Search

• Increase of the albedo causes a temperature drop of 0.09C per 0.1 rise of the albedo. • Increased albedo reduces HRM between 0.1 and 4 deaths per day. • Mortality drop is in statistically significant with albedo increase and socioeconomic parameters. Urban heat island and regional climate change raise the ambient temperature in cities and increase the levels of heat related mortality. Higher albedo values lower the ambient temperature and reduce the impact of excess urban heat on health. The present work reviews and analyses fourteen detailed studies investigating the impact of increased urban albedo on the ambient temperature and heat related mortality. It is found that the real magnitude of the afternoon temperature drop caused by the albedo increase is close to 0.09C per 0.1 rise of the albedo, and it is highly determined by the specific climatic, landscape and layout characteristic of cities. A statistically significant association of the temperature drop with the albedo increase, the greenery and street ratio in cities is found. It is observed that the levels of heat related mortality increase significantly as a function of the population size of the cities and the local poverty levels, Increased urban albedo is found to reduce heat related mortality between 0.1 and 4 deaths per day, corresponding to an average decrease of deaths close to 19.8% per degree of temperature drop, or 1.8% per 0.1 increase of the albedo. Mortality drop is found to be in statistically significant association with the initial heat related mortality levels, albedo increase and socioeconomic parameters like the local poverty levels. Accurate parametric functions to predict the magnitude of the temperature drop and heat mortality reduction are developed. [ABSTRACT FROM AUTHOR]

The urban heat island is increasing the temperature of cities up to 10 °C and has a very important impact on energy, environmental quality and health. Materials used in the building and urban fabric affect the urban thermal balance and contribute highly to urban overheating. The article presents the progress achieved on the design, development and implementation of mitigation materials presenting a low and very low surface temperature. The recent technological progress and developments concerning natural, light colour, IR reflective, PCM doped, thermochromic, fluorescent, photonic and plasmonic materials is presented. Experimental results on the cooling capacity and the thermal performance of conventional and advanced materials are described in a comparative way. It is demonstrated that innovative materials can exhibit sub-ambient surface temperatures and contribute highly to mitigate urban overheating. • New innovative mitigation materials are recently developed. • Innovative advanced materials present a superior performance. • New materials contribute to counterbalance urban overheating. • Super cool materials operate under sub ambient surface temperatures. [ABSTRACT FROM AUTHOR]

Local and global climate change increases the ambient temperature of cities by several degrees with important consequences on energy consumption, health and the economy. Advanced urban mitigation technologies contribute to decrease the ambient temperature and counterbalance the impact of urban heat islands. The present paper analyses and presents in a comparative way the mitigation potential of the known mitigation technologies using performance data from about 220 real scale urban rehabilitation projects. The average and peak temperature drop of reflective technologies, greenery, evaporative systems, earth to air heat exchangers and their combinations is calculated and presented. The mitigation potential of the main systems like cool roofs, cool pavements, green roofs, urban trees, pools and ponds, sprinklers, fountains, and evaporative towers, is analysed. It is found that the potential of the main mitigation technologies is considerable and can counterbalance UHI effects partly or fully. The average peak temperature drop calculated for all projects is close to 2 K, while the corresponding decrease of the average ambient temperature is close to 0.74 K. Almost 31% of the analysed projects resulted in a peak temperature drop below 1 K, 62% below 2 K, 82% below 3 K and 90% below 4 K. [ABSTRACT FROM AUTHOR]

Urban heat island and global warming increase significantly the ambient temperature. Higher temperatures have a serious impact on the electricity consumption of the building sector increasing considerably the peak and the total electricity demand. The present paper aims to collect, analyze and present in a comparative way existing studies investigating the impact of ambient temperature increase on electricity consumption. Analysis of eleven studies dealing with the impact of the ambient temperature on the peak electricity demand showed that for each degree of temperature increase, the increase of the peak electricity load varies between 0.45% and 4.6%. This corresponds to an additional electricity penalty of about 21 (±10.4) W per degree of temperature increase and per person. In parallel, analysis of fifteen studies examining the impact of ambient temperature on the total electricity consumption, showed that the actual increase of the electricity demand per degree of temperature increase varies between 0.5% and 8.5%. [ABSTRACT FROM AUTHOR]

