Abstract: A ventilation adapter unit or roof curb retrofit is provided for reducing energy costs in operating a building ventilation system. The unit is disposed between a traditional HVAC unit and a surface of the building, and has a plurality of internal passageways including a return air passageway, a discharge air passageway, and a supplemental discharge air passageway. Air entering the discharge air passageway from the HVAC unit is selectively routed into the supplemental discharge air passageway, where it is cooled by a cooling panel according to the position of a damper in the discharge air passageway. The cooling panel receives chilled fluid from a chiller, such as an ice storage system that operates a refrigeration unit during off-peak hours. Regardless of whether the air is routed through or around the damper, the air is then discharged from the retrofit unit and into the building.