The dome is typically installed between
rafters and joists on the roof, and the adjust-
able aluminum tube extends from the roof to
the ceiling of the interior. Sold in kits, tubular
skylights minimize heat gain and loss: the
aluminum tube radiates any collected exte-
rior heat into the attic, and the sealed shaft
allows very little interior heat to escape up.
Also, little UV is transmitted to the interior;
almost all of the UV rays are absorbed by the
dome, shaft, and diffuser materials.
Heat Gain
When buildings use glazing to admit daylight,
a single layer of ordinary glass exposed to
the sun also admits warming radiant
energy—heat. This helps in cold winters but
poses a problem in hot summers.
If buildings are properly designed to use
daylight, they reject most of the direct light
from the sun yet still admit an ample supply
of skylight. Just as the sun’s light can be
controlled, there are many ways to control
the sun’s radiant heat; it may be admitted or
excluded as seasonally required without
eliminating the benefits of daylighting.
Orientation is a primary method for
managing solar heat radiation because the
sun strikes differently oriented surfaces with
widely varying intensity. The size and place-
ment of glazed areas are also factors in cap-
turing the sun’s energy for cold-weather heat
gain.
For example, a house benefits if its walls
and roof are oriented to receive heat from
the sun in the winter and shed it in the
summer. If the principal façade of a house
faces due south or within 30° of due south,
the south-facing walls may be designed to
absorb radiation from the low winter sun; the
roof may be designed to reject the sun’s
heat by reflecting the high summer sun.
It is possible with any building orienta-
tion to achieve good quality daylighting
indoors. North light is inherently softer,
cooler, and more uniform; because of the
sun, south light is more intense and variable.
But the same high quality of illumination that
comes naturally from the north sky can be
achieved with any other orientation by the
proper use of daylight controls.Shading Devices
Shading devices used on the inside of the
building reflect some of the radiant heat
energy back outdoors, reducing the energy
gain from the sun by as much as 60 to 70
percent. Exterior shading devices can reduce
that energy penetration even more—by 90
to 95 percent. Exterior shading devices are
more expensive to build and maintain, but
with hot climates or high energy costs or
both, air-conditioning savings often give
quick paybacks.INTERIOR LIGHTING FOR DESIGNERS
Figure 5.10Tubular skylight.