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With the continuous deepening of China's rural construction and development, people's living conditions are improved day by day, while accompanied by energy and environment crisis issues. This paper mainly analyzes the energy consumption pattern and the indoor environment of rural households in China and discusses the energy-saving optimization strategies for improving the thermal environment of buildings. Questionnaire surveys and field surveys were conducted in three villages in Guanghan, China. The measurement results show that the annual indoor temperature range of the region in the summer is 15–31 °C and the relative humidity range is 34%-96%. The average indoor temperatures in summer and winter are 28 °C and 16 °C respectively. The indoor thermal environment of rural buildings is usually poor and cannot meet the requirements of Chinese standards. At the same time, the architectural design and energy consumption pattern of rural households are different from those in urban areas as countryside has unique characteristics. Finally, we put forward certain energy-saving improvement measures at the end of the article.

A transparent radiative cooling (T-RC) film with low transmittance in solar spectra and selectively high emissivity in the atmospheric window (8–13 μm) is applied on roof glazing for building energy saving. To evaluate the performance of the T-RC film, two identical model boxes (1.0 m × 0.6 m × 1.2 m, L × W × H) were constructed and the inside air temperatures were measured in August in Ningbo, China. Results show that the maximum temperature difference between the two model boxes with and without the T-RC film was 21.6 °C during the experiment. A whole building model was built in EnergyPlus for the model box. With a good agreement achieved between the calculation results and the measured temperature data, the experimentally validated EnergyPlus model was then extended to an 815.1 m2 exhibition building with roof glazing to analyze the annual air conditioning (AC) energy consumption. The results show that by incorporating both the T-RC film's cooling benefit in summer and heating penalty in winter, the annual AC energy consumption of the exhibition building can be reduced by 40.9–63.4%, varying with different climate conditions.

In order to solve the problems of low thermal conductivity and easy liquid leakage of a stearic acid (SA), the composite phase change material(PCM) was prepared by adding boron nitride (BN) and expanded graphite (EG) to melted SA, and its thermal conductivity, crystal structure, chemical stability, thermal stability, cycle stability, leakage characteristics, heat storage/release characteristics, and temperature response characteristics were characterized. The results showed that the addition of BN and EG significantly improved the thermal conductivity of the material, and they efficiently adsorbed melted SA. The maximum load of SA was 76 wt. % and there was almost no liquid leakage. Moreover, the melting enthalpy and temperature were 154.20 J • g − 1 and 67.85°C, respectively. Compared with pure SA, the SA/BN/EG composite showed a lower melting temperature and a higher freezing temperature. In addition, when the mass fraction of BN and EG was 12 wt. %, the thermal conductivity of the composite was 6.349 W • m−1 • K−1, which was 18.619 times that of SA. More importantly, the composite showed good stability for 50 cycles of heating and cooling, and the SA / BN / EG-12 hardly decomposes below 200°C, which implies that the working performance of the composite PCM is relatively stable within the temperature range of 100°C. Therefore, the composite can exhibit excellent thermal stability in the field of building heating.

Radiative cooling (RC) shows good potential for building energy saving by throwing waste heat to the cosmos in a passive and sustainable manner. However, most available radiative coolers suffer from low cooling flux. The situation becomes even deteriorated in the daytime when radiative coolers are exposed to direct sunlight. To tackle this challenge, an idea of employing both a spectrally selective cover and a spectrally selective emitter is proposed in this study as an alternative approach. A comparative study is conducted among four RC modules with different spectral characteristics for the demonstration of how the spectral profiles of the cover and the emitter affects the RC performance. The results under given conditions show that the RC module with a spectrally selective cover and a spectrally selective emitter (SC/SE) reaches a net RC power of 62.4 W/m2 when the solar radiation is 800 W/m2, which is about 1.8 times that of the typical RC module with a spectrally non-selective cover and a spectrally selective emitter (n-SC/SE). When the ambient temperature is 30°C, the SC/SE based RC module realizes a daytime sub-ambient temperature reduction of 20.0°C, standing for a further temperature decrement of 9.2°C compared to the n-SC/SE based RC module.

