Ventilation efficiency and improvements for displacement ventilation systems during heating: A case study of a ward with vertical induction units

This study investigates the ventilation mechanism and effectiveness of a displacement ventilation (DV) system under heating conditions. A method to maintain ventilation efficiency by indirectly achieving DV was proposed. A four-bed hospital ward with prototype wall-mounted induction units (IUs) and ceiling exhaust served as the case study. Full-scale experiments assessed indoor temperature and tracer gas distribution, adjusting parameters such as cubicle and window curtains, window heaters, and window heat loss. Results showed that while the vertical temperature gradient was established, downdrafts near windows disrupted DV's stratification, leading to quasi-displacement ventilation with a normalized contaminant concentration of around 0.7 near patients. To counter this, using curtains to limit air exchange between the near-window and near-bed spaces effectively prevented the horizontal movement of contaminants toward the window. This allowed the downdraft to remain clean and diffuse along the floor, thereby reducing the normalized concentration to approximately 0.3–0.5 b y indirectly achieving DV. CFD numerical studies further examined this method under varied temperature conditions and airflow patterns. Additionally, the infection risk in this ward was evaluated for reference, showing that indirect DV can reduce infection probability by one-third compared to quasi-DV. Moreover, window heat loss valued at 50–100 W/m2 achieved the best ventilation, while smaller values generated insufficient downdraft to achieve indirect DV and larger values resulted in high floor-level velocity that accelerated contaminant dispersion. • Ventilation during the heating in a hospital ward using the DV system is investigated. • DV can be indirectly achieved by the near-window downdraft during the heating season. • Blocking contaminant spread keeps the downdraft clean and enhances ventilation. • Full-scale experimental and CFD numerical study was conducted for examination. • Window heat loss and various airflow patterns' impact were addressed numerically.