Page 149 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

LEED W ater Ef ficiency 129

or

IWUD = (WCR × TWCU) + (UR × TUU) + [0.25 × TLFU]
auto i i
+ [KSR (0.25 min) × TKSU] + [SR (5 min) × TSU]
i i
+ [1.6(? min) × TPRU] for lavatory faucets with autocontrols
(metered), in gallons per year, no private applications (3.3.7)
The only differences between the base water usage rate and the design water usage
rate are the fixture flow rates. If autocontrols are used in the design case, then
autocontrols are assumed in the baseline case. This is different from LEED-NC 2.1,
and designs which meet the version 2.1 criterion might not meet the version 2.2
criterion. Also, in LEED 2009, the baseline lavatory faucet rates for commercial uses
(nonprivate rooms) are significantly reduced from the LEED 2.2 values. In fact, they
are now similar to what were previously considered to be ultra-low flow rates. In
previous versions of LEED, commercial lavatory faucet use counted for a substantial
portion of the calculated water use reductions in many cases. With this baseline
change from the 2006 UPC and 2006 IPC, lavatory faucets will no longer be as
important toward credit compliance.
As in WE credit 3.2, a reduction in potable water used for blackwater fixtures can be
from a reduction in the flows, the alternate use of nonpotable water in these fixtures, or a
combination of both. Therefore, the annual usage of other water sources, such as rainwater
or graywater, for these fixtures can be subtracted from the total design water usage rate.
The designer should provide calculations to estimate the rate of these alternative waters
available for use on an annual basis. For instance, rainwater availability is seasonal, so the
totals available during the rainy seasons may be the only opportunity for potable water
reduction. Note also that there are local and state health and other regulatory codes that
cover the use, storage, and possibly treatment of nonpotable waters in buildings. The
designers, owners, and managers should become familiar with any special health-related
requirements for use of reuse waters or rainwaters so that any special protective measures
or treatments can be included in the design and operations. The designer should include
the associated costs and systems in the design and include a narrative of them in the
submittal. Let GW be the annual graywater or other alternative water source usage in the
wastewater fixtures; then WE prerequisite (WEp1) is obtained if the following is true:

IWUD − GW ≤ .080 (3.3.8)
IWUB

In like manner, two, three, or four points for WE credit 3 are obtained if the following
are also true, respectively:

−

IWUD GW ≤ .070 or ≤ 0.65 or ≤ 0.60 (3.3.9)
IWUB
Residential Uses The building designer should declare the design occupancy (DO) for
the buildings. LEED 2009 gives some recommended residential design occupancies as
two persons per one bedroom unit and one additional person per additional bedroom.
Usually, residential facilities do not have urinals, and they typically have equal gender
distributions. Equation (3.2.2) can again be used to estimate the total water closet usage.
In this case, the transient occupancies are zero, there are no urinals, and there are no