Variable capacity binary refrigerant refrigeration apparatus

A variable capacity binary refrigerant refrigeration apparatus providing improved energy usage efficiency in an operation of a dual evaporator system. One evaporator is used for refrigerating an above-freezing fresh food zone and the other evaporator is used for refrigerating a below-freezing freezer zone. The fluid system includes a rectifier, a separator, and an auxiliary condenser, together with suitable valves for controlling the operation of the apparatus. The system further utilizes control of the cold air circulating fans in effecting the desired improved operation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is concerned with refrigeration apparatus and in particular 
to means for improving the energy usage efficiency of a binary refrigerant 
refrigeration system utilizing a refrigerant flow circuit including heat 
exchangers in the below-freezing and above-freezing zones. 
2. Description of the Background Art 
In a paper presented before the International Refrigeration Congress in 
Moscow, Russia, in 1975, A. Lorenz and K. Meutzner describe a 
non-azeotropic two-component refrigerant domestic refrigerator-home 
freezer system. As shown in FIG. 4 of the publication, it was known, in 
1975, to provide a refrigeration apparatus having a first evaporator in 
the freezer zone and a second evaporator in the above-freezing zone of a 
refrigerator, with a first heat exchanger between the condenser and the 
freezer evaporator, and a second heat exchanger between the freezer 
evaporator and the above-freezing compartment evaporator. The refrigerant 
comprised a binary refrigerant of R 22/R 11 composition. 
Another binary refrigerant system is illustrated in U.S. Pat. No. 2,799,142 
of Albert E. Schubert et al. for providing dual temperature levels of 
refrigeration in the system. The refrigerant components in the Schubert et 
al patent comprise Freon 22 and Freon 12. The system is arranged for 
selectively circulating one of the refrigerants, substantially purging the 
system of that refrigerant, and circulating the other refrigerant through 
the system, while purifying the first refrigerant during the circulation 
of the other refrigerant. The means for purifying the refrigerant 
comprises distilling means. 
SUMMARY OF THE INVENTION 
The present invention comprehends an improved variable capacity binary 
refrigerant refrigeration apparatus which provides improved energy usage 
efficiency. 
The refrigerant of the present invention is advantageously adapted for use 
with domestic refrigerator/freezer apparatuses. The system provides 
separate freezer and above-freezing compartment refrigeration, with 
continuously variable refrigeration capacity upon demand. The system is 
arranged to provide continuous operation, thereby reducing losses due to 
cycling as in conventional refrigerators. 
The improved apparatus operates automatically to shift the refrigeration 
capacity between the freezer zone and the fresh food zone as a function of 
the demand. 
The refrigeration apparatus of the present invention functions 
automatically to balance the load pursuant to the demand of the two 
different zones. When the system operates in a normal environment with the 
load on the system being due to the thermal leakage of the refrigerator 
cabinet, the binary refrigerant is selected to provide a maximum 
coefficient of performance (COP). Under this condition, the refrigeration 
system runs continuously, thereby eliminating losses due to cycling. 
The apparatus includes means for establishing preset temperatures and 
sensing means for determining the actual temperature of the freezer zone 
and the above-freezing zone, and comparing them with the preset 
temperatures. The control operates so that as long as the preset 
temperature and the actual temperature in the refrigerator and freezer 
zones are within the preset limits, the binary refrigerant is delivered 
from the condenser through a rectifier without change in the ratio of the 
constituent refrigerant fluids therein. Under these conditions, the 
refrigerant mixture flows through the two heat exchangers connected in the 
refrigerant flow circuit. 
The system is arranged so that if the temperature in the fresh food zone 
rises above a preselected temperature while the freezer temperature 
remains below a preselected temperature, a valve bypassing the second heat 
exchanger opens so as to bypass liquid refrigerant around said second heat 
exchanger directly to the expansion means of the system, thereby rendering 
the second heat exchanger ineffective so that the refrigerant leaving the 
freezer evaporator is cold and of low quality vapor as it enters the fresh 
food evaporator. The first heat exchanger, which is located in the 
refrigerator zone, superheats the refrigerant delivered from the fresh 
food evaporator before it is returned to the compressor. 
Normally, under the condition of the freezer being below the preset 
temperature, the freezer fan is de-energized. As a result of the bypassing 
of the second heat exchanger located in the freezer zone and the 
de-energization of the fan, the refrigeration effect is shifted to the 
fresh food zone. 
As a result of the de-energization of the freezer fan and the delivery of 
the refrigerant in bypassed relationship to the second heat exchanger, the 
temperature in the freezer zone slowly drifts upwardly. If the fresh food 
zone reaches the desired low temperature before the freezer zone reaches a 
preselected elevated temperature, the system is returned to the normal 
operation with the bypass valve closed. 
