How should the material selection and insulation thickness for hotel air-conditioning ducts be determined? What are the fire protection requirements?
I am an HVAC expert. The issue you raised is a core part of hotel HVAC system design and directly affects system safety, energy efficiency, operating costs, and comfort. Improper selection of duct materials can lead to air leakage, condensation, noise, or fire hazards; insufficient insulation thickness can cause cooling and heating losses and condensation problems; and fire protection requirements concern the safety of life and property and must strictly comply with codes. Below, I will provide a detailed analysis based on national standards and engineering experience.
1. Duct Material Selection
According to Article 6.5.1 of the Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings (GB 50736-2012), duct materials shall meet the requirements for fire protection, corrosion resistance, moisture resistance, strength, airtightness, and economy. As a densely occupied place, hotels should give priority to non-combustible duct materials. Galvanized steel sheet is recommended because of its corrosion resistance, high strength, and mature construction, and it is the most widely used in hotel projects. For kitchen exhaust or humid areas (such as laundry rooms), stainless steel sheet (such as 304 material) may be used to enhance corrosion resistance. For non-air-conditioned areas or auxiliary ducts, FRP or inorganic FRP may be considered, but attention should be paid to their relatively weak impact resistance. Fabric air ducts (such as Sox duct) are also used in open spaces such as hotel lobbies, but their fire rating must be ensured to meet Class A non-combustible standards.
Actual case: In a five-star hotel project, our original design used FRP ducts for guest room supply air, but it was found that their surfaces easily accumulated dust and were difficult to clean. They were later changed to galvanized steel sheet with an antibacterial coating on the inner wall, which not only met fire protection requirements but also improved air quality.
2. Determination of Insulation Thickness
The calculation of insulation thickness is based on the Guidelines for Design of Thermal Insulation of Equipment and Pipes (GB/T 8175-2008) and Article 10.1.1 of the Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works (GB 50243-2016). The core principles are to prevent condensation and reduce cooling and heating losses. For hotel air-conditioning systems, the supply air temperature is usually 13-16℃, the return air temperature is about 26℃, the ambient temperature is 28-30℃, and the relative humidity is 60%-70%. The insulation thickness shall be determined through condensation prevention calculations. The formula is based on the heat balance principle and requires the outer surface temperature of the insulation layer to be 1-2℃ higher than the ambient dew point temperature.
Taking centrifugal glass wool as an example: under conventional conditions (ambient temperature 30℃, relative humidity 65%, dew point temperature 22.8℃), the insulation thickness of the supply air duct (internal temperature 13℃) needs to reach 40 mm (density 32 kg/m³); the return air duct (internal temperature 26℃) can be reduced to 30 mm. For chilled water pipes (water temperature 7℃), the insulation thickness needs to be 50 mm. If rubber-plastic material (such as NBR/PVC) is used, because its thermal conductivity is lower (0.035 W/(m·K)), the thickness can be reduced by about 20% under the same conditions.
Actual case: In a hotel project in East China, insufficient insulation thickness (only 30 mm) once caused large-area condensation on summer supply air ducts and dripping from the ceiling. After redesign according to condensation prevention calculations, the thickness was increased to 40 mm and a moisture barrier (aluminum foil facing) was added, completely solving the problem.
3. Fire Protection Requirements
According to Article 9.3.14 of the Code for Fire Protection Design of Buildings (GB 50016-2014, 2018 edition) and Article 4.2.2 of the Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works (GB 50243-2016), the core fire protection requirements for hotel ducts include:
- Material combustion grade: Duct materials must be non-combustible materials (Class A), and insulation materials must also be Class A or B1 (flame-retardant), and materials below Class B2 must not be used. For ducts passing through fire compartments, machine rooms, and shafts, insulation materials must be Class A.
- Fire damper installation: At locations where ducts pass through fire compartments, through partition walls and floor slabs of ventilation machine rooms, and through partition walls of important rooms (such as kitchens and boiler rooms), 70℃ fusible-link fire dampers must be installed (150℃ for kitchen exhaust ducts). According to Article 6.5.7 of GB 50736-2012, the distance from the fire damper to the wall surface shall not exceed 200 mm.
- Fire resistance rating of ducts: For ducts passing through fire walls or floor slabs, the fire resistance rating of the duct itself or its external cladding structure shall not be less than 1.0 hour (fire wall) or 0.5 hour (floor slab). Fireproof board cladding or fireproof coating treatment is usually adopted.
- Smoke exhaust ducts: For smoke exhaust ducts in hotel corridors and rooms, according to Article 4.4.7 of the Technical Standard for Smoke Control and Exhaust Systems of Buildings (GB 51251-2017), the steel sheet thickness shall not be less than 1.2 mm, and a thermal insulation layer shall be provided, with a fire resistance rating of not less than 0.5 hour (horizontal) or 1.0 hour (vertical).
Summary
For hotel air-conditioning ducts, galvanized steel sheet (non-combustible Class A) is preferred; insulation thickness shall be determined through condensation prevention calculations (for example, 40 mm glass wool for supply air ducts); fire protection must strictly comply with GB 50016 and GB 50736 to ensure Class A materials, correct fire damper installation, and compliant duct fire resistance ratings. In engineering practice, it is recommended to carry out a review calculation of insulation thickness before construction and to strengthen the linkage commissioning of fire dampers.
The above are reference opinions. The actual project conditions still need to be further evaluated and implemented in combination with specific operating conditions, site conditions, and other factors.