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General: convert milk tank to thermal store?

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  1.  
    • CommentAuthorfuncrusher
    • CommentTimeSep 12th 2012
     
    Bulk milk tanks used on farms are stainless steel, insulated, and are cheap to buy when obsolete. Has anyone tried converting one to a thermal store (ie hit water)?
    • CommentAuthorEd Davies
    • CommentTimeSep 12th 2012
     
    What sort of size and shape are they?
    • CommentAuthorfuncrusher
    • CommentTimeSep 12th 2012
     
    vary. Older smaller ones are usually upright cylinders up to about 2500 litres. Later and larger ones are often rectangular or oval horizontal. Usually there are auxiliary refrigeration and other attachments.
    • CommentAuthordjh
    • CommentTimeSep 12th 2012 edited
     
    Funcrusher, have you seen Damon's http://www.earth.org.uk/milk-tanker-thermal-store.html

    Ed, about 20,000 litres according to Damon

    edit: ah, I see you said tank rather than tanker ...
  5.  
    I've seen bulk milk tanks as small as 200 lts and they go up to thousands of lts. Usually round and double walled with a refrigerant coil on the outside of the inner wall and insulated between the walls. The shape is usually squat rather than tall for ease of cleaning, but not the best shape for a TS. The insulation falls far short of what would be required of a TS (but nothing that a wrapping of 40cm of glass wool wouldn't fix)and they are open topped with a stainless steel lid which usually has a motor driven mixing paddle in the center. There will be a large tap at the base designed to completely drain any contents.
    The problem I would see with converting to a TS would be fixing a water tight top, unless you wanted to have it as the high point of the system - hmmm difficult to imagine a 2000 ltr. TS in the loft - or have the TS just a bit higher than the heat source with an open top (insulated tho) and all the outputs run off heat exchange coils or plate HXers. Some difficulties may be encountered building in coils with water tight fittings through the tank wall (brazed in fittings could be a DIY option) alternatively coils could have both input and output at the top. Central heating is not reckoned to be very effective when run off heat exchangers but they are fine for DHW.
    Sounds like an interesting project!!:bigsmile:
    • CommentAuthorfuncrusher
    • CommentTimeSep 12th 2012
     
    Peter:

    Older circular tanks have small 'manholes' in the top, and not overall lids. The manholes are easily welded up.

    Good idea about a heat exchanger though. A plate type exchange might have much better capacity than a coil.

    I'm also looking at the idea of using a vacuum system instead of a header tank. Think of the ch system as a mercury barometer, but with water instead of mercury: open milk tank at the bottom, ch pipe and rads as the glass tube filled with water held by vacuum. Create the vacuum by using an airtight pipe/reservoir in the loft. Install stoptaps at the bottom where the ch pipes enter/leave the milk tank. Fill the milk tank.Close bottom stoptaps, fill from the open top, close tap at top. open taps at bottom. Thus system filled with water and held full by air pressure like a barometer.....if plumbing is air tight it works in theory. Max head possible is 1 bar (approx 34ft).
    • CommentAuthorEd Davies
    • CommentTimeSep 12th 2012 edited
     
    Posted By: funcrusherI'm also looking at the idea of using a vacuum system...if plumbing is air tight it works in theory

    If...

    And if there's no gas (e.g., oxygen from the air over the open bit) dissolved in the water that can come out into the supposedly vacuum volume.

    Also note the lower boiling point of water at lower pressures.
    • CommentAuthorfuncrusher
    • CommentTimeSep 12th 2012
     
    Already understood. Keep the milk tank full with the lid on to prevent air absorption. Probably need a standard expansion vessel on the CH to cater for expansion. Or avoid both by heat exchanger system and standard vented CH

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