Instruction manual

KOMAC00607-09EN 27
Maximum Circuits Running
If the number of compressors running is equal to the Max Circuits Running set point, no
additional compressors will be started.
When multiple compressors are running, one will shut down if the number of
compressors running is more than the Max Circuits Running set point.
Compressor Staging in Ice Mode
The first compressor will start when evaporator LWT is higher than the target plus the
Startup Delta T set point.
When at least one compressor is running, the other compressors will start only when
evaporator LWT is higher than the target plus the Stage Up Delta T set point.
All compressors will be staged off when evaporator LWT is less than the target.
Stage Up Delay
A fixed stage up delay of one minute between compressor starts is used in this mode.
When at least one compressor is running, the other compressors will start as quickly as
possible with respect to the stage up delay.
Staging Sequence
This section defines which compressor is the next one to start or stop. In general,
compressors with fewer starts will normally start first, and compressors with more run
hours will normally stop first. Compressor staging sequence can also be determined by
an operator defined sequence via setpoints.
Next To Start
The next compressor to start must meet the following requirements:
Lowest sequence number of those compressors available to start
• -if sequence numbers are equal, it must have the least starts
• -if starts are equal, it must have least run hours
• -if run hours are equal, it must be the lowest numbered compressor
Next To Stop
The next compressor to shut down must meet the following requirements:
Lowest sequence number of the compressors that are running
• -if sequence numbers are equal, it must have the most run hours
• -if run hours are equal, it must be the lowest numbered compressor
Compressor Capacity Control In Cool Mode
In Cool mode, evaporator LWT is controlled to within 0.4 degrees F of the target under
constant flow conditions by controlling capacity of the individual compressors.
Compressors are loaded with a fixed step scheme. The rate of capacity adjustment is
determined by the time between capacity changes. The farther away from the target, the
faster compressors will be loaded or unloaded.
The logic projects ahead to avoid overshoot, such that the overshoot does not cause the
unit to shut off due to evaporator LWT dropping below the target minus the Shutdown
Delta T set point while there is still a load on the loop at least equal to the minimum unit
capacity.
Capacity of the compressors is controlled so that when possible their capacities are
balanced.
Circuits that are running in manual capacity control or running with active capacity
limiting events are not considered in the capacity control logic.