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The incident solar radiation on building facades is strongly affected by the urban characteristics, however frequently overlooked in the assessment of indoor environments due to limited data availability. Here, we show that a simplified representation of the urban environment can drastically affect the estimation of the incident solar radiation within urban canyons. We associate uncertainties with the canyon’s geometry, built surfaces, optical properties, as well as vegetation, and resort to a hybrid probabilistic-possibilistic approach to quantify the effects on thermo-visual comfort. Contrasting complex against simplified urban canyons shows that the pattern of incident solar radiation is uneven along the building facade and strongly correlated to the canyon’s characteristics. We also demonstrate that simplified models of urban canyons could underestimate the number of thermally comfortable instances by even 365 h a year (i.e., ~ 4% of the time). Similarly, a simplified canyon underestimates the visually comfortable occurrences, especially during the intermediate seasons. While a simplified canyon estimates a glare probability of 1.0, uncertainties within a complex canyon can lower the glare probability to 0.28 throughout the day. We show that for visual comfort, geometric characteristics alone, such as the canyon’s skyline, can outweigh optical properties such as the transmissivity of trees. This uncertainty, especially in the estimate of glare probability, may lead to different decisions about building envelope design, including the need for a more or less adaptable facade.

Urban overheating affects the health and wellbeing of communities, the environmental quality, and the economic performance of cities. This study demonstrates that outdoor thermal comfort can be improved in a single street by decreasing ambient (Ta) and surface (Ts) temperatures by implementing innovative and traditional heat mitigation strategies. Ten scenarios were modelled in ENVI-met and evaluated based on detailed in-situ and airborne-based meteorological data collected along Phillip Street (Parramatta) in Sydney, Australia. The best-performing scenario combining reflective materials, increased greenery, spray systems, and traditional shading provides a very significant reduction of Ta and Ts of up to 3.3 °C and 30.9 °C, respectively. On its own, radiative cooling materials applied on shading devices offer a comparable incanyon cooling capacity with maximum Ta and Ts decrease of up to 1.6 °C and 24.2 °C. Similar results are obtained by applying traditional solar control devices, which reduce peak Ta by 1.3 °C and Ts by 21.8 °C. When reflective pavements are accompanied by an increment in greenery, peak Ta and Ts are additionally reduced by 0.2 °C and 3.6 °C, respectively. When applied individually, an increase in evaporative cooling and greenery shows a strong local effect with a maximum in-canyon Ta decrease of 2.7 °C and 0.5 °C, respectively. Results show increased wind speeds have a positive impact on greenery, shading, radiative and reflective technologies and an unfavourable effect on spray systems. Future research should concentrate on examining the cooling potential of radiative coolers in different proportions and arrangements and quantifying the contributions and interactions between different strategies when applied simultaneously.

In several areas of the world, the population concentrates along the coastal regions, benefitting from the sea breeze, with warmer inland areas. However, increasing population is driving urban sprawl in traditionally low-density areas, enhancing the synergies between global and local climate change. Here we show that local climate mitigation can reduce the impacts of climate change, with the analysis of a new development area in Sydney, 50 km from the coast. With meso-scale climate modelling, we computed that by 2050 the peak summer temperature will increase by 0.8 °C and the daily average summer temperature by 1.6 °C. Mitigation with cool materials, greenery, and irrigation will lower the peak and average daily temperatures respectively by 2.2 °C and 1.6 °C with respect to the unmitigated future climate scenario. Mitigation techniques when applied in the whole Sydney area yield to cooling energy needs reductions by 6.7–8.6 kWh/m2 (13.4–19.3%) for typical residential, office, and school buildings, with a negligible heating penalty, compared to an unmitigated future scenario. Combined adaptation and mitigation can reduce the future cooling energy needs by 31.3 kWh/m2 (70%), 29.3 kWh/m2 (57.3%), and 20.9 kWh/m2 (59.4%) for typical residential, office, and school building, respectively. Our study indicates that the consolidated and widely available mitigation technologies alone cannot counteract the energy impact of both global and local climate change. A structured system of interventions at building and urban scale is necessary while developing novel and higher efficiency mitigation technologies.

Urban overheating has become a growing concern in the Northern Territory of Australia, where residents are suffering from excessive heat and frequent heatwaves. The characteristics of the local cli...

In the context of global warming, radiative coolers with high solar reflectance and strong emissivity in the atmospheric window can cool the substrate as well as the ambient air. Silica at its nano or micro-scale being randomly dispersed into a uniform transparent polymer can form scalable radiative coolers for large-scale application. Promising cooling performance has been reported for silica-polymers compared with conventional cooling materials, but their performance can be largely influenced by various fabrication parameters. So far, how fabrication parameters influence the emissivity and the cooling performance has not been experimentally demonstrated and the cooling capacity of silica-polymers reported was not substantial compared to other superior radiative coolers. In this work, random silica-polymer has been optimized experimentally. Lab measurement and experimental testing of six fabricated silica-polymers under subtropical and desert climates indicated that due to the complexity of the thermo-radiative balance, high emissivity and strong selectivity are both indispensable in the production of high cooling power. If combined with superior reflectors with higher solar reflectance and especially the emissivity in 8–13 μm enhancing the heat dissipation ability, substantial cooling capacity can be achieved: under the harsh desert climate with average peak solar radiation over 1100 Wm-2, the combination presented sub-ambient temperature of maximum 4.7 °C when air temperature reached its peak and the maximum daytime and night-time sub-ambient temperatures were 12.5 °C and 15.9 °C respectively.

