Optimisation of a theoretical 4th generation district heating network located at the town of Loughborough, UK

A cost and efficiency optimization for a net zero district heat (DH) network providing hot water and space heating for a specific urban area in the town of Loughborough, UK, was performed using a previously developed model. The model simulates a DH system with heat provided from i) renewable heat sources (RHS), i.e. heat pumps powered by PV and/or Wind and evacuated tube solar thermal collectors (ETSTCs), and ii) stored heat from centralized long duration (namely long-term water tank, LTWT) and decentralized thermal energy storage (TES) systems. Based on hourly weather data, building specifications and occupancies the model calculates a) hourly domestic heat demands for both space and domestic hot water, b) the hourly heat production from the specified RHS and c) losses from TES and pipes. The DH network simulations were performed for an 18-month period from the 01/06/2018 00:00 to 31/12/2019 23:00. The effect of parameters affecting the performance of the decentralized short-term water tanks (STWT) used for heat stores including i) the average volume of the STWT (V_STWT) per dwelling and ii) the specified STWT charging temperatures (T_{charging STWT}), on a) the DH system cost per dwelling and b) the energy efficiency of the DH system (ηDH) were assessed. The predictions showed that increasing either the V_STWT and/or T_{charging STWT} leads to i) an increase in the total cost of the DH system per dwelling, and ii) to a decrease in the ηDH. These results are mainly due to a reduced use of the LTWT, which results in a greater required installed Wind generation capacity and number of heat pumps to fully meet heat demands at certain periods of the year and as a consequence greater heat losses and increased amounts of heat being shed in the DH system.