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.

Heat exchanger system within energy piles (c) Keltbray

That translates into less energy needed to heat the building on cold days, and the system can be reversed on hot days to soak heat out of a building and pump it into the ground instead. Where it can be removed in the winter again.

In addition to being better as heat-pumps, the hollow piles need a lot less concrete in their construction, which is better — or at least, less bad, for the environment. At the moment, piles are often made from pre-assembled steel wire columns delivered to the building site and dropped into the hole, then concrete is delivered to the site to be poured down to create the solid pile.

One of the other advantages of reducing the amount of concrete used in the pile is that it’s physically lighter. Light enough that the entire pile could be built offsite and delivered, so no need to send in two sets of deliveries – one for the steel cage and one for the concrete. The other advantage of remote construction is that it’s easier to use a type of concrete made from steel industry waste products that reduce the carbon-intensive cement content by up to 70%.

The pre-cast pile segments are delivered to the construction site, lowered into a hole dug slightly wider than the piles, and then to form a tight seal, grout is poured into the gap between the ground and the pile.

Once the piles are set, they can then install the heat-pump equipment.

(c) Keltbray

The deployment of these hollow piles is part of HS2’s Innovation programme, and soon to be trialled by contractors Mace Dragados at the project’s Euston station site. Keltbray estimates its technology will harness enough energy to supply 80% of the building’s heating and hot water.

At the moment, this is being tested on just the construction site office, but if it proves its case, then there’s always the possibility that it could be used later in the railway station construction as well.

HS2’s innovation manager, Heather Donald said: “The potential benefits of this innovation are obvious. By harnessing ground heat this technology has the potential to provide both heating, cooling and hot water to HS2 stations – increasing sustainability by reducing their carbon footprint and running costs.”

HIPER piling at Euston station (c) HS2


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  1. JP says:

    What a great idea!
    It seems to have the classic simple is best philosophy behind it. Innovation in the construction industry takes an inordinate amount of time as there are so many hurdles through which to jump ~ materials standards, planning, suitable strength and of course cost. I hope that it indeed proves itself and is swiftly brought into the normal practices of the building game.

  2. alistair Twin says:

    Interesting idea, most buildings big enough to need big piles need way more heat and hot water than you can get out of the ground immediately below it. However a train station might be the right use for this. relatively little heating, some hot water, lots of piles.

    • ianVisits says:

      And yet, they predict that this system will generate 80% of the energy needed for the building being constructed — so it’s not as if the building will need “way more heat and hot water than you can get out of the ground immediately below it”

    • Alistair Twin says:

      IV I mean that usually buildings with big piles are tall offices, hotels or housing which need a lot more heating / hot water and a smaller footprint than a train station. which generally doesn’t have heating.

      I guess they dont say more than 80% because some elements like warm-air curtains over doors in waiting rooms or in kiosks are not very well suited to centralised heat pump systems.

      It all makes me think that with the vent shafts down to the northern line part of the site already, wouldn’t that be a better source of heat where the coolth generated would be actively useful. similar to the city road heat recovery shaft I guess messing with the northern line is another tin of worms (or that’s where the other 20% is coming from)

    • ChrisC says:

      The other 20% would surely come from sources such as solar panels on station rooves, maybe some wind turbines and the conventional national grid.

    • Max Ingram says:

      HS2? Stations? There aren’t any except for one at each end.

  3. Tuzie Morrison says:

    This technology should also be used to draw some of the heat away from the clay surrounding the London Underground. This clay has been heating up every since the trains began running underground (something to do with the heat released from braking etc) and the heat has nowhere to go-hence passengers are getting warmer!
    I believe TFL has started to use something similar at one tube station to heat nearby flats but do not know if this idea will be expanded.
    I appreciate that the area below the City is pretty full of pipes cables and sewers already (the latter also generates heat).

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