In most commercial and institutional buildings, lighting may directly create 20% to 30% of the electric load and is typically a significant contributor to a facility's cooling load. When an electric chiller handles that load, it may add another 10% to the building's peak demand. Where variable-speed drives control fan speeds, extra cooling loads keep them running at higher speeds, pulling even more power.

As a result, lighting is often responsible for 40% or more of a building's total electric peak load. Being able to control a portion of that load in real time through a building management system (bms) could trim the peak demand charges levied by a utility or power supplier. Fortunately, several recent developments make this goal readily achievable.

Lighting Controls More Flexible and Affordable

Most lighting systems are designed to sufficiently illuminate a space when it's dark outside. During much of the day, perimeter and common spaces that receive daylight are therefore often overlit, allowing a moderate reduction (typically 15% to 35%) in light fixture output without compromising productivity or safety. When done gradually through an automated system, most occupants are not aware that the change is occurring. Even some interior spaces not receiving any natural light can be dimmed for a few hours a day without creating a problem. How can this be done in a cost-effective way without disrupting a building's normal operations?

Dimming ballasts used to be either very expensive or, in the case of magnetic units, not always reliable or energy efficient. Many electronic dimming ballasts are now available at a much lower cost, and are quite energy efficient and reliable. When connected by low-voltage control wiring, they may be easily dimmed in groups. When done under the direction of a bms that is reading building-wide peak demand from the pulse output of a utility's meter, real-time demand control is achieved without impacting any other building operations.

The major change to fluorescent lighting systems involves replacing existing ballasts and the connecting control wiring which, in some cases, can be interfaced with a facility's Ethernet or fiber optic communication system to cut cost. Ballasts are also available that respond to power-line carrier commands, avoiding any need for new wiring. The dimming may be based on signals related to peak demand, interior daylight levels, and/or time schedules, thus providing both power demand and consumption-saving options.

One recent fixture design, the Ergolight by Ledalite, Inc., can separately reduce its uplighting component in conjunction with daylighting and its downlighting output based on occupancy. Both may also be reduced from a bms for peak demand limiting. For details, see spec sheets at: www.ledalite.com/products/ergolight/index.html.

To remotely dim existing incandescent, fluorescent, and HID lighting fixtures, area-wide dimming systems are available to control the voltage and/or power waveform at the lighting panels. Doing so reduces the wattage and light output of many fixtures without any need to modify them; no ballast changeout or new control wiring to fixtures is needed. While generally limited to a 20% to 35% reduction range (depending on the type of fixture), such systems are very cost effective due to low installation and wiring costs. Several firms offer varying types of systems. Check out products from: Electric City Corporation (www.electriccityeccc.com), Superior Electric Co. (www.superiorelectric.com), and PowerTec International (www.lightlogix.com).

An Opportunity Worth Exploring

While many plant operators have focused mainly on ways of controlling the electric loads of fans, chillers, and other centralized equipment, it now pays for them to look at ways of reducing lighting loads that force such equipment to work harder. In some states, financial incentives are available to support upgrades, making investment in this opportunity an issue to raise with senior facilities management. ES