US2047827A

US2047827A - Control mechanism

Info

Publication number: US2047827A
Application number: US716982A
Authority: US
Inventors: John F Lamb
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1934-03-23
Filing date: 1934-03-23
Publication date: 1936-07-14
Anticipated expiration: 1953-07-14

Description

CONTROL MECHANISM Filed March 23, 1934 2 Sheets-Sheet .l

WITNE SEQ 46' 1 INVENTOR wfifi FIG. 3 I JOHN F. LHM.

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' EL mmfi July 14, 1936. J, LAMB 2,047,827

CONTROL MECHANISM Filed March 23, 1934 2 Sheets-Sheet 2 WITNESSES; I FINVLENTOR OHN HMB BY m ATToRmZY UNITED STATES r 2,047,827 PATENT OFFICE common MECHANISM John F. Lamb, Pittsburgh, Pa., assiguor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 23, 1934, Serial No. 716,982

18 Claims.

My invention relates to refrigerating apparatus, more particularly to refrigerating apparatus embodying a plurality of evaporators connected to a common motor-compressor unit and whose combined rated capacity is greater than the rated capacity of the motor-compressor unit.

Such apparatus may be employed, for example, in providing comfort cooling for a house, where unit or room coolers are provided in several rooms of a house. Since it is not necessary that all of the room coolers operate at one time, and

in order to minimize cost of installation, a common refrigerating unit, that is, compressor, motor and condenser, may be used which is of less rated capacity than the combined rated capacity of the room coolers. For example, each room cooler and the refrigerating unit may have a rated capacity of 12,000 B. t. n.s an hour; that is, each room cooler may provide 12,000 B. t. u.s of

refrigeration an hour when operating against severe conditions, as on a hot and humid day, and the refrigerating unit may provide the liquid refrigerant necessary for such operation of one room cooler.

When the refrigerating load is less than full load, as on days which are not as hot and humid as that for which the room coolers are designed,-

less refrigeration is required of each room cooler, and satisfactory operation may be obtained by operating several room coolers in connection with the one refrigerating unit. It is desirable, therefore, to provide an arrangement which permits such operation. However, if more than one room cooler is operated with the one refrigerating unit when the refrigerating load is near full load, as

on a; hot and humid day, a higher suction pressure will be obtained thereby overloading the motor-compressor unit, particularly the motor. While the pressure diiierence against which the motor compressor unit operates is less, the pounds of refrigerant per unit volume is much greater, and the resultant load is greatly increased. It is desirable, in such case, tolimit the refrigerating action of the room coolers or evaporators as a whole, in order to avoid overloading of the compressor.

An object of my invention is to provide mechanism for preventing overloading of the motorcompressor unit.

A further object is. to provide control mechanism for regulating the refrigerating action of the evaporators to prevent overloading of the motor compressor unit.

A particular object is to provide control mechanism which permits a number of evaporators of greater rated'capacity than the motor compressor unit to operate at one time if the latter is not overloaded, but to restrict the refrigerating' action of the evaporators when the motor compressor unit tends to become overloaded.

"fllhey may be used wherever cooling is required,

4 of Milton Kalischer, Serial No. 698,205, filed A further object is toprovide a control mechanism which limits the number of evaporators in operation to an extent such as to obtain sufficient refrigerating action of the evaporators remaining in operation.

Another object is to provide a control mechanism which limits the number of evaporators in operation to an extent such that the evaporator remaining in operation may operate at a sumciently low temperature.

In accordance with my invention, I provide a control mechanism for restricting or regulating the total refrigeration provided by the evaporator, as by limiting the supply of refrigerant thereto, in response to a load condition of the motor compressor unit, such as the current supplied to the motor or the suction pressure of the compressor. The total supply of liquid refrigerant to the evaporators as a group may be regulated,

in which case each evaporator receives a restricted or regulated quantity of refrigerant, or

the control mechanism may cut oil the supply of Fig. 1 is a diagrammatic view of one embodi- Q ment of my invention; and,

Figs. 2 to 5 are similar views of other embodiments.

Referring to Fig. 1, I show a plurality of evaporators l0 and I l, shown as coils, connected to a common refrigerating unit 12. The evaporators may beof any suitable construction now or hereafter known in theart, and of either the dry expansion or flooded type, or any other type.

for example, they may be the evaporator ele ments of room coolers or unit air conditioners such as disclosed and claimed in the application November 15, 1933. They are shown diagrammatically only since the present invention resides in the combination defined in the claims rather than in any specific form of evaporator.

