Air Distribution and Airconditioning Apparatus.pdf

Ducts, its classification, AHU and its requirements, Duct Design Methods, Losses in Ducting, Fans and its types, Fan Characteristics, Basic elements of HVAC control system

1. Unit-5:
Air Distribution and
Air conditioning Apparatus
Prepared by:
Ankur Sachdeva
Assistant Professor, ME

2. Transmission of Air
•In an AHU, air is transmitted through various ducts and other
components with the help of fans.
• Since the fan motor consumes a large amount of power, and
the duct system occupies considerable building space, the
design of air transmission system is an important step in the
complete design of air conditioning systems.
• In the end the success of any air conditioning system depends
on the design of individual components as well as a good
matching between them under all conditions.
• In order to design the system for transmission of air, it is
important to understand the fundamentals of fluid (air) flow
through ducts.
Ankur Sachdeva, Assistant Professor, ME

3. What are Ducts
•Ducts are conduits or passages used in heating, ventilation,
and air conditioning (HVAC) to deliver and remove air.
•The needed air flows include, for example, supply
air, return air, and exhaust air.
•Ducts commonly also deliver ventilation air as part of the
supply air.
• As such, air ducts are one method of ensuring
acceptable indoor air quality as well as thermal comfort.
•Ducts work on the principle of air pressure difference. If a
pressure difference exists, air will flow from an area of high
pressure to an area of low pressure.
•The larger this difference, the faster the air will flow to the
low-pressure area.
Ankur Sachdeva, Assistant Professor, ME

4. Classification of Ducts
1.According to the pressure of air
-Low Pressure : Static Pressure <50 mm of water
-Medium Pressure : 50 mm< Static Pressure< 150 mm of water
-High Pressure: 150 mm< Static Pressure< 250 mm of water
2.According to the velocity of air
-Low Velocity: Velocity of air < 10 m/s
-High Velocity : Velocity of air > 10 m/s
3.According to the type of air
-Fresh Air : carries outside air
-Supply Air : carries conditioned air to the space to be conditioned
-Return Air : carries recirculated air from the conditioned space
Ankur Sachdeva, Assistant Professor, ME

5. Schematic Air-flow diagram for an
Air-conditioning system
Ankur Sachdeva, Assistant Professor, ME

6. AHU and its purposes
•In air conditioning systems that use air as the fluid in the
thermal distribution system, it is essential to design the Air
Handling Unit (AHU) properly.
•The primary function of an AHU is to transmit processed air
from the air conditioning plant to the conditioned space and
distribute it properly within the conditioned space.
•A typical AHU consists of:
(i)A duct system that includes a supply air duct, return air
duct, cooling and/or heating coils,
humidifiers/dehumidifiers, air filters and dampers.
(ii)An air distribution system comprising various types of
outlets for supply air and inlets for return air.
(iii)Supply and return air fans which provide the necessary
energy to move the air throughout the system
Ankur Sachdeva, Assistant Professor, ME

7. Requirements of Air Distribution
System
1) There should be enough entrainment of room air with
the supply air , so that upon reaching the occupied zone,
the air stream attains desired temperature.
2) The temperature throughout the occupied zone of the
room should be within ± 1ºC of the design temperature.
3)Only minor horizontal or vertical temperature variation
should be there in occupied zone.
4)Noise level should be below the objectionable level.
5)Effect of natural convection and radiation within the
room should be minimum.
6)The desirable air velocity is 9.1 mpm at the occupancy
level.
Ankur Sachdeva, Assistant Professor, ME

8. Terms used in Air Distribution System
1.Draft:Itisdefinedasanylocalizedfeelingofcoolnessorwarmth
ofanyportionofthebodyduetoairmovementand
temperature,withhumidityandradiationconsideredconstant.
2.BloworThrow:Thedistancetravelledbythesupplyairstream
inthehorizontaldirectiononleavingtheairoutletandreaching
avelocity15mpm.
3.Drop:- It is the vertical distance that the lower edge ofthe
horizontally projected air stream drops between theoutlet and
the end of its throw.
4.Induction or Entrainment ratio: It is defined as the ratio of total
air to primary air.
5.Spread: The angle of divergence of an air stream after it leaves the
outlet.
Ankur Sachdeva, Assistant Professor, ME

9. Throw and Drop
Ankur Sachdeva, Assistant Professor, ME

10. Terms used in Air Distribution System
1.Outlet :- It is an opening through which air is supplied to the
conditioned space.
2.Intake :- It is an opening through which air is return from the
space.
3.Grills :- Grills provide decorative covering for an outlet or inlet
4.Diffuser :- It is an outlet grille designed to guide the direction of
the air.
5.Register :- It is a grille provided with a damper or control valve.
Ankur Sachdeva, Assistant Professor, ME

11. Types ofSupply Air-Outlet
1. Grill Outlet
•Theseoutlets have
adjustable bar grills which
are the most common
types with vertical and
horizontal vanes.
2. Ceiling Outlet
•They are mounted in the
Grill Outlet
ceiling. Multi-passage
round, squareor
rectangular are most
common type
Ceiling Outlet
Ankur Sachdeva, Assistant Professor, ME

