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Kotopouleas, Alkis and Nikolopoulou, Marialena (2016) Thermal comfort conditions in airport
terminals: Indoor or transition spaces? Building and Environment, 99 . pp. 184-199. ISSN
0360-1323.
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Building and Environment 99 (2016) 184e199
Contents lists available at ScienceDirect
Building and Environment
journal homepage: www.elsevier.com/locate/buildenv
Thermal comfort conditions in airport terminals: Indoor or transition
spaces?
Alkis Kotopouleas*, Marialena Nikolopoulou
Centre for Architecture and Sustainable Environment, Kent School of Architecture, University of Kent, Canterbury, CT2 7NZ, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 October 2015
Received in revised form
10 January 2016
Accepted 21 January 2016
Available online 22 January 2016
This paper reports on the investigation of the thermal comfort conditions in three airport terminals in
the UK. In the course of seasonal field surveys, the indoor environmental conditions were monitored in
different terminal areas and questionnaire-guided interviews were conducted with 3087 terminal users.
The paper focuses on the thermal perception, preference and comfort requirements of passengers and
terminal staff. The two groups presented different satisfaction levels with the indoor environment and
significant differences in their thermal requirements, while both preferring a thermal environment
different to the one experienced. The thermal conflict emerges throughout the terminal spaces. The
neutral and preferred temperatures for passengers were lower than for employees and considerably
lower than the mean indoor temperature. Passengers demonstrated higher tolerance of the thermal
conditions and consistently a wider range of comfort temperatures, whereas the limited adaptive capacity for staff allowed for a narrower comfort zone.
© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/).
Keywords:
Airport terminal
Passengers and staff
Thermal comfort
Neutral temperature
Preferred temperature
Comfort zone
1. Introduction
Airport terminals are subject to frequent internal change and
external growth in response to the increasing passenger volumes
and the evolving nature of aircraft design. The ensuing increase in
energy demand has turned them to very energy-intensive environments and one of the greatest energy-consuming centres per
square kilometre on our planet [1]. The energy use is de-facto
comparable to that of small cities. The typical electrical energy
used in a major airport lies between 100 and 300 GWh/year, which
corresponds to the consumption of 30,000 to 100,000 households
[2]. Terminal buildings use big amounts of energy for lighting,
heating, ventilation, air conditioning, and conveyance systems.
They are characteristic of the large volume of spaces, often with
non-uniform heat gains and extensive glazing areas (e.g. glass
curtain walls) aimed at providing natural light and aesthetically
attractive facilities. The energy consumed by the HVAC systems can
exceed 40% of the total electrical energy, while excluding smaller
systems (e.g. domestic hot water) they consume nearly all the
natural gas used at an airport [3].
Due to the large differences in energy demand among airports,
* Corresponding author.
E-mail address: ak497@kent.ac.uk (A. Kotopouleas).
there is a variety of low and high-cost energy efficiency approaches
for this type of facility (periodical energy auditing, solar gain control, thermal energy storage, CHP and CHCP systems, renewable
energy sources, etc.) [3,4]. Along with the respective energy strategy implemented, energy savings can be achieved and maximised
through the fine-tuning of environmental controls for the provision
of indoor comfort conditions, particularly adjustments to space
temperature setting, as less energy would be required to maintain a
broader range of indoor temperatures. Reducing the gap between
outdoor temperature and indoor climate set-points, however, requires the consideration of the comfort requirements of the large
and diverse population typically held in these buildings.
Decades of thermal comfort research in different operational
contexts has revealed the complexity of field. Thermal comfort,
‘that condition of mind which expresses satisfaction with the
thermal environment’ [5,6] is affected by a range of parameters
both environmental (i.e. air and mean radiant temperature, relative
humidity, air movement) and personal (i.e. clothing insulation and
metabolic rate), maintaining a constant deep core temperature of
around 37 C, balancing heat losses and heat gains from the surrounding environment. This thermal exchange between the human
body and the surrounding environment has formed the basis for
current thermal standards [6,7].
Field studies, predominantly in offices and dwellings, have
demonstrated that occupants can be thermally satisfied with
http://dx.doi.org/10.1016/j.buildenv.2016.01.021
0360-1323/© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
conditions falling outside the boundaries designated by the heatbalance approach [8e10], by undertaking a range of actions to
maintain or restore their comfort. The adaptive approach to thermal comfort has highlighted that occupants can take various actions to improve their comfort state either through appropriate
control, or taking personal actions. Individual control is critical to
occupant comfort and satisfaction [11,12] and the impact of
perceived control in the determination of thermal comfort assessments has been shown to be of equal importance to the thermal
variables [13]. The personal actions include changes in clothing
levels as well as posture and activity. Clothing adjustment is among
the principal modes of adaptation, shown to moderate changes of
thermal sensation with climate [14e16] while being significantly
related to the indoor mean operative temperature [17]. Changes in
posture are also an important modifier of thermal comfort; a shift
from seated to standing/walking activity increases the metabolic
rate by an average of 0.3 met, which ultimately results to a change
in preferred temperature of about 2.4 C [18]. By associating the
adaptive actions to the subjective assessments of the thermal
environment the adaptive theory links the comfort temperature to
the conditions experienced [19,20]. Along with the physical actions,
the adaptive approach has revealed that psychological parameters
also influence thermal comfort conditions, allowing for a wider
range of comfort temperatures [17,21].
Airport terminals are designed predominantly as indoor spaces,
while the overwhelming majority is people in transient conditions.
Thus they pose a particularly challenging environment, where the
indoor microclimatic conditions are expected to provide a
comfortable transient environment for passengers without
compromising a comfortable working environment for the smaller
number of terminal staff. A number of factors, however, including
dressing code, activity levels, dwell time and overall expectations
differentiate the adaptive capacity between the two groups and
consequently their comfort requirements. The diversity of spaces
and the heterogeneous functions across the different terminal
zones are further contributing factors to potential thermal comfort
conflicts.
There has been limited work, however, on the evaluation of the
thermal environment in airport terminals and the investigation of
the thermal comfort requirements for the different user groups.
Balaras et al. took spot measurements of the thermal and visual
conditions in three Greek airports for a week during summer. The
study reported lack of proper humidity control and problems with
temperature regulation in all three buildings, while through 285
questionnaires it highlighted the different satisfaction levels between passengers and staff with all IEQ parameters [22]. The
satisfaction with IEQ was also evaluated in eight Chinese airports
where subjective and objective data were collected over a year. The
study highlighted thermal issues such as overcooling and overheating in several terminal spaces, however, the buildings were
shown to underperform more in terms of acoustic environment
and indoor air quality [23]. Environmental and subjective data were
also collected from passengers in Terminal 1 at Chengdu Shuangliu
International Airport, China, over a period of two weeks in summer
and winter. Neutral temperature was 21.4 C in winter and 25.6 C
in summer, with the respective comfort zones at 19.2e23.1 C and
23.9e27.3 C. Based on 569 questionnaires, the study reported that
78.3% of passengers were generally satisfied with the thermal
environment and 95.8% considered the thermal conditions
acceptable [24]. Another study surveyed 128 staff and passengers in
the terminal of Ahmedabad airport, India, during the summer, and
found a very high comfortable temperature range in the airconditioned part of the building, 24e32 C [25]. Ramis and dos
Santos collected temperature and humidity data from three airports in Brazil. The temperature was found below the acceptable
185
levels, which could result in thermal discomfort particularly in
occasions of prolonged dwell times [26]. In general, time of exposure is important to the context of thermal comfort [27], as
discomfort is not viewed negatively if the exposure to it is short
[28] or the individual anticipates that it is temporary [21].
