Numerical investigation of the performance of impinging jet ventilation in a four-bed ICU under heating conditions

Intensive care units (ICUs) are high-risk areas for hospital-acquired infections. Although impinging jet ventilation (IJV) shows great potential in cooling conditions, its ventilation efficiency in heating conditions remains questionable. This study numerically investigates the performance of IJV in a four-bed ICU, examining key factors such as air inlet position, outdoor temperature and air change rate. The interaction between the warm supply air current and cold air currents from exterior walls and windows determines airflow characteristics and respiratory droplet dispersion. Positioning the air inlet near the window promotes early mixing of warm and cold air currents, resulting in a more uniform temperature distribution (vertical gradients: < 0.2°C/m vs. 0.83°C/m). Lower outdoor thermal loads (e.g. 20°C vs. −10°C) enhance air mixing and droplet removal efficiency. Increasing the air change rate (ACH) from 4 to 12 ACH reduces the intake fraction of fine droplets (<5 μm) by adjacent susceptible patients from 0.48% to <0.05%. Temperature differences between patient-level air and outlet air remain within 1.0°C if ACH ≥8, ensuring thermal comfort. This study has validated IJV's potential for ICU applications and has provided theoretical guidance for its design.