What are the differences between the NFRC, EN, and ISO glass optical & thermal test methods?
There are 3 widely adopted glass optical & thermal property test methods:
- NFRC method: NFRC 100/200/300/301
- EN method: EN 410/673
- ISO method: ISO 9050/10292
This article aims to compare the 3 test methods in detail:
- How to identify the test method used in a glass specification sheet?
- Can the test method be changed without re-testing the glass?
5 examples: are they different?
In order to illustrate the result differences between the 3 test methods, listed below are the result comparisons of 5 typical glass types. Please expand one of the blocks below for the comparison.
If you are interested in the technical background, please read the theory part.
If you are interested in other glass types, please leave your comments at the bottom of the page or contact us.
Observations from the comparisons
Based on the result comparisons listed above, we have the following observations:
- The visible light transmittance/reflectance results are the same.
- The solar energy transmittance/reflectance results are different:
- The differences are small for the uncoated glasses, but are relatively larger for the low-e coated glasses
- For the low-e coated glasses, the EN and ISO results are close, but the NFRC results are noticeably different from them.
- For the low-e coated glasses, in general, the NFRC solar energy transmittance results are lower and the NFRC solar energy reflectance results are higher.
- The solar heat gain coefficient (SHGC) and shading coefficient (SC) results are different:
- In general, the EN and ISO results are close, but the NFRC results are noticeably different from them.
- For the single glazing glasses, the NFRC results are higher.
- For the clear DGU with soft low-e coating, the NFRC results are lower.
- For the tinted DGU with soft low-e coating, the result differences between the 3 methods are small.
- There is no summer condition U-value in the EN and ISO methods.
- The winter condition U-value results are close between the 3 methods.
Different result names
It is also necessary to mention the following naming differences in the EN and ISO test methods:
- Solar energy transmittance/reflectance: they are named as direct solar transmittance/reflectance in the EN and ISO methods.
- Solar heat gain coefficient (SHGC): it is named as total solar energy transmittance (TSET) in the EN and ISO methods.
- Winter condition U-value: it is simply named as U-value in the EN and ISO methods.
In this article, the default names used for the NFRC method at OTM, i.e. solar energy transmittance/reflectance, SHGC, and winter condition U-value, are used.
The theory: What are different?
As described in our glass testing procedures article, there are the testing part (Steps 2 & 3) and the calculation part (steps 4 & 5) in glass optical & thermal property testing.
Summarized below are the differences between the NFRC, EN and ISO test methods:
- Identical measurement principles
- Testing part: the NFRC method is more detailed
- Calculation part: different solvers and environmental conditions
- Results: large differences in SHGC and SC results
At OTM, the testing procedures are the same and the result differences are caused by the different calculation models for the 3 test methods.
If you are interested in more details, please expand one of the blocks below.
The practice: Which method to use?
It is important to select a right test method for fair material evaluation.
OTM: we are neutral and technically ready
At OTM, we are technically ready to test glasses according to the NFRC, EN or ISO test method.
We are neutral to the customer’s selection of the test method. We provide the relevant information in this article for customer’s decision-making, and it is the customer’s responsibility to select the right test method.
By default, we use the NFRC method if a customer does not specify a test method.
Customers: check your project requirements
In Australia and USA, it is clear that the NFRC method shall be used. However, it is not so straightforward for projects in the other parts of the world.
In such cases, a customer needs to check the project requirements or negotiate with the other relevant project members to mutually agree on a test method.
If you are interested in more in-depth information, please continue reading this article. If your concerned questions are not explained, please feel free to leave a comment at the bottom of this page. This article will be reviewed and updated regularly.
How to identify the test method used in a glass specification sheet?
Most glass manufacturers prepare their glass specifications based on the NFRC method. A small number of glass manufacturers prepare the specifications based on the EN method. Very few glass manufacturers prepare the specifications based on the ISO method.
To identify the test method used in a glass specification sheet, please read the fine prints on the specification sheet:
- If texts such as “WINDOW software” are mentioned, the specifications are based on the NFRC method.
- If texts such as “EN 410” are mentioned, the specifications are based on the EN method.
In certain cases, the glass specification sheet is based on the NFRC method, with an additional U-value result based on EN 673.
Can the test method be changed without re-testing the glass?
As explained in the theory part, at OTM, our laboratory testing work instructions are based on NFRC 300/301 and the spectral transmittance/reflectance results collected can be used for NFRC, EN or ISO calculations.
We can calculate the results according to another test method, without re-testing the glass.
In certain cases, we can issue multiple test reports based on different test methods. For example, on the customer’s request, we can issue two separate reports for one glass sample, one based on the NFRC method and the other based on the EN method.
Last update: 28/09/2020
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