Machinedesign 1344 Energy Control System200 0 0

Control system pays off in big energy cost savings

July 1, 2000
IBM got tired of paying millions in electrical and fuel bills. So the company teamed up with a controls and drives manufacturer to develop a centralized energy control system for 125 buildings.

Faced with $2 million in monthly electrical bills and $400,000 in monthly fuel costs at its Endicott, N.Y. facilities, IBM launched a multi-year program in 1985 to cut energy costs. The result is an energy management system that monitors and controls energy usage for a 125-building complex covering 5 million ft2 on two sites. Included in the complex are five large buildings used to manufacture PC chips, cables and connectors, and IC circuit boards. Several other buildings contain product development labs.

Focusing on HVAC, lighting, and chemical handling operations, this control system nets the company over $1 million annually in energy savings.

With its previous system, IBM used stand-alone manual controls and it often defined power requirements with conventional rule-of-thumb methods, which left considerable room for error.

Engineers replaced these outdated manual controls with a centralized system that monitors and controls energy usage. The new control system links personal computers (PCs), programmable logic controllers (PLCs), and adjustable speed drives with various types of HVAC, lighting, and chemical handling equipment. In addition to controlling processes, the system provides reporting and historical trends, activates alarms, and makes troubleshooting more efficient.

PLCs and drives team up

Working with engineers from Square D Co., Raleigh, N.C., IBM initially installed 12 SY/MAX 500 PLCs connected to a supervisory IBM PC. The PLCs monitored 200 analog input points, gathering energy-usage data from the various buildings. Engineers used this information to pinpoint areas of energy waste. Then they designed an energy- efficient control system in which the supervisory PC communicated with the PLCs over a token ring network that was already in place as part of an information management system. The entire system — both information management and energy control — is connected by fiber optic cables between buildings. Fiber optics was chosen for its flexibility, low cost, and ability to handle large amounts of data.

Three main objectives of the new control system were to:
• Make more efficient use of steam and chilled water to heat or cool buildings and chemical baths.
• Improve the efficiency of using compressed air to operate high-speed drills used in manufacturing circuit boards.
• Provide automatic setback of temperature and humidity levels.

For the cooling system, engineers linked PLCs to Square D’s Omegapak ac adjustable-speed drives that operate equipment in the Endicott facility’s cooling towers. The PLCs have built-in PID controls that take corrective action when temperature, flow, or pressure within the cooling tower exceeds set points. When temperatures of the water and outside air reach certain values, for example, PLCs instruct the adjustable- speed drives to turn fans on and off as needed to maintain the desired water temperature.

Other adjustable-speed drives, also controlled by PLCs, reduce the speed of chilled water pumps and decrease water flow in accordance with need, rather than operating the pumps continually at full speed and throttling the pump discharge to adjust flow. Ranging up to 250 hp, these drives reduced water flow from 25,000 gallons per minute (gpm) to 17,000 gpm in 1993.

Adjustable-speed drives are also used with PLCs for adjusting air volume in offices. In addition to monitoring and controlling temperature and humidity, the HVAC system selects the most efficient method to heat or cool the air. For example, when the outside temperature is low enough, the system uses outside air for cooling, rather than the chiller.

Other parts of the system turn lights in offices, labs, and factories on and off at selected times. And they set the lights to appropriate levels of illumination for the tasks being performed.

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System expansion

Later, IBM expanded the project to include new energy-saving projects, such as controlling the flow of process chemicals used in etching and stripping circuit boards. Because of the large number of points being monitored, engineers selected Square D’s newer Model 400 and 600 PLCs to monitor and control chemical tank farms as well as the HVAC system. Part of the PLC duties are to turn on the tank farm pumps only when needed, rather than letting them run continuously as before.

Today, a three-tiered network — based on PCs and PLCs — monitors and controls nearly 13,000 points in the Endicott building complex. The upper level of the Facilities Information System, with 40 IBM PCs on an IBM token ring network, is part of a plantwide information system.

The middle level, which is dedicated to energy management, contains a Square D SY/NET local area network and 100 SY/MAX PLCs that are connected by 7 miles of wire.

The lowest level contains all the field I/O devices, such as temperature and pressure sensors, metering equipment, adjustable-speed drives, and circuit monitors. Each PLC can scan up to 4,000 I/O points within 45 msec.

Diagnostics simplify troubleshooting

The HVAC system includes diagnostic capabilities in remotely located PLCs. These PLCs send alarms through the network to a wireless paging system that alerts both maintenance personnel and management when a problem occurs. “The communications network saves a lot of time and manpower,” says IBM controls and automation engineer Mike Magill. “Technicians can troubleshoot components throughout the facility from the control room.”

Previously, maintenance technicians would receive a call that the air conditioning wasn’t working in one of the buildings, but this call often came several hours after the system failed. Then the technicians went to the site to troubleshoot the equipment. It sometimes took an entire day to pinpoint the problem.

Today, diagnostic software in a PLC sends an immediate and specific error message to the control room, stating, for example, that a drive has shut down because incoming power is too low. In some cases, the PLCs initiate corrective action in response to data from monitoring sensors. Or the control room operator can contact any PLC in the system and make changes to a process that is miles away.

Among the 13,000 monitoring points, 1,300 are in critical areas where hazardous conditions such as chemical spills or tank overflows can occur. For these points, the PLCs send hazardous condition alarms indicating spills or overflows to key control personnel. For the remaining points, they only send routine paging messages.

Software makes it work

IBM uses several software packages to operate the energy control system. These include Intellution’s FIX DMACS, which acquires data for predictive maintenance in the chemical tank farms; USData’s FactoryLink, which provides a graphical operator interface to PLCs in a waste treatment plant; Square D’s PowerLogic for monitoring and controlling highvoltage power usage; and IBM’s Plantworks for the overall energy control system.

New customer service

Recognizing that its ability to design an extensive energy control system could be applied elsewhere, IBM now offers its design services to other manufacturers. Their engineers foresee future applications both in similar areas (HVAC and lighting) as well as for controlling the environment of clean rooms used to assemble circuit boards and ceramic chips.

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