SmartNode VAV w/ Reheat (Parallel Fan) Profile

4 Minute Read

| Overview

The VAV with Reheat (No Fan) profile is a terminal unit profile that uses a SmartNode to control a VAV terminal box. It supports both the cooling and heating requirements of a zone.

Based on the operating mode of the system-level equipment (AHU or RTU), the profile automatically adjusts the damper position and reheat operation to deliver optimal zone comfort. When the AHU or RTU is in cooling mode, the damper modulates to satisfy the cooling demand. When the system is in heating mode, the profile coordinates the damper, fans and reheat operation to efficiently meet the zone's heating requirements while maintaining occupant comfort. 

The profile also supports the Enable MySense setting, which makes the MySense universal inputs available for configuration. Each input can be enabled independently and mapped to a supported sensor or device.

| How it Works

The VAV with Reheat-Parallel Fan allows selection of dampers and reheat based on the equipment used and zone priority, which corresponds to the importance multiplier in Guideline 36.

On the heating side, the profile supports both the staged & modulating reheat controls.

| Wiring

Wiring Schematic for Modulating Hot Water Reheat

Wiring Schematic for Modulating Electric Reheat

Wiring Schematic for Staged Electric Reheat

For more wiring information, refer to the CDDs attached.

| Configuration Steps

To configure a VAV with a Reheat (Parallel Fan) profile 

• Click the pair module from the floor layout screen.

• Click the SN (SmartNode) from the select device type screen.

• Click the VAV with Reheat from the select module type, screen.

• Select the VAV Reheat- Parallel Fan.

• Click Pair, to pair the device using the pairing instructions on the pairing steps screen.

• Select the device MAC address relayed for pairing, or click connect manually to pair the device manually. For more information on manual pairing refer to Alternate/ Manual Pairing for SmartNode.

• Enter the pin displayed on the SmartNode device or an automatic pairing.
• Click Pair.

The profile configuration screen is displayed as below.

| Profile Configuration

After the SmartNode is paired, the VAV with Reheat (Parallel Fan) profile configuration screen is displayed.

The profile configuration screen contains the following sections:

• General Settings
• SmartNode I/O Configuration
• MySense Configuration
• TrueCFM Configuration
• Damper Position Configuration
• Save and Cancel

General Settings

Damper Shape

Damper Shape defines the geometry of the installed VAV damper. The selected shape determines the dimension parameters displayed in the configuration screen.

Default:

• Damper Shape: Round
• Damper Diameter: 1

Zone Priority

Zone Priority defines the weighting applied to zone-generated Trim-and-Respond requests.

Default: Normal

For additional information, refer to Damper Position & Zone Priority Driven Trim and Respond Requests.

Enable Wireless Door/Window Sensor

Enable Wireless Door/Window Sensor enables support for a compatible wireless door/window sensor.

Default: Disabled

When enabled, the Sensor Type field becomes available.

Available options:

• Door Window Sensor
• Door Window Sensor – Title 24

SmartNode I/O Configuration

The SmartNode provides physical analog outputs, relay outputs, and universal inputs that can be configured for the VAV with Reheat (Parallel Fan) profile. Depending on the profile requirements, I/O points may be fixed or configurable.

The SmartNode provides the following I/O points:

• Four Analog Outputs (AO1–AO4)
• Four Relay Outputs (RL1–RL4)
• Four Universal Inputs (UI1–UI4)

For configurable I/O points, the mapping field is available only after the corresponding I/O point is enabled.

Analog Outputs

The SmartNode provides four analog-output terminals.

AO1 is enabled by default to control the damper actuator. AO2, AO3, and AO4 are disabled by default and can be enabled as required.

Available analog-output mappings include:

• Damper (0–10 V)
• Damper (2–10 V)
• Damper (10–0 V)
• Damper (10–2 V)
• Damper (0–5 V)
• Modulating Reheat (0–10 V)
• Modulating Reheat (2–10 V)
• Modulating Reheat (10–0 V)
• Modulating Reheat (10–2 V)
• Externally Mapped

Damper and Modulating Reheat functions can be assigned to any enabled analog output.

Relay Outputs

The SmartNode provides four relay-output terminals that support Parallel Fan operation and staged electric reheat.

RL2 is enabled and mapped to Parallel Fan by default.

Available relay mappings include:

• Parallel Fan
• Stage 1 Reheat
• Stage 2 Reheat
• Stage 3 Reheat
• Externally Mapped

Mapping Validation for Relay outputs

The Parallel Fan function can be assigned to any relay output. Although multiple relay outputs can be configured as Parallel Fan, configuring a single relay output for the Parallel Fan function is the recommended configuration.

The remaining relay outputs can be configured for Stage 1, Stage 2, and Stage 3 Reheat. Reheat stages shall be assigned in sequential order. Relay outputs configured as Parallel Fan are excluded from the reheat-stage sequencing validation.

