Study on application design selection and sunshade performance evaluation of thermo-sensitive dimming glass

I. Overview1.1 Research BackgroundThe light and heat environment of buildings is periodically affected by outdoor climate conditions, so it is crucial to achieve efficient regulation of indoor lighting and solar radiation heat gain. As an intelligent material with variable light transmittance and variable heat insulation properties, thermochromic glass can dynamically regulate the visible light and near-infrared thermal radiation entering the building, and has great potential in improving the comfort of indoor light environment and reducing building energy consumption. Among them, thermochromic glass based on hydrogel materials is colorless and transparent, and the transition temperature can be freely set from 20 to 50°C. It has a high visible light transmittance, which can better meet the requirements of architectural applications for transition temperature and visible light transmittance, and has broad application prospects.However, in existing research and standards, there is a lack of clear methods for the design and selection of the optimal transition temperature of thermochromic glass under different climatic conditions; at the same time, there is no clear evaluation standard for whether thermochromic glass belongs to shading facilities and its shading potential assessment. In architectural applications, how to design and select the optimal transition temperature of thermo-dimming glass under different climates and building orientations, and how to calculate its equivalent shading area during evaluation, have become urgent issues to be solved for this material from basic research to architectural application.1.2 Research purpose and significanceThis study aims to establish a calculation model for the comprehensive impact of thermo-dimming glass on building light, thermal environment and building energy consumption through a combination of experimental testing and numerical simulation, and verify it through measured data. On this basis, the calculation method of the optimal transition temperature and equivalent shading length of thermo-dimming glass under different climatic conditions is studied to provide a reference for its design and evaluation in architectural applications. The results of this study are helpful to promote the widespread application of thermo-dimming glass in the field of architecture, improve the light and heat performance of buildings, reduce building energy consumption, and promote the sustainable development of the construction industry.2. Performance test of thermo-dimming glass2.1 Optical performance testUsing UV/visible/near-infrared spectrophotometer, the optical properties of thermo-dimming glass samples with transition temperatures of 20℃, 25℃, 30℃, and 35℃ were tested at different temperatures. The test results show that as the temperature rises, the visible light transmittance of the glass gradually decreases, and the ability to block solar radiation gradually increases. For example, at 20℃, the visible light transmittance of the glass is relatively high, allowing a large amount of visible light to enter the room; when the temperature rises to 35℃, the visible light transmittance drops significantly, and the solar radiation transmittance also drops significantly, effectively blocking the solar heat from entering the room.2.2 Heat transfer coefficient testThe heat transfer coefficient of the sample was tested using a steady-state heat flux thermal conductivity meter. The test data shows that the heat transfer coefficient of the thermo-dimming glass is relatively large in the transparent state; in the atomized state, the heat transfer coefficient is significantly reduced, which indicates that the thermal insulation performance of the glass in the atomized state is significantly improved, which can effectively reduce the heat transfer between indoor and outdoor.3. Laboratory test3.1 Laboratory designA comparable laboratory room was set up at the School of Architecture and Civil Engineering of Xiamen University. The comparison room and the laboratory room have the same size, with a length, width and height of 2.9m×2.6m×2.8m, and an external window size of 2 0.93m×1.94m. The windows of the comparison room are equipped with double-layer insulating glass and horizontal sunshades extending 50cm, and the windows of the experimental room are equipped with single-layer thermo-dimming glass with a transition temperature of 25℃.3.2 Test content and resultsThe actual measurement was carried out for 10 consecutive days, and the measurement data included outdoor weather data, indoor air temperature (natural room temperature), indoor lighting illuminance, etc. The experimental results show that in hot weather, the thermo-dimming glass installed in the experimental room gradually fogs when the temperature rises, effectively blocking solar radiation, and the indoor air temperature is significantly lower than that of the room without effective shading measures. In addition, the indoor lighting illuminance ensures the lighting needs while avoiding the discomfort caused by direct strong light. The comparison room also has a certain shading effect under the action of the sunshade, but the thermo-dimming glass experimental room has more advantages in the automatic adaptability of temperature regulation.IV. Establishment and verification of numerical simulation model4.1 Establishment of EnergyPlus modelEnergyPlus is used to establish a building performance calculation model for the comparable experimental room. Based on 10 days of measured outdoor weather data, the indoor air temperature and the lighting illuminance at the experimental measurement points are simulated and calculated. During the model establishment process, the thermal parameters of the enclosure structure, the characteristic parameters of the external windows, the indoor heat source and other related parameters are set in detail to ensure that the model can accurately reflect the actual situation of the experimental room.4.2 Model VerificationThe simulation results are compared with the experimental data. The comparison between the measured and simulated values of the indoor air temperature of the comparison room and the experimental room shows that the error NMBEs of the indoor air temperature of the comparison room is 1.99%, and the error NMBEs of the indoor air temperature of the experimental room is 1.05%. The error NMBEs of the experimental and simulated values of the illuminance at 9 measurement points in the thermo-dimming glass experimental room ranges from - 3.43% to 7.70%, and the error NMBEs of the experimental and simulated values of the illuminance at 9 measurement points in the comparison room with sunshade transparent insulating glass ranges from - 6.01% to 15.38%. The verification results show that EnergyPlus has high accuracy in calculating the indoor temperature and lighting illuminance of the comparison room and the experimental room, which can be used for further research.5. Research on the application of thermo-dimming glass under different climatic conditions5.1 Establishment of a typical office modelA typical office