US3097502A

US3097502A - Defrost control apparatus

Info

Publication number: US3097502A
Authority: US
Publication date: 1963-07-16
Anticipated expiration: 1980-07-16

Description

L. L. KRUEGER DEFROST CONTROL APPARATUS July 16, 1963 Filed Sept. '6, 1960 INVENTOR.

LOREN L. KRUEGER WflM ATTORNEY ,V// N\ M u m m R M O W m Q 8 I R 4 N 4 O 5 X I 4/ R o QT e 9 w O P r y l M M H H l O 5 u l 2\ C 5 M 3 4 M 5 7 U 5 w United States Patent 3,097,502 DEFROST CONTRtEL APPARATUS Loren L. Krueger, Hopkins, Minm, assignor to Minneapolis-Honeywell Reguiator Company, Minneapolis, MEHZL, a corporation of Delaware Filed Sept. 6, 1966, Ser. No. 54,051 19 Ciaims. (Cl. 62-156) The present invention is concerned with an improved system for controlling the defrosting operation of a heat exchanger of a refrigeration apparatus which removes heat from outdoor air.

With the advent of air-to-air heat pumps which remove heat from outdoor air for heating a dwelling, the need for an improved control or control system for initiating and terminating the defrosting operation has been recognized. When a refrigeration apparatus has an outdoor heat exchanger for receiving heat from the outdoor air as the air flows through the heat exchanger, the outdoor air heat exchanger will tend to frost over to decrease the air flow through the heat exchanger and cut down the efiiciency of the system. When the outdoor heat exchanger becomes covered with frost and a defrosting operation is started, various means have been used to defrost the heat exchanger.

Presently, there is a control device on the market which has a pair of temperature responsive bulbs connected to operate a switch to initiate the defrost cycle. The temperature bulbs are adapted to respond to the coil temperature and the outdoor air temperature, respectively. When such a control device is used, a considerable amount of difficulty is experienced in placing the one temperature responsive bulb in a representative position on the outdoor air heat exchanger. If the bulb is placed to respond to the temperature of the heat exchanger nearest the warmest portion of the heat exchanger, the defrost cycle is often commenced quite late resulting in an extensive inefiicient operation of the heat pump. Also, if the heat exchanger temperature responsive bulb is placed close to the coldest portion of the heat exchanger, other difficulties become apparent.

The present invention is concerned with the use of three representative temperatures for controlling the defrosting operation of the outdoor air heat exchanger. The defrosting operation is initiated when the temperature difference between the outdoor air temperature and the normally warmest portion of the heat exchanger reaches some predetermined value, and the defrost cycle is terminated when the temperature of the normally coldest portion of the coil reaches some predetermined high temperature.

An object of the present invention is to provide an improved defrost control system for a refrigeration apparatus having an outdoor air heat exchanger.

Another object of the present invention is to provide an improved defrost control system for a refrigeration apparatus having an outdoor heat exchanger wherein the defrosting operation is initiated by the temperature difference between the outdoor air and a first temperature of a heat exchanger and the defrosting operation is terminated by a predetermined second representative temperature of the heat exchanger.

These and other objects of the present invention will become apparent upon the study of the following specification and drawings of which a single FIGURE is a schernatic diagram of a typical refrigeration system and a defrost control device having three temperature responsive bulbs.

Referring to the single figure, the temperature of space is changed by circulating the air through an indoor coil or heat exchanger 11 which is positioned in the air flow or duct system including a fan 12. The fan is continuously driven by a motor 13 to pull air into a return duct 14, and after the air passes through the indoor coil, the air flows out of supply duct 15 into space 10. The indoor coil 11 is a part of a refrigeration apparatus 20 which is of a conventional type having a motor compressor 21, a changeover valve 22, an outdoor coil or heat exchanger 23. The system is connected so that the refrigerant flows in the following manner: from the compressor, through a pipe 24, to changeover valve 22, through a pipe 25, through coil 11, through a restriction 34, through a pipe 30, to lower side or normally coldest side 26 of the outdoor air heat exchanger 23, from the upper or normally warmest side 31 of heat exchanger 23, through a pipe 32, through a second portion of changeover valve 22, and back through a pipe 33 to the inlet side of the compressor. As connected, the refrigerant is compressed and heat is given off as the refrigerant condenses in the indoor coil 11 to supply heat to space 10. In the heat exchanger 23, the liquid refrigerant evaporates to remove heat from the outdoor air which is circulated through the heat exchanger by a fan 35 which is driven by motor 36. The vaporized refrigerant then is pulled back into the compressor through pipe 31.

