Ventilation systems aim to maintain air quality, health, comfort and safety in buildings. There are two main types of ventilation - natural ventilation, which uses pressure differences to move air without mechanical systems, and mechanical ventilation, which uses fans and ducts. Mechanical ventilation has advantages like better control over air flow and indoor air quality, but is more expensive. Different mechanical ventilation systems include natural inlet/mechanical exhaust, mechanical inlet/natural exhaust, and full mechanical inlet and exhaust. Proper ventilation is important to prevent sick building syndrome and control contaminants, odors, bacteria and temperature.

1. VENTILATION SYSTEMS

2. VENTILATION
• Ventilation is the process of changing air in an enclosed space.
• A portion of the air in the space should be continuously withdrawn and replaced by
fresh air drawn from outside to maintain the required level of air purity, health,
comfort and safety of building occupants.
• Ventilation is required to control the following:
➢ Oxygen content
➢ Carbon dioxide and moisture
➢ Other hazardous gases, such as, CO, NOx, SO2, etc
➢ Odours and contaminants
➢ Bacteria
➢ Heat
1. NATURALVENTILATION
2. MECHANICALVENTILATION

3. Sick building syndrome.
The sick building syndrome (SBS) is used to describe a situation in which the
occupants of a building experience acute health- or comfort-related effects that
seem to be linked directly to the time spent in the building. No specific illness or
cause can be identified. The complainants may be localized in a particular room or
zone or may be widespread throughout the building.
Indicators of SBS include:
• Building occupants complain of symptoms associated with acute discomfort,
e.g., headache; eye, nose, or throat irritation; dry cough; dry or itchy skin;
dizziness and nausea;
• difficulty in concentrating; fatigue; and sensitivity to odors.
• The cause of the symptoms is not known.
• Most of the complainants report relief soon after leaving the building.
Causes of Sick Building Syndrome.
The following have been cited causes of or contributing factors to sick building syndrome
• Inadequate ventilation:
• Chemical contaminants from indoor sources:
• Chemical contaminants from outdoor sources
• Biological contaminants

4. Following considerations affect the type of ventilation system selected for a
particular application and sizing of the ventilation plant:
a. The climatic zone in which the building is located is a major consideration.
b. Sitting (and orientation) of a building
c. The comfort level required is another consideration.
Factors affecting the types of ventilation systems:
ACPH – Air Changes Per Hour
❑ No. of times Volume of air is replaced in an hour
❑ E.g.

5. General Ventilation Rate for
Non Air ConditionedAreas
1. NATURALVENTILATION
2. MECHANICALVENTILATION
TYPES OF VENTILATION SYSTEMS

6. NATURAL VENTILATION
• Process of supplying and removing air through
an indoor space without using mechanical
systems.
• It refers to the flow of external air to an indoor
space as a result of pressure or temperature
differences
• The benefits of natural ventilation include:-
i. Improved Indoor air quality (IAQ)
ii. Energy savings
iii. Reduction of greenhouse gas emissions
iv. Occupant control
v. Reduction in occupant illness associated with
Sick Building Syndrome
vi. Increased worker productivity

7. MECHANICAL VENTILATION
• Mechanical ventilation systems circulate fresh air using ducts and fans rather than
relying on airflow through small holes or crack’s in a home’s wall, roof or windows.
•
• It usually consists of fans, filters, ducts, air diffusers and outlets for air distribution
within the building

8. ✓ Better indoor air quality –can remove pollutants, allergens, and moisture
that can cause mold problems.
✓ More control – provide proper fresh air flow along with appropriate
locations for intake and exhaust.
✓ Improved comfort – allow a constant flow of outside air into the home and
can also provide filtration, dehumidification, and conditioning of the
incoming outside air.
Advantages of using mechanical ventilation
✓ These systems employ an electrically driven fan or fans to provide the
necessary air movement;
✓ They also ensure a specified air change and the air under fan pressure can be
forced through filters.
✓ There are three types of mechanical ventilation systems:
1. Natural inlet and mechanical extract (exhaust system).
2. Mechanical inlet and natural extract
3. Mechanical inlet and extract

9. 1. NATURAL INLET & MECHANICAL EXTRACT
• This is the most common type of system and is used for kitchens, workshops,
laboratories, internal sanitary apartments, garages and assembly halls.
• The fan creates negative pressure on its inlet side, and this causes the air
inside the room to move towards the fan, and the room air is displaced by the
fresh air from outside the room.

10. 2. MECHANICAL INLET & NATURAL EXTRACT
• This system includes delivery of fresh air supply mechanically into the space.
• The system may be used for boiler rooms, offices and certain types of factories.
• The air may be heated in a central plant and ducted to the various rooms, or a
unit fan convector may be used.

11. 3. MECHANICAL INLET & EXTRACT
• This provides the best possible system of ventilation, but it is also the most
expensive and
• Used for many types of buildings including cinemas, theatres, offices, lecture
theatres, dance halls, restaurants, departmental stores and sports centers.
• The system is essential for operating theatres and sterilizing rooms.

12. FANS
1. Propeller/Axial Fan
• does not create much air
pressure and has limited effect in
ductwork.
• Ideal for use at air openings in
windows and walls.
2. Centrifugal Fan
• can produce high pressure and has the capacity
for large volumes of air.
• Most suited to larger installations such as air
conditioning systems.
• It may have one or two inlets..

13. Underground Car Park Ventilation
• Ventilation is essential in enclosed car parking areas to dilute the level of toxic gases
such as carbon monoxide (CO), oxides of nitrogen (NOx), presence of petrol/ diesel
fumes and smoke from engine exhaust
• The ventilation rate required for an enclosed parking facility depends primarily
on four factors:
i. Numbers of cars in operation during peak usage (N),
ii. Length of time of operation
iii. Car emission rate
iv. Contaminant level criteria
❑ For enclosed U.G car parks, a minimum ventilation rate of 6 air changes per hour shall
be provided to keep contaminants within acceptable hygiene limits.

14. Regardless of which system is used, the following elements should be
considered in planning:
a) Accounting for the contaminant level of outside air drawn in for ventilation.
b) Avoiding short circuiting supply air.
c) Avoiding a long flow field that allows contaminants to exceed acceptable levels at
the end of the flow field.
d) Providing short flow fields in areas of high contaminant emission, thereby limiting the
extent of mixing.
e) Providing efficient, adequate airflow throughout the structure.

15. The required ventilation rate, Q for a given car park may be calculated from the
following equation: