Power Reducers
What are the options?
How to make the best choice
What's on the horizon?
Power reducers are panel-mounted retrofit options for cutting energy costs in a fluorescent or high-intensity discharge (HID) lighting system. They control the voltage supplied to all of the fixtures on a given lighting circuit. When voltage is reduced, both energy consumption and light levels are reduced as well. One of the devices' main attributes is that they are panel-mounted and therefore easier to implement than many other alternatives—one need only install a single device at the panel for each lighting circuit rather than, for example, install a new ballast at each fixture.
Power reducers can deliver energy savings, but lighting retrofits often produce greater energy savings with only slightly higher first costs. Potential users should be wary of exaggerated claims for these devices, such as having the ability to cut energy use by up to 50% with little or no noticeable loss in light levels. Energy savings of this magnitude will usually be accompanied by reduced lighting levels that are quite noticeable and may affect productivity. However, there are still some niches where power reducers might provide good value, such as when users desire to shed load in response to utility requests or for overlit spaces with HID or fluorescent lighting and difficult retrofitting conditions that preclude fixture access.
Manufacturers of power reducers recommend them for illuminating generally wide open areas in large facilities. These buildings might include large retail outlets, parking garages, warehouses and distribution centres, and large manufacturing plants that use fluorescent or HID lighting systems. The manufacturers also recommend their devices for outdoor lighting in areas such as parking lots or parks. Power reducers are not recommended for individual offices or for lighting circuits with few fixtures.
In addition to energy savings, manufacturers make claims for benefits such as longer lamp and ballast life. Because less power runs through ballasts that are linked to a power reducer, they run cooler and therefore are likely to last longer, although no independent tests have confirmed that effect. Manufacturers also claim that power reducers can lengthen lamp life, but in practice a power reducer might lead to increased or decreased lamp life, depending on specific conditions. For example, in a case where line voltage is higher than nominal or a ballast with a high ballast factor is being used, the power reducer might bring the system closer to its optimum operating conditions and lamp life would be expected to increase (as long as voltage was not decreased too much). In a low-voltage, low-ballast-factor case, the operation of a power reducer might be expected to decrease lamp life. No published data are available about the effects of reduced voltage on the life of HID lamps, however, low voltage can cause a colour shift in HID lamps and specifiers should contact HID lamp manufacturers for information on the effects of low voltage for a given lamp.
What are the options?
Power reducers can be differentiated on the basis of a couple of factors.
Means of controlling voltage. The two main types of controllers are autotransformers and wave choppers. Autotransformers decrease the voltage in a circuit but preserve the voltage waveform. These devices tend to be large and heavy, often weighing more than 100 pounds. They have little or no effect on power quality. Models that use a type of autotransformer known as a torroidal autotransformer may actually produce modest improvements in power quality. Wave choppers switch power on and off to reduce voltage, effectively "chopping" a part of each voltage cycle and altering the waveform. Wave choppers are smaller and lighter than autotransformers, but may have an adverse impact on power quality.
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 about 25%, or permit the level to be varied either manually or through the use of sensors and energy management systems. Both wattage and light output are reduced by roughly the same amount.
Controllability. Some products are set by the factory to provide a single level of power reduction, whereas others can be programmed for different levels or set to respond to changing lighting conditions. Some also have the ability to communicate over the Internet or wide area networks, providing monitoring and control capability for multiple sites. The most sophisticated products also include software for managing the lighting system—setting a desired light level for a particular time of day or day of the week, monitoring and reporting on lighting energy use, and responding to load-shedding commands.
How to make the best choice
Answers to the following questions can help you decide whether power reducer technology is right for a given application.
Would another solution be more cost-effective? Although power reducers may be a viable option in a given situation, they are usually not the only one. Other ways to reduce the energy consumption in a magnetically ballasted T12 lighting system—one of the primary targets for power reducers—include the following:
- Retrofits with electronic ballasts and T8 lamps
- Reflector, lens or fixture retrofits combined with delamping
- Upgrades to low-ballast-factor or cathode cutout ballasts
- Installation of dimming electronic ballasts
To choose the best option, determine the possible savings and the payback period. Table 1 shows four 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 two T8/electronic ballast options offer the greatest life-cycle energy savings. Simple payback for the T8 option with normal ballast factor is faster than the power-reducer option and results in slightly greater light output. The T8 option also improves the colour quality of the light provided.
