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GSBN: Digest for 6/25/02

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-> Re: GSBN:More from Kelly about China
     by Derek Roff derek@...
-> Request to join GSBN
     by billc_lists@...


Date: 25 Jun 2002 14:53:38 -0500
From: Derek Roff derek@...
Subject: Re: GSBN:More from Kelly about China

Congratulations, Kelly,

It is great to hear about the careful scientific data logging showing 
the advantages of the SB houses in China.  Can someone forward this 
response to her?

>> -- Kelly, via Paul, told us:

>> They also observed that the relative humidity (RH) in
>> the straw-bale houses (SBH) is about 10% higher than in the brick
>> houses (RH in SB 61%, RH in BH 51%). The RH of the SBH is much
>> closer to the outdoor RH of 66.5%.
>> I'm postulating that the straw bale walls are more vapor permeable
>> than the brick walls and thus the interior RH follow the exterior
>> RH  humidity more closely. It may also be that thicker plaster on
>> the  straw bale walls (compared to brick walls) is acting as a
>> moisture  sink and working to balance the RH between times of high
>> RH and low  RH. Any other thoughts??

How can we explain the higher relative humidity (RH) in the strawbale 
houses, compared to brick?  Vapor permeability?  I doubt it.  Kelly 
doesn't mention the average outdoor temperature in the RH example 
above, but assuming it is pretty chilly, then the indoor air contains 
a lot more water than the colder outdoor air, at a similar RH.  Let's 
remember how relative humidity works. RH shows the amount of humidity 
in the air, relative to the maximum possible amount of humidity that 
the air could hold at that same temperature.  Air will hold much less 
moisture at lower temperatures.  If the outdoor air was at -5 degrees 
C when they measured the relative humidity of 66.5%, then moving some 
of that air indoors and warming it up to 20 degrees C will reduce its 
relative humidity to about 10% (according to the RH calculator that I 
found on the web).  If it is -18 deg. C outdoors in the winter in the 
places where Kelly is working, the RH of outdoor air, after being 
heated to indoor temperatures, would become about 5%.  Moisture won't 
be flowing from outside to inside in the winter at the RH values that 
were measured.

I also doubt the "moisture sink" explanation.  The plaster might 
moderate humidity swings over a short time period, but plaster 
couldn't store enough moisture to maintain a significantly higher RH 
over the course of a winter.  Assuming that the figures given were 
average values over time, we have to explain how  the SB house 
maintained higher average humidity than the brick house.

My best guess is that the difference has to do with the heating 
cycle, directly and indirectly.  Not knowing the details of the 
heating systems, we can't be sure of anything.  If the heating system 
exhausts air from the living space, as a fireplace or unsealed heater 
does, then an equivalent amount of air must be drawn into the house 
from outside, usually through open windows and/or small leaks and 
holes.  Assuming that the brick house and the SB house are equally 
tight (resistant to air leakage), we could explain the higher 
relative humidity of the SB house by the lower use of the heating 
system.  Here's  my reasoning:  If building a fire/running the heater 
sends some living space air up the chimney, then each time you heat, 
you will expel more inside air, and draw in more outside air.  Since 
the outside air has much less water in it, it will lower the humidity 
of the inside air, as it warms up.  The SB house requires less heat, 
so it loses less of the humid indoor air out the chimney, and brings 
in less of the drier outside air.

Another possibility is that the SB houses are a little bit tighter 
than the brick houses.  Although an unplastered bale wall would let 
more air pass than a brick wall, it may be that the plastered bale 
wall is a better air barrier than the brick wall.  Maybe the 
detailing at the wall-ceiling joint is better in the SB house.  Or 
perhaps there are other differences in construction that make the SB 
house tighter.  (It is also quite possible that the SB house is 
leakier than the brick house).  A tighter house will lose less humid 
air, and therefore maintain a higher relative humidity.  If Kelly 
doesn't have good reason to suppose that the SB house is tighter, 
then I would bet against this explanation.

Any other ideas?

Derelict Rough

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


Date: 25 Jun 2002 23:20:51 -0500
From: billc_lists@...
Subject: Request to join GSBN

Hi Folks,

I just got two requests to join the list today, one from Buddy 
Williams buddy@... (the name's not familiar to me, so I 
requested more info from him) and the one below from Tera Berland. 
I'll forward whatever I get back from Buddy to the list, unless 
someone specifically invited him.

Let me know what you think.

Original message:

I am a researcher at the University of North Dakota Energy & Environmental
Research Center. My specific interests are in the utilization of
coal-combustion byproducts and the promotion of green building products. I
am interested in learning more about the straw-building industry and hope to
conduct future research in this area.

Tera Berland
Marketing Research Specialist
University of North Dakota
Energy & Environmental Research Center
15 North 23rd Street
Grand Forks, ND 58202
Fax: (701) 777-5181
Phone: (701) 777-5296
Web: www.undeerc.org/carrc
- -- 
Bill Christensen

Green Homes For Sale/Lease:  http://SustainableSources.com/realestate/
Green Building Pro Directory:  http://directory.sustainablesources.com/
Sustainable Bldg Calendar:  http://SustainableSources.com/calendar/
Sustainable Bldg Bookstore: http://SustainableSources.com/bookstore
International Strawbale Registry: http://sbregistry.sustainablesources.com


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