HVAC systems with forced air distribution involve a lot of sheet metal work, especially for air ducts. In the US, the industry authority is SMANCA, the National Sheet Metal and Air Conditioning Contractors Association. They publish standards for all types of sheet metal work and also conduct training and public outreach.
Sheet metal work is characterized by being labor intensive and the cost of an installation is strongly influenced by the man-hours dedicated to the project. To optimize the installed cost of pipelines, working efficiently is very important.
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Designing sheet metal components for manufacturability
Design for Manufacturability (DFM) consists of specifying products so that their manufacturing process is as simple as possible. While design typically focuses on meeting project requirements, custom components such as ductwork must be specified with the manufacturing process in mind.
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Even if the ducts are well designed according to the building's needs, their cost can become unnecessarily high if the specified components are difficult to produce and assemble.
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Sheet metal designs must have adequate dimensional tolerances and all perforations and bends must be suitable for the material properties and manufacturing process.
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Assembled components must also be designed with as few parts as possible and their installation must be intuitive. If the pieces look like a difficult puzzle to put together, DFM has not been implemented successfully.
The main benefit of DFM is the reduction of labor hours dedicated to sheet metal fabrication, making the HVAC system cheaper. Building information modeling (BIM) is a powerful tool in pipeline specification since the construction details of three-dimensional components can be clearly indicated.
When sheet metal components have poor manufacturability, contractors are more likely to make mistakes. Even if there are no errors, the components will require more effort than necessary. The best HVAC engineers familiarize themselves with sheet metal fabrication procedures to design suitable facilities, even if they are not directly involved in production.
How Apps Can Simplify Sheet Metal Work
Aware of the growing role of technology in construction, SMANCA has developed several applications that simplify the work of sheet metal contractors:
HVAC Duct Construction App: This tool offers SMACNA-compliant rectangular duct options, from 1” to 120” and ranging from negative to positive 10 in.wg. The app also includes multiple options for joints, cross connections, and reinforcement. It is important to note that the app does not replace professional design services; covers some common configurations, but not the full range of possibilities allowed by SMACNA standards.
Air Duct Leakage App: This tool estimates air leakage from ducts based on specified design conditions and also determines conditions for duct air leakage testing (DALT). The method complies with many standards, including ASHRAE 90.1 and the International Energy Conservation Code (IECC).
Round industrial duct construction application: Users can select spiral or welded duct and specify material properties. The tool also allows the simulation of dynamic loads, such as snow and wind, and permanent loads, such as insulation. Air temperature and particle conditions can also be specified.
Gutter and Downspout Sizing Calculator (Non-HVAC): This tool can access rainfall intensity databases to determine the worst-case scenario for a gutter and downspout project. Based on this data, the app can optimize gutter and downspout dimensions, locations, and spacing.
Sheet metal designs are characterized by a wide range of options that meet SMACNA standards, and these tools are useful for narrowing down the available options. Once the most suitable options for a project have been found, professional HVAC engineers can find the most cost-effective configuration. It is important to highlight that the total cost of ownership goes beyond the initial construction cost, also including operation and maintenance.
Conclusion
Sheet metal work is very flexible, but this also means that the manufacturing process can become long and expensive if the specifications are poor. Ideally, ductwork should be designed to be as compact as possible without compromising HVAC performance, and components should be specified with the manufacturing process in mind.
Comfort is another important factor when designing ducts. Factors such as noise and excessive air speed must be avoided, as they are detrimental to occupant comfort – in business environments this can reduce productivity.
