張磊　馮燕珊　孟慶林　張玉

摘要：采用熱濕氣候風洞復現(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水和不補水狀態(tài)下的熱量傳遞過程.研究結果表明：試件補水后蒸發(fā)降溫效果顯著，與不補水試件相比，補水試件的外表面最高溫度和內表面最大熱流分別降低10.9 ℃和14.8 W/m2，同時，補水試件的平均熱阻比不補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的PenmanMenteith蒸發(fā)量計算模型，結合實測數(shù)據(jù)對該模型中的參數(shù)進行修正，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)計算試件外表面的熱量平衡方程.計算結果表明：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，減少進入房間的熱量，從而節(jié)省空調能耗.

關鍵詞：風洞；多孔材料；蒸發(fā)；實驗

中圖分類號：TU111 文獻標識碼：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領域.而直接且有效的建筑節(jié)能方法是設計建造低能耗建筑，將建筑設計與地域特征相結合，采用被動式建筑節(jié)能技術調節(jié)室內熱濕環(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.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，降低城市熱島強度和建筑能耗＼[4-7＼].

室外現(xiàn)場實測研究可以較為準確地描述在室外真實氣象條件下材料的蒸發(fā)降溫過程，但室外實測受自然條件的限制較大，實驗結果難以復現(xiàn)＼[8-11＼].而在實驗室開展蒸發(fā)降溫實驗研究可以獲得連續(xù)穩(wěn)定的蒸發(fā)降溫實驗數(shù)據(jù)，實驗結果可以復現(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＼].但為了真實反映室外環(huán)境，需要對全氣象要素進行模擬和控制，從而在實驗室內營造與室外氣象條件接近的實驗環(huán)境，在這種環(huán)境下開展的蒸發(fā)降溫實驗研究才具有代表性.

本文采用熱濕氣候風洞復現(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水和不補水狀態(tài)下的熱量傳遞過程，采用表面熱流計法計算補水和不補水試件的平均熱阻，引入土壤學的PenmanMenteith蒸發(fā)量計算模型，結合實測數(shù)據(jù)對該模型中的參數(shù)進行修正，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)換熱量和導熱換熱量的轉化關系.本文的研究有助于完善建筑材料蒸發(fā)降溫實驗方法，補充用于建筑蒸發(fā)降溫技術工程應用的基礎數(shù)據(jù).

1研究方法

1.1熱濕氣候風洞

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

1.2研究對象

兩個實驗試件的構造完全相同，均由飾面層、防水層和基層組成.試件構造和尺寸如圖2所示.基層構造為水泥混凝土，四周和底面粉刷防水涂料，上部設置防水層，以減少基層吸水蒸發(fā)對實驗結果的影響，防水層構造為防水砂漿，其上部為飾面層，選取紅色陶土燒結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.實驗過程中，保持一個試件不補水，稱為干試件，另外一個試件通過風洞內的補水裝置連續(xù)補水，稱為濕試件，通過記錄試件重量變化來計算試件的蒸發(fā)量.

1.4實驗環(huán)境

在風洞內復現(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)作為實驗環(huán)境的設定值.為實現(xiàn)試件一維傳熱過程，空調小室的環(huán)境溫度設定為20 ℃，實測空調小室空氣溫度在20～22 ℃之間變化.

2實驗結果分析

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，這是因為濕試件飾面磚吸水后，導熱系數(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部的熱流值有所增加.但濕試件內表面熱流仍然顯著低于干試件內表面熱流，兩者最大值相差14.8 W/m2，平均相差9.0 W/m2.

3結論

本文在熱濕氣候風洞內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，研究結果表明：

1）表面蒸發(fā)降溫對于降低試件外表面溫度和內表面熱流效果顯著.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）采用表面熱流計法，結合實驗數(shù)據(jù)，計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表面的熱流，因此濕試件計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)量計算過程，結合熱濕氣候風洞實測數(shù)據(jù)，對PM公式的系數(shù)進行了修正，采用修正后的PM公式計算了試件的逐時蒸發(fā)量，并與實測蒸發(fā)量進行了比較.比較結果表明，PM修正公式計算結果與實測結果較為接近，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%的熱量轉化為對流換熱量、長波換熱量和導熱換熱量，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化為表面的對流換熱、長波換熱和導熱換熱.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，減少進入房間的熱量，從而節(jié)省空調能耗.

致謝：感謝評審專家對本文提出的建設性意見和細致的修改建議.國家自然科學基金項目（No.51308223）、廣東省建筑節(jié)能與應用技術重點實驗室、廣州市珠江科技新星項目（2011J2200098）和華南理工大學中央高?；究蒲许椖浚?013ZM0041， 2012ZZ0070）對本文工作提供了資助.

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＼[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.

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

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