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Carrier Ultra-Low GWP HFO Heat Pumps Help Decarbonise the City of London


Carrier AquaForce® 61XWHZE high-temperature heat pumps operating on ultra-low global warming potential (GWP) Hydro-Fluoro-Olefins (HFO) 1234ze refrigerant have been chosen for E.ON's ground-breaking district heating and cooling scheme in the City of London. The project is anticipated to cut carbon emissions from heating and cooling by customers connected to E.On’s City of London network by up to 50% and will enhance air quality in the city by reducing emissions. Carrier is part of Carrier Global Corporation (NYSE: CARR), the leading global provider of healthy, safe, sustainable and intelligent building and cold chain solutions.

The project is part of a multi-million-pound programme by E.ON to improve and upgrade the Citigen energy centre, the hidden power station supporting efforts to decarbonise the city and transform how connected buildings in the Square Mile are heated and cooled. The refrigerant used in the selected heat pumps, R-1234ze, has a GWP of less than 1, significantly lower than the previous refrigerant, and therefore has only a tiny fraction of the environmental impact.

Three Carrier AquaForce 61XWHZE heat pumps will extract thermal energy from water pumped from deep boreholes in the aquifer 200 metres beneath the capital. They will also harness waste heat from the existing Combined Heat and Power plant that would otherwise be lost to atmosphere.

The Carrier units upgrade the energy harvested to produce hot water at 80 C. This will be used to provide up to 4MW of heating and 2.8MW of cooling to residential and business customers via a district-wide network of highly insulated pipes, running underground for 10 kilometers. Customers connected to E.ON’s heating and cooling network include the Barbican arts and residential complex, the Guildhall and the Museum of London.

Innovative, efficient solutions such as AquaForce heat pumps support Carrier’s aim of reducing customers' carbon footprint by more than 1 gigaton, part of its 2030 Environmental, Social & Governance (ESG) Goals.

Antony Meanwell, head of Low Carbon Solutions - City Energy Solutions at E.ON, said: “Tackling the environmental impact of heating, especially in densely populated areas, will be key to meeting the UK’s 2050 net zero targets, and by installing heat pump and geothermal technology at Citigen we’re making a powerful statement of what can be done to reduce carbon usage on a large scale.”

He added: “No project on this scale – or as pioneering in its vision – simply happens. It has required a huge team effort to develop the ideas, translate them into plans and finally make our project a reality on the ground.”

John Foster, project lead for Carrier, said: "The high temperatures required by the project are normally very challenging to achieve. However, AquaForce heat pumps are designed specifically to generate high-temperature hot water from relatively low-grade energy sources, while maintaining excellent energy efficiency. In addition, the way the units are multiplexed in the overall system ensures their capacity is fully utilised."

Carrier heat pumps are leak- and run-tested in an ISO 140001 and ISO 9001 certified facility prior to delivery. Due to the pandemic, customer witness tests for this project – to prove the units could achieve the challenging conditions required – were carried out remotely via video.

AquaForce heat pumps are designed to be exceptionally reliable and are based on Carrier's proven twin-rotor screw compressor, which has bearings with oversized rollers, oil-pressure lubricated, and a motor cooled by suction gas for extended operation, even at maximum load.

With its advanced features and performance, the heat pump is designed to be quick and easy to install for contractors, requiring only an electrical supply and water source. Streamlined electrical and hydraulic connections ensure quick set-up and commissioning.

John Foster added: "In a historical twist, Citigen's plant room once housed the ice-store for Smithfield Market. It is a happy coincidence that the site is being reborn as a centre for modern, cutting-edge low-carbon cooling and heating."

For more details on Carrier's AquaForce 61XWHZE heat pumps, visit


Carrier was selected to support E.ON’s multi-million-pound upgrade project for its Citigen site to decarbonise its network in the City of London, which is transforming how buildings are heated and cooled.


Three Carrier AquaForce® 61XWHZE heat pumps will extract thermal energy from water pumped from deep boreholes in the aquifer beneath the capital.
Image courtesy of E.ON © E.ON


The Carrier heat pumps upgrade the energy harvested to produce 4MW of hot water at 80 deg C.


The total cost of ownership of the Carrier units over their lifetime is up to 20% less than natural refrigerant-based heat pumps.