Reducing energy consumption is a bit like exercise. People tend to agree it’s a good idea and should do it regularly––but often times they don’t quite make it to the gym. Yet if energy costs keep rising, engineers won’t be able to sit on the sidelines for much longer and will have to work out new ways to trim the energy consumption of the machines they build.
This growing energy awareness was on display throughout this week’s Hannover Fair, where major suppliers and users of motion control and automation equipment showcased their energy-reduction strategies and technologies. The fair also itself featured brand new energy-efficiency displays, including an “Energy Tunnel” exhibit that highlighted ways to make common industrial processes — like pumping — more efficient.
One theme that comes up again and again is energy reduction in an industrial setting doesn’t so much require new technology as the smart application of existing technologies — which means steering clear of common design mistakes.
At Mercedes-Benz, for example, there’s an ongoing effort to save energy by turning off production machines when they’re not needed. It’s not as simple as it sounds. “You don’t just flip a switch. The machine may turn off, but will it turn on again when you need it,” says Gerhard Haeberle, an engineer with the automaker’s controls technology group. He and his colleagues have begun an analysis of the company’s manufacturing systems to see what things should be turned off and under what circumstances. Haeberle calls the strategy “intelligent shutdown” and says the goal is to implement it — ultimately as PLC function blocks — in the company-wide control standards.
The savings promise to be huge. Haeberle didn’t have energy consumption figures but he did cite a closely related metric of emissions reduction. “If you look at the life cycle of the car, 20 percent of the CO2 emissions are created during production. Our goal is to reduce that 20 percent by 20 percent through intelligent shutdown by itself,” he says. The emissions and energy savings would be even higher with the adoption of other energy-saving technologies, he says.
Consider Bosch-Rexroth, for another example of how existing technology can help cut energy consumption. The company displayed a diverse collection of drive units optimized for reduced energy consumption. Among them was a pneumatic system whose open-loop electronic controls help optimize speed and air usage for total energy savings that can reach 25 percent. Likewise, the company showed how variable speed pumps can reduce energy consumption by roughly 30 percent compared to constant speed models. And the company showed electric drive systems whose regenerative capabilities and energy exchange between multiple linked motors contributed to a 35-percent reduction in energy consumption for the 18.5 kW system used in the display.
“None of these ideas is new. Some of them have been around for years,” says Wolfgang Walter, an engineer and energy specialist with Bosch-Rexroth Drives and Controls. And in fact, many of the automation vendors at the show talked about similar approaches to reducing the energy losses associated with pneumatic, hydraulic and electric systems.
One common mistake related to designing for energy consumption involves over-sizing motors and drives. Walter says this a pervasive problem that pushes energy costs higher. “In Germany, most drives are at least 30 percent too big,” he says, adding the problem seems to be a global one. To help engineers pick the right drives for a given application, the company has developed a software sizing tool called IndraSize.
The increased use of high-efficiency motors also looms large as a relatively untapped source of energy savings. The German Electrical and Electronic Manufacturers’ Association, or ZVEI, estimates the adoption of the most efficient motor class across all possible applications would save 5.5 kWh or 440 million in power costs per year in Germany alone. The ZVEI also estimates only about 12 percent of the 30 million electric drive units in Germany use speed controls, a well-known energy-saving strategy. If 50 percent of those drives adopted speed controls, it would save 22 billion kWh of electricity per year in Germany, which is worth about 1.75 billion Euros at 0.08 per kWh.
Meinhard Schumacher, SEW-EURODRIVE’s manager for geared motors and AC drives, also likes the idea of higher-efficiency motors. But he warns they’re not a cure-all when it comes to energy reduction. “It doesn’t make sense to have a more efficient motor if the other components in the system aren’t efficient,” he says, citing inefficient gear boxes as one threat to overall energy efficiency. That systems approach led SEW-EURODRIVE to come up with its MOVIGEAR, a combination of motor, gear unit and electronics in one housing. Schumacher says its speed-control capabilities and optimized interfaces between all the components can save a significant amount of energy. For example, he says a MOVIGEAR system saves about 300W as compared to a traditional 1.5 kW AC motor and gear box.
Schumacher counsels engineers to take a systems approach and really understand their application well when trying to reduce energy consumption. For example, he says high-efficiency AC motors can actually be less efficient than their standard counterparts in applications that have only short periods where they run at constant speed and high acceleration requirements. “The message is that an energy-efficient motor is not the best solution all the time. Normally it is, but don’t assume it is every time,” he says.