System-level dynamic simulation for the design and control of energy-efficient buildings : a model library and some case studies

This dissertation, that is part of a longer term research on energy efficiency, deals with building energy systems. In particular, the thesis aims to provide a library of dynamic models capable of assisting, through system-level dynamic simulation, the design and control of energy efficient buildings. A somehow secondary (but not less important) purpose is to back up the adopted modeling choices by means of convenient case studies. To obtain the mentioned goals, the work starts by discussing the concept of “building energy system”; then, some building performance simulation tools, that today are the most used for the analysis of these systems, are reviewed. A major outcome of this review is that said software are too detailed for the purpose of a system-level analysis. The main issues generated by that characteristics are summarized below. • Statistical studies predict that for many years to come, buildings will be “structurally old”, and it will be difficult to find the necessary information for this description as required by the tools under question in general; • simulation time often turns out to be long; • much of the information required by the tools is of hardly any use for the purpose of system-level dynamic simulation for the design and control of energy efficient buildings. Moreover, mainstream simulation tools are not able to describe the entire set of multi-physical phenomena that take part in the overall energy performance of a building and, for this reason, they have to be put in the position to communicate with one another. This is typically realised by means of a co-simulator, that is often far from easy to use. To overcome these problems, we decided to create the Building Energy System library in Modelica, an object-oriented language that allows the description of a multiphisics system with the first-principle equations. After describing the features of the library and some methodological choices made, the thesis continues introducing three case studies which led to assert that the library is: • sufficiently accurate for the description at the system-level for both the design and the control of buildings. In fact, it contains all the necessary components used to characterize and to describe a whole building system through the knowledge of few information.• suitable for the analysis of the energy consumption based on user’s consumption; • able to manage complex systems while maintaining simulation times definitely reasonable.