Core Technical Requirements And Quality Control Points For Ventilation Duct Construction-Wuxi Weishan Environmental Protection Technology Co., Ltd.

1. Introduction

With the continuous improvement of building functional requirements and the increasing emphasis on indoor air quality and energy conservation, ventilation duct systems have become an indispensable part of modern buildings, widely used in commercial buildings, industrial workshops, public facilities, and residential buildings. The ventilation duct is responsible for the transmission and distribution of air, and its construction quality not only affects the indoor thermal comfort and air quality but also relates to the energy consumption and operational safety of the entire HVAC system. Poor construction quality, such as poor air tightness, insufficient structural strength, and substandard connection and sealing, will lead to air leakage, reduced ventilation efficiency, increased energy consumption, and even potential safety hazards such as duct deformation and falling.

At present, in the construction process of ventilation ducts, there are still problems such as non-standard material selection, improper fabrication technology, non-compliant installation operations, and inadequate quality inspection, which restrict the improvement of construction quality. Therefore, clarifying the core technical requirements of ventilation duct construction, strengthening quality control in each link, and standardizing the construction process are of great significance for ensuring the performance of ventilation systems and reducing long-term operation and maintenance costs. This paper focuses on the core technical requirements and quality control points of ventilation duct construction, conducts in-depth analysis and discussion, and provides a reference for the standardized construction and quality management of ventilation ducts.

2. Core Technical Requirements for Ventilation Duct Construction

The construction of ventilation ducts is a systematic project, involving material selection, duct fabrication, on-site installation, connection and sealing, anti-corrosion and thermal insulation, and other links. Each link has clear technical requirements, which are the basis for ensuring construction quality. The specific technical requirements are elaborated as follows:

2.1 Technical Requirements for Material Selection

The selection of ventilation duct materials must comply with the design requirements and relevant standards, and comprehensively consider the application environment, conveying medium, and performance requirements. The core technical requirements for material selection are as follows:

- Sheet Material Requirements: Commonly used ventilation duct materials include galvanized steel sheets, stainless steel sheets, aluminum sheets, and composite materials. Galvanized steel sheets are suitable for general ventilation systems, with a galvanized layer thickness not less than 80μm, and the sheet thickness shall be determined according to the duct diameter and working pressure (low-pressure ducts ≤500Pa: thickness ≥0.5mm; medium-pressure ducts 500~1500Pa: thickness ≥0.7mm; high-pressure ducts >1500Pa: thickness ≥1.0mm). Stainless steel sheets (304, 316L) are suitable for corrosive environments or high-hygiene requirements, with a surface roughness Ra ≤0.8μm. Aluminum sheets are suitable for lightweight and high thermal conductivity requirements, with a thickness not less than 0.6mm. The sheet must be free of cracks, scratches, rust, and uneven thickness, and its mechanical properties and chemical composition shall meet the requirements of relevant standards.

- Accessory Material Requirements: Sealing materials (such as sealants, gaskets) shall be non-toxic, odorless, high-temperature resistant, and corrosion resistant, and shall not produce harmful substances that affect indoor air quality. The sealant shall have good adhesion and elasticity, and the service life shall be consistent with the service life of the duct. Support and hanger materials shall be consistent with the duct material to avoid galvanic corrosion; for galvanized steel ducts, galvanized steel supports and hangers shall be used; for stainless steel ducts, stainless steel supports and hangers shall be used. Fasteners (bolts, nuts) shall be anti-rust and corrosion resistant, and shall meet the load-bearing requirements.

- Anti-corrosion and Thermal Insulation Material Requirements: Anti-corrosion materials shall be selected according to the corrosion level of the environment, with good adhesion and corrosion resistance. Thermal insulation materials shall have low thermal conductivity, non-combustibility, and moisture resistance, and the thermal conductivity shall not exceed 0.04W/(m·K). Common thermal insulation materials include rock wool, glass wool, and polyurethane foam, and the thickness of the thermal insulation layer shall be determined according to the design requirements of thermal insulation and energy conservation.

2.2 Technical Requirements for Duct Fabrication

Duct fabrication is the foundation of ventilation duct construction, and its precision and quality directly affect the subsequent installation and operational performance. The core technical requirements for duct fabrication are as follows:

- Cutting and Bending Requirements: The sheet shall be cut using laser cutting, plasma cutting, or shearing machines, with a smooth cut surface, no burrs, and a dimensional error not exceeding ±0.1mm. Bending shall be carried out using a hydraulic bending machine, with a bending radius not less than 1.5 times the sheet thickness to avoid cracks at the bending part. For thick-plate ducts (thickness >2.0mm), annealing treatment shall be carried out after bending to eliminate internal stress.

