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Building and Environment 37 (2002) 11391152
www.elsevier.com/locate/buildenv
Numerical simulation for optimizing the design of subwayenvironmental control system
Ming-Tsun Ke , Tsung-Che Cheng, Wen-Por Wang
Department of Air Conditioning and Refrigeration, National Taipei University of Technology, No. 1, Sec 3, Chung-Hsiao E. Rd., Taipei 106, Taiwan
Received 31 July 2001; received in revised form 7 November 2001; accepted 16 November 2001
Abstract
Subway Environmental Simulation Program (SES) was used to combine with the commercial computational uid dynamics (CFD)software to explore the inuence of various operating situations to the subway environment of Taipei Rapid Transit System in the present
study. The results show that the under platform exhaust (UPE) has a substantial inuence on the temperature and the cross-sectional area
of the ventilation shaft has quite more eect on the ventilation volume than length. The pressure distribution caused by the piston eect
and its eect on the platform screen door was also discussed and compared. ? 2002 Published by Elsevier Science Ltd.
Keywords: Computational uid dynamics; Under platform exhaust; Piston eect
1. Introduction
This paper mainly focuses on numerical simulation anal-
ysis for the environmental control system of the subwaystation area and the underground tunnel area between sta-
tions. The construction of the tunnel ventilation system is
one of the important environmental control systems aiming
at controlling the temperature inside the tunnel so that the
auxiliary system equipment of the train and the electrical
equipment in the tunnel can operate properly under accept-
able working temperature, and when emergency re occurs,
it can eectively control the direction of the spread of the
smoke and discharge the smoke out of the tunnel. On the
other hand, the ventilation shafts being installed on both
ends of the station can slow down the pressure wave in the
station platform and the inuence of the thermal load of thetunnel in the station area.
The application of SES program [1] is very popular in the
rapid transit systems of many cities in the world. The related
conceptual design of the subway can be resolved by the
thermal load analysis of the SES program and the selection
of equipment. Although there are many research reports on
the rapid transit system by using the SES program, yet the
design conditions and the weather conditions are dierent
Corresponding author. Tel.: +886-2-27712171; fax: +886-2-
27314919.
E-mail address: [email protected] (M.-T. Ke).
from those in Taiwan. There are not too many researches
that are related to the piston eect; therefore it is necessary
to use the numerical results of the SES program to combine
with the detailed simulation of the three-dimensional CFDsimulation for further studies on this subject as the reference
for the future planning of the tunnel ventilation and the
environmental control system.
2. Design conditions and theoretical model
The subway route under investigation is the Hsin Chuan
route of the Taipei Rapid Transit System. The SES soft-
ware was used to combine with the commercial CFD
package software PHOENICS (Parabolic, Hyperbolic or
Elliptic Numerical Integration Code Series) to establish
the three-dimensional numerical analysis model to proceedwith the detailed physical phenomenon simulation analysis
for the tunnel environmental control system.
2.1. Design conditions and design guidelines
According to the Taipei Rapid Transit System Planning
Handbook, the related design conditions for the environ-
mental control system are described as follows.
A.External temperature conditions
The rush hours of the Taipei Rapid Transit System are
08:00 and 17:00, and the temperature for the rush hours
0360-1323/02/$ - see front matter? 2002 Published by Elsevier Science Ltd.
