Insulation..Which way round ie. foil facing inwards or outwards?

Discussion in 'Builders' Talk' started by Lombear, Oct 11, 2007.

  1. Charlie Far!ey

    Charlie Far!ey New Member

    Oh look! Hey * you have a 'job' to do your master is here aka extremelystupidman

    Over you go and brace yourself - he's going give it big time fat boy

    [Edited by: admin5]
     
  2. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Oh the * is here
    Still kipping under the 'van then?

    Must be getting colder there now huh? Might not make
    the winter this year - We live in hope I guess

    *




    That's it Fartley, resort to smut, every time you are shown up. No wonder you post so much smut.



    Mr. HandyAndy - really

    [Edited by: admin5]
     
  3. Stoday

    Stoday New Member

    I thought everyone knew how a vacuum flask worked and how it's made.

    Lo and behold, Charlie dosn't. That's clear from his last post.

    On the other hand, maybe he's forgotten. Early onset of Alzheimer's. That explains a lot...
     
  4. ­

    ­ New Member

  5. clutters

    clutters New Member

    The foil goes on the warm side to reflect the heat back. If it is on the cold side, the smaller amount of low temperature radiation will not go directly back into the room but into the insulation where it will be absorbed. Furthermore, the adhesive holding the foil on the insulation will reduce the reflective properties. Another thing to take into account is the fact that warm air tends to hold more moisture than cold. If the foil is on the cold side, then the warm moisture-laden air will diffuse through the insulation and there will be a tendency for moisture to condense on the cold foil. This will be avoided if the foil is on the warm side and is sealed on its edges to prevent warm air entering the insulation.
     
  6. J.T. Builders Ltd

    J.T. Builders Ltd New Member

    lombear, why not draw up sum plans, put building regs in and turn it into a proper space?

    you would need a staircase etc, wack some dormers in, and you are sorted.
     
  7. Lombear

    Lombear New Member

    This is confusing, foil facing out, foil facing in! Must admit there have been some compelling arguments for both sides. Seeing as I have done half the roof so far with the foil facing towards the tiles I will leave as is. But what I have done is order some cheapo single bubble foil to put on the inside. Not only will it ensure no water can penetrate to the plasterboard (the roof isn't in great condition!) it will at least add that little bit more insulation.

    JT Builders: I am doing this conversion for only a couple of grand, whereas if I were to do it properly with stairs, fire doors, BCO approved insulation etc. the cost would escalate. I don't want anything fancy and at the end of the day when it comes to selling the house it will never be sold as an extra room.
     
  8. Stoday

    Stoday New Member

    The foil goes on the warm side to reflect the heat back.

    That conflicts with the second law of thermodynamics, which says that heat transfers from hot bodies to cold. No exceptions.

    The temperature of the room would have to be lower than the temperature of the room for this to happen.
     
  9. Tony Soprano

    Tony Soprano New Member

  10. Charlie Far!ey

    Charlie Far!ey New Member

    Toady

    *

    Thats exactly the principle of a thermos flask it refects radiant heat back into itself - The outer wall of the flask vessel is not coated with a refective surface and if the inner surface is soiled the vessel degrades in performance - Space ships are the same all foil inside so are arctic/tundra accommodations so theyre wrong and youre right?

    The foil is a radiant heat reflector, not just to make your attic look shiney and bright the outer side is to retain heat that makes it past the reflector and prevent the dew point being reached on the reflective side - an effect that is possible if put in round the wrong way - Let him do it his way and he can find that out for himself who's right or wrong.

    [Edited by: admin6]
     
  11. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Toady

    *

    Thats exactly the principle of a thermos flask it
    refects radiant heat back into itself - The outer
    wall of the flask vessel is not coated with a
    refective surface and if the inner surface is soiled
    the vessel degrades in performance - Space ships are
    the same all foil inside so are arctic/tundra
    accommodations so theyre wrong and youre right?

    The foil is a radiant heat reflector, not just to
    make your attic look shiney and bright the outer side
    is to retain heat that makes it past the reflector
    and prevent the dew point being reached on the
    reflective side - an effect that is possible if put
    in round the wrong way - Let him do it his way and he
    can find that out for himself who's right or wrong.

    [Edited by: admin6]




    Go on, chumpley fartley. I'm waiting to hear how a shiny surface works...IN THE DARK.

    Like inside a flask.



    Mr. HandyAndy - really
     
  12. Stoday

    Stoday New Member

    Y'have to spell it out so that a principle will sink into Charlie's single remaining synapse after the ravages of Alzheimer's.

    The shiny side faces the side with the biggest tenmperature difference.

    The thermos flask is double-walled. There is a vacuum between the walls. The temperature difference is greatest between the walls. The shiny side is the side of each wall that faces the vacuum.
     
  13. shut-up toad head and get back to the ****** TT forum
     
  14. Mr GrimNasty

    Mr GrimNasty Active Member

    A flask works because the vacuum stops heat loss by conduction/convection, the silvering which faces the hot contents, also stops heat loss by radiation.

