Expert in Optical & Thermal Measurement Solutions
We are able to measure glass emissivity according to EN 12898:2019, with the PerkinElmer Spectrum Two FTIR spectrometer and PIKE 10Spec 10-degree specular reflection accessory.
The total normal emissivity (εn) result is reported. The corrected emissivity (ε) is calculated and presented in the appendix. For glass U-value calculation, the corrected emissivity should be used.
We use Devices & Services AE1 RD1 emissometer for general material emissivity measurement.
The instrument is suitable for room temperature material surface emissivity measurement, according to ASTM C1371.
We had a post on the sample requirements of translucent membrane products for SRI testing before: SRI testing: Can membrane products be tested without substrate? Essentially, if a transparent/translucent material is to be laid on top of an opaque substrate, it is required to test the transparent/translucent material together with the substrate.
There are also scenarios that transparent/translucent materials are with standalone installations and without substrates, .e.g. canopies made of fabric materials. In such cases, it is sometimes necessary to determine the solar absorptance and thermal emittance of transparent/translucent materials.
According to ASTM E903, the solar absorptance of a transparent/translucent material can be calculated as:
Solar absorptance = 1 – solar transmittance – solar reflectance
The solar transmittance and solar reflectance can be measured with a UV/VIS/NIR spectrophotometer.
It is out of the scope of ASTM C1371 to measure the thermal emittance of a transparent/translucent material. A manufacturer’s technical note is available to measure the IR transmittance and thermal emittance of transparent/translucent materials, with a portable emissometer.
It is out of the scope of ASTM E1980 to determine the solar reflectance index (SRI) of transparent/translucent materials. As suggested by its title, ASTM E1980 is for “horizontal and low-slope opaque surfaces”.