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Heating and cooling: Rehau Helix Probe alternative

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    • CommentAuthorjonc_uk
    • CommentTimeSep 5th 2016
     
    Hi All,

    I have an extension which has a basement and intended to install about 20 Rehau helix probes underneath it to create an inter-seasonal heat store.

    The basement has been dug, and formwork is scheduled for the end of the week. Today I have found out that Rehau have stopped supplying them!

    Does anyone know of an alternative? This is the one opportunity I have for the heat store. I did a lot of research about methods of storing the heat and these seemed like the best solution. The floor area is about 220sqm.

    Thanks for any help.

    Jonathan
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 5th 2016
     
    Looks like you had a lucky escape.

    I would like to see some calculations for this type of ground heat store. Not seen any successful ones in the UK to date.
    The best that can be said is that you may reduce losses though the floor slightly.
    • CommentAuthorjonc_uk
    • CommentTimeSep 5th 2016
     
    Well, I did consider it 'experimental'.

    I figure I only have one go at this, and if it turned out to not work I wouldn't have been upset as the cost is not great in the scheme of things. I am sure I will be generating excess heat and thought it would be good to put it somewhere.

    The plan is to have twenty or so triple solar roof panels and a GSHP. Heating requirements for this extension should be minimal due to the ICF construction, with some heat going to maintain the temperature of the indoor pool. Excess heat was going into the ground for use when needed. I was also planning a sensor array and data logging to be able to report back with results.

    Basement slab is about 3-4m below ground, conditions are hard clay.
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 5th 2016 edited
     
    It is the amount of insulation you need, you can't rely on clay to insulate your store.

    Eventually and regardless of shape, the energy spreads out into a sphere (path of least resistance).
    Your coils are in effect cylinders, so for every doubling of diameter, you are increasing that surface area by 4, and the circumference by 2.
    So before long you would need more insulation than 'storage' if you want to hold any sort of temperature above normal ground temperature.

    I don't know what your installation would cost, but you may well find that using some PV onto a resistance heater in a large water cylinder would give you better value for money (think this has already been discussed, Ed springs to mind).
    You may also find that insulating your pool pays off better too.

    If you really want to spend some cash, send it to me and I shall do some Silly Sunday Experiments for you, not done them for a while (summer is my busy time and I am building a boat as well).
  5.  
    I don't know what research you did but there have been numerous mentions on here about it and I am pretty sure the idea filed with the design for the Hindenburg.
    • CommentAuthorEd Davies
    • CommentTimeSep 6th 2016
     
    But do you know of any in-ground heat stores for individual houses which actually work well?

    Tony's a bit disappointed with his, for example. Back of the envelope calculations and practical experience both point to it not working well at this scale. Lots of people talk about it but I've not seen any unequivocal data to show that systems work in practice beyond the thermal mass of the ground moderating the heating requirements for the winter. I.e., no real indication that you can actively extract heat back out of the ground rather than just have a bit seep out to stop you needing to heat too much.

    Larger scale stores (e.g, Drake Landing and the one on that Danish island) do seem much better. It's a matter of area to volume ratio.
    • CommentAuthorjonc_uk
    • CommentTimeSep 6th 2016
     
    Thanks for all your comments.

    I have abandoned the idea. Maybe when phase change storage systems become more accessible I will look at this again, within the thermal envelope.

    Regarding pool insulation, it is being constructed from ICF walls and with insulation between its base and the (insulated) slab. I am hoping to keep the conductive losses to a minimum and also use an auto-dosed liquid blanket system to minimise evaporative losses. Air handling will then recover the bulk of the latent heat from the humidity in the room and return it to the water.

    Jonathan.
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 6th 2016 edited
     
    Don't forget that the room that the pool is in, and any connected to it, will need stainless steel or brass fittings. There was a large centre made in St. Albans that needed loads of remedial work because they forgot that steel nails only last a few weeks in a weak chlorine/bromine atmosphere.
    • CommentAuthorjonc_uk
    • CommentTimeSep 8th 2016
     
    Thanks, I will bear that in mind.

    The pool air handling is designed to operate at a slightly negative pressure to reduce the escape of air to the surrounding rooms, plus the wet plant relies more on UV for disinfectant than chlorine dosage (although I like the taste of chlorine in a pool!).

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