This report discusses energy efficiency enhancements made to a low energy, high performance office building. The building studied is the Iowa Association of Municipal Utilities headquarters located in Ankeny, Iowa, just north of Des Moines. Monitoring the energy use of the building for over six years has revealed that it has an average annual site energy use of 29,300 Btu/ft2. This is 68% less energy than that used by the average U.S. office building and 74% less energy than the average office building in climate zone 2, the location of Ankeny.;Three areas of energy use were chosen for improvement: the ground source heat pump system's circulating pump, the energy recovery ventilator's defrost heater, and general office equipment (computers, refrigerators, coffee pot, etc.) during periods when the building is unoccupied. Before the improvements, the three items contributed to 38% of the building's annual energy use. The table below summarizes the energy use of each item before improvements were made, and the savings resulting from the improvements. The improvements have the potential of saving up to 27% of the building's annual energy use. The circulating pump's energy savings were achieved by switching it from a constant speed pump to a variable speed pump by equipping it with a variable frequency drive and installing shutoff valves on the heat pumps. Energy savings for the defrost heater were realized by decreasing its set point from an unreasonable 46°F to a recommended 5°F. The savings for the general equipment can be achieved if employees turn off all unnecessary equipment when the building is unoccupied.