US3147602A

US3147602A - Defrost method and means for refrigerated cabinets

Info

Publication number: US3147602A
Application number: US128235A
Authority: US
Inventors: Beckwith Sterling
Original assignee: Dual Jet Refrigeration Co
Current assignee: Dual Jet Refrigeration Co
Priority date: 1961-07-31
Filing date: 1961-07-31
Publication date: 1964-09-08
Anticipated expiration: 1981-09-08

Description

Sept. 8, 1964 s. BECKWITH 3,147,602

DEFROST METHOD AND MEANS FOR REFRIGERATED CABINETS Filed July 31, 1961 2 Sheets-Sheet l OOOOOOO OOOOOOO OOOOOOO FIG, 5

mmvrop. Sterlmg Beckwzih @101 BY M,%.@ MM Fm. 3 M7 Q1295 S. BECKWITH Sept. 8, 1964 DEFROST METHOD AND MEANS FOR REFRIGERATED CABINETS Filed July 51, 1961 2 Sheets-Sheet 2 lllll I WUNMQMPMG WMM l I l United States Patent "ice 3,147,602 DEFROST METHOD AND MEANS FOR REFRIGERATED CABINETS Sterling Beclrwith, Libertyville Township, Lake County,

Ill assignor, by mesne assignments, to Dual Jet Refrigeration Company, a corporation of Illinois Filed July 31, 1961, Ser. No. 128,235 16 Claims. (Cl. 62278) This invention relates to a refrigeration system and more particularly to a refrigeration system which requires occasional defrost for the removal of frost collected on the surfaces of the evaporator plates.

The invention will be described with reference to the maintenance of a refrigerated state Within a space that is enclosed except for an open side which remains open to the atmosphere for observation of the products maintained within the refrigerated space and for access into the interior thereof to remove refrigerated products or for replacement of products for refrigeration and display. It will be understood that the concepts of this invention of refrigeration and defrost will have application to refrigeration systems employed for uses other than in a refrigerated display cabinet of the type described.

In the copending application of Hagen et al., Ser. No. 54,077, filed September 6, 1960, and entitled Refrigerated Display Case, description is made of a refrigerated display cabinet having a storage space with an open side. Loss of heat from the storage space through the open side is substantially obviated by the use of a curtain of air passed continuously across the space from one edge to an opposite edge thereby to blanket the entire opening.

The air curtain is adapted to be formed of adjacent panels of air with the inner panel being a refrigerated panel while the outer panel or panels correspond more closely to the ambient temperature. For most efficient operation, it has been found desirable to recirculate at least the inner panel of cold air to conserve on the investment in refrigeration and to maintain the space in the desired refrigerated state.

In the aforementioned copending application, illustration is made of an arrangement which makes use of an inner cold air panel and an outer panel both of which are recirculated through separate systems in the cabinet whereby the outer panel acquires a temperature intermediate the cold air panel and the ambient temperature to function as a guard panel which minimizes heat loss while at the same time enhancing laminar flow. Also disclosed in the aforementioned copending application is an arrangement wherein the curtain is formed of three recirculating panels arranged in side-by-side relationship further to increase the efiiciency of operation from the standpoint of laminar flow characteristics and heat loss from the conditioned space.

Description is made of an arrangement wherein the nozzles, from which the air panels issue, extend across the bottom edge of the opening to direct the air panels upwardly across the open space towards inlets which extend across the top side of the opening. Description is also made of a preferred arrangement wherein the nozzles are located across the upper edge of the opening for issuing the air panels downwardly across the opening to inlets arranged across the bottom side. It will be understood that the air nozzles can be located across one of the lateral edges of the opening for directing the air panels across the opening towards inlets in the opposite edge. Because of the more desirable effect of gravity on the high density cold air, it is preferred to flow the air curtain downwardly from nozzles across the top to inlets across the bottom.

