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Flow Switch (Field Supplied) —
with machine off. Manually reduce water flow and observe
switch for proper cutout. Safety shutdown occurs when cut-
out time exceeds 3 seconds. Switches are required to be rated
electrically at 24 vdc, see Fig. 17.
Ramp Loading Control —
slows down the rate at which the compressor loads up. This
control can prevent the compressor from loading up during
the short period of time when the machine is started and the
chilled water loop has to be brought down to normal design
conditions. This helps reduce electrical demand charges by
slowly bringing the chilled water to control point. However,
the total power draw during this period remains almost un-
changed.
There are 2 methods of ramp loading with the PIC. Ramp
loading can be based on chilled water temperature or on mo-
tor load.
1. Temperature ramp loading limits the rate at which either
leaving chilled water or entering chilled water tempera-
ture decreases by an operator-configured rate.
2. Motor load ramp loading limits the rate at which the com-
pressor motor current or compressor motor load in-
creases by an operator-configured rate.
The TEMP (Temperature) PULLDOWN, LOAD PULL
DOWN, and SELECT RAMP TYPE may be viewed/modified
on the LID Equipment Configuration table, Config table (see
Table 2). Motor load is the default type.
Operate water pumps
The ramp loading control
Fig. 17 — 19EF Flow Switch (Field Supplied)
Capacity Override (Table 4) —
some safety shutdowns caused by exceeding motor amper-
age limit, refrigerant low temperature safety limit, motor high
temperature safety limit, and condenser high pressure limit.
In all cases there are 2 stages of compressor vane control.
1. The vanes are held from opening further, and the status
line on the LID indicates the reason for the override.
2. The vanes are closed until condition decreases below the
first step set point, and then the vanes are released to nor-
mal capacity control.
Whenever the motor current demand limit set point is reached,
it activates a capacity override, again with a two-step pro-
cess. Exceeding 110% of the rated load amps for more than
30 seconds will initiate a safety shutdown.
The compressor high lift (surge prevention) set point will
cause a capacity override as well. When the surge preven-
tion set point is reached, the controller normally will only
hold the guide vanes from opening. If so equipped, the hot
gas bypass valve will open instead of holding the vanes.
High Discharge Temperature Control —
charge temperature increases above 160 F (71.1 C) the guide
vanes are proportionally opened to increase gas flow through
the compressor. If the leaving chilled water temperature drops
5° F (2.8° C) below the control point, the machine will enter
the recycle mode.
CUT-OUT
SETTING
ADJUSTMENT
SCREW
26
These can prevent
If the dis-
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