Drying with underground air ducts Filling hall with product on floor with underground air ducts. Product in bulk. Top view of storage room. Top view of pressure chamber with hatch control. Angular cross-cut of hall with underground air ducts. Cross-cut of storage with slotted ventilation floor. Bulk storage on floor with underground air ducts. Bulk storage on floor with underground air ducts. Fan in pressure chamber. Pressure wall made of plywood and horizontal beams. Retaining wall. Use of retaining wall in practice. Outside retraining wall.