A Comprehensive Comparison between Square Ducts and Circular Ducts: How to Choose the More Suitable Ventilation Duct?

 

In the design of ventilation systems, the selection of duct shape directly affects project efficiency and cost. As the two mainstream types, square ducts (with rectangular or square cross - sections) and circular ducts have significant differences in performance and application scenarios. The following is a comparative analysis from core dimensions to help decision - makers optimize the selection plan.

 

I. Comparison of Structure and Sealing Performance

Circular ducts are formed using an integrated spiral locking or welding process, creating a streamlined duct without edges. This structure minimizes air flow resistance. Meanwhile, as the joints are equipped with factory - preinstalled air - tight connectors (usually with double - layer rubber gaskets), they can withstand a positive pressure of 3000 Pa and a negative pressure of 5000 Pa. The overall air leakage rate is significantly lower than that of square ducts. In contrast, square ducts are assembled from metal sheets. The flange or insert strip connection methods are prone to form leakage points at the corners, and the reliability of manual sealing is weaker than that of standardized circular pipe fittings.

 

II. Differences in Airflow Efficiency and Energy Consumption

The aerodynamic advantages of circular ducts enable them to perform outstandingly in long - distance air transportation. Experimental data shows that under the same air volume, the pressure loss of circular ducts is about 20% - 30% lower than that of rectangular ducts. This means that the fan power can be reduced by more than 15%, and the long - term energy - saving benefit is significant. However, due to the right - angle structure of square ducts, it is easy to generate turbulent flow. Especially in high - velocity airflow scenarios, the eddies at the corners will additionally increase the system resistance, and the efficiency loss needs to be compensated by increasing the fan power.

 

III. Analysis of Installation Cost and Economy

Although the single - piece production cost of square ducts is lower, their comprehensive installation cost is often higher than that of circular ducts. For example, under the same ventilation volume requirement, a circular duct with a diameter of 200 mm can replace a rectangular duct of 250×250 mm, reducing the material usage by about 25%. Moreover, since the single - pipe length of circular ducts can reach 3 - 6 meters (while that of rectangular ducts is only 1 - 1.5 meters), the connection nodes are reduced by more than 60%, and the labor time is greatly compressed. In addition, circular ducts do not require a complex support structure, further reducing the construction cost.

 

IV. Space Adaptability and Application Scenarios

The flattened design of square ducts is irreplaceable in specific scenarios:

1. Areas with limited floor height: When the vertical space is insufficient, such as inside the ceiling or in equipment mezzanines, the rectangular cross - section can maximize the use of horizontal space.

2. Special building structures: When it is necessary to fit the direction of beams and columns or irregular walls, the aspect ratio can be customized (it is recommended not to exceed 4:1) to achieve precise matching.

3. Parallel layout of multiple systems: When heating, ventilation, air - conditioning, fire - fighting, and smoke - exhaust ducts need to be arranged in layers, square ducts are easier to arrange in a modular way.

 

V. Considerations for Maintenance and Service Life

Due to the high structural strength (uniform distribution of circumferential stress) of circular ducts, they perform more stably in high - pressure systems (> 1500 Pa). The thickness of the galvanized steel sheet can be 0.1 - 0.3 mm less than that of rectangular ducts. However, the four corners of square ducts are easily affected by stress concentration, and the status of welds and gaskets needs to be checked regularly. Especially in dust removal systems, particles are more likely to accumulate at the right - angle parts, and the cleaning frequency needs to be increased.

 

Conclusion and Suggestions

Scenarios where circular ducts are preferred: long - distance gas transportation, high - pressure systems, and projects with priority on energy saving.

Scenarios where square ducts are preferred: areas with limited space, matching of irregular structures, and coordinated layout of multiple ducts. When making decisions, the initial investment, operation and maintenance costs, and space constraints should be comprehensively evaluated. If necessary, a mixed layout scheme can be adopted to balance technical and economic factors.