- Forming Requirements: Spiral ducts shall be formed using automated spiral forming machines, with uniform spiral pitch (20~30mm), consistent diameter, and a roundness error not exceeding 3mm/m. Rectangular ducts shall be fabricated with straight edges, right angles, and no deformation, and the diagonal error of the cross-section shall not exceed 3mm/m. The joint of the duct wall shall be locked or welded firmly, and the weld seam shall be continuous, uniform, and free of cracks, pores, and incomplete fusion. For spiral ducts, the locking structure shall be tight, and there shall be no gaps.

- Flange Fabrication Requirements: Flanges shall be fabricated using steel plates with the same material as the duct, and the thickness of the flange plate shall not be less than the thickness of the duct sheet. The flange shall be flat, with evenly distributed bolt holes (spacing 120~150mm), and the hole diameter shall be consistent with the bolt diameter. The connection between the flange and the duct shall be firm, and the welding or locking shall be tight to avoid air leakage. For stainless steel ducts, the flange shall be pickled and passivated after fabrication to improve corrosion resistance.

2.3 Technical Requirements for On-site Installation

On-site installation of ventilation ducts requires strict compliance with design drawings and installation specifications to ensure the stability, air tightness, and rationality of the duct system. The core technical requirements are as follows:

- Pre-installation Preparation Requirements: Before installation, the design drawings shall be reviewed in detail, and on-site surveys shall be conducted to confirm that the installation space, reserved holes, and structural size are consistent with the design. The fabricated ducts shall be inspected for deformation, damage, and fabrication quality, and unqualified ducts shall not be installed. The installation equipment (lifting equipment, measuring tools) shall be calibrated to ensure measurement accuracy and operational safety.

- Support and Hanger Installation Requirements: Supports and hangers shall be installed according to the design spacing and load-bearing requirements. The spacing of supports and hangers for horizontal spiral ducts shall not exceed 3m; for horizontal rectangular ducts, the spacing shall not exceed 2.5m; for vertical ducts, hangers shall be installed at each floor, and the spacing shall not exceed 3m. The support and hanger shall be installed on the building load-bearing structure, and a buffer pad (silicone rubber, PTFE) shall be installed between the hanger and the duct to reduce vibration and prevent damage to the duct surface. In earthquake-prone areas (seismic intensity ≥7 degrees), anti-seismic brackets shall be installed, with horizontal anti-seismic bearing capacity not less than 1.2 times the duct weight.

- Duct Hoisting Requirements: Hoisting shall be carried out using professional lifting equipment, and the hoisting point shall be selected reasonably to avoid duct deformation. The hoisting speed shall be stable, and collision with the building structure shall be avoided. After hoisting in place, the duct shall be fixed firmly, and the levelness and verticality shall be adjusted. The levelness error of horizontal ducts shall not exceed 3mm/m, and the verticality error of vertical ducts shall not exceed 2mm/m.

2.4 Technical Requirements for Connection and Sealing

The connection and sealing of ventilation ducts are key to ensuring air tightness, and any gaps or loose connections will lead to air leakage and reduced ventilation efficiency. The core technical requirements are as follows:

- Duct Connection Requirements: The connection between duct sections shall adopt flange connection, quick-connect joint connection, or locking connection. For spiral ducts, flange connection or quick-connect joints are preferred, and the connection shall be tight and firm. For rectangular ducts, flange connection shall be adopted, and the flange surface shall be flat and closely fitted. The bolts shall be tightened evenly, and the tightening torque shall be consistent to avoid uneven stress and air leakage. The connection between the duct and equipment (fan, valve) shall be equipped with flexible joints (length 150~200mm) to reduce vibration and noise transmission.

- Sealing Requirements: The joint between flanges shall be sealed with professional sealants or gaskets. The gasket shall be of appropriate thickness (3~5mm) and consistent with the flange size, and shall be closely fitted without gaps. The sealant shall be evenly applied along the flange edge, with a thickness of 2~3mm, and shall be fully cured before the system is put into operation. For the locking joints of spiral ducts, sealant shall be applied at the locking position to ensure tight sealing. After connection, the joint shall be inspected for air leakage, and any leakage points shall be repaired in time.