Alternatively, the invention comprehends the control of the system to shift 
capacity to the freezer zone, such as when a sudden load is added thereto, 
causing the temperature to reach a preselected high temperature. Thus, 
more of the available cooling effect will be available in the freezer to 
increase the refrigeration thereof. In the event the temperature of the 
freezer continues to rise notwithstanding the shutting down of the fresh 
food fan, the refrigeration capacity of the system is increased while 
maintaining the shift to the freezer. 
The invention comprehends the increasing of the system capacity by heating 
a portion of the binary refrigerant to boil off the lower boiling point 
constituent fluid, condensing the boiled-off fluid, and introducing the 
condensed boiled-off fluid to the binary refrigerant being circulated to 
the evaporators. The rate of heating is controlled so as to be 
proportional to the slope of the temperature/time curve. 
When the temperature conditions in the freezer and fresh food zones reach 
the desired low temperature conditions, the system is returned to the 
normal operating conditions wherein the binary refrigerant is flowed 
through the series arrangement of the heat exchangers and evaporators. 
The heating of a portion of the binary refrigerant to provide the increased 
amount of low boiling temperature refrigerant to the refrigerant fluid 
being circulated through the evaporator is effected in a rectifier. 
Suitable valves are provided for controlling delivery selectively from the 
rectifier or from a separator receiving the condensed boiled-off low 
temperature refrigerant. 
Control of the valves and fan motors may be effected by any suitable means 
as desired. 
Thus, the refrigeration apparatus of the present invention is extremely 
simple and economical of construction while yet providing a highly 
improved self-balancing, high energy usage efficient system in a two-zone 
binary refrigerant apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the illustrative embodiment of the invention as disclosed in the 
drawing, a refrigeration apparatus generally designated 10 is shown to 
comprise a domestic refrigerator having an outer cabinet 11 with internal 
wall means 12 for dividing the interior space of the cabinet into a 
freezer zone 13 and a fresh food zone 14. The freezer zone is defined by a 
space effectively maintained at a below-freezing temperature and the fresh 
food zone is defined by a space effectively maintained at a refrigerated 
above-freezing temperature. 
The invention comprehends the provision of means for providing a binary 
refrigerant in the refrigeration system generally designated 15, including 
a conventional compressor 16 and a conventional condenser 17. The 
compressor and condenser may be provided in a machinery space 18 within 
the outer cabinet 11. In the illustrated embodiment, the refrigeration 
apparatus defines a side-by-side unit wherein the freezer and fresh food 
zones are in side-by-side relationship with the machinery space 18 
disposed therebelow. 
As illustrated in FIG. 2, a first evaporator 19 is disposed in the fresh 
food zone 14 and a second evaporator 20 is disposed in the freezer zone 
13. Air moving means are provided for circulating cooling air through the 
zones 13 and 14, and as shown, include a first fan 21 for circulating air 
in heat exchange relationship with evaporator 19 to the fresh food zone 
14, and a second fan 22 for circulating air in heat exchange relationship 
to the freezer evaporator to the freezer zone 13. 
A temperature sensor 23 is disposed adjacent fan 21 for sensing the average 
temperature in fresh food zone 14 and a temperature sensor 24 is disposed 
adjacent fan 22 for sensing the average temperature in the freezer zone 
13. 
A first heat exchanger 25 is provided in fresh food zone 14 and a second 
heat exchanger 26 is provided in freezer zone 13, as seen in FIG. 2. 
Condensed binary refrigerant is delivered from condenser 17 through a 
separator 27 to a rectifier 28. The binary refrigerant liquid 29 is 
delivered through a conduit 30 provided with a shutoff valve 31 to an 
inlet conduit 32 of the heat exchanger 25. The binary refrigerant fluid is 
delivered from conduit 32 through a transfer conduit 33 to an inlet 
conduit 34 of heat exchanger 26, and through a transfer conduit 35 having 
an expansion valve 36 to the evaporator coil 37 of evaporator 20. 
The binary refrigerant may advantageously be comprised of a non-azeotropic 
refrigerant mixture of R 12/R 11. It is important to select the binary 
refrigerant mixture which will match the temperature profile of the air 
crossing the evaporator and condenser during normal operation in order for 
the system to operate at a high COP. Yet the refrigerant pair must also be 
such that a substantial difference in density at the compressor suction 
can be made to occur by adjusting the refrigerant mixture ratio in order 
to increase refrigeration capacity of the system upon demand. Other 
non-azeotropic refrigerant mixtures which may advantageously be employed 
in the disclosed apparatus and system are R 22/R 114 and R 22/R 11. 