If the configured relay stages do not meet the sequencing requirement, the CCU displays the following validation message:

"Reheat stages for relays should be configured sequentially."

Universal Inputs

The SmartNode provides four universal-input terminals. Depending on the selected mapping, a universal input operates as either a thermistor input or an analog input.

UI1, UI3, and UI4 are fixed assignments required by this profile. Only UI2 is configurable.

The available mapping options are limited to analog input types.

Analog Input

• Damper Feedback
• Voltage Input
• Current TX (0–10 Amps)
• Current TX (0–20 Amps)
• Modulating Reheat Feedback

Mapping Validation for Universal inputs

Modulating Reheat Feedback

When Modulating Reheat is assigned to an analog output, Modulating Reheat Feedback shall also be assigned to a universal input.

For this profile, Modulating Reheat Feedback shall be mapped to UI2.

If the feedback input is not configured, the CCU displays the following validation message:

"Please map the Modulating Reheat Feedback sensor to a universal input to continue."

Duplicate Sensor Mapping

Each sensor function can be assigned to only one universal input.

The following mappings are fixed for this profile:

• UI1 – Damper Feedback
• UI3 – Discharge Air Temperature
• UI4 – Entering Air Temperature

These functions shall not be assigned to UI2.

If a duplicate mapping is detected, the CCU displays the following validation message:

"Each sensor can only be mapped once. Please check your mappings."

If Modulating Reheat Feedback is not assigned when required, the Modulating Reheat Feedback validation message takes precedence over the duplicate sensor validation.

MySense Configuration

Enable MySense is disabled by default.

When enabled, three configurable MySense universal inputs are displayed.

Each input can be enabled independently. The mapping list is displayed after the corresponding input is enabled.

The following mappings are available.

• Voltage Input
• Damper Feedback
• Current TX (0–10 Amps)
• Current TX (0–20 Amps)
• Thermistor Input
• Discharge Air Temperature
• Entering Air Temperature
• Generic Alarm N/O
• Generic Alarm N/C
• Door/Window Sensor – N/O
• Door/Window Sensor – N/C
• Door/Window Sensor – N/O – Title 24
• Door/Window Sensor – N/C – Title 24
• Modulating Reheat Feedback

Control Inputs

The following mappings are used by the VAV with Reheat (Parallel Fan) control sequence.

• Door/Window Sensor – N/O
• Door/Window Sensor – N/C
• Door/Window Sensor – N/O – Title 24
• Door/Window Sensor – N/C – Title 24

All other mappings are used for monitoring only.

Configure the door/window sensor mapping to match the installed device.

Enable MySense Icon Mode

Enable MySense Icon Mode is displayed only when Enable MySense is enabled.

Default: Disabled

TrueCFM Configuration

The TrueCFM Configuration section defines the airflow limits and damper-position limits used by the VAV with Reheat (Parallel Fan) profile when Enable TrueCFM Control is enabled.

For information about the airflow calculation and damper control algorithm, refer to VAV Terminal Profile- Damper Position Calculation & Operation.

CFM Settings

The CFM settings define the airflow limits for cooling and reheating operation.

K-Factor

The K-Factor defines the airflow coefficient used by the TrueCFM control algorithm.

The K-Factor parameter is displayed only when Enable TrueCFM Control is enabled.

Damper Position Configuration

The available damper-position parameters depend on the state of Enable TrueCFM Control.

TrueCFM Enabled

When Enable TrueCFM Control is enabled, the following heating damper-position limits are available.

TrueCFM Disabled

When Enable TrueCFM Control is disabled, separate cooling and heating damper-position limits are available.

Save the Configuration

After completing all required profile settings, select Save. The SmartNode pairing and VAV with Reheat (Parallel Fan) profile configuration are then completed.

| Control System Object List

Note: For a comprehensive list of tuners and their details refer to Tuners Complete List.

| Sequence of Operation

The sequence of operation is completely driven based on Occupancy mode, Space Current Temperature, the set Cooling and Heating Desired Temperatures, CFM, and Space CO2 levels.

Let us understand the Sequence of operations based on the occupancy modes, and how the other factors contribute to the sequence of operations during different types of occupancy modes.

| Occupancy Modes

The occupancy mode (Occupied or Unoccupied) shall be determined through a user-adjustable, graphical, seven-day schedule with a holiday schedule, alongside the configurable autoaway and forced occupied options (external schedule influencers) for optimized controls and enhanced energy savings.

Based on the above aspects, factoring in the occupancy the following can be the possible applicable occupancy modes:

• Pre- Conditioning
• Occupied
• Unoccupied
• Auto-Away
• Forced Occupied

| Sequence of Operation During Pre-Conditioning

Pre-conditioning is a state just before the building enters the scheduled occupancy. It starts at more like the unoccupied state, the desired temperatures drift to unoccupied setbacks.

