To reduce weather data computer storage without loss of accuracy Discrete Fourier Series are often employed for representation of hourly Solar Radiation inputs. This paper applies a method [1] which is based on the circular convolution theorem for determining the Fourier coefficients (Gn) of the solar radiation transmittance G(t) through glazings from the coefficients τn, and lnof the discrete Fourier Series representations of the tranmittance function τ(t) and of the coefficient l(t), respectively.