DOCSLIB.ORG

Urban Climate 29 (2019) 100495

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Urban Climate 29 (2019) 100495 Urban Climate 29 (2019) 100495 Contents lists available at ScienceDirect Urban Climate journal homepage: www.elsevier.com/locate/uclim Potential energy and climate benefts of super-cool materials as a rooftop strategy T ⁎ Amir Baniassadia, David J. Sailorb, , George A. Ban-Weissc a School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, AZ, United States of America b School of Geographical Sciences and Urban Planning, Arizona State University, Tempe, AZ, United States of America c Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, CA, United States of America ARTICLE INFO ABSTRACT Keywords: For decades, refective rooftops have been used and advocated as cost-efective measures to Refective roofs mitigate the urban heat and reduce building cooling loads. However, their efectiveness has al- White roofs ways been limited by shortwave refectivity and long-wave emissivity of commercially available Urban heat mitigation technologies. Recent advances in coating materials with engineered spectral properties have Building energy consumption resulted in inexpensive “super-cool” technologies that can be applied to most surfaces and have Sensible heat fux albedo and emissivity values greater than 0.96 and 0.97, respectively. This study is an efort to Passive daytime radiative cooling quantify the potential benefts of applying the newly developed materials on building rooftops. To do so, we conducted whole-building energy simulations of archetypical residential and commercial buildings to calculate rooftop surface temperature, sensible heat fux to the ambient, cooling energy saving, and heating energy penalty in 8 U.S. cities with urban heat mitigation plans that include use of high albedo materials. Our results suggest that in all climates, the surface temperature of the super-cool rooftop remains below the ambient air temperature throughout the year, resulting in a negative average daily sensible heat fux of 30–40 W.m−2. In addition, we found that the new technology can double the cooling energy saving (and heating energy penalty) compared to typical white roofs. 1. Introduction Urban areas tend to experience higher ambient temperatures than their surroundings, a phenomenon commonly referred to as “Urban Heat Islands (UHI)” (Landsberg, 1981). Given the numerous negative impacts of urban heat, there is a large body of research on mitigation strategies that can reduce its negative impacts on energy and water demand (Touchaei and Akbari, 2015), air quality (Epstein et al., 2017), public health (Jandaghian and Akbari, 2018), and an overall reduction in quality of life for citizens. Refective surfaces (mostly applied on exterior surfaces of buildings) and urban vegetation are the two most studied methods of fghting urban heat. By reducing the absorbed solar radiation, the former has the potential to cool the near surface air (Morini et al., 2018). Because of their practicality, refective rooftops are the most studied (and applied) type of refective surfaces in the urban context (Aleksandrowicz et al., 2017), with a literature that dates back to early 90's (Rosenfeld et al., 1995). In addition, through building energy codes or other initiatives, many states around the world (especially, in mid-latitudes) already have established policies to promote (or mandate) the use of refective rooftops. For example, commercial buildings in many U.S. cities are required to implement white roofs (EPA, 2018). ⁎ Corresponding author. E-mail address: [email protected] (D.J. Sailor). https://doi.org/10.1016/j.uclim.2019.100495 Received 21 January 2019; Received in revised form 9 May 2019; Accepted 27 June 2019 2212-0955/ © 2019 Elsevier B.V. All rights reserved. A. Baniassadi, et al. Urban Climate 29 (2019) 100495 Studies on the efect of refective rooftops encompass a large range of scales. At the broadest level, Zhang et al. (2016) studied the potential impact of widespread cool roof implementation on continental and global scales and reported statistically signifcant (−0.0021 K) reductions in global mean temperature. At regional or metropolis-wide scales, examples include the work of Sailor (1995) and Vahmani et al. (2016) whose simulations suggest that wide adaptation of cool surfaces in the Los Angeles metro area can reduce daytime urban heat by 1 to 1.5 K in summer. Similarly, Li et al. (2014) showed that if 95% of rooftops in Washington- Baltimore area implement cool roofs, a 0.5 K reduction in near-surface UHI can be expected during a summertime heatwave. Based on a sensitivity analysis, Li and Norford (2016) report that in Singapore, city-wide deployment of cool roofs can reduce near-surface air temperature by up to 2 K. After reviewing the peer-reviewed literature, Santamouris (2014) concluded that the decrease in peak ambient temperature across all reliable studies is around 0.9 K per 0.1 increase in average surface albedo. At fner scales (e.g., neighborhood or a single street canyon), recent examples