2.5.1.3. Energy Code Compliance
Clearly the power densities shown in Table 2 do not even approach compliance with the
ASHRAE/IESNA Standard 90.1-2004 (see Sections 2.1.4 2.1.6). The average
calculated power density is 4.2 watts per square foot (w/sf), while the target power
density limit is 1.9 w/sf for courtrooms.
2.5.1.4. Energy Usage Kilowatt-hours
It is important to note that power density is actually a limited method of determining
actual energy usage because it does not assess hours of use. District courtrooms are not
used as frequently as most other spaces, and so the high connected load is not likely to
be as severe a problem as it could be. Unfortunately the lighting section of Standard
90.1-2004 does not have an equivalency system to determine the relative importance of
different spaces with respect to energy consumption. It is important to recognize that
true energy consumption is reflected in kilowatt-hours, which consider both connected
load and hours of use.
The issue of energy use over time and code language related to lighting controls is
being discussed in depth in the most recent ASHRAE 90.1 Lighting Subcommittee
meetings. Should the U.S. Courts want to provide data about the relative energy use of
courtrooms over time or have input to the code development process, feedback is
always welcomed by the ASHRAE Standard 90.1 Lighting Subcommittee.3
2.5.2. Energy Modeling
The immediate challenge was to determine if the use of energy efficient technologies could
sufficiently reduce consumption. Two methods of energy modeling were used to determine
possible solutions to high energy consumption. The first method was a fairly high level and
simplified investigation into the substitution of more efficient technologies. The second
method was a detailed computer modeling using point-by-point ray tracing software, to
provide a more focused solution to the obvious overuse of incandescent downlights.
2.5.2.1. ANSI/ASHRAE/IESNA Standard 90.1-2004 Models
The energy analysis utilized a pre-existing methodology that models different types of
lighting equipment in a variety of spaces. These models form the basis for lighting
power density values in the national energy standard, ANSI/ASHRAE/IESNA Standard
90.1-2004. PNNL is actively involved in supporting USDOE with respect to the
development of Standard 90.1, and as such, has experience in using these models. The
goal was to perform a broad strokes re-design in the courtrooms to determine how much
energy could be saved.4 The energy savings were roughly estimated by assuming a
replacement of the lighting technologies.
3
For information on how to provide input to the ASHRAE Standard 90.1 Lighting subcommittee,
email carol.jones@pnl.gov or eric.richman@pnl.gov.
4
The modeling process is not a simple wattage reduction or replacement; rather, it requires an
application of lighting equipment (using published data and coefficients of utilization) along with an
IESNA approved lumen method of calculating lighting levels.
March 2006
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