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General: Passive House with no tapes/membranes, no ducts, no back up heating system.

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    • CommentAuthorsinnerboy
    • CommentTimeJul 27th 2011
     
  2.  
    Posted By: fostertom(and inner plasterboard too) carried on the flatstrap noggings


    does that mean you have to put more flatstrap on the underneath of the rafters when you come to line the inside?
    •  
      CommentAuthorfostertom
    • CommentTimeAug 9th 2011
     
    Yes, but only where you'd have needed a timber noggin conventionally. There's still plenty of circumstances where pbd edges can span unsupported - not trying to make the pbd airtight, unlike the outer OSB.
  4.  
    so you make it airtight with the skim coat?
    •  
      CommentAuthorfostertom
    • CommentTimeAug 9th 2011 edited
     
    No, the glued OSB outboard of the studs/rafters is the airtight layer (no tapes/membranes, as per topic title). Then the plasterboard/skim doesn't need to be airtight (nor vapour tight, as it's breathing construction) - puncture the pbd for electrics etc as much as you like. All very relaxed.

    Note that this as breathing construction only works if about same again insulation (e.g. EWI-like EPS) lies outboard of the OSB - but that's a rule of thumb you should check to your satisfaction.
    • CommentAuthordjh
    • CommentTimeAug 10th 2011
     
    Posted By: fostertompuncture the pbd for electrics etc as much as you like.

    I thought that the rule of thumb for breathing construction was that the inner barrier should be five times less permeable than the outer barrier?

    I think that what you mean is that it's a 'warm' construction, or at least 'semi-warm'.
  7.  
    what happens where the OSB and EWI (EPS?) meets the ground Tom?
  8.  
    Viking, the first drawing you posted - just to make sure I understand - comprises from top to bottom:

    internal floor with UFH pipes buried at the lowest part
    100mm polystyrene
    Solar slab with a dpm in the middle and heating pipes running through the lowest part
    300mm polystyrene
    foundations
    heat exchanger below ground (to dump excess heat and to raise temperature of earth to reduce loss from solar slab). Is this backfilled with earth?
    •  
      CommentAuthorfostertom
    • CommentTimeAug 10th 2011
     
    Posted By: djhI thought that the rule of thumb for breathing construction was that the inner barrier should be five times less permeable than the outer barrier?
    That's right, but according to my 'what-ifs' with a Euler diagram program, that 'lnner' can in fact be up to half way thro the insulation sandwich i.e. the OSB outboard of the studs/rafters can be the airtight barrier plus modest vapour resister; everything inboard of it can be part of the interior as it were, and the more or less unbroken EPS going on outboard of the OSB is about 5x less resistant than the OSB. However, everyone check that prescription to own satisfaction.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 10th 2011
     
    Posted By: spoonandforkwhat happens where the OSB and EWI (EPS?) meets the ground Tom?
    Many ways of detailing that. Current project uses an internal loadbearing frame and the walls are effectively suspended from first floor, so don't need support at ground level, so don't really touch wet or cold ground and can unite with the slab insulation.
  11.  
    Posted By: spoonandforkViking, the first drawing you posted - just to make sure I understand - comprises from top to bottom:

    internal floor with UFH pipes buried at the lowest part
    100mm polystyrene
    Solar slab with a dpm in the middle and heating pipes running through the lowest part
    300mm polystyrene
    foundations
    heat exchanger below ground (to dump excess heat and to raise temperature of earth to reduce loss from solar slab). Is this backfilled with earth?
    That's correct, but since we found a cheaper source of collector absorbers we're reducing the size of the Solar Slabs and increasing the Solar Collectors area to make it more responsive. The Solar Slab is used as a buffer! The heat exchanger in the ground is back-filled with earth!
      UTES and Stone Solar Battery.jpg
  12.  
    Posted By: Viking HouseThe Solar Slab is used as a buffer! The heat exchanger in the ground is back-filled with earth!


    I understand the solar slab stores energy (your original design was for it to store enough for 100 days' heating). But can you draw the heat out as required to the UFH in the upper most slab? I mean, can you increase the flow rate in the pipes and this will heat the upper slab and use up the store more quickly? Or is it just passively giving off a constant background heat that can't be altered?

