This document provides an introduction to HVAC systems. It discusses the primary functions of HVAC systems to provide healthy and comfortable interior conditions while minimizing energy usage and emissions. It describes different types of HVAC systems including air systems, hydronic/steam systems, and unitary systems. It also discusses key HVAC components like air handling units, fans, pumps, ductwork, controls and their purposes.

1. HVAC Systems – UnderstandingHVAC Systems – Understanding
the basisthe basis
Table of ContentsTable of Contents
1.1. Introduction to HVAC SystemsIntroduction to HVAC Systems
2.2. HVAC System TypesHVAC System Types
3.3. HVAC Piping SystemHVAC Piping System
4.4. HVAC Air Distribution EquipmentsHVAC Air Distribution Equipments
5.5. Fans and PumpsFans and Pumps
6.6. HVAC Instrumentation and ControlHVAC Instrumentation and Control
7.7. HVAC System CommissioningHVAC System Commissioning

2. Introduction to HVAC SystemsIntroduction to HVAC Systems
 This article introduces the heating, ventilating and air-conditioningThis article introduces the heating, ventilating and air-conditioning
(HVAC) systems. The primary function of HVAC systems is to provide(HVAC) systems. The primary function of HVAC systems is to provide
healthy and comfortable interior conditions for occupants; well-healthy and comfortable interior conditions for occupants; well-
designed, efficient systems do this with minimal non-renewabledesigned, efficient systems do this with minimal non-renewable
energy and air, and water pollutant emissions.energy and air, and water pollutant emissions.

3. Introduction to HVAC SystemsIntroduction to HVAC Systems
 The purpose ofThe purpose of HVAC designHVAC design is both high indoor air quality and energyis both high indoor air quality and energy
efficiency. These dual considerations require an integrated designefficiency. These dual considerations require an integrated design
approach. Rigs heating,approach. Rigs heating,
ventilation, and air conditioningventilation, and air conditioning
system (HVAC) creates a climatesystem (HVAC) creates a climate
that allows for maximum comfort bythat allows for maximum comfort by
compensating for changing climaticcompensating for changing climatic
conditions.conditions.
 Though more costly to install and more complicated to operate, a chiller plantThough more costly to install and more complicated to operate, a chiller plant
offers a number of benefits over a large number of individual packagedoffers a number of benefits over a large number of individual packaged
cooling units, including greater energy efficiency, better controllability,cooling units, including greater energy efficiency, better controllability,
cheaper overall maintenance, and longer life. Using a comprehensivecheaper overall maintenance, and longer life. Using a comprehensive
approach to building design, designers around the world have succeeded atapproach to building design, designers around the world have succeeded at
creating highly efficient air-conditioning systems that provide excellentcreating highly efficient air-conditioning systems that provide excellent
comfort at significant savings.comfort at significant savings.

4. Introduction to HVAC SystemsIntroduction to HVAC Systems
 Heating, ventilating and air-Heating, ventilating and air-
conditioning (HVAC) systemsconditioning (HVAC) systems
reduce the environmentalreduce the environmental
impact of rigs/buildings in severalimpact of rigs/buildings in several
key ways. The most importantkey ways. The most important
function of a HVAC systems isfunction of a HVAC systems is
to provide the rig/buildings occupantsto provide the rig/buildings occupants
with healthy and comfortable interiorwith healthy and comfortable interior
conditions. A carefully designed, efficientconditions. A carefully designed, efficient
system can do this with minimal non-system can do this with minimal non-
renewable energy and air and water pollutant emissions to minimize therenewable energy and air and water pollutant emissions to minimize the
environmental impact.environmental impact.
Cooling equipment that avoids chlorofluorocarbons and hydro-Cooling equipment that avoids chlorofluorocarbons and hydro-
chlorofluorocarbons (CFCs and HCFCs) eliminates a major cause ofchlorofluorocarbons (CFCs and HCFCs) eliminates a major cause of
damage to the ozone layer.damage to the ozone layer.

5. Introduction to HVAC SystemsIntroduction to HVAC Systems
 Even the best HVAC equipment and systems cannot compensate for aEven the best HVAC equipment and systems cannot compensate for a
faulty rig design. Problems of this type cause inherently high cooling andfaulty rig design. Problems of this type cause inherently high cooling and
heating needs and consume unnecessary resources and should beheating needs and consume unnecessary resources and should be
corrected if possible. Conservation of non-renewable energy through ancorrected if possible. Conservation of non-renewable energy through an
intelligent architectural design offers the greatest opportunity for savings.intelligent architectural design offers the greatest opportunity for savings.
The most important factors in these designs are careful control of solar gain,The most important factors in these designs are careful control of solar gain,
while taking advantage of passive heating, daylighting, natural ventilationwhile taking advantage of passive heating, daylighting, natural ventilation
and cooling. The critical factors in mechanical systems' energy consumptionand cooling. The critical factors in mechanical systems' energy consumption
- and capital cost - are reducing the cooling and heating loads they must- and capital cost - are reducing the cooling and heating loads they must
handle.handle.

