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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorShevek
    • CommentTimeJul 30th 2014
     
    For various reasons UFH heating may not be the best approach for us (i.e. too much thermal mass in floor, not enough emitter area, maybe even no need for it) but I really want to use some form of radiant heating rather than convection.

    What are our options if we bale out on UFH? Is it worth thinking about running heating pipes in walls or ceiling instead? Is that (along with UFH) the only way to utilise our gas boiler for radiant heating? Is it worth investigating electric radiant heating in ceiling (when we already have a combi boiler)?
    • CommentAuthorowlman
    • CommentTimeJul 30th 2014
     
    the only wet radiant panels I know of are used commercially and may not be suitable. You've discounted UFH the only other option, I can think of is electric infra red panels. It seems most if not all domestic wet systems are convection. Trench convectors, or perimeter convectors of some description may be worth a look??
    • CommentAuthortony
    • CommentTimeJul 30th 2014
     
    Normal radiators?
    • CommentAuthorShevek
    • CommentTimeJul 30th 2014
     
    Trying to avoid convection heating Tony.
    • CommentAuthoralec
    • CommentTimeJul 30th 2014
     
    pipes in walls is increasingly common and perfectly possible, but be careful where you put the picture hooks

    Radiant heating is best for quick heat up times and infrequent use..using this heating for long periods inevitably gets on the 'thermal mass' eventually.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJul 30th 2014 edited
     
    Posted By: ShevekTrying to avoid convection heating
    What are the reasons for trying to avoid it. Have you thought of forced air heating?
    • CommentAuthorGotanewlife
    • CommentTimeJul 30th 2014 edited
     
    Posted By: alecRadiant heating is best for quick heat up times and infrequent use
    Exactly! Just had a debate with someone who wanted to keep her 1000 watts of halogens in her kitchen ceiling because it keeps her warm - she does have a point though - living on north coast of Scotland with an oil fired boiler and rads (in a minimum bldgs stds 8 year old house), she often spends a bit of time in the daytime alone in the house in the open plan kitchen/study and doesn't want to have to either heat the whole house or run around adjusting all the TRVs twice when she feels a bit chilly. I have seen infra-red panels working well in bathrooms here in Italy so I suggested infra-red heating but I have not looked further. I hope someone can suggest something for Shevek that I can look into too.
    • CommentAuthorShevek
    • CommentTimeJul 30th 2014 edited
     
    Posted By: SteamyTea
    Posted By: ShevekTrying to avoid convection heating
    What are the reasons for trying to avoid it. Have you thought of forced air heating?

    Comfort, lower air temperature, no drafts, less dust.
    • CommentAuthorMackers
    • CommentTimeJul 31st 2014
     
    Radiant ceiling, will work the same as UFH but you won't get the time lag. I'm talking about a wet system. This can be plastered into the ceiling or behind plasterboard. Viking house may have done this or maybe his was in the wall?
    •  
      CommentAuthorfostertom
    • CommentTimeJul 31st 2014
     
    Posted By: MackersRadiant ceiling, will work the same as UFH but you won't get the time lag
    Not same as - will create considerable temp stratification - hot head, cold feet, esp if used intermittently. If used continuously, would even out more, but can never match the non-stratification (if anything, slightly warmer feet - nice) of underfloor.

    Wall heating - not by panels but by smaller diam 12mm pipe array similar to UFH ways and means, is common in Europe and is intermediate in stratification effect - quite acceptable. Can be quick-response/intermittent only if part of stud/plasterboard walling, not if on masonry.
    •  
      CommentAuthordjh
    • CommentTimeAug 2nd 2014
     
    Poultry farmers use infra-red heating. If you can find a way to deal with the aesthetics, ceramic infra-red lamps appear to be efficient.
    • CommentAuthorringi
    • CommentTimeAug 2nd 2014
     
    Firstly UFH is mostly convection not radiant as is temperature is way too low for radiant heat transfer to have much effect. Even normal radiators running at 70c are mostly convection.

    Have a look at thermaskirt, it is a skirting board radiant system claimed to work most of the benefits of UFH without some of the costs.

    Also one option with UFH is to use it for “back ground” heat, with some fast responding heating. So in a well insulated and sealed building, keep the floor at about the air temperature you want and then top up with other heating. There is a design for a zero ‘U’ value wall based on this concept.
    • CommentAuthorEd Davies
    • CommentTimeAug 2nd 2014 edited
     
    Posted By: ringi: “Firstly UFH is mostly convection not radiant as is temperature is way too low for radiant heat transfer to have much effect.”

    Oh no, not this again!

    https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law

    Assume emissivity of 95% (typical of not too shiny or odd household things). Bit of Python:

    >>> s = lambda t: 0.95 * 5.67e-8 * math.pow(t + 273.15, 4)
    >>> s(21) - s(20)
    5.455793576647068

    Ie, if the floor surface is at 21 °C and the rest of the room is at 20 °C then the net radiative transfer should be just over 5 W/m². Given that the overall transfer in these conditions will be about 10 W/m² that means about half is radiative and half convective/conductive.

    PS, for a radiator at 70 °C:

    >>> s(70) - s(20)
    349.06462391695374

    That's 6.98 W/(m²·K) so, despite the T⁴ term, it's not far off linear over normal room temperature ranges, only increasing a bit for wider temperature differences.

    I'd assume that convection from the radiator would be proportionally greater, though, because a) it's got two sides exposed to the air but only one side exposed to the room and b) it's vertical so convective airflow will likely work better. Even more so with radiators with lots of fins and so on.
    • CommentAuthorEd Davies
    • CommentTimeAug 14th 2014
     
    Longer form version of above answer: http://edavies.me.uk/2014/08/radiators/

    By the way, anybody know what conditions radiators are rated at? I believe 20 °C room temperature, 70 °C mean water temperature. Is that right? Presumably they assume it's stuck up against a wall with normal sorts of reflectivity? Is the rating the amount of heat extracted from the water or the amount transferred to the room (the difference being the amount put into the wall)?
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