Urban heat island is the more documented phenomenon of climate change. Information on the magnitude and the characteristics of the canopy layer urban heat island measured in 101 cities and regions of Asia and Australia and collected through 88 scientific articles, are compiled, evaluated and presented. Data are classified in several clusters according to the experimental protocol used and the type of statistical information reported regarding the magnitude of the urban heat island. Results and detailed analysis are given for each defined cluster. Very significant differences on the UHI intensity are found between the clusters and analyzed in detail. The detailed impact of the main weather parameters and conditions on the magnitude of the UHI is also investigated. The specific influence of anthropogenic thermal fluxes as well as of the urban morphological and construction characteristics to UHI is thoroughly examined. The relation between the UHI intensity and the city size is assessed and global relationships of UHI as a function of the urban population are proposed. The seasonal and diurnal variability of the UHI is analyzed and discussed while specific features and conditions like the urban heat island characteristics in coastal cities and the existence of daytime cool islands are explored. Finally, the impact of the selected reference station and its characteristics is considered. [ABSTRACT FROM AUTHOR]

Urban heat island and global warming increase ambient temperature and modify the energy budget of buildings. The magnitude of the modification has been evaluated in a large number of articles, under different climatic and building boundary conditions. This paper collects, analyzes and classifies existing knowledge regarding the energy impact of urban heating to buildings and calculates preliminary indicators and impact figures. Based on the analysis of the impact studies, it is found that in average the cooling load of typical urban buildings is by 13% higher compared to similar buildings in rural areas. Four specific energy impact indicators, the global energy penalty per m 2 , the global energy penalty per m 2 and degree of UHI, the global energy penalty per person and the global energy penalty per person and per degree of the UHI are defined and calculated. The variability of the heating and cooling loads of typical buildings is evaluated for the period 1970–2010. The average increase of the cooling demand is 23% while the corresponding average reduction of the heating is 19%. In total, the average energy consumption of typical buildings for heating and cooling purposes increased by 11% for the same period. [ABSTRACT FROM AUTHOR]

Surface temperature measurements carried out during summer period, at canyons' facades, pavements and street inside a deep urban canyon, in the center of Athens. At the same time experimental data of air temperature were collected through extensive monitoring in the center of the urban canyon. CFD simulations performed in order to calculate surface temperature in buildings' facades and at street level as well as air temperature inside the canyon. On the first part of this study comparison carried out between the measured and calculated values for a) surface temperature for the initial coating and b) the air temperature in the center of a deep street urban canyon. The calculated data have been thoroughly analyzed and used as well for the CFD model validation. The second task of this work was the calculation of the surface and air temperature, inside the deep urban canyon, by using a "cool" coating and the possible mitigation of the heat island effect in the specific urban area. The use of "cool" coatings, providing high reflectivity of solar radiation on the materials used on pavements and walls inside a canyon, estimated able to decrease surface temperature up to 7-8°C at ground level. The decrease on walls' surface temperature estimated close to 2-3°C. Ambient air temperature inside the urban street canyon may decrease up to 1°C. The reduction of absorbed solar radiation may lead to the energy consumption and thermal comfort conditions in cities and fight the increased heat island effect. [ABSTRACT FROM AUTHOR]

Abstract: The temperature of cities continues to increase because of the heat island phenomenon and the undeniable climatic change. The observed high ambient temperatures intensify the energy problem of cities, deteriorates comfort conditions, put in danger the vulnerable population and amplify the pollution problems. To counterbalance the phenomenon, important mitigation technologies have been developed and proposed. Among them, technologies aiming to increase the albedo of cities and the use of vegetative – green roofs appear to be very promising, presenting a relatively high heat island mitigation potential. This paper aims to present the state of the art on both the above technologies, when applied in the city scale. Tenths of published studies have been analysed. Most of the available data are based on simulation studies using mesoscale modeling techniques while important data are available from the existing experimental studies. When a global increase of the city’s albedo is considered, the expected mean decrease of the average ambient temperature is close to 0.3K per 0.1 rise of the albedo, while the corresponding average decrease of the peak ambient temperature is close to 0.9K. When only cool roofs are considered, the analysis of the existing data shows that the expected depression rate of the average urban ambient temperature varies between 0.1 and 0.33K per 0.1 increase of the roofs albedo with a mean value close to 0.2K. As it concerns green roofs, existing simulation studies show that when applied on a city scale, they may reduce the average ambient temperature between 0.3 and 3K. Detailed analysis of many studies reporting a comparison of the mitigation potential of both technologies has permitted the definition of the limits, the boundaries and the conditions under which the considered technologies reach their better performance, in a synthetic way. [Copyright &y& Elsevier]