Currently, thermal comfort criteria for airport terminal buildings are provided by ASHRAE and CIBSE. ASHRAE's design criteria
suggest a temperature range of 23.0e26.0 C and a RH range of
30e40% in winter and 40e55% in summer [29], with an 80%
acceptability comfort zone. CIBSE [30] provides seasonal comfort
criteria for five terminal areas, allowing for different temperature
ranges in different facilities (Table 1).
The work presented in this paper focuses on evaluating thermal
comfort conditions in airport terminals in the UK, while also
identifying potential differences in the comfort requirements of the
main user groups. Borrowing from the methods and procedures of
thermal comfort studies in different operational contexts, it employs extensive field surveys with a large population sample in
different areas, in three airport terminal buildings in the UK.
2. Methodology
The methodology included extensive on-site surveys in three
airport terminals, London City Airport (LCY), Manchester Terminal
1 (MAN T1) and Manchester Terminal 2 (MAN T2). During the
week-long surveys, the indoor environmental conditions were
monitored across the different terminal spaces and questionnaireguided interviews were simultaneously conducted with terminal
users. Each terminal was surveyed in summer and winter in 2012
and 2013 to allow for the seasonal variations, daily from 5am to
9pm to obtain the peak and off-peak occupancy profiles.
2.1. Terminal buildings surveyed
The terminals surveyed were selected to represent buildings of
different size and typology (described in detail in Ref. [31]). The
small-scale terminal at LCY is a two-storey building of 10,000 m2
built in 1987. The linear terminal has 15 gate lounges distributed
predominantly across its two piers. In comparison with its peers,
the main terminal building is relatively small; if all the internal
walls were removed, a Boeing 747 (wingspan 64.4 m and length
70.7 m) would fit snugly nose to tail and wingtip to wingtip within
the external walls. LCY presents the highest degree of uniformity
compared to the interior of MAN T1 and MAN T2. Since 2012, it has
been the 15th busiest airport in the UK handling annually about 3
million passengers [32].
Manchester airport has been in the 3rd place since 2012, serving
around 20 million passengers a year [32]. The passenger-related
facilities in the significantly bigger MAN T1 and MAN T2 are
spread over a total floor area of 43,499 m2 and 26,063 m2
Table 1
Recommended comfort criteria for airport terminal spaces (CIBSE [30]).
Summera
Wintera
Activity (met)
Operative temperature
( C)
Baggage reclaim
Check-in areasc
Concourse (no seats)
Customs area
Departure lounge
a
b
c
21e25b
21e23
21e25b
21e23
22e24
12e19b
18e20
19e24b
18e20
19e21
1.8
1.4
1.8
1.4
1.3
For clothing insulation of 0.65 clo in summer and 1.15 clo in winter.
Based on PMV of ±0.5. At other cases based on PMV of ±0.25.
Based on comfort requirements of check-in staff.
186
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
respectively, excluding the car parks, conveyance systems and air
bridges, with an annual capacity of 11 and 8 million passengers per
year [33].
The five-storey MAN T1 is a large complex building that has
undergone consecutive overhauls and various expansions over the
years since its opening in 1962. As a result, the terminal comprises
an assortment of different terminal design trends with heterogeneous architectural features, housing a variety of spaces ranging
from the “boxed up” to modern styles. MAN T1 was the first terminal in Europe to incorporate the pier system and today it has 28
gate lounges along its finger and satellite piers. The newest among
the terminals in Manchester airport (1993), MAN T2, features the
most contemporary terminal design. Almost all the spaces are
open-plan with high floor-to-ceiling heights and abundance of
natural light through glazed curtain walls and rooflights. The fourstorey terminal utilises 17 gate lounges distributed across the two
diametrically opposed piers spanning from the central building.
Passenger dwell time is another principal differentiating factor
between the terminals. As a result of its small size and the focus on
business passengers, LCY provides short walking distances and fast
passenger processing that result in significantly shorter dwell
times, which can be down to 20 min from check-in to boarding.
All three terminals are mechanically ventilated. The indoor
environment in MAN T1 and MAN T2 is controlled through variable
refrigerant volume (VRV) and fan coil unit systems, with direct
expansion (DX) systems employed in smaller areas. In both terminals, the temperature set-point was fixed at 21.0 C throughout the
year. The spaces in LCY were conditioned by 13 air handling units
aiming for a temperature set-point of 20.0 C for winter and 23.0 C
for summer.
2.2. Environmental monitoring
For the population in transit, it was important to investigate the
immediate microclimate people experience [28,34,35]. A microclimatic monitoring station was designed to be easily transported
across the terminal spaces and dismounted for passing through
security screening when moving from landside to airside. The
equipment (Fig. 1a) consists of a data logging system, a shielded
temperature and humidity probe, an ultrasonic anemometer, a
black globe thermometer, a lux sensor and a CO2 sensor, all conforming to ISO 7726 [36]. The environmental parameters monitored included dry bulb and black globe temperature, relative
humidity, air movement, horizontal illuminance and carbon dioxide levels. The latter was used as an indicator of changes in occupancy. All parameters were measured at the average height of a
standing person, 1.7 m, and recorded at 1-min intervals. The spaces
monitored include check-in areas, security search areas, circulation
spaces, retail facilities, departures lounges, gates, baggage reclaim
areas and arrivals halls. Measurements were taken in different locations within a space to ensure readings are representative of the
conditions throughout the area under investigation, while interviews were carried out in close proximity to the equipment
(1.0e1.5 m). Due to security concerns it was not possible to leave
separate dataloggers to monitor temperatures in different spaces
concurrently.
2.3. Subjective data e questionnaire
A standardised questionnaire was developed to collect subjective data for the evaluation of comfort conditions. The questionnaire consisted of 31 questions and used a combination of openended, partially closed-ended and predominantly closed-ended
questions. Thermal sensation (TS) was assessed on the 7-point
ASHRAE scale (Fig. 1b) while a 5-point scale was used for thermal
preference (TP). Questions were also used for the evaluation of
other environmental parameters including air movement, humidity and lighting. Additional data collected include the activity level
during and 15 min prior to the questionnaire (150 met), clothing
insulation, time spent in the terminal, state of overall comfort and
demographic data. Interviewees were selected randomly to ensure
a representative sample of terminal users was achieved.
3. Data analysis
The datasets were analysed using the Statistical Package for
Social Sciences (SPSS). A statistical analysis plan was developed to
ensure uniformity in data analysis and validity of results. Data
analysis was terminal and season specific.
3.1. Indoor environmental conditions
A summary of the environmental conditions in the three terminals is presented in Table 2, while the comparison of the mean
operative temperature with the mean thermal sensation for passengers and staff across the different spaces for summer and winter
is shown in Fig. 2.
LCY had a very narrow temperature range e 4.4 C in summer
and 3.6 C in winter e indicative of its small size and uniform
spaces. The thermal environment was homogeneous across the
majority of terminal spaces (Fig. 2) where the mean temperature
ranged between 22.7 and 23.9 C in summer and between 22.9 and
23.9 C in winter. The retail area in the summer was the exception,
where the extensive spot lighting and the very low floor-to-ceiling
Fig. 1. (a) Portable microclimatic monitoring station designed for the surveys and (b) extract from the questionnaire related to the thermal environment.