PII: S 0 3 6 0 - 1 3 2 3 ( 0 1 ) 0 0 1 0 5 - 6
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1140 M.-T. Ke et al./ Building and Environment 37 (2002) 11391152
Nomenclature
AA Hsin Chuan station
BB Fu Jen University station
CC Tan Feng station
DD Hui Lung stationA net cross-sectional area of tunnel (m2)
Av cross-sectional area of ventilation shaft (m2)
C proportional constant, = 0:48
Cm ow split parameter
Cp driving pressure coecient
Cps head loss through a ventilation shaft
CHi entrance loss, = 1 for a T-junction ventilation
shaft
CHC coupling loss between the tunnel and the venti-
lation shaft
Dh hydraulic diameter (m)
E eciency of UPE
f friction factorf modied friction factor
F energy head added (m2=s2)
g gravitional acceleration (m=s2
)
hf frictional energy head loss, =(fL=D)(V2=2)
(m2=s2)
hfr minor head loss, =KV2=2 (m2=s2)
k turbulent kinetic energy, (m2=s2)
K loss coecient
Ki parameter, = 0:965
Ko parameter, = 0:9 for square tunnels
L length (m)P static pressure (Pa)
Q ventilation rate (m3=s)
Qv ventilation rate in ventilation shaft (m3=s)
R(ui) residuam vector
R0 reference base vector
Re Reynolds number
T air temperature (
C)
u velocity in x direction (m=s)
v velocity in y direction (m=s)
V air velocity (m=s)
Vv air velocity in ventilation shaft (m=s)
w velocity in zdirection (m=s)
Z elevation head (m)
Greek symbol
dissipation rate of turbulent kinetic energy,
(m2=s3)
a absolute roughness factor
air density (kg=m3
)
Table 1
Design weather conditions
Summer (17:00) Winter (17:00)
Dry-bulb temperature 32.2
C 9.7
C
Wet-bulb temperature 26.0
C 7.6
C
Atmospheric pressure 1013 mbar 1013 mbar
in the afternoon is higher, therefore 17:00 is taken to be
the design hour, and the external temperature conditions are
illustrated in Table 1.
B.The design conditions of the tunnel area
The air dry-bulb temperature in the tunnel should be keptbelow 37
C during normal operation, and should be below
43
C at conjested condition.
C.Tunnel area
The tunnel area for this research is from the cross-over
track downstream the Hsin Chuan station (AA station) to
the tunnel area of the Huei Lung station (DD station), and
the range is described as below:
(a) Hsin Chuan Station to Fu Jen University Station (BB
station) (up and down tracks),
(b) Fu Jen University Station to Tan Feng Station (CC sta-
tion) (up and down tracks),
Table 2
Tunnel dimensions
AABB BBCC CCDD Lay-up
Tunnel Tunnel Tunnel track
Length (m) 1370 1227 1416 About 600
Inclination (%) 0:3=0:53 0:3=0:36 0:47=0:3 3=3
Remark A cross-over A cross-over
near AA side near DD side
(c) Tan Feng Station to Huei Lung Station (DD station)
(up and down tracks),
(d) Extended to the reception track and the departure track
of the lay-up track of the tunnel.Tunnel sections are primarily bored tunnels except that
cross-over tracks and lay-up tracks are cut and cover
tunnels, and the geometric dimensions are shown in
Table 2.
D.The tunnel area of the cross-over track and the tunnel
portal of the lay-up track
There is a cross-over track in the CC Station to DD Sta-
tion proximate to the DD station, and behind the DD sta-
tion there is a lay-up track being extended to the ground
level to the maintenance and repair plant. The up and down
tracks are linked together by the cross-over track, making
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M.-T. Ke et al./ Building and Environment 37 (2002) 11391152 1141
Table 3
Dimensions of stations
Fu Jen Univ. Tan Feng Hui Lung
Station Station Station
Length of station area (m) 194 153 277.2
Height of concourse (m) 4.15 4.15 4.15
Height of track area (m) 6.21 6.21 6.21Width of track area (m) 16.55 16.55 17.55
Length of platform area (m) 141 141 141
Width of platform area (m) 8.7 8.7 8.9
the airow in one track to ow to another track and thus
reducing the piston eect. Therefore, jet fan should be in-
stalled to guide the airow. However, since there is a lay-up
track tunnel extending to the ground level, the hot air in the
tunnel can be exhausted, or outside air can also be induced
too.
E.Ventilation shaft
According to the design requirements, ventilation open-ings are installed on both sides of the station, which con-
nect with the environmental control system plantrooms
and the natural outdoors air, and it includes three indepen-
dent shafts: exhaust shaft, intake shaft, and pressure relief
shaft.
F.Station area geometry
The concourses and the island type platforms of Fu Jen
University station, Tan Feng station and Hui Long Station
are all located in cut and covered boxes. Platform-screen
doors are installed between the platform and the track
area. Each side of the platform is supposed to be lined
with a train with six cars and each car has four doors.
