Research matters - Illuminating Engineering Society

ENERGY ADVISOR
watts = 450 watts, for the one electronic
T8 downlight per luminaire on
a dimmer used for note taking, for a
total of 1350 watts. 1350 watts per
classroom per 750 sq ft = 1.8 watts
per sq f t for the connected load. But
the two uplights and the one downlight
can’t be on at the same time
because they are wired to a rocker
switch, which chooses one or the
other. Hence, the maximum connect-
In
Easy
Circle 54 on Reader Service Card.
ed load...general lighting is on, which
is 900 watts per 750 sq ft = 1.2
watts per sq ft, which is compliant
with the new California energy code.
Preliminary data from electronic
recording meters that measure the
actual load used on a minute-byminute
basis indicate that because of
daylight harvesting and occupancy
sensors, plus dimming control for the
single task light, and frequent use of
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video tapes by teachers, the actual
load used is less than 1.0 watts per sq
ft, about half of the connected load
and less than a third of the NEC calculated
load. What a waste of copper!
And schools, unless they are used
evenings for teaching, community
meetings and adult education,are typically
in use 200 days a year or less,
and only for about 10 hours a day.
Furthermore, according to Lisa
Heschong of the Heschong Mahone
Group, Inc., Fair Oaks, CA, daylight
harvesting can save from 40 to 80
percent of lighting energy in the
daylit zone under “toplighting” skylights.
California’s “Title 24 Energy
Code” recognizes that daylight harvesting
and bi-level lighting in intermittently
used spaces can be a useful
energy saver.
The full story on the California
PIER project will be available in July
after this school semester ends, and
hopefully, the data will be helpful to
our code writers and designers.
I have visited many offices that
use task/ambient lighting that provides
more than 50 fc with only 1
watt per sq ft, and there are some
energy saving measures, like daylight
harvesting and bi-level lighting, that
can be used to reduce energy usage
even further.
There is quite a difference
between “calculated,” “connected”
and “actual” load. Only from experiments
such as those being conducted
in the PIER project do we learn
about actual “energy usage,” which is
indicative of energy conservation.
The meaningful restrictions on usage
are not addressed by our energy
codes, which is regrettable.
Toplighting daylight harvesting can
be a significant energy saver for “big
box” retail and wholesale stores,
much more than in school classrooms.
We may be spending more
money and energy on unnecessary
copper feeders than we’re saving in
lighting. This disconnect obeys
Warren’s “Law of Unintended
Consequences.”
Willard L.Warren, PE, LC, FIESNA, is
the principal of Willard L.Warren Assoc,
a consulting firm serving industry, government
and utility clients in lighting and
energy conservation.
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