Installation and Application Analysis of Phenolic Pre-insulated Duct in Large Office Building Projects

With the continuous improvement of modern buildings’ requirements for energy efficiency, environmental protection, and HVAC system performance, HVAC composite duct systems have been widely adopted in HVAC duct engineering. Phenolic pre-insulated duct, thanks to its excellent thermal insulation performance and air tightness, is increasingly used in large public building projects. This article takes an office building HVAC project in Shanghai as an example to introduce its application and construction process.

1. Project Overview

The project is a newly constructed office building HVAC system located in Shanghai, with a total construction area of approximately 57,000 m². The building consists of 4 basement levels and 17 above-ground floors, reaching a height of 79.95 meters.

Specifically, the basement areas include a canteen, mechanical and electrical rooms, and an underground parking garage. Meanwhile, the tower area accommodates office spaces, conference centers, and activity rooms. To meet different indoor climate requirements, the office floors adopt a VAV (Variable Air Volume) all-air system with separate zoning for perimeter and core areas. In addition, the lobby and entrance hall use constant air volume all-air systems, while the restaurant area also operates with a constant air volume system.

As this project serves as a key energy-saving and environmentally friendly development, the project team carried out extensive market research and conducted detailed performance comparisons among different duct solutions. After evaluating multiple composite duct options, the team found that Phenolic Pre-insulated Duct provided outstanding thermal insulation performance, excellent airtightness, and reliable overall system efficiency.

Therefore, the project ultimately selected Phenolic Pre-insulated Duct for the supply air, return air, fresh air, and heat recovery exhaust systems.

The duct system features:

• Double-layer 0.2 mm galvanized steel sheet facing
• Core layer made of modified high-density phenolic insulation material
• Duct thickness: 22 mm
• Thermal conductivity as low as 0.18 W/(m·K) at 25°C
• B1-level flame retardant performance
• Overall compliance with Class A fire rating requirements

2. Construction Process

(1) Layout and Marking

Rectangular ducts are fabricated from panels, with dimensions marked based on the inner duct size. Edges are cut at a 45° angle, and panels are assembled to form a complete rectangular duct system. For 20 mm thick panels, an additional 40 mm is added to both sides of the inner dimension.

Depending on material usage and labor efficiency, either horizontal or vertical panel cutting methods can be adopted. Vertical cutting includes single-piece, U-type, L-type, and four-piece methods.

(2) Cutting and Fabrication

Operations include 90° V-groove cutting, 45° beveling, and stepped lap joints. Blade depth must be carefully matched to panel thickness and kept 0.5–1 mm less than the board thickness to avoid damaging the bottom facing layer.

Fabrication of elbows, tees, and straight duct sections is completed through marking, cutting, shaping, adhesive application, forming, and fixing processes.

(3) Adhesive Application, Assembly, and Sealing

During assembly, adhesive is applied to V-grooves, bevel edges, and lap joints, and allowed to dry properly before assembly. Duct sections must be assembled with strict perpendicular alignment.

Corner joints are folded over adjacent edges and fixed with rivets and adhesive. After forming, each duct section must be inspected for quality control.

Neutral transparent silicone sealant is used for internal sealing, together with reinforcement corners and flange strips to ensure airtight performance and structural strength.

(4) Duct Connection

During insertion joint installation, the connection between insert strips and flanges must be tight. If insertion is difficult, talcum powder may be applied to reduce friction and facilitate installation.

Sealant must be applied at all four flange corners before installing sealing strips to ensure airtight performance.

3. Conclusion

Phenolic Pre-insulated Ductwork is now widely used in commercial buildings such as shopping malls, hospitals, office buildings, and residential developments. It offers advantages such as lightweight construction, high strength, and excellent airtightness.

With the continuous development of modern building technologies and increasing functional requirements, Phenolic Pre-insulated Duct will continue to play a more important role in HVAC air distribution systems.