Stack Ventilation

Stack ventilation is one of the most fundamental principles in passively cooling the interior of the building.

It is free, easy to achieve, and simple. It requires a basic understanding of how air moves in general - cooler air stays below warmer air, warmer air or hot air stays above the cooler air.

Air stays on top of each other due to air pressure difference, hot air molecules move faster, have lower air pressure, less dense.

When hot air rises up and cooler air stays low, air movement is formed. The greater the difference, the greater the air movement, or the wind.

Wind forms in the atmosphere when there are air movements.

Most buildings have envelopes, microclimate is formed within, miro-atmosphere is contained.

How the air moves depend on the air pressure difference within.

When fenestration is created, indoor air links with the outdoor air, and the air pressures and temperature tend to normalize. The wind is formed by the displacement of different density air.

In a hot and humid climate, under a building envelop or a roof, you want to have fenestration at the highest possible position of the building so that the hot air that rises up and traps underneath the roof at the highest point can escape.

Cooler air can reenter the low positioned fenestration as the atmospheric air inside and outside wants to normalize with each other.

There are occasions the building room is high up from the ground level (in the sky), multi-story that cool air on the ground can no longer enter the room.

The room "in the sky" needs to consider its physical geographical region air temperature and activity within the room. Sometimes cooler air gets more than a story high, sometimes even higher. 

Allowing cross-ventilation from one end of the building to another means wanting the outdoor temperature to normalize with the indoor room temperature in the sky. 

If the outside is comforting cool, having cross-ventilation can replace the indoor air with the cooling outdoor air; the same will occurs when the outside air is warm, cross-ventilation will replace the room air with warmer air when normalize. 

You want to have options to control fenestration and have means of alternative for a full cross-ventilation windows design in the building to archive the thermal comfort.

Hot sun after morning is the crucial factor that heats up the interior via direct heat transfer and thermal conductivity through various building materials.

Hot air still rises if there is an air difference contained within a room in the sky. You want to still have high and low windows to maneuver cooler air to reenter the indoor spaces, and the hotter air to escape the room to have a cooling interior.