FAQs

Geothermal Boreholes

1) Q. How many boreholes will i need?

A. This depends on your heat loss of the building and what kilowatt your system is.

2) Q.How far apart can boreholes be?

A.We encourage boreholes to be over 10 metres apart and further if possible to maximise the efficiency of the heat pump system.

3) Q.How much room do we need to drill?

Our purpose built geothermal rig is able to fit through 5ft gaps and an area of approximately 4 parking spaces can be used per borehole.

4) Q.What type of drilling methods do you use?

A.We use a rotary drilling rig and drill using compressed air or drilling muds.

5) Q. Do i need permission for ground source heat pump boreholes?

A. Not usually however each site should be assessed individually. There are sometimes drilling restrictions from the Environment Agency, local planning departments and London Underground.

6) Q. What type of ground probes are used?

A. We use P100 virgin grade high density Polyethylene pipes with a life expectancy of 100 years, factory fitted with U-bends metre marked to ensure the correct depths are achieved.

7) Q. How deep do the borehole probes go?

A. Usually borehole probes average at 100 metres but hey can go as deep as 200 metres. It is essential that the correct amount of probe/probes are installed.

8) Q. Why use thermally enhanced grout?

A. This ensures that maximum efficiency is achieved from your borehole. Thermally enhanced grout can be up to 3 times more conductive than cheaper grouts (information below)

Geothermal Grouts – The Basics

• Thermal Conductivity of most ground is  0.8 -1.8 Btu/ft degree Fahrenheit or 1.4 - 3.1 watts/m degree Celsius
• It is logical then that the Geothermal grout should match the conductivity of the ground or be close to it.
• Less than this level the grout is acting as more of an insulator than a conductor and impairs heat pump efficiency considerably, necessitating much longer pipe lengths and deeper holes.
• Regular CE bentonite which is still widely used in Geothermal grouting can only be mixed to a maximum of 10-15% solids and then only achieves a thermal conductivity of around 0.2 Btu/ft degree Fahrenheit or .35 watts/m degree Celsius so they behave as insulators and should NOT be used for Geothermal work.
• Furthermore at low solids i.e (20%, Bentonite may loose water to formation and so dry out and crack so 30% solids should be considered the minimum for a Geothermal grout
• Proprietary grouting bentonites such as Geoseal, can be mixed and pumped at )30% solids with relative ease and permit long placement times to achieve thermal conductivities around 0.38 Btu/ft degree Fahrenheit or 0.65 watts/m degree Celsius . If these special bentonites are then enhanced with thermal conductivity improvers (eg sand ) up to 70% solids they achieve thermal conductivities up to 1.4 Btu/ft degree Fahrenheit or 2.4 watts/m degree Celsius and still deform and seal better than cement based grouts.
• One study in the magazine ‘Outside the Loop’ indicated a saving of 23% in pipe design length per ton was achieved by moving from a conductivity of .4 up to 0.85 Btu/ft degree Fahrenheit (0.65 up to 1.5 watts/m degree Celsius) and a further 19% saving in length was achieved when increasing conductivity from 0.85 – 1.4 Btu/ft degree Fahrenheit (1.5 -2.5 watts/m degree Celsius) giving a total saving of 47%. However for practical purposes most companies find little benefit in raising conductivity over .85 Btu/ft degree Fahrenheit or 1.5 watts/m degree Celsius
• In nature, clay deposits are typically 65-85% solids and contain or seal off strata containing water or oil and even radioactive material, preventing migration or contamination of the ground above. In the same way, clay grouts deform and maintain a seal irrespective of most ground movement and the sand enhanced bentonite grouts are typically 60-70% solids. Furthermore bentonite/ sand grout will not shear the pipes if the ground moves as it simply deforms.
• By contrast rigid cement based grouts do not deform with ground movement but fracture damaging any pipes buried within the grout and allowing leakage of gas or liquids around the grout mass.
• Cement on its own has relatively poor thermal conductivity ( 0.46 Btu/ft° ) due to micro pores and shrinkage so must be mixed with bentonite and thermal conductivity improvers to achieve higher values. However while cement mixtures form harder grouts which are needed for certain applications, it is felt that for Geothermal work, these are not ideal.
• To sum up, proprietary bentonite based grouts such as Geoseal mixed with sand, or pre-mixed bentonite/sand grouts like Thermoseal, are the best grouting solution available today. They can be tailored to produce efficient heat conducting mediums that protect and seal effectively and are stable long term.'

9) Q. Can i use a water borehole for water and a closed loop ground source heat pump system?

A. These systems need to be kept separate, however can be installed on the same site. In larger projects an open loop system may be used which uses the ground water and re introduces it to the ground, an abstraction licence would be required from the Environment Agency if over 20,000 litres is used per 24 hour period.

Waterwell Boreholes

1) Q. Can anyone have a water borehole?

A. Almost anyone can with a garden or free external area.

2) Q. Do you dowse for water?

A. Yes we do contact a dowser, on some occasions that helps us to find out the best place to drill and we also use the help of the British Geological Survey, they provide an accurate prognosis of groundwater depth, so we know how far down we need to drill.

  3) Q. Is groundwater always safe to drink?

  A. Usually, but not always. It may have minerals in it that can give the water an unpleasant taste or in rare cases be contaminated. We recommend that the groundwater is tested and correct filter systems are fitted as required.

  4) Q. Do i need a licence or permission?

  A. No not usually, anyone is allowed to extract up to 20,000 litres per day without licence or charge. If you do want to extract more than this, you will have to get an abstraction licence from the Environment Agency.

  5)  How deep do you need to drill?

  A. This depends on the geology of the ground and how far you need to drill to get to the water level.

    If you have a question that we have not answered on our FAQ's  pages  please contact us via email or call us with your questions and we will be happy to answer them.