Performance evaluation of personalized ventilation personalized exhaust (PV PE) system in air conditioned healthcare settings 2

2.1 Personalized ventilation Personalized Ventilation PV concept, introduced by Fanger 2000, aims to supply conditioned outdoor air to the breathing zone of occupants.. High momentum of

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This chapter consists of three parts, a holistic and critical review of PV, a review of local exhaust ventilation in the field of a ventilation type to reduce the transmission of infected air in indoor environments, the review of studies

of ventilation in healthcare centers and hospitals After summarizing in detail the three topics, knowledge gap is identified and the research motivation is discussed

2.1 Personalized ventilation

Personalized Ventilation (PV) concept, introduced by Fanger (2000), aims to supply conditioned outdoor air to the breathing zone of occupants A lot of studies have been done to investigate how to supply as much as possible PV air to the people

2.1.1 Air Terminal Device

Melikov et al (2002) developed five different kinds of Air Terminal Device (ATD) to evaluate their performance: Movable Panel (MP), Computer Monitor Panel (CMP), Vertical Desk Grill (VDG), Horizontal Desk Grill (HDG), and Personal Environments Module (PEM) (Figure 2.1) The movable panel (MP) was positioned 0.2 m front of the manikin’s face and 0.3 m above the nose It was adjustable in a wide range to supply personalized air The computer monitor panel (CMP) was mounted on the monitor at a distance of 0.4 m from the edge of the desk It was able to supply air in a changeable direction on a vertical plane The vertical desk grill (VDG) and the horizontal desk grill (HDG) were mounted at the edge of the desk, supplying a vertical and a horizontal flow of personalized air direct to the breathing zone of the

Chapter2: Literature Review

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occupant The personal environments module (PEM) consists of two nozzles mounted at the two edges of the desk and allow for changes of the direction of the personalized air in both horizontal and vertical planes A typical office workplace, with a dimension of 5 m X 6 m X 2.5 m was simulated A breathing thermal manikin was used to simulate an occupant, sitting in front of

a computer at a distance of 0.15 m from the desk Both the upright position and leaning forward position of the manikin were performed The results showed the lowest temperature of the inhaled air was achieved by VDG Movable panel (MP) performed well as well as it allowed for a change of airflow direction in relation to the occupant All the ATDs were able to reduce the amount of exhaled air re-inhaled by the manikin

Figure 2.1: CMP, MP, VDG, HDG, and PEM [Melikov et al (2002)]

Different from the movable panel, a triangular plenum box (390 mm×240 mm×150 mm) with a rectangular grille opening, the round movable panel (RMP) is developed by Bolashikov et al in 2003 It is a round front panel with an opening of Ø185 mm and a honeycomb plate attached Bolashikov (2003) also developed a new ATD named headset It is a rectangular supply

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nozzle (35 mm×8 mm) shown in Figure 2.2 The performance of both the ATDs was tested at three combinations of room air temperature and personalized air temperature: 23/23 oC, 23/20 oC and 26/20 oC respectively, and at different flow rates of personalized air, ranging from 5 to 15 l/s for RMP and 0.18 to 0.5 l/s for Headset Both the inhaled air quality and thermal comfort were evaluated The results showed that inhaled air consisting of 100% personalized air could be achieved with the RMP and up to 80% with the Headset

Figure 2.2 Round movable panel [Bolashikov et al (2003)]

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Figure 2.3: Headset [Bolashikov (2003)]

Gao (2004) used a microphone circular outlet nozzles as the PV ATD to do the experiment and simulation.The ATD is located at the microphone position beneath the chin (Figure 2.4) They conducted both experimental research and CFD modelling study of this PV ATD Desk-edge nozzle is another type of

PV ATDs, which is installed beneath the front edge of a workstation, supplying air at a proper angle (Faulkner et al, 2004) Muhic and Butala (2006) developed a personal microclimate system (PERMICS) (Figure 2.5) and demonstrated its effectiveness.Circular Perforated Panel (CPP), mounted above the computer monitor with uniformly distributed Ø5 mm holes, was used by Zhou (2005a,b), Gong (2005) and Sun (2006) Sun et al (2006) studied High Turbulence Circular Perforated Panel (High-Tu CPP) and Low Turbulence Circular Perforated Panel (Low-Tu CPP) (Figure 2.6) The impact

of turbulence on spatial distribution of the cooling effect on the facial region and whole body were investigatedthrough both experimental and subjective studies They concluded low turbulence intensity is preferred in order to achieve greater facial cooling effect,larger range of velocities at the face area andcooler facial thermal sensation Arm attached ATD (Figure 2.7) is another type of air terminal devices developed by Melikovet al (2007) The ATD was attached to an arm that could be rotated around its vertical axis Thus, the ATD itself was movable in vertical plan and the direction of the personalized flow was allowed for changing in horizontal plan This design allowed the occupant direct the personalized flow at a preferred angle as well as the target velocity at his/her face or body

