Fifth-generation district heating and cooling (5th DHC) systems offer promising approaches to decarbonizing space heating, cooling and domestic hot water supply. By using these systems, clustered buildings combined with industrial waste heat can achieve a net-zero energy balance on a variety of time scales. Thanks to the low exergy approach, these systems are highly efficient. As part of the Smart Anergy Quarter Baden (SANBA) project, the thermal energy grid simulation tool TEGSim has been further developed and used to design an ultra-low-temperature district heating (ULTDH) network with hydraulic and thermal components fitted to the specific regional characteristics of the investigated case. Borehole thermal energy storage (BTES) used as seasonal storage ensures long-term feasibility. The annual discrepancy of input of thermal energy provided by space cooling and output of energy demanded by space heating and domestic hot water is supplied by an external low-grade industrial waste heat source. This paper presents the functionality of the simulation and shows how to interpret the findings concerning the design of all components and their interplay, energy consumption and efficiencies.

CO2 blends provide tremendous advantages when used as a working fluid in transcritical power cycles with respect to pure CO2. The benefits become especially apparent if coupled with concentrated solar power since increasing the critical temperature of the blend with respect to pure CO2 allows dry condensing at high ambient temperatures in locations of high solar radiation. One key cycle component is the cooler, which in this work is designed as an air-cooled condenser with a MATLAB in-house code. The internal, condensation heat transfer model used in this paper relies on a correlation developed by Cavallini (2006). The model itself is validated against experimental data from a test rig for heat transfer measurements on a CO2 + R1234ze(E) mixture. The resulting design of the condenser is compared with the commercial software HTRI for a specific case study which is representative of the condenser of a recuperated cycle working with a CO2 + C6F6 blend. The authors also present an upgraded heat exchanger design with microfinned tubes, the DIESTA tubes, and groovy fins on the air side. The design of the heat exchanger adopting the mixture is compared to a case with pure CO2 as the working fluid.

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