DOE-2 Energy Modeling Summary - Office Building
Page 19 of 21
G. DESCRIPTION OF ENERGY EFFICIENT MEASURES
1.0 W/SF Lighting
The lighting Watts per Square Foot power consumption for all office spaces was reduced to 1.0
W/SqFt.
Daylight dimming control for perimeter office areas
Continuous daylight dimming controls can reduce the lighting output down to 10% of total lighting
output; at 10% of the total lighting output, the fixture power consumption is reduced down to 21%
of the total watts. The controls are set to maintain at least 50 footcandle at 30 inches off the finished
floor. The daylighted area is as defined in ASHRAE/IES Standard 90.1-1989 User's Manual.
Additionally, a daylight dimming system saves electricity even during nighttime. The mean lamp
output is rated at 40% of its expected life. Because of this, during the first 2-3 years of operation
lamps emit more light than specified in the design. The dimming system reduces that light level to
design specifications and saves energy whenever the lights are "on" during these first 2-3 years of
operation saving about 4% in electricity use.
Occupancy sensors in enclosed offices
Occupancy sensors are assumed to reduced lighting by 30% during occupied hours in enclosed
offices and conference rooms. The 30% Power Adjustment Factor is that given in ASHRAE
90.1-1989 Table 6-3 for occupancy sensors.
Infrared occupancy sensors detect the change in the heat patterns occurring in a room. If portions
of a room are not in direct line-of-sight with an infrared sensor, then a second sensor must be
mounted or an ultrasound sensor must be used instead of the infrared. (Ultrasound sensors emit
signals, like a bat, that bounce off obstacles in a room. These sensors "see" around partitions but are
more expensive than infrared sensors; they are also less reliable in large, open spaces with soft
enclosures, because the signals cannot bounce back very well.)
When infrared sensor technology was initially commercialized, some sensors would turn the lights
off if there was little movement in the room (e.g., only hands moved to type). This problem has long
been resolved. Today's infrared occupancy sensors have better sensing ability and, just as important,
can be set to turn lights off after specific time interval, (e.g., 1 minute, 5 minutes, 15 minutes, up to
30 minutes). A sufficiently long time interval ensures that even a sensor that does not discriminate
fine movement will still accomplish its function properly since a person that types or reads will move
the neck, back, or arm every few minutes to be comfortable.
APPENDIX J - GSA LEED COST STUDY
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