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• 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]

Income, housing unit size, number of appliances owned and other components of socio-economic status (SES), are variables generally considered to influence residential energy use. Using structural equation modeling of SES indicators from the U.S. residential energy consumption survey (RECS), we provide evidence that SES, usually modeled as a latent construct with effect indicators, is better conceptualized as including at least some causal indicators. We studied the mediating effect of housing unit size and number of owned appliances on the relationship between SES, household size and residential energy consumption (REC). We found that household size was positively associated with REC, as a direct effect. SES had a strong impact on REC, while being mediated by housing unit size and number of appliances owned. In conclusion, research must take the latent nature of SES into account to uncover its total influence on REC. [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]

The term energy poverty is used to describe a situation of a household not able to satisfy socially and materially the required levels of its energy services. Energy and fuel poverty is an increasing problem in the European Union. Although the specific conditions vary from country to country the drivers defining fuel and energy poverty are similar in all Europe. This paper aims to present the state of the art regarding the energy demand and indoor environmental quality of low income households in Europe. The characteristics of this specific population group are presented including details on the specific energy consumption, the indoor comfort and finally the impact of the specific living conditions on the occupants' health. [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]

Increase of the urban ambient temperature caused by local and global phenomena is probably the more incontestable incident of climate change. Urban warming has a very significant impact on human life increasing the energy consumption, deteriorating the comfort levels, increasing the pollution concentration, threatening the human health and affecting the urban economy. Mitigation technologies aiming to countermeasure the impact of the phenomenon are rapidly developed and applied in real scale projects. The present paper aims to present in a critical and comprehensive way the recent scientific knowledge on the causes of urban warming and also stress the main problems and inconsistencies concerning the experimental and the theoretical findings and analysis. In parallel, it classifies and summarizes the main knowledge on the energy, environmental, health and economic impacts of urban warming. Quantitative information on the energy penalties, mortality rates and environmental degradation induced by urban warming is presented. Finally, it presents the main developments regarding urban mitigation techniques and technologies and in particular, urban greenery and planted roofs, cool pavements, cool roofs and increase of the urban albedo, decrease of the anthropogenic heat and use of the ground as a sink for heat dissipation. [ABSTRACT FROM AUTHOR]

The energy performance of buildings directive (EPBD) (91/2002/EU) opened the way for member states of European Union to create and apply a holistic approach on buildings’ energy performance. Taking into consideration the reduced ratio of new buildings, energy refurbishment of existing building stock appears as a nodal point. In particular, buildings in Greece accounts approximately 4 million, while 70% has been constructed before the implementation of the first Thermal Insulation Regulation (TIR), thus they do not have any insulation. So, there is an extremely high potential for energy conservation in Greek building stock. Therefore, an extensive field study was carried out in northern area of Greece in Thessaloniki, through a detailed questionnaire. The purpose of the research is to create an integrated thermal insulation scheme in order to succeed the highest mitigation of energy losses through building envelope. Retrofitting insulation solutions were evaluated and applied through various simulation scenarios with different levels of insulation thickness. [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]

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]

Highlights: [•] Very low indoor temperatures in low and very low income housing in Athens Greece. [•] Very low energy consumption because of the energy crisis. [•] Important environmental social and health problems associated to low indoor temperatures. [ABSTRACT FROM AUTHOR]

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: This research focuses on projecting the energy demand of the building sector in Greece by calculating energy consumption, using output data from regional climate models up to 2100. More specifically, Greece was subdivided into 13 climatic zones after assessing climate model data taking into account climate change estimates for the period 2010–2100. These zones allow a detailed estimation of the effects of climate change in specific regions of the country, thus creating a database which is used to model the energy demand of the building sector in each zone. Through the use of building data from Eurostat and the European Centre for Environment, a set of three building typologies was created in relation to the building envelope, which corresponds to 85% of the building stock in Greece. These typologies were later appended to each of the 13 climatic zones and a simulation for their energy demand was calculated using climatic data from 3 distinct climatic scenarios. Results show that the energy demand for heating the building sector in Greece could decrease by about 50%, while the respective energy demand for cooling could increase by as much as 248% until 2100. These effects are more evident in the Southern part of the country. [Copyright &y& Elsevier]

