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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]

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]

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]

Cool materials have high solar reflectance (high ability to reflect sunlight), high thermal emittance (high ability to radiate heat) and stay cool in the sun. Various cool coatings have been developed recently. This paper analyses a prototype low cost cool coating using lime which shows a 15% increase in reflectance compared with a standard cool coating. Also, the ageing effect of cool coloured and white coatings are studied while they are exposed to outdoor conditions. The study shows that there is an attenuation of the white coatings' spectral reflectance while the cool coloured coatings demonstrate almost negligible loss in the visible range, thus maintaining their initial appearance. The infrared emittance of the cool and cool coloured coatings is not significantly changed by the outdoor exposure of the samples. [ABSTRACT FROM AUTHOR]

Abstract: The impact from using cool roof coatings on the cooling and heating loads and the indoor thermal comfort conditions of residential buildings for various climatic conditions is estimated. The energy cooling loads and peak cooling demands are estimated for different values of roof solar reflectance and roof U-value. The results show that increasing the roof solar reflectance reduces cooling loads by 18–93% and peak cooling demand in air-conditioned buildings by 11–27%. The indoor thermal comfort conditions were improved by decreasing the hours of discomfort by 9–100% and the maximum temperatures in non air-conditioned residential buildings by 1.2–3.3°C. These reductions were found to be more important for poorly or non-insulated buildings. For the locations studied, the heating penalty (0.2–17kWh/m2 year) was less important than the cooling load reduction (9–48kWh/m2 year). The application of cool roof coatings is an effective, minimal cost and easy to use technique that contributes to the energy efficiency and the thermal comfort of buildings. [Copyright &y& Elsevier]

Abstract: Low-income households in developed and less developed countries suffer from serious indoor environmental problems such as heat stress, lack of comfort and poor indoor air quality. Passive cooling of buildings and in particular solar and heat protection techniques, heat dissipation and heat amortisation techniques have reached a very high degree of maturity. New technological developments have proven extremely efficient in decreasing the need for cooling and improving indoor environmental conditions. Developments on the field of solar and heat protection, such as highly reflective coatings for the urban environment and the building envelope and new knowledge and developments on the field of ground and convective cooling and ventilation, may help low-income citizens to considerably improve their quality of life during the overheating period. These new developments are characterised by low cost and are easy to apply. This paper investigates the potential of the more promising new developments on the field of passive cooling, like the cool reflective coatings to improve outdoor and indoor conditions of low-income households in warm areas of the planet, ground cooling using earth to air heat exchangers, and discusses the potential of new ventilation techniques and systems for improving indoor comfort and air quality. Results show a very high potential to improve indoor environmental conditions and contribute towards higher passive survivability levels. [Copyright &y& Elsevier]

Abstract: 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 24h 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. [Copyright &y& Elsevier]

Abstract: This paper presents the results of a comparative study aiming to investigate the effect of reflective coatings on lowering surface temperatures of buildings and other surfaces of the urban environment, and thus test their suitability to lower ambient temperatures and fight the heat island effect. In total, 14 types of reflective coatings, selected from the international market were studied, from August to October 2004, on a 24h basis. These coatings are used in buildings and some of them are used or could be used in the future in other surfaces of the urban environment (sidewalks, parking lots, etc.). In order to investigate the thermal performance of the reflective coatings, surface temperature sensors and a data logging system as well as infrared thermography procedures were used. The spectral reflectance and the infrared emittance of the samples were also measured. The collected data have been extensively analyzed. It was demonstrated that the use of reflective coatings can reduce a white concrete tile’s surface temperature under hot summer conditions by 4°C and during the night by 2°C. It can be warmer, than the ambient air by only 2°C during the day and cooler than the ambient air by 5.9°C during the night. “Cool” coatings present superior thermal performance even compared to other “cool” materials. This study can assist in choosing more appropriate coatings for building envelopes and other surfaces of the urban environment, and thus contribute to the mitigation of the heat island effect as well as the reduction of cooling loads and electricity consumption of buildings. [Copyright &y& Elsevier]

This paper presents the results of a comparative study aiming to investigate the suitability of materials used in outdoor urban spaces in order to contribute to lower ambient temperatures and fight heat island effect. The study involved in total 93 commonly used pavement materials outdoors and was performed during the whole summer period of 2001. The thermal performance of the materials was measured in detail using mainly infrared thermography procedures.The collected data have been extensively analysed using statistical techniques. Comparative studies have been performed in order to identify the major advantages and disadvantages of the materials studied. Materials have been classified according to their thermal performance and physical properties into `cool'' and `warm'' materials. The impact of color, surface roughness and sizing has been analysed as well.The study can contribute to selection of more appropriate materials for outdoor urban applications, and thus assist to fight the heat island effect, decrease the electricity consumption of buildings and improve outdoor thermal comfort conditions. [Copyright &y& Elsevier]

This paper aims to investigate and present recent progress on the field of passive cooling of buildings achieved mainly through the PASCOOL research program of the European Commission. The PASCOOL group is composed by several national consortia including Belgium, France, Greece, Italy, Portugal, Spain, Switzerland, The Netherlands, UK, Slovenia, Hungary, Bulgaria and the Joint Research Centre of the European Commission at Ispra. The main scientific achievements of the project and especially the developed techniques, tools and design guidelines to promote passive cooling applications in buildings are presented. [ABSTRACT FROM AUTHOR]

The PASCOOL program was the most important European project on passive cooling of buildings. The project addressed topics included solar control, the combined effect of ventilation and thermal mass, thermalcomfort during summer and the potential of natural cooling techniques. PASCOOL put in evidence also the axes towards which future research on passive cooling should be oriented. This research, giving the continuously increasing trend of energy consumption for cooling purposes, is absolutely necessary in order to take advantage of the completepotential that passive cooling can offer to buildings, while maintaining the living standards, health and comfort of the occupants. This paper presents these future issues that comprise (a) research on the microclimatic scale in order to address the impact of outdoor environment on the cooling load of buildings, (b) investigation of comfort requirements under transient conditions during summer, (c) research onnatural ventilation in urban environments and the impact of outdoor pollution on indoor air quality, (d) development of alternative cooling systems and techniques, (e) development of integrating design concepts optimising the use of solar heating, passive cooling and naturallight in buildings. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes an effort to estimate the impact of a cool roof (characterised by increased solar reflectance compared to the initial roof and high infrared emittance) on the energy performance and thermal behaviour of a non-cooled school building in Athens, Greece. An experimental monitoring campaign has been carried out before and after the application of a white elastomeric coating with a solar reflectance of 0.89 on the roof of the building. The air and surface temperature of the building have been measured and a set of meteorological parameters have been collected. An infrared camera has been used to depict the differences in the surface temperature before and after the cool roof application. The monitoring results are complemented and supported by building simulation. The building has been modelled into TRNSYS software and the model has been calibrated and validated using the experimental data. Simulation results show a decrease in the air temperature in the classes that reaches 2.8°C and a decrease in the annual cooling load by 40%. The corresponding heating penalty (i.e. the increase of heating load) is 10%. Additionally, the impact of the cool roof on thermal comfort, peak power and surface temperature has been assessed. [Copyright &y& Elsevier]

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]