建筑多孔饰面砖蒸发降温的风洞实验研究

张磊　冯燕珊　孟庆林　张玉

摘要：采用热湿气候风洞复现广州地区夏季典型气象日环境，研究两个相同试件在补水和不补水状态下的热量传递过程.研究结果表明：试件补水后蒸发降温效果显著，与不补水试件相比，补水试件的外表面最高温度和内表面最大热流分别降低10.9 ℃和14.8 W/m2，同时，补水试件的平均热阻比不补水试件的平均热阻增大约1倍，隔热效果显著增加.此外，研究过程中引入土壤学的PenmanMenteith蒸发量计算模型，结合实测数据对该模型中的参数进行修正，将总蒸发量分解为热力蒸发量和动力蒸发量，分析三者的变化规律，采用逐时蒸发量数据计算试件外表面的热量平衡方程.计算结果表明：蒸发过程可以消耗约64.5%的入射短波辐射热量，在夏季，蒸发过程可以显著减少建筑外表面的太阳辐射的热量，降低表面温度，减少进入房间的热量，从而节省空调能耗.

关键词：风洞；多孔材料；蒸发；实验

中图分类号：TU111 文献标识码：A

Abstract： The Typical Meteorological Day of Guangzhou summer was realized in HotWet Climatic Wind Tunnel， and the thermal transfer process of two specimens with the same construction was studied in the wind tunnel. In the experiment process， one of the specimens was watered and the other one was not watered. The experiment result illustrated that the evaporative cooling effect was very significant when the specimen was watered. Compared with the nonwatered specimen， the highest outer surface temperature and the highest inner surface heat flux of the watered specimen decreased by 10.9 ℃ and 14.8 W/m2， respectively. Additionally， the thermal resistance of the watered specimen was one time bigger than that of the nonwatered specimen. It was demonstrated that the watered specimen had better heatinsulating property than the nonwatered specimen. Moreover， the PenmanMenteith model was used to calculate the hourly evaporation of the watered specimen. The total hourly evaporation was divided to thermal evaporation and dynamic evaporation. The variations of the total hourly evaporation， thermal evaporation and dynamic evaporation were analyzed. The hourly evaporation data were used to calculate the surface thermal balance equation. The result illustrated that 64.5% incoming short wave radiation was consumed in the evaporating process. In summer， evaporating process could decrease the solar radiation illuminated on the building surface， diminish the surface temperature， reduce the thermal flux flowing into the room and save the airconditioning energy consumption.

Key words：wind tunnels； porous materials； evaporation； experiments

建筑节能是全社会节能减排工作中的重点领域.而直接且有效的建筑节能方法是设计建造低能耗建筑，将建筑设计与地域特征相结合，采用被动式建筑节能技术调节室内热湿环境、节约建筑能耗＼[1-3＼].

建筑蒸发降温是一种非常有效的被动式建筑节能技术.建筑多孔材料吸水后，在自然气候要素：太阳辐射，空气温度、湿度和风速的综合作用下，多孔材料中的水分会逐渐迁移至材料层的表面，以水分蒸发的方式形成对周围环境的蒸发降温效果，降低城市热岛强度和建筑能耗＼[4-7＼].

室外现场实测研究可以较为准确地描述在室外真实气象条件下材料的蒸发降温过程，但室外实测受自然条件的限制较大，实验结果难以复现＼[8-11＼].而在实验室开展蒸发降温实验研究可以获得连续稳定的蒸发降温实验数据，实验结果可以复现，在研究建筑材料动态蒸发降温过程方面具有一定的优越性＼[4，12-13＼].但为了真实反映室外环境，需要对全气象要素进行模拟和控制，从而在实验室内营造与室外气象条件接近的实验环境，在这种环境下开展的蒸发降温实验研究才具有代表性.

本文采用热湿气候风洞复现广州地区夏季典型气象日环境，研究两个相同试件在补水和不补水状态下的热量传递过程，采用表面热流计法计算补水和不补水试件的平均热阻，引入土壤学的PenmanMenteith蒸发量计算模型，结合实测数据对该模型中的参数进行修正，将总蒸发量分解为热力蒸发量和动力蒸发量，分析三者的变化规律，建立试件外表面的热量平衡方程，分析入射短波辐射热量与对流换热量、辐射换热量、蒸发换热量和导热换热量的转化关系.本文的研究有助于完善建筑材料蒸发降温实验方法，补充用于建筑蒸发降温技术工程应用的基础数据.

