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  • 1. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-0. Duct (Types)5-3.. Duct (Shapes of Air Duct)5-3.. Flexible Connection Flexible Duct5-3.. Vertical Duct and Horization Duct5-4.. Supply Air Duct Return Air Duct and Outdoor Air Duct5-4.. Duct Layout5-5. Duct System (Classification)5-6. Duct (Duct Construction)5-8.. (Ductwork Materials)5-12.. Duct Seal5-13.. Duct (External Insulation)5-16.. Duct (Internal Insulation)5-16.. Access Doors5-17.. Duct Test Holes5-18.. Duct fittings5-18. Duct Support Hanger5-19. Duct Properties5-20.. Duct Heat Gain Duct Heat Loss5-20.. Aspect Ratio21.. (Sound Control)5-22.. (Duct leakage)5-24.. SMACNA Ductwork Testing5-25. Duct (Sizing)5-25.. Duct (Sizing)5-26.. (Friction Losses in Duct)5-28.. Head and Pressure5-28.. Friction Chart (Pressure Drop)5-31.. Calculation for Duct Static Pressure Loss by Formula5-33. Duct (Duct Design)5-37.. Design (information)5-37.. Duct Design Criteria5-39.. Design Procedure5-39. Fire Damper5-41.. Fire Compartment5-41.. Fire Damper5-42.. Fire damper5-43. Control Dampers5-44.. ( ) Two Position Duty5-48.. ( ) Capacity Control Duty5-51.. () Mixing duty5-54. Flexible Connection Flexible Duct5-10.. Air pattern5-56.. Diffuser (Air Diffusers)5-60.. Diffuser Characteristic Length5-62.. (Air Outlet) (Noise Level)5-62.. Plenum Slot Diffuser5-63. Duct cleaning5-63AIR DISTRIBUTION SYSTEMS

2. Chapter-5 Air Distribution Systemswww.acmv.org 5-1Chapter-5 Air Distribution Systems- Air Distribution SystemAir Conditioning and Mechanical Ventilation System Mechanical Ventilation (fresh air) (exhaust air) duct SystemDuct velocity duct Duct velocity (velocity) (pressure drop) (noise) (vibration) (velocity) duct ductDuctArea(A) (round) duct (rectangular)ductIP [square feet(ft2) SI [Square meters(m2)]Duct (volume flow rate)(flow) IP Cubic Feet per Minute(CFM) SI Cubic Meters per Second(CMS) Duct velocity IP Feet per Minute(FPM) SI (Metric) Meters per Sec (m/s) 3. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-2Velocity Velocity PressureWhere:VP = Velocity Pressure, inches of water (inch wg)V = Velocity, feet per minute (FPM)Frictional Lossesduct (fluid viscosity) turbulence flow duct (fr (pressure losses) Frictional LossesDynamic LossesElbow reducer transformation duct fitting (direction) (area) flow disturbances Dynamic Loss y m L (pressure losses)Duct Terms- (duct terms)Main Duct (Trunk)F F mBranch ductsB h Duct fittingsMain duct(trunk b h duct fitting (tAir Distribution Devices air distribution devices 4. Chapter-5 Air Distribution Systemswww.acmv.org 5-3. Duct (Types).. Duct (Shapes of Air Duct)Duct Duct (Round) DuctOval duct() Airflow Characteristics() Flexible duct() Air Con ductinsulation (Rectangular)Duct( (space saver)( (flexible duct)() insulationInsulatedflexibleduct( -() (installation)() (labor cost)() Metal duct() Airflow (pressure drop)() (sharp bend)Round Duct Oval Duct(automatic spiral) (round)duct (oval duct) (galvanized steel sheet) (duct length) Oval duct Major Axis(duct width, A) Minor Axis (duct depth, B) American Society of Heating, Refrigerating and Air- Conditioning (ASHRAE) Sheet Metal and Air Conditioning Contractors' National Association(SMACNA)- Oval duct- Round duct- Round duct.. Flexible Connection Flexible DuctFan (vibration) duct (transmission) fan duct fexible connection Duct (vibration) diffuser ceiling (isolation)Round duct 5. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-4metal duct diffuser flexible connector flexible ductF material (flame retardant fabric) (flame spread rating) () (smoke developed rating) () NEPA N .255 ST E84 W L S Flexible connection (air tight) flexible duct.. Vertical Duct and Horization Ductduct (vertical) duct (horization)duct.. Supply Air Duct Return Air Duct and Outdoor Air Ductduct S y Air Duct(s y supply air duct Positive pressure duct R Air Duct(r return air duct Negative pressure duct O Air Duct(outdoor) outdoor air duct E h Air Ductexhaust airDuct (Size) (Sheet Thickness)Duct (size) (sheet thickness)Ventilation DuctMaximum Size of DuctSheet Metal Thickness ( )460 mm0.56 mm (gauge)461 mm 1070 mm0.71 mm1070 mm 1530 mm0.91 mm1531 mm 2150 mm1.22 mm2151 mm1.22 mm 6. Chapter-5 Air Distribution Systemswww.acmv.org 5-5Air Conditioning DuctMaximum Size of DuctSheet Metal Thickness( )300 mm0.46 mm301 mm 760 mm0.56 mm761 mm 1400 mm0.71 mm1401 mm 2150 mm0.91 mm2151mm1.22 mm (round) duct (material thickness)Round Duct Nominal Diameter(G.I Sheet Thickness)205 mm0.6 mm (gauge)205 mm 760 mm0.8 mm760 mm 1020 mm1.0 mm1020 mm 1525 mm1.2 mmRound duct elbow center radius .5 m Vertical duct 2 m duct support- Flexible duct- Flexible duct.. Duct LayoutDuct layoutDuct layout ymmMain duct Duct (design pat)VAV system (duct loopingDuct fitting layout(exposed) duct (appearance) structure- Spide - Trunk and Branch 7. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-6- Perimeter Loop - Radial . Duct System (Classification)Duct system (velocity) (Pressure) duct system(velocity) L w V y System h Velocity Duct System Comfort air conditioning supply air velocity () (2500 feet per minute) L w V y Sy m 1200 FPM(feet per minute) 2200 FPM Supply air velocity 2500 FPM h V y Sy m- Round duct- Rectangular duct(pressure)(total pressure)Duct System Class(Pressure)(Velocity)Low pressure (Class I)3 in-wg 5 m wV y 0 m/Medium Pressure (Class II)3 6 in wg 5 m wV y 0 m/High Pressure (Class III)6 12 in wg static 5< 25 m wVelocity > 10 m/sDuct (air velocitiy)()duct duct 8. Chapter-5 Air Distribution Systemswww.acmv.org 5-7()(air velocity) (pressure drop) fan (power consumption) (operation cost)()(air velocitiy) (noise attenuator or silencer) (recommended air velocity)Recommended Maximum Duct Velocities for Low Velocity Systems (FPM)m m V y Duct Velocity) feet per minute(FPM)(Application)Controlling Factor Noise Generation Main DuctsControlling Factor Duct FrictionMain DuctsBranch DuctsSupplyReturnSupplyReturnResidences6001000800600600Apartments, Hotel Bedrooms Hospital Bedrooms10001500130012001000Private Offices, Directors Rooms, Libraries12002000150016001200Theatres Auditoriums800130011001000800General Offices, High Class Restaurants, High Class Stores, Banks15002000150016001200Average Stores Cafeterias18002000150016001200Industrial25003000180022001500From Carrier Air System Design Manual(air velocity)(residences)3 m/s 5 m/s (theatres)4 m/s 6.5 m/s(restaurants) canteen7.5 m/s 10 m/sduct (air velocity)Main duct (allowable air velocity)5 m/s 8 m/sBranche duct (allowable air velocity)4 m/s 6 m/s(allowable air velocity) 30 m/s 9. