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In the past decades, spectrally selective windows, such near-infrared absorbing (NIR) glazings, low-e glazings, and various smart windows, have been widely studied, developed, and applied in different climatic conditions for building energy-saving purposes. One major pathway of the spectrally selective glazings to achieve energy savings is through solar radiation control, either by NIR reflection or absorption. This review concerns the NIR absorbing glazings with the limited subset of ion-based and nanoparticle-based glazings. In detail, each category's spectral absorbing materials are further distinguished into sub-categories, and then their underlying mechanisms of spectral selectivity were elaborated, as well as their application status in terms of manufacturing, cost, and commercialization popularity. To further advise the application in the building sector, we comparatively evaluated the performance of each kind of glazing in terms of the light and heat decoupling ability and visual qualities (i.e., color rendering). Finally, the challenges and future directions of the NIR absorbing glazings to bridge the gap between lab research and large-scale practical applications are illustrated.

Due to superior energy efficiency and emission-reducing potential, air source heat pumps (ASHPs) have been widely used in space heating and domestic water heating. However, the heating seasons usually coincides with the serious air pollution, hence particulate fouling appears on ASHPs' outdoor coils repeatedly, despite being de-fouled periodically. In this study, four levels of fouling, namely none fouling (0 g/4 m2), mild fouling (15 g/4 m2), moderate fouling (40 g/4 m2) and severe fouling (70 g/4 m2), were concretized on a finned tube heat exchanger successively, followed by experimentally investigating the negative effects of fouling on the heat transfer performance of an air source heat pump water heater (ASHPWH). Results demonstrated that the effects of fouling on the performance of ASHPs in heating mode would be exacerbated with decreased air temperature. In addition, the frosting performances at different levels of fouling were evaluated quantitatively, by depicting the frosting evaluation plots. The frosting evaluating plots suggested that fouling would expand the air temperature and relative humidity (RH) ranges where frosting appears, and would hasten frosting process. As verification, signal factor experiments were carried at different levels of fouling. The experimental results confirmed that the increase of fouling level would result in faster frosting process, but smaller final frost accumulation mass.

Frosting has always been a crucial problem for air source heat pumps (ASHPs) operated in heating mode. Quantitative evaluation of frosting is of vital importance to the development of technologies against frosting. Although frosting maps have been developed in many studies, they are specific for unique systems. To evaluate the frosting performance of arbitrary system, a semi-experimental method, to depict frosting evaluation plot, was proposed in the present study. In the frosting evaluation plot, frosting region was clarified, and the frosting driving forces with the effect air temperature and relative humidity (RH) were evaluated, through theoretical calculation of Gibbs free energy change. After that, experiments were conducted to verify the frosting evaluation plot, and the results demonstrated the present method was feasible. In some experimental cases, the inlet segment of the heat exchanger escaped from frosting but the outlet segment frosted. As implementation of the semi-experimental method, the methodology was utilized to clarify the air temperature and RH ranges causing uneven frosting. In addition, the frosting evaluation plot with impact of air velocity was drawn. The results suggested that, increased air velocity restrained frosting, and reduced the chance of uneven frosting.

The amount and shape of intermetallic compounds (IMCs) may influence the properties of the Al–Mg dissimilar welded joints. In the present study, friction stir welding (FSW) assisted with Zn interlayer was designed to weld Mg to Al alloys. The effects of the Zn interlayer on the microstructure and mechanical properties of the joints were studied in detail. The results indicated that Zn interlayer could improve performance of the joints and inhibit the formation of Mg/Al IMCs, which were replaced by Mg–Zn and Al–Zn solid solutions. The maximum tensile strength of the joint with Zn interlayer was 102 MPa, which was elevated about 27% compared with the joint without Zn interlayer.

With the increase of welding speed from 75 to 150 mm/min, the grain size of the nugget zone first decreased and then increased, and the smallest grain size was obtained at 100 mm/min. The maximum tensile strength of 445 MPa was achieved at the welding speed of 100 mm/min, equivalent to 70% of the base metal. The hardness value of the heat-affected zone increased with the rising welding speed. Joint hardness was affected by precipitated phases and it decreased overtly from thermo-mechanically affected zone to heat-affected zone. Owing to the fact that a number of big precipitates clustered in the heat-affected zone, the strengthening effect in spray formed ultra-high strength 7055 aluminum alloy was weakened which caused the hardness of the joint to reduce remarkably. Because of the recrystallization, most of the phases in nugget zone were dissolved and the rest were similar to those in the base metal, while AlCuMg phase and Al2Cu phase precipitated in heat-affected zone. The phase precipitated in the nugget zone and heat-affected zone decreased gradually with the increase of the welding speed.

