WO1996041106A1

WO1996041106A1 - Liquid compressor cooling

Info

Publication number: WO1996041106A1
Application number: PCT/US1996/008408
Authority: WO
Inventors: Richard H. Alsenz; Timothy G. Burns; Bryan J. Ress
Original assignee: Altech Controls Corporation
Priority date: 1995-06-07
Filing date: 1996-06-03
Publication date: 1996-12-19
Also published as: AU6031196A

Abstract

The invention provides a refrigeration system which includes in a closed loop connection a compressor (14) for compressing a refrigerant, a compressor cylinder head cooling system utilizing liquid refrigerant (46) discharged into the compressor body discharge gas chamber (74) to cool the ocmpressor body (71). The compressor cylinder head cooling system decreases the cylinder head (71) operating temperature, thereby reducing the compressor discharge gas temperature (72) and improving the compressor reliability, maintenance, and efficiency, and improving the overall efficiency of the refrigeration system.

Description

LIQUID COMPRESSOR COOLING

Field of the Invention

The present invention relates generally to a refrigeration system. More particularly, this invention relates to an apparatus and method for improving the overall efficiency and reliability, and reducing the operating and maintenance costs of refrigeration system compressors by using condensed or subcooled liquid refrigerant to cool the refrigerant compressor cylinder heads.

Background of the Invention Refrigeration system compressor failures are known to be associated with high compressor body temperatures. Some common attempts to cool the compressor bodies include fans circulating air over the bodies, and injecting liquid condensate into the suction or low pressure side of the refrigeration system. Both methods result in increased energy usage and have various associated problems. Air circulation is not very effective due to the amount of heat that must be removed. Injecting liquid into the suction side of the refrigeration system has the problems associated with controlling the amount of liquid injected; too much liquid and the compressor will fail due to damage to the valving system, too little refrigerant injected will result in high temperatures which will result in bearing failure. The current invention solves the problem by injecting liquid condensate into the head of the compressor on the discharge or high pressure side of the compressor.

Summary of the Invention

The invention provides for a refrigeration system with improved compressor cylinder head cooling via the injection of liquid refrigerant into the hot compressor discharge gas in the compressor cylinder heads. The refrigeration system of the present invention also has, in a closed loop, a compressor for compressing a refrigerant, and a condenser for condensing the compressed refrigerant into a liquid refrigerant. An electronic control system is provided to control various functions of the refrigeration system, including the flow rate of the cooling liquid refrigerant injected into the cylinder head.

Examples of the more important features of the invention have thus been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended thereto. These and various other characteristics and advantages of the present invention will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention and by referring to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:

Figure 1 depicts a refrigeration system embodying the invention; Figure 2 is a simplified cross-section view of a compressor showing details of the cylinder head cooling apparatus of the present invention;

Figures 3A-3C are logic flow diagrams illustrating a control method of the invention; Figure 4 shows another embodiment of the cylinder head cooling system of the invention; Figure 5 shows another embodiment of the cylinder head cooling system of the invention; and

Figure 6 shows another embodiment of the cylinder head cooling system of the invention including a control valve in the liquid line between the condenser and condensate receiver.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For purposes of illustration and not by way of limitation, the present invention shall be described with respect to a refrigeration system and method wherein improved compressor maintenance, reliability, and efficiency are obtained by compressing a refrigerant to a high pressure and temperature, cooling the compressor cylinder heads by injection of condensed or subcooled liquid refrigerant into the cylinder heads. The refrigeration system of the present invention includes a compressor, a condenser, an evaporator, and a system by which the compressor cylinder heads are cooled by condensate or subcooled refrigerant liquid. Although subcooling of the liquid refrigerant is preferred, either condensed or subcooled liquid may be recycled to the cylinder heads for cylinder head cooling without departing from the scope of the invention. The present invention further includes a control system which controls the flow of recycled refrigerant used to cool the cylinder heads and also controls various other functions of the refrigeration system.

