Surface roughness effects on the solar reflectance of cool asphalt shingles

We analyze the solar reflectance of asphalt roofing shingles that are covered with pigmented mineral roofing granules. The reflecting surface is rough, with a total area approximately twice the nominal area. We introduce a simple analytical model that relates the “micro-reflectance” of a small surface region to the “macro-reflectance” of the shingle. This model uses a mean field approximation to account for multiple scattering effects. The model is then used to compute the reflectance of shingles with a mixture of different colored granules, when the reflectances of the corresponding mono-color shingles are known. Simple linear averaging works well, with small corrections to linear averaging derived for highly reflective materials.Reflective base granules and reflective surface coatings aid achievement of high solar reflectance. Other factors that influence the solar reflectance are the size distribution of the granules, coverage of the asphalt substrate, and orientation of the granules as affected by rollers during fabrication.     

On the development, optical properties and thermal performance of cool colored coatings for the urban environment

This paper reports the measured solar spectral properties and the thermal performance of 10 prototype cool colored coatings, developed at the National and Kapodistrian University of Athens, using near-infrared reflective color pigments in comparison to color-matched, conventionally pigmented coatings. These coatings are developed to be used in the urban environment to fight the heat island effect. The spectral reflectance and the infrared emittance were measured and the solar reflectance of the samples was calculated. The surface temperature of the coatings when applied to concrete tiles was monitored, using surface temperature sensors and a data logging system, on 24 h basis from August to December 2005 in an effort to investigate the ability of the cool colored coatings to maintain lower surface temperatures than conventionally pigmented color-matched coatings. The data obtained has been extensively analysed and indicate significant success in the development of these cool colored coatings. It was found that all the coatings containing infrared reflective pigments have solar reflectance values higher than those of standard coatings. Furthermore, it was demonstrated that cool colored coatings maintain lower surface temperatures than color-matched conventionally pigmented coatings. This temperature difference is mainly due to differences in solar reflectance. These cool colored coatings can be used on buildings (roofs and walls) and other surfaces in the urban environment. Thus, at building scale, the use of cool colored coatings with increased solar reflectance can improve building comfort and reduce cooling energy use, and at city city-scale it can contribute to the reduction of the air temperature due to the heat-transfer phenomena and therefore improve outdoor thermal comfort and reduce the heat-island effect.     

Photovoltaic roofing: issues of design and integration into buildings

In the last decade, the development of photovoltaic roofing elements has been exceptional. These efforts were not limited to merely improving the integration methods with standard PV products but were also directed towards the production of appropriate elements that could replace roof tiles or shingles. This paper reviews some of the competing technologies for photovoltaic roofing and addresses the issues raised in the total integration of PV into roofing structures. The paper also discusses the general requirements of an idealised photovoltaic roofing system and some of the relevant variables that are required for the satisfaction of the end users. It has been shown that current strategies available for the true integration of PV elements as roof tiles or shingles utilising the sloped building fabric are limited. There are however, major on-going activities to research and develop roofing systems based on the foot-print of a roof tile or shingle.     

Colored cool colorants based on rare earth metal ions

Colored pigments with high near infrared reflectance and not based on toxic metal ions like cadmium, lead and cobalt are being sought as cool colorants. Through appropriate doping two pigments Ce-Pr-Mo and Ce-Pr-Fe have been developed to offer a reddish brown and reddish orange color, respectively. These pigments have been characterized and found to be highly crystalline with an average size of 300 nm. A shift in band gap energy from 2.21 to 2.18 eV has been observed when Li₂CO₃ was used as a mineralizer. Scanning electron microscope-energy dispersive X-ray analysis (SEM-EDAX) measurement indicate a uniform grind shape and distribution of metal ion, with over 65% reflectance in the NIR region, these pigments can well serve as cool colorants.     

Procedure for measuring the solar reflectance of flat or curved roofing assemblies

The widely used methods to measure the solar reflectance of roofing materials include ASTM standards E903 (spectrometer), C1549 (reflectometer), and E1918 (pyranometer). Standard E903 uses a spectrometer with an integrating sphere to measure the solar spectral reflectance of an area approximately 0.1 cm². The solar spectral reflectance is then weighted with a solar spectral irradiance to calculate the solar reflectance. Standard C1549 uses a reflectometer to measure the solar reflectance of an area approximately 5 cm². Both E903 and C1549 are best suited to measurement of the solar reflectance of flat, homogeneous surfaces. Standard E1918 uses a pyranometer to measure the solar reflectance of an area approximately 10 m², and is best applied to large surfaces that may also be rough and/or non-uniform.We describe a technique that uses a pyranometer to measure the solar reflectance of a uniform or variegated sample with diffusely reflective surface of an area of approximately 1 m², and use this technique (referred to as E1918A) to measure the solar reflectances of low- and high-profile tile assemblies. For 10 large (10 m²) tile assemblies whose E1918 solar reflectances ranged from 0.10 to 0.50, the magnitude of the difference between the E1918A and E1918 measurements did not exceed 0.02 for unicolor assemblies, and did not exceed 0.03 for multicolor assemblies.     

