Building and Environment 37 (2002) 1139–1152www.elsevier.com/locate/buildenv

Numerical simulation for optimizing the design of subwayenvironmental control system

Ming-Tsun Ke ∗, Tsung-Che Cheng, Wen-Por WangDepartment 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 3uid dynamics (CFD)software to explore the in3uence of various operating situations to the subway environment of Taipei Rapid Transit System in the presentstudy. The results show that the under platform exhaust (UPE) has a substantial in3uence on the temperature and the cross-sectional areaof the ventilation shaft has quite more e9ect on the ventilation volume than length. The pressure distribution caused by the piston e9ectand its e9ect on the platform screen door was also discussed and compared. ? 2002 Published by Elsevier Science Ltd.

Keywords: Computational 3uid dynamics; Under platform exhaust; Piston e9ect

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 isone of the important environmental control systems aimingat controlling the temperature inside the tunnel so that theauxiliary system equipment of the train and the electricalequipment in the tunnel can operate properly under accept-able working temperature, and when emergency <re occurs,it can e9ectively control the direction of the spread of thesmoke and discharge the smoke out of the tunnel. On theother hand, the ventilation shafts being installed on bothends of the station can slow down the pressure wave in thestation platform and the in3uence 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 relatedconceptual design of the subway can be resolved by thethermal load analysis of the SES program and the selectionof equipment. Although there are many research reports onthe rapid transit system by using the SES program, yet thedesign conditions and the weather conditions are di9erent

∗ Corresponding author. Tel.: +886-2-27712171; fax: +886-2-27314919.

E-mail address: mtke@ntut.edu.tw (M.-T. Ke).

from those in Taiwan. There are not too many researchesthat are related to the piston e9ect; therefore it is necessaryto use the numerical results of the SES program to combinewith the detailed simulation of the three-dimensional CFDsimulation for further studies on this subject as the referencefor the future planning of the tunnel ventilation and theenvironmental control system.

2. Design conditions and theoretical model

The subway route under investigation is the Hsin Chuanroute of the Taipei Rapid Transit System. The SES soft-ware was used to combine with the commercial CFDpackage software PHOENICS (Parabolic, Hyperbolic orElliptic Numerical Integration Code Series) to establishthe three-dimensional numerical analysis model to proceedwith the detailed physical phenomenon simulation analysisfor the tunnel environmental control system.

2.1. Design conditions and design guidelines

According to the Taipei Rapid Transit System PlanningHandbook, the related design conditions for the environ-mental control system are described as follows.

A. External temperature conditionsThe 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: S0360 -1323(01)00105 -6

1140 M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152

Nomenclature

AA Hsin Chuan stationBB Fu Jen University stationCC Tan Feng stationDD Hui Lung stationA net cross-sectional area of tunnel (m2)Av cross-sectional area of ventilation shaft (m2)C proportional constant, = 0:48Cm 3ow split parameterCKp driving pressure coeLcientCKps head loss through a ventilation shaftCKH i entrance loss, = 1 for a T-junction ventilation

shaftCKHC coupling loss between the tunnel and the venti-

lation shaftDh hydraulic diameter (m)E eLciency of UPEf friction factorf′ modi<ed friction factorF energy head added (m2=s2)g gravitional acceleration (m=s2)hf frictional energy head loss, = (fL=D)(V 2=2)

(m2=s2)hfr minor head loss, =KV 2=2 (m2=s2)k turbulent kinetic energy, (m2=s2)

K loss coeLcientKi parameter, = 0:965Ko parameter, = 0:9 for square tunnelsL length (m)P static pressure (Pa)Q ventilation rate (m3=s)Qv ventilation rate in ventilation shaft (m3=s)R(ui) residuam vectorR0 reference base vectorRe Reynolds numberT 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 z direction (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 1Design 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 bethe design hour, and the external temperature conditions areillustrated in Table 1.

B. The design conditions of the tunnel areaThe air dry-bulb temperature in the tunnel should be kept

below 37◦C during normal operation, and should be below43◦C at conjested condition.

