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Personalized ventilation: evaluation of different air terminal devices
Arsen K. Melikov*, Radim Cermak, Milan MajerInternational Centre for Indoor Environment and Energy, Technical University of Denmark, Building 402, 2800 Lyngby, Denmark
Abstract
Personalized ventilation (PV) aims to provide clean air to the breathing zone of occupants. Its performance depends to a large extent on the
supply air terminal device (ATD). Five different ATDs were developed, tested and compared. A typical office workplace consisting of a desk
with mounted ATDs was simulated in a climate chamber. A breathing thermal manikin was used to simulate a human being. Experiments at
room air temperatures of 26 and 20 8C and personalized air temperatures of 20 8C supplied from the ATDs were performed. The flow rate of
personalized air was changed from less than 5 up to 23 l/s. Tracer gas was used to identify the amount of personalized air inhaled by the
manikin as well as the amount of exhaled air re-inhaled. The heat loss from the body segments of the thermal manikin was measured and used
to calculate the equivalent temperature for the whole body as well as segments of the body. An index, personal exposure effectiveness, was
used to assess the performance of ATDs in regard to quality of the air inhaled by the manikin. The personal exposure effectiveness increased
with the increase of the airflow rate from the ATD to a constant maximum value. A further increase of the airflow rate had no impact on the
personal exposure effectiveness. Under both isothermal and non-isothermal conditions the highest personal exposure effectiveness of 0.6 was
achieved by a vertical desk grill followed by an ATD designed as a movable panel. The ATDs tested performed differently in regard to the
inhaled air temperature used as another air quality indicator, as well as in regard to the equivalent temperature. The results suggest that PV may
decrease significantly the number of occupants dissatisfied with the air quality. However, an ATD that will ensure more efficient distribution
and less mixing of the personalized air with the polluted room air needs to be developed.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Personalized ventilation; Air distribution; Air quality; Thermal comfort
1. Introduction
Total-volume ventilation and air-conditioning of rooms is
at present the method most used in practice. Mixing and
displacement room air distribution are the main principles
applied. Displacement ventilation has been shown to provide
occupants with better air quality, especially in rooms with
non-passive, heated contaminant sources [1]. However, unlike
mixing ventilation, vertical air temperature difference in
rooms with displacement ventilation exists with low air
temperatures near the floor. High air velocities often exist
near the floor as well. Thus, if not well designed, the risk of
local discomfort due to draught and vertical temperature
difference in rooms with displacement ventilation is high
[2,3]. Studies [4,5] show that the same air is perceived by
people as being of poor quality at a high air temperature but of
better quality at a low air temperature. Therefore, assessment
of quality of the inhaled air by measurements should be based
on its temperature, humidity and gas concentration [6]. In both
rooms with mixing ventilation and those with displacement
ventilation, the temperature of the air that will reach the
breathing zone of occupants (especially under summer con-
ditions) will be relatively high. This will affect occupants’
satisfaction with the perceived air quality. A field study in
rooms with displacement ventilation found that almost 50% of
the occupants were not satisfied with the indoor air quality
[7,8]. The air quality perceived by the occupants will improve
when more fresh air is supplied to the space. However, this
may cause draught discomfort for some occupants.
In practice, rooms are used by occupants with different
physiological and psychological response, clothing, activity,
individual preferences to the air temperature and movement,
time response of the body to changes of the room tempera-
ture, etc. Thus, total-volume ventilation has limitations and
is often unable to provide each occupant simultaneously
with high level of thermal comfort and air quality. Often,
occupants in rooms with mixing or displacement ventilation
have to compromise between preferred thermal comfort and
perceived air quality, because some people are very sensitive
to air movement while others are sensitive to the air quality.
The compromise is different for each occupant and also dif-
fers in time. The disadvantage of the total-volume ventilation
Energy and Buildings 34 (2002) 829–836
Abbreviations: PV, personalized ventilation; ATD, air terminal device* Corresponding author.
E-mail address: [email protected] (A.K. Melikov).
0378-7788/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 7 7 8 8 ( 0 2 ) 0 0 1 0 2 - 0
principle is that often room air movement is changed due to
furniture rearrangement and this may increase occupants’
complaints of draught and/or poor air quality.
