Switchable Kirigami Structures as Window Envelopes for Energy-Efficient Buildings

Efficient regulation of thermal radiation is an effective way to conserve energy consumption of buildings.Because windows are the least energy-efficient part of buildings,their thermal radiation regulation is highly demanded,especially in the changing environment,but is still a challenge.Here,by employing a kirigami structure,we design a variable-angle thermal reflector as a transparent envelope of windows for their thermal radiation modulation.The envelope can be easily switched between heating and cooling modes by loading different pre-stresses,which endow the envelope windows with the ability of temperature regulation,and the interior temperature of a building model can be reduced by~3.3°C under cooling mode and increased by~3.9°C under heating mode in the outdoor test.The improved thermal management of windows by the adaptive envelope provides an extra heating,ventilation,and air-conditioning energy savings percentage of 13%to 29%per year for buildings located in different climate zones around the world,making the kirigami envelope windows a promising way for energy-saving utilization.