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Heat Pumps
Ground and air source heat pumps provide a new and clean way of heating buildings in the UK. They make use of solar energy, providing one of the most energy-efficient ways of heating buildings. They are suitable for a wide variety of building types and are particularly appropriate for low environmental impact projects. They do not require hot rocks (geothermal energy) and can be installed in most of the UK, using a borehole or shallow trenches or the air and less commonly, by extracting heat from a pond or lake. Heat collecting pipes in a closed loop, containing water (with a little antifreeze) are used to extract this stored energy, which can then be used to provide space heating and domestic hot water. In some applications, the pump can be reversed in summer to provide an element of cooling, but these systems are not currently eligible for UK grants.
What are Ground Source Heat Pumps?
The only energy used by Ground Source Heat Pump systems is electricity to power the pumps. Typically, a Ground Source Heat Pump will deliver three or four times as much thermal energy (heat) as is used in electrical energy to drive the system. For a particularly environmental solution, green electricity can be purchased.
Ground Source Heat Pump systems have been widely used in other parts of the world, including North America and Europe, for many years. Typically they cost more to install than conventional systems; however, they have very low maintenance costs and can be expected to provide reliable and environmentally friendly heating for in excess of 20 years.
Ground Source Heat Pumps work best with heating systems which are optimised to run at a lower water temperature than is commonly used in UK boiler and radiator systems. As such, they make an ideal partner for under floor heating systems.
What are Air Source Heat Pumps?
Air source heat pumps work by converting the energy of the outside air into heat. This creates a comfortable temperature inside the house as well as supplying energy for the hot water system. As with all heat pumps, air source models are most efficient when supplying low temperature systems such as under floor heating.
The efficiency of an air source heat pump is measured in Coefficient of Performance (CoP). A CoP of 4 means that for every kilowatt of electricity put in, you get 4 kilowatts of energy in the form of warm water. The flow temperature of the warm water is typically between 35oC and 45oC; much lower than achieved by a domestic boiler. The units are perfectly capable of generating higher temperatures but the CoP suffers meaning the economic and ecological benefits may be affected. Keeping the temperature at the lower end of the scale keeps the system operates at maximum efficiency.
An air source heat pump should cover the heating requirements of a well-insulated property in all but the most extreme conditions. When used in combination with an immersion heater both heating and hot water needs should be met, the immersion heater boosting water temperatures when necessary. An outside air source heat pump working efficiently can reduce energy consumption for heating by up to 50% when compared to conventional heating systems.
Heat Pump Q & A
Q. How efficient is a ground source heat pump system?
A. Modern systems are very energy efficient. For each kilowatt of electricity used to run the heat pump, three to four kilowatts of heat are delivered to the building.
Q. Why have I never heard of these systems before? Are they new?
A. Around the world, particularly in the USA and several parts of Europe, the use of GSHP systems is common. The ground source heat pump was actually invented more than 50 years ago, and continuous development has greatly improved its efficiency and reliability. It is now a proven, cost-effective, safe and environmentally friendly alternative to fossil fuels.
Q. How large are these units?
A. A typical heat pump unit for a domestic dwelling is about the same size as a large fridge.
Q. Can it supply hot water for the house?
A. Yes. Some domestic systems are able to heat domestic hot water via a modern high efficiency indirect water cylinder. An immersion heater can then boost the temperature which can be done at night using off peak rates.
Q. Can the systems provide cooling?
A. Yes. There are reverse-cycle heat pumps that can deliver both heating and cooling. Currently no grants are available for such systems.
Q. Can I use a standard domestic electricity supply?
A. Yes. There are a number of heat pumps that have been specifically designed to run on a standard UK single phase supply. However, if you do have access to a three-phase supply, which is essential for the larger units, then this is a preferable option.
Q. I am currently designing a new house which will be extremely well insulated. Would a ground source heat pump system be worth considering and is it straightforward to install?
A. Yes, absolutely. All new houses in the UK must be able to meet or exceed Building Regulations, and from April 2002, these are now the new higher standards for part L2. These mandatory regulations have been designed to conserve fuel, reduce heat losses and ensure greater energy efficiency, and so will ensure that all modern properties will lose less heat and need less heating. This means that the size of heat pump is smaller, will need smaller ground loops and will therefore be less expensive. Your plumber can connect the heat pump unit to your heating system and your builder can dig the trenches either before or whilst the footings and other ground works are being done.
Q. My architect suggests I install under floor heating in my new house. Is this OK?
A. Yes. Ground source heat pump systems are ideally matched to modern low temperature under floor heating.
Q. I have an older style property. Can I still fit a GSHP system?
Yes, you can, but your building must be well insulated for you to gain most benefit. The cost of a system is directly related to its size and with heat losses being fairly high from older buildings, this can add substantially to the capital cost of installation. Money spent on upgrading insulation levels can save a considerable amount on the capital cost. Regrettably, many older buildings can never be made sufficiently energy efficient to use a modern heating distribution system such as low temperature under floor heating, or low temperature radiators.
