The Spawn of EnergyPlus, called SOEP, is a next-generation simulation engine, for building and control energy systems. SOEP will combine

• The OpenStudio front-end for model authoring, simulation and as a workflow automation tool,

• the Modelica Buildings Library as a repository of models,

• OPTIMICA as a translator that translate models from the Modelica standard to the Functional Mockup Interface standard for simulation and for execution on control systems,

• QSS solvers, a class of new solvers that we develop for Spawn,

• PyFMI as a suite of state-of-the-art numerical solvers that conduct a time domain simulation.

The intent is for SOEP 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. Equation-based models allow SOEP to unify building energy modeling with control workflows, and allow users and manufacturers to insert their own models into SOEP.

Fig. 1 : Spawn-of-EnergyPlus (SOEP) is a next-generation BEM engine that leverages open standards for equation-based modeling (Modelica) and co-simulation (FMI).

This documentation is a working document for the design, development and implementation of the Spawn of EnergyPlus (SOEP).

To cite Spawn of EnergyPlus, use

Michael Wetter, Kyle Benne, Hubertus Tummescheit and Christian Winther.

Spawn: coupling Modelica Buildings Library and EnergyPlus to enable new energy system and control applications.

Journal of Building Performance Simulation. Pages 1-19. 2023.

Table of Contents

• 1. Preample
  • 1.1. Purpose of the Document
  • 1.2. Contributors
• 2. Download
  • 2.1. Software
    • 2.1.1. Official releases
    • 2.1.2. Development version
  • 2.2. Publications
• 3. Conventions
• 4. Requirements
  • 4.1. OpenStudio integration
  • 4.2. Mathematics
    • 4.2.1. Differentiability
    • 4.2.2. Control of Numerical Noise
  • 4.3. FMU Requirements
    • 4.3.1. FMU Capabilities
  • 4.4. QSS Implementation
  • 4.5. Master Algorithm
• 5. Software Architecture
  • 5.1. Overall software architecture
  • 5.2. Coupling of EnergyPlus with Modelica
    • 5.2.1. Assumptions and limitations
    • 5.2.2. Sizing calculations
      • 5.2.2.1. Sizing specifications
      • 5.2.2.2. Zone multipliers
      • 5.2.2.3. Sizing parameters obtained by Modelica
    • 5.2.3. Unit system
    • 5.2.4. Partitioning of the models
      • 5.2.4.1. Coupling of the envelope model
      • 5.2.4.2. Coupling of an opaque construction
      • 5.2.4.3. Coupling of a zone surface
      • 5.2.4.4. Retrieving output variables from EnergyPlus
      • 5.2.4.5. Sending input to EnergyPlus
    • 5.2.5. API used to Export EnergyPlus as an FMU
      • 5.2.5.1. Instantiation
    • 5.2.6. Time synchronization
  • 5.3. Distribution of Spawn and the Modelica Buildings Library
  • 5.4. Integration of QSS solver with OPTIMICA
    • 5.4.1. FMI Changes for QSS
      • 5.4.1.1. Setting individual elements of the state vector
      • 5.4.1.2. Getting derivatives of state variables
      • 5.4.1.3. Event Handling
      • 5.4.1.4. Getting derivatives of event indicator functions
      • 5.4.1.5. Test models
      • 5.4.1.6. SmoothToken for QSS
      • 5.4.1.7. Summary of Proposed Changes
      • 5.4.1.8. Open Topics
  • 5.5. Integration with OpenStudio
• 6. Numerical Methods of the Master Algorithm
  • 6.1. Time Integration
    • 6.1.1. QSS1
    • 6.1.2. QSS2
    • 6.1.3. QSS3
    • 6.1.4. Discussion of QSS
    • 6.1.5. LIQSS
    • 6.1.6. Discussion of LIQSS
  • 6.2. Algebraic Loops
    • 6.2.1. Software Requirements for Efficient Implementation of Newton-Raphson Method for Algebraic Loops
• 7. Benchmarks
• 8. Acknowledgments
• 9. Glossary
• 10. References