# Heat conduction from basement to earth/soil below

Hi
I have a basement in my house. The floor is about 1.5m below earth/ground level and it is concrete about 30cm thick
The floor is not insolated, so in order to save some money on the heating bill I am considering insolating it with sheets of polystyrene foam (in principle foam filled with air) with some rafters in a mesh to
lay the wooden floor on. The lastly add 20mm of wooden plates/floor
An architect has told me to break up the floor and lay a new one with 30cm of extra insolation
But, I wonder if any of you guys can help me. I am an electrical engineer and I don't like to do this without calculating the needed insolation instead.
My theory is that since the floor is 1.5m below ground level, the temperature of the soil will never be very cold. Searching the net I find something about 14degree celcius.
So if I have 60square meters of floor heated to room temperature of 20degrees, how do I calculate the heattransfer when I have the data for
the insulation and the concrete floor?
Will the earth behave as an ideal giant block that has 6degrees of tempeature. So the gradient from the room temperature to the earth can never be higher than 10 degrees (20-14)?
Numbers:
Concrete, k = ~1W/mK Polystyrene, k = 0.03W/mK Wood, k = 0.14W/mK
Power needed to keep temperature stable: P=KAT/D
Concrete using 60square meters and 30cm thick: P = 1*60*6/0.3. P 1.2kW
Adding polystyrene: k = 0.042 , P = 0.03*60*6/0.05 = 216W
The poystyrene is in parallel with the rafters. Assuming the rafters take up 5% of the floor instead of the polystyrene
P= 0.14*60*0.05*6/0.05 = 50W
So from these calculations it seems I need 250W to keep the room heated
(not counting the walls)
Any wrong doings in the calculations - comments?
Thanks
Klaus Kragelund
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Klaus Kragelund wrote:

Well, 1.5 meters is about the break even point for your question. So I would suggest worrying about the wall, but not the floor. However if you have long cold winters or long hot summers, then you might want to also work on the floor.
--
Joseph Meehan

Dia duit
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Where are you, 14c is fairly warm, I am zone 5 US where the freeze zone, 0c -32f is maybe 3.5ft, I put in 2" or R10 under a new basement floor. With that small a difference foam pad and carpet might be as good.
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Covering the ceiling with foil would give it about US R10, ie 1.76 mK/W, with E = 0.03 and a Tc = 20 C ceiling temp and a Tf = 14 C floor temp and a large air gap. This would reduce the radiation from the ceiling to the floor, es((Tc+273)^4-Tf+273)^4) W/m^2, with s = 5.6697x10^-8 W/m^2-K^4. If the upper foil surface is perfectly clean, with no dust (you are German, right? :-), this may work even better. The linearized radiation conductance is 4esTm^3 W/m^2-K, where Tm is the approximate mean absolute temp.

The English word is "insulating." InsOlation is sunlight.

The temperature of the middle of the floor might be about the same as the yearly average air temperature. The walls and the floor near the walls might be closer to the average daily outdoor temperature.

With difficulty :-) The floor surface will probably be cooler than 20 C. That's good.

The temperature difference between the room air and the middle of the floor might be 6 C. Then again, the room air will warm the floor, which has thermal capacity and resistance to downwards heatflow. Some people estimate soil's resistance to downward heatflow as US R10, ie 1.76d mK/W. Upward is less, with evaporation from lower soil layers and condensation above. And moving water can change this.

Air, k = 0.025 W/mK

Not k = 0.03, as above?

