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    A manufacturer (who will remain nameless) incorrectly manufactured or thermal store. We only found out once it was in the attic, and it is a long way to go to change it, so we are looking at options.

    The idea was that we would have a coil in the top section of the store for a small indirect gas boiler to top up the system when needed.

    They put the coil in the bottom section and left out the dhw preheat. We can use the gas coil for a preheat, but we are wondering what to do for the gas.

    The company have suggested connecting the boiler directly (it's an unpressurized store) with a filter, though the boiler manufacturer says it should only be connected indirectly.

    Then we can either draw the cool incoming boiler water from the bottom of the top section or the top of the bottom section (below the baffle). I'm leaning towards the latter as the cooler water should mean that the boiler should condense better.

    Any thoughts?
    • CommentAuthorCWatters
    • CommentTimeJun 21st 2017
    If the boiler is connected directly will you be able to dose it with corrosion inhibitor or does that water eventually come out of the taps (no coil/heat exchanger for DHW)?
    No, all the store water stays in the store, the UFH, or the back boiler coil. The potable water is heated indirectly.
    • CommentAuthorCWatters
    • CommentTimeJun 21st 2017
    Check why they said the boiler must be indirect. It's possible the boiler is expecting to be used on a sealed system and won't operate if it detects the pressure is too low/vented.
    Good point. I previously asked the technical department, but they couldn't give a reason. I will try again.
    • CommentAuthorGreenPaddy
    • CommentTimeJun 21st 2017 edited
    Can you post an drawing of the TS, with all coils and connections? I've linked a boiler into an open vented TS before, with the F&E tank on the second storey, not even in the attic, so if your boiler is on the grnd flr, it should be able to run.
    Seems like you need to pull a number of issues together, to get the overall design right, taking your other post into account re. which gas boiler. One bit at a time doesn't make it easy.
    List and detail the fixed things...therm store, log boiler, solar thermal, relative positions etc, and also list the as yet unfixed requirements. ...automated heat source, how to preheat DHW.
    Keen to help, but need the full picture.
    Thanks @greenpaddy, I'll set out as far as I can.

    On the second floor we have: TS, gas boiler. On ground floor we have stove with back boiler.

    TS has two sections. Top 400, bottom 1000. Connections are dhw preheat and heat, solar thermal coils x 2, boiler / ufh x 6, immersion x 2.

    The 'available' connections are therefore the immersion points (one in the top section, one in the bottom), and one of the stove/ufh points (depending on whether top, middle, or bottom are best for siphoning from the stove).
    If you are not going to use electricity could you get an indirect coil to fit in the top immersion point which could then be connected to the gas boiler to give you the top up to the upper part of the TS s per your original plan
    Our gas boiler is connected directly to the thermal store, we've had it fitted for 6 years now without any problems.
    • CommentTimeJun 22nd 2017
    Could you use a plate heat exchanger between the TS and the Boiler?
    Ok, I spoke with the boiler manufacturers today. The boiler I originally intended was a system boiler. This has to be in a pressurised circuit of 1.5 bar, so it sounds like that is not suitable. However, they also do an open vented boiler that sounds like it would be suitable.

    It also occurred to me that it might be possible to branch out some of the existing ports. Ie the cold water for the UFH could be branched to also be the draw point for the boiler. That would give us more flexibility for the boiler.
    @Peter, you're probably right that we could get a coil, but judging by the size of the coil that is there in the wrong place, any coil that would fit in the immersion port would be easy too small to be efficient at heat transfer.
    @steamy, yes, that is certainly possible, but presumably there is an inevitable loss of efficiency with an external heat exchange.
    • CommentAuthorGreenPaddy
    • CommentTimeJun 22nd 2017
    So here's what I think I understand, though a drawing from you would be simpler;

    1. One TS with a baffle, separating 400l top, 1000l below
    2. DHW coil inlet at base, outlet just below baffle
    3. Second DHW coil inlet just above baffle, outlet near top
    4. 2 solar coils, presumably in the lower part of the TS, ie both below the baffle, probably close to bottom
    5. connxns 2 near top, 2 close to the baffle (above/below??), 2 towards the bottom
    6. assume you have also a connxn at the very top dome to feed the F&E tank, and a return connxn near the base?

    I'm still unclear what the 1000 l at the base would be used for, and I what I mean by that is where are you getting all the energy from to heat 1400l? I don't think your solar thermal (unless you've got a large area of panels) will bring it to a particularly high temp. And if it's only making it 25/30oC, then ok it's of some use, but I question the cost/value equation. You'll still need to have additional heat input to make it useful DHW.

    OK, so what would I suggest, given my assumptions, and not a full picture by any means, so this is kind of dangerous territory;

    - connect the two DHW coils in series
    - LBS flow at top conxn1
    - gas boiler return at top conxn2
    - UFH flow at mid conxn1 above baffle (important!!)
    - LBS return at mid conxn2
    - UFH return at bott conxn1
    - gas boiler return at bott conxn2
    - forget about solar thermal and go for solar PV with immersion feed device to the top immersion and bottom if it can function selectively, unless you're planning on say 8 or 10m2 of ST, so you'll really boost the DHW in summer, and get decent prewarm rest of year, even some heating input.
    - gas boiler should be a conventional type, no need for a system boiler as you've only one heat absorber. Can it be mounted on the ground floor, so it has some better head. If the F&E tank is in the roof space, and biler on grnd floor, you're getting close to a bar, so most boilers will prob function ok...little, cheap, conventional.
    - don't worry about external plate HX's efficiency. They are more efficient than coils, tighter pinch point, but you'd need an additional pump to circ thru it. Don't think you actually need one, but you haven't got a design yet!

    There's a load still to understand on this, if you want it to work, never mind be efficient. If you want to whisper me, I'll give you my phone no. and we can discuss properly - free offer, not soliciting work :cry: but designing by internet doesn't work too well. Then you can stick my suggestion back on here, and get it disected:devil:
    • CommentAuthorGreenPaddy
    • CommentTimeJun 22nd 2017
    COP - I've just seen your other thread (might consider killing one) and you mentioned you won't use the LBS too much. That kind of backs up the question about what the 1400l is for. Indeed, why a LBS as opposed to a regular stove (unless it's purely to limit heat-to-room output)?
    Please don't take this as ill-intentioned criticism, I am keen to unpick this, and get a good answer for you, as this will be the heart of your home, and hell if it doesn't work well.
    Thanks @greenpaddy, I'll send you a PM, and post the results of any discussion here.
    Here is a working schematic from what I understand from my discussion with @greenpaddy. I may not have correctly reflected all the points correctly, for which I apologise. Any comments are welcome.
      20170630 Plumbing Schematic.jpg
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