Abstract Existing Integrated Collector Storage Solar Water Heaters (ICSSWHs) are typically simple and low-cost devices that combine heat collection and storage functions in one unified vessel. However, during non-collection periods they are affected by higher heat loss characteristics when compared to standard solar collector systems. This paper introduces the design evolution of new horizontal cylindrical ICSSWH prototypes developed at Ulster University that use novel, patented double vessel, thermal diode features (to enhance heat retention during non-collection periods) achieved by incorporating a liquid–vapour phase change material (PCM) with a very low pressure annular cavity. The energy performance evaluation and characterisation of different prototype designs under solar simulated experimental conditions has been conducted and the subsequent parametric analysis presented. A balance between performance and physical/operational considerations is necessary to ensure that new and practical design solutions (in materials, fabrication and assembly) can be formulated to improve the performance of the ICSSWHs within the limits of commercial reality. The importance of augmenting heat transfer across the annulus cavity has been demonstrated with improvement of the cold-start daily collection efficiency from around (ηcol) of 20% (no HTF), to > 55% when the annulus is evacuated to remove non-condensable gases and form a liquid–vapour phase change thermal diode. Annulus thermal diode heat transfer coefficients of around (Ufr) 35 W/m2K in forward mode and 2 W/m2K in reverse mode have been demonstrated. Diurnal thermal efficiencies ( η c o l 24 ) of 22% have been measured, but values of 39% have been identified as achievable in the longer-term development of presented ICSSWH.

中文翻译：

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不同密封水平、圆柱形双容器集成集热器存储太阳能热水 (ICSSWH) 原型的实验表征

摘要 现有的集成集热器存储太阳能热水器 (ICSSWH) 通常是简单且低成本的设备，将集热和存储功能结合在一个统一的容器中。然而，在非收集期间，与标准太阳能收集器系统相比，它们受到更高的热损失特性的影响。本文介绍了阿尔斯特大学开发的新型水平圆柱形 ICSSWH 原型的设计演变，该原型使用新颖的、获得专利的双容器、热二极管特性（以增强非收集期间的保温性），通过结合液-汽相变材料 (PCM ) 具有极低压力的环形腔。在太阳能模拟实验条件下对不同原型设计的能量性能进行了评估和表征，并提出了随后的参数分析。性能和物理/操作考虑之间的平衡是必要的，以确保可以制定新的和实用的设计解决方案（在材料、制造和组装方面），以在商业现实的限制内提高 ICSSWH 的性能。通过将冷启动日收集效率从大约 (ηcol) 的 20%（无 HTF）提高到 > 55%，当环空被抽空以去除不冷凝物时，增强环空传热的重要性已得到证明气并形成液-气相变热二极管。环热二极管传热系数在正向模式下约为 (Ufr) 35 W/m2K，在反向模式下约为 2 W/m2K。已测量到 22% 的昼夜热效率 (η col 24)，但已确定在所提出的 ICSSWH 的长期发展中可以实现 39% 的值。