In commercial buildings, air ducts are routinely used to distribute conditioned air to the various zones within the building. These duct systems carry heating, cooling, and/or ventilation air from a central location to the zones with the objective of providing for the health and comfort of the building occupants. Air systems vary in design and complexity, but insulation is routinely used on these duct systems to limit heat gains or heat losses and provide noise control.
Air systems are commonly categorized as either single-duct or dual-duct systems. Systems are further categorized as either constant air volume (CAV) or variable air volume (VAV) systems, depending on how the system adjusts to handle the changing zone loads. In general, a CAV system varies the supply air temperature in response to changes in load while keeping the air volume constant. VAV systems modulate the supply air volume while keeping the supply air temperature relatively constant. Many variations or “hybrid” systems are also used. This article will give a high-level overview of these systems. See the references at the end of this article for more details.