DAB Fully Modulating AHU - Wiring/ Configuration

4 Minute Read

| Overview

The DAB Fully Modulating AHU is a profile that is used to control an AHU, which meet the HVAC demands of a space. The AHU supported is water a cooled AHU.

The profile supports up to three analog outputs for modulating cooling, heating and Fan speed equipment. Based on the preferences for the required conditioning, the controls required can be set and used.

| How it Works

Once you select the DAB Fully Modulating AHU 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, three analog outputs, a relay, and an auxiliary relay is made available in the profile screen to enable the conditioning required based on the preferences.

The Algorithm continuously track the average current temperature of the zones mapped as terminal profiles, under the DAB Fully Modulating AHU 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 modulating equipment.

When the Average Temperature increases above the set point or desired temperature and the zones demand cooling the cooling equipment ramps up based on the modulating output.

And when the Average Temperature decreases below the set point or desired temperature, and the zones demand heating equipment ramps up based on the modulating output.

Below the profile configuration is additional parameters for adjusting the analog output voltage to each piece of equipment.  You may program min/max output voltage for min/max system operation.

| Wiring

Below is a wiring schematic for the DAB Fully Modulating AHU, 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.

| Configuration

Below is the configuration screen for the DAB Fully Modulating AHU, The relays are enabled or disabled based on the preferences.

| Configuration Parameters

Once you've configured the system profile as a DAB system, the sequences follow the proprietary 75F algorithm for operation. You will need to select a few specific configuration parameters that define the physical characteristics AHU. 

Analog-out1 - To enable the Cooling Equipment to perform or provide in a modulating range.

Analog-out2- To enable the Fan to perform or provide in a modulating range.

Analog-out3- To enable the Heating Equipment to perform or provide in a modulating range

Relay 3- To enable the Fan during the recirculation phase of the control.

Relay 7- To enable the humidifier or dehumidifier control.

Note: By default, the DCWB is disabled making the profile just a DAB fully Modulating AHU type, and below is information about usage and operation of the same.

And when the DCWB is enabled, the profile converts into a DAB Modulating AHU with DCWB, for more information on the usage and operation of profile refer to DAB Modulating AHU with DCWB

Below the profile configuration you can program the output voltage for the modulating equipment configured.

| Sequence of Operation

The sequence of operation is completely driven based on Occupancy mode, and Zone Loads (Cooling/Heating). 

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.

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

• • Pre- Conditioning
  • Occupied
  • Unoccupied

| 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 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 (Average of zones needing conditioning) are 70F and 74F for the building.
    • The operating mode is determined based on the weighted average calculation as shown in section | Sequence of Operation During Occupied

Let us assume:

• • • The operating mode determined is cooling.
    • The current temperature (Average of zones needing cooling conditioning) is 76F
    • 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 operate the damper positions optimally to receive the required conditioning to satisfy their load requirements to maintain a temperature within the deadband.

For more information on the damper operations, refer to DAB Terminal Profile- Damper Position Calculation & Operation

| Sequence of Operation During Occupied

Influencers

During the scheduled Occupied times, the AHU/RTU is influenced by two aspects of the system.

• • The Operating Mode
  • The Conditioning Mode

Operating Modes

The Operating mode is a user intent parameter that the user can specify. There are four types of operating modes.

• • Off
  • Auto
  • Cooling
  • Heating

Conditioning Modes

The Conditioning mode is a derived parameter. There are three types of conditioning modes.

• • Cooling
  • Heating
  • Deadband

Based on the influence of the aspects mentioned above, the device supplies the cooling/ heating load requirements, and the zones operate the damper positions optimally to receive the required conditioning to satisfy their load requirements,and maintain a temperature within the deadband.

For more information on the damper operations, refer to DAB Terminal Profile- Damper Position Calculation & Operation

Weighted Average Load MA (Heating /Cooling)

weightedAverageHeatingOnlyLoadMA/ weightedAverageCoolingOnlyLoadMA,  is a result of the following steps.

Conditioning Mode Determination 

Conditioning mode is determined using the following table:

| Sequence of Operation During Unoccupied

• • The range of heating and cooling desired temperature of the zones drifts further away due to unoccupied setbacks.
  • The device supplies the cooling/Heating load requirements of the zones, and the zones operate the damper positions optimally to receive the required conditioning to satisfy their load requirements to maintain the room temperature within the newly set autoaway setback temperature range, for more information on the damper operations refer to DAB Terminal Profile- Damper Position Calculation & Operation
  • If weightedAverageHeatingOnlyLoadMA/ weightedAverageCoolingOnlyLoadMA, is a positive value. The system operates in the determined conditioning mode to supply the zone cooling/heating load requirements, as shown in the | Sequence of Operation During Occupied
  • If weightedAverageHeatingOnlyLoadMA & weightedAverageCoolingOnlyLoadMA, is zero. The system is within the deadband, there is neither a cooling load nor a heating load, hence there is no conditioning that occurs at the AHU end, except for a minimum mechanical or free ventilation.

| 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, as shown in the cooling conditioning, or Heating conditioning mode.

| Sequence of Operation Zone Temp Dead

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

• • CoolingLoopOutput
  • HeatingLoopOutput
  • FanLoopOutput

| Humidifier Control

The humidifier is turned ON whenever the humidity level for the system drops below the targetMinInsideHumidty set. The humidifier will be turned OFF after being turned on when the humidity levels go humidityHysteresis above the targetMinInsideHumidty. Humidity control will not be maintained during UNOCCUPIED or VACATION modes.

| Dehumidifier Control

If the dehumidifier is selected, it turns ON whenever the humidity level for the system goes above the targetMaxInsideHumidty set. The dehumidifier will be turned OFF after being turned on when the humidity drops humidityHysteresis below the targetMaxInsideHumidty. Dehumidifier control will not be maintained during UNOCCUPIED or VACATION modes.

Note: The humidity level for the system is either the average level reported by all the zones serviced by the RTU/AHU.

| Operation Mode Summary

Test Signal - This is used for troubleshooting and testing the equipment if the configuration and the field setup are in sync, and CCU is communicating properly with the controlled equipment. Also at any point, you can override the value of the output the algorithm decides. 

We can use the test signal for relays to turn them on or for analog out to ramp up and see if the equipment works according to commands from CCU.

Test Signal Time Out - once enabled it will be active for an hour if the screen is not changed, after an hour of no interaction on the screen.  zone screen displays and the test signal will be OFF.

If the screen changes from the test signal configuration screen it will be timed out in one minute (time for the algorithm to run next).

Note: The test signal for modulating output is in deci volts ranging from 0.0dV to 100.0dV.

| 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 voltages of the modulating output that is set during the configuration.

• Cooling loop output 0-100%, the Cooling Equipment ramps up from 0-10V of analog output

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 voltages of the modulating output that is set during the configuration.

• Heating loop output 0-100%, the Heating Equipment ramps up from 0-10V of analog output

Recirculate

When the zone demands recirculation along with cooling, the system will call for Fan speed which again uses the cooling loop output 0-100% to ramp up the speed from 0-10V of analog output.

Recirculate with VFD - When recirculating with a VFD, the default output voltage will be 4v.