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Trane TRG-TRC014-EN manual period one, What Is Variable Air Volume?, VAV Systems

Models: TRG-TRC014-EN

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period one

What Is Variable Air Volume?

notes

VAV Systems

period one

What Is Variable Air Volume?

Figure 2

Avariable-air-volume (VAV) air-conditioning system varies the volume of constant-temperature air that is supplied to meet the changing load conditions of the space.

Constant-Volume,

Variable-Temperature System

supply	cooling	OA
fan	coil

thermostatRA

space

Figure 3

For the purpose of comparison, we will look at a traditional constant-volume (CV), variable-air-temperature system.

This system delivers a constant volume of air to the space and, to maintain the required space temperature at all load conditions, varies the temperature of this air. In this example, the temperature of the air is varied by controlling the capacity of the central cooling coil.

TRG-TRC014-EN

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Trane TRG-TRC014-EN period one, What Is Variable Air Volume?, Constant-Volume Variable-TemperatureSystem, VAV Systems

Contents

Air Conditioning Clinic VAV Systems One of the Systems SeriesTRG-TRC014-EN VAV Systems A publication of The Trane CompanyOne of the Systems Series Preface VAV SystemsA Trane Air Conditioning Clinic period two Contentsperiod one What Is Variable Air Volume? Components of a VAV SystemTRG-TRC014-EN Constant-Volume Variable-TemperatureSystem What Is Variable Air Volume?What Is Variable Air Volume? period oneConstant Volume-FullLoad period oneWhat Is Variable Air Volume? Constant Volume-PartLoad What Is Variable Air Volume?period one Constant Volume-MultipleSpaces Constant Volume-MultipleSpacesWhat Is Variable Air Volume? period oneTerminal Reheat System What Is Variable Air Volume?period one What Is Variable Air Volume? Variable-Air-VolumeVAV SystemVAV-FullLoad period oneWhat Is Variable Air Volume? Why VAV? Energy SavingsVAV-PartLoad Why VAV?period one Why VAV? ComfortWhat Is Variable Air Volume? quiteSystem Comparison What Is Variable Air Volume?period one What Is Variable Air Volume? VAV Building CharacteristicsVariable Thermal Load Profiles period oneWhat Is Variable Air Volume? Independent Space ControlCommon Return Air Path period oneComponents of a VAV System period twoComponents of a VAV System period twoperiod two VAV Terminal UnitsComponents of a VAV System period two Single Duct, Cooling OnlyComponents of a VAV System Single Duct, Cooling OnlySpace Heating with a VAV System Components of a VAV Systemperiod two Components of a VAV System VAV Reheatprimary air period twoperiod two Fan-PoweredTerminal UnitsComponents of a VAV System parallelParallel, Fan-Powered Parallel, Fan-Poweredplenum air Components of a VAV SystemSeries, Fan-Powered Components of a VAV Systemperiod two Components of a VAV System Parallel Versus Series Fan-PoweredSeries, Fan-Powered period twoSingle-DuctVAV Systems Components of a VAV Systemperiod two period two Dual-DuctComponents of a VAV System warm primary air cool primary air supply aircool Variable Air Volume to the Spacewarm Components of a VAV SystemComponents of a VAV System Constant Air Volume to the SpaceSingle-Fan, Dual-DuctVAV System period twoTwo-Fan, Dual-DuctVAV System Components of a VAV Systemperiod two Components of a VAV System VAV Terminal Unit ControlsUpstream Pressure Affects Airflow period twoComponents of a VAV System Pressure-DependentControlPressure-IndependentControl period twoComponents of a VAV System Primary Airflow MeasurementTerminal-UnitControl Technologies period twoPneumatic Control Components of a VAV Systemperiod two Electronic Control Components of a VAV Systemperiod two Direct Digital Control DDC Components of a VAV Systemperiod two Direct Digital Control DDC Components of a VAV Systemperiod two Electronic pressure transducer provides pressure-independentcontrolperiod two DiffusersComponents of a VAV System Diffusersperiod two Linear Slot DiffuserComponents of a VAV System CoandaCeiling-DiffuserCompatibility Components