US3350896A

US3350896A - Multiple evaporator refrigeration systems

Info

Publication number: US3350896A
Application number: US519877A
Authority: US
Inventors: James R Harnish
Original assignee: Westinghouse Electric Corp
Current assignee: YORK-LUXAIRE Inc A CORP OF DE
Priority date: 1966-01-11
Filing date: 1966-01-11
Publication date: 1967-11-07
Anticipated expiration: 1984-11-07

Description

United States Patent 3,350,896 MULTIPLE EVAPORATOR REFRIGERATION SYSTEMS James R. Hamish, Staunton, Va., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Jan. 11, 1966, Ser. No. 519,877 7 Claims. (Cl. 62200) ABSTRACT OF THE DISCLOSURE In a refrigeration system having a plurality of evaporators, all of the evaporators are fed by a single expansion valve through solenoid-controlled valves. Local thermostats control the solenoids to open the respective solenoidcontrolled valves when cooling is required. The expansion valve meters refrigerant to the active evaporator or evaporators at the rate at which the refrigerant is condensed, overfeeding the active evaporator or evaporators so gas and unevaporated refrigerant flow from the latter into an accumulator means in which liquid refrigerant is evaporated by heat from the condensed refrigerant flowing to the expansion valve.

This invention relates to refrigeration systems having multiple evaporators, and has as objects to simplify and to improve the performances of such systems.

As disclosed on pages 404-405 of the textbook Principles of Refrigeration? by R. J. Dossat,published in 1961 by John Wiley & Sons, in refrigeration systems having multiple evaporators cut in and out by solenoid controlled valves, a thermal expansion valve is usually provided for each evaporator. Such expansion valves operate to maintain constant degrees of superheat at the outlets of their respective evaporators so that all of the refrigerant supplied to the evaporators, is evaporated. Other refrigeration systems include refrigerant pumps to circulate excess liquid refrigerant through multiple evaporators so that none of the evaporator surfaces is wasted to provide superheat, and refrigerant distribution between evaporators is less critical. However, a refrigerant pump should be of the hermetic type to avoid leaks, and it, combined with its operating accessories, is expensive and requires periodic maintenance. Furthermore, since such a pump circulates nearly saturated liquid, cavitation frequently occurs at the impeller, due to changing suction pressure, and its life is relatively short.

This invention requires no refrigerant pump, and uses a single expansion valve to overfeed a plurality of evaporators, the unevaporated refrigerant from the evaporators flowing into an accumulator where it is evaporated by heat from a' coil through which the high pressure refrigerant liquid flows on its way to the expansion valve. Preferably, the expansion valve is a subcooling control valve which supplies to the active evaporators, refrigerant liquid at the rate at which the latter is condensed while providing subcooling of such liquid. Among the advantages of this invention, in addition to requiring but a single expansion valve, and not requiring a refrigerant pump, are that the internal surfaces of the evaporators are thoroughly wetted, resulting in increased heat transfer and efficiency. Oil return from the evaporators is less difiicult than in systems with thermal expansion valves since the excess refrigerant liquid fed to the evaporators washes the evaporator oil into an accumulator from which it can readily be returned to the associated compressor. Where an air cooled condenser is used, the expansion valve supplies sufiicient refrigerant to the active evaporator or evaporators at low outdoor ambient temperatures when the condensing pressure would be too 3,350,896 Patented Nov. 7, 1967 valve of FIG. 1.

A refrigerant compressor C, driven by an electric motor CM, is connected by discharge gas tube 10 containing a high pressure cut-out HPC, to one end of condenser 11. The other end of the condenser 11 is connected by liquid tube 12 to the inlet end of heat exchange coil 14 within accumulator 15. The outlet end of the coil 14 is connected by tube 16 to tube 19 containing subcooling control valve 17 which is the expansion valve of the system. The tube 19 at the outlet side of the valve 17 is also connected to tube 18 containing a valve VA, adjusted by a solenoid SA, and a hand adjustable valve 20, to one end of evaporator EA; is connected by tube 21 containing a valve VB, adjusted by a solenoid SB, and a hand adjustable valve 22 to one end of evaporator EB, and is connected by tube 24 containing a valve VC, adjusted by a solenoid SC, and a hand adjustable valve 25 to one end of evaporator EC. The other ends of the evaporators EA, EB and EC are connected by tube 27 to the top of the accumulator 15. A U-shaped tube 28 within the accumulator 15 has an open end 29, and its other end is connected by suction gas tube 30, containing a suction pressure control SPC, to the suction side of the compressor C. Portions of the tubes .12 and 30 are in heat exchange contact.