Q. Can radiators be used inside my house instead of under floor heating?
A. Yes, they can, but you will need larger radiators, sized for the typical 45° C to 50° C water temperatures obtained from GSHP systems. If your house is really well insulated they may be suitable, but check to see how big they would have to be and the space they would take up. There is now available a wide range of very stylish Italian die cast aluminium, high output radiators. These are very efficient and smaller than conventional radiators. Upstairs is usually less of a problem as bedrooms are normally kept at lower temperatures.
Q. Can a competent plumber install a heat pump to run my central heating system?
A. Yes, under most circumstances a truly competent plumber should be able to. However, unless he or she has had specific training in such installations, it can depend on whether or not the heat pump systems provided come complete with clear instructions and whether all the fittings and pipework are in place for straightforward connection to your central heating system, be it under floor, or wet radiators. Remember, there is no flue to install.
Q. Could I install the heat pump outside or in my car-port, garage or basement?
A. Yes. There is generally no problem in doing so and it normally means the pump is nearer to the pipe connections on your ground loops, which often makes the whole system easier to connect. Some home owners have made up a small, well insulated, external enclosure for the pump unit.
Q. I have been told long trenches will have to be dug on my land to house the ground loops but - my land is too rocky to dig trenches - can I still fit a heat pump system? I don't have enough land to dig long trenches - what do I do?
A. Boreholes can be used instead of trenches.
Q. How big are the trenches?
A. A typical heating-only installation for a medium sized, new build detached house would need at least two narrow trenches, each 300mm wide and 40 to 50 metres long and 1.8 metres deep. The trenches can be straight or curved and laid in any direction to suit your site, providing they are always a minimum of 5 metres apart. A standard excavator, such as the type used to dig conventional foundations and footings, can dig the trenches and backfill them after the ground loops have been installed. Your builder and/or digger driver will be able to do this work and plan it to ensure the minimum of disruption to your site. Once completed, and the ground loops pressure tested and buried, your renewable energy collection system can basically be forgotten. However, its location needs to be recorded to avoid accidentally digging it up!
Q. Can I install trenches on a downward sloping site?
A. Yes, provided you can physically dig the trenches, a moderate downward slope is not a problem. Consideration needs to be given to purging air from a system with ground loops higher than the heat pump.
Q. I have a large plot of land but the ground is quite hard. Can I dig a shallower trench?
A. Yes, the ground loop coils can sometimes be laid so that the coils lie horizontally in the trench rather than vertically. This would need a wider but shallower trench depth to at least 1.2 metres. However, this is not as satisfactory as a deep trench in which the coils are vertical and you will need a special slinky configuration and probably longer trenches. Your system supplier should be able to advise you accordingly.
Q. I have some very wet land. Can I use this?
A. Yes, wet land is better at conducting heat so, as long as you can physically dig a trench, its ideal.
Q. I have a large pond. I have a stream. Could this be used?
A. Yes, it is possible to use very large ponds and fast flowing streams as an energy heat source
Q. Are GSHP systems really environmentally friendly?
A. Yes. In the UK, there is now a strong move towards alternative technologies that are sustainable and environmentally much more acceptable. It has been calculated that 40% of CO 2 emissions are derived from the heating of buildings. By using renewable sources of energy to heat your property you can help to reduce these emissions, particularly when compared to burning fossil fuels such as oil. Most electricity suppliers are now offering 'clean green' electricity from a renewable energy source and, if you use this to power your heat pump, your property will be totally heated from renewable energy with zero carbon emissions.
Q. Are Ground Source Heat Pumps dangerous? What about servicing and maintenance?
A. There are no hazardous gas emissions, no flammable oil, LPG or gas pipes, no flue or chimney and no unsightly fuel tanks. GSHP systems have absolutely NO site emissions. There is no need for regular servicing or annual safety checks and maintenance is very low.
Q. How do running costs compare with conventional alternatives?
A. It depends what you are comparing. In a modern, well insulated house, a Ground Source Heat Pump system can offer very high efficiency and moderate running costs. An oil-fired boiler would cost considerably more to run, and electric heating would be at least three times as expensive. It is true that the very best of the modern condensing gas boilers may only be a little more expensive to run but that is on current gas prices, which are set to rise. Also, all fossil fuel boilers need regular servicing and maintenance.
Q. Are these systems expensive?
A. The initial purchase costs of a ground source heat pump system will be quite a lot more than a conventional oil or gas fired boiler. The initial one-off expense is offset by the lower running costs, lower maintenance and low servicing requirement. There is also the security of knowledge that the majority of your heating and cooling energy comes out of your ground, is under your control and will not increase in price.
Q. New buildings and drying them out!
A. The heat pump is not designed or sized to provide the greatly increased heat demand during the initialdryingout of a newly constructed building. During this period, and until the building is completely finished, supplementary heating may well have to be supplied by the owner/builder using separate equipment.
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