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In the recent years, radiative cooling has emerged as a promising technology for space cooling applications. Nevertheless, radiative cooling phenomenon is dependent on weather conditions and it presents some performance limitations, meaning that the cooling capacity is limited in some climates. The radiative cooling potential is the maximum theoretical limit that can be achieved. In this study we analyse the evolution of the radiative cooling potential in Europe under the context of climate change. Radiative cooling potential maps for the period 2020–2050 are provided. The results reveal that radiative cooling potential remains constant for this period, evidencing a resilience of this technology during the following decades. We also provide a seasonal study of the potential by regions. Summer, when cooling needs are higher, is the season with the least nocturnal energy potential and the second with the highest nocturnal power potential. Shifting to all-day radiative cooling, the energy potential increases by 1.64 in winter; 2.97 in spring; 4.03 in summer and 2.2 in autumn. [ABSTRACT FROM AUTHOR]

Radiative cooling allows to cool down surfaces in a renewable way. It can be combined with solar collection functionality to produce heat and cold in a single device known as Radiative Collector and Emitter (RCE). In this paper we propose to combine a RCE with compression heat pumps to improve its performance, producing both heat and cold. Two combined systems are studied: a peak load shifting configuration where radiative cooling and cold production for demand occur simultaneously, and a decoupled configuration with an intermediate tank. The research numerically simulates both systems in different cities and climates, and compares them to a reference system based on a conventional heat pump. The results reveal and improvement of the performance in both configurations: a greater performance of the heat pump is found in the intermediate tank configuration; but after considering the electrical consumptions of all components of the system, peak load shifting configurations exhibit the best performance in most of the cities. Denver, Lleida and Rome – cities with dry climate and moderate cooling requirements – are the top cities with the greatest improvement of the performance. In the solar heating mode, the facilities show an underutilization of the collection field. • Two combinations of radiative cooling and water-water heat pump are analyzed. • The two systems supply cooling and DHW demands in a single-family house. • Simulations of combined heat pump and radiative collector and emitter are performed. • An improvement of the COP of the heat pump in combined systems is obtained. • Electricity savings up to 33% in combined systems are achieved. [ABSTRACT FROM AUTHOR]

Polyethylene has widely been used in radiative cooling applications because of high transmittance values in the atmospheric window. However, it presents optical and mechanical degradation when exposed to environmental conditions and must be replaced every few months. This paper aims to find an alternative to polyethylene to be used in a unique device, the Radiative Collector and Emitter (RCE), that combines solar collection and night-time radiative cooling. The aging evolution analysis of five cheap and market available plastic films (two low density polyethylene, one high density polyethylene, one polypropylene, and one fluorinated ethylene propylene) exposed to environmental conditions was performed. FT-IR spectra and mechanical traction tests were performed before and after 90 days of exposure to the environment. Results confirm that polyethylene undergoes a degradation process both when it is covered by a glass and when it is uncovered. However, it maintains high average transmittance values in the atmospheric window. Polypropylene has average transmittance values slightly lower than polyethylene, but its aging behaviour is better since no oxidative processes are detected when the material is covered with glass. For all this, PP-35 is an interesting candidate for night-time radiative cooling wind-shields. [ABSTRACT FROM AUTHOR]

Radiative cooling is a promising technology for space cooling. This technology can be combined with solar heating applications, enabling the production of both energy demands –heat during daytime and cold during nighttime– in a single device; thus, reducing the non-renewable primary energy consumption for space conditioning and domestic hot water. Radiative cooling and solar heating appear in different wavelength ranges, 8–14 μm and 0.25–2.5 μm respectively, thus the device must be able to switch between ranges in each mode. An adaptive cover placed on top of the radiator/absorber can provide this switch by combining materials with suitable optical properties for each mode. Another effect derived from the usage of covers is the reduction of convective heat losses, enhancing the performance of the device. This paper aims to review the existing materials used in solar collectors, and radiative coolers as well as available smart materials used in other fields for its potential use as adaptive covers for combined radiative cooling and solar heating applications. • First review on adaptive covers for combined radiative cooling and solar heating. • Overview on radiative cooling and mixed solar collector/radiative cooling system. • Empirical correlations for convection coefficients in radiators and collectors. • Discussion on main materials used in solar collectors and radiative coolers. [ABSTRACT FROM AUTHOR]

Radiative cooling is a natural process to cool down surfaces through the rejection of thermal radiation using the outer space as a cold sink, taking advantage of the transparency of the atmospheric windows (8–14 μm), which partially matches the infrared radiation band. With the development of new materials that have a high reflectivity of solar radiation, daytime radiative cooling can be achieved. This phenomenon depends on the optical properties of the surface and the local weather conditions. In this research, climatological data from 1791 weather stations were used to present detailed nighttime and all-day radiative cooling maps for the potential implementation of radiative cooling-based technologies. The paper offers a parametric study of the variation of the potential as a result of decreasing the solar reflectivity. The results show that southern Europe is the region with the highest potential while northern Europe holds more hours of available radiative cooling. After varying the solar reflectivity from 1 to 0.5 the average power reduces from 60.18 to 45.32 W/m2, and energy from 527.10 to 264.87 kWh/m2·year. For solar reflectivity lower than 0.5, all-day radiative coolers behave as nighttime radiative coolers, but power and energy values improve significantly for high values of solar reflectivity. Small variations of solar reflectivity have greater impacts on the potential at higher reflectivity values than at lower ones. [ABSTRACT FROM AUTHOR]