If the hot water control valve is normally open (N/O) instead of normally closed (N/C), what would the control action be?

When a hot water control valve is normally open (N/O), it means that in its default state, the valve allows hot water to flow through it. In this configuration, the valve only closes or modulates when a control signal is received to divert or stop the flow of hot water, typically in response to changes in temperature or system demand.

This scenario exemplifies direct acting control. In direct acting systems, an increase in the control signal results in increased flow or output—in this case, when the system temperature reaches a certain threshold, the control mechanism would then send a signal to close the valve, thereby reducing the flow of hot water. Conversely, if the signal drops or there is a need for more heat, the valve opens further to allow more hot water to flow, directly responding to the demands of the system.

Understanding this dynamic is crucial in the context of HVAC and building controls, where valves play a significant role in maintaining comfort levels and system efficiency.