US2952991A

US2952991A - High side pressure control for refrigeration systems

Info

Publication number: US2952991A
Application number: US794669A
Authority: US
Inventors: Pierre John N St
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 1959-02-20
Filing date: 1959-02-20
Publication date: 1960-09-20
Anticipated expiration: 1977-09-20

Description

Sept. 20, 1960 J. N. ST. PIERRE 2,952,991

HIGH SIDE PRESSURE CONTROL FOR REFRIGERATION SYSTEMS Filed Feb. 20, 1959 INVENTOR. JOHN N. ST. PIERRE ATTORNEY United States Patent ,0

HIGH SIDE PRESSURE CONTROL FOR REFRIG- ERATION SYSTEMS John N. St. Pierre, North Syracuse, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Feb. 20, 1959, Ser. No. 794,669

Claims. (Cl. 62-184) This invention relates to a control for refrigeration systems and more particularly to means for controlling the high side pressure in a refrigeration system.

In refrigeration systems, the portion thereof which operates at substantially discharge gas pressure is considered the high side. This usually includes the condenser, hot gas line, liquid line and the receiver. The portion of the system that operates at substantially suction gas pressure is considered the low side and usually includes the evaporator and the suction line.

It is common to operate commercial refrigeration systems throughout the year. Very often, such refrigeration systems include air cooled condensers. In such situations, the condenser is located out of doors and is subject to a wide variation of ambient temperatures. During periods when the ambient temperature is very low, the condensing pressure within the air cooled condenser drops to an extremely low level resulting in the poor feed of liquid refrigerant fi-om the high side through the expansion means into the low side of the refrigeration system.

Various devices have been proposed to overcome these poor operating characteristics which result during periods of low ambient temperatures. One of the devices includes the use of a bypass around the condenser whereby the hot gas discharge line pressure is directly utilized ceiver, expansion means and an evaporator connected in a circuit. A fan driven by an induction motor is provided for passing air over the condenser in heat exchange relation with the refrigerant passing therethrough and means are provided for varying the volume of air passed over the condenser in response to the pressure of. the refrigerant in the condenser by decreasing the fan speed by a decrease in voltage across the motor terminals.

The attached drawing is a schematic view of a refrigeration system embodying the present invention.

Referring to the drawing, there is shown a refrigeration system which includes a compressor 2 having ex-' tending therefrom a hot gas discharge line 3 which is connected to a condenser 4. A liquid line 5 extends. from the condenser 4 to a receiver 6. The receiver 6 collects liquid refrigerant from the condenser. This liquid refrigerant passes through the expansion means 7 into the evaporator 8 wherein the refrigerant is substantially vaporized and returns through the suction line 9 to the compressor 2.

The expansion means may be the usual thermal expansion valve which includes a capillary line 10 which. connects the valve and a temperature sensing bulb 11 located on the suction line. If it is desired, other types of expansion devices may be used such as capillary tubes.

for providing the motivating force for urging liquid re-- frigerant in the receiver through the expansion means into the low side of the refrigeration system. Another device which has been proposed consists of a plurality of face dampers which restrain the passage of air over the heat exchange surface of the condenser thereby drastically reducing the heat exchange between the coolant air and the refrigerant passing through the condenser.

In the case of the bypass around the condenser, it has been found that a substantially larger amount of refrigerant is required in the system than is normally needed; so the pressure control required in this system causes a higher initial cost of the system. With respect to the face dampers, the operation of such dampers is problematic being subject to frequent breakdowns and the'initial cost of the system is also high.

The chief object of the present invention is to provide a refrigeration system having an improved control for maintaining high-side pressure.

Another object of the invention is to provide a refrigeration system wherein the amount of air passing over the condenser is regulated in response to the high side pressure.

A further object is to provide a refrigeration system having a condenser through which air is passed by a fan connected to an induction motor and including means for varying the speed of the induction motor in response to the high side refrigerant pressure. Other objects of the present invention will become more apparent from the following description.

This invention relates to a refrigeration system including in combination a compressor, a condenser, a re- With respect to the condenser 4, the drawing discloses a condenser which includes a hot gas manifold 15 which is connected to a liquid manifold 16 by means of a plurality of serpentine coils 17. These coils 17 substantially define the heat exchange surface of the condenser.

Normally, there is associated with heat exchangers such as the condenser 4 and the evaporator 8, one or more air moving means such as fans. In the present drawing the fan 20 is operatively associated with the condenser 4 and if it is desired, suitable fans may be used with the evaporator 8.

