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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentTimeNov 17th 2014
    • CommentTimeNov 17th 2014 edited
    The conductivity and diffusivity data in that paper is v useful, comparing different soils in one table.

    This paper is about the subsoil state under open ground surface under diurnal and annual variation cycles. That changes usefully when under
    a) an insulated ground cover, and
    b) a more or less constant temperature applied to the surface i.e. year-round indoor comfort temp.

    Under a), around the edge of the area covered, subsoil will be thermally coupled laterally with the surrounding uncovered subsoil and so will behave as described in the paper (though I'm v surprised to read that the depth at which annual temp variation dies out is as great as 10-15m - I understood more like 3m).

    But toward the middle of the covered area, the amplitude of the temp variation that gets through the surface insulated cover, is much smaller; therefore the depth at which annual temp stabilises is shallower. Under a very large covered area e.g. an unheated but insulated warehouse (if such exists), near its centre subsoil temp stability will happen at zero subsoil depth; approaching the perimeter that depth will increase.

    That is, under a) the temp at stabilised depth will still be same (annual average surface temp) as under open ground, but the depth at which stabilisation happens gets closer to the surface.

    Under b), same as last para, but the temp at that stabilised depth is also higher: under that same insulated warehouse, except in case b) it's heated, near its centre not only will subsoil temp stability happen at zero subsoil depth, but also its temp at that stabilised-temp depth will be near to the year-round maintained indoor air temp; approaching the perimeter that depth will increase and the temp at that stabilised-temp depth will converge with that under the surrounding uncovered ground.

    Subsoil at stabilised, or nearly stabilised temp, is what is useful as an annualised heat store (or look at it another way, as a massive stabiliser which holds floor temp steady whatever the weather or season). The question is, how deep into the subsoil do you have to go to access that stability, especially as it's only 'passively' useful if it's at zero depth i.e. right in contact with the floor slab.

    That in turn depends on a) the size and within that b) the 'path length to perimeter' of the building in question - what proportion of the slab displays 'centre' behaviour (stabilised subsoil temp at zero subsoil depth and high temp), and what proportion displays 'perimeter' behaviour (stabilised subsoil temp at increasing subsoil depth and lowering temp).

    The building's effective a) size and within that b) 'path length to perimeter' can be improved by downstand and/or 'wing' insulation; the smaller and/or narrower the building the greater the improvement for given downstand depth and/or 'wing' width.

    Don't dismiss what's possible even for this small, narrow Shetland example - model it.
    • CommentTimeNov 17th 2014
    Posted By: SteamyTeaThermal Inertia formula will tell you everything you need to know
    That kind of 'simple in principle' approach does seem to work for you - being deeply scientific you no doubt see and adjust somehow for the many complications of reality.

    But how about
    a) it's a 3D geometry problem, not 2D or even 1D - the devil is all in the detail of the corners relative to the straight walls, and
    b) it's a dynamic problem, not static or steady-state - response to diurnal and annual temp cycles is the essence of it.
    • CommentTimeNov 17th 2014
    Posted By: ringiI expect it would all come down to how much heating of the floor is done in summer. Assuming that the floor is heated all winter.
    You can assume the interior will be 'heated' in summer - we all have ways and means to 'naturally' maintain summer interior temp at much same comfort level as we do artificially in winter.
    • CommentAuthorEd Davies
    • CommentTimeNov 17th 2014
    Posted By: fostertomYou can assume the interior will be 'heated' in summer
    The air gets warm in this sort of house on a (the?) hot summer's day but the heat doesn't get stored in the floor very well at all in my limited experience. As soon as the weather cools off the interior temperature follows it down.
    • CommentAuthorringi
    • CommentTimeNov 17th 2014

    I mean the floor in summer will be heated to a higher average temperature then the outside air. (I am assuming off grid wind power that has no other useful usage.

    But heating the walls just behind the IWI may be a better usage of the power to help drying out.
    • CommentTimeNov 17th 2014
    Ah - you mean excessive floor heating in summer? The ex-turbine electricity doesn't have to flow to the floor in summer, can be sent elsewhere, or the turbine even shut down.
    Posted By: ringiheating the walls just behind the IWI may be a better usage of the power to help drying out
    Yes, thinking about that idea of yours.
    • CommentAuthormike7
    • CommentTimeNov 17th 2014 edited
    fostertom 6 hours ago edited quote
    "How would you go about simulating it mike?"

    I'll open another thread to answer. Poor Woo could probably do with more sound advice and less theorising here!
    • CommentAuthorWoo
    • CommentTimeNov 17th 2014
    Don't think I've gone away and left you all to debate heat-loss models : currently working abroad and not got as much time as I'd like to devote to all this.

    Actually quite familiar with building structures considering passive cooling methods (I work a lot in hot climates) and so while the level of tech is more than I'm used to, and the level of involvement is impressive, the general concepts that you're bringing up are comprehensible and definitely worth consideration.

    Really interested in the idea of using the turbine for electric UFH, we'd never really considered it. Also, re. IWI, has anyone any experience with the 'Matilda's Blanket' system? I can't shift the idea that it's just a slimline stud wall but maybe I'm being unfair...

    FT, how does one go about getting this kind of modelling done? This is way beyond the scope of things like building surveys. On the other hand, Orkney is quite into renewables etc. and perhaps there are outfits that can offer that service (anyone?) - it will be a question of hunting once we're there.

    Triassic, I think you've just provided me with my bedtime reading for the next week with that link, thanks.

