Occupant-centric multicriteria optimization of hybrid personalized HVAC system: Impact of supply inlet layout and return air ratio

Most studies on personalized ventilation (PV) neglected the impact of main ventilation settings. Furthermore, research often focuses on only one or two of the crucial factors in built environments: thermal comfort (TC), air quality (AQ), and energy consumption. Therefore, this study investigated and optimized the performance of hybrid personalized system (HPS), combining main and personalized ventilation, in achieving occupant-centric air quality, thermal comfort, and energy efficiency in a two-person office room. Computational fluid dynamics simulations were conducted to analyze the effects of various parameters, including main ventilation supply temperature, flow rate, return air ratio, and personalized ventilation supply temperature and flow rate. Configurations such as bottom-supply or hybrid displacement ventilation (DV-PV), near-ceiling supply or hybrid near-ceiling ventilation (NCV-PV), and a case with 100 % return air (DV-PV with 1.0 return air ratio), were explored. Using the "technique for order of preference by similarity to ideal solution" (TOPSIS), the study found that for well-designed main ventilation systems, personalized ventilation might not be necessary, as indicated by the highest TOPSIS scores across the 66 simulations. However, personalized ventilation can significantly improve inhaled CO2 concentrations in scenarios where the main system lacks proper fresh air introduction-such as those relying on slits or frequent door and window openings. This is demonstrated in the 1.0 return air ratio cases, which require a personalized ventilation flow rate of 6 L/s. As air quality, thermal comfort, and energy consumption are critical parameters in built environments, this study provides valuable insights for the design and implementation of HPS.