Ideal thermochromic smart window in a south-facing office room of China considering daylighting and energy performance

ABSTRACTThermochromic (TC) smart window which allows modulating the transmission of solar heat energy and sunlight in response to environmental conditions has great potential for improving the building energy and daylighting performance simultaneously. In this study, the multi-objective optimization method is used to determine the ideal optical properties of TC windows. Parametric assessment is firstly conducted to investigate the influence of several crucial parameters. Multi-objective optimization is then carried out by applying Non-dominated Sort Genetic Algorithm-III, maximizing daylight availability and building energy efficiency. Finally, the decision-making of the Pareto frontier is performed to achieve the ideal TC windows in 32 representative cities in different climatic zones of China. Results demonstrate that increasing the luminous transmittance at low-temperature and decreasing luminous transmittance modulation ability are beneficial to daylighting and energy performance. Lower solar transmittance at low-temperature contributes to building energy savings in Beijing, Shanghai, Guangzhou and Kunming, except for Harbin. Higher solar transmittance modulation ability is desired for building energy efficiency. The optimum value for the transition temperature is in the range of 23.67–38.85°C. The building energy consumption can be reduced by 13.01%, and the desired daylighting hours can be improved by 8.90%, relative to the clear double-glazed windows.KEYWORDS: Thermochromicdaylightbuilding energymulti-objective optimizationNSGA-III Nomenclature A=Area (m2)COP=coefficient of performance (-)E=electricity power (kWh)EUI=Energy Use Intensity (kWh/m2)G=growth rate (%)Q=energy consumption (kWh)q1=standard calorific value of coal (kWh/kgce)q2=conversion factor from electricity to standard coal (kgce/kWh)q3=standard calorific value of natural gas (kWh/m3)R=reduction rate (%)T=transmittance (-)TC=Thermochromic (-)X=vector of decision variables (-)Greek=τ=temperature (°C)η=comprehensive efficiency of the heating system with the coal-fired boiler as the heat source (-)φ=conversion coefficient of natural gas and coal (kgce/m3)Subscripts=c=coolingClear-DoubleGlazing=clear double-glazed windowsh=heatingindoor=indoorlighting=artificial lightinglum=lumsolar=solart=transitionTC-DoubleGlazing=TC double-glazed windowsDisclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis work was supported by the National Natural Science Foundation of China (No. 52108098) and the Fundamental Research Funds for the Central Universities (No. 20720220115).