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Operation Manual
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7.12.6
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 a re 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
7.12.7
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.
7.13 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, a nd
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%.
7.13.1
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%.
7.13.2
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.
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 o ff to meet
a limit lower than the minimum unit capacity.
7.13.3
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 li mit lower
than the minimum unit capacity.