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Figure 2.4:Microphone circular outlet nozzles [Gao (2004)]

Figure 2.5 Personal microclimate system (PERMICS) [Muhic and Butala

(2006)]

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Figure 2.6 Low-Tu and high-Tu Circular Perforated Panel (CPP) [Sun et

al (2006)]

Figure 2.7 Arm attached ATD [Melikov et al (2007)]

Amei et al (2007) utilized four different types of Task Ambient ATDs:

3DU+, PEM, TU, and RCU to investigate the effect of Task

Air-conditioning systems on thermal comfort in a climate chamber The Task

Air conditioning system ATDs used in the experiments are shown in Figure

2.8 TU was installed to the back surface of a desk Isothermal airflow was

supplied from the front edge of the desk The direction of the air could be

adjusted from horizontal (0–90 degree) PEM had a desktop diffuser with a

mixing box under the desk and a radiant heat panel It allowed occupants to

control the temperature of supplied air by mixing primary air and ambient

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air in a mixing box 3DU+ is non-isothermal Task Air-conditioning ATD It

has a flexible duct which allows user to adjust its position and angle freely

It is arranged along the partitions and blows out air mainly from behind a

user RCU is developed on the basis of 3DU+, which supplies air to the

user’s backwith tripod stand located behind user The ATD position can be

automatically adjusted by using remote control of surveillance camera

platform The ATD is able to move in a range of 17o upward, 27o downward

and 310o in horizontal range

Figure 2.8 TAC systems: (a) 3DU+, (b) PEM (non-isothermal airflow

desktop-based Personal Environmental Module), (c) TU (isothermal

airflow under-desk task unit), (d) RCU (remote control unit) [Amei et al

(2007)]

Niu et al (2007) developed a chair-based personalized ventilation system as shown in Figure 2.9 It is proposed that it can potentially be applied in theatres, cinemas, lecture halls, aircrafts, and even offices Experiments were conducted

to compare eight different ATDs and it was found that up to 80% of the

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inhaled air could be composed of conditioned PV air with a supply flow rate

of less than 3.0 l/s Perceived air quality improved greatly by serving cool air directly to the breathing zone Feelings of irritation and local drafts could be eliminated by proper designs PV air with a temperature below that of room air was able to bring “a cool head” and increased thermal comfort in comparison with mixing ventilation

Figure 2.9 A ventilation seat with an adjustable personalized air supply

nozzle [Niu et al (2007)]

Conceiçao et al (2010) equipped the classroom desks with PV ATDs As shown in Figure 2.10, each PV system is equipped with one air terminal device located above the desk writing area, in front to the trunk area (incident

in the trunk area), and other located below the desk writing area, in front to the legs area (incident in the knees area) Each air terminal device, made in plastic material, had a circular exit area around of 48 cm2

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Figure 2.10 Classroom desks with PV ATDs [Conceiçao et al (2010)]

Russo and Khalifa (2010) developed a novel co-flow PV nozzle (Figure 2.11) that extends the clean air “potential” core of the PV jet farther into the breathing zone The CFD simulation results showed that this kind of Co-flow

PV nozzle is far superior to a single round PV nozzle Yang et al (2010a) developed ceiling mounted personalized ventilation ATDs (Figures 2.12& 2.13), which could avoid ducting for supply of fresh air to each workplace and thus improves indoor aesthetics and have a better room layout.The ATD, made

of aluminium with a round outlet of a diameter of 95 mm, was mounted on the ceiling above the occupant The nozzle was connected to the ductwork with a diameter of 160 mm on the other side The total length of the nozzle was 140

mm High momentum of the PV air was used for this type of ATD so as to keep the core region of personalized airflow as long as possible.The ATD was able to supply air at low turbulence intensity, which helps reduce heat transfer and mass mixing between personalized air and room air so as to supply maximum cool and fresh air to the breathing zone The ATDs installed on the ceiling are well above each workplace/occupantin conjunction with mixing ventilation They conducted both subjective and objective studies of this

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newly developed PV ATD and found that ceiling mounted PV system can

improve thermal sensation, perceived air quality, and inhaled air temperature

Moreover, they analysed the energy saving potential of ceiling mounted PV

system in conjunction with mixing ventilation in hot and humid climate and

concluded that ceiling mounted PV system could decrease the total energy

consumption comparing with mixing ventilation plus desk fans Pantelic &

Tham (2010) designed a desktop PV (DPV) air terminal device (Figure 2.14),

the openings of which covered only the top half of the DPV ATD front surface There were 30 supply openings (5 vertical x 6 horizontal) and each opening on

the front surface is circular with a diameter of 8 mm Lower half of the DTV

ATD (80 mm from the table surface) was designed without any openings to

avoid interaction of PV air flow and obstacles on the surface of the table

Figure 2.11 Novel Co-flow PV nozzle and its entrainment process [Russo

&Khalifa (2010)]

