Open Access
Worldwide potential of emissive materials based radiative cooling technologies to mitigate urban overheating
(Elsevier, 2023) Carlosena Remírez, Laura; Ruiz-Pardo, Álvaro; Rodríguez-Jara, Enrique Ángel; Santamouris, Mattheos; Ingeniería; Ingeniaritza; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Radiative cooling has gained significant attention in recent years for its passive heat evacuation capabilities. Numerous materials have been developed, but comparing their cooling effectiveness has proven challenging due to inconsistent experimental conditions. This study aims to bridge this gap by evaluating the heat evacuation potential of various radiative cooling materials under consistent climatic conditions. Using a validated heat transfer model, the performance of eleven materials was simulated in twenty-two Urban Overheating-affected cities. The assessment considered factors such as radiated heat losses, solar heat gains, and convective heat losses to gauge the cooling power of each material. The simulation assumed an active system where the materials were placed on a highly conductive, uninsulated surface, akin to having a fluid at a constant temperature beneath. The ability of materials to radiate heat and cool down depends on their optical properties. The findings suggest limited benefits in equatorial climates, with an average monthly total heat exchanged (MATHE) of −19.73 kWhm−2. Materials displayed consistent behavior throughout the year in climates with high relative humidity levels. Climates with elevated ambient temperatures derived the greatest advantages from strictly selective and highly reflective materials that emitted within the atmospheric window. Arid climates showed potential during transition times (MATHE -74.5 kWhm−2), while warm temperate climes benefited during summer months (MATHE -112.1 kWhm−2). In snow zone climates, the system could be utilized year-round for cooling-intensive scenarios, with a MATHE of −203.8 kWhm−2. This study evaluates radiative cooling materials' effectiveness in different climates, informing energy-efficient cooling applications.
Open Access
Urban cooling potential and cost comparison of heat mitigation techniques for their impact on the lower atmosphere
(Springer, 2023) Khan, Ansar; Carlosena Remírez, Laura; Khorat, Samiran; Khatun, Rupali; Das, Debashish; Doan, Quang-Van; Hamdi, Rafiq; Aziz, Sk Mohammad; Akbari, Hashem; Santamouris, Mattheos; Niyogi, Dev; Ingeniería; Ingeniaritza
Cool materials and rooftop vegetation help achieve urban heating mitigation as they can reduce building cooling demands. This study assesses the cooling potential of different mitigation technologies using Weather Research and Forecasting (WRF)- taking case of a tropical coastal climate in the Kolkata Metropolitan Area. The model was validated using data from six meteorological sites. The cooling potential of eight mitigation scenarios was evaluated for: three cool roofs, four green roofs, and their combination (cool-city). The sensible heat, latent heat, heat storage, 2-m ambient temperature, surface temperature, air temperature, roof temperature, and urban canopy temperature was calculated. The effects on the urban boundary layer were also investigated. The different scenarios reduced the daytime temperature of various urban components, and the effect varied nearly linearly with increasing albedo and green roof fractions. For example, the maximum ambient temperature decreased by 3.6 °C, 0.9 °C, and 1.4 °C for a cool roof with 85% albedo, 100% rooftop vegetation, and their combination. The cost of different mitigation scenarios was assumed to depend on the construction options, location, and market prices. The potential for price per square meter and corresponding temperature decreased was related to one another. Recognizing the complex relationship between scenarios and construction options, the reduction in the maximum and minimum temperature across different cool and green roof cases were used for developing the cost estimates. This estimate thus attempted a summary of the price per degree of cooling for the different potential technologies. Higher green fraction, cool materials, and their combination generally reduced winds and enhanced buoyancy. The surface changes alter the lower atmospheric dynamics such as low-level vertical mixing and a shallower boundary layer and weakened horizontal convective rolls during afternoon hours. Although cool materials offer the highest temperature reductions, the cooling resulting from its combination and a green roof strategy could mitigate or reverse the summertime heat island effect. The results highlight the possibilities for heat mitigation and offer insight into the different strategies and costs for mitigating the urban heating and cooling demands.
Open Access
Exploring the meteorological impacts of surface and rooftop heat mitigation strategies over a tropical city
(American Geophysical Union, 2023) Khan, Ansar; Khorat, Samiran; Doan, Quang-Van; Khatun, Rupali; Das, Debashish; Hamdi, Rafiq; Carlosena Remírez, Laura; Santamouris, Mattheos; Georgescu, Matei; Niyogi, Dev; Ingeniería; Ingeniaritza
Different 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.
Open Access
Harnessing the potential of radiative cooling for the built environment: a new comprehensive protocol for materials' characterization
(Elsevier, 2024-07-26) Chiatti, Chiara; Marchini, Francesco; Fabiani, Claudia; Kousis, Ioannis; Carlosena Remírez, Laura; Pisello, Anna Laura; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
The pursuit of novel materials for radiative cooling (RC) holds immense promise in addressing building energy saving and urban overheating. RC capitalizes on the principle of dissipating heat energy into space, specifically through the atmospheric window between 8-13 μm, to achieve passive cooling of surfaces. However, the absence of a standardized and reliable methodology for characterizing RC materials has introduced inconsistencies in research findings, impeding collective advancements in the field. To address this issue, a dedicated experimental protocol is here introduced, as a unifying benchmark for the characterization of RC materials. This procedure aims to provide comprehensive, consistent, and precise data regarding crucial properties of RC cooling materials, including thermal stability, spectral radiative behavior, and thermal performance under both controlled and realistic boundary conditions. To demonstrate the effectiveness of our proposed methodology, we designed and implemented a comparative study involving an aluminum-based and a Vikuiti-based sample incorporating a silica-derived polymer as an emissive layer. Notably, our findings reveal that the Vikuiti prototype outperforms the aluminum counterpart, primarily attributable to its superior solar reflectance and thermal emittance characteristics. This research not only advances our understanding of RC materials but also offers a crucial step toward uniform characterization methods that can catalyze further research and scaling up of radiative cooling technologies.
