Heat Pumps

Eco homes 4 U  

The vast majority of us have a heat pump where we live. We just don’t always know it. The common domestic fridge has a heat pump in it, and it works in a similar way to the large scale unit used for heating a house.

The heat pump extracts heat from the air inside the fridge, and ‘loses’ the heat outside, at the back of the fridge. Check how warm the back of your fridge gets. This is an example of an ‘Air Source’ heat pump.

One of the most commonly-available heat pumps for domestic use now uses the latent heat from the soil. The soil is an excellent heat store, and effectively stores heat from the sun at approximately 10-12 degrees Centigrade all year round. This type of heat-pump is known as a Ground Source heat-pump, because that’s where it picks up its heat from.

Ground Source Heat Pumps can have a coefficient of performance (CoP) of 4 or more. That is, for each kilowatt-hour of electricity taken to run the pump, up to 4 kilowatt-hours of heat is produced.

Heat pumps will operate most efficiently when producing water at 30-40 degrees Centigrade. This temperature is ideally suited to under-floor heating systems, which run at a much lower temperature than radiators.

If you have to use radiators, they will need to be larger than you’d use with a normal boiler, because the flow temperatures will be far lower (a maximum of about 50 degrees C as against about 80 degrees C with a normal boiler). Given the cost of the equipment, Heat Pumps are not as cheap as gas heating, but can be an economic form of heating in homes which are not connected to the gas main.

In a Ground Source Heat Pump the heat is extracted from the soil by a ‘ground loop’. This is a length of plastic piping which can be buried in either a shallow trench or a deep bore-hole. The ground loop contains a glycol anti-freeze mixture. The heat collected is run through the heat pump, which raises the temperature from approximately 10-12 degrees to about 30-50 degrees.

Yes, in that it makes use of a heat-source (the earth) which will renew itself from the sun’s heat. The environmental impact depends on where you source your electricity. If you use a renewable tariff, or even use your own renewable electricity, then the impact is limited.

The refrigerants used in heat pumps are not the most environmentally-friendly materials, even though CFCs are no longer used. However, new materials are being developed which, it is hoped, will be more environmentally benign.

Because of the lower temperatures at which heat pumps operate, you will need a back-up form of water-heating, such as an immersion heater.

Yes. The Low Carbon Buildings Programme (LCBP) currently offers grants for domestic and non-domestic installations.

Energy Network (YREN) for advice on 0845 3304930. E-mail info@yren.org.uk.

david_wilkins@talktalk.net or octopustrading@freenetname.co.uk 

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Author David Wilkins.
Copyright © 2004 by [Octopus Trading]. All rights reserved.
Revised: 14 Dec 2007 12:59:35 -0000 .

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