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Figure 2.12: Ceiling mounted personalized ventilation [Yang et al (2010a)]

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Figure 2.13: Details of the jet diffuser for ceiling mounted PV ATD [Yang

et al (2010a)]

Figure 2.14: Desktop Personalized Ventilation Air Terminal Device

[Pantelic & Tham (2010)]

Seat headrest-mounted air supply terminal devices, named Seat Headrest Personalized Ventilation (SHPV),was developed by Melikov et al (2012) as shown in Figure 2.15 Experiments using a breathing thermal manikin were conductedto identify its ability to provide clean air to the inhalation zone Questionnaires were also used to collect human responses The results showed that by using the SHPV, the portion of the clean PV air in the inhalation can

be increasedup to 99% during the manikin experiments Itsuggests a dramatic improvement of inhaled air quality and a decreased risk of airborne cross-infection when SHPV is used Subjects assessed the air movement and the cooling provided by the SHPV as acceptable andno draught was reported

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Figure 2.15 The seat with ATD attached to the headrest and the breathing

thermal manikin [Melikov et al (2012)]

Makhoul et al (2013a,b) developed a ceiling-mounted low-mixing PV nozzle that provided remarkable improvements in terms of fresh air delivery and air quality The air distribution system is composed of a primary central nozzle for fresh air delivery, surrounded by an annular secondary nozzle supplying recirculated air at nearly the same velocity, and a peripheral angled diffuser to form a canopy for localizing the flow around the occupant and maintain the room macroclimate temperature

Figure 2.16 Frontal and top views of the proposed ceiling PV nozzle

[Makhoul et al (2013a,b)]

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Comparison between different kinds of PV ATDs shows that each PV ATD has some advantages over others The selection of PV ATD in a specific environment is based on the ability of PV ATD in terms of delivering more conditioned outdoor air, the function of the space and the interior design and

as well as the background ventilation type However,the ATDs are always fixed or have little flexibility to rotate/move, which never consider the occupants’ moving around the desk while they still remain seated The PV performance and inhaled air quality depend largely on the distance between

PV ATD and occupants and the fresh air core region relative to the occupants This leads to a requirement for a more flexible strategy for the fixed PV ATDs

2.1.2 Evaluation Index

To evaluate the performance of PV, a series of indices have been developed by previous researchers According to the different research purposes, the indices can be categorised into two groups, IAQ indices and thermal comfort indices Most of these indices can be used both for experimental studies and CFD studies

Since this study is focused on the improvement of inhaled air quality by using

a PV-PE system, only IAQ indices are summarized

1) Personal Exposure Effectiveness (PEE, εP)

The PEE is widely used in PV research and can be applied when a tracer gas is dosed into the background air to represent a pollutant Melikov et al (2002) first proposed the Personal Exposure Effectiveness (PEE) when doing research

on evaluating five different types of PV ATDs This index aims to identify the performance of the PV with regard to providing clean air in inhalation For this purpose, tracer gas is mixed with the supplied ventilation air in the room which will act as a marker for the pollutants and the supplied PV air is conditioned 100% outdoor air which is free of tracer gas The concentration of tracer gas in inhaled air, the air exhaust from the room, at several sampling points in the room and in the supplied PVflow need to be measured and the

et al (2003) demonstrated 100% PEE value when using RMP with a flow rate

of 15 l/s supplying PV air The headset ATD was evaluated and found to have

an 84% PEE using only less than 0.5 l/s PV air PEE of CPP was studied by Zhou (2005a) The maximum values of εp achieved with the Low-Tu CPP and High-Tu CPP at the highest flow rates were approximately 0.46 and 0.35, respectively The Desk top PV ATD (Pantelic, 2010) could achieve a PEE of 0.4 and could be increased to 0.47 if coupled with desk mounted fans

2) Air Change Effectiveness (ACE) and Pollutant Removal Efficiency (PRE)

Faulkner et al (1999) conducted numerous laboratory and field studies to evaluate the performance of two desk mounted PV in terms of inhaled air quality They utilised Air Change Effectiveness (ACE) and Pollutant Removal Efficiency (PRE) as assessment indices Air Change Effectiveness (ACE), is defined as the age of air that would occur throughout the room if the air was perfectly mixed, divided by the average age of air where occupants breathe Sincethe average age of air exiting the room is the same as the age of air that

