Expanding the applicability of daytime radiative cooling: Technological developments and limitations

Daytime radiative cooling is regarded as the gold promise of future sustainable building energy systems and a breakthrough in the fight against local climate change. Despite the fervid research interest, most literature reports exceptional theoretical performances under ideal, desert-like conditions, but overlooks the cooling impairment that occurs under low atmospheric transparency (cloudy, humid, polluted conditions) and reduced sky access (packed urban contexts). Power recovery and stabilization call for decoupling of incoming and outgoing radiation at equal wavelengths. Enhanced directionality and high-contrast, broadband asymmetric transmission have been recently proposed to expand the applicability of radiative coolers over a wider spectrum of climates, weathers and terrains. This review offers itself as a first, timely synthesis of the current technological arena. Physical principles, materials and designs, collected from a variety of applicative fields, are detailed and discussed in terms of performance and feasibility, to inspire the transition into sustainable building cooling, worldwide. Major grey areas and serious concerns on potential violations of the 2nd law of thermodynamics reinforce the need for experimental demonstrations in future research

On the energy modulation of daytime radiative coolers: A review on infrared emissivity dynamic switch against overcooling

Passive daytime radiative cooling represents one of the boldest answers to tackle the future cooling needs of the built environment and to mitigate urban heat island effects. Recent developments in the field targeted subambience with several successful examples. On the other side, heating demands may get exacerbated unless effective countermeasures against overcooling are identified, especially in wintertime or heating-dominated climates. This review aims at collecting state-of-the-art technologies and techniques to dynamically control the heat transfer to and from the radiative emitter and ultimately modulate its cooling capacity. Potential solutions are selected from different applicative fields, including spacecraft thermal control, thermal camouflage and electronics. Environmentally-responsive solutions are analyzed in depth given their perfect match with radiative cooling design requirements. Among them, VO2-tuned Fabry-Perot resonators are given particular emphasis, owing to their proven applicability. Active solutions are presented for completeness, but in less detail. Underlying principles, structural composition and experimental/simulated results are detailed and discussed to identify prominent pathways towards technically and economically effective integration in the built environment

Urban transport in the EU Mission on Climate Neutral and Smart Cities: preliminary data from applicants' expressions of interest

The EU Mission on Climate Neutral and Smart Cities is an ambitious initiative to involve a wide range of stakeholders and deliver 100 climate-neutral and smart cities by 2030. These cities will act as experimentation and innovation hubs to enable all European cities to follow suit by 2050. The results from the expressions of interest suggest that the Mission's objectives are shared by a significant number of cities: 314 EU cities (representing 18% of EU population) plus 48 non-EU cities declared their ambition and preparedness to become climate neutral. Transport is a key sector to address, with the overwhelming majority of applicant cities setting specific targets and policy measures. Electrification of urban transport appears as the main approach towards decarbonization. Nevertheless, the required investments and the repercussion on the citizens' costs for mobility are major concerns

Upscaling of SMA film-based elastocaloric cooling

A new concept of upscaling a shape memory alloy (SMA) film based elastocaloric cooling device is presented by arranging SMA films in parallel to increase the specific cooling capacity at low actuation force, while maintaining the large surface-to-volume ratio needed for rapid heat transfer. Selected materials are cold-rolled TiNiFe films that exhibit maximum adiabatic temperature changes of 27.3 and -18.1 K upon loading and unloading, respectively. Demonstrators are designed, fabricated and characterized consisting of five free-standing TiNiFe film bridges that are coupled antagonistically for work recovery. Thermomechanical cycling is performed by out-of-plane deflection of the SMA bridges, while heat transfer is established through mechanical contact with solid heat sink/source elements. The cooling capacity of the demonstrators scales with the number of active SMA films, which confirms the concept of parallelization for upscaling. Investigated demonstrators reach a maximum cooling capacity of about 900 mW compared to a maximum of about 200 mW achieved for reference devices consisting of a single TiNiFe film. The investigation also reveals a number of open issues related to narrow fabrication tolerances upon upscaling, which may cause different plastic straining and varying inhomogeneous stress accumulation among the individual SMA films

Optimization of random silica-polymethylpentene (TPX) radiative coolers towards substantial cooling capacity

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

Gamma background characterization on VESUVIO: before and after the moderator upgrade

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Towards energy efficient, comfortable and climate resilient built environment: Development and application of smart, optimized and mitigation-oriented solutions