C. Tunnel areaThe tunnel area for this research is from the cross-over

track downstream the Hsin Chuan station (AA station) tothe tunnel area of the Huei Lung station (DD station), andthe range is described as below:

(a) Hsin Chuan Station to Fu Jen University Station (BBstation) (up and down tracks),

(b) Fu Jen University Station to Tan Feng Station (CC sta-tion) (up and down tracks),

Table 2Tunnel dimensions

AA–BB BB–CC CC–DD Lay-upTunnel Tunnel Tunnel track

Length (m) 1370 1227 1416 About 600Inclination (%) −0:3=0:53 −0:3=0:36 −0:47=0:3 −3=3Remark 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 trackof the lay-up track of the tunnel.

Tunnel sections are primarily bored tunnels except thatcross-over tracks and lay-up tracks are cut and covertunnels, and the geometric dimensions are shown inTable 2.

D. The tunnel area of the cross-over track and the tunnelportal of the lay-up trackThere 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 groundlevel to the maintenance and repair plant. The up and downtracks are linked together by the cross-over track, making

M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152 1141

Table 3Dimensions of stations

Fu Jen Univ. Tan Feng Hui LungStation Station Station

Length of station area (m) 194 153 277.2Height of concourse (m) 4.15 4.15 4.15Height of track area (m) 6.21 6.21 6.21Width of track area (m) 16.55 16.55 17.55Length of platform area (m) 141 141 141Width of platform area (m) 8.7 8.7 8.9

the air3ow in one track to 3ow to another track and thusreducing the piston e9ect. Therefore, jet fan should be in-stalled to guide the air3ow. However, since there is a lay-uptrack tunnel extending to the ground level, the hot air in thetunnel can be exhausted, or outside air can also be inducedtoo.

E. Ventilation shaftAccording to the design requirements, ventilation open-

ings are installed on both sides of the station, which con-nect with the environmental control system plantroomsand the natural outdoors air, and it includes three indepen-dent shafts: exhaust shaft, intake shaft, and pressure reliefshaft.

F. Station area geometryThe concourses and the island type platforms of Fu Jen

University station, Tan Feng station and Hui Long Stationare all located in cut and covered boxes. Platform-screendoors are installed between the platform and the trackarea. Each side of the platform is supposed to be linedwith a train with six cars and each car has four doors.The station is a two-3oor underground building verti-cally connected by a concourse and the platform track-layer. The dimension of the station area is generalized inTable 3.

G. UPEIn 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 FLOWDIRECTION

Unit: m

Fig. 1. Schematic plot of the tunnel ventilation system between stations.

amount of air 3owing between the platform and the tunnelsince the gap between the train and the platform-screen dooris only 10 cm wide. The installation of screen doors servesto prevent heat in the tunnel and in the train from gettinginto the platform area and reduce the cooling load of airconditioning 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 expelledby UPE. The de<nition for the eLciency E of UPE is asfollows:

E =Heat expelled by UPEHeat released by train

= CQ: (1)

As proven by the result of the experiment, the proportionalconstant C in Eq. (1) is 0.48 when the eLciency E is under65% whereas there is no experimental data to refer to if E isgreater than 65%. However, as known through the eLciencycurve in theory, the eLciency will not exceed 80% no matterhow the discharge capacity is.

2.2. Theoretical model

The present research <rst used the SES to perform theanalysis for the underground tunnel ventilation system andobtained the important operational data, and then these datawere used as the boundary conditions to proceed with the3D CFD simulation to give us detailed and useful numericalresults. Fig. 1 shows the layout of the ventilation systemin the tunnel between each station, and Fig. 2 is the localdetailed 3D layout of the station area.

2.2.1. One-dimensional analysis modelThe installation of ventilation shaft will have an impact

on the visual landscape and the surrounding environmentbecause of the prominent vertical construction and the occu-pation of valuable land so that the design for the ventilationshaft may need to be changed. It results in the originallyplanned ventilation requirement. Therefore, we must studythe in3uence of the length and the cross-sectional area of the

1142 M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152

Fig. 2. Local detail layout of present underground station.

ventilation shaft on the piston e9ect in advance as a basisfor future reference.Bernoulli’s equation can be used for the analysis of

present subway ventilation system.

gZ1 +P1!+

V 21

2+ F = gZ2 +

P2!2+

V 22

2+ hf + hfm: (2)

In the subway ventilation system, if the height of theventilation shaft remains unchanged, and only the lengthand the cross-sectional area are considered, it will only in-3uence hf and hfm, and the relation between the frictionloss and the cross-sectional area and length is describedbelow.

