Original Date: 04/07/1997
Revision Date: 04/14/2003
Best Practice : Direct Digital Control Capabilities
Prior to 1993, all environmental cooling systems at the Rock Island Arsenal (RIA) were operated by pneumatic controls. Although the system had been in operation for many years, it had been plagued by poor reliability and inaccurate manual adjustment leading to significant fluctuations in office temperature, particularly during outside climatic changes. The system was maintained by outside contractors who did not communicate well with the Arsenal engineering department or personnel working in the affected offices. Equipment performance profiles were not developed which led to incorrect problem diagnosis.
When a new large computing center was installed in one of the buildings to support several installations within the Industrial Operations Command (IOC), it was apparent that the old control system could not meet the environmental needs of the new computer complex. This fact, coupled with the Army’s base realignment efforts which reduced support staff and mandated tighter cost control, created a need for change.
The Arsenal engineering department adapted a Direct Digital Control design to the cooling system to meet the new requirements. The basis of the design was a commercially available digital control system. However, that system did not provide precision control response or detailed equipment performance profiles and was not user-friendly to the groups that used or supported it.
The Arsenal engineers adopted a proactive attitude when they expanded the design to provide user-friendly displays and closer monitoring of chillers and air handling units. Many existing sensors were relocated, and new sensors were added to strategic locations. Software was written to accommodate the expansion, and equations were developed to combine multiple inputs and provide more timely control response based on a combination of data points. Detailed system configurations were displayed graphically (Figure 2-1) to show operating parameters at key locations allowing engineer, contractor, and user personnel to observe exactly how the system was performing. Displays at user locations provide the exact temperature of each work area. Operating parameters and system equipment status are displayed to maintenance contractors and Arsenal engineers. Modem hardware is included to display the same detailed information to off-site locations. The detail provided in this design modification provides a level of control and status information not found in any Original Equipment Manufacturer designs.
This system has benefitted the Arsenal by providing 24-hour monitoring, automatic notification of failure, and cost control by optimizing start/stop times and sequencing chiller utilization.
Figure 2-1. Chiller Schematic
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