GB2057659A - Method of operating a refrigeration system - Google Patents

Abstract

Method of operating a refrigeration system of the type having a multiple cylinder compressor (10) or multiple compressor including steps of operating the systems under normal operating conditions, sensing operating conditions, partially unloading the compressor when sensed operating conditions indicate that the ambient temperature or high side pressure exceed a predetermined limit, and continuing the operation of the refrigeration system at reduced capacity, until the sensed conditions indicate normal operating load. Unloading is achieved by flow of high pressure refrigerant passing through a by-pass line 22 to the suction side of the compressor under the control of a pressure switch 25 or temperature control. <IMAGE>

Description

SPECIFICATION Method of operating a refrigeration system This invention relates generally to a refrigeration system and to a method of operating a refrigeration system of the type having a multiple cylinder compressor or multiple compressors and more particularly to a method for regulating the operation of a refrigeration system at ambient temperatures which exceed the design temperature of the system.

In operation of a cooling system, when the ambient temperature surrounding the condenser and the evaporator is increased above predetermined limits, the temperature and pressure within the condenser are increased. As the ambient temperature increases above the design temperature range, the high side or condenser pressure may exceed the operating limits, causing the refrigeration system to shut down. However, it is desirable to maintain operation of the refrigeration system and still provide some cooling during the period that the ambient temperature exceeds the design temperature.

In known refrigeration systems having two or more compressors or two or more cylinders within one compressor, the capacity of the compressor has been changed to comply with load variations which occur when the refrigeration system is subjected to changes in ambient temperature. It has been desirable in the prior art systems to reduce the compressor capacity of the refrigeration system when the load of the system drops off and to increase the compressor capacity when the load of the system increases. During unusually hot weather the load or cooling requirements of the refrigeration system increase.

To meet these requirements it has been necessary to use a larger size motor to operate the compressor or to use a multiple compressor system. Variable capacity refrigeration systems having two or more compressors or one compressor with two or more cylinders arranged in parallel are provided with means for loading or unloading the cylinders to change the capacity of the system to correspond to the cooling requirements. In these systems the compressor is unloaded as the cooling requirements drop and the compressor is loaded as the cooling requirements increase. This may be accomplished by bypassing the discharge side of the compressor to the suction side within the compressor, or by blocking the suction side to the compressor cylinder within the compressor, or by shutting off one or more of multiple compressors.In bypass capacity unloader systems, solenoid valves are typically located in bypass lines extending between the discharge lines of each of the compressor cylinders and the compressor suction line. By opening the valve, a portion of compressed gas flows directly from the discharge line to the suction side of the compressor without passing through the condenser or evaporator thereby reducing the amount of refrigerant flow passing through the system and limiting the load on the compressor motor. To increase the capacity of the compressor one or more valves in the bypass lines are closed. These systems are designed to operate within specific ambient temperature ranges.

It is an object of.the present invention to improve refrigeration system operation when the ambient temperature increases above predetermined limits.

Another object of the present invention is to provide control means which function in response to the increase in the ambient temperature or high side pressure above predetermined limits to maintain refrigeration system in operation under conditions of high ambient temperatures.

Still another object of the present invention is to provide simple, dependable, fully automatic means in refrigeration systems to allow the systems to operate under ambient temperatures above a predetermined level.

These and other objects of the present invention are attained by sensing the ambient temperature or the refrigerant high side pressure and unloading the compressor in response to a maximum ambient temperature or high side pressure thereby reducing the refrigerant flow rate through the condor nser and decreasing the pressure in the condenser. This allows the system to operate at a relatively reduced capacity during periods of high ambient temperature.

Figure 1 is a diagrammatic view of a refrigeration system illustrating one embodiment of the invention wherein unloading of the compressor is provided by means responsive to the pressure in the high pressure side of the system.

Figure 2 is a partial diagrammatic view showing an alternate circuit wherein unloading of the refrigeration system is provided by means responsive to ambient temperature.