The refrigerating unit I! includes a compressor l3 driven by a motor ll (constituting therewith a motor compressor unit), a condenser l5 and such other apparatus as is usually incorporated therewith, such as cooling fluid circulating means (not shown) for the condenser and. a liquid receiver (not shown). The outlet ends of the evaporators are connected by a conduit It to the inlet 11 of the compressor 13, and the outlet of the compressor is connected through a conduit l8 with the condenser IS. The discharge end of the condenser is connected to a liquid refrigerant supply conduit I9, having a valve 20 therein, which conduit is in turn connected to the evaporators I 0 and I I through branch conduits 2I and 22 having valves 23 and 24, therein, respectively. Each of the evaporators is provided with an expansion valve 25 of any suitable construction. By expansion valve, I mean, in this case, any suitable flow control device between the high pressure and the low pressure side of the system, such as a thermostatic expansion valve, float valve or fixed flow resistance passage, or any other device serving the same general purpose;

The valves 23 and 24 are used to control the operation of the evaporators I 0 and II, respectively, preferably automatically in accordance with the respective refrigerating demands. may be operated, for example, by solenoids 26 and 2! controlled by

thermostats

28 and 29. The

thermostats

28 and 29 are responsive to the refrigeration demands of the respective evaporators; for example, where the evaporators are embodied in room coolers, the thermostats may be responsive to the temperature of the air in the respective enclosures which are cooled by the room coolers. Each solenoid is arranged to be energized and to open its associated valve when the thermostat closes its contacts in response to increase in temperature, and a spring 30 biases the valve to closed position when the solenoid is not energized. The motor I4 is supplied with electrical energy through conductors 3| which are connected through a switch 32 to line conductors 33. The

solenoids

26 and 21 may also derive their electrical energy through the conductors 3I.

The valve 20, constituting the novel part of the apparatus so far described, is adapted to be actuated in opening direction by a solenoid 34 and to be closed by a spring 35 when the solenoid is not energized. The energization of the solenoid is controlled by the suction pressure of the refrigerating apparatus, which pressure is communicated from the conduit I6 through a tube 36 to a bellows 31. The latter controls contacts 38 in a circuit 39 in which the solenoid 34 is connected. The arrangement is such that, when the pressure is below a predetermined maximum value, the contacts 38 are closed and the solenoid 34 is energized to open the valve 20 and, when the pressure is above said predetermined maximum value, the contacts 38 are open to deenergize the solenoid 34 and cause the valve 20 to be closed.

The operation of the above described apparatus is as follows: The refrigerating unit operates in the conventional manner of such apparatus, refrigerant being withdrawn from one or both of the evaporators through the conduit I6 into the compressor wherein it is compressed. The compressed refrigerant is conveyed through the conduit I8 to the condenser I5 wherein it is condensed and delivered to the conduit I9 to be resupplied to one or both of the evaporators. The

thermostats

28 and 29 control the valves 23 and 24, respectively, in accordance with the refrigeration demands, all as is well understood in the art. Assuming the refrigeration load not to be too great, refrigerant will be supplied to either one or both of the evaporators in accordance with their respective requirements, the refrigerating unit operating to supply refrigerant in accordance with such demands. In such case, the suction pressure will be maintained by the compressor at a relatively low value, so that the contacts 38 will be closed and the solenoid 34 energized to open They the valve 20 as long as the refrigerating unit is operating.

When the refrigeration load is relatively great, however, as on a relatively hot and humid day, the increased amount of heat supplied to the refrigerant in the evaporators when both are operating will tend to increase the suction pressure to such an extent as to overload the motor compressor unit. In accordance with my invention, I avoid such a high suction pressure by controlling the supply ofliquid refrigerant to the evaporators. This may be done in any one of a number of ways; in the embodiment in Fig. 1 it is accomplished by intermittently shutting off the common supply of refrigerant to the several evaporators.

