The majority of Aquifer Thermal Energy Storage (ATES) systems studies have been conducted in aquifer systems located in large sand aquifers. Esker formation present a more challenging geometrical complexity compared to typical sand aquifers. This study aims to conduct comprehensive and long term performance evaluation of doublet type ATES system in esker geological formation in Stockholm, Sweden. The total heating and cooling used from the ATES are 673 MWh and 743 MWh respectively during the first 3 annual storage cycles of operation. The licensed total amount of water extraction and injection is 50 liters per second with undisturbed groundwater temperature of 9.5°C. Over the first three storage cycles, the average injection and extraction temperatures for the warm side are 13.3°C and 12.1°C, and for the cold side 7.6°C and 10.5°C. The average temperature differences across the main heat exchanger from the ATES side are 4.5 K during winter and 2.8 K during summer which is 4-5 degrees lower than the optimum value. The average thermal recovery efficiency over the first 3 storage cycles were 47 % and 60 % for warm and cold storages respectively. The data analysis indicated annual energy and hydraulic imbalances which results into undesirable thermal breakthrough between the warm and cold side of the aquifer. This was mainly due to suboptimal operation of the building energy system which led to insufficient heat recovery from the warm side, and subsequently insufficient cold injection in the cold wells, despite the building heating demand and the available suitable temperatures in the ATES. The cause of the suboptimal operation is the oversizing of the heat pumps which were designed to be coupled to larger thermal loads as compared to the ones in the final system implementation. As a result, the heat pumps could not be operated during small-medium loads. Additionally, the paper discusses the limitations of currently used energy and thermal key performance indicators (KPI) for ATES and propose an additional thermal KPI named heat exchanger efficiency balance (${\mathit{\beta }}_{\mathit{HEX}}$) that connects and evaluate the optimum operational point of temperature differences from both the building and ATES prospective. In addition to ATES energy and hydraulic KPIs, ${\mathit{\beta }}_{\mathit{HEX}}$ can contribute in providing more complete picture on the ATES-building interaction performance as well as highlights if the losses in energy recovery from ATES are due to the subsurface processes or building energy system operation which has been proven to be critical for the optimum ATES performance.

大多数含水层热能储存 (ATES) 系统研究都是在位于大型含砂含水层的含水层系统中进行的。与典型的砂含水层相比，Esker 地层具有更具挑战性的几何复杂性。本研究旨在对瑞典斯德哥尔摩 esker 地质地层中的双峰型 ATES 系统进行全面和长期的性能评估。在运行的前 3 个年度存储周期中，ATES 使用的总加热和冷却分别为 673 MWh 和 743 MWh。许可的取水总量为每秒 50 升，未扰动的地下水温度为 9.5°C。在前三个存储周期中，暖侧的平均注射和提取温度为 13.3°C 和 12.1°C，冷侧的平均注射和提取温度为 7.6°C 和 10.5°C。从 ATES 侧穿过主换热器的平均温差在冬季为 4.5 K，在夏季为 2.8 K，比最佳值低 4-5 度。前 3 个储存周期的平均热回收效率分别为 47% 和 60% 的暖和冷储存。数据分析表明，每年的能量和水力不平衡会导致含水层暖侧和冷侧之间出现不希望的热突破。这主要是由于建筑能源系统的运行不理想，导致暖侧的热回收不足，随后冷井中的冷注入不足，尽管建筑供暖需求和 ATES 中可用的温度合适。次优运行的原因是热泵的尺寸过大，与最终系统实施中的热泵相比，这些热泵设计为与更大的热负荷耦合。因此，热泵无法在中小负荷期间运行。此外，该论文讨论了目前用于 ATES 的能源和热关键性能指标 (KPI) 的局限性，并提出了一个名为换热器效率平衡的额外热 KPI（${\mathit{\beta }}_{\mathit{十六进制}}$) 连接和评估建筑和ATES 预期温差的最佳操作点。除了 ATES 能源和液压 KPI，${\mathit{\beta }}_{\mathit{十六进制}}$ 如果 ATES 的能量回收损失是由于地下过程或建筑能源系统运行（已被证明对最佳 ATES 性能至关重要），则可以有助于提供更完整的 ATES 与建筑相互作用性能的图景。