HVAC Economizers 101Section #7

Central Air Handling UnitsCentral Air Handling UnitsEconomizer Controls

7-1

Section #7-Central Air Handling Units(AHU) Economizer Controls( )

7-2

Central AHU Are Custom Ordered and Built to Fit Inside the Building with and Built to Fit Inside the Building with Controls

7-3

Many Central AHU Are Standard Units with Customized Site Are Standard Units, with Customized Site Specific Designed DDC Controls

7-4

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

7-5

InputsInputs

Economizer Inspections of Actual AHU EquipmentEquipment

• Typical AHU controlsyp

• DDC controlsDDC controls

• Alerton controls• Alerton controls

• Siemens controls• Siemens controls

7-6

Many Factory Built-Up AHU Are VAV with DDC Controlswith DDC Controls

7-7

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

7-8

Typical Controls on Factory AHU Example of Economizer Program for Alerton Example of Economizer Program for Alerton Controls

C t llSensors ControllerSensors

Actuator

7-9

Typical Controls on Factory AHU Example of Economizer Program Components

SController

Example of Economizer Program Components for Alerton Controls

Sensors

Actuator

7-10

Typical Controls on Factory AHUExample of Program for Johnson ControlsExample of Program for Johnson Controls

7-11

Typical Controls AHU - Example of AutomatedLogic© Basic Graphics Display AutomatedLogic Basic Graphics Display for Central AHU Controls

7-12

What’s Wrong with the Economizer in this DDC AHU Graphics Display?this DDC AHU Graphics Display?

7-13

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?

7-14