US3314246A - Capacity control for refrigeration systems - Google Patents

Description

April 1967 N. E. HOPKINS ETAL 3,314,246

CAPACITY CONTROL FOR REFRIGERATION SYSTEMS Filed Oct. 22, 1965 2 Sheets-Sheet 1 -aH/No1/Wva1s 591 "an /wv2.Ls 59'! 01 o oog'os ooeoz O0.0'OI o (D I! I 2 'T o 3 l- IL 2 Au no" 0 m m nz m D H.

CENTRiFUGAL MAMKIM! 1 E al Dx i u ITYT. INVENTORS BY Maw ATTO R N EY April 1957 N. E. HOPKINS ETAL 5 CAPACITY CONTROL FOR REFRIGERATION SYSTEMS Filed Oct. 22, 1965 2 Sheets-Sheet 2 mokqmmzmo mmmzmo 20o a ummuomm/a mmww l m wwww uPEumZmO HH I I I I $5538 S NQ n m WK ATTO l2 N EY United States Patent C 3,314,246 CAPACITY CONTROL F OR REFRIGERATION SYSTEMS Neil E. Hopkins and Robert F. Muhleman, York, Pa., assignors to Borg-Warner Corporation, Chicago, 111., a corporation of Illinois Filed Oct. 22, 1965, Ser. No. 500,797 4 Claims. c1. 62101) This invention relates generally to absorption refrigeration systems, and more particularly to means for diluting the absorbent solution with refrigerant for the purposes of producing a fast acting capacity control means, preventing possible evaporator freezing or solution crystallization, and obtaining certain operating advantages when such absorption systems are combined with steam turbine driven refrigeration units wherein high pressure steam is first fed to the steam turbine and then to the absorption machine (or machines).

A principal object of the present invention is to provide an automatic method of capacity reduction with a speed of response so rapid that it is practically instantaneous, in contrast to the very sluggish response behavior of conventional capacity control systems.

Another object of this invention is to provide first capacity reduction, without shutting down the absorption machine, the purpose being to satisfy any safety control requirements wherein crystallization or freeze-up is threatened, while still maintaining some capacity as required by the load.

A further object of this invention is to provide a combination system including an absorption machine and a steam turbine driven centrifugal compressor system with capacity control means permitting a reduction in the capacity of the absorption system independent of the capacity of the turbine-centrifugal system to insure a better load balance between the two systems.

The further object of this invention is to provide a capacity control to satisfy any condition which calls for capacity reduction.

A further object of this invention is to provide an improved control system for a combined steam turbine driven centrifugal and absorption system which permits the absorption machines to operate as condenser for the steam exhausted from the turbine under load conditions below which the compressor would otherwise operate in an unstable region.

Still another object of the invention is to provide a system which can satisfy a need for fast acting capacity reduction, without the ordinary nuisance of complete system shutdown and the subsequent need for restarting.

Additional objects and advantages will be apparent from reading the following detailed description taken in conjunction with the drawings, wherein:

FIGURE 1 is a schematic representation of an absorption refrigeration system embodying the present invention;

FIGURE 2 is a typical performance diagram of a combined absorption and steam turbine driven centrifugal system which shows the refrigerating capacity of the combined system at various loads, the steam consumption rate, and the pounds of steam used per hour for each ton of refrigeration; and

FIGURE 3 is a schematic diagram of a combined absorption and steam turbine driven centrifugal system and the controls therefor.

It should be pointed out that one aspect of the invention concerns apparatus and method for rapidly diluting the absorbent solution to effect an almost instantaneous reduction in capacity, primarily for the purpose of safety, i.e. to prevent crystallization of solution, evaporator freeze-up, etc. This concept is applicable to all types of 3,3142% Patented Apr. 18, 1967 absorption systems and can therefore be used on simple absorption machines. The other aspect of the invention concerns the use of refrigerant to dilute the absorption solution for modulated capacity control in a combination absorption/steam-driven centrifugal system, commonly referred to in the art as a turbo topping system. It should also be understood that while this specification occasionally refers to the absorption system as using Water as the refrigerant and an aqueous solution of LiBr as the absorbent, there are numerous other refrigerantabsorbent combinations to which the invention is equally applicable.