Compressor cylinder head cooling is preferably accomplished by injecting a cooling refrigerant liquid, which is at a lower temperature than the compressor discharge gas, directly into the cylinder heads. The cooling liquid may be condensed or subcooled liquid refrigerant recycled from, for example, either the condenser outlet or condensate receiver. This cooling liquid is injected directly into the cylinder heads so as to mix with the relatively hot, compressed refrigerant vapor that is discharged from the compressor cylinder through exhaust valves.

Referring now to Figure 1, an embodiment of the refrigeration system of the present invention is shown. The system includes at least one compressor, a compressor cylinder head cooling system, at least one condenser, at least one evaporator with an expansion device, at least one cooling fan, a reservoir for holding liquid refrigerant, a temperature sensor near the outlet of the compressor cylinder head to measure the temperature of the hot discharged refrigerant, a liquid pump to recycle refrigerant liquid from a take-off point to the cylinder head through a liquid recycle line, and a control circuit containing a microprocessor to control various functions of the refrigeration system including the liquid pump. The refrigeration system may also contain a control valve disposed in the liquid recycle line to vary the flow rate of recycled cooling liquid for cylinder head cooling.

Referring to Figure 1, the refrigeration system depicted therein is a closed loop, commonly connected, multiple-stage refrigeration system. A vapor refrigerant at a low pressure is passed into parallel compressors 14 and 18 via a refrigerant line 10. The compressors 14 and 18 compress the refrigerant to a high pressure gaseous state and discharge it through refrigerant lines 22 and 24 which communicate with a condenser 28. A cylinder head temperature sensor 39 in the outlet line discharging coolant from the compressor cylinder heads preferably provides a signal representative of the cylinder head operating temperature. Cylinder head temperature sensor 39 is electrically connected to microcontroller 56.

The microcontroller circuit 56 contains a microprocessor and other circuitry which enables it to access information from various sensors used in the refrigerator system, to process these signals, and to control a variety of functions of the refrigeration system.

Referring now to Figure 2, there is shown in greatly simplified cross section a reciprocating compressor exemplary of a type which may be used with the present invention. Compressor 14 comprises a compressor block 79, containing one or more cylinder bores 76. Piston 75 reciprocates within cylinder bore 76, by the rotation of crankshaft 77 and piston rod 78. Compressor cylinder head 71 is disposed at one end of compressor block 79, perpendicular to the direction of travel of piston 75. Cylinder head 71 contains passages connected to and communicating with refrigerant suction manifold 20 and refrigerant outlet line 22, and valves controlling the flow of refrigerant being compressed, such as intake valve 72 and exhaust valve 73. Cylinder head 71 also comprises cooling liquid injection line 47, through which cooling liquid is passed into exhaust manifold 74 and mixed with hot compressed refrigerant vapor discharged from the cylinder through exhaust valve 73. Referring again to Figure 1, the condensed refrigerant leaves the condenser 28 through liquid line 38 as a liquid, and is discharged into a main fluid reservoir 44 through a main line 58. The liquid from the reservoir 44 flows through line 58 into a liquid manifold system 57, where it enters a liquid line that is connected to expansion valves 50 and 52. Each expansion valve 50 and 52 is connected to separate parallel evaporators 54 and 55 respectively. These evaporators form a refrigeration system wherein the expansion valves 50 and 52 meter the liquid refrigerant into evaporators 54 and 55 respectively. Similarly, other refrigeration systems (not shown) may be connected to the liquid manifold system 57 via lines 62 and the like. When the liquid refrigerant is metered through the expansion valves 50 or 52, it evaporates into a gaseous state within its respective evaporator at a low pressure and a low temperature. The low pressure vapor refrigerant is passed to the compressors 14 and 18 through the suction line 10 and suction manifold 20.

