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Transcript of Ventilation
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BUILDINGSERVICES-VI
Lecture -1
Contents:Need
Defne ventilation
Type:
Natural ventilation
Mechanical ventilation
Hybrid ventilation
•Air change
•Air change rate
•Air movement
•Orientation
• Temperature eects
•Minimum requirement
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NEED
• To reduce Carbon-di-oxide content and control dust and
other impurities in the air.
• To suppress odours ,smoke ,concentration of bacteria, etc.
•To maintain desired relative humidity and favorableambiance to live-in.
• The ventilation of a building can have a significant affect on
energy consumption and a thorough assessment of natural as
against mechanical ventilation should be made as the decision
could significantly affect the energy efficiency of a building.
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VENTILTI!N
Ventilation – Free passage of clean air in a structure.
• VENTILTI!N is the process of changing or replacing air in
any space to provide high indoor air "uality.
• The systematic removal of heated air, smo#e, and gases from
a structure and replacement $ith cooler, cleaner air.
• Ventilation includes both the e%change of air to the outside as
$ell as circulation of clean air $ithin the building.
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&'( VENTILTI!N
Improving thermal comfort and inoor air !"ality through
provision o resh air is !no"n to be vitally important toindividuals# perception o a space$ their health and "ell%being$and productivity&
• Any ventilation system should be 'e(ible because it "ill need to
"or! under a "ide range o conditions)
I# To remo$e e%cess heat from people an e!"ipment#II#To remo$e moist"re& smells an poll"tants 'enerate (y
people$ pets and coo!ing$ "hich can be unpleasant or ha*ardousto health and+or buildings&
III#To remo$e 'aseo"s emissions from materials& f"rnishin's&
cleaning agents and$ in aected areas$ the products o radon&IV#To act as a carrier for heatin'& coolin' an)or h"miity
control&
V#To pro$ie o%y'en for (reathin'& altho"'h the saferequirement is a tiny proportion compared to the other needs&
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VENTILTI!N T()E*
• N!"#$ V%N!&$!&'N
– +lo$ driven by $ind and temperature.
• F'#C%( &# – )%C*N&C$ V%N!&$!&'N
– E%haust ,*upply and plenum process.
• *+#&( V%N!&$!&'N
– ombinations of the above systems.
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NTL VENTILTI!N NTL VENTILTI!N
/ Natural ventilation includes the
movement of outdoor air throughintentional openings such as doors
and $indo$s and through
unintentional openings in the
building shell such as crac#s $hich
result in infiltration and e%-
filtration.
/ This ventilation type is mostly usedin smaller buildings .
/ Normally it is driven by $ind
pressure and density variations.
/ The various types are,
0 single sided ventilation
1density driven2
0 stac# ventilation 1density
driven2
0 cross flo$ ventilation
1$ind driven2
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&N$% &(%( V%N!&$!&'N
/N!"#$0
!C1 V%N!&$!&'N. /N!"#$0
C#' F$'2 V%N!&$!&'N
/N!"#$0
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 3*tac# Effect4.
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• Natural ventilation is the ventilation of a building $ith outside air $ithout
the use of a fan or any other mechanical system.
• It can be achieved $ith open-able $indo$s or tric#le vents $hen the spaces
to ventilate are small and the architecture permits.
Clerestory 0
are any high $indo$s
above eye level . Thepurpose is to bring
outside light, fresh air,
or both into the inner
space.
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5
T()E* !+
NTL VENTILTI!N !)ENIN6*
&indo$s 1&indo$s sliding vertically, sliding hori7ontally, tilting,
s$inging2.
Doors, monitor openings and s#ylights.
oof Ventilators 1$eather proof air outlet2.
*tac#s connecting to registers 1A device attached to an air%
distributing duct or the purpose o controlling the
discharge o air into the space to be heated$ cooled$ orventilated&
*pecially designed inlet or outlet openings.
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+!ED VENTILTI!N• 8echanical or forced ventilation is used
to control indoor air "uality.
• E%cess humidity, odours, and
contaminants can often be controlled via
dilution or replacement $ith outside air.
• 9itchens and bathrooms typically have
mechanical e%haust to control odours and
sometimes humidity.
• eiling fans and table fans circulate air
$ithin a room for the purpose of reducing
the perceived temperature because of
evaporation of perspiration on the s#in of
the occupants.
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T()E*
• upply ystem
– *upplying fresh air by input fans in outside $alls.
• %xhaust ystem
– reating partial vacuum by e%haust fans and blo$ers.
• )lenum process
– *upply of fresh air by inlet ducts and e%haust of vitiated air
by outlet fans.
