极端热湿地区建筑被动蒸发冷却技术应用潜力实验研究

建筑被动蒸发冷却技术能有效减少围护结构得热,有助于解决我国极端热湿地区因长年高温高湿所导致的建筑过热问题.多孔材料的实际蒸发冷却效益与气象要素作用关系密切.本文利用热湿气候风洞实验台,基于我国南海气象数据,测试以多孔陶质砖为媒介的建筑被动蒸发冷却技术的应用潜力,探索各气象要素对蒸发冷却过程的影响机理.结果显示,极端热湿气候中,被动蒸发冷却技术具有1.5～6.4℃的冷却效益潜力.在淋水时机选择方面,宜以太阳辐射强度为首要决策指标,以气温为次要决策指标,可获得较好冷却效益,并节约水耗.     

被动蒸发冷却屋面在夏热冬冷地区的应用

被动蒸发冷却屋面作为一项节能技术,在夏热冬冷地区的应用目前并不广泛。在国家大力提倡节能降耗的背景下,被动蒸发冷却技术作为一项"被动式"技术可以有效地与"主动式"技术结合起来,最终达到一个节能舒适的室内居住环境。查阅相关研究成果,主要介绍了遮挡式蓄水屋面和含湿多孔材料屋面两种常见被动蒸发冷却屋面。利用CFD软件对其进行模拟,并与普通刚性屋面进行对比,从不同的角度对被动蒸发冷却屋面技术进行简要的分析。研究了被动蒸发冷却屋面的降温幅度以及建筑体型系数对其影响,分析了被动蒸发冷却屋面的热舒适性。     

西北旱区居住建筑蒸发冷却空调适用技术类型分析

针对传统蒸发冷却空调适用性分析常忽略蒸发冷却空调实际室内状态点及机组效率综合影响,造成民用建筑中的蒸发冷却技术类型适用性与传统蒸发冷却气候适用性出现不完全匹配问题.本文以现有蒸发冷却气候适用性分区为基础,结合energyplus计算西北旱区各城市、乡村居住建筑冷负荷,综合考虑室外气候参数、实际室内状态点及各技术效率限制,得到西北旱区不同气候下与建筑类型相匹配的蒸发冷却技术类型.为在工程中直观表达,将依据冷负荷分析的结果以建筑面积展示.结果表明:蒸发冷风扇的适用性随建筑面积和室外湿度的增大而减弱;蒸发冷气机的适用性在室内温湿度要求不严格时可大大扩展;直接蒸发冷却机组不能直接满足居住建筑室内状态设计要求;各级间接冷却机组可以满足西北旱区绝大部分城市要求.     

直接蒸发冷却系统现状与展望

蒸发冷却具有节能、经济、环保等优点,在建筑热湿环境保障领域受到越来越多的关注.本文介绍了近年来直接蒸发冷却技术的相关研究和应用情况,系统总结了直接蒸发冷却器的传热、传湿与净化效能,蒸发冷却器与其他系统的结合方法,湿式冷却塔以及建筑物被动蒸发冷却等方面的最新研究进展,并探讨了蒸发冷却技术在工程应用中的制约因素,以及未来应重点关注的研究方向.     

建筑屋面利用含湿多孔材料被动蒸发降温技术研究

研究了利用含湿多孔材料被动蒸发冷却外表面的方法。建立了含湿多孔材料利用太阳能被动蒸发的热质传递过程数学模型。通过理论分析，数值模拟和实验测试，完整地提示了热过程规律，结果表明，利用太阳能被动蒸发多也材料所含水分降低建筑发面温度的方法是可行性。     

直接蒸发冷却空调系统在乌鲁木齐地铁中的应用

以乌鲁木齐地铁4号线某标准站为例,选取车站站厅、站台层公共区设计参数,分析和计算了车站公共区内热湿负荷,并确定了车站公共区采用直接蒸发冷却空调系统的送风状态点,以及消除室内热湿负荷所需的全新风量;然后利用蒸发冷却适用区域模型,验证了直接蒸发冷却空调系统在乌鲁木齐地铁中的适用性。     

夏热冬冷地区村镇建筑节能与室内热环境设计

本文基于夏热冬冷地区既有村镇建筑普遍存在的围护结构热工性能差、室内热环境恶劣的状况,以尊重当地居民的生活习惯及风俗特征为前提,充分考虑经济性、适用性、南方地区气候特点和村镇建筑特征,在建筑规划布局、围护结构、降温通风方式、被动蒸发冷却技术等方面研究成果的基础上建立了节能示范工程,并对示范工程进行了测试与模拟分析.结果表明,示范工程节能效果明显,室内热环境得到了较大改善.     

