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On 7/12/2010 11:02, Julie Lestrade wrote: Hello MariëlleTRNSYS uses the conduction transfer function method to compute the energy transfer through the wall. I would recommend looking at some of the archives of this mailing list for detailed explanations. However, to answer your direct question, the values of capacitance, density, and thermal conductivity of the various materials in the default libraries are pretty good. It is not too hard to double check them online if you are concerned. For the most part, they do NOT consider thermal bridging effects but are for the monolithic material. the TESS layer library includes some equivalent materials for typical (US) stud wall constructions. These are equivalent materials that account for the ratio of wooden stud to insulated cavity. You can do the same for other configurations of materials if you need. 2) I understood I could do that, but it's calculated by default and I don't particularly know the solar absorbance of the material. So I was wondering if the calculation was alright ?I would recommend that you run the building and look at energy use twice, once with a low estimate of the solar absorptance and once with a high estimate. That way you will be able to determine the overall sensitivity to that particular parameter and know whether it is worth spending time looking for a better estimate than the default. 5) Yes I'm adding a question here : for the ground definition, it is important to set the temperature of the earth below. By default it's 15°C. Does anybody know for which region of the world this is true ?if you don't know any better, the undisturbed deep earth ground temperature is approximately equal to the location's annual average air temperature. However, that does not account for the long term accumulation or reduction of energy in the soil directly underneath the building due to coupling with the building's conditioning. If you are using TRNSYS 17, you might look at Type49 (slab on grade); a good bit of research has gone into this area recently and that component (while slow) does a very good job of calculating what the below grade temperature is as a function of time. Best, David -- *************************** David BRADLEY Principal Thermal Energy Systems Specialists, LLC 22 North Carroll Street - suite 370 Madison, WI 53703 USA P:+1.608.274.2577 F:+1.608.278.1475 bradley@tess-inc.com http://www.tess-inc.com http://www.trnsys.com |