Conference article

Design Choices for Thermofluid Flow Components and Systems that are Exported as Functional Mockup Units

Michael Wetter
Lawrence Berkeley National Laboratory, Energy Technologies Area, Building Technology and Urban Systems, Division, Simulation Research Group, Berkeley CA, USA

Marcus Fuchs
RWTH Aachen University, E.ON Energy Research Center, Institute for Energy Efficient Buildings and Indoor Climate, Aachen, Germany

Thierry S. Nouidui
Lawrence Berkeley National Laboratory, Energy Technologies Area, Building Technology and Urban Systems, Division, Simulation Research Group, Berkeley CA, USA

Download articlehttp://dx.doi.org/10.3384/ecp1511831

Published in: Proceedings of the 11th International Modelica Conference, Versailles, France, September 21-23, 2015

Linköping Electronic Conference Proceedings 118:3, s. 31-41

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Published: 2015-09-18

ISBN: 978-91-7685-955-1

ISSN: 1650-3686 (print), 1650-3740 (online)

Abstract

This paper discusses design decisions for exporting Modelica thermofluid flow components as Functional Mockup Units. The purpose is to provide guidelines that will allow building energy simulation programs and HVAC equipment manufacturers to effectively use FMUs for modeling of HVAC components and systems. We provide an analysis for direct input-output dependencies of such components and discuss how these dependencies can lead to algebraic loops that are formed when connecting thermofluid flow components. Based on this analysis, we provide recommendations that increase the computing efficiency of such components and systems that are formed by connecting multiple components. We explain what code optimizations are lost when providing thermofluid flow components as FMUs rather than Modelica code. We present an implementation of a package for FMU export of such components, explain the rationale for selecting the connector variables of the FMUs and finally provide computing benchmarks for different design choices. It turns out that selecting temperature rather than specific enthalpy as input and output signals does not lead to a measurable increase in computing time, but selecting many small FMUs rather than a large FMU considerably increases computing time.

Keywords

FMI; Modelica; thermofluid flow

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