Question 1

What are backdraft dampers?

Accepted Answer

Backdraft dampers are a commonly used product that allow air to flow only in one direction, acting like a check valve for the air. These dampers are commonly used in ducted applications; however, they have been now repurposed on multiple fan systems. The intent of this application is to guarantee that if a fan fails, it will become isolated and not allow the adjacent fan airflow to short-cycle airflow through the failed fan opening. See this demonstrated in the "Backdraft Damper Application" section.

Question 2

Why are backdraft dampers needed?

Accepted Answer

Losing a fan in an array can present major problems in any system, with the primary concern being reduced airflow to the conditioned space. In critical applications, this reduction in airflow could be catastrophic. In other applications, reduced energy efficiency and poor space setpoint control will occur. Additionally, if the mechanical system does not have an alarm to notify facility operators of a failed fan, the air handling unit can continue to run in this condition unnoticed, wasting energy.

Question 3

What's the problem with traditional horizontal backdraft dampers?

Accepted Answer

The dampers in array applications traditionally use a horizontal blade and are gravity operated. These dampers are functional, but their use comes with a penalty in three areas:

1) Gravity – To keep the damper blades open, the fan must apply pressure to counter the effects of gravity; this added pressure requires the fan to run at a higher operating point. Most dampers try to reduce this pressure drop by adding a counterbalance mechanism to decrease the amount of force required to open the blades. The penalty of these weights is more turbulent airflow, additional length required for the damper operation (upwards of 4-8"), and pressure drop that is still substantial.

2) Blade Orientation and Application – Horizontal backdraft dampers are designed to work well in ducted applications. However, using these dampers in a fan cone inlet application poses a problem. Air flowing into a fan inlet cone takes a natural curved path towards the center of the cone. Interrupting the airflow's natural path, the parallel orientation of backdraft damper blades does not promote airflow to be thrown into the center of the cone which forces the air to make a turn, resulting in an increase in pressure drop.

3) Linkage - Backdraft damper blades are linked so that the blades open and close together which doesn’t allow the individual blades the freedom to pivot and follow the natural path of airflow. This forces the airflow to make a turn, resulting in a higher pressure drop.

The combination of these factors results in an increased air pressure drop in the system causing the fan to operate at a higher rpm and higher sound levels. The associated pressure drop can be within the range of 0.3” to 0.7” depending on the air velocity and varying standards amongst damper manufacturers. This increase in pressure forces manufacturers to increase their fan size to meet the application's required duty point.

In contrast, the Airware damper maintains a near zero air pressure drop. How is this accomplished?

1) The blades are vertical eliminating the effects of gravity. Reverse airflow closes the Airware damper. 
2) The blades are center justified on the center axis of the fan allowing all blades to open along the natural path of air flow.

3) There is no blade linkage to allow the blades to move individually following the natural path of air.

Question 4

Why not use a blank off plate?

Accepted Answer

Blank-off plates work, but they rely on several items to be true.

1) Facility operators need to be aware that a fan failed.  This requires either a BMS with monitoring of fan status or daily routine inspections. Many sites lack routine maintenance or controls to alert a facility team of a fan failure.

2) The blank-off plate needs to exist; manufacturing a blank-off when a fan motor fails isn’t the correct time. To be effective blank-off plates need to be predesigned for the specific fan inlet.

3) The blank off needs to be readily available with written procedures so that the fan can be isolated safely. Installing the plates can create a safety concern because most fan arrays will require ladder access and multiple people.

In contrast, the Airware damper closes automatically when a fan fails due to reverse air flow. Within seconds you’ve isolated your fan cell without unnecessary energy waste or facility member involvement.

Question 5

Why is the dock important?

Accepted Answer

When installing a backdraft damper on the inlet of a fan, the blades open beyond the frame of the damper and hit the inlet plate. For this reason, manufacturers must build their own stand-off out of sheet metal. This pushes the damper off the inlet plate with enough space for the blades to clear. So, why is the dock important?

1. There isn’t any engineering/design required. If you buy a 24x24 damper, you will get a 24x24 dock. Using our STEP files, it makes planning for the damper/dock simple.
2. Dampers need to be quickly removed for inspection of the fan inlet. The longer this process takes is more money operators are spending. With the Airware Dock, our damper can be removed within seconds due to 4 easily accessible mounting fasteners. The fasteners are positioned at an angle to make install and removal simple. Extension bits not required.
3. Stand-offs are inherently custom and can leak. The Airware damper/dock assembly has a built-in gaskets creating a tight seal that has been tested up to 15” wc.

Resources

FAQs

Backdraft Damper Application

No Backdraft Damper Installed

Backdraft Damper Installed

*This scenario is applicable to any number of fans within an array greater than one.

Downloads

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