Questions and answers you may have about Boreholes for Geothermal energy?
How many boreholes will I need and how deep do they need to be? (The favourite and most commonly asked one!!)
Your heat pump supplier/system installer should be able to provide you with answers to these questions; however below is a very approximate calculation based on the following assumption:
Vertical borehole collectors can provide between 25 watts (in loose gravels) and 60-70 watts (in saturated stone) per metre of active collector.
(active collector denotes the actual probe that is in contact with geothermal grout)
For the purpose of this example calculation we will assume a fairly modest figure of 35 watts per metre.
(an accurate figure can be produced via a survey, this figure becomes increasing important the larger the heat pump you are installing).
And a ground source heat pump size of 12kw.
(approx heat pump size required to heat a large 4-5 bed house with good insulation)
Assumed COP of 4 (Coefficient Of Performance of 4) – 1kw in = 4kw out = net gain of 3kw.
(I.E. for every 1kw input of electricity to drive the heat pump, 4Kw of heat is produced from the ground, so a net gain of 3)
So, using our average figure of 35 watts/metre, a heat pump size of 12kw and a COP of 4 we can apply the following calculation:
12 (heat pump size) / by 4 x 3 (COP) = 9 kW or 9000 watts / 35 (watts per metre) = 258m.
This would be 3 x 86m boreholes.
(Please note however that this could be as much as 360m or as little as 150m – depending on the watts per metre produced in the given geology)
What size loop do I need?
Borehole depths below 110m operate better and are more efficient with a 32mm diameter loop.
Borehole depths above 110m operate better and are more efficient with a 40mm diameter loop.
Borehole depths of 100-120m operate equally as well with either diameter.
How far apart should they be?
They should be spaced at least 7m apart to prevent thermal linkage (and efficiency loss) between the boreholes.
They should be at least 5m from any buildings.
Can you drill in my garden?
Yes we can drill in your garden, so long as we can get our equipment in there – our smallest rig can access with a clear space of just 1.5m.
Does it make a mess?
It can do, however Paul Havard Drilling put systems and measures in place to ensure we make as little mess as possible with as little disruption as possible.
How much does it cost?
Boreholes are usually recognised as the most expensive method, however they are also the tidiest, least disruptive and overall the most efficient way of pumping Geothermal energy into your home!
Is it safe?
Yes! It is clean and safe and has very low emissions of greenhouse gas, a negative environmental impact. In fact it is the main source of energy in Iceland, also very widely regarded as an important energy source in New Zealand and California. And has been used since ancient times as a source of hot water.
What can it be used for?
Geothermal energy has three main uses: Heating, Electricity generation and geothermal heat pumps.
Is it sustainable?
Geothermal energy doesn’t depend on the sun like other renewable energy resources, so it can run day and night using the earth’s natural heating process.