Geothermal Piles
Providing Geothermal Piles for use in ground storage systems is one way that BBGE can help with the provision of renewable energy and reduce carbon emissions.
Concrete piles are used in a ground storage system to house closed circuits made from plastic piping. The pipes are used to circulate a heat transfer fluid which transports the ground temperature to the central control system for the building services. In the central control system a heat pump is used to increase the temperature to a level suitable for heating purposes.
While the average temperature to be found in the concrete foundations is in the region of 12°C, the heat pump produces temperatures of between 25°C and 40°C in the heat transfer fluid, which is suitable for low temperature heating systems in floors and ceilings. These systems can be used for both heating and cooling purposes. BBGE can use bored, CFA, precast concrete and steel piles as geothermal piles.
In view of the complexity of the planning and engineering processes necessary for ground storage systems, the architect, structural engineer, geotechnical engineer, geothermal engineer and building services engineer need to be included right from the beginning to undertake an integrated feasibility study.
How do they work?
Within the ground, only the top 1.5m of soils are effected by temperature fluctuations in the climate and below this soils remain at a constant temperature, usually around 12 °C. Closed ground source heat loops use this temperature constant to either heat up cold water or cool down hot water by pumping a liquid solution through pipework in contact with soils at depth. At the surface, a heat exchanger is used to amplify the temperature difference in a similar way to the workings of a fridge. The heat exchanger then uses the temperature differences to either heat or cool a building via standard central heating systems.
How do you judge heat capacity from a site?
A standard thermal reponse test can be carried out on an geothermal pile installation and a calculation made relative to the heating or cooling available measured in W/m/K. A thermal response is carried out using a self contained portable test unit towed behind a 4 x 4 vehicle. A properly conducted test will take 3 to 4 hours to set up and then 3 to 4 days to complete. Anaylsis of the results and reporting will take a further 3 weeks.
Assessing heat energy for your building
As a rule of thumb, most geothermal pile installations will achieve at least 30 watts of heating and cooling energy per metre depth of soils. 1 kilowatt of energy (one 33m deep precast pile) is enough to heat and cool a well insulated 4m by 4m room. A typical two storey office arrangement for 20 people, if constructed to modern insulation standards, would require around 50kW of energy from a ground source loop. Ideally BBGE require the building heating and cooling energy requirements over a 12 month climate cycle. This is an M&E type calculation based on insultation quality and extent and type of glazing required to the building.
What happens after installation?
BBGE will provide and install co-axial piping and manifold connection to the head of each pile leaving the remainder of the infrastructure connection to the main contractor. Least disturbance to the main substructure works occurs when geothermal piles are non load bearing and installed in land around the structure such as below carparks or landscaped areas. Load bearing geothermal piles require integration with the construction sequence and careful design of in ground temperature balance. If required, BBGE can provide a design and installation service for pipework and heat exchanger systems through a joint venture.
