Choosing the best duct layout involves routing, sizing, and accounting for architectural obstacles. Software can help determine optimal duct size and estimate costs. Building constraints and access to system controls must be considered. HVAC contractors typically design duct layouts, but modifications may be necessary. Nomographs and software can calculate optimal duct sizing and routing, with more advanced software able to import CAD data. CAD programs are not a substitute for an experienced HVAC designer or engineer.
In choosing the best duct layout, the two main considerations are routing and duct sizing. A well-designed duct system will provide uniform temperatures throughout the building, minimize noise, and account for architectural obstacles. Low-cost software is available to help the designer determine an optimal duct size taking into account the building’s architecture and potential obstructions. Round ducts are inherently more efficient and less expensive to manufacture, but, in some cases, obstructions or gaps may dictate the use of rectangular ducts.
To design the best duct layout, you must first determine the volume of air required by each space in the building. Once this has been established, the number and type of outlets in each space must be calculated to provide the required volume of air. Building design constraints must also be considered. Issues such as limited ceiling-to-roof space in an existing building may require changes to the optimal duct layout. Other factors affecting ductwork design include the degree of difficulty involved in installation, as well as convenient access to dampers, filters, and system controls.
A well-designed duct layout is usually the responsibility of the heating, ventilation, and air conditioning (HVAC) contractor. In some cases, however, building managers, industrial plant designers, and even homeowners may need to modify their duct system to eliminate defects and address changing HVAC needs. These modifications may be necessary because the original design is too expensive to implement due to complex transitions or specialized and expensive fittings.
Traditionally, HVAC and sheet metal contractors have used a mechanical device called a nomoraph to establish duct sizing. It is easy to use and provides a quick calculation of the optimal size for round or rectangular ducting. The software, however, offers the designer more realistic methods for calculating optimal duct sizing and routing, and can produce an estimate of material and labor costs. When airflow issues arise with an HVAC system, some software can analyze and recommend changes to the existing duct layout by simulating the current system.
More advanced duct layout software can import data from computer-aided design (CAD) drawings, thus minimizing the data that needs to be entered into duct sizing and layout software. Most software publishers make their programs compatible with AutoCAD-based design programs. It should be noted that while CAD programs can aid in the design of the entire HVAC system, they are not a substitute for the experience and judgment of an HVAC designer or engineer.
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