Referring first to FIGURE 1, which is a schematic representation of an absorption machine emboyding the principles of the invention, the drawing shows, in general, an absorber A, an evaporator B, a generator C, and a condenser D in a dual shell configuration, although other shell arrangements are known and could also be employed in this system. A generator pump E withdraws relatively dilute (59% LiBr) solution from the absorber and forwards it to the generator through a heat exchanger -F. Relatively concentrated (64.5% LiBr) solution flows from the generator through heat exchanger F to the absorber where it mixes with a relatively dilute solution to form an intermediate strength solution (61% LiBr) which is sprayed over a heat exchanger in the absorber A where it absorbs refrigerant (water) vapor evaporated in the evaporator B. The absorber pump G continuously recirculates the intermediate strength solution formed by the mixing of the concentrated solution with the dilute solution. A refrigerant pump H withdraws liquid refrigerant from a pan underneath a chilled water coil J in the evaporator and continuously recirculates suc-h refrigerant to a spray header positioned over coil I. The dilution system to which the present invention is more particularly directed is shown generally at K and will be described in more detail below.

The automatic dilution system K comprises a line 10 interconnecting the refrigerant circuit and the solution circuit to withdraw refrigerant from refrigerant line 12 (through which refrigerant is delivered to the spray header in the evaporator) and supply it to the absorber sprays 13. Line 10 includes an automatically controlled valve 14 which controls the flow of refrigerant from the refrigerant line to the absorber in response to one or more conditions. Valve 14 may be of the modulating type, which is responsive to a pneumatic (or equivalent electrical) control signal through line 16, or a full-flow,

no-fiow solenoid actuated valve. The modulating type is preferably used in a turbo topping system for controlled reduction of capacity and the solenoid type in a simple absorption machine application where the dilution system is used as a safety feature to avoid crystallization or freeze-up. It is to be understood, however, that either type of valve may be adapted for either system.

It is obvious that by dumping refrigerant into the solution at the point Where the solution is directly feeding into the absorber, the capacity is reduced rapidly. This is an important consideration because dumping the refrigerant into the suction line of the absorber or solution pump G feeding the sprays 13, or into any other point in the pipe connections to or from the absorber pump, will result in a substantially instantaneous reduction in the concentration of solution going to the absorption sprays. In a matter of seconds, the ability of the solution to absorb water vapor over the absorber surface is drastically reduced with a corresponding reduction in the reifrigera tion capacity. The degree of capacity reduction, of

course, depends upon the amount of refrigerant which is diverted into the absorber for dilution purposes. If valve 14 is open to a position allowing maximum flow, this can be sufficient to reduce the capacity of the system to zero if required by some unusual safety control problem. In this manner, an absorption system can be made to produce zero capacity and at the same time utilize the same control device to partially reduce capacity, if such is the requirement.

The usual method employed in case safety controls indicate imminent freeze-up or imminent crystallization is to completely kill the capacity by, in effect, shutting down the system. In the shutting down process, conventional systems go into a so-called dilution cycle in which certain pumps operate; but the absorption cycle is stopped either by cutting off the condensing water flow through the absorber, discontinuing the steam supply, or shutting off the sprays over the absorber completely. By the method of this invention, the absorption capacity can be completely arrested by fully opening the refrigerant dump valve, or the capacity can be partially reduced on a modulating basis, so that the safety considerations are satisfied, but not excessively so.

