- Lawrence Berkeley National Lab – Berkeley, CA
- National Renewable Energy Lab – Golden, CO
- Modelon, Inc. – Glastonbury, CT
- Objexx Engineering, Inc. – Needham, MA
- Big Ladder Software, LLC – Denver, CO
- IBPSA-World and 42 organizations participating in IEA EBC Annex 60 and IBPSA Project 1
DOE Funding: $1,800 in FY19; $8,210,000 overall
Cost Share: In kind contributions from IEA Annex 60 and IBPSA Project 1 participants
Project Term: 2012 –
Funding Opportunity: Emerging Technologies Core Funding
Related Projects: EnergyPlus, OpenStudio, Open Building Control, Data Center Toolkit
Traditional simulation engines are “solver-based”—the governing equations of the system under simulation is implicit whereas the simulation engine itself embodies the solvers that evolve the equations in time. EnergyPlus is a traditional solver-based building energy modeling (BEM) engine—it contains equations for heat and mass balance, tightly intertwined with numerical solvers and program flow logic. Like other solver-based engines, EnergyPlus is difficult to maintain, extend, and link to other engines because it weaves together multiple solvers, each with its own structure and source-code. The tight coupling between equations and solvers also makes the models—i.e., the equations—impossible to extract and repurpose for other applications like control design and implementation.
To address these limitations while opening up BEM to new applications, BTO is building a next-generation engine with the internal name Spawn-of-EnergyPlus (Spawn). The intent is for Spawn and EnergyPlus to live side-by-side, with the OpenStudio software development kit providing access to both and insulating users and client vendors from implementation differences.
Spawn reuses the EnergyPlus modules for lighting, building envelope, and loads but re-implements the HVAC and controls modules in the equation-based modeling language Modelica. In equation-based modeling, domain (BEM) experts can focus on write the governing equations of the system to be simulated. These equations can then be simulated by domain-agnostic tools. Equations are more compact than solvers and easier to write and maintain. Equation-based component and system models can be easily composed by linking interface variables—like temperature and air flow rate—in one set of equations to interface variables in another. Equation-based models are easy to repurpose—equations implicit in a solver can only be simulated, explicit equations can be analyzed, optimized, and even automatically turned into running code for direct execution in a different environment such as a building controller.
Modelica was developed primarily by the automotive and aerospace industries, but it is making headway in the buildings space where it is especially suitable to modeling HVAC systems and building controls. Since 2012, BTO has supported the development of the Modelica Buildings Library. Library development significantly advanced through the International Energy Agency (IEA) Annex 60 “New generation computational tools for building and community energy systems based on the Modelica and Functional Mockup Interface standards”. Development coordination has now transitioned to the International Building Performance Simulation Association (IBPSA) where 20 organizations contribute to IBPSA Project 1 “BIM/GIS and Modelica Framework for building and community energy system design and operation”.
The Modelica Buildings Library provides the domain-specific content for Spawn. BTO is working with commercial partners to provide domain-agnostic pieces like a Modelica translator and a simulation manager. As of spring 2018, BTO has an "alpha" prototype of a Spawn executable which combines EnergyPlus, Modelica Buildings Library components, the JModelica compiler, the g++ C++ compiler and the pyFMI simulator and can simulate simple buildings. A beta system is expected sometime in 2020 or 2021.
The use of Modelica and equation-based modeling over imperative languages like C++ and solver-based simulators holds significant promise for the future of BEM. Anticipated advantages include:
- Ability to simulate real-world control sequences and to reuse control models in control design, implementation and verification workflows creating a natural bridge between BEM and building control. The related Open Building Control project is developing tools and processes that will form this bridge.
- Improved model scalability including the ability to simulate very large models and to integrate models with different levels of fidelity.
- Ability to leverage domain-agnostic simulation enhancements for speed and parallelization.
- Reduced development and maintenance effort for BEM-specific code and ability to leverage external efforts in BEM development such as those of IBPSA Project 1.
SOEP gains additional leverage by building on the Functional Mockup Interface (FMI) standard for co-simulation, i.e., for simulation component and engine coordination. The use of FMI is expected to yield advantages including:
- Ability to integrate with other simulation engines that support the FMI standard, a number that currently stands at 89 and is growing.
- Ability to incorporate proprietary equipment models from manufacturers. Current solver-based BEM tools have to reverse-engineer models for new equipment or fit specific equipment performance characteristics to generic models, both approaches are costly and time consuming. FMI allows manufacturers to plug in-house component models into larger simulation frameworks without compromising intellectual property or competitive advantage.
- More broadly, the use of standards provides a stable platform for buildings industry investment, and allows it to leverage technologies, tools, and investments from other related domains.
- Wangda Zuo, Michael Wetter, Wei Tian, Dan Li, Mingang Jin and Qingyan Chen. Coupling indoor airflow, HVAC, control and building envelope heat transfer in the Modelica Buildings library. Journal of Building Performance Simulation, 9(4), p. 366-381, 2016.
- Michael Wetter, Marco Bonvini and Thierry S. Nouidui. Equation-based languages - A new paradigm for building energy modeling, simulation and optimization. Energy and Buildings, 117(1), p. 290-300, 2016. Also available as LBNL Technical Report LBNL-1003383.
- Michael Wetter, Wangda Zuo, Thierry S. Nouidui and Xiufeng Pang. Modelica Buildings library. Journal of Building Performance Simulation, 7(4):253-270, 2014. Limited number of free e-prints.