    Gareth, no worries about the delicacy or otherwise of the question. If only I had an answer ... Without putting figures on it - because I can't - the quick reply is that the needed budget will be available. Just not necessarily all in one chunk. There are actually two other buildings on the property which we want to do up so anything we buy/set up as an interim measure for the main one will be used again for those places subsequently. Basically, we want a system that works and we're willing to put in the graft to pay for it / do it.
    • CommentTimeNov 17th 2014
    Had not heard of Matilda's Blanket, but apart from it doing nothing to separate floors and ceilings from potential air leakage from outside, it seems a good idea. Does take up over 3 inches on each wall installed though, and not actually sure if those electrical socket extensions are permitted under Part P, and after a quick look through the FAQ, I cannot see a U-Value, bit remiss of them that is.

    Posted By: mike7I'll open another thread to answer
    Good Idea
    • CommentAuthorWoo
    • CommentTimeNov 17th 2014 edited
    ST, it seems to me that they're missing quite a lot of info from their FAQs... :smile:

    But it looks like quite a good system, if it were installed after a building had been rendered more or less airtight.
    • CommentTimeNov 17th 2014 edited
    I would wonder how many they had actually installed.
    May be worth given them a call though.

    Found the U-Value, it is 0.28
    I came across this site from some Irish renovation builders that has lots of advice that is probably worth a read Woo.

    • CommentAuthorWoo
    • CommentTimeApr 4th 2015
    So. Orkney is lovely, and things are happening (in the periods where we are back from abroad).

    It has been interesting to live in it and find out what it's like through the winter. What I'd like to talk about today is damp :)

    When we bought the place, there were obviously patches of very limited damp around (small areas with some points of mildew ; blown interior cement render on the chimney breast and under the window in the kitchen). Notably in the window recesses, which was hardly surprising because the window frames are so rotten and the external cills mostly absent, but also a little bit in a couple of ceiling corners and on walls. Despite having had the wettest winter in 20 years, and having lost a fair few joints from between the roof tiles, damp inside the house hasn't got noticeably worse. Hurrah.

    We have started by completely repointing the roof. The external chimney breasts still need doing but the tops have them have been capped off : the amount of water on the internal chimney breasts has reduced to almost nothing. We have stripped the existing internal wall insulation and have found very little evidence of damp on the wall behind - what there is seems to be connected to cracks in the external pointing or from water ingress via the roof.
    We have a whole variety of floors, ranging from flagstones laid directly onto sand/earth, through concrete poured on top of similar flags, to concrete slab floors with a plastic sheet on top and then chipboard-type boards on top of that, some with a bit of insulation board on top of that. Where we've taken the boards and the plastic off, the concrete surface has been slightly damp or moist, but not pooling with water and without any visible sign of the moisture moving out towards the walls particularly. The kind of moisture that was dried out after one evening of the gas heater being in the room. Where we have taken the floors back to soil already, the soil was... like soil. Not bone dry dust, but not damp enough to cling to your hand either : it is pretty free-draining with a lot of sand in it. The only wetter spots have been near the base of the external wall at one point where the outside path slopes towards the house instead of away from it (that's being sorted too).

    We plan to put in wet UFH throughout, in a concrete slab floor. We don't have the foundation depth to dig out for a limecrete solution and brutally speaking, we don't have the cash for the newer systems (Ty-Mawr's Sublime, e.g.) that don't require quite so much depth. The floor would therefore be of a classic construction : DPM, insulation, pipes and screed, concrete.

    The plan for the walls is some kind of breathable internal insulation : haven't decided which, yet. What could you all advise in terms of ways to help make sure that we don't have a problem with damp displaced to the base of the walls? Air "bricks" (the walls are solid/rubble construction) or vents at the base of walls?
    • CommentAuthorTriassic
    • CommentTimeApr 5th 2015 edited
    Your walls and existing floor construction sound similar to our 1770s house. We dug out our floors and replaced them all with insulation and concrete with UFH. We used mesh reinforcement and simply zip tied the plastic UFH pipe to the mesh and then poured the concrete and floated it off, job done!

    Regarding the rubble walls, we found that lime rendering the outside walls and lime plaster inside cured any damp. I also feel the UFH helps keep the base of the wall warm and helps stop damp patches forming. We don't have air bricks, yet if we knock a hole in a wall and place a candle near the hole you can see the flame flicker on a windy day, so clearly the walls are not completely air tight and air is moving inside the rubble as was intended.

    Just one other thing, you need a small amount of air movement up the sealed off chimneys to keep them dry, so you should have a vent top and bottom.
    • CommentAuthorWoo
    • CommentTimeApr 27th 2015
    That's reassuring, Triassic. We are definitely going to lime-plaster inside - outside is still under discussion - and we had the same feeling about the effects of the UFH keeping the damp out. It's important for us because we'll probably be absent for regular periods of time.
    Getting quite excited now...
    We have similar construction to you in our listed farmhouse going back to 1650. Being on a hilltop we also have the similar problem to you of wind and horizontal rain. Our solution has been to have no opening windows and have individual (7 of) Partel heat recovery MHVR in all wet rooms and kitchens. We have used 4-16-4-16-4 argon filled 3g glass units with self cleaning on outer pane and thermal on the inside pane. The 3g units are secured direct into the stone mullions using soudal flexifoam and lead roll to protect the 3g seal from reacting to the foam. The difference has been amazing not only in elimination of draughts and heating requirement but also the increase in light by having no window frames. No issues with condensation or damp as the walls are allowed to breath with lime mortar. We have permission to install UFH which originally was going to be a wet system but now looking to go electric due to the reduced heating demand and installation of 30kw PV.
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