As the suction pressure exceeds a predetermined maximum value, the bellows 31 operates in the manner described above to shut off the supply of liquid refrigerant to the evaporator by closing the valve 20. Themotor-compressor unit continues to operate, serving first to evaporate the liquid refrigerant within the evaporators at the moment that the valve 20 is closed and then to lower the suction pressure. When the suction pressure has been reduced to said predetermined maximum value, or to a slightly lower value, the valve 20 is reopened to admit liquid refrigerant to the evaporators. As soon as the pressure again builds up to said predetermined maximum value, the valve 20 is again closed and the cycle of operation just described is repeated.

While the load on the motor-compressor unit may be increased from the moment that the valve 20 is closed until all of the liquid refrigerant is vaporized, this increased load is only temporary and may be compensated for by adjusting the bellows 31 to open the contacts 38 at a suinciently low suction pressure.

It will thus be seen that the average rate of supply of liquid refrigerant to the evaporators over a period of time is limited and avoids such an overloading of the motor-compressor unit as would cause excessive heating of the motor.

The portion of the time that the valve 20 is open varies with the refrigerating demand, becoming greater as the refrigerating demand decreases until, when thecombined refrigerating demand on the several evaporators is within the capacity of the refrigerating unit, the valve 20 will be open continuously.

Whenever the total number of evaporators in operation have a capacity not greater than the capacity of the refrigerating unit, the valve 20 will be open continuously, even though the evaporators in operation arecarrying any load up to their capacity, since the refrigerating unit will be able to provide a sufliciently low suction pressure. In the present case, each evaporator has a capacity equal to that of the refrigerating unit, so that any one evaporator may be operated with the valve 20 continuously open.

It will be apparent that the control mechanism may be arranged to close the valves 23 and 24 and the corresponding valves of all additional evaporators, instead of the valve 20.

In Fig. 2, I show a second embodiment of my invention in which the bellows 31a is directly connected to the valve 20a in the liquid refrigerant supply conduit I9. moved gradually or incrementally in response to variation in suction pressure throughout a slight range of pressure. The refrigerating apparatus to which this control is applied is identical with that shown in Fig. 1.

In this case, the valve 20a is (ill In the operation of this embodiment, as the combined refrigeration load on the evaporators Ill and I I increases and effects a higher suction pressure, such as tends to overload the motor compressoor unit, the bellows 31a begins to move the valve a in closing direction torestrlct the supply of liquid refrigerant to the evaporators and limit further increase in the suction pressure. Each evaporator, therefore, receives refrigerant continuously but at a restricted rate of supply. A constant value of the suction pressure is obtained in this arrangement, while the degree of superheat will be relatively high. When only one evaporator is in operation, the suction pressure will be sufliciently low to maintain the valve 20a in full open position, provided said one evaporator is not overloaded.

In Fig. 3, I show a third embodiment in which the refrigerating action is controlled by varying the rate of circulation of air over the evaporators I0 and H rather than by controlling the supply of refrigerant. Fans 40 and 4|, driven by electric motors 42 and 43, circulate the air to be cooled in contact with the evaporators I0 and II respectively. The motors 42 and 43 are connected in parallel to

conductors

44 and 45, in the latter of which there is interposed a variable resistance 46. The latter is controlled by a bellows 31b in response to the suction pressure in the conduit I6,

communicated through the tube 36, similarly to.

the other-embodiinentse In the operation of the embodiment shown in Fig. 3, as the refrigeration load on the evaporators tends to increase and to increase the suction pressure, the bellows 31b operates the variable resistance 46 to decrease the current supplied to the motors 42 and 43, thereby decreasing the speed of the fans 40 and 4|. Since a smaller'quantity of air is circulated over the evaporators, the re-. frigeration load on the evaporators is reduced.

Further increase in suction pressure is thereby prevented. With this arrangement, as the total refrigerating demand on the evaporators in operation becomes less, a higher speed of the several fans is provided. When the total demand is within the capacity of the refrigerating unit, the fans will operate at full speed.

If only one evaporator is in operation and carrying any refrigerating load within the capacity of the refrigerating unit, the fans will operate at full speed.

In Fig. 4, I show evaporators III, II and II, similar to theevaporators Iland II of the other embodiments, and connected .to the common refrigerating unit I2, The several evaporators are controlled by

thermostats

28, 29 and 29' as in the other embodiments. In this embodiment, the

control mechanism is arranged to successively shut off supply of refrigerant to the evaporators as the suction pressure increases.

