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Leen, The reason that thick, highly insulated walls give you a problem is that TRNBuild generates the first 20 coefficients of the transfer function that describes the thermal response of the wall. The coefficients correspond to discreet intervals of time starting with the present and moving backwards by steps of the timebase specified in TRNBuild. The default is an hour so it is my understanding that TRNBuild looks back at 20 hours worth of transfer function coefficients to determine whether the numerical stability of the wall model has been met. In very massive walls, 20 hours might not be a long enough time interval to adequately describe the wall's response. You can try to increase the wall timebase to 2 hours in order to extend how far back the wall's response is considered. However, in my experience, this can cause problems with the less massive walls in the same project (which sometimes have to be changed over to massless walls since their response time is now too short to be adequately represented with a 2 hour timebase. Best, David On 4/14/2012 17:27, leen peeters wrote:
-- *************************** 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 d.bradley@tess-inc.com http://www.tess-inc.com http://www.trnsys.com |