There are advantages to calculating the area weighted thermal properties for windows on a project. Utilizing this calculation method provides a more accurate “true to life” analysis of how the windows on the building will perform as a complete constructed unit, rather than as individual gateway size components.
Area weighted thermal properties allow custom window configurations and/or varying glazing options to be considered during the analysis. These area weighted values are of particular importance when calculating the energy performance of a building. Since the area weighted thermal property values more accurately represent the project specific window sizes and configurations, the energy models utilizing these values become more refined and accurate as well.
Another advantage of using area weighted thermal properties for each elevation, or even the whole project, is that it delivers a more accurate representation of how the project windows will actually perform. Thermal properties for windows based on gateway sizes are great when used as intended. Values based on gateway sizes allow the reviewer to make an apples-to-apples comparison of two products. However, these numbers do not represent actual project configurations or sizes. Typically window elevations on an actual project are larger and have more glass area than standard test size windows. In these situations the actual project configuration, when considered as a whole, will yield U-factors that are lower than the individual tested components at gateway sizes. By utilizing the area weighted calculations, it can often be shown that a project specific window configuration will meet the project specifications, even if the individual gateway size component could not. This can be a powerful tool.
Early in the process is often the best time to provide the area weighted thermal properties for both the envelope analysis process and project specification. EFCO has the expertise and knowledge to assist in providing these values in the early stages of your project.