Quartz 4

SOO Chilled Water System

7 min read

Glycol Chilled Water System (CHWS) - Sequence of Operation

Version: 1.0 Date: 2025-12-29 Author: Gemini Agent Related SSO: SSO Temp Sensor, SSO Pressure Sensor, SSO Flow Switch, SSO Valve Actuator, SSO Relay Output

1. Overview

This document outlines the sequence of operation for the Glycol Chilled Water System (CHWS). This is a manually-started system during the cooling season, featuring monitoring and control of multiple chilled water pumps, chillers, and associated glycol make-up units.

The system’s primary automated functions are:

  1. System Monitoring & Alarming: Upon manual activation, the control panel actively monitors pump status, water flow, temperatures, and pressures. It generates alarms for any out-of-spec conditions, including pump failure, loss of flow, or abnormal temperatures.
  2. Differential Pressure Control: A differential pressure transmitter located in the main piping loop continuously modulates a bypass valve to maintain a constant differential pressure between the supply and return mains.
  3. Glycol Make-up Automation: Dedicated glycol make-up pump systems automatically maintain pressure in their associated loops. The pump activates to build pressure and deactivates upon reaching the setpoint, with full safety and level monitoring alarms.

The system is managed by two ECL-650 controllers, which handle specific pumps, fans, and chillers but share common system sensors.

2. Point List

Note: The system is controlled by two separate ECL-650 controllers. The controller for each point is noted below.

Inputs (Physical)

  • Chilled Water Pump 1 Status (P-1-S): BI (ECL-650 (1), UI1), Dry Contact
  • Chilled Water Pump 2 Status (P-2-S): BI (ECL-650 (1), UI2), Dry Contact
  • Chilled Water Pump 3 Status (P-3-S): BI (ECL-650 (1), UI5), Dry Contact
  • Chilled Water Pump 4 Status (P-4-S): BI (ECL-650 (2), UI1), Dry Contact
  • Chilled Water Pump 5 Status (P-5-S): BI (ECL-650 (2), UI2), Dry Contact
  • Chilled Water Pump 6 Status (P-6-S): BI (ECL-650 (2), UI5), Dry Contact
  • Chilled Water System Flow Switch (Existing) (FLOW-S): BI (Both ECL-650, UI3), Dry Contact
  • Glycol Tank Low Level Alarm (GT-LL-A): BI (Both ECL-650, UI4), Dry Contact
  • Exhaust Fan 4 Status (EF-4-S): BI (ECL-650 (1), UI6), Dry Contact
  • Exhaust Fan 19 Status (EF-19-S): BI (ECL-650 (1), UI7), Dry Contact
  • Exhaust Fan 7 Status (EF-7-S): BI (ECL-650 (2), UI6), Dry Contact
  • Exhaust Fan 20 Status (EF-20-S): BI (ECL-650 (2), UI7), Dry Contact
  • Glycol Chilled Water Differential Pressure Transducer (GCHW-DP): AI (Both ECL-650, UI8), 0-10VDC
  • Chilled Water Supply Temperature (GCHWS-T): AI (Both ECL-650, UI9), 10K Type II
  • Chilled Water Return Temperature (GCHWR-T): AI (Both ECL-650, UI10), 10K Type II
  • Outside Air Humidity (OA-H): AI (ECL-650 (1), UI11), 0-10 VDC
  • Outside Air Temperature (OA-T): AI (ECL-650 (1), UI12), 10K Type II
  • Chiller 1 Common Alarm (CH-COM-A): BI (ECL-650 (1), UI13), Dry Contact
  • Chiller 2 Common Alarm (CH-COM-A): BI (ECL-650 (2), UI12), Dry Contact
  • Chiller 1 Differential Pressure (CH-1-DP): AI (ECL-650 (1), UI14), 0-10VDC
  • Chiller 2 Differential Pressure (CH-2-DP): AI (ECL-650 (2), UI13), 0-10VDC
  • Heat Exchanger 1 Differential Pressure (HX-1-DP): AI (ECL-650 (2), UI11), 0-10VDC
  • Outside Air Temperature (OA-T): AI (Via Network), Global
  • Outside Air Humidity (OA-H): AI (Via Network), Global

Outputs (Physical)

  • Exhaust Fan 4 Command (EF-4-C): BO (ECL-650 (1), UO1), 12VDC
  • Exhaust Fan 19 Command (EF-19-C): BO (ECL-650 (1), UO2), 12VDC
  • Pump 3 (Glycol Make-up) Command (P-3-C): BO (ECL-650 (1), UO3), 12VDC
  • Exhaust Fan 7 Command (EF-7-C): BO (ECL-650 (2), UO1), 12VDC
  • Exhaust Fan 20 Command (EF-20-C): BO (ECL-650 (2), UO2), 12VDC
  • Pump 6 (Glycol Make-up) Command (P-6-C): BO (ECL-650 (2), UO3), 12VDC
  • Glycol Chilled Water Bypass Valve Output (CHWS-BYP-VLV1-O): AO (ECL-650 (1), UO4), 0-10VDC
  • Glycol Chilled Water Bypass Valve Output (GCHWP-BYP-O): AO (ECL-650 (2), UO4), 0-10VDC