Compressors 14 and 18 compress the refrigerant vapor and discharge the compressed vapor into discharge line 22. The compressed vapor then passes through condenser inlet line 24 to condenser 28. Condenser 28 causes the refrigerant vapor to be cooled and condensed into a liquid phase by cooling the condenser coils with air at ambient temperature. The cooling and condensation of the refrigerant within condenser 28 may be improved by the use of one or more fan(s) 32 to increase the flow of air across the condenser coils. The liquid refrigerant may also be subcooled in condenser 28. In any case, liquid refrigerant is discharged from condenser via liquid line 38, which completes a refrigeration cycle that is continuously repeated during operation.

The flow of cylinder head cooling liquid may be effected by a pressurization member such as liquid pump 100. A control valve 49 may also be used in recycle line 46 to vary the flow of cooling liquid, in which case the position of the control valve is controlled by microcontroller 56. Microcontroller 56 varies the position of control valve 49 to control the flow of cylinder head cooling liquid in response to the cylinder head temperature sensor 39 to maintain a predetermined cylinder head operating temperature, or to maintain a head temperature just above the condensing temperature. In the latter case, microcontroller 56 controls the position of control valve 49 to maintain the temperature of the head (temperature sensor 39) a few degrees above that of the liquid line, sensed by temperature sensor 36. When the difference between the cylinder head temperature and the liquid line temperature exceeds a predetermined amount, microcontroller 56 increases the flow through control valve 49. Similarly, when the difference between the cylinder head temperature and the liquid line temperature is less than a predetermined amount, microcontroller

56 decreases the flow through control valve 49. This is illustrated in the flow diagram of Figure 3A.

In the case of multiple compressors, separate control valves (not shown) may be placed in each of the cooling liquid injection lines 47 to individually control the flow of cooling liquid to each cylinder head individually.

Referring now to both Figures 1 and 2, the present invention provides a liquid pump 100 in the liquid line 58 disposed between the reservoir 44 and the liquid manifolds 57. The liquid pump 100, when in operation, recycles refrigerant liquid from the reservoir 44, through control valve 49, via recycle line 46, through cooling liquid injection line 47, as cooling liquid for injection into the compressor cylinder head 71. The cooling liquid passes through cooling liquid injection line 47 into exhaust manifold 74, which is disposed within cylinder head 71. Relatively hot refrigerant vapor, compressed by piston 75, leaves the compressor cylinder through exhaust valve 73 and enters exhaust manifold 74. The hot compressed refrigerant vapor leaving the cylinder and the cooling liquid passing through cooling liquid injection line 47 therefore mix in exhaust manifold 74. The mixture of these two fluids has a temperature which is relatively lower than the temperature of the compressed vapor passing through exhaust valve 73. The temperature of the surfaces of exhaust manifold 74 is therefore reduced by die injection of the cooling liquid. The temperature of cylinder head 71 and other parts disposed therein is in turn reduced by the conduction of heat through the walls of cylinder head 71. Further, the temperature of compressor block 79 and parts disposed therein is also reduced by the temperature reduction effected by the cooling liquid injected to exhaust manifold 74. This is again due to the conduction of heat through the metal walls of block 79 and cylinder head 71 forming the compressor housing.

The mixing of the cool recycle liquid with the hot compressed discharge gas, as described above, will also decrease the extent to which the refrigerant entering the condenser is superheated above its condensing temperature. Decreasing the level of superheat in the vapor entering the condenser 28 reduces the condenser heat transfer surface used to desuperheat the vapor, and tiierefore increases the condenser heat transfer surfaces available for condensing and subcooling service. By thus increasing the subcooling taking place in the condenser 28 the refrigeration system efficiency and refrigerating effect are increased. In another embodiment, the present invention is also applicable in combination with enhanced subcooling of the refrigerant, such as is described in

U.S. Pat. No. 5,115,664, which is incorporated herein by reference.

