Performance evaluation of personalized ventilation personalized exhaust (PV PE) system in air conditioned healthcare settings 6

Chapter 6: Performance evaluation of PV-PE system in conjunction with background MV and DV systems — airborne infection control 6.1 Background As introduced in Chapter two, in the context of airborne infection control, it is critical that the ventilation system is able to extract the contaminated exhaled air immediately and within the shortest possible time. This will minimize the spread of the contaminated air into the room air. Studies have found that normal breathing can produce respirable contaminated droplets (Edwards et al., 2004). Gao et al. (2010) found that PV has the possibility to increase the intake fractions of exhaled air and droplets from other occupants. In order to prevent or minimise the spread of contaminated air exhaled by occupants efficiently, the ideal strategy is to exhaust the exhaled air as much as possible right around the infected person, which further supports the novel PV-PE system. The feasibility and potential of PV-PE system were studied experimentally for a particular healthcare setting consulting room geometries and the normal medical consultation positions of an Infected Person and a Healthy Person. This chapter, as well as chapter examine the issue mentioned above. In particular, this chapter deals with the originally stated Objective 2a, which is reproduced as follows: • Determine the effectiveness of airborne infection control of the combined PV-PE system in conjunction with background MV or DV systems in terms of the localized extraction of the contaminated exhaled air from an Infected Person in healthcare settings - Infected Person seated facing the seated Healthy Person. During a normal consultation process, the Healthy Person (doctor, nurse, staffs, etc.) are seated behind the desk, thus, the PV is used for providing fresh air. It is hypothesized that combined PV and PE for healthy person can achieve the highest PEE; PV for healthy person helps to reduce exposure from Infected Person; PE for Infected Person with PV for Healthy Person provides the best exposure reduction; PE for Infected Person is more effective than PV for Healthy Person. PE for Infected Person helps reduce exposure for Healthy Person. As described in Section 3.5.1, two types of PE are examined: Top-PE and ShoulderPE; two different background ventilation systems are used. It is hypothesized that Top-PE is better than shoulder-PE; and in the presence of PE for Infected Person, DV system lead to a better exposure reduction than MV system The experimental design and evaluation index are described in Chapter (Section 3.5.3). Experimental chamber is described in Section 3.4.1.1. 6.2 Performance of combined PV and PE for Healthy Person The Personalized Exposure Effectiveness (PEE) of the Healthy Person calculated based on the concentration of tracer gas measured in the experimental chamber from Equation 3.1 are shown in Figures 6.1 and 6.2. The index is used to evaluate the ability of the novel PV-PE system in bringing conditioned outdoor air and protect occupants from indoor contaminants at the breathing zone. Personal  Exposure  Effectiveness   PV  alone   PV+top-­‐PE   0.39   0.35   pv+shoulder-­‐PE   0.4   0.36   0.29   PV  5l/s   PV  10l/s   Figure 6.1 Comparison of PEE with MV 0.41   Personal  exposure  effectiveness   PV  alone   PV+top-­‐PE   pv+shoulder-­‐PE   0.58   0.52   0.32   0.34   0.3   0.24   PV  5l/s   PV  10l/s   Figure 6.2 Comparison of PEE with DV Compared with totally mixing ventilation which has value for PEE, PV alone can increase the amount of the clean personalized air to 26% and 31% when PV flow rates are l/s and 10 l/s. This means PV alone is able to protect the healthy person by supplying conditioned outdoor air in the breathing zone. The percentage of PV air or the percentage of outdoor air in the inhaled air changes when