Anybody who’s ever travelled on the London Underground will know just how hot it gets down there, with excess heat being generated by the trains’ electric motors and friction from the brakes.
Until now, all that hot air has just been vented above ground. However, Islington, a borough of London, which intends to become carbon neutral by 2030, decided that the heat was a resource to be utilized in the pursuit of this goal.
In March 2020, Islington inaugurated a world’s-first project, the Bunhill 2 Energy Centre, which sends the warm Underground air through an ammonia heat pump to assist in creating heating and hot water for more than 1,350 homes, one local primary school and two leisure centers, according to a press release from Islington's governing council. Bunhill 2, which cost £16.3 million (US$20.3 million), thereby reduces the CO2 emissions that would have been generated by oil- or gas-fired heating systems.
Bunhill 2 works with Bunhill 1 (opened in 2012), which employs a 2MW CHP (combined heat and power) engine. Together they comprise the Bunhill Heat and Power Network, a district energy provider.
Islington Council chose an ammonia heat pump for the project after conferring with engineers from German manufacturer GEA. One of the criteria was that very hot water – 75-80°C (167-176°F) – is needed for heating in the older housing units owned by the council, said Kenneth Hoffmann, GEA's Heat Pump Product Manager.
The hot-water requirement meant that an ammonia heat pump was the only viable option that would give Islington a sufficiently energy-efficient system, said Hoffmann. The solution chosen has an annual coefficient of performance (COP) of 3.5.
The energy-efficient ammonia heat pump has enabled the Islington Council to lower the heating bills for the residents in the 1,350 homes by 10% compared to other communal heating systems that use fossil fuels – which are in themselves around 50% cheaper than stand-alone systems for individual homes, according to Islington Council.
The reduced bills were a very important factor influencing Islington’s decision, as “fuel poverty” is a serious problem for many people in London, especially people living in council housing, many of whom are in low-income households.