What are the quality acceptance standards for the fabrication and installation of air-conditioning ducts? What are the air leakage rate testing requirements?
I am an HVAC expert. The quality acceptance of air duct fabrication and installation is a core part of HVAC system engineering, directly affecting the air supply performance, energy consumption, noise control, and hygiene safety of the air-conditioning system. In projects with high comfort requirements such as hotels and hospitals, excessive air duct leakage not only causes cooling loss and increases operating costs, but may also affect indoor air quality due to dust being drawn in through negative-pressure zones. Therefore, strict acceptance in accordance with the standards is essential.
According to the **Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works GB 50243-2016**, the air duct quality acceptance standards mainly cover the following aspects:
1. **Air duct fabrication quality**:
- **Materials and thickness**: The thickness of air duct sheets (such as galvanized steel sheet) must comply with Article 4.2.1 of the code. For example, for rectangular air ducts in low- and medium-pressure systems with a side length ≤630mm, the steel sheet thickness shall not be less than 0.5mm; for side lengths of 800-1250mm, it shall not be less than 0.75mm. When the side length is too large, angle steel or thin steel sheet flanges shall be used for reinforcement.
- **Connection and sealing**: The bolt spacing of air duct flange connections shall be uniform and shall not exceed 150mm (Article 4.2.6). Sealant must be applied at lock seams, riveted seams, and flange turn-ups to prevent air leakage. For medium-pressure and above air ducts, welded or flanged connections are recommended, avoiding lock seam forms.
- **Reinforcement measures**: Rectangular air ducts with side length ≥630mm, or elbows, tees, etc. with length ≥1250mm, must be provided with reinforcement frames or reinforcement ribs to prevent deformation during operation (Article 4.2.10).
2. **Air duct installation quality**:
- **Support and hanger arrangement**: The spacing of supports and hangers shall comply with Article 6.3.1 of the code. For horizontal installation, the spacing for thin steel sheet air ducts with side length ≤400mm shall not exceed 4m; when side length >400mm, the spacing shall not exceed 3m. For vertical installation, the spacing shall not exceed 4m, and each vertical pipe shall have no fewer than 2 fixing points.
- **Tightness inspection**: After installation, a light leakage test or air leakage rate test must be carried out. The light leakage test is applicable to low-pressure systems, but medium-pressure and above systems must undergo air leakage rate testing (Article 6.2.8).
- **Connection and wall penetration treatment**: Flexible short pipes shall be installed at the connection between air ducts and equipment, with a length preferably of 150-300mm (Article 6.3.6). Sleeves shall be provided where ducts pass through walls or floor slabs, and sealed with non-combustible materials.
3. **Air leakage rate testing requirements**:
- According to **Article 6.2.8 of GB 50243-2016** and Appendix C, air duct systems are divided into three grades by working pressure:
- **Low-pressure system** (P≤500Pa): allowable air leakage rate ≤0.1056×P^0.65 (m³/(h·m²)). For example, when P=500Pa, the allowable air leakage rate is about 6.0 m³/(h·m²).
- **Medium-pressure system** (500Pa<P≤1500Pa): allowable air leakage rate ≤0.0352×P^0.65. For example, when P=1000Pa, the allowable air leakage rate is about 2.1 m³/(h·m²).
- **High-pressure system** (P>1500Pa): allowable air leakage rate ≤0.0117×P^0.65. For example, when P=2000Pa, the allowable air leakage rate is about 0.9 m³/(h·m²).
- **Testing method**: Use a dedicated air leakage rate test device, seal the air duct, pressurize it to the working pressure, and measure the make-up air volume. During testing, note that the length of the test section should not exceed 100m; there must be no exposed holes or cracks on the air duct surface.
- **Practical engineering case**: In a five-star hotel project, the main air-conditioning duct was designed as a low-pressure system (P=400Pa). After installation, we conducted air leakage rate testing on each duct section as required by the code and found that the sealant at one flange connection was not fully applied, causing the air leakage rate to exceed the limit. After re-sealing, the air leakage rate dropped to 3.2 m³/(h·m²), meeting the allowable value (about 4.5 m³/(h·m²)), and the final acceptance was passed.
In summary, the quality acceptance of air-conditioning ducts requires strict control of materials, connections, reinforcement, and installation details. Air leakage rate testing is the key to verifying system airtightness and must be carried out according to the code grades. The above are reference opinions. The actual project conditions still need to be further comprehensively evaluated and implemented in combination with specific working conditions, site conditions, and other factors.