SYMPOSIA PAPER Published: 01 January 2002

An Assessment of InterLaboratory Repeatability in Fenestration Energy Ratings: 2001 NFRC InterLaboratory Test Round Robin


This paper presents the results from the 2001 Testing Round Robin. The tested fenestration thermal performance ratings (U-factors) were acquired in accordance with NFRC 100 (1997): Procedures for Determining Fenestration Product U-factors and NFRC Test Procedure for Measuring the Steady-State Thermal Transmittance of Fenestration Systems (April 1997). A total of 8 NFRC- accredited testing laboratories participated in the 2001 test round. This paper presents results from the testing laboratory round robins.

The National Fenestration Rating Council conducts a Laboratory Accreditation Program (LAP) designed to promote accuracy and uniformity among the independent laboratories providing energy rating services (simulations or tests) in accordance with NFRC procedures. NFRC has conducted annual interlaboratory round robins since 1994. The continuance of interlaboratory round robins permits the continued evaluation of the repeatability and variance among the participating laboratories when evaluating the same product. This information is also made available to ASTM C16 for precision and bias.

The round robin testing consisted of each laboratory conducting a thermal performance test on a thermally improved aluminum fixed window with high performance glazing. Each participating testing laboratory received the identical window product to be tested for thermal transmittance. Every laboratory was directed to keep all test results confidential. All questions pertaining to the testing round robin were to be directed to NFRC staff only. The testing began in February of 2001 and was completed in June of 2001. The results of each thermal test performed were reviewed and placed in a spreadsheet for analysis and comparison of data. No laboratory was provided with expected results or the relative position of their data with respect to all data presented.

Results were compiled for all participating laboratories in the test round robin. Specific data regarding various measured and calculated performance values as required by the NFRC Procedures and Program Documents are presented herein.

NFRC will continue to conduct annual interlaboratory testing round robins and simulation round robins as an on-going component of the NFRC Laboratory Accreditation Program. The round robins assist in the evaluation of the laboratories to the conformance to the procedures, repeatability between laboratories and the variance between laboratories.

Author Information

Wise, DJ
National Fenestration Rating Council, Silver Spring, MD
Shah, BV
National Fenestration Rating Council, Silver Spring, MD
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Developed by Committee: C16
Pages: 203–220
DOI: 10.1520/STP11014S
ISBN-EB: 978-0-8031-5469-8
ISBN-13: 978-0-8031-2898-9