Dampers rely on their blades to control airflow, balance air pressure, and do what needs to be done in your HVAC system. Here are the ways damper blades work in your HVAC system.
Blades make the damper. Without the blades, you just have an open frame. One of the most important parts of damper design is understanding the mechanics of damper blades. Blades close off airflow, modulate flow and pressure, and fully open to let air through.
Damper blades are a simple concept, but there are nuances that few consider when selecting dampers. Let’s discuss how damper blades work and what they can do for your HVAC system.
Damper blades rotate on their axles. This simple concept can be utilized in several ways. It all depends on what you need the damper to do.
The most common HVAC dampers have two states: fully open and fully closed. These dampers are called control dampers because they control the flow of air through ductwork. Control dampers help establish zones in your HVAC system, to concentrate the system’s efforts on areas that need air conditioning.
Balancing dampers keep a specific blade angle between open and closed, which reduces the dynamic pressure of the air stream. This reduction can help alleviate issues with air pressure in the ductwork.
Control dampers can be configured to hold blades at a specific angle, to double as a balancing damper. These are known as modulating control dampers. This requires a modulating actuator which rotates the blades between fully open, fully closed, and one or more preset blade angles.
Backdraft dampers have off-center axles designed to swing open when pushed by gusts of air. There is no actuator required. You can use a counterweight, which aids or resists the opening action. As we explain in this blog article, backdraft dampers only work for one-way airflow.
We have discussed damper blade designs at length on the Newsstand. Here is a quick overview. There are two blade profiles that make up most of the blades of air control dampers.
The two blade profiles are highly versatile. You will find these blade profiles in control dampers and balancing dampers. There are pros and cons to using one blade profile over the other, but this comes down to the damper’s purpose in your HVAC system.
Single-thickness blades close tighter, especially when configured in opposed blade action. Blade seals can be placed inside the curved edges of the single-thickness blades, so that they come together when the blades close. This creates a tight seal for the blade.
Airfoil blades provide better airflow when fully open. Their smooth profile minimizes drag on the airstream, which reduces pressure drop. Airfoil blades have small crevices near each edge of the blade for blade seals, which overlap when the blades close. They can close tightly when needed.
Single-thickness blades provide a tighter seal. Minimizing air leakage is part of maintaining efficiency across your HVAC system. Leaks can drag your system down. Learn more about how air leakage affects air performance in this Newsstand article.
Teardrop blades are unique to backdraft dampers. To visualize this profile, think of the shape of a teardrop. This blade has a bulbous part for the axle which tapers down to a thin blade edge. The teardrop design provides a smooth blade profile, so that air moves efficiently through the louver.
There is another unique blade profile, but it isn’t designed for airflow. Curtain blades are designed to close off ducts during a fire event, specifically ducts and HVAC openings inside fire barriers.
It might seem weird to bring up actuators in an article on damper blades, but actuators are an important part of blade mechanics.
Actuators rotate the blades. For control dampers, actuators provide the means of opening and closing the blades.
There are three types of actuators. There are minor differences in installation methods between each type, but they perform the same action. In this article, we will focus on electric actuators, the most common actuator type.
Actuators are fastened to the main driving blade. When the actuator rotates this blade, the damper’s linkage will translate that rotation to the rest of the blades on the damper. Linkage allows the damper to open by rotating the driving blade. In other words, all blades will rotate with the driving blade, at the same time.
Actuators can be tied directly to the blade axle, like in the picture above. Or they can be attached to the face of the driving blade. This is known as on-jamb versus on-face. On-face actuators are best for dampers installed in areas with little room around the jambs.
This provides easy access to the actuator, but it also places the actuator in the air stream during standard operation. On-jamb actuators are out of the air stream, but they typically require an extended shaft kit. Manufacturers will often provide these kits with the damper and actuator.
Dampers work because of their blades. Blades provide the means to control airflow and balance pressure. Consider the blade profile carefully and understand what each damper type can do for your system.
For more on control dampers, check out these Newsstand articles:
Starting a new HVAC project? Consider Arrow United Industries for your air control dampers. We build dampers for a variety of HVAC applications, including airflow control. Contact Arrow United today.