Abstract: This paper investigates the indoor thermal conditions in fifty low income non air conditioned houses in Athens, Greece, during the extremely hot summer of 2007. Hourly indoor temperature data have been analysed during three extended heat waves. Indoor temperatures as high as 40°C were recorded and the average indoor minimum temperature was always above 28°C. Mean indoor temperatures during the hot season were up to 4.2K above the normal climatic period, while the daily increase rate varied from 0.2K/day during the first up to 0.8K/day for the peak days of the heat wave. The exposure of inhabitants to high temperatures is very important because for almost 85% of the hot period, indoor temperature exceeded 30°C. Periods of about 216 continuous hours above 30°C, and six days above 33°C were recorded in many buildings. The dynamics and the evolution of indoor temperatures as a function of the outdoor climatic characteristics and the thermal capacitance of the buildings are analysed. Possible techniques to improve the indoor environmental quality in low income housing during extremely hot periods are discussed. [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]

The present paper investigates the impact of canyon geometry on the temperature regime and nocturnal heat island development in the very dense urban area of Athens, Greece. Detailed measurements of air temperature have been carried out within three deep urban canyons of different aspect ratios ( H/ W = 3, 2.1 and 1.7) during the night period of the summer and autumn of 2007. An analysis was carried out to investigate the relative impact of the canyon geometry, the undisturbed wind velocity, ambient temperature, and cloud cover on the development of a nocturnal heat island. A clear increase of the median, maximum and minimum values of the cooling rates has been observed for decreasing aspect ratios. Under low ambient temperatures, high wind speeds correspond to a substantial rise of the cooling rate in the urban canyons mainly because of the increased convective losses. On the contrary, cooling rates decrease substantially under high-undisturbed wind speeds and ambient temperatures because of the important convective gains. The impact of cloud cover was found to be important as cloudy skies cause a substantial decrease of the cooling rates in the urban canyons. Comparisons were performed between the temperature data collected in the three studied urban canyons and temperatures recorded in an urban as well as a suburban open space station. [ABSTRACT FROM AUTHOR]

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]

The intraurban temperature variation in the center of Athens, Greece, was investigated in relation to urban geometry. This paper describes two main tasks: 1) Air temperature was recorded in the center of Athens and at the Meteorological Service Station at the University of Athens. Experimental data were collected through extensive monitoring at four different heights inside five different urban canyons in the center of Athens during the summer period. A measurement uncertainty analysis was carried out to estimate critical threshold values of air temperature below which differences were not significant. 2) The correlation between urban–suburban air temperature differences was assessed, using the geometrical characteristics of each urban street canyon. Urban–rural air temperature differences were considered to be not important if they were below the threshold value of 0.3°C. It was concluded that the major factor controlling urban–suburban air temperature differences was the geometry of the urban area. Other factors were the orientation of the observational sites, the current weather conditions, and the inversion of air masses adjacent to the ground level. An increase in the value of aspect ratios leads to a decrease in the difference between air inside the canyons and at the suburban station. The air temperature profile in an open-space area was the most important defining factor for the stratification of the urban–rural air temperature differences. [ABSTRACT FROM AUTHOR]

