Appendix 5D: Multiple benefits in motor and fluorescent-lighting systems

This appendix for more technically inclined readers explains how premium-efficient motors can deliver about 16, and dimming electronic ballasts about 18, different benefits from a single retrofit expenditure.

Motor systems:16-for-one benefits

What answer you get depends on what question you ask. In car design (Chapter 2: Reinventing the Wheels), if you focus on just the engine of a normal car, you may find it's rated at over 30% efficient. So it is—when run under ideal conditions. Yet the suboptimal way it's typically used cuts its average efficiency to about 15%. Some more torque is lost en route to the wheels, and only 1% of the fuel energy ends up moving the driver. Electric motor systems in factories and big buildings are similar: the motor itself may be very efficient under ideal conditions, but the way it's usually used is often very inefficient, wasting most of the motor's torque before it can do the desired task. Avoiding that inefficiency requires not just an efficient motor, but applying it in an efficient system.1

When asked how to save some of the three-fifths of U.S. electricity that goes into motors, most practitioners emphasize only two improvements:
  1. premium-efficiency induction motors (the normal kind, also called "asynchronous" motors), which gain several percentage points' efficiency because they're better designed and built, using a larger quantity and higher quality of copper and iron to reduce electrical and magnetic losses; and,
  2. adjustable-speed drives (ASDS) using electronic inverters to vary the frequency of the alternating current that drives the motor in order to adjust its speed to what the task requires at the time. The output of many pumps, blowers, and fans is controlled by running them at full speed against a mechanical obstruction like a "throttling valve." Yet pumps' and fans' power consumption varies roughly as the cube of their flow rate, so if only half the full flow were needed, seven-eighths of the full input power, less minor ASD circuit losses, could be saved by removing the obstruction and halving the speed. ASDs' full use could thus save ~20%2 or ~14% to 27%3 of all U.S. motor energy, with typical paybacks estimated at about 1 to 2 1/2 years respectively.
So far, so good. But adding 33 further drivesystem improvements—in the choice, sizing, maintenance, and life of motors, in control systems of three further kinds, and in upstream electrical supplies and downstream mechanical drivetrains—can at least double the savings from these two measures.4 It can also cut total retrofit cost by perhaps fivefold5, because of the 35 combined measures, 28 are free byproducts of the other seven that must be paid for, yielding greater savings at no extra cost.6 In short, whole-system design, by capturing multiple benefits, tunnels through the cost barrier.

Immediately retrofitting an in-service standard-efficiency induction motor to a premium-efficiency model, without waiting for it to burn out, is commonly assumed to be a bad deal: the energy saved by the new motor's higher efficiency is often said to take 10–20 years to pay for the entire cost of the new motor. This comparison counts just the following single benefit:7
  1. The more efficient new motor will need less energy than the inefficient old one to produce the same torque; how much less is conventionally calculated from their full-load rated efficiencies and from how many hours a year they operate.

    But in fact, immediate retrofit usually pays for itself within just a few years, because the premium-efficiency motor yields many more benefits than just saving energy through a higher "nameplate" efficiency rating:

