SMART GRIDS | ENERGY SUPERHUB OXFORD OXFORDS BALANCING ACT Oxford is building an intelligent local grid that will allow buildings heat pumps to be connected to a smart grid that is able to charge hundreds of electric vehicles, thanks to a large-scale battery technology. Andy Pearson reports O n 5 October, a Kensa heat pump was installed in the first of 60 homes in Blackbird Leys, Oxford. The heat pumps are connected to a series of boreholes incorporating communal ground arrays. These are the first of 300 homes and commercial premises in and around Oxford that will feature ground source heating as part of the Energy Superhub Oxford (ESO). The ESO is an ambitious 41m project, partfunded by the UK governments Industrial Strategy Challenge Fund, which in addition to low carbon heating will demonstrate grid-balancing hybrid battery technology and large-scale rapid electric vehicle (EV) charging. Smart software will manage the energy storage, EV charging and heat pumps to reduce strain on the grid and allow it to accommodate more renewables. The project is being led by Pivot Power, and when complete in 2022, it is predicted that it will eliminate 10,000 tonnes of CO2 emissions a year. Heating is the single biggest contributor to UK emissions. The domestic heating element of the project will demonstrate how ground source heat pumps (GSHPs) can help minimise the carbon associated with heating homes and businesses. In advance of the heat pumps installation, housing provider Stonewater has upgraded the homes fabric through the addition of cavity wall and loft insulation, coupled with the installation of double glazing. Heat losses are generally between 4-5kW per home, so the majority of homes will be fitted with a 6kW heat pump. Each home will have a heat pump connected to the shared outside infrastructure of pipes and boreholes, says Matthew Trewhella, managing director of Kensa Contracting. The retrofit forms phase 1 of the project. Later phases will see up to 240 new-build homes fitted with GSHPs, and potentially various commercial properties too. Unusually, for the first phase the Oxford project has had to create six smaller communal arrays, one serving each cluster of homes, rather than use a single larger array. Blackbird Leys is split into six smaller clusters because groups of houses are separated by roads, and so on, says Trewhella. Similarly, the areas geology has necessitated a larger number of boreholes than usual for a scheme of this size. Normally, wed have gone with around 20 boreholes up to 220m deep, but because there is a layer of water about 100m below ground at high pressure, weve gone for 40 boreholes at about 96m depth, he says. The ground array is simple; it comprises a piped water/glycol mixfilled circuit that operates at a temperature of between 0C and 12C to connect the homes to the boreholes. The homes are being fitted with dedicated heat pumps; these incorporate a circulating pump to pass the water/glycol from the ground loop through the heat pump at the appropriate flowrate. When a householder turns on the heating, the heat pump will chill the water/glycol mix and the units circulating pump will pass this to the 38 November 2020 www.cibsejournal.com CIBSE Nov20 pp38-41 ESO Battery.indd 38 23/10/2020 16:28