VENTILATION AND ITS IMPORTANCE

Topics covered

Ventilation

• Its importance

• Factors affecting Ventilation

• Types

–Natural Ventilation, Types

–Mechanical / Forced Ventilation, Types

–HVAC

–Hybrid Ventilation, Advantages & Disadvantages

VENTILATION

Ventilation – Free passage of clean air in a structure.

• The systematic removal of heated air, smoke, and gases

from a structure and replacement with cooler, cleaner

air.

• Ventilation includes both the exchange of air to the

outside as well as circulation of clean air within the

building.`

IMPORTANCE

• To reduce Carbon-di-oxide content in the air.

• To control dust and other impurities in the air.

• To suppress odours ,smoke ,concentration of

bacteria, etc.

• To remove the body heat generated or liberated by

the occupants.

• To maintain desired relative humidity.

• To maintain favorable ambiance to live-in…..

IN INDUSTRIAL ENVIRONMENTS, VENTILATION IS NECESSARY…..

To maintain an adequate oxygen supply in the work area.

To control hazardous concentrations of toxic materials in

the air.

To remove any undesirable odors from a given area.

To control temperature and humidity.

To remove undesirable contaminants at their source before

they enter the work place air.

APPLICATION OF INDUSTRIAL VENTILATION SYSTEMS

Optimization of energy costs.

Reduction of occupational health disease claims.

Control of contaminants to acceptable levels.

Control of heat and humidity for comfort.

Prevention of fires and explosions.

MINIMUM REQUIREMENTS

Sl.No. Nature of Building Rate of fresh air in m3 per head per hour

1 Factories, Workshops 15

2 Educational Buildings 23

3 Restaurants, Dining halls 25

4 Community Buildings 28

5 Theatres, Hospitals 35

6 Residential Buildings 50

7 Gymnasiums, Amphitheatres 80

FACTORS AFFECTING VENTILATION

• Air Changes(rate of air change = 3-5)

• Humidity(at 21c relative humidity = 30-70%)

• Quality of Air(odour ,organic and inorganic dust)

• Temperature(20c and 22c w.r. to winter and

summer)

• Use of Building(no.&age of occupants, working hrs)

TEMPERATURE EFFECTS Temperature inside a structure is often different from the outside ambient

temperature.

Maximum temperature differences occur when the indoor environment is heated.

Temperature differences cause differences in air density inside and outside,

which in turn produce pressure differences.

In the winter when indoor air temperatures are high relative to those outdoors,

the warmer and less dense air inside rises and flows out of the building at its top.

During hot weather when air conditioning produces lower temperatures inside

than outside, the reverse process occurs.

GUIDELINES FOR GOOD AIRFLOW

• Maximize air velocities in occupied rooms.

• Two openings on opposite sides increase airflow.

• Locate windows on opposite sides of the house.

• An inlet window smaller than the outlet creates higher inlet velocity

(e.g. 50% smaller)

• Horizontal window openings are more effective than square or

vertical openings

• Vertical air shafts or open staircases or roof ventilation can take

advantage of “stack effects” to increase airflow

VENTILATION - TYPES

• There are mainly two types of ventilation: natural and

mechanical.

• Natural ventilation includes the movement of outdoor air

through intentional openings such as doors and windows and

through unintentional openings in the building shell such as

cracks which result in infiltration and ex-filtration.

• Mechanical or forced ventilation is intentional ventilation

supplied by fans or blowers. These fans are usually part of the

buildings HVAC system which heats, cools, mixes and filters

the air being supplied to the building.

VENTILATION STRATEGIES

• NATURAL VENTILATION

– Flow driven by wind and temperature.

• FORCED AIR – MECHANICAL VENTILATION

– Exhaust ,Supply and plenum process.

• HVAC

– Mechanical cooling, heating and air conditioning.

• HYBRID VENTILATION

– Combinations of the above systems.

NATURAL VENTILATION

NATURAL VENTILATIONNATURAL VENTILATION

• This ventilation type is mostly used in smaller buildings .

• Normally it is driven by wind pressure and density variations.

• The various types are,

– single sided ventilation (density driven)

– stack ventilation (density driven)

– cross flow ventilation (wind driven)

SINGLE SIDED VENTILATION (NATURAL)

STACK VENTILATION. (NATURAL)

This air is replaced by cold outdoor air that enters near the bottom of the building or

from the ground. This phenomenon is called the building “Stack Effect”.

CROSS FLOW VENTILATION (NATURAL)

NATURAL VENTILATIONNATURAL VENTILATION Influenced by:

– wind direction

– wind speed

– ventilation opening location

– interior/exterior temp. difference

– building geometry Etc....

19

TYPES OF NATURAL VENTILATION OPENINGS

Windows (Windows sliding vertically, sliding

horizontally, tilting, swinging).

Doors, monitor openings and skylights.

Roof Ventilators (weather proof air outlet).

Stacks connecting to registers.

Specially designed inlet or outlet openings.

MECHANICAL VENTILATION

FORCED VENTILATION• Mechanical or forced ventilation is used to control indoor

air quality.

• Excess humidity, odours, and contaminants can often be

controlled via dilution or replacement with outside air.

