自汲水蒸发冷却复合屋面的热湿迁移及其对建筑热环境的调控机理研究

Evaporative cooling roof technology is essential in eliminating urban heat island effect, reducing building cooling loads and improving the human indoor environment. However, the traditional technology of evaporative cooling roofs will increase water scarcity while they are applied to hot and arid climates. And the roof’s cooling effect is limited which should be enhanced to a higher level. To fill the deficiency, this project proposes a novel evaporative cooling roof with multi-layers composed of Metal-Organic Frameworks (MOF) and cellulose composite porous materials. Assisted by the MOF material, the novel roof can absorb water vapor from dry air without extra water supply. In addition, the effectiveness of cooling roof can be significantly improved by taking advantages of cellulose composite porous materials with high capillary performance. Through the combined approaches of numerical simulation, micro and macro-scale experimental measurements and building energy simulation, this project will investigate the heat and moisture migration mechanism of the novel roof and its effect on the indoor thermal environment. To be specified, the project will study the factors that have influences on water harvesting efficiency of the roof. Also, it will investigate heat and moisture transport process of the roof operating under repeated day and night ambient conditions. A dynamic model based on building energy simulation environment is developed by coupling with the numerical model predicting the roof’s heat and moisture transport characteristics. An experimental system will be constructed to validate the computational model. Furthermore, the validated model will be used to analyze the cooling effect of the roof operating in typical dry and arid climates. The study aims to reveal the heat and moisture migration mechanism of the novel cooling roof. The achievements of the study will provide a reference for design and optimization of the novel roof, thus will contribute to promoting the technology of passive evaporative cooling roofs in hot and arid regions.

蒸发冷却屋面对缓解城市热岛效应、减少空调负荷和改善室内热环境具有重要意义。然而，传统蒸发冷却屋面用于干热地区，需要消耗当地稀缺的水资源，降温效果也有待进一步提升。为克服以上不足，本项目拟提出一种基于金属-有机骨架与高吸水纤维材料的自汲水蒸发冷却复合屋面，新型屋面可从干燥空气中汲取水分，同时强化蒸发冷却效果。项目结合数值模拟、微观与宏观实验测试以及建筑能耗联合模拟方法，研究新型复合屋面的热湿传递特性及其对建筑室内热环境的调控机理。探索复合屋面集水效率的影响因素及其作用规律，研究周期工况作用下复合屋面的热湿传递过程，建立耦合复合屋面热湿特性的建筑能耗模型，建成自汲水蒸发冷却复合屋面模拟测试平台，分析屋面对室内的降温效果及其对干热地区典型气候环境的动态响应。研究将有利于推广蒸发冷却屋面在干热地区的应用，为新型蒸发冷却屋面的设计和优化提供参考。

蒸发冷却屋面可减少建筑空调负荷，改善室内热环境，缓解城市热岛效应。干热地区应用蒸发冷却屋面的冷却效率较高，但需要消耗当地稀缺的水资源，为此项目研究了一种基于金属有机骨架（MOFs）吸附汲水的蒸发冷却复合屋面，建立了基于MOFs的板翅式吸附床传热传质理论模型与实验测试系统，分析了工况与结构参数对板翅式吸附床的水蒸气吸脱附特性作用规律，比较板翅式与平板式吸附床在吸脱附过程的传热传质特性，搭建吸附汲水实验系统，研究其集水效率及环境工况的影响规律，建成湿纤维蒸发率实验平台，获取蒸发率经验模型，探讨湿纤维蒸发率与汲水系统释水速率的匹配程度，分析汲水蒸发冷却复合屋面的可行性。此外，项目结合模拟与现场实验测试，研究了湿纤维屋面对不同气候地区室内热环境的降温效果。主要结果和结论为：1）揭示了环境工况对多种固体吸附材料的吸脱附热动力特性的影响规律，为不同气候地区应用汲水系统筛选吸附材料；2）空气温度与相对湿度的增大提高了板翅式吸附床的吸附速率，但空气速度的影响较小。辐射强度的增大提升了吸附床的脱附速率，当辐射强度达到500W/m2以上，吸附床表面和内部温度达60℃以上，可实现脱附再生；3）当吸附床填充相同体积的吸附剂时，板翅式吸附床的吸附热高于平板式，且释热速率更快。板翅片宽高比越小，吸附速率越快。但板翅式吸附床对辐射脱附的传热效率低于平板式；4）当辐射强度达到900W/m2时，汲水装置的集水效率和循环总效率分别为70%和55%以上；5）发现蒸发实验台的湿纤维蒸发率与供水率在不同工况下可保持匹配且同步变化。当吸附温度为25℃，相对湿度为20%，辐射强度为500W/m2时，MOF-303的释水速率为0.876kg/(m2∙h)，可满足湿纤维材料的蒸发率；6）提出了湿纤维蒸发率经验模型，建成耦合蒸发率模型的建筑动态热性能模拟程序，模拟预测湿纤维屋面的室内空气降温效果，评估室内冷负荷下降率；7）在北京地区建筑的实际运行中，湿纤维屋面的室内空气峰值温度比干纤维屋面下降4.2℃，降温幅度达13%。