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
187
Table 2
Indoor environmental conditions in the surveyed terminals.
Summer
LCY
MAN T1
MAN T2
Mean
SD
Min
Max
Mean
SD
Min
Max
Mean
SD
Min
Max
Winter
Top. ( C)
Vair (m/s)
RH (%)
CO2 (ppm)
Top. ( C)
Vair (m/s)
RH (%)
CO2 (ppm)
23.3
0.9
21.4
25.8
22.0
1.5
19.1
25.4
23.0
1.3
20.6
26.3
0.12
0.06
0.04
0.58
0.15
0.05
0.04
0.32
0.18
0.11
0.04
0.55
50.4
3.0
44.7
64.1
57.5
5.8
46.6
73.8
51.1
6.8
37.6
66.6
483
138
324
1095
648
172
298
1059
726
209
490
1380
23.4
0.6
21.7
25.3
21.3
2.0
16.2
25.6
21.1
0.9
18.9
24.5
0.13
0.04
0.04
0.26
0.16
0.16
0.03
1.04
0.16
0.09
0.04
0.49
32.3
7.0
21.7
53.3
32.5
5.9
23.2
53.1
32.6
6.0
22.0
44.5
817
152
660
1333
770
107
587
1365
752
159
284
1273
height often resulted in higher temperatures, while the temperature in the gate lounges was representative of free-running
conditions.
Thermal uniformity also characterizes the thermal environment
in MAN T2, which had a wider range of operative temperatures
(Table 2) with the temperature in all spaces being 1.1e3.6 C lower
in winter (Fig. 2). More specifically, conditions in the airside spaces
(i.e. beyond the security search area), were fairly uniform in the
summer with the mean temperatures ranging between 21.9 C and
23.0 C. A higher temperature (23.7 C) was found in the search
area due to the ineffective conditioning of the space during the
occupancy peaks in the busy summer period. The warmest space in
the summer was the check-in area, 24.6 C, which reflects the
impact of external heat gains on the thermal environment, as a
result of the extensive glazed façade and rooflights. In winter, the
mean temperature was very similar between the spaces, close to
21.0 C. This was associated with the terminal's operational profile
at this time of the year. MAN T2 is serving mostly holiday destinations and as a result it was significantly busier during the summer monitoring period, whereas in winter the main occupancy
peak in the morning was succeeded by sparse passenger traffic for
the rest of the day. Consequently, there were prolonged periods of
time with very low occupancy resulting in uniformly lower temperatures very close to the temperature set-point.
On the other hand, a variety of thermal environments existed
within MAN T1 as a result of the diversity of internal spaces. The
terminal exhibited the widest temperature range in both seasons
(19.1e25.4 C in summer and 16.2e25.6 C in winter; Table 2) and
the highest mean temperature differences between its spaces
(Fig. 2). Characteristically, the arrivals hall was on average 4.7 C
cooler than the departures lounge 1 in summer and 6.2 C cooler
than the seating area in winter. The particularly cool conditions in
the arrivals hall (19.8 C in summer and 17.4 C in winter) originated from its great exposure to outdoor conditions through a
north-orientated unprotected doorway. Additionally, departures
lounge 2 was constantly cooler than its extension, the nearby departures lounge 1, with the highest mean temperature difference
between them (2.5 C) in summer due to the extensive glazing in
the latter. Other spaces of similar function but with different
thermal conditions were the check-in halls 1 and 2. Check-in 2 was
on average 1.1 C warmer in winter due to the significantly smaller
volume and very low floor-to-ceiling height.
The mean temperature in the majority of spaces surveyed in the
three terminals was within or very close to the CIBSE comfort
criteria (Table 1) for summer. In winter, however, the thermal
conditions in nearly all spaces were beyond the respective range,
with mean temperatures up to 4.2 C higher than recommended
[31,37].
The 24 h-mean outdoor temperature during the summer surveys fluctuated between 11.0 and 20.0 C for LCY, 15.0e16.0 C for
MAN T1 and 10.0e16.0 C for MAN T2. The corresponding range in
winter was 3.9e12.0 C, 0.9e6.6 C and 1.6 to 6.3 C respectively.
Indoor and outdoor temperatures were weakly correlated for LCY
and MAN T1 (Table 3). On the contrary, the (linear) relationship
between the two was strong for MAN T2 associating nearly 50% of
the temperature variance indoors to outdoor temperature. This is
largely associated with the extensive glazing areas in the terminal
and the use of indoor air quality controls.
The compact nature of LCY, although an advantage in terms of
fast passenger processing, presented a major thermal disadvantage
during busy times. The HVAC system could not cope efficiently with
the large volume of passengers handled at peak times resulting in a
largely occupancy-driven thermal environment. This was revealed
in the similarity between the mean hourly profiles of temperature
and CO2 and was reflected in the correlation between the two
variables (Table 3) (r ¼ 0.44, p < 0.01). The correlation between
operative temperature and CO2 concentration was weaker for MAN
T1 (r ¼ 0.06, p < 0.05) and MAN T2 (r ¼ 0.13, p < 0.01), while also
implying the tendency for higher temperatures with increased
occupancy levels. The effect was significant in the smaller spaces
within LCY, where a highly variable traffic was handled within the
day. Occupancy changes in LCY explain 40% of the temperature
variance in summer and nearly 30% in winter (r ¼ 0.62, p < 0.01 for
summer, r ¼ 0.55, p < 0.01 for winter). The overall effect was
weaker for MAN T1 and MAN T2 due to the considerably larger
volume of spaces and the use of air quality controls in the latter.
Seasonally, the correlation was significant only for the busy summer period (r ¼ 0.29 for MAN T1 and r ¼ 0.37 for MAN T2, p < 0.01),
as occupancy volumes did not vary much during the winter surveys; passenger traffic in MAN T2 was very low during winter,
while in the busier MAN T1 traffic had very little variance within
the day.
The mean CO2 levels in all three buildings (Table 2) were well
below the ASHRAE recommended maximum concentration range
of 1000e1200 ppm and indicate sufficient ventilation rates [38].
The higher concentrations recorded during occupancy peaks
remained close to the maximum recommended range. Although
none of the buildings include (de)humidification in their control
strategy, the mean RH (%) levels were within the ASHRAE recommended range. Draughts are the most common cause of local
discomfort and one of the most common problems encountered in
airport terminal buildings due to the large entranceways, high
ceilings and long passageways which have openings to the outdoors [29]. In all three buildings, however, air movement was very
low with average values within the range of 0.1e0.2 m/s. Readings
beyond the upper comfort boundary of 0.3 m/s occurred
188
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
LCY Winter
1
0
-1
-2
-3
Mean operative temperature (°C)
2
1
0
-1
-2
-3
1
0
-1
-2
-3
Mean operative temperature (°C)
2
3
26
25
24
23
22
21
20
19
18
17
16
2
1
0
-1
-2
-3
Mean thermal sensation vote
3
MAN T2 Winter
24
2
23
1
22
0
21
-1
20
-2
19
-3
25
3
24
2
23
1
22
0
21
-1
20
-2
19
-3
Mean thermal sensation vote
3
Mean thermal sensation vote
25
Mean operative temperature (°C)
MAN T2 Summer
Mean operative temperature (°C)
2
MAN T1 Winter
Mean thermal sensation vote
Mean operative temperature (°C)
MAN T1 Summer
26
25
24
23
22
21
20
19
18
17
16
3
26
25
24
23
22
21
20
19
18
17
Mean thermal sensation vote
3
26
25
24
23
22
21
20
19
18
17
Mean thermal sensation vote
Mean operative temperature (°C)
LCY Summer
Fig. 2. Mean thermal sensation (lines) for passengers and staff plotted against mean operative temperature (bars) in the monitored terminal spaces. Line breaks indicate insignificant number of questionnaires from the respective population group in the corresponding space.