12. Types of Supply Air Outlet
3. Slot Diffuser
•It is an elongated outlet with an
aspect ratio 25 : 1 and maximum
height of 7.5 cm. They are used in
side walls but at a higher height
of the floor.
4. Perforated Ceiling
Slot Diffuser
•In this case, confined space above
the ceiling is used as supply
plenum.
•The air from the plenum is
supplied to the room through
small holes or slots.
•The air is supplied at the rate of
0.3 to 4.5 m³/m² of the floor area.
•They are specially suited to large
zones
Perforated Ceiling
Ankur Sachdeva, Assistant Professor, ME

13. Mechanism of flow of Air
through Duct Outlet
•Themechanismofflowofairfromtheductandthroughtheoutlettothe
roomisshowninFig.
•A
cisthecoreareaortheareaofgrilleopeninginwhichtheairflowswitha
velocityC
c.
•A
faisthefreeareaofthegrillethroughwhichaircanpass.
•TheratioA
fa/A
cisR
fasothatC
fa=C
c/R
fa.
•A
0istheareaatthevena-contractaformedoutsidethegrille.
•IfC
disthedischargecoefficientoftheoutlet,andC
0isthevelocityatthe
venacontracta,
Ankur Sachdeva, Assistant Professor, ME

14. Thezoneofinterestisat25to100timesthediameterorwidthoftheoutletin
thexdirection.Inthiszone,thevelocityatanyxisgivenby
Mechanism of flow of Air
through Duct Outlet
where Qis the volume delivered by the outlet and K= 1.13 K.
Ankur Sachdeva, Assistant Professor, ME

15. Mechanism of flow of Air
through Duct Outlet
ThetestedvaluesofKaregiveninTablebelow.Theequationcanalsobeusedtocalculate
thethrowLbyputtingCx=15mpm=0.25m/s.
Ankur Sachdeva, Assistant Professor, ME

16. Mechanism of flow of Air
through Duct Outlet
•AsfarastheentrainmentratioRisconcerned,itisgivenbythefollowingempirical
relationsinwhichQxrepresentsthevolumeofthetotalairatanydistancexfromthe
outletandQisthevolumeofprimaryair.
Ankur Sachdeva, Assistant Professor, ME

17. Considerations for Selection and
Location of Outlets
1.Theamountofairtobedeliveredbytheoutletshouldbeproportionaltotheloadof
thepartofthespaceforwhichitisinstalled.
2.Theselectionofthetypeofoutletisgovernedbytheceilingheight,natureofroom
occupancy,etc.
3.Thelocationoftheoutletshouldbegovernedbytheconditionofuniformair
distributionandrapidtemperatureequalization.
4.Theselectionofsizeoftheoutletcanbemadefromthemanufacturer’scatalogdata
accordingtotheairdelivery,corevelocity,distributionpattern,soundlevels,throw,
drop,spreadetc.
•Asacorollarytothis,theoutletsshouldbelocatedsoastoneutralizetheconcentrated
loads,suchasthosethatresultfromexteriorwindows,electronicequipment,etc.
•Inbuildingsinwhichthelightingloadisheavy,i.e.,morethan55W/m2andtheceiling
heightismorethan4.5m,itisdesirabletolocatetheoutletsbelowthelightingload.
•Insuchandsimilarcasesofconcentratedloads,thereturngrillesorinletscanbelocated
adjacenttotheseloadssothatwarmair(inthecaseofcooling)iswithdrawnfromthe
sourceinsteadofbeingdissipatedintheconditionedspace.
Ankur Sachdeva, Assistant Professor, ME

18. Considerations for Selection and
Location of Outlets
•Thisarrangementisalsosuitabletoremovethefumes,pollutants,etc.,fromtheir
sourcesin the space.
•Intheirdistributionpattern,theoutletsmayhavecharacteristicsinbetweenthe
behaviouratthetwoextremes.
•Atoneextremeareceilingdiffuserswithradialflow.Asaresultofthelargeperimeter
areaoftheprimaryair,theywillhaveahighentrainmentrateandrapidtemperature
equalizationintheroom.Theairwill,however,quicklyslowdownandwillhave a
short throw.
•Attheotherextremeareslotdiffusers.Theyhavealowentrainmentrateandslow
temperatureequalization.Buttheyhavealongthrow.
•Thus,generallyspeaking,ceilingdiffuserscandelivermoreairtoaspacethangrilles
andslotdiffusers.Becauseoftheirhighentrainment,ceilingdiffusersmayalsobe
usedinsystemswithlowsupplyairtemperatures.Inspiteofthelowsupplyair
temperature,inductionwillresultinrapidtemperatureequalization.
•Thesamecannotbedoneinthecaseofslotdiffusersandgrilles.Intheircase,this
temperaturedifferencemaynotexceed11°C.Theyareusedonlywhenthethrow
required is very long.
Ankur Sachdeva, Assistant Professor, ME

19. Distribution Patterns of Outlets
The distribution patternsfollowdifferentlyforcoolingandheating.
Thebestdistributionpatternisoneinwhichthewholeroomairissetinmotion,andthere
areneitheranystagnationzonesnorzonesofdraftattheoccupancylevel.
The representation for primary air, total air, natural convection air, and stagnant zone is
shown below:
Ankur Sachdeva, Assistant Professor, ME