It is well known that in a given refrigeration system under a given load the head or high side pressure is related to the condensing temperature of the refrigerant Within the condenser. The condensing temperature is usually governed by the temperature of the coolant acting upon the condenser to abstract heat from the refrigerant gas which is discharged into the condenser through the hot gas discharge line extending from the compressor. If the temperature of the coolant which is in heat exchange relation with the refrigerant gas passing through the condenser falls to a loW temperature, a decrease in the head or high side pressure results. This decrease in pressure will lessen the rate of feed of i refrigerant through the expansion device and thereby deleteriously affect the operation of the refrigeration system.

It is envisioned that the refrigeration system which comprises the present invention will be used under circumstances where the condenser will be remote from the evaporator, that is, the condenser is an air cooled condenser which will normally be located out of doors. The evaporator will normally be located adjacent some heat load within a given structure. Under such circumstances, during certain times of the year when a low order to achieve satisfactory operation of the refrigeration system under such circumstances, the present invention visualizes decreasing the amount of coolant air whrch is passed into heat exchange relation with the refrigerant passed through the plurality of serpentine coils 17. This is achieved by varying the speed of the' fan 20. a

It is well known that varying the speed of alternating current motors is extremely difiicult. The present inthestart winding ZS-has located'inseries therewitha capacitor 36. h n h 7 Considering the electrical cir uit; of the motor' ZS; the motor is connected byv means of the lines 30-.an'd 3-1 to a source of single phase alternating; current. The line 30 is connected-tothe windingsZTand 28. Ihe opposite end of the winding 27 is connected fo the line 351. The other end of therwinding 28 is connectedtdthe line34 which as previously noted, includes therein th capacitor 36. The line 34 joins the line 35 which terminatesat the-reactor 32' which is a variable inductance including. a coi1'32 which in the present application h'as-ani'ron core. In order toachieve variation of'this inductance; a pivoted contact lever 33 isrpivotally mounted "atf'45 and is so constructed that contact maybe made'with the. windings of the reactor 32' over a plurality of points therehy pro viding a large number of contacts and thereby a large gradation of inductances. The line 31'is con'nected to the contact'lever 33 at the point 45. 7

In order to Vary the inductance of the reactor 32, a suitable pressure responsive element 40 isass'ociatedwith the reactor. This pressure responsive element includes a: bellows 42 which acts against a .biasspring 43; The bellows 42 is connected to the contact lever 33 by means ofthe member 44 so that any motion in-the bellows will ;be reflected in the rotationiof the contact lever 33 and the consequent variation in inductance in the motor circuit. I I

The bellows 42 isconnected by means of a line 41' to the hot gas manifold of the condenser 4. It will be immediately appreciated that any variations in the condensing pressures'of the condenser 4 will be sensed by the bellows and reflected ina' change of the inductance which is in'series with the windings of themotor'25i Considering the operation of the present invention, current is passed through the lines '30 and 31 and the contact lever 33 is in a positionesothat the entireinductance of the reactor is substantially removed-from the. electrical circuit of the motor 25. The currentpasses through the Winding 27 and similarly passes through the starting circuit which includes the capacitor 36 and the start winding 28. a

'9,9e2,991 V a. V, T

leaves the evaporator 8, passes through the suction line 7 system. In the present invention, however; this" decrease in condensing pressureis'sensed by the pressure responsive control 40 which is in communication with the hot gas manifold of thecondenser 4 by-' means of theline 41. This decrease in pressure-will cause the-bellows 42 to shrink in response to the decrease in pressure. This; consequently causesthe contact lever 33 to moveto the dotted position shown .in the drawing. This movement of the contact leverintroduces an increasing inductance in series with the induction motor 25.,

The reactor is an energy storing device and not an 7 energy dissipating device so that} the voltagedecreases across the motor terminals without any loss of power in the System; 3 t

It is well'khown that theitorque;of'aninductionmotor varies proportionately to thesquare of'the voltage across the motor' terminals. Likewise, it i s known that the torque requirements of fan and other moving devices increases with speed. It is also knownthatthe torque. characteristics of a motorgstart' at a; given torque for locked rotorconditions' and incfease with speed 'until a maximum is reached whereupon thetorque sharply de- Because of the phase shift providedby the capacitance inxthefstarting'circuit, the single phase motor will begin torotateand operate at a speed-slightly less than the synchronous speed of the motor field. V V V Considering the refrigerationcircuit, the compressor 2t discharges refrigerant gas through/the hot discharge gas line 3 into thehot gas'manifoldlSityf-the condenser 4.. Under normah-circumstances the gas; willpas's into the serpentine coils 17 and be in heatj'exchange relation with the coolant? air being passed' over the. serpentine;

