I have just revised a baseline and proposed model for LEED submission and the fan energy savings has changed dramatically as a result. The first go-round the fan energy savings was 27% between baseline to proposed. The formulas in G3.1.2.8 and G3.1.2.9 were used incorrectly though in the first round, so I had to revise the supply and return fan power calculations. The result is that they both were higher (0.001217556 KW/CFM supply and 0.001049567 KW/CFM return now). The baseline fan curve is the equation from G3.1.3.15 Method 2.

The proposed model fan power matches the actual units purchased, (0.001164 KW/CFM supply and 0.000435 KW/CFM return). This represents a 4.4% reduction in supply fan power and a 58.6% reduction in return fan power. The fan curve used for the proposed model is Variable Speed Drive FPLR.

There is a huge savings on the return side and a slight savings on the supply side, so I can visualize how a 60% overall savings between the two models is feasible, but is the sizing for the return fan under the baseline scenario accurate? I followed the G3.1.2.8 method of sizing them based on the supply flow minus the ventilation (or 90%) but the calculations still come out with a substantially higher return fan power than the proposed model. This may be perfectly acceptable, but USGBC always put the disclaimer on the review comment that "the comments are perceived to reduce projected savings". That would be the case otherwise, but since the fan energy has changed so dramatically after revising the baseline calculations that the savings actually increased from 17.99% to 21.77% solely on the fan energy. Does anyone have experience where, with an explanation of why this occurred, that USGBC will accept the revised results even though the savings is actually higher now?

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Bernie Hont, PE, LEED AP
Girard Engineering, P.C.
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