分析节能建筑在各种气候条件下长波辐射率和围护结构的太阳反射率的影响

分析在各种气候条件下长波辐射率和围护结构太阳反射率对建筑能耗的影响石志阳张雄1.摘要一个动态的计算机模拟对分布在世界各地的35个城市的气候进行了模拟。

研究空调节能负荷一年一度的变化和空调节能负荷由于在长波辐射的变化和建筑围护结构的研究,发现在各种气候条件下（包括热带气候，属亚热带气候，山中最合适的外部建筑饰面高原气候，寒温带气候和温带气候）太阳能反射的变化。

两者的长波发射率和太阳反射是在0.1至0.9之间，间隔设置为0.1模拟。

一年一度各城市的空调能量负载都列在一张图表。

结果表明,长波发射率和太阳的反射率在建筑围护结构的能耗中发挥了重要的角色。

在热带气候下,光学参数是影响建筑外表面建筑能耗最显著的建筑节能指标。

关键词:长波发射率;太阳能反射率;围护结构;空调能源负荷;动态仿真2.前言太阳辐射对建筑能耗有重要的影响。

近年来,许多已进行的研究利用有隔热效果的材料涂覆在凉爽的建筑围护结构上(包括外部建筑屋顶和外部(Levinsona 墙等),2007年的看法,高庆宇,Akbari苏达权等,2008年； Bretz等,Akbari,1997年,帕克和Barkaszi;1997年,苏达权等,2005a列文森对于凯等,高庆宇,2010年)。

此外,人们做了大量的研究,发展多种太阳辐射计算建筑外部表面的方法学（(Chimklai等人,2004年;弗朗西斯科·杨等人)。

冷色涂料应用在屋顶上或外观墙上增加了建筑围护结构的总太阳能反射率。

高的太阳能反射率降低了建筑物的表面温度，太阳辐射能被建筑围护结构吸收到建筑里面。

在炎热气候的地区,一年一度的空调能源负荷能能够大大降低。

然而,节能效果很好的涂料每年在空调能源负荷中减少,甚至在夏热冬冷的地区。

最后,太阳反射在寒冷的气候地区的节能因在建筑外观表面导致了负面的影响。

因此,研究利用热模拟软件来进行比较一幢教学楼的年度能源负荷与不同太阳能反射率在各种气候条件的变化(王建民苏达权等,2008年)。

然而,很少有可靠的信息影响建筑外观长波发射率在节能建筑中是怎样影响的。

本研究以exteior联合作用的建筑的说明太阳能反射率和长波发射率对建筑能耗在不同地区气候条件下的影响。

建筑物在白天收到大量的太阳能辐射。

与此同时,馆围护结构不断与热环境(包括天空、地面,其他建筑和树木等)交换热量。

当建筑物围护结构表面热交换达到稳态,表面给出了热传递的平衡关系(燕和赵,1986年):ra ca o g s q q q q q q q ++=+++B R3. 方法论能量的动态热模拟软件优先版本4.0.0.024是用于模拟。

