This paper presents and compares the results from the 1999 and 2000 NFRC interlaboratory testing round robins. The tested fenestration thermal performance ratings (U-factors) were acquired in accordance with NFRC 100: Procedures for Determining Fenestration Product U-factors (1997) and NFRC Test Procedure for Measuring the Steady-State Thermal Transmittance of Fenestration Systems (1997). A total of eight NFRC-accredited testing laboratories participated in both the 1999 and 2000 round robins. The National Fenestration Rating Council conducts a laboratory accreditation program (LAP) designed to promote accuracy and uniformity among the NFRC-accredited independent testing laboratories, which provide energy rating services (simulations or tests) in accordance with NFRC procedures. The continuance of interlaboratory round robins permits the continued evaluation of the repeatability and variance of the results among the participating laboratories when evaluating the same product. The round robin testing consisted of each laboratory conducting thermal performance tests on two nonthermal aluminum horizontal sliding windows with high-performance glazing--one for 1999 and an identical window for 2000. Each participating testing laboratory received the identical window product, which was to be tested for thermal transmittance. The test specimens were shipped to each testing facility via a common freight carrier. Each laboratory was directed to keep all test results confidential. The 1999 laboratory testing round robin began in April and concluded in August. The 2000 round robin testing was begun in February and completed in June. The thermal performance results of each thermal test performed--U_s, U_st[aw], and U_st[cts]--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. The results of this effort, as presented and compiled in this paper, indicate there is evidence that the NFRC-accredited testing laboratories, when testing to the NFRC Test Procedure (1997) and referenced ASTM standards such as ASTM C1199 and ASTM C1363, provide results that are expected to have a reproducibility limit of 5.91% from the average value, at a 95% level of confidence.

Authors: Daniel J. Wise; Bipin V. Shah

Citation: Thermal Performance of the Exterior Envelopes of Buildings VIII

Keywords: December, Florida, 2001