different PV air flow rates (10 l/s and l/s) are used. However, when comparing the PEE in pairs of 10 l/s and l/s without PE, the PEE does not change a lot. For example, with DV, PEE is 0.26 when PV flow rate is l/s while it is 0.31 when PV flow rate is 10 l/s. The difference of PEE between these two PV air flow rates is only 0.05; while the difference with MV is 0.07. Compared with the cases when PE is working together with PV, PV air flow rate has a stronger effect on the PEE with DV. It was observed that with DV, PV-PE system is always able to deliver a much higher percentage of PV air at 10 l/s flow rate. With a top-PE added, an increase of 66.7% is observed when PV flow rate increases from l/s to 10 l/s. The percentage is even higher, 79.4%, when shoulder-PE is applied. However, this obvious increase pattern is not found with MV background system. The difference of PEE is only 0.05 and 0.02 for top-PE and shoulder-PE respectively. This is because the mixing effect of MV disturbs the pulling effect of the PV-PE system. The results in Figure 6.1 and Figure 6.2 also show that the shoulder-PE performs better than top-PE in terms of pulling more PV air towards the breathing zone. For the case with l/s for PV with DV, the PEE increases at 26.9% after activating the top-PE and 30.8% if shoulder-PE is utilized instead. A similar pattern is observed with MV when better performance is achieved with combined shoulder PE-PV. This is when compared with PV alone and top PE-PV, which has a PEE of 0.01 (PV l/s) and 0.06 (PV 10 l/s) higher when shoulder PE is activated compared to top-PE 6.3 Performance of the PV- PE for preventing transmission of exhaled contaminated air during normal medical consultation process 6.3.1 Exposure Reduction The first evaluation index, Exposure Reduction, was described in Section 3.5.3. It is useful to first explain the manner in which Figure 6.3 to Figure 6.6 is plotted to display the experimental results; for each type of PE used for Infected Manikin (shoulder-PE or top-PE), there are four clusters of data. Each cluster consists of two bars representing two different PV flow rates, l/s and 10 l/s. The first cluster shows the reduction in exposure to the exhaled tracer gas from Infected Manikin when only PV is implemented. Note that the base case is when neither PV nor PE is utilized; there is only background ventilation system (MV or DV) in operation; that is, the data of exposure reduction with MV and the data with DV have different base data. Thus, the bars for the same configuration for the two manikins with MV and DV (data in Figure 6.3 and Figure 6.4; data in Figure 6.5 and Figure 6.6) are not comparable. Comparing the Exposure Reduction with MV in Figure 6.3 and Figure 6.5, it is found that the Healthy Manikin experiences roughly 25% reduction in exposure to the Infected Manikin exhaled contaminated air when PV supply air is at l/s. The reduction percentage is increased to 55% if the PV flow rate is increased to 10 l/s. The Exposure Reduction is observed with DV in Figure 6.4 and Figure 6.6 as 12.5% and 29.17% for the PV flow rate at l/s and 10 l/s respectively. This implies that the use of PV alone has the ability to protect the Healthy Manikin from inhaling contaminated air from the Infected Manikin sitting opposite. After switching on the top-PE for infected manikin while switching off the PV for healthy manikin, a more than 70% reduction of exposure is found under MV, and more than 75% for DV base case. This is encouraging not only because of the significant reduction in Healthy Manikin’s exposure, but also because of the much higher reduction than using PV alone. In this case, the exposure reductions under two different flow rates of PE not have much difference. They are almost the same with MV and a slight increase of reduction with the increase of PE flow rate with DV. For the cases of combined PV for Healthy Manikin and top-PE for Infected