www. refrigerationandaircon. co. za RACA Journal I July 2025 29
Feature
A rectangular duct section on the manufacturing line.
Dampers: An air damper is a mechanical device that regulates or stops airflow in ducts, VAV( variable air volume) boxes or air handling units. They can be operated manually or electrically and are also used to cut off air conditioning to unoccupied rooms.
Fire / smoke dampers: These specialised dampers, installed in ducts where they penetrate fire-rated barriers, are designed to prevent the spread of flame and smoke. Unlike standard dampers, they incorporate a fusible link that melts at a specific temperature, causing the blades to automatically close and seal off the duct.
Attenuators and noise: The HVAC sector uses Noise Criteria( NC) values( measured in decibels) to evaluate acceptable sound levels. While a fan ' s target range is around 30 decibels( like a whisper), fans can generate up to 80 decibels in a duct system. Noise in HVAC systems primarily comes from air velocity, fans and vibrating components. Sound attenuators( also called silencers or mufflers) are standalone components installed in ducts to reduce noise transmission using various insulating or sound-absorbing materials.
A square duct section including insulation to manage condensation challenges.
• Mild / black steel: Employed in high-temperature applications like flues, stacks and hoods, often requiring special coatings
• Copper: Rare in South Africa, primarily used for extracting air with specific chemicals that react unfavourably with other materials
• Plastic / foam board: A newer material, often aluminumsandwiched, suitable for certain chemical exhausts and underground systems. Advantages include corrosion resistance, light weight and ease of modification, but limitations include cost and fire risk
• Fabric( textile ducts): Made from permeable polyester, used in open ceilings and underfloor applications for air dispersion in new or retrofit projects. Permeable fabric prevents condensation and has shown to significantly reduce energy costs
DUCTING MATERIAL OPTIONS The choice of ducting material goes beyond simple air movement and depends heavily on the specific application and environment. For instance, corrosive conditions necessitate materials like stainless steel or copper over standard steel or fabric.
• Galvanised steel: The traditional and most common HVAC duct material, guided by SMACNA and local SANS 1238 standards for thickness and support
• Aluminum: Popular for clean rooms, moist air, special exhausts and decorative ducting
• Stainless steel: Commonly used for kitchen exhausts, moist air and fume / chemical exhaust systems
www. refrigerationandaircon. co. za RACA Journal I July 2025 29