20. High Sidewall Grilles Discharging Air
Horizontally
Distribution patterns for high sidewall grille
•Thevariationofthevanesettingmayaffecttheflowtosomeextentbutthegeneral
patternwillbethesameforbothcoolingandheating.
•Itisseenthatduringcooling,thetotalairdropsontheoccupiedzoneatsome
distancefromtheoutlet,dependingonQ,Cc,(ti–ts),deflectionsetting,ceiling
effect,andtypeofloadinginspace.
•Itmaybenotedthatthethrowisaboutthree-fourthsoftheroomwidth,andinno
caseshouldtheairoverthrowotherwisedraftconditions will result.
•Duringheating,thetotalwarmairtendstorise.Thisresultsinalargestagnation
zone.Adegreeofover-blowmaybehelpfulinminimizingthestagnationzone.
Ankur Sachdeva, Assistant Professor, ME

21. Ceiling Diffusers Discharging
Air Horizontally
Distribution patterns for ceiling diffusers projecting air horizontally
Thegeneralpatternforceilingdiffusersprojectingairhorizontallyissimilarthough
symmetricalonthetwosidesasshowninFig.(a)and(b).
Thereishardlyanystagnationzoneforcoolingapplicationthoughthesamecannotbesaidfor
thecaseofheating.
Duringheating,coldairfromthewallstendstodropbutwarmairtendstoremainnearthe
ceiling.Alargestagnationzoneresults.Anattemptmustbemadetodirecttheairtowardsthe
coldwalls.
Ankur Sachdeva, Assistant Professor, ME

22. Floor Registers
Discharging Air Vertically
Floor registers normally dischargeprimaryairinastraightverticaljetasshowninthefigure.
Ultimatelythetotalair,afterreachingtheceiling,fansout.
Inthecaseofcooling,itfallsoutsoonaftertravellingashortdistance.
Thecoolingdiagramshowsthestagnationregionabovetheterminalpointofthetotalair.Ina
largespace,thisstagnationzonemayextendmuchfartherandtoalowerlevel.
Inthecaseofheating,thetotalairfollowstheceilingandthendescendsdownifflowingalong
thecoldexteriorwalls.
Thereisabettertemperatureequalizationforheatingthanforcooling.Intheseoutlets,generally,
anincreaseinthesupplyairvelocitywillimprovetheairdistribution.
Theseoutletsaremoresuitedforheatingonly.Ankur Sachdeva, Assistant Professor, ME

23. Floor Diffusers Discharging Air in a
Spreading Jet
•Floor diffusers are similartofloorregisters.Theonlydifferenceisinthenatureofthejet
whichisspreadinginthiscase,insteadofbeingnonspreadingasseenfromthefigure.
•Althoughthecharacteristicsaresimilar,thestagnationzoneismuchlargerduringcooling
butsmallerduringheating.
•Theseoutletsaresuitablewhentheheatingrequirementissevereandprimary,andthe
coolingrequirementmoderateandsecondary.
•Flooroutletsarenotpermissiblewhenpeopleareseatedsuchasintheatres.Butwhere
peoplearemoving,asinstores,theyarequitepermissible.
•However,averylowdehumidifiedrise,say,notmorethan8°Cshouldbeused.Thiswill
requirealargevolumeflow.
•Onedisadvantageofflooroutletsisthattheybecomedustcollectors.
Ankur Sachdeva, Assistant Professor, ME

24. Low Sidewall Outlets
Discharging Air Horizontally
•As is seen from the figure,thetotalairduringcoolingremainsnearthefloorlevelresultingin
lowtemperatureintheoccupiedzoneandalargestagnationzoneabove.
•Duringheating,thewarmairrisesandtemperatureequalizationtakesplaceexceptinthe
regionoftotal air.
•Theseoutletsdischargeairdirectlyintotheoccupiedzonewithhighvelocity.Theyarenot
recommendedforcomfortairconditioning.
Ankur Sachdeva, Assistant Professor, ME

25. Ceiling Diffusers
Discharging Air Vertically
•These are ceiling diffusers whichdonotprojectairhorizontally,butverticallyasshowninFig.
•Duringcooling,thetotalairdropstothefloorandthenfansout,finallyrisingalongthewalls.
Thestagnationregionisneartheceiling.
•Duringheating,thetotalair,afterreachingthefloor,returnsbacktowardstheceiling.Thereis
nostagnationzone.
•Theseoutletshavecompletelydifferentdistributionpatternsforcoolingandheatingbecauseof
thedifferentthrowsobtained.
•Theyare,therefore,usedeitherforcoolingorforheating,butseldomforboth.
•Forcooling,werequirelowvaluesofsupplyairvolume,velocityandtemperaturedifference,
whereasforheating,thesameshouldbehightogetproperthrow.
•Nevertheless,ceilingdiffuserscanbeconvenientlyappliedtoductsorplenumsintheceilingin
largespacesandhalls/auditoriums.,
Ankur Sachdeva, Assistant Professor, ME

