What is the purpose of reheat in a single duct constant volume system?

• A. To increase cooling capacity.
• B. To offset reduced actual load.
• C. To reduce outdoor air delivery.
• D. To heat all spaces to a fixed temperature.

Answer: (B)

In a single-duct constant-volume system, reheat is used to prevent overcooling while still achieving dehumidification. The air is cooled in the air handler to remove moisture, which can leave the space too cold if it goes straight to all zones. Reheating the conditioned air after this cooling step allows the system to meet humidity control without making every space uncomfortably cold, effectively offsetting the cooling effect for zones with a lower sensible load. This keeps spaces at their desired temperature while still handling latent loads.

That’s why the purpose is to offset the cooling effect to maintain comfort and proper humidity, rather than increasing cooling capacity, reducing outdoor air delivery, or heating every space to a fixed temperature.