Manikin, Figure 6.3 and Figure 6.4 show that the best performance is found after combining PV and top-PE for cases with both MV and DV, yielding an 81% and 88% exposure reduction for case AIp!!" Hp5 with MV and case AIp!!" Hp5 with DV respectively. However, the increase in exposure reduction between the top-PE alone and combined top-PE-PV is not much, for example, the increase of Exposure Reduction with DV between case AIp!!" Hp and case AIp!!" Hp10 is only 3.4%. This shows that, not only is the top-PE system for Infected Manikin efficient, but also that it does not help a lot to use PV for Healthy Manikin while top-PE is utilized for Infected Manikin. For the case of utilizing shoulder-PE, Figure 6.5 indicates exposure reductions of 25% and 75% for the PE only cases AIp!!!" Hp and AIp!!!" Hp with MV. These results of AIp!!!" Hp are close to the case of PV alone AIpHp5. The use of shoulder-PE alone at 10 l/s in terms of reducing the exposure does not surpass the use of a small flow rate (5 l/s) of PV. PV alone for Healthy Manikin at 10 l/s (case AIpHp10) can achieve a much higher reduction of exposure than shoulder-PE alone for Infected Manikin at 10 l/s (case AIp!!!" Hp) with MV. With the increase of PE flow rate from 10 l/s to 20 l/s with MV, the advantages of shoulder-PE is seen, which shows a much higher local removal ability of 75% exposure reduction. Different performance pattern of shoulder-PE alone is found when the room is ventilated by DV. The shoulder-PE suction at 10 l/s still does not prove to be as efficient as 20l/s case (exposure reduction is 63% while shoulder-PE is 10 l/s and 78% for the case with 20 l/s), but it is able to achieve a higher exposure reduction than PV alone (case AIpHp5 and AIpHp10) . Clearly, the flow pattern of overall interaction of exhaled air, thermal plume and the PE flow are still largely influenced by the background air type, making the shoulderPE suction less effective with MV. The combined PV for Healthy Manikin and shoulder-PE for Infected Manikin also performs differently with different background ventilation systems. Figure 6.5 shows that when the shoulder-PE flow rate is 10 l/s, the exposure reduction increases with the increase of PV flow rate. However, for the case of shoulder-PE 20 l/s, Figure 6.5 indicates a 3.1% less exposure reductions when switching on the PV compared with the cases using PE alone. Considering the sitting positions of Infected Manikin which is below the supply diffusers with a distance of 0.5 m closer to the floor centre, the flow from MV four-way diffuser and the flow of PV for healthy manikin tend to pull the exhaled contaminated air further towards the healthy person. If the combined PV and shoulder-PE is applied with DV, the trend of the results is close to that of top-PE with DV, which shows a best reduction of exposure by combing PV for Healthy Manikin and PE for Infected Manikin. An additional interesting point to note is that the exposure of reduction at the higher flow rate (20 l/s) of shoulder-PE, is 13% (PV l/s) and 21.2% (PV 10 l/s) more than that at the 10 l/s flow rate of shoulder-PE (As different to the top-PE which does not have much increase between the two flow rates of PE). Indeed, Figures 6.3 through 6.6 show that the top-PE can greatly reduce the exposure of exhaled air at a lower flow rate compared with shoulder-PE. This could be attributed to the top-PE enhancing the ability of thermal plume to bring up the exhaled air towards the suction opening to mitigate the release of exhaled contaminated air to the room air. Exposure  Reduc-on   Exposure  reduc-on  with  MV   90.00%   80.00%   70.00%   60.00%   50.00%   40.00%   30.00%   20.00%   10.00%   0.00%   PV  5l/ PV   s   10l/s   PV  only   PE   PE   10l/s   20l/s   Top-­‐PE  only   PV  5l/ PV   s   10l/s   PV  5l/ PV   s   10l/s   Top-­‐PE10l/s  +PV   Top-­‐PE20l/s   +PV     Figure 6.3 Comparison of Exposure Reduction when utilizing top-PE