Near-infrared reflecting inorganic pigments based on molybdenum and praseodymium doped yttrium cerate: Synthesis, characterization and optical properties

A series of novel environmentally benign near-infrared (NIR) reflecting inorganic pigments based on yttrium cerate doped with metal ions such as Mo⁶⁺ or Pr⁴⁺ have been developed and characterized using XRD, UV-vis-NIR diffuse reflectance spectroscopy and CIE 1976 L^?a^?b^? color scales. The substitution of Mo⁶⁺ for Ce⁴⁺ in Y₂Ce₂O₇ changed the color from ivory-white to yellow and the band gap decreased from 3.01 to 2.44 eV due to O_2p-Mo_4d charge-transfer transitions. Most importantly the molybdenum doped pigments exhibit bright yellow hue with high NIR solar reflectance (>90%) in the range 700-2500 nm. In contrast, replacing Pr⁴⁺ for Ce⁴⁺ drastically shifts the absorption edge of the pigments from 410 to 725 nm and as a result the band gap of the compounds changes from 3.01 to 1.70 eV. Interestingly, the praseodymium doped pigments not only exhibits colors ranging from brick-red to dark-brown but also shows significant NIR solar reflectance. The ability of the pigments to transfer their NIR reflectance properties to a roofing material like asbestos cement sheet was evaluated.     

Solar spectral optical properties of pigments—Part II: survey of common colorants

Various pigments are characterized by determination of parameters S (backscattering) and K (absorption) as functions of wavelength in the solar spectral range of 300–2500 nm. Measured values of S for generic titanium dioxide (rutile) white pigment are in rough agreement with values computed from the Mie theory, supplemented by a simple multiple scattering model. Pigments in widespread use are examined, with particular emphasis on those that may be useful for formulating non-white materials that can reflect the near-infrared (NIR) portion of sunlight, such as the complex inorganic color pigments (mixed metal oxides). These materials remain cooler in sunlight than comparable NIR-absorbing colors. NIR-absorptive pigments are to be avoided. High NIR reflectance can be produced by a reflective metal substrate, an NIR-reflective underlayer, and/or by the use of a pigment that scatters strongly in the NIR.     

Equilibrium thermal characteristics of a building integrated photovoltaic tiled roof

Photovoltaic (PV) modules attain high temperatures when exposed to a combination of high radiation levels and elevated ambient temperatures. The temperature rise can be particularly problematic for fully building integrated PV (BIPV) roof tile systems if back ventilation is restricted. PV laminates could suffer yield degradation and accelerated aging in these conditions. This paper presents a laboratory based experimental investigation undertaken to determine the potential for high temperature operation in such a BIPV installation. This is achieved by ascertaining the dependence of the PV roof tile temperature on incident radiation and ambient temperature. A theory based correction was developed to account for the unrealistic sky temperature of the solar simulator used in the experiments. The particular PV roof tiles used are warranted up to an operational temperature of 85 °C, anything above this temperature will void the warranty because of potential damage to the integrity of the encapsulation. As a guide for installers, a map of southern Europe has been generated indicating locations where excessive module temperatures might be expected and thus where installation is inadvisable.     

New type of photovoltaic module integrated with roofing material (highly fire-resistant PV tile)

A new type of photovoltaic (PV) module integrated with roofing material (a highly fire-resistant PV tile) has been developed. It offers many attractive features, such as a lower cost, simpler construction, better design, and greater fire resistance than previous modules, and it promises to help accelerate the use of PV modules in residential applications.     

