Johnson Controls York YCAL0014E Series, Инструкция по установке, эксплуатации и обслуживанию

Страница: 101 / 216

JOHNSON CONTROLS
101
FORM 150.62-NM6 (103)
CAPACITY CONTROL
To initiate the start sequence of the chiller, all run per-
missive 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 microboard 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 reoc-
cur 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 micro 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 pres-
sure transducers are installed.
LEAvING CHILLED LIQUID CONTROL
The setpoint, when programmed for Leaving Chilled
Liquid Control, is the temperature the unit will control
to /- 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 Figure 8. Figure 8 should be utilized to aid in un-
derstanding 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 so-
lenoid. Upon energizing any compressor, the 60 second
Anti-Coincidence timer will be initiated.
If after 60 seconds of run-time the leaving chilled liq-
uid 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 5 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.
If the chilled liquid temperature drops to between Set-
point Low Limit and 0.5°F (.28°C) below the Setpoint
Low Limit, unloading occurs at a rate of 60 seconds.
If the chilled liquid temperature falls to a value greater
than 0.5°F (.28°C) below the Setpoint Low Limit but not
greater than 1.5°F (.83°C) below the Setpoint Low Limit,
unloading occurs at a rate of 20 seconds. If the chilled
liquid temperature falls to a value greater than 1.5°F
(.83°C) below the Setpoint Low Limit, unloading occurs
at a rate of 30 seconds. If the chilled liquid temperature
falls below 1°F above the low chilled liquid temperature
cutout, unloading occurs at a rate of 10 seconds.
Hot gas, if present, will be the final step of capacity. If
temperature remains below the setpoint low limit on the
lowest step of capacity, the micro will close the liquid
line solenoid or EEV, after turning off hot gas, and pump
the system down before turning off the last compressor
in a system.
The leaving chilled liquid setpoint is programmable from
40°F to 70°F (4.4°C to 21.1°C) in water chilling mode and
from 10°F to 70°F (-12.2°C to 21.1°C) in glycol chilling
mode. In both modes, the cooling range can be from
+/-1.5°F to +/-2.5°F (+/-.83°C to 1.39°C).
UNIT OPERATION
2