102
6.3 Quality of Daylighting
6.3 Quality of Daylighting
Window Size In general, the larger the windows a space has, the more daylight that space will receive. A facade’s Window Wall Ratio (WWR) is the most effective way to measure window size as it relates
=
÷
WWR
Glazing Type VT EA Single Pane
Glazing Area: 200 sf ÷ Fig. 8 - Punched Windows
Total Area: 810 sf
=
.25
.89 .22
to daylighting potential. WWR is defined as a facade’s net glazing area to its total area.
Double Pane .79 .20
Effective Aperture
Triple Pane
As discussed in Chapter 6.2, the Visible
.74 .18
Transmittance (VT) of a window’s glazing has a great impact on the amount of light allowed to enter a space. For this reason, WWR alone is not an effective measure of daylighting performance. A more accurate measurement is the glazing
=
÷
WWR
Glazing Type VT EA Single Pane
Glazing Area: 240 sf ÷ Fig. 9 - Ribbon Windows
Total Area: 810 sf
=
.30
Window Wall Ratio by the Visible Transmittance of
Double Pane .79 .24
its glazing. A higher Effective Aperture will mean
Triple Pane
more daylighting potential, however, it will also
.74 .22
mean more solar gain and glare. See Chapter 5.x
=
WWR
Glazing Type VT EA Single Pane
Total Area: 810 sf
=
.67
Triple Pane
WWR =
Glazing Area Total Facade Area
.89 .60
Double Pane .79 .53
÷
Aperture is determined by multiplying a facade’s
.89 .27
for more information on facade composition.
÷
Glazing Area: 540 sf Fig. 10 - Curtain Wall
system’s Effective Aperture (EA). Effective
.74 .50
EA = WWA x VT d =
h x 2.5