•  The process of changing or replacing air in space to provide high indoor air quality.
  •  It is used to remove bad smells excessive moisture and to provide fresh air.
  •  Ventilation includes both the exchange of air to the outside as well as circulation of air within the building.

Purposes of Ventilation:

  •  Maintain the oxygen level.
  •  Control the humidity.
  •  Eliminate odour and dirty air content.
  •  Improve the indoor air quality.

Types of Ventilation system:

  •  a)Natural type
  •  b)Mechanical type 

Natural Ventilation:

          It is the process of supplying air to and removing air from an indoor space without using mechanical systems. It refers to the flow of external air to an indoor space as a result of pressure differences arising from natural forces.

Advantages of Natural Ventilation:

1. Does not require any mechanical appliances.

2. Non-operational cast.

3. Non-maintenance cost for the appliances/equipment.

4. Silent processes.

5. Combination benefit of ventilation, lightning and esthetical value. 

Disadvantages of Natural Ventilation:

1. The system is uncontrolled:

 terms of speed and distribution.

          ..high rise building received strong velocity thus windows should be kept closed.

          ..slow wind velocity during the rainy season.

2. Internal temperature cannot be monitored:

          ..difficult to achieve the required human comfort temperature.

3. Rate of air humidity is uncontrolled:

          ..depend on the existing external humidity

4. Uneven uniform distribution:

          ..ventilation rate depend on sized of opening.

          ..distribution is maximum at the area/space nearby the opening.

          ..low ventilation rate for rooms further inside a building.

5. Quality of fresh and clean wind cannot be assured

          ..maybe contaminated from the external harmful elements such as smoke and dust.


Mechanical ventilation:

  • through an air handling unit or direct injection to a space by a fan. A local exhaust fan can enhance infiltration or natural ventilation, thus increasing the ventilation airflow rate.

Advantages of mechanical ventilation:

  • (a) Even air distribution
  • (b) Filtered air(Q↑)
  • (c) Control of humidity and temperature.
  • (d) Minimized entrance of hazardous air.

Disadvantages of mechanical ventilation:

  • (a) Involved initial, operation and machine cost
  • (b) Extra space to allocate equipment’s
  • (c) Increase noise level (sound buffer)
  • (d) Required power supply & backup systems.


CFM/Persons, CFM/Sqft, No of persons should be found according to the room given in data table.


Classroom, hotel, cinema hall, etc.


Qs = 1.08 x CFM x ΔT

Qs = sensible heat BTU/ hr

ΔT – Outdoor temperature – indoor temperature.

QL = 0.68 x CFM x ΔW

QL = Latent heat BTU/hr

ΔW = Outdoor humidity ration – Indoor humidity ratio.

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  1. Thanks for our kind of information to entire team.

  2. Thank you so much for your response.