TRG-TRC014-EN
Air Conditioning Clinic VAV Systems
One of the Systems Series
One of the Systems Series
VAV Systems
A publication of The Trane Company
A Trane Air Conditioning Clinic
Preface
VAV Systems
period two
Contents
period one What Is Variable Air Volume?
Components of a VAV System
TRG-TRC014-EN
Constant-Volume Variable-TemperatureSystem
What Is Variable Air Volume?
What Is Variable Air Volume?
period one
What Is Variable Air Volume?
Constant Volume-FullLoad
period one
period one
Constant Volume-PartLoad
What Is Variable Air Volume?
Constant Volume-MultipleSpaces
Constant Volume-MultipleSpaces
What Is Variable Air Volume?
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period one
Terminal Reheat System
What Is Variable Air Volume?
What Is Variable Air Volume?
Variable-Air-VolumeVAV System
VAV-FullLoad
period one
What Is Variable Air Volume?
Why VAV? Energy Savings
VAV-PartLoad
Why VAV?
period one
Why VAV? Comfort
What Is Variable Air Volume?
quite
period one
System Comparison
What Is Variable Air Volume?
What Is Variable Air Volume?
VAV Building Characteristics
Variable Thermal Load Profiles
period one
What Is Variable Air Volume?
Independent Space Control
Common Return Air Path
period one
Components of a VAV System
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Components of a VAV System
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Components of a VAV System
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VAV Terminal Units
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Single Duct, Cooling Only
Components of a VAV System
Single Duct, Cooling Only
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Space Heating with a VAV System
Components of a VAV System
Components of a VAV System
VAV Reheat
primary air
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period two
Fan-PoweredTerminal Units
Components of a VAV System
parallel
Parallel, Fan-Powered
Parallel, Fan-Powered
plenum air
Components of a VAV System
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Series, Fan-Powered
Components of a VAV System
Components of a VAV System
Parallel Versus Series Fan-Powered
Series, Fan-Powered
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period two
Single-DuctVAV Systems
Components of a VAV System
period two
Dual-Duct
Components of a VAV System
warm primary air cool primary air supply air
cool
Variable Air Volume to the Space
warm
Components of a VAV System
Components of a VAV System
Constant Air Volume to the Space
Single-Fan, Dual-DuctVAV System
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period two
Two-Fan, Dual-DuctVAV System
Components of a VAV System
Components of a VAV System
VAV Terminal Unit Controls
Upstream Pressure Affects Airflow
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Components of a VAV System
Pressure-DependentControl
Pressure-IndependentControl
period two
Components of a VAV System
Primary Airflow Measurement
Terminal-UnitControl Technologies
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period two
Pneumatic Control
Components of a VAV System
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Electronic Control
Components of a VAV System
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Direct Digital Control DDC
Components of a VAV System
Direct Digital Control DDC
Components of a VAV System
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Electronic pressure transducer provides pressure-independentcontrol
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Diffusers
Components of a VAV System
Diffusers
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Linear Slot Diffuser
Components of a VAV System
Coanda
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Ceiling-DiffuserCompatibility
Components of a VAV System
Ceiling-DiffuserCompatibility
Components of a VAV System
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cross T
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Supply Duct System
Components of a VAV System
Supply Duct System
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Duct Design
Components of a VAV System
Equal friction method
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Duct Design Recommendations
Components of a VAV System
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System Configurations
System Configurations
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System Configurations
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Perimeter Spaces
Perimeter Spaces
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Baseboard Perimeter Heating
System Configurations
heat loss 450 Btu/hr/ft
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Overhead Supply Perimeter Heating
System Configurations
VAV Reheat
System Configurations
period three
heat loss 250 Btu/hr/ft
System Configurations
Fan-PoweredVAV
Dual-DuctVAV
period three
System Configurations
Interior Spaces
Interior Spaces, Reheat Required
period three
System Configurations
Small Buildings
Changeover/Bypass VAV System
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period three
System-LevelControl Modes
System Configurations
System-LevelControl Modes
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Occupied Mode
System Configurations
period three
Unoccupied Mode
System Configurations
period three
Morning Warm-up/Cool-downMode
System Configurations
Fan Modulation
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Fan Modulation
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Fan Modulation
period four
System Resistance Curve
Fan Modulation
Operating Point
Riding the Fan Curve
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period four
Forward-CurvedCentrifugal Fan
Fan Modulation
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Fan Modulation Curve
Fan Modulation
Fan Modulation Curve
Fan Modulation
Fan Control Loop
VAV Fan Modulation
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Fan Modulation
Fan Modulation Methods
Discharge Dampers
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Discharge Dampers
Fan Modulation
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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 pressure
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Inlet Vanes
Fan Modulation
Inlet Vanes
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Fan-SpeedControl
Fan Modulation
Fan-SpeedControl
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Variable-PitchBlade Control
Fan Modulation
Variable-PitchBlade Control
period four
Fan Modulation Comparisons
Fan Modulation
Fan Modulation
Controlling System Static Pressure
Fan Outlet Static-PressureControl
period four
period four
Supply Duct Static-PressureControl
Fan Modulation
sensor located 2/3 down supply duct
period four
Optimized Static-PressureControl
Fan Modulation
sensor located
period four
Part-LoadComparison
Fan Modulation
period five
period five
Application Considerations
Application Considerations
Application Considerations
period five
System-LevelVentilation
period five
Ventilation Reset
Application Considerations
outdoor airflow
Application Considerations
Freeze Protection for Coils
Measures to Prevent Coil Freeze-Up
period five
period five
Part-LoadSpace Humidity Control
Application Considerations
Part-LoadSpace Humidity Control
period five
Part-LoadSupply Air Tempering
Application Considerations
Application Considerations
Building Pressure Control
Direct Pressurization Control
period five
A 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
Application Considerations
period five
Review
period six
Review
period six
fan-poweredVAV terminal unit
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Review-PeriodTwo
Review
Review
Review-PeriodThree
Review-PeriodFour
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period six
Review-PeriodFive
Review
System-levelventilation
TRG-TRC014-EN
Review
period six
Questions for Period
Quiz
Questions for Period
Questions for Period
Questions for Period
11What method of static-pressurecontrol provides the greatest power- savings potential for a VAV system?
Quiz
TRG-TRC014-EN
Answers
Glossary
parallel fan-poweredterminal unit A fan-poweredVAV terminal unit
Glossary
Glossary
supply air Conditioned air delivered to a space
The Trane Company
An American Standard Company