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• Spectrally resolved DNI was tested for an entire year in Beijing. • The spectra can be represented in five-dimensional data by an autoencoder. • Hierarchical clustering was adopted to obtain ten reference spectra in the case. • Novel local reference spectra can characterize solar resources throughout the year. • The superiority of the new reference spectra over ASTM AM1.5D was verified. The established reference spectrum (ASTM AM1.5) based on mid-latitudes is still the most frequently used standard in design and simulation in various fields worldwide, however, the solar spectrum varies with climate and time, which significantly affects the evaluations of solar energy utilization. This study proposes a novel reference spectrum analysis method to establish several local reference spectra, in this case, based on 147,374 spectra in Beijing, which can characterize solar resources throughout the year. The dataset consists of spectra of direct normal irradiance, and a deep learning autoencoder is adopted to extract the intrinsic features of each spectrum for clustering. 10 clusters are finally divided by agglomerative hierarchical clustering, and 10 local reference spectra were identified from each cluster by correlation analysis. The results show that the shape of new reference spectra shifts to the short wave as the irradiance increases, and the average photon energy increases from 1.069 eV to 1.456 eV. The new local reference spectra are compared with the standard spectrum AM1.5D to show the influence of shape variations, and it reveals 61% maximum differences among photovoltaic applications. The superiority verified new reference spectra could be further used to optimize local solar technologies design and guide photovoltaic material development. [ABSTRACT FROM AUTHOR]

Thermochromic (TC) window has been developed as an effective approach to realize building energy saving by regulating solar transmittance according to temperature stimuli; however, the non-uniform transmission and absorption of the solar spectrum result in a significant color shift and temperature increase. This study investigates the radiometric, photometric and colorimetric performances of four different TC windows with an experiment-verified model. The simulation and calculation are conducted under measured spectrum conditions in Beijing; subsequently, a comprehensive evaluation method for daylight-thermal environment method is conducted. The results show that all selected TC windows possess an energy efficiency between 3.0% and 7.9%, improve daylight availability from 2.8% to 18.8%, and reduce discomfort hours by up to 111 h. Two hydrogel TC windows improve the quality of dynamic transmitted daylight by nearly 7% considering correlated color temperature and color rendering index; the HETS hydrogel TC window is found to be the most suitable for Beijing. Finally, to increase the application potential of TC windows in Beijing, several material properties are desired, including high transition temperature with high solar modulation capability, high and uniform visible light transmittance, and low emissivity. This process for the optimization of climate-responsive material can be further adopted in other areas. • Four different thermochromic windows are compared for the Beijing climate. • The annual dynamic spectrum of Beijing is measured and adopted as a boundary condition. • The model is verified by experiments based on measured meteorological conditions. • Comprehensive evaluation, including radio, photo, and color aspects, is conducted. • Constructive suggestions on regionally suitable window characteristics are given. [ABSTRACT FROM AUTHOR]

[Display omitted] • The influences of PM 10 concentrations on SPD values are investigated. • A strong influence of PM 10 on SPD could be noticed ranging from 380 to 540 nm. • A band of 510 nm is adopted to establish models and its models has been validated. • Other bands are also validated and the band ranges from 480 to 520 nm. • Quantitative study on SPD under PM 10 levels promotes building energy-efficient design. Daylight refers to a free and valuable resource exhibiting photometric and radiometric features, and the physical parameters commonly used to represent its features are irradiance and illuminance. They are both obtained by the spectral power distribution (SPD) of global irradiance, demonstrating that values noticeably affect indoor thermal and luminous environments. Nevertheless, outdoor particulate matter (PM) significantly affects SPD conditions, and two relative spectral notions, i.e., percentage of spectral irradiance (PSI r) and percentage of spectral illuminance (PSI l), were proposed to study the effects of PM 10 concentrations in radiometry and photometry with a field measurement, Beijing. As a result, the strong impact of PM 10 on PSI r / PSI l can be noticed in the range (380 to 540 nm) (P-value < 0.01) by correlation analysis, and a wavelength of 510 nm was taken to build models between PM 10 and PSI r / PSI l based on regression analysis. With this wavelength, PSI r varies from 0.29 to 0.25%, and PSI l ranges from 0.48 to 0.42% with the increase of PM 10 concentrations from 0.01 to 0.098 mg/m3. With the verification of the model, several bands were further analyzed to comprehensively verify the monotonic correlations, and the band ranging 480 ~ 520 nm were reasonably proved that PSI r /PSI l and PM 10 can be well indicated by each other. As influenced by the complexity of spectral transmittance through the glazing, the mutual characterization between solar spectrum and particulate matters can contribute to the building energy-efficient design and develop indoor thermal and luminous environment research in the future. [ABSTRACT FROM AUTHOR]

Fine description for regional solar spectra has always been critical for improving solar energy utilization. However, it is difficult and complex to implement due to large amount and high-dimensional characteristics of the measured solar spectra. To address the above challenges, this study proposed a data-driven method to describe regional solar spectra using 211,877 global horizontal irradiance spectra in Beijing area as case data. Firstly, the dimensions of each measured spectrum were reduced from 2,221 to six using the deep autoencoder. Then, all dimensionality-reduced measured spectra were categorized into five clusters using the agglomerative hierarchical clustering. The clustering results exhibited notable variations across different months and dates. Finally, the local reference spectra were determined based on clustering results, and their effects on the performance of typical photovoltaic materials were analyzed. The maximum mismatch factor for typical photovoltaic materials under local reference spectra can reach up to 21 %. The comparisons with standard spectrum highlighted that the superior capacity of local reference spectra to describe the configuration of regional solar energy. This study provides a novel insight into the fine description for regional solar spectra, which sets a new direction for innovation in photovoltaic technology and promotes the sustainable utilization of renewable energy. [ABSTRACT FROM AUTHOR]

