Ventilation:

•  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:

          ..in 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.

Example:

Classroom, hotel, cinema hall, etc.

FORMULA:

Q_s = 1.08 x CFM x ΔT

Q_s = sensible heat BTU/ hr

ΔT – Outdoor temperature – indoor temperature.

Q_L = 0.68 x CFM x ΔW

Q_L = Latent heat BTU/hr

ΔW = Outdoor humidity ration – Indoor humidity ratio.