能量加是一个建筑节能的建模仿真程序，如关于建筑采暖、制冷、照明、通风、以及其他能量的流动,是基于BLAST 和DOE-2程序而言的。

了获得更全面地理解这个系统,太阳能反射率和长波的热辐射特性。

两者都将围护结构系数设置从0.1至0.9之间和间隔设置为0.1。

应当指出,在实际生活中,太阳能反射率高于0.8或长波发射率不到0.20以上会是很困难的。

实际的外观是纯白色建筑外观表面的太阳能反射率高于0.8。

对于长波发射率低于0.20的建筑外观表面将使用为一种磨光的金属幕墙。

结果在这两种情况下会城市会产生光污染。

所有的气象数据用于计算机仿真验中。

从数据库中下载能量加的网上。

这些气象数据产生了一段记录(典型的30年)在有代表性的那个位置是合适的，可以用于加热/冷却负荷计算。

4.对结果进行分析4.1. 各种气候参数分析热带和亚热带气候条件下，上述规律讲诉了如何影响外观光学性质空调能量负荷是相对简单的。

图表5、6显示了一个更高的太阳能反射率和长波的热辐射特性对建筑外观表面产生较低的年度空调能量负载。

空调负荷的能量收敛到某种程度上增加了太阳能反射系数,长波的重要性也随之降低。

总的来说,建筑外观表面用用浅色如太阳能反光涂料,能达到节能的目的。

高原山区的气候和寒温带气候有类似的规律。

图表7、8表明,太阳能反射率和长波发射率小的地区能够产生较低的年度空调能源负载。

因此,外部建筑用深色的颜色是比较合理的，符合节能要求的两个地区,如使用瓷砖的颜色太暗，因为长波发射率和较低比较节能。

导致这样原因是,有一个低长波陶瓷材料和黑暗的颜色可能会导致表面发射率低(太阳能反射率和德维特,2006)。

在温带气候条件下，受光学参数的影响，在一个复杂的能量负载方式中，总结了一年一度的空调负荷的趋势图之间的关系。

在举例的不同建筑围护结构太阳能反射率和长波发射率的这些城市分成四个类型。

第一类是显示在图表9中。

空调能量负载协同减少太阳能反射率，随着太阳能反射率的改变而改变。

同时,作为空调能量发散向上负载的太阳能反射系数的增加而增加。

第二类是显示在图表10中。

空调能量负载协同减少太阳能反射率随着太阳能反射率的改变出现改变同时,空调负荷的能量向上发散和随着太阳能反射率向下增加。

第三类是显示在图表11中。

随着太阳能反射率增加,每年的空调负荷最初变化很小,然后向上发散收敛后相融合到某一点上。

第四类是显示在图表12中。

随着太阳能反射率增加,每年的空调负荷一开始变小,然后分流向下，最后可收敛到某个特定的时间点上。

虽然具体的四类是不同的,但总的来说,这个模拟能够说明在温和气候环境下的要求，建筑围护结构中完成与中反射适合发射率和低长波，能够对建筑产生节能。

在这种情况下,一种金属幕墙是一个很不错的选择,因为轻微的磨光的金属有一个中等大小的反射率和低长波发射率(德维特,2006)。

4.2.每年空调节能的潜力分析对每年的空调能源载荷进行了计算分析，对应每相结合的太阳能反射率(从0.1至0.9)和长波发射率(从0.1至0.9)。

然后, 分别计算了每个城市能量挑选出来的81(理论)或56例(实际情况下)的结果，得出了数据的最高和最低的一年一度的空调负荷。

当理论条件下选择相应的最大值和最小能量荷载作用下,太阳能反射率建立和长波发射率从0.1至0.9。

实际情况中意味着只有切实可行的选项都才能实现,所以太阳能反射率在0.1至0.8之间和长波发射率是0.3 到0.9之间。

它的极限载荷减去最小负荷在城市中代表了节能潜力。

在气候能实现的条件下,通过改变光性能的围护结构就能够实现。

这些数据在图13中给出了。

从图13中可以看到,(1)城市在热带和亚热带的气候条件下(包括曼谷、新加坡、新德里,迈阿密等)看到最大的区别;(2)城市高原山区气候条件下(包括拉萨,与湖人的比赛。

