Energy analysis of an ultra-low temperature district heating and cooling system with coaxial borehole heat exchangers

The decarbonisation of society requires developing new environmentally friendly solutions for heating and cooling. Ultra-low temperature district heating and cooling (ULTDHC) allows operation with energy sources and systems hard to integrate into previous generations of district networks, making this technology more efficient and sustainable. This work analyses a novel integration of coaxial borehole heat exchangers (CBHEs) to control the temperature of the network, drastically reducing operating costs and emissions compared to existing systems. The concept is analysed based on single and double-loop networks. As a case analysis, it is studied to a ULTDH located in the south of Spain with annual heating and cooling demands of 1045 MWh and 416 MWh, respectively. The single-loop configuration requires more 100 m depth CBHEs connected, 47, whereas the double-loop layout, with a more efficient thermal balance, requires 42. In contrast, it has higher values of annualised costs. The sensitivity analysis of the main parameters proves the system is robust and effective in compensating for external variations. It operates more efficiently in warm/hot regions, increasing the possible applications and implantation expansion. The proposal is useful for new systems and for adapting the existing ones.