Refrigeration of the cold air panel is achieved by the use of a refrigeration system wherein a refrigerant liquid 3,147,562 Patented Sept. 8, 1954 is circulated through an evaporator located within the cold air passage beyond the inlet but before the outlet and through which the cold air stream must pass in heat exchange relationship. Since the air is gradually reduced in temperature as it passes progressively from the ambient atmosphere into the outer guard panels and from the outer guard panels into the inner cold air panel to form a part thereof before passing into the refrigerated space, the relative humidity of the air correspondingly increases to a point where it becomes substantially saturated with moisture by the time that it becomes part of the cold air panel. Such moisture tends to separate out and collect on the cold surfaces impacted by the cold air stream, especially when such surfaces constitute a cold surface such as the evaporator plate or coils. As aresult, moisture collects as frost on the evaporator plates and particularly on the ingoing side.

Excessive frost formation requires termination of the cold air fiow until the surfaces of the evaporator plates can be defrosted. In order properly to maintain the refrigerated state, it is desirable to minimize the number of times and the length of time that the flow of the cold air stream is shut off and for this purpose it is desirable either to minimize the amount of frost built up on the surfaces of the evaporator plates and/or else to maximize the rate at which such frost can be removed.

Thus it is an object of this invention to produce a method and means for reducing the built-up frost on the surfaces of refrigeration coils located within the path of an air stream for the refrigeration thereof.

Another object of this invention is to provide a method and means for rapid defrost thereby to minimize the length of time required to effect frost removal and replacement of the refrigeration coils back into the refrigeration cycle. 7

A further object is to provide a display cabinet having a refrigerated space which is enclosed except for an open side across which one or more streams of air are projected as an air curtain from one side to the other across the open space with the inner panel of the curtain being a refrigerated cold air panel which is continuousl recirculated and which is maintained in a refrigerated state by a refrigeration system including an evaporator plate in the path of the cold air stream passage in heat exchange relationship therewith and which embodies means for minimizing the concentration of frost built up on the surfaces of the evaporator plates thereby to lengthen the time span between the defrost cycles and/or increase the rate of frost removal thereby to minimize the length of time that the cold air stream is taken out of circulation.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, embodiments of the invention are shown in the accompanying drawings, in which- FIG. 1 is a schematic sectional elevational view of a refrigerated display cabinet embodying the features of this invention;

FIG. 2 is a schematic sectional elevational View similar to that of FIG. 1 showing a modification in the cabinet construction;

FIG. 3 is a sectional elevational view similar to those of FIGS. 1 and 2 showing a further modification in the cabinet construction;

' FIG. 4 is a flow diagram of the refrigeration system embodying the features of this invention; and

FIG. 5 is a schematic sectional elevational view of a portion of the cabinet embodying a further feature of this invention.

The concepts of this invention are found to be most eifective when used in combination with a refrigerated display cabinet of the type described wherein an air curtain is used to protect an open side of an otherwise enclosed refrigerated space to maintain the desired state of refrigeration therein. Thus the invention will be described with reference to the combination of the refrigeration system and an open refrigerated display cabinet. However, it will be understood that the concepts of the invention will have application to other refrigeration systems wherein rapid defrost finds beneficial use.

Referring now to the drawings for a description of the refrigerated display cabinet and its method of operation, the cabinet is constructed with an outer housing wall including a top wall 12, a back wall 14, a bottom wall 16, vertical side walls 18, and a front wall 20, the latter being provided with an access opening 22. The housing rests upon a suitable base 24.

Spaced inwardly from the housing walls in substantially parallel relationship is an inner wall including top, back, bottom, side and

front walls

26, 28, 30, 31 and 32, respectively, which define the interior of a storage space 34. The space between the inner walls and the housing walls is divided by a partitioning wall 36 into two separated

passages

38 and 40 which extend substantially continuously about the storage space from

outlets

54 and 56 across the bottom side of the opening 22 to

inlets

62 and 64 across the top side of the opening 22.

Located within the inner passage 40 are evaporator coils 42 through which a suitable refrigerant is circulated for indirect heat exchange to cool air passing through the cold air passage 40 into contact with the evaporator coils. Located upstream between the evaporator coils 42 and the inlet 62 is an air circulating means, such as a fan or blower 44, for causing the stream of air to flow through the passage 40 from the inlet 62 to the outlet 54 and from the outlet 54 to the inlet 62 across the open space 22 to form the inner cold air panel 58 of the air curtain.

