Why Fenestration U-factor is Important in Hot Climates

It is commonly thought that U-factor is not a key determinant in the performance of fenestration in hot climates, and generally the focus is solar heat gain.



The reason given is that the difference in air temperature between inside and outside is much lower in hot climates, so the driving force for heat transfer is less. However, the temperature difference that drives heat transfer through a window is that between the exterior surface of the window and its interior surface.



Exterior frame temperatures can exceed air temperatures by a significant amount, especially dark colored frames, because of solar absorption. This absorbed heat then transfers to the interior surfaces of the window if there is no thermal break at the frame or edge of glass. Data from a research study by the Solar Energy Research Institute of Singapore (SERIS) demonstrates how the U-factor of a window significantly impacts the energy and thermal comfort performance of fenestration systems in a hot climate.



In addition, the use of warm-edge spacer in the Space Needle renovation demonstrates how reducing thermal transfer at the edge of glass is essential for reducing the cooling load in summer, heating load in winter, and improving thermal comfort year-round.

About the Speaker: Helen Sanders - Technoform - Helen has 25 years’ experience in glass technology and manufacturing, especially in functional coatings, insulating glass and thermal zone technology for fenestration. She has a Ph.D. in Surface Science from the University of Cambridge. At Technoform North America she focuses on business development and market education. She is an active member of many industry organizations, and is president of the Façade Tectonics Institute and vice president of the Insulating Glass Manufacturers Alliance (IGMA).