The hand

adjustable valves

20, 22 and 25 are for permitting the evaporators EA, EB, and EC respectively, to be adjusted to suit operating conditions.

The compressor C has cylinders CL1, CL2, CL3 and CL4, with heads H1, H2, H3 and H4 respectively. The plungers of solenoids S2, S3 and S4 extend into the heads H2, H3 and H4 respectively, to depress the usual suction valve reeds which are not shown, for unloading the cylinders CL2, CL3 and CL4 respectively. When the solenoids S2, S3 and S4 are energized, they withdraw their plungers, permitting the suction valve reeds to close during the suction strokes of the respective pistons in the respective cylinders for loading the respective cylinders. The suction pressure control SPC has a plunger 35 pivoted to switch blade 36 between the ends of the latter. The blade 36 is pivoted at one end to fixed support 37, and its other end is curved so as to contact in succession,

switch contacts

38, 39 and 40 which are in a correspondingly curved path, on increases in suction pressure. The contact 38 is connected to one end of the solenoid S2, the other end of which is connected to electric supply line L2.'The contact 39 is connected to one end of the solenoid S3, the other end of which is connected to the line L2. The contact 40 is connected to one end of the solenoid S4, the other end of which is connected to the line L2. The switch blade 36 is connected to electric supply line L1.

The solenoid SA is connected at one end to the line L2, and its other end is connected to one end of thermostat TA, the other end of which is connected to the line L1. The solenoid SB is connected at one to the line L2, and its other end is connected to one end of thermostat TB, the other end of which is connected to the line L1. The solenoid SC is connected at one end to the line L2, and its other end is connected to one end of thermostat TC, the other end of which is connected to the line L1. The evaporators EA, EB and EC may be air cooling coils located in diiferent spaces to be ooled, and the thermostats TA, TB and TC may be space thermostats.

Starter MS of the compressor motor CM, has an energizing winding 45 connected at one to the line L2, and connected at its other end by wire 46 to switch HPCS of the cut-out HPC. The switch HPCS is connected by wire 47 to outdoor thermostat ODT which is connected to the line L1. Thus, the winding 45 is connected in series with the switch I-lPCS and the thermostat ODT to the lines L1 and L2. The motor CM is connected directly to the line L2, and is connected through switch MSS of the starter MS to the line L1.

The subcooling control valve 17, shown in detail by FIG. 2, has a diaphragm chamber 50 with a diaphragm 51 extending across its center. The chamber 50 above the diaphragm 51 is connected by capillary tube 52 to thermal bulb 53 in heat exchange contact with the liquid tube 12. The chamber 50 below the diaphragm 51 is connected by capillary tube 54 to the interior of the tube 12. The valve 17 has a valve chamber 55 below the diaphragm chamber 50, with a partition 56 extending across its interior between its inlet and outlet. The partition 56 has a valve opening 57. The top of a piston rod 58 is attached to the center of the diaphragm 51, and its bottom is attached to a valve piston 59 above the opening 57. A coiled spring 60 extends around the rod 58 between the bottom of the diaphragm chamber 50 and the top of the piston 59, and biases the latter towards the opening 57. An increase in the temperature of the liquid flowing through the tube 12 into the coil 14 tends to adjust the valve 17 towards closed position, while an increase in the pressure of the same liquid tends to adjust the valve 17 towards its open position. For an increase in the rate at which refrigerant is con-densed, if the valve 17 is not sufiiciently open, liquid will back up in the condenser 11 until the pressure has increased sufficiently or the temperature has reduced sufficiently to cause the valve 17 to open further. When the condensing rate changes, the valve 17 readjusts accordingly as do all modulating expansion valves, but it meters refrigerant to the active evaporator or evaporators at the rate at which refrigerant is condensed as does a conventional pilot operated expansion valve controlled by a pilot high pressure float. The subcooling control valve is preferred since it maintains a predetermined amount of subcooling in the condensed refrigerant, which may be, for example, F. subcooling at a condensing temperature of 100 F.