Similarly located within the outer passage 38 is another air circulating means, such as a fan or blower 46, for causing air to flow from the inlet 64 through the channel to the outlet 56 and from the outlet 56 to the inlet 64 across the open space 22 to form the outer panel 60 which flows in substantially parallel relationship with the inner cold air panel 58 to form the air curtain.

The outlet 54 of the cold air passage 40 is in the form of a vaned nozzle 55, such as a honeycomb section, which extends continuously across the bottom side of the access opening 22 in the front wall of the refrigerated display case. Similarly the outlet 56 for the outer guard air passage 38 is in the form of a nozzle 57 of a vaned or honeycomb section which also extends substantially continuously across the bottom side of the access opening in parallel side-by-side relationship with the nozzle 55.

The streams of air issuing from the

outlets

54 and 56 form continuous inner and

outer air panels

58 and 60 which extend across the access opening 22 from the

outlets

54 and 56 to the

inlets

62 and 64. The nozzle 55 is positioned to direct the inner cold air panel 58 to the inlet 62 in communication with the cold air passage 40 while the nozzle 56 is positioned to direct the outer guard air panel 68 to the inlet 64 in communication with passage 38. Both of the inlets can be provided with

screening members

66 and 68 to obviate the entrance of foreign matter, insects and the like into the passages.

From the foregoing description it will be apparent that the device provides a panel of cold air 58 adjacent to the interior of the storage space and a panel of warmer air 68 which will be intermediate the temperature of the cold air panel and the temperature of the ambient air. Thus the guard panel 60 is interposed between the inner panel of cold air and the ambient air thereby to guard the cold air from the heat of the atmosphere and whereby air entrained from the guard panel into the cold air panel will be found to be at considerably lower temperature than the air from the atmosphere which otherwise would be the component admixed therewith. To minimize heat loss into the cold air recirculated through the passage 48, it is desirable, though not essential, that the partitioning wall 36 and the outer wall 14 be provided with suitable insulation, designated by the numeral 74.

By way of still further modification, instead of making use of a single guard jet, additional guard jets may be provided whereby the air panels extending across the access opening will correspond to the number of such jets. In the modification illustrated in FIG. 3 one additional guard jet 102 is employed to provide three parallel streams of

air

58, 60 and 102 extending across the access opening. It will be understood that more than one additional. jet may be provided. Such additional jets will operate further to reduce the temperature diiferential between the air panels so that the guard jet adjacent the inner cold air panel will be at a temperature still closer to the temperature of the cold air stream such that the entrainment of air from one panel to the other will have lesser effect on the temperature thereof.

The modifications illustrated in FIGS. 2 and 3 will be the preferred modifications wherein the air streams are circulated through the passages from inlets at the bottom to outlets at the top of the access opening and downwardly from the outlets across the top of the access opening to inlets across the bottom of the access opening.

In FIG. 1, the evaporator coils 42 of the refrigeration system are located in the vertically disposed portion of the cold air passage rearwardly of the enclosed refrigerated space. In the preferred practice of the invention, illustrated in FIGS. 2 and 3, wherein the air streams are recirculated through the passages for downward flow across the access opening 22 from outlets across the top to inlets across the bottom, the evaporator coils 42 of the refrigeration system are located in the passages extending horizontally across the bottom sides of the cabinet. In either event, the evaporator coils are provided with a drain pan 188 for collecting the moisture released when the frost is melted from the surface of the evaporator coils during the defrost cycle and each drain pan is provided with a connecting hose 101 for the drainage of moisture collected in the pans.

Having described the construction and operation of the refrigerated display cabinet, description will now be made of the concepts of this invention in a system which embodies means for rapid defrost.

