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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorKieranf
    • CommentTimeJan 5th 2020
     
    Hello all,
    Hoping you kind folks could answer a few of my queries regarding my proposed hot water/heating system.
    I have bought a pile of stones in a field in Sicily which once upon a time ago was a house, I have one room habitable and a second one soon to be finished. In the next few weeks I intend to install a hot water and space heating system. It is a temporary set up until I finish more of the house, so temporary meaning several years.
    Plan as follows:
    Morso Squirrel wood burner (4kw) with 8000btu back boiler in one room for space heating and to heat 300lt direct vented thermal store with combination F&E tank located in neighbouring room on gravity circuit. 1.5kw Heat leak rad in room with the TS.
    Additional solar heating to be added next year.
    Wood burner will run 24/7 in the winter.

    Questions:
    1. How/where to vent the primary circuit? Outside? Direct to the f&e tank or will the TS self vent to the f&e tank in the unlikely event of boiling? Does it require a T&P valve or tundish?
    2. I presume 8000btu is roughly 2.5kw to water is this correct? I want to be able to drive the wood burner hard often, if the TS has reached temp will the little Morso be able to get the heat leak rad hot? Would I be better off with a smaller heat leak rad and space heating the second room with rads on their own gravity circuit?

    The aim is create a simple gravity system to space heat two rooms and provide hot water.

    Also, we are off grid, only solar for power.

    Many thanks in advance.

    Kieran
      DA342AA3-1667-4FDC-9B89-FEACBE0EB28F.jpeg
    • CommentAuthorKieranf
    • CommentTimeJan 5th 2020
     
    Rotated image
      44853F32-2EAD-4F8A-9FEA-863156B98ACF.jpeg
    • CommentAuthorKieranf
    • CommentTimeJan 5th 2020
     
    The thermal store
      7014348E-C24B-4279-BABF-3F251A72512E.jpeg
  1.  
    Kieran, have a chat with Tom at Newark, and he'll explain about the pipes supplied with his unit, that link the F&E and the TS (one from top of TS to top of F&E, and one from base of F&E to base of TS). That deals with the venting side, though you need an overflow from the F&E (which could be HOT!!) and a cold feed to it.

    You'll be quite a while burning very hard to heat the 300 litres from scratch, but I guess you'll normally be taking it from say 40oC to say 80oC, which would still be 6 hours, with no other heat draw off. Sounds like you're up for that, and a fairly constant "feeding" of the stove. Remember, the rated output is often what is achieved in a lab under controlled conditions, so may not achieve a continuous 2.3kW to water.

    Without knowing anything about how you're planning to insulate the house, and hence the heat loss / space heat requirement, I'd have thought a stove that's a bit larger, say 2kW to room, 6 or 8kW to water might be more manageable, to avoid tending it all day?

    I would personally take a couple of tall/vertical gravity rads off the TS (one for each room). That means you can use the TS as intended, ie. a store of energy to be used when you want it, rather than having to run the stove to get heat into the directly linked gravity rads. I heat my 220m2 house with one such gravity rad in the hall, so I know it works. Just add 2 more connxns top and bottom (one for each rad), in say 22mm, or whatever the local standard is for roughly 1 inch.

    I'd also keep the heat leak rad to the 20% output level (or even a bit less), so that's a 400-500W rad for the Morso you've suggested. I almost feel it's unnecessary, comparing the mini output versus the relatively large mass of water, which is open, but I'm not 100% certain about uk thermosyphon regs, never mind Scilian regs (if they bother enforcing?).

    Last point, if it's not too late, do ask this forum about insulating your house, as that ought really to be the starting point, which leads to a determination of heating system sizing. Imagine being a slave to running your stove all day every day, versus a well insulated house that only needs a few hours firing each evening, not to mention a very comfortable room temperature summer and winter...insulation and thermal mass???

    Yours jealously, GP.
    • CommentAuthorKieranf
    • CommentTimeJan 6th 2020
     
    Many thanks green paddy for such a detailed response. Funnily enough Italked to mark at Newark (before I read your post) and he did explain the internal pipe work for the thermal store. I have read here somewhere that it is not advisable to use the internal expansion and fill pipe work for venting purposes, so if anybody else could chime in on this point it would be appreciated. Mark suggested that he would expect to see the primary pipe work extended and vented into the top of the f&e tank, which is how I had planned to install the vent.

    I was starting to think on the same lines as your suggestion of using separate gravity fed rads, thank you for your real life observations.
    Tell me GP, do your gravity rads have oversized tappings? Or are they standard half inch?

    In terms of insulation, it is a typical Sicilian farm house built on solid bedrock with 600mm thick random rubble walls. We are trying to use only natural traditional materials, all lime render and a coppo tiled roof. We have used 32mm thick sarking boards as insulation and will decide after this first winter wether to add sheep’s wool between the rafters internally and lathe and plaster. The coldest it gets here is 0 degrees at night and that is not the norm usually around 4-5 for a few months a year.

    Kieran
  2.  
    Rads are just standard with 15mm connections, but over sized for the output (get about half the output rated).

    The top gets nice and hot (exactly as the top temp in the TS), but the rad base is quite cool (1800mm high vert rad). Use a standard TRV to control. The fact that the water moves so slowly through it, and the exitting water is cool, is great for stratification, and also provides a really cold base for solar thermal to be chucked in, even in winter at say 40oC. Not unusual to have 75oC at top, and 35oC at the base, in the morning, after a night's rad heat draw.

    I (and I'm sure a bus load of others here), will urge you do more on the insulation front. The roof must surely be a no-brainer, if even for the summer sun (not personally familiar with that concept here in the Highlands of Scotland). You've only one chance to do insulation and air tightness.
    •  
      CommentAuthordjh
    • CommentTimeJan 6th 2020
     
    Posted By: KieranfMark suggested that he would expect to see the primary pipe work extended and vented into the top of the f&e tank, which is how I had planned to install the vent.

    The pipework can be vented into the header tank, but you still need an overflow from the header tank. In the UK the overflow needs to be taken outside to a visible spout, or else through a visible tundish inside. You can easily get an overflow if the ballcock valve in the header tank goes wrong (don't ask me how I know!) or in the worst case you might get boiling water expanding or venting into the header tank and then overflowing.

    What GP said about insulation. :)
    • CommentAuthorKieranf
    • CommentTimeJan 6th 2020
     
    Thanks GP and Djh,

    Last question about the vent pipe, after the 28mm primary flow has been ‘T’d into the top of the TS does it need to be reduced down to 22 for the last run to to f&e tank?

    Kieran
  3.  
    Not sure it would matter. There'll be no relevant back pressure diff between a 22 and 28 over that distance. Do whatever's easier. Check how the vent will pass through the lid of the F&E - question for Tom (NCC).
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