LES (Large Eddy Simulation) has bben used to simulate cross ventilation under various wind direction angles. A new model, named local similarity model of cross ventilation, is proposed to estimate cross-ventilation flow rate and inflow angle at opening. In order to validate the proposed model, a wind tunnel experiment using a building model was carried out. The results confirm that dynamic similarity is established almost regardless of wind direction angle and position of the opening.
The study of buoyancy-driven natural ventilation in buildings requires windless conditions. It is difficult to conduct on-site measurements since the nature has few windless moments so a full-scale test room placed in a large laboratory environment can create artificially such conditions but it is an expensive method. CFD methods using two different models (RANS and LES) provide an alternative approach to study natural ventilation in buildings.
Due to the renewal of interest for solar chimneys (that convert thermal energy into the kinetic energy of air movement) , experiments were carried out in a controlled environment, with a full-scale chimney, where both air-velocity and air-temperature were measured.
The aim of the project was to get a better knowledge of :
- optimal gap to height ratio
- optimal gap to different heat input ratio
- optimal inclination angle
- methods to estimate the flow rate.
This paper develops a simple analytical model for the air flow inside a room with different discrete heating and cooling sources, established by combined localised and distributed heat input. Results from experiments are compared to simple theoretical models of the flow pattern.
In this paper, cross ventilation is evaluated by the multi zone network airflow simulation and using CFD. The distribution of indoor wind velocity by cross ventilation is influenced by the weather condition, the location of the building and the form of he building. This paper takes into account those three indexes and proposes a new evaluation method of natural cross ventilation performance
The wind tunnel experiment is the major method for cross ventilation researches. Up to now no quantitative evaluation method nor standard has been produced. This research project is to develop the quantitative method to predict cross ventilation rate driven by wind. A specially designed wind tunnel is used in the project. Conventional wind tunnel experiment is carried out in parallel with scale models of building without openings.
CFD and fluid net models used for natural ventilation designs do not consider the impacts of fluctuating characteristics to the mean airflow rate. This paper presents first a correctional method for predicting mean airflow rate of natural ventilation when the average wind velocity is more important than velocity fluctuation. A correctional coefficient for airflow resistance of multi-zone models is deduced. This method is then applied to a big atrium of a naturally ventilated five floor laboratory.
Natural ventilation is often a highly unsteady phenomenon, therefore steady criteria, very helpful for mechanical systems, cannot be used. This paper presents ideas for evaluating transient flow situations. The theory of the air exchange efficiency is extended to transient flows.
Three flow regimes encountered in hybrid ventilation systems, depending on the external temperature along with the imposed heating and cooling loads, are investigated . A theoretical model is used and small-scale laboratory experiments are visualised. The transitions between those naturally ventilated flows may vary according the seasons.
This paper presents a procedure that allows to look at the influence of atmospheric turbulence in natural ventilation. This procedure uses wind time series. The results of the estimated turbulence influence on air change rates are compared with field measurements both from the references and from the tests conducted in real buildings in order to validate that procedure.
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