Passive radiative cooling to sub-ambient temperatures inside naturally ventilated buildings

Daytime radiative cooling materials can help prevent overheating by keeping exterior roof surfaces cool, but can they passively reject heat from inside buildings, overcoming thermal gains from healthy air changes without mechanical assistance? Here we report how to produce sub-ambient interior temperatures by balancing terrestrial radiative cooling with temperature-driven ventilation and thermal mass. We present a field study with model enclosures replicating one occupant's heat balance and air changes. The reference box represents a “gold standard” in passive cooling, with thermal mass and night ventilation offsetting internal heat gains. The test box maintains an interior temperature of 3.9°C below the mean prevailing exterior temperature and 8.9°C below the gold standard, despite being actively heated from within and venting seven air changes per hour during the day. We also show with a calibrated model how to improve the cooling and ventilation performance while scaling the results to actual buildings.