Navigation:  Background > g (total solar energy transmittance)

The total solar energy transmittance (or solar factor) g is computed according to DIN 67 507, EN 410, NFRC, ISO9050:2003 or ISO52022-3 (2017). CODE can handle an arbitrary number of glass panes in a glazing. A material object of type 'Gas' has to be used between two panes.

In order to compute g CODE has to use some physical properties of the filling gas. The values have been implemented in the material type 'Gas' which allows to define all kinds of gas mixtures. Please use this type of material for all gas fillings.

g is the sum of the solar direct  transmittance τe and the secondary internal heat transfer factor qi. The quantity qi as well as the corresponding quantity qe (the secondary external heat transfer factor) are also available as integral quantities.

g can only be calculated for simulated spectra, not for measured spectra. CODE needs to compute the emissivities from parts of the layer stack. This is not possible in the case of experimental data.

CODE needs to compute the emissivity of the coated glass panes in the far infrared (200 ... 1800 1/cm). Make sure that your optical model is valid in this spectra range. In most cases it is sufficient to compute the properties of the material silver that is used in the coatings in the far infrared. We recommend to use a model for the optical constants of silver and compute the model in the range 300 ... 50000 nm with at least 3000 data points. If there are other materials that might contribute to the emssivity (like ITO or thick metallic NiCr) then you should use the recommended wavelength range for these materials as well.

If you do not have optical constants in this spectral range you can still compute g if you know the emissivity of the involved surfaces. In this case, Edit the g quantity in the list of integral quantities. This dialog will open:

 

 

Note that the individual layers are not drawn in the dialog's sketch.

 

Using the checkboxes at the interfaces you can decide if CODE should compute the emissivity at this interface from the optical model. If the option is unchecked you can type in the emissivity to be used for this interface. If the option is checked CODE will indicate (in gray) the computed value of the emissivity.

 

The computation of g-values according to standards NFRC and ISO52022-3 involves an iterative routine that determines the temperature distribution of the glazing. As a consequence one can extract the temperature of the glass panes once the computation is finished. Other quantities like the fraction of sunlight absorbed in each pane are available as well. These numbers can be extracted using optical functions or defining the wanted quantity as 'internal quantity' that is output as final result instead of the g-value.

 

Internal quantities of g_tot (ISO52022-3 (2017)):

The following quantities are available as internal quantities. Make sure you correctly type their names:

•temperature pane 1

•temperature pane 2

•temperature pane 3

•temperature pane 4

•temperature pane 5

•absorbed power pane 1

•absorbed power pane 2

•absorbed power pane 3

•absorbed power pane 4

•absorbed power pane 5

•direct solar transmission

•u-value

•gain through thermal radiation

•gain through conduction and convection

•qi