DAB External AHU Controller

| Overview

DAB External AHU Controller is a system-level profile in the 75F system. The profile is used with an external AHU (BACnet/Modbus-based).

The control of these complex external devices, can not only be based on zone load but also requires control triggers based on the Supply Air Temperature (SAT), Duct Static Pressure (DSP), and zone load-based control.

Unlike the other system profiles, the DAB External AHU controller profile does not control the external equipment directly, but indirectly the CCU contributes to the following.

Monitor, and aggregate for visualizations in portals.
Apply algorithms to calculate setpoints.
Communicate the calculated setpoint to the External device for control actions.

| Wiring

A 24V power supply powers the CCU and connects to the External communication-based device via the USB to RS485 Cable.

| Configuration

To configure the DAB External AHU Controller as a system Profile.

From the zones screen, after the CCU is registered,

Click the floor layout screen.

From the floor layout screen

Click the Settings option.

From the settings screen

Click the system profile screen icon.

Select the DAB External AHU controller option from the drop-down.

The DAB External AHU controller configuration screen is displayed.

| Configuration Parameters

The profile provides the user with different types of control options, and one can select the ones required for the building type managed.

SAT Controls

Enable the SAT Setpoint Control option to provision a supply air temperature set point reset calculation in the control algorithm.

SAT point control.png

Enabling the SAT setpoint control provides additional configuration parameters to configure from.

The table below explains the configuration parameters in detail:

Configuration Parameter	Description
SAT Heating Setpoint Min	You can set a minimum SAT heating setpoint using the drop-down, to be used in the algorithm for setpoint calculation.
SAT Heating Setpoint Max	You can set a maximum SAT heating setpoint using the drop-down, to be used in the algorithm for setpoint calculation.
SAT Cooling Setpoint Min	You can set a minimum SAT cooling setpoint using the drop-down, to be used in the algorithm for setpoint calculation.
SAT Cooling Setpoint Max	You can set a maximum SAT cooling setpoint using the drop-down, to be used in the algorithm for setpoint calculation.

Note: When the SAT setpoint control is enabled

The systemLoopOutput value is then mapped between the systemSATMinimum and systemSATMaximum to generate SAT SetPoint.

Where the Default:

systemSATMinimum = 35 (F)
systemSATMaximum = 105(F)

Enable the Dual Setpoint Control option to set the profile to dual setpoint, where the SAT setpoint minimum and maximum for the heating and cooling mode can be defined separately.

Note: When the Dual setpoint control is enabled:

The systemCoolingLoopOutput value is then mapped between the systemCoolingSATMinimum and systemCoolingSATMaximum to generate SATCoolingSetPoint.
The systemHeatingLoopOutput value is then mapped between the systemHeatingSATMinimum and systemHeatingSATMaximum to generate SATHeatingSetPoint.

Where the Default:

systemCoolingSATMinimum = 35 (F)
systemCoolingSATMaximum = 68(F)
systemHeatingSATMinimum = 85(F)
systemHeatingSATMaximum = 105(F)

Fan- Static Pressure Controls

Enable the Fan-Static Pressure Setpoint Control option to provision a duct static pressure setpoint reset calculation in the control algorithm.

Enabling the Fan-Static setpoint control provides additional configuration parameters to configure from.

The table explains the configuration parameters in detail:

Configuration Parameter	Description
Fan Static Pressure Min	You can set a minimum Fan-static setpoint using the drop-down, to be used in the algorithm for setpoint calculation.
Fan Static Pressure Max	You can set a maximum Fan-static setpoint using the drop-down, to be used in the algorithm for setpoint calculation.

Note: When the Fan-Static Pressure control is enabled.

The Fan Loop Output is calculated using the system cooling/heating loop output. This value is then mapped between the systemStaticPressureMinimum and systemStaticPressureMaximum to generate the systemStaticPressure Value.

Where the Default:

systemStaticPressureMinimum = 0.2(" wc)
systemStaticPressureMaximum = 2.0(" wc)

DCV Damper Controls

Enable the DCV Damper Control Option to provision a demand control ventilation setpoint reset calculation in the control algorithm.

Enabling the DCV Damper control provides additional configuration parameters to configure from.

The table below explains the configuration parameters in detail:

Configuration Parameter	Description
DCV Damper Min	You can set a minimum DCV damper position using the drop-down
DCV Damper Max	You can set a maximum DCV damper position using the drop-down, to be used in the algorithm for setpoint calculation.
CO2 Threshold	You can set a CO2 threshold using the drop-down, to be used in the algorithm for setpoint calculation.
System CO2 Target	You can set a CO2 target using the drop-down, to be used in the algorithm for setpoint calculation.
CO2 Damper Opening Rate	You can set a CO2 Damper opening rate using the drop-down, to be used in the algorithm for setpoint calculation.

