The working principle of the smoke exhaust composite duct mainly relies on its fire resistance and thermal insulation properties, as well as its performance during a fire situation.

The design of the smoke exhaust composite duct is intended to meet specific safety standards, particularly in terms of fire resistance and thermal insulation. This type of duct typically features a fire-resistant and insulating layer, which not only has fire and heat resistance but also thermal insulation, meeting the requirements of GB/T17428-2009 for fire resistance integrity and thermal insulation. The inner and outer protective surfaces of the duct are usually made of high-corrosion-resistant metal sheets or corrosion-resistant aluminum foil, which not only extends the service life of the duct but also effectively prevents corrosion and rust, ensuring the duct maintains stable performance over the long term.

During a fire, the role of the smoke exhaust composite duct is mainly reflected in the following aspects:

‌Smoke Prevention Function: Through mechanical pressurization, air is supplied from the exterior by the smoke prevention system (positive pressure ventilation) to prevent smoke from fires from entering stairwells, vestibules, and refuge floors, which could cause asphyxiation among the refuge population.

‌Exhaust Function: The exhaust system (negative pressure exhaust) expels smoke outside the building, effectively reducing smoke accumulation indoors, providing a better environment for personnel evacuation and rescue.

‌Make-up Air Function: Supplements the airflow of the exhaust system to maintain stable operation of the system.

Additionally, the composite exhaust ducts must be made of non-combustible materials, with fire resistance ratings and limits that comply with design specifications. The fire resistance of the ducts must meet both integrity and insulating requirements to ensure that during a fire, the ducts will not lose functionality due to flame penetration or excessive heat, thereby safeguarding the safety of the building's occupants.

In summary, the working principle of the smoke exhaust composite duct and its performance during fires highlight its crucial role in building safety. Its unique fire-resistant and insulating properties, along with its function in smoke exhaust and air supply, provide essential safety protection for those inside the building.