of studies include the work by Botham-Myint et al. (2015) who quantifed the variation of pedestrian-level efects of white roofs with respect to the arrangement and heights of buildings. Their computational fuid dynamics simulations showed that white roofs can potentially cause a near-surface air temperature reduction of 0.75 K. In another study, Taleghani et al. (2016) used micrometeorological simulations to show that, compared to cool pavements, cool roofs have a relatively low impact on thermal comfort of nearby pedestrians. In addition to the mentioned scales, there is another line of investigation that focuses on impacts at the building level. Specifcally, through measurements or whole-building energy simulations, researchers study the impacts of refective rooftops on the energy balance of buildings, and the consequent change in energy demand, thermal comfort, and heat fux into the ambient. For example, Baniassadi et al. (2018b) used EnergyPlus, a validated whole-building energy simulator, to study direct and indirect benefts of cool roofs for energy efciency and thermal comfort in residential buildings. Their work suggested that depending on the construction quality, the direct energy consumption beneft of shifting from a typical dark roof (albedo = 0.2) to a cool roof (albedo = 0.6) for a residential building in California could be up to 30%. Scherba et al. (2011) also used EnergyPlus in conjunction with a set of experimental measurements and reported that depending on the climate, a white roof can reduce total daily fux to the ambient by 75–80% compared to the baseline dark roof. While this summary covers few examples of a much larger body of work, the magnitude of benefts (regardless of the reported metric) in all previous studies is limited by the properties of commercially available products (Mastrapostoli et al., 2016). However, recent developments in Passive Daytime Radiative Cooling (PDRC) technology show the potential of a substantially diferent type of cool-roofs (Santamouris and Feng, 2018). The very recent development of an inexpensive and practical method for producing hierarchically porous poly (vinylidene fuoride-co-hexafuoropropene) coatings is one promising example. In particular, the work by Mandal et al. (2018) resulted in a coating with a substrate-independent albedo of 0.96 and emissivity of 0.97. Notably, they observed a surface temperature drop of up to 6 K below ambient air temperatures under solar intensity of 890 W/m2. This was only achievable through the extremely high albedo combined with the very high emissivity inside the atmospheric window that allow for surface cooling even in the afternoon hours. More importantly, while Mandal et al. did not scope the benefts of this coating as a rooftop strategy, they reported that the coating can be easily applied to any substrate (including rooftops). While this is the most recent and promising example, other research groups (Bhatia et al., 2018; Gentle and Smith, 2010; Gentle and Smith, 2015; Raman et al., 2014; Zhai et al., 2017) have also been working on this topic over the past few years, and achieved similar properies. Although, most are substrate-dependent and expensive solutions. There are several studies on applications of PDRC as a “free” source of cooling in buildings. Most of these studies consider the use of these materials in rooftop heat exchangers integrated within hydronic cooling and heating loops (Goldstein et al., 2017; Wang et al., 2018). For example, Fernandez et al. (2015) simulated this hybrid system (based on the coating proposed by (Raman et al., 2014)) in an ofce building in 5 US cities and reported 45–68% savings in cooling electricity demand. If this technology shows the same sub-ambient temperature performance on rooftops, it can result in a major paradigm shift in how refective rooftops interact with urban environments and individual buildings. While commonly referred to as “cool-roofs”, in reality, typical refective rooftops only reduce the daytime heat fux to the ambient (and into buildings) as opposed to actually cooling them. Hence, while they mitigate urban heat and reduce building cooling demand in comparison to dark roofs, they do not result in an actual cooling efect. In contrast, if the extremely high albedo and emissivity of the mentioned technology results in consistent sub-ambient surface temperatures, it can be considered as an actual urban cooling strategy. In addition, instead of simply reducing building heat gains, super cool roofs can passively cool the building interiors and thus, reduce the demand for mechanical cooling. To study these potential benefts, we used simulations at the building level to scope the benefts of the newly developed coating as a potential rooftop strategy (henceforth, super cool roofs). Through whole-building energy simulations, we compared roof surface temperatures and heat fuxes from super cool roofs in residential and commercial building archetypes to those of typical white (albedo of 0.7 and emissivity of 0.9) and dark (albedo of 0.2 and emissivity of 0.9) roofs.
