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[GSBN] re : 40% humidity



On Wed, 07 Nov 2007 23:56:23 -0500, GSBN GSBN@... wrote:

Date: 7 Nov 2007 10:25:30 -0500
From: jswearingen@...
Subject: Re: GSBN:40% humidity

Very interesting paper, and well written.

On Nov 6, 2007 1:03 PM, Graeme North ecodesign@... wrote:
<a  target="_blank" href="http://www.natmus.dk/cons/tp/wallbuff/wallbuff.htm";>http://www.natmus.dk/cons/tp/wallbuff/wallbuff.htm</a>

At first glance, I'd have to say that the paper looks a bit too much like junk science ... just enough technical mumbo jumbo to give it a cachet of being legitimate but upon closer inspection, not so much .

For one, in the intro it talked about an old museum in England where the ventilation channels were stuffed with cotton rope and (not surpisingly) that had some sort of effect on humidity levels.

Well, from what I understand, air-tight construction is not a typical trait even in modern-day UK buildings so of course, reducing the air leakage in an old all-masonry building by stuffing rope, will help to reduce air infiltration/exfiltration and help to stabilise the interior humidity levels.

The paper also mentions at the outset, something to the effect that "humdity buffering" (with the use of hygroscopic finish materials ) would not be effective in buildings whose air change rates exceed 0.1 ACH.

The minimum ventilation rate as set out by the American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) is 0.35 air changes per hour ... over three times the ventilation rate which the paper says is the upper limit for humidity buffering to work.

The ASHRAE limit of 0.35 ACH is the *worst* that one would want to have in a building. ie Anything below that would present a risk to occupant health. There are many who think that even the ASHRAE minimum is too low.

Obviously, the air-change rate in a home or building would need to exceed the ASHRAE minimum of 0.35 ACH. ie at times of higher-than-normal occupancy and after "odour" or "high moisture" events and these are far from being rare.

There were other points in the paper that were just as suspicious at first glance but suffice it to say that the notions espoused come across as being as iffy as the 90's notion of Porenluftung, aka "breathing walls" that function like big air-air heat exchangers, a myth that pervaded the early days of SBC and traces of which are still lingering.

That is not to say that the notion of humidity buffering via the use of hygroscopic finishes is a falsehood because it is not.

It's just that the notion of expecting hygroscopic finishes to be all that is necessary to maintain stable and healthy humidity levels in a home or building, is wishful thinking.

PS If some of you are wondering why you may have received this message in duplicate, I copied you on this message in addition to sending it to the List because from my end, it looks like the List software has not been letting my messages through.

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Rob Tom
Kanata, Ontario, Canada
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