You might cover the ceiling with foil and cover the walls with thin foil-faced foamboard over spacers and carpet the floor, with no polystyrene. Each layer of wall foil adds about US R3, plus the bulk resistance of the foamboard. If there's no vapor barrier under the concrete, you might put a layer of plastic film under the carpet.
Nick
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Here's one way to estimate the R-value of a radiant barrier based on the air gap and the emissivities and surface temps and the direction of heatflow from http://www.reflectixinc.com/pdf/RIMA_Handbook.pdf
10 SCREEN 9:KEY OFF:DIM HC(18,6) 20 DATA 0.359,0.184,0.126,0.097,0.080,0.068 30 DATA 0.361,0.187,0.129,0.100,0.082,0.072 40 DATA 0.363,0.189,0.131,0.101,0.085,0.075 50 DATA 0.364,0.190,0.132,0.103,0.087,0.078 60 DATA 0.365,0.191,0.133,0.105,0.090,0.081 70 DATA 0.366,0.192,0.134,0.106,0.092,0.082 80 DATA 0.360,0.204,0.169,0.179,0.185,0.189 90 DATA 0.366,0.267,0.223,0.233,0.238,0.241 100 DATA 0.373,0.247,0.261,0.271,0.275,0.276 110 DATA 0.380,0.270,0.292,0.301,0.303,0.303 120 DATA 0.387,0.296,0.317,0.325,0.327,0.326 130 DATA 0.394,0.319,0.339,0.347,0.347,0.345 140 DATA 0.381,0.312,0.295,0.284,0.275,0.268 150 DATA 0.429,0.381,0.360,0.346,0.336,0.328 160 DATA 0.472,0.428,0.405,0.389,0.377,0.368 170 DATA 0.511,0.465,0.440,0.423,0.410,0.400 180 DATA 0.545,0.496,0.469,0.451,0.437,0.426 190 DATA 0.574,0.523,0.494,0.475,0.460,0.449 200 FOR I=1 TO 18'read data table 210 FOR J=1 TO 6 220 READ HC(I,J) 230 NEXT:NEXT 240 T15'temperature of surface 1 (F) 250 E1=.03'emissivity of surface 1 260 T2u'temperature of surface 2 (F) 270 E2=.8'emissivity of surface 2 280 L=2'air gap (valid range: 0.5-3") 290 LI=INT(2*L+.5)'length table index 300 HF=0'heatflow 0-down,1-sideways,2-up 310 E=1/(1/E1+1/E2-1)'effective emittance 320 TM=(T1+T2)/2'mean temp (F) 330 DT«S(T1-T2)'temp diff (valid range: 5-30 F) 340 DTI=INT(DT/5+.5+6*HF)'temp diff table index 350 HR=.00686*((TM+459.7)/100)^3'radiant conductance 360 R=1/(E*HR+HC(DTI,LI))'US R-value (ft^2-F-h/Btu) 370 PRINT T1,E1,T2,E2 380 PRINT L,HF,R
T1 (F) E1 T2 (F) E2
105 .03 75 .8
gap heatflow US R-value
2" 0 (down) 7.146456
With more than one space in series (eg double-foil foamboard spaced away from a basement wall), we can't just add R-values. We only know the overall temp diff, so we have to iterate to find a solution. It's no surprise that the FTC prohibits makers from advertising R-values for radiant barriers to avoid confusing the public.
Nick
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Yea nick well if you were correct foil faced foamboard both sides would not have the R rating it has, which is verified, it would be R6 more. Foil is a Radiant barrier only, it has no R value to speak of, or gee, wouldn`t the big manufacturers like to be as smart like you and capitalise on extra performance. Nick you should go into business, mortage everything, buy 1" Polyisocyanurate foilfaced foamoard and add R6 to the rating to tell everyone its R13.2 and sell it, and see what Gov agencys come knocking to make you prove it.
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Nope. FTC rules mostly prohibit advertising installed R-values to avoid confusing people smarter than you :-)
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Nick,
How does this work out for the double bubble?
It seems to me there are two ways to go for the underfloor insulation for staple up radiant.
One is foil backed fiberglass insulation with an airspace. That is hard to find! The other would be double bubble stapled on the joists. It seems to me that would minimize heat loss through the joists themselves as they would be uninsulated elsewise. Any thoughts?
Jeff

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Haven't tried that. You might work it out, if you know the gap width, etc.

I would staple on foil or thin double-foil foamboard.
Nick
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It is?
The British Advertising Standards Authority got Actis, a French company, claiming their reflective foil insulation is 'Equivalent to 200mm of traditional Rockwoool insulation'. A complaint has been upheld after ASA went to independent technical experts.
The judgement can be seen at: http://tinyurl.com/s6c2p
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The link above does not work. Here is the ruling:
Actis Insulation Ltd Unit 1 Cornbrash Park Bumpers Farm Industrial Estate Chippenham Wiltshire SN14 6RA
Date: 31st May 2006 Media: Brochure
Sector: Household
Public Complaint From: Gloucestershire
Complaint:
Objection to a brochure for roof insulation. The brochure stated "TRI-ISO SUPER 9 Insulation for roofs ... Thermally equivalent to 200 mm of mineral wool when installed in a roof situation, as certified by the European certifying body, BM TRADA CERTIFICATION (following real building trials, certification n°0101) ... THERMAL EFFICIENCY equivalent to 200 mm of mineral wood RT = 5* ... *in situ measured values." The complainant challenged:
1. the claim "Thermally equivalent to 200 mm of mineral wool" and
2. the quoted thermal resistance "RT = 5".
Codes Section: 3.1, 7.1 (Ed 11)
1. Complaint upheld
The ASA obtained expert advice. We understood that BM TRADA had tested TRI-ISO SUPER 9 and the mineral wool in two separate roof installations. However, we noted that BM TRADA had not used the standard industry methods of testing and that the report provided by Actis did not include sufficient detail to support their own methods of testing.
We acknowledged that BM TRADA Certification was a leading multi-sector certification body accredited by the United Kingdom Accreditation Service. We considered that the BM TRADA report did not provide enough detail to support their methodology instead of the methodology employed by the internationally recognised ISO industry standards. We concluded Actis had not substantiated the claim. We noted the ad was no longer appearing but told Actis not to repeat the claim in future advertising until they were able to provide sufficient substantiation.
2. Complaint upheld
We understood that RT was a symbol of total thermal resistance and typically had the standard unit of measurement of m²K/W. We noted that the claim "RT=5" was not qualified by any recognised units of measurement e.g. m²K/W and a small footnote stated only "in situ measured values" without further explanation. Because the value of 5 was not qualified by any recognised units of measurement, we considered the claim "RT=5" was ambiguous and should be qualified in future. However, we noted that the BM TRADA report did specify an overall resistance (RT) of 5.0m²K/W derived from the in situ testing. We understood that the in situ measured values did not meet with ISO recognised international standards for determining declared and design thermal values for building materials and products.
We considered that the BM TRADA report did not include sufficient detail to demonstrate the validity or robustness of their testing methodology instead of the methodology employed by ISO standards. We concluded that the report did not substantiate the claim " RT=5". We told Actis to remove the claim until they were able to provide sufficient substantiation.
The brochure breached CAP Code clauses 3.1 (Substantiation) and 7.1 (Truthfulness).
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... ie they faulted the test documentation, vs the result.

