A test is being carried out by an HS2 contractor that could see heat being extracted out of the ground to heat buildings and railway stations.
Extracting heat from the ground is not a new technology, but it has struggled to be incorporated into large commercial construction sites. Considering that a heat pump needs lots of pipes drilled into the ground to pump cool water down, and warmed water back up, and as most construction sites dig large deep piles into the ground to support the building, it seems that combining the two would be an obvious improvement.
However, embedding ground pump heat exchangers into solid concrete piles rarely seems to work that well, often getting damaged during construction, and when they do work, concrete is a fairly poor conductor of heat from the ground to the pipes inside the pile.
What’s being tested is a hollow pile, called a HIPER Pile, that was developed by the University of London and has been recently licensed to Keltbray. The hollow pile should get around a lot of the design problems as the heat pump pipes are inserted into the hollow core, not embedded into the concrete, making post-piling installation much easier, and then the idea is to fill the empty core with water, which is a much better thermal conductor than concrete.
According to Keltbray, their tests show the hollow piles outperform traditional solid concrete piles by some 60% in capturing heat from the ground and transferring it to the surface. A recent case study by Keltbray calculated that a conventional heat pump would have extracted around 1,650MWhrs/yr of energy from the ground, but using their hollow piles means that it is actually pulling nearly double that amount of heat energy out of the ground.