Simulation of a Solar Heated House Using the Bond Graph
Modeling Approach and the Dymola Modeling Software

Abstract

Objective: To simulate a Solar Heated House using the Bond Graph modeling technique coded directly into the Dynamic Modeling Language (Dymola).

Bond Graphs: Engineers needed to find a more general symbolic (graphical) representation providing both the computational and topological structure of any kind of physical system. They found out that block diagrams and signal flow graphs only preserve the computational but not the topological structure. Thus, Henry Paynter, a professor at MIT, invented in the early sixties a new representation called the Bond Graph modeling technique applicable to a wide range of systems ranging from the usual ones such as mechanical and electrical systems, to less likely ones such as chemical, ecological, or biomedical systems. As the word says, a bond graph is a collection of elements bonded together.

Dymola: The Dynamic Modeling Language (Dymola) is going to be used in this project. It supports a variety of simulation languages and is very useful for modeling large scale systems. Dymola supports truly modular hierarchical modeling of continuous time systems. It is very well suited to implement the bond graph modeling methodology, and is able to map bond graphs into state-space descriptions and from there into simulation programs coded in several continuous-system simulation languages (Desire, Simnon).

Transformation of Bond Graph into Dymola: Once the bond graph for a certain system has been constructed, it can directly be coded into Dymola. There are several rules for this procedure that must be observed. The basic bond graph modeling elements of R, C, L, TF, GY, and Bond can be described once and for all and stored away in a Dymola model library called "bond.lib". Dymola is so powerful that it can automatically evaluate the causality of a bond graph, generate a state-space description for the system, and finally generate a simulation program in currently either Desire or Simnon, two "flat" direct executing continuous-system simulation languages.

Case Study: A demonstration of the bond graph modeling technique as well as of Dymola is performed. The system being used is a Solar-Heated House, a relatively complex system involving many different types of energy. Scientists throughout the years investigated the exploitation of the solar radiation for such houses. It is expected that, using the method described in this thesis, the physical behavior of such systems can be modeled, simulated, and evaluated in a convenient, robust, and fast manner. The investigated configuration consists of a flat-plate solar collector,two storage tanks, and the habitable space. Each part is governed by a set of first order differential equations that illustrate the energy flow through the subsystem. Each subsystem is separately transformed into an equivalent bond graph representation. The various parameters used for the simulation were taken from an older study of a similar solar-heated house performed in the late 70's.

Summary: This is a thesis touching on a modern and advanced modeling-simulation technique applied to a Solar-Heated House. The Bond Graph modeling methodology and the Dynamic Modeling Language (Dymola) are used. The goal of this study is to observe the versatility of Dymola to describe complex physical systems using the bond graph approach to dynamical system modeling.