2.5 Technical Requirements for Anti-corrosion and Thermal Insulation

Anti-corrosion and thermal insulation treatment of ventilation ducts can extend the service life of the duct and ensure the energy-saving effect of the ventilation system. The core technical requirements are as follows:

- Anti-corrosion Treatment Requirements: For ducts installed in corrosive environments (such as chemical plants, coastal areas), the inner and outer surfaces shall be treated with anti-corrosion coating. The surface of the duct shall be derusted and degreased before coating, and the derusting grade shall reach Sa2.5 level. The anti-corrosion coating shall be evenly applied, with a thickness meeting the design requirements, and no missing coating, bubbles, or cracks. For stainless steel ducts, pickling and passivation treatment shall be carried out to form a dense oxide film and improve corrosion resistance.

- Thermal Insulation Treatment Requirements: Thermal insulation shall be carried out after the duct connection and sealing are qualified. The thermal insulation layer shall be closely attached to the duct surface, with no gaps or looseness. The joint of the thermal insulation layer shall be overlapped and sealed, and the overlap width shall not be less than 50mm. The outer surface of the thermal insulation layer shall be wrapped with a protective layer (aluminum foil, glass cloth) to prevent moisture and damage. The thickness of the thermal insulation layer shall be consistent with the design requirements, and the thermal insulation effect shall meet the energy-saving standard.

3. Key Quality Control Points for Ventilation Duct Construction

Quality control of ventilation duct construction shall cover the entire process from pre-construction preparation to post-construction acceptance, focusing on key links and common quality problems, and taking targeted control measures to ensure construction quality. The key quality control points are as follows:

3.1 Quality Control in Pre-construction Preparation Stage

- Design Review and On-site Survey: Organize professional and technical personnel to review the design drawings, clarify the technical requirements, construction process, and quality standards, and put forward modification suggestions for unreasonable design contents. Conduct on-site surveys to confirm the installation space, reserved holes, and building structure conditions, and formulate a detailed construction plan according to the on-site actual situation.

- Material Inspection: Strictly inspect the incoming materials, including sheets, accessories, anti-corrosion and thermal insulation materials. Check the quality certificate, test report, and production batch number of the materials, and conduct sampling inspection for key materials (such as stainless steel sheets, sealants) to ensure that the material quality meets the design requirements and relevant standards. Unqualified materials shall be prohibited from entering the construction site.

- Construction Team Training: Conduct technical training for the construction team, explain the construction technical requirements, quality standards, and safety precautions, and ensure that each construction personnel is familiar with the construction process and operating specifications. Conduct skill assessment for key positions (such as welders, fabricators), and those who fail the assessment shall not take up the post.

3.2 Quality Control in Construction Process Stage

- Fabrication Quality Control: Establish a fabrication quality inspection system, and inspect the cutting, bending, forming, and flange fabrication of the duct. Check the dimensional precision, forming quality, and weld seam quality of the duct, and unqualified products shall be reworked or scrapped. Record the fabrication process to ensure traceability of quality.

- Installation Quality Control: Inspect the installation of supports and hangers, including spacing, load-bearing capacity, and installation firmness. Check the levelness and verticality of the duct, and adjust in time if there is any deviation. Inspect the connection and sealing of the duct, and conduct air tightness testing for key joints to ensure no air leakage. Supervise the hoisting operation to avoid duct deformation and damage.

- Anti-corrosion and Thermal Insulation Quality Control: Inspect the anti-corrosion coating process, including surface treatment, coating thickness, and coating quality. Inspect the thermal insulation layer, including thickness, adhesion, and joint sealing. Ensure that the anti-corrosion and thermal insulation treatment meets the design requirements and relevant standards.

- Safety Quality Control: Strengthen on-site safety management, ensure that construction personnel wear personal protective equipment, and strictly implement safety operating procedures. Inspect the lifting equipment and electrical equipment to ensure safe operation. Prevent safety accidents such as duct falling and electric shock.

3.3 Quality Control in Post-construction Acceptance Stage

- Visual Inspection: Conduct a comprehensive visual inspection of the entire ventilation duct system, including duct appearance, connection status, support and hanger installation, anti-corrosion and thermal insulation treatment. Check for deformation, damage, loose connections, missing coating, and other quality problems.

