I am working on a calculation to demonstrate energy savings based on the use of low flow domestic hot water fixtures for LEED EAc1. The "Advanced Energy Modeling for LEED" technical manual provides a sample calculation for this, but I cannot follow the method used to obtain the numbers presented. For instance, for a lavatory with 3 daily uses, 15 sec duration, 1 FTE, and design flow rate of 0.5 gpm, the electric heated water usage is listed as 6 gal/day. I would have expected 3 uses * 15 sec / 60 sec/min * 1 FTE * 0.5 gpm = 0.38 gal/day * some percentage of the flow being hot water = 0.xx gal/day; perhaps I am misunderstanding the calculation.

Is there a generally accepted percentage of total fixture flow rate for the hot water usage? I am anticipating that the LEED reviewer will request justification for whatever hot water flow rate I use.

Thanks in advance.

-Brian Turner