Abstract: Heat island phenomenon rises the temperature of cities, increases the energy demand for cooling and deteriorates comfort conditions in the urban environment. To counterbalance the impact of the phenomenon, important mitigation techniques have been proposed and developed. Pavements present a very high fraction of the urban areas and contribute highly to the development of heat island in cities. The use of cool pavements presenting substantially lower surface temperature and reduced sensible heat flux to the atmosphere, appears to be one of the most important proposed mitigation solutions. The present paper investigates and describes the actual state of the art on the field of cool pavements. The main thermal and optical parameters defining the thermal performance of pavements are analyzed. Almost all of the developed technologies, where data and results are available, are considered while emphasis is given on the presentation of reflective and permeable/water retentive pavements. The main technological achievements on both fields are reviewed while existing applications are described and performance data are given when available. The existing results clearly show that the mitigation and cooling potential of cool pavements is very significant and can highly contribute to decrease temperature on the urban environment. [Copyright &y& Elsevier]

Highlights: [•] Green and cool roofs are studied versus their urban heat mitigation potential. [•] Insulation level and thermal mass of cool roofs are examined. [•] Irrigation rate and vegetation type of green roofs are analyzed. [•] Free floating conditions for various climatic regions are used. [Copyright &y& Elsevier]

Abstract: Cool roof technology is an energy efficient, financially viable and sustainable solution for mitigating heat islands and reducing building energy consumption for cooling. An EU supported project called Cool Roofs has achieved to promote this technology in the EU by the implementation of an Action Plan. The work is developed in four axes, technical, market, policy and end-users. The Action Plan is steered by the development of the European Cool Roof Council that brings together all related stakeholders. The main results of the project include the creation of the European Cool Roof Council (ECRC), five cool roof pilot studies, a database of cool roofing materials, a handbook and a toolkit to assist the better understanding of the technical aspects of the technology, a market promotion plan, a proposal for a successful strategy to overcome possible policy barriers and engage with key stakeholders who could support and accelerate the creation of an EU policy and regulatory friendly environment to cool roofs, the organization of workshops and seminars and other actions of dissemination. This paper presents the main achievements at EU level regarding the establishment of cool roofs as heat island mitigation strategy and a measure for reducing cooling loads. [Copyright &y& Elsevier]

Abstract: The present paper deals with the application of 4500 m2 of reflective pavements in an urban park in the greater Athens area. The aim was to improve thermal comfort conditions, reduce the intensity of heat island and improve the global environmental quality in the considered area. To our knowledge, this has been the largest application of cool pavements in urban areas in the world. To evaluate the thermal impact of cool paving materials, specific and detailed measurements of the climatic conditions in the park have been performed before and after the installation of the new materials. Validated computerized fluid dynamics techniques have been used to homogenize the boundary conditions occurring during the two experiments and to perform direct comparisons of the climatic quality in the park. It was estimated that the use of cool paving materials contributes to the reduction of the peak ambient temperature during a typical summer day, by up to 1.9 K. At the same time, the surface temperature in the park was decreased by 12 K, while comfort conditions have been improved considerably. It is concluded that the use of reflective paving materials is a very efficient mitigation technique to improve thermal conditions in urban areas. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: The urban heat island (UHI) phenomenon is mainly caused by the differences in the thermal behaviour between urban and rural settlements that are associated with the thermal properties of urban materials, urban geometry, air pollution, and the anthropogenic heat released by the urban activities. The UHI has a serious impact on the energy consumption of buildings, increases smog production, while contributing to an increasing emission of pollutants from power plants, including sulfur dioxide, carbon monoxide, nitrous oxides and suspended particulates. This study presents the applicability of artificial neural networks (ANNs) and learning paradigms for UHI intensity prediction in Athens, Greece. The proposed model is tested using Elman, Feed-Forward and Cascade neural network architecture. The data of time, ambient temperature and global solar radiation are used to train and test the different models. The prediction accuracy is analyzed and evaluated. [ABSTRACT FROM AUTHOR]