Estimation of exposure to sunlight of the liner under a tiled roof

One construction for a pitched roof is to use tiles on battens, with a liner attached below the battens. The shape of some types of tiles is such that, at each corner where four tiles overlap, a small gap is formed. At certain positions of the sun solar radiation can penetrate through these gaps and strike the liner, accelerating its degradation. The purpose of this study is to estimate the extent and duration of the exposure. A typical gap is modelled in a ray-tracing program and the size and position of the illuminated area on the liner is calculated for given directions of the light beam relative to the roof. Analytic expressions for the size of the illuminated area are obtained using a thick slit model. The accuracy of the model was assessed by some experimental measurements. The exposure over one year of the roof liner was calculated using the Design Reference Year for Copenhagen, Denmark. Simulations were carried out for a roof tilted at 25°, 35° or 45°, facing SE, S, SW or W. For the particular roof construction and gap studied, the maximum annual exposure of a 25 mm² piece of the liner placed 150 mm below the gap (corresponding to about 100 mm below the base of the tiles) is about 140 kJ m⁻² to UV-B and 4.2 MJ m⁻² to UV-A radiation. Variations in tile size and misalignment of tiles could lead to other gap shapes and sizes, possibly leading to greater exposure. Constructions with the liner placed closer to the tiles would also lead to greater exposures. However the method developed in this study could form the basis of a standard method of assessment.     

某电厂300MW机组推力瓦磨损的诊断及处理

对某电厂300MW机组推力瓦磨损原因进行了计算分析，对推力瓦磨损作出了正确的故障诊断，提出了具体的防范措施，达到了预期效果。     

Corrosion and protection of carbon steel in low enthalpy geothermal fluids. The case of SOUSAKI IN Greece

This experimental work is aimed at evaluating first, the effect of a solution simulating the geothermal fluid of the field in Sousaki, New Korinthia, on the corrosion of bare steel, and, second, the protective performance that certain combinations of organic coatings provide. This evaluation resulted from corrosion potential measurements, mass loss measurements, corrosion rate estimates by the Tafel method, and visual ranking of the degree of rusting and blistering. Six combinations of organic coatings were tested. Four of them consisted of water-based paints as primer, as well as intermediate and topcoat. Of the two remaining combinations, the first comprised a water-based primer, including dispersed tannin and a two-component epoxy resin topcoat, while the second consisted of a two-component acrylic primer, containing chromate pigments and the same epoxy resin topcoat as above. All coating combinations tested exhibited protective performance. The results of the water-based coatings were less satisfactory than those of the two combinations containing the epoxy resin topcoat.     

新建建筑不同设置围护结构的热质耦合传递对建筑负荷的影响Ⅱ:冬季湿负荷

传统建筑室内湿负荷的计算大多不考虑围护结构内表面的散湿量,而围护结构内表面的散湿量尤其是新建节能建筑对室内湿负荷的影响是很大的。以哈尔滨地区为例,分析了严寒地区典型新建建筑不同设置的多层围护结构在最初四年内热质耦合传递对模拟房间湿负荷的影响,并与文献[5]的模拟结果进行对比。分析结果表明：新建建筑围护结构内表面粘贴墙纸或降低围护结构主体砌块的初始含湿量能够降低模拟房间冬季湿负荷;而保温层内侧隔汽层以及围护结构外表面釉面砖的使用都会增加新建建筑的模拟房间冬季湿负荷,但若延后釉面砖的粘贴时间会有所好转。     

Development and testing of thermochromic coatings for buildings and urban structures

The present study reports the development and comparative testing of thermochromic coating to be used in buildings and urban structures. Experimental results from an extensive comparative analysis of the thermal and physical behaviour of thermochromic, highly reflective (cool), and common coatings are reported and analyzed. The surface temperature was monitored on 24 h basis from August to mid-September 2007. It was revealing that the temperature of thermochromic coatings was lower than cool and common coatings. Measurements of spectral reflectance indicated that the thermochromic coatings at the colored phase (below the transition temperature of 30 °C) are energy-absorbing while at the colorless phase (above the transition temperature of 30 °C) are energy-reflecting. The data obtained was used for the calculation of solar reflectance. The results showed that the solar reflectance of the thermochromic samples was significally higher compared to the cool and common ones. A 10-day period test was also performed showing the impact of solar radiation on thermochromism.The comparative results demonstrate that the use of thermochromic coatings can both contribute to energy savings in buildings, providing a thermally comfortable indoor environment, while can contribute highly to improve the urban microclimate.     

