US3396550A

US3396550A - Arrangement for reducing compressor discharge gas temperature

Info

Publication number: US3396550A
Application number: US591227A
Authority: US
Inventors: Richard E Cawley
Original assignee: Lennox Industries Inc
Current assignee: Lennox Industries Inc
Priority date: 1966-11-01
Filing date: 1966-11-01
Publication date: 1968-08-13
Anticipated expiration: 1985-08-13

Description

Aug. 13, 1968 R. E. CAWLEY ,5

ARRANGEMENT FOR REDUCING COMPRESSOR DISCHARGE GAS TEMPERATURE 2 Sheets-Sheet 1 Filed Nov. 1, 1966 INVENTOR. R/CHARD E. CAM LEV BY fi 3, 1968 R. E. CAWLEY 3,396,550

ARRANGEMENT FOR REDUCING COMPRESSOR DISCHARGE GAS TEMPERATURE Filed Nov. 1, 1966 2 Sheets-Sheet 2 64- i 23 d 20 9 I i 24 5 3 22 1/ 4 1 f7 5: 3

S w i N If E INVENTOR fP/CHARD E. CAWLEY ATTORNE Y5 United States Patent 3,396,550 ARRANGEMENT FOR REDUCING COMPRESSOR DISCHARGE GAS TEMPERATURE Richard E. Cawley, Fort Worth, Tex., assignor to Lennox Industries, Inc., Marshalltown, Iowa, a corporation of Iowa Filed Nov. 1, 1966, Ser. No. 591,227 Claims. (Cl. 62-117) ABSTRACT OF THE DISCLOSURE Secondary throttling means for effectively reducing discharge gas temperature by introducing refrigerant into the suction gas in response to increase in the suction gas temperature above a predetermined value in order to maintain a substantially constant predetermined super-heat of the suction gas entering the compression mechanism.

This invention relates to apparatus for reducing compressor discharge gas temperature and, more particularly, to control means for providing secondary throttling of refrigerant to reduce the undesirably high temperature of the suction gas entering the cylinders during certain operating conditions, and thereby reduce the compressor discharge gas temperature.

In a conventional refrigeration system including a reciprocating compressor, a condenser, expansion means, and an evaporator interconnected with one another, it sometimes happens that the environment will add heat to the suction gas returning in the suction line from the evaporator coil to the compressor. The elevated suction gas temperature may in turn cause an increase in discharge gas temperature. Increase in discharge gas temperature above predetermined limits may cause undesirable breakdown of the lubricant and possible damage to motor insulation. Further, acid yielding reactions between Water that may be present Within the hermetic compressor and refrigerant will accelerate as the temperature increases, possibly causing corrosion within the compressor. The broad rule of thumb for compressor design is that the rate of chemical reaction in a compressor doubles for each 18 F. increase in temperature. Thus, it is apparent that it is desirable to limit discharge gas temperature.

Some hermetic compressors have been provided With discharge gas temperature controllers for terminating operation of the compressor in the event the discharge gas temperature within the compressor exceeds a predetermined maximum value, as for example, 275 F. However, when a compressor is provided with a discharge gas temperature control, compressor operation may be terminated even though there is a continued demand for cooling, due to pick up of heat by the suction gas as it passes through an elongated suction line exposed to environmental heat.

In heat pump applications, where the outdoor coil functions as an evaporator and the indoor coil functions as a condenser, the returning suction gas from the outdoor coil may be at a higher temperature than desired resulting in undesirably high discharge gas temperature. The problem is further complicated if a discharge gas temperature control is provided. If the discharge gas temperature should increase above the setting of the discharge gas thermostat or control, the compressor motor would be stopped even though heating is called for. From the foregoing, it is apparent that it is important to control discharge gas temperature and keep it below a value that would result in damage to the internal components of the compressor.

The present invention is concerned with improvements in a hermetic compressor of the type having compression mechanism resiliently supported within an outer housing spaced from the compression mechanism, the space containing suction gas which passes over the drive motor enroute to the cylinders for cooling the drive motor. One solution to the problem of reducing suction gas temperature in such compressors has been to provide a water jacket about the compressor and pass cool water through the water jacket in heat exchange relation with the suction gas to cool the suction gas. It is undesirable to require a source of water and the piping is sometimes cumbersome. Also there may be Water corrosion problems. A water jacket could not be used for heat pump applications where the compressor Was outdoors, as the Water in the water jacket might freeze.