with MV   Exposure  Reduc-on   Exposure  reduc-on  with  DV   100.00%   90.00%   80.00%   70.00%   60.00%   50.00%   40.00%   30.00%   20.00%   10.00%   0.00%   PV  5l/s   PV   10l/s   PV  only   PE  10l/PE  20l/ s   s   Top-­‐PE  only   PV  5l/s   PV   10l/s   Top-­‐PE10l/s  +PV   PV  5l/s   PV   10l/s   Top-­‐PE20l/s   +PV   Figure 6.4 Comparison of Exposure Reduction when utilizing top-PE with DV Exposure  reduc-on  with  MV   80.00%   Exposure  Reduc-on   70.00%   60.00%   50.00%   40.00%   30.00%   20.00%   10.00%   0.00%   PV  5l/s   PV   10l/s   PV  only   PE  10l/PE  20l/ s   s   Shoulder-­‐PE  only   PV  5l/s   PV   10l/s   Shoulder-­‐PE10l/s   +PV   PV  5l/s   PV   10l/s   Shoulder-­‐ PE20l/s  +PV   Figure 6.5 Comparison of Exposure Reduction when utilizing Shoulder-PE with MV Exposure  Reduc-on   Exposure  reduc-on  with  DV   100.00%   90.00%   80.00%   70.00%   60.00%   50.00%   40.00%   30.00%   20.00%   10.00%   0.00%   PV  5l/s   PV   10l/s   PV  only   PE  10l/PE  20l/ s   s   Shoulder-­‐PE  only   PV  5l/s   PV   10l/s   PV  5l/s   PV   10l/s   Shoulder-­‐PE10l/s   Shoulder-­‐ +PV   PE20l/s  +PV   Figure 6.6 Comparison of Exposure Reduction when utilizing Shoulder-PE with DV 6.3.2 Intake Fraction The second evaluation index, Intake Fraction (iF), was described in Section 3.5.3. Figure 6.7 to Figure 6.9 yield the iF results computed for Healthy Manikin based on the exhaled contaminant source from Infected Manikin. The data are divided into three groups: PE alone for Infected Manikin; PE for Infected Manikin while l/s of PV for Healthy Manikin; and PE for Infected Manikin while 10 l/s of PV for Healthy Manikin. Here, the iF results of each group have been compared with their respective PE-off case to allow the visualization of the effect of increase of PE flow rate. The first point to address is the drop of iF in all cases listed in the three figures, which means that the inhaled amount of exhaled contaminated air is reduced with the increase of PE flow rate. When considering 10 l/s of PE flow rates, the performance of shoulder-PE cases is not as good as that of top-PE, which means a higher iF is observed with shoulder-PE in the three figures. As discussed previously in Exposure Reduction section, this indicates that the top-PE performs better than shoulder-PE in terms of exhausting contaminated exhaled air before it mixes with the room air. And top-PE has an energy saving potential compared with shoulder-PE since it can achieve a lower iF with lower flow rate. An interesting feature to note in the three Figures is the comparison between iF with DV and MV when PE is not switched on. It shows that the iF values are obviously higher with DV than MV, which means more amount of contaminated air traveling to the breathing zone of Healthy Manikin. This is because the exhaled air from normal breathing process could concentrate maximally just at the breathing height level with DV and lead to a higher infection risk. This finding complies with the previous research conducted by Qian et al. (2006), Gao et al. (2008), and Pantelic (2011). Although DV may lead to a higher risk of exposure to cross-contaminated air, the performance of PE with DV does not show any weakness of infection control. In fact, after switching on the PE for Infected Person, the type of PE (top-PE or shoulder-PE) has a larger effect on the iF than the type of background ventilation system. Thus, it may be encouraging to utilize the PE system in rooms ventilated by DV to avoid the longer penetration of exhaled air. 9.00E-­‐03   Top-­‐PE  with  MV   8.00E-­‐03   7.00E-­‐03   Shoulder-­‐PE  with   MV   Top-­‐PE  with  DV   6.00E-­‐03   iF   5.00E-­‐03   4.00E-­‐03   Shoulder-­‐PE  with   DV   3.00E-­‐03   2.00E-­‐03   1.00E-­‐03   0.00E+00   PE  0  l/s   PE  10  l/s   PE  20  l/s   Figure 6.7 iF with PE for Infected Manikin 8.00E-­‐03   7.00E-­‐03   Top-­‐PE  with  MV   6.00E-­‐03   5.00E-­‐03   iF   