  2. Many U.S. motors are so grossly oversized that probably half never exceed 60%, and a third never exceed 50%, of their rated load. This oversizing often makes actual efficiency, operating at the actual loadpoint, lower than the nameplate rating implies. Quite commonly the efficient new motor, properly sized, will be one size smaller than the old inefficient motor; sometimes two sizes smaller; occasionally three. Making the new motor even one size smaller makes it cheaper—saving more capital cost than the extra cost, if any8, of making it more efficient.
  3. Motors that are too big—run at below their optimal load—not only become less efficient; they also run faster. When they are running a pump or fan, the faster speed produces more flow that's typically unwanted, but increases energy use as the cube of the flow rate. Making the motor the right size provides exactly the desired flow and eliminates this waste, so the new, right-sized motor will cost less and save more than you'd expect just be comparing rated full-load efficiencies for motors the same size.
  4. The new motor will typically stay highly efficient across a wide range of operating conditions—speed and torque. This "bigger bull's-eye" on the "efficiency map" maximizes energy savings not just at a narrowly defined operating point but through much or all of the range of conditions in which the motor will actually be called upon to operate. It can greatly increase calculated savings compared with a small-bull's-eye motor that operates most of the time at far from its optimal load.
  5. The efficient new motor, even though it's more fully loaded, will run cooler because it's typically halved the losses that route electricity into making the motor hot rather than making it turn. Heat is the enemy of motors: every 18 F° of increase in motor temperature cuts the life of the insulation and other oxidizable materials about in half. This also works backwards: every 18 F° of decrease in temperature makes these key materials last about twice as long. Running cooler therefore stretches motor life, reducing the costs of maintenance or downtime or both.
  6. Running cooler also decreases electrical resistance in the copper, boosting efficiency.
  7. Premium-efficiency motors tend to come already equipped with higher-quality bearings than standard-efficiency motors. Three-fourths of medium-sized motor failures are caused by bearing failures, so better bearings mean longer motor life.9 This means that the energy plus maintenance savings of the new motor will, over time, typically more than pay for immediately substituting it for the old motor.
  8. Cooler operation makes bearing grease last longer. This means either greater reliability on the same lubrication schedule or the same reliability with less frequent lubrication, which reduces maintenance cost. Greater liability reduces, and less frequent lubrication might reduce, downtime, which can range from a minor nuisance to a multimillion-dollar charge, depending on the nature of the process and the function of the motor.
  9. The new motor automatically eliminates any increased magnetic losses that may have been caused by improper past repair of the old motor.10 Adding this benefit to proper motor sizing yields direct electrical savings roughly twice as big as would be expected from the new motor's better nameplate efficiency alone.
  10. The high-efficiency motor generally has a better power factor11 as a free byproduct of its better design. This avoids most or all of the cost of capacitors otherwise needed to compensate for bad power factor.
  11. Higher power factor also reduces electrical losses in the wiring within the plant.
  12. The high-efficiency motor tends to heat up less when exposed to harmonics (multiples of the frequency of the alternating current). This helps it run cooler and more efficiently at variable speed.
  13. The new motor is more tolerant of improper supply voltage, which is quite common.
  14. The new motor loses much less efficiency and lifetime if the three "phases" of electricity that run it (three different power sources with different timing) don't have perfectly matched voltages—another common condition that can dramatically degrade inefficient motors.
  15. The new motor's energy savings let it draw less current than the old motor. Losses in the plant's wires, transformers, and other electrical supply equipment vary as the square of current: lower current, much lower losses.
  16. All the reduced losses, direct and indirect, release less heat into the plant. In almost all commercial buildings and an increasing number of factories, that space is air-conditioned. Less heat, less cooling and air-handling energy and capacity.
The premium-efficiency, right-sized motor thus provides at least 16 important operational advantages; but it needs to be paid for only once. However, many of these savings depend on others.12 For example, both efficiency and motor life depend on other energy-saving improvements too: reducing voltage imbalance between the phases, improving shaft alignment and lubrication practice, reducing overhung loads (sideways pulls) on the shaft that can cut bearing life by at least 5- to 10-fold, and improving housekeeping—not siting motors in the sun or next to steam pipes, not smothering them beneath multiple coats of paint, etc.

Motor choice, life, sizing, controls, maintenance, and associated electrical and mechanical elements all interact intricately. For example, suppose you're replacing an old fan motor with a right-sized, premium-efficiency motor. Most fans are driven by V-belts, which stretch, slip, wear out, require frequent maintenance, and waste about 5–15% of the torque they transmit. It would be better to use a 98–99%-efficient, virtually zero-maintenance belt-, such as a "synchronous belt" that doesn't slip because its teeth engage sprocket lugs, doesn't stretch because it has fiberglass or aramid bands inside like a radial tire, and saves so much maintenance that the electricity it saves costs about minus a dollar per kilowatt-hour. But such a belt doesn't have much "give," and fans take a lot of torque to start up, so the first time you turn it on, the belt's teeth may well strip with an awful screech. The answer is to use a stretchier but still extremely efficient flat belt, or to equip the motor with an electronic "soft-start" device—often a free feature of the ASD that most fan drives should use anyway.

But there's another catch: if you didn't carefully choose the "slip" of the motor—a measure of how fast it turns—you may find it's higher with the efficient new motor than with the old one, threatening to waste more energy through extra fan flow than the motor's higher efficiency saves. If so, then you'd better notice it in time to make the new belt sprockets a different size, or electronically adjust the fanspeed with the ASD, so you capture the full savings available from the better motor.