Environmental conditions acceptable for most occupants
in a room may be achieved by providing each occupant with
the possibility to generate and control his/her own preferred
local environment. Personalized ventilation (PV) aims to
provide each occupant with personalized clean air direct to
the breathing zone. Each occupant can control the environ-
ment at his/her workplace. Thus, occupants’ satisfaction and
productivity can be increased as a result of improved air
quality, thermal comfort and control over the environment.
Energy use may be lowered, depending on system design
and operation. In order to improve the quality of the inhaled
air, clean personalized air should reach the breathing zone
unmixed with the polluted room air. The velocity should be
low in order to avoid draught.
In a calm, comfortable environment, upward free convec-
tion movement exists around the human body due to the
temperature difference between the room air and the surface
of the clothing and of the skin of bare body parts. The free
convection flow becomes weak when the temperature differ-
ence is small. The airflow is slow and laminar with a thin
boundary layer at the lower body parts, and fast and turbulent
with a thick boundary layer at the height of the head. The free
convection movement will change the skin temperature due to
convection heat transfer and will thus affect man’s thermal
sensation. The free convection flow transports air, which
might be contaminated from the lower part of the space,
upward to the breathing zone. It also carries the bioeffluents
and vapor emitted from the human body. Furthermore, occu-
pants’ breathing generates an air movement due to exhalation.
The interaction between the airflow from the PV, the free
convection flow around the body and the airflow of exhalation
is of primary importance for occupants’ thermal comfort and
inhaled air quality [6]. The interaction is influenced by the
strength of the free convection flow and the thickness of its
boundary layer, the characteristics of the invading flow gen-
erated by the PV (mean velocity, velocity profile, turbulence
intensity, direction, temperature, etc.), the posture, shape and
area of the occupant’s body exposed to the invading flow, the
clothing design, etc.
The supply air terminal device (ATD) is an essential part
of any PV system. It plays a major role in the distribution of
air around the human body and thus, determines occupants’
thermal comfort and perceived air quality.
A study on performance of five different supply ATDs in
regard to occupants’ thermal comfort and inhaled air quality
was designed and performed. The results are presented in
this paper.
2. Experimental method
2.1. Experimental facilities and conditions
A typical office workplace, consisting of a desk with a
personal computer, was simulated in a climate chamber. The
ATDs were mounted on the desk. The climate chamber was
5 m � 6 m � 2:5 m. It is possible to maintain temperature
and relative humidity of the air inside the chamber with a
high degree of accuracy. The velocity generated by the
ventilation system of the chamber is lower than 0.06 m/s.
A detailed description of the climate chamber is given in [9].
A breathing thermal manikin consisting of 16 body seg-
ments was used to simulate a human being. The manikin sat on
an office chair in front of the computer at a distance of
approximately 0.15 m from the desk. During most of the
tests, it was in an upright position. However, several tests were
also performed with the manikin leaning forward (approxi-
mately 0.1 m from the upright position). The surface tem-
perature of the manikin was controlled to be equal to the skin
temperature of an average person in thermal comfort and heat
loss from each body segment was measured. The manikin was
dressed as specified later in this section.
The manikin was equipped with an artificial lung that simu-
lates the human breathing function. The breathing cycle (inha-
lation, exhalation and pause) and the amount of respiration air as
well as temperature and humidity of the exhaled air were con-
trolled. The artificial lung was adjusted to simulate breathing
Nomenclature
cE;N2O concentration of N2O in exhaled air (ppm)
cI concentration of SF6 in inhaled air (ppm)
cI,0 concentration of SF6 in inhaled air without
personalized ventilation (ppm)
cI;SF6SF6 concentration in inhaled air (ppm)
cI;N2O concentration of N2O in inhaled air (ppm)
cP concentration of SF6 in inhalation zone (ppm)
cPV concentration of SF6 in personalized air (ppm)
cPV;SF6SF6 concentration in personalized air (ppm)
cR concentration of SF6 in exhaust room air
(ppm)
cS concentration of SF6 in supply room air (ppm)
cS;SF6SF6 concentration in air supplied to the
chamber (ppm)
C thermal resistance offset of skin temperature
control system of thermal manikin equal to
0.054 (K m2/W)
Qt measured sensible heat loss (W/m2)
teq manikin-based equivalent temperature (8C)
Dteq,h difference in manikin-based equivalent tem-
perature for the head (8C)
Dtinh difference in temperature of inhaled and room
air (8C)
Greek letters
eP personal exposure effectiveness
eRI re-inhaled exposure index
eV ventilation effectiveness
830 A.K. Melikov et al. / Energy and Buildings 34 (2002) 829–836
of an average sedentary person performing light physical work:
breathing frequency of 10 times/min, volume of 6 l/min, breath-
ing cycle of 2.5 s inhalation, 2.5 s exhalation and 1.0 s break,
and exhaled air with a temperature of 34 8C and a relative
humidity of 95%. The air was exhaled from the nose and
inhaled through the mouth. A mixture of 90% CO2 and 10%
N2O (dinitrogen oxide) was used to mark the air exhaled by the
manikin. The two gases have the same physical properties
(same density) and do not react with each other [6]. The
temperature of the inhaled air was measured by a fast thermistor
mounted inside the mouth cavity of the manikin. The breathing
manikin is described in detail by Melikov et al. [6,10].
