US3304740A

US3304740A - Open front display case

Info

Publication number: US3304740A
Application number: US236649A
Authority: US
Inventors: Edgar V Dickson; Balk Joseph
Original assignee: Pet Inc
Current assignee: Pet Inc; Hussmann Corp
Priority date: 1962-11-09
Filing date: 1962-11-09
Publication date: 1967-02-21
Anticipated expiration: 1984-02-21
Also published as: GB1047882A; DE1301830B

Description

Feb. 2l, 1%? E. v. DICKSON ETAL 3,304,740

OPEN FRONT DISPLAY CASE Filed Nov. Q, 1962 2 Sheets-Sheet l I] n l/ U U U U H FIG! 2%,MMM

Feb. 21, 1967 E. v DlcKsoN ETAL 3,304,740

OPEN FRONT DISPLAY CASE Filed Nov. 9, 1962 2 sheets-sheet 2 United States Patent O 3,304,740 OPEN FRNT DISPLAY CASE Edgar V. Dickson, Ladue, and loseph Balk, St. Louis, Mo., assignors to let Incorporated, a corporation of Delaware Filed Nov. 9, 1962, Ser. No. 236,649 11 Claims. (Cl. 62-256) This invention relates generally to the refrigeration art, and more particularly to improvements in an open front display case especially adapted for the low temperature refrigeration of frozen food products.

The following denitions of terms are provided for disclosure purposes:

Low refrigeration temperature will refer to the refrigeration of food products, medicines or other products at temperatures below the freezing point `of water and generally in the range from about 10 F. down to 10 F .I or colder, and particular about F.

High refrigeration temperature will refer herein to the range of refrigerated temperatures between about 30 F. and 45 F. particularly about 38 F.which temperature range is ordinarily referred to in the industry as normal or standard refrigeration.

Medial refrigeration temperature is adopted as a term of reference to temperatures in the range of about F. to about 30 F. (between the low and high temperature ranges) and particularly about F. to 20 F.

The copending application of Dickson and Weber, Serial No. 68,308 (Patent No. 3,063,254) discloses an open front merchandiser having plural shelves and utilizing a low temperature main system for the product zone and a high temperature secondary system for protecting the product zone from moisture.

The principal problem in refrigeration equipment having cooling means operating at low refrigeration temperatures has been the presence of moisture in the case and ambient air, and this problem is accentuated in open front display cases which are open to the ambient air. Moisture is picked up by col-d air or migrates to the colder parts of the case and refrigeration system and condenses as frost or ice on walls, cooling coils, in air passages, etc. with the result that defrosting operation is needed to remove such frost formations to maintain the equipment in operative condition. During a case defrost, the entire coil mass and air temperature must rise above 32 F. before the frost will melt and larger coils needed for low temperatures require more heat than smaller coils. Products in an open front low temperature case are without refrigeration and not only subjected to ambient temperatures but to any heat load of the case air streams, whereby product temperature may rise a substantial amount such as 10 F. or more which product temperature rise is considered undesirable. Furthermore, all defrost heat must be removed from the case and its products after a defrost period in order to restore and maintain the normal refrigeration function of the case. Accordingly, it it desir-able to provide as short a defrost period as possible an to rapidly remove the defrost heat to minimize product temperature variations. However, too frequent defrost periods will increase the moisture problem in the case by the warmed case air carrying moisture from the evaporator Zone, so that frost and ice formations are more apt to occur in the display area and on products which is most objectionable from a merchandising point-of-view.

The principal object of the present invention is to provide improvements in air circulation and in moisture and temperature control in a two system case. Another object is to provide a display case having a minimum of condensation and frost within the display area and air passages thereof. Still another object is to provide air circulation in an open front case in a manner to prevent 3,304,740 Patented F eb. 21, 1967 uneven cooling of the products or concentration of heat loads thereon, and in which turbulence and entrainment of ambient air is minimized. These and still other objects and advantages will become more apparent hereinafter.

Briefly, the invention comprises an open front display case having a display area with la shelf and separate air distribution systems for cooling the `display area and `for providing an air wall across the open front, means for creating optimum non-turbulent air ow in the yair Wall, means for preventing localized heat loads on the shelf, and means for obviating frost formations in the display area and air distribution channels.

