Add on ESP panel (used with existing zone panel) to eliminate bypass, includes 4 zone panel and static pressure sensor. The ESP-400 electronic static pressure module eliminates the need for a bypass damper when used with the standard 24V, zone control panels and standard 3-wire, 24V dampers. Rather than using a bypass to regulate static pressure, the ESP-400 will modulate non-calling zone dampers to regulate system pressure based on the setpoint of the static pressure sensor.