KOMAC00607-09EN 29
As the signal varies from 4 mA up to 20 mA, the maximum unit capacity changes by
steps of 1% from 100% to 0%. The unit capacity is adjusted as needed to meet this
limit, except that the last running compressor cannot be turned off to meet a limit lower
than the minimum unit capacity.
Network Limit
The maximum unit capacity can be limited by a network signal. This function is only
enabled if the unit control source is set to network. The signal will be received through
the BAS interface on the unit controller.
As the signal varies from 0% up to 100%, the maximum unit capacity changes from 0%
to 100%. The unit capacity is adjusted as needed to meet this limit, except that the last
running compressor cannot be turned off to meet a limit lower than the minimum unit
capacity.
Current Limit
Current Limit control is enabled only when the current limit enable input is closed.
Unit current is calculated based on the 4-20 mA input that receives a signal from an
external device. The current at 4 mA is assumed to be 0, and the current at 20 mA is
defined by a set point. As the signal varies from 4 to 20 mA, the calculated unit current
varies linearly from 0 amps to the amp value defined by the set point.
The current limit uses a deadband centered around the actual limit value, such that unit
capacity increase is not allowed when current is within this deadband. If unit current is
above the deadband, capacity is decreased until it is back within the deadband. The
current limit deadband is 10% of the current limit.
Maximum LWT Pulldown Rate
The maximum rate at which the leaving water temperature can drop is limited by the
Maximum Rate set point, only when the LWT is less than 60°F (15°C).
If the pulldown rate is too fast, the unit capacity is reduced until the rate is less than the
Maximum Pulldown Rate set point.
High Water Temperature Capacity Limit
If the evaporator LWT exceeds 65°F, compressor load will be limited to a maximum of
75%. Compressors will unload to 75% or less if running at greater than 75% load when
the LWT exceeds the limit. This feature is to keep the circuit running within the
capacity of the condenser coil.
A dead-band placed below the limit set-point will be used to increase function stability.
If the actual capacity is in the band, unit loading will be inhibited.
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