Pacheco-Torgal / Labrincha / Cabeza Eco-efficient Materials for Mitigating Building Cooling Needs

Design, Properties and Applications
1. Auflage 2015
ISBN: 978-1-78242-401-7
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 550 Seiten

Climate change is one of the most important environmental problems faced by Planet Earth. The majority of CO2 emissions come from burning fossil fuels for energy production and improvements in energy efficiency shows the greatest potential for any single strategy to abate global greenhouse gas (GHG) emissions from the energy sector. Energy related emissions account for almost 80% of the EU's total greenhouse gas emissions. The building sector is the largest energy user responsible for about 40% of the EU's total final energy consumption. In Europe the number of installed air conditioning systems has increased 500% over the last 20 years, but in that same period energy cooling needs have increased more than 20 times. The increase in energy cooling needs relates to the current higher living and working standards. In urban environments with low outdoor air quality (the general case) this means that in summer-time one cannot count on natural ventilation to reduce cooling needs. Do not forget the synergistic effect between heat waves and air pollution which means that outdoor air quality is worse in the summer aggravating cooling needs. Over the next few years this phenomenon will become much worse because more people will live in cities, more than 2 billion by 2050 and global warming will aggravate cooling needs. - An overview of materials to lessen the impact of urban heat islands - Excellent coverage of building materials to reduce air condtioning needs - Innovative products discussed such as Thermo and Electrochromic materials

Autoren/Hrsg.

Pacheco-Torgal, F.

Labrincha, Joao

Cabeza, Luisa F.

