28 KOMAC00607-09EN
The compressor capacities are adjusted one at a time while maintaining a capacity
imbalance that does not exceed 12.5%.
Load/Unload Sequence
This section defines which compressor is the next one to load or unload.
Next To Load
The next compressor to load meets the following requirements:
Lowest capacity of the running compressors that can load up
• if capacities are equal, it must have the highest sequence number of the
compressors that are running
• if the sequence numbers are equal, it must have the least run hours
• if run hours are equal, it must have the most starts
• if starts are equal, it must be the highest numbered compressor
Next To Unload
The next compressor to unload must meet the following requirements:
Highest capacity of the running compressors
• if capacities are equal, it must have the 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 have the least starts
• if starts are equal, it must be the lowest numbered compressor
Compressor Capacity Control In Ice Mode
In Ice mode, running compressors are loaded up simultaneously at the maximum
possible rate that allows for stable operation of the individual circuits.
Unit Capacity Overrides
Unit capacity limits can be used to limit total unit capacity in Cool mode only. Multiple
limits may be active at any time, and the lowest limit is always used in the unit capacity
control.
Soft load, demand limit, and network limit use a deadband around the actual limit value,
such that unit capacity increase is not allowed within this deadband. If unit capacity is
above the deadband, capacity is decreased until it is back within the deadband.
• For 2 circuit units, the deadband is 7%.
• For 3 circuit units, the deadband is 5%.
• For 4 circuit units, the deadband is 4%.
Soft Load
Soft Loading is a configurable function used to ramp up the unit capacity over a given
time. The set points that control this function are:
• Soft Load – (ON/OFF)
• Begin Capacity Limit – (Unit %)
• Soft Load Ramp – (seconds)
The Soft Load Unit Limit increases linearly from the Begin Capacity Limit set-point to
100% over the amount of time specified by the Soft Load Ramp set-point. If the option
is turned off, the soft load limit is set to 100%.
Demand Limit
The maximum unit capacity can be limited by a 4 to 20 mA signal on the Demand Limit
analog input at the unit controller. This function is only enabled if the Demand Limit set
point is set to ON.
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