An object of the present invention is to reduce discharge gas temperature in a hermetic suction gas cooled compressor by providing the compressor with control means 'for introducing refrigerant into the suction gas in response to predetermined temperature conditions in order to cool the suction gas in the compressor and thereby reduce the discharge gas temperature.

Another object of the present invention is to provide a hermetic refrigerant compressor with means for reducing the discharge gas temperature including a conduit downstream of the condenser for communicating with the compressor, such conduit having a thermal expansion valve therein responsive to suction gas temperature internal of the compressor for controlling the amount of refrigerant passed :by the thermal expansion valve for mixture wit-h the suction gas in the compressor.

Still another object of the present invention is to provide a refrigerant compressor with secondary throttling means for reducing the compressor discharge gas temperature and for maintaining a substantially constant predetermined super heat of the suction gas entering the compression mechanism.

Yet another object of the present invention is to provide a refrigerant compressor having secondary throttling means for reducing compressor discharge gas temperature, with a portion of the conduit of the secondary throttling means disposed in a lubricant sump in the compressor for cooling the lubricant contained therein. Other objects and advantages of the present invention will become more apparent hereinafter.

The invention will be made most manifest and particularly pointed out in clear, concise and exact terms in conjunction with the accompanying drawing wherein:

:FIG. 1 illustrates schematically a refrigeration system incorporating the secondary throttling means of the present invention;

FIG. 2 is a cross-sectional view of a refrigerant compressor incorporating novel control means therein for effectively throttling refrigerant from a conduit connected downstream of the condenser for mixture with suction gas within the compressor;

FIG. 3 is a detail cross-sectional view taken generally along the line 3--3 of FIG. 2 and illustrating a portion of the conduit Within the compressor for discharging throttled refrigerant into the suction gas within the compressor to cool the same; and

FIG. 4 is an illustrative view of a modified compressor incorporating secondary throttling means for reducing the discharge gas temperature and having a portion of the conduit between the thermal expansion valve and throttled refrigerant discharge conduit disposed in the sump for cooling the lubricant therein.

Referring now to FIG. 1, there is illustrated a refrigeration system incorporating a compressor 10, a condenser 12, expansion means 14, and an evaporator 16. High pressure vaporous refrigerant is forwarded from the compressor 10 through the discharge line 11 to the condenser 12 where it is condensed into liquid. The condenser may be air cooled or Water cooled. The liquid refrigerant passes through the line 13 to the expansion means, which is illustrated as being "a' 'thermal expansion valve 14. It will be understood that capillary expansion means may be used in place of valve 14. The expansion valve 14 controls the how of liquid refrigerant from the condenser to the evaporator 16 wherein the refrigerant is vaporized. Air passing in heat transfer relationship with the evaporator 16 is cooled. The vaporous refrigerant then returns from the evaporator 16 to the compressor through a suction line 17.

If the condenser and evaporator are physically close to one another, there is little heat pick up by the suction gas due to environmental factors. However, in many applications the condenser and evaporator are far apart. Heat is picked up by the suction gas returning in the line 17 to the compressor for the elongated lengths of suction line may be disposed in a warm attic. Further, the suction line maybe heated due to solar energy, or due to other environmental factors. The elevated suction gas tempenature may result in an increased discharge gas temperature. Increased discharge gas temperature results in breakdown of lubricant within the compressor and may result in shortened life of the discharge valves, and seizure of pistons. Some compressors are provided with discharge gas temperature controllers to prevent occurrence of these problems. If the discharge gas temperature, therefore, should exceed a predetermined limit, then the controller would be actuated to terminate operation of the compressor motor. It is seen, therefore, that an elevated suction gas temperature may result in termination of compressor ope-ration, even though there may be a continued demand for cooling.