The bellows 31c is arranged to control contacts 41 in a circuit 48 extending through the thermostat 29 and the solenoid 21 of the evaporator II, and similarly to control contacts .49 in a circuit 50 extending through the thermostat 28 and the solenoid 26 of the evaporator ID. The thermostat 29' and the solenoid 21' of theevaporator I I' are connected in a circuit 5| which is directly connected to the conductors 3| and has no contacts controlled by the bellows 31c.

The operation of this embodiment is as follows:

If the refrigerating demand on all of the evaporators is within the .capacity of the refrigerating unit I2, a sufficiently low suction pressure is obtained and the bellows 31c closes the contacts 41 to shut off supply of refrigerant and. All of the thermostats are operable, therefore, to effect operation of their associated evaporators in response to the refrigerating demand. As the refrigerating demand tends to exceed the capacity of the refrigerating unit I2, the suction pressure increases and the bellows 31c operates first, in response to a first predetermined maximum pressure, to open the contacts 49, thereby opening the circuit 50 to deenergize the solenoid 26 and shut off the supply of refrigerant to the evaporator III. The refrigerating apparatus continues in operation supplying refrigerant only to the evaporators II and II'. If the refrigerating demand becomes still greater, the

suction pressure increases still further and, in response to a second predetermined maximum pressure slightly higher than the first, the bellows 31c opens the contacts "to shut off the supply of refrigerant to the evaporator II. The apparatus then continues in operation supplying refrigerant only to the evaporator II, which is first in the order of preference and always receives refrigerant whenever its thermostat calls for cooling. It will thus be apparent that by this control mechanism, liquid refrigerant is supplied to as many evaporators as the refrigerating unit l2 has capacity to supply under the existing refrigerating demand, the refrigerating demand on the remaining evaporators being not satisfied.

When the thermostat of any evaporator in operation is satisfied and shuts off the supply of refrigerant to its evaporator, the control mechanism automatically operates to supply the liquid refrigerant thus made available to the next evaporator in order of preference. For example, assume all thermostats to be calling for cooling, the evaporator II' to be in operation, and the thermostat 29 to open its contacts to shut off the supply of refrigerant to the evaporator Il'. Due to the termination of the operation of the evaporator II', the suction pressure decreases and the bellows 31c closes the contacts 41, thererator II, which is ,next in order of preference. The refrigerating apparatus then continues in operation supplying refrigerant to the evaporator II. Likewise if the thermostats of both evaporators II and I2 are satisfied, the suction pressure decreases until the bellows 31c closes contacts 49 to admit liquid refrigerant to the evaporator l0.

Similarly, assuming both evaporators II and II to be in operation and one of them to discontinue operation, the suction pressure begins to decrease until the contacts 49 are closed to admit the available liquid refrigerant to the evaporator I0.- It will be apparent that any number of evaporators may be provided in such an arrangement, and the control mechanism arranged to the several evaporators successively.

With this arrangement, the refrigerating load may be'such that the quantity of liquid refrigerant available is more than sufficient to supply, for example, one evaporator and insuflicient to sup ply two evaporators. In this case, the supply of refrigerant to the second evaporator will be intermittent. For example, assuming thermostats 29 and 29' both to be calling for cooling: and

both evaporators receiving refrigerant at the moment. The suction pressure slowly rises due to the fact that more refrigerant is being evapo-- rated in the two evaporators II and II" than can be withdrawn by the refrigerating unit at a sufficiently rapid rate to maintain the desired sucby effecting admission of refrigerant to the evapotion pressure. As the suction pressure exceeds said second predetermined maximum value, the contacts 41 are opened by the bellows 31c and the admission of liquid refrigerant to the evaporator H is shut off. 'I'he'apparatus then operates supplying refrigerant only to the evaporator II. As the amount of refrigerant evaporated in the evaporator II is slightly below the capacity of the refrigerating unit, the suction pressure slowly decreases until the contacts 41 are again closed to admit refrigerant to the evaporator ll. Under such conditions, therefore, the refrigerating demand of the preferred evaporator or evaporators is fully satisfied, while the refrigerating demand of the evaporator next in order of preference is only partially satisfied.

