OMM-0153_E
• 5/11/2023 Technical Support • (800) 526-0288 • Mon-Fri, 8 am - 5 pm EST Page 72 of 124
CENTURION Installation, Operation & Maintenance Manual
SECTION 8: WATER HEATER MANAGEMENT
8.2 WHM Principles of Operation
The WHM system communicates with the plant Water Heaters via a RS485 network utilizing
Modbus RTU protocol (8-bit, 9600 baud, no parity). Multiple baud rates (9600, 19200, 38400,
57600) options are available in WHM Cascade menu. All Modbus networks are implemented
using a “Manager” / “Client” scenario. Only one unit must be configured as a Manager and other
units must be set as Clients. Any unit can be set as a Manager to control the WHM system.
The WHM Manager monitors the Air/Fuel Valve position (VP) of all enabled units. When this
valve position (% open) exceeds a user-selectable limit (
Next On Valve Pos
), the WHM will
open the Sequencing Valve of another Water Heater in the system. Conversely, when the valve
positions of all enabled units have dropped below a different user-selectable limit (
Next Off
Valve Pos
) threshold, the WHM Manager will close the Sequencing Valve on a unit. The
philosophy behind this approach is to maintain the fire rates (Air/Fuel Valve % open) at a level
that maximizes heater efficiency.
In addition to collecting Air/Fuel Valve position data, the controlling Manager also monitors the
total accumulated operating time for each unit on the system and attempts to balance the
system so that all units operate for approximately the same number of hours.
8.3 WHM Features
8.3.1 Valve Feedback
The Valve Feedback feature is designed to confirm that the Sequencing Isolation Valve has
successfully executed either a Valve-Open or Valve-Close command from the Edge Controller.
The Valve Feedback signal from the Sequencing Isolation Valve is connected to the Edge
Controller via the I/O box. When the Edge Controller issues either a Valve-Open or Valve-Close
command to the valve, the Valve Feedback signal is monitored to confirm that the Valve has
successfully opened or closed. If there is a mismatch between the Valve Feedback signal and
the Valve-Open or Valve-Close command that lasts longer than specified
in “Valve Feedback
Timer
”, a fault is invoked.
This feature can be enabled or disabled in the Valve Feedback parameter (see
Advanced
Setup
→
WHM Cascade
→
Operating Controls
→
Sequencing Control Configuration
).
8.3.2 Valve Supervisor
This feature continually monitors the valve feedback (open or closed) to confirm operation. If the
valve supervisor detects an anomaly, the following faults/warning are displayed :
1. If the valve is stuck open, it displays the fault message VALVE STUCK OPEN but
continues operation (do not shut the unit down).
2. If the valve is stuck closed, it shuts down the unit and displays the fault message VALVE
STUCK CLOSED.