Table 3
Correlation coefficients for operative temperature, outdoor temperature and CO2.
Top. vs. Tout.
Top. vs. CO2
a
Overall
Overall
Summer
Winter
Significant at p < 0.05, all other at p < 0.01.
LCY
MAN T1
MAN T2
0.18
0.44
0.62
0.55
0.18
0.06a
0.29
n/a
0.70
0.13
0.37
n/a
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
sporadically in certain spaces exposed to outdoor wind through
openings (e.g. the gate lounges at LCY and the arrivals hall at MAN
T1).
189
destinations in warmer climates, in spite of the low mean daily
outdoor temperatures during the surveys.
3.2. The sample population
3.3. Satisfaction with the indoor environment and the link with
overall comfort
The total sample population from the three terminals consists of
3087 people, aged from less than 18 years to over 65 years and with
a 50:50 male-female ratio. Interviewees were classified into (a)
employees, (b) passengers and (c) well-wishers and other, consistent with the distinct nature of occupancy they represent (Fig. 3).
The 2333 passengers account for 74e80% of the survey participants at each terminal. They consist of arriving (3e9%) and predominantly departing passengers (91e97%). The former were
interviewed exclusively in the baggage reclaim areas and arrivals
halls and the latter across all other terminal spaces. Almost 80% of
passengers in LCY had stayed maximum an hour airside, with 40%
spending up to 30 min. The latter was comparable with only 19%
and 14% of passengers flying from MAN T1 and MAN T2, where
dwell time for the majority exceeded an hour. Over half the passengers departing from LCY (52%) were travelling on business,
whereas this percentage was significantly lower in MAN T1 (14%)
and MAN T2 (3%).
A wide range of terminal personnel, 465 in total, were studied in
their workspace and represent 14e17% of the terminals' sample
population. Reflecting staff's dwell time, nearly 80% of interviewed
employees were working full-time and 20% on a part-time basis.
Well-wishers and other account for 3e12% of the terminals' sample
population. This user group consists mainly of meters and greeters
interviewed in the landside areas of the terminals (check-in and
arrivals halls) and other short-stay visitors. The analysis focuses on
the two main user groups, passengers and staff.
Clothing insulation was evaluated using the detailed clothing
data collected from each interviewee during the questionnaire and
the insulation values for separate garment pieces provided in ISO
9920 [39]. In summer the mean clothing insulation for passengers
and staff was very similar at 0.56 and 0.60 clo (Table 4). This
increased to 0.88e1.15 clo for passengers and 0.79e0.90 clo for
staff, in winter, reflecting the greater impact of outdoor weather on
passengers' outfits. In fact, outdoor temperature explained about
20e40% of the clothing variation for employees whose outfits were
largely dependent on clothing policies, and 50% of the variance in
passenger clothing (Fig. 4). Another factor influencing passengers'
clothing was the destination. Passengers had the lowest mean
clothing insulation at MAN T2, which serves mostly holiday
The data analysis revealed a consistent satisfaction gap between
the two groups in all terminals, with dissatisfaction being considerably higher among staff in both seasons (Fig. 5). The assessment
of satisfaction with air movement and thermal comfort was based
on the assumption that a person requiring no change (in the
respective preference question) is satisfied with the prevailing
conditions.
No change in the thermal environment was required by
approximately half the passengers and by only a third of staff. In
addition, a significant fraction of employees, 60e80%, preferred
either higher or lower air movement in their workspace whereas
such requirement was expressed by 40e50% of passengers in the
three terminals. The assessment of the indoor air as “stuffy” was
widespread among employees, 40e60% of staff, compared to only
20e40% of passengers. Similar levels of dissatisfaction were reported with respect to the lighting environment. The satisfaction
gap was prevalent in all three terminals implying different comfort
requirements for the two groups and reflected in the considerably
different levels of discomfort; 23e49% among staff and 8e21%
between passengers.
The study also collected data regarding the aspects of the terminals the interviewees liked and disliked the most, using two
open-ended questions. Such data were used to assess the importance of the indoor conditions e and particularly of the thermal
environment e compared to other common concerns in such facilities. For the analysis it was assumed that a person who reports to
(dis)like a certain condition the most views that condition as
important (not necessarily as the most important).
The primary classification of the responses into “environmental”
(thermal, lighting, acoustic environment and air quality), “nonenvironmental” (all other issues) and “nothing particularly”
showed that the environmental conditions get a higher rank among
the “dislike” than the “like” statements of both groups. This implies
that the negative impact of the indoor environment on overall
comfort is stronger than the positive one, and consequently that
the indoor conditions were not considered important unless expectations were not met. Focussing on the “dislike the most” responses, the percentage of employees raising an environmental
issue (54e62%) was significantly higher than passengers (8e15%).
LCY
(818 people surveyed)
Passengers
80%
MAN T2
(1071 people surveyed)
MAN T1
(1198 people surveyed)
Wellwishers &
other
3%
Employees
17%
Passengers
74%
Wellwishers &
other
11%
Passengers
74%
Employees
15%
Fig. 3. Breakdown of the interviewees per category in the surveyed terminals.
Wellwishers &
other
12%
Employees
14%
190
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
Table 4
Mean value and standard deviation of clothing insulation (clo) for terminal users.
LCY
Total population
Employees
Passengers
Well-wishers & other
Total population
Employees
Passengers
Well-wishers & other
Clo SD
Summer
Winter
Summer
Winter
0.64
0.64
0.64
0.67
0.19
0.13
0.20
0.17
1.11
0.90
1.15
1.28
0.27
0.16
0.27
0.15
0.55
0.60
0.53
0.57
0.15
0.16
0.15
0.16
0.99
0.79
1.02
1.04
0.28
0.20
0.28
0.21
0.51
0.56
0.50
0.54
0.13
0.13
0.13
0.12
0.89
0.80
0.88
1.05
0.24
0.17
0.23
0.29
y = 1.1583e-0.03x
R² = 0.407
0
5
10 15 20 25 30
MAN T1 employees
Clothing insulation (clo)
Clothing insulation (clo)
LCY employees
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
MAN T2
Winter
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
MAN T2 employees
y = 0.829e-0.019x
R² = 0.2287
0
Outdoor temperature (°C)
5
10
15
20
25
Clothing insulation (clo)
Clo Mean
MAN T1
Summer
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
y = 0.8116e-0.021x
R² = 0.303
-5
Outdoor temperature (°C)
0
5
10 15 20 25
Outdoor temperature (°C)
(a)
y = 1.5895e-0.052x
R² = 0.496
0
5
10 15 20 25 30
Outdoor temperature (°C)
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
y = 1.171e-0.045x
R² = 0.498
0
5
10 15 20 25 30
Outdoor temperature (°C)
MAN T2 passengers
Clothing insulation (clo)
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
MAN T1 passengers
Clothing insulation (clo)
Clothing insulation (clo)
LCY passengers
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
y = 0.9243e-0.036x
R² = 0.481
-10 -5 0
5 10 15 20 25
Outdoor temperature (°C)
(b)
Fig. 4. Relationship between clothing insulation and outdoor temperature for (a) employees and (b) passengers.
