Volume 16, Number 1

January, 2005 Copyright 2005 CRITERIUM ENGINEERS

The Engineering Advisor is intended to enhance your knowledge of technical issues relating to buildings. For additional information on any subject, please feel free to call us.
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REDUCING LIGHTING COST	Energy costs for commercial buildings are estimated to run about $100 billion per year, or on average, about $1.50 per square foot of commercial floor space. The American Council for an Energy Efficient Economy (ACEEE) estimates that lighting accounts for about 40 percent of these energy costs. Lighting has an additional cost in that “waste” heat from lights must be removed by air-conditioning. ACEEE estimates that about 50 percent of the energy costs of lighting could be saved by using best-practice lighting, even in buildings that use fluorescent lighting. This represents a potential saving of $30,000 in direct energy costs per year in a 100,000 square foot commercial building. Additional benefits of the installation of energy-efficient lighting include reduced loads on air-conditioning and increased asset value. Better aesthetics and higher productivity may result as well. As energy costs continue to rise the potential benefits look even better. To gain the greatest benefits in the energy efficiency of lighting, a whole-building approach is likely to prove the most productive - there is no one best solution for every area. Areas of different use have different lighting needs and should be treated differently. For potential savings, look to re-lamping existing fixtures, replacing existing fixtures and upgrading lighting controls.
Re-lamping may be the first step	Before making any changes, it is a good idea to determine the levels of light needed in each particular use area throughout a building. Many areas may be over-lighted. Some newer recommendations suggest lighting levels as low as 65 foot candles in areas where previous levels were as high as 100 foot candles. Immediate cost savings may be realized by re-lamping with lamps of a smaller wattage. Re-lamping involves replacing existing lamps (the bulbs or tubes) with more efficient ones. In some cases it may be more practical to replace the lighting fixtures themselves. Advances in lighting technology may make the retrofitting of systems that are only 5 years old economical. The first place to look for savings in re-lamping is with the most common type of lighting found in commercial buildings, the ever-present fluorescent T-8 lamps. In common areas such as lobbies and hallways, 32-watt T-8 lamps can be replaced with 28- or 30-watt T-8’s, saving 10 - 12 percent of electricity used while providing essentially the same illumination. Replacing older ballasts with ballasts specifically developed for use with modern lamps could boost the savings to 18 percent. In areas where more illumination is required, ballasts with a higher ballast factor can be installed. A higher ballast factor overdrives the lamps to produce more illumination. In high-profile areas such as Class A offices and reception areas, T-8 fixtures can be replaced with T-5 fixtures. T-5 fixtures are smaller than T-8’s, and the T-5 lamps are glare free. High-output T-5 lamps produce almost twice the light of a T-8 lamp the same length. In high-bay areas like atriums, metal halides can be replaced with compact fluorescent lamps (CFLs). CFLs come on instantly after being shut off and maintain high color quality throughout their life. They can be dimmed down to 90 percent or more at night or on weekends when the space is unoccupied and as daylight enters the space. In warehouses, modern metal halide lamps can replace high-pressure sodium lamps yet provide the same illumination while using 15 - 25 percent less electricity. Energy consumption can be reduced by from 40 watts to 1 watt per fixture using LED (light-emitting diode) exit lights.
New control strategies create savings	Great strides have also been made in the development of lighting control. Most of the new lighting control systems have the ability to fine-tune the regulation of light levels according to the amount of light needed at a given time. Light levels can even be reduced automatically if spaces are unoccupied, as the sensors are much more capable of determining actual occupancy than the old motion sensor/timer systems. The newer control systems can also adjust the light levels to account for varying levels of daylight that enter the space. With a digital addressable lighting interface (DALI) connected to ballasts of fluorescent fixtures, lighting levels can be slowly dimmed during the day. The gradual reduction in light level is usually not noticeable. Wall-mounted sensors can detect body heat, sound and motion. These sensors are not fooled by the motion of fans or by the heat of radiators. Switches may be built into the fixtures themselves. These switches keep track of the occupants directly below and reduce lighting during a prolonged absence. Lighting levels can also be automatically balanced with daylight levels. In stairwells, new fixtures can be equipped with occupancy sensors and two-level ballasts. Stairwells are rarely occupied. When no one is in stairwells, the light level, and therefore level of power consumption, can be reduced by 50 percent. As soon as someone enters the stairwell the occupancy sensor senses their presence and brings light levels in the immediate area up to normal levels.
Timing of upgrades can be designed to coincide with routine maintenance	Using any combination of the above methods of re-lamping, replacing fixtures, and adding better lighting controls will result in direct energy savings. The capital cost of these improvements can be reduced or delayed. Lamps can be replaced as they burn out. Sometimes the labor costs of re-lamping can be reduced by replacing all the lamps in an area at once on a schedule rather than replacing them one at a time as they fail. Replacement of fixtures can take place as they fail or during remodeling and tenant turn-around. Return on investment can be high. Recently, a medical facility in New York replaced standard incandescent lights with high-efficiency fluorescents in a one-million square foot building and realized an annual saving of $485,000 on a $1,086,000 investment. A 45 percent annual return? Not bad!
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