6 Building Physics and Energy Efficiency

6Building Physics and Energy Efficiency

D-r Roman Rabenseifer

The main aim of this chapter is to make students aware of the relationship between building physics, mathematical calculations and computer-aided modelling of the future behaviour of a building, including its energy efficiency. On this occasion, it should be said that not only in the future, but even now, the assessment of the future behaviour of a designed building cannot be done without computer-aided calculations, and the software used plays a significant role. In simplified terms, it could be said that software for computer-aided building performance simulation consists of three main levels.

The deepest, almost imperceptible to the average user, is the mathematical level, often called the computational module. At this level, the physical model is first transformed into a mathematical model and then the required calculations are carried out. The transformation is mostly automatic and is based on the chosen method that is specific to the software. Numerical methods, e.g. the finite difference method or the finite volume method, are the most commonly used. Above the calculation module there is a level defining the physical model, i.e. building geometry, material properties, boundary conditions, etc. This level may or may not also be organised in the form of several separate modules. The user cannot fail to notice it, since the creation of the physical model is actually the primary objective of the software. It requires the most work and time, but also knowledge of building physics. The actual data entry or data modification is done through the third level, the interface, as in the case of any other program. Through the interface, both the physical and mathematical model can be influenced.

In conclusion, the primary focus of this chapter is not computer simulations, but the creation of building-physical models for the purpose of the correct design of the building envelope or its individual components, not only in terms of energy efficiency, but also in terms of the quality of the indoor environment. Of course, in modern design, the creation of buildingphysical models can no longer be done without computer-aided simulation tools.

We assume that the readers have a basic knowledge of building physics and thermodynamics. The aim of this chapter is mainly to review the knowledge and to complement it with the current state of knowledge in the field of building physics and thermodynamics and point out some key aspects.