22 August 2006
point calculations. These calculations indicate illuminance at specific points and are
capable of exitance and luminance calculations as well. Some programs can
incorporate objects in space to assess the lighting in a non-empty room. Many
programs generate perspective views of illuminated rooms, although due to the lack of
specular reflectivity these rooms do not have a photo-realistic appearance.
Point Calculations Using Radiosity Calculations. Commercially available
computer programs that allow for diffuse and specular room surfaces can perform point
calculations. These calculations indicate illuminance at specific points and are capable
of exitance and luminance calculations as well. Some programs can incorporate
objects in space to assess the lighting in a non-empty room. Many programs generate
perspective views of illuminated rooms, which in some cases can be quite realistic.
Daylighting Calculations. Refer to IESNA RP-21 or the Lighting Handbook.
Daylight availability can be estimated using these methods. Many point calculation
programs can also model daylight contributions. In addition, some commercially
available computer programs such as SkyCalc1 will determine the contribution of
daylight at a specific time and date and under specific weather conditions.
Task Lighting Calculations. Due to near-field photometric effects, the
illuminance patterns created by task lights are presently not accurately calculable.
Evaluate task lights on the basis of measured results or manufacturers' information.
Energy Calculations. Perform energy calculations in the manner and using
the forms described in the ASHRAE 90.1 User's Manual. Use Tables 15-11 and 15-12
for the Federal values to be used in ASHRAE 90.1 calculations. These tables provide
the federally required maximum allowable unit power density in terms of watts per
square foot, which varies with the type of area and function. These tables have been
provided here to avoid any inconsistencies in the use of the federally required values.
Commercially available software programs, such as DOE II, Energy 10, and BLAST,
simulate multiple building systems to provide a better understanding of energy benefits
and trade-offs of various design strategies. For a complete list and description of these
programs refer to the Whole Building Design Guide Energy Analysis Tools
The Heschong Mahone Group, Skylighting Guidelines, 1998.