[GSBN] Modeling or measuring mass effect of interior plaster

[Derek Stearns Roff]

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


[cid:D1FC2253-03E0-46B5-BF20-2893CBA78BF1 at domain.actdsltmp]


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<mailto:derek at unm.edu>


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