Passive cooling is a measure that uses no energy to cool buildings. It involves at least three concepts:
- Solar shading
- Thermal mass
- Ventilative cooling
One of the best known passive cooling technieques is providing natural ventilation by openable windows.
Natural ventilation uses natural forces to exchange the air in a building. The driving forces are typically wind and temperature differences. However it is important to ensure an efficient airflow through the building.
Basic principles of natural ventilation
Natural ventilation uses pressure difference that is caused by:
- difference between densities of interior and exterior air given by temperature difference
- wind velocity providing on windward façade positive pressure and on leeward negative pressure
Did you know?
Natural ventilation is also influenced by wind turbulance and flow pattern around a building (affected by neighbouring buildings, building exposure and building orientation).
Building shape also influences the natural ventilation, i.e. flow direction throughout the building and ventilation intesity.
Typical ways of natural ventilation
Aeration - air supply and exhaust is caused through inlets with proper high difference, i.e. inlet at the ground via openings and outlet via skylights in roofs. Typically used for industrial halls or stables. The ventilation is regulated by inlets and outlets openings.
A combination of inlets via typically controlled window openings and shafts as outlets, creating a stack effect and using pressure difference in different heights. Typically used for multi-floor apartment buildings.a combination of inlets via typically controlled window openings and shafts as outlets, creating a stack effect and using pressure difference in different heights. Typically used for multi-floor apartment buildings.
- stack ventilation with open windows -
- Cross ventilation with open windows
Other points to know about natural ventilation
Controls for natural ventilation can be based on sensors for indoor air quality, meteorological weather data and smart control/management systems.
Natural ventilation is often used for passive cooling at nights, where heat accumulated in the buildings throughout the day is vented out at night to avoid the building overheating.