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General: Dynamic Insulation - same principle as Airflow Windows

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      CommentAuthorfostertom
    • CommentTimeAug 15th 2007 edited
     
    Continuing from Airflow Windows http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=538&page=1#Item_9

    Posted By: biffvernonnegative U-value, i.e. they gain more heat than they lose

    Indeed - the principle can be applied to whole walls, slight internal vacuum drawing air through the pores of the wall and bringing all the escaping heat back in with it.

    Here's the reference I was looking for: http://www.forevergreen.org.uk/articles/articlesthebreat.html - the bit about Dynamic Insulation.
    • CommentAuthortony
    • CommentTimeAug 15th 2007
     
    It is a sort of good idea but there is no control. Using the air leakage of the building to ventilate is is crazy-- too much will come in on windy days and in theory if the fabric is in any way well built it shouldn't even work at all. The better idea is build tight ventilate right.
    • CommentAuthorbiffvernon
    • CommentTimeAug 15th 2007
     
    There could be something in the idea but you would need a porous wall, not a solid wall with cracks at the corners. I'm not quite sure what sort of material this would be. Strawbales? But as soon as you rendered/plastered them they would become too airtight.
    • CommentAuthorMike George
    • CommentTimeOct 12th 2008 edited
     
    Came across this. [not the multifoil article] scroll down for Dynamic Insulation piece from Mark Brinkley http://www.housebuildersupdate.co.uk/labels/Insulation.html Some good links to a system being developed. Anyone have an opinion?
    • CommentAuthortony
    • CommentTimeOct 12th 2008
     
    Cant be zero U value! The heat thrown away or lost via the depressurising fans must be added in to all calcs.

    This system has no hope -- living in a collander is never going to be thermally efficient.
    • CommentAuthorjoe.e
    • CommentTimeOct 12th 2008
     
    Presumably in order to make this idea work, you have a heat-recovery ventilation system that's set up to expel more air than it draws in through the heat exchanger, with the remaining air drawn in through the walls. The heat exchanger obviously has a certain level of efficiency in terms of how much heat it can recover from the departing air - a percentage of the heat leaves the building anyway. So the more air you suck out, the more heat you lose. The question is, how much air do you need to draw through your insulation in order to pull the heat in with it? Because if it's quite a lot, then the loss through the heat exchanger will be relatively high.
    And am I right in thinking that the relative flow rates are the wrong way round for good efficiency in the heat exchanger? If it's drawing in a lot less air than it's expelling, it won't be as efficient at getting the heat out of the departing air - is that right?
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      CommentAuthorfostertom
    • CommentTimeOct 12th 2008
     
    What a great collection of Brinkley articles. interesting that Mark's attitude to multifoils seems to have softened a bit since the 'Multifoils: last throw of the dice ' one!
    • CommentAuthorcaliwag
    • CommentTimeOct 12th 2008
     
    • CommentAuthorcaliwag
    • CommentTimeOct 12th 2008
     
  10.  
    Just noticed one of the Brinkley links doesn't work http://www.environmental-building.co.uk/dbb.shtml#energy.
    • CommentAuthorEd Davies
    • CommentTimeOct 12th 2008
     
    The references give an indication of the airflow rate through the insulation but not of the pressure differences required to create them. I wonder how they compare to the dynamic pressures created by a stiff breeze.
  12.  
    This from the BBA certificate http://www.environmental-building.co.uk/documents/4578PS1i1_web.pdf

    " Dynamic insulation
    6.6 It should be noted that ventilation air drawn through the dynamic cells will recover some of the heat which would
    otherwise be lost by conduction(1).
    (1) At the time of issue of this Certificate, a formal codified method for quantifying or using ‘dynamic U-values’ is not available, but the Certificate
    holder is currently undergoing such an assessment, in accordance with SAP 2005, Appendix Q, to enable this mechanism of heat recovery to
    be formalised and used in heat-loss calculations."

    'Some of the heat' being the interesting part
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      CommentAuthorfostertom
    • CommentTimeOct 12th 2008
     
    Well, this one certainly can't be assessed and accredited by trad hotbox methods!
  14.  
    Yes, there's quite a few cases now aren't there
    • CommentAuthorsinnerboy
    • CommentTimeOct 13th 2008 edited
     
    Jaysus ! Sorry Tom - this thread should be renamed "Dynamic Insulation - same principle as Convection Ovens"

    this is amusing - from the BBA cert

    "8 Behaviour in relation to fire
    8.1 The product is classified as ‘combustible’.
    8.2 When installed, the product will be contained by a suitable lining (eg 12.5 mm thick, Type F plasterboard), with
    all joints fully sealed and supported by timber rafters/studs/joists. Therefore, it will not contribute to the development
    stages of a fire or present a smoke or toxic hazard until the lining is compromised.
    8.3 The use of the products in pitched roofs will not affect the external fire rating of a slated or tiled roof when
    evaluated by assessment or test to BS 476-3 : 2004. The products must not be carried over junctions between those
    roofs and walls required to provide a minimum period of fire resistance."

    The single lining in item 8.2 will be punctured by elec points and vent openings . An outbreak of fire will quickly spread to the wall cavity causing flashover temperatures to be reached all over the house . Don't look to intumescents to provide an answer - they act too slowly to solve this problem

    http://uk.youtube.com/watch?v=jQV_MJwYQ3k&feature=related

    http://uk.youtube.com/watch?v=TKPfkrGDv7U
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      CommentAuthorfostertom
    • CommentTimeOct 13th 2008
     
    This is why I don't regard fire regs as a bureaucratic annoyance to be circumvented. it's cost many lives to write them, for the safety of us who've never been in a fire, as well as the firefighters'.

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