Ground Source Heat Pumps

Posted by on Dec 8, 2017 in Building Surveying

Ground Source Heat Pumps

I have recently joined GLM after 7 years at Orkney Islands Council where I gained significant experience specifying renewable energy measures to various local authority buildings.

One such project involved replacing the existing solid fuel systems to 40 housing properties with an energy efficient and low carbon means of providing heating and hot water. Following an option appraisal and feasibility study, it was determined that ground source heat pumps provided the most favourable solution.

How does a ground source heat pump work?

The ground source heat pump system works by gathering heat from solar energy stored underground using a borehole collector or ground loop buried in trenches. The earth absorbs and stores heat from the sun year after year providing a constant source of naturally renewed energy. The heat is transferred from the ground to the heat pump using a mixture of water and environmentally-friendly anti-freeze solution (brine). It circulates through the closed loop, absorbing thermal energy from the earth and carrying it to the heat pump. Refrigerant circulates in the heat pump and thus the heat from the ground is retained and converted into high-grade heat to be released into the home via the heating and hot water system.

A typical domestic home requires a 100mm borehole and suitable access for a borehole to be drilled. Retro fitting buried pipes in gardens in most instances will not be possible therefore the boreholes will be the preferred option.

 

The benefits of ground source heat pumps

  • Could lower your fuel bills, especially if you replace electric heating
  • Could provide you with income through the government’s Renewable Heat Incentive
  • Could lower home carbon emissions, depending on which fuel you are replacing
  • Can heat your home as well as your water
  • Minimal maintenance required

Unlike gas and oil boilers, heat pumps deliver heat at lower temperatures over much longer periods. During the winter they may need to be on constantly to heat your home efficiently. You will also notice that radiators won’t feel as hot to the touch as they might do when you are using a gas or oil boiler.

Is a ground source heat pump suitable for me?

To tell if an air source heat pump is right for you, there are a few key questions to consider:

  • Is your garden suitable for a ground loop? It doesn’t have to be particularly big, but the ground needs to be suitable for digging a trench or a borehole and accessible to digging machinery.
  • Is your home well insulated? Since ground source heat pumps work best when producing heat at a lower temperature than traditional boilers, it’s essential that your home is well insulated and draught-proofed for the heating system to be effective.
  • What fuel will you be replacing? The system will pay for itself much more quickly if it’s replacing an electricity or coal heating system. Heat pumps may not be the best option for homes using mains gas.
  • What type of heating system will you use? Ground source heat pumps can perform better with underfloor heating systems or warm air heating than with radiator-based systems because of the lower water temperatures required.
  • Is the system intended for a new development? Combining the installation with other building work can reduce the cost of installing the system.

Costs

Installing a typical system costs around ÂŁ10,000-ÂŁ18,000. Running costs will depend on a number of factors including the size of your home and how well insulated it is.

Savings

How much you can save will depend on what system you use now, as well as what you are replacing it with. Your savings will be affected by:

  • Your heat distribution system. Underfloor heating can be more efficient than radiators because the water doesn’t need to be so hot. If underfloor heating isn’t possible, use the largest radiators you can. Your installer should be able to advise on this.
  • Your fuel costs. You will still have to pay fuel bills with a heat pump because they are powered by electricity, but you will save on the fuel you are replacing. If the fuel you are replacing is expensive you are more likely to make a saving.
  • Your old heating system. If your old heating system was inefficient, you are more likely to see lower running costs with a new heat pump.
  • Water heating. If the heat pump is providing hot water then this could limit the overall efficiency. You might want to consider solar water heating to provide hot water in the summer and help maintain your heat pump efficiency.
  • Using the controls. Learn how to control the system so you can get the most out of it. You will probably need to set the heating to come on for longer hours, but you might be able to set the thermostat lower and still feel comfortable. Your installer should explain to you how to control the system so you can use it most effectively.

Maintenance

Heat pump systems typically come with a warranty of two to three years. Workmanship warranties for heat pumps can last up to 10 years.

Many manufacturers also offer optional extensions of warranty for a fee. You can expect them to operate for 20 years or more, but they do require regular scheduled maintenance. A yearly check by you and a more detailed check by a professional installer every three to five years should be sufficient.

Should you wish to discuss any questions raised in this blog series in more detail or need assistance with renewable energy measures, please get in touch: liam.ireland@weareglm.com or 0131 225 4235.

Liam Ireland

Building Surveyor