Proper integration topples barriers to successful energy management
The ability to reach a goal depends on accurately identifying the goal in the first place. If the goal is energy reduction, the first step toward achieving it is to determine precisely where the energy is being used. The statement "you can’t fix what you can’t measure" finds no better application than in energy management.
Historical precedent for the lack of systems integration
With the prevalence of automation in modern manufacturing facilities, one often assumes that the equipment needed to measure energy use is already in place, and that the data need only be integrated, stored, and presented for anyone to understand where energy is used and how savings can be achieved. But this is not the case for most facilities. Data integration in particular often proves very difficult, due to the nature of building and plant design.
The purpose of process systems is, quite literally, reliable control of a process. Proper control requires various field inputs, material flow meters, product counters, vision systems, and so on.
Measurement of energy flows, such as compressed air and electricity, is rarely needed to achieve an optimized production process. The measurement of energy input is generally ignored and considered part of the "utility" umbrella.
In many process facilities, the utility plant operates independently from the process. That’s because plants were originally designed to run on wood, coal, and oil, which are suited for large central utility plants, not the plant floor. Although most operations have transitioned to natural gas and electricity, facilities are still designed the traditional way. Because of this legacy, the measurements of energy flows and consumption exist in the utility plant or building automation system.
Differences between systems for process control and building automation
It’s difficult to integrate process control systems with building automation systems because they have fundamentally different design approaches. The process control system is designed for very high reliability, fast processing, and hardened input and output (I/O). The building automation system is designed to provide the maximum number of I/O at the lowest cost, integrated with low-cost field devices.
From an integration point of view, one can clearly see the division in the communication protocols. The process system is more likely to require specialized equipment from multiple vendors. The value of communication among pieces of equipment is very high, as this is where the money is made. The importance of communication has led to the adoption of specific vendor protocols as de facto standards (such as Modbus) and the development of standards (such as OPC) that permit extensive multi-vendor integration.
The equipment in central utility plants is the same regardless of industry, while building automation systems are often extremely specialized. Specialization allows one vendor to provide all the controls necessary for a central utility plant or building. Without the need for multiple vendor integration, vendors tend to select proprietary communication protocols in an effort to lower cost and secure market share. These market forces have been the primary impediment to integration of process and utility controls for data collection.
Integrating systems with open protocols
In the past decade this issue has been mitigated by the emergence of vendor-independent open protocols such as the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) BACnet protocol. Building automation vendors have also begun to adopt some industrial protocols such as Modbus and OPC, but legacy systems in existing plants are not likely to use these newer open protocols.
To bridge these systems, facilities often use protocol converters-specialized computers that convert proprietary protocols into industry standards. The converters can be very effective, but, like any specialized or custom system, they can be dif cult to con gure and support. Hardware obsolescence is a particular concern.
Leveraging the historian database
Another way to integrate data from process and utility automation systems is to combine the data from a database or historian. With this approach the measured energy use is not real-time but is derived from periodic reports drawn from each system-specific historian database. The responsibility for this type of integration falls under the IT domain, which reduces the probability of obsolescence, since most manufacturing facilities have IT support staff.
The right process control data
Once all the data is combined for measuring and tracking, it’s not uncommon to realize that the process automation systems do not collect the desired data. As stated earlier, measurement of energy flows is rarely needed to achieve an optimized production process. However, this does not mean the plant floor data is not valuable in determining energy use.
There are several accepted methods for estimating energy use based on information such as motor run time and percent of equipment utilization. These methods have been standardized in the International Performance Measurement and Verification Protocol (IPMVP). The protocol originated through efforts to measure energy savings in the building and central utility industries, but the techniques can also be used to effectively estimate equipment energy use from process automation data. Further, this protocol is well established and is accepted by the financial industry as an acceptable means to prove energy savings.
When using process and building automation data to assess energy savings, it is important to keep an eye on the goal: energy reduction. The data from each of these systems and the techniques used in the IPMVP do not provide highly accurate measures of energy or utility use. But highly accurate measures are not required. Of more importance is the relative reduction in energy use after the implementation of an energy reduction measure. Too much effort is spent in many energy reduction projects in trying to achieve exact measures of energy where relative measures will achieve the goal.
Simply put, "you can’t fix what you can’t measure" means it is time to utilize the data available from your process and utility automation systems. Review the current measurement and veri cation protocols, as well as your facility’s I/O list. It is likely that you have what you need to begin an accurate estimation of your facility’s energy use, which will give you the ability to reach your energy management goals.
Bruce Billedeaux, senior consultant with Maverick Technologies, is a licensed professional engineer. He has been involved in institutional and industrial energy optimization for more than 25 years. Edited by Control Engineering and Plant Engineering, part of CFE Media, for the October 2012, Industrial Energy Management special section.