[GSBN] Modeling or measuring mass effect of interior plaster

Tue May 14 03:43:22 UTC 2013

A few other observations worth noting:

When I checked the temperature of the interior of my strawbale house with
an IR thermometer, the concrete slab (earth coupled without insulation, on
a bed of sand) stays the same temperature as my plastered walls, near the
vaulted ceiling and at the bottom.  This suggests that either the walls
aren't cooling or heating faster than the big ol' slab floor, or the
surface of the floor is changing along with all the wall surfaces.  This is
noteworthy, as the friend with the IR video camera who came to the house,
was flabbergasted that the temperature anywhere he checked was so uniform,
as compared to the conventional construction he was used to.  As an aside,
the house with such uniform temperature regime, was so "leaky" that he
couldn't pressurize it with the blower door.  I like knowing there is lot's
of air exchange, and it still performs so well thermally.  The fact that
the floor slab is not insulated definitely adds another dimension to the
discussion in terms of the thermal lag cycles.  There is also the perceived
temperature in the house as compared to the outside.  When it's 115°
outside, the house in the high seventies or even low 80's seems
comfortable; lying down on the floor, getting conductive cooling, it feels
even better!  The same temps in winter seem warm.

Also, there has not been much mention of low-e windows in terms of solar
insolation on the mass surfaces.  I would guess that most people are using
Low-e windows today, unless specifically specifying plain glazing.
Obviously there is little heating effect due to passive solar influences
with low-e coatings.

Misha Rauchwerger

On Mon, May 13, 2013 at 1:53 PM, Derek Stearns Roff <derek at unm.edu> wrote:

>  Robert Riversong provided me with the chart below, which combines all the
> relevant factors, to come up with a Thermal Mass Index.  Soapstone is the
> winner by a large margin, so plaster your bales with soapstone.  Saturated
> sand is next in line, which would make a great plaster.  Marble is good.
>  Clay isn't great on this list, but it has so many other virtues that it is
> my first choice.
>
>  Derek
>
>
>
>
>
>  On May 13, 2013, at 9:17 AM, Van Krieken wrote:
>
> Thermal mass, like insulation, its a general expression, but in fact
> "thermal mass depends on the type of material we use.
>
> It is important to know what are the properties and thermal performances
> of the materials we want to use, because each of them have their own
> thermal characteristics.  Due to their structure and their mass they manage
> the heat in different ways:
>
>  a) Statics: conductivity or thermal capacity. How does the material
> reacts to a thermal flow, independently of the reaction time?
> b) Dynamics: diffusivity and effusivity. At what speed the material
> manages the thermal flow?
>
>  Because the exterior conditions are going to determine the interior
> changes, its essential to know how the materials react. Iron and clay, both
> thermal mass, react in a very, very different way.
>
>  1. The thermal conductivity (lambda) gives us the information concerning
> the amount of insulation a material can achieve (air passage of calories).
>
>  2. The thermal capacity, measures its aptitude to stock the heat. This
> is the key element to stock the heat in winter, as well as to absorb the
> heat in summer. They are not only heavy materials (like clay or stone, or
> cement). Straw, a much more light material, has also a thermal capacity,
> and therefore thermal mass.
>
>  3. The thermal diffusivity is the measure of thermal inertia and it increases
> with the conductivity and decreases with the thermal capacity. In a
> substance with high thermal diffusivity, heat moves rapidly through it
> (m2/hour).
>
>  4. The thermal effusivity measures its capacity to exchange its thermal
> energy with the environment. The more the effusivity is high, the more the
> material absorbs energy without warming up significantly. In contrary,
> the more the effusivity is low, the faster the material warms up.
>
>  Obviously, the thermal mass importance of a material depends on these
> characteristics, but we can help the final result with some technology. If
> in a hot climate I do not have a significant difference of temperature at
> night, then I can get 11 or 12º C of fresh air from the soil (foundations),
> colling the thermal mass; or I also can run 19ºC water in radiant walls
> made of clay. The same we can do on winter, stocking the heat on the clay
> walls.
>
>  What is the best material for thermal mass? I do not have a scientific
> knowledge to tell it, but I like to think that "clay" -- this thermally
> lazy natural and beatifull material -- is the answer.
>
>  The simple issue -- my karma its to arrive allways to a easy
> conclusion... -- it's how  to use it to keep the heat in cold seasons, and
> what to do, to cool it in hot seasons. That's it.
>
>  All the best
>
>  Jorge Van Krieken
> Portugal
>
>
> Derek Roff
> derek at unm.edu
>
>
>
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