The point should be stressed that the solution going to the absorber sprays can be diluted very quickly to that corresponding to zero capacity, while the main body of solution in the generator and absorber can still be in a highly concentrated state. For example, at full load, the solution in the generator would be, say, 64.3% and the concentration in the absorber would be, say, 59.3%. The mixture of solution going to the sprays at full capacity, using about 40% of the solution spray received from the generator, would he, say, 61.3%. This 61.3% would be flowing over the absorber and producing the full capacity condition. Now let us assume safety controls require a complete arrest of capacity. By dumping sufficient refrigerant into the solution going to the absorber pump, instead of supplying 61.3% solution to the absorber sprays, the concentration can be reduced to, say, 52%, a condition corresponding to zero capacity. This contrasts to the fact that the solution concentration leaving the generator would be at a relatively high level for some time, even though the steam valve closed immediately, due to the flywheel capacity in the generator sump. Similarly, the concentration of solution in the absorber pan will only reduce gradually. Thus, if the controls indicate that full capacity may be resumed shortly after the safety control signal was initiated, high concentrations still remain in the generator and absorber to be used for a quick resumption of high capacity operation.

It should be noted that there are several disclosures in the prior art where refrigerant is supplied to the absorber for one reason or another. In one such system described in United States Patent 2,760,350, issued on Aug. 28, 1956, to J. R. Bourne, a line between the refrigerant circuit and the solution circuit is opened when the system is shut down to clean out a purge line and dilute the solution in the absorber to prevent crystallization during the shutdown period. In another system, described in British Patent 658,914, issued to Carrier Engineering Ltd. on Oct. 17, 1951, an auxiliary tank is provided which is filled with refrigerant when the system is started up, and upon shutdown the refrigerant is drained into a concentrated solution line leading to the absorber. However, there is no suggestion that capacity can be controlled by refrigerant supplied through an automatic valve which is condition responsive to thereby insure safety of operation at any time that freeze-up or crystallization is imminent.

Combination absorption and steam turbine driven dentrifugztl system Referring now to the performance diagram shown in FIGURE 2, the operation of a combined absorption and steam turbine driven centrifugal compressor system will now be described. The lower portion of FIGURE 2 shows the percent capacity of the system over a range from to 100% of the load plotted against the tons of refrigeration produced (indicated on the left-hand ordinate) and the pounds of steam utilized (indicated on the right-hand ordinate).

One particular problem relates to the operation of the combination centrifugal and lithium bromide absorption system. While the absorption machines can operate satisfactorily throughout a complete range of capacity varying all the way from absorption system load to something in the order of 10%, the steam turbine driven centrifugal compressor system has certain operating limitations. Dropping from full load to partial load on the steam turbine system, one method of reducing the capacity is by gradual positioning of prerotation vanes in the compressor into a more throttled position. At a certain capacity reduction on the steam turbine driven refrigeration system, a point is reached where the system is unstable and refrigerant flow handled by the compressor would oscillate badly. Operation at this condition or below would not be tolerable.

At the point on FIGURE 2 designated at I, the centrifugal system is producing approximately 1150 tons of refrigeration at 100% load and using approximately 30,600 pounds of steam per hour. This same rate of steam consumption isutilized, after passing through the turbine to produce heating for the generators in the LiBr absorption system; and at 100% load, this exhaust steam will produce approximately 1510 tons of refrigeration for two absorption machines arranged in parallel.

Capacity modulation in the range from 100% load to approximately 44% load is controlled by varying the capacity of the centrifugal system by any number of well known methods. A common capacity control mechanism for centrifugal compressors, as mentioned briefly above, is what is referred to as a prerotation v-ane mechanism which comprises a plurality of radial vanes positioned on the suction side of the compressor wheel. These vanes are movable about their radial axes and are adapted to both throttle the flow of refrigerant and reduce the effectiveness of the compressor by varying the angle at which the gas is introduced into the compressor wheel. For purposes of illustration, the system to be described will be considered as having a prerotation vane mechanism (PRV) for capacity control.

