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Heating and cooling: Insulating base of copper cylinder

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    • CommentAuthorMiked2714
    • CommentTimeOct 27th 2015
     
    I'm just ordering a new copper hot water cylinder, I'm going for 100mm foam insulation as it will be located in an unheated garage. Just discovered that cylinders don't come with any insulation on the base, apparently to avoid potential build up of moisture between insulation and tank. I have to admit I never knew that, our last cylinder was encased so you couldn't see the insulation. I realise I could just stand it on a piece of celotex but would that defeat the point re moisture and it might not take the load (c.110litres, 350mm diameter). Or is it the case that heat lost downwards is minimal, somehow I doubt it. Or could I stand it on slats, then build a little tray and fill the tray with vermiculite. Sounds complicated. Any ideas, I feel I can't be first to have encountered this issue!
    • CommentAuthorCliff Pope
    • CommentTimeOct 27th 2015
     
    It will be cold, won't it? As soon as you draw off any hot water from the top, cold water will enter and form a layer at the bottom. If the tank is designed properly to minimise swirl then the layers stay at their different temperatures, hot at top, cold at bottom.
    • CommentAuthorCWatters
    • CommentTimeOct 27th 2015
     
    Data sheet says Celotex compressive strength is between 140 (GA4000) and 150kPa (FF4000) or about 150,000 N/sqm

    350mm diameter = 0.096 sqm
    So I think it can carry 0.096 * 150,000 / 9.81 = 1471Kg

    A 110L cylinder will hold 110kg of water plus weight of cylinder. Should easily be ok I think.
    •  
      CommentAuthordjh
    • CommentTimeOct 27th 2015
     
    Posted By: CWattersA 110L cylinder will hold 110kg of water plus weight of cylinder. Should easily be ok I think.

    There's no problem for a person standing on a sheet of Celotex so a water tank should be OK. Might be worth making sure it's braced against toppling over though.
    • CommentAuthortony
    • CommentTimeOct 27th 2015
     
    The bottom is likely to be convex, not flat so it will dig in with the load and stress the connections, ply or boards on sheet insulation would work
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 27th 2015
     
    I would not trust celotex, or any other sheet insulation, not to move over time.
    You could always fit flexible and expanding pipework to overcome a few millimeters of movement in all three dimensions.
    But easier to make a plinth out of a bit of floorboard, with a noggin of timber in the middle. Then fill the void with insulation fo your choice. Actually the air on its own would be pretty good.

    Also worth remembered that even on my small (200lt) cylinder at 50°C I was loosing about 2.5 kWh/day (now down to 1.5 kWh/day ish).
    I am waiting to see how our old mated JSH get on with his new phase change, vacuum insulated store before I do any further worth on mine.
    • CommentAuthorMiked2714
    • CommentTimeOct 28th 2015 edited
     
    Many many thanks for all the comments. I forgot to mention it is a thermal store not a conventional cylinder (it's actually going to be electrically heated via solar diverter switch). Sounds like a plywood base then celotex should be OK, plus a strap for safety. Or the plinth option with loose insulation.
    •  
      CommentAuthordjh
    • CommentTimeOct 28th 2015
     
    Posted By: Miked2714Or the plinth option with loose insulation.

    Raising it might be useful to give you a little extra height for when the time comes to drain it down as well.

    We have a thermal store with the bottom immersion connected to a PV diverter and the top immersion on a timeswitch currently set for one hour in the middle of the night (E7). The top immersion is also set at a lower temperature to leave maximum headroom for solar. It seems to work well.
    • CommentAuthorNewarkcyl
    • CommentTimeOct 30th 2015
     
    I would say just fill it with expandable foam, then sit on lats , the lower part of the
    tank will be about 20 to 25cc most of the time so heat loss will be a minimum.
    More importantly will be the insulation of the pipework and components.
    • CommentAuthorgyrogear
    • CommentTimeOct 30th 2015 edited
     
    I'd just super-insulate the garage (-:

    gg
    • CommentAuthorchuckey
    • CommentTimeNov 1st 2015
     
    If the outside of the tank is attacked by water, what is it doing to the inside? :-(
    Frank
    • CommentAuthorJeff B
    • CommentTimeNov 3rd 2015
     
    Our thermal store stands on a layer of cork. Better than nowt I suppose.
    • CommentAuthortony
    • CommentTimeNov 4th 2015
     
    Are we insulating the base of the cylinder from the house or the house from the base of the cylinder?
    • CommentAuthorJeff B
    • CommentTimeNov 5th 2015
     
    Posted By: tonyAre we insulating the base of the cylinder from the house or the house from the base of the cylinder?


    In my case, the former. Less insulation on the bottom of the TS as built meant that we would be losing heat to the cold concrete floor. (The TS is in an un-heated store room).
    • CommentAuthortony
    • CommentTimeNov 5th 2015
     
    I would be very surprised if the floor was closer than the incoming water temperature, does the bottom of your store get hot?

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