Five different ATDs were developed and studied. The
ATDs are schematically shown in Fig. 1. The movable panel
(MP) allows the direction of the personalized airflow in
relation to the occupant to be changed within a wide range.
The results discussed in this paper were obtained with the
MP positioned 0.2 m in front of the manikin’s face and 0.3 m
above the nose. The flow of personalized air was directed
toward the manikin’s face. The direction of the personalized
airflow from the computer monitor panel (CMP), mounted
on the monitor at a distance of 40 cm from the edge of the
desk, could be changed on a vertical plane. The results for
this ATD reported in the following were obtained when it
was inclined at 208 toward the manikin (isothermal condi-
tions) and when inclined 108 apart from the manikin (non-
isothermal conditions). The vertical desk grill (VDG) and
the horizontal desk grill (HDG) mounted at the edge of the
desk provide, respectively, a vertical and a horizontal flow of
personalized air direct to the breathing zone of the occupant
or against the occupant’s body. During the tests, two of the
ATDs, namely CMP and VDG, were tested also in modified
versions, CMP-mod and VDG-mod having a 50% larger and
a 50% smaller cross-sectional area, respectively. The last
ATD, the personal environments1 module (PEM) consists
of two nozzles mounted at the two edges of the desk. They
allow for changes of the direction of the personalized air in
horizontal and vertical planes. In this experiment, the noz-
zles were located at a distance of 0.8 m from the manikin,
generating air jets directed toward its face. This device is
described in detail in [11,12], is available on the market, and
was provided by the manufacturer.
Isothermal (winter) conditions with an operative tempera-
ture of 20 8C and a personalized air temperature of 20 8C and
non-isothermal (summer) conditions with an operative tem-
perature of 26 8C and a personalized air temperature of 20 8Cwere simulated in the climate chamber (the room air tem-
perature was equal to the mean radiant temperature). Experi-
mentswereperformedatairflowratesof less than5upto23 l/s.
During the ‘‘summer’’ experiments, the manikin was dressed
with underwear, short-sleeved T-shirt, pants, socks and shoes,
giving a total clothing insulation of 0.062 m2�8C/W (0.4 clo)
[13]. During the ‘‘winter’’ experiments, the clothing garment
was underwear, short-sleeved T-shirt, long-sleeved shirt,
sweatshirt, pants, socks and shoes, providing a total thermal
insulation of 0.155 m2�8C/W (1.0 clo). In both cases, the
manikin was seated on the office chair with an additional
thermal insulation of 0.023 m2�8C/W (0.15 clo).
2.2. Measuring procedure
A constant dose of tracer gas, sulphur hexafloride (SF6),
was used to mark continuously the air in the chamber.
Complete mixing of the tracer gas with the air supplied to
the chamber was achieved as the tracer gas was dosed to the air
long before it entered the chamber. The personalized air was
kept free of the tracer gas. As already discussed, a mixture of
CO2 and N2O was dosed in the air exhaled by the manikin.
The concentration of SF6 and N2O was measured in the air
inhaled by the breathing thermal manikin, in the air supplied
to the climate chamber and in the air supplied by the PV
system. The measurements were made by a gas monitor
based on the photo-acoustic infrared detection method of
measurement. The concentration measured under steady-
state conditions during the last 30 min of each experiment
was averaged and analyzed.
During the experiments the inhalation took 2.5 s of a 6 s
breathing cycle; only the temperature measured during the
inhalation period was averaged and used in the analyses.
