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

Wed Mar 9 00:41:28 CET 2005

Yes, Dirk, most of the lambda-value tests appear to be for heat transfer 
perpendicular to straw strand direction (i.e. the equivalent of bales on 
edge).  There are however a few with heat transfer parallel to strand 
direction - these (if I have translated documents correctly) include one 
Austrian test run, two Danish test runs and one of McCabe's results.  (I 
am not entirely clear about the Sandia tests, which used a line heat 
source rather than a hot plate method: while the test report is not 
clear on the point, I assume that the values obtained are some sort of 
average of all directions).  For the "standard" bale construction which 
I used to compare all the results, these 4 "parallel" tests give 
U-values of 0.12 to 0.14 when calculated on the assumption of purely 
conductive heat transfer.  The other 19 "perpendicular" results give 
values of 0.09 to 0.15 - in fact all but a few are in the 0.10 to 0.12 
range.
Not an enormous disparity, but probably a significant one.
I'm not sure where this takes us, though.  As noted in my previous 
message, the U-values obtained for whole-wall tests appear to be about 
0.20 for both perpendicular and parallel options.  There is therefore a 
discrepancy to explain for both configurations.  (And it's actually 
rather easier to explain for the parallel option, as convection currents 
are more favoured by that configuration.)
atb,
Mark

Dirk Scharmer - Architekturbüro WAND4 wrote:

>Okay Mark,
>Thank you very much for this excellent abstract.
>But what is about the direction of the straw blades? You cannot ignore it!
>As I know all the tests you mentioned are probable conducted with straw in
>direction of the heat transfer, aren't they?
>Or rather, the direction is not documentated.
>
>Dirk
>
> 
>-----Ursprüngliche Nachricht-----
>Von: strawbale-admin at amper....muni.cz
>[mailto:strawbale-admin at amper....muni.cz] Im Auftrag von Mark
>Bigland-Pritchard // Low Energy Design
>Gesendet: Samstag, 8. Januar 2005 19:04
>An: strawbale at amper....muni.cz
>Betreff: Re: [Strawbale]Re: Strawbale digest, Vol 1 #474 - 7 msgs
>
>
>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
>
>
>asbn wrote:
>
>  
>
>>Dear Mark
>>
>>If you want to know the difference between e.g. cellulose, sheep-wool,
>>    
>>
>flax,
>  
>
>>fiberglass and strawbale, our tests give a relevant result (all are 0,045),
>>even when the thickness of the measured probe is smaller than that of a
>>strawbale. All of these insulation-materials act different in reality or
>>when wet. But for all organic insulation-materials there is a 20% addition
>>in value by way of calculation for that reason (not so for fibreglass). And
>>all are measured under the same conditions.
>>
>>When you have to prove the insulation quality to officials to get better
>>financial supplies when you build, these tests are relevant, because this
>>paper is the only thing that matters and all common building-engineers use
>>these tests for energy-analysis.
>> 
>>We all - networkers, builders, architects, officials - know, that reality
>>    
>>
>is
>  
>
>>a different thing, even one (passive)house doesn´t act as the other one.
>>    
>>
>But
>  
>
>>as long as we have to compete with cheap prefabricated-houses or expanded
>>polystyrol-passive-houses, truth is on our side, when we rely on our tests.
>>
>>Strawbale-(passive)houses in Austria are usually build with this
>>construction / wall-system:
>>1,5  2 cm limeplaster on facade
>>3 - 5 cm magnesiabound Heraklith-plates (woodchips)
>>Wind-protection-folie
>>2,4 cm diagonal wood-boards
>>35 cm strawbale with 6 x 35 cm construction-timber (sometimes in a
>>dual-sandwich-system, isolated with 5 cm cork)
>>2,4 cm wood or OSB-boards*
>>3 - 5 cm magnesiabound Heraklith-plates (woodchips)
>>2 - 5 cm clayplaster (thickness depends on wall heating-system)
>>
>>*If OSB-boards are glued, wind-protection-folie is not necessary.
>>
>>Blower-door-test is obligatory if you want a financial (eco-)supply by the
>>government in Austria.
>>
>>This wall-system has many advantages (e.g. easy to use installation-level
>>    
>>
>in
>  
>
>>Heraklith-boards). And I´m sure, this is a passivehouse-system, U-value
>>around 0,12 - 0,14 W/m2K. For sure it is a safe (and therefore accepted)
>>system (post-and-beam-construction) for countries with much and cheap
>>wood/timber (not so for Denmark).
>>
>>Best wishes from Austria
>>Herbert Gruber, ASBN
>>
>>
>>08.01.2005 15:35 Uhr
>>
>> 
>>
>>    
>>
>>>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
>>>   
>>>
>>>      
>>>
>>
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>>
>>    
>>
>
>
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>
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