The Impact of Windows on Thermal Comfort PDF

Thermal comfort has a significant impact on the indoor environmental quality (IEQ) of a space. Windows are often selected for characteristics such as energy performance, aesthetics, noise factors and cost; however, they also have an impact on IEQ parameters, particularly thermal comfort. Poor performing windows can result in cold surface temperatures, drafts, radiant asymmetry, overheating, and other issues. Choosing the right windows for a particular building can significantly improve occupant thermal comfort and the IEQ of the space. The analysis presented herein is part of a larger study that analyzes the impact of window selection on energy consumption. As window selection can have interactive effects on a space’s IEQ, this paper will present an analysis using ASHRAE Standard 55 as a guideline to assess the thermal comfort performance of window selection. Whole building annual energy simulations are performed to compare various window and glazing types with other related variables such as window to wall ratio (WWR), orientation and shading.

The thermal comfort analysis shows that, as expected, windows with a lower U-value result in fewer occurrences of cold surface temperatures. Windows with a higher Solar Heat Gain Coefficient (SHGC) result in greater occurrences of overheating in a space. The WWR, orientation, and exterior shading also have a significant impact on the thermal comfort conditions within the space. Overheating is a particular concern due to the conflict between reducing energy consumption and improving thermal comfort. Energy modeling performed for LEED or ASHRAE 90.1 compliance often indicates that high SHGC windows will improve the energy performance of a building in heating-dominated climates by increasing passive solar heating. Selecting high SHGC windows to reduce energy consumption in buildings with high WWRs and no exterior shading can result in significant discomfort due to overheating. This paper will present an analysis of the thermal comfort performance of various window and glazing options. Guidelines for selecting windows to achieve good thermal comfort performance will be presented. Interrelationships between reducing energy consumption and achieving thermal comfort will be discussed.