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Table 28. Chiller Unit Controller Setup Variables
Chiller Controller Variable Value Description
Source Local The outputs from the remote I/O module must be able to control the chiller.
Mode Cool (not Ice or Cool/Ice) The CSM does not support the Heat, Ice or Cool/Ice modes.
Start Delta 1°F (0.6°C) Reduce the temp difference required for starting in this multiple chiller system.
Soft Load Off Soft Load control is supplied through the CSM.
Chilled Water Reset On (set to external signal) Allow chiller to accept chilled water setpoint reset from an hardwired source.
External Chilled Water Setpoint
Reset Minimum
User Defined (must match
CSM setting)
This is the chilled water setpoint when the CSM sends the chiller 2 Vdc (4 mA)
or less on its AI. This value must be set equal to the CSM’s Minimum System
Setpoint property on the Chilled Water Supply Temp screen.
External Chilled Water Setpoint
Reset Maximum (must match
CSM setting)
User Defined (must match
CSM setting)
This is the chilled water setpoint when the CSM sends the chiller 10 Vdc (20
mA) on its AI. This value must be set equal to the CSM’s Maximum System
Setpoint property on the Chilled Water Supply Temp screen.
Demand Limit On (set to external signal) Allow chiller to accept demand limiting from an hardwired source.
External Demand Limit Minimum
Amps
40% RLA This is the demand limit when the CSM sends the chiller 10 Vdc (20 mA) on its
AI.
External Demand Limit
Maximum Amps
100% RLA This is the demand limit when the CSM sends the chiller 2 Vdc (4 mA) or less
on its AI.
Evaporator Pump Recirculate
Timer
0.5 min A compressor must transition from Off to Starting within the Wait For Flow
time period after being enabled or the CSM will consider it off-line.
Hardwired Chiller Sequence of Operation
Unavailable and Available Hardwired 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. A hardwired chiller is unavailable if either of the following
conditions exist:
• All hardwired alarm digital inputs are indicating a fault alarm.
• The chiller was recently disabled and the chiller’s timers (Start-to-Start and/or Stop-to-Start) prevents the chiller
from starting. On MicroTech II chillers, the CSM receives a “chiller enable” signal from the chiller telling the CSM
the chiller is ready to run. No such signal is available to the CSM on hardwired chillers. The CSM’s Stop-to-Start
Timer (see Table 27) is used by the CSM to keep track of chiller availability on hardwired chillers. The CSM’s
Stop-to-Start Timer and the CSM’s stage timer must be set so the combined time is greater than the time a
hardwired chiller is unavailable due to its internal time delays. For example, if a hardwired chiller has a Start-to-
Start time of 20 minutes and a Stop-to-Start of 10 minutes, the combined time of the CSM’s Stop-to-Start plus the
CSM’s stage time must be greater than 20 minutes. This prevents the CSM from trying to start the hardwired chiller
while it is disabled on internal timers.
2. The chiller’s hardwired remote I/O module has lost communications with the CSM.
Chiller Startup
If the hardwired chiller is available it can be enabled normally. After the CSM commands a hardwired chiller to be
enabled, the following control takes place at the chiller’s remote I/O module:
1. Relay Output 1 is closed to enable the chiller through its Remote Start/Stop input.
a. The chiller will be enabled, but will not allow its compressors to run until its unit controller has proven evaporator
flow (it will be in a Waiting for Flow State).
b. The Proof of Evaporator Flow device to the chiller should be the same device that proves flow to the CSM (at DI
1). It is mandatory and must not be bypassed.
2. Relay Output 2 is closed to enable evaporator flow.
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