Note: When DCV damper control is enabled.

The Weighted Average CO2 is calculated using the Zone CO2 values, which are then used to calculate the Damper percentage. This value is then mapped between DCV Damper Min & max to determine the DCV Damper Set Point.

Where the Default:

systemStaticPressureMinimum = 0.2(" wc)
systemStaticPressureMaximum = 2.0(" wc)

Configuration Parameter	Description
Occupancy Mode Control	Enable to introduce occupancy-based mode control in the algorithm or system operation.
Humidifier Operation	Enable to introduce humidifier operation in the algorithm.
Dehumidifier Operation	Enable to introduce dehumidifier operation in the algorithm.

| Algorithm & Operation

CCU Aggregates the Zone temperature and priority data, to determine the required conditioning at the system level using the weighted average calculation. For more information on the weighted average calculation refer to DAB System Profile Logic & Tuners.
The resultant weighted average determines whether the External AHU should provide cooling or heating.
The resultant zone load contributes to a Loop output (Cooling/Heating)
The configuration lets the user set ranges for the Supply Air Temperature (SAT), Duct Static Pressure (DSP) & Demand Control Ventilation (DCV) set points.

Controls

Example Calculation

Supply Air Temperature (SAT) setpoint calculation.

The Loop output (Cooling / Heating) resulting from the zone load determines the Supply Air Temperature (SAT) set point using the configured Supply Air Temperature min and max values.

The determined SAT setpoint is sent to the external AHU to act upon and provide the required conditioning.

Example: For a 80% (Cooling or Heating) loop output:

When just the SAT setpoint control is enabled:

SAT setpoint Point Range=68-35= 33F

Calculated SAT Setpoint= 35+(80*33)/100= 35+26.4= 61.4F

When Dual setpoint control is enabled:

SAT Cooling setpoint Point Range=68-35= 33F

SAT Heating setpoint Point Range=105-85= 20F

For a 40% Cooling loop output:

Calculated SAT Cooling Setpoint=35+ (80*33)/100=35+26.4= 61.4F

For a 40% Heating loop output:

Calculated SAT Heating Setpoint=85+ (40*20)/100=85+8= 93F

Duct Static Pressure (DSP) setpoint calculation.

The Loop output (Cooling / Heating) resulting from the zone load determines the Fan loop output, where the Fan Loop Output= analogFanSpMultiplier* Loop output (Cooling/ Heating).

The determined Fan loop output determines the Duct Static Pressure (DSP) set point, using the configured Duct Static Pressure min and max values.

The determined Duct Static Pressure (DSP) setpoint is sent to the external AHU to act upon and provide the required conditioning.

Example: For a 80% (Cooling or Heating) loop output:

FanLoopOuput= (Cooling/Heating)* analogFanSpeedMultiplier

FanLoopOutput= 80*1=80

When just the SAT setpoint control is enabled:

Fan- Static SetPoint Range=2-0.2= 1.8"wc

Calculated Fan- Static Setpoint= 0.2+(80*1.8)/100= 0.2+1.44= 1.64"wc

Demand Control Ventilation (DCV) setpoint calculation.

CCU Aggregates the Zone CO2 data, to determine the weighted average CO2.

The resultant Weighted average CO2 contributes to the damper percentage, using the configured DCV min & max, Tuner damperopeningrate & CO2 Threshold, using the below formula.

Damper Percentage = (Weighted Average CO2-CO2 Threshold) / damperOpeningRate.

The calculated Damper percentage determines the Demand Control Ventilation (DCV) set point, using the configured DCV min and max values.

Example:

For a Weighted average CO2 of 900ppm

Damper Percentage= (900-800)/10= 100/10=10%

DCV Dmaper Setpoint= 10(100)/100= 10%

| Monitoring & Visualization

With the CCU Hayloft integration, any external equipment can be brought into CCU to configure and monitor the required parameters in the portals as visualizations.

From the configuration screen.

Select the type of the Eternal Device (Modbus / BACnet)

When device type Modbus is selected

Click Select Model drop-down to select the Modbus device.

From the pop displaying the equipment models from Hayloft,

Search & select or select the required model.

The parameters apply to the selected equipment displays.

Set a slave ID for the model using the Salve ID drop-down.
Use the toggle button to select all the parameters for monitoring and visualization in portals, as below.