E.ON Citigen Decarbonisation

Image courtesy of E.ON

Image courtesy of E.ON


Ramboll. Crispin Matson. Image courtesy of Paulina Sobczak Photography

Crispin Matson

Business Development, District Energy
T: +44 20 7631 5291


E.ON's Citigen energy centre provides district cooling, heating and electricity to the City of London and private developments.

The Citigen Decarbonisation project is expected to turn Citigen into one of the UK’s largest combined heating and cooling heat pump low-carbon energy systems.

The breakthrough: combined heating and cooling

Ramboll was commissioned by E.ON to design a heat pump solution to help decarbonise the heating and cooling supply to customers in the City of London.

The installation includes combined heating and cooling heat pumps with ground borehole storage accessing the natural warmth of the Earth and is expected to reduce carbon emissions of the energy centre by up to 50%. This innovative energy recycling principle effectively treats waste streams (excess heat) as a source.

The existing energy centre primarily uses gas powered internal combustion engines, and therefore emits carbon from the two existing 4.3MW CHPs (combined heat and power engines) and gas boilers. E.ON have recognized the opportunity to begin decarbonising their district heating network assets and Citigen was chosen as the first site to be enhanced with heat pump technology. 

The heat pumps effectively recycle low grade waste heat from both the CHP generation - capturing the waste heat from the site's cooling towers - as well as from neighboring commercial buildings which require cooling into the district heating system, reducing carbon emissions and running cost.

The district cooling abstracted heat (that would otherwise be dumped via cooling towers), can be stored in 200m deep ground boreholes and upgraded through heat pumps into useful heat, again saving cost and carbon. 

The installation of heat pumps increases Citigen’s heating capacity enabling it to connect new commercial and residential users in the City of London, while the additional cooling capacity reduces the necessary chiller operating and investment costs. 

Lord Callanan, the energy minister, said E.ON’s heat network was “a commercial vote of confidence” in low-carbon heating technologies, “meaning homes and businesses across the City of London will benefit from clean heat”.

We will be supporting E.ON throughout the project, with completion is set for early 2022.

Key benefits of the solution

  • Reduces energy waste via recycling heat that would otherwise be rejected into the urban space
  • Heat pumps that electrify Citigen’s plant, reducing dependence on fossil fuels and cutting CO2 emissions
  • Strengthens Citigen’s security of supply, while safeguarding space in the always congested city centre energy infrastructure
  • Combines heating and cooling installations into one, limiting investment and operating costs
  • Allows Citigen's district energy networks to extend to further customers, allowing greater take-up of low carbon energy in a densely populated area
  • The multi heat source approach adds flexibility to the energy system paving the way to future innovations 

Click image to expand heat pump infographic

Our approach

E.ON engaged with Ramboll to develop the concept through a feasibility study and detailed design. Extensive energy and technoeconomic modelling indicated the optimal asset sizing and heat source prioritisation to meet Citigen's growing energy needs and new customer connections, while reducing CO2 emissions. 

The scope of the project was to install 4MWth of heat pumps operating at combined heating and cooling, backed-up by three, 200m deep ground boreholes for energy balancing. A flexible heat pump concept can switch from ground source to combined heating and cooling, or waste heat recovery, as required, at different periods. The heat pumps complement the existing CHP, boilers and electric chillers to provide heat and chilled water as necessary. 

The design was developed to a level of detail commensurate with RIBA Stage 3 (Developed Design). A wide team of experts from across Ramboll were mobilised to deliver mechanical and electrical  design and services including energy modelling, air quality assessment, noise assessment, utility coordination, structural design, planning, CDM principle design, tender package support and procurement. 


Located in the heart of London, near the historic Smithfield Meat Market, Citigen feeds heating and cooling networks which extend for more than 10km under the streets of the capital, supplying 20MW of heat and 6MW of cooling to residential and commercial buildings including the Barbican and the Museum of London. 

The energy centre in Charterhouse Street, Farringdon, has had multiple uses over its long history, as marked from the listed facades of the Port of London Authority and the market's Central Cold Store.

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Tel:+44 20 7631 5291

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