The station is a two-oor underground building verti-
cally connected by a concourse and the platform track-
layer. The dimension of the station area is generalized in
Table 3.
G.UPE
In present research there are platform-screen doors that
separate the track from the platform. There is quite small
148713681758
AA station DD stationCC stationBB station
PORTAL
0.3 %
-0.3 %0.53 %-0.3 %
0.36 %
0.47 %
AIR FLOW
DIRECTION
Unit: m
Fig. 1. Schematic plot of the tunnel ventilation system between stations.
amount of air owing between the platform and the tunnel
since the gap between the train and the platform-screen door
is only 10 cm wide. The installation of screen doors serves
to prevent heat in the tunnel and in the train from getting
into the platform area and reduce the cooling load of air
conditioning in the concourse and platform layer. However,
temperature in the tunnel of the track area will rise sincethere is no air conditioning to cool down the air. Therefore,
the heat in the tunnel along the track has to be expelled
by UPE. The denition for the eciency E of UPE is as
follows:
E=Heat expelled by UPE
Heat released by train = CQ: (1)
As proven by the result of the experiment, the proportional
constantCin Eq. (1) is 0.48 when the eciencyEis under
65% whereas there is no experimental data to refer to ifEis
greater than 65%. However, as known through the eciency
curve in theory, the eciency will not exceed 80% no matter
how the discharge capacity is.
2.2. Theoretical model
The present research rst used the SES to perform the
analysis for the underground tunnel ventilation system and
obtained the important operational data, and then these data
were used as the boundary conditions to proceed with the
3D CFD simulation to give us detailed and useful numerical
results. Fig. 1 shows the layout of the ventilation system
in the tunnel between each station, and Fig. 2 is the local
detailed 3D layout of the station area.
2.2.1. One-dimensional analysis model
The installation of ventilation shaft will have an impact
on the visual landscape and the surrounding environment
because of the prominent vertical construction and the occu-
pation of valuable land so that the design for the ventilation
shaft may need to be changed. It results in the originally
planned ventilation requirement. Therefore, we must study
the inuence of the length and the cross-sectional area of the
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1142 M.-T. Ke et al./ Building and Environment 37 (2002) 11391152
Fig. 2. Local detail layout of present underground station.
ventilation shaft on the piston eect in advance as a basis
for future reference.
Bernoullis equation can be used for the analysis of
present subway ventilation system.
gZ1+P1
+
V212
+F= gZ2+P2
2+
V222
+ hf+ hfm: (2)
In the subway ventilation system, if the height of the
ventilation shaft remains unchanged, and only the length
and the cross-sectional area are considered, it will only in-
uence hf and hfm, and the relation between the friction
loss and the cross-sectional area and length is describedbelow.
hf= f L
Dh
V2
2 ; (3)
hfm= KV2
2 : (4)
To study the inuence of the ventilation shaft to the piston
eect, we need to know about the airow distribution in the
tunnel and the ventilation shaft. We can deduce the following
according to [2,3].
The ow split parameter for the airow passes throughthe ventilation shaft and inside the tunnel is dened
as
Cm=AvVv
AV =
Airow volume inside ventilation shaft
Airow volume inside tunnel :
(5)
The ow split parameter when air ows into the ventila-
tion openings is dened as
Cmi= KiAv
A
Cp
Cps: (6)
The ow split parameter when air ows out from the
ventilation openings is
Cmo= KoAv
A
Cp+ 1 CHi
Cps CHC; (7)
whereCHCcan be neglected whenCps1.
The foregoing ow split parameters are only suitable for
the tunnel that only has one ventilation shaft. However, we
can know about the relation between the airow and the area
and resistance coecient of the ventilation shaft. When the
cross-sectional area or the length of the ventilation shaft ischanged, we assume the airow caused by the piston eect
in front of the ventilation shaft is the same (that is Q2= Q1,
Cp2 =Cp1 ), and there is change in airow distribution
only in the ventilation shaft and at its downstream, and it is
known as the change of ow split parameter. Let the original
ow split parameter be Cm1 , and the ow split parameter
after changing the cross-sectional area and the length of
the ventilation shaft be Cm2 , then the relation of the airow
volume is shown below.