2.3. Criteria for assessment
Several indices have been used to assess the air distribu-
tion efficiency in rooms and around human body. Ventilation
effectiveness, eV, is widely used:
eV ¼ cR � cS
cP � cS
(1)
where cR is concentration of pollution in exhaust room air, cS
the concentration of pollution in supply room air, cP the
concentration of pollution in the inhalation zone.
This index is indefinitely large when cS and cP are equal.
Furthermore, it is difficult to compare the performance of
different ATDs based on ventilation effectiveness when a
large portion of personalized air is inhaled. Brohus [14]
Fig. 1. Air terminal devices studied: movable panel (MP), computer
monitor panel (CMP), vertical desk grill (VDG), horizontal desk grill
(HDG) and personal environments1 module (PEM).
A.K. Melikov et al. / Energy and Buildings 34 (2002) 829–836 831
defined the breathing (inhalation) zone as a semisphere with
a radius of 0.3 m. However, as shown by Melikov et al. [6]
this definition is not accurate, especially with PV, due to the
complex airflow conditions.
The aim of PV is to provide occupants with 100% clean
personalized air. In order to assess easily the performance of
PV with different ATDs, an index, personal exposure effec-
tiveness, eP, expressed as the percentage of personalized air
in inhaled air, was used [22]:
eP ¼ cI;0 � cI
cI;0 � cPV
(2)
where cI,0 is the concentration of pollution in the inhaled air
without PV, cI the concentration of pollution in the inhaled
air, cPV is concentration of pollution in personalized air.
This index is equal to one when 100% of personalized air
is inhaled and it is equal to zero if no personalized air is
inhaled. A carefully designed and properly maintained PV
system should provide clean air with no pollutants, i.e.
cPV ¼ 0. For this condition, Eq. (2) can be simplified to:
eP ¼ cI;0 � cI
cI;0(3)
During the experiments without PV, the SF6 concentration
in the climate chamber was uniform and the SF6 concentra-
tion in the inhaled air was equal to the SF6 concentration in
the air supplied to and exhausted from the chamber. There-
fore, in the present study, eP was modified as:
eP ¼ cS;SF6� cI;SF6
cS;SF6� cPV;SF6
(4)
where cS;SF6is the SF6 concentration in the air supplied to the
chamber (ppm), cPV;SF6the SF6 concentration in the perso-
nalized air (ppm), cI;SF6the SF6 concentration in the inhaled
air (ppm).
The re-inhaled exposure index [6] was used to assess the
amount of exhaled air re-inhaled by an occupant due to the
interaction of airflow of personalized air and airflow of
exhalation:
eRI ¼cI;N2O
cE;N2O
(5)
where cI;N2O is the concentration of N2O in the inhaled air
(ppm), cE;N2O the concentration of N2O in the exhaled air
(ppm).
Manikin-based equivalent temperature, teq, was used to
assess the performance of the ATDs in regard to occupants’
thermal comfort [15]. The manikin-based equivalent tem-
perature is defined as the temperature of a uniform enclosure
in which a thermal manikin with realistic skin surface
temperature would lose heat to the environment at the same
rate as it would in the actual environment. In this study, the
manikin-based equivalent temperature, teq, was calculated
by the following expression:
teq ¼ 36:4 � CQt (6)
where 36.4 is the deep body temperature (8C), Qt the
measured sensible heat loss (W/m2), C the thermal resis-
tance offset of the surface temperature control system of the
thermal manikin equal to 0.054 (K m2/W).
3. Results and discussion
The purpose of PV is to achieve the highest possible
quality of the air inhaled by occupants by providing clean air
at the breathing zone. Thus, the quality of the inhaled air
when PV is applied should be better than with a total-volume
ventilation system (mixing and displacement). Ideally, the
inhaled air should consist of 100% personalized air, i.e.
eP ¼ 1.
Fig. 2 compares the ventilation effectiveness obtained
with the tested ATDs under isothermal conditions at differ-
ent flow rates. The results show that the ventilation effec-
tiveness increases with the flow rate. However, it is rather
difficult to find the amount of personalized air inhaled by the
manikin as well as to rank the performance of the tested
ATDs. Therefore, the personal exposure effectiveness index
(Eq. (2)) was used in this study.
