Abstract In the exergy analysis of the built environment, particularly for a system with large heat capacity and low thermal conductivity, such as building envelopes, consideration of physics associated with the entropy and exergy storages is increasingly important. However, steady-state exergy analyses neglect storage-related physics. Therefore, they do not provide insights into transient processes. Moreover, the results may not be thermodynamically correct because the integrity of the physics does not hold. In this study, we first examined why unsteady-state exergy analysis is required for systems in the built environment. Then, we conducted the unsteady-state exergy analysis of externally and internally insulated building envelopes under a 24-h periodic environmental boundary condition. This was based on a methodology that numerically solves the energy, entropy, and exergy equations, where thermodynamic integrity, including exergy storage, is fully established. We compared the spatiotemporal exergetic behavior of the two envelopes from macroscopic and microscopic perspectives. In terms of exergy flow, storage, and consumption, the exergetic behavioral difference and its physical rationale were detailed. The spatiotemporal exergetic behavior of the two envelopes demonstrated a sharp contrast. In particular, the wasted exergy flow from the outer surface into the surrounding environment was significantly larger in the internally insulated envelope than in the externally insulated envelope. Additionally, the exergy stored in the internal layer, which positively affects indoor air conditioning, was much larger in the externally insulated envelope than that in the internally insulated envelope. The insights obtained can contribute to improving building thermal design and creating more efficient operation strategies for energy systems.

中文翻译：

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内外保温建筑围护结构的非稳态火用性能比较

摘要 在建筑环境的火用分析中，特别是对于具有大热容量和低热导率的系统，例如建筑围护结构，考虑与熵和火用存储相关的物理学变得越来越重要。然而，稳态火用分析忽略了与存储相关的物理。因此，它们不提供对瞬态过程的洞察。此外，结果在热力学上可能不正确，因为物理学的完整性不成立。在这项研究中，我们首先研究了为什么建筑环境中的系统需要非稳态火用分析。然后，我们在 24 小时周期性环境边界条件下对外部和内部绝缘建筑围护结构进行了非稳态火用分析。这是基于一种对能量、熵和火用方程进行数值求解的方法，其中完全建立了包括火用存储在内的热力学完整性。我们从宏观和微观的角度比较了两种信封的时空用能行为。在火用流、存储和消耗方面，详细介绍了火用行为差异及其物理原理。两个信封的时空用能行为表现出鲜明的对比。特别是，从外表面到周围环境的浪费的火用流在内部绝缘外壳中明显大于在外部绝缘外壳中。此外，储存在内层的火用对室内空调产生积极影响，外绝缘外壳比内绝缘外壳大得多。获得的见解有助于改进建筑热设计并为能源系统创建更有效的运行策略。