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    I know this info must be on here somewhere as I made the calculation that I needed 8.3 KW to heat the salon (which is 5 m x 9 m x 2.6 m) at one time ... but I can't find the right words to plug into the 'search' facility to find the info again. Can someone help?

    I'm being slightly discouraged by the folks I am talking to. I think my expectations of how much heat and hot water (solar combined systems) you can get out of solar panels and a wood burning stove are unreasonable so I'd like to get back to basics and find out how much DHW and heat I am likely to need.
    • CommentAuthorDantenz
    • CommentTimeAug 3rd 2009
    Don't know how large your hot water requirements are but 8.3kW is a huge amount of energy for 45m2 space, would have thought more like 2.5kW.
    • CommentAuthorwelshboy
    • CommentTimeAug 3rd 2009
    Might be worth trying a reality check- turn on enough electric fires to feel comfortable- then you have a fair test against theory . Please bear in mind the ambient temperature though.
    Aside from the materials which will dictate how much or how fast the heat will move through, the other key factor is the inside to outside temp difference, the greater the difference the greater the flow as like everything the highest energy will flow to the lowest energy. So estasblish your nominal inside to say worst case outside temperature.
    The other really key thing is the volume of air changes expected for a salon a lot less than the bathroom or kitchen.
    We woulkd need to know the area of internal / extaernal wall and thier construction/materials and likewise for windows and other openings
    so quite a bit of information is required.
    Even uisng old yardstick approaches i think your 8.3 Kw is too high, how did you do this? 2.5-3.5 Kw by the old guestimates

    Mike up North
    • CommentAuthordelboy
    • CommentTimeAug 4th 2009
    Hi Mrs White Cat

    Where on earth did you get 8.3KW from?

    OK there are 2 ways a building loses heat:
    1. Through the envelope
    2. Through air leakage.


    Part 1: the envelope.

    For the envelope you need to multiply the area of each element by its u-value.

    Say you have 300mm insulation in your roof. This has a rough u-value of 0.14 and an area of 45m2. So the heat loss for the roof is 0.14 x 45= 6.3w/k (ie multiply the u-value by the area).

    Repeat exercise with floor (say 80mm insulation @ 0.2w/m2k) gets you 9w/k, and walls (say 160mm insulation @ 0.18, and let's imagine that you have 5m2 of door and window giving you net wall area of 67.8m2) gets you 12.204w/k for the walls. Finally 5m2 of windows and doors @ 1.5w/m2k = 7.5w/k.

    So your total heat loss, per degree difference, is 35.004w (6.3+9+12.204+7.5).

    If the maximum degree difference is 24C, then your maximum heat loss through the building fabric is 840.1W, or 0.841KW

    Part 2: the air leakage.

    This is a little less scientific, and based more on a basic formula - others may know more precise methods of calculation.
    Here is the method I know:
    (0.33 x Volume of dwelling (m3) x air changes per hour x temp difference) / 1000 = leakage heat loss in KW

    So your salon's volume is 2.6 x 5 x 9 = 117m3
    Say you build it to 2 air changes/hour
    Say the maximum temp diff is 24C

    (0.33 x 117 x 2 x 24)/1000 = 2.78KW

    Now combine the 2 heat losses (2.78 + 0.84) and you have a total heat loss of 3.62KW.

    I seem to remember you live in France Mrs White Cat, in which case the temp difference is unlikely to get as much as 24C - but you have the maths here so you can work it out for yourself.

    Hope this gets you purring.
    • CommentAuthorRobinB
    • CommentTimeAug 4th 2009
    I'm chirping!
    I got the 8.3 kw from the 'kilowatt checker' on a Stoves online website (it then goes on to suggest boilers that might be suitable).
    • CommentTimeAug 4th 2009 edited
    t'internet's going a bit odd, I can only add stuff in short stints before getting booted out ...

    I'm not sure what the spec is of the insulation the builders have installed. All I know is that there is a lot of it because I had tony's mantra ringing in my ears. I guess I need to hunt for some generic u-values to do the sums.

    As for being leaky, the house is supposed to be airtight. The builders didn't quite 'get' air tight but they understood that I didn't want a gap even an ant could get through.
    • CommentTimeAug 4th 2009 edited
    The house is constructed (sob and believe me I argued) of earthquake proof concrete - a lot of it. There are 5 French windows in the salon, 12-4-12 argon filled double glazing comes to mind (does that sound right?)