The personal exposure effectiveness of the ATDs is
compared in Figs. 3 and 4 for isothermal and non-isothermal
conditions, respectively. The personal exposure effective-
ness as a function of the flow rate is shown in the figures. The
performance of the ATDs was different and it changed with
the flow rate. It was also affected by the air temperature
conditions. The results showed that an increase in the flow
rate from zero has no immediate effect on the personal
exposure effectiveness. Only when a certain initial flow rate
is reached does the personal exposure effectiveness for most
of the ATDs studied start to increase rapidly with the flow
rate, i.e. the personalized air penetrates the free convection
flow around the body and reaches the face of the manikin.
The initial flow rate, at which the personal exposure effec-
tiveness starts to increase, depends on the distance of the
ATD from the occupant as well as on the design and size
(cross-section) of the ATD. It is also clear from the results
Fig. 2. The ventilation effectiveness obtained with the tested ATD as a
function of the flow rate of personalized air under isothermal conditions:
personalized air temperature and room air temperature 20 8C.
832 A.K. Melikov et al. / Energy and Buildings 34 (2002) 829–836
shown in the figures that the increase in the personal
exposure effectiveness becomes marginal at a certain flow
rate until it reaches a steady-state maximum value. The flow
rate at which the maximum personalized exposure effec-
tiveness is achieved is referred to in this paper as a minimum
flow rate.
The results of this investigation showed that for the flow
rates studied (up to 23 l/s) the ATDs were not able to provide
100% of personalized air in the manikin’s inhalation. The
highest personal exposure effectiveness, i.e. the highest
amount of personalized air in the inhaled air, was reached
by CMP-mod, 0.75 at a rather high flow rate of 21 l/s under
non-isothermal conditions. The performance of this ATD is
discussed later in this paper.
The maximum personal exposure effectiveness achieved
by the VDG was 0.6 at a minimum airflow rate of approxi-
mately 10 l/s. The minimum flow rate needed in order to
achieve maximum personal exposure effectiveness for the
remaining ATDs was: 5 l/s for HDG, 10 l/s for PEM and
20 l/s for CMP and MP. The performance of VDG and MP
was high for a relatively wide range of airflow rates. These
two ATDs, especially VDG, performed best under non-
isothermal conditions. Faulkner et al. [12] compared the
performance of three ATDs similar to VDG, HDG and PEM
based on air change effectiveness and pollutant removal
efficiency indices. These indices were calculated based on
data from concentration measurements at several points
around a heated but not breathing manikin, including a
point 3 cm below the tip of the nose. They also identified
that VDG and HDG provided more personalized air to the
face of the manikin than PEM. PEM located far from the
manikin generates a turbulent jet, which is fully developed
and therefore, well mixed with the polluted surrounding air
by the time it reaches the face of the manikin.
The size of the ATDs had a different impact on their
performance. As already mentioned, two of the tested ATDs,
VDG and CMP, were modified: the cross-sectional area of
VDG was decreased by 50% and the cross-sectional area of
CMP was increased by 50%. The two new ATDs are referred
to in the following as VDG-mod and CMP-mod. Fig. 5
compares the performance of the modified and the original
ATD under isothermal conditions. The comparison shows
that for the VDG, the change in the size had almost no
impact on the personalized exposure effectiveness. How-
ever, the change of the cross-sectional area of the CMP had a
considerable impact on the performance of the ATD. Much
greater personal exposure effectiveness, up to 0.75, was
achieved by enlargement of this ATD. However, the results
in the figure also show that much higher airflow rates were
needed for this ATD in order for it to perform better than the
rest of the tested ATDs. In fact, personalized air was inhaled
by the manikin first when the flow rate from CMP-mod
increased above 13 l/s. A considerable difference in the
personal exposure effectiveness was observed for CMP-
mod under both isothermal and non-isothermal conditions.
Under non-isothermal conditions the personal exposure
effectiveness with this ATD was below 0.1 for the whole
range of tested airflow rates. Smoke visualization indicated
that under non-isothermal conditions the low-velocity
Fig. 3. Personal exposure effectiveness as a function of the airflow rate
from ATDs. Isothermal (winter) conditions: room air temperature 20 8C,
personalized air temperature 20 8C. Horizontal desk grill (HDG), vertical
desk grill (VDG), personal environments1 module (PEM), computer
monitor panel (CMP) and movable panel (MP).
