Building Automation and Lighting Control

Posted October 2008
See this whitepaper published in the fall issue of Lighting Management & Maintenance Magazine, published by NALMCO.
Demand is the sum of all electric power required to run a building’s equipment currently in operation. As equipment is turned on and off, demand rises and falls. Peak demand is the highest level of demand recorded by a demand meter during a given time period. This is the most expensive power the utility has to produce, as the utility must build sufficient capacity to satisfy these short periods or buy the power needed from other sources at market rates. Many utilities pass these costs on to their customers as a demand (kW) charge added to charges for energy consumption (kWh). According to ConsumerPowerline, in fact, demand charges can represent 40% of electric utility costs.
Utilities would rather have their customers reduce their demand peaks instead of their entire load profiles, so many utilities, Independent System Operators (ISOs) and other power providers offer incentives to curtail non-critical loads either at scheduled times or on request during a grid emergency. CAISO (California), ERCOT (Texas), PJM (Northeast), NYISO (New York) and ISONE (New England) are examples of organizations offering demand response programs. These demand response programs give utilities an alternative to building more power plants or buying expensive power from supplemental sources.
Even without tapping into such a program, building owners can reduce costs by shaving their peaks using a strategy called load shedding, either on a schedule or in response to price signals.
Lighting provides good opportunities for load shedding because it usually occurs when daylight is available and is available for year-round demand reduction. Assuming the building’s hours of operation will not change, building owners have two options to reduce peak demand with lighting.
First, they can shut off non-critical lighting loads either manually (through master switches accessible to the facility operator) or automatically (through a scheduling system such as an intelligent relay panel), and either by space or using some type of bi-level switching scheme. Second, they modify their lighting to be step-switching or dimmable with a central point of control.
Because people need light to work, dimming is preferable to ON/OFF switching in areas lacking daylight. Generally, dimming is also preferable to step-level switching (or ON/OFF switching with daylight available) in occupied spaces in which the occupants perform stationary or critical tasks, such as offices, where changes in light output should be unnoticeable to a high degree. In addition, dimming is more suitable when light fixtures are in the normal field of view and/or lamps are visible to occupants.