6. HVAC System TypesHVAC System Types
 Types of System Designs - There are several major heating, ventilating, and airTypes of System Designs - There are several major heating, ventilating, and air
conditioning system types in wide spread use today. These are air systems, hydronicconditioning system types in wide spread use today. These are air systems, hydronic
and steam systems, and unitary type systems. Most systems in use today fall into one ofand steam systems, and unitary type systems. Most systems in use today fall into one of
these categories, or are a combination or variation of them. Each type of system hasthese categories, or are a combination or variation of them. Each type of system has
advantages and disadvantages.advantages and disadvantages.
 Air cooledAir cooled
-- Air cooledAir cooled ChillersChillers

10.  Air Cooled Chiller AdvantagesAir Cooled Chiller Advantages
• Lower installed costLower installed cost
• Quicker availabilityQuicker availability
• No cooling tower or condenser pump requiredNo cooling tower or condenser pump required
• Less maintenanceLess maintenance
• No mechanical room requiredNo mechanical room required

11.  Water CooledWater Cooled
- Sea Water cooled Chillers- Sea Water cooled Chillers
- Fresh Water cooled Chillers- Fresh Water cooled Chillers

13.  Water-Cooled Chiller advantagesWater-Cooled Chiller advantages
• Higher efficiencyHigher efficiency
• Custom selection in larger sizesCustom selection in larger sizes
• Large tonnage capabilitiesLarge tonnage capabilities
• Indoor Chiller locationIndoor Chiller location
• Longer lifeLonger life

14. Purpose of an air handling systemPurpose of an air handling system
Air Handling
System
Room
With
Defined
Requirements
Supply
Air
Outlet
Air
Air Handling Systems

15. Objectives
In the following slides, we will study the components of
air handling systems in order to:
1. Become familiar with the components
2. Know their functions
3. Become aware of possible problems

16. +
Room/Cabin
Exhaust air treatment
Central air handling unit
Terminal air treatment
at production room level
Fresh air treatment
(make-up air)
Main subsystems

17. FilterSilence
r
Terminal filter
Weather louvre Control damper
FanFlow rate controller
Humidifier
Heating
coil
Cooling
coil
with
droplet
separator
Production Room
Overview components
+
Prefilter
Exhaust Air Grille
Heater
Secondary Filter
Re-circulated
air

18.  WeatherWeather
louvrelouvre
 SilencerSilencer
 Flow rateFlow rate
controllercontroller
 ControlControl
damperdamper
 To prevent insects, leaves,To prevent insects, leaves,
dirtdirt and rainand rain from enteringfrom entering
 To reduce noise caused by airTo reduce noise caused by air
circulationcirculation
 Automated adjustment ofAutomated adjustment of
volume of air (night and day,volume of air (night and day,
pressure control)pressure control)
 Fixed adjustment of volumeFixed adjustment of volume
of airof air
Components (1)

19.  Heating unitHeating unit
Cooling unitCooling unit
/dehumidifier/dehumidifier
HumidifierHumidifier
FiltersFilters
DuctsDucts
 ToTo heatheat the air to the properthe air to the proper
temperaturetemperature
 ToTo coolcool the air to thethe air to the requiredrequired
temperaturetemperature or to remove moistureor to remove moisture
from the airfrom the air
 To bring the air to the properTo bring the air to the proper
humidity, if too lowhumidity, if too low
 To eliminate particles of pre-To eliminate particles of pre-
determined dimensions and/ordetermined dimensions and/or
micro-organismsmicro-organisms
 To transport the airTo transport the air
Components (2)

20. +
Production Room
Exhaust
air
Return air
(re-circulated)
Fresh air
(make-up air)
Supply
air
Air types

21. Filter classesFilter classes
Dust filters
Standard Aerosol
FineCoarse ULPAHEPA
10 µ m > Dp > 1 µ mDp > 10 µ m Dp < 1 µ m
F5 - F9G1 - G4 U 14- 17H 11 - 13
EN 1822 StandardEN 779 Standard

