AMBIENT HEAT NETWORK | GREENSCIES pumps will be specified with variable speed compressors and drives, they will typically be set to run at constant load, charging the thermal stores as they do so. This simplifies hydraulic control of the ambient loop. The techno-economic proposition of flexible operation of the assets has been investigated through techno-economic modelling led by Chris Dunham (Carbon Descent). It has shown that, as well as making significant carbon savings, the concept can deliver affordable heating to residents and competitively priced cooling and EV charging. A number of heat pump models and refrigerant types are being considered based on coefficient of performance (COP) and capital cost. LSBUs Heating and Cooling Team, led by Graeme Maidment and Akos Revesz, carried out a detailed investigation comparing the life-cycle performance of a number of different heat pump units. The intention is to retain flexibility in the design and keep the accompanying technical specifications relatively loose to ensure that, when the scheme goes to market, supply of the heat pumps will not be confined to particular technologies, manufacturers or refrigerant types. It will also be important to future-proof the designs to allow a range of latest generation refrigerant technologies to be implemented safely and cost-effectively over the life of the network, says Riddle. Various configurations in the energy centres are being assessed, including using multiple heat pumps operating with condensers in series to reduce the temperature increase required by each individual heat pump to improve operating efficiency. LSBU found that by arranging multiple heat pumps Figure 3: Schematic of ambient loop network Chillers Buildings Annual heat demand (MWh) < = ~ 9oC HP capacity (kW) Thermal store capacity (m3) Theatre 2,182 900 110 LBI Estate 1 2,718 600 100 University Campus 1 1,946 900 95 LBI Estate 2 4,534 900 140 LBI Estate 3 3,338 900 130 University Campus 2 8,665 2,600 210 PV TfL ventilation shaft future ~ 18oC 28oC Boilers Residential customer < = 75oC, < = 55oC EV network is integrated with building-mounted PV systems and EV charging points. The decentralised energy centres effectively become the hub of a micro-grid. These could also incorporate grid electricity storage provided by the batteries from connected EVs. This will enable the system to respond to electricity grid demand and tariffs. AI will be used to help flex electricity demands from heat pumps and electric vehicle charging in response to price signals from the grid and the intermittent output of solar power. Implementing schemes like this, with its economic, community, and environmental benefits will be critical if we are to reach the target of net zero carbon for existing buildings. GreenSCIES will contribute to Londons zero carbon ambition by decarbonising the local energy system in Islington as part of its Net Zero Carbon Vision 2030, says Revesz, technical lead at GreenSCIES, who says the project is looking at scaling up the concept. We strongly believe that the implementation of schemes like this could provide a roadmap to help towns and cities across the UK and elsewhere achieve net-zero targets on time. CJ Table 1: Thermal store capacity PV GRID > = ~10oC, 16oC with condensers and evaporators in series COP could be increased by up to 30%. This arrangement has the benefit of being able to take a heat pump out of operation and still run the remaining units. The performance benefits of connecting the heat pumps in series needs to be offset against the additional capital cost and the increased requirement for plant space. Plant space is a major challenge when retrofitting the energy network to existing buildings. In general, there is insufficient space in the plantrooms of most buildings to accommodate the additional requirements, which is why the scheme has gone down the route of constructing the new energy centres. To minimise the space required by the thermal stores, the use of phase change material (PCM) thermal storage is also being considered. The distributed energy centres allow the installation of local hot networks to give heat to smaller customers without the need to connect to the loop. This has benefits where there are space limitations or where the connected loads are too small to warrant additional investment. It is in the energy centres where the heat Boilers Residential customer < = 75oC, < = 55oC Grid Heat pump Storage Energy centre EV > = ~ 15oC PV Energy centre Data centre Chillers ~ 23oC ~ 13oC Aquifer thermal energy store > = ~ 14 C ~< 8 C o o Heat pump Storage Energy centre Storage Grid EV Heat pump Boilers < = 75oC, < = 55oC ~ 6oC, 12oC Non-residential customer 36 September 2021 www.cibsejournal.com CIBSE Sep 21 pp32-34, 36 GreenSCIES.indd 36 27/08/2021 12:20