Fig. 4. Personal exposure effectiveness as a function of the airflow rate
from ATDs. Non-isothermal (summer) conditions: room air temperature
26 8C, personalized air temperature 20 8C. Horizontal desk grill (HDG),
vertical desk grill (VDG), personal environments1 module (PEM),
computer monitor panel (CMP) and movable panel (MP).
Fig. 5. Comparison of the performance of VDG and VDG-mod and CMP
and CMP-mod under isothermal conditions. VDG-mod has a 50% smaller
cross-sectional area than VDG and CMP-mod has a 50% larger area than
CMP.
A.K. Melikov et al. / Energy and Buildings 34 (2002) 829–836 833
airflow from CMP-mod dropped on the desk and the perso-
nalized air mixed with the room air. The results of the
comparison shown in Fig. 5 demonstrate the importance
of the airflow interaction at the breathing zone; this must be
carefully considered during the design of PV systems in
practice. It was found that the relationships presented in
Figs. 3, 4 and 5 depend on the posture of the manikin.
Experiments on this effect are in progress.
The present standards and guidelines recommend ventila-
tion rates from 4 to 10 l/s occupant in offices without
smoking and up to 30 l/s occupant when some smoking is
allowed [16,17]. ATD with a large outlet, providing laminar
airflow with a low velocity that will not cause draught
discomfort for the occupants, has been previously suggested
by Melikov [18] as one of the design recommendations for
PV systems. Such an ATD will make it possible to provide
the high airflow rate of 30 l/s occupant, as recommended in
the guidelines [17], at relatively low velocity without local
thermal discomfort. In practice, however, most often 10 l/s
per occupant may be required. Under these conditions, better
results will be achieved by a relatively small ATD, such as
VDG, compromising for the inhaled air quality.
The different airflow distribution achieved by the tested
ATDs had a significant impact on the temperature of the
inhaled air as well as on the amount of re-inhaled air. The
ventilation effectiveness (eV), the personal exposure effec-
tiveness (eP), the re-inhaled exposure index (eRI, in %), and
the difference in the temperature of the inhaled air with and
without PV (Dtinh), for the tested ATDs under both isother-
mal and non-isothermal conditions, are listed in Table 1(a
and b). The difference in the equivalent temperature for
the head (Dteq,h), identified with and without PV, is listed in
the table as well. This parameter will be discussed later in
the paper. The parameters are listed in the table for two flow
rates of personalized air. The first flow rate, 10 l/s, represents
the minimum amount of outdoor air typically required by the
ventilation standards and guidelines [16,17] per building
occupant today. The second flow rate corresponds to the
minimum flow rate of personalized air needed to achieve
maximum personal exposure effectiveness with each of the
tested ATDs. For VDG and PEM, these two flow rates are
identical.
Similar to the findings in [6], the results of this study show
that a rather small amount of exhaled air (<1%) was re-
inhaled with the tested ATDs. Nevertheless, in this regard
two of the tested ATDs, VDG and PEM performed best; less
than 0.3% of the exhaled air was re-inhaled by the manikin
with this ATD. For CMP and MP, the amount of re-inhaled
air increased with the increase of the flow rate. The opposite
tendency was observed for PEM. The amount of re-inhaled
air was higher under non-isothermal conditions in compar-
ison with isothermal conditions for all ATDs.