Use of near-infrared radiation for oxygenic photosynthesis via photon up-conversion

Radiation between 400 and 700 nm, used for oxygenic photosynthesis by cyanobacteria, algae and plants, represents only 44% of total solar energy while the range above 700 nm comprises 52%. An ability to use near infrared (NIR, 700–1200 nm) radiation would greatly improve the efficiency of photosynthesis, but NIR photons have too low energy to excite the photosystems of oxygenic photosynthesis. Here we show that a mechanism called photon up-conversion can turn NIR radiation into an energy source for photosynthesis. In the future, it may be possible to up-convert the NIR part of the solar energy flux to visible light for use in photo-induced biohydrogen production by oxygenic photosynthesis.     

不同配合比参数对沥青混凝土低温抗裂性能的影响

依托易县抽水蓄能电站上水库沥青混凝土面板配合比设计,通过对沥青混凝土进行低温冻断试验,研究了在沥青混凝土面板防渗层配合比设计时使用不同厂家生产的沥青、不同填料含量、不同油石比及不同天然砂掺加比例对水工沥青混凝土低温抗裂性能的影响规律。结果表明,不同厂家生产的沥青对沥青混凝土低温抗裂性能影响不同且差别很大;不同填料含量对沥青混凝土冻断温度影响显著;不同油石比对沥青混凝土冻断应力影响显著;天然砂的掺加比例会影响沥青混凝土的低温抗裂性能。结果可为沥青混凝土面板防渗层配合比参数选择提供参考。     

基于柔性晶体硅电池的光伏瓦研究

光伏瓦作为一种建筑材料,可替代屋顶陶瓦建材,且增加了发电功能,以薄膜电池为主的柔性光伏瓦具有质量轻和可弯曲的特性,但存在转换效率低、使用寿命短的问题。采用柔性晶体硅太阳电池,通过固化炉加气压釜的新型层压工艺,克服了层压过程中气泡、脱层等工艺问题,实现了基于晶体硅电池效率的柔性光伏瓦。     

磁控溅射电致变色非晶态氧化钨薄膜

利用平面磁控反应溅射在具有透明导电膜的玻璃基片上沉积氧化钨膜层。Ｘ射线衍射分析结果表明，基片在室温状态下得到的膜呈非晶态。以０．２Ｎ浓度的ＨＣｌ为电解液，用电化学方法研究了Ｈ＋注入及抽出后氧化钨膜光学性能的变化及这种变化与膜的制备参数之间的关系。获得了沉积氧化钨膜近于最佳的工艺条件。在纯氧气氛下，溅射功率密度１．２Ｗ／ｃｍ２，溅射气体压强１．３Ｐａ时，制备的非晶态氧化钨膜，在５０次电化学循环后，漂白态与着色态的可见光透射率之差约为０．５７，其电化学循环的变色寿命也长。光电子能谱（ＸＰＳ）分析表明，Ｈ＋注入后着色态膜内出现了Ｗ５＋、Ｗ４＋。对电致变色机理也作了讨论。     

Using advanced cool materials in the urban built environment to mitigate heat islands and improve thermal comfort conditions

The present paper is a review article aiming to present the actual state of the art on the development and the assessment of cool materials (i.e. materials with high solar reflectance and infrared emittance) for buildings and urban structures. The research in this field is roughly divided in four phases and includes the development and assessment of: (a) highly reflective and emissive light colored materials, (b) cool colored materials, i.e. colored materials with increased near infrared and thus overall solar reflectance compared to similarly colored conventional ones, (c) phase change materials and (d) dynamic cool materials. All major aspects related to each technology are described and the benefits and impacts of these materials at building, city and global scale are reported. The wide use of such materials can significantly contribute to the mitigation of the heat island effect and the improvement of urban environmental quality.     

The effects of TiO2 pigmented coatings characteristics on temperature and brightness of a coated black substrate

The high visible reflectivity of the cool coatings made by typical white pigment particles produces high glare, which is unpleasant to the human eye and possibly distorts the view of coated objects. A new approach to optimizing pigmented coatings considering both thermal and esthetic effects was proposed in previous works. For an accurate thermal analysis, a full spectral evaluation of radiative properties of pigmented coatings from UV to far IR wavelengths is required. We made a full spectral analysis of TiO₂ pigment particles in polyethylene resin as the host medium in the wavelength range of 0.3–36 μm. To find the spectral transmittance and reflectance of the pigmented layer, we conducted a radiation analysis using the radiation element method by ray emission model (REM²). The effects of characteristics of the coating layer, including size and volume concentration of pigment particles and coating thickness on esthetic and thermal behaviors were studied. The results show that by using the proposed optimum particle size, i.e., 0.8 μm, it is possible to design a coating with reasonable temperature and moderate brightness.