Motor compressor 21 is connected to a switch 40 which is controlled by a relay 41. When the relay 41 is energized, the compressor 21 is connected to a source of power by switch 40. Relay 41 is energized by a conventional circuit including a thermostat 42 which is located in space 10. When a switch of thermostat 42 closes, the energization winding of relay 41 is connected through a source of power or step-down transformer 43 to energize rnotor compressor 21 and deliver heat to space 1%).

Since the temperature of the outdoor coil 23 is generally quite low, and during the season of the year when heating is needed in space 10, the outdoor air temperature is low; coil 23 will tend to frost over. The frosting of the coil prevents the air flow through the coil and cuts down the efficiency of refrigeration apparatus 20. In such refrigeration apparatuses, the defrosting of the outdoor coil can be accomplished in a number of ways. One manner of defrosting the outdoor coil is the reversal of the refrigerant flow in the refrigeration apparatus by operating changeover valve 22 to a position shown by the dotted lines. When solenoid 50 is energized, lever 51 is moved clockwise to rotate the plug 52 of the changeover valve to connect pipes 24 and '32, and

pipes

25 and 33. With the changeover valve operated in the defrosting position, hot gas from motor compressor 21 is delivered directly to upper portion 31 of the coil 23. The outdoor coil is in effect reversed with the indoor coil, and within a short time, the outdoor coil will be heated up sufficiently to melt all of the frost.

Solenoid 50 is connected to source of power 43 by a normally open switch 54 which has a fixed contact 55 and a movable member 60. Movable member 60 is engaged by an operating pin 61. When pin 61 is moved upward, solenoid 50 is energized to commence the defrosting cycle.

Switch operating apparatus 62 has a first bell crank lever 63 which is attached to a floating pivot pin 64. Pin 64- is not attached to a base. The bell crank has a first portion 65 extending to the right of pivot pin 64 and a second portion 70 extending to the left of pivot pin 64. Portion 70 is free to move between a pair of adjustable stops 71 and 72. A vertical portion 73 of hell crank 63 has an adjusting screw 74 which contacts an upper portion 75 of a second bell crank lever 80. Bell crank lever '80 is pivoted on pivot pin 64 and has a second portion 81 extending to the right. Levers 63 and are connected by pin 64, but the assembly is free to move in one plane. A first output device 39 has an output member 91 to provide a movement in response to the temperature of a bulb 92 located in the outdoor air stream. Such a unit might be a liquid filled system of a conventional type wherein upon the increase in temperature of bulb 92 a bellows expands or a diaphragm moves to push member 91 upward. A second output device 93 has a pin 94 which is moved upward when the temperature of a bulb 95 located adjacent the warmest side 31 or vapor line of the heat exchanger 23 increases. Members 91 and 94 push upward on the lower side of portion 70' and portion 65, respectively, of hell crank 63. Another output device 100 has a pin 101 which moves upward in response to the temperature of a bulb 102. Each

device

90, 93, and 100 have a calibration nut 110, 111, and 103, respectively. By rotating the nuts, the position of associated pins 91, 94, and 101, respectively, can be set for a predetermined temperature of bulbs, 92, 95, 102, respectively. Bulb 102 is located on the coldest side of heat exchanger 23 to respond to the temperature of the fluid line. When the temperature of bulb 102 increases, member 101 moves upward to move bell cnank 80 in a counterclockwise direction.

When bell crank 63 moves in a clockwise direction and screw 74 pushes bell crank 80 clockwise, the upper end of portion 75 will lift pin 61 to close switch 54. Lever 80 is not restricted by pin 101 since bulb 102 is cold. A detent or cam surface 105 in upper portion 75 of the bell crank holds pin 61 upward and the bell crank 80 in the switch operating or first position even though bell crank 63 returns in a counterclockwise direction.

