80 70 60 Temperature (°F) Temperature (°F) 50 40 30 20 10 0 3/12 7:12 p Outdoor Return Mixed Discharge 80 70 60 50 40 30 20 10 3/14 4:48 a 0 3/12 7:12 p Outdoor Return Mixed Discharge 3/13 12:00 a 3/13 4:48 a 3/13 9:36 a 3/13 2:24 p 3/13 7:12 p 3/14 12:00 a 3/13 12:00 a 3/13 4:48 a 3/13 9:36 a 3/13 2:24 p 3/13 7:12 p 3/14 12:00 a 3/14 4:48 a Time Time Figure 1a (left): Plots showing outdoor-air, return-air, mixed-air and discharge-air temperatures versus time for a properly controlled economizer. Figure 1b (right): An economizer with the outdoor-air damper stuck completely closed. of the controls and making corrections, other problems with control code sequences and settings of fixed parameters can be detected. These are added to the list of faults detected and should be corrected. Following implementation of corrective actions, all operation faults identified, actions taken to correct faults, and opportunities identified for further improving the operating efficiency through future retrofits are documented in the post retuning report. This report documents all opportunities identified in the retuning process and the status of each. The faults not corrected represent opportunities for additional low-cost energy savings through follow-up actions. The savings analysis is critical to determining the degree to which retuning has succeeded in satisfying its objective of ASHRAE Journal October 2009