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would occur throughout the room if the indoor air were perfectly mixed, the ACE can be also defined as the exhaust-air age divided by the average age of air in breathing zone of heated manikins The value indicates the improvement

of fresh air that is delivered to the inhalation zone in comparisonto well-mixed ventilation The exhaust-air age is decreased if short-circuiting flow pattern occursand ACE will be less than unity ACE will be greater than unity if the breathing zone is preferentially ventilated with outside air.The calculation of ACE is based on tracer gas technique Tracer gas SF6 is injected at a steady rate into the supply air duct Concentrations of tracer gas at inhaled air, at shoulder level, at the place 15 cm in front of the nose and at the edge of the desk are measured Ages of air (τ) were determined from the SF6 tracer gas data via the Equation 2.3:

is the time elapsed since the start of tracer-gas injection

The ACE is defined as the ratio, τreturn / τbl, where τreturn is the age of the return/exhaust air and τbl is the average age of air at the breathing level

The Pollutant Removal Efficiency (PRE), also known as the ventilation effectiveness, is defined as the time-average concentration of pollutants in the exhaust air subtracting the outdoor concentration divided by the time-averaged concentration in inhaled air subtracting the outdoor concentration, shown as Equation 2.4

ply p

ply exhaust

In 2004, Faulkner et al employed ACE as an evaluation index again to study a desk-edge-mounted supply nozzle A high ACE of about 1.5 was achieved,which means a 50% increase for ventilation effectiveness compared with mixing ventilation The value of ACE highly depended on the angle of air supply nozzle (-15° ~ +45° from horizontal plane) and the temperature difference between the PV supply air and the ambient

3) Air-Quality Index (AQI)

Russo et al (2009) developed an Air-Quality Index (AQI) to computationally analyse the reduced-mixing personal ventilation jets AQI is defined as

e p

e b

point b in the breathing zone A value of 1.0 of AQI means clean air is

supplied at breathing zone, and a zero value of AQI means the air at point b is perfectly mixed

4) Personal Exposure Index (PEI)

The PEI index can be applied when the presence of a person or manikin is important It can be calculated by ventilation effectiveness but substituting the

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contaminant concentration at the point in occupied zone with the concentration

of inhaled contaminant Personal Exposure Index [PEI, (εE)] was proposed

by Brohus and Nielsen (1996) to study the personal exposure in displacement ventilated rooms This index takes the presence of a human-being into consideration since the occupant may modify the effectiveness of the air distribution It is the effectiveness of an air distribution system in removing internally generated pollutants from the ventilated space It can be expressed either as an average or overall relative effectiveness for the whole occupied zone or as a local relative effectiveness Tracer gas was dosed as passive contaminant sourceand PEI can be calculated by Equation 2.6:

PEI =!! !! !

!!!!!       (Eq 2.6)

Where CRis the concentration of tracer gas (SF6) in the exhaust/return air (ppm), CI is the contaminant concentration (SF6) in the inhaled air of a person (ppm), C∞ is the contaminant concentration (SF6) in the outdoor supply air (ppm) According to the earlierexpressionof Personal Exposure Effectiveness (εP), the Personal Exposure Index (εE) can be calculated from the PEE (εP),

by using εE =1/(1−εp) when the tracer gas is dosed at the same place

5) Intake Fraction

Intake fraction is a measure of the relationship between emission and human exposure It is able to quantify emissions-to-intake relationships The simplicity and nondimensionality of the Intake Fraction facilitates the comparison of results among investigators in an easily understandable manner

In this study, which is to quantify the link between source emissions and population exposure, Intake faction will be a good index to be used.The index

of IntakeFraction (iF) (Nazaroff, 2004) is defined as the proportion of emitted pollutant mass flow rate from an infected person which is inhaled by another healthy person The index can be stated as follows:

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iF=Ch ×M h

C i ×M i =Ch

C i       (Eq 2.7)

Ch is the inhaled tracer gas concentration for the Healthy Manikin and Ci is the

exhaled tracer gas concentration from the Infected Manikin Mh and Mi are the

mass flow rates of inhalation for the Healthy Manikin and exhalation for

theInfected Manikin respectively

6) Pollutant Exposure Reduction Efficiency (PER, ηPER)