Shoulder-­‐PE  with   MV   4.00E-­‐03   Top-­‐PE  with  DV   3.00E-­‐03   2.00E-­‐03   Shoulder-­‐PE  with   DV   1.00E-­‐03   0.00E+00   PE  0  l/s   PE  10  l/s   PE  20  l/s   Figure 6.8 iF with PE for Infected Manikin and l/s PV for Healthy Manikin 6.00E-­‐03   5.00E-­‐03   Top-­‐PE  with  MV   4.00E-­‐03   iF   Shoulder-­‐PE  with  MV   3.00E-­‐03   Top-­‐PE  with  DV   2.00E-­‐03   Shoulder-­‐PE  with  DV   1.00E-­‐03   0.00E+00   PE  0  l/s   PE  10  l/s   PE  20  l/s   Figure 6.9 iF with PE for Infected Manikin and 10 l/s PV for Healthy Manikin As depicted in Figures 6.10 through 6.13, the iF varies with different configuration for Healthy Manikin. When PE for Healthy Manikin is not activated (flow rate is l/s), the Intake Fractions are, for all the four figures, decreasing with the increase of PV flow rate for Healthy Manikin. By adding a PE working together with PV for the Healthy Manikin, it is found that the iF is further reduced. This is due to the pulling effect of combined PV-PE system, which can increase PV air in the inhaled air, thus protecting the Healthy Manikin. However, as the PE flow rate for Infected Manikin increases, the advantages of combined PV-PE for Healthy Manikin is not the same. For example, when top-PE is used for Infected Manikin with MV, the iF of the case AIp!!" Hp!!!!" is more than the case AIp!"# Hp! ; and when shoulder-PE is used for IP with DV, the iF of the case AIp!!!" Hp!!!" is higher than the case AIp!"#$ Hp! . This indicates that when PE is applied for both Healthy Manikin and Infected Manikin, the combined PV-PE for Healthy Manikin may bring more amount of contaminated air to the Healthy manikin due to the pulling and suction effect of the PV-PE system for Healthy Manikin. Considering now the cases in Figure 6.10 and Figure 6.11 of 10 l/s top-PE suction, the impact of PE for Infected Manikin on the Intake Fraction is obvious. With the further increase of PE flow rate from 10 l/s to 20 l/s, the reduction of iF begins to decrease slower as the slopes look more gentle. Different trend of the data is observed in Figure 6.12 and 6.13, a much gentler slope is found from the point where shoulder-PE is exhausting at l/s to the point where 10 l/s are set for shoulder-PE. And a sharper decrease in iF is seen from shoulder-PE 10 l/s to 20 l/s. In these cases, the shoulderPE works less effectively in terms of exhausting the exhaled contaminated air from the Infected Manikin, thereby changing the trend of the data as compared the top-PE cases. From Figures 6.10 through 6.13, it is clear that, the Intake Fraction of a Healthy Manikin is largely dependent not only on the PE flow rate, but also on the types of PE used for the Infected Manikin. Before activating the PE for Infected Manikin, the PV or the combined PV-PE for Healthy Manikin plays an important role in protecting the Healthy Manikin from exhaled contaminated air. However, after activating the PE for Infected Manikin, not much differences of Intake Fraction is found between the case with or without PV-PE for Healthy Manikin. This again indicates that in terms of airborne transmission control in health care settings, using a PE for Infected Person is more critical than using PV for a Healthy Person. MV   5.00E-­‐03   Top-­‐PE  for  IP   4.50E-­‐03   4.00E-­‐03   Top-­‐PE  for  IP  &  5l/s  PV   for  HP   3.50E-­‐03   iF   3.00E-­‐03   Top-­‐PE  for  IP  &   combined  shouler-­‐PE-­‐   PV(5l/s)  for  HP   2.50E-­‐03   2.00E-­‐03   Top-­‐PE  for  IP  &  10l/s  PV   for  HP   1.50E-­‐03   1.00E-­‐03   Top-­‐PE  for  IP  &   combined  shouler-­‐PE-­‐   PV(10l/s)  for  HP   5.00E-­‐04   0.00E+00   PE  0l/s   PE  10l/s   PE  20l/s   Figure 6.10 iF with different configurations for Healthy Manikin with top-PE for Infected Manikin with MV DV   8.00E-­‐03   Top-­‐PE  for  IP   7.00E-­‐03   6.00E-­‐03   Top-­‐PE  for  IP  &  5l/s  PV   for  HP   iF   5.00E-­‐03   Top-­‐PE  for  IP  &  combined   shouler-­‐PE-­‐  