Photo shows a vacuum system used in hospitals – also generally unmonitored and operated inefficiently.
Background
Many industries rely on electrically driven vacuum pumps for various production processes. One such industry uses a form of sand casting called vacuum molding, or “V-process.” A challenge of vacuum-based processes is that it’s generally not practical to store a vacuum, so pump capacity must always meet or exceed peak demand.
A gray iron foundry used V-process casting for most of its production and had independent vacuum systems in each of its three buildings. Each building contains two systems such that optimized vacuum levels could be provided to the molding deck and the pouring floor. These dual systems have an interlink capability so that they can back each other up in case of a malfunction.
Each building’s system used four large electric motors, two rated at 250 horsepower and two at 200 horsepower. At any moment three of the motors are active, with the fourth motor available for backup. Further, the motors are run “open-loop” without any feedback. The motors are run either full-on, or off without the benefit or efficiency of variable speed drives to manage partial loads.
Challenge
The foundry’s staff had suspected the energy-hungry vacuum pumps weren’t being operated efficiently, however, didn’t have data to confirm or quantify their suspicions.
Solution
The first step involved installing a monitoring system to track the real-time power consumption of each motor, along with the vacuum level of each system. The Sensor Synergy Energy Aware monitoring solution was selected for its low cost, ability to be self-installed, and the company’s reputation within the metal casting industry. The systems were initially installed in one of the three buildings to quantify the overall energy savings opportunity. Three-phase motor current and two pressure readings were captured every two seconds and data was stored in a secure cloud server. The Sensor Synergy Portal provided secure access to the data and visualizations by authorized users via a web browser.
Findings and Results
With 27 million data points gathered by Energy Aware at their fingertips, the correlation between power utilization and vacuum pressure was studied. The data included a power loss event where one pump lost power with no impact on system vacuum pressure. A key finding was that the system was designed with an excessive capacity margin in comparison to actual operational requirements. The staff identified opportunities for $160,000 in annual energy savings by simply taking the excessive capacity offline. The data also demonstrated an additional $70,000 of annual energy savings opportunity with a cap-ex investment for variable frequency drives. Key findings included the following.
- Operations with high-power vacuum systems should audit their “engineering margin” within a year of stabilized production. Engineering margin (also referred to as operating margin, safety margin, or simply “fudge factor”) is a design principle used in many situations to provide excess capacity to accommodate uncertainties. These uncertainties include factors such as future expansion and design requirement errors often found in equipment or process specifications.. In this case, the data demonstrated that the plant was operating with 300% excess capacity where 25% would likely be an appropriate engineering margin.
- Vacuum processes that use open-loop control systems are prone to consuming excessive energy. This is because they often rely on vacuum pressure control regulators, which open a valve to let ambient atmosphere into the header pipe to prevent the vacuum pressure from dropping too low. Since the regulator allows air to enter the system as quickly as the vacuum pumps can operate at their maximum capacity, there are no visible signs of failure in the system, except for the higher energy bill.
Conclusion
Through a combination of Industrial Internet of Things (IIoT) technology, data-driven insights, and a focus on matching actual operational capacity requirements with energy inputs required to meet them, the foundry was able to double the energy efficiency of its vacuum system. The same organization has two additional, essentially identical facilities where it will implement the same improvements. This case exemplifies how much opportunity there is for cost and efficiency improvements by measuring actual requirements in a stable production environment instead of assuming that the engineering margin designed into each part of the system remains appropriate in the actual production environment.
In this case, the payback period for the investment in Energy Aware monitoring solution was less than two weeks.