Load more

Recommended publications
  • ALBEDO ENHANCEMENT by STRATOSPHERIC SULFUR INJECTIONS: a CONTRIBUTION to RESOLVE a POLICY DILEMMA? an Editorial Essay
    ALBEDO ENHANCEMENT BY STRATOSPHERIC SULFUR INJECTIONS: A CONTRIBUTION TO RESOLVE A POLICY DILEMMA? An Editorial Essay Fossil fuel burning releases about 25 Pg of CO2 per year into the atmosphere, which leads to global warming (Prentice et al., 2001). However, it also emits 55 Tg S as SO2 per year (Stern, 2005), about half of which is converted to sub-micrometer size sulfate particles, the remainder being dry deposited. Recent research has shown that the warming of earth by the increasing concentrations of CO2 and other greenhouse gases is partially countered by some backscattering to space of solar radiation by the sulfate particles, which act as cloud condensation nuclei and thereby influ- ence the micro-physical and optical properties of clouds, affecting regional precip- itation patterns, and increasing cloud albedo (e.g., Rosenfeld, 2000; Ramanathan et al., 2001; Ramaswamy et al., 2001). Anthropogenically enhanced sulfate particle concentrations thus cool the planet, offsetting an uncertain fraction of the anthro- pogenic increase in greenhouse gas warming. However, this fortunate coincidence is “bought” at a substantial price. According to the World Health Organization, the pollution particles affect health and lead to more than 500,000 premature deaths per year worldwide (Nel, 2005). Through acid precipitation and deposition, SO2 and sulfates also cause various kinds of ecological damage. This creates a dilemma for environmental policy makers, because the required emission reductions of SO2, and also anthropogenic organics (except black carbon), as dictated by health and ecological considerations, add to global warming and associated negative conse- quences, such as sea level rise, caused by the greenhouse gases.
    [Show full text]
  • Assessing Urban Heat Island Mitigation Using Green Roofs: a Hardware Scale Modeling Approach
    ASSESSING URBAN HEAT ISLAND MITIGATION USING GREEN ROOFS: A HARDWARE SCALE MODELING APPROACH By William C. Pompeii II A Thesis Submitted to the Department of Geography and Earth Science and the Graduate Council in partial fulfillment of the requirements for the degree of Master of Science in Geoenvironmental Studies SHIPPENSBURG UNIVERSITY Shippensburg, Pennsylvania May, 2010 DEPARTMENT OF GEOGRAPHY AND EARTH SCIENCE SHIPPENSBURG UNIVESITY Upon the recommendation of the chairperson of the department of Geography and Earth Science this thesis is hereby accepted in partial fulfillment of the requirements for the degree of Master of Science in Geoenvironmental Studies Thesis Committee __________________________________________________ ________________ Committee Chairperson Date Dr. Timothy W. Hawkins __________________________________________________ ________________ Committee Member Date Dr. Claire Jantz __________________________________________________ ________________ Committee Member Date Dr. George Pomeroy Table of Contents List of Figures iii List of Tables v ABSTRACT vi Chapter 1: Introduction 1 1.1 Statement of Problem 1 Chapter 2: Review of Literature 3 2.1 Background 3 2.1.1 Urban Heat Island 3 2.2 Green Roofs 6 2.2.1 Origin and Types 6 2.2.2 Benefits of Green Roofs 7 2.3 Chicago-A Case Study City 9 2.3.1 Green Roof Case Study-Chicago City Hall Building 13 2.4 Methods of Study the Urban Heat Island and Benefits of Green Roof Mitigation 15 2.4.1. Urban Heat Island Methods-Dataloggers 15 2.4.2 Green Roof effects on Urban Heat Island
    [Show full text]
  • Radiative Cooling New Opportunities & Enabling Technologies
