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

[asbn]

Dear Mark

I agree with you in most of your arguments (except the air-circulation). And
I didn´t know the differences in testing-methods even in Europe.
Just one more word: It was a long way to acceptance and it was sometimes
hard and unfair. And I learned once again: one bad news is more efficient
than hundred good ones. All I want is a fair "procedere", so if we make
efforts to "understand" the material, why not understand it in relation to
other materials. And communicate that.

Best wishes and thanks for all the information in your email.
Herbert Gruber, ASBN


08.01.2005 19:04 Uhr

> Herbert -
> 
> I'd love to see the results of an in-situ test for U-value for your
> standard Austrian design.  The heraklith and timber layers will
> certainly result in a better figure than for some other sb
> constructions, though I also see scope for convective air circulation
> around the bale layer if the bales are not particularly well packed.
> 
> Hot-plate lambda-value testing is not the only option when it comes to
> internationally-recognised standard procedures.  Obviously, each
> government can to some extent pick and choose which international
> standards it approves, and I don't know the situation in Austria, so I
> can only note the British situation.  Here, hot-box U-value testing is
> recognised in our building regulations - the relevant test here is BS EN
> ISO 8990: 1996.  (From a cursory reading of the standard, I think some
> modifications would be necessary for a full-width strawbale wall, but
> that's not a major point.)  The By og Byg testing programme in Denmark
> included this same procedure.
> 
> Now, the relevance of all this to strawbale construction is that the
> U-value tests which have so far been carried out give somewhat worse
> values than those calculated in the standard manner from lambda-values.
> Calculations from lambda-value tests (yourselves in Austria; By og Byg
> in Denmark, FSD in Germany, abd el-Fattah Ashour in Germany, McCabe in
> the US, Sandia in the US) give U-values ranging from 0.08 to 0.16 for a
> standard bale wall with 20mm lime or clay plaster on each side.  Apply
> the official 20% fudge factor which you mention to the tests to which it
> is relevant, and that range changes only slightly:  0.10 to 0.16.  Now
> compare that to the wall-assembly U-value tests which have been carried
> out (values adjusted for same standardised bale and plaster dimensions):
>   Ship Harbour, Nova Scotia, 1995:  heat flow monitoring:
>                 U=0.20  (bales laid flat)
>   ORNL, Tennessee, 1996: guarded hot box, to US standard ASTM C236:
>      U=0.32  (bales laid flat)
>   California Energy Commission, 1997:  guarded hot box test, again to
> C236:     U=0.26  (bales laid flat)
>   California Energy Commission, 1997:  guarded hot box test, to
> C236:             U=0.19  (bales on edge)
>   ORNL, 1998: C236 again, but better-built
> wall:                                              U=0.21  (bales laid flat)
>   By og Byg, Denmark, 2001:  hot box test, to ISO
> 8990:                                  U=0.19  (bales laid flat)
>   By og Byg, Denmark, 2001:  hot box test, to ISO
> 8990:                                  U=0.22  (bales on edge)
> Both the first ORNL test and the first CEC test had well-documented
> problems, so they can be disregarded for our purposes.  That leaves us
> with virtual unanimity around U=0.20.
> 
> This represents a big difference from values calculated from
> lambda-values, and we do ourselves no favours by pretending otherwise.
> Jeff Christian (ORNL) and Joergen Munch-Andersen (By og Byg) have both
> made useful comments on the subject, and I expect to make some of my own
> when I've done a bit more data analysis.  But, however you work it out,
> I am convinced there is something happening here besides straight
> conduction through the wall.
> 
> Yes, as you say, there will be disparities between theoretical and
> actual U-values for more "conventional" types of building construction.
> If your interest is in being at least as accurate as the "competition",
> you're probably right.  Similarly, if you just have to convince building
> officials, you should be able to do so with lambda-values.
> 
> But if we want to understand how the material works, or predict building
> performance (for ourselves, so we know we are doing the best we possibly
> can), or merely do calculations to size components of the heating
> system, just working from lambda-values is, I think, going to be misleading.
> 
> atb,
> Mark