[Greenbuilding] ABout how thermal mass of ICF would work

[Russell, Richard]

I don't think I would have used the terms "heat seeks cold" and "draw"
to describe the flow of heat to the ground. They sound rather
unscientific, but in terms of what is happening aren't wrong. Heat
simply flows from one place to another that is colder. Heat flow by
conduction is proportional to the temperature difference between source
and destination, to the thermal conductivity of whatever is in the way
(ie. wall of concrete or insulation), and the area for heat transfer.

True, if there is no insulation between basement air and a concrete
wall, then more heat will be conducted down through the footing to the
ground, but much more would be conducted through the larger area of the
floor to the ground if there is no insulation under tha slab to retard
this flow of heat. On the other hand, the ground temperature is
typically well above the air temperature when heating the house is an
issue. Below 6-8 feet, ground typically reflects yearly average air
temperature over the decades.

Bear in mind that "thermal mass" is useful only to even out the
day/night outside temperature swings, and the degree it is useful is
climate-dependent. It is less effective in cold climates. I saw a study
of how this was modeled (by computer) for different wall assemblies and
climates, but I don't remember where. It addressed insulating the
exterior, the interior, and both. I think the conclusion was that in a
moderate climate having the thermal mass exposed to the inside air was
most effective, but I'd rather find it again to be sure. In either
design, the one with more total R in the wall will do better on heat
loss. It's a matter of how that R is distributed and what the climate
is.

I'll await responses from others.

Dick Russell

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Beatrice
Dohrn
Sent: Wednesday, May 14, 2008 5:13 PM
To: greenbuilding at listserv.repp.org
Subject: [Greenbuilding] ABout how thermal mass of ICF would work


Hey all. 

I'll be building a house (for myself) this summer (near Eugene Oregon). 

Some time ago -- and with some help from responses on this list -- I
decided to change from a longstanding plan to use the more common
insulating concrete forms (the ones that used EPS in and out, etc) and
have engineered to use faswall,  produced right near here by
shelterworks.  This type is demineralized woodchips,  with a slot in the
outside 1/3 of the cavity for 3" of  insulation (you can choose,  EPS,
Min wool, or Polyiso).  

I just spoke iwth the rep from the company I am NOT using,  explaining
my decision as a courtesy.  I got an annoying sales job, of course.  I
wanted to test one thing she said -- out of curiousity really as I am
not changing my plans now.  Question is this:

I believe that the faswall ICF makes the thermal mass at issue more
useful to the house's temp because it is not insulated away from the
living space -- as is the case with EPS ICFs.  The rep from the EPS co
suggested to me that "heat seeks cold" and that therefore in the winter
the walls would "draw" the heat we generate in the house down into the
ground -- since the concrete core goes below the house into the ground (
in my case a lot, as we have a basement).  This goes against about 50
things I thought to be true about how thermal mass like this will work.
Do you think it's true?


Beatrice Dohrn



      

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