Zuo et al (2002) developed pollutant Exposure Reduction Efficiency (ηPER) to

experimentally study facial air supply method for the reduction of pollutant

exposure This index quantifies the percentage of the personalized air in the

inhaled air by using a tracer gas injected in the PV nozzle Equation 2.10 is

usedto calculate the index

a L

a PV L

L F f

PER

C C

C C V

where, V F,Lis the oudoorair volume in the inhaled air V , L C PVis the tracer

gas concentration of nozzle supplied air, C ais the tracer gas concentration of

ambient air, and C is tracer gas concentration in inhaled air L

2.1.3 Air flow around occupants under PV

The general thermal environment in the micro space and the inhaled air quality

in breathing zone are strongly influenced by flow interactions around the

occupants Melikov (2004) studied the airflow around the occupants under PV

The air flow is very complex Figure 2.17 shows the air flows around the

working desk and seated person with a round movable panel PV supply There

are at least five airflows interacting with each other around human body: free

convection flow around human body, personalized airflow, respiration flow,

ventilation flow and thermal flow (Melikov, 2004)

Personalized airflow is typically a free jet, which includes core region, characteristic decay region, axisymmetric decay region and terminal region It

is suggested by Melikov (2004) that core region should reach breathing zone when the location of ATD is considered The temperature difference between jet air and surrounding air and the supply velocity will affect the buoyancy effect Reasonably increasing the diameter of jet outlet will increase the length

of core region

Respiration creates alternating inhalation and exhalation flows The dynamics

of the inhalation flow very close to the nose and to the mouth are similar

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(Haselton & Sperandio, 1988) The exhaled air has a temperature of approximately 34°C and a relative humidity close to 100% It has a relatively high velocity, and is able to penetrate the free convection flow around human body, effectively rejecting exhaled air from the flow or air that may subsequently be inhaled (Melikov, 2004) The design of personalized air should avoid mixing with exhalation, and also avoid the exhalation which will

Air-Kaczmarczyk et al (2002a, b) conducted experiments using movable panel to examine the perceived air quality, SBS symptoms and performance with 30 human subjects The flow rate of air and its direction can be controlled Four experiments were conducted: (1) PVS supplying outdoor air at 20 °C; (2) PVS supplying outdoor air at 23°C; (3) PVS supplying recirculated room air; and (4) mixing ventilation Room temperature was kept constant at 23 °C and relative humidity at 30% Results showed that the best condition in regard to perceived air quality, perception of freshness and intensity of SBS symptoms was when

PV air was at 20 °C Perceived air quality in this case was significantly better (p<0.01) than with mixing ventilation

Zeng et al (2002) conducted experiments and evaluated PV performance under more variety of thermal conditions Three levels of personalized air temperature (20, 23, and 26 °C) were supplied at four air flow rates (5, 10, 15,

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and 20 l/s/person) with three levels of ambient room air temperature (23, 26, and 28 °C) They reported that the personalized air temperature (TPV) only affected the perceived air quality during the first 30 minutes of the experiments Based on above experiments, more research was done by Zeng and Zhao (2005) to test the relationship between Personal Exposure Effectiveness, PV air flow rate and the distance between PV ATD outlet and the occupant’s breathing zone The PV air temperature was kept constant at

23 °C and the ambient temperature was 23 °C or 26 °C.The distance between the manikin’s nose and the air outlet was set at 15, 30, and 45 cm Four different flow rates of PV air (5, 10, 15, and 20 l/s) were tested at each distance The angle between the personalized air velocity and the vertical was fixed at 45 degree They concluded that the Personal Exposure Effectiveness (εp) depends more by the distance between PV ATD outlet and the occupant’s breathing zone than by the personalized air flow rate and the PEE does not change much for the PV flow rate higher than 10 l/s if the distance between the movable outlet and the occupant’s breathing zone is fixed

Melikov (2004) gave design recommendations for personalized ventilation and concluded that PV system with ATDs of high efficiency performs well at room air temperature 23-26 °C and a temperature of personalized air that is equal or 3-4 °C lower than the room air temperature

Subjective experiments with a non-isothermal task conditioning system were conducted to investigate impacts of the system on thermal comfort and productivity in a climate chamber by Akimoto et al (2004) in Japan "Default condition" was set to be 26°C with 50% RH and all the subjects took part in the test Then one half of the same subjects participated in "standard condition test: 26°C / 50% RH", and the otherhalf of the subjects participated in "task-ambient test: 30°C / 50% RH + Task-Ambient Conditioning (TAC)", just one week later again separately Subjective productivity was investigated together with thermal, humidity, comfort sensations, and other psychological factors The way the subjects controlled the task system was also monitored They found that the PEM system was able to keep people thermally comfortable