1研究方法

1.1热湿气候风洞

热湿气候风洞由华南理工大学建筑节能研究中心研发和建设.该风洞构造尺寸及其补水装置示意图如图1所示，风洞内各环境控制设备和参数如表1所示.

1.2研究对象

两个实验试件的构造完全相同，均由饰面层、防水层和基层组成.试件构造和尺寸如图2所示.基层构造为水泥混凝土，四周和底面粉刷防水涂料，上部设置防水层，以减少基层吸水蒸发对实验结果的影响，防水层构造为防水砂浆，其上部为饰面层，选取红色陶土烧结多孔饰面砖作为饰面层.该饰面砖尺寸规格为240 mm（长）×50 mm（宽）×10 mm（厚），饰面砖饱和含水率约为11.80%，半球辐射率为0.83，太阳辐射吸收率为0.76.实验过程中，保持一个试件不补水，称为干试件，另外一个试件通过风洞内的补水装置连续补水，称为湿试件，通过记录试件重量变化来计算试件的蒸发量.

1.4实验环境

在风洞内复现广州地区夏季典型气候环境，采用广州夏季典型气象日的气象参数作为实验环境的设定值.为实现试件一维传热过程，空调小室的环境温度设定为20 ℃，实测空调小室空气温度在20～22 ℃之间变化.

2实验结果分析

2.1温度、热流的变化分析

干、湿试件表面温度和热流的变化如图3，图4所示.在广州夏季典型气象日条件下，湿试件连续补水时，干、湿试件外表面温度差异显著，外表面最高温度相差10.9 ℃，干、湿试件内表面最高温度相差6.1 ℃.从图4 可以看出，湿试件外表面热流大于干试件外表面热流，这是因为湿试件饰面砖吸水后，导热系数有所增加，热阻减少，阻挡热量传递的能力有所下降，造成通过外表面流入内部的热流值有所增加.但湿试件内表面热流仍然显著低于干试件内表面热流，两者最大值相差14.8 W/m2，平均相差9.0 W/m2.

3结论

本文在热湿气候风洞内测试了多孔饰面砖与水泥混凝土组成的干、湿试件的蒸发降温过程，研究结果表明：

1）表面蒸发降温对于降低试件外表面温度和内表面热流效果显著.本研究中，干、湿试件外表面最高温度相差10.9 ℃，干、湿试件外表面平均温度相差5.0 ℃，干、湿试件内表面最高热流相差14.8 W/m2，平均热流相差9 W/m2.

2）采用表面热流计法，结合实验数据，计算得到干试件的平均热阻为0.280 m2·K/W.由于湿试件的基层不吸水，仅外表面的饰面层吸水，饰面层含水率为11.8%，在蒸发过程中降低了流入试件内表面的热流，因此湿试件计算得到的平均热阻值为0.565 m2·K/W，显示比干试件具有更好的隔热效果.

3）将估算农作物蒸散发量的PenmanMonteith公式引入到建筑多孔材料蒸发量计算过程，结合热湿气候风洞实测数据，对PM公式的系数进行了修正，采用修正后的PM公式计算了试件的逐时蒸发量，并与实测蒸发量进行了比较.比较结果表明，PM修正公式计算结果与实测结果较为接近，平均相对误差小于10%.采用PM修正公式，将总蒸发量分解为热力蒸发量和动力蒸发量，在广州地区夏季典型气象日条件下，试件热力蒸发量占总蒸发量的42.1%，动力蒸发量占总蒸发量的57.9%.

4）在白天时间段，入射到干试件外表面的短波辐射热量中，分别有64.4%，9.6%和26.0%的热量转化为对流换热量、长波换热量和导热换热量，而入射到湿试件外表面的短波辐射热量中，蒸发过程消耗了约64.5%的热量，剩余的10.8%，2.1%和22.6%短波辐射热量分别转化为表面的对流换热、长波换热和导热换热.可见，在夏季，蒸发过程可以显著降低建筑外表面太阳辐射的热量，降低表面温度，减少进入房间的热量，从而节省空调能耗.

