Energy impacts of nationwide window upgrades in commercial buildings

This report presents comprehensive estimates of the energy impacts of nationwide commercial building window upgrades in the United States, using a conservative approach.

Windows play a substantial role in determining building energy use and occupant experience. Estimates point to commercial building windows impacting loads that represent more than 6 quads (approximately 6%) of annual primary energy use in the U.S. (Harris, 2022). Beyond heating and cooling loads, windows also have effects on lighting and occupant comfort.

The fastest route to improving the energy efficiency of windows in U.S. buildings is upgrading or replacing windows in existing buildings. This is due to poor performance of windows in older existing buildings compared to most new construction, low levels of window replacement, and long window service life compared to energy-using building components.

Nationwide window upgrades were considered using the following technologies:
•    Secondary glazing systems
•    Double pane (clear and tinted)
•    Triple pane (clear and tinted)
•    Electrochromic glazing

Nationwide upgrades provide on the order of 4%–6% site energy savings in typical buildings, or up to 26% in buildings with the highest savings potential. Electrochromic windows, with their ability to adapt dynamically to environmental conditions, can provide additional benefits, ranging from median savings of 7.2% in buildings with window to wall ratio (WWR) greater than 10% and up to 28% for some buildings. Savings increase substantially for buildings with higher WWR.

This study’s approach focused on isolating the direct energy benefits from improvement in window performance, and does not take into account the following additional benefits from window retrofits, which are likely to be substantial:
•    Managing peak demand and enabling HVAC equipment downsizing.
•    Energy savings from customizing upgrades to building type and climate.
•    Energy savings and comfort improvements resulting from post-retrofit reductions in air leakage.
•    Non-energy benefits, such as occupant comfort and resilience during extreme weather.