[GSBN] Modeling or measuring mass effect of interior plaster

Tue May 7 20:25:25 UTC 2013

Well, it's hard to take seriously anyone who thinks the sun shines into
north-facing windows, but outside of that, the results are very much in
line with our observations--more mass equals temperature moderation and
comfort.  The paper stresses (over and over) that this is for mass in
visual contact with the sun, because the buildings are designed as solar
collectors.  Similar advantages in temperature moderation apply to mass
that does not have direct solar contact. (Also for wood-stove heated
buildings, when the mass can absorb excess heat in the burning cycle).

The question I have is whether you can have too MUCH thermal mass, and at
what point does that occur.  Any thick mass walls in a building with
eventually reach an average ambient temperature, and will only release (or
absorb) heat very slowly, in the long term.  In my experience, plastered
bale walls hover pretty close to room temperature, and like mass walls,
aren't experienced as cold.  A slab floor, by location, thickness and
generally low insulation values, can tend to be experienced as cold if it
isn't heated by sun or other means.

Sometimes single-level homes with a collector slab will, at night, tend to
stratify.  The efficiency of heat transfer can be improved by just a slight
level change to drive the convection loop. Even one step between the
bedrooms and living area is enough to make a significant increase in air
circulation during the night.

On Mon, May 6, 2013 at 6:05 PM, Bohdan Dorniak <bohdan at bdcoarchitects.com.au
> wrote:

> Hi All****
>
> This is a note that has been published by the Australian Institute of
> Architects regarding Thermal Mass.****
>
> I thought that you may find this interesting? Any comments John?? Laura??*
> ***
>
> Regards****
>
> Bohdan Dorniak****
>
> ** **
>
> *From:* GSBN-bounces at sustainablesources.com [mailto:
> GSBN-bounces at sustainablesources.com] *On Behalf Of *John Swearingen
> *Sent:* Tuesday, 7 May 2013 9:38 AM
> *To:* Global Straw Building Network
> *Subject:* Re: [GSBN] Modeling or measuring mass effect of interior
> plaster****
>
> ** **
>
> Laura,****
>
> ** **
>
> Modeling thermal mass is generally difficult because of the large variable
> conditions of heat transfer related to air circulation. We've done this in
> Energy-10 with some success, and usually our projections have come out on
> the conservative side--the temperature swings have been less than we
> calculated. ****
>
> ** **
>
> The other very large variable is climate--temperatures and sunshine at
> different times of the year. Everyone I know who does this successfully had
> dialed it in from years of experience in one particular climate, with which
> they are familiar.****
>
> ** **
>
> As to whether the walls make a difference,  the short answer is, I think
> it makes a big difference, and that many of the lauded characteristics of
> thermal comfort in straw bale buildings may have as much to do with the
> thermal mass on the walls as with the insulation.  Modulated temperature
> swings can influence occupant behavior positively, reducing reliance on
> mechanical systems, over and above straight Btu calculations.****
>
> ** **
>
> The ultimate efficiency of thermal mass is tied to the heat-transfer
> mechanism for exchanging heat between the mass and the rest of the building
> (air).  A floor slab is thick and of limited surface area; bale walls are
> thin with a much larger surface area. So floor slabs are longer term
> storage, and walls  function very effectively to modulate temperature
> swings on a short term (diurnal) cycle which can reduce loads on mechanical
> systems and increase comfort in passive buildings.  I don't think there is
> too much danger of over-massing, and haven't seen it in our buildings,
> because the relatively thin mass of the walls, backed by insulation and
> actively transferring heat, stays close to room temperature and so isn't
> felt as too cold or hot.****
>
> ** **
>
> Temperature modulation can result in significant changes in how mechanical
> heating and cooling are used by the occupants: if the building is slow to
> cool off at night, for instance, the occupants don't call for heat early in
> the evening.  The key here is responsiveness, which is related to surface
> area. Mass walls also help to distribute Btu's somewhat between warmer and
> cooler areas of the building: cooler walls will absorb heat more readily
> than warm walls, so they are somewhat of a magnet for warm air when located
> in cooler areas of the building.  ****
>
> ** **
>
> Well, hope this helps!****
>
> ** **
>
> John.****
>
> ** **
>
> ** **
>
> ** **
>
> On Mon, May 6, 2013 at 12:39 PM, Laura Bartels <laura at greenweaver.com>
> wrote:****
>
> Hello All,****
>
> ** **
>
> I'm writing to ask if anyone has had experience with modeling or measuring
> the mass effect of interior plaster of bale walls versus other interior
> finishes. This has come up on a straw bale project in design phase I've
> involved in which has a net zero energy goal. The project is large, about
> 6000 sf. The owners are interested in  barnwood interior wall surfaces
> (over plaster) on all or some walls. With the net zero goal, the question
> is what we might lose in having wood rather than exposed plaster. There
> will be adobe floors which will already provide direct and indirect gain
> mass.  ****
>
> ** **
>
> Anyone tackled this topic or have a guess about how to look at this? Our
> team has talked about estimating direct vs. indirect gain wall surfaces
> through sun studies in ArchiCAD as a starting point. ****
>
> ** **
>
> Looking forward to hearing any thoughts on this.****
>
> ** **
>
> Laura****
>
> ** **
>
> ** **
>
> *Laura Bartels*****
>
> *GreenWeaver Inc.*****
>
> *520 S. Third St., Suite 5 *****
>
> *Carbondale, CO 81623
> 970-379-6779
> www.greenweaverinc.com*****
>
> * *
>
>
> ****
>
> ** **
>
>
> _______________________________________________
> GSBN mailing list
> GSBN at sustainablesources.com
> http://sustainablesources.com/mailman/listinfo.cgi/GSBN****
>
>
>
> ****
>
> ** **
>
> --
> John Swearingen
> Skillful Means Design & Construction
> 2550 9th Street   Suite 209A
> Berkeley, CA   94710
> 510.849.1800 phone
> 510.849.1900 fax
>
> Web Site:  http://www.skillful-means.com
> Blog:         https://skillfulmeansdesign.wordpress.com ****
>
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>

-- 
John Swearingen
Skillful Means Design & Construction
2550 9th Street   Suite 209A
Berkeley, CA   94710
510.849.1800 phone
510.849.1900 fax

Web Site:  http://www.skillful-means.com
Blog:         https://skillfulmeansdesign.wordpress.com
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