VENTILATION

NATURAL VENTILATION MECHANICAL VENTILATION

It is the process of changing or replacing air in any space to provide high indoor air quality.

PURPOSE OF VENTILATION• To remove high concentration of body odors.

• To remove carbon dioxide.• To remove excess heat.

• To remove dust, fumes and smoke.

WIND PRESSURE EFFECT :•Wind causes a positive effect on the windward side of the building and a negative pressure on the leeward side of the building.• The inlet opening in the room should be well distributed and should be located on the windward side at the bottom.•The outlet openings should be well located on the leeward side near the top, this will allow cross ventilation

STACK EFFECT :•Stack effect is created by difference in air temperature between air inside the building and the air outside. •The warmer less dense air inside is displaced by the cooler dense air from outside.•The higher column or ‘stack’ of warm air the greater will be the air movement in side the building.•Hence, to achieve maximum advantage of stack effect the vertical distance between inlet and outlet openings should be as great as possible

EXHAUST SYSTEM :

(Natural inlet and mechanical extract)

•The most common type of system. Used for kitchens, workshops, toilets, laboratories etc.

PLENUM SYSTEM :

(Mechanical inlet and natural extract)

•Air movement in the building is created with the help of mechanical devices but extract is natural

•This system is extensively used in cold climatic conditions.

EXHAUST AND PLENUM SYSTEM :

(Mechanical inlet and mechanical extract)

•This is the combination of exhaust and plenum method

ADVANTAGES OF NATURAL VENTILATION•Simple and maintenance- free, quiet. Does not require electrical power the disadvantages of passive ventilation.•No generation of power from warmed air rising during the spring, summer and autumn.•Difficult to comply with the various norms that exist.•Does not have the capability of extracting humidity from bathrooms and laundry.

DISADVANTAGES OF NATURAL VENTILATION•Natural ventilation cannot ensure a specific air change.• It is not possible to filter the air before it enters the building.• If the air inside is at the same temperature as the air outside, and if there is no wind, natural ventilation will not occur.

ADVANTAGES OF MECHANICAL VENTILATION:

• Provide positive ventilation at all times irrespective of outside conditions.• They can ensure a specified air change.• The air under fan pressure can be forced through filters.• Use of electrically driven fan or fans to provide the necessary air movements

DISADVANTAGES OF MECHANICAL VENTILATION:

• When outdoor air is less humid than indoor air, e.g., during cool winter weather, more ventilation decreases the indoor humidity.

• Mechanical systems do not dehumidify sufficiently to counteract the effects of increased moisture entry.

ADV. BUILDING SERVICESSANJANA G. MASURKARL.S.RAHEJA S.O.AIV YEAR B.ARCH (31)

VENTILATION FILTERS

VENTILATION DAMPERS

The purpose of an air filter is to free the air from as much of air borne contaminants as in practicable. Filters are required for various dust free industrial processes.

DRY FILTERS•Dry filters use materials like cloth, paper or other fabrics to retain dust.•When air passes through the curtain of a dry filter, dust particles are trapped.•These particles trapped in these curtains can be removed by shaking/vibrating the curtains by motor run vibrator.

Dry filters are of two types: a)cleanable filters b)throw away filters

THROW AWAY FLITERS•Use curtains of cheaper fabric, glass wool, animal hair etc.•Thrown out after a specific period

CLEANABLE FLITERS•Use a curtain of a good fabric, coarse paper, wool or cellulose felt.•Periodically cleaned with the use of vibrators

VISCOUS FILTERS•These filters use materials like cloth, paper or other fabrics to retain dust.•When air passes through these curtains, dust particles get trapped.•These dust particles can be removed by shaking/vibrating the curtains by a motor run vibrator. Viscous filters are of three types: a)Throw away filters b)Manual Filters c)Automatic Filters

THROW AWAY FILTERS• Use cheaper fibrous materials.• Thrown out after a specific period

MANUAL FILTERS•Manually cleaned periodically by washing them in hot water or steam.• The contaminated oil is washed out and fresh oil is provided on the pads

AUTOMATIC FILTERS•Consists of a continuous moving roll coated with oil.•These rolls Pass over rollers and move automatically through an oil as well as through dirty air stream to be filtered.

ELECTROSTATIC FILTERS•Air is allowed to pass through oppositely charged plates connected across 1200v direct current.•Air gets ionized into positive and negative which are made to pass through another set of charged plates carrying alternate opposite charges at a potential difference of 500v.•Due to high electrical field between the collector plate the positive ions are attracted and collected on negatively charged plate or visa versa.•The collector plate are washed periodically to the collector plate are washed periodically to clean all the dust.