Qv2
Qv1=
Av2
Av1K+ f1L1=Dh1
K+ f2L2=Dh2; (8)
where the friction factor f can be calculated by the
Altshul-Tsal equation [4]:
f = 0:11
a
Dh+
68
Re
0:25
if f 0:018: f= f
if f 0:018: f= 0 :85f + 0:0028
(9)
withRe = 66:4 103DhV.
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M.-T. Ke et al./ Building and Environment 37 (2002) 11391152 1143
Table 4
Relaxation factors set in present study
Variable P u v w k T
Relaxation factor 0.3 104 104 104 0.3 0.3 0.1
2.2.2. Three-dimensional CFD model
A full-size three-dimensional model is developed accord-
ing to the actual size of the station and the tunnel area in
Cartesian coordinate. The ow is regarded as incompress-
ible, transient and turbulent. The boundary conditions are as
follows.
(a) The boundary of all kinds of solids in the model does
not consider the surface roughness and no-slip boundary
conditions are set.
(b) The boundary conditions at both sides of station and
those of the ventilation outlets all take the results
of SES simulation as in [5]. There are two tunnelventilation fans (TVFs) at each ends of the station.
The supply air volume of each TVF is 25 m3=s with
static pressure 1:2 kPa. The suction speed of UPE
is 3:48 m=s.
The turbulence model used in the numerical model is the
widely used standardk model. The relaxation factors setin the course of iteration are shown in Table 4. Except the
linear mode used in the pressure term, the rest terms all use
the false time-step mode.
PHOENICS applies the residual vector R (ui) to check
convergence. Right after each process of iteration, the preset
eective convergence criteria must be checked at once, inorder to decide whether iteration should be continued. This
preset convergence criteria is as follows:
||R(ui)||
||R0|| 6 101: (10)
3. Result and discussion
3.1. Normal operation mode
If the ventilation openings are located at the appropri-
ate positions, the natural ventilation can be accomplishedby the piston eect caused by the moving train in the
subway tunnel. There is no need to turn on the fans in
order to save the energy cost. Therefore, the train should
be able to introduce sucient air to cool down the heat
generated by the train. It must be very careful in the
planning, evaluation, and calculation for the layout of the
ventilation openings and the size of their cross-sectional
areas, and they should be conrmed with the SES
simulation.
UPE is a slot of 0:25 m wide and 1 m long on both sides
of the platform, each side has a total of 46 evenly dis-
tributed slots to capture the heat generated from the train.
There are exhaust duct under the platform and each of
the both ends has an exhaust shaft. Each exhaust shaft on
each end has two sets of fans to simultaneously proceed
with the exhaust of hot air on the same side of the both
ends.
There is platform-screen doors installed in the station plat-
form according to the present research, therefore the airowat the passenger area of the platform and that at the track area
does not have direct convection. When the train arrives a sta-
tion, and the platform-screen door opens, only small amount
of air ows in because the gap between the platform-screen
door and the carriage door is small, and hence the convection
can be ignored. Only the heat conduction generated by tem-
perature dierence inside and outside the platform-screen
door needs to be taken into consideration. The heat of such
conduction was taken into consideration in the estimation of
cooling load at the passenger area of the station and in the
SES simulation. The simulation time is peak hour of 17:00
in the afternoon, and there is a train for every 120 s, and the
train stops at a station for 25 s. The simulation duration is of
14; 400 s, and then takes the average data of the last 3600 s.
The results with various operating conditions are shown
below.
Normal operation mode with no UPE system. The SES
simulation results show that the temperature at the tunnel
area reaches up to 46:6
C and the temperature at the station
area reaches up to 48:8
C.
Normal operation mode with UPE system (suction air-
ow rate is30 m3=s). The results show that the temperature
drops signicantly, but the temperature in the tunnel area
and the tunnel adjacent to the tracks of the station area is
still as high as 3839
C, which exceeds the required designtemperature of 37
C.
Normal operation mode with UPE system (suction air
ow rate is 40 m3=s). The suction airow rate of UPE of
each track in the station area at the BB and CC stations is
40 m3=s, and at the DD stations and others is still 30 m3=s.
The simulation results show that the temperature at the tun-
nel area has dropped below 37
C, and the average temper-
ature next to the tracks in the station area also drops below
37
C.
