Dimming Demand: Lighting Control in Demand Response

The average commercial building electric bill often features a consumption and demand component. The consumption component reflects the amount of electric energy (kilowatt-hours) used, and the demand component shows the maximum demand (kilowatts) during the billing period.

Consumption of energy and demand for power are considered separately because, if a building were to require 100 kilowatts (kW) a few times per year but less than that the rest of the time, the power provider still has to build and maintain enough capacity to satisfy peak demand. Often, therefore, the monthly demand charge is ratcheted to the annual peak demand for power, which typically occurs during summer’s hottest days.

In the United States since 1940, demand for electric energy has increased almost every year. As demand stresses supply, it is in both the power provider’s and the end-user’s interests to reduce peak demand to lower costs and risk. For this reason, a strategy called demand response was developed.

The Federal Energy Regulatory Commission defines demand response as “Changes in electric usage by end-use customers from their normal consumption patterns in response to changes in the price of electricity over time, or to incentive payments designed to induce lower electricity use at times of high wholesale market prices or when system reliability is jeopardized.”

The above definition presents two primary types of demand response—economic and emergency. Economic demand response is when an end-user reduces load during times when the value of consuming electricity is less than its cost. Emergency demand response is when an end-user agrees, in exchange for a utility incentive, to reduce load during times when the power grid is stressed to the point of jeopardizing reliability.

“Demand response programs will gain prevalence over the next three years,” said Michael T. Massey, director of sales—Encelium products for Osram Sylvania. “The major driving forces behind this increased attention are the regulatory environment, a move in certain parts of the country to close or not upgrade existing power plant infrastructure, and the expansion of the smart grid.”

Demand response is covered by California’s Title 24 energy code and green building standards, such as ASHRAE 189.1 and the International Green Construction Code (IgCC), and it is expected to be featured in a new credit in the U.S. Green Building Council’s LEED rating system. Electric power system planners expect growth in demand response and energy-efficiency programs to reduce peak-power demand by up to 5 percent over the next 10 years, according to the Department of Energy (DOE).

“These codes tend to lead the way in terms of energy and environmental improvement, so you will see the same requirements spread to other states as demand response becomes part of state codes,” said Russ MacAdam, CEM, director, commercial systems development for Lutron Electronics Co. He added that incentives are available in most states; while they vary across the country, incentives are typically based on the size of the shed load in kilowatts, with up to $300 per kilowatt for initial installation and annual revenue payment of $20–40 per kilowatt.

One of the great drivers for economic demand response is expected to be growing adoption of advanced meter infrastructure (AMI), a key component of the smart grid. This equipment enables electricity producers and consumers to generate real-time consumption data and communicate about how and when to produce and consume energy. It also makes time-based pricing possible; end-users may see costs increase significantly during certain hours of the day, particularly during the late morning and early to mid-afternoon on summer days.

“The AMI adoption rate is approximately 30 percent nationwide and in the high 90 percent in California,” said Pete Horton, vice president of market development for WattStopper. “This infrastructure is essential for time of use and automatic demand response programs, both of which encourage reduction of energy consumption during utility peak usage. Because the AMI is essential to confirm results for a utility-based automatic demand response program, the smart grid will allow utilities to offer rate structures that reward energy consumption that aligns with the cost of generating and transmitting electricity.”

A role for lighting control

To reduce peak demand, end-users can turn equipment off, turn it down or use it more efficiently. Alternatively, they can use energy information to generate their own power to reduce cost and potentially sell what they saved in an energy market.

Lighting is the biggest consumer of electricity in commercial buildings, using an average of 20 percent of site energy in commercial buildings, according to the DOE. Office buildings, in particular, have more lighted floorspace than any building type and use more electricity for lighting.

Lighting can play a passive and active role in demand response. The passive role involves optimizing energy efficiency using appropriate technology and design, turning off or reducing loads when not in use, manual and automatic dimming, and institutional task tuning, in which light levels are reduced appropriate to prevailing tasks on a space-by-space basis. These steps are important low-hanging fruit for demand response in that they provide the end-user a high economic value regardless of peak demand.

“When starting a lighting demand response program, you should start with implementing basic energy-efficiency strategies,” MacAdam said. “These not only reduce your peak load, but continue to save you money all the time.”

For lighting to play an active role in demand response, it must be able to achieve substantial load reductions during emergency requests or additional reductions to reduce costs in an economic demand response program.

“The essential requirements to an effective demand response strategy are the ability to measure the available load associated with lighting at any given time and the capability to accept a signal from the utility to begin, end and measure a load shed event,” Massey said. “To optimize the effectiveness and minimize the disruption of a load shed event, it is critical that the lighting controls solution have the ability to prioritize—identify least to most invasive spaces and areas that shouldn’t participate at all—the sequence of operations, as well as take advantage of dimming technologies as opposed to simply on/off strategies.”

