greenBOX Unboxed i11: How the greenBOX Maintains Minimum Transport Air Velocities in the Main Duct and Multiple Duct Zones
Introduction
Effective airflow management in a dust collection system is essential for both safety and efficiency. This article explores how Ecogate’s greenBOX maintains the NFPA 660-mandated minimum transport air velocities throughout your entire duct system. We’ll cover essential concepts, including minimum airflow mode, transport air velocity, and practical strategies to sustain proper airflow in both main and branch ducts.
Maintaining Minimum Air Velocities in Main Duct
Maintaining Minimum Air Velocities in Duct Zones
Content
greenBOX and Air Velocities
The greenBOX system achieves this by measuring air velocities at each individual gate, calculating velocities within branch ducts, and continuously monitoring system-wide air velocity and volume. (For more detail on these measurements, see our dedicated article: What Is Not Measured Cannot Be Controlled: How Ecogate greenBOX Measures Air Velocity and Air Volume)
More than just a monitoring tool, the greenBOX actively controls your system. By strategically opening additional gates as needed and adjusting fan speed, the greenBOX ensures your duct system consistently meets minimum airflow requirements, helping prevent material settling and other potential safety hazards*.
*In some systems, such as those in pharmaceutical facilities and lab environments, opening gates at inactive workstations may not be possible. In these cases, “bleed gates” are used to maintain minimum transport air velocities, with greenBOX managing their activation as necessary.
Design Air Volume of All Gates, Workstations, Systems
During system setup, you’ll input the “Design Drop Air Velocity” for each gate. The greenBOX uses this value, along with the gate’s diameter, to calculate its “Design Air Volume.”
During system setup, you’ll input the “Design Drop Air Velocity” for each gate. The greenBOX uses this value, combined with the gate’s diameter, to calculate its “Design Air Volume.” This calculation is then extended to determine the Design Air Volume for individual workstations (which may have multiple gates) and the system’s overall Design Air Volume.
Based on each gate’s Design Air Volume, the greenBOX calculates the Design Air Volume for each workstation (which can have multiple gates) and the system-wide Design Air Volume (24,939 CFM in this screenshot).
To calculate the recommended minimum air volume, you’ll need to input the main duct diameter and desired minimum transport air velocity. Hovering over the “i” symbol provides helpful tips for selecting an appropriate minimum transport air velocity.
To calculate the recommended minimum air volume, input the main duct diameter and desired minimum transport air velocity, then adjust the Minimum Airflow Ratio to the recommended range using the slider.
Minimum Transport Air Velocity
Setting the correct minimum transport air velocity is essential and should be based on the type of material moving through your duct system. For sawdust, the general recommendation is 3,000–4,500 FPM. Use the lower range for dry, fine dust without elevation changes in the main duct, and the higher range for larger chips, wet sawdust, or ducts with elevation and/or directional changes.
For paper trim, aim for 4,500–5,500 FPM, with lower values for smaller, lighter pieces and higher values for larger or heavier ones.
For average industrial dust, a target range of 3,500–4,500 FPM is typical, adjusted based on particle size and weight. For other materials and more specific guidance, refer to Industrial Ventilation: A Manual of Recommended Practice or consult your local Authority Having Jurisdiction (AHJ).
Next, configure the "Minimum Airflow Ratio" for the main duct and select the "Minimum Airflow Mode."
Minimum Airflow Ratio
The Minimum Airflow Ratio sets the minimum percentage of gate area that must remain open to uphold the desired minimum transport air velocity. For optimal performance, follow the percentage recommended by greenBOX. The system will automatically open additional gates as necessary to achieve this ratio. Although displayed as a percentage for simplicity, this ratio represents the minimum air volume in CFM, which greenBOX calculates based on the minimum transport air velocity entered.
Adjusting Minimum Airflow
To adjust the minimum percentage of open gate area, use the slider. For optimal performance, select the displayed “Calculated Minimum %.” The acceptable range for proper function is highlighted by an orange overlay on the slider. You can retain the default “Calculated Minimum %” unless a specific need arises to increase it, such as unusually high material loading. Note that setting a higher value will increase airflow beyond the minimum transport air velocity, resulting in higher air volume and electricity consumption. greenBOX will automatically open additional gates to maintain the set ratio and will adjust fan speed accordingly.
Note: If the “Calculated Minimum” exceeds the “Calculated Maximum,” you may need to disable some “Open Only by Sensor” gates to achieve the desired airflow. greenBOX cannot use gates set to “Open Only by Sensor” for minimum airflow.
Minimum Airflow Mode (Last Used, From End, None)
The Minimum Airflow Mode determines how greenBOX selects which gates to open to maintain the required minimum transport air velocity. For most systems, “Last Used” mode is recommended, as it prioritizes recently used gates, ensuring they are readily available and enhancing operator convenience.
