11
CONTROLS AND COMPONENTS
Figure 1 shows the major components of the PPS system.
Pumpout Unit —
The pumpout unit consists of a
hermetic reciprocating compressor, a water cooled refrigerant
condenser, an oil separator, and prewired safety and control
devices. The pumpout unit comes equipped with a 4-way
transfer valve manifold to interconnect both liquid and vapor
transfer and to pressurize the chiller during transfer of refriger-
ant from chiller to storage tank.
CONTROLS — The pumpout unit has the following controls:
manual/off/automatic selector switch, transformer, .25 amp
fuses for the primary side of the transformer, 5 amp fuse for the
secondary side of the transformer, contactor, terminal strip,
high pressure cutout switch and low pressure switch.
SAFETY CONTROL SETTINGS — The pumpout unit high-
pressure switch (Fig. 3) is set to open at the settings listed in
Table 5. The switch setting is checked by operating the pumpout
condenser and slowly throttling the pumpout condenser water.
When the selector switch is in the Automatic position, the
pumpout will cycle on a low pressure/vacuum switch. This
switch will shut down the pumpout compressor when suction
pressure reaches 7 ± 1.5 psia or 15 ± 3 in. Hg vacuum
(51.7 kPa absolute). When the selector switch is in the On
position, the pumpout compressor will continue to run until
refrigerant vapor flow is so low that the compressor motor
overheats. At this time the compressor motor overload will
shut off the compressor. This is NOT recommended.
Table 5 — High Pressure Switch Settings
COMPRESSOR
—
The hermetic compressor assembly
comes equipped with internal thermal protection on the motor
and a self-regulating crankcase heater.
CONDENSER — The water-cooled condenser is a brazed
plate heat exchanger. During transfer, it condenses refrigerant
vapor to liquid.
OIL SEPARATOR — The pumpout unit includes an in-line
oil separator to remove oil that becomes mixed with refrigerant
and returns the oil to the compressor.
SUCTION AND DISCHARGE VALVES — The pumpout
unit comes with a 4-way transfer valve manifold to intercon-
nect both liquid and vapor transfer and to pressurize the chiller
during transfer of refrigerant from chiller to storage tank or
from one chiller vessel to another.
Storage Tank —
The storage tank is rated for positive
pressure refrigerants under ASME Section VIII pressure vessel
codes with a minimum of 185 psig (1276 kPa) rating. The tank
components include:
DRAIN VALVE —
Located at its lowest point of drain with a
minimum of 1 in. NPT.
DUAL RELIEF VALVES — Two relief valves and a 3-way
shut-off valve.
PRESSURE GAGE — A 30 in. Hg vacuum -0-400 psig
(101-0-2760 kPa) compound pressure gage.
LEVEL GAGE — Liquid level gage (magnetically coupled
dial type) with electronic shut-off at 90% liquid capacity.
OPERATION
Overview —
Transferring refrigerant from one vessel to
another is accomplished by using either gravity or pressure
differential. A difference in elevation between 2 vessels results
in a gravity flow of liquid; a difference in pressure forces the
liquid from one vessel to the other. The latter method requires
lowering the pressure in one vessel. If there is liquid in that
vessel, its temperature must be lowered, and the pressure in the
other vessel must be simultaneously increased.
Under most circumstances, creating the pressure differential
is not a difficult process. Some applications, such as ice
storage, outdoor installations, or installations with high tem-
perature differentials between the storage tank and the chiller
may require additional consideration. In some instances, it may
be necessary to add auxiliary heat to one of the vessels or to in-
sulate the storage tank at job sites where high ambient tempera-
ture or sun load make it difficult to reduce the temperature and
pressure in the tank. Outdoor installations must have a roof or
cover over the storage tank to ensure that the pressure in the
tank does not exceed the chiller relief pressure setting.
REFRIGERANT TRANSFER — When refrigerant is being
evacuated from the chiller cooler or condenser vessels, any
liquid refrigerant left in a vessel will flash off, lowering the
temperature in that vessel enough to freeze the fluid (usually
water) flowing through the cooler or condenser tubes. This
event, called tube freeze-up, can cause extensive damage to the
chiller; therefore, all liquid refrigerant must be removed from a
vessel before evacuation of refrigerant vapor is started. If all
the liquid cannot be removed, then the cooler water and con-
denser water pumps must be operated throughout the process
of evacuating refrigerant vapor to keep fluid moving through
the cooler and condenser tubes.
TRANSFERRING LIQUID REFRIGERANT FROM THE
CHILLER COOLER TO THE CHILLER CONDENSER
OR PUMPOUT STORAGE TANK — Chiller and pumpout
unit valves are set to permit the pumpout compressor to
discharge refrigerant vapor into the cooler vessel, lowering
pressure in the condenser vessel/storage tank. The pressure
differential forces liquid from the cooler vessel into the con-
denser vessel/storage tank. After all the liquid is transferred, the
refrigerant vapor remaining in the cooler vessel can be drawn
off by reducing pressure in the chiller and discharging the
vapor through the pumpout unit condenser into the condenser
vessel/storage tank.
NOTE: The pumpout selector switch can be placed in On
or Automatic mode. In Automatic mode, the compressor will
shut off automatically once the suction pressure drops to 7 psia
or 15 in. Hg vacuum (51.7 kPa absolute). In On mode, the unit
will continue to pumpout regardless of the suction (vacuum)
pressure.
TRANSFERRING LIQUID REFRIGERANT FROM THE
CHILLER CONDENSER OR PUMPOUT STORAGE
TANK TO THE CHILLER COOLER — Chiller and pump-
out unit valves are set to increase pressure in the chiller
condenser vessel/storage tank and to reduce pressure in the
cooler vessel. Pressure in the cooler vessel is lowered to corre-
spond to a saturated refrigerant liquid temperature 2° F (1.1° C)
above the freezing temperature of the liquid circulating through
the chiller cooler/condenser tubes (34 F [1.1 C] for water). The
valves are set so that the pressure in the cooler vessel is lower
than that of the condenser vessel/storage tank, forcing the liq-
uid into the cooler vessel.
NOTE: The pumpout selector switch can be placed in On or
Automatic mode. In Automatic mode, the compressor will shut
off automatically once the suction pressure drops to 7 psia or
15 in. Hg vacuum (51.7 kPa absolute). In On mode, the unit
will continue to pumpout regardless of the suction (vacuum)
pressure.
REFRIGERANT
HIGH-PRESSURE SWITCH
CUTOUT
CUT-IN
R-134a
185 ± 10 psig
(1276 ± 69 kPa)
140 ± 10 psig
(965 ± 69 kPa)
WARNING
During transfer of refrigerant into and out of the pumpout
storage tank, carefully monitor the storage tank level gage.
Do not fill the tank more than 90% of capacity to allow for
refrigerant expansion. Overfilling may result in damage to
the tank and personal injury. For maximum refrigerant
capacity, refer to Table 3.
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