is known, unsurprisingly, as a Ground
Source Heat Pump (GSHP for short) and the other type as an Air Source Heat Pump or ASHP.
The real benefit comes from the fact that the ground or air warms up again more quickly than the pump system cools it down, so you can keep extracting free energy continuously – usually you get at least three times as much energy back in heat as you have used in electricity.
While an ASHP simply draws fresh air in with a fan then blows it out again, GSHPs are connected to pipes which carry a circulating water-based mixture which warms up in the ground and then gives up its heat in the pump unit before returning to the ground.
Where do the pipes go?
GSHPs come in three main forms depending on the layout of the pipes in the ground. Where space
is restricted a borehole is sunk, and a single loop of pipe is run down it – the depth depends on the
heating requirements and the ground type and can be up to 200m though most installations don't
Otherwise the pipework is laid horizontally at a depth of 1 to 2m, in a single continuous run either as a simple series of long loops or in overlapping circles. There is a variation in which separate arrays of parallel pipes known as 'compact collectors' are joined by short lengths of pipe: the major disadvantage with this type is the necessity for underground joints which are difficult to service and may be the site of leaks.
Will my garden freeze or my plants be damaged?
No, the systems are designed to allow the ground temperature to remain close to normal. Naturally, you should avoid planting deep-rooted plants such as trees near to the pipework in the ground but this is to prevent damage to the pipes, not to the plants.
What's the best option for me?
You really need to work out your heating needs and investigate your ground type before trying to find an answer to this question. In practice this means talking with a qualified installer who will not only be able to assess your house and grounds but will also have up-to-date technical and cost information about all the various systems and options available.
Will my existing radiators work with a Heat Pump?
They will, though because heat pumps are most efficient when they don't raise the central heating
water to too high a temperature it is advisable to have somewhat oversized radiators for the best
A better solution, which is more practical in new buildings than in most existing houses, is to lay underfloor heating pipes. This system works best with a water temperature of about 35 to 45°C, which is ideally suited to the efficient working of a heat pump.
Will my Central Heating need any other kind of fuel?
In specifiying a system, it is usual to design for the average winter load, rather than for
exceptionally cold times: this reduces the initial cost and gives the most efficient running. It is
useful to have a reserve method of heating to cope with unusual conditions.
One very good match for a heat pump system is Solar Hot Water. Not only is solar a very good way of topping up the temperature of the stored domestic hot water – which otherwise would have to be done by running the heat pump in an inefficient way or by using an immersion heater – but in Summer when central heating may not be required for long periods it allows the heat pump system to close itself down automatically until needed again.
How much will all this cost?
The costs are very variable, as so much depends on the heating requirements of the house, whether a borehole is needed and on the type of ground. However the estimate of the Government's Low Carbon Building Programme is that a typical setup costs £7,300-£11,800 plus the price of connection to the house's heating system.
What about grants?
The situation is the same as with the Solar Heating installations I talk about here: there are some grants but they're small and you have to use a listed contractor. This usually means paying a
lot more than you would using a qualified but unlisted local installer.
It is quite time-consuming and expensive to get accredited as a contractor, as a result few firms have bothered and you will generally have to face the cost of employing one from a considerable distance away. The list of accredited suppliers is available at the Low Carbon website: but there are very few listed in Wales.
Where can I find out more?
There's some information on the Internet, though less than for Solar and Wind systems. The Low Carbon site noted above is a good place to start. The Centre for Alternative Technology sells books on all aspects of renewable energy systems, and runs courses if you are dedicated enough.
Otherwise, a specialist local contractor like West Wales Heating Ltd will be pleased to discuss your needs in general and work out an outline installation scheme for free – detailed planning and specification may cost a little, but you should see that as part of the overall cost of the job.
©West Wales Heating Ltd