That's not strictly true in the limit.
Especially with suspended floors.
Also the thermal mass implied by the load of wet soggy soil under a solid concrete floor laid on it, is a very significant thing to take into account.
No, but *relatively* small.
The building regs have some complex tables for all this relating the floor area to the external wall length etc.
The actual calculations are VERY complex. Lots of calculus IIRC..
The Natural Philosopher coughed up some electrons that declared:
OK. Now if the building is heated 10 hours out of 24, then would it be a reasonable assumption that the ground floor would tend to reach a mean temperature? Assuming a time constant in the order of days (or even a couple of weeks) the floor mass might only manage to get upto 10-15C which could explain the observations.
Cheers
Tim
Yes. Although it might not be uniform across the floor.
Yes. Even an insulated concrete floor has a time constant of several days - well mine has!
Add in a few hundred tons of soil underneath and well...its longer!
the whole efficiency of ground source heatpumps depends on the fact that the time constant of subsoil below a meter is measured in MONTHS.
Hmm. got not much better to do..let's look at concrete specific heat and do some calcs..
Assume 0.2 calories per gram per degree C.. Assume about 3 tonnes per cubic meter. Assume a 100mm screed thickness. Assume a 50mm polystyrene sheet under a block and beam floor - that's what I have..
First calc. Assuming 100W/sq meter..thats a reasonable figure for a well insulated house, how fast does it warm up?.
A square meter of 100mm thick screed is 1/10th of a tonne, so 100kg, so will need 20 thousand calories to warm by a degree C..or 23 watt hours roughly.
So at 100 watts per sq meter I should see, with no losses 4 degrees C per hour..
OK, looking at the losses downwards the U value is about 0.6 for he styrene sheet, so at say 10C difference (5C outside and under the suspended floor) and 15 C in the floor, that's 6W per square meter loss.
Not too significant. But in terms of losses, the time constant is definitely in the many hours level. 23 watts per hour per deg C is the thermal inertia...0.6 watts per degree C is the losses.. so a native time constant excluding losses to the room, of 23/0.6 hours.. a shade over 38 hours.
Now add in the chimney stacks..haha.
If the slab were in contact with the soil itself..that 100mm thick might easily be much higher. But I don't have a figure for the insulation of soil, and the path through it to the cold air outside..
Not sure what all that proves, except that people with even well insulated concrete floors have a lot of thermal inertia in their houses.
And why you need feed forward in UFH schemes to prevent temperature overshoot, especially if you have a high power to area going into them.
Another reason why it's probably better if you don't, to leave em on 24x7.
Do you really think a chipboard floor in wet conditions wont move or rot in your lifetime? I wouldnt do it :)
There may be an easier & much cheaper way, thats to use an insulating concrete slab. IOW the crete is made with a high percentage of something like perlite, which insulates. So the slab itself is a lattice of 3:1 mix and little air voids. Insulation wont be nearly as good as polystyrene, but a) it gets you a long lasting solid floor with no headroom loss b) its cheap c) its much less work/time to lay
I assume youre not wililng to dig out a few more inches.
I would also question whether if you've had concrete with no dpm for years, you need a dpm now. I know its the fashion, but lets face it, millions of us live in no dpm houses, and most are just fine. Your risk, your choice.
NT
snipped-for-privacy@care2.com coughed up some electrons that declared:
Hi
Exactly - that's why I raised the concerned regarding chip myself and started looking at insulated backer board instead (eg marmox). Maybe that post got lost.
Thing is, I don't want to dig out any inches. Only one area has been dug out, and that will get proper insulation under the screed.
The other small area is rough due to breaking off tiles but the slab is OK.
I really don't want to hack any more of the floor (I have 95m2) - so it's either what I can practically stick on top, or nothing.
This is of course true. DPM might be worse - I don't know these things for sure at the moment.
Cheers
Tim
Perlite-crete sounds even more attractive then. No need to dig up anything. Its full of half pea sized bits so will need some plain mortar to smooth it over.
NT
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