IGDB / CGDB testing

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Optical property testing for IGDB / CGDB submission

OTM is eligible to perform material optical property testing for International Glazing Database (IGDB) or Complex Glazing Database (CGDB) submission. This article aims to explain the testing procedures for IGDB or CGDB submission purposes.

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IGDB optical property testing

What is IGDB?

IGDB, or International Glazing Database, is an optical property database of specular glazing materials. The IGDB is maintained by LBNL and more information about the IGDB is available on this website.

The IGDB is primarily used in the NFRC fenestration performance rating program. It is required to submit the optical data of glasses to the IGDB before they can be used as the inputs in the NFRC certification simulations.

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IGDB testing procedures

The IGDB testing procedures are based on NFRC 300 and 301. They are identical to the procedures for single glazing optical & thermal properties testing. The details are not repeated here and please expand the block below for the key steps.

Key steps in IGDB optical property testing

The IGDB is for specular glazing materials only. Below are a few typical examples:

  • Monolithic glasses (uncoated glasses)
  • Glasses with coating
  • Glasses with window film
  • Laminated glasses

For insulating glazing units (IGUs), individual glass panes need to be tested one by one.

On completion of the test, a text file in the IGDB format is provided for submission. Shown below is an example.

An example IGDB format file

Please expand the block below for more information.

IGDB data file format

The details of the IGDB data file format are available in this document and some example data files are available on this page.

In the example data file presented above:

  • Rows 1 – 15 are the header and the following rows are important:
    • Row 2: glass thickness in mm
    • Row 3: glass thermal conductivity in W/(m⋅K)
    • Row 5: glass emissivity (when left blank, the emissivity is auto-calculated from the optical data provided below)
  • From row 16 are the optical data
    • Column 1: wavelength
    • Column 2: spectral transmittance
    • Column 3: front side spectral reflectance
    • Column 4: back side spectral reflectance

The IGDB format file can be imported to the LBNL Optics software. Refer to this blog post for the operations.

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CGDB optical property testing

What is CGDB?

CGDB, or Complex Glazing Database, is an optical property database of non-specular window shading materials (such as shade fabrics). The CGDB is also maintained by LBNL and more information about the CGDB is available on this website.

The CGDB is primarily used in the AERC window attachment rating program. It is required to submit the optical data of window shading materials to the CGDB before they can be used in the AERC certification simulations.

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CGDB testing procedures

The CGDB testing procedures are based on AERC 1.1. There are two steps in the CGDB testing:

The CGDB is for non-specular window shading materials, typically shade fabrics. A shade fabric material sample is shown in the photo below. The testing procedures described in this article are based on shade fabric materials and they may not be fully applicable to other window shading materials (e.g., insect screens, cellular shades, or Venetian blinds). OTM cannot test glass frits at this moment, due to some instrument limitations.

A shade fabric material sample

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Homogeneity testing

Unlike specular glazing materials in the IGDB, non-specular window shading materials may be with greater sample-to-sample variation. It may not be appropriate to randomly pick up a sample to present a product. The homogeneity testing is therefore required to quantity the sample-to-sample variation of a product statistically and select a representative sample.

There are 3 steps in the homogeneity testing:

  1. Sampling
  2. Visible light transmittance or reflectance measurement
  3. Homogeneity calculation

1. Sampling: 18 samples need to be sampled from different production lots and different positions (as specified in AERC 1.1).

2. Visible light transmittance or reflectance measurement: The visible light transmittances or reflectances of the 18 samples are measured.

Please expand the block below for more information.

Visible light transmittance or reflectance measurement

By default, the visible light transmittances of the samples are measured. The visible light reflectances are measured, only when the visible light transmittances of all samples are less than 0.01.

The steps described in Appendix C of AERC 1.1 are used and the instrument used at OTM is a UV/VIR/NIR spectrophotometer with 150 mm integrating sphere. The spectral transmittance/reflectance in the 380 nm – 780 nm is measured, and the visible light transmittance/reflectance is calculated from the spectral data.

UV/VIS/NIR spectrophotometer with 150 mm integrating sphere

3. Homogeneity calculation: the material product homogeneity is then calculated statistically from the measured visible light transmittance/reflectance results. Based on the homogeneity calculation results, a representative sample is then selected from the 18 samples in Step 1 for the optical property testing.

Please expand the block below for more information.

Homogeneity calculation

The homogeneity calculation essentially results in the following:

  • The mean visible light transmittance/reflectance
  • The tolerance (TvT) or confidence interval (CI) of the 95% confidence interval of all results
  • The ranks of all results

For the ranks of all results, the results are ranked from the smallest to the greatest, with a rank from 1 to 18. The two results at the center of a result set (i.e. the 9th and the 10th ranked results) are compared with the mean result to get the closer one. The sample with the closer result is then selected as the representative sample for the more detailed optical property testing.

Shown below is a sample homogeneity test calculation report (in this example, sample #3 is selected as the representative sample).

