Abstract: A novel method of combustion air control for multiple burner furnaces, whereas a pressure transducer is located in the air piping downstream of each zone air flow control device. The pressure transducer sends a feedback signal to a pressure control loop that is in a logical cascade from the furnace temperature control loop. The pressure control loop repositions the air flow control device to compensate for changes in both downstream and upstream conditions. Output from the temperature control loop is interpreted by the pressure control loop as a changing remote set-point value. In one embodiment, the system is ideally suited to compensate for the pressure drop changes that occur across a zone air flow control valve, when flow rate changes occur as burners are started or stopped, thus providing a substantially higher turndown ratio and better control at low fire settings.

Abstract: A novel method of combustion air control for multiple burner furnaces, whereas a pressure transducer is located in the air piping downstream of each zone air flow control device. The pressure transducer sends a feedback signal to a pressure control loop that is in a logical cascade from the furnace temperature control loop. The pressure control loop repositions the air flow control device to compensate for changes in both downstream and upstream conditions. Output from the temperature control loop is interpreted by the pressure control loop as a changing remote set-point value. In one embodiment, the system is ideally suited to compensate for the pressure drop changes that occur across a zone air flow control valve, when flow rate changes occur as burners are started or stopped, thus providing a substantially higher turndown ratio and better control at low fire settings.