Simmodel transformation middleware for modelica-based building energy modeling and simulation

Cao, Jun; van Treeck, Christoph Alban (Thesis advisor); Bazjanac, Vladimir (Thesis advisor)

Aachen (2018)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2018


In the Architecture, Engineering, Construction, Owners and Operators (AECOO) industry, generation of Building Energy Models (BEMs) for Building Energy Performance Simulation (BEPS) currently is a time consuming and costly process, primarily due to BEMs may be hampered by diverse inconsistencies caused by modeling failures or inconsistencies or simply due to conceptual differences between the AECOO domains and their modeling hierarchy, especially from a geometrical and topological point of view concerning the issue of space boundaries. The manual BEM development process, e.g., using traditional BEM tools such as EnergyPlus, often takes considerable effort and can result in errors and omissions, and adds to the cost of the BEM project. In order to address the challenge, this thesis provides a scientific methodology for automatically transforming a digital Building Information Model (BIM) format, SimModel, into an object-oriented acausal model in Modelica that can be readily used for advanced BEPS. The outcome of the thesis is a transformation middleware developed to link SimModel with different Modelica BEM libraries for improving the BEM development process.The acronym BIM in this thesis represents building information modeling or model. When it is used as a noun, it denotes a building information model which is an instance of the data model of buildings containing multi-disciplinary data, e.g., geometry, physics, and Heating, Ventilation, and Air Conditioning (HVAC), specific to a particular building. When it is using as a verb, i.e., building information modeling, it is the act or process of creating a building information model. Furthermore, Industry Foundation Classes (IFC) is a fully object-based open-BIM data format in the AECOO industry. SimModel is then a BIM format contains all necessary data for BEM and the structure of this model is closely aligned to the IFC data format, in order to link to incoming or outgoing IFC information data, which is also a motivation factor for using SimModel as the starting point for this work. The transformation middleware developed in this thesis focuses on automatically transforming the HVAC systems of buildings from SimModel into equation-based BEM, especially with respect to Modelica. Modelica is a non-proprietary, object-oriented, equation-based modeling language which is becoming more important in the BEM community. It allows modellers to conveniently model complex physical systems containing sub-components ofmechanics, electrics, hydraulics, etc. The typical manual BEM creation is accelerated by the transformation method proposed which avoids the prevalent tedious, cumbersome and error-prone process of manual data transformation and model generation.In summary, this thesis presents the following contributions: 1) proposed a scientific method to automatically transform a digital BIM format into an object-oriented acausal model for BEPS. To prove the concept of the proposed method, the thesis developed an open source transformation system for transforming SimModel into different Modelica libraries. This system framework converts actual HVAC component instances and their physical propertiesfrom the SimModel side into the Modelica world. 2) developed a data transformation schema, based on the XML Schema Definition (XSD), to support the data transformation to multiple Modelica BEM libraries with different model topologies and varying syntax in the meantime. The schema model defines possible data mapping logics between SimModel and Modelica. It stores generic mapping rules for transforming different levels of SimModel data intoModelica models, such as the library level for specifying a target Modelica BEM library, HVAC component level, and the internal property level of each HVAC component. Based on the schema model, simulation experts can easily define a specific data transformation process between SimModel and different Modelica libraries by re-using the generic mapping rules of the schema model. 3) presented a generic Application Programming Interface (API)for interfacing two different programming languages used in the system development. The main parts of the transformation system are implemented in the C++ programming language, in order to accelerate the system efficiency on model transformation. The Modelica data model generation is then developed in the Python language as it is widely used in the pre- or post-processing of Modelica-based BEM. This generic API, interfacing C++ and Python languages, is embedded in the transformation system, and provides control on the Modelica code generation for the Python-based modellers and simulation engineers. The proposed flexible model transformation system is an enhancement to current work by demonstrating a generic method for transforming a BIM format into different Modelica libraries in order to accelerate the BEM development. In addition, the other related works focused on linking one specific Modelica library to their BIM formats. When namingconventions, data representations or library structures of the other different Modelica libraries differ from the target library, the other works are not suitable for transforming their BIM formats into different Modelica libraries. This shortcoming was addressed in the proposed method.