NCIDQ IDFX Practice Exam

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Which system mixes hot and cool air from separate ducts?

VAV system
Dual duct system
Constant volume reheat system
Multizone system

The correct answer is: Dual duct system

The dual duct system is designed to mix hot and cool air from separate ducts in order to achieve the desired temperature in a space. In this system, there are two individual duct systems: one for heated air and one for cooled air. By blending these two streams, the system can deliver air at a precise temperature that meets the comfort needs of the occupants. This approach allows for greater flexibility and efficiency in temperature control compared to systems that operate on a single temperature. In addition, the dual duct system can accommodate varying load conditions across different zones, making it suitable for large commercial buildings with diverse space requirements. In contrast, other systems mentioned, such as the VAV system, constant volume reheat system, and multizone system, operate on different principles. For instance, a VAV (Variable Air Volume) system adjusts the amount of air supplied to a space but does not mix hot and cold air from separate ducts. Similarly, a constant volume reheat system maintains a consistent air volume with adjustments to temperature through reheat coils, and a multizone system typically serves multiple zones with separate duct runs but does not mix air streams from separate ducts.