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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.
DWCC Settings
Since the DWCC is essentially two chillers combined into one counterflow, single pass,
dual-circuit chiller, the compressor on the downstream circuit (leaving chilled water)
must always be designated as the Stage 1 compressor-first on, last off.
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.
36
Centrifugal Chillers
D-EIMWC00804-14EN
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