利用自适应双层红外膜提高低辐射率冷顶无冷凝辐射制冷的制冷量

Ke Du, Huijun Wu, Yanling Guo, G. Huang, Xin-hua Xu, Yanchen Liu
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引用次数: 2

摘要

与传统的对流冷却相比,辐射冷却已被公认为节能和热舒适的技术。然而,在湿热气候地区,辐射冷却存在制冷能力不足和冷凝风险高的问题。通过在辐射冷却板上添加双皮肤红外透明膜(DIMs),可以将空气接触表面与冷却源表面分离,从而可以在使用低温冷却源的同时保持空气接触表面高于露点温度。dim对辐射热传递是透明的,这产生了很大的冷却能力,而冷却天花板具有高发射率(例如,高于0.9)。然而,对于低发射率的金属冷顶,冷负荷对冷顶的辐射热会通过dim减少,导致制冷量不足。本文提出了一种由高发射率膜和高透明膜组成的自适应双皮红外膜(a- dims),以提高传统金属冷顶的制冷量。高发射率膜代替低发射率冷顶板作为辐射冷却面,提高了辐射热流密度,而高透明膜使冷负荷向冷顶板散发的辐射热很大。采用基于半透明表面辐射和自然对流的组合传热分析方法,对无冷凝辐射冷却的制冷量进行了预测。结果表明:采用0.96高发射率膜和0.87高透明膜组成的a- dim,冷量可达101.9W/㎡,比传统的低发射率为0.2的金属冷顶提高2倍;此外,与我们之前的研究中使用的两种红外透明dim相比,添加a- dim的冷却能力进一步提高了25%。结果还表明,在不同湿度条件下,采用a- dim辐射制冷方式可使吊顶的制冷量比传统的低辐射金属吊顶提高2倍以上。对低辐射率金属冷吊顶的高性能无冷凝辐射冷却设计和提高冷能力具有重要的指导意义。
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Improving Cooling Capacity of Condensation-Free Radiant Cooling for Low-Emissivity Chilled Ceiling via Adaptive Double-Skin Infrared Membranes
Radiant cooling has well been acknowledged as energy efficient and thermal comfortable technology compared to conventional convective cooling. However, the radiant cooling exists two serious problems (viz., insufficient cooling capacity and high condensation risk) especially in hot and humid climate zones. By adding double-skin infrared transparent membranes (DIMs) onto radiant cooling panel, the air-contact surface can be separated from the cooling source surface, which makes it possible to use a low-temperature cooling source while maintaining air-contact surface higher than dew point temperature. The DIMs are transparent to radiant heat transfer which yields great cooling capacity while chilled ceiling has high emissivity (e.g., above 0.9). However, for metal chilled ceilings having low emissivity, radiant heat from cooling load to chilled ceiling would be reduced through DIMs, which results in insufficient cooling capacity. In this paper, a type of adaptive double-skin infrared membranes (a-DIMs) consisting a high-emissivity membrane and a high transparent membrane is proposed to improve cooling capacity of conventional metal chilled ceilings. The high-emissivity membrane serves as radiant cooling surface instead of low-emissivity chilled ceiling so as to improve radiant heat flux, while the high transparent membrane permits great radiant heat from cooling load to chilled ceiling. A combined heat transfer analysis based on semi-transparent surface radiation and natural convection were carried out to predict cooling capacity of condensation-free radiant cooling. The results indicate that the cooling capacity could be up to 101.9W/㎡ by adding a-DIMs consisting of a high-emissivity membrane of 0.96 and a high transparent membrane of 0.87, which is improved by 2 times compared to conventional metal chilled ceiling with low emissivity of 0.2. Moreover, the cooling capacity by adding a-DIMs is further improved by 25% compared to that by using both infrared transparent DIMs presented in our previous work. The results also indicate that the cooling capacity could be improved by above 2 times compared to conventional low-emissivity metal chilled ceiling by using the radiant cooling with a-DIMs for various humidity. It will be of great guidance for high-performance radiant cooling design without condensation and improved cooling capacity for low-emissivity metal chilled ceiling.
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