... and they faulted the lack of explicit units in the advertised result.

Picky, picky. Reflectix does advertise some system R-values:
http://www.reflectixinc.com/script/products/product.asp?IDd http://www.reflectixinc.com/script/products/product.asp?IDw www.majorgeothermal.com/PDFs/Reflect/Solutions.pdf
The US R16.8 crawl space number is interesting.
Nick
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wrote:

An important question here is how does other insulation perform 'in-situ' if measured the same way as this product.
If this product can achieve an RT=5 'in situ', that means the overall measured insulative performance is 5 m^2-K/W. That performance includes the affects of convection and radiant heat transfer from the living space to the product, and from the product to the environs on the other side.
But what is deceptive about this, is that if I were to put a simple piece of conventional building insulation that has an RT=5 value in the same circumstance, it would undoubtedly have an 'in situ' performance that is *better* than 5. Because added to the material's own RT=5, would also be the affects of the convective layers on each side (just like this product), and the radiant transfer to/from the surfaces.
Unless this products RT value is calculated by taking the 'in-situ' performance and *subtracting* the insulative performance of those items common to *all* installations, the RT value is inflated by those other factors. Thus when compared with other materials tested in the more traditional manner, it overstates this product's performance.
daestrom
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In this case, one would hope they derived by subtracting. Nobody seems to have disputed the result that it worked as well as the rock wool did.

That number includes the other stuff, as the FTC-mandated "system R-value," with a substantial contribution from the foil surface. A non-radiant maker could also legally advertise a system R-value in the US.
Nick
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daestrom wrote:

Conventional insulation would only be between the floor joists. For 2 bys at 16" centers that means that 12.5% of the area is the insulation value of only the joist. I would think that would be around a US R6 for a 2 * 6. There will be a point of diminishing returns for conventional insulation, just because of that. Don't forget that under most floors you have a maze of plumbing and wiring and that has to be worked around with conventional insulation.
The more interesting question in my mind, is whether this would be a good afterfit for an existing structure. It certainly would be easier (crawl spaces are no fun!) to install and it would be a complete seal. It seems to me that most energy lost is in existing structures rather than new construction. The option of tearing down the old house and building a new does not exist for most people.
I would be delighted to have a US R 16.8 floor in my '20s house. At this point underfloor radiant with radiant bubble looks attractive, not sure which way I will go and I'm open to other suggestions (like foil backed iso).
Jeff
Because added to the material's own RT=5,

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wrote:

They now have TRI-ISO SUPER 10, not 9, so this judgement againast them doesn't stand anymore. They still state that it is equiv to 210mm of mineral wool. <http://www.tri-isosuper10.co.uk/tri-iso_super_10_thermal_insulator_test_data.htm
I might put a complaint in.
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Further to the above:
The UK authorities have pulled the plug on multifoils, when used on their own. The Multifoil Council) made pleaded to the Office of the Deputy Prime Minister when the last round of Part L (energy aspect) of the building regs was being assessed and had a reprieve to 01/01/2007 to give them time to show that multifoils worked as claimed. This repreive has been recinded early because of convincing evidence that the multifoil claims are exagerated. Multifoils will only be permissable if they can pass hot box tests, which they have never have. All the local authorities and the NHBC and such bodies have all been told to no longer accept multifoils.
Action may be taken against the 3rd party certifiers, principally BM Trada, who gave their stamp of approval to Actis and others.
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Rockwool has a set value and can be compounded. Makers claim all sorts of wild claim for radiant barriers. To bottom line, what is it the equivalent to in rockwool in thickness?
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News wrote:

I think that is exactly what Nick has done. But remember fiberglass blankets are temperature independant (mostly). Radiant barriers are dependant on the temperature (emisivity is T^3) and the air space can be treated as a more conventional "R" value. Note that Nick has commented the code.
Run that for a higher delta temp and you will get a higher R, just a lower delta temp gives a lower.
Jeff

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I am very sceptical of these barriers. What they need to do is have two identical houses in the same place, one with the barrier and one with rockwool. Then do data monitoring for a year or more. The British ASA ruled against Actis, a French maker, as the tests were not good enough. There is no testing model to explain. After all this time you would have thought they could have done tests on an Actis Triso9 house and an identical house without Actis with 200mm of insulation in the walls. If there was a clear difference I'm sure they would be crowing from the rooftops with all data printed and freely given out at every bus stop.
This stuff is not cheap. As far as I can see it is expensive bubble wrap - until proper meaningful realistic independent tests have been undertaken.
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