An alternative approach for assessing the benefit of phase change materials in solar domestic hot water systems
An alternative approach for assessing the benefit of phase change materials in solar domestic hot water systems
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DOI：
10.1016/j.solener.2017.10.033
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发表时间：
2017-12
期刊：
影响因子：
6.7
通讯作者：
H. Teamah;M. Lightstone;J. Cotton
中科院分区：
文献类型：
--
作者：
H. Teamah;M. Lightstone;J. Cotton
用于太阳能系统热能存储的相变材料（PCM）已经成为文献中大量研究的主题。尽管如此，有关相变材料在增强系统太阳能比例方面的功效的研究结果却好坏参半。当前的论文在系统背景下以数值方式探讨了这个问题。考虑典型的太阳能生活热水系统。 PCM 作为包含在水箱内的垂直圆柱形模块引入，从而形成混合 PCM/水蓄热装置。沿水箱长度流动的水用作传热流体。基于焓孔隙率法开发了一个模型来求解 PCM 模块内的相变过程。该模型经过彻底验证和验证，预测与文献结果吻合良好（偏差小于 5%）。混合罐模型与集热器性能相关，并且系统针对加拿大天气的典型天气和分散的需求情况进行了测试。将混合系统的太阳能部分与仅使用水作为蓄热介质的相同系统进行比较。系统分析探讨了包含和不包含 PCM 的系统中存储容量对太阳能比例的影响。该系统方法至关重要，因为它考虑到了蓄热、太阳能集热器和家庭负载的耦合效应。分析清楚地表明，将相变材料 (PCM) 纳入蓄热装置可在储罐容量相对于需求而言较小的情况下提高太阳能比例。相反，随着水箱容积的增加，PCM 的优势会减弱，并且在大容积时两个系统之间会获得相同的性能。系统的能量平衡表明，尽管混合储罐的热损失略有增加，但小存储容量的混合存储的好处是由于集热器流体入口温度的降低，这增加了泵的运行时间，从而增加了收集的太阳能并减少了集热器损失。
Phase change materials (PCM) for thermal energy storage in solar energy systems have been the subject of a great deal of research in the literature. Despite this, the research results pertaining to the efficacy of PCMs in enhancing system solar fraction are mixed. The current paper explores this issue numerically within a systems context. A typical solar domestic hot water system is considered. The PCMs are introduced as vertical cylindrical modules contained within the water tank, thus forming a hybrid PCM/water thermal storage. Water flowing along the length of tank is used as the heat transfer fluid. A model was developed based on the enthalpy-porosity method to solve for the phase change process within the PCM modules. The model was thoroughly validated and verified and predictions were in good agreement (less than 5% deviation) with results from the literature. The hybrid tank model was linked with the collector performance and the system was tested for typical days of Canadian weather with a dispersed demand profile. The solar fraction of the hybrid system was compared to that for an identical system using water-only as the thermal storage medium. The system analysis explores the impact of storage volume on solar fraction for systems with and without PCMs included. The systems approach is critical since it allows for the coupled effects of the thermal storage, solar collector, and household load to be incorporated. The analysis clearly shows that incorporation of PCMs into the thermal storage results in enhanced solar fraction at undersized tank volumes relative to the demand. In contrast, as the tank volume is increased, the benefit of the PCMs diminishes and identical performance is obtained between the two systems at large volumes. An energy balance of the system shows that, despite marginally increased heat losses from the hybrid tank, the benefits of the hybrid storage at small storage volumes are due to the reduction in the collector fluid inlet temperature which increases the pump run time and thus the solar energy collected and reduction of collector losses.