[Strawbale]Re: Strawbale digest, Vol 1 #474 - 7 msgs

[Mark Bigland-Pritchard // Low Energy Design]

Dear all,

The low lambda results in Germany, Austria and Denmark are indeed based 
on official test procedures, and appear to be reliable.  However, in 
these procedures, (i) the thickness of bale used is smaller than that 
for a wall assembly, and (ii) only very dry material is used.  Hence, if 
(a) there is any heat transfer effect which isn't proportional in its 
extent to the thickness of material, or (b) if moisture movement makes 
any difference, these tests will not be directly applicable for U-value 
calculation without some sort of adjustment factor.  There is reason to 
believe that convective effects, including moisture transfer, do make 
some difference in a real-life wall assembly.
This indeed appears to be the case when we look at the whole-wall 
U-value tests carried out by ORNL and by the Danish testing programme - 
both to variants of official test procedures in the countries 
concerned.  These give significantly higher U-values than can be 
explained by the lambda values.  There is some useful discussion of this 
in the Danish summary document:
Munch-Andersen, J & Møller Anderson, B (2004),   Halmhuse: Udformning og 
materialeegenskaber,  By og Byg resultater 033, Statens 
Byggeforskningsinstitut, Hørsholm, Denmark
which is available online in .pdf format at the By og Byg website.
Realistically, I would not assume a U-value of less than 0.2 W/m2/K for 
a 2-string-bale wall laid flat.  The results seem to me to suggest that 
you'd get much the same for the same bales laid on edge.  (Though I 
personally have big doubts about on-edge bales for other reasons...)

Mark


asbn wrote:

>Dear Jan, dear Rene
>
>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)
>
>As you can see on:
>http://www.fasba.de/info/downloads.html (Germany)
>Or
>http://www.baubiologie.at/download/zertifikate/lambda.html (Austria)
>
>I know the building market very well and I even have seen the tricks to get
>results you want (like B1 for cellulose). I think, there is no time to
>understate (or use the worst results you can get). Fact is: it is possible
>to build a passivehouse with 35 cm bales - although isolation is not all.
>
>Jan, if you need this datas for a German Passivehouse-Gathering, please use
>the german test-results!
>
>Best wishes,
>Herbert Gruber, ASBN
>
>08.03.2005 13:17 Uhr
>
>  
>
>>Some of the measurements have given figures of 0.045 but I think these
>>are not realistic. I expect though that a well executed dense
>>(>120kg/m^3) SB wall could achieve a value in the region of what you
>>seek.
>>    
>>
>
>
>
>
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