Chiller Shutdown; Hardwired Chiller Alarms; Chiller Fault Alarms - McQuay MicroTech II Operation Manual

a. If the evaporator flow switch (wired to DI 1) remains open for a time period greater than the "Waiting For Flow
Timer" property, the COMP STOP – Evaporator Water Flow Loss alarm occurs and the chiller is disabled until
the alarm has been cleared from the CSM user interface.
b. If the evaporator flow switch re-opens for longer than three seconds after flow has been initially proven, the
COMP STOP – Evaporator Water Flow Loss alarm occurs. The chiller is disabled and marked as unavailable
until the alarm has been cleared from the CSM user interface.
c. If the chiller will be controlling its own evaporator pump, Relay Output 2 is not used but DI 1 is always required
to prove evaporator flow.
3. After the compressor begins to run (defined as chiller % RLA > Running % RLA Level), Relay Output 4 is closed to
enable condenser flow.
a. If the condenser flow switch (DI 2) is open for longer than 15 seconds after flow has been enabled, the COMP
STOP – Condenser Water Flow Loss alarm occurs. The chiller is disabled and marked as unavailable until the
alarm has been cleared from the CSM user interface.
b. If the chiller will be controlling its own condenser pump, or the chiller is air-cooled, a jumper must be placed
across DI 2. Also, Relay Output 4 is not used.
4. After the chiller has been enabled, if the compressor does not begin running (defined as chiller % RLA > Running %
RLA Level) within the time period defined by the Wait For Flow Time (Chiller Seq screen) property, this chiller will
be disabled and considered Off-Line. Also, the CHILLER STOP – No Start alarm occurs. The chiller is disabled and
marked as unavailable until the alarm has been cleared from the CSM user interface.

Chiller Shutdown

After the CSM commands a hardwired chiller to be disabled, the following control takes place at the chiller's remote I/O
module:
1. Relay Outputs 1, 2, and 3 are opened to disable the chiller and pumps.
2. On a normal shutdown the chiller is marked as unavailable until the "Stop-to-Start Timer" property in the CSM for this
hardwired chiller has expired.
3. On a fault alarm shutdown the chiller is marked as unavailable until the fault alarm is cleared.

Hardwired Chiller Alarms

A hardwired chiller's remote I/O module has two digital inputs (DI) available for connection to the dry contacts of the
chiller unit controller's alarm output signal. All chillers will typically have one alarm output signal. Chillers with multiple
compressors (i.e. the McQuay MicroTech 200 series dual compressor centrifugal chiller) may have two alarm output
signals. If a chiller has two alarm outputs the Number Of Chiller Alarm Outputs (see Table 27) property must be set to 2.
Chillers with two alarm outputs will be considered 50% available if one of the two alarm outputs indicate a fault alarm.
Note: If two chiller alarm outputs are wired from the chiller to the remote I/O module, the Number Of Compressors
property on the Chiller Setup screen must be set to 2. If it is set to 1, there will be an error in the chiller availability
calculated by the CSM. Even if the Chiller has more than 2 compressors/circuits, the CSM will only associate it with 2
(representing 50% of the total capacity).

Chiller Fault Alarms

Fault alarms are defined as alarms that shut down the compressor (no available cooling capacity). If the chiller's alarm
output relay is switched (steady), this indicates to the CSM that the chiller has a Fault alarm. The chiller can indicate a
Fault alarm by either switching a contact closed or by switching a contact open. To tell the CSM which contact position
indicates a Fault alarm condition, set the Alarm Switch State (see Table 27). It is best to set the alarm signal up to indicate
a Fault alarm using a normally open contact in the open position (Alarm Switch State = Open). This provides a Fault
indication to the CSM when the chiller does not have power (the CSM will then know that this chiller is unavailable).
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