Referring now to FIG. 4 of the drawings, the evaporator located in the cold air passage is identified by the numeral 42 and the evaporator (when employed) in the guard air passage is identified by the numeral 48 and the drain pan is illustrated by the numeral 100. The other elements conventionally employed in a refrigeration system include a compressor 104, a condenser 106, and a receiver 108 whereby liquid refrigerant 110 is passed from the receiver through line 112 through a drier 114 and from the drier through line 116 through a heat exchanger 118 through line 120 to the solenoid valves 122 which control passage of the refrigerant liquid into the coils of the

evaporator

42 or 42 and 48. The refrigerant vapors from the evaporator coils pass through line 124 through the heat exchanger 118 and defrost receiver 126 to the compressor 104 where the vapors are recompressed and then advanced through line 128 to the condenser 106 wherein the compressed refrigerant vapors are condensed to the liquid state for return through line 130 to the receiver 108.

Occasionally it is necessary to shut off the refrigeration cycle to enable removal of frost collected on the surfaces of the evaporator coils. Various techniques have been employed for defrosting the evaporator coils in a refrigeration system. One such technique to which this invention is addressed is often referred to as hot gas defrost wherein the refrigerant vapors exhausted from the compressor and heated up by the work performed in compression are recirculated through the evaporator coils for condensation, to melt the frost collected on the surfaces thereof. Sometimes the heat introduced into the exhaust gases by the compressor is supplemented by external heat supplied by heat exchange relationship with the hot liquids advanced through the line 132 to the evaporator coils.

The defrost cycle using the conventional hot gas defrost requires such a length of time as to enable change in the temperature conditions existing within the refrigerated space. It has been found, in accordance with an important concept of this invention, that the defrost cycle can be markedly shortened by modification of the hot gas defrost system greatly to increase the volume of hot gases which are circulated through the evaporator coils.

For this purpose, there is provided an auxiliary supply of refrigerant liquid in communication with the

discharge line

130 or 132 from the compressor whereby the pressure conditions existing when the hot gases from the compressor are recirculated to the refrigeration coils during the hot gas defrost cycle draw the refrigerant liquid from the auxiliary supply into the return line 132. Auxiliary heaters 134 are provided for heat exchange with the line 132 to reduce the refrigerant liquid to the gaseous state thereby materially to increase the volumetric heat flow of gases to the evaporator coils. The quantity increase of heat flow of hot gases to the evaporator operates materially to reduce the defrost cycle to a matter of a few minutes compared to at least three to four times as long for conventional hot gas defrost systems.

In the illustrated modification, the auxiliary liquid refrigerant is collected in a pan 136 located within the receiver 108 and into which the end of the line 130 from the condenser extends so that the condensed refrigerant liquid is first deposited into the pan and the overflow falls from the pan into the receiver. Thus the pan is immediately refilled with refrigerant liquid during the normal refrigeration cycle and it can be dimensioned to hold refrigerant liquid in an amount desired to supply the additional volume of gases for defrost. Usually, an auxiliary supply of from to 12 pounds will be sufficient. instead of collecting the liquid in a pan forming a part of the receiver, the auxiliary liquid can be supplied in a container separate and apart from the receiver but which communicates with the line 132 through which the hot exhaust gases are advanced to the refrigeration coils for defrost.

In operation, the defrost cycle is initiated by an electrical signal which may be responsive to the frost buildup on the evaporator coils or to a temperature differential control or to a timer or other conventional means for signaling the termination of a refrigeration cycle and the initiation of the defrost cycle. In sequence with the signal, the liquid solenoid valve 122 is closed to shut off How of refrigerant liquid in the evaporator coils. After a short period for vaporization of the refrigerant liquid remaining in the coils, the suction solenoid valve 137 is closed and simultaneously the hot gas solenoid valve 138 is opened for circulation of the hot gases exhausted from the compressor through line 132 to the inlet side of the evaporator 42.

