Editing Channel Tunnel (section)

==== Ventilation, cooling and drainage ====
The ventilation system maintains greater air pressure in the service tunnel than in the rail tunnels, so that in the event of a fire, smoke does not enter the service tunnel from the rail tunnels. There is a normal ventilating system and a supplementary system. Twin fans are mounted in vertical shafts where digging for the tunnel began, on both sides of the channel: two in [[Sangatte]], France, and two more at [[Shakespeare Cliff Halt railway station|Shakespeare Cliff]], UK. The normal ventilating system is connected direct to the service tunnel and provides fresh air through the cross- passages into the running tunnels, where it is dispersed by the piston effect of the train and shuttle movements. Only one fan on each side is ever running, the second being available as a backup. The supplementary ventilating system is a separate emergency system and can be used to control smoke or supply emergency air within the tunnels. On both systems, the fans are normally run on supply mode, pulling in air from the outside, but they can also be used in extraction mode to remove smoke or fumes from the tunnels.<ref>{{Cite web |last=Dodge |first=Terence M. |title=Ventilating the English Channel Tunnel |url=https://www.aivc.org/sites/default/files/airbase_7421.pdf }}</ref>

Two cooling water pipes in each rail tunnel circulate chilled water to remove heat generated by the rail traffic. Pumping stations remove water in the tunnels from rain, seepage, and so on.{{sfn|Foreign & Commonwealth Office|1994|p=8}}

During the design stage of the tunnel, engineers found that its aerodynamic properties and the heat generated by high-speed trains as they passed through it would raise the temperature inside the tunnel to {{convert|50|C|F}}.<ref name="CoolingPost">{{Cite news|title=HFO chillers to cool the Channel Tunnel|date=14 September 2016|work=Cooling Post|url=https://www.coolingpost.com/world-news/hfo-chillers-to-cool-the-channel-tunnel/|accessdate=12 June 2016}}</ref> As well as making the trains "unbearably warm" for passengers, this also presented a risk of equipment failure and track distortion.<ref name=CoolingPost/> To cool the tunnel to below {{convert|35|C|F}}, engineers installed {{convert|480|km|mi|abbr=in}} of {{convert|61|cm|in|1|abbr=on}} diameter cooling pipes carrying {{convert|84|e6l|e6impgal|abbr=off}} of water. The network—Europe's largest cooling system—was supplied by eight [[York International|York Titan]] chillers running on [[Chlorodifluoromethane|R22]], a [[hydrochlorofluorocarbon]] (HCFC) refrigerant gas.<ref name=CoolingPost/><ref name="CoolingPost2">{{Cite news|title=Tunnel vision proves R1233zd efficiency|date=1 June 2018|work=Cooling Post|accessdate=12 June 2018|url=https://www.coolingpost.com/features/tunnel-vision-proves-r1233zd-efficiency/}}</ref>

Due to R22's [[ozone depletion potential]] and high [[global warming potential]], its use is being phased out in developed countries. Since 1 January 2015, it has been illegal in Europe to use HCFCs to service air-conditioning equipment; broken equipment that used HCFCs must be replaced with equipment that does not use it. In 2016, [[Trane]] was selected to provide replacement chillers for the tunnel's cooling network.<ref name=CoolingPost/> The York chillers were decommissioned and four "next generation" Trane Series E CenTraVac large-capacity (2,600&nbsp;kW to 14,000&nbsp;kW) chillers were installed—two in Sangatte, France, and two at Shakespeare Cliff, UK. The energy-efficient chillers, using [[Honeywell]]'s non-flammable, ultra-low GWP [[1-Chloro-3,3,3-trifluoropropene|R1233zd(E)]] refrigerant, maintain temperatures at {{convert|25|C|F}}, and in their first year of operation generated savings of 4.8{{nbsp}}[[GWh]]—approximately 33%, equating to €500,000 ($585,000)—for tunnel operator [[Getlink]].<ref name=CoolingPost2/>