Figures 4 and 5 show the take-off of recycle liquid, as cooling liquid for cooling the cylinder heads, from the liquid line 38 between condenser 28 and reservoir 44, rather than from reservoir 44 itself. The liquid leaving the condenser may be maintained at a constant level by an inverted trap 82 (Figure 4) or trap leg 83 (Figure 5), if the condenser is at a higher level than the compressor. This eliminates the need for the liquid pump shown in Figure 1, and allows the liquid to be subcooled before leaving the condenser 28.

The embodiments of Figures 4 and 5 also provide a column of liquid refrigerant of sufficient height to overcome the pressure drop through condenser 28. This ensures that liquid refrigerant will flow, due to the weight of the liquid from condenser 28, to the compressor heads 71. A control valve such as valve 49 or a restriction (not shown) may be placed in line 46

(or in lines 47) to assist in forming and controlling a liquid column in trap 82 or trap leg 83.

Referring now to Figure 6, an embodiment of the refrigeration system of the present invention is shown which also incorporates a control valve 40 disposed in liquid line 38 between condenser 28 and reservoir 44. As shown in the flow diagram of Figure 3B, control valve 40 may be operated by microcontroller 56 to regulate the flow of liquid refrigerant from the condenser 28 to the reservoir 33. In this embodiment, the position of control valve 40 is used to control the temperature in the liquid line 38.

The control valve 40 prevents the flow of the entire liquid refrigerant from the condenser 28 to the reservoir 44 thereby enabling some of the liquid refrigerant to accumulate in the liquid return line 38. The microcontroller 56 regulates the liquid refrigerant flow through the control valve 40 as a function of the difference between the liquid refrigerant temperature (ascertained by temperature sensor 36) and the ambient temperature (ascertained by temperature sensor 34) around condenser 28. When the temperature difference between the liquid refrigerant temperature and the ambient temperature ("ΔT") is greater than a predetermined value, the microcontroller 56 decreases the flow through the control valve 40. On the other hand, when the temperature difference ΔT is less than the predetermined value, the microcontroller 56 increases the flow through control valve 40. A time delay between successive decisions to alter the flow through the control valve 40 is programmed into the microcontroller 56 to smooth out the operation of the control valve 40. The operation of the method described above ensures that during operation an amount of liquid refrigerant is maintained in the condenser 28 which is sufficient to provide subcooling of the liquid refrigerant before it is discharged into the reservoir 44. The liquid refrigerant flow through the control valve 40 may be controlled by either pulse modulating or analog modulating the flow control valve 40. Further improvement in the overall system efficiency may be obtained by regulating the speed of fan 32 as a function of the discharge pressure of the gaseous refrigerant into the condenser. The microcontroller 56 thus also controls or regulates the fan 32, as shown in the flow diagram of Figure 3C, to optimize the condensation of the gaseous refrigerant entering the condenser 28. When the pressure represented by the pressure transducer 26, i.e., the discharge pressure of the gaseous refrigerant entering into the condenser 28, is above a predetermined value, the microcontroller will increase the fan speed thereby causing it to increase air flow through the condenser 28. On the other hand, when the discharge pressure is below the predetermined value, the microcontroller 56 will decrease the speed of fan 32, thereby decreasing the air flow through the condenser 28. Also, a time delay between successive speed controls is provided to avoid changing the fan speed too frequently.

The effects of these methods may be enhanced by slanting the passes within the condenser

28, allowing better draining and heat transfer within the condenser. When the last pass of the condenser 28 is tilted so that the refrigerant drains from the condenser under the influence of gravity, the gradient effect of the subcooling allows less condenser surface to be used to achieve a desired effect. While the invention has been described in accordance with air cooled condensers, one experienced in the art may easily apply the invention to water or fluid cooled condensers of all sorts. It is intended that the current patent shall apply to all sorts of condensers. These embodiments have not been specifically described because they are considered redundant in application of the invention in view of the above description.

Further, the present invention is equally applicable to condenser systems employing modulation of multiple condenser cooling fans or water flow modulation in the case of water cooled condensers. As would be obvious to one skilled in the art, many other applications of the present invention are possible and the description provided herein is intended to be limited only by the claims appended hereto.

