at two large buildings of the London South Bank University as a research and development project. Heat sources District heating networks exploit various energy sources, sometimes indirectly through multipurpose infrastructure such as combined heat and power plants (CHP, also called co-generation). Combustion of fossil or renewable fuels The most used energy source for district heating is the burning of hydrocarbons. As the supply of renewable fuels is insufficient, the fossil fuels coal and gas are massively used for district heating. This burning of fossil hydrocarbons usually contributes to climate change, as the use of systems to capture and store the CO2 instead of releasing it into the atmosphere is rare. In the case of a cogeneration plant, the heat output is typically sized to meet half of the peak winter heat load, but over the year will provide 90% of the heat supplied. Much of the heat produced in summer will generally be wasted. The boiler capacity will be able to meet the entire heat demand unaided and can cover for breakdowns in the cogeneration plant. It is not economic to size the cogeneration plant alone to be able to meet the full heat load. In the New York City steam system, that is around 2.5 GW. Germany has the largest amount of CHP in Europe. A simple thermal power station can be 20–35% efficient, whereas a more advanced facility with the ability to recover waste heat can reach total energy efficiency of nearly 80%. Some may approach 100% based on the lower heating value by condensing the flue gas as well. Nuclear fission The heat produced by nuclear chain reactions can be injected into district heating networks. This does not contaminate the district pipes with radioactive elements, as the heat is transferred to the network through heat exchangers. It is not technically necessary for the nuclear reactor to be very close to the district heating network, as heat can be transported over significant distances (exceeding 200 km) with affordable losses, using insulated pipes. Since nuclear reactors do not significantly contribute to either air pollution or global warming, they can be an advantageous alternative to the combustion of fossil hydrocarbons. However, only a small minority of the nuclear reactors currently in operation around the world are connected to a district heating network. These reactors are in Bulgaria, China, Hungary, Romania, Russia, Slovakia, Slovenia, Switzerland and Ukraine. The Ågesta Nuclear Power