Ventilation in Buildings

8/3/2019 Ventilation in Buildings

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BY: LALIT SHARMA24/CE/07


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What is Ventilation ?

y The process of removing used air by freshair frombuildings and spaces is called ventilation. This is doneby Natural or Artificial methods

y composition

Nitrogen : 78% , Oxygen : 20.9% , Co2 : 0.04 %

& CO, NH3, Inert gases, water vapour 0.06%


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Effects of Ventilation :-

To remove the used air from spaces/buildings.y To supply oxygen for humans.

y Remove excessive moisture.y Remove excessive heat.

y Cool the surroundings and freshen up the atmosphere inthe building.


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What is the need for ventilation?

y The quantity of O2 is reduced and CO2 is increased bycombustion and respiration.

y When coal is burnt it gives CO2, CO and otherimpurities.

y During breathing an average adult gives off 0.017cum/hr of CO2

y Each cum of gas on burning gives 0.017 cum of CO.y Therefore combustion and respiration both impurethe atmosphere which should be freshened by properventilation.


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Other factors affecting the air ina

spa

ce/room

yApart from increase in CO2 other factors thataffectthe atmosphere in a room/space are

y The odour and organic matter given by skin, clothingand mouth of occupants.

y Rise in temp due to heat produced bythe bodysmetabolism.

y Increase in humidity by evaporation of sweat.


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Requirements ofa good ventilation system

y Sufficient quantity offresh air be admitted and usedair extracted.

y The quantityand velocity of freshair admitted shouldbe properly controlled.

y The change ofair should be complete without leavingany stagnant pockets.

y Maximum velocity should be 15 m/min.y The incoming air should be clean and humid.

y The temp ofair should be uniform and under control.


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Types of Ventilation Systems

yNatural System.

yArtificial System.


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Natural System :-y In this system the used air which is warmer and lighter

is allowed to escape throughthe ventilators located

nearth

e ceiling wh

ile fresh

air en

ters

throug

hdoors/windows near floor level.

y A good rule is to provide a window above floorlevel and keep the area atabout 1/10th of floor area.

ySecond method is to provide fan lights which

permit ventilation even when windows are closed.Current of freshair gets mixed up with freshair and isdeflected upwards to move outthrough ventilators.


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Drawbacks of Natural System

y Reliance upon the wind direction.

y No control of volume, temperature and velocity ofincoming air.

y Chances of smoke, dust , odour entering the room.


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Artificial Ventilation System

y The Vacuum or Extraction system.

y The Plenum or propulsion system.

y Balance system.

yAir conditioning system.


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Air Conditioning

y Is the process oftreating air so as to controlsimultaneously its temp, humidity, purityand

distribution to meet requirements ofthe conditionedspace. Air conditioner gives the feeling of comfortwhich comes by comfortable temp, humidity, airmovementand elimination of body odours, gases, dust

etc.


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How does AC work :-

y Most people think thatair conditioners lower thetemperature in their homes simply by pumping coolair in. What's reallyhappening is the warm air fromyour house is being removed and cycled back in ascooler air. This cycle continues until your thermostatreaches the desired temperature.


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Vapour Compression Cycle :-

yAn air conditioner uses a material called a "workingfluid" to transfer heat from inside ofa room to the

outside. T

he working fluid w

hich

isalso c

alledRefrigerant is a material whichtransforms easily

from a gas to a liquid and vice versa over a wide rangeoftemperatures and pressures. This working fluidmoves throughthe air conditioner' s three maincomponents, the compressor, the condenser, and theevaporator in a continuous cycle.


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fig.1


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Working of Vapour Compression

Cycle :-y The compressor compresses cool Freon gas coming out

from the evaporator, causing the temp and pressure of

gasto rise (red in

the di

agram

above).

y This hot gas enters condenser which is located outsidethe room and runs througha set of snake like coils todissipate its heat, and this gas condenses into a liquid.

y

The Freon liquid runs througha narrowing pipe or anexpansion valve , and in the process it evaporates tobecome cold, low-pressure Freon gas (light blue in thediagram above).


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Continue:.

y This cold gas enters the evaporator located inside theroom and runs througha set of coils thatallow the gasto absorb heatand cool down the air inside thebuilding.

y Mixed in withthe Freon is a small amount oflightweight oil which lubricates the compressor.


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Continue:

y Pre heating :- During winter season some oftheheat lost from occupied rooms is made good by preheating the outside air. This is done by blowing hotairor passing through coil heated byhot water/steam.


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CYCLE OF OPERATION

Removal of dirt/dust by passing the air throughair

cleaner or filter,Cooling or heating air by refrigerator coils or heatingcoils respectively,Control the humidit y byadding moisture in summersa

nd removing moist

ure in wint

ers or ra

iny sea

son bypassing air throughhumidifier.Forcing of conditioned air through ducts by fans anddistributing it in rooms.


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Fig 2


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Humidification: -y This is an important part of AC system which isachieved by passing air through spray of water thenth

rough

eliminat

or plat

esto remove w

ater drople

ts. Inwinters the outside air mayhave high relative

humidity . When heated the RH becomes low and dryleading to parched feeling and scaling of skin. On theother hand air too humid can result in feeling ofdiscomfort. The proper control ofhumidity istherefore importantto human comfort.


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Fig 3


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Comfort Criteria

y Humidity:- The air should not be too dry ornearing saturation. The humidity should be between

45to 65%.

y Temperature :- It should be around surface temp ofhuman body. Atemp between 24 to 27 degree C is acomfortable temp.

y

Air velocity:- Should not exceed 15 m/min. (4.5-9%considered as ideal)

y Organicmatter :- The CO2 content should be below0.06% or 600 ppm.


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THANK YOU

Ventilation in Buildings

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