- Airtightness Testing: Airtightness testing is a key item in post-construction acceptance. The testing method shall comply with GB 50243-2016. For low-pressure ducts, the air leakage rate shall not exceed 8%; for medium-pressure ducts, it shall not exceed 5%; for high-pressure ducts, it shall not exceed 3%. For high-demand systems (such as clean rooms), the air leakage rate shall meet Class A requirements (≤2%). If the leakage rate exceeds the standard, the leakage points shall be found and repaired, and the test shall be re-conducted.

- Thermal Insulation Performance Testing: For ducts requiring thermal insulation, test the thermal insulation performance to ensure that the thermal conductivity and surface temperature meet the design requirements. Check the thickness and adhesion of the thermal insulation layer to avoid heat loss.

- Data Sorting and Acceptance: Sort out the construction data, including design drawings, material quality certificates, test reports, construction records, and inspection records. Conduct a comprehensive acceptance according to the design requirements and relevant standards, and issue an acceptance report. The system can be put into operation only after passing the acceptance.

4. Common Quality Problems and Control Measures

In the construction process of ventilation ducts, common quality problems include air leakage, duct deformation, poor connection and sealing, substandard anti-corrosion and thermal insulation, and unreasonable installation of supports and hangers. Targeted control measures are proposed for these problems:

4.1 Air Leakage

Common Causes: Loose connection between duct sections, uneven application of sealant, unqualified sealing materials, gaps in the locking structure of spiral ducts, and poor weld seam quality.

Control Measures: Strictly control the connection quality of duct sections, ensure that the flange surface is flat and closely fitted, and the bolts are tightened evenly. Use qualified sealing materials, and apply sealant evenly along the joint. Inspect the locking structure and weld seam of the duct, and repair any gaps or defects in time. Conduct air tightness testing after installation, and repair leakage points.

4.2 Duct Deformation

Common Causes: Insufficient sheet thickness, improper hoisting operation, unreasonable support and hanger spacing, and uneven stress during installation.

Control Measures: Select sheets with appropriate thickness according to the design requirements. Adopt correct hoisting methods, select reasonable hoisting points, and avoid uneven stress. Install supports and hangers according to the design spacing to ensure sufficient load-bearing capacity. Adjust the levelness and verticality of the duct in time to avoid deformation caused by uneven stress.

4.3 Poor Anti-corrosion and Thermal Insulation

Common Causes: Unqualified anti-corrosion and thermal insulation materials, inadequate surface treatment before coating, uneven application of coating, and loose thermal insulation layer.

Control Measures: Strictly inspect the quality of anti-corrosion and thermal insulation materials. Conduct thorough derusting and degreasing treatment on the duct surface before coating. Ensure that the coating is evenly applied, with a thickness meeting the requirements. Ensure that the thermal insulation layer is closely attached to the duct surface, and the joint is sealed tightly. Inspect the anti-corrosion and thermal insulation effect after construction, and rework if necessary.

4.4 Unreasonable Installation of Supports and Hangers

Common Causes: Failure to install according to the design spacing, insufficient load-bearing capacity of supports and hangers, improper installation position, and lack of buffer pads.

Control Measures: Install supports and hangers strictly according to the design spacing and load-bearing requirements. Select supports and hangers with appropriate specifications to ensure sufficient load-bearing capacity. Install the supports and hangers on the building load-bearing structure, and install buffer pads between the hangers and the duct to reduce vibration and damage.

5. Compliance with Relevant Standards and Codes

The construction and quality control of ventilation ducts must comply with relevant international standards, national codes, and industry specifications to ensure the legality and quality of the project. The main relevant standards and codes are as follows:

- International Standards: ASTM E1592 (Standard Specification for Spiral Round Ducts), ISO 16975 (Ventilation for Buildings - Performance Requirements for Ventilation Systems), EN 12237 (Ventilation for Buildings - Ductwork - Construction and Installation), EN 13403 (Ventilation for Buildings - Ductwork - Air Tightness of Ductwork Systems).

- National Codes: GB 50243-2016 (Code for Construction and Acceptance of Ventilation and Air Conditioning Engineering), GB/T 19516-2019 (Spiral Ducts for Ventilation and Air Conditioning), GB 50016-2014 (Code for Fire Protection Design of Buildings), GB 50189-2015 (Code for Energy Conservation Design of Public Buildings), GB/T 12771-2019 (Stainless Steel Tubes for Fluid Conveyance).

