Adaptive Wall-Based Attachment Ventilation: A Comparative Study on Its Effectiveness in Airborne Infection Isolation Rooms with Negative Pressure

Abstract

The transmission of coronavirus disease 2019 (COVID-19) has presented challenges for the control of the indoor environment of isolation wards. Scientific air distribution design and operation management are crucial to ensure the environmental safety of medical staff. This paper proposes the application of adaptive wall-based attachment ventilation and evaluates this air supply mode based on contaminants dispersion, removal efficiency, thermal comfort, and operating expense. Adaptive wall-based attachment ventilation provides a direct supply of fresh air to the occupied zone. In comparison with a ceiling air supply or upper sidewall air supply, adaptive wall-based attachment ventilation results in a 15%-47% lower average concentration of contaminants, for a continual release of contaminants at the same air changes per hour (ACH; 10 h^-1). The contaminant removal efficiency of complete mixing ventilation cannot exceed 1. For adaptive wall-based attachment ventilation, the contaminant removal efficiency is an exponential function of the ACH. Compared with the ceiling air supply mode or upper sidewall air supply mode, adaptive wall-based attachment ventilation achieves a similar thermal comfort level (predicted mean vote (PMV) of -0.1-0.4; draught rate of 2.5%-6.7%) and a similar performance in removing contaminants, but has a lower ACH and uses less energy.

Keywords: Air change rate; Air distribution; Attachment ventilation; COVID-19; Isolation ward; Ventilation efficiency.

Fig. 1

Adaptive wall-based attachment ventilation used in AIIR and its airflow structure. Region I: vertical attachment region; Region II: horizontal jet region; s₀: vertical attachment length; s_y: distance between Separation point I and the stagnation point; s_v: distance between the virtual origin inlet and the stagnation point; s_h: horizontal jet range; v_max: the jet axis velocity; v: velocity at different locations.

Fig. 2

Experimental validation of the axis velocity attenuation of adaptive wall-based attachment ventilation. K: the empirical coefficient related to inlet type; ΔT: the temperature difference between the supply air and the wall; h: the distance between the slot inlet and the floor; z: different height from the floor; b: the width of the slot inlet.

Fig. 3

Contaminant concentration distribution in an isolation ward with the same ACH under different air supply modes: (a) ceiling air supply; (b) upper sidewall air supply; and (c) adaptive wall-based attachment ventilation.

Fig. 4

Mean concentration of outlets under the condition of intermittent exhaled contaminants. (a) Concentration versus time; (b) accumulated concentration versus time.

Fig. 5

Removal efficiency of the air distribution mode for varying ACHs. The ACHs in the red box is the recommended range , .