Figure 3 is a partial electrical schematic showing the connection between a high pressure switch and unloaders for the refrigeration system including a plurality of banks of cylinders in accordance with the invention.

Referring now to the drawings, it can be seen that Figure 1 illustrates a refrigeration system including a multicylinder compressor 10 comprising two cylinders 11 and 12. Cylinders 11 and 12 have extending therefrom discharge lines 13 and 14 respectively which permit flow of compressed gaseous refrigerant from compressor 10 to a condenser 1 5.

It should be noted that the compressor 10 is not limited to two cylinders but may include a plurality of cylinders connected to the condenser 1 5 in the same manner as cylinders 11 and 12. A plurality of individual compressors also can be in place of the cylinders in compressor 1 0.

Hot gaseous refrigerant from compressor 10 is converted to liquid in condenser 1 5 by passing the gaseous refrigerant in heat exchange relation with ambient air or some other cooling medium. The liquid refrigerant then flows through an expansion device 16 to an evaporator 1 7. In the evaporator the liquid refrigerant evaporates absorbing heat from the medium to be cooled. The refrigerant vapors then flow to the compressor through a suction line 1 9. A check valve 1 8 is arranged in the line 14 to allow the flow of refrigerant from cylinder 12 through discharge line 14 into condenser coil 1 5 and prevent the flow of refrigerant from discharge line 1 3 into line 14.An unloading valve 20 is interposed in a bypass line 22 which connects discharge line 14 with the suction side of the compressor. A conventional solenoid valve may be used as an unloading valve 20. Typically, if the solenoid coil of the valve 20 is not energized, the plunger of the valve closes the line, and discharge gas in the discharge line 14 will not be bypassed back to suction side of the compressor Both compressor cylinders will be running and the system will be able to operate at full capacity. The solenoid coil of valve 20 may be selectively energized by an electric circuit 21, shown in Figure 1, which comprises a suitable relay switch 23 and an electric power source 24.

The electrical circuit for energizing the unloading valve may be a portion of the electrical circuit employed for the whole refrigeration system.

Switch 23 is a normally open electrical switch and is connected to a high pressure control such as pressure operated bellows 25. One end of the bellows 25 is coupled by means of linkage to the electrical contact of the switch 23. The opposite end of bellows 25 is connected to discharge line 14 of the compressor by a conduit 26 which monitors the pressure discharge line 14. An increase in pressure in line 14 will cause the bellows 25 to expand, and, upon reaching a predetermined pressure the bellows 25 will close switch 23. The bellows 25 is preset to close the switch 23 at a highest high side pressure allowable for the refrigeration system.

Although the conduit 26 is shown connected to the discharge line 14, for the purposes of this invention it may be connected to any location in the high pressure side of the system which is capable of providing a source of high pressure refrigerant.

In operation when the ambient temperature increases, there is an increase in the cooling load on the system and a corresponding increase in the condenser head pressure. Under conditions, where the ambient temperature exceeds a predetermined limit, the bellows 25 reacts by closing electrical contact of the switch 23 providing a closed electrical circuit for the flow of electricity into the coil of solenoid valve 20. Energization of the coil of the solenoid valve moves the plunger member of the solenoid valve in a direction to open the bypass line 22.By opening solenoid valve 20, a portion of a hot discharged gas flows from discharge line 1 4 through line 22 directly to the suction side of compressor 10 without passing through the condenser 15, expansion valve 1 6 and evaporator 1 7 thereby reducing the rate of refrigerant passing through the refrigeration system. This will reduce the load on the compressor and on the condenser. When the refrigerant flow to the condenser is limited, this lowers the pressure in the condenser. The lower pressure in the condenser will allow the refrigeration system to continue operating at a reduced capacity even though the ambient temperature exceeds the designed limits of the overall system.It should be noted that the compressor is unloaded or shut off by a discharge pressure switch 25 when the system approaches its maximum operating pressure. The differential of this switch is wide enough that the reduction of pressure caused by the unloading or shutting off a compressor will not reset the switch starting or loading the compressor again. Since there is a direct relationship between the outdoor temperature and the discharge pressure, a reduction in ambient will be required before the switch will reset and load or start the compressor.

