Free condensing liquid retro-pumping refrigerator system and method

A compressor, condenser, pressure control valve, condensed liquid receiver, expansion valve and evaporator are arranged in circuit to provide a refrigeration system. The pressure control valve and condensed liquid receiver are bypassed by a pump tank and a pump in circuit between the output of the condenser and the expansion valve. A float switch in the pump tank provides an actuating signal at a predetermined level for condensed liquid in the pump tank, and the actuating signal is coupled to the pump. The pump, when actuated, draws condensed liquid from the pump tank at a free condensation pressure dependent upon ambient temperature at the condenser, and provides high pressure condensed liquid to the expansion valve. An inlet/outlet line between the condensed liquid receiver and the expansion valve allows high pressure condensed liquid which is not passed by the expansion valve to be accumulated in the condensed liquid receiver. The method includes compressing a fluid in a gaseous phase and condensing the fluid to a liquid phase at a pressure corresponding to the ambient temperature of condensation. Collecting the condensed liquid phase fluid is followed by sensing the level of the collected condensed fluid and thereafter pumping the collected condensed fluid to a high pressure when the collected condensed fluid reaches a predetermined level. High pressure condensed fluid is expanded and evaporated in the refrigeration system, and/or accumulated as high pressure condensed fluid.

BACKGROUND OF THE INVENTION 
The invention relates to refrigeration systems, and more particularly to 
improved efficiency refrigeration systems utilizing ambient temperatures 
and corresponding pressures for condensation of the refrigerant. 
It is recognized that free condensation in a refrigeration circuit at 
relatively low pressures corresponding to ambient condenser temperatures 
coupled with subsequent pumping of the condensed fluid is a more efficient 
operation than condensation at a high constant pressure and subsequent 
routing of the condensed fluid through the refrigeration system at the 
high pressure. U.S. Pat. No. 2,949,750 discloses a refrigerating system of 
the evaporative type which uses an air-cooled condenser exposed to ambient 
temperatures. The system described therein is so constructed that when the 
condenser is subjected to low ambient temperatures and refrigerant 
condensed therein, satisfactory operating pressure is maintained at an 
expansion valve by pumping the condensed refrigerant to the operating 
pressure. A compressor supplies the condenser. When the compressor 
pressure falls below a predetermined level, a signal is provided which 
actuates a pump which supplies the expansion valve with condensed 
refrigerant at a sufficiently high pressure so that the expansion valve 
operates correctly. High pressure condensed liquid which is not passed by 
the expansion valve is recirculated through a relief valve to a receiver 
which contains only condensed liquid at low pressure. This recirculation 
is undesirable as unnecessary energy is expended recirculating the 
condensed liquid from a high pressure to a low pressure area and 
subsequently repressurizing the condensed liquid again before it passes 
through the expansion valve. 
Another system is known wherein free condensation of a fluid in gaseous 
form occurs in a condenser at a pressure dependent upon ambient 
temperature surrounding the condenser. Condensed fluid is thereafter 
collected in a receiver at the relatively low pressure in the condenser 
and thereafter pumped by a liquid pump to a high condensed liquid pressure 
for delivery to an expansion valve associated with an evaporator in the 
refrigeration system. The pump speed is controlled by a differential 
pressure sensor located between the compressor and the pump outputs. 
Alternatively the system uses a pump with a variable output having the 
inherent possibility of overheating the condensed fluid when operating at 
low pressure differentials and low flow rates. As before, the condensed 
liquid receiver collects condensed fluid at the relatively low condenser 
pressure, and the condensed liquid supplied to the expansion valve may 
vary somewhat in pressure as the pressure sensors are called upon to 
detect the differential in compressor and pump output pressures. 
A free condensing retro-pumping refrigeration system is needed in which the 
bulk of the condensed fluid is maintained at a substantially constant high 
pressure immediately available to the expansion valve. 
