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.

Islington Council and its net zero carbon target for 2030

Islington Council has been committed to reducing carbon emissions for many years and has declared a climate emergency. In the corresponding declaration, it committed itself to working towards a net zero target by 2030, i.e. to achieve CO2 neutrality. To achieve this goal for the benefit of its citizens, Islington is taking steps to provide citizens with cheaper and more environmentally friendly energy. 

Bunhill 2 Energy Centre - Exterior (Photo: Islington Council)
Bunhill 2 Energy Centre - Exterior (Photo: Islington Council)

One of these measures is the truly revolutionary Bunhill 2 Energy Centre, the first of its kind in the world. It represents a real blueprint for the use of waste heat from public facilities, in the specific case of the London Underground. By heating and supplying hot water for homes, a school and leisure centers in Islington, energy is saved, carbon emissions are reduced, air quality is improved, and heating costs for Islington’s residents benefiting from the scheme, many of whom are in fuel poverty, are reduced.

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.

GEA heat pump solution

In close cooperation with Islington Council, Transport for London (TfL) and the main contractor Colloide Engineering Systems, GEA installed a 1000 kW ammonia heat pump in a container at street level.

Colloide are continually looking for ways in which to achieve economic, social and environmental success. In order to ensure that our values are fully implemented into each of our projects, we have a pre-qualification system in place which assesses the sustainability policies of all Colloide’s subcontractors and suppliers. GEA and their ammonia heat pump certainly meet that criteria.”– Paddy McGuinness, Managing Director of Colloide Engineering Systems

GEA heat pump in Islington, London
GEA heat pump system installed at Bunhil 2 Energy Centre

The heat pump extracts the energy from warm exhaust air from the underground tunnels. The slightly cooler air is vented to the ambient and energy is used to heat up water by the heat pump, which  is pumped through a 1.5 km network of district heating pipes to the buildings in the neighborhood, where it is finally used to heat the buildings.

The heat pump developed and manufactured by GEA for the system consists of a combined evaporator/separator, 3 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˚C and the supply up to 80˚C.

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.

The inspiring result

The Bunhill 2 Energy Centre adds a further 550 homes and a primary school to the existing Bunhill Heat and Power district heating network, launched by Islington Council in 2012. The network already provided cheaper, greener heat every day of the year to two local leisure centers and more than 800 homes, but the new energy center gives the system the potential to supply up to 2,200 homes. The heating costs for residents connected to the network will be cut by 10 percent compared to other existing communal heating systems, which themselves cost around half as much as standalone systems heating individual homes. So, a real benefit to the environment, to residents and to Islington with the aim to end fuel poverty.

The nearby Moreland Primary School was the first school to be connected to the network that already supplies the swimming pool and facilities at Ironmonger Row Bath and Finsbury Leisure Centre. Colloide have also put in place initiatives to invest in young people in the surrounding area and have connected with local schools, colleges and universities. They aim to provide opportunities for work experience and workplace visits with a view to improving employment skills, while increasing the confidence of local children in the Islington Borough.

Bunhill 2 Energy Centre heats London homes with GEA heat pump technology
GEA's Kenneth Hoffmann (left) and Iain Eckett (right) at Bunhill 2 Energy Centre

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 by around 500 tons per year.

"This 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. We offer the most efficient solution at an attractive price," adds Iain Eckett, Technical Sales Manager, Refrigeration Technologies, GEA UK.

Thanks to the cooperation of all involved, this is 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.”– Shaun Hannon, Contracts Manager at Colloide

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.

Project data:

Start: 2017
Completion: 2019
Gross Internal Floor Area: 617m²
Contract: JCT Design and Build Contract
Architect: Cullinan Studio (design)
McGurk Chartered Architects (delivery)
Client and project manager: Islington Borough Council
Key Delivery Partner: TfL
Structural Engineer: Ramboll (design), McMahon Associates (delivery)
M&E Consultant: Ramboll
QS: Gleeds
Landscape Consultants: J&L Gibbons
CDM Co-ordinator: AECOM
Approved building inspector: Islington Building Control
Design and Build Contractor: Colloide Engineering
Artist: Toby Paterson
Heat Pump System: GEA (design, manufacture, and installation)
Testing and Commissioning: Topic Plan
Project consultants: Inner Circle Consulting
Rights of Light: Right of Light Consulting
CAD Software: MicroStation, Revit

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