Ventilation

Ventilation is the process of supplying and removing air by natural/Artificial (Mechanical means) to and from air source/any space. Change of air in a room is a must to maintain the temperature limits inside buildings and to remove vitiated by product of respiration, bacteria, and unpleasant odor. Ventilation is the process of supplying and removing air by natural/Artificial (Mechanical means) to and from air source/any space. Change of air in a room is a must to maintain the temperature limits inside buildings and to remove vitiated by product of respiration, bacteria, and unpleasant odor.

Lack of proper ventilation causes:

Nausea, Headache, Sleepiness, Laziness, Inattentiveness.

Thus, ventilation is necessary for creation of air movement and preventing undue accumulation of CO2.It also prevents flammable concentration of gas vapor and thus avoids accumulation of dust and bacteria-carrying particles.

There are two types of Natural ventilation namely Wind driven ventilation and Stack (buoyancy) ventilation. In wind driven ventilation, wind pressures are usually far greater (1 Pa to 35 Pa).In stack ventilation, the pressures generated are quite low (typical values: 0.3 Pa to 3 Pa).

A) WIND DRIVEN VENTILATION:

The static pressure of air is the pressure in a free-flowing air stream and is depicted by isobars in weather maps.

Wind = Differences in static pressure arise from global and microclimate thermal phenomena and create the air flow.

Dynamic pressure is the pressure exerted when the wind comes into contact with an object such as a hill or a building. It is related to the air density and the square of the wind speed.

The impact of wind on a building affects the ventilation and infiltration rates through it and the associated heat losses or heat gains. Wind speed increases with height and is lowered towards the ground due to frictional drag. The impact of wind on the building form creates areas of positive pressure on the windward side of a building and negative pressure on the leeward and sides of the building. Building shape is crucial in creating the wind pressures that will drive air flow through its apertures.

Benefits of Wind driven ventilation:

The wind driven ventilation has greater magnitude and effectiveness. It is readily available (natural occurring force) and user friendly (when provisions for control are provided to occupants).

Limitations of wind driven ventilation:

The wind driven ventilation is unpredictable and unreliable due to constant change. There are restrictions in design and difficulties in harnessing due to speed and direction variations .Also, the quality of air it introduces in buildings may be polluted due to proximity to an urban or industrial area.

B) STACK DRIVEN VENTILATION:

Stack effect is temperature induced. When there is a temperature difference between two adjoining volumes of air, the warmer air will have lower density and be more buoyant thus will rise above the cold air creating an upward air steam.

Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences.

also referred to as the "chimney effect", and it helps drive natural ventilation.

The driving force for the stack effect

Pressure difference ( ?P ) is the driving force:

Where: ?P = available pressure difference, in Pa

C = 0.0342 a = atmospheric pressure, in Pa

h = height or distance, in m

To = absolute outside temperature, in K

Ti = absolute inside temperature, in K

The equations apply only to buildings where air is both inside and outside the buildings. For buildings with one or two floors, h is the height of the building. For multi-floor, high-rise buildings, h is the distance from the openings at the neutral pressure level (NPL) of the building to either the topmost openings or the lowest openings.

Benefits of Stack driven ventilation:

It does not rely on wind and can take place on still, hot summer days when it is most needed. It is a natural occurring force (hot air rises) and relatively stable air flow (compared to wind) method.

Limitations of stack driven ventilation:

It has a lower magnitude compared to wind ventilation and relies on temperature differences (inside/outside).Design restrictions (height, location of apertures) may incur extra costs (ventilator stacks, taller spaces) ventilating.com fanblower.com highpressureblower.net industrialblowerfan.com industrialfanblower.net industrialfanblower.com pressureblower.net northernindustrialsupplycompany.com industrialpressureblower.com tenderall.com chicagoblowercanada.com cbblower.com buffaloblower.com buffalofan.com nis-co.com canadianblower.com olegsystems.com canadablower.com abbblower.com acmefan.net industrialblower.net fansandblowers.net americanblower.net barryfan.com cincinnatifan.net canadafans.com barryfan.net greenheck.net pennbarry.net pennfan.net tcffan.com.

Additional information can be found at the Industrial High Pressure Blower Company web site http://www.highpressureblower.net/biblower.html

Alex Todorovo
Industrial Mechanical Process Engineer
High Pressure Blower Co.
alex.todorov@canadablower.com
http://www.highpressureblower.net/howdencentrifugal.html
http://www.highpressureblower.net/airfoilblower.html


By: Oleg Tchechel

Alex Todorovo
Industrial Mechanical Process Engineer
High Pressure Blower Co.
alex.todorov@canadablower.com
http://highpressureblower.net/howdencentrifugal.html
http://highpressureblower.net/airfoilblower.html

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Article Tags: fan , blower , ventilator , high , temperature , pressure , industrial , super , transfer , air , gas , capacity , process

Submitted On Jun 20, 2014. Viewed 166 times.

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