This work is partly based on previously published papers [Borst et al., 1994, Top et al., 1995, Akkermans et al., 1995, Borst et al., 1995], and has been supported in part by the Commission of the European Communities as Esprit-III project P6521 `OLMECO' (Open Library for Models of MEchatronic COmponents). The partners in the OLMECO project are PSA Peugeot-Citroën (F), BIM (B), FAGOR (Sp), Ikerlan (Sp), Imagine (F), UT (NL) and ECN (NL). The thermal systems library has benefitted from earlier work in the EBIB project, supported by Senter, and with Kropman BV Installatietechniek (NL), ECN and the University of Twente as partners. We thank Anita Pos, Arno Breunese, Jan Broenink, Pierre-Joseph Gailly, Roger Fisset, Jacques Guyot, Bob Wielinga, Mert Alberts, Jan Benjamin, Willem Wortel and Wim Zeiler for discussions concerning various parts of our work. Furthermore,we are grateful to Kropman BV for providing data for the Schieland hospital heating system simulation.