Efficient ventilation is a critical aspect of modern building design, balancing the need for good indoor air quality and increasing energy efficiency demands. For this reason, the approach of unsteady ventilation techniques was investigated in this study, in which the supply air volume flow is varied on short timescales. This study explores the comparative performance of steady and unsteady operational modes in mechanical ventilation systems under isothermal conditions, utilising 2D Particle Image Velocimetry (PIV) and a statistical design of experiments. Time-averaged and instantaneous velocity fields in the longitudinal axis of a Reynolds-scaled model room were analysed to evaluate the influence of dynamic supply flow rates on velocities in the occupied zone, and mixing by looking at spatio-temporal dominant structures and vortices. The results of the unsteady scenarios were compared with steady ventilation scenarios and existing literature in this field, but also in the field of pulsating jets. Some considerable differences in velocities, large and small-scale flow structures were found for selected operating modes, enhancing mixing and a more homogeneous velocity distribution. But effects of the flow rate variations on the investigated area were observed in all unsteady cases, e.g. the varying number of vortices or velocity fluctuations in the occupied zone. • Velocities in the occupied zone are influenced by supply flow rate variations. • Most kinetic energy is transported through changes in the supply flow rate. • Minimum ACH (unsteady) contains more energy than maximum ACH (steady). • Vortices are more evenly distributed in the measurement plane in unsteady scenarios. • Unsteady ventilation can improve part load operation.
Mesenhöller et al. (Tue,) studied this question.