100 80 VAV Damper, % Open 100 80 VAV Damper, % Open 60 40 20 0 5/2 0:00 60 40 20 0 5/2 0:00 5/2 4:00 5/2 8:00 5/2 12:00 Time Damper 3 Damper 8 5/2 16:00 × Damper 4 5/2 20:00 Damper 5 Damper 10 5/3 0:00 5/2 4:00 5/2 8:00 5/2 12:00 Time Damper 3 Damper 8 5/2 16:00 × Damper 4 5/2 20:00 Damper 5 Damper 10 5/3 0:00 Damper 1 Damper 2 Damper 6 + Damper 7 - – Damper 9 Damper 1 Damper 2 Damper 6 + Damper 7 - – Damper 9 Figure 2a (left): Plots showing the damper positions for 10 VAV boxes, where the boxes are starved of air so the dampers are all nearly fully open. Figure 2b (right): Excess static pressure results in all dampers being nearly closed. saving energy. The authors recommend evaluating savings on a 12-month annual basis. Annual savings (Esavings) are calculated as the difference between the actual energy use in the 12 months following completion of retuning (Eactual, e.g., the sum of the energy consumption shown on monthly utility bills) and the energy that would have been used during the same 12 months if the building had not been retuned (Ebase), i.e., Esavings = Ebase – Eactual (1) Ebase should be determined from a model that captures the dependence of the building energy consumption on driving factors such as weather and building occupancy, which are sufficient to capture variations with time at the resolution of days or months for office buildings. For determination of an- October 2009 www.info.hotims.com/25209-2 ASHRAE Journal