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90 TRG-TRC016-EN
notes
period four
Chiller-Plant Control
Failure Recovery and Contingency Planning
In addition to normal chiller sequencing, the chiller-plant control system must
react when a chiller or another piece of associated equipment fails. Failure
recovery, or ensuring the reliable supply of chilled water, is a very important
part of the chiller-plant control system, and is an area where many systems
have fallen short. This is especially true in field-programmed systems because
of the difficulty of thorough debugging.
During periods of equipment malfunction, it is important to focus on the
primary goal of the system, which is to provide the required flow of chilled
water to the system at the proper temperature. It seems reasonable that the
simplest and most reliable failure-recovery sequence is to simply turn on the
next chiller in the sequence, and not try to turn several chillers on and off in
an attempt to re-optimize the system.
During an equipment failure, it is especially important to notify the operator
of the status, as well as to help the operator understand where the problem is
and what might be the cause. The control system must also allow the operator
to easily analyze the situation and to intervene if the failure condition will exist
for an extended period of time. A system that provides this information will
ensure that the system itself will be maintained and operated in proper
condition.
System Failure Recovery
▲ Maintain flow of chilled water
▲ Keep it simple
◆ Lock out failed equipment
◆ Turn on the next chiller in the sequence
▲ Notify the operator
▲ Allow the operator to intervene
Figure 98