CENTRIFUGAL FILTERS•The electrostatic filters are suited for tiny particles whereas centrifugal filters can retain heavier particles hence used for industrial purpose.•Significant features “duel function” of retaining harmful as well as useful dust can be reutilized by the manufacturer.•A whirling effect is produced by centrifugal pump blower due to which heavier particles separate.

•In ventilation systems dampers acts as a valve for the airflow. By using dampers along with or in conjunction with thermostats one can ensure that air flow only hoes to the room that needs it resulting in shorter run time for heating and cooling equipment and less spent on energy cost.•When power is applied to a closed damper, it opens allowing free air flow. Remove the power and a spring returns the damper to its original position

•Sizes available : 6”, 8”, 10”, 12”, 14” and 16” in normally open (NO) and normally closed(NC) versions

FIRE DAMPERS• In a ventilation system if the ventilation ducts lies within a protected shaft or the shaft itself serves as a ventilation duct, then the duct must be filled internally with automatic fire shutters to reduce the risk

of spreading from the compartment to other.

MECHANICAL FIRE DAMPERS• These dampers that are actuated by a fusible link and which may be used to reduce the risk of fire

spreading through ventilating ducts, they usually operate at a temperature of 70*. Mechanical fire dampers are of swinging type or drooping type.

HONEY COMB DAMPERS• This depends from its action on the property of intumescing paint which swells to many times its

original volume when Heated. • When heated the paint fills froth into a dough like mass which immediately seals and swells and

insulates the surface that is being protected from the fire.

ADV. BUILDING SERVICESSANJANA G. MASURKARL.S.RAHEJA S.O.AIV YEAR B.ARCH (31)

Building / RoomAir Change Rates

- n - (1/hr)

Garages storage 4 - 6

Homes, night cooling 10 - 18

Kitchens 15 - 60

Laundries 10 - 15

Libraries, public 4

Nightclubs 20 - 30

Malls 6 - 10

Medical Centers 8 - 12

Mills, textile general buildings 4

Mills, paper, textile dye houses 15 - 20

Municipal Buildings 4 - 10

Museums 12 -15

Police Stations 4 - 10

Post Offices 4 - 10

Precision Manufacturing 10 - 50

Pump rooms 5

Restaurants 8 - 12

School Classrooms 4 - 12

Shopping Centers 6 - 10

Shops, woodworking 5

Substation, electric 5 - 10

Theaters 8 - 15

Turbine rooms, electric 5 - 10

Warehouses 2

VENTILATION DIFFUSERSDiffusers are decisive elements for the efficiency of air conditioning and ventilation systems in rooms.They are designed to ensure a uniform distribution of the conditioned air within the room. Their proper functioning is, therefore, essential for the well-being and health of people working in air conditioned spaces.The diffuser splits the air flow emerging from the air duct into individual jets and guides them in the desired directions. This results in a rapid reduction in the velocity and temperature of the air entering the room, thus ensuring pleasant temperatures in the occupied zone.

A ROUND DIFFUSER IN HVAC SYSTEM

VENTILATION FANSAxial flow fans

•Consist of an impellor of blades with aerofoil sections rotating inside a cylindrical casing.

•The air flows through the fan in a direction parallel to the shaft and can be installed without a fan base.

•The fan can be driven mounted in air steam or lay a belt drive motor mounted outside the duct.

•Can be used to deal with large volumes of air. Preferred due to cost of installation.

Centrifugal fans

•Consists of an impellor which revolves inside a casing shaped like a scroll

•The impellor blades create high pressures & are used for forcing air through long lengths of duct work that is bulky

•The fan output can be varied with motors or by coupling it with bolt drive with change of pulley size to suit the fan speedPropeller fans

•Have 2 or more blades fixed at an angle to the hub/motor

•They develop comparatively less pressure and hence do not force air through long length ducting

•Can remove large volume of air & their installation cost is low

•Propeller fan with broad curved blades will move air and it is quieter than a fan with narrower blades

GRILLSGrills are decorative and perforated coverings at the end of a duct for outlet and inlet of air. The function of the grill is to provide a proper supply of air distribution to each area.

AIR DISTRIBUTION THROUGH GRILLS:•Floor to ceiling air distribution - It provides very good heating effects in assembly halls, auditoriums, cinema halls etc.•Ceiling to floor air distribution- It provides very good cooling effects in assembly halls, auditoriums, cinema halls etc.•Ceiling to ceiling air distribution- it is good for heating as well as cooling purposes

AIR CHANGE PER HOUROne air change occurs in a room when a quantity of air equal to the volume of the room is applied and /or exhausted.Air changes rates are units of ventilation that compare the amount of air moving through a space to the volume of space. Air change rates are calculated to determine how well a space is calculated.

ADV. BUILDING SERVICESSANJANA G. MASURKARL.S.RAHEJA S.O.AIV YEAR B.ARCH (31)