[Fwd: Re: Cob: Thermal mass and climate]

Tue Apr 23 02:08:06 CDT 2002

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I think you meant to send this to the group as a whole, to get feedback
from them.  I'll have to respond later to some items, but here you
all go:
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<th ALIGN=RIGHT VALIGN=BASELINE NOWRAP>Subject: </th>

<td>Re: Cob: Thermal mass and climate</td>
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<th ALIGN=RIGHT VALIGN=BASELINE NOWRAP>Date: </th>

<td>Mon, 23 Apr 2001 01:34:05 -0500</td>
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<th ALIGN=RIGHT VALIGN=BASELINE NOWRAP>From: </th>

<td>Kerry S Tebbetts <yourelovedbygod at juno.com></td>
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<th ALIGN=RIGHT VALIGN=BASELINE NOWRAP>To: </th>

<td>henman at it.to-be.co.jp</td>
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Darel writes: "Kerry have you ever made any temperature and humidity
measurements for both inside and outside for comparison." No, I haven't. 
I'm still in the planning stages.  We are currently living on the
land in a <gulp> mobile home and are planning to build while we live
in it.  I'm not sure any tests on my mobile home would help in my
planning since a mobile home is sooo energy inefficient anyhow.  However,
once I get a better idea of how I'm going to build, I will build a model
and do some simple experiments to see how it works before I build. Darel
suggests: "Shade.  Time to bring out the:
 >   a.) canvas tarp to spread across a frame to shade the
house, or
 >   b.) mats of reeds, etc, woven together to let the wind
through,
 > but
 > not the direct sunlight.
 >   c.) the grape vines you planted should be creating nice
shade for
 > the
 > house.
 >   d.) the bamboo you cut down in the winter has now grown
up so tall
 > it
 > shades the vertical (walls of the) sides of the house most of the
 > day?Great ideas.  Will bamboo really grow that fast?  I'm
fascinated with bamboo.  We have found several areas to harvest bamboo
for free and have used it in our garden as structural support.  (These
bamboo are about 2-3" in diameter)  But I've always been afraid to
grow it due to it's weed like tendency to get out of hand.  We are
building amidst a lot of very tall trees, and really dread having to cut
any down to get winter solar gain.  Maybe we don't have to??? >
Plants will evapotransire(?) and cool the area around the structure.
 >  If
 > your cob walls absorbed some moisture from humid weather it also
 > will
 > evaporate and cool the inside. The problem is that is with the
mean summer temp at 85 degrees and mean humidity at 71, I'm not sure much
evaporation will occur....at least not at any significant rate.  However,
that is just speculation.  I'm not sure yet as to how cob will perform. 
A fellow Arkansan has a cob house near completion and has invited me to
visit in June.  I think I will take her up on that. Regarding
external insulation Darel writes: "> Certainly not on the south side, unless
you have some other mechanism to get the solar heat inside.
 > Insulation could be done on the north, east, and west sides. That's
what I had planned. Darel writes:  "> Tell us about your attic?  
Have you put any thought to its
 > contribution to the heat in the house, during the summer? I
had planned to build only one habitable room and then add on later (which
brings up other questions I have regarding adding on to a cob house - how
do you design a house with adding on in mind if you want to have an end
product with an open layout? Building one wall with strawbale?  Making
the entrance extra wide with a sliding glass door or french doors? 
Also, is there a way to build "up" once you have built a one story room
out of cob??? Perhaps by building the room tall enough for two stories
but without the second story flooring?)  Even though I only plan to
build one room at first, I had still planned to have space in the roof
area to capture hot air and vent it out using natural convection (i.e.
vents low on the south wall and high in the north wall)  Other than
that, I haven't any other ideas. Darel writes: "Earth tubes should
be fine anywhere.  Why do you feel its
 > inadvisable?" I read an article from the U.S dept of energy
(which may be biased?).  I quote:
"Earth cooling tubes are likely to perform poorly in hot, humid areas,
because the ground does not remain sufficiently cool at a reasonable depth
during the summer months. Moreover, dehumidification, another equally important
aspect of cooling, is difficult to achieve with earth cooling. Mechanical
dehumidifiers will most likely be necessary."
Another thing I read which was very disturbing was a post on a forum. 
The person quoted some pretty ugly case scenarios of problems caused by
earth tubes.  Admittedly, I haven't checked his sources.....so who
knows, but what he said made sense.  Here's the link to the discussion
of earth tubes.  He quotes his friend who has professionally built
many alternative homes.  <a href="http://csf.colorado.edu/forums/essa/apr99/0055.html">http://csf.colorado.edu/forums/essa/apr99/0055.html</a>
In discussing the possibility of incorporating water plastic containers
"in" or "outside of" a cob wall Darel say, "> You could do either. 
Some have considered putting through the > floor
 > and/or up into the northern wall so that solar collector heat could
 > be
 > used to heat it up in the winter.
 >
I wrote: "If the {water} containers were embedded in the wall, would
condensation occur inside the cob?"
Darel responded: "I'd have to guess on this and say no.  I recall
reading >something about this and it said it wouldn't be a problem. There
may not be that
 >much of a temperature difference to cause condensation."
Yes, I was thinking the same thing. Our ground temperature here in Arkansas
is on average 67 degrees.  (I can't remember where I read that, so
I may be wrong)  Therefore, if it's 100 degrees outside and the tubing
is embedded in a 9-12" cob wall, would condensation occur?  I'm sure
there are too many unknown variables to know for sure, but what are the
unknown variables?  Also, how thick would the tubing have to be and
how close would the tubing have to be spaced?  I was thinking of using
4" diameter tubing spaced vertically every 5 feet or so?  Is that
too much.  I suppose if it was being circulated continuously, it could
be smaller tubing, but I was trying to avoid circulating continuously. 
Would the PVC pipes threaten the structural integrity of the cob walls? 
How would I prepare the surface of the pipes so that the cob would adequately
bond to them? These are just many of the questions I have.  If anyone
has built a cob water wall or radiant system using cob, let me know how
you did it.
Darel writes:  "All moisture would have to come from the cob itself,
unless you don't have the pipes sealed off."
I thought condensation occurred when a hydrogen and two oxygens bonded
when sufficiently cooled.  Since cob breathes, surely it will always
have tons of hydrogen and oxygen.  How much moisture can cob hold
before it started to break down.  Do you think I should have some
way of draining the excess condensate down through the foundation?
  
> > How would heat travel
 > > through a "cob water wall"?
 Darel asks: "This is a cob wall with water tubes in it?"
That is one idea, but, yes, that is what I had in mind with the question.
Darel writes: " Having water in the wall would slow down temperature
changes, but the amount of thermal energy stored or sank in the wall would
be the
 same. Energy out = Energy in - (Energy stored temporarily)
Ok, makes sense.  But does the wall have to be fully "charged"
before starting to radiate heat to the interior?  And does the water
fully charge before the cob?  I guess the latter question wouldn't
matter if the water was being continually cycled, but I was thinking that
the water could just be cycled one or twice a day limiting the need for
continual pumping.
Darel writes:  "Shae, You have some great ideas.  Keep it
up."
I have lots of questions =) at this point without the adequate knowledge
of science or practical know how to answer them.  Back to the research....
  
  
Thanks for all of your wonderful input!
P.S. You can call me shae
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