From evaporator coil 37, the binary refrigerant is delivered through a 
transfer conduit 38 to the outlet conduit 39 of heat exchanger 26, which 
is in heat transfer association with the inlet conduit 34 thereof. 
From outlet conduit 39 of heat exchanger 26, the refrigerant is delivered 
through a transfer conduit 40 to the coil 41 of evaporator 19. From 
evaporator coil 41, the refrigerant is delivered through a transfer 
conduit 42 to an outlet conduit 43 of heat exchanger 25 in heat exchange 
relationship with the inlet conduit 32 thereof. The refrigerant is 
returned from outlet conduit 43 of heat exchanger 25 through a transfer 
conduit 44 to compressor 16 for recompression and recirculation through 
the system. 
Separator 27 is connected through a conduit 54 having a shutoff valve 45 to 
the first heat exchanger inlet conduit 32. An auxiliary condenser 46 is 
connected between an upper portion of the rectifier 28 and an upper 
portion of the separator 27. A heating coil 47 is provided for heating the 
refrigerant liquid 29 in rectifier 28. 
A bypass conduit 48 is connected in parallel with inlet conduit 34 of heat 
exchanger 26 and is provided with a shutoff valve 49. 
The refrigeration apparatus includes a suitable control 50, which may be of 
any conventional construction, for controlling the operation of fan motors 
51 and 52 for driving fans 21 and 22, respectively, valves 31, 36, 45 and 
49, and heater 47 as a function of the temperature sensed by sensors 23 
and 24 in the zones 13 and 14. Illustratively, the control may comprise a 
Texas Instruments Model TMS7040 microprocessor wherein a number of set 
points may be stored in the memory thereof for constant comparison with 
the temperature sensed by sensors 23 and 24. In the illustrated 
embodiment, these temperatures may be sensed every two seconds by the 
control 50 so that whenever measured temperatures are outside the present 
limits set into the control, suitable associated switches (not shown) are 
actuated for controlling operation of the respective fan motors, valves, 
and heater for shifting the refrigerant system capacity or increasing the 
total system capacity, as will be brought out more fully hereinafter. 
As shown in FIGS. 3 and 4, control 50 may be set to define six preset 
temperature set points SP1, SP2, SP3, SP4, SP5 and SP6. Set points SP1, 
SP2 and SP3 are compared continuously with temperature signals received 
from fresh food zone sensor 23 and set points SP4, SP5 and SP6 are 
compared continuously with temperature signals received from freezer zone 
sensor 24. 
FIG. 3 illustrates graphically the operation of the refrigeration system 
where the temperature in the fresh food zone 14 increases to and beyond 
the different set points SP1, SP2 and SP3, and illustrates the 
corresponding small changes in the freezer zone temperature. FIG. 4 
illustrates the substantial changes in the temperature within the freezer 
zone as a result of the load introduced therein relative to the set points 
SP4, SP5 and SP6, and the relatively small changes that concurrently occur 
in the temperature within the fresh food zone. 
As pointed out above, the refrigeration system is arranged to run 
continuously so as to eliminate losses due to cycling, as in the 
conventional refrigeration systems. Referring now to FIGS. 2 and 3, as 
long as the temperature within the fresh food compartment 14 sensed by 
sensor 23 remains below SP2, the system is arranged to provide the binary 
refrigerant liquid 29 from rectifier 28 to the refrigerant circuit 15. 
Thus, at this time, valve 31 is open, valve 45 is closed, and valve 49 is 
closed to permit the normal flow of the binary refrigerant successively 
through the heat exchangers 25 and 26 and evaporators 19 and 20. The 
binary refrigerant is selected so as to provide under these conditions the 
optimum coefficient of performance, i.e. COP. 
However, if the temperature in the fresh food zone 14 rises above the set 
point SP2 of control 50, with the temperature in the freezer zone 13 
remaining below set point SP5, control 50 causes valve 49 to open so as to 
bypass warm liquid refrigerant around inlet conduit 34 of heat exchanger 
26 directly to the expansion valve 36. (In the illustrated embodiment, the 
expansion means comprises expansion valve 36, it being obvious to those 
skilled in the art that any suitable orifice or capillary tube may be 
utilized for this purpose.) 
As the bypassing of the conduit 34 renders heat exchanger 26 ineffective to 
warm the refrigerant passing outwardly through conduit portion 39 thereof, 
the refrigerant remains cold and is of a low quality vapor as it enters 
the fresh food evaporator coil 41. The refrigerant delivered from coil 41 
through heat exchanger conduit 43 is superheated by the refrigerant 
passing through inlet conduit 32 in heat exchange relationship therewith 
and, thus, is delivered to the compressor as superheated refrigerant. 
