In the illustrated single zone HVAC system, what prevents the simultaneous flow of steam through the preheat coil and flow of chilled water through the cooling coil? GS-RA-09 Illustration GS-RA-09: the U.S. Coast Guard has not released this illustration.

Correct Answer: Option C — The supply air duct thermostat controlling the steam flow is set several degrees lower than the design off-coil temperature associated with the cooling coil.

To prevent simultaneous heating and cooling, the steam preheat thermostat is set lower than the cooling coil's off-coil temperature. This sequencing ensures that the preheater only activates when the air temperature is significantly below the cooling set point, preventing energy waste and conflicting operation between the heating and cooling systems.