| Table 1: Power reducers and fluorescent lighting | |||||
|---|---|---|---|---|---|
| Base case: T12 lamps, magnetic ballasts | Power reducer | Energy-saving lamps, magnetic ballasts | T8 lamps, low-BF electronic ballasts | T8 lamps, normal-BF electronic ballasts | |
| Installed cost ($) | NA | 10,000 | 2,709 | 10,578 | 10,578 |
| Annual operating cost ($) | 11,212 | 8,807 | 9,748 | 6,804 | 8,198 |
| Annual savings ($) | NA | 2,405 | 1,464 | 4,408 | 3,014 |
| Payback (years) | NA | 4.2 | 1.9 | 2.4 | 3.5 |
| Relative light level (%) | 100 | 92 | 85 | 85 | 95 |
| Note: BF = Ballast factor; NA = not applicable Source: E Source; data from Exelon | |||||
For HID lighting systems, one alternative to lighting-circuit power reducers is a high-intensity fluorescent retrofit. In Table 2, we compare the addition of a power reducer to a metal halide lighting system with the installation of a high-intensity fluorescent system.
| Table 2: Power reducers and HID lighting | |||
|---|---|---|---|
| Standard 400 W metal halide lamp | Existing HID lighting with a power reducer | Retrofit with four 55 W biaxial fluorescents | |
| Fixture input power (watts) | 465 | 372 | 234 |
| Design lumens from fixture (lumens) | 16,800 | 13,440 | 16,445 |
| Colour rendering index | 65 | 65 | 85 |
| Annual electricity consumption at 5,000 hours per year (kilowatt-hours) | 465,000 | 372,000 | 234,000 |
| Annual electricity cost at $0.08 per kilowatt-hour ($) | 37,200 | 29,760 | 18,720 |
| Annual savings ($) | NA | 7,440 | 18,480 |
| Cost of retrofit ($) | NA | 21,750 | 42,000 |
| Simple payback (years) | NA | 2.92 | 2.27 |
| Notes: NA = not applicable; a. The $21,750 installed cost of the power reducer includes $19,000 for a 200-amp, three-phase power reducer plus $2,750 for installation. b. Installed cost of the fluorescent system with high-efficiency fixtures assumes a cost of $210 per fixture. We assumed 200 fixtures for each alternative. | |||
| Source: E Source, data from Lime Energy and Jim Rogers (independent energy consultant) | |||
Although both systems pay for themselves in less than three years, the fluorescent option saves more energy and provides more light. In addition, the fluorescent system provides a number of other benefits, including better lighting colour, faster start-up and restart time, and less glare.
Will illumination levels fall below requirements? Do not install power reducers if users will not be able to work as efficiently or as safely in the reduced light levels that will result.
Is a boost in lighting quality required? Power reducers will not improve the lighting quality in a space. If that's what you are after, other measures will be more effective, such as the use of light sources with better colour quality (higher colour rendering indexes) than the existing lamps or the use of fixtures, such as direct or indirect luminaires, that reduce glare.
How well will the technology work with particular lamps and ballasts? Power reducers aren't compatible with all types of ballasts, although some products are more versatile than others. In fluorescent lighting, some products work only with magnetic ballasts while others work with both magnetic and a few types of electronic ballasts, but none work with active front-end electronic ballasts. The active front-end ballasts, which compensate for fluctuations in incoming voltage and would therefore defeat the action of a power reducer, represent a growing share of the market for fluorescent electronic ballasts. It's not always easy to tell if a ballast features an active front end, but most often multiple-voltage ballasts, universal-voltage ballasts and ballasts with total harmonic distortion of less than 10% are made with active front ends.
For HID lighting, power reducers are compatible with both reactor-type ballasts and constant wattage autotransformer ballasts, although the savings potential is higher with reactor-type ballasts. So far, none of the power reducer products work with electronic HID ballasts, which, though rare, are becoming more common.
Will the use of this technology void lamp and ballast warranties? Potential users of power reducers should check with lamp and ballast manufacturers to make sure their equipment is compatible with a particular power reducer, and to see if use will void the lamp or ballast warranties. Conversely, the power reducer manufacturer may provide its own warranty.
If a power reducer passes each of these "tests," it may indeed be the best choice for managing energy use and responding to load curtailment signals. If you have chosen to install power reducers, then follow these guidelines:
- 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.
- When specifying a power reducer, make sure that it will not delay lamp starting or cause visible flicker.
What's on the horizon?
As manufacturers continue to develop better and less expensive dimming ballasts, power reducers will eventually become obsolete for fluorescent systems. Dimming ballasts for HID lamps are a new and growing option for HID lighting systems that 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 © 2008 E Source Companies LLC
Last Modified: May 9, 2009
