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Home , Channel Tunnel, English Channel

Ventilating the

A unique ventilation system design ensures a supply offresh air to 95 miles (150 km) of

By Terence M. Dodge Member ASHRAE

he idea of a fixed link (a tunnel) groups also put proposals together and. in Accordingly, the is the lar­ becween and 1982, French and Bricish governments gest civil engineering project incorporating was first proposed in l7Sl by the requesced feasibility studies into privately the longest tunnels the world has ever seen. TFrench Armiens Academy when funding the massive undertaking from the The underground system consists of they launched a competition to find a "bet­ banking institutions. three tunnels: north- and south-running ter means of crossing the Channel'.' In March 1983, agreement for a tunnel tunnels of 7.6 m (2S ft) internal diameter; The first tunnelling commenced in was reached and a consortium of five and, between them, a service tunnel of 4.8 1880. However, it was halted in 1882 due to French and British contractors formed to m (16 ft) internal diameter (see Figure /). a reluctant British government fearing a put forward proposals for the fixed link. The north tunnel takes shuttles and continental invasion. In October 1985, formal submissions from England co France, and the south tun­ In 1974, tunnelling started again on were made. In February 1986, an Anglo­ nel from France co England. both sides of the channel. However, it was French treaty was signed and a concession At 37S m (1,230 ft) intervals, all three abandoned in 1975 due to a change of Brit­ was granted to Eurotunnel in March 1986 tunnels are linked by 3.3 m (I I ft) internal ish government and the economic malaise for a SS-year operating contract. diameter cross-passages. At 250 m (820 ft) of the day. The contractors' formal signing of the intervals, the two running tunnels are Jinked In 1978, interest was raised when contract with Eurocunnel occurred in with a 2.0 m (6.5 ft) internal diameter piston European contractors formed a consor­ August 1986. This was followed in July relief duct (sec Figure /). tium to resurrect the tunnel. Several other 1987 by Her Majesty The Queen assenting The service tunnel is used to provide to the Channel Tunnel Bill becoming The fresh air co the running tunnels, as a safety Channel Tunnel Act. refuge in case of incidents within the run­ About the author Under the terms of the contraci, the ning tunnels, and for access for emergency Terence M. Dodge is the managing director contractors are responsible for the design, services and maintenance personnel. It also of Raxcrest Project Management Ltd., construction and commissioning of the full contains electrical and mechanical services, Birmingham, England. He graduated rrom integrated transportation system. This control rooms and pumping stations. the National College of Heating, includes modifications to the Boring and lining the tunnels com­ Ventjlating, Air Conditioning and Refrig­ to accommodate terminals in each country, menced in March 1988 and formed ISO km eration. Dodge acted as project manager with ABB Flakt for the design, procure­ integrating with and rail transporca­ (95 miles) of tunnels. The tunnelling ment and installation of the Channel Tun­ tion systems as well as the tunnelling. produced 8,000,000 ml (282,000,000 ftl) of nel ventilation system up to its final spoil in the form of liquid mud. This was installation and commissioning stage, Tunnel description pumped to settlement retention lagoons. which was completed in January 1993. The tunnel system connects , The spoil on the English site was used France, to in , England. to form 4S hectares (111 acres) of reclaimed

70 ASHRAE Journal October 1993 W fan is a axial flow fan, with sin­ land at the foot of Shakespeare Cliff, The normal ventilating system (NVS) >?i! ~j JI1d direction motors •. fitted to . When construction is completed, is connected direct to the service tunnel and ~.lb}epitch aerofoil blades. This enables this land will form a public amenity area. provides fresh air through the cross­ ~ 3._..,.- co be reversed without stopping passages into the running tunnels. There :a~ ~~ng the motor. Cooling/ventilation systems the fresh air is dispersed by the piston effea The environmental services provided of the trains and shuttle movements. t:* normal control mode, only one ~ ~ :;t:1tion operates. However, bo~h to the Channel Tunnel consist of the cool­ The piston effect causes both negative ing and ventilation systems. ~ ~ siation can be used for comnus­ and positive air pressures within the run­ ,...;,,... \"maintenance under local manual The cooling system consists of a ning tunnels with shuttle movements. The si.: - ~ refrigeration plant with dry coolers for heat piston relief ducts relieve the pressure by :..,~'Tl'i. rejection at each end of the tunnel complex. transferring air from one running tunnel The! :-lVS fans operate at a design This plant provides cooled water to feed a (via the piston relief duct) into the adjacem :'\ ·nt _,i ' $.~ ml /s (187,000 cfm~ with a pipework circulation system run into each running tunnel and then back to the shut­ ~ ~1 pressure of 2.92 kPa (12 m. wg). of the tunnels. tle running tunnel, again via the piston ~y Jl'I! fitted with 390 kW (525 hp) Heat transfer is by conduction into the relief ducts (see Figure 2). ~~'r.:. using 3.3 kV AC supply. pipework. Each cooling system and its pipe­ The supplementary ventilating system ~SYS fans operate at a design point work run to the mid-point of the tunnels. ,,: :t\1 m; s (635,700 cfm) with a system The ventilation system consists of a (SVS) is connected into both running tun­ nels. Under single-mode operation, fresh .. ._~ure 0 i t.52 kPa (6 in. wg). The fans ~re normal ventilating system (NVS) and a ;):i....J with 900 kW (1,200 hp) motors usmg supplementary ventilating system (SVS) at air can be provided to one or both running \_; kY ..\C supply. each end of the tunnels. tunnels by the selection of control dampers. Each ventilating system consists of Under dual-mode operation, both running When the fans are operated, it is essen- · · tunnels are provided with air. ~ t ll' ·ool their motors. This cooling is two fans in parallel housed in purpose-built n.. ' - k' fan stations. These fan stations are located The SVS is a separate emergency sys­ 'II\'' id1.'1 bv a ducted coolmg system ta mg at ground level and are connected via shafts tem and can be used to control smoke or h,-::h ti ~ air thro~gh a centrifugal f~n, to the tunnels. The exception is the English supply emergency air within the tunnels. ,\'llllt.'\:ti ng 10 the mam fan moto~s casmg NVS which is installed vertically in a 9.25 m On both systems, the fans are normally run ;\n,\ ~xiti ng from the exhaust casmg con- (30 ft) internal diameter shaft that is 23.5 m on supply mode, but they can also be used Continued on page 72 (77 ft) deep. in the extraction mode.

