Geothermal Boreholes For Ground Source Heat Pump Systems
If you are thinking of installing a renewable energy system for your own home or a company looking for an alternative energy source for a housing project, we in tandem with a System Design company can provide the service to drill the boreholes for open and closed loop systems.
To drill the boreholes for Ground Source Heat Pump Exchange Systems is the same process as any water well borehole. The installation of the thermal exchange pipe loop and subsequent ﬁlling of the borehole with a thermal grout is the main diﬀerence in application to a standard well construction.
Prior to drilling a desk top geological assessment is made of what is expected to be drilled into. This is done as the diﬀering rock strata all have diﬀerent thermal properties. The varying thermal properties of the rock strata can aﬀect the depth of borehole that might be required but in general the boreholes are between 60 - 120m deep.
As a guideline for borehole depth and thermal conductivity, this is generally expressed in Watts per metre borehole depth. A value range of between 40 - 80W per borehole metre is used and reﬁned by the system design company. So, a 100m deep borehole might supply up to 8KW of extractable heat.
How it works
Closed loop systems basically have within the loop pipe a thermally conductive ﬂuid which enables the heat transfer from the ground source to the loop. The ﬂuid is continuously pumped around the system until it reaches the exchange pump within the property.
Very simply, at the pump the heat from the loop ﬂuid is compressed and produces a gas which is fed via the exchanger into the household system to be used for heating water and or a central heating system.
Tp provide the amount of energy required for the system to operate the house as designed it may require more than one borehole to be drilled and these numerous boreholes connected in line to feed into the heat exchange pump.
The system design company will provide an energy rating for your property. It might be 40KW for example which would require the equivalent of approximately 4 x 100m boreholes. Various testing regimes can determine the output of the boreholes in the system to get the balance right for the heat exchanger.
Open loop systems work on the premise that the water within a borehole will act as the heat exchange ﬂuid medium. The water is drawn from one borehole to the heat exchange pump system and then discharged back into another borehole some distance away so as not to aﬀect the ingoing water and temperature.
There are potential beneﬁts over a closed loop system such as higher water temperatures but it may require more maintenance since the open water source invites its own problems with potential bacterial problems, ﬁltration may be required to stop any solids getting into the pumps as well as corrosion issues within the system. A good GSHP company will advise as to the best option for your individual situation and location.
An abstraction licence from the Environment agency may be required if more than the permitted 20,000 litres per day is required for the open loop system to provide the energy for the project in hand.