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| Overview

The Outside Air Optimization is a software profile supported by the 75F system. It controls the outside air damper to regulate the amount of outer fresh air that is brought into the building. Otherwise, known as the economizer, which is a feature of HVAC systems to use cold outside air to provide free cooling to the building. The OAO has 2 main functions, Demand Control Ventilation(DCV) and economizing. Optionally, it is also used for maintaining pressure inside the building.

| How It works

The OAO combines two primary aspects for Economizer control.

Demand Control Ventilation

It is a CO2 level-based economizing, which is used to control CO2 IAQ levels in space. If CO2 is above the threshold that is set, then the OAO control opens the outside air damper proportionately. DCV essentially sets a minimum damper position for the outside air, and it's applicable for both cooling and heating.

Comparative Enthalpy/ Dry Bulb free cooling control

It is a temperature and humidity-based economizing condition where the enthalpy of the outdoor air and the indoor air is derived to make the decision on whether to bring in outside air for free cooling, where Enthalpy determines the total amount of energy in the air based on humidity and temperature.

Enthalpy determines the total amount of energy in the air and is based on both humidity and temperature. While there is no simple math to determine enthalpy, The psychometric chart shown below is used to discover how much energy the air has.

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The 75F Outside Air Optimization (OAO) kit includes a 75F economizer controller, COsensor, Mixed Air Temperature (MAT) sensor, two 10K thermistors for SAT and OAT, and cloud computing software with predictive analytics that provides optimum positioning of the outside air damper on package HVAC units throughout the year using demand-controlled ventilation (DCV) and differential enthalpy. Economizer logic is enhanced by predictive analytics to yield increased energy savings and comfort.

| Wiring

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Below are the connection details for the wiring schematic shown above

  • Analog-in1 connects to return air CO2 sensor   
  • Analog-in2 connects to RTU current transformer 
  • Th-in1 connects to Outside Air Temperature   
  • Th-in2 connects to Supply Air Temperature 
  • One Wire sensor bus connects to the Duct Temperature/Humidity sensor for Mixed Air Temperature/Humidity 
  • Analog-out1 connects to the Outside Air Damper   
  • Analog-out2 connects to Return Air Damper 
  • Relay-1 connects to exhaust fan stage 1  
  • Relay-2 connects to exhaust fan stage 2  

| Pairing

The 75F SmartNode is used along with the CCU to achieve the Outside Air Optimization control in the buildings.

Once power is supplied to the system and all SmartNodes are displaying the default room.

From the zones page of the CCU:

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  • Click the settings mceclip1.png icon.

The floor layout screen is displayed.

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  • Disconnect the tablet from the CM and carry it with you. The device is paired via Bluetooth.
  • Press the right button on the SmartNode OAO until you reach the advertising mode screen.
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  • Click the system devices option
  • Select the OAO under System Devices.

     

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  • Click Pair Module to start the pairing process. 
  • Follow the pairing steps on the SmartNode.

Click Pair. 

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The CCU detects all the devices ready for pairing at close range, confirm the Bluetooth Pairing address of the SmartNode that needs to be paired, and select the device

The pairing pin entry screen is displayed.

 

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  • Enter the pin displayed on the advertising screen in the SmartNode and click proceed.
  • Pairing process will take a few more seconds and then complete displaying “Success” on the screen. 

| Configuration

The OAO system profile configuration screen is displayed.

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| Configuration Parameters

Parameter

Purpose

Default Value

Values in the drop-down list

Outside Damper at Min Drive (V)

To select a voltage value for the min outside air damper opening position, at minimum economizing requirement.

 

2V

Range from 0V to 10V in 1V increments 

The outside damper output signal will modulate between outsideDamperAtMinDrive and outsideDamperAtMaxDrive as the oaoFinalLoopOutput changes from 0% to 100% depending on the conditions.   

Outside Damper at Max Drive (V)

To select a voltage value for the max outside air damper opening position, at maximum economizing requirement.

10V

 

Range from 0V to 10V in 1V increments  

Return Damper at Min Drive (V)

To select a voltage value for the min return air damper opening position, at minimum economizing requirement.

2V

 

Range from 0V to 10V in 1V increments  

Return Damper at Max Drive (V)

To select a voltage value for the max return air damper opening position, at maximum economizing requirement.

2V

Range from 0V to 10V in 1V increments

The return air damper works opposite to the outside air damper and is calculated as follows  

returnAirFinalOutput = 100 - outsideAirFinalLoopOutput   

Outside Damper Min Open(%) 

To select a percentage value for the minimum outside air damper opening position

0

Range from 0 to 100 in 1% increments 

Return Damper at Min Open(%) 

To select a percentage value for the minimum return air damper opening position

0

Range from 0 to 100 in 1% increments 

Exhaust Fan Stage 1 Threshold (%)

To select a percentage value for the exhaust fan stage 1 threshold

50

Range from 0 to 100 in 1% increments 

Exhaust Fan Stage 2 Threshold (%)

To select a percentage value for the exhaust fan stage 2 threshold

90

Range from 0 to 100 in 1% increments 

Current Transformer Type

To select the type of current transformer used in the setup

0-20 (A)

0-10 (A)

0-20 (A)

0-50 (A)

CO2 Threshold  (ppm)

To select a CO2 threshold value 

1000

Range from 0 to 2000 in 10 ppm increments 

Exhaust Fan Hysteresis (%)

To select a hysteresis percentage value for the Exhaust Fan

5

Range from 0 to 100 in 1% increments

Use Per Room CO2 Sensing

To enable or disable use of per room CO2 sensing values to determine the loop output

Disabled

NA

Smart Purge Outside Damper Min open

To select a value for the minimum outside air damper opening position during the smart purge operation in the profile.

100

Range from 0 to 100 in increments of 1

Enhanced Ventilation Outside Damper Min Open 

To select a value for the minimum outside air damper opening position during the enhanced ventilation operation in the profile.

50

Range from 0 to 100 in increments of 1

  • Set the required parameters from the configuration parameters screen, using the table provided as a reference.
  • Click Set to confirm the configuration changes made.

The OAO profile is configured and the same can be visualized in the CCU and portals.

 

 

 

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