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

1



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
2

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
3

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
o
C, 23/20
o
C and 26/20
o

C 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)]

4

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.
5


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


Figure 2.5 Personal microclimate system (PERMICS) [Muhic and Butala
(2006)]
6


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

7

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 17
o
upward, 27
o
downward
and 310
o
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
8

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 cm
2
.
9


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
10

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)]

11


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

12

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.
13


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)]
14

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,
P
ε
)
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
15

data can be used to calculate the PEE. The PEE is defined by Equation 2.1,
which is expressed as the percentage of PVair in the inhaled air.
(Eq. 2.1)
Where C
I,0
is the concentration of tracer gas in the room air, C
I
is the
concentration of tracer gas in the inhaled air, C
PV
is concentration of tracer gas
in the PV air. This index is equal to one when 100% PV air is inhaled and it is
equal to zero if no PV air is inhaled. Since the PV supplies 100% outdoor air,
C
PV
=0 and, therefore, PEE can be simplified to:
𝜀
!
=

!
!,!
!!
!
!
!,!
(Eq.2.2)
In their study of the performance of five types of PV ATD for both isothermal
and non-isothermal condition, PEE of the five types ATDs were calculated
and the results showed that the VDG has a maximal PEE of 0.58. Bolashikov
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
PVOI
IOI
CC
CC
p

−
−
=
,
,
ε
16

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 SF
6
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 SF
6
tracer gas
data via the Equation 2.3:
𝜏 =
!
!
(!"#$)
𝐶
(!"#$)

− 𝐶
(!)
𝑑𝑡
!
(!"#$)
!
(Eq. 2.3)
C(t) is the tracer-gas concentration at the point, C
(tend)
is the steady-state
concentration at the end of the step up (constant injection of tracer gas), and t
is the time elapsed since the start of tracer-gas injection.
The ACE is defined as the ratio, τ
return
/ τ
bl
, where τ
return
is the age of the
return/exhaust air and τ
bl
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.
plyp
plyexhaust
CC

CC
sup
sup
−
−
=
η
(Eq. 2.4)
C
exhaust
is the contaminant concentration in the exhaust air, C
supply
is that in the
outdoor supply air, and C
p
is the contaminant concentration in inhalation zone.
Brohus (1996) defined the breathing (inhalation) zone as a semi sphere with a
17

radius of 0.3 m. However, this is not applicable for PV due to the complex
airflow conditions.
Since there are different kinds of indoor air pollutants which have different
source, PRE for each of them can be measured by different tracer gases.
During the study of PEM and ClimaDesk ATDs, the ACE values were
measured to be approximately 1.3 to 1.9 with a flow rate of 7 to 9 l/s per
occupant (Faulkner, 1999). For the measurement of PRE, three different per
fluorocarbon tracer-gases were used to simulate sources of indoor-generated
pollutants. The PRE was approximately 1.2 to 1.6.
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
ep
eb
CC
CC
AQI
−
−
=
(Eq. 2.5)
Where C
p
is the tracer gas concentration at the primary nozzle exit, C
e
is tracer
gas concentration in the exhaust, and C
b
is the tracer gas concentration at a
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

18

contaminant concentration at the point in occupied zone with the concentration
of inhaled contaminant. Personal Exposure Index [PEI, (
E
ε
)] 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 C
R
is the concentration of tracer gas (SF
6
) in the exhaust/return air

(ppm), C
I
is the contaminant concentration (SF
6
) in the inhaled air of a person
(ppm), C∞ is the contaminant concentration (SF
6
) in the outdoor supply air
(ppm). According to the earlierexpressionof Personal Exposure Effectiveness
(
P
ε
), the Personal Exposure Index (
E
ε
) can be calculated from the PEE (
P
ε
),
by using
( )
pE
εε
−= 1/1
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:
19

iF=
C
h
×M
h
C
i
×M
i
=
C
h
C
i
!!!!!!!!!!!!!!!!!!!!!!!!!!
(Eq. 2.7)
C
h
is the inhaled tracer gas concentration for the Healthy Manikin and C
i
is the
exhaled tracer gas concentration from the Infected Manikin. M

h
and M
i
are the
mass flow rates of inhalation for the Healthy Manikin and exhalation for
theInfected Manikin respectively.
6) Pollutant Exposure Reduction Efficiency (PER, η
PER
)
Zuo et al. (2002) developed pollutant Exposure Reduction Efficiency (η
PER
) 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.
aL
aPV
L
LF
fPER
CC
CC
V
V
−
−
===
,
ηη

(Eq. 2.10)
where,
LF
V
,
is the oudoorair volume in the inhaled air
L
V
,
PV
C
is the tracer
gas concentration of nozzle supplied air,
a
C
is the tracer gas concentration of
ambient air, and
L
C
is tracer gas concentration in inhaled air.
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).
20

Figure 2.17 Airflows around human body: 1 free convection flow, 2
personalized airflow, 3 respiration flow, 4 ventilation flow, 5 thermal flow.
[Melikov (2004)]

Free convection flow around the human body is an upward free convection
flow in a calm environment (Melikov & Zhou, 1996; Ozcan et al., 2003). It is
slow and laminar with a thin boundary layer at the lower parts of the body and
becomes faster and turbulent with a thick boundary layer at the higher part. A
large portion of air that is inhaled by the occupants is from this free convection
flow because it transports air from lower parts to the breathing zone. (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
21

(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

be inhaled again.
2.1.4 Study of temperature combination of PV supply air and background
air
According to American Society of Heating, Refrigerating, and Air-
conditioning Engineers (ASHRAE Standard 55-2010) standards, room
temperatures should be maintained at a temperature from 20 °C to 26 °C with
relative humidity from 30% to 60%. These thermal requirements are usually
met by using mixing ventilation or displacement ventilation. After the
introduction of PV system, quite a lot of experiments have been conducted to
investigate the PV performance under different supply temperature and flow
rate in terms of thermal sensation, inhaled air quality and energy saving.
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,
22

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 (T
PV
) 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
23

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
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an ambient temperature of 26 °C, local air velocities from 0.3 to 0.9 m/s were
preferred.
Yang et al. (2010a) assessed the thermal environment, air movement, and air
quality of ceiling-mounted PV system in a chamber at either 26 or 23.5 °C.
The personalized air had a temperature of 26, 23.5, or 21 °C. Tropically
acclimatized people were exposed to four different PV airflow rates (4, 8, 12,
and 16 l/s). The conclusion is that the local and whole body thermal sensations
were reduced when PV airflow rates were increased. Inhaled air temperature
was perceived cooler and perceived air quality and air freshness improved
when PV airflow rate was increased or temperature was reduced. The impact
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
25

mixing ventilation at 26 °C and 28 °C and desk fans for providing thermal
comfort at each workplace. At elevated room temperature up to 28 °C, the use
of desk fans for providing convection cooling to each occupant in rooms with
mixing ventilation may lead to increased energy consumption in comparison
with the energy used to keep comfortable.
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.