22. Primary panelPrimary panel
filterfilter
SecondarySecondary
filterfilter
HEPA or tertiaary filter

23. Duct heatersDuct heaters Room HetersRoom Heters
SilensersSilensers

24. Volume control damperVolume control damper
De-humidification
Filter Pressure
Gauges
AHU with fan
Variable Speed
Controller
Humid room air
Air heater
Regeneration air
Humid room air
Adsorber wheel Dry air
FireFire DampersDampers

25. Annex 1, 17.26
Regulation of room pressureRegulation of room pressure – pressure– pressure
differentials conceptdifferentials concept
Room pressure
gauges
Room pressure indication panel

26. Pressure cascade injectablesPressure cascade injectables
PProtection from micro-organisms androtection from micro-organisms and
particlesparticles
N o te : D ir e c t io n o f d o o r o p e n in g r e la t iv e to r o o m p r e s s u r e
1 5 P a
0 P a
A ir
L o c k
3 0 P a P a s s a g eD
C
A
B
D
L F
A ir L o c kA ir L o c k
4 5 P a
R o o m 3R o o m 2R o o m 1
4 5 P a6 0 P a3 0 P a

27. Pressure cascade solids
Protection from cross-contamination
Note:Directionofdooropeningrelativetoroompressure 15Pa
15Pa15P aE
30PaPassage 0PaAirLock
Room3Room2Room115Pa
AirLockAirLock
N o t e : D i r e c t i o n o f d o o r o p e n i n g r e l a t i v e t o r o o m p r e s s u r e
1 5 Pa
1 5 Pa1 5 Pa
E3 0 Pa
P a s s a g e
0 Pa
A ir
L o c k
R o o m 3R o o m 2R o o m 1
1 5 Pa
A ir L o c kA ir L o c k

32. Fan Coil UnitFan Coil Unit

33. Self Contain UnitSelf Contain Unit

34. HVAC Air Distribution EquipmentsHVAC Air Distribution Equipments
 DiffusersDiffusers
4 Way Diffusers4 Way Diffusers Two Way Diffusers One Way DiffuserTwo Way Diffusers One Way Diffuser
Round DiffusersRound Diffusers

35. Cabin UnitsCabin Units

36.  Return / Exhaust GrillesReturn / Exhaust Grilles

37. ContentsContents
 Fan DesignFan Design
 Fan PerformanceFan Performance
 Fan-duct SystemsFan-duct Systems
 Duct ConstructionDuct Construction
 Air Duct DesignAir Duct Design
Fans and Pumps

38. Fan DesignFan Design
 Common types of fansCommon types of fans

Centrifugal fansCentrifugal fans: radial, forward curved, air: radial, forward curved, air
foil (backward curved), backward inclined,foil (backward curved), backward inclined,
tubular, roof ventilatortubular, roof ventilator

Axial fansAxial fans: propeller, tube-axial, vane-axial: propeller, tube-axial, vane-axial
 Fan arrangementsFan arrangements

Motor location, air discharge orientation, driveMotor location, air discharge orientation, drive
train type (direct drive or pulley drive)train type (direct drive or pulley drive)

Centrifugal: single width single inlet (SWSI),Centrifugal: single width single inlet (SWSI),
double width double inlet (DWDI)double width double inlet (DWDI)

39. Centrifugal and axial fan components
AXIAL FANSCENTRIFUGAL FANS

40. Propeller Tube-axial
Tube-vane
AXIAL FANS

41. Tubular centrifugal fan Centrifugal roof ventilator
CENTRIFUGAL FANS
(* Note the airflow paths and impeller design.)

42. Drive arrangements and motor positions

43. Single- and double-width centrifugal fans

44. Fan PerformanceFan Performance
 Major parametersMajor parameters
 Fan volume flow rate (mFan volume flow rate (m33
/s or l/s),/s or l/s), VVff
 Fan total pressureFan total pressure ΔΔpptftf, fan velocity pressure, fan velocity pressure
ppvfvf & fan static pressure& fan static pressure ΔΔppsfsf (Pa)(Pa)

Fan power & efficiencyFan power & efficiency
• Fan power or air power (W) =Fan power or air power (W) = ΔΔpptftf xx VVff
• Fan power input on the fan shaft (brakeFan power input on the fan shaft (brake
horsepower),horsepower), PPff
• Fan total efficiency:Fan total efficiency: ηηtt == ΔΔpptftf xx VVff // PPff

Combined aerodynamic, volumetric & mechanicalCombined aerodynamic, volumetric & mechanical
efficienciesefficiencies
• Fan static efficiency:Fan static efficiency: ηηss == ΔΔppsfsf xx VVff // PPff
• Air temp. increase through fan,Air temp. increase through fan, ΔΔTT == ΔΔpp /(/(ρρcc ηη))

