Africa, with a significant portion of its territory located within the tropical latitudes, experiences high cooling demands. Addressing these requirements in a renewable way is possible thanks to Radiative Cooling (RC). RC utilizes the atmospheric window from 8 to 13 µm to emit radiation to outer space, enabling the achievement of sub-ambient temperatures. A Kriging geospatial interpolation method is applied in this work to develop maps of RC potential, considering broadband emitters, for the typical meteorological year from 1991 to 2010 and predictions for 2030–2050 based on future emissions scenarios of the Intergovernmental Panel on Climate Change. A comparison is made between nighttime and all-day RC potential. The results reveal that all-day RC power potential is at least 22% higher than nighttime potential, while in terms of energy, the difference exceeds 156%. No significant variation is observed among future emissions scenarios. The average nighttime RC power potential exceeds 70 W⋅m−2, while the average all-day potential surpasses 87 W⋅m−2. Mean values for the nighttime RC energy potential are above 294 kWh·m-2, while all-day results are over 763 kWh·m-2. The potential of RC in many regions of Africa is promising and these maps will be a useful resource to estimate this RC potential.

Nowadays, renewable energies are employed to reduce fossil fuel consumption in buildings and industrial applications. Radiative cooling (RC) technology uses the Earth's natural heat radiation to cool surfaces without any electricity supply by emitting thermal radiation to outer space through the transparent atmospheric window. RC technology can produce a cooling effect both during the night and during the day. However, daytime RC is a challenge, and special materials are to be used. Materials highly reflective in the solar spectrum (0.3-2.5 mu m) $(0.3\mbox{--}2.5\,\mathrm{\mu m})$, and highly emissive in the atmospheric IR transparency window (8-13 mu m) $(8\mbox{--}13\,\mathrm{\mu m})$ are required for daytime RC technology. This study explores the influence of several parameters in the design of the daytime RC materials testing set-up (test box), aiming ultimately at an effective measurement and evaluation of RC materials during daylight hours using a test box. The approach utilizes a test box setup to assess the materials' ability to emit thermal radiation while under the influence of direct sunlight. By employing precise measurement techniques within this controlled environment, this study contributes to the identification of key parameters affecting daytime RC materials measurements. The outcomes of this investigation contribute to the ongoing efforts in the field of daytime RC, offering practical guidance for researchers, engineers, and designers involved in developing a test box for daytime RC materials testing.

This research introduces the Adaptive Radiative Collector and Emitter (ad-RCE) device, an evolution of the Radiative Collector and Emitter (RCE). The RCE has demonstrated the dual capability of producing hot water using solar collection during the day and cold water below ambient temperature using radiative cooling at night. With the development of new materials, it is now possible to achieve radiative cooling even during daytime. To increase cold production, the ad-RCE integrates daytime radiative cooling (DRC) with nocturnal radiative cooling (NRC) and solar heating (SH) in an active system. The ad-RCE improves the previous RCE as it is designed to dynamically adjust its heat and cold production in response to daily demand. By incorporating a rotating mechanism and novel DRC materials, the ad-RCE allows the transition between radiative cooling and solar heating functions while extending the cooling operation period, representing an innovative approach to harness renewable energy sources for both heating and cooling purposes. This evolution from the RCE to the ad-RCE expands upon the capabilities of the device by increasing the cooling production while reducing the surface requirements of the ad-RCE. This makes the ad-RCE more suitable for energy production in buildings and industrial applications. The paper provides a comprehensive analysis of the ad-RCE, highlighting its benefits and improvements compared to its predecessor, the RCE.

Data centre space cooling systems consume a lot of energy and will increase over the years. Therefore, it is necessary to propose new refrigeration strategies. Radiative cooling (RC) production is a renewable alternative solution with a promising future. In this work, the energy modelling of the air conditioning system of a data centre coupled to a RC emitter is carried out to explore the benefits of this technology. The system consists of a water chiller connected to a cooling coil through which air is circulated for distribution in the data centre room. The simulations were carried out for a typical summer week in Barcelona. The RC production was carried out during the night, and this power was used during the day and was implemented directly in the energy balance of the data centre room, considering emission surfaces of 80 and 60% of the total building roof, reducing the water chiller energy consumption by 13 and 10% respectively. In the transient behaviour of the temperature in the data centre room, when the RC was used to reduce the peak cooling load, a reduction of the temperatures was observed approaching to the design setpoint, therefore, the IT equipment was not affected.

