5.(a) State THREE types of damper that may be used to control the airflow in an air conditioning system.(3)
(b) Describe, with the aid of a sketch, an automatic fire damper installed in a vertical air duct or in those that pass through bulkheads designated as fire boundaries.(7)
Types of damper that may be used to control the airflow in an air conditioning system
Air conditioning systems utilize several types of dampers to control and regulate airflow, ensuring optimal performance, energy efficiency, and comfort. Here are some of the common types of dampers used:
- Butterfly Dampers:
- Description: Circular or rectangular dampers with a central rotating disc (butterfly blade) that pivots to control the flow area.
- Operation: When fully open, the blade is parallel to the airflow, allowing maximum flow. As the blade rotates, it obstructs the flow, reducing airflow.
- Advantages: Simple design, low cost, low pressure drop when fully open, suitable for large ducts.
- Disadvantages: Less precise control at low flow rates, prone to leakage when closed.
- Typical Applications: Main supply and return ducts, zone control, and isolation.
- Multi-Blade Dampers:
- Description: Rectangular dampers with multiple parallel or opposed blades that move together to control airflow.
- Operation: The blades pivot on a central shaft, opening or closing to regulate airflow. Parallel blades maintain airflow balance, while opposed blades provide tight shut-off.
- Advantages: Good control over a wide range of flow rates, tight shut-off capability, suitable for various duct sizes.
- Disadvantages: Can be more complex and expensive than butterfly dampers, higher pressure drop compared to butterfly dampers.
- Typical Applications: Air handling units, zone control, and variable air volume (VAV) systems.
- Louver Dampers:
- Description: Consist of a series of overlapping blades or louvers that can be adjusted to control airflow direction and volume.
- Operation: The louvers pivot to open or close, allowing or restricting airflow. They can also be used to redirect airflow.
- Advantages: Excellent control over airflow direction, good sealing capabilities, suitable for outdoor applications.
- Disadvantages: Can be prone to clogging with debris, higher pressure drop compared to butterfly or multi-blade dampers.
- Typical Applications: Outdoor air intakes, exhaust vents, and areas requiring precise airflow control.
- Fire Dampers:
- Description: Designed to automatically close in the event of a fire, preventing the spread of smoke and flames through the ductwork.
- Operation: Typically held open by a fusible link that melts at a specific temperature, releasing the damper to close.
- Advantages: Essential for fire safety, can be integrated with fire alarm systems.
- Disadvantages: Requires regular inspection and maintenance to ensure proper function.
- Typical Applications: Installed in fire-rated walls and partitions where ductwork penetrates them.
- Backdraft Dampers:
- Description: Allow airflow in one direction only, preventing reverse flow or backdraft.
- Operation: A hinged flap or blades open when air flows in the desired direction and close when airflow stops or reverses.
- Advantages: Prevent unwanted airflow, protect equipment from backpressure.
- Disadvantages: Not suitable for modulating airflow or precise control.
- Typical Applications: Exhaust systems, ventilation ducts, and areas where backflow prevention is critical.
Selection Criteria:
Choosing the right damper type depends on several factors:
- Application: The specific function and location of the damper within the system.
- Duct size and shape: The size and shape of the ductwork where the damper will be installed.
- Required airflow control: The level of precision and range of airflow control needed.
- Pressure drop: The acceptable pressure drop across the damper.
- Leakage requirements: The level of airtightness required when the damper is closed.
- Cost and maintenance considerations: The initial cost, installation complexity, and ongoing maintenance requirements of the damper.
By carefully selecting and installing the appropriate types of dampers, air conditioning systems can achieve optimal airflow control, balance, and efficiency, ensuring a comfortable and healthy indoor environment.
Automatic fire damper installed in a vertical air duct or in those that pass through bulkheads designated as fire boundaries.
Let’s describe an automatic fire damper typically installed in vertical air ducts or those penetrating fire boundaries (bulkheads):
Construction and Design
- Damper Body: Usually made of galvanized steel or stainless steel for durability and corrosion resistance.
- Blades: Multiple blades (usually at least two) that pivot on a central shaft to obstruct airflow when closed.
- Actuation Mechanism:
- Fusible Link: The most common type, a heat-sensitive link that melts at a predetermined temperature (typically 72°C or 165°F), releasing the blades to close under spring pressure or gravity.
- Electric Actuator: Can be triggered by a fire detection system, allowing for remote closure and potentially faster response.
- Pneumatic Actuator: Uses compressed air to close the damper, often integrated with a larger fire suppression system.
- Seals: Gaskets or intumescent seals around the blades and frame to ensure a tight closure and prevent smoke and flame passage.
- Access Door: A small access door for inspection and maintenance of internal components.
Installation
- Location: Installed within the ductwork, either vertically or horizontally, at the point where it penetrates a fire-rated bulkhead or wall.
- Secure Mounting: The damper frame is firmly attached to the ductwork and the surrounding structure to ensure it remains in place during a fire.
- Clearance: Adequate clearance is maintained around the damper for proper operation and to allow for expansion of intumescent seals in case of fire.
Operation
- Normal Condition: The damper blades are held open, allowing normal airflow through the duct.
- Fire Detection:
- Fusible Link: When the surrounding temperature reaches the fusible link’s melting point, the link melts, releasing the spring or counterweight mechanism.
- Electric/Pneumatic Actuator: Receives a signal from the fire detection system and activates the closure mechanism.
- Closure: The blades swing shut, blocking the duct opening and preventing the passage of fire and smoke.
- Indication: A visual indicator (often a flag or lever) shows the damper’s position (open or closed).
Importance
- Fire Containment: Fire dampers play a critical role in preventing the spread of fire and smoke through ventilation systems, compartmentalizing the fire and aiding in evacuation and firefighting efforts.
- Regulatory Compliance: Their installation is mandated by safety regulations like SOLAS (Safety of Life at Sea) to ensure fire safety on board vessels.
Maintenance
- Regular Inspections: Periodic inspections are essential to verify the damper’s condition, operation, and proper installation.
- Testing: Functional tests, including drop tests and airflow tests, may be required at specified intervals to ensure the damper operates reliably.
- Cleaning and Lubrication: Internal mechanisms should be kept clean and lubricated to prevent sticking or malfunction.
- Replacement of Fusible Links: Fusible links should be replaced at recommended intervals or if they show signs of damage or corrosion.
By understanding the design, operation, and importance of automatic fire dampers, we can appreciate their crucial role in maintaining fire safety on board ships and other structures.