Without going into further detail on all the interactions, the unfavorable ones are far outweighed by the favorable ones. Their collective effect is to make the savings of the whole drivepower package far larger and cheaper than would appear from considering just a few fragmented measures, as most analyses do. The bottom line13: retrofitting approximately 35 kinds of improvements, installed in between the electric motor and the input shaft of the machine that the motor is driving, can typically save about half of the drivesystem's energy, even with no improvements further downstream (e.g., in pumps, pipes, flow reduction, etc.). These savings pay for themselves in an average of about 16 months or less at a five-cent-per-kilowatt-hour industrial rate. They're that cheap because if you pay for the right seven savings up front, you get 28 more savings as free byproducts. Seven expenditures, 35 benefits. More tunneling through the cost barrier.

Dimming electronic ballasts for commercial fluorescent lighting: 18 benefits and counting

A similar cornucopia unfolds in commercial fluorescent lighting.14 What do you do to retrofit, say, a ~65%-efficient enclosed two-by-four-foot recessed ceiling luminaire15—the most common type of major fixture? The fixture classically uses 180 watts of electricity for its four 40-watt lamps driven by two 16-watt electromagnetic ballasts. Inserting an imaging specular reflector—a very shiny, computer-designed, specially shaped piece of sheet-metal—above these lamps nearly doubles the fixture's optical efficiency. (That's because each exit ray bounces barely more than once off a very shiny surface, rather than nearly three times off a not-so-shiny surface like white enameled sheetmetal.) Half the lamps can then be removed, the rest relocated, and approximately the same delivered light obtained as before. The removed lamps appear to be still there, but they are only virtual images, and virtual lamps require no electricity or maintenance. The avoided maintenance costs end up, over time, paying for half the retrofit package. While being relocated, the lamps can also be replaced, at no extra labor cost, with new lamps whose "tristimulus" phosphors—tuned to red, green, and blue retinal cones—emit up to 18% more light per watt, with more pleas-ant and accurate color that probably helps you see better. The new lamps are also skinnier, making them up to about 25% more efficient and making it easier to control optically the exact distribution of where the light goes in the room. The two two-lamp ballasts can then be replaced with a single four-lamp high-frequency electronic ballast shared between two adjacent luminaires.

This retrofit has two important lessons. First, doing all these measures together as a package saves much more energy, at much lower cost, than fragmenting the package or omitting parts of it.16 Second, the key to success—the dimming electronic ballast and its control systems—can save electricity in at least 18 ways:
  1. The ballast wastes only two watts per lamp because it's electronic, compared with eight with a standard electromagnetic ballast or 3–4 with a "high-efficiency" electromagnetic ballast.17
  2. The lamps also produce more light at high frequency (about 20–40,000 cycles per second) than at the 60-cycle line frequency. These first two effects can boost light output per watt by upwards of 40%.
  3. Because the ballast dissipates so much less heat per lamp, circuitry for four (or perhaps even six) lamps, not just two, can be installed in a single ballast can without its overheating. This in turn means that a single ballast can control at least two adjacent fixtures, reducing capital and installation costs for both the ballast and its control systems.
  4. The more efficient lamps and ballasts can make the lampwall temperature—on which efficiency strongly depends—more nearly optimal.18
  5. The electronic ballast, depending on design, can be less sensitive to or can automatically compensate for lampwall temperature.
  6. It can also provide the same insensitivity to or compensation for abnormally high or low supply voltage. This plus effect #5 can reduce by one-eighth the overlighting normally designed as a precaution to cope with these potential conditions.
  7. The electronic ballast can continuously dim the lamps to match available daylight, often saving 50% or more of the lighting energy in the "perimeter zones" around the daylit sides of the building.
  8. The same dimming control automatically brightens the lamps as they dim with age and dirt, so they need not be too bright when young, fresh, and clean in order to provide enough light when old, tired, and dirty. This saves at least a seventh of the energy over each group relamping cycle.
  9. The reduced heat from the lamps and ballasts reduces convective air currents that deposit dust on the lamps and fixture, so more light output is maintained on the same cleaning schedule, or less frequent cleaning is needed to maintain a given light output.
  10. Dimming the lamps stretches their lifetime, saving maintenance costs.
  11. It also reduces the rate at which the lamps' efficiency deteriorates, saving energy during operations.
  12. High-frequency operation may further slow that loss of efficiency by about 2–5%.
  13. The dimming controls permit light levels to be adjusted or "tuned" in different parts of the room according to the tasks being done there (more light over your desk, less off in the corner), and easily changed if the furniture is rearranged. This saves around 12–20% of the energy.
  14. Being able to control ambient lighting levels to exactly the level you want will often mean you actually choose, especially if you're relatively young, lower light levels than official standards assume you'll want. Conversely, if you want more light than usual, you can get it without also superfluously providing it to everyone else who doesn't want it. Experiments suggest this better matching to individual preferences may save upwards of 20%.
  15. The electronic ballast facilitates smart automatic control occupancy sensors, which turn lamps down or off in empty rooms, often saving 25–50%.
  16. It's also easier to use timers to turn off lights after hours unless you turn them back on.
  17. The lamps can be slightly dimmed during peak-load periods, reducing utility peak demand charges for both the lighting energy and the associated space-cooling and fan energy needed to combat the heat of the lights. This valuable peak-dimming is imperceptible because the eye, being able to adjust by a million millionfold between sunlight and starlight, has a logarithmic response that can't detect small changes if they're gradual enough.
  18. The electronic ballast can shut down the lamps, and itself, in certain common kinds of failures, rather than wasting energy trying to restart a failed lamp or keeping energized a ballast that's providing no light.
Together, these ballast and control mechanisms can typically save about half the energy per unit of delivered light in the center of a large building, and 70% to 80% or more in a typical mix of core and perimeter zones. The better lamp phosphors and reflector optics cut electricity per unit of delivered light by a further ~15% and ~35+% respectively—a cumulative total saving of about 83% to 91%, all from a whole-system retrofit.

