BI-LEVEL
SWITCHING
Description:
Bi-level switching is a relatively simple and durable switching strategy
that can generate 10-15 percent energy savings. Bi-level switching’s
role in the Commercial Buildings Deduction provision has caused a great
deal of discussion in the lighting industry. The law offers minimal
language about bi-level switching, but it is clear. To qualify for the
Deduction as defined by the Interim Lighting Rules, bi-level switching
is required in all occupancies except hotel and motel guest rooms,
storage rooms, rest rooms and public lobbies. Due to the lack of
additional information, there is presumably some latitude in how it can
be accomplished. In existing buildings, including bi-level switching can
present application challenges. On the other hand, if it weren’t
included, the Deduction provision likely would have required 50% LPD
savings in all applications rather than 25-40%.
A number of approaches can be used to
accomplish bi-level switching, usually related to the type of controller
used to control the lights and how the lights are configured. Most
bi-level switching approaches split the lighting in a space into two
circuits that can be separately controlled. As an alternative to
switching, bi-level dimming or continuous dimming can be employed, ideal
for applications where switching or separately circuiting are not
practical.
Presumably, one could employ bi-level
switching on alternate ballasts, or alternate fixtures, or alternate
circuits; switch controlled by photosensor; manual switch controllable
by occupants; manual switch controllable by facility operator; scheduled
switching based on time or day or other factor; or bi-level or
continuous dimming.
Treasury is expected to issue final
regulations defining the Commercial Buildings Deduction shortly. Further
clarification of bi-level switching is not anticipated at this time, as
the law does not require Treasury to do so. However, Treasury will
recognize who can certify projects. This party will become the
“authority having jurisdiction” in projects seeking the Deduction, and
will approve bi-level switching strategies.
Below are two common bi-level switching
strategies that use switching.
Bi-Level Switching:
The
below graphic shows a section of an office, lighted by eight 4-lamp
fixtures. Two wall switches can be used, one to control all outboard
lamps (A and D) while the other controls the inboard lamps (B and C).
Alternately, one switch could be used to control all even-numbered
fixtures and another for the odd-numbered, or to control fixtures 1/2
and 5/6 separately from the other four. Any of these techniques permits
a 50% reduction in light output, with the best selection being that
which closely matches occupancy patterns in the space. By using four
controls, even more variations are possible. Instead of wall-switches, a
number of other controllers can be used, such as scheduling control
panels, photosensors, occupancy sensors and other devices.
Multi-Level Switching:
Another strategy is multi-level switching, which can be initiated using
a manual switch or automatically based on a control signal from a
photosensor (based on detected light level resulting from available
daylight), occupancy sensor (based on detected occupancy), or
centralized control system (based on a schedule). This graphic shows a
series of three-lamp fixtures with split-ballast wiring so that the
inboard lamps are controlled on a separate circuit than the outboard
lamps. This allows four light levels—100% (all lamps lit), 66% (2 lamps
in each fixture lit), 33% (1 lamp in each fixture lit), and 0% (all
lamps extinguished). The graphic shows two lamps being lit in each
fixture, providing 66% light output. Multi-level switching provides
greater flexibility than bi-level switching and poses a less abrupt
change in light level when automatic control is used.
see also:
Bi-Level Switching
Occupancy Sensors
Intelligent Control Panels
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