Cooling Off Energy Usage
In the heat of summer, businesses and residences crank up air conditioners in order to battle outside temperatures. As temperatures soar, so do utility bills. Most people dwell over the negative impact on their pocketbooks, but the real strain occurs at the utility plants. As energy demands increase, these plants reach peak load, placing great stress on generation, transmission and distribution. This leads to shortages, and then to brownouts, rolling blackouts and outages, as recently experienced in California.
According to a recent study released by the U.S. Department of Energy, 60 percent of all the electrical power generated in the United States is consumed by electric motors. Electric motors power not only heating, ventilation and air conditioning (HVAC) systems, but also household appliances and industrial machines. Not surprising, the industrial sector eats up 37 percent of total energy used, making it the largest consumer. The reason behind such large consumption is that industry relies on motors with over 50 horsepower capacity. These motors, which represent only five percent of the motor population, consume 72 percent of total motor energy. This demand in the industrial sector will not decrease since industry relies on these large motors for everything from treating wastewater to assembling automobiles to making paper. At the same time, residents and businesses are increasing the demand for air-conditioning, accounting for more than 50 percent of household electricity consumption during the summer m
onths, according to a recent report from the Appliance Standards Awareness Project. This is only increasing due to the large influx of businesses and residents relocating to the Sun-Belt states where temperatures will continue to soar during Summer months.
Reducing energy demands can be achieved by improving energy efficiency through motor control. Electric motors convert electrical energy into mechanical motion. These electric motors are controlled by specific types of semiconductors - microcontrollers (MCUs) and their higher performance cousins, digital signal processors (DSPs). Since they were first introduced in the early 1980's, the speed of DSPs has significantly increased from less than 5 MIPS (million instructions per second) to thousands of MIPS, while the prices of DSPs have sharply dropped from hundreds of dollars to less than five dollars each (in high volumes).
Reducing energy demands can be achieved by improving energy efficiency through motor control.
Within the cost-sensitive industrial sector, there is an increasing trend to move toward reducing the complexity of components by using high-performance, low-cost DSP controllers instead of traditional analog-relay circuitry. "While microcontrollers have been on the market for several years, the sensor technology has seen a revolution," said Neal Elliott, Industrial Program Director at the American Council for an Energy Efficient Economy.
Semiconductor companies have long offered microcontrollers for motor control applications with advanced versions offering more memory and speed. But now, companies like Motorola are merging DSP functionality with the fastest microcontroller features available. "Less components means higher reliability," said Brian Cieslak, software engineer at Rockwell Automation, a Motorola customer.
Motorola's latest line of high-performance, 16-bit DSP controllers are capable of performing the fastest, lowest cost closed-loop control of motors available today. "The DSPs pull in a lot more data and information at a much faster rate than MCUs," said Cieslak. Equipped with Flash technology, the DSP also offers higher memory capacity. DSPs will not replace MCUs, but instead target complex, high-torque profile applications, like the heavy motors used in industry.
"Industry doesn't care about energy, but what it does care about is producing a product," said Elliott. "The non-energy benefits of safety, environmental compliance, product quality, cost reduction, flexibility and labor avoidance are what concerns industry." The DSP controller accomplishes all of this through smart motor control, with the added benefit of offering a cost-effective environmental solution for the industrial sector in terms of energy efficiency. For such a small chip, these are pretty big accomplishments.
A smarter solution to pump control focuses on the source of the problem: the electric motor.
Of the many DSP controller's cost-effective environmental solutions, energy efficiency, quality control and conservation are common themes throughout various industrial applications. One of these applications is pump control. A common problem with water pumps occurs during start-up and stop of the pump. The sudden flow of water through the pump and pipes creates surge waves that send off a loud clanging sound, called "hammering." While the noise is certainly a distraction, the real problem is the negative impact on the water pipes. Hammering may cause pipes to burst or even to collapse. Efforts have been made to reduce hammering, but they have proven to be largely unsuccessful. For example, in the past, facilities have employed an electro-magnetic starter. This starter causes the flow rate to increase in a very short time, which the system cannot adequately handle. Mechanical devices have also been used, including special valves, surge chambers and air admission valves. To incorporate
these into a system requires high initial expenditure and continuous maintenance.
