Nissan Plant Reduced Energy Expenditure 30% with Daily Power-Down Regimen
In the manufacturing environment, manual processes used to stop and restart equipment can be costly due to manpower demands. The energy cost of keeping equipment running continuously may be less than that of paying employees for a daily power-down regimen. But given rising energy costs, it’s hardly an ideal solution.
Depending on the amount and nature of the equipment installed in a facility, an automated solution may be the most economically viable one. Fortunately, the modern manufacturing environment has the luxury of using many of the original “smart home devices,” with programmable logic or automation controllers (PLC or PAC).
With some creativity and a slight change in a company’s mindset, any manufacturing plant can become an energy efficient facility using minimal resources to accomplish the task. Once an energy program begins, and the benefits are realized, the savings can be used as investments to fund future projects.
PLCs are now standard on most major pieces of equipment purchased for modern manufacturing, and they provide almost infinite flexibility for modifying equipment operations. These devices are instrumental as a foundation for an automated energy reduction effort.
In fact, without purchasing a single additional component, PLCs in existing equipment panels can be used to immediately generate cost savings. Using existing inputs on machinery for monitoring the equipments’ primary function, the absence of machine or operator movement can also be monitored. If no movement is detected for a predetermined amount of time, select processes can be stopped in a controlled manner, and utility savings will begin to accumulate.
Step by step
The first step in any plant’s energy-savings development plan should be to identify the energy consumers that can be idled during non-production times without causing quality, production, or safety concerns. Many different motors, heaters, lights, and compressed air lines are energized continuously in a typical plant. Each hour a component runs without producing product is money spent in the form of utility usage that has no added value. Yearly utility budgets can be adversely affected by this wasted energy use.
Not long ago, the Nissan manufacturing plant in Smyrna, Tennessee (NNA-S) was faced with the challenge of reducing energy consumption without taking on additional resources. The 25-year old plant consumed virtually the same amount of utilities during an idled state as it did at full production. After implementing countermeasures, the Smyrna plant was able to eliminate energy consumption by over 30 percent. The plant later was named a 2010 and 2011 Energy Star Partner of the Year by the U.S Environmental Protection Agency. Although many opportunities for energy efficiency existed, the most conspicuous areas of impact were the accumulation chain conveyors, overhead lighting, and compressed air services.
Miles of conveyors ran day and night, regardless of production hours. After some planning, key inputs were identified to monitor movement throughout the chain systems using a timer for each chain motor. If one of the switches on the conveyor is made, the timer resets and begins the timing process again. If the timer exceeds the defined preset value, the conveyor motor is stopped.
Each of these conveyors supplies product to a production line. When the manufacturing line begins to run production, and the supply conveyor is in a no-activity shutdown state, an alarm sounds and the conveyor restarts. This practice was developed as a standard logic routine and replicated throughout the plant. In fact, any machine that was equipped with a PLC and inputs had a version of the standard program implemented.
Looking at lighting
Automated lighting shutdown was the next step in energy reduction strategy. Several products are currently on the market that will work with an equipment PLC to automatically turn off select lighting. Circuit breaker manufacturers have lighting panel solutions that receive inputs to monitor the running state of equipment. The task-lighting panels in the plant were changed to the smart panels, and the task lighting was automatically shut down several minutes after production had stopped for breaks and lunches. This alone produced an immediate and dependable reduction in electrical consumption.
The Body Assembly department at NNA-S also implemented a very creative automatic light reduction program. The overhead lighting was automatically shut down over robot cells when safety fences were active because robots do not need light to work. The lights automatically turn on for operators when set-up or maintenance is performed.
Although conveyors and lighting were the first areas modified because of their visibility, compressed air is also a large electrical consumer that is often overlooked.
Compressed air is one of the most inefficient energy sources in any facility. Pneumatic devices need a constant supply of compressed air to maintain a load. Most industrial compressors are very large and consume many kilowatts, especially in large facilities that have expansive air line systems. The larger the system, the larger the compressor’s electrical load. Larger systems also provide more potential for air leaks that further compound the problem.
Fortunately, automatically reducing pneumatic supply is a very simple solution. An electrically actuated ball valve can be placed in any pneumatic supply line. Using a version of the standard shutdown logic implemented on the conveyors, inputs can be monitored, and the valve can be turned off during non-production times. All compressed air consumption is immediately stopped. When a pneumatic supply is eliminated, compressor load is reduced, which ultimately saves kilowatt hours and money.
To view the savings from all of the improvements, a measuring system was developed as well. Each utility meter of every type was wired to a PLC, so usage could be monitored during idle times. Data from the meters is logged to provide trending of the numbers independent of the utility company reports. Web reports were created to display the usage data that filtering times and department. Because the data provided visibility to the energy usage data, the budget responsibilities were able to be divided more equally among consuming departments. Very similar screens were used to set the timer presets for monitoring equipment as well. This portion of the project was not essential, but the interface did provide measurable data, operator status indication, and configuration convenience.
As a precaution, cost savings should not be the only consideration when stopping equipment, turning off lights, or removing compressed air from machinery. The safety of the operators in proximity of any automated equipment should always be the top priority. No equipment can be de-energized, regardless of the savings, without considering the safety impact.
- When lighting is turned off, the required amount of lumens has to be provided with adequate safety lighting.
- Light curtains or safety scanners may be needed to protect operators in areas that will experience conveyor or machinery movement upon restart.
- Controlled stops on equipment may mean that the machinery has to be free of parts, so no damage from binding or jamming will occur to them on startup as well.
- When compressed air is depleted from cylinders, the retained load may fall. In cases such as this, a holding fixture may need to be built to support any load, tooling, or parts. The fixture can be equipped with switches that are monitored in the automatic shutdown logic.
- Regardless of the situation, each circumstance will have to be evaluated individually to assess the risk.
At first, the task of plant-wide energy reduction may seem overwhelming and could meet much initial resistance. However, using machinery PLCs, inputs and outputs already installed, a viable energy reduction program can be implemented without expending many additional resources.
Once the benefits become apparent, creativity and imagination are the only limiting factors on how far an automated utility conversation program can go. As long as safety considerations are met, any machine can be stopped in a controlled manner to provide long-term maintenance benefits, create a quieter factory, produce an environmental performance improvement, and ultimately, a significantly lower utility budget.
Josh Hauskins is a senior engineer and new-model controls-engineering project leader in the Trim and Chassis department at Nissan North America in Smyrna, TN. He has a diploma in electronics technology and a B.S. in information technology. He was one of the “Leaders Under 40” named in the November 2010 issue of Control Engineering magazine. www.controleng.com/awards