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 (BHPN) project in central London. By using waste heat from the London Underground network, 1,350 homes, a school and two leisure centers in Islington, are now heated and supplied with hot water. Due to the nature and specialisms required in this project, main contractor Colloide Engineering Systems partnered with key consulting engineers, suppliers and subcontractors to form a team very capable of delivering this project. As part of this team, GEA, a global technology specialist supplied a purpose-built heat pump solution for this flagship project. GEA, Colloide and all those involved are supporting Islington's efforts to reduce carbon emissions with the aim of achieving CO2 neutrality by 2030.

The new energy center uses state-of-the-art technology on the site of a London Underground station that has been decommissioned for almost 100 years. The remains of the station, once known as City Road, have been converted into a huge underground air extraction system that draws warm air from the tunnels underneath. The tunnels are used by London Underground's northern line.

According to Kenneth Hoffmann, Product Manager for Heat Pumps at GEA Refrigeration Technologies, there were many challenges in the design of the system during the project. These included extensive testing to ensure that dust and dirt sucked into the ventilation air would not clog the heat exchanger coil. Kenneth Hoffmann explains: "Bunhill's district heating network required hot water from the heat pump up to 80˚C. We used two-stage reciprocating compressors, also known as "pistons", to achieve a Coefficient of Performance (COP), or heat pump efficiency, of over 3.5. 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. The aim is to prevent that 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.”

Paddy McGuinness notes why this solution was chosen: “Colloide have been involved in a large number of renewable energy projects. Colloide partnered with GEA on this project for their knowledge of ammonia refrigeration and heat pump technology. Based on GEA’s experience, 95 percent of the industrial refrigeration plants installed over the last 10 years have been ammonia based. With the increasing pressure on end users to reduce energy bills, this has brought about a big increase in the interest of ammonia heat pumps.”

“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,” says Kenneth Hoffmann.

Further district heating potential in the future

The principle of heat recovery using heat pumps can be applied in London as well as in underground networks all over the world. Take London, for example: Here, investigations into the more than 150 ventilation shafts will reveal which have potential for recovering waste heat. GEA's heat pump technology, coupled with the experience gained from the groundbreaking Bunhill 2 project, makes the company the preferred partner in this respect. Take the example of underground railways all over the world: here too, GEA heat pump technology offers great potential for waste heat recovery and, consequently, for environmental and climate protection.