3 Minute Read

| Overview

The VVT-C terminal profile is a profile that controls the terminal equipment of a space, which is provided by an RTU or an AHU for its HVAC needs.

The profile is supported by a SmartNode, Smart Damper, and a Smart Damper Actuator to provide the necessary control outputs based on the profile configured.

| How it Works

Carrier Dynamic Airflow Balancing operates to help temperature balance a system without fully closing off zones and creating harmful back pressure on the AHU.

Once you select the VVT-C terminal profile under SmartNode VVT-C profiles, the configuration provides the options to define the damper types, size, shape, and zone priority. It also provides the options to define the minimum and maximum damper positions during heating and cooling along with the Temperature Offset.

Additionally, the profile provides options to modify the controls based on the Internal Air Quality and Co2, with the IAQ and Co2 control that can be enabled or disabled.

Normally the Algorithm continuously tracks the current temperature of the zone and looks for the change in the difference between the terminal level Desired Temperature and Current Temperature and provides an optimal damper opening position within the dead band range, which is a resultant of the loop output based on the PI loop for control signals.

When the Current Temperature increases above the set point or desired temperature, the zone calls for cooling from the system or building-level equipment. 

And when the Current Temperature decreases below the set point or desired temperature, the zones call for Heating from the system or building-level equipment.

The building or system-level device is an RTU or AHU which is controlled by the system-level VVT-C profiles.

For more information on the system-level VVT-C, profiles refer below.

VVT-C Staged RTU - Wiring/ Configuration

VAV Staged RTU w/ VFD Fan

VVT-C Fully Modulating AHU - Wiring/ Configuration

VVT-C Modulating AHU with DCWB

VVT-C Advanced Hybrid AHU - Wiring/ Configuration

When the Co2 or the IAQ control is enabled, the algorithm takes the target and threshold values of Co2 and VOC into consideration. An increase in the value from the threshold value results in a loop output, and it changes the minimum damper position for the actual control to the changes in percentage value.

This resultant loop output is called the Co2 loop output, which is simply the weighted average Co2 loop output for all the zones that have Co2 control enabled.

Example- If the target and threshold are 1000ppm and 800, measured Co2 is 850 and configured damper limits are 0-100.  The algorithm starts raising the minimum damper position proportionally from 800.  A Co2 measurement of 850 will yield a loop output of 25%. This raises the damper's min position so that it now varies in the range of 25 – 100 based on temperature.

| Wiring

Below is a wiring schematic for the VVT-C terminal profile, that shows the connection between the SmartNode, Damper Actuator, and the Damper.

A Temperature and Humidity only sensor, which can be a Wall Sensor/Ceiling Sensor/Duct Sensor/Flush Mount Sensor is connected to the RTS port of the SmartNode.


Points to be considered while wiring

When installing a Belimo actuator, use the 18gauge thermostat wire for connections between SmartNode and Actuator. 

For the sensors, both ends of the harness are the same male connectors. Plug one end into the Wall Sensor. Plug the other end into the RTS port on the SmartNode.

| Configuration

Below is the configuration screen for the VVT-C terminal profile.

Once you've paired the SmartNode as a VVT-C profile, and once a few specific configuration parameters that define the physical characteristics of the setup are set in the configuration screen, the Carrier sequence for the VVT-C will influence and control the setup. 


| Configuration Parameters

Damper Type

Following are the damper types the Carrier system supports


Damper 1 Type

Type of actuator being controlled on Damper port 1 or Analog out 1. Carrier Smart Dampers is controlled using an MAT actuator through Damper port 1. If you are using a modulating 0-10Vdc type, then Damper 1 Type will be Analog Out 1 and will read TH1 for the DAT. 

Damper 2 Type

Type of actuator being controlled on Damper port 2 or Analog out 2. Carrier Smart Dampers are controlled using an MAT actuator through Damper port 2. If you are using a modulating 0-10Vdc type, then Damper 2 Type will be Analog Out 2 and will read TH2 for the DAT. 

Use Reheat

It is a provision to include Reheat capability in the profile for more information on the reheat aspect refer to Reheat for VVT-C Terminal Profile

Size -Size of the associated damper. Used for calculating CFM. 

Shape - Shape of the associated damper. Also used for calculating CFM.

Zone Priority -Used in calculations for driving the AHU into heating or cooling. (Low = 1, Normal = 10, High = 50) 

Enable IAQ Control -Must have an IAQ sensor present. Nonstandard option.

Enable Co2 Control - Must have a Co2 sensor present. Nonstandard option. 

Enable Occupancy Control - Must have an Occupancy Sensor present. Nonstandard option. 

Enable CFM- To enable operation based on the Airflow in cubic feet per minute calculation. For more information refer to True CFM (Cubic Feet per Minute)

Temperature Offset -Value applied to the current temperature reading if the current temperature needs calibration. Sensors should not typically need calibration. 

Min/ Max Damper Positions -Hard limits on damper positions in a given mode. 


Once the required parameters are configured

  • Click set to confirm the configuration.

| Post Configuration

Once a VVT-C terminal profile is configured the same is visualized in the CCU as below.


And in portals as below.

| Operation

Considering there is more than one terminal profile connected to the VVT-C system profile when the zones are within the dead band the damper positions are managed using the terminal level loop output.

When the temperatures cross the dead band and zones call for cooling or heating from the system level equipment, the cooling or heating which the system level equipment provides is divided optimally for the zones, to help temperature balance a system without fully closing off zones and creating harmful back pressure on the AHU. This is achieved based on two approaches.

  • Normalization
  • Minimum overall Damper Position

Which is based on the VVT-C profile sequences and uses the aspects like the Zone priority, Damper size, and other tuner parameters for the output calculations.






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