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Green Building Bible, Fourth Edition
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Heating and cooling: recommend me a thermal store?

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  1.  
    • CommentAuthorcjard
    • CommentTimeJul 1st 2015
     
    Hi all

    having decided not to make a decision on how to heat the house (lpg/oil/xSHP/biomass) because there are jsut too darn many variables and unknowns, i'm planning to just install a large store and run it on an E7 immersion for the first year - the aim is low startup cost (budget is a concern at the mo as most of it is pouring into fabric first measures such as airtightness and insulation) and then i can monitor my usage and get a better idea of how the house performs. SAP calc currently says I'll use 26Mwh of heat and 10Mwh of electric per year

    If I have an acceptably large store then my thinking is I can plug other tech into it later - get solar panels (PV) in to reduce the E7/immersion reliance maybe, or a burning device. or both.

    So what stats and measurements do you guys need from me to help me decide a size? And next up I'll be looking for recommendations on which tank - for example an akvaterm solar plus one, 1000 litre, is a somewhat eyepopping £3200. Wow.. I wasn't quite expecting that much for an insulated cistern with a couple of copper tubes inside!
    • CommentAuthorEd Davies
    • CommentTimeJul 1st 2015
     
    26 MWh/year for a house with 500 m³ volume and 2.5 m room heights (so 200 m² floor area) works out at 130 kWh/(m²·year). Not everybody goes for Passivhaus but this is still a bit disappointing, isn't it?

    The heating required for a cold day is a different matter but, still, a guess of 1/100th of the annual load doesn't seem completely silly so 260 kWh.

    A 1000 litre thermal store operating over a temperature range of 60 °C has a heat capacity of 1000 kg × 4200 J/kg·K × 60 K = 252 MJ = 70 kWh.

    Something isn't right here.
    •  
      CommentAuthorcrosbie
    • CommentTimeJul 1st 2015
     
    When I researched manufacturers a few years ago, I came up with Akvaterm - because, in wishing to save money, I wanted a store that would last a few years, and Akvaterm best appeared to meet that criterion.
    •  
      CommentAuthordjh
    • CommentTimeJul 2nd 2015
     
    How long do thermal stores last, as compared to cylinders, and what causes them to fail?
    • CommentAuthorcjard
    • CommentTimeJul 2nd 2015
     
    Hi Ed

    Yes.. those were the figures from the SAP. A tad disappointing, but I've been assured they're conservative and the end house should perform better. The floor area in the SAP is an error - 350 sqm (more like 250 sqm) and the volume is 850 (seems arising from the previous floor error, plus assumption that the third storey is full height) and the heat demand is 24.6 so it looks more like 100kwh/sqm..

    From those figures it looks like a 11kw immersion would need to run constantly to keep up with the demand, right? hmm..
    • CommentAuthorcjard
    • CommentTimeJul 2nd 2015
     
    (no, wait.. 24.6mwh divided by 365, divided by 24, 3kw constant heat input to meet demand.. right? Better spec a 6kw immersion then!)
    • CommentAuthorcjard
    • CommentTimeJul 2nd 2015
     
    (no, wait again.. I presume it has to have enough reserve capacity to defy the increased demand on the coldest day, so maybe I should be looking at a combi boiler after all)
  8.  
    Just going down a similar route myself and have gone with a 1500lt Akvaterm store, mine was already ordered so I couldn't change my mind but a chap who used to fit them recomended Galu. Nothing wrong with Akvaterm but he said Galu were made by a former employee and are just as good but cheaper.

    Cheers, Paul

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