Resultingly, the capacity of the system is shifted from the freezer zone 
to the fresh food zone as a result of controlling the amount of subcooling 
at the expansion device 36. As a result, as seen in FIG. 3, the 
temperature in the fresh food zone 14 will normally drop to below set 
point SP2 back to the lower set point SP1. At the same time, a slight rise 
in the temperature in the freezer zone 13 occurs. Assuming that this 
operation is sufficient to handle the heat introduced into the fresh food 
zone, the system then continues to operate with the capacities matched at 
the preselected set points SP1 and SP4. 
When the freezer zone temperature is at the preselected operating set point 
SP4, which illustratively may be 0.degree. F., the control causes the 
freezer fan motor 52 to be de-energized. With the valve 49 bypassing the 
warm refrigerant liquid around the heat exchanger so as to cause the 
refrigerant passing through heat exchanger conduit 39 to not be warmed, 
and concurrently minimizing heat transfer from the evaporator coil 37, the 
refrigeration effect is shifted to the fresh food zone. 
If, however, the temperature in the fresh food zone continues to rise, 
notwithstanding this shift in the refrigeration effect thereto, the 
capacity of the refrigeration system is increased while maintaining this 
shift condition. More specifically, the capacity of this system is 
increased by energization of heater 47 so as to boil off from the liquid 
refrigerant 29 in rectifier 28 the lower temperature boiling component 
thereof. The boiled-off refrigerant component is condensed by auxiliary 
condenser 46 and introduced into the binary refrigerant in separator 27 
for delivery through the conduit 54 to the refrigerant circuit 15. In 
effecting this capacity increase, valve 31 is closed and valve 45 is 
opened concurrently with the energization of heater 47. As will be obvious 
to those skilled in the art, the energy input by heater 47 may be caused 
to be directly proportional to the slope of the temperature versus time 
curve of the system. Thus, as seen in FIG. 3, the increased capacity of 
the refrigeration system, together with the shift of the refrigeration 
effect to the fresh food zone 14 will cause the temperature in the fresh 
food zone to decrease back to the set point SP1. Concurrently, the 
temperature of the freezer zone, while rising slightly during these 
conditions, will again be brought back to the set point SP4. 
Thus, the refrigeration system provides an automatic control as a function 
of the sensed temperatures and the set points of control 50. 
Should the freezer zone temperature rise to the set point SP5 temperature 
as a result of the transfer of refrigeration effect to the fresh food 
zone, even though the temperature of the fresh food zone does not reach 
the set point SP3 temperature, the control similarly causes the above 
described increases in the capacity of the system by energization of 
heater 47 to bring the operating temperatures back to the set points SP1 
and SP4. 
Referring now to FIG. 4, a reverse operation of the automatic control 
system occurs when a heat load is introduced to the freezer zone 13. Thus, 
as shown in FIG. 4, when the temperature sensed by sensor 24 rises above 
the set point temperature SP5 while the temperature in the fresh food zone 
14 remains below set point temperature SP2, the refrigeration effect is 
shifted to the freezer zone by de-energizing the fresh food zone fan motor 
51, thereby shifting the refrigeration capacity to the heat exchanger 25 
and increasing the refrigeration capacity available to evaporator 20. As 
shown in FIG. 4, if the shift in refrigeration capacity is sufficient to 
return the temperature in the freezer zone 13 to the set point SP4 
temperature, the system will be returned to the original operating 
condition, as discussed above. 
However, should the temperature in the freezer zone 13 continue to move 
upwardly so as to reach set point SP6, the system capacity is increased by 
the above described energization of heater 47 and provision of low boiling 
point refrigerant to the binary refrigerant delivered to the refrigerant 
circuit 15. 
Control 50 functions to cause valve 49 to be closed whenever the 
temperature in the freezer zone 13 exceeds the set point temperature SP6 
concurrently with the temperature in the fresh food zone 14 exceeding the 
set point temperature SP3. 
Thus, the refrigerant system 15 provides an automatic control of the 
refrigerant flow so as to effect a shifting of the refrigeration effect to 
whichever of the zones requires such shifting, and to provide additional 
capacity in the event such shifting is insufficient to return the 
temperature of the elevated temperature zone to the desired normal 
operating temperature. The control effects this automatic shifting and 
capacity increase as a function of the temperatures sensed in the fresh 
food and freezer zones and the comparison thereof with preselected 
temperatures set into the control. 
The foregoing disclosure of specific embodiments is illustrative of the 
broad inventive concepts comprehended by the invention.