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Heating and cooling: Infrared heater staring at wall

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    • CommentAuthorgyrogear
    • CommentTimeOct 8th 2016 edited
     
    Since I retired my electric floors, our large lounge can be pretty cool of a winter morning (18.7°C on 15 November last year, which was too cold even for me...). This is no doubt due to the fact that my (purposely undersized) 7.5 kW woodstove does not last through the night... One solution is to set the alarm for 5:30, do a quick burn and go back to bed - not very "lifestyle-friendly"...

    I am therefore considering adding two low-cost infrared heaters -- dual 600/1200 watt (tubes). Since these are not very aesthetic, I want to mount them on the back side of the tie beam that connects the two roof trusses (we have a cathedral ceiling) -- the tie beam is parallel to the ridge purlin, and about 2.5 meters below it.

    The heaters would then be well above floor level, off our general trafficable route, and out of sight. They would be pointed at a partition wall, 4m x 4m and 1.5 meters distant, which is the frontage to our northern rooms (bathrooms, toilets, box-room, loftspace). The partion wall is hollow-brick with plaster over. The backside of the upper half (to loft space) is insulated with 30mm XPS.

    The idea is to use the IR to warm the partition wall, turning it into a sort of "storage radiator". This would collaborate with our ceiling fan... For just a couple of hours - once the sun gets going (around 10-ish) we are generally OK...

    If the system works, I would get the electrician to install some sort of timer control.

    Would be grateful for opinions, to see to what extent I am "off the wall".

    gg
    • CommentAuthorCWatters
    • CommentTimeOct 8th 2016
     
    Apart from the high cost of electricity that should work ok. As would a fan heater or other electric heater.
  3.  
    Have you tried any methods to make the burn last longer, such as this?

    http://thehelpfulengineer.com/index.php/2011/02/make-your-fire-last-longer-light-it-upside-down/
    • CommentAuthorEd Davies
    • CommentTimeOct 8th 2016
     
    Posted By: gyrogearThe idea is to use the IR to warm the partition wall, turning it into a sort of "storage radiator".
    That would probably work as suggested but I'm not sure it's desirable. Since what you're wanting is a bit more thermal comfort for a short time any form of storage does more harm than good as it means you have to turn the heaters on earlier and might get overheating later when the wall is still warm but the sun is coming in.

    Ideally, I think, you'd want to coat the partition wall with paint which is reflective of the thermal (long-wave) infrared put out by these heaters. That might be difficult to find, particularly as so many sources muddle up thermal (LW) radiation put out by warm objects near room temperature with the “heat” radiation of near (short-wave) thermal IR in the solar spectrum.
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      CommentAuthorfostertom
    • CommentTimeOct 8th 2016
     
    I think the storage part of the idea is good. By its nature it will be short-life storage, to prolong until getting-up time and a little beyond, the overnight output from the woodburner and to apply it not just in the room containing the IR heaters, but also in the room(s) the other side of the partition. With experience, It should be easy to adjust on and off times (by timer) to start soon enough and to stop in time for the re-fueled woodburner to kick in (or not if it turns out sunny).

    I wouldn't say a fan heater wd do just as well. The idea is to heat the (absorbent) fabric directly, by radiation, not by superheating and stirring the air. In fact I'd leave the ceiling fan off overnight.

    Do you get off-peak rate electricity at that time of day/night?
    • CommentAuthorEd Davies
    • CommentTimeOct 8th 2016
     
    Posted By: fostertomI think the storage part of the idea is good. By its nature it will be short-life storage, to prolong until getting-up time and a little beyond, the overnight output from the woodburner and to apply it not just in the room containing the IR heaters, …
    But gyrogear's original post makes it clear that it doesn't work (enough) for that - the room is too cool in the morning. I'd agree, though, that any low-e paint there would reduce any storage that's helping now but wouldn't the reduced run time of the heaters in the morning be a bigger benefit?
    • CommentAuthorCWatters
    • CommentTimeOct 8th 2016 edited
     
    Some thoughts on the storage aspect of this proposal..

    The heaters would then be well above floor level, off our general trafficable route, and out of sight. They would be pointed at a partition wall, 4m x 4m


    The specific heat capacity of plasterboard is 1090 J/kgK. A 1sqm of 12.5mm plasterboard weighs about 8kg so 16 sqm weigh 128kg.

    Lets say you were able to heat up one side of the plasterboard wall by 5C (are there cables and sound insulation in it?)

    That makes the stored energy about...

    = 5*1090*128
    = 700kJ

    That stored energy is avilable to heat the room once the heaters switch off. You didn't say what power the IR heaters would be but lets assume a single 1kW heater.

