Optimal control of critical fresh air volume based on sectional adjustment of fresh air and return air dampers

Abstract

During the regulation process of VAV systems, the supply air volume changes with the real time load changes, which will cause the fresh air volume to deviate from its set value. Insufficient fresh air results in poor IAQ, whereas an excessive fresh air increases energy consumption. Therefore, an effective method to control the fresh air volume is essential for VAV systems. Based on the differential pressure control theory, two improved control methods—the fresh air section static pressure control method and the critical air volume control method—are proposed herein. Three control methods were compared through experimental study. The results indicate that differential pressure in the first improved method is higher than that in the differential pressure control method, which increases the ease of measurement. However, both these methods have approximately 15% to 25% errors when the supply air volume is small. The critical air volume control method provides more precise control of the fresh air volume, and eliminates deviations at small supply air volumes. Furthermore, the fan power is reduced as well. Investigation has demonstrated that the critical air volume control method is energy-efficient, and can provide new insights into optimized energy-saving control methods for VAV systems. This work proposed a fresh air volume control method of VAV system, the critical air volume control method. This method improves the control accuracy and the convenience of differential pressure measurement of VAV system. The reliability of the method was verified on the test rig, and it is similar to the engineering situation. Therefore, this method has practical application value. Also this method reduces the fan energy consumption of VAV system, thereby improving energy efficiency and reducing operating costs.