In accordance with the present invention, control means are provided making use of secondary throttling for reducing the suction gas temperature and resulting in reduced discharge gas temperature. As shown schematically in FIG. 1, a conduit 20 communicates the liqiud line 13 downstream from the condenser 12 and between the condenser 12 and expansion valve 14 with the compressor 10'. Disposed in the conduit 20 is a solenoid shut-off valve 22, which may be electrically actuated so as to close when the compressor is oif and to open when the compressor is on. The solenoid coil is disposed in the circuit with the compressor motor and the compressor motor controls. In series with the solenoid shut-off valve 22 is a thermal expansion valve 24 which has a capillary sensing means 25 disposed in the compressor to sense the suction gas temperature therein. Thus, the thermal expansion valve will be operative in response to a predetermined suction gas temperature to control the flow of refrigerant introduced into the compressor for mixture withthe suction gas to reduce the temperature of the suction gas returning from the suction gas line 17. As the suction gas temperature in the compressor increases, the thermal expansion valve 24 will be actuated to permit entry of more cooled refrigerant to reduce the suction gas temperature.

Tests have been performed upon a compressor incorporating a secondary throttling arrangement and comparable tests have been run with a compressor not having such secondary throttling arrangement. The results of the tests are tabulated below.

limits is that above such limits there may be breakdown of the lubricant, which may result in accompanying malfunction of the mechanical components of the compression mechanism. Elevated temperatures in the compression mechanism might cause piston seizure and discharge valve breakage. Thus it i desirable that the compressor components be run as cool as possible. A comparison of the internal discharge gas temperature with throttling and without throttling shows that there is a significant reduction in discharge gas temperature within the compressor when secondary throttling is employed. The difference amounts to 4050 F.

Similarly, a comparison of the motor temperature with throttling and without throttling shows that there is a significant reduction in motor temperature when throttling is employed. A rule of thumb for engineering design is that for every 18 F. temperature increase in motor temperature the life of the motor is reduced one half. Stated another way, for each 18 F. increase within the compressor, the chemical reaction rate is doubled. Utilization of throttling therefore can be of material benefit in increasing the life of the motor.

It is seen from the table, that when secondary throttling is used, the internal discharge gas temperature is substantially below the internal discharge gas temperature of the compressor without throttling. Often, the refrigerant compressor of the type tested is provided with a discharge gas temperature controller. Commonly such controller is set at 275 F. It is apparent from the above table that at 135 F. condensing temperature and 45 F. evaporating temperature, the internal discharge gas temperature without throttling is 273 F. and with throttling is 230.5 F. The internal discharge gas temperature is dangerously close to the trip point, and it is readily apparent that nuisance trips could occur. Similarly, at 130 F. condensing temperature and 40 F. evaporating temperature, the internal discharge gas temperature without throttling is 274 F., again a potential nuisance trip value. At 135 F. condensing temperature and 40 F. evaporating temperature, the internal discharge gas temperature without throttling is 288.5 F. At this condition the discharge gas temperature controller would be actuated to stop the compressor. It is seen that the comparable internal discharge gas temperature with throttling is 231 F., a value well below the discharge ga temperature trip point.

Referring now to FIG. 2, there is shown in cross section a refrigeration compressor incorporating therein the secondaiy throttling control means of the present invention. Compressor 10 illustrated in FIG. 2 may be of the type shown in more detail in Patent 3,250,461 granted May 31, 1966 to Sidney A. Parker. The compression mechanism 32 is resiliently supported within the outer casing 34 of the compressor 10 by means of spring means 36.

As shown, suction gas enters the compressor through the suction valve 38 connected to suction fitting 40 that may be connected to the lower shell portion of the outer housing or outer casing 34. Suction gas enters the space between the compression mechanism 32 and the interior of the outer hermetically sealed housing 34. The space may be divided into

separate compartments

42, 44 and 46, which function to effectively muffle the suction gas noises.

TABULATED RESULTS OF TESTS WITH "SECONDARY THROTTLING Ext. Internal Ret. Gas Internal Dis. Temp, Motor Temp., F. Cond. Evap. Return Temp, F. F. Temp., F. Temp., Gas

F Temp. W/O With W/O With W/O With F. Throt. Throt. Throt. Throt. Throt. Throt.