In Fig. 5 I show a fifth embodiment of my invention in which the supply of refrigerant to the several evaporators l0, H and II is controlled by contacts 41aand 49a in a manner similar to the embodiments of Fig. 4 but in response to the current used by the motor M instead of the suction pressure. The contacts 41a and 49a are actuated by a solenoid 52 connected in one of the conductors 3| extending to the motor l4. As the load on the motor compressor tends to exceed its capacity, the solenoid 52 operates first to open the contacts 49a in the circuit 50 in response to increase in the current flowing through the motor l4 above a first predetermined maximum value, and then to open the contacts 41a in the circuit 48 in response to a second predetermined maximum value of the current of the motor M which is slightly greater than the first predetermined maximum value. The value of the current will vary in a manner very similar to the variation in suction pressure inasmuch as increase in suction pressure supplies a greater quantity of refrigerant to the compressor and thus increases the load on the motor compressor unit. The value of the current supplied to the motor may thus be used as a measure of the load on the motor compressor unit instead of the suction pressure. The construction and operation of this embodiment is in other respects similar to that of the embodiment shown in Fig. 4, the control being effected in response to value of current rather than pressure, so that further description is not necessary.

It is to be understood that the thermostats for controlling individual evaporators are shown and described only by way of example, and that either more or less control mechanism may be used in connection with my novel control mechanism which regulates or controls the supply of liquid refrigerant in accordance with a load condition of a refrigerating unit. For example, my novel control mechanism may well be combined with the control mechanism'described and claimed in the application of Lewis R. Smith, Serial No. 700,319, filed November 29, 1933, and assigned to the assignee of the present invention. On the other hand, manual control of the individual evaporators may'be substituted for thermostatic control, or individual control of the evaporators other than in response to load condition may be omitted entirely. The present invention might also be used in connection with a bank of coils arranged in parallel for cooling a single stream of air, the coils being arranged either in parallel or in series,with respect to the flow of air.

From the above description it will be seen that I have provided control mechanism whereby any combination of evaporators within the capacity of the refrigerating unit may be supplied with liquid refrigerant and whereby the total refrigerating action of the evaporators is controlled so as to limit the load on the motor compressor unit to the capacity thereof, thereby preventing overloading.

An important advantage of the present invention, in connection with air cooling for comfort, is that the evaporators operate at sufficiently low temperature to effect dehumidification of air;

The temperature of the refrigerant within the evaporators is a function of its pressure, and since the latter is controlled to a low value, the temperature is also maintained at a desirably low value.

While Ihave shown my invention in five forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications, without departing from the spirit thereof, and I desire,.

evaporators in response to a load condition of said motor compressor unit, the suction pressure being'maintained within a predetermined maximum limit in consequence of said restriction of the evaporation of refrigerant, whereby the load on the motor compressor unit is maintained within a predetermined maximum value.

2. In refrigerating apparatus, the combination of a plurality of evaporator elements, a motor compressor unit common to said evaporator elements for withdrawing vaporous refrigerant therefrom and for compressing the same, means for condensing the compressed refrigerant, means for supplying the condensed refrigerant to said evaporator elements, and means for restricting the total evaporation of liquid refrigerant in said evaporators in response to the suction pressure of said motor compressor unit, the suction pressure being maintained within a predetermined maximum limit in consequence of said restriction of the evaporation of refrigerant, whereby the load on the motor compressor unit is maintained within a predetermined maximum value.

3. In refrigerating apparatus, the combination of a plurality of evaporator elements, a motorcompressor unit for withdrawing vaporous refrigerant from said evaporator elements and compressing the same, a condenser for condensing the compressed refrigerant and providing a supply of liquid refrigerant for said evaporator elements, and means responsive to a predetermined maximum load condition of the motorcompressor unit for restricting the supply of liquid refrigerant to said evaporators.

4. In refrigerating apparatus, the combination of a plurality of evaporator elements, a motor-compressor unit for withdrawing vaporous refrigerant from said evaporator elements and compressing the same, a condenser for condensing said compressed refrigerant and providing a common supply of liquid refrigerant for said evaporator elements, and means responsive to a load condition of said motor-compressor unit for controlling said common supply to prevent overloading of said motor-compressor unit.

5. In refrigerating apparatus, the combination of a plurality of evaporator elements, a motorcompressor unit for withdrawing vaporous refrigerant from said evaporator elements and compressing the same, a condenser for condensing said compressed refrigerant and providing a supply of liquid refrigerant for said evaporator elements, and means responsive to a load condition of said motor-compressor unit for shutting off supply of liquid refrigerant to one of said evaporator elements to prevent overloading of said motorcompressor unit.

