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4.9 - COMPRESSORS & LOADERS LOADING SEQUENCE
4.9.1 - General Description
The Global chillers uses compressors which have better performance at full load than at part load. Therefore, the
loading sequence strategy will be different than for the flotronic II or for the Pro-dialog 30 G & H. The following list
applies only to capacity control. For High Ambient Unloading, it can be overridden.
1.
A compressor will not be started until all other running compressors are 100% loaded.
2.
On units with 3 compressors, both circuits cannot have their loaders off at the same time once 3 or
more of the compressors in the unit are on. Where possible, the circuit which is starting a
compressor will be the one which is to be unloaded.
3.
Any time a lag compressor in a circuit is starting, the loaders in the circuit shall be turned off
(unloading all compressors in the circuit). This shall be done 15 seconds prior to starting the new
compressor. 15 seconds after the new compressor has started, the loaders shall be set to their
desired state. When a lead compressor is starting, all loaders shall be turned off when the
compressor relay is turned on (+/- 2 seconds), and shall be set to their desired state 15 seconds
after the compressor has been started.
4.
There shall be a configuration decision for "close control", which (when selected) will cause the
control to utilize all of the loading devices to achieve better leaving water temperature control.
5.
Whenever any compressor in a circuit is going to be stopped normally, the circuit shall be fully
unloaded for 15 seconds prior to shutting down the compressor. This shall not apply when the
reason for a shutdown is due to an alarm condition.
7.
For any shutdown, all compressors and loaders will be shut down at the same time.
For more than 2 compressors, two types of sequencing are available and configurable by the user through either the
Main Interface or through the CCN network:
w
Equal circuit loading: The control shall attempt to maintain equal capacity between the circuits as the machine
loads and unloads.
w
Staged circuit loading: The control shall load the lead circuit completely before the lag circuit is started. When
the load is decreasing the lag circuit shall be unloaded first.
Circuit compressors sequence select shall try to equalize the compressor starts number. That means any
compressor in the circuit can become the lead compressor if it has the lowest starts number, however, this shall be
balanced with the operating hours.
Loaders in the same circuit are commanded simultaneously. Thus one loader variable is displayed.
When a circuit is overridden (compressor status are blinking in the synopsis) because of low suction
temperature, low or high discharge temperature or high condensing temperature (high pressure), or high
current then no capacity increase shall be allowed on the affected circuit. This circuit is selected to unload
capacity first when unloading capacity condition is required.
4.9.2- Compressor capacity determination
Each compressor has three stages capacity. Simulation had been done to determine the average capacity
corresponding to those stages as following :
No loader ON -> 40%
Only loader_1 -> 70%
Both loaders ON -> = 100%
CARRIER SA
USER'S GUIDE FOR
30GX&HX PRO_DIALOG 4 V.2
ECG-UG-02-002
Rev: Original
Page: 40/98
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