Which air distribution system includes both a warm air duct and a cool air duct and uses mixing boxes near the zone to mix the streams and achieve the desired temperature while delivering air at a near constant volume?

Which air distribution system includes both a warm air duct and a cool air duct and uses mixing boxes near the zone to mix the streams and achieve the desired temperature while delivering air at a near constant volume?

• A. Dual temperature system
• B. Multizone
• C. Dual duct
• D. Mixing box system

Answer: (C)

This question tests how a dual-duct air distribution system works. In this setup, two separate supply streams are used: one duct carries heated air and the other carries cooled air. Near each zone, a mixing box blends the hot and cold streams to produce the required space temperature, while the total amount of air delivered to the zone stays essentially constant. The zone temperature is controlled by adjusting the proportion of hot versus cold air, not by changing the overall airflow, which is why the system delivers air at a near-constant volume. This mixing-at-the-zone approach is the hallmark of a dual-duct system, giving flexibility to accommodate different zone loads quickly. Other systems either rely on a single mixed stream and reheating for zones, or use multiple dampers without separate hot and cold ducts, so they don’t match the two–duct, mixing-box-at-zone configuration described here.

This question tests how a dual-duct air distribution system works. In this setup, two separate supply streams are used: one duct carries heated air and the other carries cooled air. Near each zone, a mixing box blends the hot and cold streams to produce the required space temperature, while the total amount of air delivered to the zone stays essentially constant. The zone temperature is controlled by adjusting the proportion of hot versus cold air, not by changing the overall airflow, which is why the system delivers air at a near-constant volume.

This mixing-at-the-zone approach is the hallmark of a dual-duct system, giving flexibility to accommodate different zone loads quickly. Other systems either rely on a single mixed stream and reheating for zones, or use multiple dampers without separate hot and cold ducts, so they don’t match the two–duct, mixing-box-at-zone configuration described here.