[Cob] Passive Heating and Cooling

[Raduazo at aol.com]

I just went to the Green house exhibit at the  National Building Museum in 
Washington, DC last week. As a general rule  this should be titled Green Living 
for multi-millionaires. I did come across a  few gems though.  
Virtually everyone  wants comfort, and in a world where green house gasses 
are likely to displace  20% of the world's population or compel the massive use 
on nuclear energy,  passive solar is the only solution that will suit the 
millionaires as well as  the not so millionaires. 
    One of the books featured in the bibliography of  the show is The Solar 
House Book by Daniel Chiras. This book is great because it  gives various 
strategies to avoid over glazing, and though it does not mention  cob it usually 
mentions adobe which is an equivalent material in all  calculations.
There are some obvious flaws in the book. For example the  author states that 
a "six-inch mass wall is only 8 percent more effective than a  four-inch mass 
wall" with out telling the reader how he came to that conclusion.  Also, in 
his formula (page 108) for calculating the amount of overhang a  particular set 
of windows needs he gives the formula L (length of the overhang)  = H/F Where 
H is the height of the window and the F is a factor (listed in a  table for 
the degree of North Latitude. It is obvious from looking at his  diagram that H 
is not the height of the window but the distance of the bottom of  the window 
from the base of the overhang.
 The structures shown in the book look anything but cob-like, but  everything 
can be adapted to straw bale and cob hybrid construction.
    One of the great things about Cob is its  adaptability to different uses 
and the fact that it can be modified. For example  Adobe has only 71 percent 
of the heat storage capacity of concrete, but what if  you use cob and put lots 
of rocks in the wall? Adobe does not conduct heat as  well as concrete, but 
what if you used cob built in thin pancake-like layers and  used crushed beer 
cans in place of some or all of the straw between the  pancake-like layers?
To date I have not seen any  other books on Passive solar as complete and 
well thought out as this  one. But, for the most part The glass to mass ratio for 
particular  structures with particular insulation is still going to be a 
guess if  perhaps a better educated guess at how much glass, cob and straw bale 
you  would need to get a reasonable amount of comfort.
    

Ed