PV(5l/s)  for   HP   4.00E-­‐03   3.00E-­‐03   Top-­‐PE  for  IP  &  10l/s  PV   for  HP   2.00E-­‐03   1.00E-­‐03   0.00E+00   PE  0l/s   PE  10l/s   PE  20l/s   Top-­‐PE  for  IP  &  combined   shouler-­‐PE-­‐  PV(10l/s)  for   HP   Figure 6.11 iF with different configurations for Healthy Manikin with top-PE for Infected Manikin with DV MV   0.006   Shoulder-­‐PE  for  IP   0.005   iF   0.004   Shoulder-­‐PE  for  IP  &  5l/s   PV  for  HP   0.003   0.002   Shoulder-­‐PE  for  IP  &   combined  top-­‐PE-­‐  PV(5l/ s)  for  HP   0.001   Shoulder-­‐PE  for  IP  &  10l/ s  PV  for  HP     PE  0l/s   PE  10l/s   PE  20l/s   Figure 6.12 iF with different configurations for Healthy Manikin with shoulderPE for Infected Manikin with MV DV   0.006   Shoulder-­‐PE  for  IP   0.005   iF   0.004   Shoulder-­‐PE  for  IP  &  5l/s   PV  for  HP   0.003   Shoulder-­‐PE  for  IP  &   combined  top-­‐PE-­‐  PV(5l/ s)  for  HP   0.002   Shoulder-­‐PE  for  IP  &  10l/s   PV  for  HP   0.001     PE  0l/s   PE  10l/s   PE  20l/s   Figure 6.13 iF with different configurations for Healthy Manikin with shoulderPE for Infected Manikin with DV 6.4 Air temperature and velocity The room air temperature and mean velocity are recorded at heights of 0.1 m, 0.3 m, 0.7 m, 1.3 m, 1.65 m and 1.95 m using the DANTEC measurement system. The vertical room air temperature distribution is presented in Figure 6.14. 22.8   Temperature   22.6   22.4   22.2   22   DV   21.8   DV   21.6   21.4   0.1m   0.3m   0.7m   1.3m   1.65m   1.95m   Height  above  floor   Figure 6.14 Room air temperature with MV and DV From the data collected at the two points of the room, it can be concluded that the room air temperature is stratified along the vertical height of the room space with DV. In the region close to the floor surface, the room air temperature is cooler with the cool DV supply air. Due to the heat source (thermal manikin), the vertical temperature gradients are larger in the height from 0.7 m to 1.35 m than those in the bottom and upper part of the room. The convection flow generated in this region results in higher level of temperature gradient than in the space away from the manikin. With MV, the temperature keeps quite stable through the room height, which is due to the wellmixed flow effect. Figure 6.15 presents the profiles of the mean room air velocity during the experiments with both MV and DV. The higher air movement is observed with MV than DV. Room  air  velocity   0.18   0.16   velocity   0.14   0.12   0.1   MV   0.08   DV   0.06   0.04   0.02     0.1m   0.3m   0.7m   1.3m   1.65m   1.95m   Figure 6.15 Room air velocity with MV and DV The local air velocity at the neck/ear region of the Infected Manikin is shown in Figure 6.16 and Figure 6.17. Generally, the air velocity increases with the increase of PE flow rate. In cases without activating the PE, the air velocity at the neck/ear region is almost the same as the room air, so that the environment around the human head is mostly calm. In Cases with the flow rate 10 l/s of shoulder-PE, air is being sucked by the PE, and flow field of about 0.31m/s in velocity extends to the area around the human face with MV. A higher velocity of 0.38 m/s is observed when the PE flow rate is increased to 20 l/s. Compared with shoulder-PE, the increase of local air velocity when using top-PE instead is smaller, which is 0.24 m/s when flow rate is 10 l/s and 0.27 m/s when the flow rate is 20 l/s. Similar trend is observed with DV, the shoulder-PE tends to generate more velocity increase at neck/ear region than MV. In Cases with 20 l/s of PE flow rate, in which air is blowing at a higher velocity of 0.28 m/s and 0.17 m/s with shoulder-PE and top-PE respectively. This is because the location of shoulder-PE is closer to the neck/ear region and the air movement of the surrounding air is enhanced. MV   Air  velocity  (m/s)   0.4   0.35   0.3   0.25   0.2   0.15   0.1   0.05     