US2728197A

US2728197A - Defrosting control for refrigerating system

Info

Publication number: US2728197A
Application number: US310308A
Authority: US
Inventors: Francis R Ellenberger
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1952-09-18
Filing date: 1952-09-18
Publication date: 1955-12-27
Anticipated expiration: 1972-12-27

Description

Dec. 27, 1955 F. R. ELLENBERGER g I 2,728,19?

DEFROSTING CONTROL FOR REFRIGERATING' SYSTEM v Filed Sept. 18, 1,952

lhventOY Francis R EHenberger,

His Attorney.

United States Patent DEFROSTING CONTROL FOR REFREGERATING SYSTEM Francis R. Ellenberger, Verona, N. 5., assignor to General Electric Company, a corporation of New York Application September 18, 1952, Serial No. 310,308

3 Claims. (Cl. 62- 4) This invention relates to refrigerating systems and particularly to systems having evaporator coils for cooling air and controls for effecting defrosting of the coils automatically.

Refrigerating systems for cooling air frequently include evaporators or cooling units which must operate below the freezing point of water and on which substantial quantities of frost collect and decrease the rate of heat transfer, thereby decreasing the effectiveness of the system. It is desirable to provide some arrangement for effecting defrosting automatically without the necessity of frequent attendance of an operator and manual servicing. The defrosting operation may be accomplished in many ways; for example, operation of the cooling unit may be discontinued a sufficient length of time to permit a rise in temperature and melting of the frost, or heat may be applied artificially. The heat may be supplied either directly at the cooling unit or by heating the air circulated over the unit or by reversing the refrigerating machine to supply hot compressed refrigerant to the cooling unit. Reversed cycle refrigerating machines may be employed as year-round air conditioning equipment, and during the winter season frost collects on the outdoor heat transfer coil. It is desirable that air conditioning systems require minimum attention, and it is therefore desirable to provide defrosting automatically whenever a predetermined accumulation of frost has collected on the cooling unit. Accordingly, it is an object of this invention to provide a refrigerating machine having a cooling unit for cooling air to temperatures below freezing and an improved automatic defrosting control.

It is another object of this invention to provide a defrosting control for refrigerating systems including a simple and effective arrangement for initiating and terminating defrosting automatically.

Further objects and advantages of the invention will become apparent as the following description'proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming apart of this specification.

In carrying out the objects of this invention, a refrigerating machine is provided in an air cooling system including a cooling unit arranged in an air duct having a blower for circulating air over the surface of the unit. In order to indicate the accumulation of frost 0n the cooling unit, a small by-pass is provided to circulate air around the cooling unit and a flow responsive device is arranged in the by-pass to initiate defrosting whenever the flow of air through the by-pass is increased to a predetermined amount, this increase being caused by the accumulation of frost on the cooling unit and the consequent restriction of the main air duct. The flow responsive device may be employed to initiate defrosting by reversing the refrigerating machine to supply heat to the cooling unit.

For a better understanding of the invention, reference may be had to the accompanying drawing the single figure of which illustrates diagrammatically a heat pump installation for air conditioning provided with a control for automatically defrosting the outdoor air heat exchanger.

Referring now to the drawing, the air conditioning system illustrated includes an indoor heat transfer coil 10 arranged in a duct 11 through which air to be conditioned is circulated by a blower 12 driven by a motor 13, return air being admitted to the duct 11 through an inlet 14 and fresh air through an inlet 15, and conditioned air being returned to the rooms through an outlet 16. The heat transfer unit 10 may be connected either as the evaporator or the condenser of a refrigerating machine so that the air in the duct 11 may be either heated or cooled as desired. The refrigerating machine includes a refrigerant compressor 17 driven by an electric motor 18 and an outdoor heat transfer unit 19, the two heat transfer units and the compressor being connected in a closed refrigerant circuit provided with threeway reversing valves 20 and 21 for selecting either the heating or the cooling operation. The heat transfer unit 19 is arranged in an outdoor air duct 23 arranged to receive outdoor air from an inlet 24 in the wall of the building indicated at 25 and provided with a blower 26 driven by a motor 27 for circulating the air through the duct and returning it to the outside through a duct connection (not shown). The system is controlled by operation of a bi-metallic blade thermostat 28 arranged to engage a heating contact 30 when the room temperature is below a predetermined value and a cooling contact 29 when the temperature is above a higher predetermined yalue. The electrical control system is connected to the secondary of a transformer 35 the primary of which is connected across

