Every time we visit a new plant and chat with the folks running the dust collectors, we notice that the word “damper” means different things to different people. So we figured it’s a good time to clear things up and explain what dampers actually are, what are VFDs, and how to use them the right way.
What Are Dampers?
As systems increase in size, it may be necessary to use dampers on the ductwork
Ventilation dampers are used in dust collection systems to adjust and control airflow. Air dampers are also used to separate sections of the ductwork that are not currently operated, thus optimizing the operation of the entire system. There are different types of dampers, including manual dampers (adjusted by hand), motorized dampers (controlled by an electric motor), and automatic dampers (responding to changes in temperature or pressure). Dampers provide a way to manually or automatically adjust airflow, but they do not change the speed of the fan or motor.
In the dust collector itself, there are two main types of dampers and they adjust fan capacity with different system effects:
- Inlet Vane Damper (VIV) – Installed on the inlet of the fan, swirls the air in the same direction as the fan rotation. They are commonly modulated with electric or pneumatic actuators. This is the most efficient damper option. Power consumption can be reduced, though not as much as with a VFD.
Outlet Damper: This is the least efficient option, as it increases system pressure drop as the air flow decreases.
- Outlet Damper – Mounted on the outlet of the fan, simply “throttles” the air leaving the fan. This damper is the least efficient option, as it increases system pressure drop as the airflow decreases.
The Importance of Initial Damper Settings
You might have to readjust the dampers throughout the lifespan of the filters
When a dust collector is first commissioned, a service technician measures the total air volume and duct conveying velocity to ensure proper dust control at the hoods in the process. These measurements are typically taken when the system and filters are new, with a low differential pressure around 1.0 inch of water column. At this point, the technician sets and records the fan damper position.
Most dust collectors have a cleaning system that keeps dust from building up in the filters and helps maintain an average differential pressure. But as time goes on, pressure builds up and airflow drops, so you might have to readjust the damper a bit to keep things working right. This kind of adjustment might need to happen a few times throughout the lifespan of the filters.
When it’s time to replace the filters, the damper must be readjusted to its original position set during commissioning. If you skip that step, you could end up with too much airflow, which wears out the new filters faster, increases costs due to more frequent replacements, and could even cause some downtime in your process.
What is the difference between Dampers and VFDs?
While dampers control airflow by opening or closing to adjust the volume of air passing through ducts, VFDs control the speed of motors to regulate the output of fans.
VFDs (Variable Frequency Drives) are electronic devices used to control the speed of an electric motor by varying the frequency and voltage supplied to it. They are often used with fans to adjust the speed of the motor based on the required airflow. By adjusting the speed of the motor, VFDs can achieve energy savings by matching the output of the fan or pump to the actual demand, rather than running at full speed constantly.
This setup is great for dust collector users because it cuts down on the work needed to keep the system running—no one has to constantly mess with the outlet damper. Plus, the VFD keeps the collector working at the right air-to-cloth ratio all the time. That means there’s no risk of someone accidentally opening the damper too much and throwing things off, which can wear out the filters faster.
But the biggest perk for dust collector owners? Long-term energy savings. Since fans use variable torque, the energy they need depends on how fast they’re running. And it’s not a small difference—if you slow a fan down by 25%, it only uses about 42% of the energy. Cut the speed in half, and it only uses around 12% of the power. That adds up to serious savings over time.
Do I Need a Fan Damper or a VFD?
Simply put, it all depends on the application. What can help you decide?
PROS
In addition to reducing the power, variable frequency drives in fan applications may also result in reduced noise in heating and ventilation ductwork due to the elimination of dampers. When regulating flow rates, dampers can induce unwanted vortexes in the airflow, which create noise and vibration. In a variable frequency drive system, making flow-rate changes generally only results in slight changes to the noise levels, which are normally undetectable to the ear.
CONS
- ✳️ Full load conditions: in well-optimized applications where the process demand may already closely match the full-load capacity of the motor, then use of a variable frequency drive with its associated energy losses would only add to the overall system losses.
- ✳️ Equipment speed limitations: some equipment is not designed to operate at reduced speeds, and could be damaged if operated at a reduced speed. Check with equipment suppliers to ensure the equipment is compatible with variable speed operation.
- ✳️ Another limitation of variable frequency drives is that it is not normally possible to reduce the flow all the way to zero due to a reduction of cooling capacity in the motor; a minimum speed of around 30% is permissible, however this is dependent on the specification of the variable frequency drive and motor.
Which One is the Most Convenient for My System?
Here we have some key factors you should have in mind:
- ✔ How many hours will the fan be in operation?
- ✔ What is the cost of power in your area?
- ✔ Dampers have lower up-front costs than VFD’s, but VFD’s can provide higher long-term savings in energy costs.
- ✔ Outlet dampers may be a great option if cold-starting the fan is the only concern (when the air’s temperature at start-up is colder than the actual operating temperature).
- ✔ Dampers can be used to regulate and balance system pressure.