Fig. 6 presents the parameters disliked the most, highlighting
that the thermal environment was the highest ranked issue among
staff in all terminals for a significant fraction of employees
(34e40%). For passengers, however, it was only ranked 5th in LCY
and MAN T2 and 6th in MAN T1, with only 4e6% of passengers at
each terminal addressing thermal conditions and even then only
mentioned by those who had reported unacceptable TS. Even in
this case the percentage of passengers who considered the thermal
environment as the worst aspect of their in-terminal experience
was low (15e21%), suggesting a great extent of passengers' tolerance of thermal conditions. In fact, these percentages are comparable to common passenger-concerns such as the “amount of space/
crowding” in LCY, “seating” in MAN T1 and “speed of processing/
queues” in MAN T2.
The importance of the thermal environment for the employees
was further highlighted in their assessment of the impact of the
environmental conditions on their productivity (on a 3-point scale)
and the explanations among those reporting “negative”. A significant fraction of staff in all terminals (40e46%) reported a negative
effect, with a slightly higher percentage (47e56%) reporting
“neither positive nor negative”. For the vast majority (69e91%)
among those who reported a negative effect, this was attributed to
thermal conditions.
3.4. Perception and preference over the thermal environment
3.4.1. Thermal sensation
Correlation analysis between the physical variables and TS
shows that TS correlates better with operative temperature
(Table 5). A positive correlation was also found with CO2 levels;
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
LCY
Overall
comfort
Thermal
Comfort
100%
80%
60%
40%
20%
0%
Lighting
191
MAN T1
Air
movement
Air
freshness
Overall
comfort
Thermal
Comfort
100%
80%
60%
40%
20%
0%
Lighting
MAN T2
Air
movement
Air
freshness
Overall
comfort
Thermal
Comfort
100%
80%
60%
40%
20%
0%
Lighting
Air
movement
Air
freshness
Fig. 5. Satisfaction levels of passengers and staff with the indoor conditions in summer and winter.
higher concentrations were normally the result of overcrowded
spaces where TS had an increasing trend. Moreover, the correlation
with 150 met suggests that having performed lighter activities
people reported cooler sensation. Conversely, this demonstrates a
tendency towards warmer sensations experienced by people with
higher metabolic heat generation, associated with higher activity
levels such as walking or walking while carrying luggage.
Other variables that did not vary sufficiently to produce a statistically significant correlation with TS may still have a significant
impact through their interrelationship with other variables. To
investigate this point, but also the relative importance of the variables involved (i.e. operative temperature, air movement, RH,
clothing insulation and the activity levels during and 15 min prior
to the questionnaire) multiple (stepwise) regression analysis was
performed. All models are significant at p < 0.005.
The results (Table 6) highlighted operative temperature,
clothing and 150 met as the set of variables explaining best TS in
LCY, supplemented with the square root of air movement in the
case of MAN T1 and MAN T2. The unstandardised coefficients,
measured in the unit of the variable they accompany, indicate the
amount of change expected in TS for every one-unit change in the
value of the variable they correspond, provided that all other
quantities in the model are held constant. Thus, controlling for the
variables “clo” and “150 met”, a temperature rise of 1.0 C in LCY
would result in nearly 0.4 units change in the thermal sensation of
the terminal population. In other words, the temperature change
required to shift TS by one unit was 2.7 C. Similarly, the temperature change required to increase people's TS by a unit in MAN T1
and MAN T2 was higher at 3.3 C and 4.1 C respectively.
On the other hand, the standardised coefficients, measured in
standard deviations, enable the comparison of the relative strength
of the various predictors within the models [40]. Although clothing
correlated with TS only in LCY (r ¼ 0.21, p < 0.01), the results
indicate that it provides the second strongest unique contribution
(behind operative temperature) in explaining TS in all cases.
Similarly, controlling for the other variables, air movement makes a
significant contribution into explaining TS in MAN T1 and MAN T2.
The percentage distribution of TS for passengers and staff is
illustrated in Fig. 7. The overwhelming majority (90%) of passengers
handled in LCY were within the three central categories of the
ASHRAE scale ( 1 TS þ1) in summer, when “neutral” (41%) and
“slightly warm” (35%) were the most frequently experienced sensations. In winter, the same percentage shifted towards warmer
votes, with only 20% of passengers feeling “neutral” and the bulk of
sensations referring to “slightly warm” (42%) and “warm” (28%).
These three categories also represent the majority of passengers in
MAN T1 and MAN T2 (nearly 80%) in both summer and winter, with
“slightly warm” being the highest in most cases, representing the
thermal state of at least one out of three passengers.
Employees, however, experienced more unacceptable sensations (±2, ±3) than passengers in summer and winter. This is
demonstrated from their wider TS distribution and validated statistically from the higher standard deviation of staff's mean TS in all
cases (Table 7). More specifically, unacceptable TS expressed at
least one out of three employees in each terminal, reaching almost
half (47%) in LCY during summer. On the contrary, such sensation
was experienced from 10 to 31% of passengers with the highest
percentages found in winter, predominantly from “warm” votes.
Differentiating per season, the mean TS for staff is lower in
winter than summer in all cases, with the most significant seasonal
difference e 1 unit on the ASHRAE scale e found in MAN T2.
Conversely, and despite the lower temperatures, the mean TS for
passengers increased in winter (with the exception of T2) due to the
higher clothing insulation worn, particularly at LCY and MAN T1
(Table 4).
3.4.2. Thermal preference
Similarly to TS, TP correlates better with operative temperature
(Table 5). The distribution of TP for the two groups is illustrated in
Fig. 8, where TP has been transformed to a 3-point variable. “Prefer
cooler” corresponds to the “much cooler” and “a bit cooler” votes
and “prefer warmer” represents the preference for a “much
warmer” and “a bit warmer” environment.
About 70% of the employees in all terminals required a change in
the thermal environment, with the majority preferring to be cooler.
Although this is true for both seasons, the votes for warmer conditions were greatly increased in winter. Passengers' TP profile was
consistent among the terminals in summer e nearly 50% found the
temperature just right and the preference for a cooler environment
was dominant among those requiring a change e and varied in
winter.
The large fraction of passengers (60%) preferring cooler conditions in LCY, coupled with the significantly increased votes on the
warm side of the ASHRAE scale in winter, indicates a problem with
overheating. Yet, cooler conditions were preferred by only a third of
employees. This suggests that overheating in winter was an issue
predominantly for passengers, whilst the respective figures for
summer suggest an overheating issue for staff. In MAN T1, almost
half the passengers found the thermal environment ‘just right’ in
winter and the majority among those requiring a change preferred
192
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Fig. 6. Aspects of the terminal buildings that (a) employees and (b) passengers disliked the most in the surveyed terminals.
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
193
Table 5
Correlation coefficients for TS, TP and physical variables.
Thermal sensation
vs.
Operative temperature
CO2 levels
150 met
Operative temperature
CO2 levels
150 met
Thermal preference
vs.
a
LCY
MAN T1
MAN T2
0.25
0.23
0.18
0.27
0.16
0.12
0.40
0.06a
0.09
0.41
n/a
0.10
0.20
0.25
0.14
0.31
0.23
0.14
Significant at p < 0.05, all other at p < 0.01.
Table 6
Standardised and unstandardised coefficients for the TS predictors.