致谢：感谢评审专家对本文提出的建设性意见和细致的修改建议.国家自然科学基金项目（No.51308223）、广东省建筑节能与应用技术重点实验室、广州市珠江科技新星项目（2011J2200098）和华南理工大学中央高校基本科研项目（2013ZM0041， 2012ZZ0070）对本文工作提供了资助.

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＼[4＼]SURAKHA Wanphen， KATSUNORI Nagano. Experimental study of the performance of porous materials to moderate the roof surface temperature by its evaporative cooling effect ＼[J＼]. Building and Environment， 2009，44：338-351.

＼[5＼]NATICCHIA B， ORAZIO M D， CARBONARI A， et al. Energy performance evaluation of a novel evaporative cooling technique ＼[J＼]. Energy and Buildings， 2010，42：1926-1938.

＼[6＼]PAGLIARINI G， RAINIERI S. Dynamic thermal simulation of a glasscovered semioutdoor space with roof evaporative cooling ＼[J＼]. Energy and Buildings， 2011，43：592-598.

＼[7＼]DAVID Pearlmutter， SIGAL Rosenfeld. Performance analysis of a simple roof cooling system with irrigated soil and two shading alternatives ＼[J＼]. Energy and Buildings， 2008，40：855-864.

＼[8＼]OLIVEIRA J T， HAGISHIMA Aya， TANIMOTO Jun. Estimation of passive cooling efficiency for environmental design in Brazil ＼[J＼]. Energy and Buildings， 2009， 41：809-813.

＼[9＼]HE Jiang，HOYANO Akira. A 3D CADbased simulation tool for prediction and evaluation of the thermal improvement effect of passive cooling walls in the developed urban locations ＼[J＼]. Solar Energy， 2009，83：1064-1075.

＼[10＼]HE Jiang，HOYANO Akira. Experimental study of cooling effects of a passive evaporative cooling wall constructed of porous ceramics with high water soakingup ability ＼[J＼]. Building and Environment， 2010，45：461-472.

＼[11＼]HE Jiang. A design supporting simulation system for predicting and evaluating the cool microclimate creating effect of passive evaporative cooling walls ＼[J＼]. Building and Environment， 2011，46： 584-596.

＼[12＼]孟庆林，胡文斌，张磊，等.建筑蒸发降温基础＼[M＼].北京：科学出版社，2006：122-145.

MENG Qinglin， HU Wenbin， ZHANG Lei， et al Foundations of building evaporative cooling ＼[M＼]. Beijing： Science Press，2006：122-145.（In Chinese）

＼[13＼]PIRES L， SILVA Pedro D， CASTRO Gomes J P. Performance of textile and building materials for a particular evaporative cooling purpose ＼[J＼]. Experimental Thermal and Fluid Science，2011，35：670-675.

＼[14＼]GETTER Kristin L，ROWE D Bradley，JEFF A Andresen， et al. Seasonal heat flux properties of an extensive green roof in a Midwestern U.S. climate＼[J＼]. Energy and Buildings，2011，43（12）：3548-3557.

＼[15＼]PENG Changhai，WU Zhishen. In situ measuring and evaluating the thermal resistance of building construction＼[J＼]. Energy and Buildings，2008，40（11）：2076-2082.

＼[16＼]KHAN M I. Factors affecting the thermal properties of concrete and applicability of its prediction models ＼[J＼]. Building and Environment， 2002，37：607-614.

＼[17＼]MENDES N， WINKELMANN F C， LAMBERTS R， et al. Moisture effects on conduction loads ＼[J＼]. Energy and Buildings，2003，35（7）： 631-644.

＼[18＼]DRA E Y. An empirical simplification of the temperature penmanmonteith model for the tropics ＼[J＼]. Journal of Agricultural Science， 2010，2（1）：162-171.

＼[19＼]ALLEN Richard G，PRUITT William O，WRIGHT James L， et al. A recommendation on standardized surface resistance for hourly calculation of reference ET0 by the FAO56 PenmanMonteith method ＼[J＼]. Agricultural Water Management， 2006，81（1）：1-22.

＼[20＼]WIDMOSER Peter. A discussion on and alternative to the Penmanmonteith equation ＼[J＼]. Agricultural Water Management， 2009，96：711-721.

＼[21＼]GAVILAN P， BERENGENA J， ALLEN R G. Measuring versus estimating net radiation and soil heat flux：Impact on PenmanMonteith reference ET estimates in semiarid regions ＼[J＼]. Agricultural Water Management， 2007，89（3）：275-286.