At this reduced ambient, the unit will operate with the compressor compietely loaded. The abovedescribed method of unloading the compressor as the head pressure approaches the maximum allowed for unit operation, permits the unit to remain operational at a reduced capacity but at a higher ambient temperature.

It should be noted that although an external placement of the solenoid valve in a bypass line is shown in the preferred embodiment, the internal placement of the valve in a bypass line extending from the discharge side to the suction side within a compresser shell may also be used in the system.

Figure 2 shows a partial view of the circuit similar to that shown in Figure 1, wherein a normally open switch 23 is connected to an ambient temperature control or gauge 30.

Unloading of the compressor takes place in response to ambient temperature sensed by the temperature control 30 which is adjusted to close switch contact 23 at a predetermined maximum ambient temperature.

Figure 3 illustrates an electrical schematic showing a connection between electrical switch 23 and unloading valves 20 in a case where a compressor with a plurality of banks of cylinders or a plurality of compressors are employed in the unit. Figure 3 shows, for example, a four-cylinder compressor. As the head pressure increases to the maximum allowed for unit operation, electrical switch 23 closes, energizing the unloading valves 20.

The number of electrical switches and unloading valves used would be dependent on the particular unit and the application.

In addition, various switches 23 may be added in conjunction with other unloading valves and bypasses to produce sequential unloading of the compressors as the ambient temperature rises.

While this invention has been illustrated in accordance with a preferred embodiment it is recognized that variations and changes may be therein without departing from the invention as set forth in the claims.

Claims (6)

1. A method of operating a refrigeration system of the type having a multiple cylinder compressor or multiple compressors comprising operating the refrigeration system up to full capacity, sensing conditions which indicate the load on the system, partially unloading the compressor when conditions are sensed indicating a load on the system in excess of the normal operating load, continuing to operate the refrigeration system at reduced capacity until conditions are sensed which indicate that the load on the system is reduced to the normal operating load.

2. The method of operating a refrigeration system in accordance with claim 1, wherein partially unloading the compressor includes a step of routing the discharge gas from some of the cylinders or compressors directly to the suction line of the compressor.

3. A method of operating a refrigeration system in accordance with claim 1 or 2, wherein a high side pressure in the discharge line of the compressor is sensed and the compressor is unloaded when the sensed high side pressure exceeds the normal operating pressure.

4. A method of operating a refrigeration system in accordance with claim 1 or 2, wherein an ambient temperature is sensed and the compressor is unloaded when the sensed ambient temperature exceeds the predetermined maximal temperature.

5. A gas compressor control including a bypass conduit connecting the compressor discharge to the compressor inlet, valve means in the bypass conduit to control the flow of high pressure gas from the compressor discharge to the compressor inlet, an electrical circuit operationally connected to the valve means to open the valve means, switch means in the electrical circuit to energize and deenergize the circuit, thereby controlling operation of the valve means, and condition sensing means connected to the switch means to close the switch in response to conditions when the ambient temperature exceeds the predetermined limit allowed for the system.

6. In a refrigeration system including an evaporator, a multiple cylinder compressor or multiple compressors, and a condenser, connected into a closed circuit for the flow refrigerant, control means comprising a bypass line connecting the discharge line of one compressor cylinder or compressor with the suction line of the compressor, a solenoid valve positioned in said bypass line to open and close the bypass line, an electrical circuit having a normally closed switch and electrically connected to said solenoid valve, a pressure valve connected to the discharge line of the compressor and being operative in response to a predetermined head pressure in said discharge line, said pressure valve being operatively connected to said electrical switch to close the electrical circuit and open said bypass line for directing the discharge gas from some of the cylinders or compressors to the suction line of the compressor when discharge litre pressure exceeds the maximal operating pressure.