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re: drum wall thermal storage questions.......................
11 apr 2002
michael d  wrote:

>why is the bubblewall r2 during the day, and r20 at night?

a single layer of polycarbonate glazing is about us r1. bubbles add from
r1 to r4 per inch of thickness, depending on their size and temperature,
r1 for a 1500 expansion ratio (bubble volume to detergent solution volume) and
r4 for 1/16" bubbles with a 50 f mean temp, eg 70 inside and 30 outside.

>nick, how accurate do you think your calculations are?  have you
>validated them in any way?

my main source is a 50 page(?) report written by john groh at u arizona
in the 70s. lots of experiments with graphs, and diagrams and pictures of
a greenhouse and its foaming equipment. other sources include the us
version of the old swedish patent for insulating shop windows at night
(which does not mention specific r-values), some conversations and a 1984
report from professor otho wells on his experimental greenhouse at u new
hampshire, some discussions with richard nelson in montreal, a visit and
some discussions with bill sturm about his 12,000 ft^2 bubblewall tomato
greenhouse in calgary, and a talk with bob quist in toronto, who is now
applying bill's patented technique to venlo glass greenhouses (the most
popular style in holland), which bob invented. 


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