US3381494A

US3381494A - Frost collector evaporator coil

Info

Publication number: US3381494A
Application number: US589980A
Authority: US
Inventors: Melvin W Steelman
Original assignee: Clark Equipment Co
Current assignee: Doosan Bobcat North America Inc
Priority date: 1966-10-27
Filing date: 1966-10-27
Publication date: 1968-05-07
Anticipated expiration: 1985-05-07
Also published as: GB1187089A; DE1601018A1; DE1601018B2; DE1601018C3

Description

May 7, 1968 M. W. STEELMAN FROST COLLECTOR EVAPORATOR COIL Filed Oct. 27. 1966 FIG. 6

39 INVENTOR MELVIN w. STEELMAN m c 9 ATTORNEY United States Patent 3,381,494 FROST COLLECTOR EVAPORATOR COIL Melvin W. Steelman, Niles, Mich., assignor to Clark Equipment Company, a corporation of Michigan Filed Oct. 27, 1966, Ser. No. 589,980 7 Claims. (Cl. 62-283) ABSTRACT OF THE DISCLOSURE A refrigerated case has ductwork for carrying cool air through evaporator coils by drawing the air through a channel. Within the channel, a primary cooling coil is located downstream from a secondary cooling coil that removes most of the moisture from the air before the air reaches the primary coil. The secondary coil has individual vertical fins each in contact with several tubes in a vertical line but with only one in a horizontal line. The fins in contact with subsequent sets of tubes in a vertical line are staggered to obtain several leading edges. The ductwork and secondary cooling coil are constructed to provide a bypass air path around the secondary coil to carry the cooling air upon closing of the secondary coil by an accumulation of frost.

The present invention relates to a refrigerated case structure, and more particularly, to such a structure employing a novel finned refrigerating coil construction and arrangement.

Refrigerated cabinets and cases, particularly of the type employed in super markets and other retail stores, common-ly employ refrigerating coils by which air is cooled in movement thereover, circulated through the case to cool the products contained therein, and then returned as through a duct or passage to pass again over the coil. A plurality of coils are usually necessary, arranged one behind or downstream from the other in the air duct or passage. Moisture from the cooling air is condensed and frozen on the coil as a deposit offrost, which reduces the efficiency of the refrigerating coil, and must be removed from time to time as the accumulation increases. This is normally accomplished by supplying heat to melt the frost. It is desirable to keep the number of frequency of these defrosts to a minimum. As a practical matter, minimization of defrosting requires reduction in fro-st deposition. Many attempts have been made to solve this problem, none of them completely successful.

The solution provided by the present invention involves the use of a secondary cooling coil which is disposed in the air passage upstream from one or more primary refrigerating coils, and which is specifically constructed for accumulating a great volume of frost thereon. The secondary coil is located in the pas-sage to have most of the air flow thereover or there-through and cause deposition of moisture therefrom before it passes, in a relatively dehumidified condition, to the primary refrigerating coils, so that only relatively light frosting of such other coils occurs. The secondary cooling coil has such construction and spaced relation to the interior of the passage or duct that air may continue to flow around or past it to the primary coils, even after frost deposition on the secondary coil has reached its maximum, so that refrigeration continues with high efiiciency. Heavier frosting of the primary refrigerating coils then takes place since the air reaching these coils is not dried by the secondary coil. Frosting of the primary coils, when it increases to an undesired extent, causes defrosting of all of the coils in the case by means of known devices for this purpose. The invention increases the capacity of the refrigeration system to accumulate frost without too great a loss of 3,381,494 Patented May 7, 1968 efficiency of refrigerating capacity, and thus increases the length of the periods during which refrigeration continues without interruption for defrosting to improve the operating efliciency. The invention, as evident, also provides a novel method of controlling frosting in refrigerated cases.

Objects of the invention are the provision of a refrigerated case structure by which frequency of defrosting is greatly reduced, of a cooling coil structure having great frost-collecting capacity, and of a novel method of extending the intervals between defrosting operations in a refrigerated case or the like.

Other and further objects, advantages and features of the invention will be apparent to those skilled in the art from the following description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a vertical cross-sectional view of the lower portion of a refrigerated case embodying the present invention;

FIG. 2 is a fragmentary plan view of a cooling coil employed in the case of FIG. 1;

FIG. 3 is a vertical sectional view of the coil, taken substantially as indicated by the line 33 in FIG. 2;

FIG. 4 is a cross-sectional view of the coil, taken substantially as indicated by the line 4-4 in FIG. 2;

FIG. 5 is a fragmentary longitudinal sectional view through the case taken as indicated by the line 5-5 in FIG. 1, and showing a portion of the coil in front elevation; and

FIG. 6 is a fragmentary front elevational view of primary refrigerating coils, taken as indicated by the line 6-6 in FIG. 1.

