US3726104A

US3726104A - Refrigeration system defrost initiation apparatus

Info

Publication number: US3726104A
Application number: US00114882A
Authority: US
Inventors: L Howland
Original assignee: Thermo King Corp
Current assignee: Thermo King Corp
Priority date: 1971-02-12
Filing date: 1971-02-12
Publication date: 1973-04-10
Anticipated expiration: 1990-04-10
Also published as: FR2125401B1; AU3736071A; GB1369026A; BE779169A; DE2204722C3; AU461420B2; FR2125401A1; CA940723A; DE2204722A1; DE2204722B2

Abstract

A defrost initiation apparatus for a refrigeration system having an evaporator coil to be occasionally defrosted is comprised of an impeller to be revolved by a fluid of the system that is in motion while the system operates and a switch responsive to conditions of revolution of the impeller such as the speed or length of time of revolution to thereby initiate a defrost signal.

Description

Unite ties tet [191 Howland [451 Apr. to, 1973 GERATHON SYSTEM DEOST INITIATKON APP 1'2.

[75] Inventor: Leland L. Howland, Rosemount,

Minn.

[73] Assignee: Thermo neapolis, Minn.

[22] Filed: Feb. 12, 1971 [21] Appl. No.: 114,882

Corporation, Min- Primary ExaminerWilliam F. ODea Assistant Examiner-Peter D. Ferguson Att0rneyF. H. Henson and F. E. Blake 52 US. Cl. ..62/l40, 55/272, 55/274, [57] ABSTRACT 73/229 A defrost initiation apparatus for a refrigeration [51] lit It. Cl ..F25(] 21/02 system having an evaporator coil to be occasionally [58] Field of Search .......62/l40, 151, 155; d frost d is comprised of an impeller to be revolved 55/272, 274, 283; 3/ by a fluid of the system that is in motion while the system operates and a switch responsive to conditions [56] References C'ted of revolution of the impeller such as the speed or UNXTED STATES PATENTS length of time of revolution to thereby initiate a defrost signal. 1,984,053 12/1934 Carraway ..62/140 3,643,457 2/1972 Winkler .I ..62/l5l X 1 Claim, 4 Drawing Figures -l l W W W ,flo

'- AM i /|9 GEAR [F W I5 TRAIN 3w 8 REFRIGERATION SYSTEM DEFROST INITIATION APPARATUS CROSS REFERENCE TO RELATED PATENT APPLICATIONS So far as is known, this application is not related to any copending patent applications.

BACKGROUND OF THE INVENTION It is well known that refrigeration systems of the type having an evaporator coil require that the evaporator coil be occasionally defrosted in order to prevent the accumulation of frost on the evaporator coil in such an amount as to interfere with the operation of or cause complete failure of the system. There are numerous different known arrangements for initiating a defrost signal to periodically defrost the evaporator coil and it is of course desirable that the arrangement or apparatus be as simple as possible yet reliable under all expected conditions of operation. Depending upon the system and its operation, the defrost signal initiation apparatus may be responsive to a condition such as the accumulation of hours of operation of the system or to the accumulation of frost on the evaporator coil or to a combination of either or both of such conditions.

PRIOR ART U.S. Pat. No. 3,159,980 discloses a defrost initiation switch operated by clock timer gears driven directly by the shaft of the fan motor that is impelling the fluid to be cooled through the evaporator coil. There is no provision in the patented disclosure to make the defrost switch directly responsive to a moving fluid flow of the system. The subject invention, as will be described in detail hereinafter, provides that the defrost signal initiating apparatus and switch be operated by a moving fluid of the refrigeration system instead of being operated directly by mechanical connection to a rotating element of the system such as either the compressor or fan motor shaft. There are many advantages to having the defrost switch operated in response to the moving fluid as provided by the apparatus of the present invention. For example, one advantage is that the geared connection for the switch does not have to be in the vicinity of either the blower fan and its motor or the compressor and its motor. Another advantage is that the geared connection may be arranged to respond to either a change in speed or amount of fluid flow to be cooled through the evaporator coil or to the length of time that such fluid flows through the evaporator coil, or to both conditions in which case as the frost accumulates, the length of time of the fluid flow before defrost signal initiation could be reduced as frost accumulates.

