Energy Advisor
Your guide to energy products
for commercial buildings
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Energy Advisor Your guide to energy products |
Power reducers are a panel-mounted retrofit option for cutting energy costs in a fluorescent or high-intensity discharge (HID) lighting system. Their use produces a drop in the power consumed by the lights and in light output. Now that low-cost electronic ballasts are widely available, there usually are more cost-effective opportunities to reduce fluorescent lighting costs than power reducers. However, there are still some niches in which power reducers provide good value, such as overlit spaces with either HID or fluorescent lighting with difficult retrofitting conditions that preclude fixture access.
Autotransformer power reducers decrease the voltage to the lighting load but preserve the voltage waveform and thus have little effect on power quality. These products are primarily used in HID systems with constant-wattage autotransformer ballasts. They are heavy, often weighting more than 110 pounds.
Electronic power reducers decrease the voltage to the lights by chopping part of the voltage cycle.They are lighter and smaller but may adversely affect power quality. Some power reducers add capacitance so as to produce a leading power factor (current wave ahead of the voltage wave), which can cancel some of the effects of lagging power factors produced by inductive loads such as motors. However, the traditional means of power factor correction—an external bank of capacitors—-is usually a more cost-effective approach.
Both types of power reducers provide full voltage for several minutes to start the lamps and let them warm up; then they cut power by a defined percentage, typically 30 or 50 percent. Once installed, the percentage can only be changed by accessing the electric panel. Both wattage and light output are reduced by roughly the same amount, although manufacturers sometimes claim that power is cut more than output. Since less power runs through the ballasts that are linked to a power reducer, they run cooler and therefore tend to last longer. However, there is a downside to the same effect: reducing the supply voltage to fluorescent lamps can shorten their life by causing sputtering at the cathodes. Instant-start systems are particularly susceptible to this effect. There are no known effects of reduced voltage on the life of HID lamps; however, low voltage can cause a color shift in HID lamps and specifiers should contact HID lamp manufacturers for information on the effects of low voltage for a given lamp.
Other options for achieving similar savings. Other ways to reduce the energy consumption in a magnetically ballasted T12 lighting system—-the primary target for power reducers—include:
• Retrofits with electronic ballasts and T8 lamps;
• Reflector, lens, or fixture retrofits combined with delamping;
• Switching to low-ballast-factor or cathode cutout ballasts; or
• Installing dimming electronic ballasts.
Few alternatives to lighting circuit power reducers exist for HID lighting systems.
Calculate the payback period and savings possible with different alternatives. Although power reducers may be a viable option in a given situation, they are usually not the only one. To choose the best option, determine the savings possible and the payback period. Table 1 shows three possible upgrades to a bank of fluorescent lamps initially equipped with T12 lamps and magnetic ballasts. The quickest payback comes with an energy-saving lamp retrofit, but the T8/electronic ballast option offers the greatest lifecycle energy savings. Simple payback for the T8 is also slightly faster than that for the power reducer option. In addition, the payback period calculations include a demand savings of $10 per kilowatt. Those savings can be counted on for the new lamp options but not for the power reducers. There are several ways to disable a power reducer—for example a maintenance worker can use a key switch to bypass the savings mode—so it is difficult to count on demand savings. Without the demand savings, payback for the power reducer increases from 3.6 to 5.2 years.
This comparison of costs, savings, and paybacks for three retrofit options shows that low-energy lamps provide the quickest simple payback period however the T8/electronic ballast option provides the greatest lifetime savings, with a simple payback. Slightly faster than that for Option 3, with the Ultrawatt power reducer.
Source: Platts
Consider the effect of decreased light output on users before installing power reducers. Do not install power reducers if users will not be able to work as efficiently or as safely in the reduced lighting that will result.
If you have chosen to install power reducers, then:
• Pick a product that can interface with photosensors, time clocks, and other energy management systems. Some products are available in both autotransformer and electronic power reducer categories that can interface with other energy-saving controls.
• Check with the manufacturer for your particular application, because most power reducer manufacturers recommend that their products be used with specific lamp-ballast systems.
• When specifying a power reducer, make sure that it will not delay lamp starting or cause visible flicker.
As manufacturers continue to come out with better and less-expensive dimming ballasts, power reducers will eventually become obsolete for fluorescent systems. Manufacturers are also making progress in developing dimming ballasts for HID lamps, and although these products are still expensive, they will also eventually provide tough competition for power reducers. Meanwhile, manufacturers will continue to develop power reducers for a wider variety of voltage levels.
Copyright © 2004 - Platts, a Division of The McGraw-Hill Companies, Inc.
