Plural vertically aligned curtain sections form a first wall of a structure and are each coupled to a respective manual or powered rotary drive by means of a respective elongated, roll-up rod disposed in a lower hem, and extending the length, of the curtain section. The rotary drives are attached to horizontally spaced, vertical tracks for limiting the vertical drives, the roll-up rods and each curtain's lower hem to vertical motion in rolling up and unrolling the curtain sections. A water curtain maintained in a moist condition is disposed adjacent the inner surfaces of the curtain sections, with fans disposed on a second opposed wall of the structure for drawing air through the space occupied by the curtain sections for providing moist airflow through the structure's interior. Moist airflow and cooling are precisely controlled by controlling the gap between a pair of adjacent vertically spaced curtain sections.