RWB II ROTARY SCREW COMPRESSOR UNITS
INSTALLATION
S70-200 IOM
Page 10
OIL FILTER(S)
Use of fi lter elements other than
Frick may cause war ran ty claim
may to be denied.
The oil fi lter(s) and coalescer fi lter element(s) shipped with
the unit are best suited to ensure proper fi ltration and op-
er a tion of the sys tem.
THERMOSYPHON OIL COOLING
Thermosyphon oil cooling is an economical, effective meth od
for cooling oil on screw compressor units. Ther mosyphon
cooling utilizes liquid refrigerant at condenser pressure and
temperature that is partially vaporized at the condenser tem-
per a ture in a plate and shell vessel, cooling the oil to with in
15°F of that temperature. The vapor, at con dens ing pres sure,
is vented to the condenser inlet and reliquifi ed. This method is
the most cost effective of all cur rent ly ap plied cool ing systems
since no compres sor ca pac i ty is lost or com pres sor power
penalties in curred. The va por from the cooler need only be
con densed, not com pressed. Re frig er ant fl ow to the cooler is
automatic, driven by the ther mo sy phon prin ci ple and cooling
fl ow increases as the oil inlet temperature rises.
EQUIPMENT - The basic equipment required for a ther-
mosyphon system consists of:
1. A source of liquid refrigerant at con dens ing pressure and
temperature, located in close proximity to the unit to mini-
mize piping pressure drop. The liquid level in the refrigerant
source must be 6 to 8 feet minimum above the center of the
oil cooler.
2. A plate and shell oil cooler with:
Plate Side:
Oil 400 psi design
Shell Side:
Refrigerant 400 psi design
Due to the many variations in re frig er a tion system design
and physical layout, several sys tems for assuring the above
cri te ria are possible.
SYSTEM OPERATION - Liquid refrigerant fi lls the cooler
shell side up to the Thermosyphon receiver liquid level. See
Fig ure 7.
Hot oil (above the liquid tem per a ture) fl owing through the
cool er will cause some of the re frig er ant to boil and va por ize.
The vapor rises in the return line. The den si ty of the re frig er ant
liquid/vapor mixture in the re turn line is con sid er ably less than
the density of the liquid in the supply line. This im bal ance
pro vides a dif fer en tial pres sure that sus tains a fl ow condi tion
to the oil cool er. This relationship in volves:
1. Liquid height above the cooler.
2. Oil heat of rejection.
3. Cooler size and piping pressure drops.
Current thermosyphon systems are using two-pass oil cool-
ers and fl ow rates based on 3:1 overfeed.
The liquid/vapor returned from the cooler is separated in the
re ceiv er. The vapor is vented to the condenser inlet and need
only be reliquifi ed since it is still at condenser pres sure.
OIL TEMPERATURE CONTROL - Oil temperature will gen-
er al ly run about 15 - 35°F above condensing tempera ture.
In many cases, an oil temperature control is not re quired if
con dens ing temperature is above 65°F as oil tempera ture
can be allowed to fl oat with condenser tem per a ture.
Condensing Temperature:
65°F - 105°F
Oil Temperature:
80°F - 140°F
INSTALLATION - The plate and shell type thermosyphon oil
cooler with oil-side piping and a ther mo stat i cal ly con trolled
mixing valve (if ordered) are factory mount ed and piped. The
customer must supply and install all piping and equip ment
located outside of the shaded area on the pip ing diagram
with consideration given to the fol low ing:
1. The refrigerant source, thermosyphon or system receiv er,
should be in close proximity to the unit to minimize pip ing
pressure drop.
2. The liquid level in the refrigerant source must be 6 to 8
feet minimum above the center of the oil cooler.
3. A safety valve should be installed if refrigerant isolation
valves are used for the oil cooler.
The component and piping ar range ment shown in Figure 8, is
in tend ed only to illustrate the operating prin ci ples of ther mo -
sy phon oil cool ing. Other component layouts may be bet ter
suit ed to a specifi c installation. Refer to pub li ca tion E70-900E
for ad di tion al information on Ther mo sy phon Oil Cool ing.
HOT OIL IN
FROM
SEPARATOR
120-140 F
OIL OUT
O
TO SYSTEM CONDENSER
95 F
2.5#/FT
O
3
95 F
36#/FT
O
3
TS RECEIVER
Figure 7