45. Fan performance curves
Total pressure
Static pressure
Fan total efficiency
Fan static efficiency
Fan power input
Velocity pressure
Volume flow rate

46. Typical fan performance curve

47. Fan PerformanceFan Performance
 Fan LawsFan Laws

Speed (Speed (nn))

Volume flow (Volume flow (VV))

Total pressure lossTotal pressure loss
((ΔΔpp ))

Air density (Air density (ρρ))

For air systems thatFor air systems that
are geometrically &are geometrically &
dynamically similar:dynamically similar:
(D = impeller(D = impeller
diameter)diameter)
 c.f.: pump lawsc.f.: pump laws

48. Velocity triangle at the blade inlet and outlet of a centrifugal fan
CENTRIFUGAL FANS

49. Fan PerformanceFan Performance
 Major issues causing energy losses to aMajor issues causing energy losses to a
centrifugal fan:centrifugal fan:

Circulatory flow between the bladesCirculatory flow between the blades

Air leakage at the inletAir leakage at the inlet

Friction between fluid particles and the bladeFriction between fluid particles and the blade

Energy loss at the entranceEnergy loss at the entrance

Partially filled passagePartially filled passage

50. Operating characteristics for a backward-curved centrifugal fan

51. Total efficiency
curves for
centrifugal fans

52. Fan power curves for centrifugal fans with same impeller diameter

53. Fan pressure curves for centrifugal fans with same impeller diameter

54. Velocity triangles for a vane-axial fan
AXIAL FANS

55. Fan pressure curves for axial fans with same impeller diameter

56. Fan efficiency curves for axial fans with same impeller diameter

57. Fan power curves for axial fans with same impeller diameter

58. Performance
curves for
controllable-
pitch vane-axial
fans

59. Fan-duct SystemsFan-duct Systems
 Duct pressure changes (c.f. atmDuct pressure changes (c.f. atm
pressure)pressure)

Static pressure (SP)Static pressure (SP)

Velocity pressure (VP) =Velocity pressure (VP) = ρρVV22
/ 2 g/ 2 g

Total pressure (TP) = SP + VPTotal pressure (TP) = SP + VP
 Fan: a pumping deviceFan: a pumping device

Fan (total) pressure = pressure differenceFan (total) pressure = pressure difference
between fan inlet and fan dischargebetween fan inlet and fan discharge

At fan suction/inlet, SP = negative (c.f.At fan suction/inlet, SP = negative (c.f.
atmospheric); at discharge, SP = positiveatmospheric); at discharge, SP = positive

62. Fan-duct SystemsFan-duct Systems
 Pressure characteristicsPressure characteristics

SP and VP are mutually convertible (↑or↓)SP and VP are mutually convertible (↑or↓)

TP always decreases in the direction ofTP always decreases in the direction of
airflowairflow

For constant-area straight duct sectionsFor constant-area straight duct sections
• Velocity and VP are constantVelocity and VP are constant
• TP change = SP changeTP change = SP change

When duct cross-sectional areas are reducedWhen duct cross-sectional areas are reduced
• Velocity and VP increaseVelocity and VP increase
• Absolute value of both TP and SP decreaseAbsolute value of both TP and SP decrease
• Dynamic losses from elbow, dampers, etc.Dynamic losses from elbow, dampers, etc.

63. Fan-duct SystemsFan-duct Systems
 Fan-duct systemsFan-duct systems

Flow resistanceFlow resistance RR, pressure drop, pressure drop ΔΔpp andand
volume flow ratevolume flow rate VV

Duct sections in series:Duct sections in series:

Duct sections in parallel:Duct sections in parallel:
2
VRp ⋅=∆
o
ns RRRR +++= 21
np RRRR
1111
21
+++= 

64. Fan-duct SystemsFan-duct Systems
 Fan-duct systemsFan-duct systems

TerminologyTerminology
• Primary air (conditioned air or makeup air)Primary air (conditioned air or makeup air)
• Secondary air (induced space air, plenum air, orSecondary air (induced space air, plenum air, or
recirculating air)recirculating air)
• Transfer air (indoor air that moves from anTransfer air (indoor air that moves from an
adjacent area)adjacent area)

System curve: volume flow vs pressure lossSystem curve: volume flow vs pressure loss

