[Strawbale]realistic SB lambda values

[Rene Dalmeijer]

Herbert,

I appreciate that you support the high (low) numbers achieved in the 
tests you mention. I also agree that the MacCabe tests are not 
indicative of normally attainable Lambda values. But I have serious 
reason to doubt that actual SB buildings will achieve the 0.045 you and 
the tests mention. Nearly all other tests (not only the Mac Cabe test 
which again I think is an anomaly Check Bruce Kings website for an 
overview of the tests) show much lower values. I cannot accept that the 
relatively coarse, open, patchy SB can almost approach the same Lambda 
value as specifically fabricated insulation materials exhibiting much 
better capability to entrap air in small pockets.

I am sure the tests have not been tricked or rigged to achieve the high 
values. I just think values measured are due to the very specific 
circumstances under which these tests are executed. ie the test does 
not properly reproduce circumstances that arise under real building 
applications. I am not saying the tests have been faked, just they 
don't allow for the specific characteristics of natural building 
materials exhibiting greater variance and in-homogeneity. We are 
interested in how the system works as a whole and not what the specific 
performance is of one single component. Most conventional materials 
perform quite poorly in this respect then a SB wall system. Which is 
much more homogenous as a whole then nearly all other insulating wall 
systems. I would love to execute a few field tests using a heat 
conductance meter to verify values (to maybe even find that the 0.045 
is almost true)

In the meantime though I would not count on 0.045 as this could lead to 
a serious disappointment regarding the performance of the passive 
house.

A major issue leading to a lower performance of SB as an insulator is 
the existence of air circulation in the bales this is bigger then in 
most conventional insulation materials. Higher density bales like 
jumbos seem to exhibit a better performance in this respect then normal 
density(115kg/m^3) bales.



On Mar 8, 2005, at 16:49, strawbale-request at amper....muni.cz wrote:

> What is quite realistic? I wonder that you cannot accept, that the 
> OFFICIAL
> heat measurement-tests in Austria and Germany faced much better 
> results than
> the improvised tests of MCCabe in USA.
>
> Be sure, there were no tricks: lambda10tr = 0,038, lambdaZ = 0,045
> (lambda10tr is the value measured on the dry (tr) material at 10 
> degrees
> middle-temp., lambdaZ is the measured value + 20% addition)
>
Rene