JOHNSON CONTROLS
11
FORM 160.77-O1
ISSUE DATE: 10/22/2020
SECTION 1 - SYSTEM FUNDAMENTALS
Control Center
The chiller is controlled by a stand-alone PLC based
control center. The chiller control center provides all
the necessary controls and control logic to provide au-
tomatic start-up, operation, capacity control and safety
protection of the chiller.
Control Panel
For operator interface the control panel includes a
10.4” (264.16 mm) color active matrix display with
integral keypad. The control panel resides in a factory
wired, unit mounted, NEMA 12, gasketed enclosure.
The enclosure is fabricated 10 gauge steel and includes
full height front access doors. The panel enclosure is
painted to match the chiller color on the outside, and
gloss white on interior surfaces. All controls are ar-
ranged for easy access and internally wired to clear-
ly marked terminal strips or pre-wired PLC interface
modules for external wiring connections. Wiring is
color-coded black (control), white (neutral), and green
(ground), with each wire numerically identified at
both ends with heat shrinkable wire markers. Wiring
enclosed in shielded cables and pre-wired cables are
color coded per the wiring diagram.
The screen details all operations and parameters, using
a graphical representation of the chiller and its com-
ponents. The operator interface is programmed to pro-
vide display of all major operating parameters in both
graphical and list type screen displays. PID control
loop setpoints and Manual/Auto functions are also ac-
complished by the operator interface. Alarm indicators
on the graphic display screen provide annunciation,
and an alarm history screen is provided which shows
the most recent alarms, with the time and date of occur-
rence. Trip status screens are provided which show the
values of all analog inputs at the time of the last five
chiller safety shutdowns. The time and date of the shut-
down are also shown. A separate push button is provid-
ed on the face of the control panel for Emergency Stop.
Capacity Control System
The major components of a chiller are selected for full
load capacities at the highest design head, therefore ca-
pacity must be controlled to maintain a constant chilled
liquid temperature leaving the evaporator. The YKEP
chiller uses a combination of prerotation vanes (PRV)
located at the entrance to the compressor impeller, op-
tional hot gas bypass, and variable compressor speed to
control capacity.
The position of the vanes is automatically controlled
through a lever arm attached to an electric motor lo-
cated outside the compressor housing.
Compressor speed is controlled to overcome aerody-
namic surge and further modulated above the surge
limit as part of the capacity control routine.
Compressor Lubrication System
The chiller lubrication system consists of the oil pump,
oil filter, oil cooler and all interconnecting oil piping
and passages.
The submerged oil pump (oil sump) takes suction from
the surrounding oil and discharges it to the oil cooler
where heat is rejected. The oil flows from the oil cooler
to the oil filter. The oil leaves the filter and flows to the
emergency oil reservoir where it is distributed to the
compressor bearings. The oil lubricates the compressor
rotating components and is returned to the oil sump.
There is an emergency oil reservoir located at the high-
est point in the lubrication system internally in the com-
pressor. It provides an oil supply to the various bearings
and gears in the event of a system shutdown due to pow-
er failure. The reservoir allows the oil to be distributed
through the passages by gravity flow, thus providing
necessary lubrication during compressor coastdown.
Oil Pump
For normal operation, the oil pump should operate at
all times during chiller operation.
On shutdown of the system for any reason, the oil
pump continues operate for 150 seconds. During this
time the system cannot restart.
Oil Heater
During long idle periods, the oil in the compressor oil
reservoir tends to absorb refrigerant as it can hold, de-
pending upon the temperature of the oil and the pres-
sure in the reservoir. As the oil temperature is lowered,
the amount of refrigerant absorbed will be increased. If
the quantity of refrigerant in the oil becomes excessive,
violent oil foaming will result as the pressure within the
system is lowered on starting. This foaming is caused
by refrigerant boiling out of the oil as the pressure is
lowered. If this foam reaches the oil pump suction, the
bearing oil pressure will fluctuate with possible tempo-
rary loss of lubrication, causing the oil pressure safety
cutout to actuate and stop the system. The oil heater
maintains oil temperature above refrigerant tempera-
ture while shutdown to avoid foaming.
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