Experimental study of personalized air system for the reduction of pollutant exposure

Abstract

Current ASHRAE ventilation standard promulgates an outdoor intake around 10 1/s per person, with certain variations depending on building types. On the other hand, the metabolic human respiration rate for air is only around 0.11/s. In this thesis, we tested the concept of supplying ventilation in close proximity to nostrils and the facial area at much reduced airflow rate. A thermal manikin with a simulated lung is placed in a normal air-conditioned office. Fresh air supply is directed at the facial area of the manikin at flow rates raging from 0.1 to 41/s. The performance of personalized ventilation based on air movement in the vicinity of the occupant depends to a large extent on the supply air terminal device. Eight different air terminal devices were developed, tested and compared. CO2 was used as a tracer gas, and injected into the supply air, and the CO2 concentrations in the inhaled air, supplied air, and the ambient room air were measured, which were used to calculate two newly defined indices, i.e., the fresh air utilization efficiency 摨├ and the pollutant exposure reduction effectiveness 摨㎜ER. In the air supply flow rate range tested, the pollutant exposure reduction effectiveness increased with the increase of the airflow rate from the ATD to a maximum value. Further increase of the airflow rate appears to have reduced impact on the pollutant exposure reduction effectiveness. The effects of the airflow around thermal manikin due to heat convection, the supply airflow rate, the cross-sectional area of air terminal devices and the geometry of air terminal devices were studied. Under both isothermal and non-isothermal conditions and an airflow rate below 4 L/s, a middle size circular air terminal device achieved the highest pollutant exposure reduction effectiveness 0.8. It is perceived that such a facial air supply method may have application potentials in those work places where occupants are sitting in a fixed position for prolonged period. An optimal air terminal device was recommended which has the best performance in improving an occupants' inhaled air quality.