Placing the horizontal sunshade slightly above the upper edge of the window
can also be used to maintain body level airflow. The exact size of the gap or
placement of the overhang required depends upon the sunshade and window sizes.
Vertical Shading Devices. Vertical fins or wingwalls are the most
appropriate shading devices for east and west facing openings which receive
sun at low angles, and for southeast and southwest openings in combination
with horizontal shading. Wingwalls which increase the ventilative potential
of the building may also be utilized for shading if they are properly designed
(refer to para. 4.5.3).
Other Types. Operable exterior shutters, rolldown shades and
blinds can provide effective shading on any facade. They are most useful on
east and west openings which are difficult to shade with overhangs or vertical
shading devices. The thermal performance of closed exterior shutters depends
on how well the heat absorbed by the shade is dissipated to the outside air.
For this reason, light-colored reflective shutters are preferred in hot
climates. For naturally ventilated buildings, the specification of such
devices should be treated with care since air movement to the building
interiors is reduced when the shutters or shades are in their closed position.
If the operation of the devices is not obvious, provision should be made for
mounting instructions nearby.
Site obstructions such as buildings and trees may provide effective
building or window shading. Analysis of the site using a sunpath diagram is
recommended to determine when such shading occurs.
Glazing Type. Each glazing type provides differing amounts of
resistance to solar heat gain. Reflective and absorbing glazing types can
reduce cooling loads 15 to 30 percent below that of clear glass with some
reduction in transmitted light.
Heat-absorbing glazing is less effective than reflective glazing
because it absorbs the solar heat into the glass, thereby increasing the heat
convected and radiated into the internal space. Better performance can be
obtained with either reflective or heat absorbing glazing if they are used as
the exterior panel of a double glazed window. In general, clear glazing with
effective exterior shading shall be used unless an optional glazing/shading
system can be justified in a cost-benefit analysis.
Design Procedure. See the latest edition of Architectural Graphic
Standards for details on designing exterior solar shading.
Insulation. Insulation is used in naturally cooled buildings to
reduce the amount of solar heat transmitted to occupied areas. The designer
shall use the most appropriate and cost effective means of controlling heat
gain through the roofs and walls of the structure with a minimum recommended
composite R-value (R = thermal resistance value of the assembly) of R-20 for
roofs and R-11 for walls which are exposed to solar radiation.
The insulation systems may be located inside or outside the
building structure and should be selected using the following criteria as