supply lines

31 and 32, and upon operation of the thermostat 28 either a cooling relay 33 or a heating relay 34 is operated. Each of these relays is provided with two switches, the lower of each of which connects a coil 36 of a solenoid switch 37 across the

lines

31 and 32 and energizes the

motors

13, 18 and 27, thereby starting the operation of the air conditioning system.

During the cooling season, the refrigerating machine operates to supply hot compressed refrigerant to the outdoorheat exchange unit 19 through the valve 21, and the indoor heat exchange unit 10 is connected as an evaporator to cool the air circulated through the duct 11. This operation is effected upon movement of the thermostat 28 to engage the left-hand contact 29 and actuate the cooling switch 33, to close the normally open upper contacts thereof. The upper contacts of the switch 33 completea' circuit from the line 31 through a connection 38, then in parallelthrough lower solenoid coils 39 and 40 of the three-way: valves 20 and 21, respectively, and thence back to the'line 32 through a connection 41. The compressor 17 then operates to discharge hot compressed refrigerant to the valve 21, thence through the lower outlet of the valve and a conduit 42 to the unit 19 where the refrigerant is cooled and liquefied upon giving up heat to the air circulated by the duct 23. The liquefied refrigerant then flows through a connection 43 and a check valve 44 to a liquid receiver 45. From the liquid receiver, the refrigerant flows through a liquid line 4-6 under control of a thermostatic expansion valve 47 to the unit 10 through a connection 48. The liquid refrigerantin the unit 10 is vaporized by the absorption of heat from the air flowing through the duct 11, and the vaporized refrigerant is returned to the compressor through the upper inlet of the valve 20 and a suction line .49 connecting the outlet of the valve 20 and the intake of the compressor.

During the heating season when the temperature falls to .a predetermined value below the range of operation- Patented Dec. 27, 19 55 during. the coolingv season, the bimetallic blade thermostat 28 engages the contact 30 and energizes the coil of the switch 34, this coil being connected across the secondary of the. transformer through the thermostat and a normally closed set of contacts of a. solenoid switch-51 having four sets of

contacts

50, 52,53 and 54 respectively. Upon energization of the switch 34, its lower contacts close the circuit of the coil 36 to actuate the switch 37 and initiate operation of the refrigerating machinev and air circulating system. The upper set of. contacts of the switch 34 energizes the circuit of actuating solenoids 55 and 56 of the valves 20 and 21. This: circuit may be traced. from the line 31 through the upper contacts of the switch 34, a connection 57, the coils 55 and 56in parallel, and thence to the line 32 through the connection 41. Energization of the coils 55 and 56 shifts the valves 20 and 21 so that the compressor 17 delivers hot compressed refrigerant to the unit 10 through connection 48, the thermostatic valve 47 automatically closing to prevent passage of refrigerant into the line 46. The refrigerant is liquefied in the unit 10 by the cooling of the. air passing through the duct. The air is thereby warmed and returned to the rooms. The liquefied refrigerant then flows through a line 58 and a check valve 59 to the receiver 45 and then flows from the receiver through the line 46 to the unit 19 under control of a thermostatic expansion valve 60. The refrigerant in the unit 19 is vaporized by the absorption of heat from the outdoor air flowing through the duct 23, and the vaporized refrigerant is returned to the compressor through a suction con nection comprising the line 43, a connection 61, the valve 20, and the suction connection 49. The operation of. the system continues to eflect heating of the air in the rooms supplied by operation of the blower 12 until the thermostat 28 reaches a predetermined high temperature at which it moves away from contact 30 and stops operation of the system.