    Radiative Cooling New Opportunities & Enabling Technologies Aaswath P. Raman, Ph.D. [email protected] Research Associate, Fan Group, Ginzton Laboratory ARPA-E Alternative Power Plant Cooling Workshop, May 12, 2014 1 An opportunity to tap an underutilized resource Use the cold of outer space to cold outer space! (-80°C ! -270°C)! radiatively pump heat from the ground through sky access New: Possible at all hours of the day through photonic design of thermally emissive layers Heat Atmosphere Thermal Meaningful cooling power that EM Waves scales with area: analogies to PV Radiative Cooling Surface! 2 I. INTRODUCTION Radiative cooling is a technique that exploits a natural transparency window for electro- magnetic waves in the Earths atmosphere to transport heat from terrestrial objects into cold space. As a result, objects with the appropriate radiative properties can passively cool them- selves down to temperatures well below the ambient. The atmospheric transparency window is found in the 8-13µm wavelength range, as shown in Fig. 1, and fortuitously overlaps with the blackbody spectralAtmospheric radiance corresponding to typical terrestrialtransmittance temperatures (0-50C), thus enabling objects at these temperatures to emit more power than they absorb. 1 Atmospheric Transmission Radiative cooling is enabled by 0◦C blackbody 50◦C blackbody an atmospheric transparency 0.5 window between 8 – 13 μm 0 7 9 11 13 15 Blackbody spectrum of typical λ [µm] Earth temperature objects overlap with window FIG. 1. Atmopheric Transmissioncold in the outer zenith space direction! vs. wavelength; normalized blackbody spectral radiance of a 0◦C and a(upper 50◦C blackbody atmosphere) emitter ! Varies with cloud cover, Prior work in radiative cooling has almost entirely focused on nighttime cooling,geographic where location and one aims to maximize emission in the atmospheric transparency window, without having to contend with solar radiation.
    [Show full text]
  • Concentrated Radiative Cooling Arxiv:2010.02426V1 [Physics.App
    Concentrated Radiative Cooling Joseph Peoples,1 Yu-Wei Hung,2 Xiangyu Li,1 Daniel Gallagher,1 Nathan Fruehe,1 Anil Yuksel,3 James Braun,1 Travis Horton,2 Xiulin Ruan1∗ 1School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, USA, 2School of Civil Engineering, Purdue University, West Lafayette, IN 47907, USA, 3IBM Corporation, Austin, TX, 78758, USA ∗To whom correspondence should be addressed; E-mail: [email protected]. A fundamental limit of current radiative cooling systems is that only the top surface facing deep-space can provide the radiative cooling effect, while the bottom surface cannot. Here, we propose and experimentally demonstrate a concept of \concentrated radia- tive cooling" by nesting a radiative cooling system in a mid-infrared reflective trough, so that the lower surface, which does not con- tribute to radiative cooling in previous systems, can radiate heat to deep-space via the reflective trough. Field experiments show that the temperature drop of a radiative cooling pipe with the trough arXiv:2010.02426v1 [physics.app-ph] 6 Oct 2020 is more than double that of the standalone radiative cooling pipe. Furthermore, by integrating the concentrated radiative cooling sys- tem as a preconditioner in an air conditioning system, we predict electricity savings of > 75% in Phoenix, AZ, and > 80% in Reno, NV, for a single-story commercial building. 1 Introduction In 2018, 9.3% of the total generated electricity in the United States went to space cooling and refrigeration of commercial buildings, equating to 164.7 million metric tons of carbon dioxide emission, just for commercial cooling (1).
