In recent years, as the need for development of low-carbon architecture increases, practical use of the natural energy that surrounds buildings is attracting attention. Heat/cool trench systems make use of one such natural energy, subterranean heat. These systems reduce the fresh air load by introducing outside air through trench that pass beneath the bottom floor-slab before blowing the air indoors. This study involves a year-round measurement survey of outside air and indoor outlet temperature and humidity at school building. The effectiveness of using subterranean heat in a building is examined by calculating heat extraction in summer and heat addition in winter.