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Renewable Energy: heat exchangers?

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  1.  
    • CommentAuthorkinley
    • CommentTimeJun 23rd 2008
     
    hi, am installing woodchip boiler mini district heating system into 5 buildings. conflicting advice about necessity or not of having heat exchangers in each building. unpressurised system not on mains water so low pressure. would be great to hear what anyone in the know knows about why we should use them (they cost £1000 EACH) so would prefer not to. thanks
    •  
      CommentAuthornigel
    • CommentTimeJun 23rd 2008
     
    I have done this with 3 flats and a shop and the biggest problem is the DHW. How do you intend to deal with this.
    Will they have their own supplies or are they shared.
    You could otherwise just treat as a system with 5 zones but you will have to think about how you control each zone.
    • CommentAuthorkinley
    • CommentTimeJun 23rd 2008
     
    70 kW woodchip boiler will heat the DHW in each unit with heat meters which will monitor each cottage use so we can charge guests according to what they use. they need to be individually controlled I think tho I did visit one installation where the room stats were in the boiler room and only way guests could control how warm they were was with the thermostats on the rads. so we were assuming each cottage will have its own controls.
    •  
      CommentAuthornigel
    • CommentTimeJun 23rd 2008
     
    If you can get suitable controls for each zone then I dont think there is a benefit from having heat exchangers.
    They are designed for large flat developments where they have separated water supplies and the controls work independently.

    If you are always going to be in control of the whole development I would avoid using heat exchangers, they are expensive for what they are.
    • CommentAuthorkinley
    • CommentTimeJun 23rd 2008
     
    thanks for that. So one last question if you dont mind! If something needs repairing in one unit - say leaking radiator or similar, would we be able to isolate that unit without having to turn off whole system without heat exchanger installed?
  6.  
    Hi, there are a lot of water stations out there. Was this for dHW only or DHW plus heating. There are numerous combinations and they can get pricy. Yhe thing is that they would assume an infinite supply as per a larger district heating system such that individual units could pretty much draw what they want. From your boiler you would need a large accumulator buffer to cope with this variance and decouple the user demands from the boiler.
    Cheers, Mike up North
    •  
      CommentAuthornigel
    • CommentTimeJun 24th 2008
     
    Many of the system are direct anyway so the same problem of isolation is involved anyway, particularly the cheaper units.

    So long as you build in isolation valves then you should be able to isolate parts of the system.

    The one thing I wish I had installed is a constant pressure system which keeps the system pressure at a constant level.
    It makes bleeding the system so much easier as on larger systems you seem to be always topping them up.
    • CommentAuthorkinley
    • CommentTimeJun 24th 2008
     
    thanks mike up north, its both heating and DHW..we will have 2200L accumulator tank as buffer. it is only for few weeks in winter that full heat and DHW will be required so trying not to oversize for rest of year.
    thanks nigel, will talk to our plumber about constant pressure system and go from there.
    • CommentAuthorArnold
    • CommentTimeJun 24th 2008
     
    Are you also fitting solar thermal if not why not?

    THANKS
    • CommentAuthorkinley
    • CommentTimeJun 24th 2008
     
    got solar thermal on own all year round dwelling which is great. experience so far with one already fitted on our holiday accommodation is that guests not necessarily as keen to time their hot water usage to when the sun has been shining as we might be. my conclusion thus far is that solar benefits are more efficient with 100% committed end users which regretfully not all guests are.
    • CommentAuthorkinley
    • CommentTimeJun 24th 2008
     
    just re read this and maybe you are suggesting solar feeding into accumulator tank? would that be possible?
  12.  
    From what I understand - it is. I'm not sure how (but I'm pretty sure it doesn't matter that your thermal store is 2200 litres). Hopefully one of the techier members of the forum will draw you up a schematic of how it's done.
    • CommentAuthorkinley
    • CommentTimeJun 25th 2008
     
    that would be good wouldnt it? I ll keep my fingers crossed!
    • CommentAuthorspynappels
    • CommentTimeJun 26th 2008
     
    Do you have a lot of room available for solar panels? You could pump quite a lot of heat into your accumulator, especially if you have a large collector array, 20msq+. This option can even be retrofitted if required, although this would not be the easiest option. It would involve running the solar through a plate heat exchanger and heating the water from the thermal store on the other side of the plate heat exchanger. Not the best way of explaining it, I'll see if I can sort out a diagram for you if you like.

    Stefan.
    • CommentAuthorkinley
    • CommentTimeJun 26th 2008
     
    hi stefan thanks for your input. we have good south facing roof which could take that size panels but at a distance (20m) across the yard from the boiler room site where the accumulator will be. I THINK i understand about the plate heat exchanger and the water. I m off for a week tomorrow so wont be accessing forum til we get back. will think about it while I m away.

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