The proposed control method is to provide energy into or to extract from a perimeter zone as a counterbalancing heat against the window heat gain estimated with thermal load calculations. This paper describes a part of the proposed perimeter control method; real time spliting the solar radiation into beam and diffuse, solar transmittance of glazing and window systems, thermal dynamic response model of the perimeter spaces. An applied example to the all-air systems, constant-air-volume perimeter AHU system, is also presented.