It seems to me that there is a large discrepancy in the baseline for gallons per minute versus gallons per cycle.
The LEED Online template states "When using the metering lavatory faucet, please convert all flow rates in gallons per minute (GPM) to gallons per cycle (GPC) based on duration from the product specifications. Provide a narrative or calculations to support the installed flow rate."
A .5 GPM aerator evaluated in gallons per minute is right at the baseline for public lavs. However, that very same aerator metered with an automatic sensor at a standard duration of 10 sec. uses water at a clip of .083 GPC (at 0.5GPM x 10sec/60min), which is only 33% of the metered faucet baseline.
This is a critical question for a health care TI project that we are pursuing as a LEED-CI. Due to concerns about bacterial growth, the state health regulations (OSHPD) prohibit any aerators except for laminar flow type, which bottom out at about a 1.5 GPM flow rate (i.e. there is no .5 GPM faucet we can legally use in this application). This is triple the LEED GPM baseline. However when metered with automatic controls on a 10 second cycle, it hits right at the .25 GPC baseline for metered faucets (at 1.5GPM x 10sec/60min). The faucet meter we've specified can be factory set for a cycle duration as low as 5 seconds (we have a manufacturer cut sheet to verify this); therefore the water use in GPC drops to 0.125.
It seems odd that an aerator which, evaluated in one compliance path, is three times over the baseline, but evaluated another way is half the baseline. And yet I can't see where either the math or the logic behind this is flawed. Obviously, this has a huge impact on our water calcs.
Does anyone out there have some insight that I might be missing, or is there truly that big a discrepancy between the two compliance paths?
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
March 2, 2010 - 3:43 am
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.
Andrea Traber
Director, Sustainable Buildings and OperationsKEMA
62 thumbs up
March 5, 2010 - 5:28 pm
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!
Andrea Traber
Director, Sustainable Buildings and OperationsKEMA
62 thumbs up
March 9, 2010 - 12:31 pm
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.
Hannah Pham
20 thumbs up
March 9, 2010 - 6:05 pm
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.
Tristan Roberts
RepresentativeVermont House of Representatives
LEEDuser Expert
11478 thumbs up
March 12, 2010 - 3:19 pm
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.
Dave Intner
Firmitas Architecture & Planning90 thumbs up
March 12, 2010 - 6:49 pm
Shoot, that's a bummer they have it on the back burner. Depending on how they rule on this, it could be a six point swing for our project; possibly more. I wonder if submitting a formal CIR would expedite it.
There is precedent within LEED for multiple analysis paths leading to different outcomes; for example, EAc1.1 (Lighting Power Density) in LEED CI 2009 allows you to use either a Space-by-Space Method or an overall Building Area Method. Same fixtures, same floor area, but potentially different results due to varying baselines.
Just sayin'.