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even under ambient condition of temperature at 30°C and relative humidity at 50% Local thermal sensation was improved as well with TAC operation Sekhar et al (2003a, 2003b, 2005) conducted both objective and subjective studies on PV performance in tropics The experiments consisted of different combinations of room ambient temperature at both 23 °C and 26 °C, personalized air temperature at 20 °C, 23 °C, and 26 °C, and the personalized air flow rate at 7, 11, and 15 l/s/person The experiments were performed in a controlled environmental chamber having 6 workstations, each provided with

a movable panel type PV ATD Eleven human subjects participated in the experiment Air velocity, air temperature and ventilation effectiveness were measured in the breathing zone of each occupant The experimental results showed that a warmer room temperature such as 26 °C, accompanied by a PV air temperature of 23 °C or 20 °C, could achieve a significantly lower breathing temperature than a room air temperature at 23 °C without PV Furthermore, a warmer room temperature at 26 °C with a PV air at 23 °C was found to reduce the space cooling load compared with a conventional air-conditioning system in which the space is typically maintained at 23 °C

Gong et al (2005, 2006) studied the draft perception of tropically acclimatized people 24 subjects (male and female), performing normal office work in a room equipped with six workstations, were exposed to local airflow from the front and towards the face at six air velocities (0.15, 0.3 0.45, 0.6 0.75 and 0.9 m/s), at ambient temperatures of 26 and 23.5°C and localair temperature of

26, 23.5 and 21 °C The air terminal device was fixed on top of the computer monitor Other than at workstations, the room air velocity was measured to be less than 0.1 m/s Humidity in the chamber was not controlled but was monitored; it varied between 40% and 55% during the experiments The study found that air movement was preferred by the subjects even when the room air temperature is below 26 °C Subjects preferred air movement within a certain range, the values of which were dependent on the particular combination of ambient and local temperatures At an ambient temperature of 23 °C, people in the tropics preferred local air velocities ranging from 0.3 to 0.45 m/s, while at

of the PV air temperature was stronger A warmer space temperature, such as

26 ˚C, accompanied by a PV air temperature of 23.5 ˚C, implies that space cooling load is reduced by spot cooling in comparison with total mixing air-conditioning system in which space is uniformly maintained at 23.5 ˚C Based

on above energy saving potential conclusion, Yang et al (2010n) analysed the energy consumption of PV with ceiling mounted ATD in conjunction with mixing ventilation for tropical climates The energy calculations were performed for a room with dimensions 11.7 m×7.2 m×2.7 m 16 ceiling mounted PV ATDs were equipped at 16 workstations, supplying PV air which

is conditioned by a Primary AHU Another 6 diffusers supply air for the ambient, which is conditioned by using a Secondary AHU The energy consumption of the PV in conjunction with mixing ventilation is compared with the energy consumption obtained when mixing ventilation is used alone and when in addition to the mixing ventilation occupants are provided with desk fans for increased convection cooling at elevated room air temperatures They concluded that the use of ceiling mounted PV in conjunction with mixing ventilation at elevated room temperature of 26 °C will decrease the total energy consumption in comparison with the energy consumption with mixing ventilation only aiming at room air temperature of 23.5 °C The energy saving may not be great The use of PV with ceiling mounted ATD in conjunction with mixing ventilation at room air temperature of 26 °C will lead

to the use of substantially less energy in comparison with energy used with

Li et al (2010) examined the PV performance with UFAD ventilation They studied the PV system at 2 levels of supply air temperature (22 °C and 26 °C) The UFAD system supplied recirculated room air either at 22 °C or 18 °C, respectively at 480 l/s and 360 l/s, to keep the ambient room temperature at 26°C They observed that the supply air temperature of PV air has stronger effect on the PEE and PEI than PV air flow rate The PEI increases with the decrease of PV supply air temperature However, they concluded that the cooler UFAD supply air temperature tends to result in lower PEE and PEI This is because of the thicker thermal plume generated by the occupants In addition, when supplying the PV air at 26 °C due to buoyancy effect, a small part of the fresh air might rise up with the thermal plume before reaching the manikin’s breathing zone

Skwarczynski et al (2010) found that with the PV elevating the air velocity around the face, the acceptability of the air quality at the room air temperature

of 26 °C and relative humidity of 70% can be significantly improved They designed three experimental conditions, covering three combinations of relative humidity and local air velocity under a constant air temperature of

26 °C, 70% relative humidity without air movement, 30% relative humidity without air movement and 70% relative humidity with air movement PV air

of 26 °C with 70% RH was supplied from front toward the upper part of the body The results support the idea of supplying relatively high temperature (26 °C) and high relative humidity (70%) in the background for energy saving consideration

A summary of temperature combination studies of PV and background ventilation is listed in Table 2.1

23 °C Best condition in regard

to perceived air quality, perception of freshness and intensity of SBS symptoms was when PV air was at 20 °C

at the first 30 minutes of the experiments

Melikov

(2004)

