Iain Trent, project engineer, Land Securities

With the Merton Rule requiring 10% of energy to come from renewable sources, we knew we’d need something special for such a largescale project. Consultants Arup and Hoare Lea had looked at photovoltaics, but found that would barely make a dent in the requirements, maybe 1%, and a biomass system physically wouldn’t fit.

The only viable option was geothermal energy. We’d previously trialed an open loop borehole system at an office refurbishment at 40 Eastbourne Terrace in Paddington, but the system experienced problems with the aquifer gradually rising in temperature. There are also risks related to not knowing the amount of water you’ll find underground, which even detailed geographical surveys can’t reveal.

So at One New Change, to minimise the risks associated with open loop boreholes, we opted for a hybrid system, linking the open loop to Energy Piles to help balance temperatures. Energy Piles are similar in structure to typical concrete piles but embedded with long plastic pipes through which water is run to act as a thermal store for geothermal energy. When the foundation works are finished, the sections of pipework embedded in the pile are plumbed into the heating/cooling system.

At One New Change the initial design had incorporated five pairs of open loops and 106 Energy Piles, but that still wouldn’t generate our 10%. So to boost efficiency, energy pile developers Skanska Cementation and Geothermal International, working with the design team, refined the system, cutting down the number of thermal loops to just one pair and increasing the number of Energy Piles to 219, which is the majority of the piling.