冷却塔-内嵌管式相变屋面复合降温系统的性能研究

Performance of an integrated cooling system combining a cooling tower and a pipe-embedded phase-change-material slab roof

为提高相变屋面的性能,本文提出了一种冷却塔-内嵌管式相变屋面复合降温系统。基于焓法,建立了系统的数值计算传热模型,数值研究了该系统在福州地区的热性能及节能潜力,探讨了相变材料相变温度、相变材料导热系数以及内嵌管间距的影响,并与传统的无内嵌管相变屋面进行了对比分析。研究发现,相变温度越高,复合降温系统的相变材料越容易完成凝固,但潜热利用率随相变温度的升高呈现先增加后降低的趋势。当相变温度由35℃升高到41℃时,屋面的累计冷负荷由383 k J/m^(2)增大到400 k J/m^(2),增加了4.4%。相变材料导热系数越高、内嵌管间距越小,复合降温系统相比于传统无内嵌管相变屋面的潜热利用优势越显著。当导热系数由0.2 W/(m·K)增加到0.8 W/(m·K)时,复合降温系统的潜热利用率和屋面累计冷负荷分别增加了36.3%和5.1%,而无内嵌管相变屋面的潜热利用率和屋面累计冷负荷分别升高了33.1%和6.3%。当内嵌管间距由500 mm减少到100 mm时,复合降温系统比传统无内嵌管相变屋面的潜热利用提高率由2.7%增大到16.3%,累计冷负荷降低率由3.8%升高到10.9%。研究结果可促进建筑节能和双碳目标的实现。

To enhance the performance of phase-change-material(PCM)slab roofs,this study proposes an integrated cooling system combining a cooling tower with a pipe-embedded PCM slab roof.Further,leveraging the enthalpy method,the study establishes a computational heat transfer model of the developed integrated cooling system.Subsequently,the thermal performance and energy-saving potential of a similar system in Fuzhou city,China,are numerically investigated.Furthermore,the impacts of the phase-change temperature and thermal conductivity of the PCM and the pipe interval are explored,and the developed system is compared with a traditional PCM slab roof without embedded pipes.The results reveal that higher phase-change temperatures of the PCM lead to more significant solidification of the PCM within the integrated cooling system.However,with increasing phase-change temperatures of the PCM,the utilization rate of the PCM's heat of fusion within the system initially increases and subsequently decreases.Specifically,increasing the phase-change temperature of the PCM from 35℃to 41℃leads to a corresponding rise in the accumulated cooling load of the roof from 383 kJ/m^(2) to 400 kJ/m^(2),presenting an increase of 4.4%.Furthermore,higher thermal conductivities of the PCM and narrower pipe intervals improve the utilization rate of the PCM's heat of fusion within the integrated cooling system compared to that within traditional PCM slab roofs without embedded pipes.Specifically,increasing the thermal conductivity of the PCM from 0.2 W/(m·K)to 0.8 W/(m·K)boosts the utilization rate of the PCM's heat of fusion and the accumulated cooling load of the roof by 36.3%and 5.1%,respectively.Conversely,the corresponding values of the traditional PCM slab roof increase by only 33.1%and 6.3%,respectively.Moreover,when the pipe interval is decreased from 500 mm to 100 mm,the utilization rate of the PCM's heat of fusion in the integrated cooling system surpasses that in the traditional PCM slab roof by 2.7%—16.3%.Concurrently,the reduction in the accumulated cooling load of the roof increases from 3.8%to 10.9%.Overall,these findings demonstrate the potential of integrated cooling systems in promoting building energy savings and contributing toward the realization of dual-carbon goals.