Abstract: In this study the performance of organic PCMs used as latent heat storage materials, when incorporated in coatings for buildings and urban fabric, is investigated. Thirty six coatings of six colors containing different quantities of PCMs in different melting points were produced. Accordingly, infrared reflective (cool) and common coatings with the same binder system and of the same color were prepared for a comparative thermal evaluation. The samples were divided in six groups of different color and eight samples each: three PCM coatings of different melting temperatures (18 °C, 24 °C, 28 °C) each one of two different PCM concentrations (20% w/w, 30% w/w), an infrared reflective and a common coating of matching color. Surface temperature of the samples was recorded at a 24 h basis during August 2008. The results demonstrate that all PCM coatings present lower surface temperatures than infrared reflective and common coatings. Analysis of the daily temperature differences showed that peak temperature differences occur between PCM and common or cool coatings from 7 am to 10 am. Investigating the temperature gradient revealed that for this time period the values for PCM coatings are lower compared to infrared reflective and common. From 10 am to 12 pm, temperature gradients for all coatings have similar values. Thus coatings containing PCMs store heat in a latent form maintaining constant surface temperatures and discharge with time delay. PCM doped cool colored coatings have the potential to enhance thermal inertia and achieve important energy savings in buildings maintaining a thermally comfortable indoor environment, while fighting urban heat island when applied on external surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Data from 25 fixed temperature stations placed in the major Athens area have been used to analyse the characteristics of the heat island phenomenon during the summer season. The city has been divided in five geographic zones presenting different thermal balances and it is found that the differences between the mean and maximum daily air temperatures, among the five areas, were statistically significant, showing that the five areas of this analysis had definitely different temperature conditions. Higher air temperatures are found in the industrial western part of the city and also the center while the lower values were presented at the northern and the eastern parts. The intensity of the phenomenon is found to be close to 5C. Statistical methods have been developed and the mean and maximum nocturnal air temperatures as well as the number of hours where air temperature exceeds 30°C, can be estimated using the corresponding diurnal temperature values. The overall analysis is important to identify energy and comfort problems in the city and plan in a sustainable way the rehabilitation of the zones presenting important thermal problems. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to study the urban micro-climatic conditions in the historic centre of Tirana in order to integrate the information in the rehabilitation of specific open spaces. The process included field measurements of the thermal characteristics in the examined area, bioclimatic design and use of passive cooling techniques (cool materials, green spaces, water, solar control & earth to air heat exchangers). Advanced simulation tools were used to evaluate and optimize the planed microclimatic modifications. CFD calculations with model PHOENICS have been applied for the simulation of the air flow and the temperature field at the concept design stage. The proposed design solutions included the increase of vegetation (planting of trees), the use of shading, as well as the use of cool materials with appropriate thermal and optical properties. In parallel, earth to air heat exchangers, are proposed to supply cool air during the summer period and preheat the ambient air during the winter. Simulations have shown that the use of the proposed bioclimatic measures can decrease the peak summer ambient temperatures up to 3°C, while surface temperatures are decreased seriously. In parallel, the calculation of appropriate bioclimatic indices showed that the thermal comfort conditions were significantly improved with the application of interventions mainly because of the increase of shading as well as because of the use of construction materials with high emissivity and reflectivity values. [Copyright &y& Elsevier]

The urban heat island effect and its consequences is one of the most important problems cities worldwide have to face in an effort to become more sustainable. This paper presents a study of a major open area in a densely built and populated area in the centre of Athens that was part of a Municipality of Athens program to improve thermal comfort conditions in open spaces. The bioclimatic rehabilitation design process was based on a specific strategy involving detailed monitoring of the thermal characteristics and climatic conditions in the area, extensive analysis of the results in order to define the problem, design and use of efficient passive cooling techniques (cool materials, green spaces, solar control and earth to air heat exchangers), and the use of advanced simulation tools to evaluate and optimise the planed microclimatic improvements. The results indicate that the proposed measures contribute to a decrease in local temperatures of up to 2°C for summer conditions.Practical application:• The knowledge on perceptions of microclimate in outdoor space can serve as a basis for urban spatial design.• To evaluate the application of cool materials in public urban squares.• Strategies to improve local microclimate with monitoring and modelling the design features. [ABSTRACT FROM PUBLISHER]