Capacity within the aforementioned range is controlled by the PRV unit in response to some variable, preferably the temperature of chilled water being forwarded to the load. This also has the effect of reducing the rate at which the exhaust steam is supplied to the LiBr absorption units. At approximately 44% load, steam consumption is approximately 13,500 pounds per hour, indicated at point II; and this rate will produce approximately 665 tons of absorption capacity and 505 tons turbine capacity for a total of 1170 tons. This area of operation from 100% down to 44% of maximum load is within the stable operating zone of the centrifugal system. Below this figure, of approximately 505 tons of centrifugal capacity, unstable operation would be encountered. A further drop in total load, therefore, must be handled in such a way that the centrifugal capacity is not allowed to drop. As shown in FIGURE 2, from 44% to 29% of full load, the centrifugal unit is permitted to put out about 505 tons of capacity, and the reduction in total tons is met by reducing the absorption system tonnage. However, this raises a problem which is One of the reasons for the use of the refrigerant dump valve. It is not possible for the lithium bromide absorption system to utilize the amount of steam put out by the centrifugal system unless some unusual operation is developed. An important aspect of the invention thus concerns the use of a refrigerant dump valve, so that the lithium bromide absorption system will continue to use the amount of steam forwarded from the turbine while the capacity of the lithium bromide system is reduced. Consequently, from a condition of 44% total load to a condition of 29% total load, the amount of refrigerant dumped increases on a gradual basis. Below 29% load, it is found that it is more economical to shut off the centrifugal system completely and run the absorption machines alone, either one or both as required. The triangular area defined within the dotted lines in FIG- URE 2 represents the tons of refrigeration capacity dumped by diluting the solution. A steam economy curve shown in the upper part of FIGURE 2 can be constructed. Over the range from 100% load (I') to 44% load (11), the combined systems are using about twelve pounds of steam per hour per ton of useful refrigeration. Between 44% load and 29% load (111'), the dump valve is permitted to operate to balance the two systems. The steam consumption increases gradually to break-even point encountered at 29% load where steam consumption is then that of the absorption systems, namely 17.5 pounds steam per hour per ton. This explains, the economy of operation from the combination of turbo systems with absorption systems. It should be recognized that without the device, it would be necessary to go to the absorption systems by themselves at 44% load, wherein the steam consumption would jump immediately to approximately l7 /2 pounds steam per hour per ton. On many systems there is a further reason for not wanting to go to the absorption systems so soon. Sometimes the absorption systems do not have sufiicient capacity to take care of the load, and it is necessary to delay the change to the absorption systems by themselves until a load condition well below the stable operation of the turbo system is reached.

The arrangement for the combined absorption and steam turbine driven centrifugal system, and the controls therefor, are shown schematically in FIGURE 3. Where applicable, the same reference characters used in FIG- URE 1 will be applied to the components in FIGURE 3. The system to be described may be generally characterized as one which employs the steam turbine driven centrifugal system in series with two lithium bromide absorption machines which are connected in parallel with each other.

Chilled water returning from the load 20 is directed first to the chilled water coils in the evaporators of both absorption machine M and absorption machine N through pump 21 and line 22 which is connected to two parallel supply lines 23, 23' for the chilled water coils J and J. The chilled water leaves the absorption machines M and N through lines 23, and 28 respectively, both of which are connected with line 32 which leads to the chiller P in the centrifugal refrigeration system V. The chilled water is further cooled in the chiller P and leaves through line 36 to be returned to the load 20.

Cooling water for both the absorption machines and the condenser Q in centrifugal system V is supplied from a cooling tower L which includes a first section 40 supplying the absorption machines, and a second section 42 supplying the condenser Q. For the absorption machines, the cooling water is directed from cooling tower section 40 to a pump 44 through line 46 where it flows through line 48 to parallel lines 50 and 50 supplying the absorber tube bundle (not shown) in both of the absorption machines. After passing through the absorbers, the cooling water is then forwarded to the respective condensers D and D through lines 52 and 52. After passing through the condenser, the water is conducted through lines 54 and 54 to return line 56 leading to the cooling tower. A relatively constant temperature for the cooling water supplied to the absorption machine is maintained by means of a temperature responsive three-way valve 58 and a bypass line 60. If the cooling water drops below a predetermined temperature as sensed by capillary bulb 62, a portion of the returning cooling water in line 56 is bypassed around the cooling tower through line 60. Cooling water for the condenser Q in the centrifugal system is supplied by pump 64, supply line 66, and return line 68.

