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Cooling terrestrial objects for thermoregulation is a significant challenge in this decade due to the rapidly increasing world energy consumption and human daily life demands. Furthermore, the conventional cooling technologies are energy-intensive, as predominantly vapor compression-based cooling systems consume a substantial amount of electricity. Therefore, the development of energy-efficient alternative cooling techniques with fewer environmental footprints is desirable. Here, we present a porous polymer coating with P(VDF-HFP) as a passive radiative cooler to investigate the cooling performance under various conditions. The reflectivity within the visible wavelength range (0.38-0.78 μm) and the ultraviolet visible-near infrared wavelength range (0.25–2.5 μm) of a 2.0 mm thick porous polymer radiative coating (PPRC) are about 98% and 94%, while the emissivity in the main atmospheric window (8–13 μm) is up to about 97%, indicating that the proposed PPRC is a potential candidate to achieve a notable radiative cooling performance. By taking the meteorological location of Shanghai, China, as an example, the radiative cooling performance is tested for a whole year. The PPRC cooler can constantly exhibit excellent cooling performance throughout all-year and show the best in winter, followed by spring, autumn, and summer under typical fine weather conditions. We investigated quantitatively the impact of different environmental conditions, including cloud amount, air quality, relative humidity, and ambient temperature on the performance of the radiative cooler, which is essential for real-world deployment. For example, the PPRC cooler can achieve a temperature drop of up to about 6.9 °C at the relative humidity of 38% and only 3.9 °C at the relative humidity of 68% at 15:00–17:00 in summer when other environmental conditions are similar. As the passive cooling technique is expected to play an increasing role in the future, this work facilitates the fabrication of environmentally friendly PPRC cooler for energy-saving applications.

Sub-ambient diurnal radiative cooling is an effective, environment-friendly and energy-saving passive cooling approach as it cools a surface without anthropogenic energy input. The cooling power of a radiative cooler is strongly influenced by the meteorological conditions, in particular humidity, on which quite a few investigations have been conducted so far. However, the cooling power evaluation of a radiative cooler usually considers the radiative cooler to be isothermal, which ignores the interior temperature difference resulted from the low thermal conductivity of the prevalent radiative materials, leading to an overestimation of the cooling power. Therefore, this work focuses on the theoretical evaluation of the radiative cooling power along with the interior temperature distribution under varying humidity conditions through incorporating coupled heat and radiation transfer approach. The results show that higher relative humidity leads to less cooling power and minor interior temperature difference in the radiative cooler. In addition, the position of the lowest temperature inside the radiative cooler, which is usually taken at the bottom of the radiative cooler, gradually approaches the surface facing outer space with the increase in humidity during the diurnal time. Our work provides a unique viewpoint for predicting the cooling power by taking interior temperature non-uniformity resulted from the low thermal conductivity into account, which elaborates a vivid picture of the evolution of radiative cooling power as well as the internal temperature distribution with the variation of humidity. Such an approach is beneficial for the further design, efficiency enhancement and on-site deployment of radiative coolers.

Porous liquids (PLs) have both liquid fluidity and solid porosity, thereby offering a variety of applications, such as gas sorption and separation, homogeneous catalysis, energy storage, and so forth. In this research, canopies with varying structures were utilized to modify porous silica nanoparticles to develop Type I PLs. According to experimental results, the molecular weight of canopies should be high enough to maintain the porous materials in the liquid state at room temperature. Characterization results revealed that PL_1_M2070 and PL_1_AC1815 displayed low viscosity and good fluidity. Both low temperature and high pressure positively influenced CO

Paraffin waxes are organic phase change materials possessing a great potential to store and release thermal energy. The reversible solid–liquid phase change phenomenon is the under-lying mechanism enabling the paraffin waxes as robust thermal reservoirs based on inherently high latent heat (i.e., ~200–250 J/g). However, the main drawback of paraffin waxes is their inability to expedite the phase change process owing to low thermal conductivity (i.e., ~0.19–0.35 Wm−1 K−1). This drawback has long been documented as a technological challenge of paraffin waxes especially for temperature-control applications where faster thermal storage/release is necessitated, encompassing thermal management of batteries, thermoelectric modules and photovoltaic panels. Besides, sustaining the solid-like form of paraffin waxes (shape-stability) is also recommended to avoid the liquid drainage threats for crucial applications, like thermal management of buildings and fabrics. These objectives can be met by developing the paraffin wax-based thermal composites (PWTCs) with help of various thermal reinforcements. However, PWTCs also encounter severe challenges, probably due to lack of design standards. This chapter attempts presenting the recent advances and major bottlenecks of PWTCs, as well as proposing the design standards for optimal PWTCs. Also, the fundamental classification of phase change phenomenon, paraffin waxes and potential thermal reinforcements is thoroughly included.

Evaporative cooling of the dehumidified air in a desiccant cooling system with the aid of solar energy is an attractive energy saving option to cool the process air for air conditioning purposes. This paper is concerned with the dynamic simulation and performance analysis of three configuration schemes of a solar-based ventilation mode desiccant cooling system energized by a photovoltaic-thermal (PV/T) solar collector for the weather conditions of Lahore (31.52°N, 74.36°E). In configuration-1 (C-1), the auxiliary heater is installed in the air conditioning loop to heat the return air up to the desired regeneration temperature. In configuration-2 (C-2), the auxiliary heater is installed in the solar heating loop to raise the temperature of the liquid water to a certain elevated temperature. The configuration-3 (C-3) is similar to C-2 except there are no evaporative coolers and all the cooling is achieved via conventional vapor compression chiller. The primary energy savings, solar fraction, and the thermal efficiency of the solar collector are the energetic performance parameters which are used to compare the performance of three configuration schemes and to analyze the influence of various parameters such as regeneration temperature, solar collector size and tilt, flow rates, and storage volume. The simulation results demonstrated that the C-1 scheme performs best in terms of solar fraction and primary energy savings while C-3 schematic resulted in the least values of primary energy savings.

The enhanced cooling performance and the reduced operational cost of the integrated radiative sky coolers are essentially necessitated in a wide range of applications, such as cooling of buildings, electronic devices, solar cells, power plants and personal wears, etc. The radiative sky coolers are enabled by radiating heat into deep space and reflecting sunlight without external energy input, thereby providing passive cooling. Previously, radiative sky cooling was limited to nocturnal applications; however, recent advancements in nanotechnology and metamaterials have altogether led to achieve sub-ambient temperatures under direct solar irradiation, creating diurnal applications. In addition to elaborate radiative heat transfer mechanism and evaluate the corresponding limitations, this review puts forth an in-depth study on the structural characteristics of broadband and selective band radiative sky coolers, the latest advancements in radiative materials and emerging applications of the radiative sky coolers. Most importantly, valuable insights are discussed regarding the barriers and scalability of radiative sky coolers on the commercial scale. It is therefore anticipated that a broader picture of the recent progress about radiative sky cooling as presented herein provides a great potential to boost up energy-saving, resolve water-scarcity, maximize power generation, minimize urban heat effects and so forth.