Only in Cologne by Duncan J.D. Smith

116 42 Innenstadt A Road under the Rhine Innenstadt (Deutz) (Borough 1), the District Heating Tunnel (Fernwärmetunnel) at the corner of Messeplatz and Kennedyufer Stadtbahn 1, 7, 9 Deutzer Freiheit An inconspicuous concrete cylinder in Deutz, at the corner of Messe- platz and Kennedyufer, provides an entrance to one of Cologne’s technological wonders. Beyond a flood-proof door is a spiral staircase, leading downwards for twenty five metres. At the bottom is a tunnel conveying pipes for the city’s District Heating Network (Fernwärme­ netz) from one side of the Rhine to the other. The tunnel is walkable and can be visited on an exciting tour by appointment with Cologne’s power provider, RheinEnergie AG (tel. 0049-(0)221-178-4660, www. rheinenergie.com ). Cologne’s District HeatingTunnel (Fernwärmetunnel) , which is four hundred and sixty one metres in length, connects the heating network of the Innenstadt with Deutz on the east bank. Water heated in the city’s three power stations (Niehl, Merkenich, and Innenstadt Süd) is pumped through a network of underground feed and return pipes, of which those in the tunnel are part, to around six thousand homes and businesses on both sides of the river, providing them simultane- ously with heating and hot water. The pipes are so well insulated that the water cools by only five degrees between power station and end user. The concept of District Heating (Fernwärme) was first introduced into Cologne in the early 1960s. Over time the city’s traditional, coal- fired power stations have been supplemented by four combined heat and power (‘cogeneration’) plants (Kraft-Wärme-Kopplung) , namely the three already mentioned, and another in Merheim. Running costs are cheaper in cogeneration plants because steam is used both to propel the turbines that generate power and to heat the water in the District Heating Network (heat that was traditionally lost to the atmosphere). The facility in Niehl, for example, converts 86% of its fuel input into power and heat, as opposed to less than 50% in a coal-fired power sta- tion that generates electricity alone. Atmospheric pollution is also significantly reduced. At the time of writing, more than 80% of heat in Germany’s district heating networks is provided by cogeneration plants, of which over 40% are powered by natural gas. To see a co-