Equal or 3–4°C lower than the room air temperature

23 °C - 26 °C PV system performs well

(no draught discomfort)

at room air temperature 23–26 °C and a

temperature of personalized air that is equal or 3–4 °C lower than the room air temperature

temperature of 30°C Sekhar et al

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at 23 °C without PV 2) Reduce space cooling load compared with a conventional system

in which the space is typically maintained

26 °C Air movement is preferred even when the

room air temperature is below 26 °C Local air velocities ranging from 0.3 to 0.45 m/s is preferred with an ambient temperature of 23 °C, 0.3

to 0.9 m/s are preferred with an ambient

temperature of 26 °C Yang et al

A warmer space temperature, such as

26 °C, with PV air of 23.5 °C, can reduce space cooling load by spot cooling in comparison with total mixing air-conditioning system in which space is uniformly maintained at 23.5 °C Yang et al

(2010) 21°C; 23.5°C;

26°C

26 °C ; 23.5°C The use of PV with ceiling mounted ATD in

conjunction with mixing ventilation at room air temperature of 26 °C will lead to substantial energy saving compared with energy used with mixing ventilation at 26 °C and

28 °C and desk fans for providing thermal comfort at each workplace

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18 °C (360 l/s), to keep room at 26 °C

PEI

2) When supplying the

PV air at 26 °C, due to buoyancy effect, a small part of the fresh air might rise up with the thermal plume before reaching the manikin’s breathing zone

Skwarczynski

et al (2010)

26°C, 70% RH without air movement,

without air movement and 70% RH with air movement

26°C with 70% RH

1) PV can improve the acceptability of the air quality at the room air temperature of 26°C with 70% RH

2) Supplying relatively high temperature (26°C) and high relative humidity(70%) in the background can be considered for energy saving

2.1.5 Study of transmission of exhaled air between occupants using PV 2.1.5.1 Droplets in exhaled air

It has been demonstrated that airflow pattern plays an important role in some airborne transmissible diseases (Li et al 2005) When there is one infected person in a room, the respiratory activity of this infected person will become one of the most important pathogen sources Thus, the study of the airflow pattern and the transmission of exhaled air are of great importance

Exhaled air normally comprises small droplets and these exhaled air and droplets may carry airborne pathogens and thereby magnify the spread of certain infectious diseases (Sattar et al., 1987; Papineni & Rosenthal, 1996; Edwards et al 2004; Johnson and Morawska, 2009)

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Bjorn and Nielsen (2002) studied the influence of the human exhalation on flow fields, contaminant distributions, and personal exposure in displacement ventilated rooms experimentally and numerically They stated that the exhaled air from mouth can be trapped in a thermally stratified layer and the exhaled air from nose could flow to the upper part of the room The exhalation air from both nose and mouth is able to penetrate the breathing zone of another person standing nearby The results also indicate the possibility of high exposure of exhaled air in rooms with displacement flow

Experiments carried out by Qian et al (2006) supported the above conclusion They examine how the exhalation flows interact with different room ventilation system, i.e mixing, downward and displacement ventilation Two breathing thermal manikins were used to simulate an infectious patient and a receiving patient in a full-scale experimental ward with the dimensions of 4.2

m x 3.6 m x 2.5 m N2O was used as tracer gas to simulate the droplet nuclei from the infectious patient Both the local ventilation effectiveness and personal exposure index were used here to examine the efficiency of an air distribution system in removing contaminants The results showed that the exhaled air of the infectious manikin could penetrate a longer distance with displacement ventilation because of the thermal stratification along the exhaled air direction created by displacement ventilation

Similar statement was made by Gao et al (2008) that exhaled air and sneeze/cough droplets are diluted much slower in DV/UFAD than MV, which might lead to higher exposure risk for other co-occupants This is because the exhaled droplets from normal breathing process could concentrate maximally just at the breathing height level under DV and UFAD and lead to a higher infection risk The conclusion is made by a series of CFD simulation with three different air distribution strategies MV, DV, and UFAD The supply air temperature was 17 ℃ in MV and 19 ℃ in DV and UFAD, with an air change rate 5.7 times per hour A 5% mass fraction of CO2 was added in the exhaled air The simulation results also showed that the respiratory droplets smaller than 10.0 µm disperse like tracer gases

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He et al (2011) conducted CFD study of exhaled droplet and air transmission under different ventilation strategies with PV and the conclusion is that PV has the possibility to increase the intake fractions for both exhaled air and particles They stated that PV enhanced mixing degree of exhaled particles under DV and UFAD much stronger than under MV Furthermore, for particles with diameter smaller than 0.8 µm, the concentration profile is similar with gas, which supports the results simulated by Gao et al (2008)

Johnson and Morawska (2009) examined the aerosol size distribution in exhaled breath Aerosol size distributions in the diameter range 0.5-20 µm were measured using an Aerodynamic Particle Sizer (APS) Normal breathing, varied breath holding periods and contrasting inhalation and exhalation rates are studied as different exhaling patterns They used an APS to measure the aerosol droplet size distribution in the exhaled air The results showed the peak of size distribution was between 0.8 and 0.9 µm