    Unhappily I'm not in the south of France at the moment but the temperature there at the moment is 30C, 20% humidity, 6mph easterly wind. I've known it to go to 40C - but we're at a teensy bit of altitude so we always get a bit of a breeze.

    In the winter it gets down to -3C. I've known -5C and snow on the palm trees. We're not in the path of the Mistral but it can get quite parky.
    • CommentAuthorCWatters
    • CommentTimeAug 5th 2009
    The magic words to google are "heat loss calculator". To maintain a stable temperature the heating system needs to match the losses. There are various calculators around that vary in complexity.
    That calculator is way off - I just tried your dimensions and it does come up with 8300. The old fashioned rule of thumb which would not take into account decent insulation levels etc etc is vol in cu feet x 3 = BTUs/hour. You have 4131 cu ft so that about 12k BTU/hr which is about 3.6 kw/hr. Which by modern standars quite a bit anyway.
    Mike up North
    • CommentAuthormarktime
    • CommentTimeAug 5th 2009
    I'm surprised Ms Pussycat that you haven't gone back to your architect. He, or someone in the permission stream to build your house must have provided calcs to satisfy EU based (although locally modified, see the UK) regs. To quote New Age, it's a holistic excercise and although your salon is part of it, the results are whole house. Simply put, there is loss due to the fabric and loss due to the air you heat but allow to be replaced to keep the air fresh.

    I´m puzzled that you want to get involved at such a level when you tells us quite clearly that you are out of your depth. Let the guys that you paid do it, then secretly pass the calcs here where they can be digested to your hearts content. :bigsmile:

    Caring for cats (my favourite charity).
    Mike (Up North) : is the 8300 you came up with the same as my 8.3 Kw? (I'm gratified to learn I'm not such a div after all).

    marktime : I'd dearly love to know where the original architect is. We hunted high and low for him and he appears to have fallen off the face of the earth.

    We bought the land with planning permission for this house from our neighbour who is the Maire's secretary - so I guess you might say any documentation regarding heat loss calcs may not have existed and certainly didn't make it our way - we didn't even get the original house plans!
    • CommentAuthormarktime
    • CommentTimeAug 5th 2009
    Then you need to get a copy of the plans that you have indicating the floor, wall and roof fabric, plus the spec for the type of insulation that is indicated on them, plus the spec for the windows and doors that are actually being fitted.

    In addition, you need to know the area climate detail which will indicate the number of 15 deg days that will require the house to be warmed in its separate areas, e.g. bedrooms at 18 deg, salon at 21 deg, bathrooms at 23 deg plus the number of air changes that you require, depending again on whether you are actually going to fit a heat recoverable air trunking system, factored by the orientation of the house with respect to the sun, and when you have got all that, you can calculate how many kw of heat you require and then how you plan to supply that heat and direct it to those areas that require heating.

    The DHW demand is much easier to satisfy but then again, if you are combining with solar you need to do the calcs to engineer an optimum solutiion.

    I'd find a heating engineer, (not a plumber), that you can trust and hand the problem to him: probably save you the cost of an 8.3 kw heat source that surely won't come cheap. You can also discuss with him the cost benefit of increasing/substituting the insulation from all that you have learnt here.

    But I don't think any of this can be done long distance. Just my point of view, of course.
    >how do I work out the heat demand for my house?

    Houses don't demand heat. It's the people inside. Tell 'em to put some clothes on.
    Hi, yes thats 8.3kw that what the site calculator produced which is completly wrong. You need to list out each room, each wall constuction/materials, thickness etc plus the higth/width, areas of window doors etc, and for each room the expected tempertaure. Give all of this to a heating engineer and ask for the heat load.
    Its not a difficult set of sums with all the info, and can be estimated, but the basics are the wall/floor sizes and what they are made of.
    Mike up North
    • CommentAuthordelboy
    • CommentTimeAug 6th 2009
    Sod it - just get a 8KW boiler and be done with it. You can do all the sums in the world but ultimately that is roughly what you'll end up needing.

    As Biff says, stick on some extra clothes on those occasional freezing winter's days if needed. If it doesn't go below zero more than 10 days a year, it's not worth getting a boiler which can hit the demands of those rare days anyway.
    delboy - that so makes sense to me, just get the stove I like the look of and worry about the rest later (especially since it's beginning to sound like I can't integrate it with a thermal store anyway).

