Investigating the annual energy-saving and energy-output behaviors of a novel liquid-flow window with spectral regulation of ATO nanofluids

Building envelopes with energy-generation from renewable sources are highly promising for the green development of buildings. Recently, a new concept of energy-efficient window i.e., the water flow window (WFW), that can capture solar energy for domestic water heating, was reported. However, the output heating capacity of the WFW is inferior due to the limited absorption bandwidth of water. In this study, the ATO-based liquid filled window (LFW) was newly conceived for broadband solar harvesting and effective indoor solar regulation, and then a transient model was developed to figure out the annual performance of ATO-based LFW. By comparing the performance of ATO-based LFW with different ATO concentrations, it was found that an ATO mass fraction of 100 ppm is a positive solution for feasible luminous transmittance about 52%, and excellent monthly output heating capacity between 19 and 60 MJ/(m²_·month) in Beijing. With the 100 ppm ATO-based LFW nanofluids, the output heating capacity and the annual solar heat gain coefficient (SHGC) of the ATO-based LFW in four cities with different climatic conditions were discussed. The results indicate that the 100 ppm ATO-based LFW shows the highest level of output thermal energy in Hong Kong, the highest output water temperature in Beijing, the lowest output heating capacity in Harbin, and the lowest cooling energy-saving potential in Chengdu. We believe that the ATO-based LFW is a feasible and applicable solution for achieving carbon neutrality in buildings, especially for buildings in hot regions.