HEAT NETWORK | CITIGEN Greening the City The City of London is adding heat pumps and boreholes to its Farringdon energy centre and hopes to encourage more commercial buildings to plug into its low carbon heat network T he faades of the Port of London Authority building and its neighbour The Central Cold Storage, built to hold animal carcasses for Smithfield meat market opposite, stand as a reminder of Londons commercial past. Now behind these venerable walls is a state-of-the-art energy centre that includes an innovative heat pump and borehole solution, which is claimed to cut the carbon emissions associated with heating and cooling by up to 50%. The energy centre, owned and run by E.ON, is the latest development on a site where power was first generated in 1893. Back then, when electric power was still in its infancy, the Cold Storage building housed one of Londons first coal-fired power stations, built to power the market and its refrigerators and purchased by the City of London. A century after it first started to produce power, the power station now has two combined heat and power (CHP) engines and two absorption chillers, which together form a centralised energy centre capable of providing up to 39GWh of electricity, 40GWh of heat energy and 7GWh of cooling per year for the corporations buildings in the City. In 2013, and now known as Citigen, its two 16MW dual-fuel (gas/diesel) CHP engines were replaced by two new, smaller and more efficient 4.3MW gas-reciprocating CHP engines, as part of a 27m investment programme. The energy centres three, 3MW oil-fired back-up boilers were also converted to run on gas, while a 320m3, 50m-high thermal store, which can store up to 8MWh of heat, was installed. If the heating load on the network is larger than 9MW, the boilers will kick in as top-up, explains Leke Oluwole, general manager of the Citigen district energy scheme. In a normal year, 92% of the heat is reclaimed from the CHP, with an 8% contribution from the boilers. Three, 1.1MW low-voltage screw chillers, and a 3MW high-voltage screw chiller, were installed to replace the absorption chillers mentioned above. The low-grade heat rejected by the replacement chillers was discharged to the atmosphere via eight cooling towers. The final intervention was the addition of a new control room above the energy centre, to enable staff to run it and the 70 other district heating schemes operated by E.ON around the country. The energy centres CHP engines generate high-voltage electricity to power the chillers and network pumps, with surplus power sold to the Grid or direct to customers via a private wire network. Heat reclaimed from the CHP engines and their exhausts is used to heat the water in the thermal store, up to a temperature of 105C. The energy centre runs 24/7 to serve the mix of residential and commercial properties on the network, says Oluwole. From Smithfield, 11km of insulated pipes weave their way underground, buried beneath public roads and hidden in basements and tunnels. These also deliver heating and cooling to the City of Londons buildings, including the Guildhall, Barbican Centre, and the Museum of London. Heat from the thermal store is carried through 6km of pipes at a temperature of 95C flow, 72C return to 27 substations, for distribution to buildings served by the plant. Seven of the substations also provide cooling; chilled water leaves the energy centre at a temperature of 6C and returns at approximately 11C-12C, depending on demand. In June 2021, E.ON announced the start of a 4m project to decarbonise the energy centre and increase its heating and cooling The Port of London Authority building, which houses the energy station CHP engines generate high-voltage electricity to power the chillers and network pumps, with surplus power sold to the Grid or direct to customers 46 May 2022 www.cibsejournal.com CIBSE May 22 pp46-48, 50-51 Citigen Supp.indd 46 22/04/2022 15:56