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| Overview

Active Chilled Beams (ACB) is a terminal-level equipment that uses the chilled water supply from the chiller and the air from an AHU to condition the space. Active Chilled Beam+ Dedicated Outside Air System (DOAS) is a terminal profile under the VAV system profile using SmartNode.

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The SmartNode in CCU-connected mode/ the fail-safe mode provides the necessary controls to support the operation of the Active Chilled Beam equipment.

| How it Works

Cooling Operation

When the system is cooling, the box acts like a single duct VAV and supplies the airflow from the air handler to maintain room temperature.

Similar to other VAV terminal profiles, it can also provide occupancy-based control and damper controls based on, CO2 & VOC levels, and true CFM.

A condensation sensor is used to detect condensation in the pipings and drive the chilled water shut-off valve and the modulating valve to avoid overcooling and equipment pipe damage. Once condensation is detected the valves will be closed irrespective of the cooling loop output.

Additionally, a hysteresis tuner (Relay activation Hysteresis) controls the shut-off valve, on the activations side of the loop output. 

And a modulating chiller water valve control based on the cooling loop output.

Heating Operation

The system or the AHU will not have any heating capability, the system will be either Off or Cool Only

When the desired temperature of the zone falls below the heating desired, there is no heating coil to turn ON hence the damper will stay at its minimum position, and the chilled water valve of the ACB will remain shut.

| Wiring & Schematics

 

  • Analog-out1 connects to the modulating damper actuator 
  • Analog-out2 connects to the modulating water valve
  • Relay-1 connects to the shutoff valve
  • Thermistor-1 connects to discharge air temperature sensor to a chilled beam
  • Thermistor-2 connects to condensation; Normally Open/Normally Closed Contacts. Normally Open: When no condensation then resistance will be infinite, when there is condensation, then contact will close reading 0 resistance.
  • A Differential pressure sensor connects to the Sensor bus, or a  Multi Sensor connects to the Sensor bus to provide CO2, IAQ, and occupancy sensing.

  • Optionally a HyperSense also can connect to the RS485 port to provide CO2, IAQ, and occupancy sensing.

| Pairing

From the Floor layout screen,

  • Click the Pair Module+ option.

The select device type screen is displayed.

  • Select SN SmartNode as the device option.

The select module type screen is displayed.

  • Select Active Chilled Beam+ DOAS

The Pairing steps screen is displayed.

  • Click Pair.

The broadcasting window is displayed.

  • Put the SN in the pairing mode from the Installer options screen.

  • Click the MAC ID of the SN to start pairing /Click Connect Manually if the expected device MAC address is not displayed in the list. For more information on the Alternate or Manual pairing steps refer to Alternate/ Manual Pairing for SmartNode.
  • Enter the PIN from the SN.
  • Click Pair to complete pairing.

The Active Chilled Beams + DOAS configuration screen is displayed.

| Configuration

  • Select the Damper Type from the drop-down list.

  • Select the Damper Size from the drop-down list.

  • Select the Damper Shape from the drop-down list.

  • Select the modulating Valve Type from the drop-down list.

  • Select the Zone Priority from the drop-down list.

  • Select the Thermistor-2 type from the drop-down list.

| Configuration Parameters

The below table provides more information on the configuration parameters.

Parameter Description Default value Value in the drop-down list
Damper Type To define the damper type used 0-10V

0-10V

2-10V

10-2V

10-0V

SmartDamper

0-5V

Damper Size To set the damper size used 4 4 to 22 in increment of 2
Damper Shape To set the damper shape used round

round

square

rectangular

Valve Type To define modulating chiller water valve type not installed

not installed

0-10V

2-10V

10-2V

10-0V

Zone Priority

To set zone priority, that influences the request numbers to the system-level equipment (Yet to be implemented in the Algo, for now does not affect the cooling side of the operation)

Note: These are only applicable for the DAB systems and VAV systems when it’s in heating.

normal

none

low

normal

high

Thermistor 1 To sense discharge airflow temperature Discharge Airflow NA
Thermistor 2 To define the type of condensate sensor used. N/O Condensation Sensor

N/O Condensation Sensor

N/C Condensation Sensor

K-Factor

To define the K-factor for the PI loops

Note: It is used only for the CFM PI loop

2

1 to 3 in increments of 0.1

Temperature Offset To set a temperature offset  NA

-10.0 to 10.0 in increments of 0.1

Max Damper Pos Cooling To set the maximum damper position during cooling operation NA