    [Show full text]
  • The Application of Passive Radiative Cooling in Greenhouses
    sustainability Article The Application of Passive Radiative Cooling in Greenhouses Chia-Hsin Liu 1, Chyung Ay 2, Chun-Yu Tsai 3 and Maw-Tien Lee 1,* 1 Department of Applied Chemistry, National Chia Yi University, Chiayi 60004, Taiwan; [email protected] 2 Department of Biomechatronic Engineering, National Chia Yi University, Chiayi 60004, Taiwan; [email protected] 3 Program of Agriculture Science, National Chiayi University, Chiayi 60004, Taiwan; [email protected] * Correspondence: [email protected]; Tel.: +886-5-2717691 Received: 31 October 2019; Accepted: 24 November 2019; Published: 27 November 2019 Abstract: At present, greenhouses are used to grow a variety of crops around the world. However, with the change of climate, the increasingly harsh weather makes it more and more disadvantageous for people to work inside, and plants are difficult to grow. Previous research has illustrated that radiative cooling can be realized by using certain nonmetal oxide particles created for emission in an infrared atmospheric transparency window, which is an environmentally friendly cooling method due to reducing energy consumption. Polyethylene (PE)-based formulations with a UV stabilizer and nonmetal oxide particles (NOP) were first granulated and then formed a monolayer film by co-injection molding. The experimental results show that due to passive radiative cooling, under the environmental conditions of 35 ◦C, and only considering the natural convection heat transfer, the net cooling power of the greenhouse film developed in this study is 28 W m 2 higher than that of · − the conventional PE film. The temperature inside the simulated greenhouse cladded with the new greenhouse covering was on average 2.2 ◦C less than that of the greenhouse with the conventional PE film.
    [Show full text]
  • Urban Heat Islands
    11 Urban Heat Islands 11.1 Introduction .............................................................................................................................143 11.2 Principles ...................................................................................................................................144 Urban Scales • Conceptual Framework • Heat Island Types, Characteristics, and Underlying Processes • Heat Island Controls 11.3 Methods of Analysis ................................................................................................................151 Observations • Models 11.4 Impacts and Applications ...................................................................................................... 154 Solutions to Mitigate Urban Heat Islands • Human Comfort and Health • Forecasting Urban Weather and Climate and Developing UHI Mitigation Strategies • The Urban Heat Island and Global Climate Warming 11.5 Major Challenges .....................................................................................................................157 M. Roth Science • Observations National University of Singapore References .............................................................................................................................................158 11.1 Introduction heat-related illness and mortality, air pollution, energy demand for air conditioning, and indirectly greenhouse gas emissions. For millions of people living in cities, increased temperatures Heat waves, for example, which heat islands can
    [Show full text]
  • Implementation of Passive Radiative Cooling Technology in Buildings: a Review
    buildings Review Implementation of Passive Radiative Cooling Technology in Buildings: A Review Suhendri , Mingke Hu * , Yuehong Su * , Jo Darkwa and Saffa Riffat Department of Architecture and Built Environment, University of Nottingham, Nottingham NG7 2RD, UK; [email protected] (S.); [email protected] (J.D.); saffa.riff[email protected] (S.R.) * Correspondence: [email protected] (M.H.); [email protected] (Y.S.) Received: 29 October 2020; Accepted: 21 November 2020; Published: 26 November 2020 Abstract: Radiative cooling (RC) is attracting more interest from building engineers and architects. Using the sky as the heat sink, a radiative cooling material can be passively cooled by emitting heat to the sky. As a result of the development of material technology, RC research has been revived, with the aim of increasing the materials’ cooling power as well as finding reliable ways to utilize it in cooling for buildings. This review identifies some issues in the current implementation of RC technologies in buildings from an architectural point of view. Besides the technical performance of the RC technologies, some architectural aspects, such as integration with architectural features, aesthetic requirements, as well as fully passive implementations of RC, also need to be considered for building application. In addition, performance evaluation of a building-integrated RC system should begin to account for its benefit to the occupant’s health and comfort alongside the technical performance. In conclusion, this review on RC implementation in buildings provides a meaningful discussion in regard to the direction of the research. Keywords: radiative cooling; architectural application; combination; passive design architecture 1.