LCY
MAN T1
MAN T2
(Constant)
Top ( C)
Clothing (clo)
150 activity (met)
(Constant)
Top ( C)
Clothing (clo)
150 Activity (met)
Sqrt Vair
(Constant)
Top ( C)
Clothing (clo)
150 Activity (met)
Sqrt Vair
Unstandardized
coefficients
Standardized coefficients
B
Beta
Std. error
9.240
0.369
0.613
0.556
6.492
0.305
0.512
0.251
0.958
5.760
0.246
0.803
0.588
1.257
0.996
0.042
0.103
0.096
0.436
0.018
0.102
0.091
0.305
0.658
0.027
0.145
0.105
0.319
Significance level
0.284
0.196
0.190
0.000
0.000
0.000
0.448
0.133
0.072
0.083
0.000
0.000
0.006
0.002
0.315
0.188
0.173
0.122
0.000
0.000
0.000
0.000
to be cooler. MAN T2 presented the highest thermal satisfaction
rate for passengers in winter as well as in summer with over 60% of
passengers preferring “no change”.
Further scrutiny of the TS and TP votes found that neutral
(“neither cold nor hot”) was not the desired thermal state for the
over half the passengers and staff. Assuming that preference for no
change denotes thermal satisfaction, the results showed that 51%,
64% and 62% of passengers and 53%, 57% and 61% of the employees
satisfied with the thermal environment in LCY, MAN T1 and MAN
T2 had reported TS other than neutral.
3.4.3. The space-to-space thermal conflict
The thermal conditions in the terminal spaces were often
evaluated differently by passengers and staff (Fig. 2), with the
respective mean TS difference reaching up to 2.1 units. As indicated
by the spatial profiles of mean TS in all terminals, employees' TS
profile fluctuates significantly between the spaces whereas for
passengers it is considerably more stable. This demonstrates passengers' wider adaptive capacity as opposed to the rigid working
conditions for the vast majority of staff.
Interestingly, employees' TS profile did not always fluctuate in
accordance with the temperature changes between the spaces, but
reflected the diverse activity levels between the various types of
staff associated to the nature of work they perform. For instance,
security staff working in the search area of LCY in summer (0.74 clo)
experienced a mean temperature of 23.4 C and reported a mean TS
of 1.7. In the nearby seating area (0.70 clo), with just 0.2 C higher
temperature staff's mean TS was 0.5, while inside the warmer
retail facilities (24.6 C, 0.64 clo) staff reported neutral TS. The
comparison between staff in the check-in hall, search area and arrivals hall of MAN T2 in winter is also representative. The mean
temperature in these spaces was nearly identical at 21.0 C and
employees had a very similar mean clothing insulation (0.84e0.92
clo). Nevertheless, three distinct mean sensations were
reported; 1.1 in the check-in area, 0.4 in the arrivals and 1.1 in
the search area. Similarly, staff in the check-in 2 (0.74 clo) and
search area (0.66 clo) at MAN T1 experienced a mean temperature
of 22.4 C in summer and reported a mean TS of 0.2 and 1.1
respectively. The figures for the search areas are fairly consistent
between the three terminals. In most cases, the mean TS for both
groups was among the highest reported while overall comfort was
lower than in other spaces. This suggests that the particular function has an increasing effect on TS and decreasing effect on comfort
due to staff's mental concentration leading to increased metabolic
rate and passengers' stress in a confined space.
3.5. Quantifying the thermal conflict
3.5.1. Neutral temperatures
Neutral temperatures, i.e. the temperature where people are
neither warm nor cool but are in a state of thermal neutrality
[8,41,42], were calculated using weighted linear regressions [43].
Working with half-degree ( C) increments of operative temperature, the mean TS of the two groups was determined for each bin.
The mean TS was regressed against operative temperature (Fig. 9)
and neutral temperatures were subsequently obtained by solving
the regression equations for TS ¼ 0. All models were significant at
the 99% level.
The gradient of the regression models, representing thermal
sensitivity [43], demonstrates that employees were on average 1.6
times more sensitive to temperature changes than passengers in
both seasons. This means that the rate of TS change differs significantly. For example, in summer, a unit increase in staff's TS would
require 2.5 C temperature rise in LCY, 2.2 C in MAN T1 and 2.4 C
in MAN T2, whilst passengers' TS would not be altered with temperature changes below 4.1 C, 3.5 C and 3.7 C respectively.
The results demonstrate the discrete thermal requirements of
the two groups, who consistently achieved neutrality at different
temperatures (Table 8). Neutral temperature for staff was
0.6e3.9 C higher than for passengers, with the highest differences
met in winter. For both groups, neutrality was found at temperatures cooler than the mean indoor temperature (except from the
winter case of staff in MAN T2), with employees' neutral temperature being closer to it in all cases. More specifically, the difference
between mean and neutral temperature was only 0.6e1.2 C for
staff and 1.5e2.7 C for passengers.
3.5.2. Preferred temperatures
Weighted linear regression models were generated to associate
the thermal preference votes with temperature1 [44,45]. Using the
sample size of each temperature bin as weighting factor, the percentages of “prefer cooler” and “prefer warmer” votes were
1
Probit analysis confirmed the results obtained from linear regression in some
cases but was ineffectual where the temperature range was very narrow. The
alternative method of linear regression was used to retain uniformity in data
analysis (Personal communication with Humphreys M.A. [46]).
194
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
MAN T1 Summer
-3
-2
-1
0
1
2
MAN T2 Summer
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
3
% of Observation
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
% of Observation
% of Observation
LCY Summer
-3
ASHRAE Thermal Sensation Scale
-2
-1
0
1
2
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
3
-3
ASHRAE Thermal Sensation Scale
-2
-1
0
1
2
3
ASHRAE Thermal Sensation Scale
(a)
MAN T1 Winter
-3
-2
-1
0
1
2
MAN T2 Winter
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
3
% of Observation
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
% of Observation
% of Observation
LCY Winter
-3
ASHRAE Thermal Sensation Scale
-2
-1
0
1
2
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
3
-3
ASHRAE Thermal Sensation Scale
-2
-1
0
1
2
3
ASHRAE Thermal Sensation Scale
(b)
Fig. 7. Percentage distribution of thermal sensation for passengers and staff in summer and winter.
Table 7
Mean score and standard deviation of TS for staff and passengers and percentage of unacceptable TS.
Employees
Mean TS
Summer
Winter
LCY
MAN
MAN
LCY
MAN
MAN
T1
T2
T1
T2
0.65
0.50
0.32
0.38
0.44
0.31
Passengers
SD
% of unacceptable TS
Mean TS
SD
% of unacceptable TS
1.59
1.44
1.51
1.39
1.65
1.54
47%
33%
35%
35%
44%
36%
0.42
0.53
0.63
0.97
0.66
0.58
0.90
1.08
1.09
0.96
1.17
1.16
10%
21%
23%
31%
28%
28%
calculated for each half-degree ( C) increment and regressed
separately against operative temperature. Preferred temperature
was obtained from the intersection of the two regression lines as
shown in Fig. 10.
The results demonstrate that both groups preferred a cooler
environment than the one experienced (Table 8). Passengers,
however, preferred constantly lower temperatures than employees,
by as little as 0.4 C (in MAN T1 in summer) to 2.0 C (in MAN T2 in
winter). In accordance with the profile of neutral temperatures, the
greatest differences were encountered in winter while in both
seasons staff's preferred temperature was closer to the mean
temperature experienced.
