In order for industry to control energy use and its associated environmental impacts, it is first necessary to understand how and when energy is used. Citect is meeting this requirement with an energy management system that is allowing a major manufacturer with widely distributed site facilities, to both understand and control his energy use.
Based upon a CitectSCADA platform, the total plant energy management system provides not only usage information for each building in the manufacturing facility, but also assists operations managers in controlling energy consumption and costs and contract compliance. In addition, the system allows plant managers to track greenhouse gas emissions and tie them directly to the energy requirements of specific production facilities.
Developed by Centric Design a Citect Integration Partner (CIP) in the United States, the SCADA-based energy management system was first commissioned in 2002 by a major US manufacturing company that required a tool to understand electrical use in multiple buildings on its large manufacturing campus.
The facility has a 13kv distribution system consisting of multiple feeders that provide electricity to multiple buildings. Most feeders on the system feed multiple transformers, so the building load cannot be determined simply by reading individual feeder loads. Furthermore, the complexity of the distribution system and the building transformers is such that most building loads could not be defined simply by installing meters on a limited number of connection points.
The client had already chosen an electrical meter manufacturer and was installing their meters at the start of the system project. This made it necessary that the energy management system provide an open architecture and support for multiple protocols.
The client also required access to the system from multiple locations around the facility so that key personnel to check electrical system conditions in real-time from their daily work locations.
The initial system was designed using CitectSCADA 5.41. Communication to I/O devices was achieved through a combination of Ethernet and serial channels. The system initially connected 20 advanced electrical meters and two electric utility billing meters to the power monitoring system. The advanced electrical meters were installed on each of the 13kv feeders in the facility's electrical substation and at selected locations around the plant to provide the ability to calculate individual building usage.
Adding natural gas and Steam
In 2004, facility energy managers decided to add gas and steam monitoring to the energy system. The addition was complicated by the desire to use available transducers to minimise installation cost. Steam lines had flow transducers. Gas lines had only pulse outputs from the gas utility billing meters. The client desired to have consumption, demand, and flow data for high and low pressure gas connections and various steam lines feeding the plant. I/O devices were connected to the various inputs to collect this raw data, which is processed in a PLC to calculate the required consumption, demand, and flow data.
Supply contract management
Changes in the electrical energy market resulted in additions to the system in 2005, when the facility changed its energy supplier. To improve its ability to stay in compliance with the new energy contract, the facility energy manager decided to make two major changes to the energy system.
First, the system was modified to automatically report energy usage to the energy supplier every fifteen minutes. Total electric and gas energy consumption for each 15 minute interval is captured. At the end of each interval, the system automatically connects to the energy supplier's servers via an Internet connection and downloads the consumption data. For each interval the system reports total imported electric energy, total on-site electric generation, and total gas consumption.
Second, the new energy contract had a specified monthly limit in kwh. In order to ensure that the facility does not exceed this limit, the system tracks energy consumption for each day and month to date.
Generation and net metering
Further alterations to the electrical supply contract, in 2007, resulted in changes to the method of operation of two large co-generation units installed by the company in 2002. The new contract gave the company the ability to sell generation onto the electrical system. As a result, the facility needed to be able to track energy into and out of the plant. To achieve this, the system was modified to gather pulse outputs from the billing meters for energy flow in both directions, rather than only incoming energy. The system tracks energy in each demand interval and calculates demand and peak demand in each direction. The usage numbers are tracked monthly and stored to provide a record of energy use and sales. Also in 2007, facility managers decided to integrate additional data into the energy system, from the Wonderware system that was originally installed to monitor and control the co-generation units; and a Honeywell EBI system that is used for facility management.
The data pulled from the Wonderware system enables plant management to better monitor the conditions of the co-generation facility and the load-shed control system. As a result of this addition, plant management has identified a problem with the load shed system that prevents it from fully protecting the plant for the loss of the utility feed.
The data pulled from the Honeywell system is used to provide plant floor views of electrical use. The new views also provide real-time access to electrical conditions at machine tools located throughout the facility.
In 2008, the facility added a new heat-treat furnace. This furnace is fuelled by natural gas and electricity. Plant and corporate management desired to track both energy inputs and the results of inputs for the furnace. As a result, the Citect Energy System connected to an EIG Shark electrical meter and a Mercury Instruments gas meter. Data from both meters has been added to the system. The system collects energy inputs to the furnace and calculates daily and monthly energy use.
This article is a shortened version of a Citect White Paper entitled: Energy Monitoring: A Foundation for Effective Energy Management.
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