The current Ph.D. thesis deals with new advanced methods of air distribution in occupied places aimed to improve the inhaled air quality and to reduce the risk from airborne cross infection among the occupants. The existing ventilation strategies nowadays are not able to provide enough clean air to the occupants and can even enhance the risk from cross-infection from airborne diseases indoors. Clearly new advanced methods are needed to improve the current situation. The subject is especially important because of the energy issue as well as the increased possibility of random mutations of known airborne pathogens. The threat from possible bio-terrorist attacks in the last decade makes the topic quite important. So far the existing methods of indoor air cleaning rely on several basic strategies: dilution, filtration and Ultra Violet Germicidal Irradiation (UVGI). Dilution utilizes ventilation at high flow rates to reduce the concentration of pollutants/pathogens to levels that would not deteriorate the air quality or be harmful for the occupants. It is also connected to certain energy limitation issues. Filtration and UVGI are efficient in protecting occupants provided the sources are located outdoors. However, these methods are not very efficient, if the contaminant sources are indoors and especially if the source is a sick individual. The current thesis focuses on two ways to provide reduced risk from airborne infections: by providing personal protection of each individual in an office environment and by protecting medical staff, patients and visitors from cross-infection in hospital wards. The first part of the thesis focuses on improvement of inhaled air quality and thus reduction in the risk from cross-infection by advanced ventilation, providing clean air close to the occupants with personalized ventilation (PV) by applying control over the airflow interaction at the breathing zone. Two new control methods, namely control over the free convection layer around the human body and control over the personalized flow are studied when applied for different PV designs. The first method aims to reduce the strength of the free convection layer via blocking or local exhausting, and thus make possible its penetration by the personalized flow at low velocity (low flow rate). The second method aims to control the way the PV flow is supplied so that it is less affected by the flow interaction around the human body: by immersing it within the convection flow or by simply substituting the boundary layer with a PV flow adjacent to the body. Both methods helped greatly increase the performance of the employed PV systems with respect to the amount of clean air supplied into the breathing zone of the occupant compared to the case when the PV was used alone. These methods also show great potential for energy savings, due to the reduced PV flow rate. The suggested designs are easy for implementation in occupied spaces, where people spend most of the time seated, e.g. offices, theaters, cinemas, busses, trains, airplanes, etc. The second part of the thesis focuses on a novel ventilation strategy for reduction the risk of cross-infection for medical staff, visitors, and patients in hospital wards. The novel ventilation strategy is implemented by a specially developed device, named Hospital Bed Integrated Ventilation Cleansing Unit (the device is part of a patient application in Europe (EP 09165736.1) and in the United States of America (US 61/226,542). The HBIVCU helped to provide improved protection to doctor and other patients, present in a space, from a sick individual with highly contagious airborne transferred disease, by locally evacuating the air coughed by the sick patient. Apart of increased protection the use of the HBIVCU leads to decrease of the background ventilation rate. This technique of local exhaust and cleaning of the coughed air can provide solution to the existing problems in a hospital environment related to control and, handling the spread and treating patients with contagious airborne diseases, as well as problems with insufficient space in hospital wards in times of epidemics and pandemics.
Main Research Area:
Dtu Civil Engineering Report
Technical University of Denmark, Department of Civil Engineering, 2010