The exception was the winter of MAN T1 and MAN T2, where the
lowest temperatures were observed and employees' preferred
temperature was slightly higher than the mean temperature. These
cases provide evidence of tolerance to cool conditions, which appears to be considerably higher among passengers. With the mean
temperature at 21.3 C in MAN T1, employees preferred 21.7 C but
were still comfortable at 20.6 C demonstrating limited adaptation
to the cooler conditions. On the other hand, passengers preferred
20.6 C, yet they were still comfortable at 19.2 C. Similarly, with
the mean temperature at 21.1 C in MAN T2, employees preferred a
slightly warmer temperature, 21.9 C, and achieved neutrality at
22.3 C, while passengers preferred 19.9 C but were also
comfortable at 18.4 C, demonstrating higher adaptation to cooler
temperatures.
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
MAN T1
LCY
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
36%
41%
57%
57%
33%
51%
31%
195
38%
31%
12%
8%
5%
Employees Passengers Employees Passengers
Summer
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
33%
42%
45%
47%
MAN T2
27%
34%
49%
46%
31%
19%
18%
9%
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Employees Passengers Employees Passengers
Summer
Winter
45%
26%
38%
28%
32%
34%
62%
53%
42%
22%
10%
9%
Employees Passengers Employees Passengers
Winter
Summer
Winter
Fig. 8. Percentage distribution of binned thermal preference votes for passengers and staff.
LCY Summer
MAN T1 Summer
3
2
1
0
y = 0.243x - 5.2295
R² = 0.6708
-1
-2
Mean Thermal Sensation Vote
y = 0.3894x - 8.5844
R² = 0.6062
Mean Thermal Sensation Vote
3
3
Mean Thermal Sensation Vote
MAN T2 Summer
y = 0.4613x - 9.7319
R² = 0.7392
2
1
0
-1
y = 0.2822x - 5.7681
R² = 0.8234
-2
-3
-3
21
22
23
24
25
26
27
Operative Temperature (°C)
2
y = 0.2741x - 5.682
R² = 0.7212
1
0
-1
y = 0.4212x - 9.431
R² = 0.3007
-2
-3
19 20 21 22 23 24 25 26
20 21 22 23 24 25 26 27
Operative Temperature (°C)
Operative Temperature (°C)
Fig. 9. Relationship between thermal sensation and operative temperature for passengers and staff at in summer.
Table 8
Summary of mean, neutral and preferred temperatures and acceptable temperature ranges for passengers and staff (within brackets is the % of time the respective range was
met).
Summer
Employees
Passengers
Winter
Employees
Passengers
LCY
MAN
MAN
LCY
MAN
MAN
LCY
MAN
MAN
LCY
MAN
MAN
T1
T2
T1
T2
T1
T2
T1
T2
Mean Top. ( C)
Gradient
R2
Tneutral ( C)
Tpref ( C)
80% Accept. ( C)
90% Accept. ( C)
23.3
22.0
23.0
23.3
22.0
23.0
23.4
21.3
21.1
23.4
21.3
21.1
0.389
0.461
0.421
0.243
0.282
0.274
0.756
0.342
0.362
0.407
0.304
0.219
0.61
0.74
0.3
0.67
0.82
0.72
0.38
0.46
0.21
0.86
0.77
0.75
22.1
21.1
22.4
21.5
20.5
20.7
22.5
20.6
22.3
21.1
19.2
18.4
22.1
21.3
22.5
21.4
20.9
21.1
22.8
21.7
21.9
21.5
20.6
19.9
19.9e24.3
19.3e23.0
20.4e24.4
18.0e25.0
17.4e23.5
17.6e23.8
21.4e23.6
18.1e23.1
19.9e24.6
19.1e23.2
16.4e22.0
14.5e22.3
20.8e23.4
20.0e22.2
21.2e23.6
19.5e23.6
18.7e22.2
18.9e22.6
21.9e23.2
19.2e22.1
20.9e23.7
19.9e22.4
17.6e20.9
16.1e20.7
3.5.3. Acceptable temperature ranges
Based on the acceptance of the statistical assumptions underlying PMV/PPD heat-balance model [6], the TS regression models
were used for the calculation of the operative temperature ranges
in which 80% and 90% of passengers and staff find the thermal
environment acceptable. Accordingly, it was assumed that a mean
(86%)
(79%)
(83%)
(95%)
(83%)
(68%)
(66%)
(70%)
(92%)
(39%)
(60%)
(93%)
(57%)
(49%)
(61%)
(66%)
(63%)
(52%)
(38%)
(47%)
(69%)
(5%)
(28%)
(28%)
TS of ±0.85 and ± 0.50 corresponds to 80% and 90% general
acceptability respectively.
The results reveal a considerable difference in the adaptive capacity of the two groups, with passengers demonstrating consistently wider ranges of acceptable temperatures (Table 8). The 80%
acceptability range was on average 4.0 C wide for staff and 6.0 C
196
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
MAN T1 Summer - Passengers
y = 0.1991x - 3.9401
R² = 0.9124
y = -0.1019x + 2.479
R² = 0.6125
19
20
21
22
23
24
25
% of Passengers
% of Employees
MAN T1 Summer - Employees
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
21
22
23
24
25
26
MAN T1 Winter - Passengers
% of Passengers
% of Employees
y = 0.1137x - 2.0844
R² = 0.751
20
Operative Temperature (°C)
MAN T1 Winter - Employees
y = -0.1294x + 3.1949
R² = 0.7098
y = -0.0913x + 2.1764
R² = 0.7228
19
26
Operative Temperature (°C)
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
y = 0.1071x - 1.98
R² = 0.7882
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
y = -0.0969x + 2.3056
R² = 0.7946
y = 0.0943x - 1.6318
R² = 0.7883
16 17 18 19 20 21 22 23 24 25
16 17 18 19 20 21 22 23 24 25 26
Operative Temperature (°C)
Operative Temperature (°C)
Fig. 10. Preferred operative temperatures for passengers and staff at MAN T1 in summer and winter.
wide for passengers, reducing to 2.4 C and 3.5 C respectively for
the 90% acceptability range. This difference is predominantly due to
the higher acceptance of cooler conditions that passengers
demonstrated in all terminals (Fig. 11). On the contrary, it was
employees' comfort zone that stretched to higher temperatures in
some cases (at MAN T2 in summer and at all terminals in winter)
and passengers' in others (at LCY and MAN T1 in summer).
4. Discussion
The data analysis showed that thermal discomfort was common
in the three terminals, as demonstrated by the high percentages of
unacceptable TS (passengers 10e31%, staff 33e47%; Table 7) and
the percentage of people requiring changes in the thermal environment (50% of passengers in summer and 38e62% in winter, 70%
of staff in both seasons; Fig. 8). In all terminals the thermal profile
was close to the upper boundary of the acceptable temperature
ranges, occasionally falling outside the comfort zone (Fig. 11). The
mean TS for the two user groups was predominantly on the warm
side of the ASHRAE scale (Table 7) and preference for cooler conditions was dominant among those requiring a change (Fig. 8).
These results demonstrate that warm rather than cool conditions
can be an issue in both summer and winter in such facilities, where
neutral is not the desired thermal state for over half the passengers
and staff.
Furthermore, the findings revealed a consistent discrepancy
between the thermal comfort conditions for passengers and staff.
