The control system will be a PLC-based Supervisory Control and Data Acquisition (SCADA) system designed to centralize the monitoring and control of the production and distribution of chilled water in the District Cooling Plant (DCP), Heat Exchanger Buildings (HEX), and Energy Transfer Stations (ETS). A SCADA system programmable logic controller (PLC) will perform monitoring and control functions within the DCP. A local PLC mounted at each HEX or ETS location will perform monitoring and control functions for that HEX or ETS and utilize Ethernet communication for communication with the SCADA system.
Operators will monitor and control the DCP, HEX, and ETS processes through SCADA system operator workstations configured with dynamic graphics for each process. Alarm summaries, selective input/output trends, and historical data will be stored on application, management, and information servers.
An engineering workstation will provide SCADA system application and development capability. Open communication protocols will allow integration with the Island Operation Center and National Operation Center.
Packaged equipment control will be performed by a local controller mounted in a local control panel. Each packaged equipment controller will be integrated into the SCADA system through Modbus or other approved communication protocol.
Q06024-IDCP-RPT-CI-001-REV 3 7-3 Stanley Consultants
Chiller pairs will include a local control panel with HMI that will provide manual and automatic operation of the chiller pairs for starting, operation, normal shutdown, and emergency shutdown of the chiller pair, and safety protection interlocks for the chiller pair. The chiller control panels will be integrated into the SCADA system utilizing Modbus communication protocol.
Local chiller control panel will provide the following control functionality:
• Support local and remote control modes by means of Owner's control system. • Maintain leaving water temperature within 0.5ºF of setpoint.
• Maintain internal refrigerant processes and chiller equipment within acceptable operating bounds through operating range of 25-100 percent of capacity.
• Limit chiller electric demand to setpoint within range of 40 percent to 100 percent.
• Incorporate protective controls with local alarm status and reset capability for high oil temperature, low differential oil pressure, high and low refrigerant pressure, low condenser water and chilled water differential pressure, chilled water low temperature, and condenser water high and low temperature.
• Have demand limit of 10 percent to 100 percent FLA based on setpoint. Local Operation:
• “Local-Off-Remote” mode selections on HMI: “Local,” start initiated at chiller; “Remote,” start initiated from Owner’s control system.
• Emergency Stop Pushbutton.
• Provide local LCD or LED displays for HMI. • Local Alarms:
- Low Chilled Water Differential Pressure - Low Condenser Water Pressure
- Low Condenser Water Temperature - High Oil Temperature
- Low Oil Differential Pressure - High Refrigerant Pressure - Low Refrigerant Pressure - Low Refrigerant Temperature - Starter Fault
• Alarm Horn, 100 dB minimum. • Horn Silence Switch.
Q06024-IDCP-RPT-CI-001-REV 3 7-4 Stanley Consultants
Hardware and software for Modbus communication interface to communicate with Owner’s control system for remote control, monitoring, trending, system diagnostic, and troubleshooting.
• Preliminary I/O list shall include, but not be limited to the following points. Vendor to add additional points as necessary for proper remote operation and control. Final list is subject to Owner’s review and approval.
- Discrete Outputs: • Chiller Run Status • Chiller Alarm Status • Refrigerant Leak Detection • Mode Selector Switch In “Local” • Mode Selector Switch In “Remote” • Compressor Started Fault
• Low Oil Pressure • High Oil Pressure • Purge Pump Run Status • Low Oil Level Status - Analog Outputs:
• Leaving Chilled Water Temperature Setpoint • Demand Limit Setpoint
• Leaving Chilled Water Temperature • Entering Chilled Water Temperature • Chilled Water Differential Pressure • Leaving Condenser Water Temperature • Entering Condenser Water Temperature • Condenser Water Differential Pressure • Evaporator Refrigerant Temperature • Condenser Refrigerant Temperature
• Compressor Discharge Refrigerant Temperature • Evaporator Refrigerant Pressure
• Evaporator Differential Pressure • Condenser Refrigerant Pressure • Oil Temperature
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• Oil Differential Pressure • Actual Guide Vane Pressure • Oil Sump Differential Pressure
• Compressor Thrust Bearing Temperature • Inboard Motor Bearing Temperature • Outboard Motor Bearing Temperature • Inboard Compressor Bearing Temperature • Outboard Compressor Bearing Temperature • Motor Amperes
• Demand kw
HEX and ETS control will be performed at each remote location by a local PLC with HMI. The SCADA system will provide supervisory control data to each HEX or ETS PLC and receive process data from the HEX or ETS PLC through Ethernet communication.
Digital communication connections will utilize UTP copper or fiber-optic media depending on the distance between each communicating device.
Chilled Water System
The chilled water system will employ a direct primary pumping scheme with constant speed pumps.
Each chilled water pump is dedicated to a chiller pair. Chilled water pump suction and chilled water supply discharge piping from each chiller will connect to common headers. When operating in Automatic Mode, the SCADA system will start and stop chiller pairs based on the following:
• When the sum of the plant energy meter and plant HVAC energy meter indicates that total demand increases to full capacity of the currently operating chiller pair(s), the main plant PLC shall start the next chiller in the operator selected pre-defined starting sequence that has the “AUTO” mode selected and one of the following occurs:
- Differential pressure between the chilled water supply header and chilled water return header increases to or above the field adjustable setpoint for a field adjustable time period.
- Chilled water supply header temperature increases to or above ½°F (field adjustable) above the current leaving chilled water temperature setpoint for the currently operating chillers for a field adjustable time period.
- Power input to the currently operating chiller pairs increases to or above the field adjustable setpoint.
Q06024-IDCP-RPT-CI-001-REV 3 7-6 Stanley Consultants
Cooling Towers
Each cooling tower cell has a dedicated condenser water pump and variable speed cooling tower fan. Condenser water supply and return headers allow the selection of any cooling tower cell to operate with any chiller pair. Cooling tower fan speed is controlled based on condenser water supply temperature. Low gear box oil and high fan vibration switches will de-energize and stop the fan should abnormal conditions be present.
Make-Up Water System
Each tower basin will be equipped with an automated make-up water system. The plant control system modulates the make-up water valve to maintain tower basin level. These valves are closed to prevent water flow to each tower when the operator has placed the tower out-of-service. The control system will monitor basin level and make-up water flow rate.
Blowdown System
The control system will monitor and control the blowdown rate based on condenser water conductivity. The operator will determine and adjust conductivity set point.
Electrical System
The SCADA system will provide hardwired inputs and outputs for motor control. Profibus DP communication protocol will allow the SCADA system to monitor, store and trend additional process information from starters, variable frequency drives, and multifunction relays.