Performance evaluation of personalized ventilation personalized exhaust (PV PE) system in air conditioned healthcare settings 1

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PERFORMANCE EVALUATION OF

PERSONALIZED VENTILATION -

PERSONALIZED EXHAUST (PV-PE) SYSTEM IN AIR-CONDITIONED HEALTHCARE SETTINGS

YANG JUNJING

(Bachelor of Eng., Tongji University;

Master of Science, University of Reading)

A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

DEPARTMENT OF BUILDING NATIONAL UNIVERSITY OF SINGAPORE

2013

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Declaration

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Acknowledgements

I would like to acknowledge and extend my heartfelt gratitude to the following individuals who have made the completion of this thesis possible

Firstly I would like to express my deepest acknowledgement to my supervisor Professor S.C Sekhar for his vital guidance, constant support, valuable advice and encouragement He was also very accommodating in allowing me

freedom to pursue my interests which were out of my research scope I feel lucky to have been one of his PhD students

I am also grateful to my thesis committee members: A/P Cheong Kok Wai, David, and A/P Benny Raphael, whose doors are always open, for freely sharing with me their valuable knowledge, experience and expertise on any issues related to my research

I would like to thank Professor A.K Melikov from DTU for his suggestions and comments for the Qulify Exam Report of my PhD study which gives me ideas for experimental design

I want to thank Ms.Wu Wei Yi, Mr Zaini bin Wahid, Mr Tan Cheow Beng,

Mr Tan Seng Tee for assisting with the laboratory equipment and instruments during the experiments in my research

I am grateful to Dr Jovan Pantelic and Dr Wang Junhong for sharing their knowledge about CFD simulation I also wish to thank Dr Li Ruixin and Huang Shuguang for sharing their experience during the experiments

Gratitude goes out to the National University of Singapore for funding this effort and providing much needed apparatus during the course of this thesis

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Lastly, I would like to express my sincere gratitude to my husband, my daughter and my parents for their understanding, support and unconditional love

Singapore, Final submission May 2014

Yang Junjing

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Summary

Severe Acute Respiratory Syndrome, H1N1 and other flu-related outbreaks in recent times have highlighted the issue of short-range aerosol transmission between healthcare workers and the patients Concerns about the ventilation system design in healthcare centres in the field of control of airborne transmission of infection have become topical and important Personalized Ventilation (PV) has been introduced in indoor air distribution for more than a decade and the concept involves delivering 100% conditioned outdoor air directly to the occupant breathing zone The primary aim of a PV system is to supply fresh air to the breathing zone to enhance Inhaled Air Quality At the same time, it can also be seen as a solution to prevent the spread of contaminated air Whilst a conventional PV system would fulfil most of these requirements, it may not be able to adequately prevent the spread of contaminated air as the PV air would go past an infected person and mix with the room air In order to maximize the advantages of a PV system in delivering personalized air to the breathing zone, it is interesting to explore the use of a personalized exhaust (PE) device that is integrated with the chair and assists in pulling the PV air flow towards the seated person Not only is the inhaled air quality improved further but the exhaled contaminated air is extracted locally and its spread into the room air is minimized by adding the local exhaust working together with the PV system Experimental study using two types of tracer gases have been conducted to evaluate the performance of this novel PV-PE system in conjunction with two different background ventilation systems Two types of PE: top-PE and shoulder-PE are evaluated and four different arrangements between the Healthy Person and the Infected Person were studied Three indices: Personalized Exposure Effectiveness; Intake Fraction; and Exposure Reduction were used to evaluate the system The main hypothesis is that the Top-PE is better than Shoulder-PE and in the presence of PE for patient, Displacement Ventilation system leads to a better exposure reduction than Mixing Ventilation system

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The results indicate that there is a good potential for improving inhaled air quality by having the combined PV-PE system to pull the clean air towards the seated person, especially under displacement ventilation When the PE is set at

