Ventilation

VENTILATION
QSB 1714
Prepared by: Mariatul Liza bt Meor Gheda

Introduction
 Definition:

 The process of changing air in an enclosed space.  A proportion of air within the enclosed space should be continuously withdrawn and replaced by fresh air.
 Drawn in from a clean external source:
• At as high an elevation as practical…where more polluted air occurs at the relatively low levels found in congested towns and cities.

Why do we need ventilation?

Ventilation is needed to maintain air purity…

which is......

1. Preservation of oxygen content
• This should be maintained at approximately 21% of air volume.

2. Removal of carbon dioxide
3. Control of humidity
•

30 – 70% relative humidity (RH) is acceptable for human comfort.

4. Prevention of heat concentrations from machinery, lighting & people.

5. Prevention of condensation
6. Dispersal of concentrations of bacteria
7. Dilution & disposal of contaminants
•

Smoke, dust, gases & body odours

8. Prevention of heat concentrations from machinery, lighting & people.
9. Provision of freshness
•

An optimum air velocity lies between 0.15
& 0.5 m/s.

Natural ……… mechanical
 It can be natural or mechanical ventilation.
Natural ventilation affected by

 pressure variations due to wind & stack effects. Wind
 The movement of air takes place smoothly well away from the earth’s surface.
 Velocity is reduced towards the ground, direction of movement is affected by relief of hills and mountains and vegetation resulting in turbulence of airflow.
 Admiral Beaufort devised a scale in 1806 primarily for classification of winds at sea.

A Typical Pattern of Pressure
Distribution

In high buildings above ten floors, wind and stack effect become apparent. The Stack
Effect In a
Tall Building

key requirement

The for ventilation is the need to maintain adequate indoor air quality.

An efficient ventilation system must