Performance of Intermittent Personalized Ventilation Assisting Mixing Ventilation in the Presence of Indoor Disturbance

Abstract

Abstract In this work, an office space is considered, equipped with an intermittent personalized ventilation (PV) system assisting a conventional mixing ventilation system. In ideal offices with no disturbances, it was proven that an intermittent PV average flow rate of 7.5 L/s and frequency of 0.86 Hz could enhance comfort compared to a steady PV and provide protection against contaminants present in the macroclimate. However, office spaces are subject to many disturbances, which could deteriorate the performance of air ventilation systems. In this work, an office door is considered to open disturbing the flow field by establishing pressure gradients. To conduct this study, a 3D computational fluid dynamics model was developed to predict the airflow field variables as well as contaminants’ concentration in the occupant-breathing zone. The model was used to assess the ability of the ventilation systems in maintaining its optimal operating parameters (0.86 Hz) obtained in ideal conditions. Results showed that the optimal PV frequency did not assure the same level of air quality. In fact, ventilation effectiveness decreased by 18% due to the opening door which pulled the PV jet away from the occupant’s breathing zone (BZ). Therefore, in office spaces with high disturbance levels, it is better off to operate the PV under steady state conditions to avoid further disturbance of the jet, or to operate the intermittent PV at low frequencies of 0.3 Hz to 0.5 Hz to minimize turbulence intensities created by the jet fluctuations.