Passive cooling

Passive cooling is an important tool for design of buildings for climate change adaptation – reducing dependency on energy-intensive air conditioning in warming environments.

The building structure's thermal mass acts as a sink through the day and absorbs heat gains from occupants, equipment, solar radiation, and conduction through walls, roofs, and ceilings.

[18] For optimal performance, the nighttime outdoor air temperature should fall well below the daytime comfort zone limit of 22 °C (72 °F), and should have low absolute or specific humidity.

[19] For the night flushing strategy to be effective at reducing indoor temperature and energy usage, the thermal mass must be sized sufficiently and distributed over a wide enough surface area to absorb the space's daily heat gains.

There are numerous benefits to using night flushing as a cooling strategy for buildings, including improved comfort and a shift in peak energy load.

By implementing night flushing, the usage of mechanical ventilation is reduced during the day, leading to energy and money savings.

There are also a number of limitations to using night flushing, such as usability, security, reduced indoor air quality, humidity, and poor room acoustics.

For natural night flushing, the process of manually opening and closing windows every day can be tiresome, especially in the presence of insect screens.

This design relies on the evaporative process of water to cool the incoming air while simultaneously increasing the relative humidity.

[32] An innovative passive system uses evaporating water to cool the roof so that a major portion of solar heat does not come inside.

Earth coupling uses the moderate and consistent temperature of the soil to act as a heat sink to cool a building through conduction.

A traditional Iranian solar cooling design using a wind tower
This ancient Roman house avoids gaining heat. Heavy masonry walls, small exterior windows, and a narrow walled garden oriented N-S shade the house, preventing heat gain. The house opens onto a central atrium with an impluvium (open to the sky); the evaporative cooling of the water causes a cross-draft from atrium to garden .
A pair of short windcatchers ( malqaf ) used in traditional architecture; wind is forced down on the windward side and leaves on the leeward side ( cross-ventilation ). In the absence of wind, the circulation can be driven with evaporative cooling in the inlet. In the center, a shuksheika ( roof lantern vent), used to shade the qa'a below while allowing hot air rise out of it ( stack effect ). [ 13 ]
A courtyard in Florence, Italy . It is tall and narrow, with a fountain spouting very thin streams of water at the bottom, and upper rooms opening onto it. Night flushing of the courtyard happens automatically as the night air cools; evaporative cooling cools it further and can be used to create drafts and change the air during the day. Windows can be left open around the clock.
The infrared atmospheric window , frequencies in which the atmosphere is unusually transparent, is the large blueish block on the right. An object that is fluorescent in these wavelengths can cool itself to below ambient air temperature.
Radiative cooling energy budget in Iranian Architectural element, yakhchāl
A salasabil (currently dry) in the Red Fort in Delhi , India. A salasabil is designed to maximize evaporative cooling; the cooling, in turn, may be used to drive air circulation.
A qanat and windcatcher used as an earth duct, for both earth coupling and evaporative cooling. No fan is needed; the suction in the lee of the windtower draws the air up and out.