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71 (Circle No. 37 on Reeder Service Cam) ASHRAE Journal October 1993 The English Channel Tunnel eliminated by the addition of special anti­ As system pressure increases to Continued from page 71 stall rings. This unique ring-shaped stabiliz­ approach the fan stall point, air flow at the ing device is one of only a handful of its rotating fan blade tips is reversed as the stall type in operation in the world. It is incor­ progresses. This backflow rotates with the nection via ductwork to atmosphere out­ porated into the fan casing entry but impeller and imposes a pre-rotation of the side the fan station. located outside the main flow stream adja­ entering air, which also affects the blade On the NVS system only, an electric cent to the fan blade tips (see Figure 3 ). roots causing severe stress in a conventional air heater battery system, with a rating of 1.2 MW (4,000,000 Btu/ h), is installed to maintain temperature control of the tunnel Piston Relief Duct ventilation air. With the large volume of air, 2.0 m· Diameter the heater battery gives a 10 °C (18 °F) rise over the battery. Each electric heater battery consists of modules of smaller heater batteries. These are switched on and off by a thyrister con­ trol system fitted to one of the battery mod­ ules when deviation from the control setpoint occurs. On a temperature fall, the thyrister Figure 1. Cross-section view 9f the three tunnels. module switches on and modulates up to 100% capacity output. If heat demand is still required, the thyristor switches on a fixed output module (with the thyrister controlled unit returning to zero output), whence the cycle recommences until all modules required are in operation. On rise of temperature, the control system acts in reverse manner.

Ventilation system operation The principle of the NVS ventilation to the Channel Tunnel is relatively straight­ forward. However, the scale of operation and the fact that the running shuttles cause extreme pressure variations as they pass through the tunnels combine to create sig­ nificant problems for most conventional ventilation systems. The fan feeding the air supply into the ~ I Channel Tunnel complex would run at con­ stant speed, volume and pressure if there were no shuttle movement. But with the movement, both volume and pressure will Figure 2. Air flow through the piston relief ducts. vary, and the system operating point will ' move up and down the fan performance curve. With the computer control system, the Channel Tunnel fans adjust the fan blade pitch to continue supplying air at the required volume. If the pressure increases due to shuttle movement, then the system resistance will increase until the fan reaches its stall limit. At that point, a conventional axial flow fan will start operating in an unstable mode and the volume and pressure output will fail. This situation will cause severe stress to occur in the fan and it may be damaged, causing a breakdown to the whole system. However, with the Channel Tunnel fan .: system, this stalling problem has been Continued on page 74

ASHRAE Journal October 1993 rJ I The English Channel Tunnel of air intake louvres, air heater (NVS only) and displayed on a VDU. The system is Continued from page 72 acoustic attenuators and isolating dampers totally separated from the EMS. Level 3 is I to each side of the main fans, cooling sys­ used primarily for maintenance purposes. tem and an integrated control system linked The electrical power to the ventilation I ·l fan system. Once induced, this pre-swirl to the principal engineering management stations is provided from two independent reduces air flow and the pressure capacity system (EMS). grid supplies (one domestic, the other over­ of the fan. 'I Each fan station has installed a con­ ), each connected to its own switch I I The introduction of the anti-stall ring eliminates the air flow reversal at blade tip trol panel that can operate at three levels: board. The primary supply is the domestic I I supply using the overseas supply for back­ I , by means of turning vanes incorporated • Level I allows the control panel to into an annular chamber of the anti-stall up in case of failure. . operate the fan station automatically under The domestic primary supply to the ring. The air stream off the ring is returned normal operation, with monitoring and fan station control system is fed through an into the main air stream in a completely operating commands direct from the engi­ I I axial sense. Therefore, the blade tip uninterruptable power supply. The overseas I neering management system operator supply is connected direct to the control still receives high axial flow vector and con­ located in the Channel Tunnel central con­ tinues to support pressure generation, and system. trol. The operating point of the fans is the problem of backflow causing pre-swirl selected by the EMS operator using the pro­ The domestic supply feeds the run­ in the fan inlet is eliminated. ning fan system whilst the overseas supply At certain times, shuttle movement grammable logic controller within the fan station panel which confirms back to the runs the standby fan system. Should a will cause abnormal pressure resistance to failure occur in the running system, then I EMS when its commands are achieved. ~ occur within the Channel Tunnels, leading the overseas supply to the standby system the fans to operate well beyond the system • Level 2 allows operation from the automatically takes over and the current design pressure. However, the anti-stall sys­ fan station local control panel with the running system closes down. tem will prevent the tunnel fans from stall­ EMS only able to the operations The overseas supply can be used to j I ing and maintain air flow into the tunnels. I I and functions carried out. feed the running system by selection of the \ switchgear by the EMS operator. Ventilation control system • Level 3 operation of equipment is Operational life of the ventilation sys- The tunnel ventilation system consists again from the fan station but by keyboard tem is designed for 25 years. •

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