What aspect does a duct NOT include in its definition?

A duct is primarily defined as a conduit or channel designed for conveying air, whether cooled or heated, as part of a heating, ventilation, and air-conditioning (HVAC) system. The definition encompasses the movement of air to regulate temperature and maintain comfort within a space.

Cooled air conveyance and heated air movement are integral functions associated with ducts, as they are specifically designed to transport conditioned air. Similarly, air quality control is an essential aspect of duct systems since they often incorporate filters and ventilation strategies that play a crucial role in ensuring good indoor air quality.

In contrast, compressed air systems operate under different principles and are typically found in industrial or mechanical applications, not directly related to the conventional definition of a duct within an HVAC context. Compressed air systems involve the delivery of air under pressure for tools or equipment, separating them conceptually from what ducts are designed to do. Hence, this aspect is not included in the standard definition of a duct.