Effectiveness of External Window Attachments Based on Daylight Utilization and Cooling Load Reduction for Small Office Buildings in Hot Humid Climates

Abstract

This study explored the effectiveness of selected external shading devices and glazing treatments used to minimize the total annual energy consumption in small office buildings in hot humid climates. The external shading devices included a permanent horizontal overhang and a light shelf. The selected types of glazing included clear, reflective, tinted, low-emissivity coating, and heat-mirror glass. One concern about using external window attachments is that while reducing the solar heat gains, they also reduce the amount of the daylight needed to supplement interior lighting. Therefore the objective of this study was to explore which strategy would give a balance between solar heat gain reduction and daylight utilization and result in the most energy savings in the building. Computer simulations using an hourly energy calculation model were conducted to predict the building's total energy consumption using each strategy. The economics of each strategy were analyzed with lifecycle costing techniques using the present value technique. Results show that properly designed overhangs that shade clear glazing are slightly more cost-effective than specialized low-e glazing systems. These results are unique for hot humid climates where winter heating is not an issue. On the contrary, when used in cold climates, external shading devices tend to increase the building's energy consumption.