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Kiko Denzer on Art
Thermal performance, was Cob sledgehammers and heat retentionBob Bolles bbolles at cts.com
Sat Dec 6 16:33:13 PST 1997
Hello All Normally I don't participate in these discussions - I have little to offer in terms of cob expertise. However this particular area is one that fascinates me - Thermal characteristics. It is also one about which I can only claim a superficial knowledge. For the sake of clarification, I would note that I consider "knowledge" or "understanding" from three distinct points of view: First is that type I gain from reading, observing, discussing, researching, etc - kind of "intellectual" knowledge. The second is that which I have gained from personal experience. The third is the exploration of the possible, taking what I "know" and projecting that into different situations or conditions. I "know", for example, the thermal characteristics of a material can really only be measured as a function of conductivity - when a material does not conduct heat well, it is said to "insulate". That is type 1 knowledge. Something that I can personally relate to is a solid brick house that I had the misfortune of living in during one winter in central Missouri. It was a wonderful old (built in the 1860's) two story house with 16 inch thick walls. The heat was provided by a monster fireplace in the living room and an equally large gas furnace in the basement. We moved into the house in the fall, and one of the first things we did was to have the 300 gallon propane tank filled (took about half of our life savings ;-). When the first real cold front came through, we supplemented the fireplace with the furnace. Two weeks later the propane tank was empty. That was the beginning of the most miserable winter of my life. We ultimately moved into the living room where the fireplace was, and I spent a large amount of my time just cutting and hauling firewood. That was my introduction to the negative aspects of thermal mass. That is type 2 knowledge. Another interesting thing that I have "learned" (type 1) is about how "Adobe" buildings function. My understanding is that "Adobe" is more about the form of the material ( a block) rather than the material itself (clay. sand, and maybe some fiber material - or not). The block, and resulting wall, are typically of similar thickness that seems to be used with cob. My understanding is that Adobe works particularly well in a climate with hot days and cool nights. The theory is that when the sun strikes the thermal mass, it begins to absorb the heat, which slowly moves to the interior surface of the wall. When the sun goes down and the air cools, the heat radiates into the interior (and of course the exterior) of the building, warming it. In the morning, the process repeats itself. While the outside surface of the wall is absorbing the solar heat, the wall is also absorbing heat from the inside air (ambient ?), keeping the interior cool. So let's add one more ingredient. Concrete block houses, which are very prevalent in northern Mexico, are very hot in the summer, and cold in the winter. In the areas where the heat and humidity are high, and the night-time temperatures remain high, high mass building hove no opportunity to cool - they actually gain heat over the hot months. One more example: In the high-rise (typ. Brick/tenement) buildings in New York, Chicago, Kansas City, and St. Louis we hear of occupants who die every year due to the excessive heat and cold that builds up over the season. (BTW, My AR Quotient is not so high that I really think in these type 1,2, and 3 terms - it just seemed to be an interesting way to express this stuff, and, of course, have a little fun with it ;-) Now all of this leads me to believe that Cob and other high-thermal-mass buildings are more appropriate in some areas than others. So, re: > As well, do you know if a cob home would be energy efficient in > heating costs in a region where winters are cold with a mean temp. of 22 > degrees F in January- where it's not very sunny? Is there a place where Cob has been used that is similar in climate? How about you-all in England? How does the climate compare? How cold does it get in the areas where Cob construction was prevalent? As Pat asked, how big a factor is sun in your area, April? And you folks in England? And you, Pat - what are the climatic conditions in GA? And you-all in Oregon? Anyone else who has built with Cob and has some experience to relate regarding thermal performance? This summer we will be building with Cob in El Valle (see web page - shameless plug) just to see what it is all about. Between now and then, I need to figure out just what we want the building(s) to accomplish (form does follow function, don't you know ;-). We won't be able to simulate your conditions, April, but we should be able to come up with some meaningful testing and design exploration. Any suggestions, all? Just as a follow-up note, WE are in earthquake country, so what ever we build will have to have some sort of structural skeleton I'm guessing. Regards Bob ------------------------------------------------------------ Sustainability International Bob Bolles - Director Promoting Sustainable Building Through Demonstration Visit our Sustainable Community Demonstration Project site at: http://www.geocities.com/RainForest/Vines/8290/ Please reply to (619) 486-6949 (619) 748-4680 Fax - bbolles at cts.com 13446 Poway Rd. #236, Poway, CA 92064 "Experience is a hard teacher because she gives the test first, the lesson afterwards." -- Vernon Sanders Law
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