[GSBN] Imperial to SUI conversion Vapour Permeance

RT ArchiLogic at yahoo.ca
Mon Sep 1 22:58:31 CDT 2014


On Mon, 01 Sep 2014 20:48:20 -0400, <GSBN-request at sustainablesources.com>  
wrote:

> Date: Mon, 1 Sep 2014 21:33:40 +0000
> From: Derek Stearns Roff <derek at unm.edu>
> To: Global Straw Building Network <GSBN at sustainablesources.com>
> Subject: Re: [GSBN] Perms and Grains?
[snip]
> The SI unit for permeance is kilograms per second per square meter per  
> pascal, and is roughly equal to 1.74784x10+10 US perms.  If I?m  
> calculating correctly, I think that?s over 17 billion US perms.  Perhaps  
> not the most useful unit for builders.

Can't say for certain what those Murricans in the deserts of New Mexico  
are measuring when they look at the vapour permeance of materials but here  
in MooseLand where nous sommes bilingues, both in terms of language as  
well as weights and measures, many of us like to speak in terms of " ng/Pa  
* s * m^2 " for the SI units of vapour permeance, ie "nanograms" rather  
than "kilograms". That may help to explain the billions that the Derelict  
was talking about.

If a material allows kilograms of water to pass through an area of a  
square metre, then one is probably talking about bailing with buckets (as  
in "HARRRR-RR_RRR !!!, Avast, me mateys, we's a-goin' down fast unless ye  
grabs them buckets and commences t' bailin' !" ) as opposed to vapour  
transmission rates when building with bales.

And generally speaking, geek to geek, the conversion factor is 57 (57.2148  
if you want to get fussy about it) for Imperial (grains/(hr·in Hg· ft2) to  
Metric perms.


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Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at  Y a h o o  dot  CA >
(manually winnow the chaff from my edress if you hit REPLY)

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