Canopy urban heat island and its association with climate conditions in Dubai, UAE

The impact that climate change and urbanization are having on the thermal-energy balance of the built environment is a major environmental concern today. Urban heat island (UHI) is another phenomenon that can raise the temperature in cities. This study aims to examine the UHI magnitude and its association with the main meteorological parameters (i.e., temperature, wind speed, and wind direction) in Dubai, United Arab Emirates. Five years of hourly weather data (2014–2018) obtained from weather stations located in an urban, suburban, and rural area, were post-processed by means of a clustering technique. Six clusters characterized by different ranges of wind directions were analyzed. The analysis reveals that UHI is affected by the synoptic weather conditions (i.e., sea breeze and hot air coming from the desert) and is larger at night. In the urban area, air temperature and night-time UHI intensity, averaged on the five year period, are 1.3 °C and 3.3 °C higher with respect to the rural area, respectively, and the UHI and air temperature are independent of each other only when the wind comes from the desert. A negative and inverse correlation was found between the UHI and wind speed for all the wind directions, except for the northern wind where no correlation was observed. In the suburban area, the UHI and both temperatures and wind speed ranged between the strong and a weak negative correlation considering all the wind directions, while a strong negative correlation was observed in the rural area. This paper concludes that UHI intensity is strongly associated with local climatic parameters and to the changes in wind direction

Analysis of the indoor air quality in greek primary schools

The exposure of children to indoor air pollutants in school classrooms might cause them adverse health effects. In order to confront this issue, the in-depth study and evaluation of the indoor air quality in classrooms is necessary. The aims of this study are to characterize the environmental factors that affect indoor air quality. Several indoor air pollutants such as the concentrations of the particulate matter (PM) of several different size ranges, carbon dioxide (CO2), carbon monoxide (CO) and VOCs, were simultaneously measured in classrooms as well as the outdoor environment in nine primary schools in Athens, Greece during April 2013. Measurements were performed for more than 7 hours per day, for a period of one to five days in a classroom, per school. The first results indicate extreme PM10 concentrations in many cases with varying fluctuations throughout the day, mainly attributed to the presence of students, inadequate level of ventilation and chalk dust while the ultrafine particles (UFP) remained in rather low levels. In most of the cases the indoor concentrations exceeded the outdoor ones by more than ten times. Carbon dioxide concentrations in many cases exceeded the recommended limit value indicating inadequate levels of ventilation

Energy Performance of Cool-colors and Roofing Coatings in Reducing the Free Solar Gains during the Heating Season: Results of an In-Field Investigation☆

Abstract Today, it is not well-known the impact of cool roofs during heating season in balanced climates. Proposed study tries to quantify the increase of energy demands of buildings characterized by high-reflective and high-emissive coatings of roof, by means of experiments and numerical simulations. Three coatings are investigated with different solar absorptance and thermal emittance. The experiments have been carried out at the living lab of the University of Sannio, a full-scale test-room, provided with a large flexibility in terms of variability of the thermal envelope and air-conditioning system. Moreover, numerical evaluations of heating and annual energy consumptions are presented

On the energy potential of daytime radiative cooling for urban heat island mitigation

The objective of this paper is to present the potential of daytime radiative cooling materials as a strategy to mitigate the Urban Heat Island effect. To evaluate the cooling potential of daytime radiative cooling materials, 15 theoretical materials and seven existing materials were simulated: two radiative cooling materials, a coolmaterial, two white paints, a thermochromic paint and a construction material. The novelty of this study is that it shows that the optimal spectral characteristics of radiative cooling materials depending on the climate conditions and the type of application. A sensitivity analysis was performed to evaluate the impact of each wavelength emissivity on the ability to achieve sub-ambient radiative cooling. The sensitivity analysis comprised a total of 90 theoretical materials with 15 different wavelength combinations and 6 emissivity values. The heat transfer model, which includes conduction, convection, and radiation, was developed using a spectrally-selective sky model. Two conditions were considered: a very conductive surface and a highly insulated one. All the materials were simulated in two cities that suffer from the Urban Heat Island effect—Phoenix and Sydney. The mean surface temperature reduction achieved was 5.30 ◦C in Phoenix and 4.21 ◦C in Sydney. The results presented suggest that the type of application (active or passive) is a determinant factor in the design of radiative cooling materials. Modifying the spectra of the materials led to a substantial change in the cooling potential. A material that performs well in a dry climate as a passive solution could perform poorly as an active solution.Laura Carlosena would like to acknowledge the funding of the Government of Navarre for an industrial Ph.D. research grant "Doctorados industriales 2018–2020" file number 0011-1408-2017-000028 at the University of the Basque Country that takes place in the R + D department of Alonso Hernández & asociados arquitectura S.L

Experimental development and testing of low-cost scalable radiative cooling materials for building applications

Urban overheating has a serious impact on building energy consumption. Daytime radiative cooling materials are an interesting passive solution for refrigeration. However, their costs and complex manufacturing hinder their current application. In this study, a series of scalable and lowcost daytime radiative cooling (DTRC) materials were designed, fabricated, and tested in a moderate climate (Cfb-Köppen-Geiger classification) and compared to aluminum and Vikuiti. The methodology was: i) material selection and design, (ii) optimization, (iii) fabrication, (iv) characterization, and (v) testing. The materials were fabricated using different substrates, aluminum and Vikuiti, and two kinds of formulations for the emissive layers based on silica-derived polymer polymethylsilsesquioxane (PMSQ) with embedded silica nanoparticles. The resulting aluminum DTRC materials had a mean solar reflectivity of 0.7 and 0.34 emissivity in the atmospheric window, the samples with Vikuiti had 0.97 and 0.89, respectively. During the experiment, the samples were exposed to different ambient conditions without a convection barrier and were contained in an extruded polystyrene board to eliminate conduction. The samples reached 7.32 °C and 9.13 °C maximum surface temperature reduction (below ambient) during the day and night, respectively. The samples with the commercial substrate achieved a mean reduction of 3.72 °C below ambient temperature. Although the aluminum samples did not achieve subambient cooling throughout the entire day, the emissive layer reduced the sample's surface temperature by an average of 1.7 °C. The PMSQ radiative cooling materials show great potential for future building applications. Suitability under different climates and experimental settings should be done to test broad applicability.The materials development in this research received a grant from the Government of Navarre "Convocatoria proyectos I + D 2019" file number 0011-1365-2019-000051; and financial support from Alonso Hernandez & asociados arquitectura, S. L