Operation When the outdoor temperature increases to a predetermined temperature, the outdoor thermostat ODT energizes through the closed switch HPCS of the cut-out HPC, the starter MS which closes its switch MSS, energizing the compressor motor CM, and starting the compressor C. The latter supplies discharge gas through the tube 10 and the cut-out HPC to the condenser 11. Refrigerant liquid flows from the latter, through the tube 12, the coil 14 within the accumulator 15, the subcooling control valve 17 and the tube 19 into the active evaporator or active evaporators. If the thermostat TA is calling for cooling, it energizes the solenoid SA which opens the valve VA to supply refrigerant to the evaporator EA. If the thermostat TB is calling for cooling, it energizes the solenoid SB which opens the valve VB to supply refrigerant to the evaporator EB. If the thermostat TC is calling for cooling, it energizes the solenoid SC which opens the valve VC to supply refrigerant to the evaporator EC. The valve 17 overfeeds the active evaporator or evaporators, gas and unevaporated refrigerant flowing from each active evaporator through the tube 27 into the accumulator 15. Gas separated from the liquid within the latter flows into the open end 29 of the tube 28 into the latter, and then through the suction gas tube 30 to the suction side of the compressor C. Heat from the liquid flowing through the coil 14 in contact with the liquid within the accumulator evaporates the refrigerant liquid flowing from the active evaporator or evaporators into the accumulator, the liquid flowing through the coil 14 being subcooled by this action. Any refrigerant liquid which may enter the suction gas tube 30 will be evaporated by heat from that portion of the tube 12 which is in heat exchange contact with the tube 30, the liquid flowing through the tube 12 being further subcooled by this action.

At its minimum load, the compressor C will operate with its cylinder CL1 loaded and its other cylinders unloaded. As the load increases, the suction gas pressure will increase, and the switch blade 36 of the control SPC will move against the contact 38 to energize the solenoid S2 which will withdraw its plunger to load the compressor cylinder CLZ. On a further increase in load, a further increase in the suction gas pressure will cause the switch blade 36 to move against the contact 39 to energize the solenoid S3 which will withdraw its plunger to load the compressor cylinder GL3. On a further increase in the load, the increased suction gas pressure will cause the switch blade 36 to move against the contact 40 to energize the solenoid S4 which will withdraw its plunger to load the compressor cylinder CL4.

If the thermostat ODT should start the compressor when none of the thermostats TA, TB or TC is calling for cooling, the suction gas pressure would decrease below normal, and the usual low pressure cut-out which is not shown, would open its switch, stopping the compressor motor.

While the subcooling control valve disclosed herein is a direct acting one, it could, and for relatively large systems, would be a pilot operated valve such as is disclosed in my copending application, Ser. No. 508,736, filed Nov. 19, 1965, for Controls for Refrigeration Systems now Patent No. 3,320,763 issued May 23, 1967.

What is claimed is:

1. A refrigeration system comprising a refrigerant compressor, a condenser, accumulator means, a heat exchange coil arranged to heat liquid Within said accumulator means, an expansion valve, a discharge gas tube connecting the discharge side of said compressor to said condenser, a liquid tube connecting said condenser to said coil, a third tube connecting said coil to the inlet of said expansion valve, a fourth tube connected to the outlet of said expansion valve, 21 fifth tube connected to said accumulator means, first and second fluid cooling evaporators connected at their outlet ends to said fifth tube, a suction gas tube connecting said accumulator means to the inlet of said compressor, a tube containing a first valve connecting the inlet end of said first evaporator to said fourth tube, a tube containing a second valve connecting the inlet end of said second evaporator to said fourth tube, a first thermostat responsive to the temperature of the fluid cooled by said first evaporator, means including said thermostat for opening said first valve when said first thermostat calls for cooling, a second thermostat responsive to the temperature of the fluid cooled by said second evaporator, means including said second thermostat for opening said second valve when said second thermostat calls for cooling, and means for adjusting said expansion valve to supply refrigerant from said coil into said fourth tube at the rate at which refrigerant is condensed in said condenser.

