US3097503A

US3097503A - Automatic defrost control for refrigeration systems

Info

Publication number: US3097503A
Authority: US
Publication date: 1963-07-16
Anticipated expiration: 1980-07-16

Description

July 16, 1963 J. LIEBERMANN 3,097,503

AUTOMATIC DEFROST CONTROL FOR REFRIGERATION SYSTEMS Filed Dec. 15, 1961 INVENTOR JOHN LIEBERMANN ATTORNEY United States Patent 3,097,503 AUTOMATIC DEFRUST (ZONTROL FUR REFRIGERATION SYSTEMS John Liebermann, Columbus, Ohio, assignor to Rance Incorporated, Columbus, Ohio, a corporation of @2320 Filed Dec. 13, 1961, Ser. No. 159,126 5 Claims. ((31. 62156) This invention relates to improvements in automatic control means for electric motor driven mechanical refrigerating systems of the compressor-condenser-expander type in which defrosting of the evaporator of the system is effected at the beginning of each refrigerating cycle.

It is a principal object of this invention to provide improved control means in a refrigerating system of the compressor-condenser-expander type having a cycling thermostatic switch for controlling operation of the compressor to produce refrigerating cycles and an electrically controlled valve which may be opened upon energization thereof to pass hot compressed refrigerant directly from the compressor to the evaporator to effect removal of frost therefrom, the control of the valve being effected by circuit means including a switch in series with the cycling thermostatic switch, the valve control switch being thermostatically operated to close upon a reduction in temperature of the evaporator below a given temperature and to open upon a rise in temperature of the evaporator above the melting point of frost to terminate passage of hot gas through the evaporator, and means to prevent reenergization of the valve as long as the compressor is in operation and irrespective of the reduction in temperature of the evaporator.

Another object of this invention is the provision of an improved refrigeration control system of the above mentioned character wherein the defrosting, or valve control switch is preferably operated by thermally responsive means such as a bellows connected to a bulb located at the evaporator, the defrosting switch means having two operative positions one of which connects the electrically operated valve in series with the cycling thermostatic switch so that the valve is energized and opened to commence defrosting when the compressor is started by the cycling thermostat, the defrosting switch means being moved by the resulting increase in temperature in the evaporator to a predetermined temperature above 32 F. to its second operative position to break the circuit of the valve, thereby allowing the valve to close and establish the cooling cycle and to energize means for preventing reenergization of the defrost valve until the cycling thermostat has terminated the refrigerating cycle. In. one preferred form of the invention the means for preventing reenergization of the defrosting valve comprises a relay switch in the circuit between the defrosting switch means and the valve, the relay being effective, when energized, to prevent energization of the valve and having a holding circuit including the cycling thermostat switch, so that although the defrosting switch means be returned to its valve energizing position, the relay will remain energized and prevent reenergizing and opening of the defrosting valve until. the cycling thermostat switch has opened to break the holding circuit.

Other objects and advantages of this invention will become apparent, from the following detailed description of a presently preferred embodiment thereof described with reference to the accompanying sheet of drawings forming a part of this specification, and in which the single view provides a schematic illustration of a refrigerating system embodying the present invention.

The present invention is described hereinafter with reference to embodiment in a mechanical refrigerating system generally indicated at 19, such as may be used in domestic refrigerators, although it will be understood that ice this use is intended only as an example and that the invention may be embodied in similar cooling systems for use in commercial freezers, coin operated vending units, an conditioning systems for habitable buildings, and the like. Refrigerating system 10 comprises a compressor 13 which is driven by a prime mover such as an electric motor 14 and is operative to withdraw vaporized refrigerant through a tube 15 from a cooling unit or evaporator 16, and to compress the refrigerant and direct it through. a tube 17 to a condenser 18.

The refrigerant is cooled and liquified in condenser 18, from which the condensed refrigerant is led by a tube 20 through a suitable expansion means, such as a capillary tube 21, into the evaporator 16 where the refrigerant vaporizes and cools the walls of the evaporator, as is well understood in the art. Motor 14 is connected by

conductors

24, 25, and a compressor cycling thermostatic switch 26 to power lines L1 and L2. Thermostatic switch 26 is responsive to temperatures in the refrigerator compartment, or other space being tempered by the cooling effect of the evaporator 16, and is adapted to energize and deenergize motor 14 to start and stop the compressor to produce refrigerating cycles as may be necessary to maintain the compartment temperature within predetermined desired limits.

