Experimental Study On Personalized Ventilation For Lying Infant

This master thesis experimentally analyzed the performance of personalized ventilation designed for use in the condition of a lying infant.The main purposes of this study included finding the optimal personalized ventilation strategy,analyzing the features and effect of infant’s thermal plume,and comparing the performance of personalized ventilation with mixing ventilation.An infant thermal manikin was built up in this research to be used as the occupancy in experiments.As the infant thermal manikin had the similar geometric size and heat generation power to a real human infant,it was reasonable to be used to simulate the real condition.A movable personalized ventilation system was also built up in this study,whose diffuser’s position and flow rate was adjustable for the purpose of testing different ventilation strategies.A textile ventilation system,which was a typical model of mixing ventilation,was also built up in the study,and was used for comparison experiment.Anemometers and thermocouples were used to collect air velocity and temperature data separately,based on which the airflow distribution in the infant’s breathing zone was observed and quantitatively analyzed.N₂O was used in this study as tracer gas to analyze the ventilation effectiveness and the age of air under different ventilation strategies.The highest velocity of thermal plume was 0.094 m/s,which was observed 10 cm above infant manikin’s mouth.The temperature above infant manikin’s mouth was 27.5℃,showing that thermal plume dominates the microenvironment above infant’s face.When the supply air flow rate was 3 l/s,the air velocity above infant manikin’s mouth with thermal plume was 67.8%of that without thermal plume,and the ventilation effectiveness was 87.2%of that without thermal plume,showing obvious obstacle effect.Five different supply air flow rates were tested in the study,including 3l/s,5 l/s,7 l/s,9 l/s and 11 l/s.Three different diffuser’s relative heights were tested in the study,including 50 cm,70 cm,and 90 cm.According to the experimental result,if flow rate was below 3 l/s,the supply air could hardly penetrate thermal plume.But if flow rate was higher than 7 l/s,the thermal environment would be uncomfortable for human.Comprehensively considering the thermal comfort and ventilation effectiveness,we believed that L2 case was the optimal strategy for personalized ventilation,in which the flow rate of supply air was 5 l/s and the relative height of diffuser was 50cm.In this case,the age of air at breathing zone was 28.0 min,and the ventilation effectiveness was 2.46,and the highest draught rate was 20.1%.Compared with mixing ventilation,personalized ventilation’s performance on diluting pollutant was much better.When the contaminant source was outside the bed,the performance ranking was 40 l/s mixing ventilation≈11 l/s personalized ventilation>11 l/s mixing ventilation>no ventilation.When the contaminant source was inside the bed,the performance ranking was 11 l/s personalized ventilation>40 l/s mixing ventilation>11 l/s mixing ventilation>no ventilation.In order to achieve the same ventilation performance,personalized ventilation would save at least 70%of airflow rate,and consume much less energy.