Paper Conference

Proceedings of SimBuild Conference 2006: 2nd conference of IBPSA-USA


Modelica Versus TRNSYS - A Comparison Between an Equation-Based and a Procedural Modeling Language for Building Energy Simulation

Michael Wetter, Christoph Haugstetter
United Technologies Research Center, 411 Silver Lane, East Hartford, CT 06108, USA

Abstract: We present the implementation of a multizone building energy simulation model in the equationbased modeling language Modelica and compare it to an implementation with comparable modeling detail in TRNSYS. Our development time comparison indicates a five to ten times faster development through use of the equation-based modeling language Modelica. The development time for TRNSYS was extrapolated using data from BuildOpt and comparison between BuildOpt and TRNSYS since TRNSYS data were not available. We provide a comparative model validation of the Modelica and TRNSYS implementation, and compare their numerical performance. The difference in predicted annual heating and cooling energy usage between our Modelica model and TRNSYS is 5% to 20%, which we primarily attribute to our simplified window model. The computation time of the Modelica model was three to four times longer than TRNSYS, but we believe that dismissing equation-based modeling languages as computationally inefficient is a premature conclusion.
Pages: 262 - 269