Geothermal Wells & Ground Source Heat Pumps

Dunelm Well Drilling installing ground loops for a ground source heat pump for a new school in Northumberland.
The job comprised 40 x 100m boreholes.

Ground-source heat pumps (GSHP) are an increasingly popular option for delivering low-carbon space heating (and cooling) for commercial, public and domestic buildings.

The principle of GSHP technology is long-established and is based on the same process as the common domestic refrigerator. A quantity of thermal energy is removed from one source and transferred to another. In the case of a refrigerator, the energy is removed from the inside of the appliance (cooling the air inside as a consequence) and transferred to the heat dissipation coils on the back of the cabinet. In the case of GSHP, the energy is removed from the ground and transferred into the interior of a building. In both cases the energy source becomes chilled, and the energy sink is warmed.

There are two principal methods for supplying thermal energy to the source-side loop in GSHP applications:

(a) Closed loop systems, in which the source-side loop is long, and is buried in the earth, either: i. as coils of HDPE pipework to depths of > 1.5m in cut-and-fill trenches, or ii. suspended in vertical boreholes.

(b) Open loop systems, in which the source-side loop is covered in pumped groundwater, which is typically re-pumped to the subsurface via another borehole well after passing through the heat pump.

In both cases, the energy source generally approximates to the local average annual air temperature, which in the lowland UK is typically between 10°C and 12°C. The fluid in the source-side loop will typically be chilled to around 6°C after passing through the heat exchanger. The exchanger typically delivers heat at around 55°C. The system can be coupled to closed circuits of water pipes supplying conventional 'wet' radiators or underfloor heating systems. The under floor heating been the system far better suited to GSHP applications.

There are many environmental problems associated with the installation of geothermal wells and it is important to undertake the drilling and installation with due to regard to the environment and the surroundings. Examples of potential problems include but are not limited to the following:

• pollution due to leakage of refrigerant liquids
• ground freezing, with associated impacts for buried infrastructure and blockage of aquifer permeability.
• reductions in effective hydraulic conductivity due to localised excessive chilling of groundwater.
• discharge of chilled or saline water to natural surface watercourses, with negative ecological impacts.
• interconnection of naturally distinct aquifers, leading to undesirable cross-aquifer flows with potential negative impacts.

In order to prevent interconnection between aquifers and potential cross contamination the closed loop system is often adopted and the loop grouted with a high conductivity grout comprising high grade silca sand, premium thermal bentonite based grout and water.

Dunelm Well Drilling has therefore a dedicated team specialising in the drilling of geothermal wells for ground source heat pumps.