Chilled-Water VAV Systems - HVAC.Amickracing

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PrefaceAs a leading HVAC manufacturer, we deem it our responsibility to serve thebuilding industry by regularly disseminating information that promotes theeffective application of building comfort systems. For that reason, weregularly publish educational materials, such as this one, to shareinformation gathered from laboratory research, testing programs, andpractical experience.This publication focuses on chilled-water, variable-air-volume (VAV) systems.These systems are used to provide comfort in a wide range of building typesand climates. To encourage proper design and application of a chilled-waterVAV system, this guide discusses the advantages and drawbacks of thesystem, reviews the various components that make up the system, proposessolutions to common design challenges, explores several system variations,and discusses system-level control.We encourage engineering professionals who design building comfortsystems to become familiar with the contents of this manual and to use it asa reference. Architects, building owners, equipment operators, andtechnicians may also find this publication of interest because it addressessystem layout and control.Trane, in proposing these system design and application concepts, assumes noresponsibility for the performance or desirability of any resulting system design. Design ofthe HVAC system is the prerogative and responsibility of the engineering professional.“Trane” and the Trane logo are registered trademarks, and TRACE, System Analyzer andTAP are trademarks of Trane, a business of Ingersoll-Rand.© 2009 Trane. All rights reserved Chilled-Water VAV Systems SYS-APM008-EN
ContentsPreface .................................................................................................iiOverview of a Chilled-Water VAV System ........................... 1Basic System Operation ................................................................... 3Benefits of Chilled-Water VAV Systems ........................................... 6Drawbacks/Challenges of Chilled-Water VAV Systems .................... 9Common Building Types That Use Chilled-Water VAV Systems ..... 10Primary System Components .................................................. 11VAV Air-Handling Unit ...................................................................... 11Indoor versus outdoor air-handling units...................................... 12Chilled-water cooling coil............................................................. 15Maximum face velocity to prevent moisture carryover ........ 17Freeze prevention ................................................................. 18Evaporative cooling ............................................................ 21Heat source inside the VAV air-handling unit ............................... 23Heating coil (electric, hot water, or steam) .......................... 23Gas-fired burner ................................................................... 24Recovered heat ................................................................... 26Fans (supply, return, relief) .......................................................... 26Supply fan only .................................................................... 26Supply fan and relief fan ...................................................... 29Supply fan and return fan .................................................... 30Should the system use a relief fan or a return fan? ............. 30Fan types ............................................................................. 32Blow-thru versus draw-thru? ................................................ 35Supply fan capacity modulation ........................................... 38Air cleaning .................................................................................. 40Particulate filters .................................................................. 40Gaseous air cleaners ........................................................... 46Biologicals ........................................................................... 48Water management ..................................................................... 50Casing performance (leakage and thermal) ................................. 51VAV Terminal Units ......................................................................... 54Types of VAV terminal units ......................................................... 55Cooling-only VAV terminal units ........................................... 55VAV reheat terminal units .................................................... 56Fan-powered VAV terminal units ......................................... 58Dual-duct VAV terminal units ............................................... 62Minimum primary airflow settings ............................................... 62Perimeter versus interior zones ................................................... 63Typical combinations used in chilled-water VAV systems ............ 66SYS-APM008-EN Chilled-Water VAV Systems iii
Page 3: Chilled-WaterVAV SystemsJohn Murphy
Page 8 and 9: VAV terminal units ................
Page 10 and 11: Overview of a Chilled-Water VAV Sys
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Page 40 and 41: Primary System ComponentsFan typesV
Page 42 and 43: Primary System ComponentsTo allow a
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Primary System Componentssystem. So
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Primary System ComponentsPhotocatal
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Primary System ComponentsPCO techno
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Primary System Componentsand upstre
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Primary System ComponentsThermal pe
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Primary System ComponentsFigure 47.
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Primary System ComponentsFan-powere
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Primary System Componentspowered VA
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Primary System Componentsinterfere
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Primary System ComponentsIf the des
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Primary System ComponentsTypically,
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Primary System ComponentsInterior z
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Primary System ComponentsInterior z
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Primary System ComponentsEqual fric
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Primary System Components• If nee
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Primary System ComponentsIn additio
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Primary System ComponentsAir-cooled
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Primary System Componentstemperatur
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Primary System ComponentsVariable-
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Primary System ComponentsFreeze pre
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Primary System Componentsrow coil i
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Primary System ComponentsThermal st
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Primary System Components(although
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Primary System ComponentsA variable
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System Design Issues and Challenges
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System Design VariationsThis chapte
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System Design Variationspressure dr
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System Design VariationsImpact on o
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System Design Variations• Run 7 v
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System Design Variationsmechanical
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System Design Variations• Impleme
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System Design Variationsconventiona
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System Design VariationsFigure 113.
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System Design Variationsbuildings (
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System Design VariationsFor most ap
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System Design VariationsWhile the s
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System Design VariationsFigure 120.
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System ControlsThis chapter discuss
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System Controlssensor from being in
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System ControlsFigure 126. Modulate
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System Controlsfixed enthalpy contr
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System ControlsIf the air-handling
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System ControlsFigure 133. Floor-by
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System ControlsVAV terminal unitsSi
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System Controlspeople in a zone, an
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System ControlsAlternatively, if th
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System Controlsvariable-speed drive
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System ControlsFigure 137. System-l
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System ControlsTable 31. Example of
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System ControlsFigure 139. Morning
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System Controlszone to the unoccupi
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System ControlsThe optimal starting
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System ControlsFigure 143. Fan-pres
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System ControlsTable 36 lists condi
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System Controlsreset to be used dur
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System ControlsFigure 147. Ventilat
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System Controlsdecrease overall sys
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System ControlsFigure 150. Optimize
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GlossaryACH. Air changes per hour.A
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Glossarycondensing boiler. A type o
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Glossaryelectronic air cleaner. Par
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GlossaryMERV. Minimum Efficiency Re
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Glossarypump-pressure optimization.
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GlossaryTR. Cold-spot thermal resis
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ReferencesAir-Conditioning and Refr
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References______. 2009. Direct-Driv
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References______. 2008. “ASHRAE S
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Indexchilled-water system 79air-coo
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Indexhumidifiers 126humidity contro
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IndexVAV controlpressure-dependent
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Tranewww.trane.comFor more informat
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