Abstract: Climatic change and heat island effect in combination with the non-proper design of buildings have increased substantially the cooling load of buildings. Night ventilation appears to be one of the more promising passive cooling techniques. Many important theoretical and experimental studies have been performed however the existing information is presented in a segmented way. The present paper analyses energy data from two hundred fourteen air conditioned residential buildings using night ventilation techniques. The specific absolute energy contribution of night ventilation has been calculated. The relation of the cooling demand of the buildings with the specific contribution of night ventilation has been investigated. It is found that the higher the cooling demand of the building, the higher the potential contribution of night ventilation under specific boundary conditions. The role of air flow rate is investigated as well. It is found that the global utilisability of the energy stored during the night increases as a function of the air flow rate and the tilt of the regression line between the energy contribution and the air flow rate increases significantly with the air flow rate applied, although the energy contribution per unit of air flow is decreasing. The whole analysis contributes towards a better understanding and evaluation of the expected energy contribution of night cooling techniques. [Copyright &y& Elsevier]

High-spatial resolution multispectral satellite images collected over the metropolitan Athens area in Greece were used to generate (a) a shortwave albedo map depicting the albedo spatial variations across the metropolitan area, (b) a fractional vegetation cover map showing the spatial distribution of urban vegetation and (c) a daytime and night-time land surface temperature (LST) map depicting the spatial variations of the surface temperature across the city. From LST maps, cooling and heating regions were identified and analysed to reveal relationships between surface heat islands and urban surface characteristics. Based on the data acquired with the use of satellite images and in order to better define the heat island problem and the mitigation measures that need to be taken, the most common building and paving materials used in the urban fabric of Athens were examined. Their optical properties were measured using a UV/VIS/NIR spectrophotometer fitted with an integrating sphere, an emissometer and their thermal performance was evaluated. Furthermore, measurements of the spectral reflectance help explore the possibility of increasing the near-infrared reflectance of materials in order to increase their total solar reflectance. The solar reflectance index of the samples was calculated in order to characterise them as 'cool' or 'warm'. Cool materials, with high albedo and thermal emittance values, attain lower surface temperatures when exposed to solar radiation, reducing the transference of heat to the environmental air. [ABSTRACT FROM AUTHOR]

Heat island is a very well documented climatic phenomenon that has an important energy and environmental impact in the urban environment. The main energy problems are related to the important increase of the energy consumption for cooling purposes as well as to the important increase of the peak electricity load. Heat island in Athens, Greece, is measured during the last decade and its energy impact is calculated in details. The aim of the present paper is to estimate the direct and indirect environmental impact of the heat island effect in Athens. This is achieved through the estimation of the additional ecological footprint caused by the urban heat island phenomenon over the city. The ecological footprint estimation is performed at a first step by calculating the increase of the cooling demand caused by the heat island over the whole city and then by translating the energy to environmental cost. Two years annual experimental data from many urban stations have been used. The results show that the ecological footprint because of the heat island ranges 1.5-2 times the city's political area that have to be reserved every year to compensate the additional CO2 emissions caused by the presence of the heat island effect while the maximum potential ecological footprint, provided that all buildings are air conditioned, is almost 110,000 hectares. [ABSTRACT FROM AUTHOR]