hf = fLDh

V 2

2; (3)

hfm = KV 2

2: (4)

To study the in3uence of the ventilation shaft to the pistone9ect, we need to know about the air3ow distribution in thetunnel and the ventilation shaft.We can deduce the followingaccording to [2,3].The 3ow split parameter for the air3ow passes through

the ventilation shaft and inside the tunnel is de<nedas

Cm =AvVvAV

=Air3ow volume inside ventilation shaft

Air3ow volume inside tunnel:

(5)

The 3ow split parameter when air 3ows into the ventila-tion openings is de<ned as

Cmi = KiAvA

√CKp

CKps: (6)

The 3ow split parameter when air 3ows out from theventilation openings is

Cmo = KoAvA

√CKp + 1− CKH i

CKps − CKHC; (7)

where CKHC can be neglected when CKps�1.The foregoing 3ow split parameters are only suitable for

the tunnel that only has one ventilation shaft. However, wecan know about the relation between the air3ow and the areaand resistance coeLcient of the ventilation shaft. When thecross-sectional area or the length of the ventilation shaft ischanged, we assume the air3ow caused by the piston e9ectin front of the ventilation shaft is the same (that is Q2 =Q1,CKp2 = CKp1 ), and there is change in air3ow distributiononly in the ventilation shaft and at its downstream, and it isknown as the change of 3ow split parameter. Let the original3ow split parameter be Cm1 , and the 3ow split parameterafter changing the cross-sectional area and the length ofthe ventilation shaft be Cm2 , then the relation of the air3owvolume is shown below.

Qv2Qv1

=Av2Av1

√#K + f1L1=Dh1#K + f2L2=Dh2

; (8)

where the friction factor f can be calculated by theAltshul-Tsal equation [4]:

f′ = 0:11(

aDh

+68Re

)0:25

if f′¿ 0:018: f = f′

if f′ ¡ 0:018: f = 0:85f′ + 0:0028

(9)

with Re = 66:4× 103DhV .

M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152 1143

Table 4Relaxation factors set in present study

Variable P u v w k T

Relaxation factor 0.3 10−4 10−4 10−4 0.3 0.3 0.1

2.2.2. Three-dimensional CFD modelA full-size three-dimensional model is developed accord-

ing to the actual size of the station and the tunnel area inCartesian coordinate. The 3ow is regarded as incompress-ible, transient and turbulent. The boundary conditions are asfollows.

(a) The boundary of all kinds of solids in the model doesnot consider the surface roughness and no-slip boundaryconditions are set.

(b) The boundary conditions at both sides of station andthose of the ventilation outlets all take the resultsof 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 withstatic pressure 1:2 kPa. The suction speed of UPEis 3:48 m=s.

The turbulence model used in the numerical model is thewidely used standard k− model. The relaxation factors setin the course of iteration are shown in Table 4. Except thelinear mode used in the pressure term, the rest terms all usethe false time-step mode.PHOENICS applies the residual vector R (ui) to check

convergence. Right after each process of iteration, the presete9ective convergence criteria must be checked at once, inorder to decide whether iteration should be continued. Thispreset convergence criteria is as follows:

||R(ui)||||R0|| 6 10−1: (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 e9ect caused by the moving train in thesubway tunnel. There is no need to turn on the fans inorder to save the energy cost. Therefore, the train shouldbe able to introduce suLcient air to cool down the heatgenerated by the train. It must be very careful in theplanning, evaluation, and calculation for the layout of theventilation openings and the size of their cross-sectionalareas, and they should be con<rmed with the SESsimulation.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 ofthe both ends has an exhaust shaft. Each exhaust shaft oneach end has two sets of fans to simultaneously proceedwith the exhaust of hot air on the same side of the bothends.There is platform-screen doors installed in the station plat-

form according to the present research, therefore the air3owat the passenger area of the platform and that at the track areadoes not have direct convection. When the train arrives a sta-tion, and the platform-screen door opens, only small amountof air 3ows in because the gap between the platform-screendoor and the carriage door is small, and hence the convectioncan be ignored. Only the heat conduction generated by tem-perature di9erence inside and outside the platform-screendoor needs to be taken into consideration. The heat of suchconduction was taken into consideration in the estimation ofcooling load at the passenger area of the station and in theSES simulation. The simulation time is peak hour of 17:00in the afternoon, and there is a train for every 120 s, and thetrain stops at a station for 25 s. The simulation duration is of14; 400 s, and then takes the average data of the last 3600 s.The results with various operating conditions are shownbelow.

