[GSBN] Straw bale lambda

[Derek Roff]

Hi, André,

In my edition of Bruce's book, on page 185, Footnote A, the general 
conversion factor is given as 5.678, for converting between metric and 
"Murrican" U-values.  Inversely, the conversion factor for R-values is 
given as 0.1761.  (Since 5.678 and 0.1761 are inverses, either of these 
numbers is sufficient for converting both U-values and R-values in both 
directions, if you set up the equation properly).  Bruce's conversion 
factor is in agreement (of course) with several web sources, including 
Wikipedia on R-value: 
<http://en.wikipedia.org/wiki/R-value_(insulation)> (Click on item 1 
"Units") in the pages Contents.)

On page 187, Bruce's book gives an R-value of 1.45 per inch for 
strawbale.  It goes on to say that the thermal resistivity was found to 
be higher for bales stacked on edge than flat.  It doesn't say which 
orientation the 1.45 figure refers to.  Using the R-value conversion 
constant of 0.1761 from page 185, I set up the equation like this:

(Murrican R-value) 1.45/inch x 0.1761 (Murrican R-value to metric 
conversion factor) x 39.37 (inches to meters) = 10.05 (metric R-value 
per meter)

1.45 x 0.1761 x 39.37 = 10.05

That seems to confirm Rob Tom's calculation.  Not that I ever doubted 
it.

Derek

PS.  I wonder if Graeme North might have transposed two digits in his 
message.  5.678 rounds nicely to 5.68, which is in agreement with all 
the sources that I looked at.  "5.86" looks like it might be the same 
number with the last two digits transposed.


--On Monday, June 15, 2009 8:22 PM +0200 contact at lamaisonenpaille.com 
wrote:

> Hello,
>
> For the purpose of publishing Bruce Kings book "Design of SB
> Buildings" in french I would appreciate someone from this list
> confirming Rob Tom's conversion below (for page 187):
>> A thermal resistivity of 1.45 ft2*hr*degF/Btu*inch (Murrican)
>> converts to 10.05 m2*degC/W*m (SIU).
>>
>> The thermal conductivity, or lambda value = 1 / thermal resistivity
>> = 1 / 10.05 m2*degC/W*m
>> = 0.0994 W/mK lambda (?)
>
> Thanks,
>
> André de Bouter
> La Maison en Paille
> www.lamaisonenpaille.com
> _______________________________________________
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Derek Roff
Language Learning Center
Ortega Hall 129, MSC03-2100
University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek at unm.edu