Faucets at Gallons per Cycle vs. Gallons per Minute

I didn't check your math, but recently also spec'ed a metering faucet for 0.125 GPC which I rounded to 0.13. It could be that the baseline GPC of 0.25 is based on a much more realistic cycle time of 15 seconds or 12 seconds with autocontrol. 5 seconds is about 33% of 15 seconds.

I wish I did have insight as to why the baseline methodology was changed to GPC, and I concur that you have in fact discovered a significant gap for this fixture type, we have too. One suggestion is to leverage your contact with your assigned review team, provided that your project is registered, and ask them to clarify the methodology, and ask if they are aware of the intent of the GPC calcs. Additional contact with USGBC LEED staff may be helpful. Yet another reason the CIR process needs to come back!

I inquired with GBCI and this issue has been identified as needing investigation. It will be presented to the WE TAG, though I'm not sure of timing. The thinking is that there is a discrepancy in the baseline calculation methodology. Stay tuned and I will post if a clarification is announced.

Dave makes a great point and there is definately a discrepancy here! The .25 GPC baseline for metered faucets, when converted to GPM, equals 1.5 GPM (three times the baseline for public lavs). Perhaps the assumption is that, if the faucet doesn't shut off automatically, people will leave it running three times as long, therefore using three times as much water. I seriously doubt the accuracy of this type of assumption. As Tristan commented above, "Published studies have tended to show that fixtures with sensors use more water on average than those without." At least, if there is no conclusive evidence to the contrary, the baseline GPM should be the same for metered and non-metered faucets. This would also avoid a lot of confusion.

We heard from TAG support staff on this question. They have been hearing the same question from several sources but don't have a ready answer. They also noted that based on the TAG's current schedule and workload, we may be in for a waiting game.