The above simulations show that when the station area
does not have the UPE system, the temperature will rise to
49
C approximately. When the operation is performed inan environment with the temperature higher than 45
C, the
performance of the electrical equipment, air conditioning
system and auxiliary equipment of the train itself in the
tunnel will drop to below 50%. When the temperature of the
environment further rises over 55
C, they will not be able to
operate. Therefore, it is necessary to install the UPE system
to prevent the operation eciency of system equipment in
the tunnel from being seriously inuenced by the extreme
environment.
Since there is a crossover on the up track departing
from the AA station, when the suction airow rate of UPE
is 30 m3=s for each side of the platform the piston eect
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1144 M.-T. Ke et al./ Building and Environment 37 (2002) 11391152
Distance from AA Station (m)
DryBulbTemper
ature(C)
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Distance from AA Station (m)
0 500 1000 1500 2000 2500 3000 3500 4000 4500
29
30
31
32
33
34
35
36
37
38
39
40BB/CC/DD UPE=15 m3 /s, Headway=120 sec.
BB/CC UPE=20 m3 /s, DD UPE=15 m3 /s, Headway=120 sec.
BB/CC/DD UPE=15 m3 /s, Headway=120 sec.
BB/CC UPE=20 m3 /s, DD UPE=15 m3 /s, Headway=120 sec.
BB Station
BB Station CC Station DD Station
CC Station DD Station
DryBulbTemperature(oC)
29
30
31
32
33
34
35
36
37
38
39
40
(a)
(b)
Fig. 3. Temperature distributions in up track and down track tunnels.
cannot function as expected. In the down track the DD
station is the terminal station and has no entrance or exit
passing through the ground surface. When the train departs
the DD station, it will immediately meet the cross-over and
reduce the function of the piston eect. Although there is a
signicant drop in the air temperature in the tunnel, yet it
still does not meet with the design requirement. More partic-
ularly, the temperature reaches up to about 39
C on the track
in the BB station and the CC station. Since the piston eect
cannot accomplish the expected result, only reinforcing the
performance of UPE system can be considered. Therefore,
suction airow rate at the BB and the CC stations will rise
to 40 m3=s on each side of the platform and still keeps at
30 m3=s for the DD station. The comparison of the simu-
lation results is shown in Fig. 3. The average temperatures
in dierent location according to the present conditions are
shown in Table 5. The simulation results show that the av-
erage temperature of the air next to the track in the tunnel
Table 5
Average temperature in tunnel and station areas (UPE suction rates:
BB=CC stations= 40 m3=s, DD station= UPE30 m3=s)
Tunnel area Up track (
C) Down track (
C)
AABB 36.4 35.1
BBCC 36.5 35.5CCDD 35.8 35.2
DDPortal 31.7 30.6
Station area
BB 36.9 35.6
CC 36.4 35.7
DD 34.2 30.5
and the station area is below 37
C. Therefore, it is recom-
mended to increase the suction airow rate of UPE system
at the BB and CC stations to 40 m 3=s on each side of the
platform.
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M.-T. Ke et al./ Building and Environment 37 (2002) 11391152 1145
3.2. The inuence of the cross-sectional area and length
of the ventilation shaft on the piston eect
Studying and understanding the inuence of the
cross-sectional area and the length of the ventilation tun-
nel to the piston eect serves as the reference basis for
the design change and reduces the impact on surroundingenvironment and the visual landscape in the future.
In the present research, the cross-sectional area and the
length of the upstream and downstream ventilation shafts in
the BB station are separately changed, and the case analy-
ses by comparing the results with the theoretical values are
shown below.
3.2.1. Eect of the cross-sectional area of the ventilation
shaft
The cross-sectional area of the ventilation tunnel at the
BB station is set to 15, 20, 25, and 30 m 2, and the length is
maintained at 60 m to investigate its impact. All of the UPEsystems are closed to avoid inuences to the analysis of the
piston eect.
