Volkswagen and Mercedes-Benz study energy savings potential with PROFIenergy
By Bill Lydon, Editor
During the 17th Annual PI North America General Assembly Meeting in Phoenix, AZ on October 4-6, 2011, Dr. Frithjof Klasen, professor from the Institute for Automation & Industrial IT at Cologne University made a presentation describing results of a study at a Volkswagen and a Mercedes-Benz plant focused on PROFIenergy. He noted that PROFIenergy was developed in response to calls from the AIDA (Automation Initiative of German Automobile Manufacturers) Group (members include Audi, BMW, Daimler, Porsche and Volkswagen) to reduce energy consumption. Participating plants were the Daimler Sindelfingen Plant (mixed production of sedan and T-model) and the Volkswagen Hanover Plant (Porsche Panamera body production).
PROFIenergy is a profile of the PROFINET communications protocol that allows the power consumption of automation equipment to be managed over a PROFINET network. The PROFIenergy profile was published in 2010 with a key concept of enabling energy consuming devices to go into sleep-modes during non-productive periods.
PROFIenergy is the enabling technology for deploying energy-saving strategies. The elaborate engineering required for energy-saving functions must often be carried out specifically for each device, which, to date, has been a major obstacle for the implementation of energy-saving measures. This is where the engineering beauty and simplicity of PROFIenergy shines. When the application engineer is designing the control logic for a machine they build the logic for reporting and controlling to one of three states:
- Brief Pauses – Usually planned and lasting up top one hour.
- Longer Pauses – Typically hours or days.
- Unscheduled Pauses – Typically caused by equipment failure.
PROFIenergy enables centrally controlled switchover of individual devices or portions of a production plant to energy-saving modes. The profile then allows a coordinated restart behavior from energy saving modes. PROFIenergy also defines models for monitoring energy consumption data to normalize data at the unit level that is either monitored directly (by instrumentation) or calculated (by knowing the electrical parameters).
Dr. Klasen’s measurement study examined the savings potential in the automotive industry in cooperation with Volkswagen and Mercedes-Benz by recording load profiles for equipment in work cells.
Professor Klasen used the analogy of the power management in a laptop computer to illustrate the concept behind PROFIenergy. Laptop users define when the screen will dim, when the monitor will be switched off, when the drive will be switched off, and when the computer will be put in standby energy-saving mode. In a similar way, the states defined in the PROFIenergy profile are to save energy in production plants based on the production state.
Using instrumentation, the study measured and recorded load profiles of work cells along with logging operating states of production. Operating states of production are full production, planned pauses, and unplanned pauses to identify relevant energy savings from running equipment in ways to match those states. In addition to electrical energy, the energy consumption of pneumatic devices was measured because it account for a large percentage of energy use in plants. Energy was measured down to the device level.
Power analyzers acquired and simultaneously recorded all power supply system characteristics, transients, alarms, and waveforms. Measuring devices were time synchronized with PLCs to capture the operating state of the production line and machines. Continuous recording of voltage, current, and power parameters over a time period of 7 days with a measuring interval of 1 second was used. Measurements were also recorded at the infeed of the plant, sub-distributions to plant units, 400 Volt energy bus and 24 V DC energy buses. Examples of units monitored included assembly robot, part delivery robot, and screwing machine. PLC log data provided information on the operating modes:
- Plant Level: Plant ready to operate, plant in operation, or plant fault.
- Station Level: Single station operation.
- End Device level: Robot in motion, tool in operation, etc.
Data was logged along with operating modes for energy analysis and to capture energy consumption/load curves for the entire operation, sections and devices. Other information recorded for the entire operation, sections, and devices included maximum energy consumption, average basic energy consumption and energy consumption during idle times. Data was further marked for planned idle times of plant (breaks, weekend), unplanned idle times of plant (fault), operational idle times of plant (e.g., maintenance), and model-related idle times (mixed production).
Qualitative and quantitative analysis of operating modes and the associated energy consumption of plant units was derived from the data including energy consumption of individual plant units, reduction of energy consumption during idle times, duration of idle times, and pauses (planned, unplanned, operational, model-related). Based on this information potential savings were determined. For example one of the production lines had average power consumption during production of 32.62 kW and during idle time 17.74 kW. The study calculated a 33% potential energy savings per year for the production line using PROFIenergy based on a 2-shift operation, 5 work days + 2 weekend days. The potential savings per work cell results in savings of 5,700 euro and 33.250 kg of CO2 emissions per year. Typical plants have over 100 cells which would yield a savings of more than 500,000 euro per year.
Dr. Klasen noted that full utilization of savings potential requires adequate plant concepts to save energy. Plant operators must define requirements for plant builders, equipment manufacturers, and device manufacturers. Also, standby mode is only useful if trouble-free startup of equipment can be assured.
Thoughts & Observations
This was an excellent example of applied engineering leading to understanding. Mike Bryant, Executive Director of PI North America noted, “We were all in a meeting and I just said why don’t we get some empirical data…”
I was impressed by the care and precision of Dr. Klasen’s study and the openness of Volkswagen and Mercedes-Benz to make their production lines available for the study. This is an example of productive cooperation to improve industry.
PROFIenergy is a clever idea that provides the kind of framework required to configure control and automation systems to save energy in concert with production flow.
The next step is for the enterprise IT systems to exploit PROFIenergy capabilities to improve operating efficiencies.
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