/**
  * Evaluates superior surface temperature
  *
  * @param $tsr total solar reflectance
  * @param $g heat solar flux
  * @param $t_ext exterior temperature
  * @param $h_ext external heat transfer coefficient
  * @param $e thickness of the sandwich panel
  * @param $y thermal conductivity of the insulation material
  */
function evaluateSupSurfTemp($tsr, $g, $t_ext, $h_ext, $e, $y)
{
    // External thermal resistance
    $r_ext = 1 / $h_ext;
    // Internal thermal resistance
    $r_int = (1 / 7.7) + (($e/1000) / $y);

    $surf_sup = (((1-$tsr) * $g) + (($t_ext + 273.15)/$r_ext) + ((21 + 273.15)/$r_int)) / ((1/$r_ext) + (1/$r_int));
    return $surf_sup;
}