The compressor R for the centrifiigal system is driven by a steam turbine S which is provided with a speed control governor 69 and supplied from a source of high pressure steam through lines 70 and 72. After passing through the turbine, the steam is forwarded through line 74, which preferably includes an override to prevent the steam pressure from rising above a predetermined maximum, and then through parallel lines 76 and 76 to the heat exchangers in the generators C, C. Condensate from the generator is withdrawn through lines 78, 78 respectively.

It will be understood that the centrifugal machine is representative of many types. In the one illustrated, refrigerant gas is compressed in the compressor R and forwarded through hot gas line 80 to the condenser Q. The liquid refrigerant is withdrawn through line 82 to a receiver and intercooler 84. A portion of liquid vapor refrigerant from said intercooler is supplied back to the compressor through line 86. The remaining portion of the liquid refrigerant is supplied to the evaporator or cooler P through line 88 where it comes in contact with a heat exchanger 96 through which chilled water is flowing from the absorption machines. Cold suction gas is returned to the compressor inlet through line 92.

Control of the system is maintained primarily by a temperature responsive element T which senses the chilled water being returned to the load through line 36. A typical pneumatic control for such a system is one manufactured by Johnson Service Corporation, Milwaukee, Wis. and designated as T900. The control unit produces a pneumatic output pressure which is supplied both to the PRV control for compressor R and via lines 16, 16' to valves 14, 14' in the refrigerant dump valve systems in absorption units M, N.

The chilled water flows through the two lithium bromide machines M and N in parallel and then through the centrifugal system V. Although the values for temperature and load requirements are not critical, representative values will help to illustrate the operation of the system. A control temperature of 39 F. is maintained by the use of temperature control unit T If the temperature of the leaving chilled water should start to fall below 39 F., and indicate that there has been a decrease in the cooling load, the pneumatic signal supplied to the PRV will adjust the prerotation vanes to reduce compressor performance. As a result, less steam goes to the absorption machines and their performance is similarly reduced. When the prerotation vanes in the compressor reach a predetermined minimum position below which unstable compressor operation will commence, they cannot be throttled any further because of a limit mechanism which is previously set to establish this minimum PRV position. This would occur, as indicated with the above reference to FIGURE 2 at a load of approximately 44%. As the temperature sensed by control unit T drops still further, the control air pressure will begin to open valves 14, 14' in the refrigerant bleed or dilution system K, K. These valves will withdraw refrigerant from the discharge side of the refrigerant pumps to the suction side of the absorbent pumps and, thus, begin diluting the lithium bromide solution in the absorber. This will have the effect of immediately reducing the refrigeration capacity of the absorption machines, but will have no effect on their capacity as steam condensers for the steam supplied to the generator. As the temperature of the chilled water returning from the load approaches approximately 43 F., a load condition occurs at which it is more economical to shut down the centrifugal system entirely and continue to run with the absorption machines alone. The point at which this occurs is approximately 29% of the maxim-um load. At this time, the valve 102 in steam supply line 72 is closed and valve 104 between the main steam supply and the absorption machines is opened to permit steam to flow through reducing valve 106 to the control valves 18, 18'.

When the turbo system is shut down, capacity is controlled by varying the fiow of steam to the generators C, C by means of temperature sensing elements T T responsive to the temperature of chilled Water leaving the absorption machines for actuating control valves 18, 18'. It can, therefore, be seen that the dump valve may be used to advantage on a turbo topping system to permit operation of the steam turbine driven refrigeration system over a greater range of operation with the steam turbine operation limited only in the interests of economy. At the point where it ,is more economical to operate lithium bromide systems alone, from the standpoint of steam consumption, then the turbo system is shut down. At the point where unstable operation of the turbo system would normally be encountered, and before the load is reduced to the point where absorption systems alone would operate, the refrigerant bleed valve is used to balance out the systems.