Operation The normal operation of the refrigeration apparatus 20 is shown. Upon thermostat 42 calling for heat, relay 41 is energized to initiate operation of the motor compressor. The hot gas is delivered to the indoor coil 11, and upon the hot gas losing some heat, the gas condenses and the liquid passes through the restriction 34- to vaporize in outdoor coil 23. The heat of vaporization is obtained from the outdoor air which passes through the coil. The lower end 26 of coil 23 receives the liquid refrigerant and is normally the coldest portion of the coil.

As the liquid refrigerant enters the lower side of coil 23, the evaporation will normally take place in the lower twothirds of the coil. The vapor in the upper portion of the coil will be at a temperature relatively close to the temperature of the outdoor air; therefore, the temperature of bulb 95 will be relatively close to the temperature of bulb 92. By the proper calibration of

devices

90 and 93 the position approximately as shown of bell crank 63 for relatively equal temperature of

bulbs

92 and 95 is selected. As frost begins to form .on coil 23, the evaporation of liquid refrigerant is not confined to the lower two-thirds of the coil since the heat transfer to the air in the frosted portion of the coil is cut down. As evaporation begins to take place in the upper portion of coil 23, the temperature of bulb 95 will drop. Upon a predetermined difference in the temperature of

bulbs

92 and 95 being reached as selected by screw 74, lever 63 will have moved clockwise a sufiicient amount to pivot lever 80 until pin 61 is in detent 105. The switch 54 is then closed to initiate the defrost cycle.

Once the defrost operation is started by closing switch 54, any increase in temperature of bulb 95 has no effect upon the termination of the defrosting operation as pin 61 is locked in the upward position by the detent 105 on bell crank 80. In order to move the portion 75 to the left, bell crank 80 has to be pivoted about pin 64 by an upward movement of member 101.

When the defrost operation is started and the upper portion of coil 23 receives the hot gas, the gas will lose [heat by melting the frost off of coil 23. As the coil becomes free of frost, the hot gas will increase the temperature of bulb 102, and member 101 will move upward to pivot bell crank 80 in a counterclockwise direction to 4 allow pin 61 to open switch 54 to terminate the defrosting operation.

While the invention has been shown in one particular form, the invention should only be limited by the scope of the appended claims in which I claim:

1. In a defrost control system, a refrigeration apparatus comprising an indoor coil for delivering heat to a space, an outdoor coil for obtaining heat from outdoor air, a motor driven compressor, and means connecting said compressor, said indoor coil, and said outdoor coil into a series system, said outdoor coil having a liquid conduit and a vapor conduit connected thereto whereby liquid refrigerant fiows into said outdoor coil through said liquid conduit and vapor refrigerant leaves said outdoor coil through said vapor conduit after heat is obtained from the outdoor air, defrosting means adapted to heat said outdoor coil to remove frost from the coil by changing the flow of refrigerant in the system to deliver hot gas to the outdoor coil, first temperature responsive means responsive to the temperature of said liquid conduit, second temperature responsive means responsive to the temperature of said vapor conduit, air temperature responsive means responsive to the temperature of said outdoor air, means connecting said second temperature responsive means and said air temperature responsive means to said defrosting means to initiate operation of said defrosting means when the temperature difference between said vapor conduit temperature and said air temperature reaches a selected value, and means connecting said first temperature responsive means to said defrosting means to terminate the operation of said defrosting means when the temperature of the liquid conduit reaches a selected value as hot refrigerant passes therethrough.

2. In a defrost control system, a refrigeration apparatus comprising an indoor coil for delivering heat to a space, a second coil for obtaining heat from a source of cold air, a motor driven compressor, and means connecting said compressor, said indoor coil, and said second coil into a series refrigeration system, said second coil having a first portion which is first to receive liquid refrigerant from a conduit and a second portion from which vapor refrigerant leaves said second coil, defrosting means adapted to heat said second coil to remove frost from the coil, first temperature responsive means responsive to the temperature of said first portion, second temperature responsive means responsive to the temperature of said second portion, air temperature responsive means responsive to the temperature of said air, means connecting said second temperature responsive means and said air temperature responsive means to said defrosting means to initiate operation of said defrosting means when the temperature difference between the temperature of said second portion and said air temperature reaches a selected value, said second portion decreasing in temperature as said coil becomes frosted, and means connecting said first temperature responsive means to said defrosting means to terminate the operation of said defrosting means when the tempenature of said first portion reaches a selected value as said defrosting means is operated.