Claims

WE CLAIM:

1. A method of cooling a compressor in a close loop refrigeration system comprising the steps of: supplying liquid from the condenser, elevating the liquid to a higher pressure and then discharging the liquid into the head of the compressor body on the discharge gas side of the compressor.

2. The method of claim 1 further including the step of elevating the pressure of the liquid using a liquid pump.

3. The method of claim 1 further including the step of elevating the pressure of the liquid using a liquid column.

4. A method of cooling a compressor housing for a refrigeration system comprising the steps of: injecting a liquid refrigerant into the exhaust chamber of the housing of the compressor; mixing the liquid refrigerant with the compressed refrigerant which has been compressed by the compressor; cooling the compressed refrigerant; and cooling the compressor housing.

5. The method of claim 4 further comprising the step of controlling the flow rate of the liquid refrigerant into the exhaust chamber of the compressor housing so as to maintain the temperature of the compressor housing at a predetermined value.

6. The method of claim 4 further including the steps of: measuring the temperature of the compressor housing; sending signals representing such temperature to a control circuit; and controlling the flow of liquid refrigerant into the exhaust chamber to control the temperature by means of the control circuit.

7. A refrigeration system, comprising: a compressor for compressing a refrigerant, said compressor having a housing with an exhaust chamber for receiving the refrigerant after the refrigerant is compressed; a condenser for receiving and condensing the compressed refrigerant into a liquid refrigerant; and a conduit member transporting liquid refrigerant from said condenser to said exhaust chamber whereby the liquid refrigerant cools said compressor housing.

8. The apparatus of claim 7 wherein said liquid refrigerant mixes and desuperheats the compressed refrigerant.

9. The apparatus of claim 8 further comprising a liquid reservoir for receiving the liquid refrigerant from said condenser.

10. The apparatus of claim 9 wherein said conduit member extends from said liquid reservoir to said exhaust chamber.

11. The apparatus of claim 10 further comprising a pump disposed in said conduit member for transporting liquid refrigerant through said conduit member.

12. The apparatus of claim 8 wherein said exhaust chamber serves as a mixing chamber or mixing the liquid refrigerant with the compressed refrigerant.

13. The apparatus of claim 12 wherein said exhaust chamber is disposed within a cylinder head of said compressor.

14. The apparatus of claim 11 further including a temperature sensor producing a signal representative of the temperature of said compressor housing.

15. The apparatus of claim 14 further comprising a control member electrically connected to said temperature sensor and said pump for controlling the flow through said conduit member as a function of the signal produced by said temperature sensor.

16. The apparatus of claim 15 wherein said control member includes a microprocessor.

17. The apparatus of claim 15 further comprising: a level sensor disposed in said reservoir and electrically connected to said control member for producing a signal representative of said level of liquid refrigerant in said reservoir; and said control member disabling said pump if said level sensor signal reaches a first predetermined value and enabling said pump if said level sensor signal reaches a second predetermined value.

18. The apparatus of claim 7 wherein said conduit member receives liquid refrigerant from said condenser.

19. The apparatus of claim 7 further comprising: a liquid reservoir for receiving liquid refrigerant from said condenser; an electrically operable control valve for controlling the flow of liquid refrigerant into said reservoir; a variable speed fan for providing airflow over said condenser; a first temperature sensor for providing an electrical signal that is representative of the temperature of the liquid refrigerant discharging from said condenser; a second temperature sensor for providing an electrical signal representative of the ambient temperature around said condenser; a third temperature sensor for providing an electrical signal that is representative of the temperature of the liquid refrigerant in said exhaust chamber; a microprocessor based control circuit electrically connected to said temperature sensors, fan, and control valve, said control circuit controlling the discharge through said control valve as a function of the temperature difference between the ambient temperature and die temperature of the liquid refrigerant at said condenser, so as to regulate the cooling of the compressed refrigerant, the cooling of said compressor housing, and the condensing temperature in said condenser.