cross-ventilation

A working group for natural ventilation and cross-ventilation at the Architectural Institute of Japan (AIJ) was established in 2005 by researchers and designers with an interest in this topic. One of the tasks of the working group is to review and classify related research papers. This paper introduces the activities of the working group and presents some results of the review work.

A simulation study on the reduction of cooling loads by utilizing cross-ventilation was performed for a typically shaped house as defined by the Architectural Institute of Japan. A reduction in cooling load of around 50% could be achieved when the windows were opened liberally at night compared with the cooling load when all the windows remained closed, regardless of building coverage ratio.

Recently, natural ventilation, which is a traditional cooling method in Japan, has become considered as the key method for cooling energy conservation. The results of experiments are presented to measure the indoor thermal environment and cooling power consumption in an experimental dwelling by simulating occupants' life-style including thermal control with natural ventilation and air conditioning. Based on the experimental results the cooling power consumption from July to September has been estimated.

This study is focused on the efficient use of cross-ventilation in a densely populated area by using roofwindows in particular. Wind tunnel experiments were conducted to understand not only the relationbetween the building coverage ratio and the coefficient of wind pressure (Cp) but also the relationbetween the roof slope of a residence and Cp value. To simulate an urban area, dummy models wereplaced around a target model, and the building densities were set to 0, 10, 20, and 40%. The roofslopes of residences were set to 0 (flat roof), 15, and 26.7.

This paper presents a study of the impact of urban warming upon energy consumption forair-conditioning in the home, using a numerical simulation model. The results are as follows. 1) In citiesother than Sapporo and Sendai, about 50% of the total hours of occupancy were ventilation hours, andabout 20% to 40% were cooling hours. As a result, the total energy consumption for cooling wascomparatively large. 2) In these other cities, cooling hours increased in the summer as the outdoortemperature rose.

Conventional method to predict ventilation rate induced by wind is based on the orifice equationassociated with the discharge coefficient and wind pressure coefficient. In the cross-ventilationphenomena, however, this method has a problem due to the difficulty to predict resistance of thebuilding related with total pressure loss. In this paper, therefore, the stream tube caught by the inletopening is analyzed to investigate the pressure loss due to the transformation (and possiblyconvergence and divergence) of the stream tube.

Variation of discharge coefficients with wind direction and opening position is one of the main factorsdebasing accuracy of cross-ventilation flow rate prediction. The local dynamic similarity model wasdeveloped to solve this problem, and previous studies had validated it for inflow openings. In thepresent study, two experiments were carried out to investigate its validity for outflow openings.