Trane TRG-TRC014-EN manual System-Level Ventilation

Page 74

period five

Application Considerations

notes

System-Level Ventilation

RA

OA

 

 

 

PA

 

 

 

 

 

 

 

 

 

VAV #1

 

VAV #2

 

VAV #3

 

 

primary air (PA)

1000 cfm

 

1000 cfm

 

1000 cfm

 

3000 cfm

[0.47 m3/s]

+ [0.47 m3/s]

+ [0.47 m3/s]

=

[1.41 m3/s]

 

OA required

200 cfm

+

200 cfm

+

300 cfm

=

700 cfm

 

[0.09 m3/s]

 

[0.09 m3/s]

 

[0.15 m3/s]

 

[0.33 m3/s]

ventilation fraction

0.20

 

0.20

 

0.30

 

Figure 96

 

 

 

 

 

 

 

System-Level Ventilation

During operation, a typical VAV system delivers a mixture of outdoor air and recirculated air to the multiple spaces it serves. The volume of supply air that enters a space is controlled by a temperature sensor in that space.

In contrast, the ventilation requirement for a space typically remains constant as the supply airflow varies with thermal load. The challenge is to maintain the proper amount of ventilation air to each individual space while varying the supply air to that space in response to its load.

ASHRAE Standard 62–1999,Ventilation for Acceptable Indoor Air Quality, includes a procedure that can be used to calculate the quantity of outside air required at the central air-handling unit in order to satisfy the ventilation requirements of the individual spaces. At part-load conditions, VAV systems typically require a constant quantity of ventilation air, resulting in an increased percentage of outdoor air at the air handler. Fixed-position dampers will result in underventilated VAV systems.

TRG-TRC014-EN

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Image 74
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

The Trane TRG-TRC014-EN is a comprehensive technical resource guide that serves as an essential tool for HVAC professionals and engineers looking to enhance their understanding of Trane's commercial HVAC systems. This guide provides an in-depth examination of Trane’s advanced technologies, key features, and design characteristics that position their products as industry leaders in heating, ventilation, and air conditioning.

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