Expert in Optical & Thermal Measurement Solutions
We’ve just released our Q1/2023 OTM Insights newsletter, with the main article “Curtain wall system thermal property calculation procedures“.
Please click the image below to read the newsletter. For the past issues, please proceed to our branding & publications page.
We are a Singapore-based third-party test laboratory, providing lab test services of material optical & thermal properties. We use Konica Minolta CM-2500d portable spectrophotometer, with the following key information.
We have a post on the measurement of thin paint and coating thermal conductivity with the ASTM D5930 method. Many surfaces are coated with multiple layers of coatings. How to determine the apparent thermal conductivity of such multilayer coating systems?
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:
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.
Can the standard NFRC/EN/ISO glass test methods still be employed to determine the optical & thermal properties 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:
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.
The requirements on daylight reflectance by BCA are available in this circular dated 27/06/2016. Please refer to Section P.3.2 of the document (pages 5-6) for the requirements.
Below is a flowchart prepared by us for your easy reference:
For a specific scenario, you may click one of the blocks below for more elaborations.
Due to the availability of ASTM C518-21, we’ve updated our SAC-SINGLAS accreditation schedule to ASTM C518-21. New test reports will be issued based on ASTM C518-21 accordingly.
Please also refer to the updated sample test report.
We’ve just released our Q1/2023 OTM Insights newsletter, with the main article “Glass color, color difference & color rendering“.
Please click the image below to read the newsletter. For the past issues, please proceed to our branding & publications page.
We are a Singapore-based third-party test laboratory, providing lab test services of material optical & thermal properties. We use Xiatech TC3000E transient hotwire thermal conductivity meter, with the following key information.
The instrument is equipped with two probes, a thin film probe, and a needle probe.
The thin film probe is mainly for flat plate solid samples:
The thin film probe is mainly for bulk gel or soft soil samples:
Thermal conductivity, thermal resistance, and thermal transmittance are the 3 commonly used properties related to material or system thermal insulation performance. The 3 properties and their differences are explained below.
Thermal conductivity represents the ability of a material to conduct heat.
Thermal conductivity is also called K-value and its unit is W/(m⋅K). The smaller the thermal conductivity, the better the thermal insulation performance.
Listed in the table below are the typical thermal conductivity ranges of selected building material types.
| Building material type | Typical thermal conductivity range |
|---|---|
| Insulation material (e.g. polyurethane/polystyrene foam, mineral wool) | 0.02 – 0.04 W/(m⋅K) |
| Wood, plywood, and gypsum board | 0.1 – 0.5 W/(m⋅K) |
| Coating (e.g. paint), plastics, and rubber | 0.1 – 0.5 W/(m⋅K) |
| Glass | 1 W/(m⋅K) |
| Concrete (light weight or heavy weight), brick, and tile | 0.5 – 2.5 W/(m⋅K) |
| Metal (e.g. stainless steel or aluminum) | 15 – 200 W/(m⋅K) |
Thermal conductivity is typically for homogeneous materials. For inhomogeneous materials (e.g. concretes or composite panels), their average thermal conductivity is referred to as the apparent thermal conductivity.
Thermal resistance represents the ability of a material layer to resist heat transmission. Thermal resistance is calculated as:
Thermal resistance is also called R-value and its unit is (m2K)/W. The greater the thermal resistance, the better the thermal insulation performance.
Thermal resistance is always in terms of one or multiple material layers with fixed thicknesses:
Thermal transmittance represents the ability of a wall, roof or fenestration system to transmit heat. Thermal transmittance is calculated as:
Thermal transmittance is also called U-value and its unit is W/(m2K). The smaller the thermal transmittance, the better the thermal insulation performance.
Thermal transmittance is always in terms of a complete wall/roof/fenestration system and air-to-air thermal transmission.
OTM provides two online thermal transmittance (U-value) calculators:
The discussions above follow typical engineering practices. In the academic context, the practices could be different.
If we use double glazing unit (DGU) glasses as an example, the engineering practice is to use its thermal transmittance (U-value), instead of the other two, for performance evaluations, though in the academic context it is still correct to calculate the apparent thermal conductivity and thermal resistance of a DGU glass.
After testing, a test sample is retained by the lab for a certain period. The following sample retention periods are implemented at OTM:
| Sample type | Size range | Retention period |
|---|---|---|
| Small samples | Smaller than 10 cm × 10 cm × 3 cm | 3 years |
| Large samples | Larger than 10 cm × 10 cm × 3 cm Smaller than 30 cm × 30 cm × 5 cm | 1 year |
| Oversize samples | Larger than 30 cm × 30 cm × 5 cm | 3 months |
At the end of the retention period, the sample will be disposed of by the lab. The lab may further retain some samples for internal quality control purposes.
Upon the customer’s request (indicated in the test request form or in writing), a test sample can be returned to the customer.