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

Abstract: Air flow and the associated indoor carbon dioxide concentrations have been extensively monitored in 62 classrooms of 27 naturally ventilated schools in Athens, Greece. The specific ventilation patterns as well as the associated carbon dioxide concentrations, before, during and after the teaching period are analysed in detail. During the teaching period, only 23% of the measured classrooms presented a flow rate higher than the recommended value of 8l/p/s while the mean daily fluctuation was close to 40%. About, 52% of the classrooms presented a mean indoor CO2 concentration higher than 1000ppm. The specific experimental data have been compared against existing ventilation rates and carbon dioxide concentrations using published information from 287 classrooms of 182 naturally ventilated schools and 900 classrooms from 220 mechanically ventilated schools. The relation between the air flow rates and the corresponding indoor carbon dioxide is analysed and then compared to the existing data from naturally and mechanically ventilated schools. It is found that all three data sets present a CO2 concentration equal to 1000ppm for air flows around 8l/p/s. Specific adaptive actions to improve the indoor environmental quality have been recorded and the impact of indoor and ambient temperatures as well as of the carbon dioxide concentration on window opening is analysed in detail. A clear relation is found, between the indoor temperature at which the adapting action takes place and the resulting air flow rate. In parallel, a statistically significant relation between window opening and the indoor–outdoor temperature difference has been established. [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: This paper deals with the experimental investigation and analysis of the energy and environmental performance of a green roof system installed in a nursery school building in Athens. The investigation was implemented in two phases. During the first phase, an experimental investigation of the green roof system efficiency was presented and analysed, while in the second one the energy savings was examined through a mathematical approach by calculating both the cooling and heating load for the summer and winter period for the whole building as well as for its top floor. The energy performance evaluation showed a significant reduction of the building''s cooling load during summer. This reduction varied for the whole building in the range of 6–49% and for its last floor in the range of 12–87%. Moreover, the influence of the green roof system in the building''s heating load was found insignificant, and this can be regarded a great advantage of the system as any interference in the building shell for the reduction of cooling load leads usually to the increase of its heating load. [Copyright &y& Elsevier]

Abstract: Social, financial, energy and technical data from about 1110 households have been collected during 2004 in the major Athens area. The sample has been divided in seven income groups and a detailed analysis has been performed. Important conclusions have been drawn regarding the quality of households, the operational conditions and the energy spent per income group. Low income people are more likely to be living in old buildings with poor envelope conditions. The cost per person and unit area is much higher for the low income group for both heating and electricity. Fuel poverty is quite high, especially when the actual oil prices are considered. [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]

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]

Abstract: The present paper deals with the energy performance, energy classification and rating and the global environmental quality of school buildings. A new energy classification technique based on intelligent clustering methodologies is proposed. Energy rating of school buildings provides specific information on their energy consumption and efficiency relative to the other buildings of similar nature and permits a better planning of interventions to improve its energy performance. The overall work reported in the present paper, is carried out in three phases. During the first phase energy consumption data have been collected through energy surveys performed in 320 schools in Greece. In the second phase an innovative energy rating scheme based on fuzzy clustering techniques has been developed, while in the third phase, 10 schools have been selected and detailed measurements of their energy efficiency and performance as well as of the global environmental quality have been performed using a specific experimental protocol. The proposed energy rating method has been applied while the main environmental and energy problems have been identified. The potential for energy and environmental improvements has been assessed. [Copyright &y& Elsevier]

Abstract: The present paper aims to present a distant-learning training module that concerns the environmental design of urban buildings. The whole approach attempts to integrate topics that concern the design of urban buildings from various points of views, e.g. active and passive systems, automation systems, indoor air quality, economic aspects, energy and resources management. The package offers both printed and electronic material that gives the possibility to the students to study the various topics by using different educational methods. Additionally, the present package contains software tools that permit the students to examine real or hypothetical situations and to study further the influence of various parameters that concern the environmental building design. [Copyright &y& Elsevier]

Abstract: The utilizability or ϕ-curve method is a design method for some types of solar energy systems that use flat-plate solar collectors. It can be a very useful design tool, for the preliminary design or the design of small systems, cases where methods easy to use and apply are required. In this paper, a simple method to calculate monthly average hourly and daily flat plate collector utilizability is presented. It is based on empirical correlation of ϕ with independent variables that separate meteorological and collector parameters, making possible quick evaluations of changes in collector design and collector inlet temperature. In general, the method reduces the calculations required to determine ϕ, and gives good results compared to long-term hourly simulations as well as to existing hourly and daily utilizability calculations methods. [Copyright &y& Elsevier]