基于湿能理论的空气能量转换方法和实践

运用湿能理论探讨了利用自然空气,在无需外界能量输入的情况下实现制冷与制热,包括直接蒸发冷却、间接蒸发冷却、多级间接蒸发冷却、液体除湿蒸发冷却,以及利用自然空气的能量实现液体再生等.该方法突破了传统的蒸发冷却露点温度的限制,同时将自然空气的利用由制冷拓展到制热.     

不同属性蓄水屋面的气候适用性研究

借助风洞试验台控制实现多种温湿度气候条件,分别研究50、100、150 mm三种深度的蓄水屋面及具有0、5%、10%水面反射物覆盖率的蓄水屋面在不同工况条件下的被动蒸发换热状况,通过热湿特性参数的分析探讨两者的气候适用性。结果显示:低温中湿(25℃、60%)和中温低湿(30℃、40%)环境下,100 mm深蓄水池具有较强适用性;低温高湿(25℃,80%)和中温中湿(30℃,60%)环境下,蓄水深度与蒸发降温效果关联性较弱。水面设置反射物在低温(25℃)和高温(35℃)环境均有助于降低空调负荷,且高温时较大覆盖率效果更显著。     

西北干旱地区空调系统节能研究

西北地区特殊的气候条件下,依据室温条件的不同,夏季可采取的空气处理方案,有直接蒸发冷却、间接蒸发冷却和间接蒸发冷却与直接蒸发冷却相结合的二级蒸发冷却空气处理方案.通过对三种空气处理方案的过程、特点及原理的认真分析,并以兰州地区为例,比较三种方案的参数,确定出在西北地区夏季特殊气候条件下,最节能的空调方案及其适用性.     

Roof cooling effect with humid porous medium

A method of laying a layer of humid porous medium on roof to gain free cooling effect by passive water evaporation is proposed. Numeric model for simulating cooling effect is built with the help of experimental results of physical properties for humid porous medium, which shows advantage over analytical solutions because of the supposition of constant physical properties in the latter. Through the comparison between simulated and experimental results, the model is validated. And the method of evaporation cooling effect with humid porous medium on the roof is tested to be feasible.     

太阳能供暖与蒸发冷却技术适用性分析

根据设计规范提供的室外气象参数 ,分析了在冬季采暖和夏季空调设计条件下 ,太阳能供暖与蒸发冷却技术在我国各地应用的可行性 ,由此选择了一种既节能又节省投资的空调方案 .指出了利用天然能源 ,冬季供暖、夏季供冷 ,是最大限度地节约能源、保护环境、改善室内空气品质的重要举措 .     

各气候区被动建筑节能技术适用性分析

被动式建筑节能,是通过利用自然气候资源的生态建筑设计原理,赋予建筑本身节能自然特性而实现的建筑节能,因而更为绿色环保,更有利于人类生存环境的可持续发展,成为建筑节能积极倡导的方向。针对中国各气候区典型城市的气候特点进行被动式太阳采暖、自然通风、蓄热墙体、诱导+夜间通风、直接蒸发冷却和间接蒸发冷度这六种被动式建筑节能技术适用性进行分析,并对各气候区的各种被动式建筑节能技术的适用性进行对比。     

多孔介质应用于建筑结构的热质传递及制冷性能分析

本文将含湿多孔介质床层应用于建筑围护结构,利用多孔介质内水分蒸发的吸热作用,为房间提供部分冷量。本文在建立非饱和多孔介质热质迁移过程数学模型的基础上,分析了室外环境参数及多孔介质床层结构对床层内温度分布、蒸发量场及水蒸气迁移的影响,为多孔介质蒸发制冷板应用于建筑结构的推广和应用提供了理论指导。     

Sensitivity analysis of predicted night cooling performance to internal convective heat transfer modelling

The potential of night cooling, a passive cooling technique of growing interest, is typically investigated by numerical means. In particular multi-zone energy simulation is currently appraised for building design. Unfortunately, in addition to the inaccurate approximation of an ideally mixed room, the implemented empirical convective heat transfer coefficients (CHTCs) only apply to specific flow regimes - forcing to use arbitrary correlations and, thus, possibly limiting the usefulness of the simulation results. Therefore, the authors of this paper investigate the sensitivity of the night cooling performance to convection algorithms. First, the authors examine the applicability of convection correlations for real building enclosures, extracted from literature. Subsequently, simulations of a night cooled office room during summertime of a moderate climate (Belgium) are carried out in TRNSYS, using different convection correlations in addition to varying design parameters. The results show that the choice of the convection algorithm strongly affects the energy and thermal comfort predictions. More importantly, the convection algorithm is of the same importance as the design parameters - making an exact definition of the CHTC crucial. Therefore, additional research by experiments or airflow codes, based on fluid dynamics, is regarded necessary.     

