[GSBN] R value export straw blocks?

[Rene Dalmeijer]

John and others,

One of the issues I might have missed in this discussion is the effect of convection in specifically walls in fibrous insulation materials. This effect is common to all open cell and fibrous insulation materials with increasing importance with increasing insulation thickness, an effect that is not accounted for in the thin specimen hot box tests. 

I am sure the increase in insulation value found with higher densities (to a certain limit) is due to the increased resistance to convection. Where convection is a function of the density (air resistance) temperature differential, thickness and height of wall, ie meaning there is no single optimal density value. I would be nice to find the relative effects of the various factors including moisture but this would mean a very extensive amount of measurements.

Pondering an optimal basking time in the reclaimed swamp at an old branch of the Rhine
Rene Dalmeijer

On Jan 27, 2015, at 14:46, John Straube wrote:

> 
> I am beginning to think that the fiber diameter of SB varies sufficiently between types to explain results that vary almost 50% from 0.040 to 0.060. A value of 0.04 is hard to imagine achieving in practise as it basically what most stone wool products achieve, an they have a lot more control of fiber orientation and diameter.  Running some fibers through a light hammer mill to split and open the fibers, remove dust, then rebale until we find a good way to make the fibers fine long but smaller diameter would be a thought Worth it? Doubt it, but then we could perhaps identify which straw in the field is best for thermal performance, and which is not..  
> 
> 
>> Hi All,
>> 
>> I have recently joined as a posting member to GSBN so thought I'd add to the conversation on thermal conductivity of straw at different densities. Colleagues of mine at the University of Bath have done some testing in this area and published the findings - details here: http://opus.bath.ac.uk/30137/ 
>> 
>> The paper includes a graph (copied below) of tests done at Bath Uni and others, including FASBA. The results suggest that below a density of 120kg/m3 thermal conductivity is less sensitive to deceasing density than might be expected. It appears that the thermal conductivity of straw is actually more sensitive to the temperature of the straw and it's moisture content. Hope this is of interest.