The invention also consists in the parts and in the arrangements and combinations `of parts hereinafter described and claimed. In the accompanying drawing which forms a part of this specification and wherein like numerals refer to like parts wherever they occur:

FIG. 1 is a front elevational View, partly broken away, of a display case embodying the present invention, and

FIG. 2 is a vertical transverse sectional view taken substantially through the center of FIG. 1.

Referring now to the drawings, a display case 10 embodying the present invention includes an insulated outer cabinet having a base 11, a low front wall 12, a high rear wall 13, a top wall 14 extending forwardly from the rear wall 13 and end walls 15. The front of the'display case 10 is open between the front wall 12 and top wall 14 for direct accessibility to the interior of the case.

Positioned within the outer cabinet and extending longitudinally between the end walls 15 thereof is `an intermediate insulated cabinet which includes a bottom wall 17 in spaced relation within the base 11 to provide a bottom ue 13, a front wall 19 spaced from the low front wall 12 to provide a front ue or return duct 20 in communication with the bottom iiue 18, la rear wall 21 spaoed from the back or rear wall 13 to provide a rear flue 22 also in communication with the bottom flue 18, and a short top wall 23 spaced below the top wall 14 and deiining :an air curtain refrigeration c-hamber 24 therebetween. In FIG. 2 it will be seen that the wall 23 slopes downwardly toward the rear wall 13 for draining moisture during defrosting as will be ySet out hereinafter. The forward end of the top Wall 23 has :an upwardly projecting flange member 25 extending toward the top wall 14 for forming a restricted pass-age 26 therebetween, and a lower flange member 27 extends downwardly from the top wall 23. The top wall 14 of the outer cabinet has a short vertical front wall 29 extending downwardly therefrom in spaced relation with the upper fl-ange member 25 to form a vertical discharge chamber 28 :and diverging anguilarly outwardly from the end of the top wall 23 and lower flange member 27 to form an enlarged discharge opening 30 from the chamber 28. Air straightening means in the form of -a honeycomb grid 28 is positioned in the vertical chamber 28, and a perforated plate 31 is provided between the lower end of the wall 29 and the lower member 27 through which refrigerated air is discharged. The plate or =air discharge -grill 31 is set angularly to vertical and the air discharge p'ath therethrough is in the direction of the arrows in FIG. 2. Another perfor-ated plate or lair control grill 32 is provided in the enlarged opening area 30 on the inner side of the air discharge path adjacent to the case interior and extends horizontally from the lower flange 27 yto the discharge grill 31. The air control grill 32 functions as an fair velocity restrictor on the inner portion of air discharged through the discharge 4grill 31, as will be more fully explained hereinafter.

The refrigeration chamber 24 houses a fan 33 or similar air circulating means 'and the chamber 24 is divided by a partition 34 extending between the rear wall 21 and the top wall 14, the partition having an opening 35 in which the fan blade 36 is mounted for efficiently moving air through the refrigeration chamber to the discharge plate 31 and forming a wall or curtain of -this air across the open front of the display case to the return duct 20. The chamber 24 preferably houses an evaporator coil 37 or like cooling means of a closed refrigeration sytsem (not shown), the evaporator coil 37 being shown positioned forwardly of the fan 33 and extending longitudinally of the display case so that the air wall is refrigerated.

The return duct 2l), bottom and

rear lues

18 and 22, refrigeration chamber 24 and discharge chamber 28 form an air cooling and circulatory system for continuously forming the air wall and recirculating refrigerated air. This refrigeation system will be referred to as a secondary system inasmuch as the wall of air merely defines the front of the case 10 and does not directly cool food products therein. The coil 37 is adapted to cool the air at `least to high refrigeration temperatures (as will be discussed more fully), and the fan 33 is adapted to create a negative pressure through the rear, 'bottom and front ues to draw previously cooled air into the front flue 20 through a perforated plate or air return gill 38 and to force refrigerated air of the secondary system out of the dischage chamber 2S and across the display case 10 in the refrigerated air wall extending between the perforated plate 31 at the discharge and the perforated plate 38 covering the return duct 20. A heating element 38 of the socalled epoxy type is mounted in t-he return duct 20 -adjacent to the perforated grill 38, and this heating element 38 operates continuously to prevent the grill perforations from becoming blocked by a frost or ice formation as will lalso be discussed more fully hereinafter.

