Trane TRG-TRC014-EN manual Fan Modulation Comparisons, BI fan with Discharge Dampers

Page 68

period four

Fan Modulation

notes

In response to reduced airflow and rising system static pressure, the variable- pitch vaneaxial fan responds similarly to a centrifugal fan with either inlet-vane or variable-speed capacity control.

By changing the angle of the fan blades, the performance curve for the fan shifts downward, and the airflow and resulting pressure decrease until the operating point (B) balances along the fan modulation curve.

Fan Modulation Comparisons

 

100

 

 

BI fan with

 

 

 

 

 

 

90

 

 

discharge

 

 

 

 

 

 

80

 

 

dampers

 

 

 

 

 

 

power

70

AF fan with

 

 

 

 

 

 

 

60

inlet vanes

 

 

 

 

FC fan with

% design

50

FC fan with

 

 

 

 

 

 

 

 

inlet vanes

40

discharge

 

 

 

fan-speed

 

 

30

dampers

 

 

 

 

 

 

20

 

 

 

 

 

control

 

 

 

 

 

 

 

variable-pitch

 

 

 

 

 

10

 

 

 

 

 

 

 

 

 

 

 

vaneaxial

 

 

 

 

 

 

0

 

 

 

 

 

 

 

 

 

10

20

30

40

50

60

70

80

90

100

 

 

% design airflow

Figure 89

These curves describe the performance characteristics of each fan modulation method, in terms of the fan power required versus the percent of design airflow. Realize that these are generalized curves based on an arbitrary set of test conditions.

On a generalized basis, the forward-curved (FC) centrifugal fan with inlet vanes, the variable-pitch vaneaxial fan, and fan speed control are similar in performance.

To obtain a more accurate comparison for specific operating conditions, a life- cycle cost analysis should be performed.

TRG-TRC014-EN

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Image 68
Contents Air Conditioning Clinic VAV Systems One of the Systems Series Publication of The Trane Company Preface VAV SystemsContents TRG-TRC014-EN What Is Variable Air Volume? Constant-Volume Variable-Temperature SystemConstant Volume-Full Load Constant Volume-Part Load Constant × Supply AirflowConstant Volume-Multiple Spaces FineTerminal Reheat System Variable-Air-Volume VAV System VAV-Full LoadReduced fan energy Reduced refrigeration energy Why VAV? Energy SavingsVAV-Part Load Why VAV? Comfort Dedicated terminal units Dedicated thermostatsSystem Comparison VAVVAV Building Characteristics Variable Thermal Load ProfilesIndependent Space Control Common Return Air PathComponents of a VAV System Components of a VAV SystemVAV Terminal Units VAV Terminal UnitsAir Heating coil Filter Mixing fan Single Duct, Cooling Only Primary air irSpace Heating with a VAV System VAV Reheat Primary airFan-Powered Terminal Units SeriesParallel, Fan-Powered Series, Fan-Powered Parallel Versus Series Fan-Powered Single-Duct VAV Systems Dual-Duct Variable Air Volume to the Space Cool Primary airConstant Air Volume to the Space Single-Fan, Dual-Duct VAV SystemTwo-Fan, Dual-Duct VAV System VAV Terminal Unit Controls VAV Terminal Unit ControlsUpstream Pressure Affects Airflow Pressure-Dependent Control Pressure-Independent ControlPrimary Airflow Measurement Terminal-Unit Control TechnologiesPneumatic Control Electronic Control Direct Digital Control DDC Components of a VAV System Diffusers DiffusersLinear Slot Diffuser EffectCeiling-Diffuser Compatibility Components of a VAV System Supply Duct System Supply Duct SystemStatic regain method Duct DesignEqual friction method Duct Design Recommendations System Configurations Perimeter P Versus InteriorPerimeter Spaces Perimeter SpacesBaseboard Perimeter Heating Overhead Supply Perimeter Heating Heat loss 250 Btu/hr/ft Fan-Powered VAV Dual-Duct VAVInterior Spaces Interior Spaces, Reheat RequiredSmall Buildings Changeover/Bypass VAV SystemOccupied mode Unoccupied mode Morning warm-up/cool-down mode System-Level Control ModesOccupied Mode Unoccupied Mode Morning Warm-up/Cool-down Mode Fan Performance Curve Fan ModulationFan Performance Curve System Resistance Curve System Resistance CurveOperating Point Riding the Fan CurveForward-Curved Centrifugal Fan Fan Modulation Curve Fan Modulation CurveFan Control Loop VAV Fan ModulationFan Modulation Methods Discharge DampersStatic pressure Discharge damper SP loss Inlet Vanes Fan-Speed Control 0 r p mVariable-Pitch Blade Control Fan Modulation Comparisons BI fan with Discharge DampersControlling System Static Pressure Fan Outlet Static-Pressure ControlSupply Duct Static-Pressure Control Sensor located Down supply ductOptimized Static-Pressure Control At fan outletPart-Load Comparison Application Considerations Period fiveSystem-Level Ventilation System-Level VentilationVentilation Reset Freeze Protection for Coils Freeze Protection for CoilsMeasures to Prevent Coil Freeze-Up Part-Load Space Humidity Control Part-Load Space Humidity ControlPart-Load Supply Air Tempering Building Pressure Control Building Pressure ControlDirect Pressurization Control Application Considerations Review Review-Period OneReview-Period Two Review-Period Three Review-Period FourReview-Period Five Trane Air Conditioning ManualReview Quiz Questions for PeriodQuiz TRG-TRC014-EN Answers Glossary Glossary Glossary Trane Company

TRG-TRC014-EN specifications

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