Page 134 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

114 Cha pte r T h ree

Water Management Draft: Table 1-3: Mid-Summer Daily Reference ET (Grass Reference)
0
Based on Climate for Midday Mid-Summer Air Temperature and Relative Humidity on
the IA (Irrigation Association) website, January 2006 (www.irrigation.org/about_et_
list.htm). The values are based on typical July daily high temperatures (degrees
Fahrenheit) and associated relative humidities (RHs).
These factors and ET are used to determine the baseline and the design
0
evapotranspiration rates for each landscape area (area i) on the site, ETB and ETD .
Li Li
ETB = (k )(k )(k )(ET ) for landscape area i (3.1.1)
Li sB dB mcB 0
ETD = (k )(k )(k )(ET ) for landscape area i (3.1.2)
Li sD dD mcD 0
There are two other factors that influence irrigation and are included in the calculations.
The first is the irrigation efficiency (IE) factor, which is representative of the type of
irrigation system used. A drip irrigation system usually has an irrigation factor of 0.90 and
is much more efficient at delivering the water more directly to the plants as needed than a
typical sprinkler system which has an IE of around 0.65. For the baseline case, a
“conventional irrigation” system type of the region should be used (conventional irrigation
is defined as per LEED-NC 2.2 in App. B). The second factor, the controller efficiency (CE),
has to do with using special sensors to control the sprinkler use based on conditions such
as soil moisture. If no special sensors are used, then CE is equal to 1; otherwise the factor
used should be supported by the manufacturer’s literature and is less than 1, but
significantly greater than 0. Some typical or representative values are given in Table 3.1.5.
The baseline and the design evapotranspiration rates for each landscape area A on
i
the site (ETB and ETD ) together with the baseline and design irrigation efficiencies
Li Li
(IEB andIED ), and the controller efficiencies (CE ) for each landscape area i, are used to
i i i
calculate the baseline and design total water applied (TWAB and TWAD ) for each
i i
landscape area, and the baseline and design total water applied (TWAB and TWAD) for
the project. Typically the controller efficiency for the baseline case remains at 1.0.
TWAB = (A ) (ETB )(1.0/IEB ) for landscape area i (3.1.3)
i i Li i
TWAD = (A ) (ETD )(CE /IED ) for landscape area i (3.1.4)
i i Li i i
TWAB = ∑
TWAB i (3.1.5)
i
TWAD = ∑
TWAD i (3.1.6)
i

Irrigation Irrigation Controller
System Efficiency (IE) Irrigation Controller Efficiency (CE)
Drip irrigation 0.90 None 1
Types
Sprinkler 0.65 Per manufacturer 0 <<CE < 1
Conventional 0.65 None 1
Baseline
irrigation
TABLE 3.1.5 Other Irrigation Factors: Some Representative Values