Simulation of air flow distribution in rooms by a systemic approach

In order to achieve a satisfactory level of hygiene and comfort in premises aid to assess the pollutant transfers, it is necessary to control the air flow distribution. The research on air distribution in rooms involves full-scale experiments, scale-model experiments and Computational Fluid Dynamics (CFD) tools. An intermediate approach between predictive numerical simulation and experimental determination of aerodynamic parameters is the systemic approach. The paper proposed presents the main features of the MTS code recently developed and based on the principles of the systemic approach. A model is built from a combination of elementary systems representing basic flows as piston, mixing flow, recirculation, short circuiting; each elementary system is characterized by specific parameters such as the residence time and the volume of the unitary system. The adjustment of the model is derived from the comparison of the responses to a signal injected into the model with a tracer emission realized at the room inlet; these responses depend on the internal fluid flow patterns. The difficulty consists in finding quickly the most representative adjustment and the associated parameters. The code IDTS is constituted then by two main subroutines, whose functions are described: a subroutine in order to solve the algebra differential equations characterizing the unitary systems, and a subroutine in order to optimise the structural adjustment design respecting some defined numerical and physical constraints. Furthermore, the computational tool has been tested from a ventilated laboratory enclosure (2 300 m3 volume). Helium stimulus corresponding to pulse is realized in the blowing duct, and the helium concentration is monitored at the exhaust duct of the test enclosure. The experimental results are then analysed and compared with the IDTS identifications. The IDTS code thus constitutes a computer-aided design tool of flow models to improve the knowledge about the gaseous transfers in a ventilated indoor space. So, a preliminary qualification from several experimental data has been achieved and is quite encouraging. (authors)