3. In a defrost control system for a refrigeration system having a compressor, an indoor heat exchanger normally furnishing heat to a space and an outdoor air heat exchanger connected in a refrigerant filled series system with defrosting apparatus for heating the outdoor heat exchanger when frost forms thereon, first responsive means having an output indicative of the temperature of the normally coldest portion of said outdoor coil, second responsive means having an output indicative of the temperature of the normally warmest portion of the outdoor coil, third responsive means having an output indicative of the temperature of the air entering the outdoor heat exchanger, means responsive to a predetermined difference in the output of said second responsive means and said third responsive means for starting the operation of the defrosting apparatus by reversing refrigerant fiow to said coils to remove frost from the outdoor heat exchanger,

and means responsive to the output of said first responsive means for terminating the operation of the defrosting apparatus.

4. In a defrost control system for a refrigeration system having a refrigerant compressor, and first heat exchanger and second heat exchanger connected in a series system and having defrosting apparatus for defrosting the second heat exchanger when frost forms thereon, first responsive means having an output indicative of the temperature of one portion of the second heat exchanger, second responsive means having an output indicative of the temperature of another portion of said second heat exchanger, third responsive means having an output indicative of the temperature of the medium entering the second heat exchanger, means responsive to a predetermined dilference in the output of said second responsive means and said third responsive means for starting the operation of the defrosting apparatus to remove frost from the second heat exchanger, and means responsive to a predetermined output of said first responsive means for stopping the operation of the defrosting apparatus.

5. In a defrosting control device for starting and stopping a defrost cycle of an outdoor air heat exchanger of a refrigeration apparatus, a base member, a first bell crank lever pivotally supported on a pivot for movement in a plane parallel to said base, a first and a second mechanical output member engaging said bell crank on opposite sides of said pivot, air temperature responsive means adapted to respond to the outdoor air temperature, means connecting said air responsive means to said first output means to have an output movement indicative of outdoor air temperature, second temperature responsive means adapted to respond to the normally warmest portion of the heat exchanger, means connecting said second responsive means to said second output member to have an output indicative of the temperature of the warmest portion of said heat exchanger, a second bell crank pivotally supported on said pivot, a second portion of said first bell crank engaging a first portion of said second bell crank to move said second bell crank to a first position when said output of said first output member exceeds said output of said second member as the temperature of said warmest portion drops below the temperature of the air, switch means mounted on said base, said switch being adapted to start the defrost cycle when said second bell crank is in said first position, locking means on said second bell crank to hold said second bell crank in said first position even though said first bell crank moves away, a third output member, first temperature responsive means adapted to respond to the temperature of the normally coldest portion of said heat exchanger, and means connecting said first temperature responsive means to said third member to have an output indicative of temperature whereby when said output of said third member rotates said second bell crank from said first position said defrost cycle is terminated.

6. In a defrosting control device for starting and stopping a defrost cycle of an air heat exchanger of a refrigeration apparatus, said defrost cycle being initiated by reversing the refrigerant flow to heat said air heat exchanger, a base member, a first bell crank lever pivotally attached to a pivot for movement in a plane parallel to said base, said bell crank having a first portion moving between a pair of stops mounted on said base, a first and a second mechanical output members engaging said bell crank on opposite sides of said pivot, temperature responsive means adapted to respond to the air temperature, means connecting said responsive means to said first output member to move said bell crank upward upon an increase in air temperature, first temperature responsive means adapted to respond to the temperature of one portion of said heat exchanger, second temperature responsive means adapted to respond to the temperature of another portion of the heat exchanger, means connecting said second responsive means to said second output memher to move said bell crank upward upon an increase in temperature, a second bell crank pivotally attached on said pivot, a second portion of said first bell crank engaging said second bell crank to move said second bell crank to a first position when said output of said first output member exceeds said output of said second member, switch means mounted on said base, said switch being adapted to start the defrost cycle when said second bell crank is in said first position, a third output member, and means connecting said first temperature responsive means to said third member to move said second bell crank from said first position when the temperature of the one portion increases to stop the defrost cycle.

