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    • CommentAuthorEd Davies
    • CommentTimeApr 1st 2016
     
    All other things being equal [¹] I (and, I gather, DJH and Rhamdu) think that the radiant temperature of the walls, ceiling, floor, furniture, etc, are about equally as important as the air temperature for determining thermal comfort. SteamyTea, on the other hand, seems to think that the radiant temperatures are unimportant.

    The reasons I think radiant temperature is important are, in no particular order:

    1) Because various references say so. For example: https://en.wikipedia.org/wiki/Operative_temperature

    2) Because calculations (similar to the ones I did here: http://edavies.me.uk/2014/08/radiators/) indicate that it is.

    3) Because that's what it feels like in the real world: sitting next to a cold single glazed window is uncomfortable as you can feel the heat being “sucked” from you way beyond the immediate effects of any drafts.

    It'd be interesting if Steamy could explain why he takes his view.

    [¹] Humidity, drafts, sunlight, etc.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 1st 2016
     
    I think it's something like, ST thinks that human bodies are warmed by their environment; in fact the environment's temp serves to regulate the body's constant loss of heat. If the body doesn't continually dissipate its heat, we soon die. So higher temp walls slow down the rate of loss - there's a comfortable rate of loss, varying for different circumstances.

    Any light shone?
    • CommentAuthorgravelld
    • CommentTimeApr 1st 2016
     
    How much does the volume of a room matter? The larger the room, the less radiative loss matters?
    •  
      CommentAuthordjh
    • CommentTimeApr 1st 2016
     
    Posted By: gravelldHow much does the volume of a room matter? The larger the room, the less radiative loss matters?

    Does it matter at all? It's only the air that's in contact with you and the angle subtended by the walls, which is always 4π steradians. The volume will affect things like convective drafts and have obvious psychological effects but I don't think it changes the heat transfer in and of itself.
    • CommentAuthorEd Davies
    • CommentTimeApr 1st 2016
     
    I think the same as DJH, it's the solid angle subtended by surfaces of different temperatures that matters. If the surfaces are at uniform temperatures then that's 4π steradians wherever you are in the room and however large it is.

    If the surfaces are not at a uniform temperature then it does matter where you are. If, say, there's a cold window then being close to it and somewhere approximately normal to its surface will result in it having a larger solid angle, compared with being further away or round closer to its wall, and therefore decreasing the average radiant temperature you see, particular noticeable on your side facing the window.

    Still, even in that case it doesn't matter how large the room is. Double all the dimensions, including your distance from the window and the effect is more-or-less the same (give or take slight perspective effects unless you double all your dimensions as well).
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 2nd 2016 edited
     
    I think I better clarify my thoughts on this before I get all upset again. :bigsmile:

    Within normal household temperatures (so we are not talking about extreme differences), of just a few degrees C difference, my argument is that it makes no measurable difference.
    The reason being that the 'cost' of heating up the walls is greater than any benefit.

    I shall do a Tom here, and ask others to conduct some experiments to show that a wall that is varied by 2 or 3°C, really makes a difference to a person that is sitting in a room with a comfortable air temperature.
    Once that experiment is conducted, I will be willing to replicated it and show my results (as long as it is a cheap experiment).
    Until then, it is just using anecdotal evidence, which is another way of saying no data.
    • CommentAuthorgravelld
    • CommentTimeApr 2nd 2016
     
    But small temperature differences are perceptible by humans. 18.5C is fine for me in the lounge. 17.5C isn't. (Air temp only, might be other factors)
    •  
      CommentAuthorfostertom
    • CommentTimeApr 2nd 2016
     
    Posted By: SteamyTeaWithin normal household temperatures... of just a few degrees C difference, my argument is that it makes no measurable difference
    Assuming 'it' means radiant temp not air temp, do you mean no difference in perceptible effect on the body, clothed or not - or no difference in in fuel 'cost'?

    If the former, is that where 'anecdotal' comes in i.e. it's what you notice about yourself/your walls?
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 2nd 2016
     
    Do the experiments, show your data and then justify why it did not work, got to be better than not doing any experiments, not collecting data but justifying why it does work. :devil:
    • CommentAuthorEd Davies
    • CommentTimeApr 2nd 2016
     
    Posted By: SteamyTeaI think I better clarify my thoughts on this before I get all upset again.
    Good, that was what I was hoping.

    Within normal household temperatures (so we are not talking about extreme differences), of just a few degrees C difference, my argument is that it makes no measurable difference.
    OK, but given the list of reasons I gave in my first post, why do you think the wall temperature is less important than the air temperature?

    The reason being that the 'cost' of heating up the walls is greater than any benefit.
    This depends to some extent on the construction of the building and the usage profile. If we're talking about poorly insulated external walls then I'd agree, keeping their surfaces cool would save energy. For internal walls and well-insulated external walls I don't think this matters anything like as much.

    For a room which is only used intermittently (for an hour or two a day) then just warming the air will also make more sense. However, for a well-insulated room used for long periods the heat capacity of the surface layers of the walls is small so there's a lot to be said for keeping them warm and the air a bit cooler as you're going to dump the heat in the air every two hours or so (give or take any heat recovery).

    I shall do a Tom here, and ask others to conduct some experiments to show that a wall that is varied by 2 or 3°C, really makes a difference to a person that is sitting in a room with a comfortable air temperature.
    Once that experiment is conducted, I will be willing to replicated it and show my results (as long as it is a cheap experiment).
    Until then, it is just using anecdotal evidence, which is another way of saying no data.
    It's more than anecdotal evidence - it's the widely accepted view based on previous experiments and experience. It could be wrong, of course, but the onus on those saying it is is to produce some evidence or argument as to why or in what way it's wrong.

    It's mildly tricky to experiment with as it's all about perceptions which are influenced by recent history (over the last few minutes to weeks) and rather awkward to double blind. Still, starting with a cold house it ought to be feasible to track what air temperatures are needed for comfort as the air is warmed and the solid surfaces rise in temperature.
    • CommentAuthortony
    • CommentTimeApr 2nd 2016
     
    Yes but too slowly, I like temperature, it gives me the feeling of comfort.

    Wind chill should not be a problem indoors

    Radiative cooling to low temperature surfaces can cause less than comfortable perceptions.
  1.  
    This is purely anecdotal but I've always found our house, even before any improvements, more comfortable in this way than my parents one even heated to similar temperatures.

    Ours is entirely dry lined so the walls are always fairly warm to the touch while their's is built from an outer layer of stone and an inner one of brick (no cavity between) and in winter are always cold.

    Ed
    • CommentAuthorEd Davies
    • CommentTimeApr 2nd 2016
     
    Posted By: tonyWind chill should not be a problem indoors
    Indeed it shouldn't. However, it's worth noting that a minor disadvantage of the warm-walls/cool-air strategy would be that any drafts (e.g., air blowing from the ventilation) would be more of a nuisance.
    •  
      CommentAuthordjh
    • CommentTimeApr 2nd 2016
     
    Posted By: tonyWind chill should not be a problem indoors

    Wind chill is exactly what causes the problems in the offices I've been describing.

    But offices are different to houses.
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