26. Duct Design
•A duct system is also called ductwork.
•Duct Design of a system involves:
–Planning (laying out),
–Sizing,
–Optimizing,
–Detailing, and
–Finding the pressure losses
Ankur Sachdeva, Assistant Professor, ME

27. Aspect Ratio
•Aspect Ratio is the ratio of the dimensions of
the two adjacent sides of a rectangular duct.
•Mathematically, Aspect ratio = a/b
b
a
A rectangular duct section with an aspect ratio close to 1 yields the most
efficient rectangular duct shape in terms of conveying air. A duct with
an aspect ratio above 4 is much less efficient in use of material and
experiences great pressure losses.
Ankur Sachdeva, Assistant Professor, ME

28. Material of the Duct
Type Advantages
Galvanized IronZinc coating of this metal prevents rusting and avoids
cost of painting
Aluminium Lightweight, Quick to install, Easily fabricated into
different shapes
Flexible PlasticConvenient for attaching supply air outlets to the rigid
ductwork
Fiber-Glass Built-in thermal insulation and the interior surface
absorbs sound
Wood Used in applications where moisture content is less in
air
Ankur Sachdeva, Assistant Professor, ME

29. Recommended Thickness of GI
Sheets for the Ducts
Ankur Sachdeva, Assistant Professor, ME

30. Duct Design Methods
•There are mainly three methods which are
commonly used for duct design.
1)Velocity reduction method
2)Equal friction loss method
3)Static regain method
Ankur Sachdeva, Assistant Professor, ME

31. Velocity Reduction Method
•In this method the duct designed in such a
way that the velocity decreases as flow
proceeds.
•The pressure drops are calculated for this
velocities for respective branches and main
duct.
•The duct size are determined for assumed
velocities and known quantities of air to be
supplied through the respective ducts
Ankur Sachdeva, Assistant Professor, ME

32. Recommended maximum duct velocity
for low-velocity system (mpm)
Ankur Sachdeva, Assistant Professor, ME

33. Equal Friction Method
•In this method, the frictional pressure drop
per unit length of duct is maintained constant
throughout the duct system.
•The procedure is to be select a suitable
velocity in the main duct from the sound level
consideration.
•Knowing the air flow rate and the velocity in
the main duct, the size and friction loss are
determined from the friction chart.
Ankur Sachdeva, Assistant Professor, ME

34. Static Regain Method
•For the perfect balancing of the air duct layout system,
the pressure at all outlets must be made same.
•This can be done by equalizing the pressure losses in
various branches.
•This is possible if the friction loss in each run is made
equal to the pressure gain due to reduction in velocity.
•Advantages :
•It is possible to design long run as well as short run for
complete regain.
•It is sufficient to design the main duct for complete
regain
Ankur Sachdeva, Assistant Professor, ME

35. Flow of Air through Ducts
•The fundamental equation to be used in the analysis of air
conditioning ducts is the Bernoulli’s equation.
•Bernoulli’s equation is valid between any two points in the
flow field when the flow is steady, irrotational, inviscid and
incompressible.
•The equation is valid along a streamline for rotational,
steady and incompressible flows.
•Between any two points 1 and 2 in the flow field for
irrotational flows, the Bernoulli’s equation is written as:
Ankur Sachdeva, Assistant Professor, ME

36. Flow of Air through Ducts
•The above equation implies that for frictionless flow through
a duct, the total pressure remains constant along the duct.
•Since all real fluids have finite viscosity, i.e. in all actual
fluid flows, some energy will be lost in overcoming friction.
•This is referred to as head loss, i.e. if the fluid were to rise
in a vertical pipe it will rise to a lower height than
predicted by Bernoulli’s equation.
• The head loss will cause the total pressure to decrease in
the flow direction. If the head loss is denoted by H
l then
Bernoulli’s equation can be modified to:
Ankur Sachdeva, Assistant Professor, ME

37. Fan Total Pressure (FTP)
•To overcome the fluid friction and the resulting head, a fan
is required in air conditioning systems.
•When a fan is introduced into the duct through which air
is flowing, then the static and total pressures at the section
where the fan is located rise.
•This rise is called as Fan Total Pressure (FTP). Then the
required power input to the fan is given by:
Ankur Sachdeva, Assistant Professor, ME

38. Fan Total Pressure (FTP)
•The FTP should be such that it overcomes the pressure drop
of air as it flows through the duct and the air finally enters
the conditioned space with sufficient momentum so that a
good air distribution can be obtained in the conditioned
space.
•Evaluation of FTP is important in the selection of a suitable
fan for a given application
Ankur Sachdeva, Assistant Professor, ME

39. Estimation of Pressure Drop
•As air flows through a duct its total pressure drops in
the direction of flow. The pressure drop is due to:
1.Fluid friction
2.Momentum change due to change of direction
and/or velocity
•The pressure drop due to friction is known as frictional
pressure drop or friction loss, Δp
f
•The pressure drop due to momentum change is
known as momentum pressure drop or dynamic loss,
Δp
d
•Thus the total pressure drop Δp
t is given by:
Ankur Sachdeva, Assistant Professor, ME