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*))L( *(*TE8*
Components3
ir inlet section
+ilters
'eating and:or cooling e"uipment
+an
Ducts
egister:grills for distributing the air $ithin the $or# space
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E;'*T *(*TE8*
4urpose3
n e%haust ventilation system removes the air and airborne
contaminants from the $or# place air
The e%haust system may e%haust the entire $or# area, or it may
be placed at the source to remove the contaminant at its source
itself
!ypes of exhaust systems3
6eneral e%haust system
Local e%haust system
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6ENEL E;'*T *(*TE8*
sed for heat control in an area
by introducing large "uantities
of air in the area. The air may
be tempered and recycled.
sed for removal of
contaminants generated in an
area by mi%ing enough outdoor
air $ith the contaminant so that
the average concentration is
reduced to a safe level.
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L!L E;'*T *(*TE8*1LE*2
The ob<ective of a local e%haust system is to remove the
contaminant as it is generated at the source itself.
dvantages3
8ore effective as compared to a general e%haust system.
The smaller e%haust flo$ rate results in lo$ heating costs
compared to the high flo$ rate re"uired for a general e%haust
system.
The smaller flo$ rates lead to lo$er costs for air cleaning
e"uipment.
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&'T I* T'E DI++EENE =ET&EEN
E;'*T ND *))L( *(*TE8*>n E%haust ventilation system removes the air and air borne contaminants
from the $or# place, $hereas, the *upply system adds air to $or# room to
dilute contaminants in the $or# place so as to lo$er the contaminant
concentrations.
Plenum Process
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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.
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Hybrid -entilation%Advantages
• 'ybrid ventilation systems offer many advantages?
– elative lo$ 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
– elative lo$ maintenance
– educed use of mechanical e"uipment compared to mechanically
ventilated building
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Hybrid -entilation%Disadvantages
• Disadvantages include?
– elative high initial costs
– Depending on climatic conditions, hybrid ventilation is not suitable
for many types of buildings $here mechanical ventilation might be
the only solution
– oom space for e"uipment might be needed 1space for ducting2
– =uilding design might impose restrictions to the use of hybrid
ventilation
– The urban aspects 1noise, outdoor pollution, $ind velocity,humidity2 might limit its use
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SELECTING T*E VENTIL+TI,N STR+TEG
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SELECTING T*E VENTIL+TI,N STR+TEG
B+SIC D,.ESTIC SC+LE .V*R SSTE.
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B+SIC D,.ESTIC SC+LE .V*R SSTE.#
+DV+NT+GES +ND DIS+DV+NT+GES ,/ N+TUR+L +ND .EC*+N
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+DV+NT+GES +ND DIS+DV+NT+GES ,/ N+TUR+L +ND .EC*+N
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I 'N6E*
The volume o resh air .ma!e up air/ required or proper
ventilation is determined o the si*e and use o the space&
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The air change rate refers to the number of times in a 1-hr eriod that thevolume of air in a sace is renewed.
Design Consideration:
The factors affecting air change rate are!
• The resence of air oc"ets or dead sace in the #ontrolled area.
• The relative ositioning of $uly and %eturn air grills.
• Tye of Machine and &quiments laced inside the area
I 'N6E TE
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I 8!VE8ENT
'ir movement is affected by the following!
(ifferences in air ressure as air moves from areas of high ressure toareas of low ressure.
Circulation- heating and cooling equiment both
use blowers to distribute conditioned air throughout
buildings.
Ventilation fans for bathrooms) laundries
all vent conditioned air to the outside which must be relaced.
Combustion processes- aliances such
as boilers) furnaces) heating stoves and
water heaters ull air from the home
interior as they e*haust the roductsof combustion to the e*terior.
.
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I 8!VE8ENT
(ifferences in temerature
Thermal buoyancy- describes the action ofair as it is heated. +ecause heated air is less
dense it rises) moving from a cool) high-
density area to ward a warm) low-density
area.
Stack effect- describes the action of warm
air rising through a building. 's warm airrises) it ulls cold ma"e-u air into the home
through the lower building enveloe and
ushes warm air out through the uer
building enveloe.
Convection currents- The movement ofcooler air moving in to relace rising warm
air will establish convection currents any
lace in the home in which temerature
differentials e*ist) with main areas of concern
being the living sace and attics.
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E+RT* TUBES
One urther approach to the provision o resh air to a building$ and that can be used "itheither a mechanical or natural system$ is the earth tube& The temperature o the ground a e"metres belo" the surace is typically similar to the mean annual air temperature & This meansthat i the supply air is brought to the building via a long tube buried in the ground its "ill
ad0ust is temperature closer to the ground temperature& Thus in "inter cold air "ill be slightly"armed and in summer hot incoming air "ill be slightly cooled& Thus ree heat o cooling isprovided$ but is ar more popular in locations "here there is a much greater s"ing in annualtemperature&
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TE8)ETE E++ET*
Temperature inside a structure is often different from the outside
ambient temperature.
8a%imum temperature differences occur $hen the indoor environment
is heated
In the $inter $hen indoor air temperatures are high relative to those
outdoors, the $armer and less dense air inside rises and flo$s out of
the building at its top.
During hot $eather $hen air conditioning produces lo$er
temperatures inside than outside, the reverse process occurs.