One other feature of the dump valve with reference to turbo topped applications should be mentioned. This is the very important point of possible safety shutdown of the lithium bromide absorption systems, which can be avoided, in many instances, by using the dump valve. For example, on an ordinary lithium bromide absorption system Without the dump valve, safety controls might require that the absorption system be shut down, as might be the case with low refrigerant temperature indicated. With the dump valve in the system, the low refrigerant temperature can signal for the dump valve to open, rather than for the absorption systems to shut down. This permits the steam turbo system to continue operation with the absorption system permitted to operate and serve as a steam condenser for the steam turbine system.

By using various known control elements, such as temperature or fluid flow responsive switches, motor interlock switches, etc., a safety control system may be incorporated into the absorption machines which will automatically activate the dilution cycle according to a predetermined sequence. A typical control sequence is illustrated in the table below.

with a certain specific embodiment thereof, it is to be understood that this is by way of illustration and not by way of limitation; and the scope of this invention is defined solely by the appended claims which should be construed as broadly as the prior art will permit.

What is claimed is:

l. In a method for operating an absorption refrigeration machine, said machine comprising an evaporator, an absorber, a generator, and a condenser connected to provide a closed circuit refrigeration system, means for supplying a heating medium to said generator, a solution circuit including spray means in said absorber and means for circulating absorbent solution to said spray means, and a refrigerant circuit including means for circulating refrigerant to and from said evaporator, the steps including: maintaining a supply of heating medium to said generator and a supply of absorbent solution to said absorber during normal operation throughout the entire capacity range of said system; continuously monitoring the operation of said machine to determine the presence of an abnormal condition which is indicative of imminent solution crystallization or evaporator freeze-up; withdrawing refrigerant from said refrigerant circuit and supplying it to said solution circuit directly upstream from the absorber spray means such that the refrigerant mixes with the absorbent solution just prior to being directed into said spray means.

2. A refrigeration system comprising an absorption refrigeration machine including an evaporator, an absorber, a generator, and a condenser in combination with a steam turbine driven refrigeration unit including a steam turbine, a compressor, a condenser, and a chiller; means for circulating a liquid to be chilled through said evaporator and through said chiller in series; means for supplying high pressure steam [first to said turbine and then to said generator; means for varying the capacity of said compressor in response to varying load conditions down to a level where compressor operation is unstable; means CONTROL SEQUENCE These Results Follow- When Those Conditions Occur- Steam Rel'rig. Chilled Cooling Dilution Flow 1 Solution Pump Pump Water Water Bleed Flow Flow Valve 1 Steam Flow Stops Ofi On 2 Solution Pump Stops From "Stop Button 3 Solution Pump Stops From Overload 4 Refrigerant Pump Steps From Overload, Chilled Water Pump Running.

5 Refrigerant Pump Stops From Overload, Chilled Water Pump Not Running.

6-.." Chilled Water Flow Stops 7 Cooling Water Flow Stops..-

Low Refrigerant Temperature Dilution Cycle 0n Off Off Dilution Cycle Off Dilution Cycle On On 0 On 1 stoppage of chilled water or cooling water flow shuts ofi steam.

- Dilution cycle controlled by timing relay which allows pump to run for predetermined time (about 7 minutes).

Referring to the last column in the table above, it Will be apparent that the dilution system is actuated when .any of the following situations occur:

(a) Solution pump stops from stop button (normal :shutdown).

(b) Refrigerant pump stops from overloadchilled Water pump running.

(c) Refrigerant pump stops from overloadchilled water pump not running.

(d) Chilled water flow stops.

(e) Cooling Water flow stops.

(f) Low refrigerant temperature.

Conditions (a) to (e) inclusive are accompanied by steam flow shut-off; but under low refrigerant temperature conditions, the steam flow is continued while the capacity is reduced.

While this invention has been described in connection for diluting absorbent solution supplied to said absorber in controlled quantities in response to further decreases in cooling requirements below said unstable level; and means for discontinuing operation of said turbine driven refrigeration unit at cooling load level within the maximum capacity of the absorption unit.

