Use of steady and intermittent personalized ventilation in indoor environments: Thermal comfort and Indoor air quality

Abstract

The wellbeing and productivity of occupants in indoor spaces are correlated to their satisfaction with their thermal environment and their breathable air quality. This is highly dependent on the installation of carefully designed and energy-efficient air distribution systems such as personalized ventilation. These systems are individual devices consisting of a ducting network, which outlet delivers conditioned clean fresh air towards the occupant. As the issuing jet is adjustable in flow rate, direction and temperature, personalized ventilators respond to each occupant’s thermal preferences while improving the inhaled air quality compared to standalone total volume ventilation. Research on personalized ventilation has investigated its performance under steady state conditions. In other words, its adjustable operating conditions were constant over prolonged periods of time. The first part of this work integrates for the first time, the concept of personalized ventilation with dynamic cooling, known to enhance comfort in warm indoor conditions. This is done by supplying the personalized flow rate in a time-dependent sinusoidal profile that fluctuates between a minimum and a maximum at frequencies of 0.3-1 Hz. The occupant is hence given additional freedom to adjust the jet frequency to their liking or revert to steady supply. This device is denoted as intermittent personalized ventilation. This work studies through experimentally validated CFD models, the performance of intermittent personalized ventilation in a space equipped with typical mixing ventilation and another equipped with a chilled ceiling, in enhancing occupants’ thermal comfort. Breathable air quality will also be assessed, and possible energy savings evaluated in comparison with a steady system. It was found that intermittent personalized ventilators enhanced thermal comfort especially in warm indoor conditions (26 C) with increasing frequency. It did not perform well in neutral conditions (24 C). Moreover, due to increased jet turbulence, it provided lower, but nonetheless satisfactory breathable air quality compared to steady personalized ventilation. Energy savings of 16% and 8% were achieved in the case of mixing ventilation and chilled ceiling. Personalized ventilation has always been viewed as a means to improve indoor quality for the person using it by reducing exposure to gaseous or particulate matter pollutants. However, in the presence of particle emissions, personalized ventilation can contribute to particle deposition on occupants’ clothing, which can act as subsequent sources if triggered by occupants’ physical activities. Hence, personalized ventilation can contribute to second-hand clothing-mediated exposures. This work also investigates through experimentally validated CFD models the effect of different air terminal devices in reducing inhalation exposure while contributing to second-hand clothing exposure. Results showed that a computer mounted panel showed the best performance as it simultaneously decreased all types of exposure. Vertical desk grills decreased inhalation exposure while having negligible effect on second-hand exposure. Round movable panels decreased inhalation exposure but significantly increased clothing mediated exposures.