This display case 1t) also includes an inner cabinet delining a display area 39 in which frozen food products are positioned for refrigeration. The inner cabinet also extends longitudinally between the end walls of the outer cabinet and includes a bottom plate or Wall 40 spaced above the -bottom wall 17 of the intermediate cabinet to form a rst or front refrigeration chamber 41 for a main or prima-ry refrigeration system. A front panel 42 is spaced from the front wall 19 of the intermediate cabinet and provides a cold air return flue or duct 43 therebetween, the panel 42 having an angularly-positioned perforated end plate or grill 44 secured to the front wall 19 and forming a return or inlet for the front ue 43. Another heating element 44 is mounted in the return flue 43 adjacent to the grill 44 to prevent frost and ice formation in the perforations and this heater also performs an important function of raising the temperature of the return air in order to lower the relative humidity to minimize moisture precipitation or snowing in the front return ue 43. The inner cabinet also includes a lower rear panel 45 spaced forwardly from the rear wall 21 of the intermediate cabinet and defining rea-r or second refrigeration chamber 46 therebetween, which chamber 46 also forms part of th-e main or primary vrefrigeration system.

The 'return flue 43 is in communication with the refrigeration chamber 41, which houses an evaporator coil 48 extending longitudinally of the display case 10. The refrigeration chamber 41 is divided by a. partition 49 having an opening 50 therein, and a fan 51 or like air circulating means is mounted in -the chamber with its blade 52 positioned in the opening, although more than one fan 51 may be provided if desired. The rear chamber 46 is in communication with the refrigeration chamber 41 through the fan blade opening 50, and the rear chamber houses an auxiliary or second cooling coil 53 through which air is forced by the fan 51. The

coils

48 and 53 may be part of a single closed refrigeration system (not shown) and `the coils 48 :and 53 are positioned on opposite sides of the fan 51.

Still referring to FIG. 2, it is clearly shown that the

chambers

41 and 46 together form an L-shaped main refrigeration -chamber positioned at the bottom and rear of the display case 1t) and having inlet and outlet ends in communication with the air return flue 43 and

air delivery ducts

54 and 62, respectively. Inasmuch as the

coils

48 and 53 may be connected in a single closed refrigeration system, the first evaporator section 48 adjacent to the inlet end and second evaporator section 53 adjacent to the outlet end will be provided with a common refrigerant coil arranged to provide the second evaporator section 53 with lower temperatures relative to the temperatures of the rst evaporator section 48 in order that the air temperature is further lowered as the air passes through the second section S3. It will be noted that the partition 49 forms a supporting plate for mounting the fan or blower 51 in the opening 5t), and that the partition extends from the plate 49 to the wall 17 so that all of the air circulated in the chamber is drawn through the first evaporator section 48 by the -fan and discharged through the second evaporator section 53. The fan blade 52 is shown in an angular position, more nearly horizontal than vertical, for directing air in a downward path toward the wall 17 and producing a more uniform dispersion of air through evaporator 53 than when t-he fan is in a more vertical position.

It is now apparent that lair is drawn into the return ue 43 by the negative pressure developed by the fan 51 and passed through the coils 48, and is then forced upwardly through the secondary evaporator coil 53 whereby the air is refrigerated to the low temperatures required for maintaining food products in frozen condition. This refrigeration system is a portion of a primary system for providing low temperature refrigerated air directly to food products in the -display area 39.

The bottom plate 40 and front and

rear panels

42 and 45 of the inner cabinet and the end wall 15 of the outer cabinet define a lower portion or well 55 of the display area 39 in which food products may be positioned in a conventional manner. The display area 39 also includes an upper shelf portion 56 which may be provided with lower and

upper shelves

57 and 58, respectively, or additional shelves (not shown). The upper portion 56 also extends between the end walls 15 of the outer cabinet and is delimited at the rear -by an upper rear panel 59 and at the top by atop panel 60.

The upper rear panel 59 is spaced from the rear wall 21 of the intermediate cabinet by suitable means (not shown) t0 provide the rear cold air delivery flue or duct 54 therebetween, the duct S4 being in communication With the second refrigeration chamber 46 and receiving a stream of low temperature air therefrom. As shown in FIG. 2, the rear panel 59 is offset relative to the vertical plane of the panel 45 so that the rear duct 54 is directly in communication with a portion of the chamber 46, the rearward portion of the lower shelf 57 overhanging the refrigeration chamber 46 and acting as a baille for deflecting a portion of the main air stream from the chamber 46 into the chamber 62 through a perforated air diffuser 62.

