Managing energy costs in large offices offers an opportunity to trim energy costs that account for 19 percent of an office building’s total expenditures. In the US, large office buildings of more than 100,000 square feet (ft2) use an average of 20 kilowatt-hours of electricity and 24 cubic feet of natural gas per ft2 annually. To cut those costs, energy managers in large offices should target their biggest energy users: lighting, heating, and cooling systems, which consume almost 70 percent of a building’s total energy demand. Here, we provide five tips to help you lower your energy bill—and improve employee comfort and building aesthetics, too.
1. Switch to LEDs. LED prices have been falling quickly, and their advantages over traditional incandescents and tubular fluorescents are significant. LEDs last up to 10 times longer than other lamps and use at least 75 percent less energy while providing higher-quality and more-direct lighting.
For the needs of large offices, there are very few applications for which the benefits of LEDs don’t at least merit some consideration. In office spaces, where lights are left on for extended periods of time, LEDs will offer distinct advantages in lifespan and energy use over halogen lamps or CFLs and will require fewer replacements. LED troffers (2- to 4-foot-long recessed lighting fixtures where the opening is flush with the ceiling and the inner surface serves as a reflector), can compete with typical fluorescent fixtures in quality while providing energy-saving and longevity benefits.
Yet when buying LEDs, caveat emptor (let the buyer beware) remains the key consideration. Not all LED products available on the market are equally effective or offer the savings they describe. Visit the US Department of Energy’s (DOE’s) LED Lighting Facts Products web page to determine which LED products have been verified to perform as promised.
2. Install advanced rooftop unit (RTU) controllers. Retrofitting existing RTUs with advanced packaged controllers improves functionality and offers potential savings of 20 to more than 50 percent, with a typical payback of one to four years. Onboard energy-saving strategies include variable or multispeed supply fan control, demand-controlled ventilation (DCV), and improved economizer control. Other energy-saving features that are included to improve RTU performance and increase savings are demand response, remote monitoring, and fault detection and diagnostic (FD&D), which notifies facility operators of equipment status changes.
For RTUs serving large spaces with intermittent occupancy, like auditoriums, cafeterias, parking garages, and conference rooms, DCV can offer big savings. The system detects occupancy by measuring the level of carbon dioxide present in the return airstream. High levels of carbon dioxide indicate the presence of people; low levels indicate their absence. This strategy decreases the amount of ventilation produced by the HVAC system during low-occupancy periods and can result in energy savings of as much as $1 per ft2.
Economizers save energy by drawing in outside air to cool the building instead of using mechanically refrigerated air. In many applications, a fully functioning economizer can cut a building’s total energy consumption by as much as 10 percent or up to 20 percent in mild coastal climates. It’s important to note, however, that economizer performance can degrade over time and pose a risk of wasting much more energy than the device was originally intended to save. The linkage on the damper can seize up or break, causing the economizer to become stuck in an open position. When this occurs, the economizer lets in hot air during air-conditioning season and cold air during heating season. The cost of conditioning this outside air can increase a building’s annual energy bill by an additional 50 percent. The key solution is regularly scheduled maintenance and repair. Hire a licensed technician to check and clean your economizer, lubricate the linkage, and calibrate the controls about once a year, and repair it if necessary.
3. Commission your building. When done well, commissioning or retrocommissioning can yield energy savings and increase occupant comfort in a building by improving the energy system’s performance. For a standard 50,000-ft2 building, commissioning can often uncover around $17,000 in annual savings and deliver a one- to two-year payback period. Additionally, a 2004 Lawrence Berkeley National Laboratory (LBNL) study (PDF) that retrocommissioning is “one of the most cost-effective means of improving energy savings in commercial buildings, with average whole-building energy savings of 15 percent and a simple payback of 0.7 years for the building owner.” Commissioning a new building is the process of ensuring that building systems are designed, installed, functionally tested, and capable of being operated and maintained according to the owner’s operational needs. Existing buildings that have never been commissioned undergo the process of retrocommissioning to upgrade building performance to optimal levels. Because building energy systems are dynamic and tend to fall out of calibration over time, it’s important to recommission them—typically every three to five years—to maintain top performance. You can also install monitoring equipment to provide continuous diagnostics that can identify system problems before they have a chance to degrade performance; this is called ongoing commissioning.
4. Install lighting controls. Lighting controls can provide the right amount of lighting where and when it’s needed by turning lights off and dimming them to reduce unnecessary lighting levels. Depending on the baseline conditions and the strategies used, lighting controls can reduce lighting energy use by 5 to 60 percent. Implementing lighting controls allows end users to participate in utility demand-response programs, since it enables them to manage their own energy behavior. Advanced lighting control systems can improve maintenance by signaling lamp outages as well as monitoring output levels to indicate when they fall below required or desired levels. When improved light sources such as LEDs are used in addition to lighting controls, savings can be even more significant. A Sacramento Municipal Utility District program saw lighting energy savings of 50 to 90 percent in several projects that used both lighting-source and control upgrades.
5. Cut down on overlit parking lots. Big savings can be found by installing higher-efficiency light sources and occupancy-sensing lighting controls in overlit parking lots. Traditional light sources used for outdoor lighting such as high-intensity dischargE Sources, fluorescents, and induction lamps are being out phased by more-efficient LEDs. The DOE Better Buildings Alliance estimates that using LEDs can cut energy use by 40 percent or more, depending on the application. In addition to offering energy savings, the other benefits of LEDs are the bulbs’ ability to direct light output, which reduces light pollution and glare and makes the lamps a good choice for parking lot illumination, both in terms of aesthetics and energy-saving potential. Additional information on LED application in parking lots, including a sample specification and case studies, can be found on the DOE Better Buildings Alliance’s Adopt High-Efficiency Lighting for Your Parking Lot and Lighting Energy Efficiency in Parking Campaign web pages.