Page 147 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

LEED W ater Ef ficiency 127

Using these variables, the equations for total lavatory faucet use (TLFU), total
kitchen sink use (TKSU), and total shower use (TSU) are

TLFU = [ND ∑ (FTE × LFU )] + [ND (TOW × LFU )]
FTE j i TOW i
over all shifts j and for each type of use i (3.3.1)
TKSU = [ND ∑ (FTE × KSU )] + [ND (TOW × KSU )]
FTE j i TOW i
over all shifts j and for each type of use i (3.3.2)
TSU = [ND ∑ (FTE × SU )] + [ND (TOW × SU )]
FTE j i TOW i
over all shifts j and for each type of use i (3.3.3)

The equations for water volume usage based on lavatory faucet, shower, prerinse
spray, and kitchen sink uses have an additional variable that was not included in the
equations for blackwater generation. Unlike toilets and urinals, where the uses are
calculated on a volume per flush or use, sink and shower volumes per use are often
based on both flow rates from the fixture and a time or duration that the fixture is
kept turned on. The applicable durations are given in Table 3.3.1. Note that Table 3.3.1
gives different durations for residential and commercial uses. The baseline EPAct
1992 (conventional) flow rates as updated for the 2006 Uniform Plumbing Code (UPC)
and the 2006 International Plumbing Code (IPC) revisions and water-efficient flow
rates from the LEED-NC 2009 Reference Guide for lavatory faucets, kitchen sinks,
prerinse sprays, and showers (LFR , KSR , PRR , and SR , respectively) are given in
i i i i
Table 3.3.2, as are the previously given baseline values for the water closets and
urinals from Table 3.2.2.
A special note is again needed for some of the blackwater generation rates in Table
3.2.2. Composting toilets and nonwater urinals do not use water for regular usage. They
are not currently customary fixtures in the United States. Therefore, they have different
maintenance and waste collection needs than more common water closets and urinals.
The designers and owners should be very cognizant of the different maintenance needs,
and it is recommended that they determine a way to meet these special needs early in the
design phase of a project so that there are no additional concerns, costs, or changes later
in the project.
Now both the baseline and the design annual water volume usage rates for the
fixtures applicable to WE prerequisite 1 and WE credit 3 can be determined.
Durations for typical prerinse spray usages will need to be provided by the project
team. The following equations also do not address private (hotel or hospital room)
lavatory use in commercial facilities and these would also need to be added in.
The applicable indoor water usage baseline (IWUB), in gallons per year, can be
calculated using the durations in Table 3.3.1 and the fixture flow rate numbers in
Table 3.3.2 as follows:

IWUB = (1.6 × TWCU) + (1.0 × TUU) + [0.5(0.25 min) × TLFU]
no-auto
+ [2.2(0.25 min) × TKSU] + [2.5(5 min) × TSU] + [1.6(? min) × TPRU]
for lavatory faucets without autocontrols, in gallons per year ,
no private applications (3.3.4)