System operating pointSystem operating point

65. Fan-duct SystemsFan-duct Systems
 System effectSystem effect ΔΔpptsts

Its additional total pressure loss caused byIts additional total pressure loss caused by
uneven or non-uniform velocity profile at theuneven or non-uniform velocity profile at the
fan inlet, or at duct fittings after fan outletfan inlet, or at duct fittings after fan outlet

Due to the actual inlet and outlet connectionsDue to the actual inlet and outlet connections
as compared with the total pressure loss of theas compared with the total pressure loss of the
fan test unit during laboratory ratingsfan test unit during laboratory ratings
Inlet Outlet

66. Fan system operating point & system effect

67. Fan-duct SystemsFan-duct Systems
 Modulation of air systemsModulation of air systems

Constant volume systemConstant volume system
• Volume flow rate remains constantVolume flow rate remains constant
• Supply temperature is raised during part loadSupply temperature is raised during part load

Variable-air-volume (VAV) systemVariable-air-volume (VAV) system
• Volume flow rate is reduced to match part loadVolume flow rate is reduced to match part load
operationoperation
• Modulation curveModulation curve

68. Fan modulation curve

69. Fan-duct SystemsFan-duct Systems
 Fan modulation methodsFan modulation methods

DamperDamper (vary the opening of the air flow(vary the opening of the air flow
passage)passage)
• Waste energyWaste energy

Inlet vanesInlet vanes (opening & angle of inlet vanes)(opening & angle of inlet vanes)
• Low cost; less efficient than following typesLow cost; less efficient than following types

Inlet coneInlet cone (peripheral area of fan impeller)(peripheral area of fan impeller)
• Inexpensive; for backward curved centrifugal fanInexpensive; for backward curved centrifugal fan

Blade pitchBlade pitch (blade angle of axial fan)(blade angle of axial fan)

Fan speedFan speed (using adjustable frequency(using adjustable frequency
drives)drives)
• Most energy-efficient; but usually cost moreMost energy-efficient; but usually cost more

70. Damper, inlet vanes & fan speed modulation

71. Inlet vane
modulation

72. Fan speed
modulation using
AC inverter

73. Fan-duct SystemsFan-duct Systems
 Fan surgeFan surge (in centrifugal fan)(in centrifugal fan)

Occurs when air volume flow is not sufficient toOccurs when air volume flow is not sufficient to
sustain the static pressure difference betweensustain the static pressure difference between
discharge & suctiondischarge & suction
• Discharge pressure is reduced momentarilyDischarge pressure is reduced momentarily
• Volume flow & pressure fluctuationsVolume flow & pressure fluctuations
• Create noise & vibrationCreate noise & vibration

Surge region: shall avoid operation in itSurge region: shall avoid operation in it
 Fan stallFan stall (in axial fans)(in axial fans)

When smooth air flow suddenly breaks & pressureWhen smooth air flow suddenly breaks & pressure
difference across the blades decreasesdifference across the blades decreases

The fan loses pressure capability drasticallyThe fan loses pressure capability drastically

74. Stall and stall region of an axial fan

75. Fan-duct SystemsFan-duct Systems
 Fan selectionFan selection

Select fan type + determine fan sizeSelect fan type + determine fan size

Important factors:Important factors:
• Pressure-volume flow operating characteristicsPressure-volume flow operating characteristics
• Fan capacity modulationFan capacity modulation
• Fan efficiencyFan efficiency
• Sound power levelSound power level
• Airflow directionAirflow direction
• Initial costInitial cost

77. Duct ConstructionDuct Construction
 Types of air ductTypes of air duct

Supply air ductSupply air duct

Return air ductReturn air duct

Outdoor air ductOutdoor air duct

Exhaust airExhaust air
 Duct sectionsDuct sections

Header or main duct (trunk)Header or main duct (trunk)

Branch duct or runoutBranch duct or runout

79. Duct ConstructionDuct Construction
 Duct systemsDuct systems

Max. pressure difference (between air insideMax. pressure difference (between air inside
the duct and the ambient air)the duct and the ambient air)
• 125, 250, 500, 750, 1000, 1500, 2500 Pa125, 250, 500, 750, 1000, 1500, 2500 Pa

Commercial buildingsCommercial buildings
• Low-pressure duct system: ≤ 500 Pa, max 12 m/sLow-pressure duct system: ≤ 500 Pa, max 12 m/s
• Medium-pressure system: 500-1500 Pa, max 17.5Medium-pressure system: 500-1500 Pa, max 17.5
m/sm/s