40. Flow of Air in a Duct
Ankur Sachdeva, Assistant Professor, ME

41. Flow of Air in a Duct
Ankur Sachdeva, Assistant Professor, ME

42. Flow of Air in a Duct
Ankur Sachdeva, Assistant Professor, ME

43. Flow of Air in a Duct
•For Actual case,
•Where p
L is the total pressure drop between
section 1-1 and 2-2
•If a fan is installed between the two sections
then, above equation changes into
•Where p
TF is the Fan Total Pressure
Ankur Sachdeva, Assistant Professor, ME

44. Some Important Points
•Pressures in the duct are usually expressed in mm of water
•Properties of standard air in the duct:
–Temperature of air, T
a = 20°C,
–Pressure of air, P
a = 1.01325 bar
–Density of air, ρ
a, at 20°C = 1.2 (kg/m
3)
Ankur Sachdeva, Assistant Professor, ME

45. Evaluation of frictional
pressure drop in ducts
•Frictional pressuredrop in internal flows are
calculated using Darcy-Weisbach equation:
•Where
–f is the dimensionless friction factor,
–L is the length of the duct and
–m is the hydraulic mean depth
–Friction factor is a function of Reynolds number
Ankur Sachdeva, Assistant Professor, ME

46. Estimation of Pressure Drop
But
Therefore
For Circular Duct
Ankur Sachdeva, Assistant Professor, ME
For Rectangular Duct

47. Calculation of Friction factor
Ankur Sachdeva, Assistant Professor, ME

48. Surface Roughness of Materials
Ankur Sachdeva, Assistant Professor, ME

49. Moody’s Chart for friction factor
(Circular Ducts/Pipes)
Ankur Sachdeva, Assistant Professor, ME

50. Equivalent Diameter of a Circular
duct for a Rectangular Duct
Two cases:
(i)When quantity of air, Q , passing through the circular and rectangular duct is same
(ii)When velocity of air, V , passing through the circular and rectangular duct is same
Case (i) When Quantity of air, Q, is same
Ankur Sachdeva, Assistant Professor, ME

51. Equivalent Diameter of a Circular
Duct for a Rectangular Duct
Pressure Loss due to friction,
Hydraulic mean depth,
Ankur Sachdeva, Assistant Professor, ME

52. Equivalent Diameter of a Circular
Duct for a Rectangular Duct
Pressure loss due to friction in rectangular duct,
Since the pressure loss, friction factor, length, density and quantity of air for the circular
and rectangular duct is same , we have
Ankur Sachdeva, Assistant Professor, ME

53. Equivalent Diameter of a Circular
Duct for a Rectangular Duct
Case (ii) When Velocity of air, V, is same
,
Pressure loss due to friction in circular duct,
Pressure loss due to friction in rectangular duct
Since the pressure loss, friction factor, length, density and velocity of air for the
circular and rectangular duct is same , we have
Ankur Sachdeva, Assistant Professor, ME

54. Part-2: AIR CONDITIONING APPARATUS
Ankur Sachdeva, Assistant Professor, ME

55. Introduction
•Fansandblowersprovideairforventilationand
industrialprocessrequirements.
•Fansgenerateapressuretomoveair(orgases)against
aresistancecausedbyducts,dampers,orother
componentsinafansystem.
•Largecapacityfanunitstypicallyconsistofabladed
rotatingimpellerenclosedinastationarycasing.
•Therotorsystemcausesthemotionoftheair/gasand
thecasingdirectstheairflow.
•Thefanrotorreceivesenergyfromarotatingshaftand
transmitsittotheair.
Ankur Sachdeva, Assistant Professor, ME

56. Difference between Fan, Blower,
and Compressor
•Asper“ASME”Dependingonthespecificratioandrisein
systempressure.
Ankur Sachdeva, Assistant Professor, ME

57. Types of Fans and Blowers
Ankur Sachdeva, Assistant Professor, ME

58. Centrifugal Fans
•Rotatingimpellerincreasesairvelocity.
•Airspeedisconvertedtopressure.
•Thisfanproduceshighpressurewhichranges
from550mmwcto1400mmwc.
•Efficiencyvariesfrom60-83%.
•Usedfordirtyairstreamconditioningand
materialhandlingapplications.
•Wheneverasystemhasductwork,centrifugal
fanshavetobeusedasthestaticpressuredropis
considerable.
•Butwhenthereisnoductwork,propellersor
axialflowfanscanbeused.
•Nevertheless,inwindow-typeandpackage
units,simpledrum-typecentrifugalfansareused,
whereasmostexhaustfansareoftheaxialtype,
astheyoccupylessspace,andcanhandlelarge
volumes
Ankur Sachdeva, Assistant Professor, ME

59. Types of Centrifugal Fans
These are categorized by blade shapes as:
(a)Radial
(b)Forward Curved
(c)Backward Curved
Ankur Sachdeva, Assistant Professor, ME

60. Radial fans
Characteristics:
•Usuallycontains6to16impellerblades.
•Highstaticpressuresupto1400mmwc
canachievewithlowflowrates.
•Low/mediumairflowratesonly.
•Efficiencyrangesfrom69%-75%.
•SimpleinDesign.
Applications:
•Suitableforhandlingheavily
contaminatedairstreamslikedust-laden,
sawdust,etc.
•Thesearewidelyusedincorrosiveand
high-temperatureenvironments.
Ankur Sachdeva, Assistant Professor, ME

