[GSBN] Modeling or measuring mass effect of interior plaster

Tue May 14 09:15:52 UTC 2013

The "standard" low e window which the window companies in the US push, soft coat low e glazing, has too low a solar heat gain coefficient  to be very effective for passive heating. However there are two types of low e glazing. There is "heat receiving" low e that utilizes a hard coat film that is very effective for passive gain with a SHGC of >65 or greater. Its harder to get window companies in much of the USA  to supply the second type because of lazy marketing. One type makes it easy for them however if one persists you can usually get the second type. If you can't its better to use double glazed clear if you want passive heating. The Canadian companies are much better in offering a wider range of options I've found. 

Ken Haggard San Luis Sustainability Group  
On May 13, 2013, at 8:43 PM, Misha Rauchwerger wrote:

> 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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San Luis Sustainability Group 
16550 Oracle Oak Way
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