“Though it is possible to implement a demand response program in a commercial building using switches and the ‘sneaker net,’ having workers run around the building turn off lights can be very costly and very hazardous to the productivity of the business,” MacAdam said. “Of course, in an emergency condition, this would be better than a complete blackout.” Nonetheless, automating the process minimizes these effects.

MacAdam pointed out that multilevel switching can work well in transient areas in hallways, bathrooms, copier rooms and the like. In these applications, light level can be reduced without significantly affecting productivity. In occupied spaces, dimmable ballasts or drivers can work well to temporarily reduce light levels.

“In all the above cases, you should be able to tie into a central location to receive the demand response signal,” he said. “The most basic way is through a dry contact closure that can be closed when the facility manager gets a call or email requesting demand response, but usually there is a lighting management system, energy management system or building management system that the facility manager can use to implement the demand response or that automatically receives a signal to implement it.”

For spaces where light levels will be reduced through dimming in response to a load-shedding event, a critical question is how deep, how fast and over what period lighting can be dimmed before occupants notice and are adversely affected. These questions were explored in a National Research Council Canada-Institute for Research in Construction (NRC-IRC) study. The researchers first studied various dimming scenarios with typical office workers in two full-scale office mockups. Later, they conducted a field study over the course of a summer that included an open-plan office with 330 dimmable luminaires and a college campus with 1,850 dimmable luminaires in several buildings.

Load shedding was executed during the afternoon hours over several days. The rate of dimming spanned one to 30 minutes with dimming reductions up to 40 percent. Occupants were informed that an experiment would be conducted during the summer involving afternoon dimming but were not told on which days.

In the field study, lighting loads were reduced by 14–23 percent without occupant complaint. Based on this data coupled with the lab study data, NRC-IRC developed several recommendations:

•Stage 1: This type of demand response involves dimming by amounts the large majority of occupants will not notice. Dimming can occur rapidly, over as little as 10 seconds, by 20 percent with no daylight, 40 percent with low prevailing daylight, and 60 percent with high prevailing daylight. If dimming occurs slowly, over 30 minutes or more, and with no immediate expectation of dimming occurring, levels may drop by 30 percent with no daylight and 60 percent with high prevailing daylight.

•Stage 2: This type of demand response involves more load reduction, with steeper reductions in light levels but still acceptable to a large majority of occupants. Dimming can occur as quickly as 10 seconds, by 40 percent with no daylight and 80 percent with high prevailing daylight. If dimming occurs slowly, over 30 minutes or more, with no expectation of immediate dimming, levels may drop by 50 percent with no daylight and 80 percent with high prevailing daylight.

The researchers emphasized that these recommendations relate only to situations where load shedding is performed to alleviate the effect of temporary—and infrequent—grid stress events, with dimming lasting a few hours at most. The recommendations are not intended to replace current lighting practice and support daily load shedding.

Incorporating demand response into an existing building is possible but more economically challenging. For this application, load-shedding ballasts can be effective, providing hi-lo continuous or step dimming in response to low- or line-voltage control signals. In new construction projects using a centrally managed digital lighting control system, adding demand response dimming can be relatively easy with a marginal premium.

“The market drivers for these systems go beyond just the simple return on investment that an ASHRAE 90.1 2010-compliant system achieves,” Horton said. “These drivers include confirming the performance of the systems, leveraging information such as occupancy states for space utilization analysis or to integrate with the HVAC system, remote adjustment such as occupancy sensor setting, or monitoring energy consumption in real time.”

“As time goes on, lighting controls and demand response strategies are going to become prevalent in a great number of your projects,” Massey said. “It is critical you are familiar with the technologies in the marketplace and comfortable with the installation of the various systems. This familiarity and comfort level with both objectives will allow you to differentiate yourself in the marketplace, allow you to more accurately quote projects, and ensure higher levels of client satisfaction.”

“Most modern lighting control systems are now digital and have options to connect to the IT infrastructure with IP connectivity, servers and databases,” Horton said. “Control systems will soon become an extension of the Internet, and each sensor and control device will have its own unique address and bar code to identify its operating characteristics and service history.”

Some progressive electrical contractors, he said, have moved from the “plan and spec” market to offer design/build services, while the most competitive contractors are moving to an “operate and maintain” business model—owning the customer for life.

“ECs have to understand that, just like the Internet, the data these control systems generate will be valuable in generating profits,” Horton said. “So whether it’s digital sensors, sequences of operation or demand response programs, the EC must get involved with managing the data to lead the industry.”

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