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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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    • CommentAuthoran02ew
    • CommentTimeMay 25th 2021
     
    Posted By: Dominic Cooney
    Posted By: an02ewextending the EWI down the face of the external wall is only equal to the Leca wing insulation when it extend beyond 600mm deep.


    This is very interesting to me, in situations where the existing foundations may not be 600mm deep but there is enough room around the (existing) building to create a perimeter wing.


    Interestingly the numbers stay very simular if the same 2 bags are used to in a different configuration stretched out from the build 1 bag deep (see pic) so the lenght of the insulated path is not all that counts?
      Capture leca 3.0.JPG
  1.  
    Hi An02ew, thanks for posting these!

    SAP10 uses a value of 0.32 W/mk for a wall-to-ground-floor junction. Any ideas why Therm is predicting so much worse performance for the LECA insulated junction? The SAP figure is supposed to be a conservative high default value.

    For context, if the wall was insulated to U=0.2W/m2K and was one storey high, each metre length of the wall would lose ~0.5W/mK. So Therm is predicting that the wall-floor LECA junction is losing nearly 4x as much heat as the whole wall itself does :shocked:

    The heat loss from the centre of a solid floor is almost all 'sideways' under the wall/floor junctions. To what extent does Therm allocate this heat loss to the junction, and how much of the heat loss is allocated to the general floor area?

    If you change the dimensions of the floor, does your junction heat loss figure change? Eg if the room was say only 2.5m wide wall-to-wall like a lean to bathroom, do you get the same junction heat loss results as you do for a 5m wide room?
    •  
      CommentAuthorfostertom
    • CommentTimeMay 25th 2021
     
    In Therm, every rectangle (incl the subsoil) which forms the perimeter of the diagram has to be told
    either what temp its outer edge will be (like inside face of wall is held at 21C),
    or that its face is adiabatic i.e. no heat passes thro that face.
    What did you assume for the under-edge of the subsoil rectangle, and how 'high' (or deep) is that rectangle below FL?
    • CommentAuthoran02ew
    • CommentTimeMay 25th 2021
     
    Posted By: WillInAberdeenSAP10 uses a value of 0.32 W/mk for a wall-to-ground-floor junction.


    Hi Will. Probably because SAP is modelling the heat loss through the juction and assumes an insulated floor, the Therm model is modelling the heat loss through both floor and junction. With an uninsulated floor the HL through the slab is so great that when deducted from the L2D it creates an negetive psi for the junction. so i removed the W/m2k for the slab from the sum resulting in a HL for the floor through the perimeter as a linear W/mk these condition are the same for the different senarios.

    This figure will change with different floor lenghts so building dims with get a more accurate result but i started with the standard 4M



    Posted By: fostertomWhat did you assume for the under-edge of the subsoil rectangle, and how 'high' (or deep) is that rectangle below FL?


    i used the EN standard 8m house but only draw 1/2 that 4m and 2.5x the ground out and down (20m out and 20m down) when the slab is drawn alone to get the u value it has a NIL boundry condition but when the wall and slab are put together the ground is added and tha condition is lost and become adiabatic.
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