Normal operation mode with no UPE system. The SESsimulation results show that the temperature at the tunnelarea reaches up to 46:6◦C and the temperature at the stationarea reaches up to 48:8◦C.

Normal operation mode with UPE system (suction air-:ow rate is 30 m3=s). The results show that the temperaturedrops signi<cantly, but the temperature in the tunnel areaand the tunnel adjacent to the tracks of the station area isstill as high as 38–39◦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 air3ow rate of UPE ofeach track in the station area at the BB and CC stations is40 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 below37◦C.The above simulations show that when the station area

does not have the UPE system, the temperature will rise to49◦C approximately. When the operation is performed inan environment with the temperature higher than 45◦C, theperformance of the electrical equipment, air conditioningsystem and auxiliary equipment of the train itself in thetunnel will drop to below 50%. When the temperature of theenvironment further rises over 55◦C, they will not be able tooperate. Therefore, it is necessary to install the UPE systemto prevent the operation eLciency of system equipment inthe tunnel from being seriously in3uenced by the extremeenvironment.Since there is a crossover on the up track departing

from the AA station, when the suction air3ow rate of UPEis 30 m3=s for each side of the platform the piston e9ect

1144 M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152

Distance from AA Station (m)

Dry

Bu

lb T

emp

erat

ure

(°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

Dry

Bu

lbT

emp

erat

ure

(o C)

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 DDstation is the terminal station and has no entrance or exitpassing through the ground surface. When the train departsthe DD station, it will immediately meet the cross-over andreduce the function of the piston e9ect. Although there is asigni<cant drop in the air temperature in the tunnel, yet itstill does not meet with the design requirement. More partic-ularly, the temperature reaches up to about 39◦C on the trackin the BB station and the CC station. Since the piston e9ectcannot accomplish the expected result, only reinforcing theperformance of UPE system can be considered. Therefore,suction air3ow rate at the BB and the CC stations will riseto 40 m3=s on each side of the platform and still keeps at30 m3=s for the DD station. The comparison of the simu-lation results is shown in Fig. 3. The average temperaturesin di9erent location according to the present conditions areshown in Table 5. The simulation results show that the av-erage temperature of the air next to the track in the tunnel

Table 5Average 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)

AA–BB 36.4 35.1BB–CC 36.5 35.5CC–DD 35.8 35.2DD–Portal 31.7 30.6

Station areaBB 36.9 35.6CC 36.4 35.7DD 34.2 30.5

and the station area is below 37◦C. Therefore, it is recom-mended to increase the suction air3ow rate of UPE systemat the BB and CC stations to 40 m3=s on each side of theplatform.

M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152 1145

3.2. The in:uence of the cross-sectional area and lengthof the ventilation shaft on the piston e;ect

Studying and understanding the in3uence of thecross-sectional area and the length of the ventilation tun-nel to the piston e9ect serves as the reference basis forthe 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 inthe BB station are separately changed, and the case analy-ses by comparing the results with the theoretical values areshown below.

3.2.1. E;ect of the cross-sectional area of the ventilationshaftThe cross-sectional area of the ventilation tunnel at the

BB station is set to 15, 20, 25, and 30 m2, and the length ismaintained at 60 m to investigate its impact. All of the UPEsystems are closed to avoid in3uences to the analysis of thepiston e9ect.The simulation results are shown in Fig. 4. When the

cross-sectional area of the ventilation shaft is doubled, theair3ow rate in it will increase by 1.4 times, and the theoret-ical value of the 3ow should also be doubled. It is becausethe theoretical result only takes one ventilation shaft intoconsideration and there is no in3uence from any other, butthe SES simulation accounts the in3uence of all ventilation

Cross-Sectional Area of Ventilation Shaft (m2)

Vo

lum

e F

low

rat

e in

Ven

tila

tio

n S

haf

t (m

3/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. E9ect of the length of ventilation shaft on the air3ow rate (cross-sectional area = 20 m2).