SUMMARY AND OBJECTS OF THE INVENTION 
In general, the disclosed refrigeration system has a compressor, a 
condenser, a pressure control valve, a receiver, an expansion valve and an 
evaporator connected in circuit. A pump tank providing no back pressure is 
connected to receive and collect condensed fluid from the condenser, so 
that fluid in a gaseous state may be delivered by the compressor to the 
condenser at a pressure corresponding to the ambient temperature at the 
condenser. A level sensing switch is provided in the pump tank which 
produces an output signal when the condensed fluid therein reaches a 
predetermined level. A pump is coupled to the pump tank and is actuated by 
the output signal, so that the condensed fluid in the pump tank at the 
relatively low condenser pressure is provided at the pump output at a high 
pressure. The high pressure condensed fluid is delivered to the expansion 
valve, and that fluid which is not passed by the expansion valve is 
accumulated in the receiver at the high pump pressure. Thereafter, high 
pressure condensed fluid is immediately available to the expansion valve 
from the receiver and directly from the pump when the pump is operating. 
A method of providing a condensed fluid at a high pressure to an expansion 
valve connected to supply an evaporator is disclosed which includes the 
steps of compressing the fluid in gaseous form from the evaporator to a 
pressure which is dependent upon ambient temperature, and condensing the 
fluid at ambient temperature to a liquid phase. Collecting the liquid 
phase fluid and sensing the level of the collected liquid phase fluid is 
followed by pumping the condensed fluid to a high pressure when the 
collected condensed fluid level reaches a predetermined level. High 
pressure condensed fluid is delivered to the expansion valve. 
It is an object of the present invention to provide a free condensing 
retro-pumping refrigeration system with improved efficiency, and with a 
stabilized supply of high pressure condensed liquid for a system expansion 
valve. 
It is another object of the present invention to provide a free condensing 
retro-pumping refrigeration system which absorbs full pump flow during the 
retro-pumping operation. 
Another object of the present invention is to provide a free condensing 
retro-pumping refrigeration system which avoids short cyling of the 
retro-pump. 
Another object of the present invention is to provide a free condensing 
retro-pumping refrigeration system which maintains receiver pressure as 
high pressure condensed fluid is received therein. 
Additional objects and features of the invention will appear from the 
following description in which the preferred embodiment has been set forth 
in detail in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The term "retro-pumping" as used herein refers to pumping of liquid phase 
refrigerant as opposed to gaseous phase. The free condensing retro-pumping 
system of FIG. 1 includes a compressor, a condenser, a condensed fluid 
receiver, a pump, an expansion valve and an evaporator in circuit. The 
compressor provides refrigerant in gaseous phase to the condensor at a 
pressure determined by the ambient temperature at the condenser. 
Refrigerant is condensed to liquid phase and collected in the system 
condensed fluid receiver. A pump is placed in the outlet from the 
condensed fluid receiver for pumping the liquid phase refrigerant to a 
high pressure which is connected to the expansion valve associated with 
the evaporator. A differential pressure sensor 11 is located between the 
high pressure sides of the compressor and the pump, and provides power to 
a pump motor for driving the pump at predetermined pressure differentials. 
A description of the disclosed refrigeration system will now be undertaken 
with reference to the block diagram of FIG. 2. A compressor 12 is driven 
by a motor 13 receiving driving power as shown. A line 14 is provided for 
conducting refrigerant in gaseous phase to a condenser 16. Condenser 16 
has the usual motor powered fans 17 associated therewith for driving air 
at ambient temperature through the condenser 16. Condenser 16 has an 
outlet line 18 which is connected to a pressure control valve 19 situated 
between condenser 16 and a condensed fluid receiver 21. Pressure control 
valve 19 will not pass condensed fluid until a predetermined pressure 
exists at condenser outlet line 18 relative to atmospheric pressure. Thus, 
the pressure condensed fluid receiver 21 is maintained at the 
predetermined pressure. An inlet/outlet line 22 couples condensed fluid 
receiver 21 to an expansion valve 23. Expansion valve 23 is of the type 
which requires liquid phase refrigerant to be delivered at adequate 
pressure for proper operation. Expansion valve 23 is connected through 
line 24 to an evaporator 26. Evaporator 26 in turn emits refrigerant in 
gaseous phase which is conducted through a line 27 to the low pressure 
side of compressor 12 to complete a refrigerant circuit. Expansion valve 
23 is the usual thermostatic type having a control associated with line 27 
as shown. 
Condenser outlet line 18 is also connected to a pump tank 28. A shut-off 
valve 29 is positioned in the inlet to pump tank 28. Pump tank 28 receives 
condensed fluid therein from condenser 16 at the pressure in condenser 16. 