    Tom, what heat source is going in your project pictured above?
  13.  
    also, do you have any more info / links to using the walls of a building as an equivalent to the solar slab described above?
  14.  
    Hi Spoon, I'd planned to let the heat escape from the solar slab passively into the house to avoid over complicating the plumbing. The calculations show that a 12m2 solar array alone will deliver enough energy to heat the Passive houses in Oct, Nov and Feb, Mar. When I subtract the heat loss to the ground I'm short 200kW in December and 50kW in January. In reality this is all I need to store so if the Solar Slab is heated to just 30 degrees it should be more than sufficient! The warmer the Solar Slab is the more heat it will lose!
  15.  
    Posted By: spoonandfork Do you have any info on using the walls of a building as an equivalent to the solar slab described above?
    Using wall pipes behind 100mm external insulation to deliver low grade heat at temperatures between 14-18 degrees; 14 degree water makes the wall act like it had 200mm of insulation and 18 degree water makes the wall act like it had 400mm of insulation.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 12th 2011 edited
     
    Unh? 14oC water is actually cooling the interior! It will keep the extg wall/EWI interface a lot cooler than if there was no such cooling input at the interface.

    If the idea is to pump quite a lot of 'free' heat into that interface as a substitute for adequate EWI thickness, well what happens in Dec/Jan when the free heat is extremely scarce? Your backup fuel burner will be working flat out!
  17.  
    My figures come from this document showing the effect of the different water temperatures pumped through a wall! I know, before you say it, that the document shows the pipe in the middle of an ICF wall, but its interesting none-the-less to see the effect of the different water temperatures.
    The 16-18 degree water pumped through the pipes on non sunny winter days will come from the heat store beneath the house, where excess summer heat is dumped all summer long.
      Temperature Barrier.jpg
    •  
      CommentAuthorfostertom
    • CommentTimeAug 12th 2011 edited
     
    I think it's because the 'interface' where the heat's being input is half way towards the outside of the insulation sandwich, whereas inputting it at the extg wall/EWI interface is near enough at the inside, insulation-wise. They're maintaining the mid part of the sandwich at higher temp than it wd be without heat input there - throwing presumably 'free' heat away outward in lieu of insulation.

    But applied to the extg wall/EWI interface, if the input temp is any less than desired internal temp, that nearly-interior part of the sandwich is being maintained at lower temp than it wd be without that cooling input there. That does mean less outward loss from the interface, but also means the interior is cooled below desired temp, so extra internal input from rads etc has to be applied and you're back to square one.

    Best thing is to input heat at the extg wall/EWI interface, 1K or so higher than desired internal temp - say 19C flow, 17C return =18C mean, for 17C internal temp.
  19.  
    Posted By: Viking HouseThe 16-18 degree water pumped through the pipes on non sunny winter days will come from the heat store beneath the house, where excess summer heat is dumped all summer long


    so you're able to pull warm water from underneath the ground when you like, so it's not passive like the solar slab?

    *

    Posted By: fostertomBest thing is to input heat at the extg wall/EWI interface


    (i assume extg = external)

    why's that better than lower temperatures closer to the exterior in the wall?
  20.  
    Posted By: spoonandfork So you're able to pull warm water from underneath the ground when you like, so it's not passive like the solar slab?
    I call this the "Heatloss Barrier" construction method, with just 100mm of insulation in the external walls and roof and wrapping an average house with 1km of Under Floor heating pipe costing €500, you can build or renovate a house to performs like a Passive House for a fraction of the cost.
    Because airtightness levels, window U-values and cold bridging details are less critical it seems to be an excellent solution for renovation projects.

    So the "Heatloss Barrier" method is not "Passive" like a Passive House with a Solar Slab wrapped in 300mm of insulation, but with just 100mm of insulation in the walls/floor/roof along with water pipes in the walls and roof, it exploits Low Grade heat storage and usage methods to potentially reach similar energy usage levels, but it is more active in the use of pumps and controls etc.
    • CommentAuthordjh
    • CommentTimeAug 15th 2011
     
    Posted By: spoonandfork
    Posted By: fostertomBest thing is to input heat at the extg wall/EWI interface


    (i assume extg = external)

    why's that better than lower temperatures closer to the exterior in the wall?

    I was curious, so I wrote a simplistic spreadsheet, which I hope is attached.

    It has, outside-to-inside, insulation, pipes, insulation, blocks. By varying the thicknesses and conductivities you can simulate heated pipes on the inside of EWI and heated pipes on the outside of EWI as well as heated pipes in the middle of the EWI.


    "You are not allowed to upload (heat-loss.ods) the requested file type: application/vnd.oasis.opendocument.spreadsheet"
  22.  
    good stuff, can you process it via google docs and try again?
    • CommentAuthordjh
    • CommentTimeAug 16th 2011
     
    Posted By: spoonandforkgood stuff, can you process it via google docs and try again?

