Office buildings can be good candidates for commercial and industrial (C&I) demand-response (DR) programs because these programs provide owners with a way to trim ever-increasing energy costs and to boost their market position by promoting a “green” image. When office owners and managers use green measures to reduce operating expenses for their tenants, it makes the space more attractive for leasing and ultimately improves the profitability of all parties involved.
Office buildings tend to have highest occupancy from early morning through late evening. Many have peak demands coincident with utility peaks on summer afternoons, as air conditioning use increases. As a result, it is likely that an office building will be occupied during DR events.
The largest energy users in office buildings are, in decreasing order: space cooling, lighting, office equipment, and space heating—making HVAC the best target for DR. Some buildings have special-purpose rooms, such as cafeterias, auditoriums, and recreational facilities, in which lighting and plug loads can be curtailed without inconvenience. Many modern office buildings have a sophisticated building automation system (BAS) that controls HVAC, lighting, and other systems. A BAS provides a centralized way to control an automated DR strategy throughout a building, which is vital because office buildings do not typically have facility or energy managers on-site to react to DR events.
A San Francisco office building achieved a noticeable load reduction through participation in a DR program (Figure 1). Lights were dimmed or turned off in unused areas and HVAC settings were adjusted to reduce demand.
Office buildings have indoor air quality and comfort requirements that must be considered for a DR program. Because office occupants tend to remain in the same location for relatively long periods of time, they are prone to noticing and being inconvenienced by alterations in the environment. However, within these requirements, office buildings can reduce loads in many ways, such as by adjusting HVAC setpoints, reducing lighting, and turning off plug loads. Some office buildings also have backup generators, which, depending upon local environmental regulations, may be used to offset the building’s load during a DR event.
Office buildings can successfully participate in load reduction events using several proven strategies.
Adjusting thermostats. During a DR event, thermostats can be adjusted to decrease electricity demand. Some DR programs offer day-ahead notification of events, allowing facility operators to warn building occupants that indoor temperatures may be somewhat higher on the day of the event. However, control designers claim that people can tolerate a temperature rise of around one or two degrees Fahrenheit (F) over a four-hour period without feeling inconvenienced and without even noticing in many cases.
Adjusting chiller setpoints. The temperature setpoint of the chilled-water system can be adjusted to decrease air conditioning electricity demand. With this strategy, overall building temperatures will rise slightly although ventilation systems will remain at their normal level. This strategy must be used carefully because other equipment within the chilled-water system may be forced to work harder to compensate for the chiller’s higher setpoint.
Decreasing fan speeds. Office buildings often have ventilation systems with variable-frequency drives and fan speeds can be slowed during DR events. This can be implemented successfully in conjunction with other HVAC strategies such as setpoint adjustments.
Precooling. Office buildings are good candidates for precooling, a strategy in which the building is over-cooled in advance of a DR event—usually overnight or during the early morning. An office building’s thermal mass helps store the cooling energy, which is slowly released throughout the day, allowing thermostats to be set higher during the afternoon peak.
Curtailing lighting. Lighting can be turned off in special-purpose rooms such as cafeterias, auditoriums, and recreational facilities, as well as in selected hallways and other areas during DR events. In addition, overhead lights in occupied areas can be selectively turned off, with occupants relying on task lamps if necessary. Office buildings can use dimming ballasts to dim the lights—studies show that building occupants usually cannot detect lighting level reductions of up to 20 percent. Turning off lights also reduces cooling loads, which can provide demand relief during the summer.
Manually reducing or eliminating key equipment loads. During a DR event, building staff can turn off unused office equipment, vending machines, air handlers, and exterior lighting or signage. This strategy requires a concerted effort on the part of building occupants to meet load reduction goals, so it may not be feasible in all office settings.
Switching to on-site generation. Some office buildings have on-site backup generation. Such customers are good candidates for DR programs that allow the shifting of the building’s load onto these generation sources. Switching to backup generation is usually immediate so it causes no interruptions to service.
Using a building automation system (BAS). Found in the vast majority of modern office buildings, a BAS uses sensors and controllers to monitor and optimize temperature, pressure, humidity, and flow rates while minimizing the energy use of fans, pumps, HVAC equipment, dampers, mixing boxes, and thermostats. The BAS is programmed to curtail predetermined loads upon notification (either day-ahead or early the same day) from the energy service provider (ESP)—typically a utility, independent system operator, or DR provider—eliminating the need to manually turn equipment down or off. Global temperature reset is a DR strategy that can be implemented using a BAS. Upon receipt of notification of a DR event, the BAS adjusts the setpoint temperature either up or down, usually by 2° to 8°F.
If a building does not have a facility manager, its occupants may need education from an ESP on how to program their BAS. The existing BAS may need to be retrofit to enable communication of curtailment requests from the ESP to the BAS to the end-use equipment.
Based in San Jose, California, Echelon is no stranger to demand response—or to high-tech. The company designs and produces control systems and software for advanced metering, building automation, and DR. Therefore, it seemed natural to include a cutting-edge communications center when the company built its new headquarters in 2000.
The building’s developer, Kenmark, included the latest in DR technology after hearing about the state’s Automated Critical Peak Pricing Pilot Study. This endeavor, involving investor-owned utilities and research institutions, set out to measure dozens of C&I customers’ voluntary energy-use reduction. This reduction occurs in response to time-based pricing signals from utilities on summer afternoons when electricity demand on the grid reaches a critical level. Through a process dubbed Auto-DR, a signal is sent straight from the utility—Pacific Gas and Electric (PG&E), in Echelon’s case—to a BAS, triggering demand reduction. No intervention from building staff is necessary and customers can opt out of any events.
Echelon has achieved sizeable load reductions using HVAC and lighting curtailment strategies through Auto-DR. The building regularly sheds around 30 percent of its total electric load during DR events. The BAS shuts down one air handler and lights in offices that have windows. It also dims lights in other offices, hallways, and conference rooms.
PG&E provides notice of a critical peak event a full day in advance, so Echelon employees receive word that they should dress for warmer temperatures the following day. Such communications are important because temperature changes are noticeable, although Echelon was careful to adopt strategies that were designed to have minimal effect on building occupants.
These strategies have not only saved the company money, but allowed its employees to feel that they are helping avoid future brownouts. Echelon won an Early Adopter Innovator Award from the California Energy Commission’s Demand Response Research Council, the agency that partially funds the research and development of Auto-DR.
Dynamic Controls for Energy Efficiency and Demand Response: Framework Concepts and a New Construction Study Case in New York, Lawrence Berkeley National Laboratory and The New York Times (2006)
Introduction to Commercial Building Control Strategies and Techniques for Demand Response (PDF), Lawrence Berkeley National Laboratory (2007)
Reducing Barriers to Use of High Efficiency Lighting Systems (PDF), Lighting Research Center (2002)
Enhancing Price Response Programs Through Auto-DR: California’s 2007 Implementation Experience (PDF), Lawrence Berkeley National Laboratory (2008)
Green Buildings: Beyond Materials and Into Energy, automatedbuildings.com (2007)
Echelon Wins Energy Award from the California Energy Commission, Business Wire (2007)