TDI Energy Solutions

Controlling Energy Hogs #2

Foundry Analysis (Vacuum Pump Air Handling System)

Project Overview

A large gray iron foundry wanted to explore energy use by electric motors in their vacuum pump generation area. These pumps are required to create the vacuum needed for V-Process casting operations. At the start of this AFS R&D project, plant management indicated felt that there may be energy savings opportunities involved with the motors driving the vacuum pumps but they had no “hard numbers” to prove that.

In order to monitor electric power usage, we instrumented the motors driving the vacuum pumps to
measure electric power usage, as well as monitoring vacuum pressure at the production floor. This monitoring system allowed us to examine and correlate vacuum pressures and electric power usage continuously, at 2 second intervals.

The vacuum pumps are operated in an “open loop” configuration - with no feedback control signals generated by the actual vacuum pressure at the production floor. In addition, the motors are running in an “on-off” mode; that is either running at full power, or not at all. Since air handling systems are present in virtually every foundry environment, this was a good candidate to include as an R&D project.

Project Goals

Research team developed 4 key project goals hoping to reveal savings opportunities with vacuum system “energy hogs”:

• Determine the cost-benefit ratio for adding variable frequency drives to the vacuum pump drive motors.
• Observe the correlation of vacuum pressure changes with power consumption changes
• Measure short-term fluctuations of the vacuum pressure on the pouring floor.
• Identify opportunities for saving power by monitoring weekend pump turn-on/turn-off times

What We Looked At

Four large electric motors driving separate vacuum pumps provided partial vacuum pressures to production areas at the host foundry. Electric power consumption at the motors and vacuum pressures at the pouring floor and shakeout area were measured using the Sensor Synergy monitoring system. 

It took approximately 3 hours of time to setup the sensors and other system components. Participants could then observe and evaluate power usage and vacuum pressure, with updated measurements every two seconds.

The target equipment, location of the sensors, the measurement rate, and other project details were selected by the project's joint technical team, involving staff from both Sensor Synergy and the host foundry.

Key Discoveries

Vacuum pressure on the foundry floor was very stable showing few fluctuations no matter what activities occurred on the foundry floor. These observations caused us to question whether the capacity of the system was sized correctly.

• Measurements of vacuum pressure during a vacuum pump failure highlighted extra capacity in the system:
• When one of the 4 pumps was out for refurbishing, and another one of the remaining 3 pumps failed, our electronic pressure monitors revealed virtually no fluctuations in vacuum pressure.
• This demonstrated that the 3rd and 4th  motor-pump systems were  unnecessary in most operating modes.
• Insight: Excess capacity for “design margin” is a common practice but can be very costly in the long term. The principles of "engineering margin" cause systems to be designed with more capacity than predicted needs indicate. Often the penalty costs for correcting an implemented system with less capacity than needed is so expensive that systems are generally designed and implemented with significantly more capacity than actually needed. Many types of systems (air pressure, vacuum, cooling fluid, HVAC, ....) must be operated for 1 or 2 years before the actual needs are determined so that production and seasonal variations are properly accommodated.
• Weekly measurements correlating foundry operations with vacuum pump operations highlighted time inconsistencies when pumps were turned off with the time in which the foundry completed work for the week. During the course of this four month study, we found that on average, equipment was left on unnecessarily for several hours each week - adding additional unnecessary usage costs.

Examples of Project Savings Recommendations

• Reducing excess vacuum pump capacity will result in an estimated savings of $50,000-90,000/year at each facility
• Install a variable frequency drive on one of the vacuum-pump drive motors to serve as a feedback controlled trim vacuum-pump.
• Consistently, turning off pumps on the weekends at more appropriate times will save an estimated  $8500/year/facility.