7. In a control device, a base, a pivot pin, a first lever pivotally mounted on said pivot pin, a first and a second output means engaging said lever to move said lever in opposite directions about said pin, said first output means having an upward movement indicative of the temperature of the air passing through a heat exchange coil of a refrigeration system, said second output means having an upward movement indicative of the temperature of the normally warmest portion of the heat exchanger, a switch operating lever adapted to initiate a defrost cycle by applying heat to said heat exchanger, said first lever moving said switch operating lever clockwise when said first output exceeds said second output to move said switch lever to a switch operating position, a third output means having an output indicative of the temperature of the normally coldest portion of the exchanger, and means connecting said third output means to said switch lever to move said lever from said switch operating position to terminate the defrost cycle, when said coldest portion is warm.

8. A defrost control system for a refrigeration system wherein heat is removed from air by a heat exchanger having a conduit for normally receiving liquid refrigerant and a conduit for vapor refrigerant to normally leave the exchanger and having a heating means to heat the exchanger to defrost the heat exchanger comprising, first temperature responsive means responsive to the temperature of the heat exchanger nearest the liquid conduit, second temperature responsive means responsive to the temperature of the heat exchanger nearest the conduit of the leaving vapor, third temperature responsive means responsive to the temperature of the air, control means adapted to control the heating device, means connecting said second temperature responsive means and said third temperature responsive means to said control means to start defrosting the heat exchanger when the temperature of the vapor conduit exceeds the temperature of the air a predetermined amount, and means connecting said first temperature responsive means to said control means to stop the defrosting of the heat exchange when the heating means increases the temperature of said first responsive means.

9. A defrost cycle control system for a refrigeration apparatus having a heat exchanger removing heat from air as air passes in thermal contact with the heat exchanger, the heat exchanger receiving liquid refrigerant at a first portion and losing refrigerant vapor from a second portion comprising, first responsive means having an output responsive to the temperature of the first portion, second responsive means having an output responsive to the temperature of the second portion, third responsive means having an output responsive to the temperature of the air, means connecting the outputs of said second and third responsive means to initiate a defrost cycle of the heat exchanger when the temperature of the second portion exceeds the temperature of the air, and further means connecting the output of said first responsive means to terminate the defrost cycle.

10. In a defrost control system for a refrigeration system having a compressor, an indoor heat exchanger and an outdoor air heat exchanger connected in a refrigerant filled series system and having a defrosting apparatus for for starting the operation of the defrosting apparatus to remove frost from the outdoor heat exchanger, and means responsive to a predetermined output of said first responsive means for stopping the operation of the de- 5 frosting apparatus.

References Cited in the file of this patent UNITED STATES PATENTS 2,666,298 Jones Jan. 19, 1954

Claims

3. IN A DEFROST CONTROL SYSTEM FOR A REFRIGERATION SYSTEM HAVING A COMPRESSOR, AN INDOOR HEAT EXCHANGER NORMALLY FURNISHING HEAT TO A SPACE AND AN OUTDOOR AIR HEAT EXCHANGER CONNECTED IN A REFRIGERANT FILLED SERIES SYSTEM WITH DEFROSTING APPARATUS FOR HEATING THE OUTDOOR HEAT EXCHANGER WHEN FROST FORMS THEREON, FIRST RESPONSIVE MEANS HAVING AN OUTPUT INDICATIVE OF THE TEMPERATURE OF THE NORMALLY COLDEST PORTION OF SAID OUTDOOR COIL, SECOND RESPONSIVE MEANS HAVING AN OUTPUT INDICATIVE OF THE TEMPERATURE OF THE NORMALLY WARMEST PORTION OF THE OUTDOOR COIL, THIRD RESPONSIVE MEANS HAVING AN OUTPUT INDICATIVE OF THE TEMPERATURE OF THE AIR ENTERING THE OUTDOOR HEAT EXCHANGER, MEANS RESPONSIVE TO A PREDETERMINED DIFFERENCE IN THE OUTPUT OF SAID SECOND RESPONSIVE MEANS AND SAID THIRD RESPONSIVE MEANS FOR STARTING THE OPERATION OF THE DEFROSTING APPARATUS BY REVERSING REFRIGRANT FLOW TO SAID COILS TO REMOVE FROST FROM THE OUTDOOR HEAT EXCHANGER, AND MEANS RESPONSIVE TO THE OUTPUT OF SAID FIRST RESPONSIVE MEANS FOR TERMINATING THE OPERATING OF THE DEFROSTING APPARATUS.