In a calm environment, people inhale mainly the air from
the free convection flow around the body. Therefore, the
temperature of the inhaled air is higher than the ambient air
temperature. The inhaled air temperature without PV mea-
sured during this experiment was 21.6 8C at a room air
temperature of 20 8C and 28.1 8C at a room air temperature
of 26 8C. The results of the present study show that the
temperature of the inhaled air generally decreased with an
increase in the flow rate from the ATDs, under both iso-
thermal and non-isothermal conditions. The personalized air
was able to penetrate the free convection flow around the
body. However, under isothermal conditions, the inhaled air
temperature with PV was measured only slightly lower than
the inhaled temperature without PV and nearly the same for
Table 1
Ventilation effectiveness (eV), personal exposure effectiveness (eP), re-inhaled exposure index (eRI), inhaled air temperature difference (Dtinh) and manikin-
based equivalent temperature difference for the head (Dteq,h) identified with the tested ATDs under isothermal and non-isothermal conditions
Air terminal device Flow rate of personalized air (l/s) eV eP eRI Dtinh (8C) Dteq,h (8C)
(a) Isothermal (winter) conditionsa
HDG 10 1.61 0.38 0.19 �0.6 �4.5
5 1.54 0.35 0.21 �0.3 �0.8
VDG 10 1.92 0.48 0.03 �0.6 �3.9
PEM 10 1.45 0.31 0.20 �1.0 �3.1
CMP 10 1.35 0.26 0.46 �0.8 �0.8
20 1.82 0.45 0.35 �0.9 �3.1
MP 10 1.69 0.41 0.56 �0.3 �0.7
20 2.38 0.58 0.66 �0.5 �2.5
(b) Non-isothermal (summer) conditionsb
HDG 10 1.30 0.23 0.49 �2.2 �3.2
5 1.32 0.24 0.48 �2.1 �0.7
VDG 10 2.27 0.56 0.30 �5.1 �6.0
PEM 10 1.52 0.34 0.25 �3.3 �3.1
CMP 10 1.39 0.28 0.67 �2.9 �2.0
20 1.59 0.37 0.75 �4.5 �3.6
MP 10 1.47 0.32 0.61 �3.2 �2.4
20 2.00 0.50 0.74 �4.6 �4.2
aRoom air 20 8C, 30% RH; personalized air 20 8C, 30% RH.bRoom air 26 8C, 30% RH, personalized air 20 8C, 30% RH.
834 A.K. Melikov et al. / Energy and Buildings 34 (2002) 829–836
all ATDs studied. The inhaled air temperature decreased
substantially by increasing the temperature difference
between the personalized air and the room air
(Table 1(b)). Under non-isothermal conditions (room air
temperature 26 8C), the ATD with the greatest ability to
decrease the inhaled air temperature was VDG. The inhaled
air temperature decreased by 5 8C from the inhaled air
temperature without PV. The decrease of inhaled air tem-
perature by MP and PEM was also high, whereas HDG
decreased the inhaled air temperature by only about 2 8C.
Increasing the temperature difference, the inhaled air tem-
perature may further be decreased; however, this may
decrease the amount of personalized air in the inhaled air,
due to a buoyancy effect, and may also cause thermal
discomfort for the occupant due to local cooling of the body.
The quality of the inhaled air is the most important
criterion for performance assessment of PV systems. How-
ever, it is also important that at comfortable temperatures the
PV does not affect occupants’ thermal comfort and that in a
warm environment it provides the body with cooling. As
already mentioned, the manikin-based equivalent tempera-
ture was used in the present study to assess the performance
of the ATDs in respect to occupants’ thermal comfort. The
equivalent temperature for the whole body and some of the
16 body segments decreased when the flow rate of perso-
nalized air increased. The ability of the ATDs tested to affect
the whole-body heat loss was evaluated by calculating the
difference in the manikin-based equivalent temperature
caused by the PV and the equivalent temperature measured
without a PV system. The results obtained at the minimum
flow rate for each of the tested ATDs are compared in Fig. 6.
The equivalent temperature measured without PV (reference
condition) was 21.1 and 26.6 8C at room temperatures of 20
and 26 8C, respectively.
The comparison in Fig. 6 shows that under isothermal
(winter) conditions the cooling effect is low, 0.4 8C for HDG
and CMP, and 0.8 8C for VDG and PEM. Thus, occupants
may feel slightly cooler with VDG and PEM. Occupants
may decrease the flow rate through these two ATDs, which
will improve their thermal comfort, but will also decrease
the personal exposure effectiveness, i.e. the quality of the
inhaled air. Under non-isothermal (summer) conditions (26/
20 8C), the cooling effect of all ATDs, except MP, is around
1 8C. Under these conditions, the cooling effect of MP is
almost twice as high, 1.9 8C. This cooling effect, even
though small, may be sufficient for many occupants who
need only minor adjustment of the local thermal environ-
ment. Tszuki et al. [11] tested two ATDs and reported
differences in the cooling power as well. A decrease of
the personalized air temperature (if possible) can further
increase the cooling effect of the body caused by the PV
system.
