BS2 Hvac ventilation 1

BUILDING SERVICES TWO (BLD60503)

HVAC Systems & Building

BUILDING | SERVICES | TWO (BLD60503)

Ventilation

Prepared by Tan Hee Chai

Ventilation RequirementsThe effect of air on health and comfort depends upon:Movements;Humidity andTemperature

Ventilation systemRatio Main Elements in Dry atmospheric

Oxygen 21%

Carbon dioxide 0.03%

Nitrogen NeonHelium HydrogenWater Vapour79%

Ventilation Requirements

Air change important for two reasons:

1.Maintain a satisfactory level of oxygen content – essential for life2.To remove impurities

Ventilation Requirements

BUILDING | SERVICES | TWO (BLD60503)Ventilation System

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

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

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:

Ventilation System

Ventilation SystemVentilation 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

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

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

Ventilation System

Desirable characteristics of atmosphere:•Air change•Proper means of ventilation

Undesirable characteristics of atmosphere:•Cubic space•Excessive cubic space

Ventilation SystemVentilation principles:

To prevent undue concentrations of odours,

Bacteria carrying particles andNoxious gases

To remove heat from products of combustionBody heat and heat from electrical equipment, motors, heat from solar radiation etc

To remove fumes, dust etc produced by industrial process

Ventilation principles:To maintain the relative humidity within reasonable limits

Ventilation SystemVentilation 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%

Ventilation SystemVentilation principles: Relative Humidity

Ventilation principles:

To create air movement

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.

Natural Ventilation

Pressure Patterns caused by wind

Passive stack ventilation (PSV)

PSV Consist of Extract grilles at ceiling height Ducts to terminal at roof

Passive stack ventilation (PSV) Types of vent

Natural Ventilation System

Building Regulation

Habitable or occupiable rooms located on an external wall

Requirements require a window

opening with permanent background ventilation

Non-habitable rooms in domestic buildings

Maybe ventilated mechanically or by passive stack ventilation system

Building Regulation

Rooms with no openable windows in non-domestic buildings

Requirements Mechnical ventilated

or air-conditioning

Kitchen,bathrooms,utility rooms etc

Open window and mechanical extract ventilation or by passive stack ventilation system

Mechanical Ventilation System

Artificial methods of preserving the purity and controlling the temperature of the atmosphere.

Method: Extract Supply Combined extract and input

Extractor fan system

Extractor fan

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

Supply system

• Air delivered under pressure.

• Include air heater battery with automatic

control over temperature of air delivered

into rooms

• An air filtration device

Supply system

• Easy to install in existing buildings• Can be included when designing new

building.• Eliminates draughts by building up

pressure inside the spaces

Supply system

Combined supply & extract system with propeller fans

BUILDING | SERVICES | TWO (BLD60503) Heat Exchanger

Components:FanFiltersDuctworkFire dampersDiffusers

Types of Fan Cross-flow or tangential Propeller Axial flow Centrifugal

Wall mounted propeller fan

Axial-flow fan

Bifurcated axial flow fan

Centrifugal fan

Cross-flow or tangential fan

Filters

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

Dry Filters

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

Viscous or Wet Filter

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

Electrostatic Filter

Activated carbon Filter

made of •Disposable elements of glass fibrous matting containing charcoal granular

Ventilation duct design

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

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

BUILDING | SERVICES | TWO (BLD60503)Ventilation duct design

Ventilation duct design - Chart

BUILDING | SERVICES | TWO (BLD60503)Ventilation duct design

Ventilation Design – Duct conversion

Ventilation Design – Duct conversion chart

The End

BS2 Hvac ventilation 1

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