Multiphysics simulation in buildings

Abstract

Numerical simulation play an important role in the design, engineering, operation and management of buildings. It can help reducing energy consumption, improving indoor air quality and thermal comfort and provide quantitative data supporting decision making, e.g. choosing the best solution for designing, retrofitting or choosing the optimal HVAC system. Besides, buildings are composed more and more of different complex elements and systems which make the simulation of only thermal physics in buildings not enough to evaluate their whole performance. All the involved physical phenomena like moisture, airflow and pollutants should be considered and coupled in order to reproduce the reality with the highest possible level of details. In this context, this PhD thesis presents the models and the simulations of multi-physics inside buildings using an in-house developed modular and object oriented tool called NEST. All the physics of the coupled heat, moisture, airflow and pollutants transfer that take place inside buildings are considered and solved. In addition, the software allows the simulation of a building system as a collection of different numerical elements, like walls, rooms, HVAC systems, outdoor, etc., connected with each other and able to exchange boundary conditions. In this manner any building configuration can be set and simulated. The physical and mathematical formulations of the implemented elements are presented. Then, in order to assure the credibility of the developed software, the implemented models are validated and verified with different test cases from the literature. The list of test cases cover all the aspects of heat, moisture, airflow and pollutants transfer in the whole building and it can be used as a reference list for the validation of other buildings simulation tools. Special emphasis is placed on the simulation of buildings performance in real applications. First, the hygrothermal behaviour in different public buildings with different climates conditions are analysed before retrofitting them. Several weak points in the thermal and moisture resistance of the façades layers are identified and thermal and moisture loads before and after the expected retrofitting solutions are evaluated. Second, a residential building (semidetached house) in Netherlands is simulated and the airflow, heat and CO 2 transfer inside it is studied in order to optimize the energy consumption while maintaining acceptable levels of thermal comfort and indoor air quality.