US3487654A - Deicing control apparatus for forced air refrigeration system - Google Patents

Description

J 6 197 J. LORENZ 3,487,654

DEICINCT CONTROL APPARATUS FOR FORCED AIR REFRIGERATION SYSTEM Filed May 14, 1968 v INVENTOR.

JEROME L. LORENZ BY WM M ATTORNEYS United States Patent 3,487,654 DEICING CONTROL APPARATUS FOR FORCED AIR REFRIGERATION SYSTEM Jerome L. Lorenz, Columbus, Ohio, assignor to Ranco Incorporated, Columbus, Ohio, a corporation of Ohio Filed May 14, 1968, Ser. No. 728,953 Int. Cl. F25d 21/02, 21/08 US. Cl. 62-140 5 Claims ABSTRACT OF THE DISCLOSURE A forced air circulation type refrigerator is shown in which air is forced over the surfaces of a heat exchange unit normally maintained at below freezing temperatures. A device is provided for initiating a defrost cycle of the unit and comprises a control circuit which responds to a change in voltage at the junction of a voltage divider to actuate a control device and initiate a defrost cycle. The bridge circuit includes two self-heated resistance elements located in separate air flow paths of a fluid amplifier device and which air flow dissipates heat from the respective resistance element according to the volume of flow through one or the other paths. The fluid amplifier comprises a main flow inlet passage and two alternate flow outlet passages arranged to pass air from the high pressure air upstream of the chilling unit to the lower pressure downstream side of the unit. The main stream is directed into one or the other outlet passages by two opposed control jets effective according to the pressure differential of air on opposite sides of the chilling unit and operative to shift the main flow in response to an increase in air pressure differential. The actuation of the deice device locks out the initiating control circuit and renders a thermostatically actuated switch effective to restore normal refrigeration operation after the chilling unit reaches a predetermined ice melting temperature. The fluid amplifier device can be easily installed and adjusted for operation in a wide variety of forms of forced air refrigeration systems.

The present invention relates to a control apparatus for automatically deicing or defrosting the heat transfer surfaces of an air chilling unit of a refrigerating system in which system air is forced over heat exchange surfaces of the unit which are maintained below freezing temperatures causing moisture to condense and freeze thereon.

The invention is an improvement over the types of automatic control apparatuses which initiate an automatic deicing cycle of air chilling units in response to an increase in air pressure differential between air at the entrance of the chilling unit and air discharge side of the unit. Examplary systems of this type are disclosed in US. Patents 3,004,399, 3,066,496 and 3,309,887.

The principal object of the present invention is the provision of an automatic deicing control for refrigerating systems of the character mentioned which can be easily installed in conventional refrigerating systems with a minimum of alteration of the system and which has an air ressure differential responsive mechanism which is inexpensive to manufacture, positive and accurate in action and which can be readily installed in various forms of 3,487,654 Patented Jan. 6, 1970 amplifier circuit for actuating a deicing device and which circuit responds to a change in resistance of a voltage divider circuit including two heat sensitive electrical resistance elements connected to a common junction, the resistance elements being normally heated and heat is dissipated therefrom by locating the resistances in two alternate air flow paths, the air flow through one or the other of the alternate paths being established according to the air pressure differential between the air inlet and outlet sides of the chilling unit. In the preferred form of the invention the alternate air flow paths in which the respective resistance elements are located are part of an air flow passage device having a main flow inlet communicating with the high air pressure side of the chilling unit and the flow outlet, including the alternate air flow passages, communicating with the low air pressure side of the chilling unit. The flow of air from the main flow to one or the other of the alternate paths is determined by first and second control jets of air discharging into the main stream transversely of and on opposite sides thereof. The sources of air for the control jets are from the main stream and from the low air pressure side of the chilling unit respectively. The flow of air in the first control jet may be adjustably set to provide for deflection of the main flow into one alternate path when the air flow through the chilling unit is relatively free and when ice accumulates on the surfaces of the chilling unit sufficiently to appreciably impede the flow of air through the chilling unit, the pressure differential at the inlet and outlets of the main air stream increases causing the jet air in the first control jet to increase in influence on directing the main stream to the second alternate air flow passage. This shifting of air flow from one passage to the other occurs more or less proportional to the increase of air from the first control jet whereby the resistance element formerly having heat thereof carried away by the air stream increases in temperaturewhile the other resistance element is cooled by the airflow now passing thereover. By reason of the relatively substantial changes in temperatures the electrical resistances of the elements affecting the amplifier controlling the deice cycle initiating device readily responds to the change in voltage of the divider circuit. When the deice cycle control device is actuated, the amplifier circuit is bypassed and control of the device is established through a thermostatic switch which is actuated in response to a deice temperature in the chilling unit to re-establish normal refrigeration cycles in the chilling unit.

