Al-musaed, A.
Bibliographic info:
28th AIVC and 2nd Palenc Conference " Building Low Energy Cooling and Ventilation Technologies in the 21st Century", Crete, Greece, 27-29 September 2007

Human has developed a board rang of passive cooling techniques in various parts of the world up to a very impressive level of maturity: cliff dwellings through the world (ground cooling), wind towers (convective and mass cooling), sprinkling water with fountains (evaporative cooling), and whitewash (sun protection). All these cooling techniques were based on careful design in which heat and mass transfer principles did not make use of any mechanical energy: they were totally passive. The concept of evaporative cooling is that when water evaporates it absorbs a large quantity of heat from its surroundings. Evaporation occurs at whatever time the vapor pressure of water is lesser that the water vapor in the surrounding atmosphere. The phase change of water from liquid to the vapor state is accompanied by the release of a large quantity of sensible heat from the air that lowers the temperature of air while its moisture comfortable increases. The most familiar example of this is the cooling effect of evaporating perspiration on the human skin. In Iraqi, climates, body temperature is partially controlled by the rapid evaporation of perspiration from the surface of the skin. In hot climates with high atmospheric moisture the cooling effect is less because the high moisture content of the surrounding air. In both situations, however, the evaporation rate is raised as air movement is increased. Both of these facts can be applied to natural cooling of structures. The provision of shading and the supply of cool, dry air will enhance the process of evaporative cooling. Evaporative cooling is only effective for comfortable cooling in dry climates. When outdoor humidity rises, the cooling capability of direct evaporative systems declines unless occupants are willing to suffer with high humidity. Evaporative cooling techniques can be broadly classified as passive and hybrid.