    That much stored energy is would be equivalent to running the 1kW IR heater for around

    700/(1000*60) = 11.6 minutes

    eg...

    With a 5C rise in the plasterboard wall you are effectively storing the equivalent of 11mins worth of energy from a 1kW IR heater.

    Your mileage may vary.
    • CommentAuthorCWatters
    • CommentTimeOct 8th 2016 edited
     
    I suppose you might boost that by a factor of four? eg by doubling the thickness of the plaster board and achieving a 10C temperature rise? However it's not easy to calculate what temperature rise would occur.

    Since there is no such thing as a free lunch storing heat in the wall really only makes sense if you can store off peak electricity for use during peak period.

    In addition having to switch the heating on earlier (because of the thermal mass of the wall) means the room is warmer longer so losses are higher. This is/was an issue for old leaky storage heaters that keep your room unnecessarily hot at night while they charge up.
    • CommentAuthorEd Davies
    • CommentTimeOct 8th 2016
     
    Posted By: gyrogeartwo low-cost infrared heaters -- dual 600/1200 watt (tubes).


    Posted By: gyrogearThe partion wall is hollow-brick with plaster over.
    But, yes, the storage is both small and (slightly) harmful.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 8th 2016 edited
     
    Posted By: CWattersLets say you were able to heat up one side of the plasterboard wall by 5C
    It's not - it's
    Posted By: gyrogearThe partition wall is hollow-brick with plaster over
    •  
      CommentAuthorfostertom
    • CommentTimeOct 8th 2016
     
    Posted By: Ed DaviesBut gyrogear's original post makes it clear that it [the undersized woodburner which doesn't make it thro till the morning] doesn't work (enough) for that - the room is too cool in the morning
    Eh? so that's what the IR is for - to input some heat back into what's stored (but running out) ready for geting-up time - instead of doing same by refuelling the woodburner at 5.30am.
    • CommentAuthorEd Davies
    • CommentTimeOct 8th 2016
     
    Sorry for being unclear. I meant:

    Posted By: Ed DaviesBut gyrogear's original post makes it clear that it [the storage part of the idea] doesn't work (enough) for that - the room is too cool in the morning.
    I don't understand why anybody would want to store heat from an instant heater when all that's wanted is actual instant heat for a few hours. Unless electricity is significantly cheaper earlier in the morning, of course.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 8th 2016
     
    Fair comment - tho by storing it into the partition, it emits into rooms on both sides. Or does it? (rate of heat soak thro the partition)
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 9th 2016
     
    Why not just put a storage heater in. You can get a 4 element one that you can play about with by switching the number of elements that are active. That could be an easy way to vary the temperature and the energy stored.

    Depending on the partition wall being load bearing or no, you could fit it into the wall, rather than have it 'sticking out'
    •  
      CommentAuthordjh
    • CommentTimeOct 9th 2016
     
    Why not point the IR heaters downwards at the floor instead of the wall? Then storage would probably be unnecessary.
    • CommentAuthorgyrogear
    • CommentTimeOct 9th 2016 edited
     
    First off, thanks to one and all for the great feedback !

    Posted By: fostertomI think the storage part of the idea is good.


    Thank you Tom, so did I LOL :devil:

    Posted By: fostertomDo you get off-peak rate electricity at that time of day/night?


    Yes, we get off-peak from 1.30 am till 7.30 am - that is the period I am aiming at using... Perhaps, say, one hour x 600 Watts per heater, for two heaters.

    Posted By: fostertomthat's what the IR is for - to input some heat back into what's stored (but running out) ready for geting-up time - instead of doing same by refuelling the woodburner at 5.30am.


    Precise and in a nutshell !

    ==== I ought to mention that we have EWI, and are "adept fans" of our... ceiling fan, which we use at various times of the day to help heat in and out of thermal mass... ====

    Posted By: SteamyTeaWhy not just put a storage heater in.


    Very Good Point ! I did not actually want to go that far, as it looks "retrograde" since we have stepped back from (= abandoned...) 100 sq. m of infloor electric...

    And for those who asked, we have no available wall area for "traditional" heating units - the house is split level (3 staggered half-floor heights, if anyone can imagine that...), meaning that we have no full-height walls (apart from the partition in question) (which of itself causes problems in furnishing) (translation: all lower wall areas are precious).

    Hiding the IR behind roof timbers gets over that problem...

    Posted By: djhWhy not point the IR heaters downwards at the floor instead of the wall?


    Another nice try ! However, (and no abolutely no offence meant), this is our main living floor (lounge/dining/kitchen) and I'd rather not have it resembling my local garage or something in an industrial unit :devil:

    Guess I now need to move on to the Testing Phase !

    Many thaks again, all, great feedback !

    gg

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