During the operation of the refrigerating machine to supply heat to the air through duct 11, it is necessary at times to operate the unit 19 as an evaporator below the freezing point of water, and the moisture condensed on the surface of the unit 19 is frozen and builds up a layer of frost. In order to maintain the efiicient operation of the, unit 19, it is necessary to remove the frost before it accumulates to an extent that heat transfer is seriously impeded. In order to detect the accumulation of frost, an air duct 62 is provided constituting a by-pass around the unit 19. The duct 62 receives air through an; inlet 63 and returns the air to the duct 23 through an outlet 64. As frost accumulates on the surface of the unit 19, the flow of air through the unit is decreased by. the de creased effective cross-sectional area of the duct and an increased flow of air occurs through the by-pass 62. Thisincreased flow of air may be employed. as an indication of the presence of a predetermined accumulation of. frost on the surface of the evaporator 19, and, for this purpose, a device dependent upon the change of the flow Off air in the duct 62 is employed to initiate the defrosting operation of the system.

In the system illustrated in the drawing, a snap-acting switch 65 is arranged to be actuated by a vane 66mount ed in the by-pass 62. The vane is normally biased to a position toward the intake 63 of the by-pass .by an. adjustable compression spring 67. The vane is therefore normally in a position opposing the flow of air from the inlet 63 toward the outlet 64. As the passage of air through the duct 23 is restricted by the accumulation of frost on the unit, increased air flows through by-pass 62 until the force thereof is sufficient to move the vane 66' to the left about its pivot indicated at 68 and thereby compress the spring 67 and move an'arm 6.9 of the switch 65 to the right: until. a spring 70.passesovercenten with respect to a pivot 71 and causes actuation of av switch arm 72. The-switch arm 72 normally restsagainst a stop. 73 and: upon actuation is snapped bysthe'. over:

center. action. Of the spring 70 to engage a contact 74. This closes a circuit from one side of the secondary of the transformer 35 through a line 75, the switch arm 72, and contact 74, and thence through a line 76, a coil 77 of the switch 51, and back to the other side of the primary through a connection 78. The coil 77 is thereby energized and actuates the switch 51 to open its contacts 50 and thereby prevent energization of the coil of the switch 34 and close its contacts 52 to energize the switch 33. It is thus apparent that the operation of the refrigerating machine will be reversed by de-energizing of the coils 55 and 56 and energizing the coils 39 and 40. Thereupon, the hot compressed refrigerant will be delivered to the unit 19 through the connection 42 and the heat will melt the frost on the surface thereof, the resulting water being drained off through any suitable connection, not shown.

During this defrosting operation, circulation of cold outdoor air through the duct 23 is prevented by stopping the blower motor 27 the circuit of which is opened when the coil 77 is energized to actuate the switch 51, the normally closed contacts 53 being in the circuit of the motor 27. At the same time the normally open contacts 54 are closed to shunt the vane actuated switch 65,

through a lead 78 and a switch 79 actuated by a temperature responsive bellows 80. Thus, even though the vane 66 is restored to its normal position, separating the contacts 72 and 74 due to interruption of airflow through duct 23 when blower motor 27 is stopped, thev defrosting operation will be continued because the coilv 77 will be energized through the shunt or holding cit:- cuit. The temperature responsive bellows 80 is provided with a temperature feeler element 81 adjacent the outlet.

line 43 of the coil 19, and when the, temperature of the refrigerant withdrawn from the coil exceeds a predetermined value the, bellows 80 expands and opens the switch 79, thusv terminating the defrosting operation, the switch 65 being open at this time since it will have been restored by the stopping of air flow through the duct 62 when contacts 53 are opened. Deenergization. of the switch coil 77 opens

contacts

52 and 54 and closes.

contacts

50 and 53 thereby deenergizing the coil of the switch 33 and energizing the coil of the switch 34' provided there is a call for heating by the thermostat 28.

The temperature responsive bellows 80 and holding circuit including switch 79 have been illustrated byway of example, it being obvious to those skilled in the art that other mechanisms may be employed to continue the defrosting operation for the desired period.