An example homogeneity test calculation report

There are also additional procedures defined in AERC 1.1 for the following scenarios: 1) newly developed materials; 2) materials in a material product family; 3) materials under the recertification process. Please expand the block below for more information.

Additional Homogeneity testing procedures for special scenarios

1) Newly developed materials: by default, the 18 samples of a material shall be from 3 different manufacturing lots, with 6 samples from each lot. For newly developed materials, it is permitted to test 6 samples from 1 single lot for the initial homogeneity testing and test the remaining 12 samples later.

2) Materials in a material product family: a simplified homogeneity testing process is available if there are multiple materials in a product family. It is permitted to select two materials from the product family, one with light colour and one with dark colour (if there are multiple openness factors, one with the lowest openness factor and one with the highest). If the homogeneity tolerances of the two selected materials are within the homogeneity limits specified in AERC 1.1, it is possible to proceed to the optical property testing with a single sample for all materials. Otherwise, homogeneity testing needs to be performed for all materials.

3) Materials under the recertification process: if the homogeneity tolerance of a material meets the requirements lists in AERC 1.1, it is possible for the material to be recertified, with some written affirmation and without re-testing. If the requirements are not met, the optical properties of a single new sample need to be re-tested. If the visible light transmittance/reflectance result is within the homogeneity tolerance, all material optical properties are updated to the new sample’s results (without homogeneity testing). Otherwise, the homogeneity testing needs to be re-performed and a new representative sample needs to be selected again and tested accordingly.

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Optical property testing

As the CGDB is for non-specular window shading materials, there is a diffuse component of the spectral transmittance/reflectance.

The are 3 steps in the optical property testing:

  1. Direct-hemispherical and diffuse spectral transmittance/reflectance measurement
  2. Thermal emissivity and infrared (IR) transmittance measurement
  3. CGDB format file generation

1. Direct-hemispherical and diffuse spectral transmittance/reflectance measurement: there are in total 4 measurements for each sample. The instrument used at OTM is a UV/VIS/NIR spectrophotometer with 150 mm integrating sphere. The wavelength range is 300 nm – 2500 nm.

Please expand the block below for more details.

Direct-hemispherical and diffuse spectral transmittance/reflectance measurement
Specular and diffuse transmission
Specular and diffuse reflection

As illustrated above, for the incident light (the black color ray) transmitted/reflected by a surface, there are two components:

  • Specular transmission/reflection (the blue color ray): the transmission in the same direction of the incident light or the mirror-like reflection in the direction opposite to the incident light
  • Diffuse transmission/reflection (the red color rays): the general transmission/reflection scattered in all directions

The sum of the specular transmission/reflection and diffuse transmission/reflection is the total transmission/reflection.

The instrument, UV/VIS/NIR spectrophotometer with 150 mm integrating sphere, can be configured to measure the direct-hemispherical and diffuse spectral transmittance/reflectance in the 300 nm – 2500 nm wavelength range. The direct-hemispherical transmittance/reflectance is equivalent to the total transmittance/reflectance.

UV/VIS/NIR spectrophotometer with 150 mm integrating sphere

2. Thermal emissivity and infrared (IR) transmittance measurement: the thermal emissivity and IR transmittance of the both sides of a sample are measured with a portable emissometer.

Please expand the block below for more details.

Thermal emissivity and infrared (IR) transmittance measurement
Portable emissometer

A special method is described in Appendix E of AERC 1.1 on fabric material thermal emissivity and IR transmittance measurement. The method is also described in a technical note by the emissometer manufacturer.

3. CGDB format file generation: the measurement results in the previous two steps are written to a text file in the CGDB interim file format for submission.

Shown below is a sample text file in the CGDB interim file format.

An example CGDB format file

Please expand the block below for more information.

CGDB data file format

The details of the CGDB interim file format is available in this document.

In the example data file presented above:

  • Rows 1 – 13 are the header and the following rows are important
    • Row 2: sample thickness in mm
    • Row 3: sample thermal conductivity in W/(m⋅K)
    • Row 4: sample IR transmittance
    • Row 5: sample thermal emissivity
  • From row 14 are the optical data
    • Column 1: wavelength
    • Column 2: front side specular spectral transmittance (Tf_n-dir)
    • Column 3: front side diffuse spectral transmittance (Tf_n-dif)
    • Column 4: back side specular spectral transmittance (Tb_n-dir)
    • Column 5: back side diffuse spectral transmittance (Tb_n-dif)
    • Column 6: front side specular spectral reflectance (Rf_n-dir)
    • Column 7: front side diffuse spectral reflectance (Rf_n-dir)
    • Column 8: back side specular spectral reflectance (Rb_n-dir)
    • Column 9: back side diffuse spectral reflectance (Rb_n-dif)

For the row header in row 13, below are the meanings of the abbreviations:

  • T: transmittance
  • R: reflectance
  • f: front side
  • b: back side
  • n-dir: normal-to-directional, i.e. specular
  • n-dif: normal-to-diffuse, i.e. diffuse

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Last update: 24/04/2022

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