Air Currents: Air Diffusion Inside a Home
superadmin
April 26, 2017
Air currents in a natural ventilation system
Traditionally, natural ventilation has been used to renew the indoor air of homes. This type of ventilation can occur in three ways: unilateral ventilation, cross ventilation, and thermal lift ventilation.Unilateral ventilation occurs due to the pressure and temperature differences between the outside and inside of a home. This difference arises in the gaps and leaks found in the exterior envelope of the facade walls. When the air pressure is higher on one side of the enclosure, a flow is generated in which the air circulates from the area with higher pressure to the area with lower pressure. This system is activated when a window is opened. On the other hand, when air is heated, it rises, generating air currents in the form of whirlwinds near the facade opening. This effect is used to renew air in boiler rooms and kitchens where gas is used for fuel, employing lower and upper ventilation grills.
Cross ventilation occurs when air currents are activated between an intake and an outlet located in opposite enclosures of the building's envelope. They are activated by pressure differences, creating positive pressure at the intake and negative pressure at the outlet.
Thermal lift ventilation through vertical ducts is activated by the difference in densities within the air caused by variations in temperature and humidity content. Hot air weighs less than cold air, and humid air weighs less than dry air. This system is used for vertical air extraction through ducts such as shunts and chimneys.
Air diffusion in rooms
Once sufficiently clean air has been obtained for incorporation into the ventilation system, it is necessary to distribute it evenly throughout the different rooms in the home at a speed that does not cause unpleasant noise. To carry out this process, it is essential to understand certain concepts well:- Diffusion is the distribution of air through an outlet that discharges in several planes and different directions.
- Diffuser is an air outlet that supplies air in multiple directions and planes.
- Efficiency is the ratio between the concentration of a contaminant at the extraction point and its average concentration in the occupied area. In cases of air induction by mixing, this efficiency reaches unity.
- Reach is the length to which the propelled air flow reaches before its speed drops to the terminal, which is usually 0.25 m/s.
- Axial jet is the air current along a line.
- Drop is the vertical distance between the air outlet and the end of its vertical displacement.
- Effective area is the net space of an air discharge or inlet. It is equal to the outlet section multiplied by the discharge coefficient.
- Drag is the effect induced in the indoor air by the propelled air current.
Siber Ventilation
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