Communication Loss Control At The Chiller - McQuay MicroTech II Operation Manual

Sensor rate will be displayed on the Misc page. This variable applies only to MicroTech II chillers. Default = No .

Communication Loss Control at the Chiller

If the communication between the chiller and the CSM that is commanding the chiller is lost, the chiller's L
communication module provides configuration properties which may be used to set the commandable variables to default
values. The variables you use to define communication loss and set the default values are Receive Heartbeat, Comm
Loss/Power Up State and Comm Loss Cool Setpoint.
Receive Heartbeat
The Receive Heartbeat variables tell the chiller unit controller's L
without receiving a communication from the CSM before determining that communications have been lost. The CSM has a
Maximum Send Time of 100 seconds, which means that it will update its commands to each chiller at least once every 100
seconds. The chiller's L
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the CSM. If this time ever reaches a value greater than the Receive Heartbeat, the L
determines that network communication has been lost and resorts to its Comm Loss states for Chiller Enable, Cool
Setpoint, and Capacity Limit. The values for Chiller Enable and Cool Setpoint are discussed below. The Comm Loss State
for Capacity Limit is always 100%.
A value of "0" (default) for Receive Heartbeat means that the Comm Loss features of the chiller's L
communication module are disabled. This means that the chiller will use the last commands it received from the CSM until
communications have been restored and the CSM sends it a different command. For example: if the chiller was enabled
when communications was lost, it will stay enabled.
If you will be using the communications loss feature at the chiller, set the Receive Heartbeat value to a number greater than
200 seconds. This will allow multiple communication attempts before the chiller switches to its Comm Loss settings.
Since the CSM's maximum commanded property update time is 100 seconds, setting the chiller's Receive Heartbeat to 200
seconds would allow for a minimum of 2 communication tries before communication has been determined to be lost.
Normally higher Receive Heartbeat times in the range of 300 seconds are acceptable.
Comm Loss/Power Up State
The Comm Loss/Power Up State variables tell the chiller unit controller's L
to be in if communication is lost with the CSM. See the Receive Heartbeat section above for definition of loss of
communications. If this value is set to DISABLE, the chiller will be disabled whenever communication is lost between it
and the CSM. If this value is set to ENABLE, the chiller will be enabled whenever communication is lost between it and
the CSM.
A sometimes-confusing effect of setting the Comm Loss/Power Up State to Enable is that this feature will put that chiller
into the Enabled State whenever the chiller is powered up. As soon as a newly powered chiller unit controller begins
communicating with the CSM, the CSM will disable the chiller. This may take up to the 100-second maximum
commanded property update time. This power up control is necessary since the chiller cannot prove communications with
the CSM until it has power.
If you want to start or stop any chiller that has lost communications, you can enable or disable it locally.
If the Receive Heartbeat value = 0 (default), the chiller will ignore the value of this Comm Loss/Power Up State input and
continue to run with its last received chiller enable setpoint from the CSM. This will be the desired configuration on many
chiller system applications.
Comm Loss - Cool Setpoint
The Comm Loss - Cool Setpoint variables tell the chiller unit controller's L
setpoint to use if communications is lost with the CSM. See the Receive Heartbeat section above for definition of loss of
communications.
If the Receive Heartbeat value = 0 (default) the chiller will ignore the value of this Comm Loss Cool Setpoint input and
continue to run with its last received cooling setpoint from the CSM.
Example #1: You want a chiller to be enabled with a Cool Setpoint of 50 if communication is ever lost between that chiller
and the CSM:
• Set that chiller's Receive Heartbeat to 250 seconds
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