Lochinvar 1.5 - Manual (Page 14)

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5
Unit Operation
Unit Operation with ModBus Communications
To control a Crest boiler through a Building Management System communicating through ModBus, the Crest Demand
Confi guration must be set to one of three options. These confi gurations allow different control points for a variety of applications.
The confi guration can be set by selecting Main Menu>>Setup>>BMS.
Holding Registers Defi nition Bit Value (HEX) Action
40001 Confi guration 00 01 Set Confi guration to read 40002
40002 Coils 00 01 Enables unit (00 00 disables unit)
NOTE: To ensure proper operation re-send the confi guration bits to holding register 40001 prior to issuing a command.
The Crest boiler is equipped with a ModBus communication timer. This timer is programmable from 0 - 120 seconds. The
timer can be programmed from the ModBus Setup Menu by selecting Main Menu>>Setup>>ModBus. The purpose of the
timer is to ensure proper temperature data is communicated to the boiler in a timely manner. Additionally, it will provide for
fail safe operation should ModBus communication be lost. This timer will cause the unit to revert back to internal unit controls
should the ModBus communication be interrupted longer than the ModBus timer. The timer is reset every time a ModBus write
command is received with updated temperatures or commands. It is the recommendation of Lochinvar that this timer be set to
the shortest value possible.
When controlling a Crest boiler through a Building Automation System (BAS), it is very important to ensure that the correct
confi guration bits are sent to holding register 40001, and that the correct data and enable signals are sent to holding registers
40002 - 40007, per the demand confi guration.
Demand Confi guration: ENABLE = ACTIVE; BMS = INACTIVE
In this confi guration the unit is controlled by setting the setpoints locally on the boiler and providing an enable signal through
ModBus communications.
All sensors and limiting devices should be hardwired to the terminal strip on the back of the unit excluding the enable signal.
This signal will be sent to the unit via ModBus.
The holding registers will need to be set as follows:
ModBus Instructions