McQuay IM 743 User Manual

Page 112 OM 780-2
No Chilled Water Flow
If the Pump Control Option is not equal to “None (Load Flow Control screen), the no chilled water flow alarm occurs
whenever all cooling load pumps have failed. A pump is considered “failed” if its digital input is open while its digital
output is closed for any continuous period of time equal to the Pump Status Check Delay Time variable (Load Flow
Control screen). If the No Chilled Water Flow alarm occurs, the system immediately shuts down and remains shut down
until the alarm is manually cleared at the user interface.
Problem Alarms
Comm Loss Between CSM and Chiller X (x could be any commissioned chiller #)
When the communications between the CSM and a chiller on the CSM’s L
ONWORKS network is lost; two types of Comm
Loss control take place; 1) Comm Loss control at the CSM, and 2) Comm Loss control at the chiller.
Comm Loss control at the CSM
If the CSM loses communications with a chiller the comm loss between CSM and chiller X alarm occurs, where
x
is the
number of the affected chiller. When communications are restored, the alarm automatically clears.
If the affected chiller would normally be enabled at this point of the chiller sequencing logic, the Chiller Off-line alarm will
occur (see “Warning Alarms” below).
Comm Loss Control at the Chiller
The CSM continually updates all commanded properties at the chiller every 100 seconds (max). The commanded
properties are Chiller Enable, Cool Setpoint and Chiller Capacity Limit. If communication is lost between the CSM and
chiller these points will no longer be updated and the chiller will operate in the last enable/disable, cool setpoint and
capacity limit commands it received from the CSM. For example: if the chiller was enabled when communications were
lost it will stay enabled until communications are restored. This is an acceptable control strategy on many chiller systems.
The operator can program the chiller’s Comm Loss states for Chiller Enable and Cool Setpoint. The Comm Loss default
for Chiller Capacity Limit is 100 % and is not changeable through the CSM. To change the Comm Loss conditions of
Chiller Enable or Cool Setpoint, see Communication Loss Control at the Chiller on page 26.
Comm Loss Between CSM and Remote Module X (x could be any commissioned remote I/O module)
When the communications between the CSM and a commissioned remote I/O module on the CSM’s L
ONWORKS network
is lost control of the devices connected to that module is lost.
• When communications is lost with Remote Module A, B, or C control of the cooling load pumps will be lost. This will
typically cause the No Chilled Water Flow fault alarm to occur and shut down the system. If the module is operating
properly except for loss of communication with the CSM, the following conditions will be locally set after
communications has been lost for 200 seconds.
The pump output relays will be turned off.
The pump VFD speed output signals will be set to 0% speed.
• When communications is lost with any of the Remote Modules E through H, cooling tower control will be reduced or
lost. If the module is operating properly except for loss of communication with the CSM, the following conditions will
be locally set after communications has been lost for 200 seconds.
The tower output relays on all non-communicating modules will be turned off.
The tower VFD speed output signal on all non-communicating modules will be set to 0% speed.
If Remote Module B looses communication the tower bypass valve will hold current position.
• When communications is lost with Remote Module D, control of the loop bypass valve will be lost. If Module F is
operating properly except for the loss of communications with the CSM, the loop bypass valve position will be locally
set to 100% (full bypass) after communications has been lost for 200 seconds.
When communication is re-established, the alarm automatically clears.

McQuay IM 743 Specifications

General

Brand	McQuay
Model	IM 743
Category	Controller
Language	English