Open Access
Towards cooling concrete: evaluation of cement and cement composites under realistic climatic conditions
(Elsevier, 2025-04-15) Torres García, Alicia E.; Agbaoye, Ridwan O.; Carlosena Remírez, Laura; Goracci, Guido; Lezaun Capdevila, Carlos; Dolado, Jorge S.; Beruete Díaz, Miguel; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería; Ingeniaritza
Finding scalable, cost-effective and environmentally safe solutions for Passive Daytime Radiative Cooling (PDRC) is essential for addressing energy and climate challenges. This study demonstrates the feasibility of achieving PDRC using only cement-based compounds, without the need for additional whitening agents or other additives. Unlike previous approaches that rely on external additives, the proposed solution leverages two fundamental cement phases—portlandite and tobermorite—offering a scalable and low-impact alternative. The research evaluates the radiative cooling potential of these phases, along with two widely used cements—white cement (WC) and ordinary Portland cement (OPC), by analyzing and comparing their homogenized complex permittivities, derived using the Kramers-Kronig (KK) method. Simulations were conducted to assess the cooling power over one year across three different climates using actual meteorological data. The portlandite exhibits positive Pcool, maintaining a temperature equal to or below the ambient temperature more than 90 % of the time in dry desert and warm temperate locations. Indoor controlled measurements results reveal that portlandite (CH) may exhibit temperatures 15 °C lower than OPC and 5 °C lower than WC.
Open Access
Monitoring the thermal potential of low-cost radiative cooling materials under static and dynamic conditions of exposure
(Morlacchi Editore University Press, 2023) Chiatti, Chiara; Kousis, Ioannis; Fabiani, Claudia; Carlosena Remírez, Laura; Pisello, Anna Laura; Ingeniería; Ingeniaritza
Reflecting the radiation of the sun while emitting thermal radiation to cold outer space has proven to be an effective solution against urban overheating. The latter severely impact the energy consumption of buildings, outdoor pollution levels, and heat-related morbidity and mortality, which is why recent research has focused on new advanced mitigation technologies to be implemented in cities. Passive radiative cooling (PRC) has the potential to provide a temperature lower than ambient without any energy consumption. While conventional cooling prototypes reject heat to the air, PRCs reject heat to the outer atmosphere emitting radiation mainly in the 8-13 ¿m range, i.e., the so-called atmospheric window. This work investigates the thermal behavior of different radiative cooling materials under various exposure conditions to examine their effective cooling potential. The basic structure of the samples comprehends a highly reflective substrate (aluminum or Vikuiti) and a silica-derived emissive layer. After a preliminary characterization under controlled environmental settings, the samples were exposed outdoors, and their superficial temperature was monitored during the central hours of the day. Comparisons among samples and a benchmark aluminum reference layer were made, also considering the weather data collected during the days of exposure. Although the samples did not reach sub-ambient temperatures during the monitoring, the emissive layer significantly reduced the surface temperature. Furthermore, the effect of a tunable intermediate layer placed between the substrate and the emissive element was demonstrated to positively impact the thermal performance of the sample, thanks to its capability of changing the emissivity spectrum with temperature.
Open Access
Evaluating the cradle-to-gate environmental impact and cooling performance of advanced daytime radiative cooling materials to establish a comparative framework for a novel photonic meta-concrete
(Springer, 2024-10-08) Adams, Nick; Carlosena Remírez, Laura; Allacker, K.; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
Background By the end of 2050, it is expected that 68% of the population will live in urban areas. A higher density of people living in cities generates an increased urban heat island. Radiative cooling (RC) materials are proposed as a key strategy to mitigate global warming and urban heating. The Horizon 2020 project MIRACLE aims at developing a new RC material based on conventional concrete. This paper presents a framework developed for comparing both the cradle-to-gate environmental impact and cooling potential of the newly developed photonic meta-concrete (or any other new RC material) with existing RC materials. The framework is applied to various RC materials using the generic Ecoinvent v3.6 database. The impact assessment method is in line with the Belgian life cycle assessment method for buildings and covers the 15 environmental impact categories of the EN15804:A2. The cooling performance is assessed by implementing the material spectral emissivity into a thermal model for Brussels and Madrid. Results The study shows that the sputtering process contributes over 75% to the cradle-to-gate environmental impact of several RC materials, while materials produced without this process, have significantly lower impacts. The assessment of the cooling potential showed that convection heat gains make it difficult to create an all-year round cooling material. The comparison with a conventional building material, a concrete roof tile, hence shows great potential for these RC materials as heating gains during summer are significantly reduced. Analysing cooling performance alongside environmental impact, the study identified two RC materials, i.e. D6 and D10, as the most preferred in both Brussels and Madrid, considering their lower environmental impact and superior performance. Conclusions The literature review revealed that a standardised way to assess and benchmark RC materials based on their cradle-to-gate environmental impact and cooling performance is lacking to date. This paper hence presents, for the first time, a method to compare RC materials considering these two characteristics. This method allows to identify the most competitive RC materials, which will serve in our study to benchmark the newly developed photonic meta-concrete.