The lower shelf 57 is secured to the lower end 61 of the panel 59 and extends forwardly therefrom in spaced relation above the rear panel 45. The chamber 62 is provided below the lower shelf 57 and is defined by a bottom and front forming wall 63 secured to a suitable structural member on the lower surface of the shelf 57 and to the upper end of the lower rear panel 45. The chamber 62 is in communication with the refrigeration chamber 46 and the chamber wall 63 has spaced

apertures

64 and 65 in the bottom forming wall portion through which refrigerated air from the coil 53 is expelled into the display area Well 55 and is drawn across the food product in the Well 55 toward the return inlet plate 44 of the Vfront flue 43 of the primary refrigeration system. The front forming portion of the wall 63 is perforated, at 66, and has its upper portion connected to an imperforate air channeling guide 67 which extends upwardly and forwardly to form a narrow air passage 68 immediately adjacent to the undersurface of the front of the shelf 57. Air is discharged from the passage 68 through an opening 69 behind a price tag molding 70 or the like forming a downward baffle directed toward the return grill 44 of the front flue 43. A light fixture 7l is mounted below the front of the lower shelf 57 to illuminate the well area S5, and lit will be noted that the guide 67 channels a predetermined portion of air between the lamp 71 and the shelf 57 in order to prevent any heat load of the fixture from being imposed directly on the shelf and the food product thereon. The low temperature air dis-charged through the openings 66 at the front of the wall 63 will tend to fall into the well 55, but the forward movement of air discharged from rearwardly in the case and the velocity at which air is expelled through the perforations 66 cause a forwardly moving air layer to be formed under the shelf 57 and light fixture '7]l.

The upper rear panel 59 is provided with lower air outlet openings 72 and with upper air outlet openings 72', and lower and upper air restricting or deiiecting baffles 73 and 73 are positioned in the rear duct S4 and secured to the wall 21 for deflecting a portion of the primary air stream through the

openings

72 and 72.

The upper shelf 58 is mounted on the rear panel 59 and extends forwardly therefrom into the upper shelf portion 56 of the display area 39. In FIG. 2 it will be seen that each

shelf

57 and 58 is angularly positioned relative to horizontal and has aback plate 74 secured at substantially right angles thereto so that the plates 74 are angularly positioned relative to the rear panel 59. This shelf means is especially adapted to receive frozen food packages thereon and prevents them from falling forwardly on the shelves.

The primary air distribution means also includes an air duct 75 below the shelf 58 and is defined by a bottom and front forming wall 76 secured to the shelf 58 and to the rear panel 59. The duct or chamber 75 is in communication with the rear air delivery duct 54 through the openings 72, and the bottom portion of the wall 76 has air discharge means therefrom. The wall 76 has a perforated vertical step 77 adjacent the rear panel 59 and another perforated vertical step 78 spaced forwardly toward the front of the shelf 58. The front portion of the wall 76 is curved and has perforations 79, and is lconnected adjacent to the shelf 58 with an imperforate -air channeling guide 80 which extends forwardly to form a narrow passage Si next to the undersurface of the shelf 58. Air is discharged from the passage 81 through an outlet opening 8l behind a price tag molding 82 or the like forming a downward baffle directed toward the return grill 44 of the front flue 43. A light fixture 83 is mounted below the front of the upper shelf 58 to illuminate the lower shelf 57, and it will be noted that the guide 80 channels a predetermined portion of air between the lamp 83 and the shelf 58 to prevent any direct heat load from the lamp on the shelf. The low temperature air -of the primary steam defiected by the baffle 73 through the openings 72 in the rear panel 59 moves forwardly in the duct 75, and portions of this are discharged through the perforations 77 and 78 in a forward path to wipe or scrub the bottom surfaces of the wall 76 to prevent frost formation. The air discharged through perforations 79 at the front portion of the wall 76 tends to fall but for the forward movement of air discharged from the rearward perforations 77 and 78 and the velocity at which the air stream is moved through the duct 75 and expelled through the perforations 79. The result is a forwardly moving -air layer under the shelf 58 and l-amp 83. It should also be noted that the

ducts

62 and 75 slope upwardly with the

shelves

57 and 58 toward the front edges whereby the uphill movement of the cold air tends to retard or slow the velocity and is a factor in determining the discharge velocity of the air layers.

