Directional thermal emission enables efficient energy savings

Thermal radiation, a fundamental heat transfer mechanism, is crucial for energy exchange across various applications. However, conventional radiative heat transfer systems rely on omnidirectional thermal radiation, causing energy dissipation in undesired directions and limiting radiative heat transfer efficiency. Here, we show that perfectly matched directional thermal emission between an emitter and absorber can reach a theoretical efficiency up to 100%. In a parallel-plate configuration, replacing a conventional system with a customized directional system raises efficiency from 29% to 100%. We further experimentally demonstrate directional radiative heat transfer realizes substantial energy savings of 67.8% in vacuum and 28.7% in non-vacuum conditions. Moreover, directional radiative heat transfer enables efficient heating in diverse scenarios, including vehicle heating, car paint drying, human body heating, and rail car thawing, achieving 17-46% energy savings. Our work highlights the broad applicability and energy-saving potential of directional radiative heat transfer, opening new avenues for efficient energy utilization.