Referring to the drawing, there is shown in FIG. 1 a refrigerated case, generally designated 10, comprising thermally insulated front and rear walls 11 and 12 connected by an insulated bottom 13, these walls and bottom extending between end walls, one of which is shown at 14 in FIG. 5, also of thermally insulated construction. The case body provided by the walls and bottom may be supported in any suitable manner on a base 15.

Within the case body there is provided a well or product compartment extending between the end walls 14 of the case 10 defined by a front panel 16, a rear panel 17, and a bottom panel 18, of a suitable sheet material or the like. The front panel 16, bottom 18 and rear panel 17 are spaced respectively from the front Wall 11, bottom 13 and rear wall 12 of the case to define a duct or passage generally indicated as 19. Air may be circulated through this duct by means of a fan or blower 20 driven by electric motor 21 and suitably mounted in an opening in a fan panel 22 extending across the air duct or passage 19. The fan 20 draws air through a preferably screened inlet aperture 23, defined between the upper edge-s of the front wall 11 and front panel '16, to pass downwardly in a forward vertical portion of the duct, under the bottom panel 18 of the product compartment, and upwardly in the rear portion of the duct defined between the rear panel 17 and rear wall 12. From the rear duct portion, the air is discharged through any suitable outlet structure for cooling of the product compartment and its contents, returning through the inlet aperture 23 to the duct 19 for recirculation.

In the portion of the passage or duct 19 forwardly or upstream of the fan 20, there is provided a refrigerantevaporating coil generally designated 25, which may be referred to as a secondary or cooling coil, or frost-collecting coil, to distinguish from primary or refrigerating coils hereinafter mentioned. The coil 25 comprises a suitable number of pipe or tube portions 26 in two groups or series each consisting of a pair of sets, the particular construction illustrated employing four tube portions in each set, the four tube portions of each set being disposed in substantially the same vertical plane. The tube portions 26 in each set of each group or series are offset vertically from those in the other set of that group, as is clearly evident from FIGS. 1, and 3 to inclusive. Header plates 27, which may have oppositely directed upper and lower flanges, mount the tube portions. Return bends 28 at opposite ends of the coil each connect a tube portion of one set with a tube portion of the other set of a group, providing a continuous flow path for a fluid refrigerant through each of the two groups of tube portions 26 and bends 28. A tube portion at one end of each group has a suitable connection to a refrigerant inlet line or conduit 29 common to the two groups, and a tube portion of each group at the end opposite the tube portion connected to the inlet conduit 29 has a suitable connection to a common refrigerant return line 30.

The refrigerant, in accordance with commercial practice, is supplied under pressure from a suitable source through the inlet conduit 29, and is returned through line 30 after expansion and evaporation in the coil 25 to effect cooling thereof. The refrigerant is then compressed and condensed by any well-known means, not shown, to be again supplied to the coil as desired. In the present case, the tube portions extend horizontally in a direction transverse of the air path, with adjacent sets of tube portions spaced apart in the direction of air flow.

A plurality of fins 31 are secured on the tube portions 26 of each set, the fins being relatively narrow and elongated as best evident from FIGS. 3 and 4. An appreciable space is provided between the fins of the several sets in the direction of air flow. As best shown in FIGS. 2 and 5, the fins 31 of one set are offset laterally, or longitudinally of the tube portions, from the fins of the adjacent set. The fins of alternate sets are also offset vertically relative to each other, as is best shown in FIGS. 4 and 5. At one or more points along the length of the coil 25, plates 32, which may be flanged at their upper and lower ends and preferably of the same width as the fins, but of greater height or length, are secured on the four sets of tube portions in the same plane transverse of the coil. These plates replace fins 31 on two of the sets and are interposed between fins of the other two sets. Tie elements 33, shown as angle members, are bolted or otherwise secured to the upper and lower ends of the plates 32. This construction, best shown in FIGS. 2, 3 and 5, assures that the tube portions will be maintained in the desired spaced and offset relation throughout their length, and rigidifies the coil assembly.