6. In refrigerating apparatus, the combination of a plurality of evaporator elements, a motorcompressor unit for withdrawing vaporous refrigerant from said evaporator elements and compressing the same, a condenser for condensing said compressed refrigerant and providing a supply of liquid refrigerant for said evaporator elements, and means for shutting off supply of liquid refrigerant-to a number of said evaporator elements successively in response to successive increases in load of said motor compressor unit.

7. In refrigerating apparatus, the combination of a plurality of evaporator elements, a common refrigerating unit for withdrawing vaporous refrigerant from said evaporator elements and for supplying liquid refrigerant thereto, and means responsive to the suction pressure of said refrigerating unit for controlling the supply of refrigerant to said evaporators in such manner as to limit the value of said suction pressure.

8. In refrigerating apparatus, the combination of a plurality of evaporator elements, a compressor connected to said evaporator elements, a condenser for condensing the compressed refrigerant, means for supplying condensed refrigerant to said evaporator elements, and means responsive to the suction pressure of said compressor for controlling the last-mentioned means to limit' said suction pressure.

9. In refrigerating apparatus, the combination of a plurality of evaporator elements, a compressor for withdrawing vaporous refrigerant from said evaporator elements and compressing the same, a motor for driving said compressor, a condenser for condensing said compressed refrigerant and providing a common supply of liquid refrigerant for said evaporator elements, and means responsive to suction pressure of said compressor for controlling said common supply of liquid refrigerant during the operation of the compressor to prevent overloading of said motor.

10. In refrigerating apparatus, the combination of a plurality of evaporator elements, a compressor for withdrawing vaporous refrigerant from said evaporator elements and compressing the same, a condenser for condensing the compressed refrigerant and providing a supply of liquid refrigerant for said evaporator elements, and means responsive to the suction pressure of said compressor for incrementally controlling the supply of liquid refrigerant to the several evaporator elements to limit said suction pressure to a predetermined maximum value. r

11. In refrigerating apparatus, the combination of a plurality of evaporator elements, a compressor for withdrawing vaporous refrigerant from said evaporator elements and compressing 12. In refrigerating apparatus, the combination of a plurality of evaporator elements, a compressor for withdrawing vaporous refrigerant from said evaporator elements and compressing the same, a condenser for condensing said compressed refrigerant and providing a supply of liquid refrigerant for said evaporator elements, and means for shutting off the supply of liquid refrigerant to a number of said evaporator elements successively in response to successive increases in the suction pressure of said compressor.

13. In refrigerating apparatus, the combination of a plurality of evaporator elements, a common refrigerating unit for withdrawing vaporized refrigerant from said evaporator elements and for supplying liquid refrigerant thereto, and means for limiting the maximum value of the suction pressure of said refrigerating unit by controlling the supply of liquid refrigerant to said evaporators in response to said suction pressure.

14. The method of operating refrigerating apparatus including a plurality of evaporator elements and a common refrigerating unit for withdrawing vaporized refrigerant from said evap- .orator elements and for supplying liquid refrigerant thereto, which comprises reducing the supply of liquid refrigerant to the evaporator elements in response to increase in suction pressure of the refrigerating unit.

15. The method of operating refrigerating apparatus including a plurality of evaporator elements and a common refrigerating unit for withdrawing vaporized refrigerant from said evaporator elements and for supplying liquid refrigerant thereto, which comprises reducing the supply of liquid refrigerant to the evaporator elements in response to increase in load on the refrigerating unit.

16. The method of operating refrigerating apparatus including a plurality of evaporator 'elements and a common refrigerating unit for withdrawing vaporized refrigerant from said evaporator elements and for supplying liquid refrigerant thereto, which comprises shutting off the supply of liquid refrigerant to one evaporator element in response to increase in suction pressure of the refrigerating unit.

17. In refrigerating apparatus, the combination of a plurality of evaporator elements, a compressor connected to said evaporator elements, a condenser for condensing the compressed refrigerant, means for supplying the condensed refrigerant to the evaporator elements, and means for reducing the supply of condensed refrigerant to the evaporator elements in response to increase in suction pressure of the compressor.

18. In refrigerating apparatus, the combination