Carrier POSITIVE PRESSURE STORAGE SYSTEM 19XB - Manual (Page 11)

CONTROLS AND COMPONENTS
Figure 1 shows the major components of the PPS system.
Pumpout Unit — The pumpout unit consists of a spring-
mounted direct motor-driven reciprocating compressor, a water-
cooled refrigerant condenser, an oil separator, suction and
discharge valves to control refrigerant flow, 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 trans-
fer of refrigerant from chiller to storage tank.
CONTROLS — The pumpout unit has the following con-
trols: an on/off switch, a 3-amp fuse, compressor overloads,
an internal thermostat, a compressor contactor, and a refrig-
erant high pressure cutout.
SAFETY CONTROL SETTINGS — The pumpout unit high-
pressure switch (Fig. 1) 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 con-
denser water.
Table 5 — High Condition Pressure Switch Settings
English
REFRIGERANT
HIGH-PRESSURE SWITCH
Cutout CutIn
R-134a 161 ± 5 psig
+ 0
130 − 5 psig
R-22 220 ± 5 psig
+ 0
185 − 5 psig
SI
REFRIGERANT
HIGH-PRESSURE SWITCH
Cutout Cut-In
R-134a 1110 ± 34 kPa
+ 0
896 − 34 kPa
R-22 1517 ± 34 kPa
+ 0
1276 − 34 kPa
NOTES:
1. R-22 units use high-pressure cutout switch HK01UA181.
2. R-134a units use high-pressure cutout switch HK01UA187.
COMPRESSOR — The pumpout compressor assembly has
a positive displacement of 1750 rpm (29 r/s) and 8.7 cfm
(0.004 m
3 /s). It comes equipped with thermal protection on
the motor and an in-line oil separator.
CONDENSER — The water-cooled condenser is fully ASME
constructed. During transfer, it condenses refrigerant vapor
to liquid. The condenser transfer tank safety relief valves com-
ply with ASHRAE 15 standards.
OIL SEPARATOR — The pumpout unit includes an in-line
oil separator to remove oil that becomes mixed with refrig-
erant and returns the oil to the compressor.
SUCTION AND DISCHARGE VALVES — The pumpout
unit comes with a 4-way transfer valve manifold to inter-
connect 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 ves-
sel codes with a minimum of 300 psig (2068 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.-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.
During transfer of refrigerant into and out of the pump-
out 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 maxi-
mum refrigerant capacity, refer to Table 2.
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 re-
sults 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 liq-
uid 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 differ-
ential is not a difficult process. Some applications, such as
ice storage, outdoor installations, or installations with high
temperature differentials between the storage tank and the
chiller may require additional consideration. In some in-
stances, it may be necessary to add auxiliary heat to one of
the vessels or to insulate the storage tank at job sites where
high ambient temperature or sun load make it difficult to re-
duce the temperature and pressure in the tank. Outdoor in-
stallations 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 condenser 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 dis-
charge refrigerant vapor into the cooler vessel, lowering pres-
sure in the condenser vessel/storage tank. The pressure dif-
ferential forces liquid from the cooler vessel into the condenser
vessel/storage tank. After all the liquid is transferred, the re-
frigerant 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 con-
denser vessel/storage tank.
TRANSFERRING LIQUID REFRIGERANT FROM THE
CHILLER CONDENSER OR PUMPOUT STORAGE TANK
TO THE CHILLER COOLER — Chiller and pumpout unit
valves are set to increase pressure in the chiller condenser
vessel/storage tank and to reduce pressure in the cooler ves-
sel. Pressure in the cooler vessel is lowered to correspond 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
liquid into the cooler vessel.
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