The secondary or cooling coil 25 is so dimensioned and located relative to the interior of the duct or passage 19, specifically the horizontal portion thereof below the bottom panel 18 of the product compartment, as to leave a space or spaces through which air may flow about or around, rather than through or over, the coil. In the present instance, the coil is mounted in the duct so as to be spaced from at least one of the end walls 14, as shown in FIG. 5. As frost builds up on the coil 25, it tends to block passage of air through the coil, and may accumulate in a sulficient volume to present a substantially solid barrier to air flow. The coil 25 may be mounted in the duct or passage 19 in any suitable manner, as by securement of the bottom flanges of the headers 27 and the lower tie elements 33 to the bottom 13 of the case by any appropriate means. Upper flanges of the headers and the upper tie elements 33 may be disposed in supporting relation to the bottom panel 18 of the product compartment, if desired, as shown in FIGS. 1 and 5.

On the leading or upstream side of the coil 25, there are suitably mounted a plurality of vertical brackets 34 which support elements of an electrical resistance heater 35 in the form of one or more wires or rods extending horizontally along the cooling coil 25. The heater 35 is of a known construction, and is connected to a suitable source of electricity for activation in a predetermined manner.

In the vertical rear portion of the duct or passage 19,

downstream from the secondary or cooling coil 25 and fan 20, there is provided at least one primary or refrigerating coil 36, two such coils appearing in FIG. 1, suitably supported for flow therethrough of air which has been drawn through the inlet 23 by the fan 20. The refrigerating-coils 36 are of conventional construction, comprising tube elements 37 supported on headers 38, and carrying fins 39 common to all the tube elements and spaced longitudinally therealong. The refrigerating coil or coils 36 may provide the greater portion of the refrigerating capacity of the case 10, the cooling coil 25, providing the balance. Defrosting of the coils is controlled in accordance with the frosting of the primary coils 36, by means of any of several known devices for this purpose, although in the alternative, defrosting may be initiated by time mechanism set in accordance with knowledge of the number of defrosts required during a given period of time, corresponding to a given frost accumulation, based upon trial and/or experience. The coils 36 may be supplied with refrigerant from the same source as the coil 25.

The refrigerating coil structure has preferably each coil successively downstream from the first 0r farthest upstream refrigerating coil 36 provided with a fin spacing less than that of the preceding or immediately upstream coil, as shown in FIG. 6. Thus if the farthest upstream coil 36 has a fin spacing of the next coil downstream might have its fins spaced /2" apart, the third /3, and so on within practical limits. Because the air becomes progressively drier as it passes through the successive coils 36, it deposits less and less frost on the coils as it moves over them. The progressively closer spacing of the fins allows more fins to be used, improving refrigerating efficiency by affording maximum heat transfer surface area for the coils within a given space, but bridging or clogging of the fins and coils by frost is not accelerated.

In coil 25, the fins 32 of each set are equally spaced from each other along the tube portions 26 by a distance considerably greater than the spacing of the fins 39 of the refrigerating coils 36, as for example double that spacing. Fewer fins are employed, reducing the refrigerating capacity of the coil 25, since its heat transfer surface area is less than otherwise, but the secondary coil 25 is primarily a frost-collecting or dehumidifying coil and not a refrigerating coil. The primary or refrigerating coils 36 are relied upon for the major portion of the refrigerating capacity of the case, as already mentioned. In a specific embodiment, the spacing of the fins 32 of the coil 25 is 1 /2" as compared to for the fins 39 of that refrigerating coil 36 disposed farthest upstream.

The wide spacing of the fins of the secondary coil 25 provides for accumulation of a heavy frost deposit thereon without bridging the space between the fins. The laterally offset arrangement of the fins of one set relative to those of the adjacent set, and the provision of relatively narrow fins so that each fin is in contacting relation with only one set of tube portions rather than being common to all of the tube portions of the coil, affords a maximum number of leading fin edges for presentation to the air flowing therepast. Frost builds up somewhat in a teardrop or streamlined formation on fins of refrigerating coils, there being a greater accumulation on and adjacent the leading or upstream edge than at the trailing edge, so that it is advantageous to provide as many fins as possible without close spacing thereof. The spacing apart of the fins on the several sets of tube portions in the direction of the air flow, so that the rear or downstream edges of each set of fins are spaced forwardly of the forward or upstream edges of the set of fins behind or downstream thereof, allows a buildup of frost on the leading fin edges without bridging thereof to the trailing edges of the forward fins, particularly since the alternate sets of fins are laterally offset. The vertical offsetting of the sets of fins further increases the volume of frost which may be deposited on the coil 25, since the fins of two of the sets have portions projecting above the level of those of the other set, so that the air may impinge directly thereon without interference by or contact with other fins. The upwardly projecting fin portions also have a maximum of space to accumulate frost thereon. Thus a maximum accumulation of frost on these projecting fin portions may be effected. A similar result is achieved by the lower portions of the fins of the other set, as will be evident. The vertical offsetting of the tube portions of alternate sets effects changing of direction of the air, for increased contact and hence greater moisture deposition.

