Green Building Bible, Fourth Edition |
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Posted By: WillInAberdeenThat method is from BRE Information Paper 3/90, which like Nessie, many people talk about, but I have never managed to see myself...!
The assumptions are equally mysterious.
Legend has it that BRE did lots of finite element models of buildings with concrete slabs, with lots of different variations like shape, soil, water table, edges, etc. They plotted them all on a graph and drew a best-fit line through them, U=0.05+1.65(p/A)-0.6(P/A)Â² to give a very wet finger estimate.
I also assume that BRE would have included the resistance of the concrete, and the surface resistances, in their model, but your pic seems to show them being added on separately (double counting?).
IIUC their method refers to the P/A of the whole slab, however many people seem to look at individual rooms, giving very high or low P/A (like your example?)
Posted By: LFNot read fully as should be working but I think there is a lot of benefit in insulating around the slab/footings. The heat loss through building to 14 C soil in the middle of the slab is low so difference is low and driving force for heat loss. Ignore if not valid input.
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