SUMMARY According to the invention, an impeller is arranged to be revolved responsive to fluid that is moving during operation of the refrigeration system. The moving fluid is preferably the fluid to be cooled by passing through the heat exchange fins of the evaporator coil but it could be other moving fluids such as the refrigerant. The defrost initiation switch is connected to the revolving impeller through suitable gearing such that the switch will be operated in response to a condition of revolution of the impeller such as after a predetermined number of revolutions of the impeller corresponding to the length of time of operation of the system or such as a change in speed of revolution of the impeller corresponding to a change in condition of the fluid flow through the system. For example, the impeller may be located in a bypass around the evaporator coil and under such circumstances the switch may respond to a predetermined number of impeller revolutions as indicated by clock timer gearing driven by the impeller to thus indicate a total time of operation of the system. With the foregoing arrangement, the impeller and clock timer gearing is driven faster by the increased fluid flow through the bypass around the evaporator coil as the evaporator coil plugs with frost to thereby operate the defrost signal switch sooner than it would be operated if the coil is not plugged with frost. Alternatively, the switch may be a centrifugal switch connected by gearing to the impeller and the gearing would not be clock timer gearing but instead would be suitable reduction or step up gearing for obtaining the required rotation of the centrifugal switch when the impeller is revolving at a predetermined speed indicative of the rate of fluid flow through the evaporator coil which corresponds to the condition of an objectional build up of frost on the evaporator coil. When the switch is a centrifugal switch and the impeller is located in the bypass around the evaporator coil, the switch would be operated by an increase in speed of revolution. Alternatively, if the impeller is located in the direct flow of fluid either before or after it flows through the evaporator coil, the centrifugal switch would respond to a reduction in speed of revolution of the impeller for initiating a defrost signal because of frost buildup.

Further features and advantages of the invention will be apparent with reference to the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevational view, partly in section, of

a preferred form of the invention in which the defrost initiation switch is driven by a clock timer gear train responsive to fluid flow through the evaporator coil;

FIG. 2 is a view similar to FIG. I but showing a modified arrangement in which the defrost initiation switch impeller and gear train is positioned within a bypass conduit around the evaporator coil;

FIG. 3 is a diagrammatic illustration of yet another form of the invention in which the impeller and defrost initiation switch are arranged to respond to the movement of gaseous refrigerant in the refrigeration system.

FIG. 4 is a fragmentary side elevational view, partly in section, of a modified form of the invention in which the defrost initiating switch is a centrifugal switch driven by a gear train connected to the impeller that is positioned downstream of the evaporator coil; and

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, the evaporator coil 10 is shown to be mounted on a transverse panel wall 11 within the duct 12 of the refrigeration system. The fluid, usually air, to be cooled by the refrigeration system is blown by the blower fan 13 in the direction of the arrows through the evaporator coil 10. The transverse duct wall or partition 11 is provided with an opening 14 to one side of the evaporator coil in which is positioned the rotatable impeller 15 connected by the gear train 16 to the defrost initiation signal switch 17. In the preferred form of the invention, the gear train 16 is a simple clock timer gear train that is driven by the impeller 15 instead of the conventional clock spring. It will be understood that the impeller 15 will be continuously revolved so long as the blower fan 13 is revolving to move the fluid to be cooled through the evaporator coil 10. Thus after a predetermined number of revolutions for the impeller 15 corresponding to a predetermined length of time during which fluid to be cooled is moved through the evaporator coil 10, the gear train 16 will be effective to close the defrost initiation switch 17 and transmit a signal through the

conductors

18 and 19 to the appropriate apparatus for reversing the operation of the refrigeration system for purposes of defrosting the evaporator coil 10 in a manner well known to those skilled in the art. A feature of the preferred form of the invention being described in connection with FIG. 1 of the drawing is that as the evaporator coil 10 becomes plugged with frost, the air flow through the coil 10 is reduced, thus increasing the flow of air past the impeller 15 around the bypass coil 10 and thereby increasing the speed of operation of the revolution of the impeller 15 and the timer gear train 16 to cause the switch 17 to be operated sooner than it would be if no frost had accumulated on the evaporator coil 10.

Although as previously described for the preferred embodiment, the gear train l6is a clock timer gear train for integrating the total number of revolutions of the impeller 15, the arrangement may be modified by providing that the defrost switch 17 is a centrifugally operated switch responsive to the speed of rotation of the shaft 21. In such case, the gear train 16 would preferably be a reduction gearing to allow the impeller 15 to rotate at considerable speed and with very little effort before the shaft 21 is rotated at sufflcient speed to close the centrifugal switch 17. With such arrangement, as the evaporator coil 10 becomes plugged with frost, the increased fluid flow past the impeller 15 would increase the speed of the impeller 15 and also the speed of rotation for the centrifugal switch shaft 21 until the predetermined increased speed corresponding to an undesired condition of plugging for the evaporator coil 10 is such as to cause the centrifugal switch to operate and initiate the defrost signal. It will be obvious to those skilled in the art that the centrifugal switch 17 can be either of the normally open or normally closed variety depending upon the type of signal circuits with which the switch is connected. Therefore, whether or not the switch is normally open or normally closed, it will be operated from its normal condition to its operated condition only when the speed of revolution of the impeller 15 is such as to indicate the condition of a plugged evaporator coil.

