From Fig. 3, one can see that the solar heat gain coefficient for the plain clear glass is dependent on the solar profile angle.
It has the maximum value of 0.836 at zero solar profile angle and the value is slowly decreased as the solar profile angle is increased up to about 60 degree.
Then its value is rapidly decreased to 0 at 90 degree of solar profile angle.
When the blind is installed behind the glass window the value of the solar heat gain coefficient of the combined glass window system is decreased compared to value of the plain glass window.
The variations of the solar heat gain coefficient of the combined glass window system are dependent on slat angle.
At 45º slat angle the value of the solar heat gain coefficient is at 0.5036 at 0º solar profile angle.
The value of the solar heat gain coefficient is continuously decreasing when the solar profile angle is increasing.
For 0º slat angle, the value of the solar heat gain coefficient is at 0.801 at 0º solar profile angle.
The value of the solar heat gain coefficient is continuously decreasing when the solar profile angle is increasing.
For -45 º slat angle, the value of the solar heat gain coefficient is at 0.5044 at 0º solar profile angle.
The value of the solar heat gain coefficient is continuously increasing when the solar profile angle is increasing until it reaches 45º.
Then the solar heat gain coefficient is continuously decreased when the solar profile angle is further increased.
The explanation of the increasing of the solar heat gain coefficient for the case of -45º slat angle is that when the solar profile angle is increasing from 0 to 45º, more solar radiation beam can be penetrated through the blind into the room. Once the solar profile angle is greater than 45º the slat starts to block the solar radiation beam from entering into the room causing the value of solar heat gain coefficient to decrease.