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


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


Combined supply & extract system with propeller fans

BUILDING | SERVICES | TWO (BLD60503) Heat Exchanger

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


Centrifugal 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


Electrostatic Filter


Activated carbon 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

air.



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


BUILDING | SERVICES | TWO (BLD60503)Ventilation duct design


Ventilation duct design - Chart








Ventilation Design – Duct conversion


Ventilation Design – Duct conversion chart


The End

Art & Photos

BS2 Hvac ventilation 1