A float switch 31 is situated in pump tank 28 operating to sense the level 
of condensed fluid therein. Float switch 31 serves to provide an actuating 
signal which connects power to a motor 32 when the condensed fluid reaches 
a predetermined upper level in pump tank 28. Motor 32 drives a pump 33 
which is situated in an outlet line 34 from pump tank 28. When the 
predetermined upper level of condensed fluid in pump tank 28 is sensed by 
float switch 31 motor 32 is operated until a predetermined lower level of 
condensed fluid is reached in pump tank 28, thereby avoiding short cycling 
of pump 33. The level differential between the upper and lower levels is 
set at float switch 31. Condensed fluid at a high pressure is provided in 
a high pressure line 36 at the output of pump 33, and delivered through a 
high pressure shut-off valve 37 to the expansion valve 23. When expansion 
valve 23 is controlled to the closed position, high pressure condensed 
fluid is delivered through inlet/outlet line 22 to condensed fluid 
receiver 21. As a consequence, condensed fluid is pumped during a pumping 
cycle at a constant rate from pump tank 28 between the upper and lower 
predetermined levels therein, and delivered at a high pressure to 
expansion valve 23 and/or condensed fluid receiver 21. Condensed fluid 
receiver 21 operates as an accumulator for the high pressure condensed 
fluid which is not passed through expansion valve 23 during a pumping 
cycle for pump 33, and therefore determines the pressure in high pressure 
line 36. 
High pressure condensed fluid in line 36 is delivered at a point enroute to 
expansion valve 23 such that it is not necessary for the high pressure 
condensed fluid to pass through condensed fluid receiver 21. This avoids 
cooling of condensed fluid receiver 21, and consequent pressure drop in 
the space above the high pressure condensed fluid contained therein. 
However, when high pressure condensed fluid is passed from high pressure 
line 36 through inlet/outlet line 22 to condensed fluid receiver 21 as the 
system transfers the full storage of condensed refrigerant from pump tank 
28, some cooling and consequent pressure reduction in condensed fluid 
receiver 21 will occur. A pressure sensor 38 is provided to sense the 
pressure of the condensed fluid in condensed fluid receiver 21 and to 
provide an output signal indicative of such pressure. The output signal 
from pressure sensor 38 is coupled to a heater 39 adjacent to condensed 
fluid receiver 21 to elevate the temperature of the high pressure 
condensed fluid therein and thereby reestablish the desired high pressure 
above the fluid. As a result, expansion valve 23 always has sufficiently 
high pressure condensed fluid feed, which is a characteristic requirement 
for proper operation of such valve. 
In the event pump 33 fails or the path for condensed refrigerant through 
pump tank 28, line 34, pump 33, and high pressure line 36 becomes 
unsuitable for conducting refrigerant, shut-off valve 29 may be actuated 
to the closed position and the refrigeration system of FIG. 2 will 
continue to function, though less efficiently. Compressor 12 will be 
required to provide refrigerant in gaseous phase to condenser 16 at a 
predetermined high pressure determined by pressure control valve 19. 
Condensed liquid phase refrigerant will thereafter pass pressure control 
valve 19 only when the concenser pressure is at or above the predetermined 
pressure above atmospheric pressure. It may be desirable to also close 
high pressure shut-off valve 37 in the event the discrepancy is in the 
form of a leak in high pressure line 36. In this fashion, the refrigerant 
circuit through pump tank 28 and pump 33 will be isolated at each end 
thereof and the refrigeration system will function as a conventional 
refrigeration system. 
The manner in which the apparatus of FIG. 2 operates will now be described 
further in conjunction with the refrigerant cycle shown in FIG. 4 of the 
drawings. Beginning the cycle at line 14 at the high pressure side of 
compressor 12 the cycle is entered at point 41 of FIG. 4. Free 
condensation is shown occuring at about 40.degree. F until the refrigerant 
in gaseous phase at point 41 assumes a condensed liquid phase at point 42. 
A free condensed liquid phase appears in condenser outlet line 18 at a 
pressure dependent upon the ambient temperature surrounding condenser 16. 
