The document discusses ventilation systems for buildings. It describes the importance of ventilation for maintaining oxygen levels and removing impurities from indoor air. It provides recommendations for ventilation rates based on space volume and occupancy. Both natural ventilation utilizing wind and stack effects, and mechanical ventilation using fans and ductwork are covered. Key components of mechanical ventilation systems like fans, filters, ducts and diffusers are defined. Design principles for sizing ventilation ducts based on air flow rates are also presented.

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(BLD60503)
HVAC Systems &
Building

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(BLD60503)
Ventilation
Prepared by Tan Hee Chai

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(BLD60503)
Ventilation
Requirements
The effect of air on
health and comfort
depends upon:
Movements;
Humidity and
Temperature

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Ventilation system
Ratio Main Elements in Dry atmospheric
Oxygen
21%
Carbon
dioxide
0.03%
Nitrogen
Neon
Helium
Hydrogen
Water
Vapour
79%

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Ventilation
Requirements
Air change important for two reasons:
1.Maintain a satisfactory level of
oxygen content – essential for life
2.To remove impurities

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Ventilation
Requirements

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Ventilation System
Rate of air change = ratio of fresh air
supplied each hour to volume of the
enclosed space

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Ventilation System
Example:
A private office of 30 m3 volume designed for 2
persons:
Recommended m3/hour per person is 43
43/30 x 2 = 2.86 air change per hour

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Ventilation System
Ordinary
conditions
Fresh air supply
of 30 -35m3 per
person per hour
• 1.5 air
changes per
hour for family
of 4
Normal living
room 45 m3:

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Ventilation System

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Ventilation System
Ventilation rates requirements:
Normally based on recommendations
by authorities or code of practice e.g:
•Department of Occupational Safety & Health
(DOSH)
•Malaysian Standard Code of Practice

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Ventilation System
Apart from fresh air,
movement of air over surface
of body necessary to remove
surplus
•heat,
•water vapour,
•carbon dioxide and
•organic vapours from body

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Ventilation System
Desirable
characteristics of
atmosphere:
•Cool
•Dry
•Diverse in
temperature in
different parts and at
different times
•Moving
Undesirable
characteristics of
atmosphere:
•Hot
•Damp
•Uniform and
Monotonous
•Still

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Ventilation System
Desirable
characteristics of
atmosphere:
•Air change
•Proper means of
ventilation
Undesirable
characteristics of
atmosphere:
•Cubic space
•Excessive cubic
space

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Ventilation System
Ventilation principles:
To prevent undue
concentrations of
odours,
Bacteria carrying particles and
Noxious gases

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Ventilation System
Ventilation principles:
To remove heat from products of
combustion
Body heat and heat from
electrical equipment, motors,
heat from solar radiation etc

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Ventilation System
Ventilation principles:
To remove fumes, dust etc
produced by industrial process

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Ventilation System
Ventilation principles:
To maintain the relative humidity
within reasonable limits

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Ventilation System
Ventilation principles:
Percentage saturation
= Weight of moisture in the air/weight
of moisture if air were saturated at
the same temperature x 100%
Relative humidity (RH)
= Vapour pressure of moisture
present/ Vapour pressure if air were
saturated at the same temperature x
100%

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Ventilation System
Ventilation principles: Relative Humidity

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Ventilation
principles:
To create
air
movement

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 Natural Ventilation
• Natural ventilation systems rely on pressure
differences to move fresh air through buildings.
• Pressure differences can be caused by wind or the
buoyancy effect created by temperature
differences or differences in humidity.

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Natural Ventilation

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 Pressure Patterns caused by wind

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 Passive stack ventilation (PSV)
PSV Consist of
 Extract grilles at ceiling height
 Ducts to terminal at roof

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 Passive stack ventilation (PSV)
 Types of vent

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Natural Ventilation System

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Building Regulation
 Habitable or
occupiable rooms
located on an
external wall
Requirements
 require a window
opening with
permanent
background ventilation
Natural Ventilation System
 Non-habitable
rooms in domestic
buildings
 Maybe ventilated
mechanically or
by passive stack
ventilation system

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Building Regulation
 Rooms with no
openable
windows in non-
domestic buildings
Requirements
 Mechnical ventilated
or air-conditioning
Natural Ventilation System
 Kitchen,bathrooms
,utility rooms etc
 Open window and
mechanical extract
ventilation or by
passive stack
ventilation system

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Mechanical Ventilation System
Artificial methods of preserving the
purity and controlling the temperature
of the atmosphere.

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Mechanical Ventilation System
Method:
 Extract
 Supply
 Combined extract and input

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 Extractor fan system

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 Extractor fan

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Extract system
• Cheap to install and operate
• Definite volume of air is removed from
buildings
• Air entering to replace cannot be controlled.
• Draughts are created

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Supply system

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Supply system

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• Air delivered under pressure.
• Include air heater battery with automatic
control over temperature of air delivered
into rooms
• An air filtration device
Supply system

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• Easy to install in existing buildings
• Can be included when designing new
building.
• Eliminates draughts by building up
pressure inside the spaces
Supply system

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 Combined supply & extract system with propeller
fans

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 Combined supply & extract system with propeller
fans

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 Heat Exchanger

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 Heat Exchanger

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Mechanical Ventilation System
Components:
Fan
Filters
Ductwork
Fire dampers
Diffusers

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Mechanical Ventilation System
Types of Fan
 Cross-flow or tangential
 Propeller
 Axial flow
 Centrifugal

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Wall mounted propeller fan

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Axial-flow fan

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(BLD60503)
Bifurcated axial flow fan

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Centrifugal fan

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Centrifugal fan

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Centrifugal fan

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Cross-flow or tangential fan

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Filters
Dry Filter
made of
•Paper
•Fine woven fabrics
•Foamed plastics or
fibreglass

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Dry Filters

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Filters
Viscous or Wet
Filter made of
•A bank or rows of
corrugated metal sheets
with surface coated in
non-flammable, non-
toxic odourless oil

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Viscous or Wet Filter

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Electrostatic Filter
consist of
•Pre-filter
•Power pack
•Ioniser
•Rows of
opposing
charged plates

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Electrostatic Filter

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Electrostatic Filter

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Activated carbon Filter

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Activated carbon Filter
made of
•Disposable elements of glass
fibrous matting containing
charcoal granular

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Ventilation duct design

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Factors influencing the size of ducts for air
transport are:
 The volume of flow rate of the air
 The friction of the air against the walls of the
ducts and any turns and protrusions.
 The pressure available for the movement of
air.

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Calculation of air volume flow rate:
Q = Room volume x air changes per
hour/time in seconds
Where
• Q is the volume of flow rate in m3/s
Ventilation duct design

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Ventilation duct design

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Ventilation duct design - Chart

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Ventilation duct design

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Ventilation duct design

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Ventilation duct design

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Ventilation duct design

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Ventilation Design – Duct conversion

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Ventilation Design – Duct conversion chart

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The End