10 l/s, the PEE of 5 l/s PV and 10 l/s PV are 27% and 50% higher with DV than MV at the nearest position (0.2 m and 0 degree) respectively It is also seen that this kind of personalized exhaust can prevent the spread of contaminated air by exhausting the exhaled air directly before it mixes with the room air; especially the top-PE has a better performance than shoulder-PE Furthermore, the use of PE is a more efficient way to protect the healthy person than using PV After using 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 However, the Healthy Manikin only enjoys about 25% reduction in exposure to the Infected manikin exhaled contaminated air when PV fresh air is at 5 l/s, and 55% if the

PV flow rate is increased to 10 l/s This thesis contributes to the knowledge of ventilation systems by addressing a few limitations of PV systems as well as controlling the short range aerosol transmission between healthcare workers and patients in healthcare settings

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Nomenclature

Abbreviations

ACE Air Change Effectiveness

ACH Air Change Rate

AHU Air Handling Units

ASHRAE American Society of Heating, Refrigerating and Air- Conditioning

AQI Air-Quality Index

ATD Air Terminal Device

BTM Breathing Thermal Manikin

CFD Computational Fluid Dynamic

CMP Computer Monitor Panel

CPP Circular Perforated Panel

CSP Computer Simulated Person

CTM Computational Thermal Manikin

CV Central Ventilation

DDV Desk Displacement Ventilation

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DPV Desktop Personalized Ventilation

DR Draught Rating

DV Displacement Ventilation

FCU Fan Coil Unit

HBIVCU Hospital Bed Integrated Ventilation and Cleaning Unit HDG Horizontal Desk Grill

HEPA High-Efficiency Particulate Air

HP Healthy Person

HVAC Heating Ventilation and Air Conditioning

IAQ Inhaled Air Quality

ICAS Infection Control at Source

iF Intake Fraction

IP Infected Person

ISO International Organization for Standardization

LEV Local Exhaust Ventilation

MV Mixing Ventilation

PE Personalized Exhaust

PEE Personal Exposure Effectiveness

PEI Personal Exposure Index

PER Pollutant Exposure Reduction Efficiency

PEM Personal Environment Module

PRE Pollutant Removal Efficiency

PV Personalized Ventilation

RH Relative Humidity

RMP Round Movable Panel

RNG Re-Normalisation Group

SARS Severe Acute Respiratory Syndrome

SBS Sick Building Syndrome

SHPV Seat Headrest Personalized Ventilation

SIMPLE Semi-Implicit Method for Pressure-Linked Equations TAC Task-Ambient Conditioning

TAM Task Air Module

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TV Total Volume Ventilation

UFAD Under Floor Air Distribution

VDG Vertical desk grill

Symbols

Δt Temperature Difference

C Constant dependent on clothing, body posture, chamber

characteristicsand thermal resistance offset of the skin surface temperature control system (K.m2/W)

C∞ Contaminant concentration in the outdoor supply air (ppm)

CI Contaminant concentration in the inhaled air of a person (ppm)

CPV Concentration of the tracer gas in personalized air (ppm)

CR Contaminant concentration in the exhaust/return air (ppm) Tracer gas concentration of ambient air

Ch Inhaled tracer gas concentration for the Healthy Manikin

Ci Exhaled tracer gas concentration from the Infected Manikin

Cpvpe off Tracer gas (N2O) concentration in the inhaled air of the Healthy Person when both the PV and PE are turned off

a

C

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Con Tracer gas (N2O) concentration with the particular PV or PE or both turned on

D Hydraulic diameter (m)

I Turbulence intensity (%)

k Turbulent kinetic energy (m2/s2)

L Flow rate(l/s)

Mp Mass flow rates of inhalation for the healthy manikin (kg/s)

MI Mass flow rate of exhalation for the infected manikin (kg/s)

Qt Dry heat loss

T Temperature (°C)

VF,L Fresh air volume (l)

Inhaled air volume (l)

t*eq Manikin-based equivalent temperature in reference conditions (°C)

t0 Supply air temperature (°C)

teq Manikin-based equivalent temperature in an actual environment (°C)

ɛ Turbulent kinetic energy dissipation rate (m2/s3)

ɛp Personal exposure effectiveness (dimensionless)

ɛe Personal exposure index (dimensionless)

ηPER Pollutant exposure reduction efficiency (%)

Φ Diameter

τ Reynolds stress (kg/m/s2)

