Billions lack air conditioning as heat-related mortality rises globally. Conventional AC consumes large amounts of energy, relies on refrigerants that leak about 720 million metric tons of CO₂-equivalents annually, and remains unaffordable for much of the world. This entry presents a passive daytime radiative cooling (PDRC) tent that delivers 8–10°C below-ambient cooling with zero electricity, refrigerants, or greenhouse gas emissions.

The atmosphere is relatively transparent to infrared (IR) radiation in the 8–14 μm wavelength range, known as the atmospheric window (ATMW). Objects emitting strongly in this band exchange radiation with the cold sink of outer space. Materials that maximize ATMW emissivity, minimize absorption outside of the ATMW, and maximize reflectivity for incoming solar radiation — selective emitters (SE’s) — can cool below ambient temperature even under full sunlight.

Prior PDRC systems treated exterior surfaces with SE coatings, exposing them to ambient air. Our design eliminates this parasitic convective heat gain by enclosing the SE within an air duct between outer and inner duct walls, so only the air we wish to cool contacts the SE. Intake air flows through the duct, transporting heat into the SE. The SE radiates heat to outer space through an IR-transmissive outer duct wall, while cooled air flows into the tent interior. This roughly doubles available cooling power versus prior implementations.

A conceptual image of an example tent in cutaway view is attached.

Two innovations differentiate this system. First, isolating the SE from ambient air eliminates parasitic convective heat gain, substantially increasing cooling power. Second, we are developing a proprietary SE comprising a nonwoven nanofiber mat with an emissivity-enhancing coating. Initial samples achieved about 97% solar reflectivity, matching the best published values. The SE adds negligible weight and contains no PFAS or VOCs. The emissivity enhancing coating also improves SE mechanical durability. Both innovations are protected by U.S. and international patent filings, granted and pending.

Tent fabrication would be outsourced to established manufacturers. A technology partner produces the nonwoven nanofiber material to our specification. We are developing the emissivity-enhancing coating in-house and expect to apply it using established coating methods. The outer duct wall uses a commercially available ATMW-transmissive film, though we believe an improved nano-textile variant can be developed.

Primary markets include disaster relief housing, camping and backpacking, military field shelters, and shelters for anyone exposed to the effects of global warming who lacks access to vapor compression air conditioning.

As validation of our approach, Better Stuff LLC was named a finalist and use-case winner in the DHS/FEMA Cooling Solutions Challenge. Our prize funded COMSOL Multiphysics modeling (results attached) of an axisymmetric conceptual model. Analysis confirmed target cooling 10°C below ambient of the tent interior was achievable under 1,000 W/m² solar irradiance, while maintaining ASHRAE fresh-air requirements (a solar-powered fan helps move air through the system).

Beyond reducing power demand for disaster relief and military shelters, we are truly excited that our technology could bring cooling to populations priced out of conventional solutions who are increasingly exposed to extreme heat.