Optimized Layouts of Borehole Thermal Energy Storage Systems in 4th Generation Grids

• Main Authors: Hoofar Hemmatabady, Julian Formhals, Bastian Welsch, Daniel Otto Schulte, Ingo Sass
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: Energies
• Subjects: district heating and cooling; borehole thermal energy storage; dynamic exergoeconomic method; TRNSYS; MATLAB; coupling
• Online Access: https://www.mdpi.com/1996-1073/13/17/4405

Borehole thermal energy storage (BTES) systems are a viable option to meet the increasing cooling demand and to increase the sustainability of low-temperature district heating and cooling (DHC) grids. They are able to store the rejected heat of cooling cycles on a seasonal basis and deliver this heat during the heating season. However, their efficient practical implementation requires a thorough analysis from technical, economic and environmental points of view. In this comparative study, a dynamic exergoeconomic assessment is adopted to evaluate various options for integrating such a storage system into 4th generation DHC grids in heating dominated regions. For this purpose, different layouts are modeled and parameterized. Multi-objective optimization is conducted, varying the most important design variables in order to maximize exergetic efficiency and to minimize levelized cost of energy (LCOE). A comparison of the optimal designs of the different layouts reveals that passive cooling together with maximizing the heating temperature shift, accomplished by a heat pump, lead to optimal designs. Component-wise exergy and cost analysis of the most efficient designs highlights that heat pumps are responsible for the highest share in inefficiency while the installation of BTES has a high impact in the LCOE. BTES and buffer storage tanks have the lowest exergy destruction for all layouts and increasing the BTES volume results in more efficient DHC grids.