Indoor Air. 2015 Apr;25(2):176-87. doi: 10.1111/ina.12127.

Performance evaluation of a novel personalized ventilation–personalized exhaust system for airborne infection control

 

Yang Junjing1, Chandra Sekhar1, David Cheong Kok Wai1 and Benny Raphael2

1 Department of Building, School of Design and Environment, National University of Singapore

2 Indian Institute of Technology, Chennai, India

 

Abstract

In the context of airborne infection control, it is critical that the ventilation system is able to extract the contaminated exhaled air within the shortest possible time. To minimize the spread of contaminated air exhaled by occupants efficiently, a novel personalized ventilation (PV)–personalized exhaust (PE) system has been developed, which aims to exhaust the exhaled air as much as possible from around the infected person (IP). The PV–PE system was studied experimentally for a particular healthcare setting based on a typical consultation room geometry and four different medical consultation positions of an IP and a healthy person (HP). Experiments using two types of tracer gases were conducted to evaluate two types of PE: Top-PE and Shoulder-PE under two different background ventilation systems: Mixing Ventilation and Displacement Ventilation. Personalized exposure effectiveness, intake fraction (iF) and exposure reduction (e) were used as indices to evaluate the PV–PE system. The results show that the combined PV-PE system for the HP achieves the lowest intake fraction; and the use of PE system for the IP alone shows much better performance than using PV system for the HP alone.

KEYWORDS: Airborne transmission; Exhalation air; Healthcare setting; Infection control; Personalized exhaust; Personalized ventilation

PMID: 24810200

 

Supplement  

A novel Personalised Ventilation (PV) – Personalised Exhaust (PE) system to aid in the ventilation design of consultation rooms in healthcare centers and hospitals to obtain better infection control as well as better inhaled air quality is the subject of this study. With different configurations of the Infected Person and the Healthy Person, PV and PE air terminal devices, PV and PE flow rates, as well as the background ventilation/air distribution type, there were 84 scenarios studied with each experimental set up as shown in Figure 1.

 fig1

Figure 1. Experimental set up and the two novel PE systems. (Right: Top-personalized exhaust (PE); right: shoulder-PE)

(Yang, J., Sekhar, S. C., Cheong, K. W. D. and Raphael, B. (2015), Performance evaluation of a novel personalized ventilation–personalized exhaust system for airborne infection control. Indoor Air, 25: 176–187. doi:10.1111/ina.1212. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd)

 

The experimental duration was 30 minutes and the readings were taken at 10 minutes, 20 minutes and 30 minutes. Considering a continuous exposure of 30 minutes as being reasonable, the results at 30 minutes are reported in the Indoor Air paper. Yang et al. (2015)4 reported that although the Intake fraction of the healthy person increases with time, the first 10 minutes have seen the more rapid increase. Consequently, the exposure reduction at 10 minutes for the 54 scenarios under CASE A is shown as supplement in Figure 2. We can see that, for the first 10 mins, the PV-PE system is able to achieve good exposure reduction, which also shows the same trend as the results at 30 minutes. Comparing the exposure reduction with MV, the exposure reduction observed with DV is higher for most of the cases. It is seen that the use of PV alone with low flow rate has very limited ability to protect the healthy person from inhaling contaminated air from the infected person sitting opposite. The Top-PE can greatly reduce the exposure of exhaled air compared with the shoulder-PE at the same flow rate. The highest exposure reduction is obtained with the combined PV-PE system.

 

fig2

Figure 2. Comparison of exposure reduction at 10 minutes when utilizing PE

 

Since the Top-PE has a better performance compared with shoulder-PE, as shown in Figure 2, a more detailed analysis on intake fraction (iF) with 0l/s-10l/s-20l/s comparison is shown as Figures 3 & 4. The first point to address is that the reduction of iF from PE 0l/s to PE 10l/s is much more significant than that from PE10l/s to PE 20l/s in all cases, which means that the use of 10l/s of top-PE is able to achieve efficient exposure reduction. An interesting feature to note in Figure 3 is that, with the increase of PE flow rate with MV, the addition of PV does not help with exposure reduction. As shown in Figure 3, lines with light blue and green have seen an increase of iF when PE is operated at 10l/s and 20l/s.

fig 3 and 4

 

While the application of PE, on the one hand, assists in pulling the PV air flow towards the healthy person when working together with PV as a system, on the other hand, it also extracts the exhaled contaminated air locally to minimize its spread into the room air. The elevated air velocity at face/ear region due to the location of the PE should be considered. In this study, Dantec Dynamics comfort Sense system, was used to measure the mean air velocity, temperature, turbulence intensity and Daft Rating (DR) at face/ear region. The results in Figures 5 and 6 show that the Infected Person was prone to higher air velocities at face/ear region where the PE were switched on than without PE. The velocity increases as the PE flow rate increases. When the results obtained with shoulder-PE are compared with the results obtained with the top-PE, it is observed that shoulder-PE generated higher velocity at face/ear region of the Infected Manikin, especially with DV. This implies that the shoulder-PE which is located near to the face/ear region may lead to higher air movement around the head. Meanwhile, further consideration is needed when using PE regarding the draft risk.

fig 5 and 6

 

References

  1. Melikov, A.K., Cermak, R. and Majer, M. (2002) Personalized ventilation: evaluation of different air terminal devices, Energy and Buildings., 34, 829–836.
  2. Nazaroff, W.W. (2008) Inhalation intake fraction of pollutants from episodic indoor emissions, Build. Environ., 43, 269–277.
  3. Dygert, R.K. and Dang, T.Q. (2010) Mitigation of cross-contamination in an aircraft cabin via localized exhaust, Build. Environ., 45, 2015–2026.
  4. Junjing Yang, Chandra Sekhar, David K.W. Cheong & Benny Raphael (2015) A time-based analysis of the personalized exhaust system for airborne infection control in healthcare settings, Science and Technology for the Built Environment, 21:2, 172-178

 

Funding: The project was funded by National University of Singapore under research grant R-296-000-138-112.

 

Contact

Chandra Sekhar, PhD, Fellow ASHRAE, Fellow ISIAQ

Professor and Programme Director, MSc (Building Performance and Sustainability)

Co-Director, Centre for Integrated Building Energy and Sustainability in the Tropics (CiBEST)

Department of Building, School of Design and Environment

National University of Singapore, 4 Architecture Drive, Singapore 117566

bdgscs@nus.edu.sg

 

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