The thermal requirements of the two groups were shown to vary
considerably (Table 8) resulting in thermal conflict across the terminal spaces. Passengers achieved neutrality at lower temperatures
than staff by 0.6e3.9 C, which was lower by an average of 1.0 C in
summer and 2.2 C in winter. The respective difference in preferred
temperature further highlights the thermal conflict between the
two groups, with passengers preferring constantly lower temperatures by 0.4e2.0 C. On average, passengers' preferred temperature was lower than staff's by 0.8 C in summer and by 1.5 C in
winter. The differences in comfort temperatures were smaller in
summer when clothing insulation values were similar and greater
in winter when clothing was higher for passengers (Table 4).
The comfort temperatures for employees were in all cases closer
to the indoor mean temperature, reflecting their long-term acclimatisation to the terminals' thermal environment that results from
the long dwell times and the continuous experience with it.
However, despite staff's familiarity with the indoor thermal environment, it was passengers that demonstrated greater adaptation
to the thermal conditions. Employees were on average 1.6 times
more sensitive to temperature changes than passengers (Table 8),
whose TS profile was more stable across the terminal spaces
demonstrating a greater adaptive capacity (Fig. 2). In this context,
the 80% and 90% acceptability temperature ranges were significantly wider for passengers in all cases. Considering the 80%
acceptability range, this was on average 6.4 C wide in summer and
A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
MAN T1 Summer
27
26
26
24
23
22
21
20
19
25
24
23
22
21
20
19
18
18
17
17
28/05/2012 to 03/06/2012
Operative temperature (°C)
26
24
23
22
21
20
19
18
29/01/2013 to 04/02/2013
24
23
22
21
20
19
17
22/08/2012 to 28/08/2012
MAN T1 Winter
27
25
25
18
27
26
25
24
23
22
21
20
19
18
17
16
15
03/12/2012 to 10/12/2012
29/08/2012 to 06/09/2012
(a)
MAN T2 Winter
Operative temperature (°C)
25
Operative temperature (°C)
27
26
LCY Winter
Operative temperature (°C)
MAN T2 Summer
27
Operative temperature (°C)
Operative temperature (°C)
LCY Summer
197
26
25
24
23
22
21
20
19
18
17
16
15
14
11/12/2012 to 18/12/2012
(b)
Fig. 11. Continuous operative temperature monitored across the terminal over the survey periods and 80% acceptability temperature ranges of passengers (continuous lines) and
staff (dashed lines) in (a) summer and (b) winter surveys.
5.8 C wide in winter for passengers, reduced to 4.0 C for staff in
both seasons (Table 8). Even when the operative temperature was
within the acceptable range for both groups, the percentage of
unacceptable TS was consistently higher among employees, while
also indicating difficulties in coping with thermal discomfort.
Characteristically, 30e40% of employees at each terminal rated the
clothing policy as inflexible (on a 3-point scale) in maintaining their
thermal comfort, while the vast majority (86e94%) reported no
control over the indoor environmental conditions.
The different perspective of the two groups towards the thermal
environment was also expressed in the significantly different
weighting of the thermal conditions as the worst aspect of their interminal experience (4e6% of passengers and 34e40% of employees; Fig. 6). This implies a difference in the perceived importance of the thermal conditions and consequently a different
impact on overall comfort. In fact, the highest discomfort levels
among staff emerged in the terminal spaces identified as the most
thermally-problematic (e.g. arrivals halls in MAN T1 and security
search area in MAN T2). On the other hand, the highest discomfort
levels among passengers were associated with processing activities
including security screening and flight boarding; discomfort was
increasing in the search areas, dropping in the departures lounge
and slightly rising again in the gate lounges while boarding.
Comparing the results with the relevant guidelines for designers, the comfort zone for passengers is considerably wider than
the range recommended by CIBSE for the majority of terminal
spaces. Alongside the 80% acceptability ranges, preferred
temperatures suggest that lowering the heating set-points in
winter e when overheating was more apparent e would improve
thermal comfort while leading to energy savings. To ensure, however, that employees' comfort is not compromised, appropriate
control strategies, perhaps with localised control, for terminal staff
could be considered. On the contrary, the results for summer suggest that increasing the cooling set-points would deteriorate thermal comfort conditions. As shown in Fig. 11, the thermal profile of
all terminals was close to the upper limit of the 80% acceptability
range with preferred temperatures implying that more cooling was
required (Table 8). To provide energy savings for cooling without
compromising thermal comfort different strategies can be investigated, from increasing air movement, to reducing peak temperatures, e.g. with the use of phase change materials (PCM). The
application of PCM was modelled in an airport terminal in the UK
and it was shown to prevent overheating in the summer months
reducing peak temperatures up to 3.0 C [47,48]. Additionally,
thermal comfort could also be improved by increasing staff's
adaptive capacity, e.g. through more flexible dress codes.
Overall, the findings highlight the perceived difference of the
terminal as transition vs. indoor workspace, which is also reflected
in the considerably different overall discomfort levels reported by
the two groups (8e21% of passengers and 23e49% of employees;
Fig. 5). The results are consistent with the broader context of
adaptation to the thermal environment, where expectations, time
of exposure and perceived control increase thermal tolerance and
therefore adaptive capacity [30]. Employees have a limited adaptive
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A. Kotopouleas, M. Nikolopoulou / Building and Environment 99 (2016) 184e199
capacity originating from the rigid working conditions associated
to the terminals' functions. On the contrary, when and where
required in the terminal, passengers can take adjustment actions
(e.g. moving to another space, altering clothing levels, etc.) that
allow them to cope effectively preventing thermal discomfort.
5. Conclusions
This work investigated the nature of thermal comfort conditions
in three airport terminal buildings of different size and typology.
The indoor environmental conditions were extensively monitored
in different terminal areas along with questionnaire-guided interviews with 3087 people across different seasons. Thermal
sensation was predominantly determined by the combination of
temperature, clothing insulation and activity levels. The latter two
are among the parameters differentiating the comfort conditions of
passengers and staff along with the variation in dwell time and
overall expectations.
The two user groups presented different satisfaction levels with
the indoor conditions, both preferring a different thermal environment to the one experienced. Warm rather cold conditions were
most commonly the cause of discomfort, although this was affected
by the particularities of each terminal. Passengers' neutral and
preferred temperatures were lower than staff's and significantly
lower than the mean indoor temperature in all cases, which has
significant implications for energy conservation. Viewing the terminal as a transition space, passengers consistently demonstrated a
wider adaptation potential through the wide range of acceptable
temperatures. On the other hand, employees were more sensitive
to temperature changes and their limited adaptive capacity resulted in a narrower comfort zone. From the energy conservation
perspective, the results indicate little scope for increasing the
cooling systems set-points in summer and alternative methods
should be sought. In winter, however, there is a greater potential for
energy savings by lowering the heating set-points, provided that
more control over the thermal environment is provided to terminal
staff. Soft policies such as more flexible dressing codes would also
improve thermal comfort for staff.
Ultimately, understanding the differing comfort requirements of
the key population groups in airport terminals is important to
improve thermal comfort conditions and identify appropriate
strategies for reducing energy consumption. Such knowledge can
influence the design and potential refurbishment of this energyintensive sector to maintain occupants' well-being without jeopardising the terminals' environmental performance.
Acknowledgements
This work was funded by the UK Engineering and Physical Sciences Research Council (EPSRC) as part of the project “Integration
of active and passive indoor thermal environment control systems
to minimize the carbon footprint of airport terminal buildings”,
grant no. EP/H004181/1. The assistance from the airports' authorities and terminal staff at the three terminals is gratefully
acknowledged.
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