Rainfall identification and estimation in Guangzhou area used for building energy simulation

In uncomfortably warm areas and seasons of the year, passive cooling effects resulting from natural rainfall evaporation can greatly cut down on building energy consumption. To simulate the passive evaporation cooling effect and evaluate the relevant energy-saving potentials, hourly rainfall data are needed. However, in currently used building energy simulation software, such as DOE, EnergyPlus and DeST, no rainfall information is provided in the climatic database. This paper uses a limited set of monthly and daily rainfall distribution data in Guangzhou area to identify and model monthly, daily and hourly rainfall patterns. For a current weather database used by building energy simulation software, rainy days and rainy hours are distinguished using distance discriminant analysis, which uses measured data samples for rain identification. According to an autocorrelation analysis of rain sequences, a one-order AR model is suitable for monthly rainfall estimation by AIC criterion judgment. Distribution of daily rainfall month-by-month shows a Gamma distribution model agrees well with daily rainfall distribution. Using a Gamma distribution model and monthly total rainfall, daily rainfall is assigned stochastically. Analysis shows distribution patterns of hourly rainfall percentage, both in the rainy season and non-rainy season, coincide well with the Beta distribution. Using a Beta distribution model and daily total rainfall, hourly rainfall is assigned stochastically. A comparison of statistics features of simulated data to that of measured data validates the method.     

Experimental study of cooling effects of a passive evaporative cooling wall constructed of porous ceramics with high water soaking-up ability

As a passive cooling strategy aimed at controlling increased surface temperatures and creating cooler urban environments in summer, the authors developed a passive evaporative cooling wall (PECW) constructed of porous ceramics. These ceramics possess a capillary force to soak water, which means that their vertical surface is wet up to a level higher than 100 cm when their lower end is placed in water. The present paper describes an experiment that clarifies the cooling effects of a prototype PECW constructed of pipe-shaped ceramics. The PECW is capable of absorbing water and allows wind penetration, thus reducing its surface temperature by means of water evaporation. Passive cooling effects such as solar shading, radiation cooling, and ventilation cooling can be enhanced by incorporating PECWs into the design of outdoor or semi-outdoor spaces in parks, pedestrian areas and residential courtyards. The following findings were understood from an experimental data collected over a summer period. Wet vertical surfaces of the ceramic pipe reached a height of over 1 m at an outdoor location exposed to solar radiation. Wet surface conditions can be maintained throughout successive sunny days during summer. A slight difference in the vertical surface temperatures of the ceramic pipe was found. The air passing through the PECW was cooled, and its temperature can be reduced to a minimum value by several degrees during summer daytime. It was also found that the surface temperature of the shaded ceramic pipe can be maintained at a temperature nearly equal to the wet-bulb temperature of outdoor air.     

A numerical study of daytime passive radiative coolers for space cooling in buildings

A passive daytime radiative cooler is made of a sky facing surface which can preserve the indoor air temperature below ambient without energy consumption by simultaneously reflecting solar radiation and emitting thermal radiation to the universe through the atmospheric window located between 8–13 μm of the electromagnetic spectrum. After the first demonstration of radiative cooling under direct sunlight, a solar mirror coated with a mid-infrared (MIR) emissive thin film has become the standard device architecture. This study firstly reviews recent developments in daytime passive radiative cooling, followed by describing the development of an energy balance mathematical model to study the potential application of passive radiative coolers in HVAC systems of buildings. Some micro-channels are fabricated on the back side of the passive radiative cooler, allowing fluid to flow in an isolated loop such that the coolant can be chilled and transported to the demand side for spacing cooling. This leads to the partial replacement of conventional vapor compression refrigeration by the radiative cooling panel. Considering the steady state energy balance within the radiative cooling panel integrated HVAC systems, the cooling performance and indoor air temperature are evaluated by numerical analysis. A 100 m2 passive radiative cooling panel could chill water for the cooling of air, reducing indoor air temperature by 10 °C, equivalent to a net cooling power of 1600 W. This study suggests that the proposed passive radiative cooling system should be used to pre-cool the ambient hot air such that the overall energy consumption of a traditional air-conditioning system can be reduced. The findings promise the application of passive daytime radiative cooling in building HVAC systems.