Questa tesi riporta una serie di attività di ricerca che indagano, sotto diversi aspetti spaziali e temporali, i temi di efficienza energetica, comfort e resilienza al cambiamento climatico relativi al settore edilizio. Il primo macroblocco tematico è incentrato sul design di logiche di controllo ottimizzate a servizio di svariati componenti edilizi, nella fattispecie: radiatori elettrici (logiche on-off, PID e fuzzy), finestre (algoritmi di comfort adattivi basati su qualità dell’aria e comfort termico), serre solari (ventilazione meccanica controllata a logica termoigrometrica) e ventilconvettori (modelli fuzzy e predittivi per la gestione degli apporti solari). Il secondo macroblocco indaga le ripercussioni del cambiamento climatico sulla performance energetica ed ergonomica dell’ambiente costruito, partendo dal singolo edificio fino a coinvolgere fenomenologie su scala urbana. Vengono dapprima presentati i risultati dello studio di quattro mesi condotto su territorio europeo nell’ambito dell’edizione 2015 del WISBA (Wienerberger Sustainable Building Academy): la resilienza di un edificio low-tech (rappresentato dal Building 2226, Austria) è investigata nel contesto delle condizioni climatiche attese nel 2050 per approdare ad una strategia di redesign anti obsolescenza prematura. In seguito, sono esposti e discussi i risultati di uno dei progetti di mitigazione dell’effetto isola di calore urbana, condotti in collaborazione con la University of New South Wales (Sydney, Australia): il caso limite rappresentato da una capitale tropicale (Darwin) è oggetto di monitoraggio, analisi, modellazione e sviluppo di contromisure specifiche. Nel complesso, l’intero percorso di ricerca mira a definire e testare su campo soluzioni ad elevato potenziale di risparmio energetico e comfort (indoor ed outdoor) tramite logiche smart e tecnologie orientate alla mitigazione dei fenomeni di surriscaldamento globale. Comun denominatore è l’inclusione di una robusta fase sperimentale.This thesis addresses a series of research activities spanning the different spatial and temporal aspects of energy efficiency, comfort and climate change resilience throughout diverse scales of the built environment. The first macro-topic deals with the design of optimized control logics of specific building components, notably: electric radiators (on-off, PID and fuzzy controllers), windows (indoor air quality and thermal comfort driven adaptive comfort algorithm), sunspaces (smartly controlled mechanical ventilation) and fan coil units (fuzzy and model-predictive logics to counteract overabundant solar gains). The second macro-topic focuses on how climate change phenomena impinge on the energetic and ergonomic performance of buildings and cities. Firstly, the outcomes of the four-month experience in Europe, as a member of the 2015 WISBA edition (Wienerberger Sustainable Building Academy), are presented: the low-tech concept of Building 2226 (Austria) was tested in the frame of the actual climatic conditions and in view of the expected climate change to come in 2050. A re-design strategy was developed to enhance its resilience. Secondly, the results of one of the Urban Heat Island (UHI) mitigation projects run during the last year in collaboration with the University of New South Wales (Sydney, Australia) are illustrated and discussed: the borderline case of a tropical city (Darwin, Northern Territory) was monitored, analysed, modelled and tackled by developing customized counterbalance measures. Indeed, the overarching aim of the whole research path is to provide and field-test smart, optimized and mitigation-oriented solutions towards more efficient and liveable indoor and outdoor spaces. Special focus was given to the collection of on-site validated data, by planning robust monitoring campaigns and properly selecting the sensor networks

Visions for climate neutrality and opportunities for co-learning in European cities (Supplementary Material)

The two files of this Supplementary Material are provided in the scope of the original research article Kılkış, Ulpiani, & Vetters (2024) titled “Visions for climate neutrality and opportunities for co-learning in European cities” in Renewable and Sustainable Energy Reviews. This first Supplementary Material (SM1) is composed of additional original analyses that are performed by city groupings in support of the findings of this article. These original analyses focus on the scale and status of implementation (Figure S1) and scope of key mitigation measures (Figure S2) as well as collaboration with stakeholders who are involved in formulating and implementing climate change mitigation policies (Figures S3, S4). In subsequent figures, text analysis of the cities’ visions for climate neutrality by thematic grouping (Figure S5), correlation matrices on the main barriers to determine similarities and differences (Figure S6), and evolution of current climate governance structures and plans for the future (Figure S7) are provided. The tables are organised to provide the descriptive statistics (Table S1), Kruskal-Wallis H Test (Table S2), summary of overarching approaches and cross-cutting patterns in 2030 city visions for climate neutrality (Table S3), and application of Z-score and Wilcoxon signed-rank test statistic to contextual factors (Table S4). The second Supplementary Material (SM2) contains the official Expression of Interest questionnaire (EOI questionnaire) of this study with the relevant questions used in the various analyses highlighted. SM2 that is also uploaded to the OSF server is accessible from the same link as contained in the article