This paper presents temperature and airflow measurements proving that ground-coupled fresh air intake ducts can have a significant cooling effect. Measurements at two Norwegian schools with such ducts, Jaer School and Medi School, show that the actual cooling performance after a three-day warm period is about 100 Wh/m2 of exposed concrete surface in the duct, with air velocity passing the surfaces of about 0.15 m/s. Our calculations indicate that this can rise to at least 200 Wh/m2 by increasing the air flow rate during the night. This method of passive cooling is well suited for handling considerable peak cooling loads. The main mechanism of cooling in these ducts is exploiting thermal storage with nighttime precooling, exploiting the diurnal swing in outdoor temperature. The paper concludes by giving a number of design criteria.