DAMPERS IN HVAC SYSTEMS

In HVAC systems, dampers are mechanical devices installed within ductwork or Air Handling Units (AHUs) to control airflow, enhance safety, and maintain indoor air quality. They play a vital role in ensuring energy efficiency, fire protection, and occupant comfort in buildings like hotels, offices, and hospitals.

Fire Dampers

Function

Fire Dampers are passive fire protection devices designed to prevent the spread of fire through HVAC ductwork in the event of a fire. They automatically close when exposed to high temperatures, sealing off ducts to maintain fire-rated compartmentation in buildings.

• Primary Role: Restrict fire from traveling between fire-rated walls or floors via ducts, ensuring compliance with safety codes (e.g., NBC 2016 in India).
• Operation: Triggered by a fusible link (melts at ~74°C) or a thermoelectric sensor, closing the damper blades via a spring mechanism.

Design and Components

• Blades: Single or multiple curtain-style or multi-blade (steel, ~1-2 mm thick), folding or sliding to block airflow.
• Frame: Galvanized steel or stainless steel, fire-rated (e.g., 1.5-3 hours per UL 555).

Closure Mechanism

• Fusible Link: Melts at a set temperature, releasing blades.
• Spring: Ensures rapid, tight closure.
• Optional Actuator: For motorized reset in accessible locations.
• Seals: Intumescent strips (expand when heated) for airtight closure, preventing fire leakage.
• Sizes: Match duct dimensions (e.g., 300×300 mm to 1200×1200 mm for hotel AHUs).

Standards and Testing

• India: National Building Code (NBC) 2016, Part 4 (Fire and Life Safety), mandates fire dampers for fire separations.
• International: UL 555 (1.5-3 hour fire rating), IS 16471 (Indian standard for fire dampers).
• Testing: Must withstand fire exposure (e.g., 800-1000°C) without deformation, ensuring no flame passage.

Fire & Smoke Dampers

Function

Fire & Smoke Dampers combine fire protection with smoke containment, preventing both fire and toxic smoke from spreading through ductwork. They are critical in high-occupancy buildings like hotels, where smoke inhalation is a leading cause of fire-related injuries.

• Primary Role: Block fire (like fire dampers) and seal against smoke leakage, maintaining safe evacuation routes.
• Operation: Close via: –
• Fusible Link (~74°C) for fire.
• Smoke Detector or Building Management System (BMS) signal for smoke, using a motorized actuator.

Design and Components

• Blades: Multi-blade (interlocking, 1.5-2 mm steel) for tighter seals vs. curtain-style fire dampers.
• Frame: Heavy-duty galvanized or stainless steel, rated for 1.5-3 hours (UL 555 for fire, UL 555S for smoke).
• Seals: Silicone or rubber gaskets for smoke-tightness, plus intumescent strips for fire.
• Actuator: Electric or pneumatic motor (24V/120V) for smoke-triggered closure and remote testing/reset.
• Sensors: Integrated smoke or heat sensors (e.g., 135°C reset) for automatic operation.
• Sizes: Similar to fire dampers, customized for ductwork (e.g., 600×400 mm for hotel AHUs).

Applications

Installed in smoke barriers or combined fire-smoke partitions, such as hotel lobby ducts or escape corridors.

Standards and Testing

• India: NBC 2016 (Clause 3.4.8.3) requires fire & smoke dampers in critical zones. ISHRAE guidelines emphasize smoke control.
• International: UL 555 (fire) and UL 555S (smoke leakage, <4 cfm/sq.ft. at 0.5 in. WG).
• Testing: Must pass fire endurance and smoke leakage tests, ensuring no smoke penetration at 200°C.

Volume Control Dampers (VCDs)

Function

Volume Control Dampers (VCDs) regulate airflow volume in HVAC ductwork to balance air distribution, optimize energy use, and maintain comfort. They adjust airflow manually or via actuators based on zone requirements.

• Primary Role: Control air volume (e.g., CFM) to specific areas, ensuring proper cooling/heating (e.g., for your hotel’s FCUs or AHUs).
• Operation: Blades rotate to open/close (0-90°), manually via a quadrant or automatically via motorized actuators (linked to BMS or thermostats).

Design and Components

• Blades: Single or opposed/parallel multi-blades (galvanized steel or aluminium, 1-1.5 mm), pivoting on bearings for smooth adjustment.
• Opposed Blades: Reduce turbulence, better for precise control in hotel rooms.
• Parallel Blades: Simpler, for on/off applications.
• Frame: Galvanized steel or aluminium, flanged for duct mounting.
• Seals: Neoprene or silicone gaskets for low leakage (e.g., <10 cfm/sq.ft. at 1 in. WG).
• Actuator: Optional electric/pneumatic motor (e.g., Belimo, 24V) for automated VCDs in large AHUs.
• Sizes: From 100×100 mm (branch ducts) to 2000×1000 mm (main ducts), matching 2,000-40,000 CFM AHU fans.

Applications

Used in duct branches or AHU outlets to balance airflow.

Collar Dampers

Function

Collar Dampers (also called duct collar dampers or backdraft dampers) are simpler devices installed at duct terminations (e.g., grilles, diffusers) to control airflow direction or prevent unwanted backflow. They are often used in exhaust or ventilation ducts.

• Primary Role: Allow airflow in one direction (e.g., exhaust out) while blocking reverse flow (e.g., outdoor air entering), or regulate flow at duct outlets.
• Operation: Gravity or spring-loaded blades open with positive pressure and close when airflow stops. Can be manual or motorized for control.

Design and Components

• Blades: Lightweight aluminium or mild steel (0.5-1 mm), single or multi-flap, pivoting freely or spring-assisted.
• Frame: Aluminium or mild steel, circular or rectangular, fitting duct collars (e.g., 100-300 mm diameter).
• Seals: Optional foam or rubber strips for tighter closure, reducing leakage.
• Actuator: Rarely motorized; manual quadrants for adjustable models.
• Sizes: Small (100-400 mm), matching duct ends or diffusers in hotel bathrooms or kitchens.

Applications

Installed at exhaust ducts (e.g., hotel bathrooms, kitchens) to prevent backdraft

Used in supply ducts for fine-tuning airflow at room diffusers, complementing VCDs in your hotel’s FCU zones.

Standards and Testing

• India: No specific NBC mandate, but ISHRAE suggests low-leakage dampers for ventilation.
• International: AMCA 500-D (backdraft performance), UL 2043 (low smoke for plenum use).
• Testing: Focus on leakage (e.g., <20 cfm/sq.ft. at 0.5 in. WG) and pressure loss (<10 Pa).

Aman Taluja is a dedicated professional in the HVAC industry, currently involved in operations at Brightflow Engineers Pvt. Ltd. Based in Kundli, Haryana, the company specializes in manufacturing Evaporative Cooling Units, Dry Scrubbers, and Air Handling Units. With a proven track record, Aman has successfully contributed to various prestigious projects, including installations at NTPC Dadri, Le Meridien Hyderabad, Marriott Amritsar, and Ambience Creacions Gurgaon.