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GSBN:Re: 40% humidity



It's easy for our clients to be confused by humidity numbers, so I think it bears repeating:

Humidity of the air and moisture content of the straw are not the same, and will have vastly different values in most building situations.

The 40% relative humidity (RH) of the air in a building, which André mentions, is a good value for comfortable human respiration. As Jim says, if there are no other sources of moisture, this RH in the air would result in a moisture content (MC) of the straw below 10%.

For a client who has read that straw moisture must stay below 20%, an RH of 40% looks scary. How can we best explain the distinction between relative humidity of the air and moisture content of the straw? The relationship between RH and MC varies with temperature and atmospheric pressure, resulting in a complex psychrometric chart filled with various intersecting curves. These charts would be baffling to the average person.

Perhaps John Straube or Don Fugler can comment on how to effectively convey the essential concepts to a confused client. In my climate, I can assure people that at normal household temperatures, an interior RH under 70% will present no risk to the straw. Leaks, cracks and rain striking the plaster can still cause moisture risks, of course.

This online moisture content calculator might help in some cases. It's designed for wood, but I think the numbers for straw are almost identical. I hope Don and John will correct me if I am wrong about that similarity.

<<a  target="_blank" href="http://www.woodbin.com/ref/wood/emc.htm";>http://www.woodbin.com/ref/wood/emc.htm</a>>

Derelict

Derek Roff
Language Learning Center
Ortega Hall 129, MSC03-2100
University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek@...


--On Tuesday, November 6, 2007 9:58 AM +0000 Jakub Wihan kuba@... wrote:

Hi Andre,

As Jim writes, worldwide expert on passive climate control in
buildings such as archives and museums is Tim Padfield. His extensive
research is available for free on his remarkable website.

You might be particularly interested in:

<a  target="_blank" href="http://www.padfield.org/tim/cfys/musmic/musmicbuf.pdf";>http://www.padfield.org/tim/cfys/musmic/musmicbuf.pdf</a>

Materials creating all the surfaces (including equipment, furniture
,etc.) in the room seem to play crucial role in passive humidity
(relative humdity) control as well as maintaining constant
temperature. One might assume that straw bale building could be ideal
for this purpose, because it won't need much energy for maintaining
constant temperature in temperate climate of France and on top of it,
according to Padfields research, earth plaster seems to create
excellent surface for humidity buffering:

<a  target="_blank" href="http://www.padfield.org/tim/cfys/wallbuff/wallbuff.php";>http://www.padfield.org/tim/cfys/wallbuff/wallbuff.php</a>

Plastered straw bale walls, according to Padfields e-mail, has
enormous water vapour capacity:

<a  target="_blank" href="http://www.jakubwihan.com/pdf/thesis.pdf";>http://www.jakubwihan.com/pdf/thesis.pdf</a> , pg. 267

Personaly, I think that winery monitoring done by Straube and
Schummacher won't help you much in this case, because the room
designed for maintaining constant relative humidity of 80% was air
conditioned. I would be very interested, if anyone out there did a
monitoring that would more directly shed some light on the subject of
using straw bale walls for passive maintainance of constant relative
humidity. The monitoring that I'm familiar with (monitoring widely
available for free on internet) suggests that palstered straw bales
seem to make a very promising solution in case of various archives
and museum buildings.



Love

Kuba



----- Original Message ----- From: "Andr&eacute; de Bouter"
forum@...
To: "GSBN" GSBN@...; "ACHTE Christophe"
achte_christophe@...
Sent: Tuesday, November 06, 2007 7:56 AM
Subject: GSBN:40% humidity


Hello everyone,

Christophe Achte (that same army engineer student I mentioned
earlier) told me of a project of the French army were electronical
material will be stalled (for future use) in buildings that should
keep the humidity at a constant 40% to avoid corrosion of the
material. He wondered if SB with earthen plasters could be used
instead of airtight 'modern' materials. The need to keep the straw
under 20% makes me hesitate to give an answer. But someone who
participated in the discussion told us that 70% humidity in wine
cellars is quite common.
Do we have any info, from the Ridge Winery for instance, that might
shed light on this subject?

Andr&eacute; -hic- de Bouter
France
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Derek Roff
Language Learning Center
Ortega Hall 129, MSC03-2100
University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek@...