Influence of portable air cleaner discharge orientation and placement on aerosol exposure in a ventilated hospital patient room

Poor ventilation in hospital patient rooms increases the risk of aerosol transmission from infected occupants. Portable air cleaners (PACs) with high-efficiency particulate air (HEPA) filters can complement conventional ventilation systems (VS), but their performance depends strongly on diffuser design and spatial configuration. This study experimentally evaluated PAC outlet types (square diffuser, SQD; swirl diffuser, SWD; and rotated configuration, RAC), placement relative to the patient (near or far), and airflow distribution between the PAC and the VS (100–0%, 60–40%, 40–60%, 0–100%). The results showed that combining a PAC and a VS reduced aerosol exposure compared with ventilation alone, although the performance varied significantly with configuration. The SWD and RAC configurations located near the patient and operated with a 40–60% PAC-VS airflow distribution achieved the greatest reductions in particle concentration. In contrast, the SQD configuration operating alone yielded the highest size-specific Hygienic Air Delivery Rate-to-power ratio (ηHADR) (4.9 m3 h ⁻¹  W ⁻¹ ). Overall, aerosol exposure was highly sensitive to PAC placement, discharge configuration and interaction with the ventilation system. These findings indicate that PAC-VS hybrid operation can improve indoor air quality under the tested conditions, but the performance depends on the system configuration. Performance metrics such as the ηHADR and HADR provide complementary insight into contaminant removal and energy use under realistic mixing conditions.