[ Heat Recovery ]
[ Heat Recovery ]
Behind its red-metal skin, the Bunhill 2 Energy Centre in Islington, London, hides advanced heat recovery technology in plain sight: a piece of functional infrastructure that not only delivers warmth, but also defines the neighborhood’ s identity. Photo © Nicole Kinsman
Ammonia is used as the refrigerant for its high efficiency, especially when lifting water temperatures to 70 ° C or more, as required for older buildings in Islington. Unlike many common refrigerants, ammonia is also environmentally benign; it has zero global-warming potential, and, does not deplete the ozone layer. The heat pump is powered on-site by two gas-fired combined heat and power( CHP) units, which also feed heat into the district network. Water returning from the network at 55 ° C enters the heat pump and is reheated to 75 ° C before being circulated back to homes. In summer, when the outside air is warmer than the air in the tunnels, the fan’ s direction can be reversed and air cooled by the system can be blown into the Underground. While the evaporator at Bunhill 2 is made of Type 316 stainless steel, the condenser is made from a 6 % molybdenum stainless steel, chosen for its combination of high strength and corrosion resistance under demanding conditions: 60 bar pressure, relatively high temperature, and exposure to London’ s city water, which contains more than 50 ppm of chlorides. The system saves around 500 tonnes of CO2 per year compared with an oil- or gas-fired one. More remarkably, residents connected to the network benefit from about 10 % lower heating costs than other communal systems, which themselves already cost roughly half as much as standalone systems for heating individual homes. The project also highlights London’ s untapped potential: the Greater London Authority estimates that waste heat could meet as much as 38 % of the city’ s heating demand. The Bunhill 2 Energy Centre is groundbreaking as it provides a practical model for decarbonizing heat in dense cities worldwide.
Recycling heat across Malmö Sweden’ s third-largest city, Malmö, is one of a few places in the world with district heating on a truly city-wide scale. About 90 % of the coastal city’ s heat is provided through a network that also serves the neighboring municipality of Burlöv.
Most of this energy is heat directly recovered from waste incineration, treated wastewater, and other industrial processes as well as renewable sources. A small share of fossil fuel oil is used only during the coldest days. This integrated grid allows Malmö to supply most of its buildings with efficient heat while steadily reducing emissions.
Reuse from refuse The city’ s waste incineration plant provides around 60 % of the district heating for Malmö and Burlöv, using thermal energy from burning trash that would otherwise be unused. In addition to heat generated from burning waste, energy is also captured from the exhaust gases. To improve air quality, harmful compounds are scrubbed from the exhaust gases in a flue-gas cleaning process that removes hot, acidic condensate rich in chlorides and other corrosive compounds. Heat from this condensate is channeled into the district-heating network through a series of plate heat exchangers made from 6 % molybdenum stainless steel.
38 Stainless Steel World May 2026 www. stainless-steel-world. net