Curcija, D.
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| Certification of building products has been practiced for many years as a means of assuring that product conforms to minimum performance criteria, as prescribed by standards. More recently, certification of selected building components, like windows and other fenestration systems (i.e., skylights, curtain walls, etc.) has assumed new meaning through the use of product labeling. The very first building product label in United States was for thermal performance of fenestration products, and now there is an action to develop same type of label for wall and roof systems. The National Fenestration Rating Council (NFRC), an independent, non-profit organization, which was founded by voluntary action of fenestration industry, academia, and government, does the rating and labeling of windows in United States. One of the most important considerations for the introduction of window labels was that the process needs to be economical, and one of the major contributors to the overall cost was the cost of the assessment of window thermal performance. Cost of testing was very high, and it was not feasible to test every window combination. At the time, computer simulation appeared as a reasonable low cost alternative to testing and was immediately embraced after some initial validation studies showed that the agreement between test ing and computer simulation was very good.
Not coincidentally was National Fenestration Rating Council born at the dawn of the introduction of first "user friendly" PC based computer programs for simulating thermal performance of windows (e.g., Jonnson 1985, WINDOW, KOBRU, FRAME, etc.) While first editions of these programs had very limited functionality, they represented a leap in convenience of use, consistency of results and even accuracy. This has created favorable conditions for the establishment of the national rating system that was sufficiently accurate and fair, while low cost and affordable. The United States and Canada started using computer modeling for its certification process 10 years ago, and the number of certified products had exponentially increased ever since. Today, more than 60,000 products have NFRC certified labels in U.S. alone.
Today, the latest generation of computer tools (THERM 2.1, WINDOW 5, OPTICS 5, and RESFEN 4) offers significant improvement in accuracy, ability to model wider range of different products (e.g., projecting products, commercial systems, etc.), to provide new indices, like condensation resistance, and finally improvements in user friendliness and ease of use. It is clear that continued and expanded use of computer modeling tools will continue and will be backbone of successful rating and certification system, and improvement in products design. |
