Refrigeration accounts for the majority of a refrigerated warehouse’s total electrical costs, often up to 70 percent of a plant’s total operating expenses. As energy costs continue to increase, more and more food distributors are realizing the need for energy optimization and monitoring as a way to increase productivity and lower energy costs. The most effective way to reduce energy costs is by employing an integrated approach to mechanical and automation controls.
The keys to managing energy efficiency are reducing operational costs, utilizing existing systems to reduce equipment costs, analyzing the ROI for new energy savings projects, and conducting a power quality assessment. Most refrigeration systems are designed to optimize the efficiency of each individual component rather than looking at the entire system as a whole. An all-inclusive equipment approach ensures the system works together efficiently.
Many users add new equipment with little regard to the impact on the total system, leading to wasted energy and operational inefficiencies. If a facility is preparing for an expansion, or simply adding a new compressor, it’s important to obtain baseline data to compare against future results and install energy monitoring controls prior to making any changes. If a facility is embarking on a new construction project, mechanical engineers and automation engineers can work together to install state-of-the-art controls and energy-monitoring capabilities that can actually decrease a plant’s energy cost over the long term.
Consider incorporating some of these operational efficiencies into your energy management plan:
1. Ensuring that equipment is the right size is important to control efficiency. Compressors need to match the load so they can be staged and sequenced effectively. Condenser capacity should be sized so that energy efficient variable frequency drives (VFDs) on fan motors can be implemented. Sequencing of compressors in the machine room, in conjunction with condensers, helps lower the amount of energy consumption.
2. Install VFDs on compressors to optimize mechanical efficiencies of the machines. The best approach is to set the slide valve position at 100 percent and vary the RPM of the motor according to the refrigeration needs of the machine, allowing it to run more efficiently.
3. Install VFDs on condenser motors to stabilize head pressure and prevent the motors from heavy repeats and intense start/stop cycles. This will allow the fans to change speeds so they don’t continually stop and start, which requires additional energy and results in mechanical wear. The algorithm that is established on the VFDs, or how you fine tune the fans in and out of operation, is the real key.
4. Use of floating head pressure to maintain the ideal temperature for compressor and condenser operations is important. Based upon ambient conditions and wet bulb calculation, a system can run at a lower head pressure. Higher condensing temperatures require more compressors to work harder while lower temperatures require less power. You can find the optimal break-even point where the condenser and compressor are working together to reduce overall horsepower requirements.
5. A two-stage system takes advantage of mechanical efficiencies. By commissioning a booster compressor for the low stage system and an intermediate compressor for the high stage system, a facility can see up to a 20 percent or more improvement in mechanical efficiency.
6. A completely integrated automation system can run your machine room to ensure efficiency and automate temperature controls within zones. Automating defrost cycles to sequence at different times can result in significant energy savings. Automated controls also provide the ability to control evaporators in cold zones.
7. Remote monitoring can have a significant impact on your bottom line, reducing energy, maintenance and overall operating costs. If you’ve recently upgraded your refrigeration controls system or are in the process of upgrading, it’s important to ensure your new system offers remote access. This will allow for speedy diagnostics, offsite troubleshooting capabilities, and constant monitoring, all with a “big picture” view of the entire system and allow you to run reports in real-time, including trend analyses, alarm logs, and energy management data. Working with a vendor who has expertise in both refrigeration and controls will help your team identify inconsistencies and trends that could be wasting energy so you can make the necessary changes to improve efficiency.
Kevin Frantz is an automation manager with Stellar, online at www.Stellar.net.