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-8Duct system industry ASHRAE Handbook SMACNA HVAC Duct System Design Manual (reference) v duct N v duct supply air fan duct v exhuast air fan duct duct Negative PressureDuct system (air velocity)Coil (filter) (air velocitiy) 1000 fpm(5.08m/s) 000 m 5.24m/Duct System Sheets reinforcements seals joints duct duct element- Duct system. (Duct Construction)Duct (duct strength) (deflection) (leakage) duct (pressure) (velocity) (noise) (vibration) (friction loss) (velocity) 10. Chapter-5 Air Distribution Systemswww.acmv.org 5-9()(standards) SMACNA duct construction standards 2005 ASHRAE standard local codes()y()h (support)()Welding grinding()Double-wall and lining())()(material types)()Sh N S NDuct Construction Manuals:()SMACNAHVAC Duct Construction Standards Metal and Flexible (Third Edition)()SMACNAFibrous Glass Duct Construction Standards (Fifth Edition)()SMACNARectangular Industrial Duct Construction Standard (First Edition)()SMACNARound Industrial Duct Construction Standard (First Edition)()SMACNAThermoplastic Duct (PVC) Construction Manual (First Edition)Duct (toilets) Return air duct supply air streamSupply air duct return air duct A(ceiling space) return air air plenum (ceiling and the side-walls) (plastering) (painting) Masonry ductrigid duct steel aluminium glass-fibre batt mineral wool v mDuct duct lining glass fibre batt mineral wool air stream erosion of fibresDuct (supported hanger bracket (metal) Duct covering duct lining flexible connection material - m 11. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-10 (combustible material)( ) (methods) surface flame spread rating (class 1)(flame spread rating) class zero duct lining material class zero( )ductVentilation ductwork terminal unit ventilation grilles air diffuser flexible connection (2 m) (thermal movements) flexible joint 250 mmFlexible joint ('not easily ignitable') British Standard BS 476: Part 5Duct opening Air duct air duct support fitting plenum ( joints seam stiffening reinforcing and access opening ) ASHRAE Handbook, Institution of Heating and Ventilating Engineers(IHVE) guide books SMACNA Manuals duct (construction standards).. (Ductwork Materials) v SV (applications) Galvanized steel sheets ASTM A90, A525, and A5224" Breechings flues stacks (carbon steel) ASTM A56924" Breechings flues stacks (carbon steel) ASTM A569 m mm m y h ASTM B209 Sh h fume hood exhaust S Stacks h 304 304L 316 or 316L stainless steel sheets ASTM A167 12. Chapter-5 Air Distribution Systemswww.acmv.org 5-11SHEET METAL GAUGESSheet Metal GaugeThickness InchesRemarksSheet Metal GaugeThickness InchesRemarks00.3125Welded Ductwork Only190.0437SMACNA Ductwork Construction10.2810200.037520.2650210.034330.2500220.031240.2340230.028050.2187240.025060.2030250.021870.1875260.018780.1720270.0170Gauges Not Permitted for Ductwork Construction90.1560280.0156100.1400290.0140110.1250300.0125120.1090310.0109130.0937320.0100140.0780330.0093150.0700340.0085160.0625SMACNA Ductwork Construction350.0078170.0560360.0070180.0500Duct (Duct Material)UL (Underwriters Laboratory) standardClass 0() ( zero flame spread) () (zero smoke developed)Iron galvanized steel aluminum concrete masonry clay tileClass 1() m 25 () ( m v 50)Fiberglass many flexible ductsClass 2() m 50 () ( m v 00).. Duct SealDuctwork and plenum sealeDuct Seal (leakage) 13. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-12ASHRAE Minimum Duct Seal LevelDuct LocationDuct TypeSupplyExhaustReturn 2 . w. .> 2 in. w.c.OutdoorsAACAUnconditioned SpacesBACBConditioned SpacesCBBCASHRAE Standard 90.1-2001 and ASHRAE Standard 90.1-2004 Ductwork Seal ClassesSeal LevelSealing Requirements *Seal Class AAll transverse joints and longitudinal seams, and duct wall penetrations. Pressure-sensitive tape shall not be used as the primary sealant.Seal Class BAll transverse joints and longitudinal seams. Pressure-sensitive tape shall not be used as the primary sealant.Seal Class CAll transverse joints onlySealing Ductwork (ASHRAE Standard 90.1) American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ASHRAE.org)SMACNA Ductwork Seal ClassesSeal ClassApplicable Static Pressure Construction ClassA4" WC and higherB3" WCC2" WCC1/2" WC and higher for all ductwork upstream of VAV terminal unitsSealants and AdhesivesW s v(outside (Underground solvent based S (resistant to weather (ultraviolet raysSMACNA Recommended Ductwork Seal ClassesSMACNA Pressure Class (in. WC)1/21234610Supply DuctworkOutdoorsAAAAAAAUnconditioned SpaceBBBAAAAConditioned SpaceBBBAAAA 14. Chapter-5 Air Distribution Systemswww.acmv.org 5-13Return DuctworkOutdoorsAAAAAAAUnconditioned SpaceBBBBAAAConditioned SpaceBBBBAAAExhaust DuctworkOutdoorsBBBBAAAUnconditioned SpaceBBBBAAAConditioned SpaceBBBBAAASMACNA-HVAC Ductwork Seal Classes()Seal Class A: 25 percent total system leakage (all transverse joints, longitudinal seams, and duct penetrations).()Seal Class B: 310 percent total system leakage (all transverse joints and longitudinal seams).()Seal Class C: 520 percent total system leakage (all transverse joints).