An intelligent “data-driven” method is used in the present study for investigating, analyzing and quantifying the urban heat island phenomenon in the major Athens region where hourly ambient air-temperature data are recorded at twenty-three stations. The heat island phenomenon has a serious impact on the energy consumption of buildings, increases smog production, while contributing to an increasing emission of pollutants from power plants, including sulfur dioxide, carbon monoxide, nitrous oxides and suspended particulates. The intelligent method is an artificial neural network approach in which the urban heat island intensity at day and nighttime are estimated using as inputs several climatic parameters. Various neural network architectures are designed and trained for the output estimation, which is the daytime and nighttime urban heat island intensity at each station for a two-year time period. The results are tested with extensive sets of non-training measurements and it is found that they correspond well with the actual values. Furthermore, the influence of several input climatic parameters measured at each station, such as solar radiation, daytime and nighttime air temperature, and maximum daily air temperature, on the urban heat island intensity fluctuations is investigated and analyzed separately for the day and nighttime period. From this investigation it is shown that heat island intensity is mainly influenced by urbanization factors. A sensitivity investigation has been performed, based on neural network techniques, in order to adequately quantify the impact of the above input parameters on the urban heat island phenomenon. [ABSTRACT FROM AUTHOR]

Studies the existence of the heat island effect in urban places in Athens, Greece. Thermal structures between the urban and rural environments; Measurement of climatic parameters; District variations of the heat island intensity.

• Urban Overheating affects energy generation and demand, pollution, health and vulnerability. • It increases the energy demand for cooling and decreases the efficiency of power plants. • Rises the concentration of ground level ozone. • Increase indoor temperature in low income housing. • Increases heat related mortality and morbidity. Urban overheating is documented for more than 400 major cities in the world. Numerous experimental data show that the magnitude of the average temperature increase may exceed 4-5 C, while at the peak may exceed 10 C. Increased ambient temperatures cause a serious impact on the cooling energy consumption, peak electricity demand, heat related mortality and morbidity, urban environmental quality, local vulnerability and comfort. Synergies between urban heat island and heat waves increase further the amplitude of urban overheating The present paper reviews and reports the recent progress and knowledge on the specific impact of current and projected urban overheating in energy, peak electricity demand, air quality, mortality and morbidity and urban vulnerability. In parallel, it discusses new findings related to the characteristics and the magnitude of urban overheating, and reports and analyse the recent knowledge on the synergies between urban heat island and heat waves. [ABSTRACT FROM AUTHOR]

Cities face important overheating problems caused by the local and global climate change. Detailed mitigation and adaptation plans and strategies, are designed and applied to counterbalance the impact of the overheating challenges. Albedo management seems to be among the more considered mitigation strategies. A barrier to the wider use of reflecting technologies is the lack of quantitative experimental data and concrete knowledge about their mitigation contribution. Up to now, the performance of the reflective mitigation technologies is assessed based on simulation results considering the initial optical properties of the materials and neglecting ageing and weatherization phenomena. The article present information on the global performance of reflecting mitigation technologies, as measured in a large scale urban mitigation project employing several types of reflecting technologies. It is shown, that because of the weatherization effects, the mitigation potential of the materials is reduced, during the first year after their installation, by at least, 25%. Despite the ageing effects, reflective pavements have found to contribute in reducing the peak summer ambient temperature up to 1,7 K, while their surface temperature was up to 12,3 K lower than that of conventional pavement reducing considerably the sensible heat released to the atmosphere. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the energy performance of a medium scale green roof system installed on a two-story commercial building in Athens, Greece and its possible contribution to the mitigation of the urban heat island phenomenon. For the purpose of this research, in-situ measurements of temperature and humidity took place during the cold period of the year. The surface temperature of the conventional concrete floor of the roof was found to be up to 21.9 K higher than the one of the planted area during the day, while at the first hours of the day, the surface temperature of the green roof appeared to be up to 1.6 K higher than the one of the cement floor of the roof. Differences of the surface temperatures of the varying plants of the green roof were measured and led to a proposal of an optimum selection among them for the best performance of such a green roof system. Furthermore, simulations for this building were performed by using the EnergyPlus program. It was calculated that, the indoor air temperature, for a non air conditioned status of the building, was decreased up to 1.1 K during a typical summer day and was increased up to 0.7 K during a typical winter day. Lastly, an overall saving of 15.1% for a whole year on the energy consumption of the building was calculated. [ABSTRACT FROM AUTHOR]