0 to 100 in increments of 1

Min Damper Pos Cooling To set the minimum damper position during cooling operation NA

0 to 100 in increments of 1

Max Damper Pos Heating To set the maximum damper position during heating operation NA

0 to 100 in increments of 1

Min Damper Pos Heating To set the minimum damper position during heating operation NA

0 to 100 in increments of 1

 

Additionally, the profile also provides occupancy-based control with the Auto forced Occupied and Auto Away options available as configurable options.

 

When CFM-based control is included in the profile additional parameters are made available, as below:

Parameter Description Default value Value in the drop-down list
Max CFM Cooling To set the minimum CFM for a cooling operation NA

0 to 5000 in increments of 5cfm

Max CFM Cooling To set the maximum CFM for a cooling operation NA 0 to 5000 in increments of 5cfm
Max CFM Heating To set the maximum CFM for a heating operation NA

0 to 5000 in increments of 5cfm

Min CFM Heating To set the minimum CFM for a heating operation NA

0 to 5000 in increments of 5cfm

Configure the required parameters for the profile, as below:

  • Click SET to confirm the configuration.

| Post Configuration in CCU

Once configured, the profile displays in the zones screen of the CCU as below:

| User Intents in CCU

User intents available in the CCU are as below:

The status message is based on the equipStatus point (DEADBAND, HEATING, COOLING, OR TEMPDEAD). If the zone is not dead, the same is determined using information in the following table:

Equi Status Conditions System Mode
HEATING if currentTemp < heatingDesiredTemp not OFF
COOLING if currentTemp > coolingDesiredTemp not OFF
DEADBAND if the currentTemp is in deadband OFF

 

Note: Only the cooling stages are configured at the system level, and hence the zones display only the cooling desired temperature. It is because the active chilled beams just provide cooling conditioning for the zone and do not have heating conditioning capability.

| Widgets in Portals

Once configured the profile displays the portal widgets screen as below:

.

 

Note: Only the cooling stages are configured at the system level, and hence the widgets display only the desired cooling temperature and the related parameters. It is because the active chilled beams just provide cooling conditioning for the zone and do not have heating conditioning capability.

| User Intents in Portals

User intents available in the Portals are as below:

 

Note: Only the cooling stages are configured at the system level, and hence the zone setting also displays only the desired cooling temperature. It is because the active chilled beams just provide cooling conditioning for the zone and do not have heating conditioning capability.

| Controls Trigger & Operations

When the Zone demands cooling and the system provides cooling.

If No Condensate is detected If Condensate is detected
  • The box acts like a single duct VAV and supplies the airflow from the air handler to maintain room temperature.
  • The chilled water shut-off valve control opens once the cooling loop output is above the Chilled water shut-off relay activation hysteresis.
  • The modulating chilled water valve is scaled for the resultant cooling loop output at Analog out 1.
  • The Damper position is scaled from the Minimum to the Maximum position ( Configured parameters), based on the resultant PI loop (Cooling), that uses the current and desired temperatures (Cooling).

Example: 

 Let us Assume the PI loop output signal is 80%, the same is translated to Damper Positions as

  • Min Damper Position=20%
  • Max Damper Position=100%
  • Range of the Damper Position= 80%
  • 80% loop output signal scaled for Damper position range (80)= 80*80/100= 6400/100= 64%
  • Actual Damper Position= 20 (Minimum Damper Position) + 64% = 84%
  • The chilled water shut-off valve control closes.
  • The Modulating chilled water valve control is also brought to a minimum.
  • The Damper position is scaled for the Cooling Loop output.

When the Zone demands Heating and the system provides Cooling.

If No Condensate is detected If Condensate is detected
  • The Damper position is set to a minimum position.
  • The chilled water shut-off valve control closes.
  • The Modulating chilled water valve control is also brought to a minimum.
  • The Damper position is set to a minimum position.
  • The chilled water shut-off valve control closes.
  • The Modulating chilled water valve control is also brought to a minimum.

When the Zone demands Cooling and the system provides Heating.

The chilled water modulating and shut-off valve will be closed, and the damper position will be brought to a minimum, regardless of whether the condensate is detected.

