[Ferro List] Supertherm Insulation

[Uwe Brunjes]

Hi Jon,

You seem to know quite a lot about heat transfer
(particularly radiation), desert climate and other
subjects of my interest, so I would like to ask a few
questions (or rather express doubts) if you don't
mind. I happen to live in a desert myself, and never
could find any good, convincing info for building in
this kind of climate.

For many people it’s hard to believe that during the
daytime temperatures can be well above 100F, while a
few hours later they are around 50F. And it’s more the
rapid change than the absolute temperatures what makes
our climate so unpleasant. So that’s something very
important to consider.

That means, thermal mass is a major issue here, as the
air has hardly any. Oxygen, nitrogen and the other
gasses in the air can’t provide too much of it, and if
there is no humidity in the air, we are out of luck.
If we are inside a house, we can do something about
that with humidifiers, insulation and mortared walls,
but if outside temperatures are too different from the
inside, our body temperature will still be affected
via radiation.

My feeling is that to control all this, the exterior
wall of a desert home has to have five distinct
layers: a huge insulating core (against thermal
conduction), both an inside and outside thermal mass
(stucco/mortar) and a radiation barrier that could be
part of the paint.

In my opinion, the thermal mass inside the house
shouldn’t receive or give any (or too much) heat via
radiation. Conduction and convection between the
mortar and the air should be enough to help keep
temperatures stable. Heating up this thermal mass with
the heat radiated from our bodies is obviously not
desirable, and if temperatures are ok or too high, we
don’t need any heat radiated from the walls either.

On the other hand, if the radiation from the sun and
nearby objects doesn’t penetrate the outside thermal
mass, it shouldn’t heat up too much during the
daytime, while not losing too much heat to the
environment at night either. It would only lose that
part that would be transmitted via
conduction/convection, but nothing via radiation. - Of
course these absolute terms are not quite correct, but
they give an idea.

So if the face of the inside thermal mass is covered
with a radiation barrier, that should help keeping our
body heat to ourselves when outside temperatures go
down rather abruptly. And as they shoot up in the
morning, our bodies won’t receive too much radiated
heat either, as the first layer of the outside thermal
mass is a radiation barrier. And these two aspects of
thermal comfort in a desert house are what hasn’t been
addressed very well in all the literature I’ve seen so
far.

I don’t know if I managed to explain myself correctly
and completely (in fact, I don't like my own writing),
and can only hope that you see what I mean. If not,
please ask me all the questions that come to your
mind, and if yes, let me know what you think about
this theory, what to add, what to trash, etc. It's
about time to clear all my confusion and to eliminate
all doubts.

Thank you!

Uwe
P.S. Of course, these (implied) questions are for
everybody else, too.


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