When the evaporator is operated at temperatures below the freezing point of water, moisture in the air surrounding the evaporator is condensed and frozen on the surface of the evaporator in the form of frost. Because accumulations of such frost act as an insulation between the evaporator and the surrounding air, the efficiency of the refrigerating system would be impaired if the frost were permitted to remain. In the refrigerating system shown, however, such frost is melted at the beginning of each refrigerating cycle, and for this purpose an electric solenoid actuated, normally closed valve 30 is connected between tubes 17 and 22 by

tubes

31 and 32, and hence is adapted to provide a path for directing hot compressed refrigerant coming from the compressor 13; directly into evaporator 16 so as to raise the temperature thereof to remove formations of ice and frost therefrom. Valve 39 may be of any well known type such as asolenoid operated valve of the type disclosed in my copending patent application Serial Number 8,3 3 6- filed February 12, 1960; Valve 30 is actuated to an open condition each time the thermostatic switch 26 closes to start compressor 13 for a refrigerating cycle, and is heldopen by control means, described more fully as the description proceeds, until the evaporator has attained a temperature at which the frost is. melted. Thereafter, the valve is closed and the evaporator is cooled in the normal manner until thermostatic switch once again opens.

The control means for valve 30 includes: a thermally responsive defrosting switch, generally indicated at 34, and a relay 35. Switch 34 may be of any single pole, double throw, snap acting type well known in the art, and is here shown as comprising a movable contact arm 36 which is fixed at one end and carries adouble contact 31 at its movable end. Contact 37' is movable between spaced staionary contacts 38 and 39 with a snap movement effected by a toggle mechanism including a bowed tongue 40, struck out of the center of arm 36 and having a free: end engaged in a notch 41 of a toggle member 42 which is pivoted at 43 to a suitable frame 44. It willbe recognized that movement of toggle member 42 in a counterclockwise direction from its illustrated position so as to bring notch. 41 to the other side of arm 36, will cause the latter to be snapped upwardly to bring contact 37 into engagement with contact 38. Conversely, movement of toggle member 42 in a clockwise direction so as to bring notch 4 .1 past arm 36, will cause. contact 37 to be returned into engagement with contact 39 with a snap action.

A compression spring 46 is disposed between toggle member 42 and frame '44, and biases toggle member 42 in a counterclockwise direction about pivot 43. An expansible power member in the form of a bellows 487is mounted on frame 44 and has a post 49 in engagement with toggle member 42. Bellows 48 is connected by a capillary tube 50 with a temperature sensing bulb 51 disposed adjacent evaporator 16. Bulb 51 contains a volatile liquid, such as Freon which is in a liquid state for the normal temperatures encountered during operation of the refrigerating system so that the vapor pressure corresponds to the lowest temperature of the thermostatic system, which is generally the bulb 51. Such changes in pressure are transmitted by capillary tube 50 to bellows 48 to effect expansion and contraction thereof, through the action of spring 46, and actuation of the toggle mechanism so as to move contact 37 into engagement with contact 39 as shown in the drawing. The force exerted by spring 46 is such that when the temperature of evaporator 16 is reduced below the freezing point of water the reduction in pressure in the bellows permits the spring to depress bellows 48 and thereby shift contact 37 to engage contact 38.

Relay 35 which cooperates with switch 34 to control actuation of valve 30, comprises a solenoid 53, normally closed contacts 54, and normally open contacts 55. Assuming the refrigerating apparatus to have bee-n standing idle and to be entirely at room temperature, the various parts of the refrigerating system would be positioned as shown in the drawing. Upon supplying lines L1 and L2 with current such as 110 v. A.C., motor 14 is energized to start operation of compressor 13 as previously described, and the temperature of evaporator 16 is brought to a temperature somewhat below freezing. As evaporator :16 passes into the freezing temperature zone, switch 34 is actuated to bring contacts 37 into engagement with contact 38, or into what will hereafter be referred to as the first operative position of this switch. When the refrigerator has been suificiently cooled, thermostatic switch 26, which is shown schematically as a bimetal switch, opens to deenergize motor 14 and terminate the first refrigerating cycle and also deenergizes relay solenoid 53 to cause reclosing of switch 54 and reopening of switch 55.

