A novel solar-based human-centered framework to evaluate comfort-energy performance of thermochromic smart windows with advanced optical regulation

Thermochromic windows provide a promising and practical solution to lower building air conditioning energy via automatically reducing window-through solar radiation which imposes large cooling loads on air conditioning systems. The conventional framework for evaluating thermochromic windows assumes that the solar radiation passing through smart windows is immediately absorbed by indoor air, which ignores the deviated occupant comfort by indoor solar radiation and leads to a biased comfort-energy performance of thermochromic windows. This study proposes a novel solar-based human-centered framework to evaluate the comfort-energy performance of hydrogel thermochromic smart windows (HTSWs) via integrating human-solar modelling, solar-based indoor set-point correction, and building simulations. The comfort-energy performance of HTSWs are evaluated with different warm climates and compared to that of normal windows. The main results indicate that, the conventional framework, which ignores solar radiation on indoor human bodies, underestimates the discomfort time duration of indoor occupants by 55.0% and 75.2% when evaluating normal windows and HTSWs, respectively. Under the human-centered framework, with solar-based set-point correction, indoor occupants with HTSWs regulating solar radiation will be comfortable during more than 95% of working hours; and HTSWs reduce nearly 50% of the discomfort hours compared to normal windows. In addition, the average energy saving potential of HTSWs under the human-centered framework is extended by 35.0% compared to that under the conventional framework. To be specific, the air conditioning energy savings of HTSWs under the conventional framework are 9.9%–20.3% (average 14.5%); under the human-centered framework, the energy savings are 13.5%–25.6% (average 19.5%, which is 35% higher than that under the conventional framework). The considerably improved comfort-energy performance of HTSWs under the human-centered framework will further contribute to the wide adoption of HTSWs.