Case Study - Office Lighting Retrofit

Jackson EMC discusses the ins and outs of a lighting retrofit project.

Nearly 30 percent of your energy bill goes toward lighting, according to the U.S. Department of Energy. Examples of unique high-efficiency lighting applications seem to be everywhere — from compact fluorescent lamps in the lobby, LED exit signs and flashlights, and even HID lamps in car headlights.

With improvements in lighting system efficiencies, new technologies, and light sources, lighting retrofits remain one of the most cost-effective energy conservation measures a commercial facility can implement. So when a customer asked about replacing light fixtures in their office building as part of a general renovation, we punched in the numbers to see how the savings measured up. In our study, we found a range of options to choose from and a whole vocabulary to master.

The Site:

  • A 25-year-old, 7,400 sq. ft., single-story office
  • Total electric
  • Offices occupied from 8 a.m. to 6 p.m., five days a week and a half-day on Saturdays

The Lighting System:

Current office space uses 150, 4-lamp surface-mounted fluorescent fixtures with magnetic ballasts and a combination of 40-Watt and 34-Watt T-12 fluorescent lamps. The office standard was 40-Watt lamps until the mid-1990s when manufacturing of 40-Watt lamps was halted. The 34-Watt lamps were legislated as replacements. However, the company continues to use 40-Watt lamps until their supply is depleted. To calculate savings, we'll assume that they are all 34-Watt lamps, though the savings are higher for 40-Watt lamps. The latest technology touts 32-Watt T-8 lamps in fixtures with electronic ballasts, offering improved performance, lifespan and energy savings.

Let's Examine Our Options:

  1. Re-work the existing fixtures, replacing the old magnetic ballasts with high-efficiency electronic ballasts and install 32-Watt T-8 lamps. However, the fixtures are old — some were damaged during removal and the customer wanted to install lay-in fixtures to fit the new ceiling grid rather than use surface-mounted fixtures.
  2. Install new 4-lamp fixtures with 32-Watt T-8 lamps and standard electronic ballasts. New T-8 lamps produce more light than their older T-12 counterparts. The new fixtures will be 15 percent brighter and use 76 percent of the energy. Most offices don't need more light or glare on computer screens.
  3. Install new 4-lamp fixtures with 32-Watt T-8 lamps and low-ballast factor electronic ballasts. Low-ballast factor ballasts reduce the light output to the same level as the original system and consume 68 percent of the energy. However, some experts have voiced concern over reduced lamp life.
  4. Install new 3-lamp fixtures with 32-Watt T-8 lamps and standard electronic ballasts. This fixture will provide 86 percent of the light of the original, but consume only 58 percent of the power.
  5. Install new 4-lamp fixtures with 28-Watt T-8 lamps and standard electronic ballasts. This fixture will provide 10 percent more light than originals but consume only 57 percent of the power.

More efficient lights save energy and reduce the building's peak electrical demand, which accounts for most of the savings. In addition, if the lights are operating more efficiently, there is less heat gain that air conditioners must remove. Since many office buildings require air conditioning year-round due to heat gain from lights, equipment and people, the air conditioning savings from lighting energy reduction can be significant. Finally, though harder to quantify, there can be some maintenance savings from lighting replacement. With older lamps and fixtures, it seems that lamp and ballast replacements occur frequently, causing disruption of work as well as time and hassle. Also, if a contractor must be brought in each time, the costs can mount. A new lamp has a rated life of 20,000 hours, so you may not need to worry about lamp replacement for years.

CalculatorWhen calculating energy and demand savings, it's important to use the incremental cost of energy and demand, not the average cost. Under Jackson EMC's General Service rate, the last kilowatt-hour of energy you use or save doesn't cost the same as the first few. This is due to the block structure of the rate and depends on your specific energy use and electrical demand profile. Your Jackson EMC C&I representative can explain this in detail and help you calculate your incremental costs. For this office building, the average cost of electricity is $0.0632/kWh but the incremental cost of electricity is $0.0317/kWh. Each 1 kW reduction in peak electrical demand is worth $12.30/month.

What should you look for in a retrofit project?

Get prices for each option. Jackson EMC can help you calculate energy use for your proposed changes. Then talk to a contractor to get an installed cost. We found that sometimes, 3-lamp fixtures actually cost more than 4-lamp fixtures.

Shop around. We found options that were within a few dollars of each other. As long as you're comparing the same fixture types, consider a wide variety before making a final decision. Thirty-two Watt lamps are less expensive than 28-Watt lamps. If the office is too bright, a 3-lamp fixture may be a good option. If you want the same light levels as before, the low-ballast factor 4-lamp fixture may be the ticket. As production of 28-Watt lamps increases, their cost will decline, offering the best blend of light output and efficiency.