Growing environmental awareness has prompted a resurgence in traditional building techniques that rely on natural or recycled materials since many believe that structures made from these resources are ecologically friendly. Using Life Cycle Assessment (LCA) for construction materials offers valuable insights into the impacts produced during their production and construction processes. This study aims to assess the environmental impacts of two different constructions—an Earthbag Building (EB) and a conventional Sahrawi Cement Blocks Building (CBB). It also determines whether it is more environmentally beneficial to construct traditionally, utilizing local materials and aligning with the principles of the circular economy, which is one of the Sustainable Development Goals (SDGs) in Europe. This study specifically examines a cradle-to-gate LCA, using the software Simapro v. 9.4.0.1. Results show that in 21 out of the 22 impact categories analyzed, the CBB performs worse, in some cases presenting an impact of 70% higher than the EB. The highest impact is obtained for fine particulate matter formation and Global Warming related to Human Health categories, whilst impact categories related to water consumption and eutrophication obtained an impact of less than 0.001 for both constructions.

This study assesses existing literature on radiative cooling through bibliometric and keyword analyses, shedding light on both quantitative and qualitative aspects of the subject. The research adheres to a systematic methodology, encompassing query formulation, data extraction, data curation, and analysis, accompanied by author interpretations and discussions. The evaluation encompasses the scrutiny of radiative cooling patents and scientific publications. For patents, trends, and geographic distribution are analyzed, while for scientific publications, a comprehensive overview of subtopics, subject areas, top journals of publication, distinctive trends, geographical distribution, affiliations, document types, and the central focus of previous studies are examined. From the results, the main questions on research diversity, dimensions, dominance, methodological approach, evolution, trends, and commercial relevance among others are discussed.From this investigation, it was found out that, although research on radiative cooling dates to the 1880 s, it is in the last decade when substantial growth was experienced across multiple disciplines. China and the United States of America emerged as the top contributors in this research domain.

The building sector is one of the main consumers of energy, being the heating and cooling, as well as the Domestic Hot Water (DHW), the highest demands.The Radiative Collector and Emitter (RCE) is a renewable technology capable of providing both heating and cooling in a single device.This innovative technology reduces the dependency on fossil fuels, as well as diminishes the carbon footprint.An evolution of the RCE, the adaptive RCE (ad-RCE), which allows night-time radiative cooling and either daytime solar collection or daytime radiative cooling is presented for a single-family house in Johannesburg, South Africa.This new concept is capable to adapt its behaviour to the energy requirements, producing either heat or cold during daytime, as well as cold during night-time.Thus, the production of heat and cold adapts to the demands of the building.By means of numerical simulation, the relation between cooling and Domestic Hot Water (DHW) demands are compared with the renewable energy produced by the ad-RCE to determine the suitability of such technology to cover the energy demands of buildings by means of renewable energy.Results show that with a proper decision on the number of hours in solar collection mode and the rest for daytime or night-time radiative cooling, the ad-RCE field could yield to annual coverages of the cooling demand of 83% and of 100% for the DHW.

Server power densities are foreseen to increase, and conventional air-cooling systems will struggle to cope with thermal demand. Single-phase immersion systems are a promising alternative to operate very intensive workload such as high-performance computing, cryptocurrencies mining or research activities. However, few companies deal with this kind of system and there is a lack of energy models that can reproduce an accurate analysis of the system behaviour. This study addresses the experimentation, data collection, and model validation of a single-phase immersion cooling system where 54 open compute project servers, each with a peak power of 400 Watts that are submerged and operated in a dielectric coolant. Results show the evolution of the thermal profile of the system under static and dynamic workloads, and it provides a correlation of server energy use under various system temperatures. The energy model is presented, validated against real data, and exploited to investigate the system response to different cooling conditions. In conclusion, the study demonstrates the validation of the energy model and supports the basis for further investigation.

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.

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 mu m and 0.25-2.5 mu m 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.