The free condensed liquid phase of point 42 is collected in pump tank 28, 
as described hereinabove, until the predetermined upper level is reached 
therein. When the predetermined upper level is sensed, pump 33 is driven 
by motor 32 and condensed liquid in pump tank 28 is pumped in liquid phase 
to a high pressure as seen at point 43 in FIG. 4. A condensed liquid is 
substantially imcompressible and therefore there is no temperature change 
with the pressure change between the points 42 and 43 of FIG. 4. The high 
pressure liquid phase refrigerant at point 43 at the outlet of pump 33 is 
allowed to expand through expansion valve 23, thereby traversing that 
portion of the refrigerant cycle in FIG. 4 from point 43 to point 44. 
Expansion is accompanied by a rapid drop in refrigerant temperature from 
40.degree. to approximately -26.degree. F in the particular example of 
FIG. 4. Thereafter free evaporation takes place within evaporator 26 at a 
substantially constant pressure and temperature to a point 46 in the 
cycle. Thereafter, the refrigerant in gaseous form is no longer a 
saturated vapor and evaporation continues at constant pressure and 
increasing temperature to a point 47 in the cycle. Refrigerant in this 
condition is located in outlet line 27 from evaporator 26. Compression 
then takes place within compressor 12 between cycle points 47 and 41 of 
FIG. 4 to provide the refrigerant in gaseous form to condenser 16 at a 
pressure corresponding to the ambient temperature at condenser 16. Free 
condensation within condenser 16 then takes place, thereby repeating the 
portion of the refrigerant cycle between cycle points 41 and 42 as 
described above. 
It may be seen by reference to FIG. 3 that compressor 12 need only provide 
refrigerant in gaseous form in line 14 of FIG. 2 at a pressure 
corresponding to the ambient temperature existing for the particular 
season of the year. FIG. 3 shows that the mean ambient temperature on 
approximately March 1 at the latitude represented by the graph of FIG. 3 
is 40.degree. F. A pressure of approximately 95 lbs. per square inch is 
required to be produced by compressor 12 in refrigerant *Freon 502, for 
example, in gaseous phase delivered to condenser 16. On January 1 
compressor 12 need only provide a pressure of approximately 85 lbs. per 
square inch for *Freon 502 in the gaseous phase delivered to condenser 16 
due to the lower mean temperature of approximately 36.degree. F. On the 
other hand, on July 1, with a mean ambient temperature of approximately 
70.degree. F, compressor 12 must provide a pressure of approximately 155 
lbs. per square inch in the gaseous phase refrigerant *Freon 502 delivered 
to condenser 16. It is clear therefore, that a refrigeration system 
requiring an outlet pressure of 155 lbs. per square inch the year around 
in *Freon 502 refrigerant would consume excess energy comparatively and be 
relatively inefficient as compared to a system of the type disclosed, 
wherein the pressure corresponds to the ambient temperature at the 
condenser 16 and free condensation occurs therein. Moreover, they system 
herein described requires only a relatively small volume compared to total 
system volume of the condensed refrigerant to collect in pump tank 28 
prior to total transfer of the relatively small volume at full flow 
through pump 33 to expansion valve 23 and/or accumulator or condensed 
liquid receiver 21. Condensed refrigerant, once pumped to a high pressure 
by pump 33 is either utilized for refrigeration by being passed through 
expansion valve 23, or accumulated and retained at high pressure in 
condensed fluid receiver 21 for immediate future supply to expansion valve 
23. Efficiency is enhanced by pumping liquid phase refrigerant as opposed 
to gaseous phase refrigerant, by pumping liquid phase refrigerant to a 
high pressure a full flow through pump 33 during a pumping period, by 
retaining all high pressure liquid phase refrigerant at high pressure 
until utilized for refrigeration, and by reducing the outlet pressure of 
gaseous phase refrigerant at the compressor to a pressure corresponding to 
the ambient temperature existing at the condenser. 
FNT *Trademark 
There are different ways of accomplishing the normal refrigeration cycle 
during cold weather which do not utilize the pressure control valve 19 of 
FIG. 2. Such ways are known to those skilled in the art. The disclosed 
improvements to the basic refrigeration cycle apparatus may be used in 
conjunction with those different of accomplishing the normal refrigeration 
cycle.