OPERATION STRATEGY AND ENERGY PRICES The dynamic demand profiles for each end-user were obtained using a stochastic approach and the results were validated by comparing these to typical UK profiles available in literature for similar buildings, occupancy and use. The strategy implemented to optimally operate the CES was focused on a cost optimisation to maximise the local use of the generated electricity both for direct use and storage/export, and as a consequence to minimise the import of electricity from the main grid. Three main scenarios were evaluated, considering the system operation under different operating temperatures: 55/25 °C, 50/25 °C and 45/25 °C. Yearly simulations were performed with energyPRO assuming the UK retail electricity price for 2016. This is composed of the day- ahead price (spot market) (47 % of total cost) and the remaining 53% of grid costs, taxes and commodities. When exporting electricity, the ESCO receives only the day ahead electricity price, hence it is important to carefully identify when the system should import or export electricity. The heat tariffs associated with DH networks are site-dependent and vary within the UK heat market. This was set to 95 £/MWh for this investigation by assuming that this is the average price an end-user would pay in the UK for useful MWh of heat using a typical individual gas combi boiler. The tariff includes the average gas price, the cost of the boiler and its efficiency and maintenance.
Figure 1: Schematic of the multi-vector energy system
Heat is supplied to each end-user through de-centralised heat interface units (HIU). Two dedicated plate heat exchangers (PEXs) will be installed for SH and DHW, and a ∆ T of 5 °C was assumed between the heat network and the secondary loops. UFH and LTRs are the chosen heat emitters for the SH systems, so supply temperatures in the range of 35-45 °C would be adequate to guarantee indoor comfort. For the instantaneous DHW preparation, a 32 kW PEX will be installed and an electric heater will also be placed on the secondary side of the DHW loop to boost the temperature if below the required limit of 50 °C. This will add more flexibility in the system operation, as supply temperatures even lower than 50 °C could be possible in the heat network, without any risks associated with Legionnaires' disease.
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