ASHRAE - American Society of Heating@ Refrigerating and Air-Conditioning Engineers@ Inc.
Latest
ASHRAE IJHVAC 16-4-2010
Scope
INTRODUCTION A personalized ventilation system@ installed in classrooms desks@ made with upper and lower air terminal devices@ has been developed in the last years (Concei??o et al. 2007@ 2008a@ 2009). The main idea is the introduction of new air to the face@ in order to promote good air quality conditions in the respiration area@ and a uniform airflow around the body@ in order to guarantee acceptable thermal comfort conditions. This kind of philosophy@ which uses a new localized ventilation concept instead of the non-localized traditional ventilation@ has the potential for energy savings (Schiavon and Melikov 2009). In previous works (Concei??o et al. 2007@ 2008a@ 2009) experimental and numerical studies of personalized ventilation systems installed in classrooms desks using a combination of air terminal devices located above and below the desk writing area was made. In these three works@ the personalized ventilation airflow was obtained using a combination of three ventilators: a bigger one placed before the desk ducts systems@ a smaller one placed in the exit upper air terminal device@ and a smaller one placed in the exit lower air terminal device. In Concei??o et al. (2007@ 2008a)@ the air terminal devices located above the desk writing area@ in front of the trunk area@ and incident in the head area and the air terminal devices located below the desk writing area@ in front of the legs area@ and incident in the knees area. More recently Concei??o et al. (2009)@ in accord to previous results@ presented a study which also utilized two air terminal devices; nevertheless@ the air terminal device located above the desk writing area@ in front to the trunk area@ was incident in the trunk area. Concei??o et al. (2007) measured four values at 90? angles in different human body sections. In accordance with the obtained values the mean difference of the air velocity around each section is@ in general@ lower than 0.2 m/s (0.66 ft/s)@ and the measurement made in front to the manikin surface is@ in general@ representative of each section. In similar studies@ but only with measurements made in front of the manikin surface@ Concei??o et al. (2008a) verified that the design used with two air terminal devices@ installed in the classroom desk@ guarantees a relatively uniform air velocity field around the manikin. The presence of the small ventilators@ located in the exit air terminal devices@ increases the thermal comfort levels; nevertheless@ the airflow turbulence levels also increase. Concei??o et al. (2008a) suggested to put other grids in the exit air terminal devices area@ so as not to use small ventilators placed in the exit air terminal devices and to change slightly the upper air terminal devices exit direction. In Concei??o et al. (2009)@ in order to evaluate all of the chamber's internal airflow@ a developed computational fluid dynamic numerical model was also applied. This kind of study@ that analyzes in detail the airflow around the occupants@ was also used to evaluate the airflow topology inside the experimental chamber. Different philosophies of personalized ventilation systems@ using experimental@ numerical@ or combinations of numerical and experimental means@ were studied in the past few years. Personalized ventilation systems with only one air terminal device present the highest number of studies; nevertheless@ recently@ more than one air terminal device placed in the desk has been introduced. Cermak et al. (2002)@ Kaczmarczyk et al. (2004)@ Zeng and Zhao (2005)@ Sekhar et al. (2005)@ Pan et al. (2005)@ Muhic and Butala (2006)@ and Sun et al. (2007)@ are some examples. The influence between the environmental variables around the body and the human thermal response can be evaluated through the multi-node thermal regulation model. This kind of numerical methodology was developed in the last years@ as an example@ by Stolwijk (1970)@ Thellier et al. (1994)@ Huizenga et al. (1999)@ Fiala et al. (1999)@ Farrington et al. (2001)@ Fiala et al. (2001)@ Tanabe et al. (2002)@ Ozeki et al. (2004)@ and Gao et al. (2006). These methodologies@ and others@ were used in the analysis of cold@ moderate@ or warm environments. In slightly warm environments@ which are also analyzed in this work@ Thellier et al. (1994)@ Fiala et al. (2001)@ Tanabe et al. (2002)@ Arens et al. (2006a)@ and Arens et al. (2006b)@ and others@ applied and developed numerical models used for better understanding of the human thermal response in these kinds of conditions. To evaluate the thermal comfort level in moderate environments@ the multi-nodal human thermal comfort numerical model uses the PMV (Predicted Mean Vote) and the PPD (Predicted Percentage of Dissatisfied) indexes (Fanger 1970; ISO 2005). This philosophy considers four environmental variables (air temperature@ air velocity@ air relative humidity@ and mean radiant temperature) and two personal parameters (activity and clothing levels). For acceptable thermal comfort conditions@ the ISO 7730 (2005) defines three comfort categories: A (6% of unsatisfied people)@ B (10% of unsatisfied people)@ and C (15% of unsatisfied people). The aim of this study is to investigate turbulent and mean airflow in the exit air terminal devices and around an occupant seated in classroom desks equipped with personalized ventilation systems with upper and lower air terminal devices@ for slightly warm environments. In the study@ a desk is equipped with one air terminal device located above the desk writing area@ in front of the trunk area@ and incident in the trunk area@ while another air terminal device is located below the desk writing area@ in front to the legs area@ and incident in the knees area. The airflow in the upper and lower exit air terminal devices is obtained using only one ventilator placed before the personalized ventilation system@ depending on the ventilator airflow rate and the duct geometry.