    Obviously silvering/foil is designed to reflect back infra-red (heat energy) (non-visible spectrum - dark!), although it also happens to reflect visible light pretty well too.
     
  15. Stoday

    Stoday New Member

    A flask works because the vacuum stops heat loss by
    conduction/convection, the silvering which faces the
    hot contents, also stops heat loss by radiation.

    The inside is in contact with the contents, therefore at the same temperature. You can't have heat loss by radiation if there's no temperature gradient. It's the silvering that faces away from the contents that stops heat loss by radiation. The temperature difference is that between the two walls.
     
  16. Mr GrimNasty

    Mr GrimNasty Active Member

    You can't have heat loss by
    radiation if there's no temperature gradient.

    There is a temperature gradient - inside to outside flask. But I don't think (can't remember) a heat gradient is necessary to lose heat by radiation (black body radiation blah blah) anyway.

    The silvering reflects heat radiation back into the flask contents. Hence if you shine a torch inside it looks silver. The outside of the glass vessel appears silver too, to stop radiant heat getting absorbed from outside - so cold contents stay cold.

    The silvering is applied to the glass surfaces inside the vacumm - so if you could see inside the vacuum the 2 glass surfaces would look like the back of a miror.
     
  17. Mr GrimNasty

    Mr GrimNasty Active Member

  18. Stoday

    Stoday New Member

    There is a temperature gradient - inside to outside
    flask.
    Through the double wall. The gradient is between the walls.

    But I don't think (can't remember) a heat
    gradient is necessary to lose heat by radiation
    In that case you're heading for the Nobel physics prize having found the second law of thermodynamice is not true.

    The silvering reflects heat radiation back into the
    flask contents. Hence if you shine a torch inside it
    looks silver.
    It reflects the light of the torch because the filiament is at a higher temperature than the surroundings. Hence there is energy flow in the form of light/heat. In keeping your tea hot, there's no temperature difference between the inner wall and the tea. Hence no heat reflected back into the tea.

    The outside of the glass vessel appears
    silver too,
    Because the flask is made of glass & you can see the silver deposited on the vacuum side of the two walls, through the glass.

    to stop radiant heat getting absorbed from outside -
    The outside of the flask is at room temperature. The silvering stops the radient heat flow between the walls, where there is a temperature difference.
    so cold contents stay cold.

    The silvering is applied to the glass surfaces inside the vacumm
    Yes.

    - so if you could see inside the vacuum
    the 2 glass surfaces would look like the back of a miror.

    No. The back of a mirror is covered with a film to protect it. The inside walls of a vacuum flask don't need protection and are shinier than the outer surfaces.
     
  19. Mr. Handyandy

    Mr. Handyandy Screwfix Select

  20. Mr GrimNasty

    Mr GrimNasty Active Member

    Handy - inside the flask is clearly the active mirror surface - you can search the hundreds of other images out there if you don't believe it!

    Stoday -

    Through the double wall. The gradient is between the
    walls.

    The flask contents are being insulated from ambient temperatures outside. Ergo the inner and outer leaves of glass will match contents and air temperature respectively. There is (usually in use) a temperature gradient. Not sure of your point? Conduction/Convection prevented by vacuum. Radiation reflected back by mirrored surfaces. So no heat exchange (assuming a perfect flask etc).

    In that case you're heading for the Nobel physics
    prize having found the second law of thermodynamice
    is not true.

    As we have actually discussed on here before, heat loss through radiation can cause objects to cool BELOW the ambient temperature (but not deep space!). Unfortunately this is well known and won't win me any prizes. Don't think it's relevant here though.

    It reflects the light of the torch because the
    filiament is at a higher temperature than the
    surroundings. Hence there is energy flow in the form
    of light/heat. In keeping your tea hot, there's no
    temperature difference between the inner wall and the
    tea. Hence no heat reflected back into the tea.

    A load of nonsense - heat radiation is just 'light' outside of the visible spectrum. If you could see infrared you could see the tea losing heat. The physics of light/heat reflection has nothing (in this sense) to do with temperature. If the glass wasn't mirrored heat radiation would pass through the vacuum(either way) just like (most of) the light of the torch would pass. Heat radiation from hot tea is reflected back from the mirrored internal underside of the inner glass leaf and cannot escape, just like torch light.

    Because the flask is made of glass & you can see the
    silver deposited on the vacuum side of the two walls,
    through the glass.

    Both leaves of glass are mirrored. The silvering process makes the opposite face of the glass to which it is applied the mirror. The silvering is applied to the glass surfaces which become the inside the vacuum - else the flask contents would likely corrode it. The inside of the silvered surfaces (that you cannot see) would look like the back of a mirror (without addition protection if that makes you happy - and I suppose the back of the deposit may not be oxidised like a mirror in air, but it will still be rough/matt and a poor reflector).
     

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