coils 17 by thefan 20. The gaseous refrigerant issubstantially liquified in the serpentinefc'oi-ls and collected in" the liquid'manifold 16 This liquid refrigerant'is passed through the liquid line 5 and collected within the re ceiver"6.' This liquid refrigerant then passes 'from the high side through expansiongvalve 7 'intd -the low"side which ineludes the evaporator: 82 The refrigerant-as it creases until a no torque condition is reached-at synchronousspeed. U I' By introducing the inductance in T theci'rcuit which pro-- vides a'voltage drop in thesupply line there is a; consequent reduction" in voltage across the motor terminals. Since as previously noted, motor torque: is proportional to the 'square of the voltage across 'the I terminals; there will be a decrease inspeed of the rnotor'i This-decrease in speed will diinini'shfthe amount of'coolant air placed in heat exchange relation with refrigerant passing through the condenser 4. Accordingly,'there will beat tendency of the refrigerant in the condenser to reach-normal condensing temperatures and pressnrestomaintainf an adequate feed of refrigerant through'the-ternia-l' expansion valve into the evaporator; 7

By meansof a reactor or variahle inductanceandla head pressure responsiveelement; thef'present'invention permits satisfactory operation: of the refrigeration system under conditions where low ambieii'tjternperatures 'may" induction motor. This is alsoachiev'ed:withoutthe-use of expensive facedampers 'or expensive bypass systems wherein large amounts of refrigerant are needed tofcom' pensate for flooding conditionswhichioccurfinftliecon denser when a bypass is utilized} 5 7 f While I have described"a' 'preferredi'ernbodiinent of limited thereto since i't-fni a'y be otherwise employedwith in. the scope of'therfollowin'g' clahnsi 1'. Q17 .1? 1. In a refrigeration sy s'tem,'- the combination or; acompressor, a condenser; areceive'r; expansion-means and an evaporator connected fir'f'ac'ircnitg the condenser comprising a hotflgas header having a plurality or heat exchange surfaces extending therefrom withr efiigerant paths passing therethro igh; j said heat ex nange i iur'faces being connected to'a liquid'heade atleasfiofie fanfor passing air, into heat exch ge re1 atierr the condens er, said fanlhein'g connected to treasuresreater. a variable inductanc'e'being cbnneeted{ induction motor; and means responsiv th ressure i j of the refrigerant passing through;the condenserfsaid pressure respo s ea s heinlgiopera'tiveli eonnected e ie was said with said hot gas header and with said variable inductance whereby when the pressure in the condenser decreases to a predetermined point the variable inductauce connected in series with the induction motor increases the amount of inductance in the circuit to decrease the volume of air passing into heat exchange relation with the condenser by decreasing the fan speed permitting the pressure of the refrigerant in the condenser to increase.

2. In a refrigeration system, the combination of a compressor, a condenser, expansion means, and an evaporator connected in a circuit, said condenser including a heat exchange coil with a path for refrigerant therethrough; fan means for passing air over said heat exchange coil for condensing refrigerant vapor passing therethrough; an induction motor connected to said fan means; a variable inductance connected in series with the induction motor for varying the speed of the fan means; pressure responsive means; means connecting the pressure responsive means with the heat exchange coil to impose refrigerant pressure upon the pressure responsive means, and means operatively connecting said pressure responsive means to the variable inductance Whereby a decrease in refrigerant pressure increases the amount of inductance in series with the induction motor to decrease the amount of air passing over said heat exchange coil by decreasing the speed of said fan means.

3. A refrigeration system as in claim 2 wherein said pressure responsive means comprises a bellows.

4. A refrigeration system as in claim 3 wherein said bellows is expanded in one direction upon an increase in refrigerant pressure in the condenser and is spring biased in an opposite direction upon a decrease in pressure to collapse the bellows.

5. In a refrigeration system, the combination of a compressor, a condenser, expansion means, and an evaporator connected in a circuit, said condenser having a heat exchange coil through which refrigerant passes, fan means for passing air into heat exchange relation with the condenser, said fan means being connected to an electric motor, a variable inductance connected in series with said motor, pressure responsive means, means connecting said pressure responsive means with said condenser, and means connecting said pressure responsive means with said variable inductance whereby when the pressure in the condenser decreases to a predetermined point the variable inductance connected in series with the electric motor increases the amount of inductance in the circuit to decrease the volume of air passing into heat exchange relation with the condenser by decreasing the speed of the fan means permitting the pressure in the condenser to increase.

References Cited in the file of this patent UNITED STATES PATENTS 2,705,404 Malutich Apr. 5, 1955