At the initiation of every subsequent refrigerating cycle, defrosting valve 30 will be opened to direct hot gas into evaporator 16 to remove frost therefrom. Thus, when the refrigerator temperature rises sutficiently to close thermostatic switch 26 for energization of compressor motor 14, a circuit is closed which may be traced from conductor 25 through

conductors

60, 61, arm 36, now closed con tacts 37 and 38, conductor 63, normally closed contacts 54 of relay 53, conductor 64, electrically operated defrosting valve 30, and a conductor 65 to line L2. Valve 30 is therefore energized and opened to commence the defrosting action. When evaporator 16 attains a predetermined temperature which will assure the removal of frost therefrom, the liquid in bulb 51 is vaporized causing expansion of bellows 48 and actuation of switch 34 from its first operative position to a second operative position by snapping contact 37 from contact 38' to contact 39.

Opening of contacts 37 and 38 interrupts the energization of valve 38 which therefore closes to terminate defrosting of the evaporator and to permit the commencing of the cooling portion of the cycle. Closing of contacts 37 and 39 completes a

circuit including conductors

60, 61, arm 36, now closed contacts 37 and 39, solenoid 53, and a conductor 67 to line L2. Relay 35 is thereby actuated causing contacts 54 to open and contacts 55 to close. Closing of contacts 55 establishes a holding circuit for relay 35, which circuit may be traced from conductor. 60 through conductor 68, contact 55, a conductor 69, solenoid 53, and conductor 67 to line L2. This holding circuit maintains relay 35 energized even though switch 34 is then actuated to its first operative position (opening contacts 37 and 39) as the evaporator is reduced to a temperature below freezing during the remainder of the refrigerating cycle. Because relay 35 remains energized, contacts 54 are held open and prevent the reopening of valve 30 upon closing of contacts 37 and 38.

When the cooling eflects of the evaporator 16 reduce the temperature within the refrigerator sufliciently to open thermostatic switch 26, the holding circuit for relay 35 is broken allowing contacts 55 to open and contacts 54 to close. Switch 34 and relay 35 are therefore conditioned to energize valve 30 once again upon the next closing of thermostat 26 to initiate another refrigerating cycle. The above described sequence of events, including the operation of switch 34 and relay 35 to open valve 30 at the beginning of each refrigerating cycle, is continuously repeated, thereby maintaining evaporator 16 free of frost and at peak efiiciency.

Inasmuch as evaporator 16 and bulb 51 are, during defrosting, raised to a temperature somewhat above that in the remainder of the refrigerator, a small electrical resistance heater 71 is disposed adjacent capilliary 50 and bellows 48 so that bulb 51 will always be the coldest part of the volatile liquid containing system. This is necessary since such a system is responsive only to temperature changes in the coldest portion thereof, as is well understood by those skilled in the art to which the inven tion pertains. Heater 71 is conveniently energized by connection between conductor 61 and line L2 by

conductors

72 and 73, as shown.

From the foregoing detailed description of a presently preferred embodiment of the invention, it will be recognized that there has been provided thereby a particularly effective refrigerator control system which maintains the evaporator substantially free of frost by effecting hot gas defrosting upon the initiation of each refrigerating cycle. It will also be recognized that the invention may be practiced by the utilization of relatively simple and reliable components such as switches and relays which are inexpensive and require little or no adjustment other than that performed at the factory upon fabrication.

Although the invention has been described in considerable detail and with specific reference to a refrigerating system embodying the invention, it is understood that the invention is not limited thereto, but rather the invention includes all those changes, modifications, and uses as are reasonably embraced by the scope of the claims hereof.

Having thus described my invention, I claim:

1. In a refrigerating system comprising:

(a) a cooling unit,

(b) an electrically powered means to circulate refrigerant through said unit,

(0) a thermostatically operated first switch controlling said electrically powered means according to temperatures effected by said cooling unit,

(d) electrically powered valve means to selectively direct a fluid of relatively high temperature through said cooling unit to melt frost therefrom,

((2) means to control said electrically powered valve means comprising a circuit connecting said valve means in series with said first switch,

(1) a second switch in said circuit in series with said valve,

(g) thermostatic means responsive to the temperature of said cooling unit and operative to close said second switch in response to a decrease in temperature below a given temperature and open said second switch in response to an increase in temperature of said cooling unit substantially above 32 F., to deenergize said valve, and

(h) means responsive to opening of said second switch during an operating cycle of said refrigerant circulating means to maintain said valve deenergized for the remainder of said opera-ting cycle and until the beginning of the next cycle irrespective of the reduction in temperature of said evaporator and closing of said second switch during said remainder of said operating cycle.