PE  0l/s   PE  10l/s   PE  20l/s   shoulder-­‐PE   0.16   0.31   0.38   top-­‐PE   0.16   0.24   0.27   Figure 6.16 Local air velocities at neck/ear region with MV DV   Air  velocity  (m/s)   0.35   0.30   0.25   0.20   0.15   0.10   0.05   0.00   PE  0l/s   PE  10l/s   PE  20l/s   shoulder-­‐PE   0.07   0.28   0.29   top-­‐PE   0.07   0.15   0.18   Figure 6.17 Local air velocities at neck/ear region with DV In the space close to the manikin’s neck/ear region (1.2 m), draft rating (DR) at the face is presented in Figure 6.18 and Figure 6.19. Draft is an unwanted local cooling of the body caused by air movement. The figures show that the activation of PE always brings a higher value of DR at the neck/ear than the cases without PE. Although the velocities are higher with MV, there is not much difference between the DR with MV and DV. This means that the effect of the background ventilation type on DR is not strong. After activating either top-PE or shoulder-PE, the DRs increase to more than 15%, even with the lower flow rate of 10 l/s; and a flow rate of 20 l/s of PE would result in a slightly higher DR. This means that the use of either shoulder-PE or top-PE may lead to some draft discomfort. DraE  Ra-ng  with  MV   shoulder-­‐PE   17.34%   top-­‐PE   18.85%   19.35%   16.08%   6.38%   6.51%   PE  0l/s   PE  10l/s   PE  20l/s   Figure 6.18 Draft rating at neck/ear region of Infected Manikin with MV DraE  Ra-ng  with  DV   shoulder-­‐PE   top-­‐PE   17.64%   17.30%   19.55%   18.50%   6.51%   6.64%   PE  0l/s   PE  10l/s   PE  20l/s   Figure 6.19 Draft rating at neck/ear region of Infected Manikin with DV 6.5 Key Findings The Infected Manikin keeps exhaling the tracer gas into the room air, which is cooled by 90% re-circulated air. During the half hour of experiments (the maximum duration of a typical consultation process), there is no steady-state achieved. In this chapter, only data at the end of the 30 minutes of each experiment were used for analysis; The Intake Fraction and Exposure Reduction at 10 mins and 20 mins after the start of each experiment are listed in Appendices and 2. As a summary, the key findings in this chapter and Appendices and are listed as follows: During a normal consultation process in healthcare centers, where the Infected Person and the Healthy Person are sitting face to face, the results indicate that the combined PV and PE for HP can achieve the highest PEE. And the shoulder-PE performs a little better than top-PE in terms of increasing PV air in inhaled air. In the context of airborne transmission control, the use of PV alone has a potential to protect the HP; the use of combined PV-PE alone for HP can achieve the lowest Intake Fraction; and the use of PE for IP alone shows much better performance than using PV for HP alone. However, after activating the PE for IP, the use of PV for HP may lead to higher or lower exposure. The increase or decrease depends on the effects of background ventilation type, PE type and PV flow rates. For better airborne transmission control, top-PE is preferred than shoulder-PE because it can achieve better exposure reduction and lower Intake Fraction with a lower flow rate.   [...]... Figure 6. 18 Draft rating at neck/ear region of Infected Manikin with MV DraE  Ra-ng  with  DV   shoulder-­‐PE   top-­‐PE   17 .64 %   17.30%   19.55%   18.50%   6. 51%   6. 64%   PE  0l/s   PE  10l/s   PE  20l/s   Figure 6. 19 Draft rating at neck/ear region of Infected Manikin with DV 6. 5 Key Findings The Infected Manikin keeps exhaling the tracer gas into the room air, which is cooled by 90% re-circulated air. .. Figures 6. 10 through 6. 13, it is clear that, the Intake Fraction of a Healthy Manikin is largely dependent not only on the PE flow rate, but also on the types of PE used for the Infected Manikin Before activating the PE for Infected Manikin, the PV or the combined PV-PE for Healthy Manikin plays an important role in protecting the Healthy Manikin from exhaled contaminated air However, after activating... pulling and suction effect of the PV-PE system for Healthy Manikin Considering now the cases in Figure 6. 