Note: This is a negative case, where the dampers will be maintained at their minimum position by the zone algorithm. On the system side when the system is doing heating and all zones are kept at minimum damper position owing to the contradicting zone and system conditioning, normalization will open the dampers from minimum towards 100%. 

| IAQ-Based & CO2 Damper Position

Based on additional parameters enabled for the profile, the damper position calculation, during cooling operation varies.

The Damper position is scaled from the Minimum to the Maximum position (Configured parameters), based on the resultant PI loop (Cooling), that uses the current and desired temperatures (Cooling/Heating).

Where the minimum position is altered based on the breach in CO2 or VOC levels. Below is an example of the same.

Example: 

Let us Assume there is a CO2 breach in the system

  • zoneCO2Threshold=800 ppm
  • zoneCO2Target=1000 ppm
  • Zone CO2 Breach Range = 200 ppm
  • Zone Current CO2=900 ppm
  • Actual Breach= 100 ppm
  • CO2 loop output= 100/200*100= 50%

The Damper position calculations are as below:

In non-True CFM, the minimum damper position changes from:

  • config minimum (20%) at 0% CO2 loop
  • config maximum (100%) at 50% CO2 loop

That would work out to:

  • 20% damper at 0% CO2 loop
  • 40% damper at 12.5% CO2 loop
  • 60% damper at 25% CO2 loop
  • 80% damper at 37.5% CO2 loop
  • 100% damper at 50% CO2 loop and above

The same applies to VOC breaches as well:

Example: 

Let us Assume there is a VOC breach in the system

  • zone VOC Threshold=400 ppb
  • zone VOC Target=500ppb
  • Zone VOC Breach Range = 100 ppb
  • Zone Current VOC =450 ppb
  • Actual Breach= 50 ppb
  • VOC loop output = 50/100*100= 50%

The Damper position calculations are as below:

In non-True CFM, the minimum damper position changes from:

  • config minimum (20%) at 0% VOC loop
  • config maximum (100%) at 50% VOC loop

That would work out to:

  • 20% damper at 0% VOC loop
  • 40% damper at 12.5% VOC loop
  • 60% damper at 25% VOC loop
  • 80% damper at 37.5% VOC loop
  • 100% damper at 50% VOC loop output and above

Note: When both CO2 and VOC are enabled for control, the highest loop percentage among both is considered for the minimum damper position, for the actual damper position calculation.

| CFM-Based Damper Position

When only the CFM is enabled, the system uses CFM setpoints and no damper positions anymore. Here we replace the minimum damper position with the minimum airflow setpoint. 

The below table talks about how CFM-enabled control affects different scenarios in the profile operations.

Operation Calculation
Zone demands cooling & system is in Cooling

On the cooling side the PI loop (Cooling Loop Output), which uses the current and desired temperatures (Cooling) is used to determine the Airflow setpoint.

Let us Assume the PI loop output signal is 80%, the same is translated to Airflow Setpoint as

The Loop output signal is scaled for configured Minimum and Maximum CFM to determine the Airflow setpoint.

Example: 

  • Min CFM(Cooling)=50 cfm
  • Max CFM(Cooling)=250 cfm
  • Airflow CFM Range = 200 cfm
  • 80% loop output signal scaled for Airflow CFM Range (200)= 200*80/100= 16000/100= 160 cfm
  • Actual Airflow Setpoint= 50 (Min CFM(Cooling))+ 160= 210 cfm

The resultant CFM Loop Output Signal, which uses the Airflow Setpoint and calculated actual CFM, as shown above. is directly mapped to the Analog Out 1.

For more information on the Actual CFM calculation refer to True CFM (Cubic Feet Per Minute) VAV.

Zone in Deadband system in cooling

The cfmTarget is the minReheatCfM and PILoop(cfmTarget, curCfm) determines the effective damper position.

For more information on the Actual CFM calculation refer to True CFM (Cubic Feet Per Minute) VAV.

Zone demands heating & system is in Cooling

The heatingLoop is less than 50% or dischargeTemp <= (roomTemp + reheatZonetoDATMinDifferential (default value 9 F )).

The cfmTarget is the minReheatCfM and PILoop(cfmTarget, curCfm) determines the effective damper position.

