Although CO₂-based ventilation control often is used in new construction,retrofits of existing buildings involving CO₂ controlare less common. This is probably because retrofit projects typicallyneed a high degree of documentation of possible savings andbenefits. In addition, control retrofits are perceived as complex.Ironically, the most significant opportunity for energy savings is inexisting buildings where a clear track record of energy usage patternsis available for analysis.

This article presents a methodology for assessing the potentialfor a CO₂ retrofit on an existing building. Discussion includes anactual assessment and retrofit of a Class-A office building that uses this methodology and the resultingperformance enhancements. The subject building is a U.S. Environmental Protection Agency (EPA) EnergyStar®-rated building that has a state-of-the-art direct digital control (DDC) system.