Important advantages of the invention include the use of relatively inexpensive resistance elements and circuit amplifying components because of the shifting of the cooling stream of air from one resistance element to the other which produces a wide swing in temperature and resistance, Furthermore, the operation of the deice control apparatus is not readily affected by abnormal temperature and pressure changes which may occur temporarily in the refrigeration system. In addition, the air stream fiow control may be conveniently located and may be readily adjusted to produce deicing in response to given icing conditions.

Other objects and advantages of the invention will be apparent from the following description of a preferred form thereof, reference being made to the accompanying drawings wherein:

FIG. 1 is a schematic fragmentary sectional view of a refrigerator embodying the invention;

FIG. 2 is a sectional view taken substantially along line 22 of FIG. 1, and on a larger scale; and

FIG. 3 is a Wiring diagram of the deicing control apparatus embodying the form of the invention disclosed.

Referring to the drawings, a refrigerator R is shown, which may be of conventional construction and comprises a cabinet having a partition 11 across the upper portion thereof which divides the cabinet into an air chilling compartment 12 and a food storage compartment 13. A wall 14 between the upper wall of the cabinet and the parti' tion 11 further defines the compartment 12. Air passage openings 15, 16 are formed in the partition 11 and an air passage opening 17 is formed in the wall 14.

An air chilling unit 20 is located in the compartment 12 and comprises the evaporator of a conventional compressor-condenser-expander refrigerating system in which the compressor is driven by an electric motor 21. For sake of brevity, the compressor and condenser are not shown and the motor 21 is shown schematically. The chilling unit 20 comprises a refrigerant pipe 22 formed to extend in closely spaced parallel reaches across the compartment 12, the reaches having metal fins 23 attached thereto to form numerous air passages, the walls of which provide considerable heat exchange surfaces. Normally, the temperature of the chilling unit is maintained well below freezing temperature by conventional control means, not shown.

Air is withdrawn from the compartment 13, forced through the air passages of the chilling unit 20 and returned to the compartment -by a fan 24 which is supported in the opening 17. The fan 24 is driven by an electric motor 25 so as to draw air from the compartment 12 through the openings 15, 17 and into the upstream side of the chilling unit 20. Chilled air from the unit 20 passes from the compartment 12 to the compartment 13 through the opening 16. It will be appreciated that the pressure of the air between the fan 24 and chilling unit 20 is relatively higher than the air pressure on the air discharge of the chilling unit 20 and in both compartments 12 and 13. As water condenses and freezes on the tubes 22 and fins 23, the passage of air through the unit 20 becomes impeded and the air pressure at the inlet side of the chilling unit increases relative to the air pressure downstream from the chilling unit 20 in compartments 12, 13.

The ice accumulated on the heat exchange surface of the unit 20 is adapted to be melted by an electric heater 26 suitably positioned adjacent the surfaces of the unit, but not shown in detail. The heater 26 and the compressor motor 21 are controlled by a deice control device comprising a double throw, solenoid actuated switch 27. The switch 27 comprises a movable contact 30 which is shifted between alternate contacts 31 and 32 by an armature 33 normally biased to move contact 30 to engage contact 31 and which is attracted to an electro-magnet 34 by energization of a solenoid coil 35. Electric power for the motor 21 and heater 26 is supplied by a conventional three-wire 240 v. line system L1, L2 and N. It will be seen that when the solenoid coil 35 is energized, switch 30 is moved to break the motor circuit at 31 and to complete the circuit for the heater 26 at 32 to produce heating of the unit 20. When the solenoid coil 35 is de-energized, the heater circuit is broken and the motor circuit is closed at contact 31 to provide normal refrigeration in the unit 20. A diode D1 is connected in parallel with the coil 35 to provide a discharge path for current induced upon de-cnergization of the solenoid.

The circuit for the solenoid coil 35 includes a center tap transformer 36, the primary winding 37 of which is connected to a suitable v. A.C. source, a secondary winding 38, conductors 40, 41 and a transistor 42, the collect r 43 of which is connected with the conductor 41.

A full Wave rectified current is provided in conductors 40, 41 by the provision of a diode 45 between conductor 40 and one end terminal of the secondary winding 38, a diode 46 connected between the conductor 40 and the other terminal of the secondary winding and connection of conductor 41 to the center tap of the secondary winding.

