Cob: Re: Thermal mass works, PAHS works, Insulation works

[Mark Piepkorn]

	Amanda's subject line summed it up, IMO.

	That said, I offer a couple comments anyway: not because I have all the 
answers (or any of them, even)... but because the way this mass stuff works 
-- both above-ground and below -- is far from obvious and simple.


At 10:07 PM 1/30/2003, Darel Henman wrote:
 >Ernest Martinson mentions that:
 >"John Hait in Passive Annual Heat Storage suggests the 20 foot
 >perimeter insulation because heat requires 6 months to travel 20
 >feet and at a depth of 20 feet the temperature approaches a
 >constant that is a reflection of the average annual air temperature
 >for the site..."

	The research of the U of MN Underground Space Center, which was cited (and 
deemed "excellent") in a quote in the original response, indicates that:

"...the lines of heat flow [through the earth] follow lengths which are on 
the order of 10 to 20 m (33 to 66 ft)..."



 >> Also, looking at the figure in "The Hand-Scupted House" that compares cob
 >> to straw bales, they point out that cob (earth) is not a good insulator.
 >
 >Again, you are not considering the thermal mass function.


	I can't think of a single material or method that doesn't have proponents 
trotting out the old saw (read sing-song like a bored class of 
fourth-graders), "Warm in the winter, cool in the summer." The effect of 
the mysterious "thermal mass (wall) function" truly seems magical under the 
right conditions -- but in practice varies from climate to climate, even 
building to building. This is also true of PAHS.

	On the other hand, the effects of insulation are more predictable. 
Above-ground, the best compromise in unspecified (that is, imprecisely 
defined) conditions for unspecified occupants is going to be 
diurnally-moderating insulated mass.



 >Here's more information for you from:
 >http://www.thenaturalhome.com/frostwalls.htm
 >"The Underground Space Center at the University of Minnesota did some
 >excellent research in the late 70's and early 80's pointing to the fact that
 >horizontal "wing" insulation was preferable to vertical foundation wall
 >insulation..."


	The outcome of that research, in dollars, was that with a "wing" of 5.6 ft 
(as opposed to putting that insulation vertically against the walls), 
"...energy savings of $8.60 to $28.70 per year are possible..." based on 
energy costs of $0.03 to $0.10/kW-hr. How much would a 20-foot wing cost? 
Would it pass the test of diminishing returns? (I know Don Stephens has 
done it with a subterranean strawbale "umbrella" protected with plastic 
sheeting, but I suspect most people would use sheet foam.)