ASHRAE LO-09-036

Abstract

<strong>INTRODUCTION</strong> <br>Personalized ventilation aims to provide clean and cool air in the vicinity of the breathing zone of human body and thus to improve inhaled air quality. Occupants' thermal comfort is also improved, especially at relatively high room temperatures (Gong et al. 2005, Kaczmarczyk et al. 2006). Most often, personalized ventilation systems (PV) with desk mounted air terminal devices (ATD) have been studied (Faulkner et al., 1999, Tszuzuki et al. 1999, Melikov et al. 2002, Kaczmarczyk et al. 2004, etc.). The idea of ceiling mounted PV ATD provides more flexibility in arranging the furniture in the occupied zone. It also improves the indoor aesthetics because extended air ducts for transporting of clean and cool air to different workstations are not needed. Occupants may be provided with individual control of the PV airflow rate in order to obtain preferred micro-environment in term of thermal comfort and indoor air quality. <br>The cooling effect of ceiling mounted nozzle depends on the PV airflow rate and the temperature of the PV supply air (Yang et. al. 2008). The size of the nozzle (its diameter if it is circular nozzle) and the initial airflow conditions at the exit define the size of the target area in contact with the body. The system can be regarded as one kind of individual spot cooling system by vertical air jet, which can provide occupants with acceptable thermal comfort conditions (Azer et al. 1971, 1972; Azer and Nevins 1974; Olesen and Nielsen 1980, 1983; Ma and Qin 1991; Melikov et al. 1994, 1994a). At constant airflow rate, the increasing of the nozzle outlet diameter will reduce air velocity of the personalized airflow but will increase the size of the target area of the jet (target area is defined as the cross section of the jet where it first meets the occupant) while decreasing nozzle diameter will increase airflow velocity at the target area but will decrease its size, i.e. the airflow will not cover occupant's body (Melikov et al. 1994a). Human body will affect the personalized airflow as an obstacle and with the generated thermal plume. The characteristics of the thermal plume generated by human body depend on the body posture (standing and seated), clothing design and thermal insulation, type of the chair, surrounding air and radiant temperature, etc. (Hyldgaard 1998, Zukowska et al. 2007, 2007a). The interaction of the personalized airflow with the thermal plume generated by the human body is of major importance for the body cooling. It may also affect the air distribution pattern in the entire space. In reality, people at workplaces will move and may not be located directly below the nozzle. The asymmetric exposure of the body, i.e. the changes in positioning of the thermal plume will affect its interaction with the personalized airflow, which will result in a non-uniform cooling of the body. Thus the whole body cooling effect of the personalized airflow will decrease while the local cooling of some body parts may increase leading to draught discomfort. These effects need to be studied for proper design of ceiling mounted personalized ventilation. <br>The interaction of the personalized airflow from ceiling mounted PV nozzle with the thermal plume from human body and its whole body and local cooling effect was studied under different conditions. The impact of occupant's movement on the airflow interaction and thus on the body cooling was explored. The results are presented and discussed in this paper. <br>It may be noted that CFD tools could be employed in studies involving room air distribution. A validated CFD model is useful for parametric variation studies in which refine grids become essential, especially for simulating thermal plume around human body. However, this is beyond the scope of the present paper.