    [Show full text]
  • Significance of Aerosol Radiative Effect in Energy Balance Control on Global Precipitation Change
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Central Archive at the University of Reading Significance of aerosol radiative effect in energy balance control on global precipitation change Article Published Version Creative Commons: Attribution 4.0 (CC-BY) Open Access Suzuki, K., Stephens, G. L. and Golaz, J.-C. (2017) Significance of aerosol radiative effect in energy balance control on global precipitation change. Atmospheric Science Letters, 18 (10). pp. 389-395. ISSN 1530-261X doi: https://doi.org/10.1002/asl.780 Available at http://centaur.reading.ac.uk/72369/ It is advisable to refer to the publisher's version if you intend to cite from the work. To link to this article DOI: http://dx.doi.org/10.1002/asl.780 Publisher: John Wiley & Sons All outputs in CentAUR are protected by Intellectual Property Rights law, including copyright law. Copyright and IPR is retained by the creators or other copyright holders. Terms and conditions for use of this material are defined in the End User Agreement . www.reading.ac.uk/centaur CentAUR Central Archive at the University of Reading Reading's research outputs online ATMOSPHERIC SCIENCE LETTERS Atmos. Sci. Let. 18: 389–395 (2017) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/asl.780 Significance of aerosol radiative effect in energy balance control on global precipitation change Kentaroh Suzuki,1* Graeme L. Stephens2,3 and Jean-Christophe Golaz4 1Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Japan 2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA 3Department of Meteorology, University of Reading, Reading, UK 4Lawrence Livermore National Laboratory, Livermore, CA, USA *Correspondence to: Abstract K.
    [Show full text]
  • Full Daytime Sub-Ambient Radiative Cooling with High Figure of Merit in Commercial-Like Paints
    The work below was included in a provisional patent application filed on October 3, 2018 and a non-provisional international patent application (PCT/US2019/054566) filed on October 3, 2019 and published on April 9, 2020.1 Full Daytime Sub-ambient Radiative Cooling with High Figure of Merit in Commercial-like Paints 1,2 1,2 1,3 1 1,4,5 1,2,* Xiangyu Li, Joseph Peoples, Zhifeng Huang, Zixuan Zhao, Jun Qiu and Xiulin Ruan 1 School of Mechanical Engineering, Purdue University, West Lafayette, IN, USA. 2 Birck Nanotechnology Center, Purdue University, West Lafayette, IN, USA. 3 School of Power and Mechanical Engineering, Wuhan University, Wuhan, China. 4 School of Energy Science and Engineering, Harbin Institute of Technology, Harbin, China. 5 State Key Laboratory for Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan, China. *Correspondence: [email protected] SUMMARY Radiative cooling is a passive cooling technology by reflecting sunlight and emitting radiation in the atmospheric sky window. Although highly desired, full daytime sub-ambient radiative cooling in commercial-like single-layer particle- matrix paints is yet to be achieved. In this work, we have demonstrated full daytime sub-ambient radiative cooling in CaCO3-acrylic paint by adopting large bandgap fillers, a high particle concentration and a broad size distribution. Our paint shows the highest solar reflectance of 95.5% among paints and a high sky- window emissivity of 0.94. Field tests show cooling power exceeding 37 W/m2 and lower surface temperature more than 1.7˚C below ambient at noon. A figure of merit RC is proposed to compare the cooling performance under different weather conditions.
    [Show full text]
  • For the Mitigation of Urban Heat Island and Urban Noise Island
    TOPICAL REVIEW • OPEN ACCESS Recent citations For the mitigation of urban heat island and urban - A Mobile Vehicle-Based Methodology for Dynamic Microclimate Analysis noise island: two simultaneous sides of urban Ioannis Kousis et al discomfort - More Than Just Concrete: Acoustically Efficient Porous Concrete with Different Aggregate Shape and Gradation To cite this article: I Kousis and A L Pisello 2020 Environ. Res. Lett. 15 103004 Louena Shtrepi et al - Intra-urban microclimate investigation in urban heat island through a novel mobile monitoring system Ioannis Kousis et al View the article online for updates and enhancements. This content was downloaded from IP address 170.106.33.22 on 30/09/2021 at 21:30 Environ. Res. Lett. 15 (2020) 103004 https://doi.org/10.1088/1748-9326/abaa0d Environmental Research Letters TOPICAL REVIEW For the mitigation of urban heat island and urban noise island: OPEN ACCESS two simultaneous sides of urban discomfort RECEIVED 13 May 2020 I Kousis1 and A L Pisello1,2 REVISED 1 CIRIAF - Interuniversity Research Center, University of Perugia. Via G. Duranti 67—06125—Perugia Italy 22 July 2020 2 Department of Engineering—University of Perugia. Via G. Duranti 97—06125—Perugia Italy ACCEPTED FOR PUBLICATION 28 July 2020 E-mail: [email protected] PUBLISHED Keywords: UHI mitigation, urban noise mitigation, urban discomfort, energy efficiency, cool materials, sound absorption, solar reflection 28 September 2020 Original Content from this work may be used Abstract under the terms of the Creative Commons Urban environment well-being has become a crucial public issue to face, given the huge Attribution 4.0 licence.
