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Trane TRG-TRC014-EN manual Fan Modulation Methods, Discharge Dampers, period four

Models: TRG-TRC014-EN

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period four

Fan Modulation

notes

The system static pressure controller senses this higher pressure and sends a signal to the supply fan to reduce capacity. Modulating the fan capacity results in a new fan performance curve and the system balances at an operating point (B) along the fan modulation curve, bringing the system static pressure back down to the set point.

Fan Modulation Methods

▲Discharge dampers

▲Inlet vanes

▲Fan-speed control

▲Variable-pitch blade control

Figure 80

Fan Modulation Methods

The four methods commonly used to modulate fan capacity are: discharge dampers, inlet vanes, fan-speed control, and variable-pitch blade control. We will examine these now.

Discharge Dampers

supply

fan

discharge dampers

Figure 81

Discharge dampers match the static pressure supplied by the fan with the static pressure required by the system. They accomplish this by adding static- pressure loss to the system a little bit downstream of the fan.

58	TRG-TRC014-EN

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Trane TRG-TRC014-EN manual Fan Modulation Methods, Discharge Dampers, period four

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 Components of a VAV System Contentsperiod one What Is Variable Air Volume? period twoTRG-TRC014-EN period one What Is Variable Air Volume?What Is Variable Air Volume? Constant-Volume Variable-TemperatureSystemConstant Volume-FullLoad period oneWhat Is Variable Air Volume? Constant Volume-PartLoad What Is Variable Air Volume?period one period one Constant Volume-MultipleSpacesWhat Is Variable Air Volume? Constant Volume-MultipleSpacesTerminal Reheat System What Is Variable Air Volume?period one period one Variable-Air-VolumeVAV SystemVAV-FullLoad What Is Variable Air Volume?Why VAV? Why VAV? Energy SavingsVAV-PartLoad What Is Variable Air Volume?quite Why VAV? ComfortWhat Is Variable Air Volume? period oneSystem Comparison What Is Variable Air Volume?period one period one VAV Building CharacteristicsVariable Thermal Load Profiles What Is Variable Air Volume?period one Independent Space ControlCommon Return Air Path What Is Variable Air Volume?period two period twoComponents of a VAV System Components of a VAV Systemperiod two VAV Terminal UnitsComponents of a VAV System Single Duct, Cooling Only Single Duct, Cooling OnlyComponents of a VAV System period twoSpace Heating with a VAV System Components of a VAV Systemperiod two period two VAV Reheatprimary air Components of a VAV Systemparallel Fan-PoweredTerminal UnitsComponents of a VAV System period twoComponents of a VAV System Parallel, Fan-Poweredplenum air Parallel, Fan-PoweredSeries, Fan-Powered Components of a VAV Systemperiod two period two Parallel Versus Series Fan-PoweredSeries, Fan-Powered Components of a VAV SystemSingle-DuctVAV Systems Components of a VAV Systemperiod two warm primary air cool primary air supply air Dual-DuctComponents of a VAV System period twoComponents of a VAV System Variable Air Volume to the Spacewarm coolperiod two Constant Air Volume to the SpaceSingle-Fan, Dual-DuctVAV System Components of a VAV SystemTwo-Fan, Dual-DuctVAV System Components of a VAV Systemperiod two period two VAV Terminal Unit ControlsUpstream Pressure Affects Airflow Components of a VAV Systemperiod two Pressure-DependentControlPressure-IndependentControl Components of a VAV Systemperiod two Primary Airflow MeasurementTerminal-UnitControl Technologies Components of a VAV SystemPneumatic 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 Electronic pressure transducer provides pressure-independentcontrol Components of a VAV Systemperiod two Direct Digital Control DDCDiffusers DiffusersComponents of a VAV System period twoCoanda Linear Slot DiffuserComponents of a VAV System period twoCeiling-DiffuserCompatibility Components of a VAV Systemperiod two cross T Components of a VAV Systemperiod two Ceiling-DiffuserCompatibilitySupply Duct System Supply Duct SystemComponents of a VAV System period twoEqual friction method Duct DesignComponents of a VAV System period twoDuct Design Recommendations Components of a VAV Systemperiod two period three System ConfigurationsSystem Configurations period threePerimeter Spaces period threePerimeter Spaces System Configurationsheat loss 450 Btu/hr/ft Baseboard Perimeter HeatingSystem Configurations period threeOverhead Supply Perimeter Heating System Configurationsperiod three heat loss 250 Btu/hr/ft System Configurationsperiod three VAV Reheatperiod three Fan-PoweredVAVDual-DuctVAV System Configurationsperiod three Interior SpacesInterior Spaces, Reheat Required System Configurationsperiod three Small BuildingsChangeover/Bypass VAV System System ConfigurationsSystem-LevelControl Modes System-LevelControl ModesSystem Configurations period threeOccupied Mode System Configurationsperiod three Unoccupied Mode System Configurationsperiod three Morning Warm-up/Cool-downMode System Configurationsperiod three period four period fourFan Modulation Fan Modulationperiod four System Resistance CurveFan Modulation period four Operating PointRiding the Fan Curve Fan ModulationForward-CurvedCentrifugal Fan Fan Modulationperiod four Fan Modulation Curve Fan Modulation CurveFan Modulation period fourperiod four Fan Control LoopVAV Fan Modulation Fan Modulationperiod four Fan Modulation MethodsDischarge Dampers Fan ModulationAs 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 pressure Fan Modulationperiod four Discharge DampersInlet Vanes Inlet VanesFan Modulation period fourFan-SpeedControl Fan-SpeedControlFan Modulation period fourVariable-PitchBlade Control Variable-PitchBlade ControlFan Modulation period fourFan Modulation Comparisons Fan Modulationperiod four period four Controlling System Static PressureFan Outlet Static-PressureControl Fan Modulationsensor located 2/3 down supply duct Supply Duct Static-PressureControlFan Modulation period foursensor located Optimized Static-PressureControlFan Modulation period fourPart-LoadComparison Fan Modulationperiod four Application Considerations period fiveApplication Considerations period fiveperiod five System-LevelVentilationApplication Considerations outdoor airflow Ventilation ResetApplication Considerations period fiveperiod five Freeze Protection for CoilsMeasures to Prevent Coil Freeze-Up Application ConsiderationsPart-LoadSpace Humidity Control Part-LoadSpace Humidity ControlApplication Considerations period fivePart-LoadSupply Air Tempering Application Considerationsperiod five period five Building Pressure ControlDirect Pressurization Control Application ConsiderationsApplication 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 period six period sixReview ReviewReview period sixReview-PeriodTwo fan-poweredVAV terminal unitperiod six Review-PeriodThreeReview-PeriodFour ReviewSystem-levelventilation Review-PeriodFiveReview period sixReview 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 Glossary parallel fan-poweredterminal unit A fan-poweredVAV terminal unitsupply air Conditioned air delivered to a space GlossaryAn American Standard Company The Trane Company