Indoor environments are susceptible to contaminant exposure, as contaminants can easily spread in the air. Human breathing is one of the most important biological contaminant sources, as the exhaled air can contain different pathogens such as viruses and bacteria. This paper addresses the human exhalation flow and its behavior in connection with different ventilation strategies, as well as the interaction between two people in a room. This is a key factor for studying the airborne infection risk when the room is occupied by several persons. The paper only takes into account the airborne part of the infection risk.

Several guidelines recommend the downward ventilation system to reduce the risk of cross-infection between people in hospital rooms. This study shows that this recommendation should be taken into careful consideration. It is important to be aware of people position, position to other thermal loads in the room, and especially be aware of the distance between people if the exposure to the exhaled contaminants wants to be reduced.

No abstract

This study is focused in determine the convenience of the use of displacement ventilation strategy in airborne infection isolation rooms (AIIRs). Comfort of the occupants of the chamber, IAQ indices and the exposition of the health worker (HW) to the contaminants emitted by the confined patient (P) are considered in a typical AIIR set up with a hot radiant wall representing an external wall. Three air ventilation rates are tested to determine their influence in the studied variables. Results show that IAQ indices associated with ventilation and general comfort indices for both manikins performs well in the cases studied. Lockup phenomenon associated to displacement ventilation occurs above P but it has a low influence on contaminant exposition of HW because of the influence of the convective boundary layer of HW. The influence of the radiant wall derives part of the fresh air directly to the exhaust and has a low influence the comfort of the manikins.

ACH Air changes per hour (h-1) AIIR Airborne infection isolation room CFD Computational fluid mechanics CP Patient D Exhaust grille placed on the lower part of the West wall DR Percentage of dissatisfied people as a result of draught DV Displacement ventilation G Supply grille diffuser placed on the East wall of the room GD Ventilation system configuration combining G supply and D exhaust GU Ventilation system configuration combining G supply and U exhaust IHR Individual hospital room Intake fraction Maximum intake fraction 125% Peaks average intake fraction S Supply swirl diffuser placed on the ceiling of the room SD Ventilation system configuration combining S supply and D exhaust SU Ventilation system configuration combining S supply and U exhaust U Exhaust grille placed on the upper part of the West wall ⟨ ̅ ⟩ Mean tracer gas concentration of contaminant of the chamber (ppm) ̅ Average tracer gas concentration of the exhaust air (ppm) ̅ Average tracer gas concentration in a determined point (ppm) ̅ ,125% Average peaks tracer gas concentration in a determined point (ppm) , Maximum tracer gas concentration in a determined pint (ppm) ̅ , ℎ Average contaminant concentration emitted through the CP exhalation (ppm) ̅ Average tracer gas concentration in the supply air (ppm) Local relative exposure coefficient ,125% Local relative average peaks concentration exposure coefficient , Local relative maximum exposure coefficient ,125% Local maximum exposure frequency (h-1) H Total height of the chamber (m) Air change efficiency index Local air change index for a determined point Contaminant removal effectiveness index ⟨ ⟩ Mean age of air in the room (min) Nominal time constant (min) Local mean age of air in a determined point (min)