Comfort Ventilation

Provides a direct physiological cooling effect

Even when outside air is hotter than indoors, it can feel cooler because of higher air velocity


Convective Cooling

Cools the structural mass of the building by ventilation at night

“During the day, the building must be closed, eliminating ventilation possibilities.”

Can be achieved only if the outdoor air is cooler than indoor. Therefore typically only used at night

Good for places with big diurnal temperature range

Can still provide cooling during day if stored in building mass from night 75

Building needs to be well insulated

Building must have sufficient mass to store and surface area to collect “coolness”

Challenges include bigger windows left open at night (security and privacy concerns) and lack of control over night temperatures

“Whenever convective cooling is applicable, it is the simplest and the least expensive of all the natural energy sources for cooling.”



Direct Evaporated cooling

“Outdoor air is directly cooled as it enters the built structure. The air is humidified while its temperature is simultaneously lowered and the indoor water content level is elevated above the outdoor level.”

“Direct evaporative cooling requires either a mechanical device or the passive utilization of the wind, when the wind is blowing in a more or less constant direction. The mechanical device is usually an inexpensive, compact unit which consumes less energy than conventional air conditions.” [fan draws ambient air over fiber pads, for example—swamp cooler]

Requires very high rates of outdoor air flow: 15-30 air changes per hour (= high and concentrated indoor air flow with high variability of indoor air speed distribution) 76

Can be passive (window evaporative pads, which can also filter dust but require water flow)


Indirect Evaporative Cooling 77

Permanent insulated shading structure over roof pond

Requires “perfect” waterproofing


Radiant Cooling

Expose roof to night sky

Dense concrete roof externally insulated during day, exposed at night (“operable insulation remains an obstacle”) 78


Earth Cooling

“If the average annual is above 50F, the soil needs to be cooled”

“In order to lower the soil temperature below the natural level, the soil must be protected from direct solar radiation and there must be provisions for evaporation from the surface of the earth.”

“In dry summer regions, cover the spoil with a layer of gravel, at least 10cm thick, which is insulated.”

Passive – Bury building so earth provides direct passive cooling effect

Active – Install air pipes in soil; circulate ventilation air or air from building through pipes; cooler earth mass serves as heat sink, cooling air as it enters building 79

B Givoni and L Orlick, Planning for Comfort in Hot Dry Climatic Regions, in Desert Development: Man and Technology in Sparse-lands, Y. Gradus, ed., Boston: D. Reidel Publishing Company, 1985, 60-80.