In dwellings there is a desire to reduce ventilation heat loss, by reducing uncontrollable air infiltration, at the same time as providing adequate indoor air quality by controllable background ventilation. In England and Wales, the background ventilation requirements in part F of the Building Regulations at present are expressed in prescriptive terms. The adopted European Standard, EN13141-1:2004, provides a means of assessing the performance of background ventilation devices, such as trickle ventilators, and gives a standard method of measuring the equivalent area of the ventilator.
This paper reviews the current literature on discharge coefficients (CD) of openings and compares different studies for wind-driven cross-ventilation. Considerable variation of discharge coefficients with opening porosity, configuration (shape and location in the faade), wind angle and Reynolds number is shown. Consequently, the use of a constant CD value such as that given in textbooks or other sources might be an invalid simplification.
In the present study, a numerical simulation to simulate an experiment for evaluating the cross-ventilation performance at an inflow opening by using Large Eddy Simulation (LES), the standard k-e model, and Durbin's k-e model was performed. Results showed that too much turbulent kinetic energy was produced at the leeward opening frame in the standard k-e model. However , Durbin's k-e model improved this defect , and reproduced the wind tunnel results fairly well, as did the LES approach.
A Local Dynamic Similarity Model, applicable to dynamic similarity of cross-ventilation, has been applied to outflow openings. Cross-ventilation performance at the openings on the outflow side has been evaluated, and the structure of air flows around the outflow openings has been studied by LES and wind tunnel experiments. It was found that LES reproduces the wind tunnel experiment results fairly well, such as the extensive increase of discharge coefficient in a small region where dimensionless room pressure, PR*, is low.
This paper deals with techniques aiming at reducing noise entering into naturally ventilated buildings while reducing airflow path resistance.The description of the combined experimental and theoretical approach is made. A method is suggested to enable the acoustic and airflow performance of apertures for natural ventilation systems to be designed simultaneously.
We performed numerical simulation of the inflow characteristics at an opening by using LES,the standard k- emodel, and the improved k- emodel that was applied Durbins limitation (hereafter, it is described as Durbins k- emodel in this paper). As a result of this simulation, Durbins k- emodelreproduced the experiment result fairly well as in case of LES. Accordingly, by using Durbins k- emodel, the analysis was carried out on the air flow characteristics at some openings. As a result, the static pressure increase was induced by the collision of the air flow with the leeward opening frame.
The authors recently reported the detailed experimental results on that the discharge coefficient of the openings exposed to the wind driven airflow clearly changes depending upon the windangle and consequent conditions. A full-scale building model in a wind tunnel has been used for theexperiment. In this paper, the mechanism of the change is discussed more deeply, and the predictionmethods of the discharge coefficient are tested by the new experimental results for different conditions of opening size and location.
As part of an investigation into single-sided natural ventilation, a computational fluid dynamics study was performed to analyse the impact on the airflow rate of the dimensions and position of a large rectangular opening and of the temperature difference between inside and outside air. An empty room with a rectangu-lar opening in the external wall was assumed and the Bernoulli formula used to calculate discharge coefficients Cd. The vertical position of the opening was found to have the greatest impact on the discharge coefficient.
In this paper, after theoretical considerations, two ventilation openings are analysed : an opening with top-hinged flap and a wall inlet with central flap. The analysis shows that it is possible to split artificial resistance coefficients from literature into pure resistance and pure contraction coefficients .