Referring to FIG. 2 of the drawing, a modified form of the invention is shown wherein the impeller 15, gear train 16 and switch 17 is enclosed in a bypass duct 25 connected through the main duct wall 12 on both sides of the evaporator coil 10. Thus a portion of the fluid to be moved by the blower 13 through the evaporator coil 10 is diverted through the bypass duct 25 around the evaporator coil. When the evaporator coil 10 becomes plugged with frost, the amount of fluid moving through bypass duct increases in pressure and therefore causes the impeller 15 to revolve at increased speed to either accelerate the gear train 16 for purposes of timing the number of revolutions of the impeller 15 or for purposes of responding to the increased speed of rotation of the impeller 15 and operate the defrost initiation switch 17 as previously described.

In the modified form of the invention shown by FIG. 4 of the drawing, the impeller 15, gear train 16 and defrost initiation switch 17 are positioned within the duct downstream of the evaporator coil 10. Thus as the evaporator coil becomes plugged the fluid moving through the evaporator coil to be cooled decreases causing the impeller 15 to rotate at lower speed and the I centrifugal switch 17 would be arranged to respond to a decrease in speed of rotation of the impeller 15 for purposes of initiating the defrost signal. Instead of locating the impeller 15 and its associated apparatus downstream of the evaporator coil 10 as shown by FIG. 4 of the drawing, the impeller 15 and associated apparatus may be positioned upstream of the evaporator coil 10. In such arrangement the effect would be substantially the same in that the plugging of the evaporator coil with frost would cause a reduction of fluid flow past the impeller 15 and through the evaporator coil 10 so that the impeller would rotate at lower speed to cause the appropriate operation of the defrost initiation switch 17.

Referring to FIG. 3 of the drawing, in another modification of the invention is shown as it may be applied to a refrigeration system in which a compressor such as shown at 30 is connected by the relatively large diameter suction line 31 to the discharge of the evaporator coil 32. Compressed refrigerant gas from the compressor 30 is connected by the line 33 to the condensing coil 34 whose discharge is connected by the line 35 to the expansion device or valve 36 and the inlet of the evaporator coil 32. The revolving impeller 40 is mounted within the suction line 31 in any suitable manner not shown in detail and is connected through the gear train 41 to the defrost initiation switch 42. Thus the impeller 40 is revolved by the motion of the gaseous refrigerant in the line 31 being drawn into the intake of the compressor 30 during operation of the refrigeration system and the gear train will therefore function to integrate the total time of operation of the system between periods of defrosting to be initiated by the defrost signal initiating switch 42.

In addition to the modifications specifically shown and described above, it should be understood that various other modifications will occur to those skilled in the art. For example, the impeller 40 may be arranged to respond to the motion of the refrigerant fluid whether or not it is in the gaseous or liquid state throughout the system.

I claim as my invention:

1. A defrost initiation apparatus in combination with a refrigeration system having an evaporator coil to be occasionally defrosted, the refrigerator system having a fluid in motion passing in heat exchange relation to be cooled by said coil during its operation, a bypass passage around said coil for a portion of said fluid, an impeller enclosed within said bypass passage and whereby said switch means is adapted to count the number of revolutions of said impeller and is actuated to thereby initiate a defrost cycle for said system after a predetermined number of said revolutions.

Claims

1. A defrost initiation apparatus in combination with a refrigeration system having an evaporator coil to be occasionally defrosted, the refrigerator system having a fluid in motion passing in heat exchange relation to be cooled by said coil during its operation, a bypass passage around said coil for a portion of said fluid, an impeller enclosed within said bypass passage and adapted to be revolved by the motion of said fluid passing therethrough, and switch means connected to said impeller to be actuated in response to a condition of revolution of said impeller, said switch means including a clock timer gear train driven by said impeller, whereby said switch means is adapted to count the number of revolutions of said impeller and is actuated to thereby initiate a defrost cycle for said system after a predetermined number of said revolutions.