Cross-Sectional Area of Ventilation Shaft (m2)

Vol

ume

Flow

rat

e in

Ven

tilat

ion

Sha

ft (m

3 /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. 4. E9ect of the cross-sectional area of ventilation shaft on the air3owrate (length = 60 m).

shafts. Therefore, there is a di9erence in the results, and theSES simulation is used as the basis for the analysis.

3.2.2. E;ect of the length of the ventilation shaftThe length of the ventilation shaft at the BB station

is separately changed to 40, 60, 80, and 100 m, and the

1146 M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152

Fig. 6. Coupling e9ect of the cross-sectional area and length of ventilation shaft on the air3ow rate.

Tunnel Distance (m)

Tem

per

atu

re in

Tu

nn

el (

oC

)

500 100030

32

34

36

38

40

42

44

46

48

5020 km/hr40 km/hr60 km/hr80 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 UPEsystems are closed to avoid any in3uence to the analysis ofthe piston e9ect.

The simulation results are shown in Fig. 5. When thelength of the ventilation shaft is increased to 2.5 times, theair3ow rate at the downstream of the ventilation shaft at

M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152 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 theupstream of BB station is reduced to about 0.95 times. Sincethe in3uence at the upstream ventilation shaft is smallerthan that at the downstream due to the change of length,theoretically the change in air3ow rate due to the change inlength is very small and is about 1%.

3.2.3. Coupling e;ect of the cross-sectional area and thelength of the ventilation shaftThe design speci<cation basically regulates the cross-

sectional area of the ventilation shaft that cannot be greaterthan 20 m2, and the length should not exceed 60 m, butsometimes the length of the ventilation shaft has to be in-creased due to the problem of limiting land and the positionof 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 and100 m, the cross-sectional area should be increased ac-

cording to the simulation to obtain the same air exhaustvolume.The simulation results are shown in Fig. 6. When the

length of the upstream and downstream ventilation shafts atthe BB station are increased to 80 m, the cross-sectional areashould be enlarged to 22:5 m2 to accomplish the originallydesigned total intake and exhaust air volume (at 20 m2, and60 m) caused by the piston e9ect. When the length of theventilation shaft is increased to 100 m, the cross-sectionalarea should be enlarged to 25 m2.

3.3. The in:uence of train velocities on environmenttemperature in the tunnel and track areas

Di9erent piston e9ects caused by di9erent train velocitieswill in3uence the induction and exhaust of the air3ow in theventilation shaft, and further impact the thermal exchangeof the hot air in the tunnel with the external air and hence

1148 M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152

Fig. 9. Pressure and velocity distributions when the train passing through the ventilation shaft under various speeds.

a9ects the temperature distribution in the tunnel. The heatin the tunnel is generated from the equipment such as lights,indicating lights, and electric equipments, and the majorsource comes from the train due to its acceleration heat,braking heat, and the heat discharged from air-conditioningequipment and its accessory equipment.The SES program is used to separately simulate di9erent

piston e9ects caused by di9erent train velocities (20, 40, 60,and 80 km=h) passing through the tunnel for the analysis oftemperature 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 of40–60 km=h, the temperature in the tunnel is lower. Whenthe velocity is at 20 km=h, it has more cars in the tunnel dueto the slow speed and causes a drastic rise in temperaturedue to the weak piston e9ect. When the train velocity isat 80 km=h, although there is a better piston e9ect, yet the

larger heat released from the high speed of the train causesthe air temperature in the tunnel higher than those at thevelocities of 40 and 60 km=h.

3.4. The in:uence of train velocities on pressuredistribution in the station area

Due to the safety and economic considerations, all stationsin the Hsin Chuan route will be designed to install platformscreen doors. However, the addition of screen doors easilycauses the piston e9ect when the train arrives the station.A large pressure at the train head will be produced, and thethickness of the glass and the anti-pressure capability of theplatform 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. Bothsides of the model are tunnels, and the length at the end of

