Local ventilation for general patient rooms

Numerous studies on ventilation of general patient rooms have been performed, while most of the studies have focused on total volume air distribution (mixing or displacement). This study presents results of local ventilation (LV) aimed to efficiently protect a lying person from cross-infection due to airborne respiratory viruses. Experiments performed in a climate chamber (4.7 m × 4.7 m × 2.6 m) included LV when used alone and when coupled with background mixing ventilation (MV). A thermal manikin and a heated standing dummy were used to simulate respectively a patient lying in bed and an infected doctor or nurse standing beside the bed. The LV was able to reduce substantially the exposure of the patient to the infected air exhaled by the doctor. The results show that the efficiency of the LV depended mostly on its supply airflow rate. An increase of the background ventilation's supply flow rate, i.e. increase of the air change rate in the room, was less important. At 15 L/s supplied by LV the concentration of a contaminant at the patient's mouth decreased by 76%. The findings of the paper give insights for researchers and designers in developing a novel ventilation system to be used during a pandemic in general patient rooms.publishedVersio

Particle deposition in a realistic geometry of the human conducting airways: Effects of inlet velocity profile, inhalation flowrate and electrostatic charge:Effects of inlet velocity profile, inhalation flowrate and electrostatic charge

AbstractUnderstanding the multitude of factors that control pulmonary deposition is important in assessing the therapeutic or toxic effects of inhaled particles. The use of increasingly sophisticated in silico models has improved our overall understanding, but model realism remains elusive. In this work, we use Large Eddy Simulations (LES) to investigate the deposition of inhaled aerosol particles with diameters of dp=0.1,0.5,1,2.5,5 and 10μm (particle density of 1200kg/m3). We use a reconstructed geometry of the human airways obtained via computed tomography and assess the effects of inlet flow conditions, particle size, electrostatic charge, and flowrate. While most computer simulations assume a uniform velocity at the mouth inlet, we found that using a more realistic inlet profile based on Laser Doppler Anemometry measurements resulted in enhanced deposition, mostly on the tongue. Nevertheless, flow field differences due to the inlet conditions are largely smoothed out just a short distance downstream of the mouth inlet as a result of the complex geometry. Increasing the inhalation flowrate from sedentary to activity conditions left the mean flowfield structures largely unaffected. Nevertheless, at the higher flowrates turbulent intensities persisted further downstream in the main bronchi. For dp>2.5μm, the overall Deposition Fractions (DF) increased with flowrate due to greater inertial impaction in the oropharynx. Below dp=1.0μm, the DF was largely independent of particle size; it also increased with flowrate, but remained significantly lower. Electrostatic charge increased the overall DF of smaller particles by as much as sevenfold, with most of the increase located in the mouth–throat. Moreover, significant enhancement in deposition was found in the left and right lung sub-regions of our reconstructed geometry. Although there was a relatively small impact of inhalation flowrate on the deposition of charged particles for sizes dp<2.5μm, impaction prevailed over electrostatic deposition for larger particles as the flowrate was increased. Overall, we report a significant interplay between particle size, electrostatic charge, and flowrate. Our results suggest that in silico models should be customized for specific applications, ensuring all relevant physical effects are accounted for in a self-consistent fashion

Local ventilation for general patient rooms

Numerous studies on ventilation of general patient rooms have been performed, while most of the studies have focused on total volume air distribution (mixing or displacement). This study presents results of local ventilation (LV) aimed to efficiently protect a lying person from cross-infection due to airborne respiratory viruses. Experiments performed in a climate chamber (4.7 m × 4.7 m × 2.6 m) included LV when used alone and when coupled with background mixing ventilation (MV). A thermal manikin and a heated standing dummy were used to simulate respectively a patient lying in bed and an infected doctor or nurse standing beside the bed. The LV was able to reduce substantially the exposure of the patient to the infected air exhaled by the doctor. The results show that the efficiency of the LV depended mostly on its supply airflow rate. An increase of the background ventilation's supply flow rate, i.e. increase of the air change rate in the room, was less important. At 15 L/s supplied by LV the concentration of a contaminant at the patient's mouth decreased by 76%. The findings of the paper give insights for researchers and designers in developing a novel ventilation system to be used during a pandemic in general patient rooms

Localized Ventilation Method for Providing Clean Air to Hospitalized Patients

Three novel air terminal devices (ATDs) for localized ventilation were designed (ATD with perforated inner plate, ATD with honeycomb diffuser, and ATD with lobbed nozzle). The ability of the ATDs to provide clean air to the breathing zone of a person lying in a hospital bed was studied. Experiments were performed in a simulated full-scale hospital patient room. A thermal manikin was used to simulate a patient. The ATD was located above the head of manikin. Heated dummy simulated a doctor standing beside the bed. Tracer gas was used to simulate contaminated air exhaled by the doctor. The supply and the exhaust flow rates were controlled at 15.3 L/s and 14.8 L/s, respectively. The supply air temperature and room temperature were kept at 23 °C and 25.3 °C, respectively. Increase of the supply air speed resulted in a cleaner air supply to the breathing zone but also increased the risk of draught. The ATD with a lobbed jet nozzle was able to reduce contaminants by more than half in the breathing zone and to provide the lowest draught risk at the face. This ATD is a better solution to supply clean air in practice comparing to the other two ATDs

Impact of room airflow interaction on metabolic CO₂ exposure

CFD simulations were performed to investigate occupants’ exposure to metabolic CO2 in a room with mechanical ventilation. A meeting room occupied by six adult people performing sedentary activity was simulated. Five of the six occupants were simulated to exhale air with realistic CO2 content, while one occupant was inhaling, i.e. the exposed occupant. Both exhalation and inhalation were simulated with constant flow rates. Two air distribution patterns were considered, mixing and displacement air distribution, each was combined with chilled ceiling, as summer conditions were simulated. For both air distribution patterns, the influence of solar gain of 200 W, which was simulated as heated vertical surface (window), and the distance between the occupants facing each other were studied. The simulation results revealed the importance of buoyancy flows generated by heated vertical surfaces for the pollution distribution. It was found out that compared to the case without solar heat gain, the presence of solar gain increased the inhaled CO2 level by 26.9 % in the case of displacement ventilation, while it reduced the exposure by 4.5 % when the outdoor air was distributed by mixing ventilation. The distance between the occupants facing each other did not affect considerably the exposure