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Housing - New Build: Using floors as thermal mass

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    • CommentAuthorJohan
    • CommentTimeSep 27th 2007 edited
     
    Posted By: Paul in Montreal
    Posted By: JohanNo, they are not using multifoil insulation. They use an Al/polyester based vapour barrier (see page 37 in the report), is that what you mean?


    I was just yanking the chain of the multifoilers :wink:
    Paul in Montreal.
    Ok, sorry I didn't get it! :cry: I find the whole multifoil discussion a bit blasé... :shocked:
    •  
      CommentAuthorfostertom
    • CommentTimeSep 27th 2007
     
    You know what they say - any yank is a good yank.
  3.  
    Paul,
    Thanks for the digging on ESP-r. Good to know that the bug was fixed.

    Mark
    •  
      CommentAuthorfostertom
    • CommentTimeSep 27th 2007 edited
     
    When American troops arrived in London 1943, they brought to their English girlfriends not only wondrous nylons, but bras with nice fastening hooks, instead of awkward ties. They were advertised: Easily undone by a smart yank. After protest, this was amended to: Easily undone by a quick jerk.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 12th 2007
     
    A thought about wide skirts or 'umbrellas' of insulation around the building, laid horizontally a bit below garden surface level:
    The soil above the skirt, cut off from that mass of year-round stable-temperature soil a metre or two down, will fluctuate much more than usual, in temp. It will bake in summer and freeze soild in winter. Poor plants. Any pointers as to what kinds of plants would tolerate that? Presumably shallow-rooted ones wouldn't mind, as the top 6" of soil probably fluctuates like that anyway. Shrubs and trees, especially if existing, could have the insulation fitted around their stems, so their roots would actually be extra-warm - however in such areas, you'd have to leave out the waterproof membrane that's part of the formula, intended to eliminate downward water percolation that could carry the stored heat away - the soil shd be dry - in fact forget the whole idea if there's moving ground water, of even a water table, within 2-3m of the surface under the area of the 'umbrella'.
  6.  
    I wonder how shallow groundwater would need to be before it has a negative effect? Do you think within 2m? I have also tried to find data about groundwater conditions [depth] across the UK. Anyone know of where this can be found?
    • CommentAuthortony
    • CommentTimeOct 12th 2007
     
    Ground water is only a problem if it is running and then running water under a house -- well problems all of its own.

    Rising and falling levels may not necessarily be a problem either and water has good ability to store heat.


    Not all bad.
  8.  
    Sorry, I should have said running groundwater, so how common is this in the UK?
    •  
      CommentAuthornigel
    • CommentTimeOct 12th 2007 edited
     
    Posted By: tonyand water has good ability to store heat


    Water is actually a good conductor of heat. It conducts heat about 3 times as well as brick for example.
    A high water table will significantly increase heat losses through a ground floor slab regardless of whether it is running or not.
    • CommentAuthortony
    • CommentTimeOct 12th 2007
     
    Nigel, Where is the heat going and how fast? I am not sure that I agree with you notion that more heat will be lost through the ground floor slab if there is wet underneath it.

    In my view the heat losses through a ground floor slab in steady state are very considerably lower than almost all the models and theories predict.
    •  
      CommentAuthornigel
    • CommentTimeOct 12th 2007
     
    Conduction is the process of heat transfer through matter. Therefore the heat transfer rate will depend on the conductivity of the material. The unit SI: W/(m*K) and as watts are joules per second this measures heat transfer over time.
    As water conducts better than dry sand for example heat losses will higher as the heat is transferred into the surrounding ground.

    I know that heat losses through floors are lower due to the high level of thermal mass in the ground, my point is that regardless of this heat losses will be greater where the ground is wet.
    • CommentAuthorMike George
    • CommentTimeOct 12th 2007 edited
     
    Posted By: nigelConduction is the process of heat transfer through matter. Therefore the heat transfer rate will depend on the conductivity of the material. The unit SI: W/(m*K) and as watts are joules per second this measures heat transfer over time.
    As water conducts better than dry sand for example heat losses will higher as the heat is transferred into the surrounding ground.


    There also has to be a temperture difference. What is the external temperature and where is it located for a ground bearing slab? Is it so far away that by the time heat energy gets close to the external environment the temperature differential has reversed and it is on its way back? I think groundwater movement is a consideration for these reasons.

    Steady state u-values cannot accurately predict the many heat flow paths present in any solid floor, and are therefore only good for approximate predictions. In order to be anywhere near accurate, we need to consider heat loss dynamically.

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