For more information on the Actual CFM calculation refer to True CFM (Cubic Feet Per Minute) VAV.

Note: There might be cases with the ACB profile where the current temperature of the zone dips below the heating desired temperature and the heating loop output is more than 50% but as the discharge temperature is not hot enough because of no reheat present, the cfmTarget will be the minReheatCFM and PI loop will operate with the same.

Zone demands heating & System is in Heating

The cfmTarget is the minReheatCfM and PILoop(cfmTarget, curCfm) determines the effective damper position.

For more information on the Actual CFM calculation refer to True CFM (Cubic Feet Per Minute) VAV.

Note: For a negative CFM loop the Damper position remains at the minimum. 

| IAQ, CO2 & CFM Based Damper Position

When CO2 & IAQ controls are enabled alongside CFM controls minimum CFM set point is influenced as below.

Min CFM setpoint will be the highest of the following:

Configured min CFM setpoint with CO2 Control:

  • Configured min CFM setpoint when CO2 is <= CO2Threshold
  • Halfway between min and max configured CFM setpoints when co2 is 50ppm above threshold
  • Configured max CFM setpoint when CO2 is 100ppm above the threshold

Configured min CFM setpoint with IAQ Control:

  • Configured min CFM setpoint when VOC is <= vocThreshold
  • Halfway between min and max configured CFM setpoints  when VOC is 25ppm above threshold
  • Configured max CFM setpoint when VOC is 50 ppb above threshold

In this configuration, the Damper Position calculation would have four calculation stages.

  • The Breach percentage on the CO2& VOC breaches, as in the above section.
  • The Breach Percentage translated to the new minimum cfm.
  • The airflow set point calculation using the new minimum and maximum airflow cfm, and the temperature-based PI loop output.
  • The CFM loop output calculation from the airflow set point and actual airflow, which is translated to the Damper position minimum and Maximum.

Below is an Example calculation for the same

Example:

The Breach percentage on the CO2 breach

Let us Assume there is a CO2 in the system

  • zoneCO2Threshold=800 ppm
  • zoneCO2Target=1000 ppm
  • Zone CO2 Breach  = 200 ppm
  • Zone Current CO2=825 ppm
  • Actual Breach= 25 ppm
  • CO2 loop output = 25/200*100= 12.5%

The Breach percentage on the VOC breach

Let us Assume there is a VOC breach in the system

  • zone VOC Threshold=400 ppb
  • zone VOC Target=500ppb
  • Zone VOC Breach Range  = 100 ppb
  • Zone Current VOC =475 ppb
  • Actual Breach= 75 ppb
  • Breach Percentage= 75/100*100= 75%

Note: When both CO2 and VOC are enabled for control, the highest breach percentage among both is considered for the minimum damper position, for the actual damper position calculation.

As per the above, let us consider the Breach Percentage from VOC = 75% for the new minimum cfm calculation

The Breach Percentage translated to the new minimum cfm.

  • Min CFM(Cooling/Heating)=50 cfm
  • Max CFM(Cooling/Heating)=250 cfm
  • Airflow CFM Range = 200 cfm
  • 75 % Breaches Translates to =75*200/100= 15000/100= 150 cfm
  • The New minimum CFM= 50 (Min CFM(Cooling/Heating)) +150= 200 cfm

The airflow set point calculation

Let us Assume the PI loop output signal is 80%, the same is translated to Airflow Setpoint as

  • New Min CFM(Cooling/Heating) =200 cfm
  • Max CFM(Cooling/Heating) =250 cfm
  • Airflow CFM Range = 50 cfm
  • 80% loop output signal scaled for Airflow CFM Range (50) = 50*80/100= 4000/100= 40 cfm
  • Actual Airflow Setpoint= 200 (Min CFM(Cooling/Heating)) + 40 = 240 cfm

The CFM loop output calculation from the airflow CFM set point and actual airflow CFM, which is translated to the Damper position minimum and maximum.

For more information on the Actual CFM calculation refer to True CFM (Cubic Feet Per Minute) VAV.

| Failsafe Mode

When the Smartnode loses the connection with the CCU, the system enters the failsafe mode where the required controls are still made available from the SmartNode itself.

The Occupancy, IAQ and VOC controls will not be available in Fail Safe, only CFM and all its tuners and configs will work as intended in Fail Safe.

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