Heat Pumps

General Description

Heat Pumps use the same technology as fridges. Whereas fridges pump heat from their inside, heat pumps take it from outside to heat a home. The heat can come from the air, the ground or a body of water such as a lake or stream. For every unit of electricity used to power a heat pump up to 3-4 units of heat can be produced from a good system.

Air Source Heat Pumps (ASHP)
These can extract useful heat from air that is as cold as -15 Centrigrade.
There are 2 types:
1. Air to Air systems provide warm air for fans to distibute around a ventilation system
2. Air to Water systems heat water instead and pump this through under flooring heating or radiators. The water produced is typically 35 to 40 Centrigrade and this makes under floor heating the most suitable distribution system.

ASHP can be used to pre-heat domestic hot water which can then be further heated by another means such as electric immersion. Some ASHP systems can domestic heat water to full temperature on their own although this takes more electricity per unit of heat to do.

Could I benefit from this ?
1. What are the alternative fuels available ? If its electricity, oil, Liquid Petroleum Gas (LPG), or coal, the payback from an ASHP will be more favourable. ASHP is a good option where mains gas is unavailable or a connection to the mains expensive.
2. You will need space on an external wall outside your home for the part of the system that collects the heat from the air. This could be an outbuilding such as garage.
3. It is cheaper and easier to install under floor heating for an air to water system when building a new home or carrying out major renovation of an old one.
4. With all heat pump technologies, it is normally cheaper to insulate your home well in order to reduce the heat demand. This should reduce running costs and may reduce up-front costs as the size of heat pump needed should be smaller. Low Carbon Buildings Programme grants (see later) are also only available when certain insulation measures have been taken.

Advantages
1. Running costs are likely to be cheaper than for other fuel sources where mains gas is not available.
2. If the electricity used to power the heat pump is from renewable sources, this should reduce your homes CO2 emissions.

Disadvantages
1. Gas boilers are currentlly cheaper to install and cheaper to run where mains gas is connected.
2. Poorly designed, manufactured or maintained units can be noisy according to anecdotal evidence.

Cost
The Energy Savings Trust website says that a typical 6Kw domestic system, suitable for a well insulated detached property, costs in the range of £7000 to £10000 installed. Savings in running costs depend on the type of fuel that ASHP is being compared against ranging from £185 pa (gas) to £760 pa (electricity). Site accessed 2/8/08 :
http://www.energysavingtrust.org.uk/generate_your_own_energy/types_of_renewables/air_source_heat_pumps
On 2/6/08 ASHP became eligible for Low Carbon Building Programme grants of up to £900 or 30% of allowable costs (whichever is lower). But do not assume that the total price for a system with grant will be less than that without. There is some anecdotal evidence of quotes for systems with grants being increased by the amount of the grant. And, as its early days for ASHP under the Low Carbon Building Programme, many installers are not yet registered to install under the LCBP.

Sources
1. Energy Savings Trust website as quoted above.
2. Low Carbon Buildings Program http://www.lowcarbonbuildings.org.uk/micro/
0800 915 0990
3. National Energy Action ( a charity aiming to end fuel poverty in the UK) has been involved in the installation of ASHPs in several homes in the north of England. Search http://www.nea.org.uk/ by air source heat pump.

Local Installers
1. Nibe Energy Systems Ltdm Chesterfield 0845 095 1200
2. Trianco Heating Products, Chapeltown S35 0114 257 2300
3. Eco Heat Pumps Sheffield S3 0114 270 3900

Ground Source Heat Pumps
The ground is a more stable source of heat than the air. The temperature does vary slowly with the seasons near the surface but below about 10 metres is stable all year around and typically 10-12C in the UK. Other things being equal heat pumps extract more heat per unit of electricity the higher the temperature of the source. And more heat tends to be needed in homes when outside air temperatures are lower. So a GSHP that uses a vertical borehole to extract heat from 10 or more metres below the surface will tend to have higher efficiency than an Air Source Heat Pump. But a GSHP tends to cost more to install than an ASHP though there is a slightly higher grant ceiling from the Low Carbon Buildings Programme of £1200.

Where there is sufficient land available, collecting heat from a ground coil buried in a trench typically 1 to 2 metres below the surface is an intermediate option both in terms of cost and performance. Temperatures at this depth vary with the seasons but fluctuate much less than the air.

The Energy Savings Trust website quoted below gives a broad range of £6000 - £12000 for a typical 8 - 12 kW system not including the system used to distribute the heat around the home(accessed 30/8/08).

South Yorkshire Energy Centre near Heeley City Farm have installed a GSHP using a borehole to collect heat and over-sized radiators to distribute it around a refurbished house. See
http://www.syec.co.uk/ for current opening hours. Over-sized radiators are a way of compensating for the lower temperature of the water from a heat pump compared to that from a boiler. However, talking to a senior member of staff on a visit some time ago, I was told that the radiators had not been able to raise the temperature to a high enough level for the comfort of office staff on the first floor. However, thermal comfort is subjective and it would be interesting to find out what others with radiator distribution systems attached to heat pumps feel because this type of distribution system is more easily fitted to existing properties than under floor heating.

Local installers * :
1. Andrews Engineering Ltd, Chesterfield 0845 126 7873
2. Eco Heat Pumps Ltd, Sheffield 0114 270 3900
3. Blue Flag Ltd, Halifax 01422 248613

* 30/8/08 from Low Carbon Buildings Programme, certified installers list for Yorks & Humber.

Sources :
(1) Energy Savings Trust
http://www.energysavingtrust.org.uk/generate_your_own_energy/types_of_renewables/ground_source_heat_pumps
(2) Low Carbon Buildings Program http://www.lowcarbonbuildings.org.uk/home/
Re grants http://www.lowcarbonbuildings.org.uk/about/hfaqs/
(3) Renewable Energy, 2nd Edition, Oxford University Press 2004, Edited by Godfrey Boyle p348 and pp364-8. This book can be viewed at Sheffield Central Library in the Business,Science & Technology section.


Water Source Heat Pumps
If you have a spring, stream, river, lake or large pond on or by your land, it is possible to extract heat from the water. However, properties with such natural assets are relatively uncommon, there are no grants from the Low Carbon Buildings Programme at the time of writing (2/9/08) and we know of no local installer - though if you have such an asset you might like to contact one of the local installers of ASHP & GSHP systems to see if they can help and add a comment to this blog.

Source : Energy Savings Trust http://www.energysavingtrust.org.uk/generate_your_own_energy/how_renewable_energy_works
Further Info : John Cantor Heat Pumps http://www.heatpumps.co.uk/ This is a commercial site but looks comprehensive, worth exploring and although the principal is based in Machynlleth, mid-Wales does consultancy.

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