The degree of frosting of the evaporator necessary to actuate the switch 65 may be adjusted by adjustingv the. compression of the spring 67 by turning of, a knob 82. Theamount of air flowing through the duct 62 may also be variedto adjust the setting of the control by varying the. position. of adamper 83 arranged. to restrict the passage through the. inlet 63. The damper 83 may be adjusted by turning its threaded stem, indicated at 84.; From the foregoing, it is readily apparent that a.-

simple and effective arrangement has been provided for initiating defrosting of the evaporator of a refrigerat ing machine automatically upon the accumulation of a predetermined amount of frost on its surface. Furthermore, the amount of accumulation of frost which is to be permitted may readily be determined by adjust- What I claim as new and desire to secure by Letters Patent of the United States is:

1. A refrigerating machine including a cooling unit, means for circulating over said unit air to be cooled, means for operating said machine to cool said unit below the freezing point of Water whereby frost tends to collect on the surface of said unit, duct means providing a by-pass around said unit whereby an increased rate of flow of air occurs through said by-pass upon restriction of the path of flow through said unit upon the accumulation of frost thereon, a movable vane in said by-pass in the path of the air flowing therethrough, means for biasing said vane to a position toward the inlet of said by-pass, means dependent upon movement of said vane away from said position for effecting the defrosting of said unit, means responsive to the temperature of the refrigerant in said cooling unit to terminate the defrosting operation, and damper means in said by-pass for varying the effective inlet area of said by-pass for determining the degree of frosting of said coil required to actuate said vane.

2. A refrigerating machine including a compressor and a condenser and an evaporator connected in a closed refrigerator circuit, means for circulating air to be cooled over said evaporator, means for operating said machine to cool said evaporator below the freezing point of water whereby frost tends to collect on the surface of said evaporator, means including a switch for reversing the refrigerant circuit of said machine to interchange the functions of said evaporator and said condenser and supply heat to said evaporator to defrost the surface thereof, duct means providing a by-pass for conducting air around said evaporator whereby an increased rate of flow of air occurs through said by-pass upon a restriction of the path of flow through said evaporator upon the accumulation of frost, a movable vane in said by-pass connected to actuate said switch, means for biasing said vane in a direction resisting the flow of air through said by-pass whereby upon the occurrence of a predetermined fiow of air through said by-pass said vane actuates said switch to initiate defrosting of said evaporator, and means responsive to the temperature of the evaporator during defrost to terminate the defrosting operation.

3. A refrigerating machine including a compressor and a condenser and an evaporator connected in a closed refrigerant circuit, means for circulating air to be cooled over said evaporator, means for operating said machine to cool said evaporator below the freezing point of water whereby frost tends to collect on the surface of said evaporator, means for reversing the refrigerant circuit of said machine to interchange the functions of said evaporator and said condenser and supply heat to said evaporator to defrost the surface thereof, duct means providing a by-pass for conducting air around said evaporator whereby an increased rate of flow of air occurs through said by-pass upon a restriction of the path of flow through said evaporator upon the accumulation of frost, means including an electrical switch for reversing said refrigerating machine to effect defrosting of said evaporator, a movable vane in said by-pass connected to actuate said switch, means for biasing said vane in a direction resisting the flow of air through said by-pass whereby upon the occurrence of a predetermined flow of air through said by-pass said vane actuates said switch to initiate defrosting of said evaporator, means responsive to the temperature of the refrigerant in said cooling unit to terminate the defrosting operation, and damper means for adjusting the effective inlet area of said by-pass to determine the degree of restriction of air through said evaporator necessary to initiate defrosting.

References Cited in the file of this patent UNITED STATES PATENTS 2,015,249 Benesh Sept. 24, 1935 2,060,848 Boyle Nov. 17, 1936 2,143,687 Crago Jan. 10, 1939 2,303,857 Numero et a1. Dec. 1, 1942 2,323,511 Baker July 6, 1943 2,633,004 Leeson Mar. 31, 1953 2,654,227 Mufliy Oct. 6, 1953 2,662,380 Sutton Dec. 15, 1953