Installing a ground source heat pump

Last updated Wednesday 30 April 2008

A groundbreaking way to harvest heat

An underground heat pump can save you money and cut your CO2 emissions by sucking the heat from your soil and distributing it round your house. But is your home suitable?

A heat pump takes low temperature 'ground heat' from underneath your lawn and upgrades it to a higher, more useful temperature to heat the rooms and the water supply in your home. It has the potential to cut your annual emissions by up to 50% and, depending on the fuel you're currently using, cut your heating bills even further.

Installation costs may be a bit daunting (7,300 upwards) but a pump requires no annual servicing, will last 25 years-plus and saves you money from day one.

Because of their high cost, heat pumps are usually installed in houses which are not on the gas network. Houses which are heated with electricity, oil or coal will also see the highest carbon savings from installing a heat pump.

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Photo: Installing a ground source heat pump

Saves up to 6,400kg of CO2 a year

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CO2 reduction 4 out of 5

Cheapness 5 out of 5

Popularity 2 out of 5

Cost 7,300 - 11,800

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It's Not Easy Being Green: ground-source heat pumps

An engineer discusses the pros and cons of heating your home with a heat pump

In this article:

How does it work?

Pub Fact

  • The temperature of the earth 7.5m below our feet is constant all year round
  • The earth absorbs 47% of the sun's energy amounting to 500 times more energy than mankind needs every year
  • A typical system will provide 95-100% of a household's heating requirements

A ground source heat pump uses lengths of pipe - placed either vertically in a borehole or horizontally in a trench - filled with a mixture of water and antifreeze to extract heat from the ground around your home. The mixture is pumped round the pipes where it absorbs heat, which is gathered in a hot water tank and then pumped into a distribution system - underfloor heating, radiators or water storage if it's going to be used to pre-heat your hot water. Ground source heat pumps are most commonly used with underfloor heating systems.

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How will it make a difference?

Getting your heat from the back garden is a big saver - both of money and CO2.

  • A ground source heat pump can save on average about four tonnes of CO2 a year, and up to 50% of your annual carbon footprint
  • It produces about 75 per cent of the CO2 of a modern gas-fired condensing boiler
  • The pump does require electricity to run - but for every unit of electricity used, three to four units of heat are produced
  • If you're replacing a system fuelled by oil, LPG or electricity, it could save up to 300-600 a year. If it's replacing a gas-fired system it will be more like 200

Of course, all your best efforts will be undone if you haven't insulated your home properly first.

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What's stopping me?

"Have I got room for one?"

It may simply be a non-starter where you live. It depends on whether you opt for a vertical or horizontal heat pump, what type of soil or rock there is below your house and the size of heat pump you buy. The area below the garden also needs to be free of inconvenient obstructions like sewerage pipes and access for machinery will be required. Speak to an installer to find out if your garden is suitable. The Low Carbon Buildings Programme has a list of certified installers.

"A bit steep, isn't it?"

The price tag might put you off too (and vertical pumps for smaller gardens are more expensive) but you can get grants of up to 1,200 at Low Carbon Buildings and you'll start making your money back immediately.

"Sounds like a lot of bother"

To keep disruption to a minimum, it's a lot easier if your pump is installed when your house is being constructed - but they can be added to old homes. There will be less aggravation if you already have underfloor heating - the system can work with oversized radiators, but underfloor heating is better as it works at a lower temperature.

If you're not well situated for a ground source heat pump, less disruptive 'air source heat pumps' are available and are becoming more popular. Or you could investigate biomass heating.

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How do I do it?

  • Make sure your property is suitable - get a ground survey to identify underground obstacles
  • Install insulation measures before installing the heat pump - wall, floor and loft insulation will lower your heat demand and make the system more effective and also are required in order to qualify for a grant
  • Get a grant from Low Carbon Buildings
  • Contact an accredited installer and find accredited products

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Comments

Greenjoe 2009-04-21

Ground Source heat pumps are great. All my heating and hot water needs are provided by the heat pump. I've also got solar panels, and the great thing is that I grants to help with the installation cost. I used a government approved installer (MCS accrediated) called Better Planet. All in all i'd recommend ground source heat pumps. Saving me money in the long run, and saving carbon emissions the whole time.

Baz, Shrewsbury 2009-01-28

Heat pumps are a great idea, especially if you have enough garden to allow a horizontal collector rather than the more expensive vertical borehole. Expect an energy gain of 3:1 or more, that is for every 1 kW the system uses, it will supply 3 kW to the heating system. As the system is sealed, no real maintenance will be required other than cleaning the dust from filters and checking the antifreeze solution. Heat pumps are best used for underfloor heating.

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Glossary terms used on this page
CO2
CO2, or carbon dioxide, is made up of the elements carbon and oxygen. It exists quite naturally in our atmosphere, as part of the carbon cycle. Everyday processes in the plant and animal world both add CO2 to the atmosphere and take it out. However, because it is a greenhouse gas - meaning it affects the temperature of the earth - the exact level of CO2 is important. Burning fossil fuels releases CO2 into the atmosphere, hence the anxiety that extensive use of these fuels is causing climate change.
Carbon
Carbon is the fourth most common chemical element in the universe, and carbon compounds - in other words, carbon chemically combined with other elements - are the basis of all known life forms on earth. Pure carbon appears in many apparently diverse forms, from diamond to graphite to charcoal, but it is much more commonly found in substances such as coal, oil, natural gas, wood and peat that we use for fuel. When we burn these substances to provide energy - either directly in our homes as heat, or in power stations to produce electricity - the combustion process produces 'oxides' of carbon, including the gas CO2.
Carbon footprint
A person's carbon footprint (or that of a particular household, business or entire community) refers to the CO2 for which they are responsible - whether directly, via their home energy use, their transport use, or indirectly via the embodied energy in the products and services they buy and use. You can work out your carbon footprint using calculators such as the Government's Act On CO2 Calculator.
Condensing boiler
A condensing boiler captures and uses energy contained in the water vapour given off when gas or oil is burned. In a non-condensing boiler this vapour leaves via a heat-resistant gas tube, or 'flue', and its energy is wasted. A condensing boiler cools the combustion gases sufficiently that the water vapour condenses back into liquid and its heat is recaptured. Approximately 10% of the energy value of the fuel is contained in this water vapour, so a condensing boiler converts far more of the fuel's energy into heat.
Emissions
Emissions are the CO2 (and other greenhouse gases) produced by energy use, usually calculated and stated as an annual tally: also referred to as your carbon footprint. Your personal emissions can be direct - such as the gas you personally use to heat your home or the petrol you burn to power your car - or indirect - meaning the energy use that has gone into the products or services you buy. The latter, such as the emissions caused by the manufacture of your new TV, or the packaging your food comes in, are also referred to as embodied emissions.
Ground source heat pump
Electrically powered systems that tap the stable, residual heat stored immediately below the surface of the earth to provide heating and hot water for homes and offices. Also known as geothermal heat pumps. See also geothermal energy.
Liquid petroleum gas (LPG)
Liquid (or 'liquefied') petroleum gas (LPG) is a mixture of butane, propane and other light hydrocarbons produced either as a by-product of oil refining or from natural gas fields, and used as a vehicle fuel with lower CO2emissions than petrol. At standard temperature and pressure, it's a gas but the mixture can be cooled, or subjected to moderate pressure, and is then transformed into a liquid for ease of storage and transportation. LPG is used in dual-fuel vehicles, where it operates alongside a conventional petrol tank. It is also used in heating appliances.

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