Wall finishes with high solar reflectance and thermal emittance, commonly known as cool walls, can reduce the exterior surface temperatures of façades, and consequently the building cooling energy needs and power demand, and lower the sensitivity to degradation. Aging, though, may affect their performance. To investigate this risk, we exposed for four years in Milan, Italy, two series of façade finish coats, white and beige, facing north and south, in vertical and vertical-sheltered position, and we measured their solar spectral reflectance and thermal emittance before and after aging. The solar reflectance of the white finish coats drops from 0.75 to 0.55 in four years, and from 0.46 to 0.38 for the beige coats, while the thermal emittance is unchanged. Then, for a typical residential building with white walls, we computed that the cooling energy needs increase with walls aging by 5% and 11%, respectively, with or without exterior wall insulation. The exterior surface temperature is increased even by 6 °C, and the number of sudden surface temperature variations in one hour is boosted. Finally, the moisture content in the external layers is reduced, showing the impact on the heat and mass balance because of the uncertainty in solar absorption due to aging. © 2017 Elsevier B.V.

Indoor thermal comfort and air quality in school classrooms are of interest worldwide, primarily because of their potential impacts on students’ health, learning performance and productivity. Further, increasing concerns with changing climate and building energy efficiency highlight the importance of ventilation and comfort in educational settings. The existing literature on indoor air quality (IAQ), ventilation, and thermal comfort in classrooms in subtropical regions of Australia is sparse. Here, we present the results of a field study conducted in secondary school classrooms in Sydney during the school year in 2018 and 2019. We collected data with subjective surveys through questionnaires and with field measurements related to IAQ the thermal comfort in two adjacent similar classrooms. The infiltration and ventilation rates were measured during the non-occupied period using the concentration decay method. We analysed the performance of a cloud-connected demand-controlled mechanical extract ventilation system (DCV), which was installed in one of the two surveyed classrooms during mid-season. Before application of the DCV, CO2 levels were similar in both classrooms with a maximum concentration of approximately 2418 ppm during cold season. The DCV reduced the peak CO2 concentration to 1335 ppm, while CO2 raised to 2981 ppm in the classrooms without DCV during mid-season. Further, Volatile Organic Compounds (VOCs) analysed from air samples show improved air quality in the classroom with DCV. Our results highlight the impact of both indoor temperature and CO2 concentration on students’ feeling of fatigue. Students showed adaptability to indoor temperature change. A period of one week is needed for students’ adaptation to a step change in the mean outdoor temperature. Understanding classroom indoor air quality and thermal environment, as well as students’ perceived comfort, is vital to develop child-based design guidelines for schools.

Climate change is one of the most significant environmental issues facing communities, while poor construction and absence of effective air-conditioning (AC) predominantly cause indoor overheating. Although AC may help meeting indoor comfort, it increases the vulnerability of low-income residents, triggers large energy consumption, and generates anthropogenic heat, which worsens heat stress outdoor. The capacity of buildings to maintain comfortable thermal conditions without mechanical cooling is the key factor protecting occupants against the rising temperature. Residents of Darwin, Australia, will be largely affected by increasing temperature where the annual peak ambient temperature may increase by 7.4 °C in 2060, while the number of hours above 30 °C will rise by 70%. Based on regional climate modelling for the Australian area and using a building energy simulation platform, we computed that by 2060 the indoor air temperature in a typical residential building may exceed 30 °C for over 4000 h under free-floating condition, with a peak daytime and night-time temperatures of 39 °C and 36.5 °C, respectively. The sensible thermal energy need for cooling per unit area under thermostatically controlled condition will increase from the current level of 110.7 kWh/m2 to 196.8 kWh/m2 in 2060. Different adaptation techniques when applied to the typical residential building yield to the peak indoor air temperature drop by 3.3–12 °C, and cooling energy needs reductions by 23.5–195.3 kWh/m2 (12–99.7%) for low, medium, and high retrofit buildings compared to the typical residential building in 2060. Our study indicates that improved building quality is necessary to enhance survivability and energy efficiency in Darwin considering the role of building adaptation measures to counterbalance the impacts of global warming.