The simulation results are shown in Fig. 4. When the
cross-sectional area of the ventilation shaft is doubled, the
airow rate in it will increase by 1.4 times, and the theoret-
ical value of the ow should also be doubled. It is because
the theoretical result only takes one ventilation shaft into
consideration and there is no inuence from any other, but
the SES simulation accounts the inuence of all ventilation
Cross-Sectional Area of Ventilation Shaft (m2)
Volume
Flow
rateinVentilationShaft(m3/s)
15 20 25 303
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Downstream BB Station, ExhaustDownstream BB Station, IntakeUpstream BB Station, ExhaustUpstream BB Station, IntakeTheoretical Value
Fig. 5. Eect of the length of ventilation shaft on the airow rate (cross-sectional area = 20 m 2).
Cross-Sectional Area of Ventilation Shaft (m2)
VolumeFlowrateinVentilationShaft(m3/s)
15 20 25 30
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Downstream BB Station, ExhaustDownstream BB Station, Intake
Upstream BB Station, Exhaust
Upstream BB Station, Intake
Theoretical Value
Fig. 4. Eect of the cross-sectional area of ventilation shaft on the airowrate (length = 60 m).
shafts. Therefore, there is a dierence in the results, and the
SES simulation is used as the basis for the analysis.
3.2.2. Eect of the length of the ventilation shaft
The length of the ventilation shaft at the BB station
is separately changed to 40, 60, 80, and 100 m, and the
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1146 M.-T. Ke et al./ Building and Environment 37 (2002) 11391152
Fig. 6. Coupling eect of the cross-sectional area and length of ventilation shaft on the airow rate.
Tunnel Distance (m)
TemperatureinTunnel(oC)
500 100030
32
34
36
38
40
42
44
46
48
5020 km/hr
40 km/hr60 km/hr
80 km/hr
BB Station CC Station
Fig. 7. Temperature distributions in tunnel under various train speeds.
cross-sectional area remains at 20 m2, and all of the UPE
systems are closed to avoid any inuence to the analysis of
the piston eect.
The simulation results are shown in Fig. 5. When the
length of the ventilation shaft is increased to 2.5 times, the
airow rate at the downstream of the ventilation shaft at
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M.-T. Ke et al./ Building and Environment 37 (2002) 11391152 1147
Fig. 8. Pressure and velocity distributions when the train entering the station area under various speeds.
the BB station is reduced to 0.75 0.85 times, and that at the
upstream of BB station is reduced to about 0.95 times. Since
the inuence at the upstream ventilation shaft is smaller
than that at the downstream due to the change of length,
theoretically the change in airow rate due to the change in
length is very small and is about 1%.
3.2.3. Coupling eect of the cross-sectional area and the
length of the ventilation shaft
The design specication basically regulates the cross-
sectional area of the ventilation shaft that cannot be greater
than 20 m2, and the length should not exceed 60 m, but
sometimes the length of the ventilation shaft has to be in-
creased due to the problem of limiting land and the position
of the exit of the ventilation opening has to be changed.
Therefore, when the original design with an area of 20 m2
and length of 60 m is changed to the lengths of 80 and
100 m, the cross-sectional area should be increased ac-
cording to the simulation to obtain the same air exhaust
volume.
The simulation results are shown in Fig. 6. When the
length of the upstream and downstream ventilation shafts at
the BB station are increased to 80 m, the cross-sectional area
should be enlarged to 22:5 m2 to accomplish the originally
designed total intake and exhaust air volume (at 20 m2
, and60 m) caused by the piston eect. When the length of the
ventilation shaft is increased to 100 m, the cross-sectional
area should be enlarged to 25 m2.
3.3. The inuence of train velocities on environment
temperature in the tunnel and track areas
Dierent piston eects caused by dierent train velocities
will inuence the induction and exhaust of the airow in the
ventilation shaft, and further impact the thermal exchange
of the hot air in the tunnel with the external air and hence
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1148 M.-T. Ke et al./ Building and Environment 37 (2002) 11391152
Fig. 9. Pressure and velocity distributions when the train passing through the ventilation shaft under various speeds.
aects the temperature distribution in the tunnel. The heat
in the tunnel is generated from the equipment such as lights,
indicating lights, and electric equipments, and the major
source comes from the train due to its acceleration heat,
braking heat, and the heat discharged from air-conditioning
equipment and its accessory equipment.