Residential buildings: 125 Pa or 250 PaResidential buildings: 125 Pa or 250 Pa

Industrial duct system:Industrial duct system: ΔΔP can be higherP can be higher

80. Duct ConstructionDuct Construction
 Duct material: e.g. UL (Underwriters’Duct material: e.g. UL (Underwriters’
Laboratory) standardLaboratory) standard

Class 0: zero flame spread, zero smokeClass 0: zero flame spread, zero smoke
developeddeveloped
• Iron, galvanized steel, aluminum, concrete,Iron, galvanized steel, aluminum, concrete,
masonry, clay tilemasonry, clay tile

Class 1: flame spread ≤ 25, smokeClass 1: flame spread ≤ 25, smoke
developed ≤ 50developed ≤ 50
• Fiberglass, many flexible ductsFiberglass, many flexible ducts

Class 2: flame spread ≤ 50, smokeClass 2: flame spread ≤ 50, smoke
developed ≤ 100developed ≤ 100

81. Duct ConstructionDuct Construction
 Shapes of air ductShapes of air duct

RectangularRectangular
• More easily fabricated on site, air leakageMore easily fabricated on site, air leakage

RoundRound
• Less fluid resistance, better rigidity/strengthLess fluid resistance, better rigidity/strength

Flat ovalFlat oval

FlexibleFlexible
• Multiple-ply polyester film w/ metal wire or stripsMultiple-ply polyester film w/ metal wire or strips
 SMACNA (Sheet Metal and AirSMACNA (Sheet Metal and Air
Conditioning Contractors’ NationalConditioning Contractors’ National
Association) standardsAssociation) standards

82. Rectangular duct Round duct w/ spiral seam
Flat oval duct Flexible duct
(Source: Wang, S. K., 2001. Handbook of Air Conditioning and Refrigeration)

83. Transverse joint reinforcement
(Source: Wang, S. K., 2001. Handbook of Air Conditioning and Refrigeration)

84. Duct ConstructionDuct Construction
 Duct specificationDuct specification

Sheet gauge and thickness of duct materialSheet gauge and thickness of duct material

Traverse joints & longitudinal seamTraverse joints & longitudinal seam
reinforcementsreinforcements

Duct hangers & their spacingDuct hangers & their spacing

Tapes & adhesive closuresTapes & adhesive closures

Fire spread and smoke developedFire spread and smoke developed

Site-fabricated or factory-/pre-fabricatedSite-fabricated or factory-/pre-fabricated

85. Duct ConstructionDuct Construction
 Duct heat gain or lossDuct heat gain or loss

Temperature rise or dropTemperature rise or drop

Duct insulation (mounted or inner-lined)Duct insulation (mounted or inner-lined)
• Reduce heat gain/loss, prevent condensation,Reduce heat gain/loss, prevent condensation,
sound attentuationsound attentuation
• Minimum & recommended thicknessMinimum & recommended thickness

See ASHRAE standard or local codesSee ASHRAE standard or local codes

Temperature rise curvesTemperature rise curves
• Depends on air velocity, duct dimensions &Depends on air velocity, duct dimensions &
insulationinsulation

86. Temperature rise from duct heat gain
(Source: Wang, S. K., 2001. Handbook of Air Conditioning and Refrigeration)

87. Duct ConstructionDuct Construction
 Frictional lossesFrictional losses

Darcey-Weisbach EquationDarcey-Weisbach Equation
• HHff = friction head loss, or= friction head loss, or ΔΔppff = pressure loss= pressure loss
• ff = friction factor (dimensionless)= friction factor (dimensionless)
• LL = length of duct or pipe (m)= length of duct or pipe (m)
• DD = diameter of duct or pipe (m)= diameter of duct or pipe (m)
• vv = mean air velocity in duct (m/s)= mean air velocity in duct (m/s)

88. Mode of airflow when air passes over and around
surface protuberances of the duct wall
δ >ε
δ <ε

89. Duct ConstructionDuct Construction
 Duct friction chartDuct friction chart

Colebrook formulaColebrook formula
 Roughness & temperature correctionsRoughness & temperature corrections
 ΔΔppff == KKsrsr KKTT KKelelΔΔppf,cf,c
• KKsrsr = correction factor for surface roughness= correction factor for surface roughness
• KKTT = correction factor for air temperature= correction factor for air temperature
• KKelel = correction factor for elevation= correction factor for elevation

90. Friction chart for round duct

92. Duct ConstructionDuct Construction
 Circular equivalentCircular equivalent
 Hydraulic diameter,Hydraulic diameter, DDhh = 4= 4 AA // PP
• AA = area (mm= area (mm22
);); PP = perimeter (mm)= perimeter (mm)

