Optimal control of combined air conditioning system with variable refrigerant flow and variable air volume for energy saving

•A VRF and VAV combined system is proposed to take merits of both parts.•An optimal control strategy is proposed for the combined system for energy saving.•The strategy effectively reduces total energy consumption and improves efficiency.•Characteristics of the system energy efficiency are revealed.

An optimal control strategy for minimizing the energy consumption of variable refrigerant flow (VRF) and variable air volume (VAV) combined air conditioning systems was presented. The combined system was proposed to take advantages of VAV systems to solve the ventilation problem of VRF systems. The VAV part consists of an outdoor air processing unit and air supply and distribution devices. To determine set-point of the optimal control variable, i.e. outdoor air supply temperature, this paper proposed an optimal control strategy based on adaptive predictive model and recursive least squares estimation technique. Typical days in summer and winter were selected to test the strategy. Results indicated that the optimal control strategy reduces energy consumption of the combined system by 32.17% in summer and 2.47% in winter. The overall energy efficiency is enlarged by 12.18% in summer and 3.37% in winter, compared with the benchmark operation strategy.

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