    Sorry, that would require me to create an account, login etc. I don't understand why .ods is blocked - does it get used a lot for pr0n files? :shamed:
    •  
      CommentAuthorSteamyTea
    • CommentTimeAug 16th 2011
     
    You could just change the extension to a .txt or .jpg, post it up with a note to change it back to .ods
    •  
      CommentAuthorfostertom
    • CommentTimeAug 17th 2011 edited
     
    Posted By: spoonandforki assume extg = external
    extg = existing - sorry for 'trade' abbreviation! So I'm saying heat input at external face of existing wall, with EWI applied outboard of that.
    Posted By: spoonandforkwhy's that better than lower temperatures closer to the exterior in the wall?
    To answer that, determine the temp gradient thro the wall thickness, from interior, thro the existing wall, thro the EWI, to exterior.

    Wherever in that sandwich you place your heat input layer, if the heat is input hotter than that point wd naturally be (on the gradient you've just determined), then it will have the effect of warming the interior (as well as warming the external world as a substitute for adequate insulation outboard of the heat input layer).

    If the heat is input colder than that point wd naturally be , then it will have the effect of cooling the interior (as well as still warming the external world as a substitute for adequate insulation outboard of the heat input layer).

    So if the heat is input hotter than that point wd naturally be, then the wall can act as a significant (or the sole) source of heating to the interior. Whereas if the heat is input colder than that point wd naturally be, then it's actually adding to the heat load that will have to be provided to the interior by other means.

    NB when we say 'hotter than', it need be only about 1K hotter, in a superinsulated airtighted building.
  26.  
    Agree with Tom.

    Specifically, if the heat input layer is put at the interface of the super-structure and external insulation then it will effectively be at the same temperature as the internal air temperature (assuming constant internal temperature). In this case, the heat needs to be applied at, or slightly above, internal room temperature. Anything lower will make it worse than having no heat input.
    •  
      CommentAuthorSteamyTea
    • CommentTimeAug 17th 2011
     
    Or it is the scalar field where:

    Steady state is equal to:
    T=T(x,y,z)

    Dynamic state is equal to:
    ΔT=δT/δx,δT/δy,δT/δz

    Or think of it as the more it has to spread out the cooler it gets as governed by:
    PV/T=C but in this case P and V become the wall thickness and area (the x,y,z)

    Use thermal conductivity to establish the temperature gradient of your wall.
    λ = − Q/(∂T/∂n)

    and has the units W m−1 K−1

    Purely out of interest (and I think Mike George may be interested too), has anyone does a condensation analysis on this idea?
    •  
      CommentAuthorfostertom
    • CommentTimeAug 17th 2011 edited
     
    Posted By: MarkBennettif the heat input layer is put at the interface of the super-structure and external insulation then it will effectively be at the same temperature as the internal air temperature
    Not quite - about a 1K drop thro a 500 stone wall, assuming 200 of EPS outboard (with 16K drop), thus 17K inside to outside difference.

    So for 17C inside air temp, inside wall face needs to be 18C, mean temp at heat input layer 19C, so 20C flow/18C return temp to your solar collector. Or figures of that order.

    Note, that's an incredibly low temp to be running your solar collector, which brings unheard-of solar collection/conversion efficiency and also goes a long way to minimising the simultaneous heat loss from solar collector back to external scenery, which usually knocks cold-weather (Dec/Jan) collection on the head.
  29.  
    I did see one comment on a forum about using the new breed of vacuum flat panel solar collectors as EWI. You get the (near) vacuum as a highly efficient insulator, all heat collected at the rear surface, i.e. near the superstructure and as much solar hot water as you can make use of. The panels are also close to vertical so maximise winter collection.

    Connect the cavities of the panels together so that any air leakage can easily be pumped back out again. Sounds an expensive but interesting idea, which is not too dissimilar from what is being proposed here.

    Found a paper during a quick search: http://www.ibpsa.org/proceedings/BS2009/BS09_0805_810.pdf
    •  
      CommentAuthorfostertom
    • CommentTimeAug 17th 2011
     
    Vacuum helps with loss by conduction/convection to cold outside air but radiation loss to (often even colder) solid objects/sky is unaffected by vacuum. Low frequency re-radiation loss can be greatly reduced by multiple front glazing with selective coatings that are as transparent as poss to high frequency incoming radiation - alternatively multiple low-iron glass is all-round more transparent but less selective wavelength-wise.

    Remains to be seen which approach - vacuum (incl tubes) and/or multiple glass - is better on balance for collection at ultra-low flow/return temp in mid winter - but for sure vacuum is much more expensive, whereas built-in-situ methods such as Viking illustrated plus patent glazing in front can be cheap, maximised-area, and can be part-financed from the roof-covering budget.

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