The SES program is used to separately simulate dierentpiston eects caused by dierent train velocities (20, 40, 60,
and 80 km=h) passing through the tunnel for the analysis of
temperature distribution, assuming the length of the tunnel,
the length, dimension and position of the ventilation shaft,
and the train schedule interval are constant.
The simulation results are shown in Fig. 7. The simulation
results show that when the train velocity is in the range of
4060 km=h, the temperature in the tunnel is lower. When
the velocity is at 20 km=h, it has more cars in the tunnel due
to the slow speed and causes a drastic rise in temperature
due to the weak piston eect. When the train velocity is
at 80 km=h, although there is a better piston eect, yet the
larger heat released from the high speed of the train causes
the air temperature in the tunnel higher than those at the
velocities of 40 and 60 km=h.
3.4. The inuence of train velocities on pressure
distribution in the station area
Due to the safety and economic considerations, all stations
in the Hsin Chuan route will be designed to install platform
screen doors. However, the addition of screen doors easily
causes the piston eect when the train arrives the station.
A large pressure at the train head will be produced, and the
thickness of the glass and the anti-pressure capability of the
platform screen door must be taken into consideration.
To simulate the situations of the train passing the station,
the actual dimensions of the station and tunnel are consid-
ered as detailed as possible into the numerical model. Both
sides of the model are tunnels, and the length at the end of
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M.-T. Ke et al./ Building and Environment 37 (2002) 11391152 1149
Fig. 10. Pressure and velocity distributions upon the train arriving the platform screen door area under various speeds.
the entrance to the tunnel is 171 m, and the length at the
end of the exit of the tunnel is 150 m. The total length of
the station is 198 m, wherein the platform screen door area
is 141 m, the height of the station is 5 :31 m, and they are
of the actual size. The 46 UPE slots under the platform are
simplied into 5, but the total opening area and the suction
air volume remain unchanged. In the mean time, in order
to simplify the model, and since the station is symmetrical
sideway, only the track on one side is considered for the
CFD simulation in order to reduce the CPU time.
The by-pass and the ventilation shafts are taken into con-
sideration, and they are put into the model for simulation.
A 29:5 m 3:2 m 141 m block represents the train of theTaipei Rapid Transit System. A theoretical reference value
can be derived by the calculation according to the design data
[2]. When the train is traveling at the velocity of 80 km=h,
the length of the tunnel is 1400 m, and the blockage ratio is
42.5%, the pressure dierence generated by the train head
is 1132 Pa. 3D CFD simulation results are shown in Fig. 8
when the train entering the platform area and traveling at the
velocity of 80, 65, and 55 km=h, respectively. The contour
diagram represents the pressure, and the vector diagram rep-
resents the velocity. Fig. 9 shows the pressure and velocity
distributions of the train passing the ventilation shaft with
dierent velocities. Fig. 10 shows the pressure and veloc-
ity distributions of the train just entering into the platform
screen door area. Fig. 11 shows the pressure and velocity
distributions when the pressure generated by the head of the
train reaches the maximum.
The maximum pressure at 80 km=h is 1727 Pa, as can
be seen from these gures and the head of the train gener-
ates the maximum pressure of 1119 Pa at 65 km=h. Further-
more, Fig. 12 shows the pressure and velocity distributions
of the train just departing from the platform screen door
area at dierent velocities, and it shows the pressure and ve-
locity distributions at each location. When the train passes
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1150 M.-T. Ke et al./ Building and Environment 37 (2002) 11391152
Fig. 11. Pressure and velocity distributions when the pressure on the train head reaches maximum under various speeds.
through the platform at dierent velocities, the maximum
pressure caused by the trains displacement is shown in Fig.
13. When the train enters the platform area from the circular
tunnel, the maximum pressure generated by the train head
starts to drop, and it is because the eects of the by-pass
and the ventilation shafts. After the train passes the by-passand the ventilation shafts, the pressure starts to accumulate.
When the velocity of the train is 80 km =h, the maximum
pressure of 1727 Pa of the entire simulation process approx-
imately occurs at the second car of the train when it enters
the platform screen door area, and the pressure will progres-
sively decrease thereafter. When the velocity of the train is
65 km=h, the maximum pressure generated by the train head
is up to 1119 Pa, and at the velocity of 55 km =h, the maxi-
mum pressure is 782 Pa.
