OM 780-2 Page 41
Chillers That Go Off-line Without Being Enabled
In condition 1 the term unavailable means that the CSM cannot start the chiller. If a chiller is unavailable when it would
normally be enabled by the CSM, this chiller is skipped and the next available chiller with an equal or higher sequence
number will be enabled. This chiller goes off-line when it is skipped. The Chiller Off-line alarm will occur without the
chiller ever being enabled.
Enabled Chillers that Go Off-line and Forced Stage-Ups
Conditions 2 through 4 deal with a chiller that has been enabled by the CSM and then goes off-line. An enabled chiller that
goes off-line will be compensated for to help maintain system capacity. In this case the CSM will immediately enable the
next available chiller. This is called a forced stage-up. Forced stage-ups will occur even if some form of Stage-Up
Inhibiting is active. The CSM will also disabled the newly off-line chiller. The Chiller Off-line alarm will occur when the
chiller is disabled.
Note: In the case of a running chiller that loses communications a forced stage-up could result in an excess of capacity
because the chiller may remain running.
Unavailable and Available Chillers
A chiller is unavailable when the CSM cannot influence its start/stop operation. This can occur for either of two reasons:
1. All compressors (or circuits) on a chiller are unable to run. MicroTech II chiller compressor controllers send the CSM
an indicator; AVAILABLE (1) if the CSM can influence it’s stop/start operation. The indicator is cleared (0) when the
following conditions exist:
IF Compressor is OFF because of an alarm
OR
If Compressor is OFF due to the Pump Down Switch
OR
The Unit is OFF because of a Unit alarm
OR
The Unit has been disabled at the keypad display
OR
The Remote Switch has disabled the Unit
OR
The Control Source does not = BAS Network
OR
The front panel switch has disabled the Unit
OR
The compressor switch has disabled the Compressor
OR
An air-cooled unit is below it’s outside air temperature setpoint and all compressors are off
OR
The Compressor is in the Waiting Low Sump Temperature State
OR
The Compressor is in the Anti-recycle State (start-start, stop-start, etc.)
OR
The Unit has low source water temperature on a Templifier.
For example, if a chiller has a Fault alarm, the alarm must be cleared; if a chiller’s remote stop switch input is opened,
the input must be closed again; if a chiller is set for a local source to enable it, it must be returned to network control.
2. The chiller has lost communications with the CSM.
Conversely, a chiller is available when none of the above conditions apply to it.
Chiller Availability can be viewed on the Misc screen of the user interface. A value of “0” means the chiller is Unavailable,
“1” means the chiller is fully Available, “0.5” means 50% of the chillers compressors (or circuits) are available, etc. Each
compressor (or circuit) sends its availability signal to the CSM. If the value for a chiller’s availability seems high, check
that the chillers Number of Compressors value has been set properly on the Chiller Setup screen.
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