2. Control means in a refrigeration system of the type including a compressor, a prime mover for said compressor, a condenser and an evaporator connected to said compressor to form a closed path for refrigerant, and an electrically operated valve for directing hot gas from said compressor to said evaporator to effect defrosting thereof; said control means comprising:

(a) a first thermally responsive switch means for start ing and stopping operation of said compressor by said prime mover,

(b) a second thermally responsive switch means connected in series with said first switch means and with \said electrically operated valve so that said valve is opened when both switches are closed,

(c) said second switch being adapted to open in response to a temperature rise in said evaporator to a predetermined defrosting temperature whereby said valve is closed and cooling of said evaporator started, and

(d) electrically actuated means for preventing said second switch from effecting reopening of said valve upon a decrease in temperature of said evaporator until the next opening and closing of said first switch means.

3. Control means in a refrigeration system of the type including a compressor, a prime mover for said compressor, a condenser and an evaporator connected to said compressor to form a closed path ior refrigerant, and an electrically operated valve for directing hot gas from said compressor to said evaporator to effect defrosting thereof; said control means comprising:

(a) a first thermally responsive switch means for starting and stopping operation of said compressor by said prime mover,

(b) a second thermally responsive switch means having a first operative position connecting said valve to said first switch means so that closing of said first switch means to start .said compressor will also effect opening of said valve to effect defrosting,

(c) said second switch means being responsive to attainment of a predetermined defrosting temperature of said evaporator to shift from said first operative position to a second operative position and to effect closing of said valve,

(d) electrically actuated holding means connected in series with said first switch means and operative to prevent said second switch means from effecting reopening of said valve upon reduction of said evaporator temperature below said predetermined temperature until the next opening of said first switch means to release said holding means.

4. Control means in a refrigeration system of the type including a compressor, a prime mover for said compressor, a condenser and an evaporator connected to said compressor to form a closed path for refrigerant, and an electrically operated valve for directing hot gas from said compressor to said evaporator to effect defrosting thereof; said control means comprising:

(b) a second thermally responsive switch means having a first operative position connecting said valve to said first switch means so that closing of said first switch means [to start said compressor will also effect opening of said valve to effect defrosting,

(c) said second switch means being responsive to attainment of a predetermined defrosting temperature of said evaporator to shift firom said first operative position to a second operative position and to effect closing of said valve,

(d) electrically actuated holding means connected in series *with said first switch means and operative to prevent said second switch means from effecting reopening of said valve upon reduction of said evaporator temperature below said predetermined temperature and until the next opening of said first switch means which is operative upon said next opening to release said holding means,

(2) said electrically actuated holding means comprising a relay having contacts connected between said second switch means and said valve, said relay being actuated to open said contacts and hence to close said valve upon movement of said second switch means from said first operative position to said second operative position, and said relay having holding means to prevent reclosing of said contacts until said next opening of said first switch means.

5. Control means as defined in claim 4 and wherein said holding means comprises an electrical holding circuit through second contact means of said relay.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

2. CONTROL MEANS IN A REFRIGERATION SYSTEM OF THE TYPE INCLUDING A COMPRESSOR, A PRIME MOVER FOR SAID COMPRESSOR, A CONDENSER AND AN EVAPORATOR CONNECTED TO SAID COMPRESSOR TO FORM A CLOSED PATH FOR REFRIGERANT, AND AN ELECTRICALLY OPERATED VALVE FOR DIRECTING HOT GAS FROM SAID COMPRESSOR TO SAID EVAPORATOR TO EFFECT DEFROSTING THEREOF; SAID CONTROL MEANS COMPRISING: (A) A FIRST THERMALLY RESPONSIVE SWITCH MEANS FOR STARTING AND STOPPING OPERATION OF SAID COMPRESSOR BY SAID PRIME MOVER, (B) A SECOND THERMALLY RESPONSIVE SWITCH MEANS CONNECTED IN SERIES WITH SAID FIRST SWITCH MEANS AND WITH SAID ELECTRICALLY OPERATED VALVE SO THAT SAID VALVE IS OPENED WHEN BOTH SWITCHES CLOSED, (C) SAID SECOND SWITCH BEING ADAPTED TO OPEN IN RESPONSE TO A TEMPERATURE RISE IN SAID EVAPORATOR TO A PREDETERMINED DEFROSTING TEMPERATURE WHEREBY SAID