Granqvist, Claes-Göran

Leseproben

2 Coating materials to increase pavement surface reflectance
N. Xie; H. Wang; D. Feng    Harbin Institute of Technology, Harbin, China Abstract
Asphalt pavement constitutes more than 40% of urban land areas, which largely accounts for the urban heat island phenomenon in most cities. This number keeps increasing annually with the increase of urbanization. Therefore, it is important to develop new technologies to mitigate the heat island effect in urban areas. Currently, some technologies have been developed and applied in pavement engineering to mitigate the heat island phenomenon, including porous concrete pavement and high thermal reflective coating overlays. In this chapter, the materials used as coating overlays of pavements for heat island phenomenon mitigation are introduced. Three types of materials are highlighted as the main components of the coating materials for pavement to mitigate the heat island effect. Organic polymers applied as the main part of the overlay coating materials, inorganic metal oxide powders used as the solar energy reflective fillers, and fine aggregates used to increase the durability of the reflective coatings are systematically introduced. In addition, the advantages and disadvantages of the current coating materials are analysed. This chapter may help readers understand the background of solar energy reflective coatings for pavements; furthermore, it may help in designing and developing new materials that can overcome the shortcomings of the current reflective coating materials, and thus increase their applications in the field. Keywords Heat island Cool pavement Solar energy reflectance Materials Acknowledgments
This work is financially supported by the ministry of education program for New Century Excellent Talents (NCET-08-0163) and the China Postdoctoral Science Foundation (No. 20110491065). 2.1 Introduction
The urban heat island (UHI) effect is a common environmental problem occurring in metropolitan areas in which the air temperature is significantly higher than in suburban areas. The UHI effect also leads to a smoggy climate. The UHI effect mainly results from high-density infrastructures, which not only limit air flow but also emit heat stored from solar energy. In addition, the reduction of vegetation and wetlands further weakens the heat-releasing capacity of cities. It is urgent to mitigate the UHI effect, as it has become a huge threat to the environment and human health (Santamouris, 2007; Santamouris et al., 2011; Stathopoulou, 2008; Mirzaei and Haghighat, 2010). Previous studies indicated that the optical and thermal characteristics of urban structures have a strong relationship with urban climate and temperatures (Chen et al., 2009; White et al., 2010). In many cities, the roofs and pavements comprise about 60% of the total urban area, with roofs contributing about 20–25% and pavements contributing about 40% (Akbari et al., 2003). Cantat indicated that the reflectance of Paris is 16% lower than the surrounding suburban district (Cantat, 1989). Another study claimed that the increase of the solar energy absorption in urban areas is affected by the urban geometrical structures (Aida, 1982; Aida and Gotoh, 1982). Cool pavement is an effective technology to solve the UHI problem. The primary three types of cool pavements are (1) light color aggregates pavement, (2) permeable pavement, and (3) solar-reflective coating pavement. The albedo of normal asphalt pavement is only about 5%. By using white or light color aggregates, the albedo can be increased to about 30% (Doulos et al., 2004). Recent case study results from Portland State University (Oregon, USA) show that if you increase the albedo of the pavement in a bare courtyard from 37% (black) to 91% (white), the mean radiant temperature will increase 2.9 °C, but the air temperature will decrease 1.3 °C (Taleghani, 2014). Cotana et al. (2014) believes that using high solar reflective surfaces is an effective way to mitigate the UHI problem and reduce greenhouse gas emission in urban areas. It has been found that albedo coatings can reduce CO2 emissions. Simulation results indicated that a 115,000 m2 high-albedo coating area could reduce 16,000 tons of CO2eq, releasing and effectively mitigating global warming if applied for 30 years. Akbari and Matthews (2012) also estimated that using cool roofs and cool pavements could increase urban albedo by about 10%, and reduce CO2 emissions by at least 40–160 Gt. Yu’s study claimed a similar result based on a life cycle assessment model (Yu and Lu, 2012). Experimental results indicated that 4500 m2 cool pavements in an urban parking lot could decrease the ambient temperature about 2 °C, and at the same time decrease the surface temperature by 12 °C during a typical summer day (Santamouris et al., 2012). Rosenfeld et al. (1998) claimed that cool surface techniques could save at least half a billion dollars if used in the Log Angeles basin, and up to five billion dollars if applied in the entire U.S. by the year 2015. Akbari et al. (2009) estimated that urban albedo could be increased about 10% by using cool roofs and cool pavements, and the increased urban albedo could reduce 44 Gt of CO2 emissions and save 1.1 trillion dollars worldwide. To implement the high-reflectance surface coating technology, proper cool material selection plays the most important role. In general, the selection rule is governed by two main parameters: solar reflectance and heat emittance (Asaeda et al., 1996; Synnefa et al., 2006). Carnielo and Zinzi (2013) tested the emissivity and solar reflectance of five different albedo samples with colors of green, red, blue, gray, and off-white. It was found that, compared with thermal emittance, the effect of solar reflectance is more evident on mitigating the urban heat island phenomenon. The spectral emissivity values of those samples are similar to the normal asphalt, which are all above 90%, while the solar reflectance of each sample varies a lot, with a maximum difference of about 61% compared to the normal asphalt sample. The visible light reflectance of the coating is mainly governed by its visible color and surface roughness, which are determined by the inorganic fillers. Uemoto et al. (2010) claimed that the visible light reflectance of the coating will decrease when the color is more dark than light. Other than the visible light reflectance, the near-infrared (NIR) light reflectance is also important for cool pavements. In the NIR reflective region, the colors of the materials are not the dominant factor. High NIR reflectance can be realized in various colors of inorganic fillers. Synnefa et al. (2011) investigated five asphalt pavement overlay coatings with various colors. The results indicated that the reflectance of the coatings with all colors are higher than the asphalt pavement without coatings. The NIR reflectance of these coating ranges from 27% (red and green) to 55%, which could maximally decrease the pavement temperature about 12 °C compared with the noncoated asphalt pavement surface. Kinouchi et al. (2003) developed a new pavement coating with high reflectance and low brightness, which has a relatively low reflectance (20%) in the visible light region (350–750 nm) and high reflectance (83%) in the NIR region (750–2100 nm). The results showed that this coating could decrease the pavement temperature by 15 °C compared with normal asphalt pavement. Wan et al. (2012) also developed a cool pavement coating with high NIR reflectance (81%), low thermal conductivity (0.252 W/m K), and high emissivity (82.8%). The results demonstrated that this pavement could decrease surface temperature about 17 °C compared with conventional asphalt pavement and 5 °C compared with cement concrete pavement. Unlike cool roofs, which have no traffic safety and traffic load concerns, cool pavement coatings with high reflectance have to satisfy the requirements of a pavement overlay. Therefore, they are generally composed of three main parts: the organic polymer substrate, inorganic fillers, and antiskid aggregates. The polymer substrate is mainly for providing bonding capacity to guarantee the durability of the coatings; the inorganic fillers are mainly used for providing the solar reflectance; and the aggregates are used for transportation safety and wear resistance concerns. The following sections will discuss how these can be used as cooling pavement materials. 2.2 Organic polymers used as coating overlay materials for pavements
In the past decades, various polymers were used as coating overlay materials to protect bridge decks and pavements from chemical attacks and freeze/thaw damage. The bonding or adhesive property is the most important factor to consider before these polymers can be used as coating overlays. Recently, it was reported that 2724 polymer-based overlays were applied on bridge structures in the United States (Federal Highway Administration, FHWA, 2010). Since 2008, the polymer overlay has increased 24.2%, whereas other surface overlays keep decreasing every year (Young and Durham, 2012). The requirements of cool pavement are more critical than cool roof because cool pavement must satisfy the requirements of a pavement,...