[Greenbuilding] Relative humidity in heated houses

[John Straube]

What absolute humidity level?  Humidification we know is needed in very leaky houses and very dry climates. 

John Straube
519 741 7920
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-----Original Message-----
From: "JOHN SALMEN" <terrain at shaw.ca>
Sender: greenbuilding-bounces at lists.bioenergylists.org
Date: Wed, 27 Oct 2010 14:42:01 
To: 'John Straube'<john at buildingscience.com>; 'Corwyn'<corwyn at midcoast.com>
Cc: 'Greenbuilding'<greenbuilding at lists.bioenergylists.org>
Subject: Re: [Greenbuilding] Relative humidity in heated houses

Here is a link to the pnas published article (09).
http://www.pnas.org/content/early/2009/02/09/0806852106.full.pdf+html

Shaman and Kohn Absolute humidity modulates influenza...

Basic discussion is that though previous studies of affect of increasing rh
were compromised by the limited association of relative humidity with
influenza - the stronger relationship found between absolute humidity and
influenza suggests that humidification may be warranted.

JOHN SALMEN ENVIRONMENTAL DESIGN
4465 UPHILL RD,. DUNCAN, B.C.  CANADA, V9L 6M7
PH 250 748 7672 FAX 250 748 7612 CELL 250 246 8541
terrain at shaw.ca


-----Original Message-----
From: John Straube [mailto:john at buildingscience.com]
Sent: October 27, 2010 2:07 PM
To: JOHN SALMEN; Corwyn
Cc: Michael O'Brien; Greenbuilding
Subject: Re: [Greenbuilding] Relative humidity in heated houses

As far as I know, the studies referenced in the Sterling paper are not the
problem, the translation of the results in those references studies from
glove boxes to buildings, and single data points to linear lines.  The
beautiful graphic is very compelling, and has received the most  criticism.
And the takeway of "the best RH is between 40 and 60%" is dangerously
simplified and not correct. I dont know the Oregon study John, and would be
glad to hear more of this one.

A lot of knowledge is not written down in widely available papers. Most of
what I know on this topic comes from attending ASHRAE conferences, and IAQ
meetings over the last almost 20 years not the paper reference below, or
several more that I have.  The reason for my "scorn" is that this is a very
common question, Sterlings drawing is widely quoted, yet people in the
business know this is not a good basis of design.  I have seen many people
with serious health impacts because of too high a humidity, and never seen
low humidity actually connected to health problems (lots of people claim
this, but people are not hospitalized, you cant measure any IgE or similar
in blood, etc etc ).  My experience is shared by every forsensic building
scientist I have spoken to.  Really low RH (like <20 or so) regularily cause
discomfort, although good proportions of  people are unable to identify if
the air is dry or normal between 15 and 25% (based on student surveys).

The only more recent paper I have on my laptop (other than the
aforementioned ASHRAE Standard 55, 62, and Handbook of Fundamentals 2009) at
the moment is which has some nice relevant quotes:
Baughman, A, and Arens A,"Indoor Humidity and Health: Part 1: Literature
Review of HEalth Effects of Humidity-Influenced Indoor Pollutants" in ASHRAE
Transactions 1996, Vol. 102, Part 1
"A paper'by Sterling et al. (1985)also addressesthe topic
humidityandhealthin buildingsandis the onlycited reference pertinent to
humidity in ASHRASEtandard 62-1989. This paper includes a figure that has
received wide circulation within the HVAC engineering profession. It
graphically depicts humidity impact zones using bars that decrease in width,
suggestinga decreasein the effect for eachof the eight environ- mentalhealth
factors addressed. Thesebars convergefor all of the eight categories into a
nat~'owrecommende"doptimum" zone between 40%and 60%RH;both low- and
high-humidity effects are addressed. There is clearly a need for' such a
summary because it has appeared in numerousjournals and
conferences(Arundelet al. 1986,1992).It is alsoarrestingly drawnandeasyto
grasp, whichaddsto its appeal. ....For the purpose of setting humidity
standards, the figure is clearly inadequate."
Who writes the paper is also important to me. Arens is a researcher with a
long record of good work that has borne the test of time.

On the cold or influenza front: colds are spread in water droplets from
sneezes and coughs . Drier air causes these droplets to evaporate more
quickly, and the virus therefore desiccates more quickly and loses viability
more quickly. To have this effect noticeable it helps to have low RH.
Apparently viral and bacteria viability does not vary much above 50%RH (does
not get worse that is).  The Sahara desert is very dry, and yet people dont
have a lot of colds there.  They have lots of colds when packed together
indoors where they exposed to each other.  The problem is, essentially none
of the viability studies of virus and bacteria that consider RH were
conducted in buildings.  This changes how the air actually moves from host
to site, other factors that affect viability, etc. Most importantly, it
ignores that in cold climates, an air RH of 50% means an RH of 80%+ at most
windows, in corners, etc.   Some disease agents are not affected by RH, and
some, in the lab, seem counter intuitively to like drier air.  So even here
the evidence is less than equivocal.



On 2010-10-27, at 3:11 PM, JOHN SALMEN wrote:

> I was just going to reference that article as well. It is from the 80's
but
> I wasn't aware it was 'widely debunked'?? Are the 24 studies it references
> also debunked? I have an article in front of me 2008 that references it as
> well as the humidity/influenza studies. And what about the stuff from
Oregon
> a couple of years ago that retested data and did establish low absolute
> humidity as the control.
>

Dr John Straube, P.Eng.
Building Science Corporation
Somerville MA     Waterloo ON
www.buildingscience.com






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