    [Show full text]
  • The Role of Cloud Heating Within the Atmosphere on the High Cloud Amount and Top-Of-Atmosphere Cloud Radiative Effect Bryce E
    JAMES, VOL. ???, XXXX, DOI:10.1002/, The role of cloud heating within the atmosphere on the high cloud amount and top-of-atmosphere cloud radiative effect Bryce E. Harrop,1 Dennis L. Hartmann,1 Key Points. ◦ ACRE both enhances high cloud amount through direct destabilization of the cloud layer and reduces high cloud amount by stabilizing the troposphere to deep convection ◦ ACRE produces more high, optically thin clouds relative to high, optically thick clouds, increases TOA CRE Abstract. The effect of cloud radiation interactions on cloud properties is examined in the context of a limited domain cloud resolving model. The atmospheric cloud radia- tive effect (ACRE) influences the areal extent of tropical high clouds in two distinct ways. The first is through direct radiative destabilization of the elevated cloud layers, mostly as a result of radiation heating the cloud bottom and cooling the cloud top. The sec- ond effect is radiative stabilization, whereby cloud radiative heating of the atmospheric column stabilizes the atmosphere to deep convection. In limited area domain simulations, the stabilizing effect is the dominant role of the cloud radiative heating, thus reducing the cloud cover in simulations where ACRE is included compared to those where it is removed. Cloud radiative heating increases cloud amount, decreases cloud optical depth, and increases cloud top pressure. The combination of these effect increases the top-of- atmosphere cloud radiative effect. In mock-Walker circulation experiments, the decrease in high cloud amount owing to radiative stabilization tends to cancel out the increase in high cloud amount owing to the destabilization within the cloud layer.
    [Show full text]
  • Radiative Cooling and Thermoregulation in the Earth's Glow
    Manuscript - Radiative Cooling and Thermoregulation in the Earth’s Glow- Mandal et. al. Radiative Cooling and Thermoregulation in the Earth’s Glow Jyotirmoy Mandal, 1* Sagar Mandal,2 John Brewer,1 Arvind Ramachandran,3 Aaswath Pattabhi Raman1* 1 Department of Materials Science and Engineering, University of California, Los Angeles, California, USA 2 Independent Researcher, 523 Broadway E, Seattle, Washington, USA 3 Department of Civil, Environmental and Sustainable Engineering, Arizona State University, Tempe, Arizona, USA Contact: Jyotirmoy Mandal ([email protected]) and Aaswath Raman ([email protected]) Abstract Passive radiative cooling involves a net radiative heat loss to the cold outer space through the atmospheric transmission window in the long-wave infrared (LWIR) wavelengths. Due to its passive nature and net cooling effect, it is a promising alternative or complement to electrical cooling. For efficient radiative cooling, an unimpeded view of the sky is ideal, with prior work thus focused on roofs and sky-facing surfaces. However, much of the surface area of typical buildings are vertically oriented, with ≳50% of their field of view subtended by terrestrial features. Under sunlight, these features become warm and thermally irradiate vertical facades of buildings. Since building facades are made of materials that are broadband emitters and absorbers of thermal radiation, this heating effect can dramatically counter heat loss to the sky, diminishing or even reversing the radiative cooling process. We show that selective LWIR emitters on vertical building facades can experience higher cooling than achievable by using conventional broadband thermal emitters. They achieve this enhancement by exploiting the differential transmittance of the atmosphere towards the sky and between terrestrial objects.
    [Show full text]