Rectangular duct:Rectangular duct:

Flat oval duct:Flat oval duct:

93. Duct ConstructionDuct Construction
 Dynamic lossesDynamic losses

Result from flow disturbances caused by duct-Result from flow disturbances caused by duct-
mounted equipment and fittingsmounted equipment and fittings
• Change airflow path’s direction and/or areaChange airflow path’s direction and/or area
• Flow separation & eddies/disturbancesFlow separation & eddies/disturbances

In dynamic similarity (same Reynolds numberIn dynamic similarity (same Reynolds number
& geometrically similar duct fittings), dynamic& geometrically similar duct fittings), dynamic
loss is proportional to their velocity pressureloss is proportional to their velocity pressure

94. Duct ConstructionDuct Construction
 Local or dynamic loss coefficientLocal or dynamic loss coefficient

Ratio of total pressure loss to velocityRatio of total pressure loss to velocity
pressurepressure

95. Duct ConstructionDuct Construction
 Duct fittingsDuct fittings

ElbowsElbows

Converging or diverging tees and wyesConverging or diverging tees and wyes

Entrances and exitsEntrances and exits

Enlargements and contractionsEnlargements and contractions
 Means to reduce dynamic lossesMeans to reduce dynamic losses

Turning angle, splitter vanesTurning angle, splitter vanes
 ASHRAE duct fitting databaseASHRAE duct fitting database

Fitting loss coefficientsFitting loss coefficients

97. Region of eddies and
turbulences in a round elbow 5-piece 90o
round elbow

98. Rectangular elbow, smooth radius, 2 splitter vanes
Mitered elbow and its secondary flow

99. Airflow through a
rectangular converging
or diverging wye

100. Entrance Exit

101. Abrupt enlargement Sudden contraction

102. Duct ConstructionDuct Construction
 Flow resistance,Flow resistance, RR
 Total pressure lossTotal pressure loss ΔΔpptt at a specific volume flowat a specific volume flow
raterate VV

Flow resistance in series:Flow resistance in series:

Flow resistance in parallel:Flow resistance in parallel:
2
VRpt
⋅=∆
ns RRRR +++= 21
np RRRR
1111
21
+++= 

103. Total pressure loss and flow resistance of a round duct section

104. Flow resistance in series
Flow resistance in parallel

105. Flow resistance for a Y connection

106. Air Duct DesignAir Duct Design
 Optimal air duct designOptimal air duct design

Optimal duct system layout, space availableOptimal duct system layout, space available

Satisfactory system balanceSatisfactory system balance

Acceptable sound levelAcceptable sound level

Optimum energy loss and initial costOptimum energy loss and initial cost

Install only necessary balancing devicesInstall only necessary balancing devices
(dampers)(dampers)

Fire codes, duct construction & insulationFire codes, duct construction & insulation
 Require comprehensive analysis & care forRequire comprehensive analysis & care for
different transport functionsdifferent transport functions

107. Flow characteristics of a supply duct system

108. Air Duct DesignAir Duct Design
 Design velocityDesign velocity

Constraints: space available, beam depthConstraints: space available, beam depth

Typical guidelines:Typical guidelines:
• Main ducts: air flow usually ≤ 15 m/s; air flow noiseMain ducts: air flow usually ≤ 15 m/s; air flow noise
must be checkedmust be checked
• With more demanding noise criteria (e.g. hotels),With more demanding noise criteria (e.g. hotels),
max. air velocity: main duct ≤ 10-12.5 m/s, returnmax. air velocity: main duct ≤ 10-12.5 m/s, return
main duct ≤ 8 m/s, branch ducts ≤ 6 m/smain duct ≤ 8 m/s, branch ducts ≤ 6 m/s

Face velocities for air-handling systemFace velocities for air-handling system
componentscomponents

110. Air Duct DesignAir Duct Design
 Reduce dynamic losses of the critical pathReduce dynamic losses of the critical path

Maintain optimum air velocity through ductMaintain optimum air velocity through duct
fittingsfittings

Emphasize reduction of dynamic lossesEmphasize reduction of dynamic losses
nearer to the fan outlet or inlet (high airnearer to the fan outlet or inlet (high air
velocity)velocity)

Proper use of splitter vanesProper use of splitter vanes

Set 2 duct fittings as far apart as possibleSet 2 duct fittings as far apart as possible
 Air duct leakageAir duct leakage

Duct leakage classificationDuct leakage classification
• AISI, SMACNA, ASHRAE standardsAISI, SMACNA, ASHRAE standards

111. Air Duct DesignAir Duct Design
 Fire protectionFire protection

Duct material selectionDuct material selection

Vertical ducts (using masonry, concrete orVertical ducts (using masonry, concrete or
clay)clay)

When ducts pass through floors & wallsWhen ducts pass through floors & walls

Use of fire dampersUse of fire dampers

Filling the gaps between ducts & bldgFilling the gaps between ducts & bldg
structurestructure

Duct systems for industrial applicationsDuct systems for industrial applications
 Any other fire precautions?Any other fire precautions?

