<div dir="ltr">Laura,<div><br><div><div>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. </div>
<div><br></div><div>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.</div>
</div><div><br></div><div>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.</div>
<div><br></div><div>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.</div>
<div><br></div><div>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. </div>
<div><br></div><div style>Well, hope this helps!</div><div style><br></div><div style>John.</div><div style><br></div><div style><br></div>
</div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, May 6, 2013 at 12:39 PM, Laura Bartels <span dir="ltr"><<a href="mailto:laura@greenweaver.com" target="_blank">laura@greenweaver.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px">Hello All,</div>
<div><br></div><div>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. </div>
<div><br></div><div>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. </div>
<div><br></div><div>Looking forward to hearing any thoughts on this.</div><div><br></div><div>Laura</div><div><br></div><div><br></div><div><span style="text-indent:0px;letter-spacing:normal;font-variant:normal;text-align:-webkit-auto;font-style:normal;font-weight:normal;line-height:normal;border-collapse:separate;text-transform:none;font-size:medium;white-space:normal;font-family:'Times New Roman';word-spacing:0px"><span style="text-indent:0px;letter-spacing:normal;font-variant:normal;text-align:-webkit-auto;font-style:normal;font-weight:normal;line-height:normal;border-collapse:separate;text-transform:none;font-size:medium;white-space:normal;font-family:'Times New Roman';word-spacing:0px"><span style="text-indent:0px;letter-spacing:normal;font-variant:normal;text-align:-webkit-auto;font-style:normal;font-weight:normal;line-height:normal;border-collapse:separate;text-transform:none;font-size:medium;white-space:normal;font-family:'Times New Roman';word-spacing:0px"><span style="border-collapse:separate;font-variant:normal;letter-spacing:normal;line-height:normal;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><span style="text-indent:0px;letter-spacing:normal;font-variant:normal;font-style:normal;font-weight:normal;line-height:normal;border-collapse:separate;text-transform:none;font-size:medium;white-space:normal;font-family:'Times New Roman';word-spacing:0px"><span style="text-indent:0px;letter-spacing:normal;font-variant:normal;font-style:normal;font-weight:normal;line-height:normal;border-collapse:separate;text-transform:none;font-size:medium;white-space:normal;font-family:'Times New Roman';word-spacing:0px"><span style="font-family:Helvetica;font-size:18px"><span style="text-indent:0px;letter-spacing:normal;font-variant:normal;font-style:normal;font-weight:normal;line-height:normal;border-collapse:separate;text-transform:none;font-size:12px;white-space:normal;font-family:Helvetica;word-spacing:0px"><div class="MsoNormal">
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<span style="color:rgb(76,114,29);font-family:'Times New Roman';font-size:16px;font-style:italic;font-weight:bold">Laura Bartels</span></div><div class="MsoNormal"><font color="#4C721D" face="'Times New Roman'" size="4"><span style="font-size:16px"><b><i>GreenWeaver Inc.</i></b></span></font></div>
<span style="font-size:12pt;font-family:'Times New Roman';color:rgb(76,114,29)"><b><i>520 S. Third St., Suite 5 </i></b></span></div><div style="font-style:normal;font-size:12px;font-family:Helvetica;font-weight:normal">
<span style="font-size:12pt;font-family:'Times New Roman';color:rgb(76,114,29)"><b><i>Carbondale, CO 81623<br><a href="tel:970-379-6779" value="+19703796779" target="_blank">970-379-6779</a><br><a href="http://www.greenweaverinc.com" target="_blank">www.greenweaverinc.com</a></i></b></span></div>
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<br></blockquote></div><br><br clear="all"><div><br></div>-- <br><font face="'trebuchet ms', sans-serif"><span style="font-size:x-small"><font color="#666666">John Swearingen<br>Skillful Means Design & Construction<br>
2550 9th Street Suite 209A<br>Berkeley, CA 94710<br>510.849.1800 phone<br>510.849.1900 fax<br><br>Web Site: <a href="http://www.skillful-means.com" target="_blank">http://www.skillful-means.com</a><br>Blog: <a href="https://skillfulmeansdesign.wordpress.com" target="_blank">https://skillfulmeansdesign.wordpress.com</a></font></span></font>
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