cross ventilation

As natural wind is continuously fluctuating in both speed and direction, quantifying instantaneous wind-driven natural ventilation rate can be difficult, and often an average effect is used to stabilize the fluctuations. This work performs an experimental investigation to assess the validity of assumptions often used in quantifying airflows through an opening under cross natural ventilation condition. In the experiment, the three velocity components are analyzed for flows approaching and through an open window exposed to natural wind.

In Japan where is located at the hot humid climate region, houses have been built considered hot summer life from ancient times. It is said that comfortable and cool feelings by cross-ventilation were more important. However, the characteristics of cross-ventilated air flow are unclear, and that it has yet to be revealed how they affect the psychological and physiological factors that influence comfortable feeling. So, in this study, time-series data of cross-ventilated indoor air flow velocity were measured by field measurement at the actual detached house in Japan.

The convective heat transfer coefficient around the human body is important for evaluating the effects that airflows exert on thermal comfort. However measuring it is generally difficult. Therefore, in this research, a thermal manikin was set up inside a wind tunnel simulating a ventilation environment. This was used to measure the convective heat transfer coefficient around the human body and the relationship between the effects of airflows and the thermal resistance of clothing under various clothing conditions.

The reduction of carbon dioxide emission due to energy consumption in the household sector is an urgent task, worldwide. As a measure to respond to the task, a new regulation has just been enforced since April 2009, in Japan. This regulation evaluates the energy performance of detached houses by estimating the primary energy consumption for different uses, namely, heating, cooling, ventilation, domestic hot water and lighting.

In the light of global environmental problems, it is vital for buildings to conserve energy and make use of natural energies. Natural ventilation is one important method for achieving this. In houses, natural ventilation is a very attractive way to control the indoor environment. Compared to this, mid- to high-rise buildings include many closed spaces where windows cannot be opened and internal heat is trapped inside, which increases the cooling load. Based on this situation, consciousness of environmentally friendly buildings and utilization of natural energy becomes high.

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.

The mechanism of cross ventilation is dealt with in this paper. The results are obtained by a combination of wind tunnel studies and CFD predictions using a Reynolds stress model as the turbulence model. All buildings have been exposed to a uniform velocity field and therefore the reference flow rate for an opening is equal to the velocity multiplied by the opening area. The openings were located at or close to the position of the stagnation point on the corresponding sealed building.

The purpose of this study was to clarify differences between evaluations of thermal environment undercross ventilation and airflows from air-conditioning systems and electric fans. Nine subjects evaluatedthermal sensation, thermal comfort sensation, airflow sensation and humidity sensation in anexperimental room in the summer of 2006. The surrounding ambient temperatures, relative humidity,and air velocity were measured simultaneously.