Design and operation of Borehole Thermal Energy Storage systems

在钻孔储能系统中，目标是将地面温度提高到高于其正常值，并长期储存能量。BTES系统还没有得到广泛的研究，需要科学发展来更好地设计和操作这些系统。该研究计划的长期目标是开发知识和模型，以更好地了解BTES系统的性能，以便工程界能够广泛使用它们来充分利用可再生能源的潜力。用于预测井筒传热的换热系数通常基于标准关联式计算。然而，对于减流条件，目前的自然对流和混合对流关联式不适用于井眼。有人建议开发一种热流传感器，它将能够确定井筒内的局部换热系数。将在小型钻孔测试设施中进行测试，以开发适用于钻孔的通用换热系数关联式。*已经提出了更先进的BTES系统，其中使用在电网温室气体排放量最低的夜间运行的电动热泵，将热量从外环钻孔转移到中心核心钻孔。在这些系统中，将在单个钻孔上进行热注入/收集，以迅速提高(或降低)BTES某些区域的存储温度。这将为建筑物提供灵活性，使其可以直接从中央核心供暖或从外环冷却。为了提高计算效率，将开发一种新的载荷聚合方案，以处理每个钻孔的热历史的时间叠加。*行业需要制定指导方针和工具来评估BTES的设计和运行。首先，工程师需要知道BTES可以预期的最大传热率。提出了用变换热器效率作为BTES荷电状态的函数来表示井筒换热的方法。工程师面临的第二个设计问题是确定最佳的BTES运行温度，以最大限度地节约能源和最大限度地减少温室气体排放。这种最佳化是在足以直接提供空间供暖的足够高的温度和足够低的温度以限制BTES热损失和由此对热泵施加的温升之间的折衷。因此，需要进行参数研究，以找到特定应用的最佳参数集。*随着我们朝着共享存储资源以实现能源灵活性和弹性的社区规划迈进，BTES系统将发挥更大的作用。这里提出的项目将加深我们对BTES热行为的了解，并为更好地设计这些系统提供严格的计算方法。

In a Borehole Thermal Energy Storage (BTES) system, the goal is to increase the ground temperature above its normal value and to store energy over long periods. BTES systems have not been studied extensively and scientific developments are required to better design and operate these systems. The long-term objective of the research program is to develop knowledge and models to better understand the performance of BTES systems so that the engineering community can use them extensively to fully utilise the potential of renewable energy.******Heat transfer coefficients used to predict borehole heat transfer are typically calculated based on standard correlations. However, for reduced flow conditions, current natural and mixed-convection correlations are inadequate for boreholes. It is proposed to develop a heat flux sensor that will enable the determination of local heat transfer coefficients inside borehole tubes. Tests will be performed in a small-scale borehole test facility to develop general heat transfer coefficient correlations applicable to boreholes. ******More advanced BTES systems have been proposed where electric heat pumps, operating at night when greenhouse gas emissions from the grid are the lowest, are used to transfer heat from an outer ring of boreholes to the central core boreholes. In these systems, injection/collection of heat will be performed on individual boreholes to rapidly increase (or decrease) the storage temperature in certain regions of the BTES. This will provide flexibility for buildings to operate on direct space heating from the central core or cooling from the outer ring. A new load aggregation scheme will be develop to handle temporal superposition of the thermal history of each borehole to improve computational efficiency. ******There is an industry need to develop guidelines and tools to asses the design and operation of BTES. First, engineers need to know the maximum heat transfer rate that can be expected from a BTES. It is proposed to represent borehole heat transfer using the concept of variable heat exchanger efficiency as a function of the BTES state-of-charge. The second design problem facing engineers is the determination of the optimum BTES operating temperature for maximum energy savings and minimum greenhouse gas emissions. This optimum is a compromise between a high enough temperature to provide space heating directly and a low enough temperature to limit BTES heat losses and the resulting temperature lift imposed on the heat pump. Thus, parametric studies will be needed to find the best set of parameters for particular applications. ******As we advanced towards community planning where storage resources are shared for energy flexibility and resilience, BTES systems will play a larger role. The projects proposed here will enhance our understanding of the thermal behaviour of BTES and provide rigorous calculation methods to better design these systems.