10 and Figure 6. 11 of 10 l/s top-PE suction, the impact of PE for Infected Manikin on the Intake Fraction is obvious With the further increase of PE flow rate from 10 l/s to 20 l/s, the reduction of iF begins to decrease slower as the slopes look more gentle Different trend of the data is observed in. .. as follows: During a normal consultation process in healthcare centers, where the Infected Person and the Healthy Person are sitting face to face, the results indicate that the combined PV and PE for HP can achieve the highest PEE And the shoulder-PE performs a little better than top-PE in terms of increasing PV air in inhaled air In the context of airborne transmission control, the use of PV alone has... in Figure 6. 12 and 6. 13, a much gentler slope is found from the point where shoulder-PE is exhausting at 0 l/s to the point where 10 l/s are set for shoulder-PE And a sharper decrease in iF is seen from shoulder-PE 10 l/s to 20 l/s In these cases, the shoulderPE works less effectively in terms of exhausting the exhaled contaminated air from the Infected Manikin, thereby changing the trend of the data... higher air movement is observed with MV than DV Room air  velocity   0.18   0. 16   velocity   0.14   0.12   0.1   MV   0.08   DV   0. 06   0.04   0.02   0   0.1m   0.3m   0.7m   1.3m   1 .65 m   1.95m   Figure 6. 15 Room air velocity with MV and DV The local air velocity at the neck/ear region of the Infected Manikin is shown in Figure 6. 16 and Figure 6. 17 Generally, the air velocity increases with the increase... from exhaled contaminated air However, after activating the PE for Infected Manikin, not much differences of Intake Fraction is found between the case with or without PV-PE for Healthy Manikin This again indicates that in terms of airborne transmission control in health care settings, using a PE for Infected Person is more critical than using PV for a Healthy Person MV   5.00E-­‐03   Top-­‐PE  for  IP... for Infected Manikin with DV 6. 4 Air temperature and velocity The room air temperature and mean velocity are recorded at heights of 0.1 m, 0.3 m, 0.7 m, 1.3 m, 1 .65 m and 1.95 m using the DANTEC measurement system The vertical room air temperature distribution is presented in Figure 6. 14 22.8   Temperature   22 .6   22.4   22.2   22   DV   21.8   DV   21 .6   21.4   0.1m   0.3m   0.7m   1.3m   1 .65 m... air During the half hour of experiments (the maximum duration of a typical consultation process), there is no steady-state achieved In this chapter, only data at the end of the 30 minutes of each experiment were used for analysis; The Intake Fraction and Exposure Reduction at 10 mins and 20 mins after the start of each experiment are listed in Appendices 1 and 2 As a summary, the key findings in this... Infected Manikin with MV, the iF of the case AIp!!" Hp! is more than the case AIp!"# Hp! ; and when shoulder-PE is used for IP !!!" with DV, the iF of the case AIp!!!" Hp! is higher than the case AIp!"#$ Hp! This !!" indicates that when PE is applied for both Healthy Manikin and Infected Manikin, the combined PV-PE for Healthy Manikin may bring more amount of contaminated air to the Healthy manikin . Chapter 6: Performance evaluation of PV-PE system in conjunction with background MV and DV systems — airborne infection control 6. 1 Background As introduced in Chapter two, in the context of airborne. combined PV-PE system in conjunction with background MV or DV systems in terms of the localized extraction of the contaminated exhaled air from an Infected Person in healthcare settings - Infected. to the pulling effect of combined PV-PE system, which can increase PV air in the inhaled air, thus protecting the Healthy Manikin. However, as the PE flow rate for Infected Manikin increases,