Dictionary --‘intentional movement of air from outside

a building to inside’

Excess of ventilation - discomfort

Control of the quality of air - by modifying the

temperature, humidity and purity

Aim –

a. provide an environment, which is thermally

controlled and comfortable,

b. gives a sense of well-being and

c. reduces the risk of transmission of airborne

diseases.

VENTILATION AIR

The air used to provide acceptable indoor air

quality

It removes the bad odours

Delivered either naturally or by means of

mechanical ventilation

Can change the temperature of air or its moisture

content depending on the requirement inside

the building.

Air exchange rate.

VENTILATION STANDARDS

To achieve a sense of freshness in a room and remove body

odours.

(a)Floor space :

the product of the length and breadth

optimum floor space requirements per person - 50 to 100 feet.

(b) Cubic space of area :

Earlier prescriptions - fresh air supply of 3000 cu feet of air

per person per hour.

beyond 12 feet, not taken into account

Current standards - 1000 to 1200 cu feet per person per hour

(c) Air change

The recommended number of air changes

living room - 2 to 3 in an hour,

Work rooms and assemblies - 4 to 6 per hour.

NATURAL

forces of nature such as wind,

ambient temperature and air

pressure

• Diffusion / infiltration

• Wind driven

• Stack driven

DIFFUSION / INFILTRATION

Through openings, joints and cracks

Buildings - kept under slightly positive pressure

Helps in moisture management and humidity

control inside the rooms

WIND DRIVEN VENTILATION

Perflation

Aspiration

Cross ventilation.

It creates areas of positive pressure on the windward side of

the building and negative pressure on the leeward side

and the sides of the building.

The shape of the building is crucial in creating wind

pressures that will drive air flow through its apertures.

Simple shapes - improve the ventilation

Complex shapes - turbulent air flows

Adv - readily available, economic to implement, could be

controlled

Dis- unpredictability in speed and directions, air quality is

not controlled and could introduce pollutants & may

create draughts and discomfort

STACK DRIVEN VENTILATION

The warmer air will have lower density and be more buoyant and thus will rise above the cold air, creating an upward stream.

To have optimum ventilation – the inside and outside air temperatures must be different

The greater this temperature difference the greater the stack effect.

ADV - does not rely on wind , flow is relatively stable with a greater control.

DIS - lower magnitude, reliance on temperature differences, restrictions due to building designs & may introduce pollutants.

Used in mills, boiler rooms, warehouses and industrial plants.

CEILING FANS, TABLE OR FLOOR FANS

Used to circulate air within a room for the purpose

of reducing the perceived temperature,

because of evaporation of perspiration from the

skin of occupants.

Do not introduce outside air inside the room

Air-coolers are used in hot & dry conditions

They comprise of a chamber whose walls are

made of straw, which is kept cool by pouring

water & evaporation of water .

A cool environment is thus created inside the

chamber and a fan blows cool air inside the

room

EXHAUSTS

The indoor air is extracted out with the help of mechanically driven fans.

Used in combination with the doors and windows since exhaustion of air outside the room creates a vacuum and this needs to be replaced by fresh air

Exhausts are useful in industries especially where excess heat is generated.

In residential areas - for extricating smoke or odours.

The exhaust blades should be cleaned & well maintained to ensure Their long life

PLENUM VENTILATION

Air is blown inside a room by the use of fans and

it enters through ducts.

Creates a positive air pressure inside the room.

Combined with exhaust mechanism it creates

‘balanced ventilation’.

Used along with air conditioners, to supply air

inside the building such that fresh air is

circulated to leave out the odours and

pollutants.

AIR CONDITIONING

A system which provides a combination of cooling,

ventilation and control of humidity

The system has a refrigerant providing cooling through

a ‘refrigeration cycle’. This cycle comprises of four

elements

Compressor , condenser, Evaporator-dehumidifier &

fan.

Can be stand-alone systems or a part of central air-

conditioning systems.

Central air-conditioning system should be installed at

the time of construction,

The split air-conditioning where the fan coils are

connected to remoter condenser unit using piping

instead of ducts.

DEMAND CONTROLLED VENTILATION

Reduces the energy consumption in a building,

while maintaining adequate air quality.

No fixed air replacement rate

Carbon-dioxide sensors control the ventilation

rate dynamically

based on emissions of actual building occupants.

HVAC

HVAC stands for ‘Heating, Ventilation and Air-

Conditioning’.

Important in those places where humidity and

temperature must be closely regulated while

maintaining healthy and safe conditions inside

buildings.

To ensure thermal comfort, accessible indoor

quality at reasonable installation, operation and

maintenance costs.

HVAC systems determine the room air

distribution i.e. how air is delivered to and

removed from room spaces.

VENTILATION REQUIREMENTS

. The factors which determine the difference in

ventilation are :

●● Type of buildings

●● Size of the buildings and the floor areas.

●● Type of roof

●● Locally prevalent wind directions

●● Number of persons occupying the room

●● Proximity to commercial or industrial areas

●● Sanitation of the surrounding area

●● Nature of work being carried out inside the

buildings

●● Geographical locations such as closeness to

sea, large water bodies, hilly areas