Solar-Powered Critical Cooling: A Theoretical Feasibility Study for Human Thermal Regulation

Abstract

Over the last 50 years, the leading global environmental hazard has not been hurricanes, lightning, tornadoes, floods, or earthquakes, but extreme heat events. With climate models projecting an increase in the frequency, intensity, and duration of heatwaves in the coming decades this threat to life is expected to only increase. Air conditioning has been demonstrated to reduce mortality during heatwaves yet uses an order of magnitude more energy than necessary to keep a human cool. Using principles of similitude to extrapolate the capability of existing vapor compression equipment, an objective function to maintain energy balance in a human exposed to extreme heat is developed across a design space. The function shows that in a standard forced convection air conditioning system, there no opportunity to provide emergency cooling of a human due to the slow mass flow rate needed to cool air in a single stream. As such, status-quo attempts to cool humans with general-purpose air conditioning will always be an inefficient use of energy. By focusing on keeping people cool, not spaces, we propose three paths forward for critical human cooling that appropriately match the energy needs of humans: radiative cooling, liquid cooling devices, and low-mass flow air conditioning.