In conjunction with the opening of the hot gas solenoid 138, a discharge pressure drop occurs which draws or otherwise forces the small quantity of auxiliary refrigerant liquid from the auxiliary supply pan 136 into the discharge line 130 and the hot gas line 132. As the auxiliary liquid is advanced through the air cooled condenser 106 and the hot gas line 132 provided with the heating means 134, such as an electrical resistance heater or other heating means, the liquid boils and absorbs heat whereby the auxiliary refrigerant liquid is converted into a large volume of heated gases or vapor. The total heat of the hot gases exhausted from the compressor and the hot gases of the converted liquid is advanced through the line 132 to the evaporator since evaporation is at a lower temperature and pressure. The heat from the total volume of hot gases is absorbed by the evaporator coils to cause rapid melting of the frost collected on the surfaces thereof.

It is preferred that the heating means 134 be a low energy source such that it will not evaporate the rapid flow of liquid from the supply pan 136 unless it has, over a period of time, which is a substantial portion of the time between defrosts, stored thermal energy in the mass of metal which constitutes the hot gas line 132. Under such circumstances there will be a relationship between the volumetric capacity of supply pan 136 and the mass of hot gas line 132. Also line 132 should have adequate inside surface area to transfer its heat rapidly to the liquid flowing from pan 132.

The hot gases are, in turn, condensed for reconversion into liquid form which accumulates in the evaporator suction line side of the evaporator. A capillary tube 140 which bypasses the suction solenoid 137 operates to discharge the accumulated liquid into the suction line 124 for return to the compressor and recycling.

A further concept of this invention resides in the construction and arrangement of the evaporator whereby the build up of frost is spread over a larger area of the surface of the refrigeration coils thereby to extend the length of time between the defrost cycles. For this purpose, as illustrated in FIG. 5, the passage 40 leading to the inlet end of the evaporator is dimensioned to have a crosssection greater than the cross-section of the evaporator with the walls 142 of the passage converging to engage the evaporator walls intermediate the inlet and outlet ends so that a fractional portion of the air stream will impact the evaporator at the inlet end while the remaining portions will impact the evaporator for passage therethrough along the side walls beyond the inlet thereby materially to increase the surface area of the evaporator on which moisture can condense to form frost.

' Such distribution of frost over a greater surface area of the evaporator coils has been found proportionately to increase the amount of time that the evaporator can remain in the cooling cycle before initiation of the defrost cycle and it also inversely reduces the amount of time required to defrost the coils since there will be a lesser build up of frost per unit area .of surface and greater surface area is available for heat transfer from the hot gases advanced through the coils during the defrost cycle.

It will be apparent from the foregoing that I have provided a method and means for materially shortening the defrost cycle thereby to minimize the length of time that the refrigeration system is taken out of operation. It will be apparent that this material reduction in the time required to defrost the evaporator coils will operate beneficially to maintain the refrigerated state within the storage space of a refrigerated display cabinet of the type to which this invention is principally addressed thereby materially to enhance the utility of the refrigerated display cabinet for the display and storage of refrigerated products.

It will be understood that changes may be made in the details of construction, arrangement and operation Without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. In a refrigeration system having an evaporator, a compressor, a condenser and a receiver wherein refrigerant liquid is circulated from the receiver to the evaporator and wherein the refrigerant vapors are circulated from the evaporator to the compressor for recompression and from the compressor to the condenser where the compressed vapors are condensed for return to the receiver, a defrost system comprising a passage communicating the discharge from the compressor with the evaporator for circulation of the hot vapors exhausted from the compressor to the evaporator, an auxiliary supply of refrigerant liquid in communication with the passage whereby refrigerent liquid is drawn from the auxiliary supply into said passage responsive to the circulation of the hot vapors exhausted from the compressor through the passage to the evaporator, and heating means in heat exchange relationship with the auxiliary liquid advanced to the passage to convert said refrigerant liquid to the vapor state and for heating same whereby the total volume of hot vapors advanced to the evaporator for defrost comprises the hot vapors exhausted from the compressor plus the large volume from the so converted auxiliary refrigerant liquid to cause rapid defrost of the evaporator.

2. A refrigeration system as claimed in claim 1 which includes a shut-off valve for stopping the flow of refrigerant liquid from the receiver to the evaporator prior to the circulation of the hot vapors from the discharge and the auxiliary refrigerant liquid to the evaporator.

