Cross Ventilation
From Swikipedia
Introduction
Cross ventilation is obtained by having windows in both sides of the room, causing airflow across the space. Positive pressure on the windward and/or a vacuum on the lee side of the building causes air movement across the room(s) from the windward to the lee side, provided the windows on both sides of the room are open.
Designing for cross ventilation in buildings allows for passive cooling and reduces the reliance on air-conditioning. The cross ventilation principle is, like all Natural Ventilation principles, based on the requirement of ensuring a fresh and comfortable indoor climate. This is done with minimal energy consumption and at low cost.
Brief Description
Requirements for air motion in the early summer and late post-monsoon periods are usually small. These can be easily met by providing adequate cross ventilation through rooms. When a building is cross ventilated during the day, the temperature of the indoor air and surfaces closely follow the ambient temperature. Therefore ventilation in daytime should be considered only when indoor comfort can be experienced at the outdoor air temperature (with acceptable indoor speed).
The indoor wind speed varies due to factors such as the area and location of windows in the room, direction of incident wind, weather shades such as louvers, chhajjas, verandahs, etc., and the type of interconnection between different rooms of a building. For example, the available wind velocity in a room with a single window on the windward side is about 10% of the outdoor velocity at points up to a distance of one-sixth of room width from the window. Beyond this, the velocity decreases rapidly and hardly any air movement is produced in the leeward end of the room. Therefore, it is better to provide two windows on adjacent or opposite walls to improve ventilation. The window area and the direction of wind affect the performance of cross ventilation. For example, for windows that are 20 percent of floor area, the average indoor wind velocity is about 25 percent of outdoor velocity.
References:
http://www.windowmaster.com/regado.jsp?type=page&id=39
http://www.energysave.sg/index.php?option=com_content&view=article&id=51&Itemid=111