An important consideration in reducing discharge gas temperature and maintaining same within desired design The suction gas then passes from compartment 46 through an opening (not shown) in the top of the suction muflie shroud 48, over the motor 49 to cool same, and into the compression mechanism. The suction gas is compressed by the piston means 45 operatively connected to the crankshaft 43 by connecting rods. Crankshaft 43 is driven by the motor means 49 secured to the upper end thereof within the compression mechanism. Gas is discharged from the cylinders into a discharge gas mufiling chamber 50 formed within the compression mechanism. From the discharge gas mufiiing chamber disposed annularly within the compression mechanism the discharge gases pass through the discharge line 52 and exit through the discharge fitting 54 to the discharge line exterior of the compressor.

The control means for providing secondary throttling includes a thermal expansion valve 24 disposed within the compressor and operatively connected to solenoid valve 22 which is in turn connected to the conduit 20. The outlet end of the thermal expansion valve 24 is connected by conduit 59 to an annular tube or conduit 60 (FIGS. 2 and 3) suitably supported within the compressor in compartment 46. The annular tube 60 is provided with a plurality of openings 61 therein for permitting discharge of refrigerant from the annular ring-like conduit 60 into the compartment 46 for mixture with the suction gas therein prior to passage of the suction gas into the compression mechanism. On one side, the annular ring-like member 60 may be supported by a bracket 62 and diametrically opposed, the ring-like member 60 may be supported by a bracket 64, connected to the outer shell or outer housing 34 of compressor 10, or as shown, connected to a sound rnufiling sleeve afiixed to shell 34.

The expansion bulb or thermal sensitive element 25 of the secondary expansion valve 24 is oriented so as to sense the temperature of the suction gas in the motor compartment just prior to entry of the gas into the cylinder prior to compression thereof. If desired, the expansion bulb 25 may be disposed within the compartment 46 downstream of the entry of suction gas into the compartment and also downstream of the entry of secondary refrigerant into the suction gas.

The solenoid valve 22, which -for example, may be a Sporlan, Type 108, is normally closed so as to'prevent liquid refrigerant from entering the compressor during the off cycle. Whenever the compressor motor 49 is energized, the solenoid 23 of the valve 22 will be energized to open the valve and permit flow of refrigerant to thermal expansion valve 24.

In operation of the compressor 10, high pressure vaporous refrigerant will be compressed by the pistons operative within the compression mechanism and will be discharged from the cylinders into discharge gas mufiiing chamber 50, then through discharge line 52 and fitting 54 to the refrigeration system. The temperature of the suction gas returning to the compressor will be sensed by the bulb 25. In the event the temperature exceeds a predetermined value, or stated in other words, in the event the superheat exceeds a predetermined value, the secondary expansion valve 24 will be operative to permit passage of cooled refrigerant through the conduit member 60 and the openings 61 therein into the space 46 for mixture with the suction gas prior to entry of the suction gas into the compression mechanism 32. The control means of the present invention function to maintain a substantially constant superheat under varying operating conditions. By adding cool refrigerant to the suction gas, the temperature of the incoming suction gas is reduced. As a consequence, the discharge gas temperature will also be reduced. Chemical reaction within the compressor is held within acceptable limits and the life of the compressor is prolonged. Where a discharge gas temperature controller is employed, the discharge gas temperature will normally be maintained below the trip value and the control will then function as a safety control and without undesirable nuisance trips.

In FIG. 4, there is shown a modification of the arrangement of FIGS. 2 and 3 wherein the conduit 60 is supplied with refrigerant by an elongated loop portion 66 adapted to extend into the lubricant sump defined in the bottom of the outer casing between the compression mechanism and the outer casing. The conduit 66 is imper-forate. By virtue of this arrangement, cooled refrigerant will pass from the thermal expansion valve 24 through the conduit 66 prior to discharge from the openings 61 in the conduit member 60. The cool refrigerant in the loop 66 is in heat transfer relationship with the lubricant or oil in the sump and accordingly the oil will be cooled.

While the invention has been illustrated in connection with a conventional refrigeration circuit, it will be understood that the secondary throttling control mechanism for reducing compressor discharge gas temperature will have equal applicability with a compressor utilized in a heat pump system. The secondary throttling arrangement of the present invention will effectively reduce discharge gas temperature Whether the compressor is utilized in a conventional refrigeration system or in a heat pump system. The introduction of gas from the secondary expansion valve into the compressor will not cause a measurable reduction in system cooling capacity. Chemical reaction within the compressor will be maintained within acceptable limits and compressor life will be increased without increasing operating costs.

