Methods for rejecting daytime waste heat to outer space

We report that outer space constitutes an extremely low temperature (T ~ 4 K) thermodynamic reservoir of boundless thermal capacity, with the potential to serve as a cold reservoir for cooling objects to sub-ambient temperatures in the daytime. For example, assuming a perfect emitter at 300 K, the theoretical black-body heat transfer rate to space can be calculated to be 450 Wm-2 [1]. However, for terrestrial objects, the atmosphere serves as a highly effective infrared (IR) insulator, as well as a heat source via radiation, convection and conduction to the object when cooled to sub-ambient temperatures.