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Trane TRG-TRC014-EN period six, Review-PeriodTwo, fan-poweredVAV terminal unit, dual-ductVAV

Models: TRG-TRC014-EN

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period six

Review

notes

Review—Period Two

fan-powered VAV terminal unit

single-duct, cooling-only	dual-duct VAV
VAV terminal unit
	terminal unit	Figure 106

A simple VAV system is comprised of the following components:

nCentral air handler

nSupply duct

nVAV terminal unit with thermostats and supply diffusers for each independently controlled space

nThermostat and unit controller for each terminal unit

nReturn plenum or duct

There are various types of VAV terminal units, each one unique in its response to changing space loads.

TRG-TRC014-EN

Page 82

Image 82

Trane TRG-TRC014-EN period six, Review-PeriodTwo, fan-poweredVAV terminal unit, single-duct, cooling-only, dual-ductVAV

Contents

One of the Systems Series Air Conditioning Clinic VAV SystemsTRG-TRC014-EN A publication of The Trane Company VAV SystemsOne of the Systems Series VAV Systems PrefaceA 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 oneperiod one Constant Volume-FullLoadWhat Is Variable Air Volume? What Is Variable Air Volume? Constant Volume-PartLoadperiod one Constant Volume-MultipleSpaces Constant Volume-MultipleSpacesWhat Is Variable Air Volume? period oneWhat Is Variable Air Volume? Terminal Reheat Systemperiod 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? quiteWhat Is Variable Air Volume? System Comparisonperiod 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 twoVAV Terminal Units period twoComponents of a VAV System period two Single Duct, Cooling OnlyComponents of a VAV System Single Duct, Cooling OnlyComponents of a VAV System Space Heating with 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 SystemComponents of a VAV System Series, Fan-Poweredperiod two Components of a VAV System Parallel Versus Series Fan-PoweredSeries, Fan-Powered period twoComponents of a VAV System Single-DuctVAV Systemsperiod 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 twoComponents of a VAV System Two-Fan, Dual-DuctVAV 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 twoComponents of a VAV System Pneumatic Controlperiod two Components of a VAV System Electronic Controlperiod two Components of a VAV System Direct Digital Control DDCperiod 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 CoandaComponents of a VAV System Ceiling-DiffuserCompatibilityperiod 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 methodComponents of a VAV System Duct Design Recommendationsperiod two period three System ConfigurationsSystem Configurations period threeSystem Configurations period threePerimeter Spaces Perimeter Spacesperiod three Baseboard Perimeter HeatingSystem Configurations heat loss 450 Btu/hr/ftSystem Configurations Overhead Supply Perimeter Heatingperiod 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 ModesSystem Configurations Occupied Modeperiod three System Configurations Unoccupied Modeperiod three System Configurations Morning Warm-up/Cool-downModeperiod three Fan Modulation period fourFan Modulation period fourSystem Resistance Curve period fourFan Modulation Fan Modulation Operating PointRiding the Fan Curve period fourFan Modulation Forward-CurvedCentrifugal Fanperiod 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 Fan Modulation Comparisonsperiod 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 locatedFan Modulation Part-LoadComparisonperiod four period five period fiveApplication Considerations Application ConsiderationsSystem-LevelVentilation period fiveApplication 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 ControlApplication Considerations Part-LoadSupply Air Temperingperiod five Application Considerations Building Pressure ControlDirect Pressurization Control period fiveperiod five Application ConsiderationsA 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-levelventilationperiod six ReviewTRG-TRC014-EN Questions for Period QuizQuestions for Period Questions for PeriodQuiz 11What method of static-pressurecontrol provides the greatest power- savings potential for a VAV system?Questions 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

period six

Review—Period Two

fan-powered VAV terminal unit

single-duct, cooling-only

dual-duct VAV

VAV terminal unit

terminal unit