By David P. Tryling
Saving the environment. To call that a pretty big topic is a gross understatement. Perhaps we can narrow our focus a bit. Whether you believe in global warming or you don’t, it seems only practical to be prudent with our resources. Maybe one of the best things that we can do in industry is energy conservation. Starting back in the late 1970’s with the rise in energy costs, energy conservation became a much-touted method for improving the company’s bottom line. Now, in addition to saving money, energy conservation can contribute to a healthier environment through the reduction of necessary energy generation and fossil fuel consumptions. These are a few ideas that may provide some energy savings for you or your customers through the application of existing industrial electronic technologies.
Using Your PLC for Load-Shedding
Most people don’t think of it, but a PLC that’s already running equipment and operations may be easily adapted to save some energy. Below is a list of potential load shedding ideas that can easily be programmed into your PLC. For these ideas, the PLC does not need to be measuring energy usage. The primary assumption is that the PLC will only allow energy-using devices to be turned on when they are actually needed. If these devices are then inactive, for a period of time, they are turned off. That’s the energy savings key – turning them off.
- Shutdown inactive conveyors / motors
- Cycle pumps when not needed
- Reduce heating / cooling temperatures when processes are inactive
- Create production calendar to power machinery on / off outside of scheduled times
- Reduce office lighting and heating during non-business hours
What is helpful about this type of application is that usually the programming involves adding simple relays and timers to existing logic. This means the implementation is fairly quick and painless.
Reducing Large Motor Loads
The second concept for energy savings is an application, which will reduce energy usage by reducing large motor loads. Many facilities have large blowers, fans, pumps or other devices that run continuously. These devices may not be able to be shut off completely, but yet may not need to run at full capacity at all times. Accepted practice in these applications is to supply these motors with variable frequency drives that throttle back the motor speed, thus reducing energy usage to a lower level that is required by the current load. While this involves financial investment for the variable speed drive and the sensing electronics, with the current cost of variable speed drives continuing to decrease and the cost of energy continuing to increase, this type of application is becoming more cost effective in lower horsepower installations.
Most service shops are familiar with this type of installation, since it has been a fairly popular energy saving concept for a number of years.
Water and Chemicals
Our third energy saving idea is not directly discernable as energy savings. However, it still is. Over the last decade, most municipalities have been strictly monitoring manufacturers waste runoff for chemicals and other impurities in water and sewage. Almost all manufacturing processes use some sort of chemicals. These chemicals not only can be harmful to the environment, but also can be expensive to clean up. The clean up, or better still prevention of chemicals in waste runoff is the responsibility of the manufacturer. The obvious recommendation is for the most exact measurement of chemicals and hazardous materials used and for the implementation of a process for effective cleaning. In most cases this can be as simple as pH balancing of wastewaters, possibly stripping off suspended solid metals or in some cases, the collection of uncleanable liquids for disposal by a third party. So, why should we be concerned about the costs of chemicals and chemical treatment? The reason is simple. Although manufacturers spend a significant amount of money on chemicals, the cost of management, safety and most of all, cleanup far exceeds the cost of the chemicals themselves. Thus, these become high profile operations in the manufacturing plant. Minimizing the impact of chemicals involves a significant amount of energy for both the manufacturer and the local municipality.
Power Factor Correction
One of the single largest cost reduction factors for several decades has been the installation of power factor correction equipment. Power factor is the relationship between real and reactive power caused by inductive loads such as motors. The installation of power factor correction capacitors is the most widely accepted practice for this. Poor power factor can have a direct impact on a facility’s energy usage. Most utilities charge a premium for service to manufacturers with a poor power factor. Correcting this directly affects the bottom line of the utility bill.
Less common however is an associated utility related item – that is the control of peak demand usage. Utilities also charge a premium for peak usage in a manufacturing facility. These calculations can be complex and may be differently applied from utility to utility, depending on the where you are in the country. However, generally there can be price points for the peak usage and any usage that exceeds a pre-established peak. By monitoring this electric usage, a manufacturer can decide in their process or facility to turn off certain loads at a certain peak time in order to avoid some of these costs. Additionally, some utilities offer different rates for industrial usage in off peak hours when residential demand is at a lower point.
Controlling peak loads for utilities and users is important because it affects the utility’s power generation requirements. This in turn affects the usage of renewable and non-renewable energy sources and the utility’s need to build new power generation capabilities.
Energy management has long been a key topic in the financial departments of manufacturers. With the advent of the worldwide consciousness about environmental issues, reducing energy usage moves beyond just an economic consideration and into a broader consideration of society as a whole.