• Kitchens and bathrooms typically have mechanical exhaust

to control odours and sometimes humidity.

• Ceiling fans and table fans circulate air within a room for

the purpose of reducing the perceived temperature because

of evaporation of perspiration on the skin of the occupants.

TYPES

• Supply System

– Supplying fresh air by input fans in outside walls.

• Exhaust System

– Creating partial vacuum by exhaust fans and blowers.

• Plenum process

– Supply of fresh air by inlet ducts and exhaust of

vitiated air by outlet fans.

SUPPLY SYSTEMS

Components:

Air inlet section

Filters

Heating and/or cooling equipment

Fan

Ducts

Register/grills for distributing the air within the work space

EXHAUST SYSTEMS

Purpose:

An exhaust ventilation system removes the air and airborne

contaminants from the work place air

The exhaust system may exhaust the entire work area, or it may

be placed at the source to remove the contaminant at its source

itself

Types of exhaust systems:

General exhaust system

Local exhaust system

GENERAL EXHAUST SYSTEMS

Used for heat control in an area by introducing large

quantities of air in the area. The air may be tempered and

recycled.

Used for removal of contaminants generated in an area by

mixing enough outdoor air with the contaminant so that

the average concentration is reduced to a safe level.

LOCAL EXHAUST SYSTEMS(LES)

The objective of a local exhaust system is to remove the

contaminant as it is generated at the source itself.

Advantages:

More effective as compared to a general exhaust system.

The smaller exhaust flow rate results in low heating costs

compared to the high flow rate required for a general exhaust

system.

The smaller flow rates lead to lower costs for air cleaning

equipment.

What is the difference between Exhaust and Supply systems?

An Exhaust ventilation system removes the air and air borne contaminants

from the work place, whereas, the Supply system adds air to work room to

dilute contaminants in the work place so as to lower the contaminant

concentrations.

Plenum Process

MECHANICAL VENTILATION

HVAC

• Heating, ventilating, and air conditioning.

• The three central functions of heating, ventilating, and air-

conditioning which are interrelated, and provides thermal

comfort, acceptable indoor air quality, within reasonable

installation, operation, and maintenance costs.

• It can provide ventilation, reduce air infiltration, and

maintain pressure relationships between spaces.

Contd…• Heating

– Necessary in winter to supply heated air.

– Done by warm air furnaces, hot water circulation.

• Cooling

– Necessary in summer to supply cool air.

– Done by refrigeration, sprayers, cool water circulation.

• Air Conditioning

– Necessary for producing--CONDITIONED AIR

– Done by filters, precipitators, coolers ,humidifiers

A.C. - CLASSIFICATION

Hybrid ventilation is a two mode system combining of natural ventilation and mechanical ventilation.

Mechanical ventilation is used when natural driving forces cannot fulfill the required ventilation level.

Hybrid Ventilation-Advantages

• Hybrid ventilation systems offer many advantages:– Relative low running costs for energy conditioning the ventilation

air

– Energy savings compared to full mechanical ventilation systems

– Easily controlled by the inhabitants compared to natural ventilation

– Relative low maintenance

– Reduced use of mechanical equipment compared to mechanically ventilated buildings

– Possibilities for night or passive cooling

Hybrid Ventilation-Disadvantages

• Disadvantages include:– Relative high initial costs

– Depending on climatic conditions, hybrid ventilation is not suitable for many types of buildings where mechanical ventilation might be the only solution

– Room space for equipment might be needed (space for ducting)

– Building design might impose restrictions to the use of hybrid ventilation

– The urban aspects (noise, outdoor pollution, wind velocity, humidity) might limit its use

THANK YOU

1. Outdoor air2. Supply air3. Indoor air4. Transferred air5. Extract air6. Recirculation air7. Exhaust air8. Secondary air9. Leakage10. Infiltration11. Exfiltration12. Mixed air

Air flow in Mechanical ventilation

The air change rate refers to the number of times in a 1-hr period that the volume of air in a space is renewed.

Design Consideration:

The factors affecting air change rate are:

• The presence of air pockets or dead space in the Controlled area.

• The relative positioning of Supply and Return air grills.

• Type of Machine and Equipments placed inside the area

Air change rate

NATURAL VENTILATION• Natural ventilation is the ventilation of a building with outside air

without the use of a fan or any other mechanical system.

• It can be achieved with open-able windows or trickle vents when the

spaces to ventilate are small and the architecture permits.

• In more complex systems warm air in the building can be allowed to

rise and flow out upper openings to the outside (stack effect) thus

forcing cool outside air to be drawn into the building naturally

through openings in the lower areas.

• These systems use very little energy but care must be taken to ensure

the occupants' comfort.

NATURAL

NATURAL VENTILATION• Natural ventilation is the ventilation of a building with outside air

without the use of a fan or any other mechanical system.

• It can be achieved with open-able windows or trickle vents when the

spaces to ventilate are small and the architecture permits.

• In more complex systems warm air in the building can be allowed to

rise and flow out upper openings to the outside (stack effect) thus

forcing cool outside air to be drawn into the building naturally

through openings in the lower areas.

• These systems use very little energy but care must be taken to ensure

the occupants' comfort.

NATURAL