112. Air Duct DesignAir Duct Design
 Design procedure (computer-aided or manual)Design procedure (computer-aided or manual)

Verify local codes & material availabilityVerify local codes & material availability

Preliminary duct layoutPreliminary duct layout

Divide into consecutive duct sectionsDivide into consecutive duct sections

Minimise local loss coefficients of duct fittingsMinimise local loss coefficients of duct fittings

Select duct sizing methodsSelect duct sizing methods

Critical total pressure loss of tentative critical pathCritical total pressure loss of tentative critical path

Size branch ducts & balance total pressure atSize branch ducts & balance total pressure at
junctionsjunctions

Adjust supply flow rates according to duct heat gainAdjust supply flow rates according to duct heat gain

Resize duct sections, recalculate & balance parallelResize duct sections, recalculate & balance parallel
pathspaths

Check sound level & add necessary attenuationCheck sound level & add necessary attenuation

113. Air Duct DesignAir Duct Design
 Duct layoutDuct layout

Symmetric layout is easier to balanceSymmetric layout is easier to balance
• Smaller main duct & shorter design pathSmaller main duct & shorter design path

For VAV systems, duct looping allows feedFor VAV systems, duct looping allows feed
from opposite directionfrom opposite direction
• Optimise transporting capacity (balance pointsOptimise transporting capacity (balance points
often follow the sun’s position)often follow the sun’s position)
• Result in smaller main ductResult in smaller main duct

Compare alternative layouts & reduce fittingsCompare alternative layouts & reduce fittings

For exposed ducts, appearance & integrationFor exposed ducts, appearance & integration
with the structure is importantwith the structure is important

114. Typical supply duct system with symmetric layout & looping

115. Air Duct DesignAir Duct Design
 Duct linerDuct liner

Lined internally on inner surface of duct wallLined internally on inner surface of duct wall

Mainly used for noise attenuation & insulationMainly used for noise attenuation & insulation

Fiberglass blanket or boardsFiberglass blanket or boards
 Duct cleaningDuct cleaning

Prevent accumulation of dirt & debrisPrevent accumulation of dirt & debris

Agitation device to loosen the dirt & debrisAgitation device to loosen the dirt & debris

Duct vacuum to extract loosened debrisDuct vacuum to extract loosened debris

Sealing of access openingsSealing of access openings

116. Duct breakout noise

117. HVAC Piping SystemHVAC Piping System

118. HVAC Instrumentation and ControlHVAC Instrumentation and Control

119. HVAC System CommissioningHVAC System Commissioning
 The key elements of commissioning include:The key elements of commissioning include:
 Installation checks.Installation checks. Check installed equipment to ensure that all associatedCheck installed equipment to ensure that all associated
components and accessories are in place.components and accessories are in place.
 Operational checks.Operational checks. Verify and document that systems are performing as expected,Verify and document that systems are performing as expected,
and that all sensors and other system control devices are properly calibrated.and that all sensors and other system control devices are properly calibrated.
 Documentation.Documentation. Confirm that all required documentation has been provided, such asConfirm that all required documentation has been provided, such as
a statement of the design intent and operating protocols for all building systems.a statement of the design intent and operating protocols for all building systems.
 O&M manuals and training.O&M manuals and training. Prepare comprehensive operation and maintenancePrepare comprehensive operation and maintenance
(O&M) manuals, and provide training for rig operations staff.(O&M) manuals, and provide training for rig operations staff.
 Ongoing monitoring.Ongoing monitoring. Conduct periodic monitoring after the school is occupied toConduct periodic monitoring after the school is occupied to
ensure that equipment and systems continue to perform according to design intent.ensure that equipment and systems continue to perform according to design intent.
 Correctly implemented, commissioning is extremely cost-effective, and shouldCorrectly implemented, commissioning is extremely cost-effective, and should
improve the delivery process, increase systems reliability, improve energyimprove the delivery process, increase systems reliability, improve energy
performance, ensure good indoor environmental quality, and improve operation andperformance, ensure good indoor environmental quality, and improve operation and
maintenance of the facility.maintenance of the facility.