Metallic nanoparticles exhibit localized surface plasmon resonance, which gifts them with enhanced solar energy absorption in a special band. With an adjustable plasma resonance band from the visible light to the infrared, silver nanorods (AgNRs) are potential candidates for energy saving application. In this research, the optical properties of AgNRs were investigated by the Discrete Dipole Approximation (DDA) approach, and the spectral response of AgNR/PMMA nanocomposites were studied by a Monte Carlo method. Meanwhile, the ideal window for high luminous transmittance and high thermal radiation insulation was identified, and then eight hybridizations of AgNRs were proposed to match the ideal window. Based on these eight hybridizations, related performance comparisons were conducted. The cases study shows that when the diameter of AgNRs decreases from 30 to 10 nm, both the radiation shielding performance and luminous transmittance can be improved. While as the diameter of AgNRs decreases from 10 to 5 nm, there are insignificant changes in radiation shielding performance or luminous transmittance. The optimal AgNR/PMMA nanocomposites proposed in this study were demonstrated to be positive solutions for light/heat splitting, as they can ensure higher luminous transmittance than 50%, while blocked the solar radiation by about 80%.

High cell temperature of PV modules would reduce electrical efficiency and hinder the development of photovoltaic application. Many potential cooling channels have been proposed for PV modules cooling but perform inefficiently, due to the insufficient heat transfer between the cooling water and PV modules. In current research, a PV/T system with a special cooling channel based on field synergy theory, was designed to optimize the performance of PV/T systems. The performance of the new PV/T system was studied numerically, and mathematical models were validated with the experimental data. Results indicated that electrical efficiency of PV modules increased by 0.5% (from 11.4% to 11.9%) when the solar radiation decreased from 1200 to 300 W/m2. The electrical efficiency increased 1.11% (from 10.8% to 11.9%) as the inlet mass flowrate of cooling water increased from 0.0018 to 0.018 kg/s at the inlet temperature of cooling water of 20 °C. Additionally, the special channel with shark dorsal fin type sawtooth or regular type sawtooth, had the optimal parameter values, with the channel depth of 0.05 m, the sawtooth peak of 0.035 m and the sawtooth width of 0.01 m. The average cell temperature with the optimized channel was 6.05 °C lower than the conventional smooth channel, and the new cooling channel performed better with a high solar radiation.

The influence of wire feeding speed during laser welding with a filling wire was investigated by high-speed imaging and mechanical analysis of the droplet. A force relationship was found to analyze the droplet transition behavior at the end of the welding wire in the narrow-gap groove. Welding defects, mainly including nonfusion and porosity, were studied to reveal the formation mechanism and propose affective solutions. In this paper, it was found that the droplet transition was determined by the position of the melting end of the wire in the narrow-gap groove under the same parameters. The sidewall transition, the liquid bridge transition, and the spreading transition were found at different wire feeding speeds. As the wire feeding speed increases from 3 to 6 m/min, the weld depth increased 40%, the maximum weld width decreased 16%, and the minimum weld width increased 8%. More nonfusion and porosity defects and poor weld formation would appear at excessive wire feeding speed.

Air source heat pumps (ASHPs) have worldwide applications due to their superior performance in energy saving and environmental friendliness. Two challenges of frosting and fouling for outdoor coils of ASHPs were of attention individually. This study investigated the effect of PM2.5 air pollution on the frosting process of the outdoor evaporator of ASHPs. The system performance and frosting characteristics of ASHPs with different environmental parameters were measured experimentally. The results showed that PM2.5 could significantly promote the frosting process when the concentration was greater than 146 μg/m3. Under the condition of severe pollution, both the experimental data and evaporator surface images reflected the shortening of the frost column generation period and frost layer growth period. On the theoretical basis of the three periods of the frosting process, the frost layer growth period was further divided into transition period and frost thickening period. At the same time, in order to quantitatively analyze the difference of frosting rate between severe pollution condition and no pollution condition, frosting rate ratio (FRR) was defined to reflect the influence of PM2.5 on frosting in different periods. Based on the analysis of the experimental results under different temperature and humidity conditions, it was considered that the frosting zone could be divided into two regions. In the Region I where the moisture content of the air was very low, the effect of PM2.5 on the frosting was weakened, and the FRR was positively correlated with the moisture content of the air. While in Region II with a relatively high moisture content of air, the FRR was positively correlated with the mass ratio of PM2.5 to moisture.