This article deals with the energy performance of eight new and existing museum buildings located around Europe. Various energy efficiency and microclimate improvement measures have been adopted to reduce the energy consumption of the buildings and improve the comfort conditions. The investigation was implemented in two principal phases. During the first phase, energy simulation studies were performed in all buildings to evaluate the efficiency of the proposed measures and the various design possibilities. The energy consumption for heating, cooling, lighting and other electrical devices was calculated with and without the application of the proposed techniques and the corresponding energy conservation was estimated. Therefore, the proper measures from the energy point of view were adopted. During the second phase, measurements of the energy consumption were performed in the buildings after the finalization of the construction and the implementation of the proposed measures. The energy conservation was again calculated to evaluate the energy efficiency of the final construction. In addition to the energy aspect, the environmental impact of the final construction of the museums was investigated by calculating the reduction of the CO2 emissions due to the applied energy conservation techniques. Finally, the economic efficiency was examined by assessing the payback period of the adopted measures.The results of the present work show that the adaptation of energy conservation techniques in museums buildings can reduce significantly the energy consumption by respecting at the same time the requirements of the exhibition spaces and the comfort conditions of the visitors. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses how neural networks, applied to predict energy consumption in buildings, can advantageously be improved, guided by statistical procedures, such as hypothesis testing, information criteria and cross validation. Recent literature has provided evidence that such methods, commonly used independently, when exploited together, can improve the selection and estimation of neural models. We use such an approach to design feed forward neural networks for modeling energy use and predicting hourly load profiles, where both the relevance of input variables and the number of free parameters are systematically treated. The model building process is divided in three parts: (a) the identification of all potential relevant input, (b) the selection of hidden units for this preliminary set of inputs, through an additive phase and (c) the remove of irrelevant inputs and useless hidden units through a subtractive phase. The predictive performance of short term predictors is also examined with regard to prediction horizon. A comparison of the predictive ability of a single-step predictor iteratively used to predict 24h ahead and a 24-step independently designed predictor is presented. The performance of the developed models and predictors was evaluated using two different data sets, the energy use data of the Energy Prediction Shootout I contest, and of an office building, located in Athens. The results show that statistical analysis as an integral part of neural models, gives a valuable tool to design simple, yet efficient neural models for building energy applications. [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]

Abstract: Detailed experiments have been carried out in a deep canyon in Athens during the summer period. The aim of the experimental campaign was first to evaluate the potential of natural ventilation in the urban environment and second to better understand the air flow and thermal phenomena in deep urban canyons. Extensive measurements of the surface and air temperature as well as the wind speed in the middle and close to the canyon façades have been measured in a continuous basis. In parallel, the undisturbed temperature, wind speed and direction above the canyon have been measured as well. Measurements of the airflow rate in single side and cross ventilation configurations have been carried out using tracer gas techniques, in a naturally ventilated building located in the canyon. It is found that the potential of natural ventilation for both single side and cross ventilation configurations in buildings located inside urban canyons, is seriously reduced. It is estimated, that in the specific canyon, the airflow rate for single side and cross ventilation configurations, is reduced by 82 and 68%, respectively compared to an undisturbed location. The mechanism of the air flow and temperature distribution inside the canyon is extensively analysed and the specific phenomena that determine the wind speed and direction inside the canyon are described in details. [Copyright &y& Elsevier]

Abstract: The present paper aims to examine the application of night ventilation techniques to 10 urban canyons, situated in the extended region of Athens, Greece. As the climatic conditions in the urban environment frequently present important variation in different locations of the same urban area, the outdoor air temperature and the wind profile have been measured inside and outside the experimental canyons. The present work determines the impact of the urban environment on night ventilation energy performance, by studying a typical room located in the urban domain, under air-conditioned and free-floating operation, when single-sided and cross-ventilation are considered, during the night period. The influence of the urban microclimate on the efficiency of the technique has been examined by considering the typical zone inside the canyons and under undistributed conditions. The comparison of the results permits to evaluate the impact of the urban environment on the effectiveness of night ventilation techniques. The performed analysis shows that due to the increase in air temperature and the decrease in wind velocity inside the canyons, the efficiency of the studied techniques is significantly reduced compared with the situation that considers the undistributed conditions, dominating outside the urban canyons. [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]

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]