In long or less efficient duct systems, the “From End” mode is often more suitable. Since gates closest to the fan are entered first during greenBOX setup, this mode prioritizes gates farthest from the fan, maximizing airflow throughout the duct system.
Select “None” if maintaining minimum transport air velocities is unnecessary, as in most fume collection systems.
Maintain Minimum Airflow in Main Duct
Enable this option to allow greenBOX to actively sustain the minimum required air velocity in the main duct by automatically opening additional gates and adjusting fan speed as necessary. If your system configuration includes branch ducts that connect directly to the filter, with no main duct, disable this option as main duct airflow control will not be needed.
Maintaining Minimum Air Velocities in Duct Zones
Building on the setup of minimum transport air velocity for the main duct, this section guides you through assigning gates to specific duct zones and configuring the minimum air velocity for each zone. While the principles mirror those applied to the main duct, each gate must be assigned to its respective duct zone.
Duct Zones Explained
A duct system is divided into branches, or duct zones, each of which may contain multiple gates. You can divide your system into up to ten zones, using only as many zones as necessary for your setup.
Assigning Gates to Duct Zones
To assign gates, go to the "Workstation" page, click on the gate icon, and access the gate’s "Advanced Gate Configuration" section. Select the desired gate and assign it to its corresponding duct zone, choosing numbers 0 through 9. Make sure all gates within the same branch duct are assigned to the same zone number. Once assigned, greenBOX will automatically calculate the "Total Design Air Volume" for each duct zone.
Assign gates to duct zones 0–9 in “Advanced Gate Configuration.” All gates on the same branch duct must share the same zone number.
Duct Zone Diameter
For each zone, specify the diameter of its main duct, where all gates within that specific duct zone are connected.
greenBOX Calculations
Design Air Volume: The sum of the design air volumes of all gates assigned within a zone.
Minimum Air Volume: Calculated based on the user-defined minimum transport air velocity (previously entered for the main duct) and the specific duct zone diameter.
Minimum and Maximum Airflow Range
greenBOX calculates each zone’s minimum and maximum airflow based on gate diameters and the user-defined design air velocity.
Minimum Airflow: Determined by the minimum transport air velocity and the zone’s duct diameter.
Maximum Airflow: Limited by gates set to "Open Only by Sensor," as greenBOX cannot directly open these gates.
Adjusting Minimum Airflow
To adjust the minimum percentage of open gate area, use the slider. For optimal performance, select the displayed "Calculated Minimum %." greenBOX will automatically open additional gates and adjust the fan speed to maintain this ratio. If the "Calculated Minimum" exceeds the "Calculated Maximum," you may need to disable some “Open Only by Sensor” gates to reach the desired airflow or consider adding bleed gates to the system.
Calculated Minimum and Maximum
Calculated Minimum: The ratio of the minimum air volume to the design air volume for the specific zone.
Calculated Maximum: Calculated as 100% minus the percentage of design air volume from all "Open Only by Sensor" gates within the zone.
Closing Unused Duct Zones
When a duct zone has no active gates, maintaining minimum air velocity is unnecessary since there is no material flow. In such cases, it is advisable to close all gates within these zones to increase the system’s dynamic capacity and improve energy efficiency. However, this feature can be disabled if closing unused zones is impractical for your application.
User interface for adjusting minimum airflow in duct zones 0, 1, 2.
Summary
This document has outlined the setup process for maintaining minimum airflow throughout the duct system. Accurate readings of gate air velocity and main duct velocity are essential for optimal performance. Calibration procedures for these measurements are detailed in a separate article. While the system operates, you can monitor how greenBOX maintains minimum transport air velocities via the workstation user interface. Gates used for this purpose are displayed as open, marked by a blue “wave” icon instead of the active sensor icon.
The greenBOX control unit is exceptionally robust, capable of managing multiple dust collection systems while maintaining minimum transport air velocities across the entire duct system in each.
For over twenty-five years, Ecogate has pursued a mission to enhance dust collection systems by improving functionality and efficiency. In that time, we have achieved substantial advancements in system performance, simplified setup and monitoring, and ensured a user-friendly experience. With Ecogate's intelligent automation, dust collection becomes virtually effortless, allowing users to focus on their core tasks. Our dynamic system operates with a fraction of the energy consumption compared to traditional static systems, while also reducing noise levels and extending filter lifespan. This is the next generation of dust collection—fully automated, energy-efficient, dynamic systems with enhanced capacity—setting a new standard for the industry and establishing how every new system should be designed and operated.
Are there features or options that would further enhance the usability of minimum transport air velocities? The greenBOX team welcomes your feedback and ideas to help us continue improving greenBOX to meet real-world needs.
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