The method described in the post is only applicable to one single layer of coating. For a surface coated with two or more layers of coatings, the method can only measure the top layer, but cannot determine the apparent thermal conductivity of multiple layers.
To determine the apparent thermal conductivity, the calculation method needs to be used. In this post, we use a two-layer coating system as an example:
Measure the thermal conductivity of each layer individually (k1 and k2). Note: the samples need to be prepared individually too, as the method can measure the top layer only.
Calculate the overall thermal resistance: R = d1/k1 + d2/k2, where d1 and d2 are the thickness of each layer.
Calculate the apparent thermal conductivity: k = (d1 + d2)/R
For the calculation of the overall thermal resistance, our online ETTV U-value calculator can be used. The R-value result reported is the overall thermal resistance of all layers in the system.
As an alternative to glasses, several transparent plastic materials are utilized as window glazing panels. Transparent polycarbonate sheets and transparent acrylic sheets are two examples of such transparent plastic materials.
The NFRC/EN/SIO glass test methods are for glazing materials, which are not limited to glasses. Plastics are a type of glazing material. Transparent plastic sheets can be tested by the NFRC/EN/ISO methods when the following conditions are met:
With specular transmission and reflection only: materials with significant diffuse transmission/reflection are out of the scope (for example, frosted glasses, glasses with ceramic frits, and hazy plastic sheets).
Note: in the latest NFRC methods (2020 version), diffuse materials are supported, but our lab is not ready to test such diffuse materials.
Homogenous and flat sheet: corrugated plastic sheets and double-wall (multiple-wall) polycarbonate sheets are out of the scope.
Without far-infrared transmission: plastic sheets with significant far-infrared transmission in the 5 µm to 50 µm range are out of the scope.
Note: in the NFRC methods, it is possible to test materials with far-infrared transmission, but our lab is not ready to test such materials.
In principle, the scope of the NFRC/EN/ISO glass optical & thermal property test methods is based on the optical characteristics, but not on the material type. Transparent plastic sheets with the same optical characteristics as transparent glasses are within the scope.
We recently supplied an ISO 9060 spectrally flat Class A albedometer with a data logger and tripod to a customer in Singapore. Shown below are a photo of the system and a screenshot of the data logging software.