Dear Achim and group, thank for the information, but sorry for the question: what do you mean with: "...the other two are called heat flux upwards and downwards, it should be a good approximation" what are these values? I normally define the same value for all the three resistances? I also saw that it is possible to define (in the constructions menu) "non-linear properties" with a "thermal configurations file". Do you have any idea of that? Maybe I can define a polynomial function for the temperature dependence of the resistance. But I am not sure! Thank you very much in advance Francesco -- Dr. Francesco Frontini, MEng PhD in Buildings Engineering ---------------------------------------- Fraunhofer Institut für Solare Energiesysteme ISE Heidenhofstr. 2, 79110 Freiburg, Germany M1: [+39] 333-3097826 M2: [+49] (0)1522-1624691 Phone: [+49] (0)7614588-5358 FAX: [+49] (0)7614588-9358 @1: <a href="mailto:francesco.frontini@ise.fraunhofer.de">francesco.frontini@ise.fraunhofer.de</a> @2: <a href="mailto:francesco.frontini@polimi.it">francesco.frontini@polimi.it</a> ---------------------------------------- The information transmitted is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon, this information by persons or entities other than the intended recipient is prohibited. If you receive this in error, please contact the sender and delete the material from any computer.