＼[4＼]SURAKHA Wanphen， KATSUNORI Nagano. Experimental study of the performance of porous materials to moderate the roof surface temperature by its evaporative cooling effect ＼[J＼]. Building and Environment， 2009，44：338-351.

＼[5＼]NATICCHIA B， ORAZIO M D， CARBONARI A， et al. Energy performance evaluation of a novel evaporative cooling technique ＼[J＼]. Energy and Buildings， 2010，42：1926-1938.

＼[6＼]PAGLIARINI G， RAINIERI S. Dynamic thermal simulation of a glasscovered semioutdoor space with roof evaporative cooling ＼[J＼]. Energy and Buildings， 2011，43：592-598.

＼[7＼]DAVID Pearlmutter， SIGAL Rosenfeld. Performance analysis of a simple roof cooling system with irrigated soil and two shading alternatives ＼[J＼]. Energy and Buildings， 2008，40：855-864.

＼[8＼]OLIVEIRA J T， HAGISHIMA Aya， TANIMOTO Jun. Estimation of passive cooling efficiency for environmental design in Brazil ＼[J＼]. Energy and Buildings， 2009， 41：809-813.

＼[9＼]HE Jiang，HOYANO Akira. A 3D CADbased simulation tool for prediction and evaluation of the thermal improvement effect of passive cooling walls in the developed urban locations ＼[J＼]. Solar Energy， 2009，83：1064-1075.

＼[10＼]HE Jiang，HOYANO Akira. Experimental study of cooling effects of a passive evaporative cooling wall constructed of porous ceramics with high water soakingup ability ＼[J＼]. Building and Environment， 2010，45：461-472.

＼[11＼]HE Jiang. A design supporting simulation system for predicting and evaluating the cool microclimate creating effect of passive evaporative cooling walls ＼[J＼]. Building and Environment， 2011，46： 584-596.

＼[12＼]孟庆林，胡文斌，张磊，等.建筑蒸发降温基础＼[M＼].北京：科学出版社，2006：122-145.

MENG Qinglin， HU Wenbin， ZHANG Lei， et al Foundations of building evaporative cooling ＼[M＼]. Beijing： Science Press，2006：122-145.（In Chinese）

＼[13＼]PIRES L， SILVA Pedro D， CASTRO Gomes J P. Performance of textile and building materials for a particular evaporative cooling purpose ＼[J＼]. Experimental Thermal and Fluid Science，2011，35：670-675.

＼[14＼]GETTER Kristin L，ROWE D Bradley，JEFF A Andresen， et al. Seasonal heat flux properties of an extensive green roof in a Midwestern U.S. climate＼[J＼]. Energy and Buildings，2011，43（12）：3548-3557.

＼[15＼]PENG Changhai，WU Zhishen. In situ measuring and evaluating the thermal resistance of building construction＼[J＼]. Energy and Buildings，2008，40（11）：2076-2082.

＼[16＼]KHAN M I. Factors affecting the thermal properties of concrete and applicability of its prediction models ＼[J＼]. Building and Environment， 2002，37：607-614.

＼[17＼]MENDES N， WINKELMANN F C， LAMBERTS R， et al. Moisture effects on conduction loads ＼[J＼]. Energy and Buildings，2003，35（7）： 631-644.

＼[18＼]DRA E Y. An empirical simplification of the temperature penmanmonteith model for the tropics ＼[J＼]. Journal of Agricultural Science， 2010，2（1）：162-171.

＼[19＼]ALLEN Richard G，PRUITT William O，WRIGHT James L， et al. A recommendation on standardized surface resistance for hourly calculation of reference ET0 by the FAO56 PenmanMonteith method ＼[J＼]. Agricultural Water Management， 2006，81（1）：1-22.

＼[20＼]WIDMOSER Peter. A discussion on and alternative to the Penmanmonteith equation ＼[J＼]. Agricultural Water Management， 2009，96：711-721.

＼[21＼]GAVILAN P， BERENGENA J， ALLEN R G. Measuring versus estimating net radiation and soil heat flux：Impact on PenmanMonteith reference ET estimates in semiarid regions ＼[J＼]. Agricultural Water Management， 2007，89（3）：275-286.