01432nas a2200121   4500008004100000245005900041210005900100520100900159100002001168700002001188700001801208856008401226       2018                        eng d00aSimplifications for hydronic system models in Modelica0 aSimplifications for hydronic system models in Modelica3 a<p>Building systems and their heating, ventilation and air conditioning ow networks, are becoming increasingly complex. Some building energy simulation tools simulate these ow networks using pressure drop equations. These ow network models typically generate coupled algebraic nonlinear systems of equations, which become increasingly more difficult to solve as their sizes increase. This leads to longer computation times and can cause the solver to fail. These problems also arise when using the equation-based modelling language Modelica and Annex 60 based libraries. This may limit the applicability of the library to relatively small problems unless problems are restructured. This paper discusses two algebraic loop types and presents an approach that decouples algebraic loops into smaller parts, or removes them completely. The approach is applied to a case study model where an algebraic loop of 86 iteration variables is decoupled into smaller parts with a maximum of 5 iteration variables.</p>1 aJorissen, Filip1 aWetter, Michael1 aHelsen, Lieve  uhttps://simulationresearch.lbl.gov/publications/simplifications-hydronic-system