55 research outputs found
Exploring the meteorological impacts of surface and rooftop heat mitigation strategies over a tropical city
Get PDFDifferent heat mitigation technologies have been developed to improve the thermal environment in cities. However, the regional impacts of such technologies, especially in the context of a tropical city, remain unclear. The deployment of heat mitigation technologies at city-scale can change the radiation balance, advective flow, and energy balance between urban areas and the overlying atmosphere. We used the mesoscale Weather Research and Forecasting model coupled with a physically based single-layer urban canopy model to assess the impacts of five different heat mitigation technologies on surface energy balance, standard surface meteorological fields, and planetary boundary layer (PBL) dynamics for premonsoon typical hot summer days over a tropical coastal city in the month of April in 2018, 2019, and 2020. Results indicate that the regional impacts of cool materials (CMs), super-cool broadband radiative coolers, green roofs (GRs), vegetation fraction change, and a combination of CMs and GRs (i.e., “Cool city (CC)”) on the lower atmosphere are different at diurnal scale. Results showed that super-cool materials have the maximum potential of ambient temperature reduction of 1.6°C during peak hour (14:00 LT) compared to other technologies in the study. During the daytime hours, the PBL height was considerably lower than the reference scenario with no implementation of strategies by 700 m for super-cool materials and 500 m for both CMs and CC cases; however, the green roofing system underwent nominal changes over the urban area. During the nighttime hours, the PBL height increased by CMs and the CC strategies compared to the reference scenario, but minimal changes were evident for super-cool materials. The changes of temperature on the vertical profile of the heat mitigation implemented city reveal a stable PBL over the urban domain and a reduction of the vertical mixing associated with a pollution dome. This would lead to crossover phenomena above the PBL due to the decrease in vertical wind speed. Therefore, assessing the coupled regional impact of urban heat mitigation over the lower atmosphere at city-scale is urgent for sustainable urban planning.DN acknowledges the William Stamps Farish Chair through the Jackson School of Geosciences at University of Texas; and funding from NOAA NIHHIS NA21OAR4310146, NASA Interdisciplinary Sciences (IDS) Program (NNH19ZDA001N-IDS and 80NSSC20K1268), and DOE Urban Integrated Field Labs (IFL)
1997-2002-2007 Link Input-Output Tables of China
Get PDFapplication/pdf序 1.1997年・2002年・2007年名目産業連関表の整理 2.統合中分類35部門の対応物価指数および最終需要のデフレーター 3.付加価値ID （Implicit Deflator） 4.中国1997-2002-2007年接続産業連関表の作成 結departmental bulletin pape
On the energy potential of daytime radiative cooling for urban heat island mitigation
Get PDFThe 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
On the winter overcooling penalty of super cool photonic materials in cities
Get PDFDaytime radiative coolers appear to be the most triumphant and promising technology for urban thermal management, as they could improve the thermal field of the cities, especially during the summertime. However, during
the colder months, it can lead to an overcooling penalty, a widely overlooked phenomenon. This study aims to
determine the cooling penalty derived from using super-cool materials (SCMs) at a city scale. We used a mesoscale
urban modeling system to assess the overcooling of three broadband SCM emitters with different reflectivity and
emissivity values. A significant change was found in radiation and energy balance compared to the control case
(CTRL) during the daytime and nighttime. Under the most reflective and emissive SCM scenario, the maximum
decrease of net radiation at peak hour was 354.9 Wm−2, therefore choosing a scenario with lower albedo values
for walls and ground would be more beneficial. The mean decrease of ambient temperature, surface temperature, roof temperature and canopy were 2.8 °C, 4.7 °C, 12.9 °C and 6 °C, respectively. This SCMs assessment is
a first stride to understand better the unexplored behavior of the boundary layer meteorology and its depiction
in the mesoscale climate model for winter seasons. The implementation of SCMs during winter could create an
inversion layer near the surface, leading to a buildup of stagnant air over the urban environment, resulting in
heating during the night in the winter seasons as usual with SCMs as with the CTRL. Further research is needed
on material development to modulate materials’ spectral configuration to address overcooling during the winter
and improve SCMs’ year-round performance at city scale
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