Airflow window units are a combination of energy-efficient fenestration and solar collectors. They typically consist of a double-glazed outer sash and a single-glazed inner sash, with venetian blinds in between. Return air from the room is admitted to the window through a gap at the inner sash, then air is returned to the central HVAC system of the building.

The airflow window system not only provides improved thermal properties and space comfort both in winter and summer conditions, but it also gives excellent daylighting utilization . In addition to energy savings of heating, cooling, and daylighting, considerable initial cost savings are also obtained in the reduction of capacity of the HVAC equipment.

This paper discusses the evaluation of the airflow window system and shows how the window system has been used with different air-conditioning systems to achieve energy efficiency.

The TRNSYS simulation program has been modified to make accurate energy and performance analyses of the window system available for different building applications. Results of locations comparative calculations concerning window system performance at three different and climates in the United States are presented in the last part of the paper.