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
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
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
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.

Carlosena Remírez, Laura

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