Since ancient times, raw earth has been used worldwide as a construction material. Today, it is well known for its good environmental properties of recyclability and low embodied energy along the production process. Earthen walls regulate the interior temperature of the buildings, providing comfortable temperatures with a very low carbon footprint. As a result of those advantages, earthen building techniques have been revived and used for contemporary architecture. The aim of this paper is to review the state of the art about the thermal behaviour of earthen building, including all the monitoring and simulation analysis of real earthen constructions up to now. The paper presents the different earthen techniques known nowadays, analysing the most important thermal parameters and the thermal comfort achieved with each technique. Regardless the wide differences among the analyzed cases, the authors conclude that earth building is a suitable solution in hot and arid climates, since it preserves the indoor temperature within the thermal comfort limits most part of the time without any active system.

Thermal energy storage (TES) systems can store heat or cold to be used later, under varying conditions such as temperature, place or power. TES systems are divided in three types: sensible heat, latent heat, and thermochemical. Clues for each TES system are presented in this chapter and requirements for each technology and application are given. An overview of system types and description of particular and novel applications are presented. The potential for energy saving and climate change mitigation using TES with a 10-year scenario is presented for specific cases. Finally, the CO2 mitigation potential of TES in different applications is presented.

A Radiative Collector and Emitter (RCE) is a technology which combines solar collection and radiative cooling to provide both heat and cold from renewable sources. Solar collection uses radiation coming from the Sun to heat up a fluid, while radiative cooling takes advantage of the atmospheric window to emit thermal radiation to the sky with no interference with the atmosphere to cool down a fluid. However, temperatures achieved by radiative cooling are not always suitable for cooling applications. Combining the RCE with a compression heat pump (HP) can improve the coefficient of performance (COP) of the heat pump by using a colder heat sink for the condenser, the cold produced by the RCE. A numerical analysis using TRNSYS is done to determine the improvements in the COP of the HP when combined with an RCE. Results show an increase of the COP of both the heat pump and the whole system when combined with the RCE. The COP of the heat pump is the one with a higher increase, from 2.5-3.5 to 3.5-5.

Radiative cooling is a promising technology for space cooling which can be combined with solar heating applications, enabling the production of both energy demands -heat during daytime and cold during nighttimein a single device; reducing the non-renewable primary energy consumption for space conditioning and domestic hot water. An adaptive cover allows a mode switch, enabling heat or cold production, 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. Glass covers have been used in solar heating applications; polyethylene has been widely proposed in radiative cooling applications while zincbased compounds are transparent enough to solar and infrared radiation in the atmospheric window to be used in RCE applications. Smart materials show tunability of properties of radiative surfaces but upon this time, they have not been used as covers neither in radiative cooling applications, nor in combined radiative cooling and solar heating applications.

Nowadays, climate change impact is becoming more important in our daylife and the use of renewable energy sources to cover the space conditioning and Domestic Hot Water (DHW) demands is growing every year. In this study, a new device that works with renewable energies and combines two different concepts, radiative cooling and thermal solar collection, is presented. The device is called Radiative Collector and Emitter (RCE) and it consists of a modified solar collector based on an adaptive cover. The absorber is covered by a polyethylene film and the glass of the solar collector is removed during the night to allow the radiative cooling effect. Due to this adaptive cover, during daytime the greenhouse effect is allowed because of the glass cover, favoring the solar collection; and during nighttime, radiative cooling is allowed through the polyethylene film in the same device. The adaptive cover allows the different properties of the materials to be used according to its mode of operation. This equipment has been experimentally tested during summertime 2019, in the University of Lleida, where the climate corresponds to a Semi-Arid Climate (BSk according to Koppen and Geiger climate classification). Results show that the RCE performs similarly to a solar collector during the day, with average heating values of 573.69 W/m(2), and is able to provide extra cooling at night, at an average cooling rate of 15.57 W/m(2).

Nowadays space conditioning with renewable energy is one of the highest challenges of our society. Solar collection is a suitable source of energy for domestic hot water and space heating, but there is no green source to cool the spaces during hot periods or for hot climates. Radiative cooling seems to be a feasible solution for it. Elsewhere the Radiative Cooler Emitter (RCE) is presented, a device with an adaptive cover concept that combines both functionalities: solar collection during daytime and radiative cooling during nighttime. In this study, the solar and IR transmittances are analyzed for five samples: polycarbonate, methacrylate, and three commercial samples of low density polyethylene (LDPE): 17 mu m, 50 mu m and 200 mu m). The aging of 50 mu m low density polyethylene film is also studied during two months of environmental exposure in a RCE prototype (summer 2019). Presence of double bonds and C=O groups are detected, which implies a degradation of the polyethylene during the experimental campaign.