Post on 11-Dec-2016
HVAC Economizers 101Section #7
Central Air Handling UnitsCentral Air Handling UnitsEconomizer Controls
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Section #7-Central Air Handling Units(AHU) Economizer Controls( )
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Central AHU Are Custom Ordered and Built to Fit Inside the Building with and Built to Fit Inside the Building with Controls
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Many Central AHU Are Standard Units with Customized Site Are Standard Units, with Customized Site Specific Designed DDC Controls
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Typical Controls on Central AHU
Return-Air Fan
Exhaust-Air DamperNormally Closed Return-Air Fan
FromZones
2424
24
Recirculation-AirDamper Normally
Open
DamperMotor
Return-AirTemperatureand Humidity
T & H
S l Ai F24
Open
Filter
Supply-Air Fan
T & H
Outdoor-AirTemperatureand Humidity Heating
Coil
Supply FanStatusHeating
Coil Status
Supply-Air Fan
AB
AB
24
24 2424Outdoor-Air Damper
Normally Closed CoolingABAB
Normally ClosedMixed-Air
Temperature
CoolingCoil Supply-Air
Temperature
Air-Handling Unit Controller
Outputs
I t
CoolingCoil Status
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InputsInputs
Economizer Inspections of Actual AHU EquipmentEquipment
• Typical AHU controlsyp
• DDC controlsDDC controls
• Alerton controls• Alerton controls
• Siemens controls• Siemens controls
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Many Factory Built-Up AHU Are VAV with DDC Controlswith DDC Controls
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http://www.mmtmagazine.org/page/indexa916.html?id=44
Typical Controls on Factory AHUExample of Schematic for Alerton ControlsExample of Schematic for Alerton Controls
ActuatorSensors Controller
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Typical Controls on Factory AHU Example of Economizer Program for Alerton Example of Economizer Program for Alerton Controls
C t llSensors ControllerSensors
Actuator
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Typical Controls on Factory AHU Example of Economizer Program Components
SController
Example of Economizer Program Components for Alerton Controls
Sensors
Actuator
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Typical Controls on Factory AHUExample of Program for Johnson ControlsExample of Program for Johnson Controls
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Typical Controls AHU - Example of AutomatedLogic© Basic Graphics Display AutomatedLogic Basic Graphics Display for Central AHU Controls
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What’s Wrong with the Economizer in this DDC AHU Graphics Display?this DDC AHU Graphics Display?
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Exercise #7 (Provide Answers below on notes page)(Provide Answers below on notes page)
1. The previous slide shows that a typical AHU has a problem in the program code What is it?problem in the program code. What is it?
2. The Automatic Logic Graphic display shows the % of OSA, what is it?
3. How does Alerton programming compare to Siemens programming? Explain.
4. Some central AHU will have two OSA dampers. Why is this designed this way?
5 The controls on a central AHU typically shows all of the5. The controls on a central AHU typically shows all of the dampers being tied together from one control signal. Why?
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