Geothermal Heating

Often referred to as 'Ground Source Heating' - is a developing ‘green’ technology which utilises the heat energy which is present in all near surface soils and rocks. This heat energy source within the ground can be harnessed to provide heating for buildings. During summer months and depending on the type of system installed, the heating arrangement can be reversed to provide building cooling systems.

The transfer of heat energy from the ground is carried out by circulating cold water (with an anti-freeze additive) through small diameter pipes or loops installed in trenches or boreholes. The temperature of the circulated water rises to the ambient ground temperature (in the region of 12°C) and it is then passed through a heat pump unit producing a temperature in the heat transfer medium (e.g. methanol) in the region of 48°C or above. This can then be used to provide the heat source for building heating systems i.e. through radiator, underfloor or ducted air systems, and may also be used to partially heat domestic hot water.

With the heat extracted at the heat pump unit, the now cold water is then re-circulated back into the ground loops to be reheated.

The key to producing an efficient & cost effective geothermal heating installation which meets defined design parameters is to ensure that there is a continuous thermal conductivity medium between the ground and the water circulation loops to allow effective heat transfer. In boreholes, which may be up to 150m deep, this is often difficult to achieve due to the nature of the strata and the problem of hole degradation and blocking both during drilling, loop installation and hole grouting. This can result in incomplete holes, holes not drilled to the design depth, inability to install loops to the correct depth due to hole collapse or in-hole debris and the inability to achieve a fully grouted surround to the loops. Heating installations based on such risks will be inefficient and unable to meet design outputs.

It is essential, therefore, when considering borehole based solutions that the correct drilling methods are used to ensure properly installed and efficient systems.

Forkers operate a number of multi-functional Casagrande C6S and M9 ‘Dual Head’ rotary drilling rigs which allow holes to be simultaneously cased to depths of up to 350m. The dual head facility enables one-pass, steel cased borehole drilling through all types of strata including voids, broken, unstable or loose ground to provide a ‘clean hole’ for installation of the water circulation loops. These rigs are equipped with bespoke cuttings collection systems mounted below the lower drill head allowing collection of wet or dry cuttings to either dust collector or sealed skip thus enabling clean drilling in any location.

The fully cased hole method also enables grout injection tubes to be easily inserted to the base of the boreholes and the holes grouted from the bottom up thus ensuring the loops are fully grout surrounded with a thermally conductive clay based grout for the full hole depth. Compliance monitoring and validation of loop installation and grout injection can therefore be assured.

Installing a ‘field’ of Geothermal Heating Loops in 100m deep Boreholes on a PFI Hospital Development