The use of a thermal expansion valve 24 in the conduit 20 provides for accurate control over a wide range of operating conditions. A fixed resistor or a capillary tube type throttling control in conduit 20 might pass too much or too little refrigerant into the suction gas within the compressor and would therefore be incapable of providing precise control over a wide range.

While I have shown a preferred embodiment of the invention, it will be understood that the invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

What is claimed is:

1. In a refrigeration system including a compressor, a first heat exchanger, expansion means and a second heat exchanger, said compressor comprising a sealed housing having compression mechanism therein for compressing refrigerant and discharging hot vaporous discharge gas into a discharge line for passage to the first heat exchanger, the refrigerant being returned from the second heat exchanger to the compressor via a suction line, the improvement comprising control means responsive to the temperature of the suction gas for selectively introducing throttled refrigerant taken from between the first heat exchanger and the expansion means into the suction gas to (1) maintain a substantially constant superheat and (2) cool the suction gas and thereby reduce the temperature of the discharge gas.

2. Apparatus as in claim 1 wherein the control means includes a conduit communicating the refrigeration system between the first heat exchanger and the expansion means with the suction gas in the compressor, and thermal expansion means for throttling the hot liquid refrigerant in the conduit in response to a predetermined suction gas temperature condition to control the introduction of refrigerant from the conduit into the suction gas so as to cool the suction gas.

3. Apparatus as in claim 2 wherein said thermal expansion means includes a valve and thermal sensing means responsive to the temperature of the suction gas in the compressor for controlling the valve.

4. Apparatus as in claim 2 including a shut-off valve in said conduit, said valve being closed when the compression mechanism is inoperative and said valve being open when the compressor is operative.

5. Apparatus as in claim 1 wherein the control means includes a conduit communicating the liquid line in the refrigeration system with the compressor and a thermal expansion valve in said conduit for controlling flow of refrigerant therethrough, the thermal expansion valve including a thermal sensing member responsive to the temperature of suction gas in the compressor.

6. Apparatus as in claim wherein the thermal sensing member is within the compression mechanism for sensing the temperature of the suction gas prior to entry into the cylinders for compression thereof.

7. Apparatus as in claim 1 wherein said control means includes a conduit member disposed in the space between the compression mechanism and the outer housing, said conduit member having opening means therein for discharging refiigerant from the conduit member into the space to reduce the temperature of suction gas in the space prior to passage over the motor in the compressor for cooling same.

8. Apparatus as in claim 7 wherein a lubricant sump is formed in the bottom of the outer housing between the compression mechanism and the outer housing and an imperforate portion of the conduit member is disposed in the sump for cooling lubricant therein.

9. The method of maximizing operation of a refrigerant compressor by controlling discharge gas temperature, the refrigerant compressor having compression mechanism spaced from and resiliently supported within a sealed outer casing, the space between the compression mechanism and the outer casing containing suction gas, which suction gas is utilized to cool the compressor drive motor within the outer casing, said compressor being disposed in a refrigeration system including a condenser, expansion means, and an evaporator, comprising the steps of throttling refrigerant from downstream of the condenser and discharging same into the suction gas within the compressor in response to increase of suction gas superheat within the compressor above a predetermined value to hold the superheat below a predetermined limit under varying operating conditions.

10. A refrigeration system as in claim 1 wherein said compression mechanism is spaced from the sealed housing to define a suction gas compartment therebetween receiving suction gas from the suction line, said compression mechanism including an electric drive motor, the suction gas from said suction line passing into said compartment and then over said electric drive motor into the cylinder means within the compression mechanism, said control means including a conduit having openings in the portion thereof disposed in said compartment for discharging vaporous refrigerant fromsaid conduit into said compartment for mixture with the suction gas returning from the suction line to maintain a substantially constant superheat under varying operating conditions of the gas entering the compression mechanism and to cool the gas entering the compression mechanism to thereby reduce the temperature of the discharge gas.

References Cited UNITED STATES PATENTS 3,109,297 11/1963 Rinchart 62197 3,150,277 9/1964 Chubb et a1. 6250'5 2,261,172 7/1966 Grant 62117 LLOYD L. KING, Primary Examiner.