When the train passes through the platform screen door
area, the maximum pressure occurs at the position near the
train head, since the cross-sectional area of the station is
descending when it enters the platform screen door area,
and the pressure obviously starts increasing. Meanwhile, it
can be observed that only when the train passes through the
neighborhood of the by-pass and the ventilation shafts, it has
signicant pressure releasing eect. After the train passing
by-pass and the ventilation shafts, it has no eect on therelease of pressure.
4. Conclusions
This study combines the SES program and the CFD soft-
ware PHOENICS for detailed simulation and analysis of
subways environmental control system as a reference for
design. The conclusions of the analysis of the present re-
search are described below:
The temperature change in tunnel under dierent piston
eects and train velocities. When the velocity of the train
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M.-T. Ke et al./ Building and Environment 37 (2002) 11391152 1151
Fig. 12. Pressure and velocity distributions when the train head leaving the station area under various speeds.
is at 4060 km=h, the air temperature in the tunnel is lower
than that at the velocity of 80 km=h by 12
C, and when the
velocity is at low speed of 20 km=h, the temperature will
rise due to the weak piston eect.
The inuence of cross-sectional area and length of the
ventilation shaft on the piston eect. If the height of the
exit of the ventilation shaft and the minor head loss remains
unchanged, the increase in length of the ventilation shaft will
increase the friction. When the length is increased from 40
to 100 m, the airow rate will decrease by 1525%. Theincrease in cross-sectional area of the ventilation shaft will
signicantly reduce the friction resistance and the resistance
due to the reduction in velocity. When the cross-sectional
area is increased from 15 to 30 m2, the airow rate will be
increased by about 40%. When the length of the ventilation
shaft is increased to 80 m, the cross-sectional area has to be
increased to 22:5 m2 in order to maintain the original piston
eect. If the length of the ventilation shaft is increased to
100 m, the cross-sectional area has to be increased to 25 m 2.
The inuence to the platform-screen door when the train
passes through the station.The CFD simulation result of the
maximum pressure when the train that passes through the
platform screen door with a velocity of 80 km=h is 1727 Pa,
which is higher than the result of 1132 Pa obtained from
the empirical correlation, which is a simplied model with
less parameters. The value diers from the simulation results
obtained by the PHOENICS by approximately 30%.
The CFD simulation results show that when the train is
traveling at 80 km=h, the train head generates the maximum
pressure of 1727 Pa, which approximately occurs at the sec-
ond car of the train when it enters the platform-screen door
area. When the velocity slows down to 65 and 55 km=h,
the maximum pressures are decreased to 1119 and 782 Pa,
respectively, which also occurs at the second car of the
train when it enters the platform-screen door area. The
foregoing results recommend a speed of less than 55 km =h
when the train passes through the platform without a
stop.
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1152 M.-T. Ke et al./ Building and Environment 37 (2002) 11391152
Position (m)
Pressure(Pa)
10 20 30 40 50 60 700
200
400
600
800
1000
1200
1400
1600
1800
2000Speed= 80 km/hrSpeed= 60 km/hrSpeed= 55 km/hr
Fig. 13. Pressure distribution along distance when the train head arriving the station area under various speeds.
The pressure generated by the train head can only be re-
leased when the train is passing through the by-pass and the
ventilation shafts. After the train passes through the by-pass
and the ventilation shafts, the pressure starts to increase
quickly.
References
[1] Subway environmental design handbook, vol. II, Subway
environmental simulation computer program, Version 4, Part 1, Users
manual. DOT of USA, 1997.
[2] Subway environmental design handbook, vol. I, Principles and
applications. DOT of USA, 1975.
[3] ASHRAE applications handbook. ASHRAE, 1999 [Chapter 28].
[4] Tsal RJ, Adler MS. Evaluation of numerical methods for ductwork
and pipeline optimization. ASHRAE Transactions 1987;93(1):1734.
[5] Cheng TC. Simulations of ventilation and smoke system for subway
tunnel. MS thesis, National Taipei University of Technology, Taiwan,
2000.