Double walled ducts are essentially a type of ductwork that has two walls and liner in between. There are a few reasons why these ducts would be chosen instead of a traditional single walled duct:
- Acoustical Considerations: One of the main reasons to use double walled ducts is for acoustical reasons. Often if there is a room with ductwork where containing noise is a high priority, for example in a movie theatre or concert hall, then double wall ducts will be an option. The layer of lining in between the two walls creates an acoustic buffer and prevents noise from travelling. There are ways to insulate a duct once it is already installed that involves wrapping insulation around the ductwork, but this is expensive and not as effective as insulating it on the inside.
- Air Quality: As mentioned in a previous blog post, after a bacteria spread through the duct system causing a pneumonia outbreak in 1976 steps were taken to improve the quality of air travelling through ducts. One of these steps was to introduce double walled ducts. The second wall and liner created a much stronger barrier to air contaminants. Additionally, in single walled ductwork the insulation or liner is put on the inside of the duct, creating a higher possibility of trapping contaminants in the liner. With the double walled duct design the air flow only comes in contact with the inner wall of ductwork rather than the liner and as a result fewer contaminants become trapped.
Due to the fact that these ducts have two walls they are often two to three times more expensive to manufacture. They require not only more labour but also an increased amount of material usage to make the three components. Due to this higher rate of material usage it is extremely important to have sophisticated nesting software to ensure material optimization. ShopData software provides advance nesting capabilities for HVAC applications, and includes fittings layouts that include designs for double walled ducts. It features not only the layout for the outer and inner wall, but also the liner as well.