Energy control system combines PCs, PLCs, and adjustable-speed drives with processmonitoring sensors to control HVAC and lighting systems, plus electrical power usage.
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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Engineers replaced these outdated manual controls with a centralized system that monitors and controls energy usage.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.

PLC Model 600 controls a chemical waste recovery system. This rack-mounted unit contains both digital and analog I/O cards, plus a network interface module and power supplies.
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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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