Design and operation of Borehole Thermal Energy Storage systems

在钻孔热能储存（BTES）系统中，目标是将地面温度提高到正常值以上，并长时间储存能量。 BTES系统尚未得到广泛研究，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，以便工程界可以广泛使用它们，充分利用可再生能源的潜力。用于预测钻孔热传递的热传递系数通常基于标准相关性来计算。然而，对于减少流量的条件下，目前的自然和混合对流的相关性是不够的钻孔。建议开发一种热通量传感器，该传感器将能够确定钻孔管内部的局部传热系数。试验将在小规模钻孔试验设施中进行，以开发适用于钻孔的一般传热系数相关性。 ** 已经提出了更先进的BTES系统，其中电热泵在电网温室气体排放最低的夜间运行，用于将热量从钻孔的外圈传递到中心核心钻孔。在这些系统中，将在各个钻孔上执行热的注入/收集，以快速增加（或降低）BTES的某些区域中的存储温度。这将为建筑物提供灵活性，使其能够从中央核心直接供暖或从外环制冷。将开发一种新的载荷聚合方案来处理每个钻孔的热历史的时间叠加，以提高计算效率。** 行业需要制定准则和工具，以评估BTES的设计和运作。首先，工程师需要知道可以从BTES预期的最大传热速率。 建议使用可变热交换器效率作为BTES荷电状态的函数的概念来表示钻孔热传递。工程师面临的第二个设计问题是确定最佳BTES工作温度，以实现最大的节能和最小的温室气体排放。该最佳值是在直接提供空间加热的足够高的温度和限制BTES热损失的足够低的温度以及施加在热泵上的所得温度提升之间的折衷。因此，将需要进行参数研究，以找到特定应用的最佳参数集。 ** 随着我们朝着社区规划的方向发展，在社区规划中，存储资源将被共享，以实现能源灵活性和弹性，BTES系统将发挥更大的作用。 这里提出的项目将提高我们对BTES热行为的理解，并提供严格的计算方法，以更好地设计这些系统。

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.