建筑多孔飾面磚蒸發(fā)降溫的風(fēng)洞實(shí)驗(yàn)研究

張磊　馮燕珊　孟慶林　張玉

摘要：采用熱濕氣候風(fēng)洞復(fù)現(xiàn)廣州地區(qū)夏季典型氣象日環(huán)境，研究兩個相同試件在補(bǔ)水和不補(bǔ)水狀態(tài)下的熱量傳遞過程.研究結(jié)果表明：試件補(bǔ)水后蒸發(fā)降溫效果顯著，與不補(bǔ)水試件相比，補(bǔ)水試件的外表面最高溫度和內(nèi)表面最大熱流分別降低10.9 ℃和14.8 W/m2，同時，補(bǔ)水試件的平均熱阻比不補(bǔ)水試件的平均熱阻增大約1倍，隔熱效果顯著增加.此外，研究過程中引入土壤學(xué)的PenmanMenteith蒸發(fā)量計(jì)算模型，結(jié)合實(shí)測數(shù)據(jù)對該模型中的參數(shù)進(jìn)行修正，將總蒸發(fā)量分解為熱力蒸發(fā)量和動力蒸發(fā)量，分析三者的變化規(guī)律，采用逐時蒸發(fā)量數(shù)據(jù)計(jì)算試件外表面的熱量平衡方程.計(jì)算結(jié)果表明：蒸發(fā)過程可以消耗約64.5%的入射短波輻射熱量，在夏季，蒸發(fā)過程可以顯著減少建筑外表面的太陽輻射的熱量，降低表面溫度，減少進(jìn)入房間的熱量，從而節(jié)省空調(diào)能耗.

關(guān)鍵詞：風(fēng)洞；多孔材料；蒸發(fā)；實(shí)驗(yàn)

中圖分類號：TU111 文獻(xiàn)標(biāo)識碼：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

建筑節(jié)能是全社會節(jié)能減排工作中的重點(diǎn)領(lǐng)域.而直接且有效的建筑節(jié)能方法是設(shè)計(jì)建造低能耗建筑，將建筑設(shè)計(jì)與地域特征相結(jié)合，采用被動式建筑節(jié)能技術(shù)調(diào)節(jié)室內(nèi)熱濕環(huán)境、節(jié)約建筑能耗＼[1-3＼].

建筑蒸發(fā)降溫是一種非常有效的被動式建筑節(jié)能技術(shù).建筑多孔材料吸水后，在自然氣候要素：太陽輻射，空氣溫度、濕度和風(fēng)速的綜合作用下，多孔材料中的水分會逐漸遷移至材料層的表面，以水分蒸發(fā)的方式形成對周圍環(huán)境的蒸發(fā)降溫效果，降低城市熱島強(qiáng)度和建筑能耗＼[4-7＼].

室外現(xiàn)場實(shí)測研究可以較為準(zhǔn)確地描述在室外真實(shí)氣象條件下材料的蒸發(fā)降溫過程，但室外實(shí)測受自然條件的限制較大，實(shí)驗(yàn)結(jié)果難以復(fù)現(xiàn)＼[8-11＼].而在實(shí)驗(yàn)室開展蒸發(fā)降溫實(shí)驗(yàn)研究可以獲得連續(xù)穩(wěn)定的蒸發(fā)降溫實(shí)驗(yàn)數(shù)據(jù)，實(shí)驗(yàn)結(jié)果可以復(fù)現(xiàn)，在研究建筑材料動態(tài)蒸發(fā)降溫過程方面具有一定的優(yōu)越性＼[4，12-13＼].但為了真實(shí)反映室外環(huán)境，需要對全氣象要素進(jìn)行模擬和控制，從而在實(shí)驗(yàn)室內(nèi)營造與室外氣象條件接近的實(shí)驗(yàn)環(huán)境，在這種環(huán)境下開展的蒸發(fā)降溫實(shí)驗(yàn)研究才具有代表性.

本文采用熱濕氣候風(fēng)洞復(fù)現(xiàn)廣州地區(qū)夏季典型氣象日環(huán)境，研究兩個相同試件在補(bǔ)水和不補(bǔ)水狀態(tài)下的熱量傳遞過程，采用表面熱流計(jì)法計(jì)算補(bǔ)水和不補(bǔ)水試件的平均熱阻，引入土壤學(xué)的PenmanMenteith蒸發(fā)量計(jì)算模型，結(jié)合實(shí)測數(shù)據(jù)對該模型中的參數(shù)進(jìn)行修正，將總蒸發(fā)量分解為熱力蒸發(fā)量和動力蒸發(fā)量，分析三者的變化規(guī)律，建立試件外表面的熱量平衡方程，分析入射短波輻射熱量與對流換熱量、輻射換熱量、蒸發(fā)換熱量和導(dǎo)熱換熱量的轉(zhuǎn)化關(guān)系.本文的研究有助于完善建筑材料蒸發(fā)降溫實(shí)驗(yàn)方法，補(bǔ)充用于建筑蒸發(fā)降溫技術(shù)工程應(yīng)用的基礎(chǔ)數(shù)據(jù).

1研究方法

1.1熱濕氣候風(fēng)洞

熱濕氣候風(fēng)洞由華南理工大學(xué)建筑節(jié)能研究中心研發(fā)和建設(shè).該風(fēng)洞構(gòu)造尺寸及其補(bǔ)水裝置示意圖如圖1所示，風(fēng)洞內(nèi)各環(huán)境控制設(shè)備和參數(shù)如表1所示.