The preconditioning uses an algorithm to start the conditioning before the building is scheduled for occupancy, from the heating side or cooling side, to bring the building to an optimum level ( within the occupied heating & cooling desired temperatures) exactly at the time of occupancy start.

A cooling and heating coolingPreconditioningRate and heatingPreconditiningRate tuners defaulted to 15 minutes, are used alongside the occupied heating/cooling desired temperature breach to determine when the pre-conditioning should start.

Example Calculation:`

When,

• The heating & cooling desired temperatures are 70F and 74F for the building,
• The current temperature is 76F (Average of zone temperatures),
• 8:00 AM is the time the building is scheduled to be occupied.

Then the preconditioning start time is calculated as follows:

Cooling Desired Temperature Breach= 76-74=2F

Preconditioning duration= coolingPreconditioningRate (mins) * Cooling Desired Temperature Breach

                                        = 15*2

                                        = 30 mins

The preconditioning starts 30 minutes before the building is scheduled to be occupied, which is = 7:30 AM.

The zones would operate as shown below to accommodate the preconditioning from the system equipment.

During Warm-up:

• If the space temperature is below the occupied heating desired temperature, the space utilizes the warm-up via HeatingLoopOutput as below.

• The CO2 loops are disabled. (If configured for)
• The CFM loop is disabled. (If configured for)

During Pre-cooling:

• If the space temperature is below the occupied cooling desired temperature, the space utilizes the morning pre-cooling via CoolingLoopOutput, as below.

• The CO2 loops are disabled. (If configured for)

| Sequence of Operation During Occupied

At all occupied times: (based on a set schedule)

• The device maintains a space temperature within the Heating Desired Temperature and Cooling Desired Temperature Range.

During Deadband:

During deadband, the damper operation is influenced, based on the configuration of the profile, as follows.

During Heating:

• When the space current temperature falls below the HeatingDesiredTemperature the HeatingLoopOutput is enabled as below as below.

During Cooling:

• When the space current temperature is above the Cooling Desired Temperature the CoolingLoopOutput is enabled,  as below

| Sequence of Operation During AutoAway

• The range of Heating Desired Temperature and Cooling Desired Temperature drifts further away.
• The device maintains a space temperature within the newly set Heating Desired Temperature and Cooling Desired Temperature Range.

During Deadband:

• CoolingLoopOutput, HeatingLoopOutput, CFM LoopOutput, CO2 Loop Output, and Reheat Stages are disabled.

During Heating:

• When the space current temperature falls below the heating autoaway setback temperature, the HeatingLoopOutput is enabled as below.

• The CO2 loop is disabled. (If configured for)
• The CFM loop is disabled. (If configured for)

During Cooling:

• When the space current is above the cooling autoaway setback temperature, the CoolingLoopOutput is enabled,  as below.

• The CO2 loop is disabled. (If configured for)

| Sequence of Operation During Unoccupied

• The range of Heating Desired Temperature and Cooling Desired Temperature drifts further away.
• The device maintains a space temperature within the newly set Heating Desired Temperature and Cooling Desired Temperature Range.

During Deadband:

During deadband, the damper operation is influenced, based on the configuration of the profile, as follows.

During Heating:

• When the space's current temperature falls below the heating unoccupied setback temperature, the HeatingLoopOutput is enabled as below.

• The CO2 loop is disabled. (If configured for)
• The CFM loop is disabled. (If configured for)

During Cooling:

• When the space current temperature is above the cooling unoccupied setback temperature, the CoolingLoopOutput is enabled, as below.

• The CO2 loop is disabled. (If configured for)

| Sequence of Operation During Forced Occupied

• The device maintains a space temperature within the Heating Desired Temperature and Cooling Desired Temperature Range.

During Deadband:

During deadband, the damper operation is influenced, based on the configuration of the profile, as follows.

During Heating:

• When the space current temperature falls below the Heating Desired Temperature the HeatingLoopOutput is enabled as below.

• The CO2 loop is disabled. (If configured for)
• The CFM loop is disabled. (If configured for)

During Cooling:

• When the space current temperature is above the Cooling Desired Temperature the CoolingLoopOutput is enabled as below,

• The CO2 loop is disabled. (If configured for)

| Sequence of Operation During Emergency Conditioning

When zone limits are violated, and the recorded temperature is within the zone limit plus leeway the conditioning will happen in the direction of zone load.

| Sequence of Operation During Zone Temp Dead

And, when the zone temperature breaches the zone limits, beyond the leeway limits all the following loops are disabled:

• CoolingLoopOutput
• HeatingLoopOutput
• Reheat Stages
• FanLoopOutput
• CO2 & IAQ LoopOutput
• CFM LoopOutput

| Control Mode Summary