Page 325 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

LEED Indoor Envir onmental Quality 287

RAT The total floor area of all regularly occupied room areas
WA The sum of the areas of window type i in room area j
ij
The glazing factor of regularly occupied room area j can be determined as
( ∑ CDFi) ×( WAij)

GF = i
j for all window types i in regularly occupied area j (6.8.1)
RAj
The total floor area of all regularly occupied room areas can be determined as
RAT = ∑ RAj for all regularly occupied room areas j
(6.8.2)
j

In LEED 2.2 Option 1, daylighting compliance for the project can be calculated as
⎛ ∑ RAj⎞
DC = 100 × ⎜ j ⎟ ⎟ for all regularly occupied areas j where GFj ≥ 0.02 (6.8.3)
⎜
⎜ ⎝ RAT ⎟ ⎠

For either version and all options, the project complies with IEQc8.1 if
DC ≥ 75 (6.8.4)

Simulation and Measurement Options These options are based on a horizontal illumination
level. The requisite amount is at least 25 horizontal footcandles by natural lighting in a
minimum of 75 percent of the regularly occupied areas. Illumination engineers are
experienced in providing isoluxes of areas. Isoluxes are plan views giving horizontal
illumination contours. For many exterior applications, these illumination contours are
usually given at ground level, but for the simulation options (Option 1 in LEED 2009
and Option 2 in LEED 2.2) and either version of the measurement option (Option 3), the
isoluxes would be on the horizontal plane at 30 in above the floor. This elevation
corresponds more closely to the level of a worktable or desktop. Isolux stands for “same
light,” and the term lux (abbreviated lx) is also the SI unit for illuminance. One footcandle
equals approximately 10.764 lx. In the 2.2 version, these simulations or measurements
are based on natural light that would be expected or is measured on a clear day at noon
on the equinox (either vernal or autumnal). In LEED 2009, the time has been changed to
both 9 a.m. and 3 p.m. on the equinox for the simulation option, but is not specified for
the measurement option, so it is assumed that the times for the measurements have also
been changed to 9 a.m. and 3 p.m. to be consistent with the simulation option.

Special Circumstances and Exemplary Performance
Since the location of windows and other daylighting features is an intricate part of the
architecture of a building, this credit has been labeled with an EB from the USGBC. It is
more difficult to change in an existing building. Figure 6.8.2 shows an area with natural
daylighting at a LEED-NC-certified building in Columbia, S.C. Figure 6.8.3a and b
shows the outdoor and indoor views of skylights at a mall in South Carolina.