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| Dual-duct system
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A central plant heating , ventilation and air conditioning (HVAC ) system that produces conditioned air at two temperatures and humidity levels. The air is then supplied through two independent duct systems to the points of usage where mixing occurs. |
| Dual-paned (double-glazed)
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Two panes of glass or other transparent material, separated by a space. |
| Duckbill pliers
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Pliers with jaw ends that are tapered to a horizontal flat wedge. |
| Duckboard
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Board that is placed over a muddy area to provide firm walking surface. |
| Duct
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A pipe or closed conduit made of sheet metal, fiberglass board, or other suitable material used for conducting air to and from an air handling unit. A passageway made of sheet metal or other suitable material used for conveying air or other gas at relatively low pressures. |
| Duct fan
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An axial flow fan mounted in a section of duct to move conditioned air. |
| Duct tape
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This (initially) sticky tape is unfortunately the most common material used to seal duct connections. Care must be taken when it's applied. For effective sealing, the surface it is applied to must be clean--free of dust, dirt, oil, or other substances. Duct tape has a tendency to lose adhesion with age, especially when used on ducts in unconditioned spaces. |
| Ductile
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Workable. Material, as metal, able to be stretched or hammered thin without breaking, something not brittle, easily molded. |
| Ductility
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The property of a material, often metal, which allows it to be formed and reformed, stretched or hammer, etc. |
| Ductwork
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Network of ducts that has been installed, usually as part of an HVAC system. Ductwork is typically constructed from sheet metal. |
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