Resource issues

GSHPs utilise energy stored in the earth’s crust. The temperature difference between the ground and circulating fluid in a closed loop system or the temperature of circulating water in an open loop system affect heat transfer thus it is vital to determine the temperature of the ground or the circulating water.

Ground characteristics will determine configuration and design of GSHP systems and can create a number of problems such as:

  • Precipitation of minerals, which results in scaling of heat exchangers and clogging of wells;
  • Corrosion of piping and heat exchangers;
  • Bio-fouling of the well intake area;
  • Clogging of aquifer as a result of precipitation of minerals within the aquifer or transport of precipitation into the aquifer.

The problems can be avoided if considered at early stages of the system design. As experienced Well Drillers, H.D. Services have much experience of such issues and will be able to identify any potential problems which may arise following site investigation and hydro-geological study.

It is also important to know ground water levels when considering design of a GSHP system. Understanding of ground water levels is required to establish required depth of boreholes. The deeper the borehole is the more pumping energy will be required, which can have considerable effect on overall efficiency of the system but will also influence the capital costs of the system. The projected depth of a borehole can be determined following a hydro-geological survey and will be communicated to the client via a budge quotation. We charge on a by metre basis, so we always look to over estimate the required depth.

Regulatory Issues

The Environment Agency (EA) controls water abstraction and discharges of pollutants and heat/energy to the environment. There are no specific requirements regarding the control of heat detailed in legislation or statutory guidance. The EA has the option to control discharges with a permit where appropriate, to avoid pollution or failure to achieve Water Framework Directive (WFD) objectives.

Control of thermal changes

The EU Habitats Directive requires the EA to have specific regard to potential adverse effects on protected species and/or ecosystems when consenting a discharge of heat to controlled waters. The Groundwater Directive also states that energy/heat can cause pollution and that pollution should be prevented (although its application in UK law is not clear). This may limit the upper limit of any single cycle open loop cooling system that is discharged to surface water to around 30ºC and also limits the upper temperature of a closed loop system as this will affect shallow soil temperatures to a greater degree.

Abstraction licences and discharge consents

For installation of an open loop system, the EA requires an investigation and consenting under the Water Resources Act as amended by the Water Act 2003.  NB: The act confirms that an abstraction licence is not required for abstractions less than 20,000 litres per day.

Other issues and barriers

Apart from the aforementioned potential technical and regulatory issues, there are other issues and barriers which slow down the development of GSHP systems.

Construction practice is centred on traditional trades providing electrical and plumbing skills, however, as GSHP systems are not yet so popular a specialist is required to deal with all of the problems of trades interfacing and planning activities in the construction phase. H.D. Services Ltd are specialist Open-Loop GSHP installers utilising ground water from boreholes as a heat source. Although we do not install the heating systems within properties (UFH, controls etc) we have qualified plumbers and electricians on our staff and ensure that we liaise directly with the heating installers and provide them with the information they require to both understand the role of the heat pump and to connect the system to the heat pump. H.D. Services are experienced in working on construction sites and can assist in the interfacing of trades and the planning of activities during construction.

The supply of electricity into domestic properties can have implications on the level of installed systems. The issues are two-fold. First the specification of the heat pump benefits from the availability of a three-phase electricity supply (most domestic supply is a single phase) because a three phase supply helps with the operation of the pump. Three phase motors are more efficient, less complicated and more reliable than single phase motors. Single phase motors are not easily available in sizes larger than about 10 horsepower. Three phase motors can be used with variable frequency drives (VFDs) to provide adjustable speed operation and controlling air or liquid flow by controlling the speed of a fan or pump is more efficient than using dampers or throttling valves. H.D. Services Ltd would recommend to any self-builder considering an open-loop GSHP to keep a 3-phase supply, as this allows the system to run more efficiently. However, we understand that this may not be preferable and are fortunate enough to have a partnering agreement with a manufacturer how can provide both single and three-phase heat pump units for the domestic market.

(Taken from NERA Report 2009 – Renewable Heat Technologies for Carbon Abatement: Characteristics and Potential. Pages 32-36)