American society of heating, refrigerating and air-conditioning engineers

Abstract

Many special purpose computer programs for simulation of physical systems are in operation today.In industrial applications, they dominate completely over general purpose simulation environments.To gain runtime efficiency, often on yesterdays computers, the mathematical models of the tailored tools are frequently intertwined with the coded solution procedure, creating a monolithic structure.This makes it difficult to understand and improve the implemented models, also for the original developers.In the field of building simulation, researchers agree that the monolithic programs will be impossible to upgrade and maintain in the long term.This thesis treats the design of the general purpose simulation environment IDA, and of the Neutral Model Format (NMF), a program independent language for modelling of dynamical systems using differential-algebraic equations with discrete events.IDA and NMF are used to effectively develop special purpose GUI-based tools that (1) are easy to use for end users without simulation expertise, and that (2) have good prospects for long term maintenance and reuse.IDA and NMF also serve as a general modelling and development environment for the sophisticated user.The development of IDA commenced in 1987 at the Swedish Institute of Applied Mathematics.IDA has been used externally since 1990, primarily for simulation of building and energy systems.IDA applications and NMF model libraries have been developed for, e.g., district heating substations, fire scenarios in offshore structures, natural ventilation of buildings, building energy and loads simulation, refrigeration systems, ventilation of road tunnels under normal and fire conditions.NMF component model descriptions can be automatically translated into the format of a number of simulation environments.Translators have been developed for ESACAP, HVACSIM+, IDA, MS1, SPARK, and TRNSYS.Some of these have computer algebra capability for automatic model processing.This thesis consists of seven introductory chapters and seven separate papers.The main design issues for IDA and NMF are listed and briefly discussed in the introductory sections.Among them are: algebraic solution techniques, field models, implementation form and languages, equation based model description languages, modelling language translatability, and access to foreign subroutine based models.The papers give historical overview and insight into selected applications and topics.