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MicroTech II Operator Interface Touch Screen (OITS) Settings
Settings for any type of linked multiple compressor operation must be made to the MicroTech II controller. Settings on
a dual compressor unit are made in the factory prior to shipment, but must be verified in the field before startup. Settings
for multiple chiller installations are set in the field on the Operator Interface Touch Screen as follows:
Maximum Compressors ON – SETPOINTS - MODES screen, Selection #10 ‘= 2 for a dual, 4 for 2 duals, 3 for three
separate, single compressor chillers, etc. If all compressors in the system are to be available as normal running
compressors, then the value entered in #10 should equal the total number of compressors. If any compressors are for
standby and not operated in normal rotation, they should not be included in the compressor count in Selection #10. The
Max Comp ON setting can be made in only one toucDHSCreen, the system will observe the highest number set on all
chillers-it is a global setting.
Sequence and Staging – SETPOINTS - MODES screen, Selection #12 & #14; #11 & #13. Sequence sets the sequence
in which compressors will start. Setting one or more compressors to “1” evokes the automatic lead/lag feature and is
the normal setting. The compressor with least starts will start first and the compressor with maximum hours will stop
first, and so on. Units with higher numbers will stage on in sequence.
The Modes setpoints will do several different types of operation (Normal, Efficiency, Standby, etc.) as described in the
operating manual.
The same Modes setting must be replicated on each chiller in the system.
Nominal Capacity – SETPOINTS - MOTOR screen, Selection #14. The setting is the compressor design tons.
Compressors on dual units are always of equal capacity.
Operating Sequence
For multiple-chiller, parallel operation, the MicroTech II controllers are tied together by a pLAN network and stage and
control compressor loading among the chillers. Each compressor, single or dual compressor chiller, will stage on or off
depending on the sequence number programmed into it. For example, if all are set to “1”, the automatic lead/lag will be
in effect.
When chiller #1 is fully loaded, the leaving chilled water temperature will rise slightly. When the Delta-T above setpoint
reaches the Staging Delta-T, the next chiller scheduled to start will receive a start signal and start its pumps if they are
set up to be controlled by the Microtech controller. This procedure is repeated until all chillers are running. The
compressors will load-balance themselves.
If any of the chillers in the group are dual compressor, they will stage and load according to the staging instructions.
See
OM CentrifMicro II-3
for a complete description of the various staging sequences available.
