Air Shock Absorbers: A Detailed Guide

An air damper is a device that uses valves or plates to stop or regulate the flow of air within a duct, chimney, variable air volume (VAV) box , air handling unit or other similar equipment. Dampers are also used to stop airflow in unoccupied or unused rooms where air conditioning is not needed. Furthermore, dampers can also be used as protective measures against smoke or fire.

An air damper is a complex mechanism with many moving elements. Its main components are the blades, which adjust their position to control the air flow. In addition, shock absorbers include structures, connections, shafts, bearings, seals, blade pins, actuation motors, flanges, secondary shafts and sleeves, among other components.

Types of air dampers

Based on their construction, air dampers can be classified into parallel-blade and opposing-blade dampers. Each configuration has unique performance capabilities and is intended for different applications.

1) Parallel Blade Dampers

In this type of air damper, the blades rotate in the same direction, parallel to each other. The parallel blade configuration is typically used when the damper operates in two positions: open or closed.

These dampers redirect airflow throughout the first few degrees of rotation as they transition from fully open to closed, and therefore control is achieved throughout the first 20-30% of movement. Instead of modulating airflows, these dampers change direction, which is the main reason they are preferred for open-close operation or fixed flow control.

Parallel leaf dampers are typically used in applications where the damper represents an important part of the overall system pressure loss. They should not be used before critical components due to their uneven airflow.

2) Opposing Blade Shock Absorbers

In this type of air damper, the blades rotate in opposite directions, modulating the air flow. These air dampers are primarily used when the system requires air flow control rather than open and close operation, but can also be used for on-off service.

Opposed leaf dampers are typically used in the following applications:

1. When the damper does not represent the majority of the overall system pressure loss.
2. Systems required to maintain uniform airflow downstream of the damper.
3. Ducted terminals.

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Classification of Shock Absorbers by Control Method and Application

Air dampers can also be classified based on the control method they implement and the intended application. Based on their control method, shock absorbers can be automatic or manual:

• Automatic dampers are similar to automatic control valves in terms of operation.

• Manual dampers are manually adjusted depending on the required airflow, as their name implies.

Shock absorbers can also be classified based on their application, with some of the main types being:

• Balancing dampers (volume dampers)
• Front and bypass shock absorbers
• Fire dampers
• Smoke dampers
• Combined fire and smoke dampers
• Gravity dampers (backdraft or barometric)
• Mixture dampers
• Multizone shock absorbers
• Round bumpers
• VAV boxes (variable air volume)

Note how dampers are not only used for air balancing in ventilation systems, but also for safety in fire protection applications.

Why are we worried about shock absorbers?

Air dampers are an important element of MEP engineering design , since their use is subject to code requirements. They must also be designed to minimize energy losses, by preventing heat exchange between them when in the closed position, whilst maintaining the pressure conditions required in the different spaces.

In New York, air dampers are subject to the following codes and standards:

1. National Fire Protection Association (NFPA) standards:
1. NFPA 90A Standard for Installation of Air Conditioning and Ventilation Systems
2. NFPA 92A Standard for Smoke Control Systems Using Barriers and Pressure Differences
3. NFPA 101 Life Safety Code
2. Underwriters Laboratories (UL) standards:
1. UL 555 Standard for Fire Dampers
2. UL 555S Standard for Smoke Dampers
3. UL 555C Standard for Ceiling Dampers
3. New York Building Code
4. New York Mechanical Code

The primary locations where air dampers are required to meet code are as follows: stairwell enclosures, elevator shafts, common hallways, mechanical rooms, fire walls, building exterior walls, shaft enclosures, horizontal assemblies, and ducts and transfer openings.

Air dampers in fire protection applications

The three main types of dampers used in fire protection applications are fire dampers, smoke dampers and combined fire/smoke dampers. This section provides an overview of each type and their applications.

Fire Dampers

Fire dampers automatically interrupt the flow of air through the duct, restricting the passage of flames. To fulfill their function, these dampers are installed in ducts that cross fire protection sets or fire walls. They can be installed in horizontal and vertical ducts and can be curtain or multi-blade types.

The fire damper has the following components:

1. Mango
2. curtain blade
3. Burst joints
4. Fuse link
5. Access door to inspect the fire damper

All fire dampers are installed in the open position, with fuse. When the temperature in the ducts exceeds a specified value, the fusible link melts and the damper shuts off, either by gravity or a spring. To ensure that they fulfill their function, fire dampers need to pass several tests.

Fire damper selection is based on three main factors: fire resistance rating, temperature and operating range. Fire rating depends on the length of time a damper will withstand the heat associated with a fire. For walls, partitions and barriers with a fire resistance rating of less than 3 hours, 1.5 hour fire dampers are used. For fire barriers rated for 3 hours or more, 3 hour fire dampers are used. This procedure ensures compliance with the building code, which requires that the fire resistance rating be maintained throughout the area of ​​walls, partitions and floors.

Exceptions to the use of fire dampers are parking garages, kitchen exhaust ducts, and dryer exhaust ducts.

Smoke dampers

Smoke dampers prevent the spread of smoke in HVAC systems designed to automatically shut down in the event of a fire and have only two positions: open and closed. These dampers are installed in a slotted section of duct – they are installed wherever a duct penetrates a smoke partition or smoke barrier inside the building. They can be applied in passive smoke control systems or as part of an engineered smoke control solution.

In passive systems, smoke dampers close and prevent the circulation of air and smoke through ducts or ventilation openings that pass through a smoke barrier. On the other hand, in engineered smoke control systems, the spread of smoke is controlled by the building's HVAC system or by dedicated fans that create pressure differences. Smoke dampers can be controlled by heat sensors, smoke sensors, fire alarms , or any other method that meets the design intent.

The smoke damper has the following components:

1. Mango
2. Smoke blades (parallel)
3. Burst joints
4. Duct Mounted Smoke Detector
5. damper actuator
6. Access door

It is important to decide which ratings are required for UL listed fire dampers. They are summarized in the following table:

• SD-1320 and SD-1330 smoke dampers are UL/cUL leak rated dampers, listed to the latest UL 555S standard.
• SD-1620 smoke dampers meet UL Class II. Leakage is less than 20 cfm per square foot at 4 inches wg and 350°F (177°C).
• SD-1630 smoke dampers meet UL Class I. Leakage is less than 8 cfm per square foot at 4 inches wg and 350°F (177°C).

Fire and Smoke Damper (Combined)

As the name suggests, this type of damper is a combination of a fire damper and a smoke damper, and is installed in ducts that cross partitions classified as fire and smoke barriers. This type of shock absorber must be qualified under UL555 and UL555S.

Selection of a combined fire and smoke damper depends on 4 factors: fire resistance rating, leakage rating, temperature, and operational ratings.

Combined fire and smoke damper applications include walls, floors and partitions required by local building code. For walls, partitions and barriers with a fire resistance rating of less than 3 hours, 1.5 hour fire/smoke dampers are used. For fire barriers rated for 3 hours or more, 3 hour fire/smoke dampers are used.

The UL 555S standard identifies the three leak classes given in the following table. It provides leakage in cfm per square foot for each class and for various static pressure values:

It is generally suggested that designers choose a very low leakage category.

Conclusion

Air dampers have a wide range of applications, from modulating airflow under normal operating conditions to providing a reliable barrier against smoke or fire during emergencies. However, code compliance is an important aspect to consider regardless of the application, so working with qualified HVAC professionals is highly recommended.