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
Optically modulated passive broadband daytime radiative cooling materials can cool cities in summer and heat cities in winter
(MDPI, 2022) Khan, Ansar; Carlosena Remírez, Laura; Feng, Jie; Khorat, Samiran; Khatun, Rupali; Doan, Quang-Van; Santamouris, Mattheos; Ingeniería; Ingeniaritza
Broadband passive daytime radiative cooling (PDRC) materials exhibit sub-ambient surface temperatures and contribute highly to mitigating extreme urban heat during the warm period. However, their application may cause undesired overcooling problems in winter. This study aims to assess, on a city scale, different solutions to overcome the winter overcooling penalty derived from using PDRC materials. Furthermore, a mesoscale urban modeling system assesses the potential of the optical modulation of reflectance (ρ) and emissivity (ε) to reduce, minimize, or reverse the overcooling penalty. The alteration of heat flux components, air temperature modification, ground and roof surface temperature, and the urban canopy temperature are assessed. The maximum decrease of the winter ambient temperature using standard PDRC materials is 1.1 ◦C and 0.8 ◦C for daytime and nighttime, respectively, while the ρ+ε-modulation can increase the ambient temperature up to 0.4 ◦C and 1.4 ◦C, respectively, compared to the use of conventional materials. Compared with the control case, the maximum decrease of net radiation inflow occurred at the peak hour, reducing by 192.7 Wm−2 for the PDRC materials, 5.4 Wm−2 for ρ-modulated PDRC materials, and 173.7 Wm−2 for ε-PDRC materials; nevertheless, the ρ+ε-modulated PDRC materials increased the maximum net radiation inflow by 51.5 Wm−2 , leading to heating of the cities during the winter.
Open Access
On the energy potential of daytime radiative cooling for urban heat island mitigation
(Elsevier, 2020) Carlosena Remírez, Laura; Ruiz-Pardo, Álvaro; Feng, Jie; Irulegi, Olatz; Hernández-Minguillón, Rufino J.; Santamouris, Mattheos; Ingeniería; Ingeniaritza
The 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.
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
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.
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
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
Experimental development and testing of low-cost scalable radiative cooling materials for building applications
(Elsevier, 2021) Carlosena Remírez, Laura; Andueza Unanua, Ángel María; Torres, Luis; Irulegi, Olatz; Hernández-Minguillón, Rufino J.; Sevilla Moróder, Joaquín; Santamouris, Mattheos; Ingeniaritza; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería; Ingeniería Eléctrica, Electrónica y de Comunicación; Gobierno de Navarra / Nafarroako Gobernua
Urban overheating has a serious impact on building energy consumption. Daytime radiative cooling materials are an interesting passive solution for refrigeration. However, their costs and complex manufacturing hinder their current application. In this study, a series of scalable and lowcost daytime radiative cooling (DTRC) materials were designed, fabricated, and tested in a moderate climate (Cfb-Köppen-Geiger classification) and compared to aluminum and Vikuiti. The methodology was: i) material selection and design, (ii) optimization, (iii) fabrication, (iv) characterization, and (v) testing. The materials were fabricated using different substrates, aluminum and Vikuiti, and two kinds of formulations for the emissive layers based on silica-derived polymer polymethylsilsesquioxane (PMSQ) with embedded silica nanoparticles. The resulting aluminum DTRC materials had a mean solar reflectivity of 0.7 and 0.34 emissivity in the atmospheric window, the samples with Vikuiti had 0.97 and 0.89, respectively. During the experiment, the samples were exposed to different ambient conditions without a convection barrier and were contained in an extruded polystyrene board to eliminate conduction. The samples reached 7.32 °C and 9.13 °C maximum surface temperature reduction (below ambient) during the day and night, respectively. The samples with the commercial substrate achieved a mean reduction of 3.72 °C below ambient temperature. Although the aluminum samples did not achieve subambient cooling throughout the entire day, the emissive layer reduced the sample's surface temperature by an average of 1.7 °C. The PMSQ radiative cooling materials show great potential for future building applications. Suitability under different climates and experimental settings should be done to test broad applicability.
Open Access
The trend of heat-related mortality in Spain
(Springer Nature, 2022) Carlosena Remírez, Laura; Carlosena Remírez, Alicia; Ingeniería; Ingeniaritza
Rapid urbanization, increasing and aging population combined with rising temperatures and extreme weather events present severe worldwide challenges for the near future. Spain is not an exception; characterized by one of the highest life expectancies in Europe and a very high urban density in its cities. Moreover, its diverse climate, ranging from arid to wet, hot, and cold regions, is affected by heatwaves during the summertime. Increases in temperatures require physiological adaptation and can be a health burden. People suffering from obesity, respiratory, cardiovascular diseases, diabetes, or renal failures have greater difficulty adapting to heat events. Moreover, the Spanish built environment presents some overheating challenges, as half of its building stock was constructed before 1980. Green infrastructure enhances the urban climate and thermal comfort; however, the distribution of green areas in Spain is insufficient. This chapter presents the current trends of heat-related mortality in Spain, summarizing the most relevant findings in research. A total of 27 published papers on heat-related mortality are reviewed and discussed. Additionally, data on heatwaves and mortality due to excess heat are presented. Current mitigation techniques, such as implementing heathealth prevention plans and other solutions, are discussed to establish systems to cope with heatwaves and to improve the quality of life of the Spanish population. However, more research with standardized procedures is needed. Furthermore, we need to quantify the effectiveness of the already implemented strategies to determine the most suitable for every Spanish climate and city condition.
Open Access
On the winter overcooling penalty of super cool photonic materials in cities
(Elsevier, 2021) Khan, Ansar; Carlosena Remírez, Laura; Khorat, Samiran; Khatun, Rupali; Doan, Quang-Van; Feng, Jie; Santamouris, Mattheos; Ingeniería; Ingeniaritza
Daytime 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.