拉,等等)看到很大的差异;(3)在亚寒带气候条件下的城市(包括旧金山、莫斯科等),看到一个可观的但较小的差异;(4)城市在温带气候(包括上海、纽约、武汉等。

看到一个更小的差异。

在曼谷,与实际情况相比,差异达到670.0 MJ/m2左右,与理论条件差异达到873.5 MJ/m2.。

在洛杉机与实际的数值之间差异也到达了371.4 MJ/m2，与理论数值到达了446.6 MJ / m2。

这些数据揭示了显著节能数据，在热带和山地高原地区的建筑采用高反射率的潜力和高长波发射率才能够达到如此数据。

在莫斯科,与实际的情况下两者的区别达219.2 MJ/m2,在理论的条件下,差异达到278.4 MJ/m2的差距。

因此,在亚寒带气候条件下低反射率和低发射率的城市可以减少空调负荷较大的能量损失。

在上海,与实际情况的差异相比,差别是35.7,MJ/平方米,在理论的条件下,两者的区别等于58.7美兆/平方米。

以上结果表明，大多数气候温和的城市外建筑物的表面只有一个有限的通过改变效果能实现光学节能的参数。

5.结论本研究的目的是要研究一种被动的解决方案，通过改变建筑物围护结构表面在各种气候条件下太阳能反射率和长波的热辐射特性来减少一年一度的空调负荷变化的能量。

动态计算机模拟了分布在世界各地的35个城市的气候。

通过参数分析得出了下列几点。

（1）在热带和亚热带气候条件下,高太阳能反射率和高长波表面发射率对于建筑节能是最有利的，而且高太阳发射率是最主要的影响因素。

（2）在高原山区的气候条件下和副极带气候条件下, 低太阳能反射率和表面发射率较低的长波是最好的选择。

（3）在温带大陆气候和温带海洋气候条件下,介质反射率和合适的低发射率的节能要求长波。

低长波发射率是主要因素。

当长波能量负载率高的时候，反射率的变化仅仅有一点影响。

通过分析一年一度的空调负荷的潜力,得出结论：(1)热带气候条件下的城市有最大的节能潜力,(2)高原山区气候条件下的城市和副极带气候条件下的城市也有可观的节能潜力；(3)在温带大陆和温带海洋气候下的城市只有有限的节能潜力。