61. Forward Curved Blade Fans
Characteristics:
•Usually contains 24 to 64 impeller blades.
•Produces low pressure up to 5 in wg.
•Large airflow rates against relatively low
static pressure.
•Efficiency ranges from 60% -65%.
•Lighter in construction and less expensive
Applications:
•Suitable for clean air environment as blades
easily accumulate dirt
•Well suited for low-pressure HVAC such as
packaged air conditioning equipment
•Not constructed for high pressures or harsh
service.
Ankur Sachdeva, Assistant Professor, ME

62. Backward Curved Blade Fans
Characteristics:
•Usuallycontains6to16impeller
blades.
•Produceshighpressure(40inwg)with
highflowrates.
•Moreefficientthanforwardcurved
bladeefficiencyrangesfrom79%-
83%.
•Highmaintenancecost.
Applications:
•Onlyrecommendedforcleanair
streamscontainingnocondensable
fumesorvapours.
•Acommonapplicationisaforced
draft.
Ankur Sachdeva, Assistant Professor, ME

63. Comparison of Characteristics of Backward
and Forward Curved Blade Fans
Ankur Sachdeva, Assistant Professor, ME
Forward-curved fans develop highest pressure for a given diameter and speed. They are also
available as high volume flow fans.

64. Ankur Sachdeva, Assistant Professor, ME
Backward-curved fans are commonly used in air conditioning.
However, a backward-curved fan must run at a higher speed to develop the same pressure as a
forward-curved fan. Accordingly, forward-curved fans are smaller and slower running. Thus
they tend to be quieter and cheaper for FTP up to 750 N/m
2
Comparison of Characteristics of Backward
and Forward Curved Blade Fans

65. Axial Flow Fans
•Airispressurizedbybladeswhichcreate
aerodynamiclift.
•Typicallyprovidelargeairvolumesatrelatively
lowpressuresrangingfrom250mmwcto500
mmwc.
•Efficiencyvariesfrom45%-85%.
•Popularintheindustryascompact,low-cost,and
lightweight.
•Axialfansarefrequentlyusedinexhaust
applicationswithsmallairborneparticulatesizes,
suchasduststreams,smoke,andsteam.
•Itiscategorizedas,
1.PropellorAxialFan
2.TubeAxialFan
3.VaneAxialFan
Ankur Sachdeva, Assistant Professor, ME

66. Propeller Axial Fans
Characteristics:
•Havetwoormorebladesthatgenerate
veryhighairflowvolumes
•Produceslowstaticpressure(20-50)
mmwc.
•Verylowefficienciesof
approximately50%.
•Lightweightandinexpensive.
•Noiselevelsarehigherthantubeaxial
andvaneaxialfan.
Applications:
•Aircirculationwithinaspaceor
ventilationthroughawallwithout
attachedductwork.
•Ideallyusedformakeupor
replacementairsupply.
Ankur Sachdeva, Assistant Professor, ME

67. Tube Axial Fans
Characteristics:
•Tube axial fans have a wheel inside a
cylindrical housing which improves the
air flow efficiency.
•Numbers of blades range from 4 to 8.
•Capable of developing a more useful
static pressure range(250-400 mmwc).
•Efficient up to 65 %.
Applications:
• Frequently used in exhaust applications.
• Also used in some industrial
applications such as drying ovens and
paint spray.
Ankur Sachdeva, Assistant Professor, ME

68. Vane Axial Fans
Characteristics:
•Vane-axialfansaresimilartotube-
axialfanswithguidevanesthat
improveefficiencybydirectingthe
flow.
•Typicallyhave5to20aerofoil-type
bladeswithalargehubdiameter.
•Suchfansaregenerallyusedfor
pressure(upto500mmwc).
•Theycanachieveefficienciesupto
85%.
Applications:
•Typicallyusedinhigh-pressure
applications,suchasinduceddraft
serviceforaboilerexhaust.
Ankur Sachdeva, Assistant Professor, ME

69. Tube Axial and Vane Axial Fans
Ankur Sachdeva, Assistant Professor, ME

70. Types of Fans, Characteristics and
their Applications
Ankur Sachdeva, Assistant Professor, ME

71. Blowers and their Types
•Blowerscanachievemuchhigherpressures
thanfans,ashighas1.20kg/cm
2
.
•Theimpelleristypicallygear-drivenand
rotatesasfastas15,000rpm.
•Theyarealsousedtoproducenegative
pressuresforindustrialvacuumsystems.
Types:
1.Centrifugalblowers
•Typicallyoperateagainstpressuresof0.35
to0.70kg/cm
2
.
•Theyaremostoftenusedinapplicationsthat
arenotpronetoclogging.
2.Positive-displacementblowers
•Theyareespeciallysuitableforapplications
pronetocloggingsincetheycanproduce
enoughpressureupto1.25kg/cm
2
-toblow
cloggedmaterials.
Ankur Sachdeva, Assistant Professor, ME

