New build house, GSHP



  • Cardew
    Cardew Posts: 29,036 Forumite
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  • peeta
    peeta Posts: 16 Forumite
    an update for you -- we managed to have a conversation with the system installers who agreed to commission the system and they will use an accredited company to provide the certification.

    On a slightly separate issue the heating engineers commented on the design of the ground collectors.
    The four boreholes join as two sets to two manifolds.
    There is about 200m of surface level pipework to and from the manifolds, which includes outflow and inflow pipework which is laid side by side to each other.

    The heating people said that all outflow and inflow pipework must be separated with either a 1m gap or be thermally insulated to prevent thermal loss in the incoming pipes.
    What is the industry-standard for the pipework, were the borehole people wrong to the lay them side by side?
    many thanks once again
  • matelodave
    matelodave Posts: 8,605 Forumite
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    I'm not an expert but I would think that as the heatpump relies on the differential temperature between the incoming and outgoing water flow that running them side by side would reduce that differential, especially over 200m.

    The outgoing pipe is likely to be at zero or even below and would be cooling the ground area around it whereas you want the incoming to be as warm as possible so you can extract as much heat as possible from it, Running the incoming pipe through cooled ground seems counter intuitive unless it was insulated to reduce heat loss.It may not be significant but any heat loss could affect the overall system efficiency

    That's my view, others with more experience may differ.
    Never under estimate the power of stupid people in large numbers
  • lovesgshp
    lovesgshp Posts: 1,413 Forumite
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    Bit confused here. You have 200mtrs of feed pipes running on the surface, with no insulation and no real separation?
    The input heating lines should should have insulation on them, otherwise they will suffer from heat loss.
    Even from a horizontal layout, where the supply lines go to 60cm depth to the property, they are insulated against this.
    As Manuel says in Fawlty Towers: " I Know Nothing"
  • peeta
    peeta Posts: 16 Forumite
    sorry if I didn't explain the setup - the four boreholes are about 15-30m from the house and there are 8 pipes going to and from them. these are in a 4-foot deep trench.

    in this trench these pipes are laid next to each other and basically touching.

    the two manifolds are about 3m from the house, and from these we have 4 pipes coming into the house -- again these 4 pipes are laying in a trench, next to each other and touching
  • matelodave
    matelodave Posts: 8,605 Forumite
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    Even though the pipe runs may be shorter the flow and returns are all located together and touching so any heat in the return pipes will be reduced by the fact that they are running next to the refrigerated flow pipes in ground that will get colder over time, because of the refrigerated flow pipes.

    I guess the returns should be separated if possible but at the very least insulated to keep as much heat in them as possible.

    Perhaps lovesgsp could comment whether it would help by insulating the flow (cold) pipes as well where they are in close proximity to the returns to reduce cooling the surrounding ground.
    Never under estimate the power of stupid people in large numbers
  • lovesgshp
    lovesgshp Posts: 1,413 Forumite
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    edited 13 August 2016 at 10:52AM
    The pipes in the 4ft deep trench should have at least 30cm between each of them and preferably be bedded in sand. Depth is fine, as they will be acting like a horizontal system.
    From the collectors into the house, the inlet pipes only should be insulated, as midwinter you will quite possibly have sub zero flows out. It is not normally required to insulate the out lines, as they need to pick up as much heat as they can on return flow.
    As Manuel says in Fawlty Towers: " I Know Nothing"
  • peeta
    peeta Posts: 16 Forumite
    *** Update ***
    The commissioning process was very slow, the installers couldn't get good flow in one (of four) ground loops. In the end we got an engineer from the manufacturer and the borehole company to come and have a look.

    Although the other 3 loops were fine (there are two sets of loops, with antifreeze solution is mixed for each set at the manifold.
    In other words, the faulty loop with the poor flow has a joint circulation with another loop that flows fine.

    When testing the faulty loop we isolated it and used a petrol-power pump which achieved good flow. The circulating pumps on the GHSP units however could only manage about 10L/min. The other loop on the same manifold can reach almost 40L/min when isolated.

    The other strange thing with the faulty loop was that there seems to be a pressure build-up.
    After using the petrol-powered pump (which can achieve 90L/min), by disconnecting the flow pipe a back wash of antifreeze jets out with force. If we disconnect the return pipe there is minimal flow.
    It seemed that the loop had a blockage that acted like a valve.

    The decision was made to rod the loop. The borehole company used a cobra pipe and checked the whole depth (incase there was a cavern collapse) of the borehole. It was fine, reached the full depth.

    The borehole company stated that the problem with the ground loop was the antifreeze solution (a dense blob of solution at the bottom of the loop acting like an obstruction).
    Their position is that they want to make a charge for the remedial work they did to sort the problem, and suggested that installer should cover the cost.

    I am aware this isn't a clear cut situation. The facts of this are as follows:

    - The ground loop appears fine, ie there are no kinks etc.
    - There was no definite blockage removed during the problem-solving by the borehole company
    (if there was a stone or a piece of copper twirl flushed out, then we know where the 'blame' lies).
    - There was only very soft evidence for the problem. The borehole company said dense antifreeze was causing the issue.
    - I witnessed the loop being flushed and the cobra did bring up some grit and the pump flushed some brown stuff up. Could this have been a clump of dirt that was broken up and flushed out?
    - It seems impossible to prove or disprove that actual cause for the blockage.

    The flip side of this situation is that I, as the customer, have already paid for a functioning system.
    The contract was for a good collector system, and a commissioned set of pumps. Yes, there was a minor problem that was fixed without huge upheaval -- but who is responsible to cover this cost?
  • lovesgshp
    lovesgshp Posts: 1,413 Forumite
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    I must admit, that in 11 years of installing gshp systems I have never heard of antifreeze thickening in a ground loop.
    What are the models of the pumps that you have? I have the installer manuals for all the IVT/WB so I can check the flow rates.
    Did they use bio-ethanol, or propylene glycol as the antifreeze medium, as propylene glycol is slightly thicker, therefore reducing flow rates?
    As Manuel says in Fawlty Towers: " I Know Nothing"
  • peeta
    peeta Posts: 16 Forumite
    we used Killfrost GEO, i think the concentration is normal about 30% i'd say. their argument is that it wasn't mixed thoroughly and parts of it is much denser causing the apparent flow problems.

    as I said, there's no way to prove this claim, but they feel that I, or someone has to cover their costs.
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