A smarter solution to pump control focuses on the source of the problem: the electric motor. To meet this need, Rockwell Automation created the Smart Motor Controller Plus. "This product minimizes the surge caused by the pump during starting and stopping," said Jerry Watkins, marketing manager of Rockwell Automation's Components and Packaged Applications Group. The microprocessor monitors the speed of the electric pump motor and adjusts the voltage and current applied to it accordingly. The end result is a closed loop system, allowing for smooth motor acceleration without excessive acceleration torque. Although Rockwell has relied on microcontrollers in the past, they are considering the advantages of Motorola's latest family of DSP controllers to reduce the size of the product and increase its functionality and reliability. "The DSP controller's algorithms are more robust, making it less error-prone and improves overall performance and reliability," said Cieslak. Thus, controlli
ng the initial influx of electricity will contribute to energy savings and the elimination of hammering will prolong the life of the pumps and pipes, which means less waste for landfills.
Another application that consumes a great deal of energy at start-up is HVAC systems. "Electrical circuits experience a lot of stress when they are turned on," said Kraig Knutson, Assistant Professor in ASU's College of Engineering. "If you can reduce the stress on them, you can prolong the life of the motor." Knutson is part of a joint research project focused on DSP controlled HVAC systems.
A surefire way of reducing the stress and maximizing both heating and cooling systems is to avoid cycling, which occurs when the system turns on and off to adjust to the set temperature. According to a July 2000 study released by the Appliance Standards Awareness Project, cycling is one of the primary strains on power plants. High summertime temperatures negatively affect the performance of electricity generation, transmission and distribution equipment. It is precisely at this weakest moment that air conditioning systems kick on to battle the outside heat, placing even more strain on the equipment and on the electrical system.
Control, Reduce, Improve
This problem would be alleviated if the system maintained a constant temperature through speeding up or slowing down the compressor, rather than turning it on and off. DSPs can adjust the speed of the motor to match the required temperature. Knutson compares this solution to a light dimmer. Instead of an on and off light switch, the amount of light can be adjusted through a dimmer. At night it would be brightest, but during the day, the light can be dimmed, conserving both energy and the life of the bulb. Steve Neale, president of Syntronix Inc., sees the DSP as the only available technology that can provide for a continuously variable output to set the exchange rate in the room. "This will allow for greater comfort at a lower cost," said Neale.
Controlling electric motors with DSPs also helps reduce waste and conserve raw material usage. For example, DSPs can improve upon the entire extrusion process. An extrusion process begins with bulk material that is liquefied by water, heat and/or pressure. The extrusion process squeezes the raw material though a narrow slot (for flat rolled materials like paper rolls, rolls of steel, or rolls of plastic sheeting) or through a small diameter hole (to create different gauges of wire).
Controlling electric motors with DSPs also helps reduce waste and conserve raw material usage.
For paper, the raw material (trees) are run through a chipper at the sawmill site in the woods or in the centralized lumber processing plant. This material normally consists of the by-product of the lumber mills (sawdust, limbs, bark and the areas at the edge of the trees that can't be used for lumber production, etc.). Once all this material is reduced to fine "chips," the raw pulp is mixed in large vats with acid and water to break down the pulp into cellulose fibers. The cellulose is bleached to enable the paper mill to control the color and is then mixed with other pulps and chemicals to determine the type of paper to be made (60# craft, 20# copier, 30# fine, etc.). At this point, the liquefied paper is at very high temperatures (150-200 degrees Fahrenheit) to keep the gelatinous mass moving. It is then extruded by a motor-driven spreader onto a conveyor belt, fine enough to hold the fiber, but porous enough to allow excess moisture to fall through.
The speed at which the screen is driven and the rate at which the spreader extrudes raw product onto the screen helps determine the thickness of the paper. Of the pulp actually spread onto the screen, only about 20 percent is actually pulp, and the rest is liquid which will be removed through the drying process. By controlling the mix of pulp-to-water, the cost of the paper is directly controlled. Small percent changes in mix ratio can reduce the amount of pulp needed to make the paper, while also producing consistent high-quality products. Improving the process then leads to an improved product, cost savings and energy savings.
With many motors running on multiple lines at the same time at an industrial site, the power factor of energy supplied to the site can become skewed. This creates power inefficiencies that increase power consumption and costs, while reducing its effectiveness, whether it's processing paper or assembling cars. If all the motors at the site were connected to a communications network, the motors could essentially "talk" to one another to control the phase shift of the energy being used by each motor and thus enable the power factor to be optimized throughout the entire facility. The result includes optimized power utilization that reduces cost, extends motor life, and minimizes the possibility of brownouts, rolling blackouts and the other power outages that can occur when power demand exceeds the ability to deliver.
This article appeared in the April 2001 issue of Environmental Protection, Vol. 12, No. 4, on page 53.
This article originally appeared in the 04/01/2001 issue of Environmental Protection.