Analyzing the effect of the longwave emissivity and solar reflectanceof building envelopes on energy-saving in buildings in various climatesZhiyang Shi , Xiong Zhang1.AbstractA dynamic computer simulation is carried out in the climates of 35 cities distributed around the world. The variation of the annual air-conditioning energy loads due to changes in the longwave emissivity and the solar reflectance of the building envelopes is studied to find the most appropriate exterior building finishes in various climates (including a tropical climate, a subtropical climate, a mountain plateau climate, a frigid-temperate climate and a temperate climate). Both the longwave emissivity and the solar reflectance are set from 0.1 to 0.9 with an interval of 0.1 in the simulation. The annual air-conditioning energy loads trends of each city are listed in a chart. The results show that both the longwave emissivity and the solar reflectance of building envelopes play significant roles in energy-saving for buildings. In tropical climates, the optical parameters of the building exterior surface affect the building energy-saving most significantly. In the mountain plateau climates and the subarctic climates, the impacts on energy-saving in buildings due to changes in the longwave emissivity and the solar reflectance are still considerable, but in the temperate continental climates and the temperate maritime climates, only limited effects are seen.2010 Elsevier Ltd. All rights reserved.Keywords:Longwave emissivity; Solar reflectance; Building envelope; Air-conditioning energy loads; Dynamic simulation2. IntroductionSolar radiation has a significant effect on the energy loads of buildings. Recently, many studies have been performed to research the heat insulation effects of using cool coatings on exterior building envelopes (including roofs and exterior walls) (Levinsona et al., 2007; Yu et al., 2008; Akbari et al., 1997; Bretz and Akbari, 1997; Parker and Barkaszi, 1997; Levinson et al., 2005a,b; Kai et al., 2010). In addition,much research has been done to develop various solar radiation calculation methodologies for the exterior surfaces of buildings (Chimklai et al., 2004; Francisco et al., 2005; Yang et al., 2006). The cool coatings used on the roof or the exterior he exterior building envelopes. High solar reflectance decreased the temperature of the exterior building surface and the solar radiation heat absorbed by the building envelopes. In hot climate regions, the annual air-condition energy loads could then be decreased considerably. However, the energy-saving effect of cool coatings on the annual air-condition energy loads is reduced and even obliterated in hot summer and cold winter regions. Finally, high solar reflectance of the building exterior surface results in a negative effect on building energy-saving in cold climate regions. Therefore, studies have been performed using thermal simulation software to compare the annual energy loads of one building with different solar reflectances in various climatic conditions (Wang et al., 2008; Synnefa et al., 2007). However, there is little information available about the effect of the building exterior longwave emissivity onenergy-saving in buildings. This study focuses on the joint effect of the building exteior’s solar reflectance and longwave emissivity. Buildings receive a great deal of solar radiation in the daytime. At the same time, the building envelopes constantly exchange heat with the thermal environment (including the sky, the ground, other buildings and trees, etc.). Fig. 1 depicts the thermal interaction between the building envelopes and the environment. When the exterior surface of the envelopes reaches a thermal steady-state, the surface thermal transfer balance is given by the relation (Yan and Zhao, 1986):3.MethodologyThe dynamic thermal simulation software Energy Plus version 4.0.0.024 is used for the simulations. Energy Plus is a building energy simulation program for modeling building heating, cooling, lighting, ventilating, and other energy flows and is related to both the BLAST and DOE–2 programs.To get a more complete understanding of this system,the solar reflectance and the longwave emissivity of the building envelope are both set from 0.1 to 0.9 and the interval interval is set to 0.1. It should be mentioned that, in reality, it would be difficult for the solar reflectance to be higher than 0.8 or the longwave emissivity to be less than 0.20 on the actual building exterior. For the solar reflectance to be higher than 0.8, the color of the building exterior surface would be pure white. For the longwave emissivity to be less than 0.20, the building exterior surface would use highly polished metal as a curtain wall. Both of these cases would result in light pollution in an urban environment.All meteorological data used in the computer simulation are downloaded from the database of the energy plus ebsite.These meteorological data are carefully generated from a period of record (typically 30 years) to be representative of that location and be suitable for use in heating/cooling load calculations.4. Analysis of the results4.1. Parametric analysis in various climatesIn tropical and subtropical climates, the rules dictating how the exterior optical properties affect the air-condition energy loads are relatively simple. Figs. 5 and 6 indicate that a higher solar reflectance and longwave emissivity of the building exterior surface result i lower annual air-condition energy loads. For the air-condition energy loads to converge to some extent with an increase in solar reflectance, the importance of longwave emissivity on energy-saving decreases in the high solar reflectancecondition.Overall,building exterior finishes with a light color, near-infraredreflectance and high longwave emissivity, such as solar reflective coatings, can comply with the nergy-saving requirements of the region.Mountain plateau climates and frigid-temperate climates have similar rules. Figs. 7 and 8 show that a smallersolar reflectance and