Monthly Archives: February 2014

A Closer Look at Energy Conservation Measures – Window Replacement

As promised, here are more highlights from a recent energy audit and retro-commissioning assessment project. The energy conservation measure (ECM) I’d like to highlight this time is upgrading a facility’s windows.

The majority of the existing windows in our case study are single pane with wood frames in fair to poor condition. With window replacement there is an opportunity for thermal efficiency improvement with the installation of windows with better insulating properties. Typically, energy savings from window replacement are a result of reduced infiltration from gaps and cracks around window frames and glazing and from reduced heat transfer during the heating and cooling season. For a conservative savings estimate associated with this measure, the calculations below are only based on improvements to the windows’ thermal properties.

Overall, we calculated a savings of approximately $5,857/year (based on improvements to the windows’ thermal properties) with a simple payback of nearly 200 years! What can be recommended with these stats? Window replacement was considered, but the economic payback did not justify implementation as an ECM. Therefore, we suggest that when window replacement is required, high performance windows should be used. Replacement windows should have insulated frames (with thermal breaks), two or more layers of glazing with an inert gas “air” gap between and solar heat gain coefficient appropriate for the window orientation and desired level of solar heat gain.

Although not all ECMs end with a recommendation for implementation, this facility can now plan appropriately for the future. When putting together their budgetary needs, they can now reference this study to plan more accurately and most efficiently.

What are some lessons learned from your building energy studies? Have you recently replaced your windows? How did you choose the best fit? Share your thoughts and questions in the comments below.

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