1.2研究對象

兩個實(shí)驗(yàn)試件的構(gòu)造完全相同，均由飾面層、防水層和基層組成.試件構(gòu)造和尺寸如圖2所示.基層構(gòu)造為水泥混凝土，四周和底面粉刷防水涂料，上部設(shè)置防水層，以減少基層吸水蒸發(fā)對實(shí)驗(yàn)結(jié)果的影響，防水層構(gòu)造為防水砂漿，其上部為飾面層，選取紅色陶土燒結(jié)多孔飾面磚作為飾面層.該飾面磚尺寸規(guī)格為240 mm（長）×50 mm（寬）×10 mm（厚），飾面磚飽和含水率約為11.80%，半球輻射率為0.83，太陽輻射吸收率為0.76.實(shí)驗(yàn)過程中，保持一個試件不補(bǔ)水，稱為干試件，另外一個試件通過風(fēng)洞內(nèi)的補(bǔ)水裝置連續(xù)補(bǔ)水，稱為濕試件，通過記錄試件重量變化來計(jì)算試件的蒸發(fā)量.

1.4實(shí)驗(yàn)環(huán)境

在風(fēng)洞內(nèi)復(fù)現(xiàn)廣州地區(qū)夏季典型氣候環(huán)境，采用廣州夏季典型氣象日的氣象參數(shù)作為實(shí)驗(yàn)環(huán)境的設(shè)定值.為實(shí)現(xiàn)試件一維傳熱過程，空調(diào)小室的環(huán)境溫度設(shè)定為20 ℃，實(shí)測空調(diào)小室空氣溫度在20～22 ℃之間變化.

2實(shí)驗(yàn)結(jié)果分析

2.1溫度、熱流的變化分析

干、濕試件表面溫度和熱流的變化如圖3，圖4所示.在廣州夏季典型氣象日條件下，濕試件連續(xù)補(bǔ)水時，干、濕試件外表面溫度差異顯著，外表面最高溫度相差10.9 ℃，干、濕試件內(nèi)表面最高溫度相差6.1 ℃.從圖4 可以看出，濕試件外表面熱流大于干試件外表面熱流，這是因?yàn)闈裨嚰椕娲u吸水后，導(dǎo)熱系數(shù)有所增加，熱阻減少，阻擋熱量傳遞的能力有所下降，造成通過外表面流入內(nèi)部的熱流值有所增加.但濕試件內(nèi)表面熱流仍然顯著低于干試件內(nèi)表面熱流，兩者最大值相差14.8 W/m2，平均相差9.0 W/m2.

3結(jié)論

本文在熱濕氣候風(fēng)洞內(nèi)測試了多孔飾面磚與水泥混凝土組成的干、濕試件的蒸發(fā)降溫過程，研究結(jié)果表明：

1）表面蒸發(fā)降溫對于降低試件外表面溫度和內(nèi)表面熱流效果顯著.本研究中，干、濕試件外表面最高溫度相差10.9 ℃，干、濕試件外表面平均溫度相差5.0 ℃，干、濕試件內(nèi)表面最高熱流相差14.8 W/m2，平均熱流相差9 W/m2.

2）采用表面熱流計(jì)法，結(jié)合實(shí)驗(yàn)數(shù)據(jù)，計(jì)算得到干試件的平均熱阻為0.280 m2·K/W.由于濕試件的基層不吸水，僅外表面的飾面層吸水，飾面層含水率為11.8%，在蒸發(fā)過程中降低了流入試件內(nèi)表面的熱流，因此濕試件計(jì)算得到的平均熱阻值為0.565 m2·K/W，顯示比干試件具有更好的隔熱效果.

3）將估算農(nóng)作物蒸散發(fā)量的PenmanMonteith公式引入到建筑多孔材料蒸發(fā)量計(jì)算過程，結(jié)合熱濕氣候風(fēng)洞實(shí)測數(shù)據(jù)，對PM公式的系數(shù)進(jìn)行了修正，采用修正后的PM公式計(jì)算了試件的逐時蒸發(fā)量，并與實(shí)測蒸發(fā)量進(jìn)行了比較.比較結(jié)果表明，PM修正公式計(jì)算結(jié)果與實(shí)測結(jié)果較為接近，平均相對誤差小于10%.采用PM修正公式，將總蒸發(fā)量分解為熱力蒸發(fā)量和動力蒸發(fā)量，在廣州地區(qū)夏季典型氣象日條件下，試件熱力蒸發(fā)量占總蒸發(fā)量的42.1%，動力蒸發(fā)量占總蒸發(fā)量的57.9%.

4）在白天時間段，入射到干試件外表面的短波輻射熱量中，分別有64.4%，9.6%和26.0%的熱量轉(zhuǎn)化為對流換熱量、長波換熱量和導(dǎo)熱換熱量，而入射到濕試件外表面的短波輻射熱量中，蒸發(fā)過程消耗了約64.5%的熱量，剩余的10.8%，2.1%和22.6%短波輻射熱量分別轉(zhuǎn)化為表面的對流換熱、長波換熱和導(dǎo)熱換熱.可見，在夏季，蒸發(fā)過程可以顯著降低建筑外表面太陽輻射的熱量，降低表面溫度，減少進(jìn)入房間的熱量，從而節(jié)省空調(diào)能耗.

致謝：感謝評審專家對本文提出的建設(shè)性意見和細(xì)致的修改建議.國家自然科學(xué)基金項(xiàng)目（No.51308223）、廣東省建筑節(jié)能與應(yīng)用技術(shù)重點(diǎn)實(shí)驗(yàn)室、廣州市珠江科技新星項(xiàng)目（2011J2200098）和華南理工大學(xué)中央高校基本科研項(xiàng)目（2013ZM0041， 2012ZZ0070）對本文工作提供了資助.

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＼[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＼]孟慶林，胡文斌，張磊，等.建筑蒸發(fā)降溫基礎(chǔ)＼[M＼].北京：科學(xué)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.

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