The idea is as ingenious as it is unique and has the potential to become a global role model: the Bunhill Heat and Power Network project in central London.
By using waste heat from the London Underground network, 1,350 homes, a school and two leisure centres in Islington are now heated and supplied with hot water as part of the council’s efforts to reduce carbon emissions and achieve CO2 neutrality by 2030.
In partnership with the main contractor, Colloide Engineering Systems, global technology specialist GEA supplied a purpose-built heat pump solution for this flagship project – the first of its kind.
Bunhill 2 Energy Centre represents a real blueprint for the use of waste heat from public facilities, taking advantage of state-of-the-art technology on the site of the former City Road London Underground station which was decommissioned nearly 100 years ago.
The remains of the station have now been converted into a massive underground air extraction system that draws warm air from the tunnels underneath, still used by the London Underground's Northern Line.
In close cooperation with Islington Council, Transport for London and Colloide, GEA installed a 1000 kW ammonia heat pump, housed within a container at street level.
The heat pump extracts the energy from warm exhaust air from the underground tunnels. The slightly cooler air is vented to the ambient and the rest is harnessed as energy and used to heat up water via the heat pump, which is then pumped through a 1.5 km network of district heating pipes which provide heating to various buildings in the neighborhood.
Developed and manufactured by GEA the heat pump system consists of a combined evaporator/separator, three compressors and four heat exchangers in the heating circuit.
The heat exchangers optimize the heating circuit according to criteria based on the return of heating water at 55 degrees Celsius and the supply up to 80 C.
Kenneth Hoffmann, product manager for Heat Pumps at GEA Refrigeration Technologies, said a key challenge in finalizing the system design was the extensive testing required to ensure that any dust or dirt sucked into the ventilation air would not clog the heat exchanger coil.
“Since the project was located next to a residential building, the installation also included a scrubber technology to filter the ventilation air from the plant room,” he said.
“In the very unlikely event of a small amount of the natural refrigerant ammonia escaping into the plant room, the local residents would not be exposed to the ammonia in the air, as it would be absorbed in the scrubber before being vented to ambient.
“The use of heat pumps is much more environmentally friendly than the use of gas boilers, especially in big cities, as they do not emit nitrogen oxides (NOx). Heat pumps therefore lead to cleaner air in cities and pay off financially. Moreover, ammonia is a natural refrigerant that does not contribute to global warming.”
Paddy McGuinness, managing director of Colloide Engineering Systems, said the company has been involved in several renewable energy projects.
“We partnered with GEA. on this project given their knowledge of ammonia refrigeration and heat pump technology,” he said.
“Based on GEA’s experience, 95 per cent of the industrial refrigeration plants installed over the last 10 years have been ammonia based. Increased pressure to reduce energy bills for end users is driving a lot of interest in ammonia heat pumps.”
The Bunhill 2 Energy Centre now connects an additional 550 homes and a primary school to the existing Bunhill Heat and Power district heating network, launched by the Islington Council in 2012. Heating costs for residents connected to the network will be cut by 10 per cent when compared to other existing communal heating systems, which themselves cost around half as much as standalone systems for heating individual homes.
The new system is a win-win for the environment and for the residents of Islington and aligns with the council’s aim to end fuel poverty.
The heating system is particularly environmentally friendly as it reuses heat that would otherwise be wasted. Supplying the connected households and public facilities with the upgraded waste heat will help to reduce CO2 emissions in the Islington Borough by around 500 tonnes per year.
Colloide contracts manager, Shaun Hannon, described it as a ground-breaking district heating scheme.
“The main technology used is the ammonia heat pump and as a result, this project provides cheaper, greener energy for the local community,” Hannon said.
GEA UK technical sales manager for refrigeration technologies, Iain Eckett, said it was a very ambitious task.
“But we have shown that GEA has the knowledge, the technology and the ability to successfully implement innovative projects to generate cleaner and cheaper heating,” he said.
The principle of heat recovery using heat pumps can be applied in London and in underground networks all around the world.
London alone has more than 150 ventilation shafts where waste heat could potentially be recovered.