3. A refrigeration system as claimed in claim 2 in which the passage communicating the discharge from the compressor with the evaporator communicates with the evaporator beyond the shut-off valve and which includes another shut-oti valve in the passage between the discharge from the compressor and the evaporator.

4. A refrigeration system as claimed in claim 1 in which the heating means comprises a heater in heat exchange relationship With the passage between the discharge from the compressor and the evaporator.

5. A refrigeration system as claimed in claim 1 which includes a container within the receiver of smaller capacity than the receiver and a passage having one end in communication with the condenser and the other end terminating in the container for the delivery of refrigerant liquid from the condenser to the container to fill the container before overflow from the container into the receiver.

6. A refrigeration system as claimed in claim 1 in which the auxiliary supply of refrigerant liquid comprises a container Within the receiver.

7. In a refrigerated display cabinet having a refrigerated space provided with an access opening communicating the otherwise enclosed space with the outside atmosphere, means for projecting a continuous curtain of refrigerated air across said access opening from an outlet across one side of said opening to an inlet across the opposite side of said opening, a passage in said cabinet communicating the inlet with the outlet for recirculating the air from the inlet to the outlet, and evaporator located within said passage and a refrigeration system in communication with said evaporator including a compressor, a condenser and a receiver wherein refrigerant liquid is circulated from the receiver to the evaporator and wherein the refrigerant vapors are circulated from the evaporator to the compressor for recompression and from the compressor to the condenser where the compressed vapors are condensed for return to the receiver, a defrost system comprising a passage communicating the discharge from the compressor with the evaporator for circulation of the hot vapors exhausted from the compressor to the evaporator, an auxiliary supply of refrigerant liquid, in communication with the passage whereby refrigerant liquid is drawn from the auxiliary supply into said passage responsive to the circulation of the hot vapors exhausted from the compressor through the passage to the evaporator, and heating means in heat exchange relationship with the auxiliary liquid advanced to the passage to convert said refrigerant liquid to the vapor state and for heating same whereby the total volume of hot vapors advanced to the evaporator for defrost comprises the hot vapors exhausted from the compressor plus the large volume from the converted auxiliary refrigerant liquid to cause rapid defrost of the evaporator.

8. A refrigerated display cabinet as claimed in claim 7, which includes a shut-ofi valve for stopping the flow of refrigerant liquid from the receiver to the evaporator prior to the circulation of the hot vapors from the discharge and the auxiliary refrigerant liquid to the evaporator.

9. A refrigerated display cabinet as claimed in claim 8 in which the passage communicating the discharge from the compressor with the evaporator communicates with the evaporator beyond the shut-off valve and which .includes another shut-off valve in the passage between the discharge from the compressor and the evaporator.

10. A refrigerated display cabinet as claimed in claim 7 in which the heating means comprises a heater in heat exchange relationship with the passage between the discharge from the compressor and the evaporator.

11. A refrigerated display cabinet as claimed in claim 7 which includes a container within the receiver of smaller capacity than the receiver and a passage having one end in communication with the condenser and the other end terminating in the container for the delivery of refrigerant liquid from the condenser to the container to fill the container before overflow from the container into the rece ver.

12. A refrigerated display cabinet as claimed in claim 7 in which the auxiliary supply of refrigerant liquid comprises a container within the receiver.

13. A refrigerated display cabinet as claimed in claim 7 which includes a drain pan underlying the evaporator for drainage of the liquid defrost.

14. A refrigerated display cabinet as claimed in claim 7 which includes means for terminating the flow of air through said passage during the defrost cycle.

15. A refrigerated display cabinet as claimed in claim 7 in which the passage about the ingoing side of the evaporator is of larger dimension than the evaporator to provide an access space about the leading end portion of the evaporator whereby the circulating air may enter the evaporator for passage theret-hroug-h about the side wall portions in addition to the leading end portion.

16. A refrigerated display cabinet as claimed in claim 15' in which the passage is defined by walls which are spaced from the outer surfaces of the evaporator in the leading end portion and converged to engage the evaporator mtermediate its ends.

References Cited in the file of this patent UNITED STATES PATENTS