This feature provides central system warm-up (or cooldown) support. Warm-up occurs when the AHU serving a set of VAV boxes provides warm air (typically 85 to 90°F [29 to 32°C]) to the boxes. This feature is often used first thing in the morning on cool days before occupants arrive. The control action on the flow setpoint control is reversed to prevent overheating the spaces. The minimum flow setpoint may be independently specified for warm-up and cooldown. Warm-up is triggered either based on writing to the Network Input when the AHU is commanded to warm up, or by each VAV sensing the actual temperature of the air supplied by the AHU and automatically switching to warm-up.