A cold weather cooling tower bypass valve should not be fully closed until the temperature reaches:

• A. the compressor setpoint
• B. the point at which drift stops
• C. +5C
• D. about 27C

Answer: (D)

In cold weather, the bypass valve on a cooling tower is used to control how much water bypasses the tower so the condenser water temperature stays in a safe, efficient range. If the water is still relatively cool, you keep part of the flow bypassed to avoid overcooling and potential freeze risk in the tower and piping. As the condenser water warms and approaches the desired operating temperature, you can start closing the bypass to route more water through the tower so it can do the cooling work efficiently.

Reaching about 27C is chosen as the point to avoid overcooling while still letting the tower do its job. Below that temperature, bypass helps prevent excessive cooling; at around 27C, you’re at a practical point to close the bypass and maximize tower cooling. The other options aren’t the control signal for this valve: they don’t relate to how the bypass should be managed to protect the system or optimize cooling in cold weather.