Following advancement in urbanization, outdoor thermal comfort is receiving increasing attention, with radiation being an influencing factor. To determine the shading preference, instead of a subjective questionnaire survey, an objective foot vote approach was proposed using remote sensing images. Subsequently, the meteorological data of cities were obtained from the Bureau of Meteorology. From the results, the foot vote was approximately consistent with the PMV, and pedestrians tended to move to the shaded area if it was hot and to the non-shaded area if it was cold. However, people do not move if the foot vote value ranges from 1 to 2, and the thermal acceptance range of PET is 19.2–29 °C in Beijing when using the definitions of foot vote. The outdoor thermal acceptance differs significantly with the types of outdoor sites and climates, and pedestrians in Beijing are significantly more sensitive than those in Wuhan if the outdoor thermal environment changes. Compared to transportation hubs and shopping malls, pedestrians in public buildings are less sensitive, whereas those in scenic spots are more sensitive. Results from this study will be beneficial to policymakers in urban designing to renovate and improve thermally comfortable urban environments at the pedestrian level. [Display omitted] • An objective foot vote approach from remote sensing images is proposed. • The foot vote approach is tested and consistent with PMV approach. • Air temperature and global radiation are important factors affecting foot votes. • Thermal acceptance range of PET is 19.2–29 °C in Beijing under foot vote approach. • Outdoor thermal sensitivity differs with the types of outdoor sites and climates. [ABSTRACT FROM AUTHOR]

• The influence of adjacent room heat transfer on heating load is investigated. • Both measurement and simulation are adopted to validate the model accuracy. • Three factors are proved to have great impacts on adjacent room heat transfer. • Adjacent room heat transfer could takes up 40%–70% of the total heating load. • Quantitative study on adjacent room heat transfer promotes household heat metering. Household heat metering plays a significant role in building energy efficiency and has become an inevitable trend in northern China. Precise supplying aims to ensure indoor thermal comfort while realizing energy saving with occupants' behavior. Due to the different indoor temperature, interior envelope material and occupancy rate of each room, the Adjacent Room Heat Transfer (ARHT) will greatly affect the fair heating charging under household heating metering. This study takes an office building in Beijing as the object to measure the indoor and outdoor temperature in winter. EnergyPlus is adopted to establish a building model and calculate the heating load. The time-dependent temperature of the simulated room is compared with the hourly measured temperature to validate model accuracy. The validated model is further adopted to calculate the ratio of ARHT under three different conditions. The result indicates all these three factors have important impacts on ARHT. The ratio of ARHT to the real total heating load could stay around 40% and even reach up to 70%. The result shows an unexpected influence of ARHT, while it provides a case study for fair allocation of heat charges, which is vital to the implementation of household heat metering in China. [ABSTRACT FROM AUTHOR]

Electrochromic (EC) glazing provides a promising solution to actively adjusting the sunlight and radiant heat through windows in response to building visual and thermal environmental requirements, and control strategies play a critical role in the application of EC technology in buildings. However, there is a conflict between the visual and thermal environmental requirements for EC regulation during a cooling season. To solve this problem, this paper developed a predictive control strategy for EC glazing. It was achieved based on two theoretical models which could predict the energy performance of EC glazing at different tint states, including the solar radiation heat transmitted through the glazing and lighting energy consumption. The optimum glazing state was determined based on real-time minimized energy consumption. Study results showed that the predictive control strategy outperformed the rule-based control strategy, with percentage energy saving of an office room in Beijing, China from 8.04% to 12.78% over an entire cooling season. In addition, the paper evaluated the energy-saving of using EC glazing under the predictive control strategy in 28 Chinese cities. The results indicated that EC glazing was highly applicable in most of cities with energy saving from 2.35 kWh/m2 to 5.04 kWh/m2 over an entire cooling season. • A predictive control strategy for EC glazing was developed. • Theoretical models were established to predict the EC glazing energy performances. • Real-time minimized energy consumption determined the optimum EC glazing state. • Balance between the visual and thermal environment requirements was achieved. • The energy-savings of using EC glazing in 28 Chinese cities were assessed. [ABSTRACT FROM AUTHOR]

Solar spectral irradiance distributions have a great impact on the photoelectric conversion performance of photovoltaic materials. By average photon energy, this paper assessed the practical conversion performance of ten types of photovoltaic materials based on the spectral measurements of Beijing and Changsha, China. Photon energy utilization efficiency was proposed to assess the practical conversion performance of photovoltaic materials at the same aperture area. Monocrystalline silicon had the best energy utilization efficiency when the spectrum is the red-rich or close to the reference spectrum. However, gallium arsenide would outperform it if the average photon energy exceeded 1.95 eV. Mismatch factor was used at the same rated output power of photovoltaic materials. It is found that the mismatch factor of perovskite with a 1.22 eV bandgap energy ranks the first place when the spectrum is the red-rich or close to the reference spectrum. However, the perovskite with a 1.83 eV bandgap energy has the optimal conversion performance at the average photon energy over 1.83 eV. Moreover, an ideal photovoltaic material with advanced properties was proposed for optimal performance with the regional spectra, which might provide useful instruction for photovoltaic industries to produce the most suitable photovoltaic material considering the annual regional spectrum. [ABSTRACT FROM AUTHOR]