Abstract In this study, an innovative thermal energy storage design method was developed by adding the combination of metal foam and fin to phase change materials (PCMs). A numerical model was built and verified based on the comparison among the present model prediction, experimental measurements, and numerical results in open literature. To highlight the novel design method, four cases including fin-PCM, foam-PCM, fin-foam-PCM, and PCM unit were compared by means of solidification features. The temperature distribution, solidification front propagation, and buoyancy-induced convection in the liquid PCM were accounted for. Numerical results demonstrated that metal foam outperformed fin regarding the improvement on solidification phase change. The combination of foam and fin achieved the best performance, leading to a 90.5% reduction in complete energy release time in comparison with the PCM unit. The proposed design method provided reference potentials for advancing energy storage engineering. However, buoyancy-induced convection in the liquid PCM before solidification was harmful to the formation of solidification front and its movement. A maximal 11.5% prolonging time for the complete solidification was found.

Photovoltaic (PV) windows have received more and more attention in recent years since their active energy-saving advantages. Considering the surface covered with solar cell modules, the indoor daylight environment of PV windows is obviously different with clear glass windows. However, despite many scholars have studied the indoor daylight environment of PV windows, there few investigations study it from the perspective of human subjective visual perception. In this paper, the indoor daylight environment and human visual comfort of building with Cadmium Telluride Photovoltaic (CdTe-PV) window were investigated. Firstly, the parameters of indoor daylight environment and subjective questionnaires in rooms with CdTe-PV window and clear glass window were analyzed respectively. On the basis of this, combined with indoor working surface illuminance and results of subjective questionnaires, the daylight illuminance threshold of human visual comfort was investigated by the method of Mean Bias Degree (MBD). Finally, an evaluation model for indoor daylight environment of buildings with CdTe-PV window was developed by Fuzzy Comprehensive Evaluation Method. The results showed that the working surface illuminance of CdTe-PV window was lower than that of clear glass room, the CCT of different windows room had a minor gap and the CdTe-PV window room was closer to the recommended range that was 3300-5000K. As for CRI, both the CdTe-PV window room and the clear glass room could meet the visual comfort requirements of office staff. Furthermore, it was found that the requirement of human visual comfort was met when indoor working surface illuminance varies between 500-2200lx in the room with CdTe-PV window. At last, according to the comprehensive evaluation model proposed in this paper, it was found that the indoor daylight environment of buildings with CdTe-PV window was excellent in the present experiment.

Renewable paper reusing plays a significant role in the sustainable environment under the background of the shortage in forest resources and the pollution from the paper industry. The conventional reusing stream of waste office paper appears to have low reusing rates while consuming massive amounts of energy in intermediate steps. In this study, we developed a novel portable renewable desktop paper reusing system based on font area detection and greyscale sensor. The proposed system consists of two main parts, namely, a greyscale sensor and font area detection model and a polishing mechanism. Acting as an ink mark detector for waste desktop paper, the greyscale sensor and font area detection model can detect the font in the waste desktop paper using an adaptive dynamic compensation schematic. The polishing mechanism will grind the font area of the wasted desktop paper, and this paper reusing processing is non-chemical, energy saving and environmentally friendly. The proposed system is demonstrated through simulations and experimental results, which show that the proposed renewable desktop paper reusing system is portable and is effective for reusing waste office paper in the office. An accuracy of 99.78% is demonstrated in the greyscale sensor and font area detection model, and the average reuse rate of one piece of paper is 2.52 times, verifying that the proposed portable system is effective and practical in renewable desktop paper reusing applications.

In this work, a series of nanoencapsulated phase change materials (NanoPCMs) with paraffin wax (PW) as core and melamine-formaldehyde (MF) as shell were synthesized by the in-situ polymerization method. The morphology, chemical structure and thermal properties of prepared NanoPCMs were characterized by scanning electron microscope, Fourier transform infrared, differential scanning calorimetry and thermogravimertic analyzer. The results show that the PW is successfully encapsulated in the MF without chemical interaction, and the NanoPCMs present regular spherical shape with the average diameter of 260–450 nm. The encapsulation efficiency of the NanoPCMs increases with the augment of the supplied amount of core material. The maximum encapsulation efficiency of the NanoPCMs can reach up to approximately 75%. The NanoPCMs can maintain excellent thermal reliability and stability after 2000 thermal cycling. The prepared NanoPCMs can be well applied in the latent heat thermal energy storage and thermal management systems due to their remarkable encapsulation efficiency and thermal properties enable them to.