The transistor 42 is adapted to be rendered conductive and energizes the solenoid coil 35 by the output of amplifier circuit connected with the base 47 thereof. The amplifier circuit comprises a transistor 50 having its emitter 51 connected with the conductor 41 through a potentiometer 52, fixed resistor 53 a conductor 54 and resistor R1. A resistor 56 balances the resistor 53. The collector 55 is connected with conductor 40 through a resistor 57. The base 48 of the transistor 50 is connected through a diode 59 with a junction 60 of a voltage divider comprising resistance elements 61, 62. The resistance element 61 is connected with conductor 40, and junction 60 and conductor 54. The resistance elements 61, 62 are temperature sensitive resistors which increase in resistance as the temperature thereof increases, and vice versa, and are heated by the passage of current therethrough. As is explained hereinafter, arrangements are provided for maintaining the temperatures of the resistor 61 substantially equal while the chilling unit 20 is relatively free of frost and the voltage at the junction 60 and base 58 is sulficiently high to prevent conduction through transistor 50. When the surfaces of the unit 20 becomes coated with ice to an extent to appreciably impede air flow and heat exchange between the unit and air passing between the fins 23, the resistor 61 is then cooled at a greater rate than the resistor 62 which reduces the resistance of the resistor 61 and increases the resistance of the. resistor 62. This change in resistance values causes the voltage at 60 to appreciably decrease, lowering the voltage at base 58 and causing conduction of the transistor 50.

The collector 55 of the transistor 50 is connected with the base 47 of the transistor 42 and when the transistor 50 conducts, the voltage at base 47 is increased and causes conduction through the transistor 42 which energizes the solenoid coil 35. Transient spike triggering of the transistor 50 is obviated by a condenser 63, one plate of which is connected to the conductor 40 through a resistor 64 and the other plate of which is connected with the base 47 to provide a high frequency negative feed-back. Coil 35 actuates the switch 27 to open the circuit of compressor motor 21 and 31 and closes the chilling unit heater element 26 at 32, thus initiating a deicing cycle.

The armature 33 is adapted to close a normally open switch 65, when the coil 35 is energized, which connects the base 47 of transistor 42 with the conductor 54 through a resistance 66 and provides a circuit to maintain the transistor 42 conductive regarless of the conduction of transistor 50 so that changes in voltage at the junction 60 as determined by the temperatures of the elements 61, 62 will not affect the transistor 42.

The deicing cycle is terminated and normal refrigeration is restored by the closure of a normally open thermostatically activated switch 70 which is adapted to be closed when a part of the chilling unit reaches a predetermined temperature at which ice will have melted from the unit, and to open when the temperature of the chilling unit returns to below freezing or thereabout. Suitable thermally responsive switches are well known in the art and need no further description. When the switch 70 closes, the voltage at base 47 is reduced to that of the conductor 40 causing the transistor 42 to turn off and deenergize the coil 35 which opens switch 65, breaking the circuit for heater 26 and reclosing the circuit for motor 21 at 31. When sub-freezing refrigeration temperatures,

or thereabouts, are again restored in the chilling unit 20, the switch 70 reopens.

A suitable voltage limiting resistor R1 is provided as shown. Resistor R2 provides regenerative feed-back f r positive switching.

The temperatures of the resistors 61, 62 are controlled according to ice conditions on the chilling unit 20 by a fluid flow control device 72. The device 72 comprises a known form of fluid amplifier such as that disclosed in US. Patent 3,122,165 and in its present form comprises a relatively flat rectangular block 73 formed of a suitable moldable material, such as a plastic, having recesses formed therein to provide fluid flow passages. The recesses are covered by a suitable cover plate attached to the block to complete the closure of the sides of the passages. The block 73 is suitably attached to the underside of the partition 11.

The recesses in the block 73 comprise a circular main flow inlet 75 having a throat-like outlet 76 which opens into a fan shape intermixing chamber 77. The inlet 75 has a tubular extension 78 which extends through an opening through the partition 11 and is open to the air in the compartment 12 upstream of the chilling unit 20, i.e. between the fan 24 and the chilling unit. Three diverging passages 80, 81, 82 lead from the chamber 77 and discharge from the right-hand end of the block 73 into the compartment 13. The capacity of the passages 80, 82 are such as to carry the main flow individually.

A first control jet flow passage 83 opens into one side of the throat 76 and communicates with the inlet passage 75 through a valve chamber 84 in which a rotatable flow regulating member 85 is positioned. A passage 86 leads from the valve chamber 84 to the inlet 75, and the valve member 85 more or less blocks the opening between the chamber and passage according to its angular position, to regulate the flow from the inlet to the jet flow passage 83. The angular position of the valve member 85 may be adjusted by inserting a screw driver into a transversely slotted end of the valve member (not shown) exposed through an opening in the bottom of the block 73, as viewed in FIG. 1.

A second control jet passage 90 opens-into the side of the throat 76 opposite the opening of jet 83. The jet passage 90 leads to an inlet chamber 91 which has a connector collar 92 extending from the bottom of the block 73 and which is connected by a tube 93 with the area of the compartment 12 at the air discharge side of the chilling unit 20 so that air from the discharge or downstream side of the chilling unit is directed into the jet passage 90.