Having broadened the size range to be examined, different results were found

by Holmgren et al (2010) They studied the size distribution of exhaled particles in the range from 0.01 to 2.0 µm, which is the first time exhaled particles smaller than 0.4 µm were observed The results showed that the size distribution peaks at around 0.07 µm during tidal breathing, and an additional broad and strong peak was found between 0.2 and 0.5 µm

2.1.5.2 Study of dispersion of exhaled air and droplets under PV

Zhao and Guan (2007) focused their study on the particle dispersion in a room with personalized ventilation They simulated the dispersion characteristics of particles with aerodynamic diameter of 0.5-10 µm in a room ventilated by a

PV system with MV system The results showed that PV was effective to remove particles smaller than 2 µm, and that PV might not be the best ventilation mode for particles bigger than 7.5 µm due to resulting obvious particle accumulation on the floor

Pantelic et al (2009) examined the protective role of PV for an exposed manikin against droplets released from a “coughing machine” in three

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distances experimentally They found that PV combined with Total Volume Ventilation (TV) could both reduce the peak aerosol concentration levels in the breathing zone and shorten the exposure time compared with TV alone Halvonova and Melikov (2010a) studied the performance of “ductless” personalized ventilation in conjunction with displacement ventilation Two pollution sources with different behaviour in the space were simulated: the air exhaled by the polluting manikin (active pollution) and a point passive pollution source (not heated) placed on the table in front of the polluting manikin The results show that the use of personalized ventilation causes mixing and increases the concentration of tracer gas at a lower level However, the personalized ventilation may increase mixing and transportation of pollution generated in the vicinity of its supply ATD and in general will decrease the quality of the inhaled air More research was conducted by Halvonova and Melikov (2010b) to investigate the impact of disturbances due

to walking person on the performance of ‘‘ductless’’ personalized ventilation

in conjunction with displacement ventilation They found that the walking person introduced mixing in the room and therefore the concentration of the exhaled air inhaled by the polluting manikin increased

He et al (2011) investigated the transmission of respiratory droplets between two seated occupants equipped with round movable panel (RMP) PV in an office room.The office was ventilated by three different ventilation strategies: mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD) system respectively as background ventilation methods Three diameters of particles: 0.8 µm, 5 µm, and 16 µm, as well as tracer gas were numerically studied to examine their concentration Intake Fraction (iF) and a steady-state concentration uniformity index RC were utilized as indices

to evaluate the performance of ventilation systems The dimensions of the simulated office room were width (X) 4.8 m x length (Y) 5.4 m x height (Z) 2.6 m Two numerical thermal manikins (75 W each) were identical in shape and were seated upright at the tables inside the office One was a polluting manikin which exhaled infected airflow at 6 l/min through the mouth The

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other one was an exposed person which inhaled airflow at 6 l/min through the mouth It was found that without PV, DV performed the best concerning protecting the exposed manikin from the pollutants exhaled by the polluting manikin In MV, when the exposed manikin opened RMP the inhaled air quality could always be improved In DV and UFAD, application of RMP might sometimes, depending on the personalized airflow rate, increase the exposure of the others to the exhaled droplets of tracer gas, 0.8 µm particles, and 5 µm particles from the infected occupants

Makhoul et al (2013a,b) investigate the particle transport in offices equipped with ceiling mountedpersonalized ventilators using CFD and experiments.They found that the PV nozzles integrated with peripheral diffusers were able to form a canopy of conditioned air around the occupant.The canopy was effective in reducing the migration of particles from the macroclimate to the microclimate region and low intake fractions of 1.9e-4 and 5.9e-4 were achieved for particle sizes of 1 mm and 0.01 mm, respectively The PV jet was capable of maintaining an intake fraction of 3.6e-4 for fine particle sizes (1 mm) and 2.95e-4 for ultrafine particles (0.01 mm) when the particle-emitting source is in the proximity of the occupant

Cermakand Melikov (2007) studied the protection of occupants from exhaled infectious agents and floor material emissions in rooms with personalized and underfloor ventilation The results showed that the transmission of exhaled pollution between the two workplaces is independent of the location of the workplace where the pollution was generated when VDG is used A small difference in exposure was found for the RMP in conjunction with the short throw The reason is largely due to airflow direction, which caused the pollution to spread below and above the breathing zone, respectively, with the two terminals The free convection flow around the human body projected the spatial differences near the floor to the inhaled air (RMP), whereas below the ceiling the air was exhausted (VDG).The results of this study also imply that the exposure of occupants to exhaled air is independent of the location of the polluting workplace This result makes it possible to extend the research to