Draught, defined as unwanted local cooling of the body
due to air movement, is one of the most frequent complaints
in practice. Studies show that the neck and the feet are the
body parts most sensitive to draught [19]. The body parts
directly exposed to the personalized air can be cooled more
than is acceptable for the occupants. For example, if occu-
pants’ arms and hands are exposed to cool air supplied
upward from the edge of the table, the occupant will feel
uncomfortable and his/her performance may decrease even
when the whole body feels thermally comfortable. The
draught sensation increases when mean velocity and turbu-
lence intensity increase and air temperature decreases.
Furthermore, airflow toward the front of the body causes
less discomfort than airflow from the back [20,21]. The
tested ATDs distribute the air with relatively high velocity
mainly at the front of the body, i.e. the head, the chest, the
arms and the hands. For most of the tested ATDs (except
HDG), the equivalent temperature measured for the head at
the minimum airflow needed to achieve maximum perso-
nalized exposure effectiveness was lower than the other
body segments of the manikin, i.e. the head was cooled
most. The performance of the tested ATDs in this regard can
be seen in Table 1(a and b). The difference in the equivalent
temperature for the head (Dteq,h), measured with PV and
without PV is listed in the table. The greatest cooling effect
was measured with VDG under both isothermal and non-
isothermal conditions. The cooling effect measured with
CMP and MP under non-isothermal conditions was high as
well. In general, it may be expected that occupants, in order
to decrease draught discomfort, will use PVat low flow rates,
and this will cause a decrease in the amount of inhaled
personalized air (the personal exposure effectiveness
decreases when the flow rate decreases) and an increase
in the inhaled air temperature. These changes will have a
negative impact on the quality of the air as perceived by
occupants.
In general, it may be expected that two of the tested ATDs,
namely VDG and MP, will perform well in practice since
they will not affect occupants’ general thermal sensation
significantly and will provide more personalized air in
Fig. 6. Decrease in the whole-body manikin-based equivalent temperature
caused by personalized ventilation from the reference condition (without
personalized ventilation). The effect of the tested ATDs is compared. The
comparison is made for the minimum flow rate (shown in the figure)
needed to achieve maximum personal exposure effectiveness. Winter
conditions (room and personalized air temperature of 20 8C) and summer
conditions (room air temperature of 26 8C and personalized air
temperature of 20 and 23 8C) are compared.
A.K. Melikov et al. / Energy and Buildings 34 (2002) 829–836 835
inhalation. Occupants may reduce the warmth sensation in
summer using the cooling power of MP. However, human
response to these designs needs to be identified before
applying them in practice. This research is in progress.
The tests performed and reported in this paper were limited
to only a few of many possible conditions that would occur in
practice. The performance of HDG and VDG will depend on
the posture of the occupant (seated upright or leaning forward
or backward) which may change in time. In the case of MP, the
preferences of the occupants in regard to the distance between
their face and the ATD may be different. Occupants may
change flow rate, temperature and direction of personalized
air during the day and this will affect the performance of PV. It
may be possible in the future to introduce a control system that
will to some extent compensate for these changes. The results
of this study reveal that further research is needed in order to
develop ATDs with better performance than those tested and
reported in this paper.
4. Conclusions
The performance of five ATDs for a PV system was tested
in regard to occupants’ thermal comfort and quality of
inhaled air. A breathing thermal manikin was used to
simulate a human being. Both isothermal and non-isother-
mal conditions were examined.
An index, personal exposure effectiveness, expressed as
the percentage of personalized air in inhaled air, was used to
assess the performance of the tested ATDs. The personal
exposure effectiveness increased with the increase of the
airflow rate from the ATDs to a constant maximum value,
which was not affected by a further increase of the airflow.
Under both isothermal and non-isothermal conditions and an
airflow rate below 15 l/s, the highest personal exposure
effectiveness, 0.6, was achieved by a VDG providing per-
sonalized air upward to the occupant’s face. A MP allowing
for a change of airflow direction in relation to the occupant,
had a high performance as well.
The amount of exhaled air re-inhaled by the manikin was
rather small with all tested ATDs.
The temperature of the inhaled air decreased with the
increase of the personalized airflow. The lowest temperature
of the inhaled air was achieved by VDG.
The VDG provided greatest cooling of the manikin’s
head. In practice, this may cause draught discomfort for
the occupants.
Further research on the development of ATDs that gen-
erate airflow with minimum mixing of the personalized air
with the polluted room air is recommended.
Acknowledgements
This research was performed with support from the
Danish Technical Research Council (STVF).
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