It will be understood by those familiar with the art that when the flow through the jet 90 exceeds that of the flow through the jet 83, the main stream flow from the chamber 75 will be directed more or less by the jet from 90 into the passage 82 and when the flow from jet 83 exceeds the flow from jet 90, the main flow through throat 77 is deflected more or less through passage 80.

To stabilize the flow of the main stream into either one or the other of the alternate passages 80, 82, notch- like recesses 95, 96 are formed in opposite sides of the intermixing chamber 77 and bleed through openings in the bottom of the block 73 into chamber 13. The intermediate passage 81 further promotes the stability mentioned by permitting excess air flow in the flow resulting from injection of the control streams to exit the block 73.

The resistor 61 is located in passage 80 and is cooled by air passing therethrough and the degree of cooling thereby is dependent upon the volume of fluid flowing through the passage. The resistor 62 is similarly located in passage 82 and is like-wise cooled by air flowing through this passage. When air is flowing through one or the other of the passages 80, 82 little, if any, air fl ws through the other passage resulting in an appreciable rise in temperature of the resistor in the latter passage.

It will be seen that when the refrigerating system is operating as described and the unit 20 is relatively free of ice, the differential in air pressure at the upstream .and downstream sides of the unit is relatively low. The valve member 5 is initially adjusted, when the device 72 is installed, so that the volume of air from control jet 90 balances that from the jet 83 and the main flow of air from the inlet chamber 75 will be divided to flow in equal volumes through the passage 80, 82. Both resistors 60, 61 will be cooled to the same degree and their electrical resistances will be equal. As explained previously, under these conditions the deicing control switch 27 remains in its normal position.

As ice collects on the fins 23 and coils 22, the flow of air through the unit 20 is impeded, causing the upstream air pressure to increase and the downstream air pressure to decrease which diminishes the air discharging from jet 90 and correspondingly increases the air discharge from jet 83 causing the main stream to be deflected to a greater degree into the passage 80. This shift of flow of the main stream from the passage 82 into passage decreases the cooling effect on the resistor 62 and increases the cooling effect on the resistor 61 resulting in an appreciable decrease in resistance of the resistor 61 and an increase in resistance of the resistor 62. Accordingly, the voltage at the junction 60 will be materially decreased.

The degree of the air pressure differential at which the fluid amplifier device 72 shifts its flow from the passage 82 to the passage 80 can be rather precisely determined for various forms of forced air refrigerating equipment by setting of the valve member 85. The adjustment of valve member 85 is easily accomplished when the control apparatus is installed in any particular refrigeration system. Thus, the control apparatus can be readily adapted to control refrigerating systems having widely diifering air flow characteristics of their air chilling units.

It 'will also be appreciated that the device 72 may be located in convenient positions by extending air tubes to convenient upstream and downstream locations.

The fact that the cooling air stream is shifted from one thermistor to the other provides "a wide range of voltage change to indicate need for deicing thereby enabling the employment of reliable yet inexpensive components in the control cricuits. In addition, the deice control is unaffected by changes in fan speed or stoppage of the fan, sudden loads on the chilling unit, and the like.

I claim: ,1

1. In a refrigerating system having an air chilling unit operating at sub-freezing temperatures and having means for forcing a stream of air over heat exchange surfaces of said unit, means to initiate a deicing cycle of said chilling unit comprising, an electrically actuated control device, circuit means for energizing said device including two electric resistance elements connected with a junction, said elements having electrical resistance which varies according to temperature variations thereof, means heating said elements, means establishing a flow of air over said elements adapted to dissipate heat from said elements, and means responsive to an increase in the differential in air pressures .in said air stream upstream and downstream of said chilling unit to change the proportion of said flow of air over one of said elements relative to the air flow over the other of said elements.

2. A refrigerating system of the type defined in claim 1 further characterized by said means establishing a flow of air over said elements comprising a fluid amplifier control device including a main fluid flow stream arranged to discharge into one or the other of alternative flow passages, control jets on opposite sides of said main flow passage adapted to discharge into opposite sides of said main flow and cause said main flow to move towards one or the other of said alternate passages, one of said control jets being in communication with the source of fluid for 7 said main flow passage and the other of said control jet passages being in communication with the downstream side of said chilling unit.

3. A refrigerating system as set forth in claim 2 further characterized by means to regulate the flow of air through one of said control jets.

4. A refrigerating system as defined in claim 3 in which said regulating means comprises a modulating valve in the passage between the main flow source and said control jet associated therewith.

5. A refrigerating system as defined in claim 4 in which said modulating valve is a manually settable valve.

References Cited UNITED STATES PATENTS 0 MEYER PERLIN, Primary Examiner US. Cl. X.R.

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