The increasing frequency of extreme hot days has a considerable impact on health and energy. Heat stress related to high temperatures cause increased rates of mortality and morbidity, particularly amongst vulnerable populations such as those belonging to lower socio-economic groups. Most studies on heat related mortality and morbidity generally use temperatures from weather stations that do not consider the urban heat island (UHI) effect, leading to inaccurate predictions, particularly during heat waves. This study uses data collected by citizen scientists in predicting outdoor thermal comfort as well as indoor heat stress and peak cooling energy for low income housing in Australia. The results show that the outdoor Universal thermal climate index (UTCI) values estimated during hot afternoon ranged from 26 °C to 46 °C which equate to moderate to extreme heat stress. The indoor Discomfort index (DI) values calculated inside the living and bedrooms were below the heat stress limits (DI

In building performance simulations it is typically assumed that outdoor HVAC equipment is exposed to air at the outdoor ‘ambient’ temperature, obtained from a weather file. However, in reality, significant spatial variations in the outdoor air temperature can exist close to buildings. This simplification may lead to significant errors, especially when comparing simulations of buildings with and without cool roofs, since the colder surface of the cool roof would reduce above-roof air temperatures, thereby influencing the energy consumption of rooftop HVAC equipment. Above-roof temperature variations were measured in detail at three shopping centre buildings, and the experimental data was used to develop a model that can estimate air temperatures above hot or cold roof surfaces. The model requires only four input variables, all of which are available in typical building simulation tools. Implementation of the model in a set of case-study simulations revealed that above-roof air temperatures can have a large effect on the predicted performance of cool roofs. In cases where cooling equipment and ventilation inlet ducts were both located on the roof, the electricity savings and gas ‘penalties’ attributable to cool roofs would have been underestimated by 44–85% (61% on average) if above-roof air temperature variations had not been modelled accurately.

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 CO2, 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.

The physical integrity and photocatalytic performance of titanium dioxide (TiO2) deteriorate with aging. Here we propose a pre-treatment with nitric or sulfuric acid of commercial TiO2 nanopowders used in coating, mortars, or paints. The diffuse reflectance is increased between 1500 and 2500 nm by 0.04 and 0.06, respectively, with nitric and sulfuric acid (unaffected by neutralization). Nitric acid causes a decrease in crystallinity and photocatalytic activity, which drops by almost 20%; this drawback is prevented by post-treatment neutralization, which allows to recover initial photocatalytic efficiency and even increase it. Treatment with sulfuric acid shows no significant effect on photoactivity, instead.

Cities often show nighttime air temperatures higher by 3–4 °C than adjacent non-urban areas. This yields to cooling loads in average higher by 13% for urban than rural buildings. Here we assess the hygrothermal performance and the heating and cooling loads of a reference building representative of the Italian stock. We compare its performance calculated with hourly urban weather data (2002–2008) with the performance of the same building using a rural dataset instead. Milan’s Urban Heat Island reduces the heating loads by 12% and 16%, for the non-insulated and insulated building, respectively, while the cooling loads are increased by 41% and 39%. The urban building also shows dehumidification loads 74–78% lower than the rural building. Moreover, during the 2003 heat wave, the indoor air temperature is computed to be 1.5 °C–2.2 °C higher in a non-conditioned urban building than in the rural one. This increases the wakefulness, occupants’ vulnerability to overheating, and impacts the overall hygrothermal performance. Our findings highlight the need of a different design concept for urban with respect to non-urban buildings, even though they are, by law, in the same climate zone.

International audience; The development of photoactive materials with self-cleaning and depolluting qualities is a hot topic in materials science, given their impact on several technologies, in a wide range of contexts of applications. Anatase phase titanium dioxide (TiO2) is the largest used photocatalyst, with increasing applications ranging from air quality control to renewable energies, to green building materials for zero energy communities. Yet, it is partially transmissive in the near infrared (NIR), which negatively affects the solar reflectance of TiO2 containing materials. In this contribution we describe an unexpected increase in anatase near infrared (NIR) reflectance observed during environmental exposure. We unveil its complex mechanisms, based on the contact with nitric acid generated by NOx photocatalytic degradation, which causes partial reduction and decrease in crystallinity to TiO2. This may open the way for introducing multiple environmentally beneficial effects on TiO2 pollutants degradation, self-cleaning, and energy performance.

Cool materials represent an interesting and acknowledged solution able to produce a threefold benefit: the reduction of cooling energy needs in buildings, the mitigation of the urban heat island phenomenon, the counterbalance of global warming trend at larger scale. In fact, they are environmentally friendly and relatively cost-effective materials characterized by high solar reflectance and infrared thermal emittance properties. Therefore, they are helpful to mitigate the urban microclimate by decreasing air and surface temperature when applied over building envelopes, i.e., roofs and walls, and urban paving surfaces. This chapter will discuss about the key research contributions to the development and testing of such cool materials’ effectiveness with a specific focus on the material engineering and characterization. More in details, the recent nanoscale developments will be addressed and the main applications of cool materials will be discussed in order to provide quantitative and quantitative assessment of the effectiveness of such technology for building energy efficiency.