Functional mock-up unit for co-simulation import in EnergyPlus

TLDR

The functional mock‑up interface (FMI) standard defines FMUs as open‑format packages that can contain models, descriptions, source code, and executables for multiple platforms, enabling links between disparate simulation programs. The article aims to develop and implement an FMU co‑simulation import interface in EnergyPlus, detailing the FMI mathematical basis, its application, and the architecture of the implementation. The implementation uses EnergyPlus as a master simulator that imports FMUs, controls simulation time, and coordinates data exchange, with a typical workflow involving pre‑processing and co‑simulation; for example, an HVAC system and its controls can be modeled in Modelica, exported as an FMU, and linked to a building envelope model in EnergyPlus for runtime data exchange. The new FMU import capability enables EnergyPlus to co‑simulate with diverse FMU‑packaged programs, as demonstrated by use cases of a ventilation system and a shading controller.

Abstract

This article describes the development and implementation of the functional mock-up unit (FMU) for co-simulation import interface in EnergyPlus. This new capability allows EnergyPlus to conduct co-simulation with various simulation programs that are packaged as FMUs. For example, one can model an innovative Heating, Ventilation, and Air Conditioning (HVAC) system and its controls in Modelica, export the HVAC system and the control algorithm as an FMU, and link it to a model of the building envelope in EnergyPlus for run-time data exchange. The formal of FMUs is specified in the functional mock-up interface (FMI) standard, an open standard designed to enable links between disparate simulation programs. An FMU may contain models, model description, source code, and executable programs for multiple platforms. A master simulator – in this case, EnergyPlus – imports and simulates the FMUs, controlling simulation time and coordinating the exchange of data between the different FMUs. This article describes the mathematical basis of the FMI standard, discusses its application to EnergyPlus, and describes the architecture of the EnergyPlus implementation. It then presents a typical workflow, including pre-processing and co-simulation. The article concludes by presenting two use cases in which models of a ventilation system and a shading controller are imported in EnergyPlus as an FMU.