of a VAV Systemperiod two Ceiling-DiffuserCompatibility Components of a VAV Systemperiod two cross Tperiod two Supply Duct SystemComponents of a VAV System Supply Duct Systemperiod two Duct DesignComponents of a VAV System Equal friction methodDuct Design Recommendations Components of a VAV Systemperiod two period three System ConfigurationsSystem Configurations period threeSystem Configurations period threePerimeter Spaces Perimeter Spacesperiod three Baseboard Perimeter HeatingSystem Configurations heat loss 450 Btu/hr/ftOverhead Supply Perimeter Heating System Configurationsperiod three VAV Reheat System Configurationsperiod three heat loss 250 Btu/hr/ftSystem Configurations Fan-PoweredVAVDual-DuctVAV period threeSystem Configurations Interior SpacesInterior Spaces, Reheat Required period threeSystem Configurations Small BuildingsChangeover/Bypass VAV System period threeperiod three System-LevelControl ModesSystem Configurations System-LevelControl ModesOccupied Mode System Configurationsperiod three Unoccupied Mode System Configurationsperiod three Morning Warm-up/Cool-downMode System Configurationsperiod three Fan Modulation period fourFan Modulation period fourperiod four System Resistance CurveFan Modulation Fan Modulation Operating PointRiding the Fan Curve period fourForward-CurvedCentrifugal Fan Fan Modulationperiod four period four Fan Modulation CurveFan Modulation Fan Modulation CurveFan Modulation Fan Control LoopVAV Fan Modulation period fourFan Modulation Fan Modulation MethodsDischarge Dampers period fourDischarge Dampers Fan Modulationperiod four As the VAV terminal units modulate shut, the system resistance curve shifts upwards. The fan begins to “ride up” the constant-speedperformance curve, from the design operating point A, trying to reach the balance point with this new system resistance curve. As a result, the fan delivers a lower airflow at a higher static pressureperiod four Inlet VanesFan Modulation Inlet Vanesperiod four Fan-SpeedControlFan Modulation Fan-SpeedControlperiod four Variable-PitchBlade ControlFan Modulation Variable-PitchBlade ControlFan Modulation Comparisons Fan Modulationperiod four Fan Modulation Controlling System Static PressureFan Outlet Static-PressureControl period fourperiod four Supply Duct Static-PressureControlFan Modulation sensor located 2/3 down supply ductperiod four Optimized Static-PressureControlFan Modulation sensor locatedPart-LoadComparison Fan Modulationperiod four period five period fiveApplication Considerations Application Considerationsperiod five System-LevelVentilationApplication Considerations period five Ventilation ResetApplication Considerations outdoor airflowApplication Considerations Freeze Protection for CoilsMeasures to Prevent Coil Freeze-Up period fiveperiod five Part-LoadSpace Humidity ControlApplication Considerations Part-LoadSpace Humidity ControlPart-LoadSupply Air Tempering Application Considerationsperiod five Application Considerations Building Pressure ControlDirect Pressurization Control period fiveApplication Considerations period fiveA sensitive static-pressurecontroller directly compares the variations between the space static pressure and the outdoor reference static pressure. The controller modulates the capacity of a central relief fan to maintain a fixed static-pressuredifference, usually a slightly positive building pressure. The space static-pressuresensor is typically located in the lobby or near the main entrance Review period sixReview period sixfan-poweredVAV terminal unit period sixReview-PeriodTwo ReviewReview Review-PeriodThreeReview-PeriodFour period sixperiod six Review-PeriodFiveReview System-levelventilationReview period sixTRG-TRC014-EN Questions for Period QuizQuestions for Period Questions for Period11What method of static-pressurecontrol provides the greatest power- savings potential for a VAV system? QuizQuestions for Period TRG-TRC014-EN Answers Glossary parallel fan-poweredterminal unit A fan-poweredVAV terminal unit GlossaryGlossary supply air Conditioned air delivered to a spaceThe Trane Company An American Standard Company