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? Illustration GS-RA-09

Illustration GS-RA-09: the U.S. Coast Guard has not released this illustration.

Question

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? Illustration GS-RA-09

Illustration GS-RA-09: the U.S. Coast Guard has not released this illustration.

Accepted Answer

Option A: 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.. Staggering the setpoints of heating and cooling coils ensures deadbands that prevent energy-wasteful simultaneous operation and thermal conflict during air conditioning cycles.