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Bi-level Switching Study Demonstrates Energy Savings

While automatic shutoff of general lighting, required by prevailing energy codes, has received a significant amount of attention by the lighting specification community, bi-level switching is another frequent code requirement that can play an important role in energy conservation.

While energy savings with bi-level switching can be less than automated control strategies due to reliance on human initiative, it is a simple, durable switching strategy, with no special user training or maintenance to maintain its functionality.

In this special report by the Lighting Controls Association, we will describe bi-level switching code requirements, its role in the Commercial Buildings Deduction, methods and equipment, and the results of a study of typical energy savings achievable with bi-level switching in popular applications.

Bi-Level Switching and IECC

While ASHRAE/IESNA 90.1 is the national energy standard, many states have adopted an alternative—the International Energy Conservation Code (IECC) developed by the International Code Council (ICC), a membership association dedicated to building safety and fire prevention. The IECC is a model energy code that covers lighting in addition to other energy-using building systems. States have adopted various versions of the IECC, including the 2000 version (with 2001 supplement), 2003 version (with 2004 supplement), and 2006 version (with 2007 supplement), with the 2003 version being the most prevalent. The 2003 and 2006 versions of the IECC, covered in this report, require bi-level switching in interior spaces.

A number of states have developed state-specific codes that may or may not also require bi-level switching. For example, California’s Title 24 energy code requires bi-level switching in interior spaces.

Below is a table that reflects state-by-state adoption of IECC as of April 8, 2007. Confirm your state’s status by clicking here and scrolling down to the commercial code section of the page. Note that the 2003 and 2006 versions of IECC reference ASHRAE 90.1 as an alternative standard. ASHRAE 90.1 versions up to 2004 do not require bi-level switching in interior spaces.

IECC requires at least one manual control for lighting in all interior spaces enclosed by ceiling-height partitions, with few exceptions. If the space …

* has more than one light fixture
* is not controlled by an occupancy sensor
* is not a corridor, storeroom, restroom or public lobby
* has a lighting power density (lighting W/sq.ft.) >0.6W/sq.ft.
* is not a guestroom/sleeping unit

… then it must have bi-level switching. IECC defines bi-level switching as providing occupants the ability to reduce lighting load in a reasonably uniform pattern by at least 50%, and recognizes four methods (see “Methods of Bi-Level Switching” below).

IECC bilevel switching decision tree

Bi-level Switching and the Commercial Buildings Deduction

The Commercial Buildings Deduction created by the Energy Policy Act of 2005 established the Interim Lighting Rule, which enables an accelerated tax deduction of $0.30-$0.60/sq.ft. proportional to lighting power density savings of 25-40% below ASHRAE 90.1-2001.

There are several other requirements, one of which is bi-level switching must be installed in all occupancies except hotel and motel guest rooms, store rooms, restrooms and public lobbies.

Methods of Bi-level Switching

IECC recognizes four methods of light level reduction control:

* Controlling all lamps or fixtures (e.g., dimming or light level switching)
* Dual switching alternate rows, fixtures or lamps
* Switching middle lamp independent of outer lamps (3-lamp fixtures)
* Switching each fixture or each lamp

Suitable solutions include dimming controls, manual switches and daylighting controls. Other methods are acceptable if approved by the authority having jurisdiction.

Below is an example of the dimmer control option:

bilevel switching - dimmer option

Another option for controlling all lamps and fixtures is to use step-dimming or light level switching ballasts, which provide a uniform change in illumination in the space. For example, a light level switching ballast incorporates two hot power leads for control with two standard switches or relays; switching one lead on provides 50% power while having both switches on provides 100% power. Alternatively, if only one switch is available or desired, the light level switching ballast can provide 100% power when the switch is first turned on and 50% after toggling down and back up.

Below is an example of bi-level switching based on separately circuiting and switching alternate fixtures:

bilevel switching - alternate fixtures option

Below is an example of bi-level switching based on separately circuiting and switching alternate lamps (a/b).

Another approach based on lamps would be multi-level switching, which enables three levels of light output and power input using three-lamp fixtures: all lamps OFF (0% light output), one lamp on in each fixture (33%), two lamps on in each fixture (66%), and all lamps ON (100%). Multi-level switching provides greater flexibility than bi-level switching and poses a less abrupt change in light level when automatic control is used. Greater granularity is possible depending on the lighting equipment and need.

Note that the term “bi-level switching” often refers to both bi-level and multi-level switching strategies.

Study of Bi-Level Switching Use and Energy Savings

In May 2002, “Lighting Controls Effectiveness Assessment: Final Report on Bi-Level Lighting Study” was published by the California Public Utilities Commission (CPUC), prepared by ADM Associates for Heschong Mahone Group, project managers for the Southern California Edison Company on behalf of the CPUC.

This is one of only a few field studies that have actually examined the use and utility of bi-level switching as a means to reduce energy costs. Two specific goals of the study were:

* Study how occupants used manual bi-level switching controls, including behaviors that reduced savings potential; and
* Estimate energy and demand savings.

The researchers measured data for bi-level switching applications in 256 open and private office, retail and classroom spaces in 79 buildings. The fixtures contained three lamps that were switched in a multi-level switching scheme, providing four lighting states: all lamps OFF, 1/3 lamps operating, 2/3 lamps operating and all lamps ON.

Table 2 below shows the breakdown of use of different bi-level switching conditions (high-wattage or 2/3 lamps switch only ON, low-wattage or 1/3 lamps switch only ON, or both switches ON or OFF).

Table 2. Use of bi-level switching conditions at 3PM on weekdays by space type. Source: ADM Associates

ADM Associates discovered that private offices demonstrated the highest level of energy savings derived from using bi-level switching at 21.6% (with bi-level energy savings defined as occurring at 1/3 or 2/3 power). Open offices came in second at 16.0%, followed by retail at 14.8% and classrooms at 8.3%.

One of the factors of bi-level switching use that was studied was daylight contribution. Use of bi-level switching and subsequent energy savings in open offices and retail spaces showed a positive correlation with daylight availability. Private offices did not show a positive correlation. Classrooms did, but demonstrated the opposite of researcher expectations: Classrooms with the lowest amount of daylight also had the lowest level of use of lighting.

In the end, the study demonstrated that manual bi-level switching results in energy savings, which could be increased with occupant education, and with the limitations on the use of only one switch offset by the simplicity and economy of the approach.

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