Comparative study of outdoor airflow requirement and distribution in multi-zone VAV system with different control strategies

Owing to design and operation limitations, most multi-zone variable air volume (VAV) systems in existing buildings still follow traditional techniques for ventilation. In recent ventilation research, most studies focused on comparing a traditional strategy with a superior one, and the comparison studies among traditional strategies are relatively rare. In this paper, four traditional outdoor airflow control strategies that are commonly used in existing VAV systems are introduced and discussed. The results illustrate that the phenomenon of uneven distribution for outdoor airflow among conditioned spaces often occurs, irrespective of the strategies with which the system operates. Compared to constant outdoor airflow fraction strategies, variable outdoor airflow fraction strategies can meet system outdoor airflow requirements while the occupancy number varies. On this basis, performance with respect to IAQ and energy-savings of variable outdoor airflow fraction strategies is compared. The results indicate that the two strategies have the same control effect on the IAQ. Furthermore, the multiple spaces equation-based strategy (MSE-V) shows energy reductions of 6.76% and 9.88% in the heating and cooling seasons, respectively, compared to the maximum outdoor airflow fraction-based strategy (MaxY-V) when the system operates under the same operation conditions.