Context and Criteria
The standard method for determining U-factor values is used to establish basic criteria, allowing a comparison of products during the preliminary stages of a project, or to ensure compliance with the NECB’s prescriptive requirements. U-factor data determined by this approach are ubiquitous in the commercial building and fenestration industry. It is imperative to understand the context in which the values were determined to better assess how the results may be influenced.
Two components emerge in the standard method for determining U-factors:
1. The protocol, which is the procedure to be followed to carry out the computer simulation or the physical test; and
2. The specimen, which is the product itself.
It is expected that all parameters of these two components will be exhaustively defined, allowing an equal comparison of fenestration products.
Among the protocol’s many criteria are:
• The calibration of measuring devices;
• The software versions to be used in case of simulation, or the installation of the specimen in the case of a physical test;
• The indoor and outdoor temperature differentials;
• The location of temperature reading points on the simulated or physical specimen;
• The wind speed(s); and
• Any additional reference standards.
As for the specimen, the objective is to measure its performance; however, other factors also have an impact on the resulting U-factor. Some of these factors may not be integral or consistent with the product’s design. The variations in these factors can be especially important in the case of curtainwall systems. Curtainwall offers many options to customize commercial building envelopes’ appearance and performance. Reviewing Figure 2, one can see how non-standard fenestration systems can impact an overall U-factor and why specifiers must carefully review their data.