Software Points & Setpoints

  • Chiller 1 Differential Pressure Setpoint (CH-1-DP-SP): Setpoint (ECL-650 (1))
  • Chiller 2 Differential Pressure Setpoint (CH-2-DP-SP): Setpoint (ECL-650 (2))
  • Exhaust Fan 4 Failure (EF-4-FAIL): Alarm (ECL-650 (1))
  • Exhaust Fan 19 Failure (EF-19-FAIL): Alarm (ECL-650 (1))
  • Exhaust Fan 7 Failure (EF-7-FAIL): Alarm (ECL-650 (2))
  • Exhaust Fan 20 Failure (EF-20-FAIL): Alarm (ECL-650 (2))
  • Glycol Chilled Water Differential Pressure Setpoint (GCHW-DP-SP): Setpoint (Software)
  • Glycol System Normal Operating Pressure (GCHW-Press-SP): Setpoint (Software)
  • Glycol System Low-Low Pressure Alarm Limit (GCHW-Press-LOLMT): Setpoint (Software)
  • Glycol System High-High Pressure Alarm Limit (GCHW-Press-HILMT): Setpoint (Software)
  • Chilled Water Return Temp High Alarm (GCHWR-T-HILMT): Setpoint (Software) (e.g., SP+10°F)
  • Chilled Water Return Temp Low Alarm (GCHWR-T-LOLMT): Setpoint (Software) (e.g., SP-10°F)

3. Safety Devices & Interlocks

  • Glycol Pump Pressure Safety: The glycol make-up pump will be de-energized if the system pressure drops below a low-low limit setpoint (GCHW-Press-LOLMT) or rises above a high-high limit setpoint (GCHW-Press-HILMT). An alarm is generated in both cases.
  • Glycol Pump Start Failure: If a make-up pump is commanded ON (P-3-C or P-6-C) but its corresponding status contact (P-3-S or P-6-S) does not prove flow within a defined time, the pump command will be stopped and a malfunction alarm will be generated.
  • Glycol Tank Low Level: If the glycol tank low level float switch (GT-LL-A) activates, the associated make-up pump will be stopped, and an alarm will be generated to prevent the pump from running dry.

4. Modes of Operation

Chilled Water System Operation

  • Activation: The chilled water pumps (P-1, P-2, P-4, P-5) and chillers are started manually for the cooling season.
  • Monitoring: Once the system is active, the DDC controller monitors all associated points. All alarm functions become active.
  • Differential Pressure Control:
    • The GCHW-DP transmitter continuously measures the differential pressure across the supply and return mains.
    • The controller modulates the normally open bypass valve (CHWS-BYP-VLV1-O / GCHWP-BYP-O) to maintain the GCHW-DP-SP.
    • As system load increases (VAV boxes open), system DP will tend to drop, causing the bypass valve to modulate closed to force more flow out to the system.
    • As system load decreases (VAV boxes close), system DP will tend to rise, causing the bypass valve to modulate open to relieve pressure.

Glycol Make-up Pumps (Typical of P-3, P-6)

  • Monitoring: The analog pressure transmitter in the expansion tank feed line is continuously monitored.
  • Pump Activation:
    • If system pressure drops below the GCHW-Press-SP, the corresponding make-up pump (P-3-C or P-6-C) is commanded ON.
  • Pump Deactivation:
    • The pump runs continuously until the system pressure rises to meet or exceed the GCHW-Press-SP. At this point, the pump is commanded OFF.

5. Alarms & Fault Conditions

All alarms shall be annunciated at the User workstation.

  • Pump Failure:
    • Condition: Status contact (P-1-S, P-2-S, etc.) indicates a pump is off when it should be running.
    • Priority: High.
  • Loss of Chilled Water Flow:
    • Condition: The chilled water system flow switch (FLOW-S) opens while the system is expected to be active.
    • Priority: High.
  • Chilled Water Temperature Out of Range:
    • Condition: The GCHWS-T or GCHWR-T reading exceeds the high (GCHWR-T-HILMT) or low (GCHWR-T-LOLMT) alarm limits.
    • Priority: Medium.
  • Glycol Pump Pressure Alarm:
    • Condition: System pressure drops below GCHW-Press-LOLMT or rises above GCHW-Press-HILMT.
    • Priority: High.
  • Glycol Pump Malfunction:
    • Condition: A make-up pump fails to prove status after being commanded ON.
    • Priority: High.
  • Glycol Tank Low Level:
    • Condition: The low level float switch (GT-LL-A) is activated.
    • Priority: Critical. Prevents pump operation.
  • Chiller Common Alarm:
    • Condition: The common alarm contact from either chiller (CH-COM-A) is activated.
    • Priority: High.

6. Commissioning & Verification Checklist

  • Verify that all pump status points (P-1-S, P-2-S, etc.) correctly report the ON/OFF status of each pump.
  • With the system running, manually open the FLOW-S circuit and verify a “Loss of Chilled Water Flow” alarm is generated.
  • Adjust the high and low alarm limits for GCHWR-T and verify that an alarm is generated when the temperature goes out of range.
  • Verify the GCHW-DP reading is accurate. With the system running, manually adjust VAV box dampers and observe the CHWS-BYP-VLV1-O modulating to maintain the GCHW-DP-SP.
  • Simulate a drop in system pressure and verify the correct glycol make-up pump (P-3-C or P-6-C) activates.
  • Verify the make-up pump deactivates once the GCHW-Press-SP is achieved.
  • Simulate a system pressure drop below GCHW-Press-LOLMT and verify the make-up pump is stopped and an alarm is generated.
  • Simulate a system pressure rise above GCHW-Press-HILMT and verify the make-up pump is stopped and an alarm is generated.
  • With a make-up pump commanded on, disconnect its status input (P-3-S or P-6-S) and verify a “Glycol Pump Malfunction” alarm is generated.
  • Manually activate the GT-LL-A float switch and verify the make-up pump is de-energized and a “Glycol Tank Low Level” alarm is generated.
  • Activate the CH-COM-A dry contact and verify a “Chiller Common Alarm” is generated.

Graph View

Backlinks