Heat conduction from basement to earth/soil below

[Klaus Kragelund]

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

[Joseph Meehan]

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.

[m Ransley]

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.

[nicksanspam]

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

[nicksanspam]

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

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=105'temperature of surface 1 (F) 250 E1=.03'emissivity of surface 1 260 T2=75'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=ABS(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

[Edwin Pawlowski]

Su, what the f*ck does all that gibberish mean? Oh, I know, it means Nick can show off he knows a couple of equations and has a calculator. So, rather than impress us with all of your learning, why not take the time to explain if this is good or bad and translates to dollars (or Euros) saved.

Yes, that closed cell EPS will be a good insulator.

[m Ransley]

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.

[m Ransley]

Gibberish is right, "Covering the ceiling with foil gives you R10" Covering nick with foil and putting him in " Nicks Lightbulb Sauna" [easybake oven] of previous fame, for a month would do it, or maybe he just got out of his Easy Bake Oven [sauna].

[Jeff]

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

[Klaus Kragelund]

Thankyou for the very good points

The basement is going to be used for office, so it will be heated all year round.

I should have said I'm situated in Denmark (just north of Germany :-)

Perhaps then my number of 6 degrees gradient is overly optimistic due to fringe effects near the outer walls. I want as little insulation as possible since adding too much to the floor will limit the height of the doors.

Currently no mostiture film is used. I want to add a wooden floor with a carpet on top of this. The basement is dry, but my intention was to add ventilation holes in the wooden floor and use no platic film to allow the construction to"breathe". But adding plastic film might be a good idea since this also limits heat flow caused by travelling moisture.

Thanks

Klaus

[nicksanspam]

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

[nicksanspam]

That's called "elementary engineering" :-) The OP Klaus is an engineer.

Nick

[nicksanspam]

m Ransley errs again:

Nope. FTC rules mostly prohibit advertising installed R-values to avoid confusing people smarter than you :-)

Nick

[nicksanspam]

You are welcome.

Danish people might permit a tiny amount of dust on the upper foil. Then again, they build airtight houses, so excess moisture could be a problem in summertime.

You may not need the wood.

Upwards heatflow could be nice in wintertime.

Nick

[News]

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:

Think hard before you buy.

[News]

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?

[Jeff]

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

>

[News]

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.

[News]

"News" wrote in message news:44ca5155$0$17961$ [e-mail]...

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

1. the quoted thermal resistance "RT = 5".

Codes Section: 3.1, 7.1 (Ed 11)

Adjudication:

Actis Insulation Ltd (Actis) said they had stopped advertising TRI-ISO SUPER

9 because it had been replaced with their new product TRI-ISO SUPER 10. They said the efficiency of their products was demonstrated by their track record in the market. Actis said they had commissioned BM TRADA Certification Ltd (BM TRADA) to test, assess and report on the TRI-ISO Super 9 product. They provided us with a copy of the BM TRADA Certification and Report dated August 1997 and said that it substantiated their claims. Actis explained that TRI-ISO Super 9 was different from traditional bulk insulation because it was a multi-foil product that used layers of reflective foils spaced with synthetic wadding and foams. They said the product required less space than traditional bulk insulation and, therefore, internal insulation cavities could be made smaller and internal useable spaces could be enlarged without compromising efficiency of insulation. Actis argued that traditional methods of testing were not appropriate for their product because traditional methods measured thermal efficiency mainly by conduction and did not take into account the influences of convection, radiation and change of phase. They said their product combined various energy transfers of radiation, conduction, convection and change of state rather than just conduction. Actis also argued that traditional methods of testing did not allow representation of the real behaviour of building materials once used on site. They pointed out that BM TRADA had used "in situ" testing involving a real external environment with variations in temperature, humidity, etc. rather than the traditional methods of laboratory testing. Actis maintained that the BM TRADA Certification demonstrated the thermal efficiency of their product and provided proof of their claims.

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.

1. 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).

[nicksanspam]

... 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:

?ID=77www.majorgeothermal.com/PDFs/Reflect/Solutions.pdf

The US R16.8 crawl space number is interesting.

Nick