York YCAL0014E Series, Установка, эксплуатация и обслуживание

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JOHNSON CONTROLS
113
FORM 150.62-NM8 (1020)
3
CAPACITY CONTROL
To initiate the start sequence of the chiller, all run
permissive inputs must be satisfied (flow/remote start/
stop switch), and no chiller or system faults exist.
The first phase of the start sequence is initiated by the
daily schedule start or a remote cycling device. If the
unit is shut down on the daily schedule, the chilled water
pump I/O Board contacts (TB5 3-4) will close when the
daily schedule start time has been reached. Once flow
has been established and the flow switch closes, capacity
control functions are initiated.
If unit cycling is accomplished with a remote cycling
device wired in series with the flow switch, the chilled
water pump contacts will always be energized as long
as the Unit Switch is turned ON . When the flow switch
and remote cycling contacts are closed, the capacity
control functions will be initiated.
It should be noted that the chilled water pump contacts
(TB5 3-4) are not required to be used to cycle the chilled
water pump. However, in all cases the flow switch must
be closed to allow unit operation.
The control system will evaluate the need for cooling
by comparing the actual leaving or return chilled liquid
temperature to the desired setpoint, and regulate the
leaving or return chilled liquid temperature to meet that
desired setpoint.
SUCTION PRESSURE LIMIT CONTROLS
The anticipatory controls are intended to prevent the
unit from ever actually reaching a low-pressure cutout.
Loading is prevented, if the suction pressure drops
below 1.15 x Suction Pressure Cutout. Load may reoccur
after suction pressure rises above the unload point and
a period of one minute elapses. This control is only
operable if the optional suction pressure transducers
are installed.
DISCHARGE PRESSURE LIMIT CONTROLS
The discharge pressure limit controls unload a system
before it reaches a safety limit due to high load or dirty
condenser coils. The microprocessor monitors discharge
pressure and unloads a system, if fully loaded, by
one compressor when discharge pressure exceeds the
programmed cutout minus 15 psig. Reloading will occur
when the discharge pressure on the affected system
drops to 85% of the unload pressure and 10 minutes
have elapsed.
This control is only applicable if optional discharge
pressure transducers are installed.
LEAVING CHILLED LIQUID CONTROL
The setpoint, when programmed for Leaving Chilled
Liquid Control, is the temperature the unit will control
to within plus or minus the cooling range. The Setpoint
High Limit is the setpoint plus the cooling range. The
Setpoint Low Limit is the setpoint minus the cooling
range
(see Fig. 8)
. Figure 8 should be utilized to aid
in understanding the remainder of the description of
Leaving Chilled Liquid Control.
If the leaving chilled liquid temperature is above the
Setpoint High Limit, the lead compressor on the lead
system will be energized along with the liquid line
solenoid. Upon energizing any compressor, the 60
second Anti-Coincidence timer will be initiated.
If after 60 seconds of run-time the leaving chilled liquid
temperature is still above the Setpoint High Limit,
the next compressor in sequence will be energized.
Additional compressors will be energized at a rate of
once every 60 seconds if the chilled liquid temperature
remains above the Setpoint High Limit and the chilled
liquid temperature is dropping less than 3°F/min. The
lag system will not be allowed to start a compressor until
the lead system has run for five minutes .
If the chilled liquid temperature falls below the Setpoint
High Limit but is greater than the Setpoint Low Limit,
loading and unloading do not occur. This area of control
is called the control range.
SECTION 3 - UNIT OPERATION