longwave emissivity of the building exterior surface result in lower annual air-condition energy loads. Thus, exterior building finishes with a dark color,near-infrared-absorption and low longwave emissivity can comply with theenergy-saving requirements of the two regions, such as use of ceramic tiles of a dark color. The causes are that ceramic materials have a low longwave emissivity and the dark color surface could result in low solar reflectance (Incropera and Dewitt, 2006). In temperate climates, the optical parameters affect the energy loads in a complicated way. Summarizing the annual air-condition loads trend chart in relation to the solar reflectance and the longwave emissivity of the building envelopes, these cities are divided into four categories.The first category is shown in Fig. 9. The air-conditioning energy loads converge with decreasing solar reflectance and diverge with increasing solar reflectance. Also, the air-conditioning energy loads diverge upward as solar reflectance increases The second category is shown in Fig. 10. The air-conditioning energy loads converge with decreasing solar reflectance and diverge with increasing solar reflectance. Also, the air-conditioning energy loads diverge upward and downward at the same time as the solar reflectance increases.The third category is shown in Fig. 11. As the solar reflectance increases, the annual air-conditioning loads converge initially and then diverge upward after converging to a certain point.The forth category is shown in Fig. 12. As the solar reflectance increases, the annual air-conditioning loads converge at the beginning and then diverge downward after converging to a certain point.Although the specifics of the four categories are different,on the whole the building finishes with medium reflectance and low longwave emissivity fit the energy-saving requirements in the temperate climates. In this case, a metalcurtain wall is a good choice since slightly polished metal has a medium reflectance and low longwave emissivity (Incropera and Dewitt, 2006).4.2. The annual air-conditioning energy-saving potential analysisThe annual air-conditioning energy loads are calculated corresponding to every combination of the solar reflectance (from 0.1 to 0.9) and the longwave emissivity (from 0.1 to 0.9). Then, the maximum and minimum data of the annual air-conditioning energy loads in every city are selected out of the 81 (theoretical condition) or 56 (actual condition) results, with results calculated separately. The theoretical condition means that when selecting the maximumand the minimum energy loads, the solar reflectance and the longwave emissivity are set from 0.1 to 0.9. The actual condition means that only practically feasible options are considered, so the solar reflectance is set from0.1 to 0.8 and the longwave emissivity is set from 0.3 to 0.9. The maximum load minus the minimum load in one city represents the energy-saving potential in that climate condition that could be achieved by changing the optical properties of the building envelope. These data are presentedin Fig. 13.As seen in Fig. 13, (1) the cities in tropical and subtropical climates (including Bangkok, Singapore, New Delhi, Miami, etc.) see the biggest difference; (2) the cities in mountain plateau climates (including Lhasa, La. Paz,etc.) see a large difference; (3) the cities in subarctic climates (including San Francisco, Moscow, etc.) see a considerable but smaller difference; and (4) the cities in temperate climates (includingShanghai, New York, Wuhan, etc.) see a much smaller difference. In Bangkok, with actual conditions, the difference reaches 670.0 MJ/m2 and with theoretical conditions, the difference reaches 873.5 MJ/m2. In LaPaz, the difference reaches 371.4 MJ/m2 with the actual conditions, and 446.6 MJ/m2 with the theoretical conditions. These data reveal the significant energy-saving potential of using high reflectance and high longwave emissivity finishes in tropical and mountain plateau region buildings. In Moscow, with actual conditions, the difference reaches 219.2 MJ/m2, and with theoretical conditions, the difference reaches 278.4 MJ/m2. Thus, in subarctic climate cities, low reflectance and low emissivity finishes can reduce air-conditioning energy loads considerably. In Shanghai, with actual conditions, the difference is equal to 35.7 MJ/m2, and with theoretical conditions, the difference is equal to 58.7 MJ/m2. These results demonstrate that in most temperate climate cities, only a limited energy-saving effect could be achieved by changing the optical parameters of the exterior building surface.5. ConclusionsThis study aims to research a passive solution to reduce the annual air-conditioning energy loads by changing the solar reflectance and longwave emissivity of the exterior building surfaces in various climates. The dynamic computer simulation is carried out in climates of 35 cities distributed around the world. The parametric analysis indicates the following points. (1) In tropical and subtropical climates, the high solar reflectance and the high longwave emissivity exterior surface is the most favorable to building energy-saving. And the high solar reflectance is the major factor. (2) In the mountain plateau climates and the subarctic climates, the low solar reflectance and the low longwave emissivity exterior surface is the best choice. (3) In the temperate continental climates and the temperate maritime climates, the medium reflectance and the low longwave emissivity fit the energy-saving requirement. The low longwave emissivity is the major factor. The change of reflectance have only a little effect on the energy load when the longwave emissivity is high. By analyzing the annual air-conditioning energy load potential, it is concluded that (1) the tropical cities have the greatest energy-saving potential, (2) the mountain plateau and subarctic cities also have considerable energy-saving potential, and (3) the temperate continental and temperate maritime cities only have limited energy-saving potential.。