()Unsealed: 1040 percent total system leakage.()SMACNA recommended seal classes.- Benefits of insulation and sealing ductsAir Conditioning duct AC duct Mechanical Ventilation duct MV duct Air Conditioning duct duct insulation Mechanical ventilation duct Duct external insulation duct internal insulationAir conditioning duct mechanical ventilation duct Air conditioning duct (heat transfer) 15. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-14(internal insulation)- Duct- Fire rated duct.. Duct (External Insulation)Insulation(vapor barrier) external insulation fiber glassmineral wool materialinsulation (thermal conductivity) 0.0332 W/m2 K 16. Chapter-5 Air Distribution Systemswww.acmv.org 5-15(mean temperature) 24C insulation (thickness) 25mm (density) 32 kg/m3 air c supply duct return duct exhaust duct Air con (non air conditioning area) duct insulation supply air 50mm return exhaust air 25mm Air con (non air conditioning area) (air conditioning area) insulation.. Duct (Internal Insulation)Internal insulation (noise level) insulation (vapor main duct(density) 140 kg/m3 rockwool material Main duct () internal Insulation Duct rockwool (0.46mm) (perforated) (aluminum shee m m h (perforation holes) (total surface) % %- External Insulation ductDuct (construction) (type) (dimension) SMACNA guide line SMACNA Sh N SDuct and plenum insulation (Ref Singapore Standard SS 553:2009)Minimum duct insulation R-values for cooling only supply ducts and return ductsDuct LocationDuct location R-value (m2K/W)*Exterior1.06Ventilated attic1.41Unvented attic above insulated ceiling1.77Unvented attic with roof insulation1.06Unconditioned space1.06Buried1.06(thermal conductivity (insulation) 17. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-16.. Access DoorsEquipment duct damper fire damper access door Access door ( (welding method) Access door duct insulation material 1.00mmAccess door 12mm neoprene rubber gasket Duct fire rating access door (fire rating) Access door lock (latch) h vy y (galvanized) (chromium)- Oval Duct Access Door- Access door Access door frameAccess door duct (size)Duct (size)access door1200mm duct300mm x 400mm1200mm duct450mm x 450mmAutomatic Damper or Fire Damper450mm x 600mm.. Duct Test HolesDuct (velocity) (pressure) T T (location) (dawing) (hole diameter) 25mm top screw braged 40mm 5mm braged Bar sheet metal v- Duct test holes- Duct test hole air flow.. Duct fittingsduct duct duct fitting duct fitting 18. Chapter-5 Air Distribution Systemswww.acmv.org 5-17()Elbows()Enlargements and contractions()Converging or diverging tees and wyes()Means to reduce dynamic losses()Entrances and exits()Turning angle, splitter vanes(Source: ASHRAE Handbook Fundamentals 2001)ASHRAE duct fitting database fitting loss coefficients duct fitting()Fitting Types Elbows Mitered vanes()Fitting Types Divided Flow Y-Branch()Mitered no vanes()Reducing Y-Branch()Fitting Types Elbows Gored long radius()Divided Flow Laterals()Fitting Types Elbows Gored Standard()Divided Flow Laterals()Fitting Types Divided Flow Straight Tee()Duct fitting -Branch()Fitting Types Divided Flow Conical Tee()Duct fitting -Branch()()()()()()()()()()()()- Duct fitting. Duct Support HangerMaximum ductwork hanger spacing(a.) SMACNA minimum requirements(1)Horizontal: 8 to 10 feet maximum.(2)Vertical: One- or two-story intervals-12 to 24 feet. 19. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-18(horizontal) duct hanger rod Hanger rod lock nutCross-Sectional Perimeter of DuctMaximum Spacing Between Hanger(Hanger )1.5 m duct2.4 m1.6 m 2.5m1.8 m2.5 m duct1.2 m(b.) Recommended(1)Horizontal ducts less than 4 square feet: 8 feet maximum.(2)Horizontal ducts 4 to 10 square feet: 6 feet maximum.(3)Horizontal ducts greater than 10 square feet: 4 feet maximum.(4)Vertical round ducts: 12 feet maximum.(5)Vertical rectangular ducts: 10 feet maximum.Ductwork SupportDuctwork (Type)Maximum Hanger Spacing FeetHorizontal Ducts Less than 4 Square Feet8Horizontal Ducts 4 to 10 Square Feet6Horizontal Ducts Greater than 10 Square Feet4Vertical Round Ducts12Vertical Rectangular Ducts10(vertical) duct continuous length support- Dcut hanger- Dcut supportFirst cost (installation cost) Operating cost Duct system (first cost) (operating cost) 20. Chapter-5 Air Distribution Systemswww.acmv.org 5-19( )Duct (cool air) duct (heat) duct (hot air) (heat loss )( )Aspect ratio of the duct (duct aspect ratio)()duct (friction rate)()Fitting (type). Duct Properties.. Duct Heat Gain Duct Heat LossAir con duct air con (duct heat gain) (duct heat loss) Supply air (temperature) (cooled air duct duct (heat) )duct (allowance) supply air (air quantity)Duct duct aspect ratio duct duct aspect ratio duct (heat gain) (air flow rate) (velocity) (heat gain) (heat loss)U value 0.12 insulation (duct heat gain) %.. Aspect Ratio- Aspect Ratio 1.0 Aspect Ratio 4.0 duct(velocity) duct (duct heat gain) (duct heat loss) 21. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-20Aspect ratio duct (long side) haspect ratioAspect Ratio(installation cost) (operation cost)Duct Class Max; Size of Duct(inch) Semi Perimeter1 6 - 17 1/2" 10 - 232 12 - 24 24 463 26 - 40 32 - 464 24 - 88 48 - 945 48 - 90 96 - 1766 90 - 144 96 - 238 (capacity) duct duct(gate of metal sheet) Materialinsulation insulation- Small Aspect Ratio - Large Aspect Ration.. (Sound Control)() (acceptable noisecriteria (NC))() m() (resultant sound level criteria)() ( vduct consultant dust class Aspect RatioAspect Ratio (friction loss)Duct c Duct (area)capacity duct system (total pressure) duct cDuct (size) duct cDuct work (first cost) (installationcost) (material) 22. Chapter-5 Air Distribution Systemswww.acmv.org 5-21()(appropriate) N v- Duct System AcousticsDesign guidelines for HVAC system noise in unoccupied spaces(Room Types)RC / NCPrivate Residences25-35Hotels/MotelsIndividual rooms or suites25-35Meeting/banquet rooms25-35Corridors, lobbies35-45Service/support areas35-45Office BuildingsExecutive and private offices25-35Conference rooms25-35Teleconference rooms< 25Open-plan offices< 40- With sound masking< 35Corridors and lobbies40-45Hospitals and Clinics Private rooms25-35Wards30-40Operating rooms25-35Corridors and public areas30-45Performing Arts SpacescDrama theaters25Music teaching studios25Music practice rooms30-35SchoolsdClassrooms25-30 23. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-22Large lecture rooms25-30Large lecture rooms, without speech amplification25Laboratories (with Fume Hoods)Testing/research, minimal speech communication45-55Research, extensive telephone use, speech communication40-50Group teaching35-45Church, Mosque, SynagogueGeneral assembly25-35With critical music programs cLibraries30-40CourtroomsUn-amplified speech25-35Amplified speech 30-4030-40Indoor Stadiums, GymnasiumsGymnasiums and natatoriumse40-50Large seating-capacity spaces with speech amplificatione 45-5545-55.. (Duct leakage)(leakage) ANSI SMACNA ASHRAE standard(Impact of Leakage )(leakageEnergy Cost Example Cost/year = [CFM x TP]/[8,520 x Eft] x Hours/Year x $/kwhLeakage (%)CFM (Cu ft/min)RPM (rev/min)SP (in wg)VP (in wg)TP (in wg)BHP (hp)Oper/yr (5/year)Extra Oper/yr (5/year)Increased Oper/yr WO020,0005301.500.391.896.685,600--521,0005571.650.432.087.736,48188115.71022,0005831.820.472.298.897,4521,85233.31523,0006101.980.522.5010.168,5152,91552.12024,0006362.160.562.7211.549,6754,07573.03026,0006892.540.663.2014.6812,3016,701120.0 24. Chapter-5 Air Distribution Systemswww.acmv.org 5-23(assumedElectric rate $0.15/kWh0.1552 wk x 6 d/wk x 24 hr7,488 hrFan/motor Efficiency89initial velocity2,501(Suggested Leakage Levels)Leakage LevelsTest Pressure (in wg)SMACNA Class 3(CFM/100 sq ft)Leakage (%)0-13.021 -24.622-36.013-47.414-69.60.56-1013.50.5Annual Operational CostsCost/Year=system first year operating cost ($)Qfan=system volume flow rate (cfm)FTP=system total operating pressure (in wg)Hours/Year=number of hours the system operates in one year $/kwh = cost of energyEfficiency=fan/motor drive combined efficiency8,520=conversion factor to kWh (kilowatt hours).. SMACNA Ductwork Testing()-4 W pressure r (test)(1.5 X Pressure Rating)()- W W w()4 W pressure rating (test)(1.5 X Pressure Rating)()ASHRAE Standard 90.1-200 2004 static pressures +3" Water Gauge y m y-()200 2006 S N V m wstatic pressures +3" Water Gauge y m y-. Duct (Sizing)y m 25. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-24()(space availability)()(space air diffusion)()(noise levels)()Duct (duct leakage)()duct (duct heat gain) (duct heat loss)()(air balancing)()(fire and smoke control)()(initial investment cost)()(system operating cost)(discomfort) S(construction) (leakage) (terminal) air diffuser h h system loss y mDuctwork Sizes()4 4 ()8 4 (smallest recomm() 24 2 0 6 2 6 48 2 v m )()4:1 m m m mm() m.. Duct (Sizing)( )Pressurized Method( )Equal Friction Sizing Method(Constant Pressure Loss Method)()Static Regain Method()Total Pressure Method( )Velocity Reduction Method( )Constant Velocity Method 26. Chapter-5 Air Distribution Systemswww.acmv.org 5-25v m h()Velocity Reduction Method()Equal Friction Method()Static Regain MethodPressurized Methodduct duct duct (size)Equal Friction Sizing Method (Constant Pressure Loss Method)Equal friction (method) (flexibility) Duct (pressure loss) ductSystem duct 1 Pascal (1Pa/m) duct Eq F h Supply extract duct system Eq F h ASHRAE duct (high and low limits for pressure loss per unit length) (velocity) duct (pressure loss per unit length)Eq F h ( )friction loss per unit of length duct 1 Pascal( 1Pa/m)( )friction loss(1 pa/m) (air flow rate) duct Friction loss chart duct (size)()(pressure loss) (section) friction loss (duct section) elbow fitting friction loss()duct (size) friction loss coefficient duct (size) SystemEq F (air balancing) 27. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-26 S Regain Sizing MethodS R h duct (equal friction method ) (material)S R h terminal branch duct section (pressure loss) duct branch duct section (pressure loss) branch duct section (pressure loss)duct (section) duct (section) (pressure losses) duct section duct (size) duct (section) duct (size) (p S R h iteration process T S hT m h m hV y Reduction Sizing MethodVelocity reduction duct (air velocity) (velocity) (noise) Duct (acceptable velocity) (velocity) duct duct (size) (round) duct (rectangular) duct (size) (pressure losses)(high noise level) (velocity) (noise level) ASHRAE SMACNA V S V y S hConstant velocity method duct (tender) (specified) (velocity) duct duct (pressure losses).. (Friction Losses in Duct)Friction loss fluid viscosity v y m m m F 28. Chapter-5 Air Distribution Systemswww.acmv.org 5-27Eq m h y m hF()Duct (size) (velocity) friction loss()Duct (interior surface roughness) friction loss()(Air flow rate) friction loss()Duct (length) friction loss.. Head and Pressurem ("Head" is the height of a fluid co m y w. w q He (cloum liquid)m Hea 5 meter of water cloum(WC)q mAir pressure 1 Pound per Square Inch (PSI) = 51.71 millimeter of mercury( mmHg ) 51.71 mm of mercury (mmHg)y-W h Eq f pipe d (pressure drop f (f y-W h Eq fully developed flowDarcy and Colebrook EquationsDuct (pipe) fluid (pressure drop) 29. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-28f( )Fluid laminar flow Reynolds () (Reynolds numbers less than 2000) Friction factor Reynolds number( )Fluid turbulent flow friction factor Reynolds (Reynolds number) (duct surface roughness) jointFriction factor (Reynolds number) (duct surface roughness) hydraulic diameterN m w noncircular duct laminar flow hydraulic diameter Duct (Noncircular Duct)hy mRectangular DuctR Flow resistance round ducthy m roun square rectangular duct w q m v 30. Chapter-5 Air Distribution Systemswww.acmv.org 5-29Flat Oval DuctA = major axis of flat oval duct (mm)a = minor axis of flat oval duct (mm)P = perimeter of flat oval duct (mm)Friction f R y m h hy m (Graph)Hydraulic diameter(D) Reynolds Number(dimensionless) Duct (turbulent or laminar) Reynolds NumberReynolds Number () Laminar flow (Laminar if Re < 2300)Reynolds Number () () Transient flow (Transient for 2300 < Re < 4000)Reynolds Number () Turbulent flow (Turbulent if Re > 4000).. F h (Pressure Drop)S R E friction ch()Friction losses ( Pa/ m)()Air Quantity (Liter per Second)()Velocity (m/s)()R m mm() Friction losses ( Pa/m) h 0.1 Pa/m 00 /m 0. /m 5 /m F()Air Quantity (Liter per Second) (vertical li 20 L/ 200 000 L/()Velocity (m/s)()Round Duct Diamaeter (mm) 31. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-3025 000 ( m (maximum f /m round duct () total f (air quantity 25 000 (air quantity L S 25 000 L S- ASHRAE friction chart25,000 CHM x 1000 Liter per meter cube = 25,000,000 Liter per hour/ 3600 6 44 L/ m m F /m 6 44 L/ /mm 50mm m v y 0.2 m/ S R E mm v y 32. Chapter-5 Air Distribution Systemswww.acmv.org 5-31v y 0.2 m/ recommend duct vel y 50mmv y mType of DuctComfort SystemsIndustrial SystemsHigh Speed Systemsm/sftmm/sm/sftmMain ducts4 - 7780 - 13808 - 121575 - 236010 - 181670 - 3540Main branch ducts3 - 5590 - 9855 - 8985 - 15756 - 121180 - 2360Branch ducts1 - 3200 - 5903 - 5590 - 9855 - 8985 - 1575(outlets (inlets (velocit (unacceptable noise)(air flow rate) 8 000 450mm 00mm (frictioin losses - Pa/m)Air Flow Rate 18,000 CMH Liter per SecondAir Flow Rate 18,000 CMH = 5,000 L/sRectangular d 450mm 00mm Eq v Rectangular Eq h 808mm 800(air quantitie) 5,000 L/s 800mm R m (frictioin losses - Pa/m) . /mFriction Loss Estimate1.5 X System Length (ft./100) X Friction Rate (in.W.G./100 ft.)... S L y F mS L (Formula) Ref: 2001 ASHRAE Fundamentals Handbook (SI), Chapter 34, Equation No:11WhereDe =Circular Equivalent of Rectangular duct for equal lengthQ =Air flow rate (L/sec)2001 ASHRAE Fundamentals Handbook (SI), Chapter 34, Eq N (air flow rate) R S V y V S R E (air flow rate) / L S 0.001 33. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-32A = (3.14 x De2 /4 roun round duct d m Rectangular duct (formula) circular eq v m()Ref: 2001 ASHRAE Fundamentals Handbook (SI), Chapter 34, Equation No:25(velocity) velocity Pressure (formula)Ref: 2001 ASHRAE Fundamentals Handbook (SI), Chapter 34, Equation No:09Rv=Velocity Pressure ()V=Fluid mean Velocity (m/s) y m mm)Ref: 2001 ASHRAE Fundamentals Handbook (SI), Chapter 34, Equation No: 24 F R h FRef: 2001 ASHRAE Fundamentals Handbook (SI), Chapter 34, Table No: 01absolute roughness factor 2001 ASHRAE Fundamentals Handbook (SI), Chapter 34, Table No: 01() Reynolds numberRef: 2001 ASHRAE Fundamentals Handbook (SI), Chapter 34, Equation No:23Re=Reynolds numberDh=Hydraulic Diameter (mm)V=Velocity (m/s) 34. Chapter-5 Air Distribution Systemswww.acmv.org 5-33() Pressure Drop Ref: 2001 ASHRAE Fundamentals Handbook (SI), Chapter 34, Equation No:21 () orRef: 2001 ASHRAE Fundamentals Handbook (SI), Chapter 34, Equation No:19=1.204 kg/m2 (for air)Dh=Hydraulic Diameter, mmV=Velocity (m/s)If()For Ducting,For Fittings,E internet a d whttp://www.acmv.org/lecture/file/Duct_Static_Loss_calculation.xlsA. Ductwork Sizing Criteria Table (Ductwork Size Criteria)System TypeMaximum Friction Rate in.W.G./100 ft.Minimum Velocity ft./min.Maximum Velocity ft./min.Comments/ReasonsGeneral Air Handling SystemsLow Pressure Ducts0.10 (0.15)----1,500 1,800When CFM > 6,000 velocity governs;when CFM < 6,000 friction rate governs; applicable for supply, return, exhaust, and outside air systemsMedium Pressure Ducts0.20 (0.25)----2,000 2,500When CFM > 6,000 velocity governs; when CFM < 6,000 friction rate governs; applicable for supply systems onlyHigh Pressure Ducts0.40 (0.45)----2,500 3,500When CFM > 5,000 velocity governs; when CFM < 5,000 friction rate governs; applicable for supply systems only 35. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-34Transfer Air Ducts0.030.05----1,000When CFM > 3,200 velocity governs; when CFM < 3,200 friction rate governsOutside Air Shafts0.050.10----1,000When CFM > 1,200 velocity governs; when CFM < 1,200 friction rate governsGravity Relief Air Shafts0.030.05----1,000When CFM > 3,200 velocity governs; when CFM < 3,200 friction rate governsGeneral Exhaust and Special Exhaust SystemsGeneral Exhaust Ducts0.10 (0.15)----1,500 1,800When CFM > 6,000 velocity governs; When CFM < 6,000 friction rate governsToilet Exhaust Ducts0.10 (0.15)----1,500 1,800When CFM > 6,000 velocity governs; When CFM < 6,000 friction rate governsKitchen Hood Exhaust Ducts----1,5002,2002003 IMC: 1,500 FPM min.; 2006 IMC: 500 FPM min.; NFPA 96-2004: 500 FPM min.Dishwasher Exhaust Ducts0.10 (0.15)1,5002,200Acid, Ammonia, and Solvent Mains0.50 (0.60)1,0003,000Mains and risers 1,5003,000 FPM; Branches and lateral 1,0002,000 FPMAcid, Ammonia, and Solvent Stacks----3,0004,000Silane Ducts----250----Velocity across the neck of the cylinder or cabinet window or access portLouversIntake--------500Maximum velocity through free area; assuming 50% free areamax. velocity 250 FPM through gross louver areaExhaust or Relief--------700Maximum velocity through free area; assuming 50% free areamax. velocity 350 FPM through gross louver areaNotes:(1) Maximum aspect ratio 4:1; unless space constraints dictate greater aspect ratios.(2) Duct velocities should not exceed 1,500 FPM or noise will result. 