An important example of effects not included in the above list of 18 engineering-economic benefits, but vital to users, is that since the high-frequency operation of the lamps eliminates both flicker and hum, fatigue is much reduced, typically requiring less light per person-hour of work to achieve the same visual performance.

Such large savings are not unusual even in awkward cases, because further opportunities are available too from other aspects of the whole lighting system (not just what's in the fixture):
  • reducing endemic overlighting (most offices are lit not only far above official recommendations, but at levels that actually violate those standards by making it difficult to read computer screens);
  • concentrating local light on the visual task with a user-controllable swing-arm task lamp that lets you spill light evenly across the paper tasks on your desk without also washing out the computer screen;
  • making the light more visually effective by bouncing light off the ceiling and walls so it doesn't wash out the contrast between paper and ink, or by equipping overhead downlights with radial polarizers that reduce veiling glare;
  • using lighter-colored surfaces to bounce light around better in the room;
  • bouncing daylight several times as far into the room (via lightshelves, top-reflective blinds, glass-topped partitions, etc.); and
  • improving maintenance, such as replacing lamps all at once before they lose too much efficiency.
In all, 70% to 90% or greater savings on electricity used for lighting are typically available from comprehensive retrofits, with the same delivered light and great improvements in quality and attractiveness. The cost of such a retrofit is typically equivalent, at a six-cent-per-kilowatt-hour commercial rate, to about a one-year payback if you count saved air-conditioning savings and long-term maintenance savings (from having only half as many lamps and a quarter as many ballasts to maintain). If you didn't count those savings, the payback could be up to about three years. A three-year payback is equivalent to an aftertax annual return on investment of about 32%.

As with motors, however, achieving both such large lighting savings and such improved quality of service depends on harnessing complex thermal, optical, and electrical interactions between all the components. It requires including all the right parts, and combining them into something greater than their sum. It demands doing the right things, in the right order, at the right time. This isn't as complicated as it sounds, but it isn't simply plugging in one "magic-bullet" gadget and turning it on. Rather, it requires new ways to deliver integrated packages of modern hardware plus managerial and cultural changes.19 That isn't easy; but neither is expanding electrical supplies.

1 The original analysis is in Lovins, A.B., Neymark, J., Flanigan, T., Kiernan, P.B., Bancroft, B., & Shepard, M. 1989: The State of the Art: Drivepower, COMPETKTEK / Rocky Mountain Institute, Snowmass CO 81654-9199. For later, less thorough, but somewhat more up-to-date versions, see Nadel, S., Shepard, M., Greenberg, S., Katz, G., Almeida, A. 1991: Energy-Efficient Motor Systems: A Handbook on Technology, Program and Policy Opportunities, American Council for an Energy-Efficient Economy ( ), Washington, D.C. and current DTA Howe, B., Shepard, M., Lovins, A.B., Stickney, B.L. & Houghton, D.J. 1996: Drivepower Technology Atlas. Such data are periodically updated by the comprehensive MotorMaster database sponsored by USDOE (800/862-2086, FAX 360/586-8303, Motor Challenge Information Clearinghouse, Box 43717, Olympia WA 98504-3171).

