A coordinate control approach for energy saving of central variable- frequency air conditioning systems

This paper presents a coordinate control approach for energy saving of central variable-frequency air conditioning systems. The major contributions of this paper are composed of four parts. First, optimal driving conditions of induction motors used for central air conditioning systems are established to reduce motor losses. Second, the optimal operation condition of the air condition system under rated loading is used to find the optimal flow rates of the cooling water pumps using Lagrangian approach, thereby providing the optimal input frequencies of the induction motors under consideration. Third, the coordinate control algorithm is proposed to minimize total power consumption and determine the optimal cooling water temperatures under rated loading condition. Finally, the multi-adjustable speed drives controlled by PI controllers with the optimal setting and a wet ball temperature compensation strategy are used to conduct experimentation. Experimental results for a small-scale variable-frequency air conditioning system show that the proposed coordinate control is capable of achieving satisfactory energy saving.