Experimental study on a duty ratio fuzzy control method for fan-coil units

This paper presents a novel energy-efficiency control method for a fan-coil unit, the duty ratio fuzzy control method (DRFCM), which employs the concept of duty ratio on the electric valve control to fully utilize the cooling and dehumidifying capacity of a fan-coil unit when the control valve is closed. By means of mamdani-type fuzzy rules and functioning-fuzzy-subset inference methods, the duty ratio of valve and fan speed signals are decided according to the deviation and deviation changes of the room temperature. This paper adopts a two-water-pipe FCU system with a three-fan speed control and an electric water valve on-off control as test objects to verify the application effect of DRFCM. Program controllers and software tools are employed to conduct DRFCM. The conventional control method is applied by individual FCU controllers. Experimental results show that DRFCM could obtain at least 30% energy savings (not including chilled pump power savings) over the conventional control method. A preferable room temperature control effect could be achieved as well.