τ Return age of the return/exhaust air(s)

τbl Average age of air at the breathing level(s)

y+ Near wall distance unit (dimensionless)

L

V

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Chapter 1: Introduction

1.1 Background and motivation

With Several Severe Acute Respiratory Syndrome outbreaks, SARS in 2003,

Pandemic Influenza A (H1N1/2009), and the more recent Influenza A (H5N1) in

2010, concerns about the airborne transmission of infection have become important During the epidemics of Severe Acute Respiratory Syndrome (SARS) in China, 917 out of 4698 infected person were hospital/healthcare workers; this has highlighted the issue of short range aerosol transmission between healthcare workers and the patients

Li et al (2007) reviewed the evidence for the effects of ventilation on the

transmission of infectious diseases They concluded that there was good evidence (as demonstrated by the contemporary technology available at the time of the studies) for aerosol transmission influenced by ventilation factors in outbreaks involving measles, chickenpox, the pneumococcus (Streptococcus pneumonia), SARS-CoV, tuberculosis, influenza and smallpox Therefore, ventilation systems in healthcare environments should be carefully designed to reduce the risk of aerosol transmission, in particular those causing respiratory and gastrointestinal infection

Mixing ventilation, displacement ventilation and under-floor air distribution (UFAD) are at present the methods most applied in mechanically ventilated healthcare centers Mixing ventilation involves mixing of the high momentum supply air with room air completely so that the temperature is uniform either in the entire space or in a specific zone of the space It is able to provide uniform air quality in rooms and relatively great freedom in terms of interior decoration However, the supply air at a low

contaminant concentration is mixed with the contaminated room air by the time it reaches the inhalation zone of the healthy person Displacement ventilation involves the supply of cool air at a low velocity through air inlets that are installed in the lower portion of the room, at the wall or floor While it has been shown to provide

occupants with better air quality and has good energy saving potential, the risk of drafts and contaminant issues have been raised Another ventilation approach is the under-floor air distribution (UFAD) concept The basic idea of the UFAD system is to supply air through a pressurized plenum to the occupants’ area UFAD has the

potential to increase the flexibility of space subdivision and reduce the zone sensible

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load by not conditioning the upper part of the zone (Eng., 2009) However, despite all the advantages of UFAD, there are some disadvantages, such as cold feet and draft discomfort Under UFAD, mixing ventilation and displacement ventilation systems, the fresh air cannot be delivered into the occupants’ breathing zone Hence, the

personalized ventilation concept was introduced in indoor air distribution more than a decade ago It supplies clean, cool and dry outdoor air at low turbulence directly to the breathing zone of occupants Different types of PV air terminal devices have been developed and their performance evaluated The ability to provide local cooling and thereby enhance thermal comfort as well as improve inhaled air quality has been examined together with different types of background ventilation systems It has been demonstrated that PV system is able to improve indoor air quality and potentially increase occupants’ satisfaction (Melikov et al, 2002; Kaczmarczyk et al., 2004; Sekhar et al, 2005; Gong et al, 2006; Yang et al, 2010a; Li et al, 2010)

Despite all the advantages of PV, there are some disadvantages The PV ATDs are typically either fixed in a place or have little flexibility to rotate and move However, the inhaled air quality and thermal sensation depend on the distance between PV ATD and human being Once the occupant starts moving around the desk, the distribution

of personalized air cannot change accordingly Although personal control was

introduced to allow occupants to change the flow rate according to their preference, the angles and direction could not be manually adjusted easily, especially for some ATD such as vertical desk grille (VDG)

In order to maximize the advantages of a PV system in delivering personalized air to the breathing zone at all times, it is interesting to explore the use of a localized

exhaust device that is integrated with the chair and assists in pulling the PV air flow always towards the chair i.e the seated person Thus, in the case of a seated person moving within certain limits around the workstation, the chair integrated localized exhaust device will serve to provide directional control for the PV air plume A

certain minimum gauge pressure of the localized exhaust system is necessary to be able to divert the personalized air within the range of movement of the seated person And most importantly, in the context of airborne infection control, it is critical that the ventilation system is able to extract the contaminated exhaled air immediately and