Multi-mode ventilation: An efficient ventilation strategy for changeable scenarios and energy saving

The advanced air distribution methods such as displacement ventilation and personalized ventilation attempt to seek a balance between better indoor air environment and energy efficiency. However, multiple demand scenarios including variable locations of occupants and indoor sources may exist in daily operation of the ventilation system. Most of existing airflow patterns are single mode and cannot always be efficient when responding to changeable scenarios. In this paper, a novel ventilation strategy, i.e., multi-mode ventilation (MMV), is proposed to address multiple scenarios. MMV is designed by the combination of several single airflow patterns and aims to utilize the individual advantages of each airflow pattern in controlling specific scenarios. The energy saving potential of MMV is demonstrated by numerical studies of a meeting room. An indexed local cooling load (LCL) is adopted to evaluate the performance of airflow patterns. As a key parameter in LCL calculation, the required supply temperature to maintain the set temperature at the target zone is determined by computational fluid dynamics (CFD) method. The results show that each single airflow pattern can only be efficient for part of 8 scenarios. MMV performs better by combining single airflow patterns 1 and 2 regardless of the changes of the location and magnitude of the occupied zone as well as the location of the heat source. MMV achieves a reduction rate of up to 56.8% in cooling load compared with airflow pattern 4. MMV may provide a reference for real projects in controlling temperature, humidity and contaminant concentration under changeable scenarios.