How NFRC's Thermal Rating and Certification Program Works
The NFRC program is comprised of two newly-adopted ASTM test standards which are C1199 and E1423 and two computer modeling programs which calculate the heat flow through the center of glass (Window 4.0, developed by Lawrence Berkeley Labs, through sponsorship by the U.S. Department of Energy) and the edge of glass, frame, and sash members (Frame 3.0, developed by an engineering firm based in Canada, sponsored by the Canadian government). In the NFRC program, a manufacturer contracts with an NFRC-accredited computer simulator to model its products in all the possible combinations which the product may be manufactured. The product line's simulated U values are verified by thermal testing, which is performed on two products representing the best and worse case U values obtained through the simulation process. If the test and simulation results are within a specified tolerance, as established by NFRC, the manufacturer is allowed to use the computer simulation results for product labeling on each distinct product designation. If the results between these two procedures are outside the tolerance, a testing alternative is required. This procedure is designed to provide a higher degree of accuracy and repeatability, direct comparison of thermal performance between manufacturer's products, and reduced cost. The reduced cost comes from computer modeling individual product options versus having a complete thermal test performed on every product. When manufacturers are required to certify each individual product for thermal performance, then computer simulations become an economical and accurate alternative. After a manufacturer obtains all the thermal performance values on its product lines and options, it must enter into an agreement with an NFRC-certified inspection agent (IA) for obtaining labels, in-plant inspections, and product listings in a certified products directory. This is very similar to the AAMA program. In fact, the primary elements of the AAMA program and the NFRC program are not too different with respect to testing, lab accreditation, and product certification. What makes the programs different are the methods of determining U-values and the scope of NFRC's program, which is to put other thermal performance characteristics on the certification label consisting of air leakage, condensation resistance, solar heat gain, solar optical properties, durability, and annual energy use. NFRC is also developing a means to combine all these numbers into a common sense rating scheme which may provide total heat loss/gain and energy dollar information as well.
FENESTRATION MAY/JUNE 1993 Vol 6, No. 5
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