[Display omitted] • A total of 95 papers systematically reviewed cool material as a mitigation strategy for urban heat island (UHI). • Based on the type of reflection and the spectral range, the analysis found 7 material technologies (UV–Vis-NIR). • Optical properties such as reflectance (ρ), absorptance (α), and emittance (ε) are key factors in cool materials design. • Technological setbacks constitute a key limitation to scale cool material technologies and low-cost alternatives. • DRC and super cool materials represent the most efficient innovations amongst current technologies. The challenging urban expansion represents a pressing need to implement climate mitigation strategies for the urban heat island (UHI) effects and significant threats to the environmental quality, energy consumption, and human health. Thus, this manuscript systematically evaluates 95 relevant studies through a robust evidence-based analysis centered on the latest advances in cool materials, their potential, technological innovation, and global trends. The results showed studies in 21 countries, 81 cities, and 16 climate zones, of which the majority belong to Humid subtropical climates (Csa) including 29 % of studies, Oceanic climates (Cfb) with 15 %, and Mediterranean climates (Cfa) with 13 %. Spectrophotometry analysis is used in 48 % of the studies, while the most studied technologies are the Daytime Radiative Cooling (DRC); 22 %, followed by Thermochromics (TC); 19 %, Cool-Colored (CC); 17 %, Phase Change Materials (PCM); 17 %, Retroreflectives (RR); 11 %, Light-colored (LC); 5 % and Fluorescents (FL); 5 %. Finally, DRC reported the highest cooling power of up to 136 W/m2, however, the latest developments advocate for climate-dependent dynamic modulation techniques of Super Cool Materials (SCM) with Passive Daytime Radiative Cooling (PDRC) attributes and engineered spectral properties to dissipate urban heat to outer space in different meteorological conditions and wavelengths levels of the atmospheric window (8–13 μm). [ABSTRACT FROM AUTHOR]

Buildings are responsible for about the 40% of the global annual energy consumption, therefore, innovative strategies for buildings’ energy efficiency are under development. Strategies of re-roofing with “cool” materials have a non-negligible cooling energy saving potential, as they contribute to the reduction of the peak ambient temperatures during summer and, moreover, they contribute to the improvement of the urban microclimate by decreasing the intensity of heat island phenomena. In this paper, the experimental characterization and optimization of a new membrane for buildings’ roof is carried out. To this aim, laboratory measurements were performed to determine its optic-energy properties and, therefore, to optimize its “cool roof” behavior. A full scale field test was also setup in order to measure the global solar radiation reflected by each membrane, before and after optimization, with varying boundary conditions, e.g. time during the day, seasonal period, and weather conditions. The in-field experimental campaign allowed to characterize the optic-energy behavior of the cool membranes in real boundary conditions, showing non-negligible variation of measured solar reflection capability with varying environmental constraints in winter conditions. The research showed interesting results from the in-lab optimization campaign, and non-negligible unreliability due to environmental agents affecting in-field albedo measurement. [ABSTRACT FROM AUTHOR]

[Display omitted] • A repository of 171 UHI papers were systematically reviewed to address relevant questions. • An endogenous research geospatial distribution, disadvantaging UHI most vulnerable regions was observed. • UHI strategies, tools, techniques, indexes and data source trends were identified through through data curation. • Seven major urban fields of impact were identified and multidimensionally analyzed. • Future research opportunities on UHI regulatory framework development were proposed. Scientific research on Urban heat islands (UHI) and urban. overheating has set new challenges for societies regarding risk and vulnerabilities, energy demands and mitigation strategies to favor urban environmental quality conditions against urban pollution. This review manuscript addresses systematically 171 relevant studies to identify and characterize gaps in the field of knowledge, through a robust evidence-based analysis focused on identifying taxonomic recurrences, trends in the study of urban fields of impact, global leaderships, mitigation strategies, methodological divergences, remote sensing indexes, data sources, legal frame, among other significant aspects on the context of environmental degradation and energy. The results showed that studies were carried out in 37 countries and 92 cities, mainly in North America (33%), Europe (31%), and Asia (27%) although mainly concentrated in five countries (59%) with an endogenous bias towards domestic microscale purposes. Prevailing topics, multidisciplinary interactions and regulations are focused on the study of Urban Environmental Quality degradation (95%) and on issues related to Energy (25%) demand and efficiency with applications on land cover with high interest on material science, and urban design and planning. The need to implement multiscale studies, motivate policies oriented to prevent health vulnerability and promote energy safety for urban resilience is imperative. [ABSTRACT FROM AUTHOR]