- Michael Wetter. Modelica-based Modeling and Simulation to Support Research and Development in Building Energy and Control Systems. Journal of Building Performance Simulation, 2(2):143-161, 2009. Also available as LBNL Technical Report LBNL-2740E.pdf.
- Michael Wetter. A View on Future Building System Modeling and Simulation. Published in Building Performance Simulation for Design and Operation, 2011, Jan L. M. Hensen and Roberto Lamberts (editors), Routledge, UK, ISBN: 978-0-415-47414-6.
- Michael Wetter, Thierry S. Nouidui, David Lorenzetti, Edward A. Lee and Amir Roth. Prototyping the next generation EnergyPlus simulation engine. Proc. of the 14th IBPSA Conference, p. 403--410, Hyderabad, India, December 2015.
- Michael Wetter, Marcus Fuchs, Pavel Grozman, Lieve Helsen, Filip Jorissen, Moritz Lauster, Dirk Müller, Christoph Nytsch-Geusen, Damien Picard, Per Sahlin and Matthis Thorade. IEA EBC Annex 60 Modelica Library - An international collaboration to develop a free open-source model library for buildings and community energy systems. Proc. of the 14th IBPSA Conference, p. 395--402, Hyderabad, India, December 2015.
- Michael Wetter, Marco Bonvini, Thierry S. Nouidui, Wei Tian, and Wangda Zuo. Modelica Buildings library 2.0.
Proc. of the 14th IBPSA Conference, p. 387--394, Hyderabad, India, December 2015.
- Marco Bonvini, Michael Wetter and Thierry Stephane Nouidui. A Modelica package for building-to-electrical grid integration.
Proc. of 5th BauSim Conference, p. 6-13, Aachen, Germany, September 2014.
- Wangda Zuo, Michael Wetter, Dan Li, Mingang Jin, Wei Tian and Qingyan Chen. Coupled Simulation of Indoor Environment, HVAC and Control System by Using Fast Fluid Dynamics and the Modelica Buildings Library. Proc. of ASHRAE/IBPSA-USA Building Simulation Conference, p. 56-63, Atlanta, GA, September 2014.
- David H. Blum and Leslie K. Norford. Dynamic Simulation of Regulation Demand Response by VAV HVAC Systems.
Proc. of ASHRAE/IBPSA-USA Building Simulation Conference, p. 402-409, Atlanta, GA, September 2014.
- Michael Wetter. Fan and pump model that has a unique solution for any pressure boundary condition and control signal.
Proc. of the 13th IBPSA Conference, p. 3505-3512, Chambéry, France, August 2013.
- Xiufeng Pang, Raj Dye, Thierry Stephane Nouidui, Michael Wetter, and Joseph J. Deringer. Linking interactive Modelica simulations to HTML5 using the Functional Mockup Interface for the LearnHPB platform. Proc. of the 13th IBPSA Conference, p. 2823--2829, Chambéry, France, August 2013.
- Donghun Kim, Wangda Zuo, James E. Braun, and Michael Wetter. Comparisons of building system modeling approaches for control system design. Proc. of the 13th IBPSA Conference, p. 3267-3274, Chambéry, France, August 2013.
- Thierry Stephane Nouidui, Kaustubh Phalak Wangda Zuo, and Michael Wetter. Validation and Application of the Room Model of the Modelica Buildings library. Proc. of the 9th International Modelica Conference, Munich, Germany, September 2012.
- Gregory Provan and Alberto Venturini. Stochastic Simulation and Interference using Modelica.
Proc. of the 9th International Modelica Conference, Munich, Germany, September 2012.
- Roberta Ansuini, Roberto Larghetti, Massimo Vaccarini, Alessandro Carbonari, Alberto Giretti, Sara Ruffini, Hongliang Guo, and Sian Lun Lau. Hybrid Modeling for Energy Saving in Subway Stations. Proc. of the First Building Simulation and Optimization Conference, Loughborough, UK, September 2012.
- Thierry Stephane Nouidui, Michael Wetter, and Wangda Zuo. Validation of the Window Model of the Modelica Buildings library.
Proc. of the 5th SimBuild Conference, Madison, WI, USA, August 2012.
- Bryan Eisenhower, Kazimir Gasljevic, and Igor Mezic. Control-Oriented Modeling and Calibration of Building Energy Models Using Modelica. Proc. of the 5th SimBuild Conference, Madison, WI, USA, August 2012.
- Michael Wetter, Wangda Zuo, and Thierry Stephane Nouidui. Modeling of heat transfer in rooms in the Modelica "Buildings" library.
Proc. of the 12th IBPSA Conference, p. 1096--1103. Sydney, Australia, November 2011.
- Michael Wetter, Wangda Zuo, and Thierry Stephane Nouidui. Recent developments of the Modelica buildings library for building energy and control systems. Proc. of the 8th International Modelica Conference. Dresden, Germany, March 2011.
- Michael Wetter. Modelica Library for Building Heating, Ventilation and Air-Conditioning Systems. Proc. of the 7th International Modelica Conference. Como, Italy, September 2009.
- Michael Wetter. A Modelica-based model library for building energy and control systems. Proc. of the 11th IBPSA Conference, p. 652--659. Glasgow, Scotland, July 2009.
- Michael Wetter. Multizone Airflow Model in Modelica. Proc. of the 5th International Modelica Conference, p. 431--440. Vienna, Austria, September 2006. (The models that are described in this paper have been implemented in Buildings library in the package Buildings.Airflow.)