地道风与相变平板空气集热器复合系统的实验研究

Experimental Study of a Coupled System Combing a Phase Change Flat-Plate Solar Air Heater with an Earth-to-air Heat Exchanger

为提高冬季地道风出口温度以满足建筑供热要求,现有研究中开发了地道风和太阳能平板空气集热器复合系统。针对该系统因太阳辐射间歇性和不稳定性导致出口风温不够稳定,易出现过热且集热器工作时间仅限于日间的问题,本文提出在集热器中耦合相变材料以构成地道风和相变平板空气集热器复合系统。为评估该系统热性能,本文通过实验测试分析了系统出口风温、集热器工作时间和相变材料温度的变化特性,并与传统系统进行了比较。实验结果显示该系统可在近4. 5 h内将出口风温维持在33~35. 8℃,并将最大出口风温降低8℃,集热器夜间工作时间延长近5. 5 h。此外,常用矩形封装结构易导致相变材料无法完全融化,从而显著降低其利用率,而针对此的一种可能解决方法是采用楔形封装结构代替矩形封装结构。上述结果表明本文所开发系统可有效抑制太阳辐射波动对系统出口风温的影响,避免出口空气过热并延长集热器工作时间。在未来实际应用中应根据建筑负荷和系统运行时间选择合适的相变材料容积,以进一步延长系统出口风温稳定时间和运行时间。

A coupled system combining a flat-plate solar air heater with an earth-to-air heat exchanger was developed in this study with the aim of increasing the outlet air temperature of the sole earth-to-air heat exchanger,so as to meet the heating demand of the building in winter.However,owing to intermittent and fluctuating solar radiation,the developed system has some drawbacks,such as unstable outlet air temperature,overheating and running period being limited to daytime.To cope with these problems,PCM(phase change materials)was proposed to apply in the flat-plate solar air heater coupled with the earth-to-air heat exchanger.To assess the thermal performance of the proposed system,a series of experimental tests were conducted to investigate the outlet air temperature,running duration of the collector and temperature change characteristics of PCM.In addition,these results were compared with those of conventional system without PCM.Experimental results show that the PCM integrated system can maintain an outlet air temperature between 33℃ and 35.8℃ for nearly 4.5 hours,reduce the peak outlet temperature by 8℃,and extend the running hours in the nighttime by 5.5 hours.Moreover,it's found that PCM encapsulated in commonly-used rectangular structures cannot fully melt,that is,its utilization rate is significantly reduced.One possible solution is to encapsulate PCM in the wedge-shape structure rather than in the rectangle structure.In conclusion,experimental results demonstrate that the proposed system coupling the PCM-integrated flat-plate solar air heater and the earth-to-air heat exchanger can effectively suppress the impact of fluctuating solar radiation on outlet air temperature,avoid overheating and prolong the running period.For future practical applications,the type and volume of PCM should be carefully selected according to building thermal loads and system running time,so as to improve the stability of the outlet air temperature and the running period.