Energy Efficiency Measures

LIGHTING

High-efficiency lamps, such as T-5 and T-8 fluorescent lamps with electronic ballasts, provide the same or improved illumination as do fixtures with T-12 lamps and magnetic ballasts. Combined with de-lamping and high-efficiency reflectors, retrofit savings can approach a factor of two. Depending on usage patterns, installation costs, and other factors, paybacks for many lighting retrofits are often three years or less. Additional benefits of energy-efficient lighting include lowered cooling costs since less waste heat must be removed by the air conditioning system.

A wide range of compact fluorescent lighting (CFL) fixtures are now available whose characteristics are far superior to earlier models. Modern versions typically have zero hum, long-life electronic ballasts, excellent color rendering, are four times more efficient than incandescents, a lifetime of up to 10,000 hours, and bulk prices of less than $3 apiece. Since a CFL outlasts a typical incandescent by a factor of 10 or more, their upfront costs are now about the same. Lifetime savings of a 25-watt CFL over a 100-watt incandescent is 750 kWh—and maintenance costs are reduced as well. The ENERGY STAR program lists over 1,400 CFL bulbs that are “qualified” as high-performance by their criteria (which include lifetime, efficiency, and surface temperature limits), as well as about 10 percent of that number that have been deemed “unqualified.” These are shown by manufacturer and model number at www.energystar.gov/ia/products/prod_lists/cfl_prod_list.pdf.

Light emitting diodes (LEDs) last a long time (ten years or more) and are quite energy efficient. Accordingly, they are ideal for use in exit signs. Since exit signs operate for 8,766 hours in an average year, efficiency improvements can result in substantial savings. Old-style exit signs used 40 watts of power and bulbs had to be replaced often. ENERGY STAR qualified exit signs use less than five watts per face; over 500 that meet this criterion are listed at www.energystar.gov/ia/products/prod_lists/exit_signs_prod_list.pdf.

In general, lighting distribution is more efficient and visually comfortable in light-colored spaces, especially those in which the ceilings are white. This applies across a wide range of buildings from chicken coops and schools to offices and industrial facilities. In each of these cases, lighting quality improvements by the addition of white paint are frequently accompanied by improved productivity.

Whenever feasible, retrofit lighting design strategies should be combined with daylighting controls to maximize energy efficiency. Such controls may locate a sensor outside to measure the amount of light entering spaces through windows or skylights, or be placed above the work plane to dim electric lights in response to the amount of natural light falling on key surfaces. Furthermore, a task/ambient lighting design strategy that provides an appropriate level of general light and task-level light where it is needed reduces the overall electricity load required for lighting. Good designs also enhance working and learning environments.

The ability to control the daylight entering a building is critical to a daylighting design’s success. Studies show that school classrooms with skylights designed with manually-operated internal louvers result in a dramatic increase in student performance. At the same time, it is important to minimize glare caused by uncontrolled daylighting. Daylight tends to penetrate from a window into an interior space about 1.5 times the head height of the window. Light shelves and similar devices reflect natural light onto white-colored ceilings, which both controls for glare and allows diffuse light to illuminate the interior space. For such spaces, it’s best to install dimmable light fixtures and associated daylighting controls.

Older industrial facilities often incorporate rooftop windows, either vertical or at an angle to the vertical, in a saw-tooth fashion. Sometimes these windows can be opened to enhance ventilation, but their main function is to supply natural light. Oftentimes, they perform this function too well, allowing direct beam sunlight to fall on work spaces below where they cause unwanted glare and produce harsh shadows. One solution is to redirect sunlight up on a light-colored ceiling as illustrated below.

This system uses specular reflectors which can become dusty unless cleaned regularly. A simple way to accomplish this task is to install several copper tubes with holes in them that will direct a blast of compressed air over the reflective surfaces for several seconds at the close of production each day. Enhancements include using specularly-selective glazing to provide adequate daylight with relatively low solar heat gain and installing insulating shutters to limit thermal losses through the roof windows on cold winter nights. In all cases, energy-efficient electric lighting should be controllable so that it can be ramped up as needed when solar daylighting is diminished by cloud cover or for night-time lighting needs.

To learn more about daylighting, visit www.daylighting.org/what_is_cool_daylighting.htm.

Occupancy sensors are electronic devices that detect the presence of people. They turn on lights or associated equipment such as computer monitors or copiers when people are detected, and turn things off if no people are detected after a programmable period of time, typically 5 to 15 minutes. Their sensitivities and areas of coverage may be adjusted to a degree, dependent upon on the technology used by the sensor, its location, and control settings.

Ultrasonic sensors are quite sensitive and react to small motions. They are sensitive over large areas, but are subject to false triggering. Passive infrared sensors are less susceptible to false triggering, but their sensitivity drops off with the square of the distance. Some dual technology systems are available that incorporate the virtues of both technologies, but they are somewhat more expensive. In general, ultrasonic occupancy sensors are best used in large areas, infrared in smaller areas.

Mounting occupancy sensors toward the tops of walls is best for smaller spaces like offices, copy rooms, and bathrooms. Ceiling-mounted sensors are best for larger open spaces.

In recent years, the quality and performance of occupancy sensors has become higher while costs have come down. Accordingly, for many applications they can save substantial energy and are quite cost-effective. The trick is to match the right sensor to the right circumstance to maximize energy saving performance while minimizing people hassle and cost. This is a judgment call that is a strong function of the patterns of the people that are using a given space. This is why potential energy savings for various kinds of spaces has such a broad range, as illustrated in the following table.

Range of savings from the use of occupancy sensors

Occupancy controls are also quite useful in hotels and motels where they permit thermostat adjustments on the heating and cooling system as a function of occupancy.

Efficient parking lot lighting fixtures can reduce the energy use on the site without compromising safety or illumination. “Hockey puck” fixtures, which use 175-watt metal halide bulbs, require fewer poles, cut down on light pollution, have better color rendering, and use 70% less electricity than “cobra head” fixtures using 250-watt high-pressure sodium bulbs.

Source: Clayton Engineering

Use timers and daylight sensors and controls in parking lots.

Metal halide lamps provide light at relatively high efficiency, have excellent color rendering, and have a long lifetime. With suitable fixtures and electronic ballasts, metal halide lamps have a luminous efficacy over 80 lumens per watt. The down side is their propensity to change color properties over their lifetime, and their relatively long re-strike time; the lamp and ballast must cool for several minutes if power is lost before they can turn back on.

Metal halide lamps are often used in “high bay” applications such as in factories, warehouses, or sports arenas, as well as for outdoor lighting. Also, metal halide lamps are sometimes used in grocery stores, home supply centers, and other “low bay” applications.

An attractive application of high-efficiency metal halide fixtures is to supply indirect lighting in a range of spaces, from open offices to factories. Metal halide lamps are mounted on pillars aimed upwards, allowing diffusely-reflected light to illuminate work spaces below. This produces virtually shadow and glare-free lighting environments that are consistent with computer work and many production activities. Task lights are sometimes used to provide supplementary illumination as needed.

Dimmable metal halide fixtures are becoming more common, with systems dimming in response to daylight availability, user needs, or in response to high peak demand periods experienced by the electric utility. In general, dimming much lower than 50% results in color shifts and diminution of luminous efficacy.

© 2006 Southwest Energy Efficiency Project
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