The spacing of the secondary coil from the interior surface of duct 19 assures that the air will be properly circulated in the volume and at the velocity required to maintain the case and its contents at the desired temperature for a period additional to that required to effect the maximum frost buildup on the coil. This additional period depends upon the time required for the air flowing through the primary or refrigerating coils 36, not substantially dehumidified by the coil 25, to provide such accumulation or deposit of frost on the primary coils as to diminish fiow or circulation of air to a point which would not maintain the refrigerating temperature. At or before this point, defrosting is effected in any of a number of known ways, by closing of a circuit or circuits through the heater 35, so that the air circulated through the case is warmed and melts the frost from the

coils

25 and 36. Upon termination of the defrosting operation, the refrigerating operation is resumed.

The secondary or cooling coil 25, disposed in the path of cooling air upstream of the primary or refrigerating coils 36, is constructed to collect frost and thus retard 0r largely prevent frost deposition on the primary coils. At the same time, it is so dimensioned and arranged in the air duct that air may pass thereabout in the event it becomes blocked or clogged by frost, so as to maintain refrigeration. By also providing for defrosting in accordance with the frost condition of the primary refrigerating coils, the number and frequency of defrosts required to maintain the case in eficient refrigerating condition is greatly reduced. The condition and appearance of the product in the case are never adversely affected. In addition, economy of operation is achieved over what would otherwise be possible.

It will be evident that the invention, in addition to the novel structure, provides a novel method for controlling frosting of refrigerated cases and the like, and more specifically of lessening the frequency of defrost or lengthening the intervals between defrosts.

The embodiment of this inventive concept illustrated herein is exemplary and not exhausive, the invention not being limited thereto since modifications and variations thereof may be made through a wide range without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim:

1. A refrigeration structure having a primary refrigerating coil in a duct for flow of cooling air and a secondary finned cooling coil upstream of said primary refrigerating coil,

said secondary coil comprising a plurality of generally parallel tube portions extending generally normal to the direction of air flow and arranged in sets extending generally in a plane normal to the direc tion of air flow with said sets spaced apart along the direction of cooling air flow, and a plurality of groups of spaced apart relatively narrow elongated fins arranged generally parallel to the direction of air flow, with each group of fins respectively secured on the tube portions of each set in heat-conducting relation, with said fins of each group having each fin connected only to tubes: of one set, with said fins offset laterally relative to the fins of each adjacent set, with each group of fins spaced apart from each other along said flow direction, and with said lateral fin spacing of each group of said secondary coil being considerably greater than that of said primary coil; and

said secondary coil dimensioned and located relative to said duct to provide passage for a continuing flow of air to the primary refrigerating means in the event of impedance of air fiow through the secondary coil as by frost accumulation thereon.

2. A structure as defined in claim 1 in which said secondary coil fin spacing is greater than that of the fins of the primary refrigerating means by a multiple of the order of two.

3. A structure as defined in claim 1 in which the fins of adjacent sets are offset from each other in a direction substantially normal to said air flow direction and to said direction of lateral offset.

4. A structure as defined in claim 1 in which the tube portions of adjacent sets are offset from each other in a direction substantially normal to said air flow direction and said direction of lateral offset.

5. A structure as defined in claim 1 in which said primary refrigerating means comprises a plurality of finned refrigerating elements arranged one substantially directly downstream of another with the fins extending generally in said direction of air flow.

6. A structure as defined in claim 5 in which the spacing of the fins of the farthest upstream of said refrigerating elements is greater than that of at. least one of the elements downstream thereof.

7. A structure as defined in claim 5 in which the spacing of the fins of at least some of said refrigerating elements is progressively smaller in the downstream direction.

References Cited UNITED STATES PATENTS 2,929,229 3/1960 Detwiler 62-426 3,091,942 6/1963 Dickson et a1. 62--80 3,099,914 8/1963 De Witt et al. 62-283 X 3,199,581 8/1965 Kritzer -151 X 3,209,553 10/1965 Sohda 62283 3,267,692 8/1966 Pfeiffer et a1. 62-272 X 3,333,437 8/1967 Brennan 62-256- ROBERT A. OLEARY, Primary Examiner. W. E. WAYNER, Assistant Examiner.