2 Fickett, A.P., Gellings, C.W., & Lovins, A.B. 1990: "Efficient Use of Electricity," Scientific American 263(3):64–74, Sept.

3 Lovins et al. 1989, op. cit., updated and supplemented by Howe et al. 1996, op. cit.

4 Lovins et al. 1989, op. cit.

5 Fickett et al. 1990, op. cit.

6 Lovins et al. 1989, op. cit.

7 Actually this is two benefits, because saving electricity reduces both energy charges and demand charges, but it might be considered just the single benefit of "saving electricity and hence reducing the utility bill."

8 Actually, as Chapter 12 mentioned, there is no such extra cost of efficiency up to at least 100 horsepower. However, even if the usual rule-of-thumb were right about how much extra you have to pay for a more efficient motor, making the new motor the right size would typically reduce the payback of immediate retrofit to about three years.

9 Changing to a premium-efficiency motor also makes it easy to add at the factory some "bearing seal isolators" that keep traces of water or other contaminants from getting into the bearing and causing it to fail—cheap insurance that can greatly increase motor life at very low cost.

10 Normal rewinding methods cook the nonrotating iron parts of the motor in an oven, often causing subtle and irreversible magnetic damage that wastes about $1–3 billion a year worth of electricity in the United States. Better methods that are faster, cheaper, and nondamaging are on the market but little-known.

11 Power factor is the cosine of the phase angle between current and voltage. It reflects the degree to which the utility must provide out-of-phase current that it must generate and transmit but cannot charge for. Induction motors cause this problem to a degree which, if not adequately compensated by in-plant capacitors, may incur a utility penalty charge.

12 Lovins et al. 1989. op. cit.

13 Id., Fickett et al. 1990 op. cit., Nadel et al. 1991 op. cit. The first reference provides the most detailed scoping calculation, although it conservatively omits effect #3 above.

14 The original analysis is in Lovins, A.B. & Sardinsky, R. 1988: The State of the Art: Lighting, COMPETITEK / Rocky Mountain Institute, Snowmass CO 81654-9199. Its fourth update, Audin, L., Houghton, D., Shepard, M., & Hawthorne, W. 1998: Lighting Technology Atlas, E SOURCE, Boulder CO., is considerably more up-to-date. Fluorescent lighting in the late 1980s was using about half of U.S. lighting energy. The remaining savings are chiefly in incandescent systems and to a much lesser extent in high-intensity discharge lighting. For all lighting retrofits, total cost is typically negative because most replacements of incandescent lamps by compact fluorescents or other longer-lived alternatives are more than paid for by saved maintenance costs (Lovins & Sardinsky 1988). New construction shouldn't use downlights—indirect uplights are more visually effective, attractive, flexible, and cost-effective—and retrofits should consider converting to indirect lighting, but this may not be feasible in some situations such as with low ceilings.

15 The "luminaire" is the light fixture together with the equipment that produces the light. Its efficiency is how much of the produced light comes out.

16 Installing just a reflector duplicates the relamping labor, adds labor for reballasting later, and may save nothing if the reflector is badly designed. Installing a nondimming electronic ballast captures about 3–4 kinds of savings but loses about 14 others; it delivers only one-third the savings of a dimming ballast, but doesn't save enough capital cost to justify that sacrifice. Not switching to the better lamps means unpleasant light, wasted electricity, and a need to change the lamps and ballast later, duplicating labor on both, to correct those problems. (Using 34-watt "energy-saving" lamps also introduces additional technical problems.) Leaving out the controls slashes the savings, and usually requires a costly retrofit later to make computer screens readable and the space reconfigurable. Remarkably, most lighting retrofits make one or more of these mistakes, partly because many utility rebate programs reward specific pieces of hardware rather than integrated packages.

17 This interim technology uses copper instead of aluminum wire, but is still much less efficient than an electronic ballast. It also runs at line frequency, so it hums and the lamps flicker, and it can't dim. In essentially no applications is it a wise choice.

18 Mainly for this reason, starting with three 34-watt "energy-saver" lamps and two "high-efficiency" electromagnetic ballasts in a modern louvered parabolic fixture will save, within a few percentage points, the same amount of energy as replacing the less efficient initial equipment assumed in this example.

19 With motors, for example, an important cultural need is to change lubrication from a low-caste, dirty-hands occupation to a high-caste, white-lab-coat occupation.

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