M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152 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 theend of the exit of the tunnel is 150 m. The total length ofthe station is 198 m, wherein the platform screen door areais 141 m, the height of the station is 5:31 m, and they areof the actual size. The 46 UPE slots under the platform aresimpli<ed into 5, but the total opening area and the suctionair volume remain unchanged. In the mean time, in orderto simplify the model, and since the station is symmetricalsideway, only the track on one side is considered for theCFD 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 valuecan 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 is42.5%, the pressure di9erence generated by the train head

is 1132 Pa. 3D CFD simulation results are shown in Fig. 8when the train entering the platform area and traveling at thevelocity of 80, 65, and 55 km=h, respectively. The contourdiagram represents the pressure, and the vector diagram rep-resents the velocity. Fig. 9 shows the pressure and velocitydistributions of the train passing the ventilation shaft withdi9erent velocities. Fig. 10 shows the pressure and veloc-ity distributions of the train just entering into the platformscreen door area. Fig. 11 shows the pressure and velocitydistributions when the pressure generated by the head of thetrain 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 distributionsof the train just departing from the platform screen doorarea at di9erent velocities, and it shows the pressure and ve-locity distributions at each location. When the train passes

1150 M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152

Fig. 11. Pressure and velocity distributions when the pressure on the train head reaches maximum under various speeds.

through the platform at di9erent velocities, the maximumpressure caused by the train’s displacement is shown in Fig.13. When the train enters the platform area from the circulartunnel, the maximum pressure generated by the train headstarts to drop, and it is because the e9ects of the by-passand 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 maximumpressure of 1727 Pa of the entire simulation process approx-imately occurs at the second car of the train when it entersthe platform screen door area, and the pressure will progres-sively decrease thereafter. When the velocity of the train is65 km=h, the maximum pressure generated by the train headis 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 thetrain 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, itcan be observed that only when the train passes through theneighborhood of the by-pass and the ventilation shafts, it hassigni<cant pressure releasing e9ect. After the train passingby-pass and the ventilation shafts, it has no e9ect on therelease of pressure.

4. Conclusions

This study combines the SES program and the CFD soft-ware PHOENICS for detailed simulation and analysis ofsubway’s environmental control system as a reference fordesign. The conclusions of the analysis of the present re-search are described below:

The temperature change in tunnel under di;erent pistone;ects and train velocities. When the velocity of the train

M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152 1151

Fig. 12. Pressure and velocity distributions when the train head leaving the station area under various speeds.

is at 40–60 km=h, the air temperature in the tunnel is lowerthan that at the velocity of 80 km=h by 1–2◦C, and when thevelocity is at low speed of 20 km=h, the temperature willrise due to the weak piston e9ect.

The in:uence of cross-sectional area and length of theventilation shaft on the piston e;ect. If the height of theexit of the ventilation shaft and the minor head loss remainsunchanged, the increase in length of the ventilation shaft willincrease the friction. When the length is increased from 40to 100 m, the air3ow rate will decrease by ∼ 15–25%. Theincrease in cross-sectional area of the ventilation shaft willsigni<cantly reduce the friction resistance and the resistancedue to the reduction in velocity. When the cross-sectionalarea is increased from 15 to 30 m2, the air3ow rate will beincreased by about 40%. When the length of the ventilationshaft is increased to 80 m, the cross-sectional area has to beincreased to 22:5 m2 in order to maintain the original pistone9ect. If the length of the ventilation shaft is increased to100 m, the cross-sectional area has to be increased to 25 m2.

The in:uence to the platform-screen door when the trainpasses through the station. The CFD simulation result of themaximum pressure when the train that passes through theplatform screen door with a velocity of 80 km=h is 1727 Pa,which is higher than the result of 1132 Pa obtained fromthe empirical correlation, which is a simpli<ed model withless parameters. The value di9ers from the simulation resultsobtained 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 maximumpressure of 1727 Pa, which approximately occurs at the sec-ond car of the train when it enters the platform-screen doorarea. 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 thetrain when it enters the platform-screen door area. Theforegoing results recommend a speed of less than 55 km=hwhen the train passes through the platform without astop.

1152 M.-T. Ke et al. / Building and Environment 37 (2002) 1139–1152

Position (m)

Pre

ssu

re (

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 theventilation shafts. After the train passes through the by-passand the ventilation shafts, the pressure starts to increasequickly.

References

[1] Subway environmental design handbook, vol. II, Subwayenvironmental simulation computer program, Version 4, Part 1, User’smanual. DOT of USA, 1997.

[2] Subway environmental design handbook, vol. I, Principles andapplications. 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):17–34.[5] Cheng TC. Simulations of ventilation and smoke system for subway

tunnel. MS thesis, National Taipei University of Technology, Taiwan,2000.