A hybrid ventilation system combines both mechanical and natural ventilation modes. The natural ventilation mode, especially, causes some challenges for analysis tools since the varying nature of naturally driven flow means that transient calculations should be used to predict the flow fields. Analysis tools based on CFD have some advantages for detailed investigations since, in addition to evaluating the flow and temperature fields, it is possible to use CFD methods to calculate air exchange efficiency and other flow indices.
This paper presents a study of the dynamics of the turbulent mixing of a hot or cold air stream with the air in the interior of a building zone. Observations and CFO results of transient temperature behaviour in a fully developed jet flow field are presented. A simple model for the characteristic time-constant of the mixing process in a room is derived. The mixing of a turbulent jet, as a function of position inside the room, is also discussed. This mixing time-constant plays an important role in total system dynamic behaviour and stability.
This paper is concerned with the numerical modelling and investigation of the performance of air curtains employed to reduce air flow and heat transfer across open doors and between conditioned and unconditioned spaces. It has been found that the model based on a commercial Computational Fluid Dynamics software package can successfully predict the critical velocities and efficiencies of air curtains and the influence of external parameters such as wind speed.
Results from testing of a simple model in a wind tunnel are used to validate two computational fluid dynamics mathematical models. The results show that only the Reynolds-stress model provides a reasonably accurate representation of the inlemal flow, and that both models fail to predict the flow at the opening of the model
The air flow in a Passive Downdraught Evaporative Cooling (PDEC) tower has been modelled using a Computational Fluid Dynamics (CFD) code. Water is injected into dry warm air and the interaction between the water and the air is represented using a particle transport model. This models the transfer of mass, momentum and heat between the water particles and the air in addition to predicting individual particle trajectories.
The results presented here supply values for the room ventilation efficiency of a number of configurations covering as many as possible of the ventilation systems encountered in actual practice. The study is based on experimental results and numerical simulation. Using a few configurations experimented-on, simulations were performed using CFD code, which in particular allowed the reliability of calculations to be checked. The simulation tool was then used in such a way as to arrive at results that could be applied in practice.
Applicability of CFD simulation to designing passive architectures was investigated using a passive solar room with a Trombe wall system inside it. In the investigation non-steady numerical simulation was performed to predict thermal environment in the test room. Two weather models assuming a typical fine winter day were compared, one was the model based upon the data in Osaka and the other was that in Sapporo. The test room has glazing in the south side wall and in the north side one. Each glazing was covered with an insulating door during night.
The potential for using a large eddy simulation (LES) computational fluid dynamics (CFD) model to analyze building indoor air quality (IAQ) and ventilation problems was investigated. The LES model was developed by the Fire Science Division of NIST to simulate the transport of smoke and hot gases during a fire in an enclosure.
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