As the engineering profession comes under increasing pressure to be more sustainable and cut carbon emissions, foundation specialists are doing their bit by installing geothermal piles to harness the energy of the ground.
This is the process where the sun heats the ground - and anything in the ground, such as piled foundations – so that it becomes a huge heat sink.
This heat energy is then absorbed by water contained in a U shaped pipe installed in the pile. Water returns to the building above ground about 4°C warmer.
Heat from this water is then passed through a heat pump containing a “heat transfer medium” or refrigerant which, through a cycle of evaporation, compression, condensation and expansion increases the temperature to 550C.
This heat can then be used to warm water for heating the building.
Piling contractor May Gurney has just finished installing piles containing these U-pipes at Bracknell College in Berkshire on a £500,000 contract.
Cost benefits of using piling specialist Geothermal International to install geothermal piles were part of Morgan Ashurst’s proposal to make whole life cost savings in the development.
The college will be fitted with two Water Furnace EKW 130 heat pumps which will immediately cut savings by 70% compared to conventional heating systems.
And for every 1kW of power used to operate the pump, 6kW of energy can be used to heat and cool the building.
Carbon emissions for the building will also be reduced by up to 50%, according to Geothermal International project manager Mike Palmer.
The scheme at Bracknell involves maximising the surface area of all 190 piles and the underside of the basement slab to achieve the maximum energy potential of the ground.
The U tubes are actually tied in with the reinforcement cage and cast into the piles. The inlet end and return ends are then connected to a main pipe system before the warm water enters the heat pump.
The piles here are 400mm diameter, installed to a depth of 17m and on the morning.
“One rig and two site workers are boring, concreting and installing over 10 ‘energy piles’ a day,” says Palmer.
Testing on site has been rigorous and his assiduous scrutiny of piling ensures that water runs through the loops unimpeded.
The structural integrity of the piles was also subject to rigorous checks. Each was load tested under pressures equivalent to two and half times that likely to be exerted by the weight of the building.WHAT ARE GEOTHERMAL PILES?
Geothermal piles uses structural piles to transport and store geothermal energy from the surrounding ground. As required, the energy from these piles is used to heat or cool the building above.
Flexible plastic pipes are fitted to the pile reinforcement cages installed in the piles. Once the piles are constructed, these pipes are linked to further piping embedded in the concrete floors and walls of the building using a closed circuit of pipework (similar to domestic central heating) allowing the piles to transfer geothermal energy via a heat pump for use in the structure.
The naturally high thermal conductivity and storage properties of concrete offer an ideal energy transfer medium. During construction, the pipes in the piles are simply filled with water and capped off to ensure integrity. This ensures that the pipework can safely withstand the head of wet concrete.
A simple flush test can be carried out before, during and after concreting and setting to verify the condition of pipework. Low temperature heating systems in floors and ceilings are most appropriate for use with geothermal energy.
Although originally conceived only to heat buildings, with the aid of the heat pump these technologies have also now been developed to be able to cool using a refrigerator unit where the capacity of the ground is inadequate for direct cooling. The financial return on investment of any ground storage system is dependant on a whole raft of variables including the building design and the ground conditions.