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, Michael, Marcus Fuchs, and Thierry Stephane Nouidui
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 nine small FMUs rather than a
large FMU increases computing time by 70%

LBNL Report Number

LBNL-1002826