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| Overview

The VVT-C staged RTU is a profile that is used to control an RTU, which meet the HVAC demands of a space. The RTU can be a cooling only/Heating Only or Both cooling and Heating, the profile has its all to control.

The profile supports up to five stages of cooling, Heating and Fan speeds and humidification. Based on the type of RTU used and type of conditioning and controls required, the options can be set and used.

| How it Works

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Once you select the VVT-C Staged RTU profile from the system selection, from all the relays, analog inputs and output that are available as a part of the CM board of the CCU, six output relays and an auxiliary relay is made available in the profile screen to enable and select the stages of conditioning required based on the preferences.

The Algorithm continuously track the average current temperature of the zones mapped as terminal profiles, under the VVT-C Staged RTU system profile, and looks for the change in the difference between the system level Desired Temperature and Average Current Temperatures and provides the required conditioning via Staged equipment.

When the Average Temperature increases above the set point or desired temperature and the zones demand cooling the cooling stages are activated

And when the Average Temperature decreases below the set point or desired temperature, and the zones demand heating the Heating stages are activated.

| Wiring

Below is a wiring schematic for the VVT-C Staged RTU, that show the connection from the CM board of the CCU to the RTU.

Note: The wiring schematic would differ for different staged control options set during the configuration.

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| Configuration

Below is the configuration screen for the VVT-C staged RTU, The relays are  enabled or disabled based on the preferences.

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Once a Relay is enabled the drop down next to the relay is enabled for selection as below

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Relays 1-6

By default are configured as a traditional thermostat connection. However, depending on your equipment, you can reconfigure (Mapping) any of these relays to act as heating, cooling, or fan. 

Relay 7

Auxillary relay for humidifier or dehumidifier contact. This is a wet contact. If your equipment needs a dry contact, please see wiring information for which jumper to pull from the CM board. 

Test Signal

At any point you can override the value the output the algorithm decided. This is used for troubleshooting and testing your equipment. 

| Operations

Cooling

When the zones demand for cooling the algorithm calculates a loop output, which is based on the Proportional and Integral loop for control signals, called cooling loop output. This loop output which is in percentage is scaled to the different stages of cooling as below.

  • Cooling loop output > 0%, Cooling Stage 1   Turns On
  • Cooling loop output > 50%, Cooling Stage 2   Turns On
  • Cooling loop output <= 0%, Cooling Stage 1 Turns Off
  • Cooling loop output <= 40%, Cooling Stage 2  Turns Off

Heating

When the zones demand for heating the algorithm calculates a loop output, which is based on the Proportional and Integral loop for control signals, called Heating loop output. This loop output which is in percentage is scaled to the different stages of Heating as below.

  • Heating loop output > 0%, Heating Stage 1   Turns On
  • Heating loop output > 50%, Heating Stage 2   Turns On
  • Heating loop output <= 0%, Heating Stage 1  Turns Off
  • Heating loop output <= 40%, Heating Stage 2  Turns Off

Recirculate

When the zone demands recirculation along with cooling, the system will call for the stage-1 fan and so on for fan speed which is also based on the loop output that is calculated.

 

 

 

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