72. FAN CHARACTERISTICS
•Fancharacteristicscanberepresentedintheformoffancurve(s).
•Thefancurveisaperformancecurvefortheparticularfanunderaspecificsetof
conditions.
•Typicallyacurvewillbedevelopedforagivensetofconditionsusually
includingfanvolume,systemstaticpressure,fanspeed,efficiencyandbrake
horsepowerrequiredtodrivethefanunderthestatedconditions.
•Theintersectionofthesystemcurveandthestaticpressurecurvedefinesthe
operatingpoint.
•Whenthesystemresistancechanges,theoperatingpointalsochanges.
•Oncetheoperatingpointisfixed,thepowerrequiredcouldbefoundby
followingaverticallinethatpassesthroughtheoperatingpointtoanintersection
withthepower(BHP)curve.
•Ahorizontallinedrawnthroughtheintersectionwiththepowercurvewillleadto
therequiredpowerontherightverticalaxis

73. FAN CHARACTERISTICS
Ankur Sachdeva, Assistant Professor, ME
•Therequiredfanworkcanbecalculatedby
knowingtheflowrateandfantotalpressure
usingthefollowingequationandincludingthe
fanefficiencyinit.
•Point A on the fan total pressure-volume flow curve
represents the condition of the open inlet and outlet.
•At this point FSP = 0 and FTP = FVP
•It is seen that as Qdecreases, FTP increases.
•IntermsofthediameterDandspeedNofthe
fan,itisseenthatthefantotalpressure,FTPor
pTisproportionaltothedensityandsquareofthe
velocity,whichinturnisproportionaltothe
productDN.Thus
•Sucharelationcanalsobeobtainedby
dimensionalanalysis.Thevolumeflowrateis
proportionaltothefanareaandvelocity.

74. Fan Arrangement
•Thefanarrangementsarestandardizedforthedrive,rotation,motorposition,
suctionanddischarge.
•Thus,therecanbeabeltordirectdriveandbearingsononesidewiththe
wheeloverhungorbearingsonbothsides.
•Therotationmaybeclockwiseorcounter-clockwise.
•Thedischargemaybetophorizontalorbottomhorizontal,
•upblastordownblast,topangulardownorup,orbottomangulardownorup.
•Thesuctioniscommonlyfromonesidebutmaybefrombothsidesalso.
•Further,amultiplenumberoffansmaybeused.
•Thearrangementforthepurposewillbeeitherinseriesorinparallel.
Ankur Sachdeva, Assistant Professor, ME

75. Fans in Series
•Whentwofansareemployedinaseries,
•TheflowrateQthrougheachfanisthesame,and
•(ii)TheoverallfantotalpressurepTisequaltothe
sumofindividualFTPsminusthelossesinthe
connections.
•Thecombinedcharacteristicoftwofansinaseries
can,therefore,bedrawnbyaddingtheFTPofeach
fanforeachQasshowninFig.
•Toobtainthecombinedcharacteristic,itisassumed
thatthecharacteristicofeachfanisknownfor
volumesgreaterthanthosethatareachievedbyfans
whenrunningwithsuctionanddischarge
unconnectedtothesystem.Thisinformationis
rarelyavailable.
•Thecharacteristicinthisregionmaybeextrapolated
asshowninFig.
•Further,itispreferabletouseidenticalfanunitsin
seriesasitisunlikelythatefficientoperationwould
resultotherwise.
Ankur Sachdeva, Assistant Professor, ME

76. Fans in Parallel
•When two fans are employed in parallel,
(i) The total pressure pTacross each fan is the same,
and
(ii) The total volume handled Q is equal to the sum of
the volumes handled by individual fans.
•Thecombinedcharacteristicoftwofansinparallel
can,therefore,bedrawnbyaddingQofeachfan
forthesamepTasshowninFig.
•Again,inordertodrawthiscombined
characteristicinfull,itisnecessarytoknowthe
reverse-flowcharacteristicofoneofthefanswith
theimpellerrunninginthenormaldirectionwhich
isnormallynotknown.
Ankur Sachdeva, Assistant Professor, ME

77. Suction line, Discharge line and
Liquid line
Ankur Sachdeva, Assistant Professor, ME

78. HVAC Piping
HVACpipingorheatingventilationandair-conditioningpipingdelivershot
water,coolwater,refrigerant,condensate,steam,andgastoandfromtheHVAC
components.
HVACSystemsprovidethermalcomfortfortheoccupantsaccompaniedby
indoorairquality.Theyareusedinindustrial,commercial,residential,and
institutionalbuildingsfordifferentpurposeslike
•To add or remove heat from the air inside the building.
•Control the humidity.
•Filter the air in the building.
•Bring fresh air into the building.
Ankur Sachdeva, Assistant Professor, ME