The method presented in this paper is a practical procedure for the derivation of a street canyon’s albedo, by taking into account the angle-dependent optical properties of a typical coated (SnO2) glazing. The development of the method is based on the flux transfer theory and can be easily implemented in a computer code permitting exploitation of a series of possibilities, such as street canyon geometry and window to wall ratios (WWRs). [Copyright &y& Elsevier]

A neural network approach is used in the present study for modelling and estimating the energy consumption time series for a residential building in Athens, using as inputs several climatic parameters.The hourly values of the energy consumption, for heating and cooling the building, are estimated for several years using feed forward backpropagation neural networks. Various neural network architectures are designed and trained for the output estimation, which is the building’s energy consumption. The results are tested with extensive sets of non-training measurements and it is found that they correspond well with the actual values.Furthermore, “multi-lag” output predictions of ambient air temperature and total solar radiation are used as inputs to the neural network models for modelling and predicting the future values of energy consumption with sufficient accuracy. [Copyright &y& Elsevier]

Assesses the impact of the urban climate on the energy consumption of buildings using climatic measurements from urban and suburban stations in Athens, Greece. Relative position of the measuring stations; Spatial and hourly distribution of the cooling degree hours in Athens for August 1996; Impact on the natural ventilation potential.

Investigates the potential of deterministic mathematical modeling in representing related physical phenomena with sufficient accuracy. Importance of prediction of air velocity field in a naturally ventilated space; Phenomena resulting to occurence of single-sided ventilation; Parameters affecting air flow in natural ventilation.

Three methods for analyzing and modeling the global shortwave radiation reaching the earth's surface are presented in this study. Solar radiation is a very important input for many aspects of climatology, hydrology, atmospheric sciences, and energy applications. The estimation methods consist of an atmospheric deterministic model and two data-driven intelligent methods. The deterministic method is a broadband atmospheric model, developed for predicting the global and diffuse solar radiation incident on the earth's surface. The intelligent data-driven methods are a new neural network approach in which the hourly values of global radiation for several years are calculated and a new fuzzy logic method based on fuzzy sets theory. The two data-driven models, calculating the global solar radiation on a horizontal surface, are based on measured data of several meteorological parameters such as the air temperature, the relative humidity, and the sunshine duration. The three methods are tested and compared using various sets of solar radiation measurements. The comparison of the three methods showed that the proposed intelligent techniques can be successfully used for the estimation of global solar radiation during the warm period of the year, while during the cold period the atmospheric deterministic model gives better estimations. [ABSTRACT FROM AUTHOR]

Presents a study on the transfer of radiation and air flow through partly covered external building openings, while suggesting that solar control devices disturb air flow and radiation transfer. Research methods employed in this study; Statistical data gathered in this study; Results of this study.

States that passive cooling techniques applied to thermostatically controlled buildings can contribute to reducing their cooling load significantly. Method for calculating the contribution of earth-to-air heat exchangers to the cooling load of such buildings; Description of procedural steps to the implementation of cooling techniques; Reference to the principle of `balance point temperature.'

Presents information on the construction of mathematical models to assist in the anticipated variation measurements of multi-year ground surface temperatures. Information on ground surface modelling; Conditions resulting from test.

Urban overheating affects the energy, health, power, survivability and environmental quality of cities. We calculated the magnitude of overheating in Sydney, Australia, at close to 9 °C, which causes a cooling penalty of up to 16% and an increase in the indoor overheating levels of up to 56%. We developed and evaluated eight heat mitigation scenarios based on the use of reflective surfaces, additional greenery, an increase in the evapotranspiration rate and several combinations of these factors. We estimated that mitigation can decrease the peak ambient temperature by up to 2.9 °C, reduce the maximum annual cooling consumption by up to 1.5 TWh, decrease the CO2 emissions by as much as 1.21 MT CO 2 , reduce indoor overheating by up to 80%, decrease the heat-related morbidity by 1.07–1.49, and decrease the heat-related mortality anomaly by as much as 1.39 per 100,000 citizens. We estimated the associated water penalty range to be between 80 and 100 Gl/year or between 13 and 16.7% of the water consumption in Sydney. [ABSTRACT FROM AUTHOR]