is selected for modeling, and the calculation method verified by experiments is adopted. Under different climatic conditions, the operating parameters such as thermal parameters of the enclosure structure, lighting power density, equipment density, personnel density, personnel occupancy rate, and room air conditioning set temperature are selected according to the provisions of the current relevant building energy-saving design standards in my country.5.2 Simulation and analysis of building physical performanceThe full-year dynamic building physical performance simulation method based on typical meteorological year data is used to calculate the effective daylight illumination (UDI), indoor expected average thermal perception index (PMV) and building unit area energy consumption (EUI), and analyze the influence of thermo-dimming glass on the building light environment, thermal environment and building energy consumption in typical office applications. The simulation results show that in different climate zones, the influence of thermo-dimming glass on the building light and heat environment and energy consumption is different. In hot areas, thermo-dimming glass can effectively reduce indoor temperature in summer, reduce air conditioning energy consumption, and at the same time ensure certain lighting needs and improve indoor comfort; in cold areas, the glass remains transparent at low temperatures in winter, which is conducive to increasing indoor solar radiation heat gain and reducing heating energy consumption.VI. Research on the design and selection of thermo-dimming glass6.1 Comparison of performance of different glassesTypical meteorological data of 203 cities in my country were selected to compare and analyze the building performance of single-layer thermo-dimming glass, Low-e double-layer insulating glass (high transmittance in the north and low transmittance in the south), and Low-e single-layer thermo-dimming glass in four directions of east, west, south and north. The research results show that the building energy efficiency performance of single-layer thermo-dimming glass in most areas (95%) is not as good as that of Low-e double-layer insulating glass, while the building energy efficiency performance of Low-e single-layer thermo-dimming glass in most areas (82%) is worse than that of Low-e double-layer insulating glass.6.2 Mapping of optimal transition temperature design selectionBased on the above research, a map of optimal transition temperature design selection of Low-e single-layer thermo-dimming glass under 4 building orientations was drawn. The map intuitively shows the optimal transition temperature of thermo-dimming glass applicable to different regions and different building orientations, providing an important reference for architectural designers. For example, in the hot southern regions, the optimal transition temperature of Low-e single-layer thermo-dimming glass for east-west oriented buildings is around 35-38℃; while in the cold northern regions, the optimal transition temperature of south-oriented buildings is relatively low, between 28-32℃.VII. Study on the sunshade performance evaluation of thermo-dimming glass7.1 Comparison with fixed external shading facilitiesTypical cities in 5 building thermal climate zones in my country (Harbin, Beijing, Nanjing, Kunming, Xiamen) were selected to compare the effects of single-layer thermo-dimming glass and fixed external shading facilities (horizontal external shading and vertical external shading) on indoor light and heat environment and building energy consumption. The analysis and calculation cases cover 5 typical urban climate conditions, 4 building orientations of east, west, south and north, single-layer thermo-dimming glass with a transition temperature of 20-50℃, fixed horizontal external shading with a length of 0-3.6m, and fixed vertical external shading with a length of 0-3.6m. Among them, the windows of fixed external shading use double-layer insulating glass, and the selection of 0-3.6m shading length takes into account the building self-shading structures including balconies, corridors, and building protrusions.7.2 Method and results for determining equivalent shading lengthThe determination process of equivalent shading length of thermo-dimming glass is proposed: first determine the minimum building energy consumption of thermo-dimming glass at different transition temperatures, and the transition temperature at the lowest building energy consumption is the optimal transition temperature of thermo-dimming glass; then, when the minimum building energy consumption of thermo-dimming glass is closest, the length of fixed external shading is the equivalent shading length of thermo-dimming glass. Taking the comparison between thermo-dimming glass and horizontal external shading in Xiamen as an example, under the climate conditions of Xiamen, the optimal transition temperature of single-layer thermo-dimming glass is 36-37℃. In the four directions of east, west, south and north, the equivalent horizontal external shading lengths of thermo-dimming glass with the optimal transition temperature are 0.5m, 0.9m, 0.4m and 1.6m respectively. The research results show that thermo-dimming glass can achieve building energy saving and light and heat environment improvement effects similar to those of fixed external shading facilities.VIII. Conclusion and Prospect8.1 Research ConclusionThrough experimental tests and numerical simulations, this study established a calculation model for the comprehensive impact of thermo-dimming glass on building light, thermal environment and building energy consumption, and verified the accuracy of the model through measured data. The study obtained the calculation method of the optimal transition temperature and equivalent shading length of thermo-dimming glass under different climatic conditions, and drew a design selection map for the optimal transition temperature. The results show that thermo-dimming glass has good light and heat regulation potential in building applications, can effectively improve the comfort of indoor light and heat environment, reduce building energy consumption, and in most areas, the building energy efficiency of Low-e single-layer thermo-dimming glass is better than that of traditional glass. At the same time, thermo-dimming glass can achieve building energy saving and light and heat environment improvement effects similar to those of fixed external shading facilities.8.2 Research ProspectsFuture research can further expand the application research of thermo-dimming glass in different types of buildings, such as residential buildings, hospitals, schools, etc., and deeply analyze its performance under different building function requirements. At the same time, optimize the material properties and production process of thermo-dimming glass, improve its stability, durability and dimming accuracy, and reduce production costs to promote its wider application. In addition, combined with artificial intelligence, big data and other technologies, the intelligent linkage between thermo-dimming glass and other building systems can be realized to further improve the intelligence and energy saving level of buildings.