    However, 'due care and diligence' tells me to persist in trying to get the heat calc figures despite the fact that I don't know what the spec for the insulation is (despite asking for this detail - say fortnightly - for the last 12 months). The plumber in our case, is the heating engineer. That's the way they do it there. Same guy hooks up your septic tank, solar panels and UFH.

    The Mairie on the other hand keeps a complete record of weather conditions - so that bit's easy.
    Just thought I'd mention biff that my hubby is a complete tyrant with the thermostat in our current house which is why he benefits from so many roast dinners and cakes in the winter.
    I think this is going to be like drawing teeth - I've been offered the information the the manufacturer of the insulation materials is a German company called Knauf. Hopefully if I persist I'll eventually learn what the builders have used and where.
    Hi, very well known name and they are one of the biggest suppliers. They along with the other big suppliers have very comprenhive web sites that offer all the info and technical detail as well as most usual combinations of materials/thicknesses so you'll easily get what you need. plus its all downloadable.
    If you can state the material (or closest thing) and what the build up is (eg render/block 215mm/PU insulation 100mm/plaster 20mm etc etc) you can email that to Kingspan technical desk who will do the u val calc and condensation risk. Youll get an email back with U value etc. This you can use with the sq m walls and temp diff to "estimate" the heat loss - Thats what you are after the loss, for example "how much heat am i losing when internal = 20deg and when its 0 deg out side". Subtract areas of doors and windows (do the same calc for them and add it back in).
    Best done in a little spreadsheet.
    There is a useful U and R value calculator at vesma dot com under tools, downloaded it works off line as well.
    I'm sure the boffins will have better, but for simplicity you need to develop a basic model you can if you wish introduce enhancements later. When the basics are right a reality check will confirm where its going.
    I suspect you doubted the on line calculator all along, that gave you the funny answer, so a simple assessment will put it into perspective and be ok if say 90% accurate.


    Mike up north
    Many thanks for that. I haven't had a chance yet to run through the Kingspan or Vesma calculations but as you say, I did think the 8.3 Kw was a bit high, but mainly because the Charnwood technical guy I spoke to was adamant the boiler I was talking to him about would be working well within its capacity while looking at the technical spec, it would seem to be not quite man enough for the job.

    It would be useful to have some kind of idea / scale of what Kw / BTus equate to in the same way as they have for decibels eg 60db = normal conversation and 105db = rock concert ... something along the lines of sitting within x metres of a heat source with x kw output means you still need to wear a fleece and slippers, x means cat can sleep next to it and not get fur singed, x melts chocolate, x fries an egg & etc.
    A bit more info re the insulation. The Knauf stuff is in the floor apparently. On the walls and ceilings is a combined plasterboard and insulation product from St Gobain. The stuff that is on the inside of the internal walls is something with a resistance thermique of 2.55 and (all Greek to me) the lambda of the insulation is 0.032. There is something from the same family of products on the inside of the external walls.
    • CommentAuthorneelpeel
    • CommentTimeSep 23rd 2009
    I've also been trying to calculate the heat demand (or heat loss I suppose) for my cottage conversion (the 'conversion' being from 4 dodgy stone walls into a liveable space).

    I put through calcs for the U-values of all my walls/floors/roof (as per Delboy's method above) and came up with a 1.1kW loss. The air leakage heat loss estimate though was coming out as 3kW.

    I'm just wondering, if I intend to try and seal as well as I can using all the 'best practice' as mentioned on many threads...and intend to fit MHRV then is there a more accurate way of estimating the air leakage heat loss?

    For ref - the space I have is 189m^3 (45m^2, 2 floors).
    • CommentAuthorCWatters
    • CommentTimeSep 25th 2009
    I've heard that MHRV is normally set up for between 0.25 to 0.7 air changes per hour and that trickle vents can provide upto three air changes per hour or more on a windy day.

    I guess if you know the volume of air in the house, the specific heat capacity of air and the internal and external air temperatures you can work it out.
    • CommentAuthorneelpeel
    • CommentTimeSep 30th 2009
    Ah, I hadn't really thought of it that way, but yes you're quite right.
    Using a volumetric heat capacity of 0.001297 J/(cm3.K) and a worst case air change of 0.7 per hour I now get a more respectable figure of 1.14kW loss from air leakage.

    But with MHRV do I not get most of that heat loss back from the exchanger so the figure would be much lower still? or does the 0.25 to 0.7 figure take that into account?
    • CommentAuthorCWatters
    • CommentTimeSep 30th 2009
    Yes should get most of that back.
    • CommentAuthornikhoward
    • CommentTimeMar 5th 2013
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