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...distribution pollutants associated exhaled air and floor material emissions was evaluated various combinations of personalized and underfloor airflow rates. Compared to underfloor ventilation alone, personalized and underfloor ventilation provided excellent protection of seated occupants from any pollution, while the concentration of exhaled air pollution increased in the room. The two types of personalized ventilation performed differently. Subsequent analyses of airborne infection transmission risk indicated that personalized ventilation could become a supplement to traditional methods of infection control.
INTRODUCTION
Air exhaled by people when coughing, sneezing, or talking contains aerosol droplets up to 100 [micro]m in diameter (Brosseau et al. 1994; Duguid 1945) and respirable particles 0. 1-1 [micro]m in diameter (Hinds 1999) that may carry viral and bacterial agents. After expulsion, the larger droplets (larger than 60-100 [micro]m) settle out from the air or evaporate to droplet nuclei (up to 10 [micro]m). Such nuclei have very low settling velocities and, together with respirable particles, are transported by the room air. Thus, there is a possibility for the airborne transmission of respiratory infectious agents between occupants. A recent literature review shows strong evidence that the airborne transmission of some infectious diseases is associated with building ventilation (Li et al. 2006).
Floor surface area is typically large compared to other objects in rooms. Studies (Mendell 1993; Wolkoff et al. 1995; Jaakola et al. 1999, 2000) have associated the prevalence of building- related symptoms with the presence of carpeting, polyvinyl chloride (PVC), and linoleum, which emit a variety of gaseous pollutants, including phthalates. Phthalates in home dust have been shown to increase the risk of asthma and allergies among children (Bornehag et al. 2004). Therefore, studying exposure to floor material emissions is very important.
Personalized ventilation (PV) is an air distribution principle that supplies air at each workplace, aiming to improve the inhaled air quality as well as the thermal comfort of each occupant. Because occupants are allowed to adjust the rate and sometimes temperature of the supply air, other means of ventilation and air conditioning, e.g., total-volume ventilation, must be provided together with PV to ensure acceptable air quality and thermal environment in the room.
The inhaled air quality depends on the interaction of personalized airflow, room airflow, and pollution sources (Melikov 2004a, 2004b). PV supplying clean air at the breathing zone is able to decrease the inhaled pollutant concentration 2 to 50 times compared to total-volume ventilation alone (Melikov et al. 2002; Cermak 2004; Cermak et al. 2006). At the same time, PV was shown to promote mixing of room air in non-uniform environments. Cermak et al. (2006) documented that in a room with personalized and displacement ventilation, occupant exposure to agents associated with exhaled air could increase.
Underfloor ventilation, also referred to as underfloor air distribution (UFAD), delivers air directly to the occupied zone through floor diffusers or grilles. Air is returned at the ceiling. The height above the floor where the supply airstream velocity decreases to 0.25 m/s is referred to as the maximum penetration height or the throw height. A short throw has been associated with a displacement-like airflow pattern, while a long throw is said to promote mixing. An extensive report on UFAD was given in Bauman and Daly (2003).
Knowledge concerning the performance of PV in conjunction with UFAD is limited. A pilot study (Cermak and Melikov 2003, 2004) suggested an overall similarity between personalized and displacement ventilation (Cermak et al. 2006). Detailed analyses of the airflow and pollutant interactions on the air quality remain to be made.
In this study, the performance of two PV systems was tested in conjunction with a UFAD system generating two different throw heights in a full-scale test room. The system performance was tested with regard to the pollutants released through human exhalation and emitted by the floor surface. The measurements of inhaled air concentrations and vertical profiles of concentration, temperature, and velocity are reported for different scenarios of PV use. The risk of airborne infection transmission was assessed based on the model by Rudnick and Milton (2003).
METHOD
Measurements were performed in a full-scale experimental room (5.4 x 4.8 x 2.6 m) in which there were two workplaces. Each workplace consisted of a desk with an air terminal device for PV, a computer tower and monitor, a lamp, and a seated breathing thermal manikin (Figure 1). Six fixtures located on the ceiling provided the overall lighting. The room was built in a laboratory hall in which the air temperature was maintained close to the room air temperature in order to reduce the heat flux through the walls. The walls were sealed prior to the measurements. The room was ventilated by means of a combination of PV and a UFAD system.
[FIGURE 1 OMITTED]
Personalized Ventilation
Two types of air terminal devices for PV were tested (Figure 2). The round movable panel (RMP) consisted of an air distribution box with a round supply opening mounted at the end of a movable arm duct. The supply opening had a diameter of 0.185 m and was equipped with a honeycomb flow straightener. The second type was a vertical desk grille (VDG), which was a slot diffuser sized 0.02 x 0.22 m mounted at the front desk edge. Units of the same type were mounted on the desks at the same time and tested. They were adjusted to discharge air directly to the breathing zone of the seated occupants. The positioning (also the studied airflow rate, see Table 1) corresponded to the settings most often preferred by occupants (Kazcmarczyk et al. 2002, 2004).
Underfloor Ventilation
The UFAD system consisted...
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