[Greenbuilding] Precision for Air Permeance numbers (was Re: insulating on sheathed roof)

[Robert Tom]

On Thu, 03 Jan 2008 17:29:04 -0500, Bob Korves <bkorves at winfirst.com>  
wrote:

> I have a problem with is the fact that the Canadian government test
> results are listed in six significant figures.  Anyone who has taken a
> quantitative analysis class would know immediately that this sort of  
> testing is not reportable to six significant figures.


I've never taken a "quantitive analysis" class but I don't have a problem  
with the 4 decimal place precision of the test data in the report.

The numbers that I cited for "Q-avg" (average air flow) were determined  
 from test data for Q-min and Q-max.

There were 12 materials tested whose air flow numbers were too low to  
measure.

Of the 24 materials that demonstrated measurable air flows, the Q-min (@75  
Pa) readings ranged from 0.0006 to 75.2354 L/s-m^2 for 23 of those 24.
The first measured 0.0000 for Q-min. (My guess is that the test equipment  
probably yielded readings to 5 or possibly even 6 decimal places.)

I don't know anything about the external research contractors who did the  
study (AIR-INS Inc., St. Laurent, QC) for CMHC but they did validate their  
test method against that developed by IRC (no slouches on the  
international scientific research stage) according to the preamble in the  
report.

I'm not here to defend AIR-INS,  CMHC( http://cmhc-schl.gc.ca ), IRC/NRC
( http://irc.nrc-cnrc.gc.ca  ) or that now-almost-20-year-old report
but I seriously doubt that they "made up" the 4-decimal-place-precision  
numbers listed in the tables.


-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at chaffY a h o o  dot  c a >
manually winnow the chaff from my edress in your reply