Passive ventilation
It refers to the flow of external air to an indoor space as a result of pressure differences arising from natural forces.
Differences in static pressure arise from global and microclimate thermal phenomena and create the air flow we call wind.
In practical terms wind pressure will vary considerably creating complex air flows and turbulence by its interaction with elements of the natural environment (trees, hills) and urban context (buildings, structures).
Vernacular and traditional buildings in different climatic regions rely heavily upon natural ventilation for maintaining thermal comfort conditions in the enclosed spaces.
As observed in the equation (1), the air exchange depends linearly on the wind speed in the urban place where the architectural project will be built.
CFD (Computational Fluid Dynamics) tools and zonal modelings are usually used to design naturally ventilated buildings.
If there are lower apertures then colder, denser air from the exterior enters the building through them, thereby creating upflow displacement ventilation.
Buoyancy-driven ventilation can be implemented in ways that air inflow in the building does not rely solely on wind direction.
For example, air can be drawn through the backside or courtyards of buildings avoiding the direct pollution and noise of the street facade.
In climates where the mean absolute difference between inside and outside temperatures exceeds ~10K the energy conservation argument for choosing natural over mechanical ventilation might therefore be questioned.
The device was found to provide sufficient ventilation air flow for a single family home and heat recovery with an efficiency around 40%.
The device was however found to be too large and heavy to be practical, and the heat recovery efficiency too low to be competitive with mechanical systems of the time.
[8] Later attempts have primarily focused on wind as the main driving force due to its higher pressure potential.
[10] Liquid coupled run around loops have also been tested to achieve indirect thermal connection between exhaust and supply air.
While these tests have been somewhat successful, liquid coupling introduces mechanical pumps that consume energy to circulate the working fluid.
This might explain the apparent lack of market impact of these commercially available products claiming to deliver natural ventilation and high heat recovery efficiencies.
[16] These requirements are for "all spaces intended for human occupancy except those within single-family houses, multifamily structures of three stories or fewer above grade, vehicles, and aircraft.
The mechanical system is to be used when windows are closed due to extreme outdoor temperatures noise and security concerns".
"[16] Another reference is ASHRAE Standard 62.2-2010: Ventilation and Acceptable Indoor Air Quality in low-rise Residential Buildings.
