The Impact Of Ventilation On Airborne Infection In Naturally Ventilated Hospital Wards

Natural ventilation is believed to be of great potential in view of controlling airborne transmission of infection in hospital environments.Therefore,understanding ventilation characteristics and transmission mechanisms in naturally ventilated hospital wards is of great importance.In this thesis,on-site measurement,numerical simulation and theoretical analysis are used to investigate the ventilaiton characteristics and airborne transmission in general hospital wards withn atural ventilaiton.First,a multi-zone simulation was conducted to evaluate the effectiveness of types of natural ventilation systems which were proposed by World Health Organization for controlling airborne infection.It is found that the central-corridor type may result in cross transmission between hospital wards.Second,an on-site measurement was done in a central-corridor naturally ventilated general hospital ward in Nanjing.Carbon dioxide exhaled by human was recorded and its variation throughout a year was analyzed.Then the ventilation rate and airborne infection risks were also predicted on the basis of the CO2 concentration.The results show that during transition period,natural ventilation could maintain indoor CO2 concentrantion significantly lower than those of heating or cooling period.Meanwhile,the ventilaiton rate is much higher in transition period than in heating or cooling period.In addition,the predicted infecion risk could be low by natural ventilation.Then,a CFD simulation was conducted based on a field measurement in a hospital ward.Specifically,cross infection in such a central-corridor hospital ward with natural ventilation was investigated.The results support WHO's recommendation.Finally,jet mechanics theory was applied to study the dispersion characteristics of exhaled flow in a naturally ventilated hospital ward.The non-dimensional governing equations of the jet flow were derived.The dispersion characteristics in thermally uniform environment and thermally stratified environment were copmared and the mechanism of lock-up phenomenon was revealed.It is found that the Ar number and temperature gradient would have impact on the lock-up height in a thermally stratified environment.