A review of recent development in variable refrigerant flow systems

This article presents a comprehensive research review on variable refrigerant flow systems. The content includes four main parts: (1) a comprehensive introduction of variable refrigerant flow systems; (2) a review of recent experimental studies, including testing of the heat pump variable refrigerant flow system, heat recovery variable refrigerant flow system, and new variable refrigerant flow systems under various operation modes; (3) a review of steady-state modeling of variable refrigerant flow systems, including history, modeling approach, and model accuracy; and (4) a review of a dynamic modeling study of variable refrigerant flow systems, including modeling approach, control design, and fault detection and diagnosis techniques. It is suggested that the experimental study of variable refrigerant flow systems should include occupants’ thermal comfort. In addition, it is recommended that the steady-state simulation should take the internal gain of buildings into consideration. To improve the accuracy of the steady-state variable refrigerant flow model, more field testing would also be necessary. For dynamic modeling research, it is suggested to include heat recovery variable refrigerant flow and new variable refrigerant flow systems. Development of advanced controllers and effective fault detection and diagnosis algorithms would also be necessary.