2. A refrigeration system as claimed in claim 1 in which said expansion valve is a subcooling control valve, and in which said means for adjusting said expansion valve responds to the pressure and the temperature of the liquid flowing through said liquid tube.

3. A refrigeration system as claimed in claim 2 in which said means for opening said first valve comprises a solenoid, and includes means including said first thermostat for energizing said solenoid; and in which said means for opening said second valve comprises a second solenoid, and includes means including said second thermostat for energizing said second solenoid.

4. A refrigeration system as claimed in claim 1 in which said means for opening said first valve comprises a solenoid, and includes means including said first thermostat for energizing said solenoid; and in which said means for opening said second valve comprises a second solenoid, and includes means including said second thermostat for energizing said second solenoid.

5. A refrigeration system as claimed in claim 4 in which said tube containing said first valve also includes a throttling valve, and in which said tube containing said second valve also includes a throttling valve.

6. A refrigeration system as claimed in claim 1 in which said tube containing said first valve also includes 6 a throttling valve, and in which said tube containing said second valve also includes a throttling valve.

7. A refrigeration system as claimed in claim 6 in which said expansion valve is a subcooling control valve, and in which said means for adjusting said expansion valve responds to the pressure and the temperature of the liquid flowing through said liquid tube.

References Cited UNITED STATES PATENTS 2,472,729 6/1949 Sidell 62503 X 3,234,752 2/1966 Quick 62196 X MEYER PERLIN, Primary Examiner.

Claims

1. A REFRIGERATION SYSTEM COMPRISING A REFRIGERANT COMPRESSOR, A CONDENSER, ACCUMULATOR MEANS, A HEAT EXCHANGE COIL ARRANGED TO HEAT LIQUID WITHIN SAID ACCUMULATOR MEANS, AN EXPANSION VALVE, A DISCHARGE GAS TUBE CONNECTING THE DISCHARGE SIDE OF SAID COMPRESSOR TO SAID CONDENSER, A LIQUID TUBE CONNECTING SAID CONDENSER TO SAID COIL, A THIRD TUBE CONNECTING SAID COIL TO THE INLET OF SAID EXPANSION VALVE, A FOURTH TUBE CONNECTED TO THE OUTLET OF SAID EXPANSION VALVE, A FIFTH TUBE CONNECTED TO SAID ACCUMULATOR MEANS, FIRST AND SECOND FLUID COOLING EVAPORATORS CONNECTED AT THEIR OUTLET ENDS TO SAID FIFTH TUBE, A SUCTION GAS TUBE CONNECTING SAID ACCUMULATOR MEANS TO THE INLET OF SAID COMPRESSOR, A TUBE CONTAINING A FIRST VALVE CONNECTING THE INLET END OF SAID FIRST EVAPORATOR TO SAID FOURTH TUBE, A TUBE CONTAINING A SECOND VALVE CONNECTING THE INLET END OF SAID SECOND EVAPORATOR TO SAID FOURTH TUBE, A FIRST THERMOSTAT RESPONSIVE TO THE TEMPERATURE OF THE FLUID COOLED BY SAID FIRST EVAPORATOR, MEANS INCLUDING SAID THERMOSTAT FOR OPENING SAID FIRST VALVE WHEN SAID FIRST THERMOSTAT CALLS FOR COOLING, A SECOND THERMOSTAT RESPONSIVE TO THE TEMPERATURE OF THE FLUID COOLED BY SAID SECOND EVAPORATOR, MEANS INCLUDING SAID SECOND THERMOSTAT FOR OPENING SAID SECOND VALVE WHEN SAID SECOND THERMOSTAT CALLS FOR COOLING, AND MEANS FOR ADJUSTING SAID EXPANSION VALVE TO SUPPLY REFRIGERANT FROM SAID COIL INTO SAID FOURTH TUBE AT THE RATE AT WHICH REFRIGERANT IS CONDENSED IN SAID CONDENSER.