The owners of this seven story, 53,000 square foot condomimium tower built in the late 1960s felt that their energy bills were too high and asked for an energy audit by BPT. As is somewhat usual, no information was available for HVAC systems, or wall, window and roof construction. BPT's careful survey of the facility included assessment of actual construction materials and measurement of major HVAC equipment performance. That information was then incorporated into an energy model with the actual weather data for the most recent 12 months and "tuned" to match the actual energy bills, resulting in an excellent correlation between predicted and actual energy use (shown below). This calibration of the energy model allowed much greater confidence for savings projections. The audit resulted in identifying that the makeup air unit serving the common spaces was operating poorly and dramatically oversized. Replacement of that unit with an appropriately sized, newer unit promised a payback in less than 2 years. Although other opportunities were also identified, the return on investment did not merit implementing them.