Design choices for thermofluid flow components and systems that are exported as Functional Mockup Units

TitleDesign choices for thermofluid flow components and systems that are exported as Functional Mockup Units
Publication TypeJournal Article
Year of Publication2015
AuthorsWetter, M, Fuchs, M, Nouidui, TStephane
Abstract

This paper discusses design decisions for exportingModelica thermofluid flow components as FunctionalMockup Units. The purpose is to provide guidelinesthat will allow building energy simulation programsand HVAC equipment manufacturers to effectively useFMUs for modeling of HVAC components and systems.We provide an analysis for direct input-output dependenciesof such components and discuss how these dependenciescan lead to algebraic loops that are formedwhen connecting thermofluid flow components. Basedon this analysis, we provide recommendations that increasethe computing efficiency of such components andsystems that are formed by connecting multiple components.We explain what code optimizations are lost whenproviding thermofluid flow components as FMUs ratherthan Modelica code. We present an implementation ofa package for FMU export of such components, explainthe rationale for selecting the connector variables of theFMUs and finally provide computing benchmarks fordifferent design choices. It turns out that selecting temperaturerather than specific enthalpy as input and outputsignals does not lead to a measurable increase in computingtime, but selecting nine small FMUs rather than alarge FMU increases computing time by 70%

LBNL Report Number

LBNL-1002826