Lighting accounts for 30 to 40 percent of the total energy use for
most office facilities. In industrial facilities, lighting will account
for five to 10 percent of the total energy use due to the heavier process
and motor loads. In either case, it is an attractive cost reduction
strategy and is commonly the first option selected.
Start with a lighting audit to evaluate the current lighting systems
and assess how well the systems perform compared to state-of-the-art
systems. The benchmark is lighting power density (LPD), which is expressed
as watts per square foot (W/ft2). A state-of-the-art T8 fluorescent
lighting system in an office space is at or below 1 W/ft2. Compare that
to a typical office building LPD of 2 W/ft2 or more, and one can see
the savings potential.
If you think lighting upgrades are old hat, more T12 fluorescent lamps
are produced each year than any other type of fluorescent lamp. Converting
T12 fluorescent systems with magnetic ballasts to T8 fluorescent systems
with electronic ballasts offers energy savings of 40 to 60 percent,
and a 30- to 50-percent return on investment. Also consider using low
mercury fluorescent lamps. They cost the same, perform as well or better
than those with high levels of mercury, and are not considered hazardous
waste. While mercury is a critical component for a fluorescent lamp,
it isn't needed in your tuna sandwich. Using low-mercury lamps in your
lighting retrofit will increase your rebate, if you are a Florida Power
& Light customer from $75/kW in reduced demand, to $100/kW.
Add occupancy sensors to an upgrade from T12 to T8 fluorescent lighting
and the return on investment soars to levels that will make a CFO break
out into song. The logic is simple. Keep the lights off when nobody
is in the room. The typical private office is empty 53 percent of the
day, storerooms 56 percent, meeting rooms 66 percent, and restrooms
are empty 70 percent of the time.
Don't forget that by reducing the lighting load you can reduce the HVAC
load at the same time. One kW is equal to 3,412 BTUs and 12,000 BTUs
equal one ton of air-conditioning.
In South Florida, FPL and ASHRAE have adopted the following standard:
For each kWh of electricity saved by lighting, an additional 32% is
saved on HVAC costs, due to the reduced heat generated by energy efficient
lighting equipment. This factor of .32 is reduced somewhat, however,
if return air is ducted, rather than returned in the plenum.