CADOUEST SA (Prilly)

**DISTRICT HEATING

THEN AND NOW

District heating in the Greater Lausanne area began with the Pierre-de-Plan plant. Initially dedicated to the production of town gas for public lighting, it was converted in 1934 into a single boiler room for the buildings of the nearby hospital, now the CHUV.

Over the course of its history, the network has benefited from technological innovations and its production facilities have evolved: in addition to a gas turbine, boilers were installed to meet the needs of the heating network; coal-fired boilers were replaced in 1965 to produce directly at the distribution temperature, which was 180ºC at the time. Supplementary electric boilers were also abandoned, in favor of gas or oil-fired boilers.

Since winter 2006, the Tridel plant has replaced the former household waste incineration plant, producing 220 GWh of heat compared with 80 GWh previously. This transformation has brought CAD into an era where fossil fuels are no longer the main source of supply**. Various production stations have also been added to the network, including a sewage sludge combustion station at the STEP de Vidy.

After decades of expansion, CAD in the Greater Lausanne area now has over 1,300 connected buildings and more than 100 km of network.

To encourage development in the western part of the conurbation, CADouest SA was created in 2011, with the mission of promoting district heating and taking charge of network extension work.

CAD OPERATING PRINCIPLE

Heat is produced by several industrial-scale production units serving a network of consumers. The heat is distributed throughout the city via an underground network of high-temperature pipes, supplying the connected buildings. The superheated water circulating in the pipes is used to heat the secondary network inside each connected building, via a heat exchanger. The water cooled by the heat transfer returns to the power plant to be heated again.