Designing a Closed Loop Ground Source Energy Systems
A successful ground source energy (GSE) system provides a renewable energy solution to a buildings heating and cooling needs. These benefits depend on a reliable and efficient design of the ground loop energy source.
For the system to be successful it is important that the ground loop design and size matches the profile of energy use for the building. ESI can provide the specialised skills and knowledge to ensure that the proposed ground loop size matches these needs, taking into account the balance between winter heating and summer cooling.
Site Check
An initial desk based Site Check can identify typical values of thermo-geological parameters for the site location based on a postcode and site plan. This will give an indication of the closed loop or open loop options available for the site and an indication of the size of ground loop required. For smallest systems this might provide adequate information to feed into simple design tools and enable a suitable conservative design to be chosen.
Numerical Modelling
On most schemes,ESI bases the design on site specific numerical modelling to confirm the long term performance of the design. The layout and depths of the borehole heat exchanges are accounted for explicity and long term ground temperatures are predicted. For larger schemes, FEFLOW modelling allows more detailed and accurate modelling to be undertaken accounting for complex layered geology and the role of groundwater flow.To build confidence in model predictions, it is recommended that site specific thermal properties are obtained. Whichever modelling approach is taken, the circulation pump requirements are assessed using ESI's custom head loss calculation tools, designed specifically for ground source energy applications. This allows the overall system performance factors to be evaluated as a key part of an integrated system design.
Thermal Response Testing
A Thermal Response Test (TRT) is a standard measurement of the ground thermal conductivity and the borehole resistivity, and will confirm the local geological properties enabling the site specific geological setting to be taken into account. A Thermal Response Test would also quantify the consequences of a unsaturated zone and might also help identify potential benefits from groundwater flow past the array. Tests can take place during drilling of the array and the results delivered in time for a judgement on whether an additional borehole is required when less conservative designs are initially being proposed.
It is highly recommended that ESI work with Installers to design the ground loop to match the requirements of heat pump and the energy demand of the building. ESI’s design services support installations to take best advantage of the available ground area and geological setting.
