4 Minute Read
| Overview
The 75F® DAD Dual Duct is a custom terminal profile that is introduced to support the VAV dual-duct systems. It consists of an air handling unit that has two coils, a continuously operating cooling coil, and a continuously operating heating coil.
| Advantages
- The System Dual duct variable air volume (DDVAV)) is used to obtain zone-level temperature control by mixing the cold and warm air in various volume combinations.
- The fan used is of a size that anticipates the maximum hot or cold air volume, and not the sum of the instantaneous peaks.
- With control provided with a customized DAB Dual Duct Terminal zone, we can install 75F products in Buildings that have VAV dual-duct systems.
| How it works
Once you select the DAB Dual duct terminal profile under SmartNode DAB profiles, the configuration provides the options to define the damper actuator types for the analog outputs, made available from the SmartNode for controlled output.
Additionally, the profile provides options to modify the controls based on the Internal Air Quality, CO2, and occupancy, with the IAQ, CO2, and Occupancy control that can be enabled or disabled.
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 deadband range, which is a result 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 the cooling coil of the system-level device supplies via the Cooling Deck to support the zone.
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, and the heating coil of the system level device supplies via the Heating Deck to support the zone.
The building or system-level device is an RTU or AHU which is controlled by the system-level DAB profiles.
For more information on the system-level DAB, profiles refer below.
DAB Staged RTU - Wiring/ Configuration
DAB Fully Modulating AHU - Wiring/ Configuration
DAB 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.
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 DAB Dual duct terminal profile, that shows the connection from the smart node to the Airflow and Reheats damper actuators.
| Configuration
Below is the configuration screen for the DAB Dual duct terminal profile.
Once you've paired the Smart Node as a DAB Dual duct profile, and once a few specific configuration parameters that define the physical characteristics of the setup are set in the configuration screen, the 75F sequence for the DAB will influence and control the setup.
Analog-out1- set to 'Composite Damper Actuator' by default
Drop Down Options include Not Used, Composite Damper Actuator, Cooling Damper Actuator, Heating Damper Actuator
Analog-out2- set to 'Not Used' by default
Drop Down Options include Not Used, Composite Damper Actuator, Cooling Damper Actuator, Heating Damper Actuator
Thermistor-1- connects to Discharge airflow 10K sensor
Thermistor-2- connects to Supply Air Temperature
Optionally differential pressure sensor connects to the Smart Node 1-wire sensor bus
Optionally SmartSense connects to the RS 485 port to provide CO2, IAQ, and occupancy sensing
Below the profile configuration, you can program the output voltage for the modulating equipment configured.
| Operation
The cooling coil feeds chilled air into a cold air duct and the heating coil feeds hot air into a hot air duct; the ducts run parallelly throughout the building. The air is tapped from the two ducts by a terminal unit at each space. The terminal unit can have a hot or cold air damper. When the zone requires heating, the hot air damper opens. When cooling is required, the cold air damper opens.
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