- Industry Specifications: JGJ/T 141-2017 (Technical Specification for Installation of Ventilation and Air Conditioning Ducts), CECS 207-2006 (Technical Specification for FRP Ventilation Ducts in Buildings), HG/T 20696 (Code for Construction and Acceptance of Stainless Steel Piping Engineering), JGJ 142-2012 (Technical Specification for Energy Conservation of Ventilation and Air Conditioning in Residential Buildings).

In the construction process, it is necessary to strictly implement the requirements of the above standards and codes, combine the actual situation of the project, formulate a scientific and reasonable construction plan, and strengthen quality control to ensure that the construction quality of ventilation ducts meets the standards.

6. Practical Engineering Case Analysis

To verify the effectiveness of the core technical requirements and quality control points proposed in this paper, a large-scale commercial complex ventilation duct construction project is selected for case analysis.

6.1 Project Overview

A large-scale commercial complex with a total construction area of 180,000㎡, including shopping malls, office buildings, and catering areas. The ventilation system of the project adopts spiral ducts and rectangular ducts, with a total length of 2500m, including low-pressure and medium-pressure duct systems. The design service life is 25 years, and the air tightness level of the medium-pressure duct is Class B. The project requires strict control of construction quality to ensure ventilation efficiency and energy-saving effect.

6.2 Implementation of Technical Requirements and Quality Control

- Material Selection: Galvanized steel sheets (thickness 0.7mm) are selected for medium-pressure ducts, and 304 stainless steel sheets (thickness 0.8mm) are selected for catering area ducts. Sealing materials adopt high-temperature resistant silicone sealants, and thermal insulation materials adopt rock wool (thickness 50mm). All materials are inspected and sampled, and meet the design requirements and relevant standards.

- Duct Fabrication: Spiral ducts are fabricated using automated spiral forming machines, with uniform spiral pitch and precise dimensions. Rectangular ducts are fabricated with straight edges and right angles, and the weld seam is inspected by non-destructive testing to ensure no defects. Flanges are fabricated with the same material as the duct, and the bolt holes are evenly distributed.

- On-site Installation: Supports and hangers are installed according to the design spacing (2.5m for horizontal ducts), and anti-seismic brackets are installed in earthquake-prone areas. The duct is hoisted stably, and the levelness and verticality are adjusted to meet the requirements. The connection between duct sections adopts flange connection, and the joint is sealed with sealant. The connection between the duct and the fan is equipped with flexible joints.

- Quality Control: Establish a full-process quality control system, inspect the fabrication and installation quality of the duct, and conduct air tightness testing after installation. The average air leakage rate of the medium-pressure duct is 2.8%, meeting the Class B requirement. The anti-corrosion and thermal insulation treatment is inspected, and the thermal insulation effect meets the design requirements.

6.3 Project Effect

After the completion of the project, the ventilation duct system operates stably, with no air leakage, deformation, or corrosion. The ventilation efficiency meets the design requirements, and the energy consumption of the ventilation system is 16% lower than the national standard. After 3 years of operation, the duct system is in good condition, and the maintenance cost is low. The project has achieved good economic and social benefits, verifying the rationality and effectiveness of the core technical requirements and quality control points proposed in this paper.

7. Conclusion

The construction quality of ventilation ducts is crucial to the operational efficiency, energy conservation, and service life of the entire ventilation system. This paper systematically elaborates on the core technical requirements of ventilation duct construction, including material selection, duct fabrication, on-site installation, connection and sealing, and anti-corrosion and thermal insulation, and points out the key quality control points in the pre-construction, construction, and post-construction stages. At the same time, it analyzes common quality problems and proposes targeted control measures, combined with relevant standards and practical engineering cases, to provide practical technical guidance for ventilation duct construction.

In the actual construction process, it is necessary to strictly implement the core technical requirements, strengthen full-process quality control, standardize the construction process, and ensure that the construction quality of ventilation ducts meets the design requirements and relevant standards. With the continuous development of HVAC technology and the increasing stringency of energy conservation and environmental protection requirements, the construction technology and quality control level of ventilation ducts will continue to improve. It is hoped that this paper can provide a reference for the standardized construction and quality management of ventilation ducts, and promote the sustainable development of the ventilation and air conditioning industry.