36. Chapter-5 Air Distribution Systemswww.acmv.org 5-35. Duct (Duct Design).. Design (information)(client requirements)(supply air condition)(space availability)(installation cost)(air friction loss)Duct system configuration (type) duct layout(noise level)(duct heat transfer and airflow leakage)(ambient conditions)(material)Duct insulationDuct system layout(codes and standards requirements)Key design inputsDesign outputs v m w m3/s) S h m w y & L m /m S h h L miting flow velocity (m/s)Duct()( (duct material)()duct (sudden changes in directions) (pressure loss) turning vane()Duct Angle of divergence 20()Aspect ratio () () Aspect ratio ( duct duct duct Aspect ratio () duct()Duct (vibration) (noise) (air velocity) duct()(frictional loss) (duct material) 37. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-36- Transfer ductDuct( )m S yDuct (shape) (strength) (deformation) dimensional stability( )(Leakage Control)Positive pressure duct (air loss) Negative presure duct leakage control()(Noise)Duct (noise generation) (noise transmission) (noise)()(Exposure)(weather) duct (corrosive a m h ) (biological contamination) (underground basement) (outdoor) exposure( )Duct SupportDuct support alignment (position) duct support( )Thermal ConductivityDuct duct (heat t (heat gain) h duct (condensation) (thermal conductivity)Duct (expericence) 38. Chapter-5 Air Distribution Systemswww.acmv.org 5-37(technical knowledge) (good practices)Duct (workshop) (fabricate) (site) Drawing duct (dimension) internal dimension duct (size) w (dimemsion)..()Life-cycle cost(LCC) duct duct()Damper duct (duct) duct (size) configuration(sound level) VAV box (pressure) (excess pressure) Sound attenuation()(critical path) duct (critical path) duct fitting equipment (local loss coefficients) (surplus pressure)()Supply air (volume flow rate) duct heat gain VAV system (volume flow rate) diversity Fan (discharge pressure) critical path.. Design ProcedureAir duct system(supply volume flow rate)(space air diffusion) (supply outlets) (return inlets)cold air (volume flow rate) warm air(volume flow rate)air duct system duct design software Computer-aided duct design (precise calculation) m m air duct system duct designDesign Procedure()Verify local codes & material availability()Preliminary duct layout 39. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-38()Divide into consecutive duct sections()Minimise local loss coefficients of duct fittings()Select duct sizing methods()Critical total pressure loss of tentative critical path()Size branch ducts & balance total pressure at junctions()Adjust supply flow rates according to duct heat gain()Resize duct sections, recalculate & balance parallel paths()Check sound level & add necessary attenuationdesign procedure ()() (client requirement) (tender specification) (local codes) (material availability)()duct layout (preliminary) (supply outlets) (return inlets) fan main ducts branch takeoffs air duct (duct) (space available)()Duct layout (duct sections) Duct segment () critical path critical path()Critical path duct fitting local loss coefficient()Air duct system characteristics duct (sizing methods) duct system space available noise energy use initial cost maximum design air velocity critical path duct section duct()Critical path (total pressure loss) Air duct system (total pressure loss)()Branch duct Junction duct fitting component total pressure loss()The supply volume flow rates supply outlet duct heat gain (adjusted)()duct section (resizes) total pressure loss()Duct section(paths) (airborne sound level) (noise) sound attenuator 40. Chapter-5 Air Distribution Systemswww.acmv.org 5-39. Fire Damper.. Fire CompartmentFire compartment (zone) Fire compartment Fire compartment- Fire compartment ( )- Fire rated partitions contain fire damage to the compartment of fire origin.- duct fire damperDuct fire damper Duct fire damper fusible link blade fire damper 41. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-40(horizontal) duct (vertical) duct horizontal fire damper (floor mounted) vertical fire damper (duct or wall mounted)(horizontal) duct vertically fire damper Fire damper (fire resisting rating) v (wall) (compartment floor) (fire resisting rating)- Fire damperCode of Practice for Fire Precautions in BuildingsWall Mounted Fire Damper and Floor Mounted Fire DamperFloor mounted fire damper blade bland (spring)- Horizontal fire damper Multiple Blade Wall mount or In line Duct Curtain Type- V and HFloor mounted fire damperFusible Links 42. Chapter-5 Air Distribution Systemswww.acmv.org 5-41.. Fire DamperF m (galvanized steel frame fusible link Fusible link ( 65 F damperS m dynamic damperFire RatingFire r Fire r hAccess Door: F m Fire Damper InstallationFire d m fire-rated walls - --Standard Fire Damper Static Fire DamperStandard fire damper static fire damper Fire Mode duct.. Fire damper- Fire damperDynamic Fire DamperDynamic fire damper Fire Mode duct Dynamic fire damper (moving air) static fire damper 43. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-42()Type-A fire damperType-A fire damper (low-pressure part of y m 2 w. .()Type-B fire damperType-B fire damper Type-A fire damper (free area) ( pressure drop)()Type-C fire damper (100% free area)100% free area Type-C fire damperMedium-to-high air velocities (3,000 fpm) W. Type-C fire damper. Control Dampers(air volume) (air flow) Volume Control Damper (VCD) Volume damper Volume Control Damper (VCD) Manual or balancing dampers motor operated dampersDamper CharacteristicsOpposed blade Bala mixing modulating 2- position control applicationsParallel blade: Two-position applications (open/closed).2000 F 0.15" W.Gm w 200 500 F / q.Damper (air flow) (control) Damper (round) (rectangular) (oval) duct (round) damper (oval) damper (rectangular) damper Blade () ()HVAC damper galvanized steel extruded aluminium (outdoor air intake) damper m m (aluminium) (industrial facilities) (stainless steel) 44. Chapter-5 Air Distribution Systemswww.acmv.org 5-43Airfoil dampers- Figure 3-28 Triple V and Airfoil dampers(frame) blade Damper (shaft) (bearing) (friction)Damper blade()Flat, one-piece(single metal sheet) blade()Single skin blade with a triple-v-groove shape()Double- skin air foil-shaped blade (-) Triple V airfoil blade Damper F1 ( ) F2 ( ) (frame depth) Blade width frame depth (flat) blade (round) duct (oval) duct blade (single blade) damper damper blade (rectangular) damperTriple V groove blade (velocity) 2000 FPM 1500 FPM Blade (overlap) (tight closure)Air foil damper Air foil blade (pressure drop)(control) (valve) (control) damper Valve damper (selection principle) Damper valve (stable) accurate control 45. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-44Blade (edge) compressible sealing strip (leakage) sealing strip m silicon rubber v y Silicon rubberSeal damper (fully open) (fully closed) (performance) (frame) blade seal Damper (standard leakage) 50 F q h(249 Pa damper 50 CFM Air foil blade low leakage damper 6 damper 10CFMHVAC System shut off damper (low leakage) damper 24 damper 2 CFM (2 CFM per square foot at 1 inch wg) (reading) controlled variable control(le Damper (minimum leakage) ANSI/ ASHRAE/ IESNA Standard 90.1-2004 )Ultra-low leak damper Low leak damperCooling load system ultra-low leak damperBlade (linkage) (-) blade (linkage) damper (linkage) ( ) (pressure drop) (corrosion)damper damper (seal) Blade Damper (maintenance)Damper actuator damper m (oversized) 46. Chapter-5 Air Distribution Systemswww.acmv.org 5-45Actuator damper actuator damperDamper actuator damper (linkage) damper Blade damper multiple blade damper Multiple blade damper blade parallel blade opposed blade (-)()Parallel blade operation blade (same direction) ()Opposed blade operation blade blade damper (operating characteristic) Blade (single blade) damper (operating characteristic) parallel opposed blade damperActuator damper operator damper motor (fully open) damper actuator (power) damper- Figure 3-31 Fans in Parallel- Centrifugal Fan with Inlet Vane damperModulating damper small increment ( m modulateLower leakage damper seal (friction) (friction) damper motor (damper actuator) parallel blade damper actuator (opposed blade damper )Actuator torque h- Damper torque h- Damper (1 square foot) h- 47. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-46(friction) actuator minimum torque minimum 20inch-lb 8 inch-lbs per square foot of damper areadamper damper actuator Normally open operation(NO) (set up) power (fail) damper (flow)Coil freezing hazardous waste system isolation damper Normally Open(NO) N m y NDamper y damper damper application( )Two position only(fully open/fully closed) position two position Fan isolation (out door air intake) (shut-off)( )Capacity control dutycapacity damper control VAV discharge damper air balancing damper()Mixing dutyEconomizer damper.. ( ) Two Position DutyFan system duct Outdoor air intake fan intake discharge F damper fan damper (position) (wind pressure) stack effect fan (out door air intake) damper supply air fan interlock coil (freezing)h (heating energy cost)damper m motorized damper gravity damper Gravity damper Back Draft Damper(BDD) barometric damper Non Return Damper(NRD) Gravity damper actuator(motor) motorized damper (fight seal) Gravity damper Supply (return) N R m 48. Chapter-5 Air Distribution Systemswww.acmv.org 5-47Exhaust fan back draft damper fan fan exhaust air fan discharge point- Figure 3-33 Installed Characteristic Curves of Parallel blade dampers(air pressure) damper exhaust system make up air gravity damper motorized dampergravity damper motorized damper (-) fan damper (isolate) fanVariable Air Volume (VAV) application low load fan high load fan shut-off damper fan fan Parallel pumping system check valve motorized damper damper 49. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-48Fan damper fan fan w h fan wheel fan fan direction q m v- Figure 3-35 Two Parallel blade Triple V dampers From Different Manufacturers- Figure 3-36 Two Opposed blade Triple V dampers From Different ManufacturersFan damper fan plenum (pressure) application gravity back draft damper F (pressure) gravity damper Back draft damper fan discharge Fan 50. Chapter-5 Air Distribution Systemswww.acmv.org 5-49h (velocity) back draft damper heavy duty damperParallel blade damper Damper damper actuator parallel damper actuator opposed blade damper ( ) HVAC designer two position application (vendor) (contractor)Two position damper two position damper modulateShut off damper duct m. ( ) Capacity Control DutyAir system terminal (air flow) duct Volumer control damper balancing damper branch duct selection diffuser grille (design air flow) (pressure) (adjust ) Volume control damper static damper Static damper actuator (air flow) Volume control damper(fully open position) ( h Volume control damper single blade single skin damper ductdamper OTwo position damper (size) (leakage) (pressure drop) (energy)Two position parallel blade damper opposed blade damper Two position damper (fully open) (fully close position) damper performance 51. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-50VAV System fan capacity control damper Damper style inlet guide vane discharge damper (-) inlet guide vane fan inlet m Fan (inlet) damper blade - hDamper (entering air) ( - Damper fan wheel direction fan wheel direction wheel air volume unload fan y m inlet guide vane (maximum capcity) % (air flow) (pressure)Discharge damper paraller pump check valve Discharge damper fan (fan pressure) VAV box stabl (air flow) controlDischarge damper fan performance Discharge damper h VAV system discharge damperDamper performance()Manufacturer()Damper relative size()Damper situation()ManufacturerDamper (design) (material) (linkage) blade seal damper (performance)()Damper Relative SizeDamper (size) duct (size) wall opening damper (performance) damper duct duct damper w damper damper flow characteristic damper (performance)()Damper SituationDuct device d damper direction damper direction damper 52. Chapter-5 Air Distribution Systemswww.acmv.org 5-51performance- Figure 3-37 Effect of Inlet Louver on an Opposed blade damper Characteristic(-) opposed blade damper performanceCapacity control (throttling) application damper position pressure drop across the damperDamper throttling (air flow rate) duct system (frictional losses) (frictional losses) (air flow rate) Fan (pressure) volume flow rate fan curve Two way valve hydronic system(-) parallel blade damper (air steam direction) (deflect the air steam) down steam(down stream) elbow duct fitting ymm v y (pressure drop) (down stream) diffuser outlet throw pattermOpposed blade damper throttling application linear characteristic pressure drop across the damper total system pressure drop % opposed blade damper down steam throttling applicationThrottling application parallel blade damper linear characteristic damper ( pressure drop) system (total pressure drop) % 53. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-52- Air flow through parallel- Air flow opposed dampers- (3-38) Flow Pattern through opppsed dampers and parallel Damper(air outlet) diffuser neck diffuser opposed blade damper.. () Mixing duty(air steam) damper (out door air) return air m opposed blade damper throttling (mixing)mixing application parallel blade damper mixing throttling air streamThrottling application damper hydronic system control valve y (pressure drop) Damper (size) controllability (pressure drop) Damper (size y (pressure drop) 54. Chapter-5 Air Distribution Systemswww.acmv.org 5-53Parallel blade damper (air steam) (deflect) throttling mixing (-) m air stream (deflect mO m (air steam) m (- )- Various Mixing Box Arrangements(air steam) S (air steam) Duct (outdoor air 55. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-54temperature) return air temperature S Ventilation system effectivenessDamper damper scheduleDamper Identification TagBlade typeLocationVelocity Pressure DropDamper TypeFail PositionDamper Size & QuantityActuator identification TagDuct SizeActuator type & quantityArrangementMounting. Air Distribution DevicesDiffuser register grille (air distribution devices)Primary AirPrimary air (supply outlet)Total AirTotal Air primary air entrained room air Cooling (supply outlet) m y.. 56. Chapter-5 Air Distribution Systemswww.acmv.org 5-55-ThrowTh w (outlet face v y (air outlet m -)v y 50 0. 5 m/ 00 0.50 m/ 50 m 0.25 m/ v y m v yTh w m w v y h w m w v y- S v . Th w v w (Plan view)- Space air diffusion with overhead cooling 57. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-56- O h w-Drop- T m y m y y y m m m v m w y w d- hSpreadv h m v h m S m ySurface Effect(supply air velocity) (moving air mass) v w 58. Chapter-5 Air Distribution Systemswww.acmv.org 5-57Occupied Zone 6 .8 m v w m v - Spread and Throw- Active and inactive sections(Pressure Drop)m m y h . w. .y m- Space air diffusion with overhead heating- Upward deflection- Sidewall application(air flow (air outlet) (pressure loss) 59. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-58- Ceiling diffuser free space mounting- Sidewall outlet free space mounting- Ceiling diffuser- Slot diffuser.. Diffuser (Air Diffusers)air con system (air outlet)( ) Grilles and RegistersLouver (air outlet) (intake) (square) face size neck size (adjustable louvers) (stationary louvers) single deflection grille double deflection grille horizontal verticalGrille v m m V register( )Linear Bar Grillegrille linear bar grille 60. Chapter-5 Air Distribution Systemswww.acmv.org 5-59()Linear Slot DiffuserLinear Slot DiffuserSlot ( in. [13 mm]) ( in. [19 mm])(1 inch [25 mm]) Slot () () Linear slotdiffuser (ceiling)Round ceiling diffuser Square ceiling diffuser Louvered face diffuserRound plaque diffuser Square plaque diffuser Perforated ceiling diffuserRound Twist Diffuser Plenum slot diffuser Light troffer diffuser- Diffuser- Linear bar grille[6mm]spacing- Return grille - Linear slotdiffuser- Double deflection supply grille - Return grilleIndustrial VentilationIndustrial supply grille Drum louver Nozzle 61. Air Conditioning and Mechanical Ventilation System (Vol. 1)www.acmv.org 5-60Industrial return grilleSecurity grille-Slot diffusers light troffer diffusers (low air volumes) throws VAV applications.. Diffuser Characteristic LengthCharacteristic length for various diffuser typesDiffuser TypeCharacteristic Length, LHigh Sidewall GrilleDistance to wall perpendicular to jetCircular CeilingDiffuser Distance to closest wall or intersecting air jetSill GrilleLength of room in the direction of the jet flowCeiling Slot DiffuserDistance to wall or midplane between outletsLight Troffer DiffusersDistance to midplane between outlets, plusdistance from ceiling to top of occupied zonePerforated, Louvered Ceiling DiffusersDistance to wall or midplane between outlets.. (Air Outlet) (Noise Level)(air outlet) (noise level) Noise Criteria (NC) sound pressure value based on an industry standard 10 dB default for room absorption.(air outlet) (noise level) (air outlet) (air outlet) ASHRAE recommended NC level valuesDiffuser24 in. x 24 in. module [610 mm x 610 mm], 380 cfm [180 L/s], 700 fpm [3.6 m/s] neck velocityDiffuserTypeNC LevelDiffuserTypeNC Level()Square Cone17()Perforated Curved Vane28()Square Plaque18()Louvered Face31()Round Cone22()Perforated Face Deflector33()Modular Core26()Perforated Neck Deflector37.. Plenum Slot Diffuser1 in. slot, 4 ft [1.2 m], 270 cfm [127 L/s], 8 in. [203 mm] neck, 800 fpm [4.1 m/s] neck velocityDiffuserTypeNC LevelDiffuserTypeNC Level()Linear Slot31()Linear IceTong39()Linear Fixed Curved36()Linear Wiper Blade46 62. Chapter-5 Air Distribution Systemswww.acmv.org 5-61. Duct cleaningDuct duct (duct cleaning)- Duct -End-