Ventilating the English Channel Tunnel A unique ventilation system design ensures a supply offresh air to 95 miles (150 km) of tunnels By Terence M. Dodge Member ASHRAE he idea of a fixed link (a tunnel) groups also put proposals together and. in Accordingly, the Channel Tunnel is the lar­ becween France and England 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 trains 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 London National College of Heating, includes modifications to the infrastructure 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 road 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 Sangatte, The spoil on the English site was used France, to Folkestone in Kent, 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 Dover. 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 lte~ 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. Introducing our new 5-yr. \Vnrrnnty On Commercial/ Industrial Boilers! . , n.: than half a century, Colum- .,11 110 . ' Ih in's built a better boiler-and now we re ·'·in•' our boilers better, too. Now you I) Ill.:" 0 • ' • cull specify and buy Americas pre~ier 1ler' ror hydro nic or steam heat, high- _, orI'" \ow-pressure steam, or .instantaneous ter and get unsurpassed five-year 111 I Wa • I . - · Iprotection . Ask your c.o umb1a 0 1sm- hutor for complete details. COLUMBIA ,,, Columbia Boiler Co. Box G, Pottstown, PA 19464 Phone: (215) 323-2700 Fax: (215) 323-7292 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.