3. In a method for operating an absorption refrigeration machine, said machine comprising an evaporator, an absorber, a generator, and a condenser connected to provide a closed circuit refrigeration system, means for supplying steam to said generator, a solution circuit including means for circulating absorbent solution to said absorber and a refrigerant circuit including means for circulating refrigerant to and from said evaporator, the steps including: regulating the capacity of said absorption refrigeration machine by withdrawing a regulated stream of refrigerant from said refrigerant circuit and supplying said refrigerant to said solution circuit to dilute said solution while continuing to supply steam to said generator, whereby said generator continues to function as a condensing unit for the steam supplied thereto while the capacity is being reduced.

4. An absorption refrigeration machine comprising an evaporator, an absorber, a generator, and a condenser connected to provide a closed circuit refrigeration system, means for supplying a heating medium to said generator, a solution circuit including spray means in said absorber and means for circulating absorbent solution 'to said spray means, a refrigerant circuit including means for circulating refrigerant to and from said evaporator, means for circulating a liquid to be chilled through said evaporator; means for supplying cooling water for said absorber and said condenser; means for transferring refrigerant in said refrigerant circuit to said solution circuit, said last-named means including a conduit connecting said refrigerant circuit to said solution circuit at a point just upstream from said solution spray means, valve means in said conduit for controlling flow between said refrigerant circuit and said solution circuit, valve actuating means for controlling the operation of said valve, and means for continuously monitoring the operation of said absorption machine to determine the presence of an abnormal condition which is indicative of imminent solution crystallization or evaporator freeze-up to fully open said valve and permit maximum flow of refrigerant to said absorber, said abnormal conditions including stoppage of refrigerant flow in said refrigerant circuit, stoppage of flow of said liquid to be chilled, stoppage of flow of said cooling water supplied to said absorber or condenser, or when the temperature of said refrigerant or said liquid to be chilled falls below a predetermined level.

References Cited by the Examiner UNITED STATES PATENTS 2,722,806 11/1955 Leonard 62-489 X 2,855,765 10/1958 Smith et al. 62-494 X 2,983,117 5/1961 Edberg et al. 62476 References Cited by the Applicant UNITED STATES PATENTS 2,760,350 8/ 195 6- Bourne.

FOREIGN PATENTS 65 8,914 10/ 1951 Great Britain.

LLOYD L. KING, Primary Examiner.

Claims (1)

1. IN A METHOD FOR OPERATING AN ABSORPTION REFRIGERATION MACHINE, SAID MACHINE COMPRISING AN EVAPORATOR, AN ABSORBER, A GENERATOR, AND A CONDENSER CONNECTED TO PROVIDE A CLOSED CIRCUIT REFRIGERATION SYSTEM, MEANS FOR SUPPLYING A HEATING MEDIUM TO SAID GENERATOR, A SOLUTION CIRCUIT INCLUDING SPRAY MEANS IN SAID ABSORBER AND MEANS FOR CIRCULATING ABSORBENT SOLUTION TO SAID SPRAY MEANS, AND A REFRIGERANT CIRCUIT INCLUDING MEANS FOR CIRCULATING REFRIGERANT TO AND FROM SAID EVAPORATOR, THE STEPS INCLUIDING: MAINTAINING A SUPPLY OF HEATING MEDIUM TO SAID GENERATOR AND A SUPPLY OF ABSORBENT SOLUTION TO SAID ABSORBER DURING NORMAL OPERATION THROUGHOUT THE ENTIRE CAPACITY RANGE OF SAID SYSTEM; CONTINUOUSLY MONITORING THE OPERATION OF SAID MACHINE TO DETERMINE THE PRESENCE OF AN ABNORMAL CONDITION WHICH IS INDICATIVE OF IMMINENT SOLUTION CRYSTALLIZATION OR EVAPORATOR CIRCUIT AND DRAWING REFRIGERANT FROM SAID REFRIGERANT CIRCUIT AND SUPPLYING IT TO SAID SOLUTION CIRCUIT DIRECTLY UPSTEAM FROM THE ABSORBER SPRAY MEANS SUCH THAT THE REFRIGERANT MIXES WITH THE ABSORBENT SOLUTION JUST PRIOR TO BEING DIRECTED INTO SAID SPRAY MEANS.

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