79. Types of HVAC Pipingand Material Used
Ankur Sachdeva, Assistant Professor, ME
•HVACPipingsystemcanbeclassifiedintotwoparts;thepipinginthecentral
plantequipmentroomandthedeliverypiping.
•Thecentralplantequipmentroomconsistsofthepipenetworksconnectedto
therotatingequipmentandtanks.
•Theyareconnectedtodifferenttypesofequipmentlikeheatexchangersand
pumpsoverthepumproomfromtheseregionsthepipingnetworktransportsthe
processliquidtotheotherpartsofthebuildingusingthedeliverypiping.
•Theeffectivenessofthepipingisinfluencedbythematerialsusedtomakeit.
CopperandsteelarethetwomajortypesofmetalsusedforHVACpiping.
•Copperisusedmostlyforsmallerpiping,andtransportingwaterinACunitsas
theuseofcopperisveryexpensivethanthatofothermaterialsavailable.
•Steelontheotherhandismuchcheaperandisusedforlargesizes.Itcanalso
withstandhigherpressurethancopperandisidealforbothhotandcoldwater.It
usuallyallowsforarangeoftemperaturesandpressure

80. Noise and Vibration in HVAC
•Thebuilding'sHVACsystemcanmanuallyorintelligentlycontrolthe
comfortofthehumanlivingenvironmentinthebuilding.
•TheequipmentoftheHVACsystemgeneratesacertainamountofvibration
andnoiseduetothemechanicaloperationduringoperation,whichaffectsthe
comfortofhumanlivingandthestructuralstabilityofthebuilding.
•Inbuildingstructuredesign,themaindesigntypesaredividedintoseismic
design,durabilitydesign,andfatiguedesign.
•Inthedesignprocessofpreventionandcontrolofcommonproblemsin
buildings,themaincommonproblemisvibration.
•Theshapeandfrequencyofvibrationgeneratedbyequipmentandhuman
activitiesinthebuildingwilldamagethebuilding.
•ThedesignoftheHVACsystemfullyconsidersthestructureofthebuilding,
thecharacteristicsoftheequipment,thefrequencyofuseoftheequipment,
andtheformandstabilityofvibration.
•Thesearethemainsourcesofnoiseandvibrationinthedesignprocessand
arenecessarytoensurethesafetyofthesystem.
•Atthesametime,itprovidespeoplewithacomfortablelivingenvironment.
Ankur Sachdeva, Assistant Professor, ME

81. •Thenoiseandvibrationofthebuilding'sHVACsystemaremainlycausedby
airconditioningterminals,suchasairconditioningunits,circulatingwater
pumps,coolingtowers,fans,andairconditioningwindowcabinets.
•Thesetypesofequipmentarepronetonoiseandvibrationduringuse.
•Whentheimpactofnoiseandequipmentvibrationindecibelsexceedsthe
allowablelimit,itwillaffectpeople'scomfort,andthenoiseandvibrationof
thebuilding'sheating,ventilation,andair-conditioningsystemwillhavea
significantimpactonpeople'sproductionandlife.
•Atthesametime,continuousvibrationcancausepermanentdamagetothe
equipment,reducetheefficiencyoftheequipment,andshortenitsservicelife.
•Inaddition,thenoiseandvibrationofthebuilding'sHVACsystemwill
increasethecostofsubsequentmaintenance.
•Therefore,thepersonnelinvolvedinthedesignandconstructionshouldpay
closeattentiontothenoiseandvibrationofthebuilding'sHVACsystem
Ankur Sachdeva, Assistant Professor, ME
Origin & Effects of NoiseandVibration

82. Noise and Vibration Control
•VibrationisthesourceofnoisefromHVACsystems,managementofthose
conditionsisimperativetoaquietdesign.
•Systemdesignthatneglectstoproperlyaddressvibrationmayresultin
malfunctioningcomponents,noise,and,insomecases,catastrophicfailure.
•Therearetwofacetsofvibrationmanagement:isolationanddamping.
•Isolationisthepreventionofvibrationfromenteringthesystemand
dissipatingitbychangingkineticenergyofvibrationintoadifferentformof
energy,suchasheat.
•Vibrationisolationsystemsformechanicalcomponentsrequiresomeamount
ofdamping.
•Dampingdissipatesmechanicalenergyfromthesystemandattenuates
vibrationsmorequickly.
•Withoutdamping,thesesystemsmayvibrateforsometimebeforecomingto
rest.
•Thefluidinautomotiveshockabsorbersisakindofdamper,asisthe
inherentdampinginelastomeric(rubber)equipmentmounts.
Ankur Sachdeva, Assistant Professor, ME

83. Basic Elements of HVAC Control
In simplest terms, the control is defined as the starting, stopping, or regulation of
heating, ventilating, and air conditioning systems.
Controlling an HVAC system involves three distinct steps:
1)Measure a variable and collect data
2)Process the data with other information
3)Cause a control action
Elements ofHVACControls
AnHVACcontrolsystem,fromthesimplestroomthermostattothemost
complicatedcomputerizedcontrol,hasfourbasicelements:sensor,controller,
controlleddeviceandsourceofenergy.
1)Sensormeasuresactualvalueofcontrolledvariablesuchastemperature,
humidityorflowandprovidesinformationtothecontroller.
2)Controllerreceivesinputfromsensor,processestheinputandthenproduces
intelligentoutputsignalforcontrolleddevice.
3)Controlleddeviceactstomodifycontrolledvariableasdirectedbycontroller.
4)Sourceofenergyisneededtopowerthecontrolsystem.Controlsystemsuse
eitherapneumaticorelectricpowersupply
Ankur Sachdeva, Assistant Professor, ME

84. Ankur Sachdeva, Assistant Professor, ME