The top panel 60 delimiting the top of the display area 39 is spaced below the top wall 23 of the intermedi-ate cabinet and provides a forwardly extending discharge ue or duct 84. The top panel 60 is secured to the rear panel 59 above the openings 72' through which a portion of air is deected by bafe 73', but most of the air is pushed forwardly into the duct 84. The top panel 60 is stepped longitudinally intermediate its front and rear edges to provide a vertical wall 8S which has apertures 86 through which a .portion of the remaining air stream is expelled into the display area 39. The forward edge of the panel 60 is spaced away from the lower ange member 27 of the intermediate cabinet and defines an angularly positioned discharge fiue 87 therebetween through which the remaining portion of the primary low temperature air stream is discharged.

The display case 10 has a top display front S8 mounted in front of the front wall 29 and forming a cavity 89 housing an upper light fixture 90, which is located outside the display area 39 and does not product any heat load therein.

In the secondary system the evaporator 37 is provided with a defrost heater 92 positioned upstream or on the leading edges of the fins of the evaporator 37 so that air movement past the heater 92 will carry the heat through the evaporator and produce rapid defrosting thereof. The water resulting from the melting of frost and ice lon the coil 37 will run down the inclined wall 23 and rear duct 22 to a suitable drain in the bottom wall 11. In the primary system defrost heaters 93 are provided upstream of the

evaporators

48 and 53 to rapidly raise the temperature of the coil mass and surrounding area to melt frost and ice formations from the evaporators and the refrigeration chambers. In addition, a defrost heater 94 is mounted on a spa-cer element 95 in the front return ue 43 adjacent to the front panel 42 and near the return grill 44. The heater 94 assures that any frost formation in the return flue 43 is melted during the time the

evaporators

48 and 53 are being cleared by defrost heaters 93 to obviate the need for extending the defrost cycle in order to circulate hot air from the

refrigeration chambers

41 and 46 through the front flue 43.

In the operation of the display case 10, the primary system and the secondary system cooperate to provide low temperatures in the display area 39 for keeping food products in frozen condition and for providing a cold front or wall of refrigerated air obviating the necessity for doors or glass panels to close the front of the case or a glass retaining wall or barrier extending above the low front wall 12 of the outer cabinet, The two systems reduce to a minimum the .amount of ambient room temperature air that becomes intermixed with the refrigerated air wall so that the case can operate efficiently `and perform its function of providing low temperatures for frozen food products. In addition, moisture is substantially eliminated from the display area 39 so that condensation on the display area walls and the food products is minimized; and condensation, and consequent frosting, is substantially reduced on the evaporator coils 48 and 53 of the primary system.

In the operation of the primary system, the primary or

main coils

48 and 53 are part of a typical closed refrigeration system (as shown in fcopending application' of Dickson and Weber, Serial No. 101,782) and the temperature of these coils in the main refrigeration chamber is approximately 40 F. in order that the air and prodduct temperature in the display area 39 can be maintained about 0 F. The fan 51 draws cold air into the return duct 43 from the display area 39 and past refrigeration coil 48 to dehumidify the return air, and pushes this refrigerated air downwardly against the wall 17 to cause turbulence and lateral air distribution endwise of the case. The air then is pushed upwardly through the coil 53 in the chamber 46 so that the temperature of the air is lowered to the required degree of coldness. The

primary air stream forced through the coil 53 is divided and a portion of the air passed into the rear delivery duct 54 and another portion of the air is deflected forwardly into the chamber 62 and through the

openings

64 and 65 into the well area 55 as well as forwardly through the perforations 66 and into the air passage 68 whereby the lamp 71 is circumscribed by this cold air. The air from air passage 68 is discharged through opening 69 against the baie 70 and is deliected downwardly to merge with the other air from the duct `62 and be returned to the front return duct 43. The heat from the lamp 71 is absorbed by the primary air stream and is not imposed on the shelf 57 to cause localized heating of products thereon, and the lower portion 55 of the display area 39 is cooled and the forward direction of the air discharged from the Ichamber 62 assists in supporting the front wall of air of the secondary system.

The portion of air forced upwardly into the rear duct 54 is further divided by the batiies 73 and 73 into three streams, the llower stream passing through openings 72 into duct 75 under the upper shelf 58 and outwardly through the perforated steps 7'7 and 78 for cooling the lower shelf 57 and scrubbing the wall '76. The air is also discharged from the duct 75 outwardly through the openings 79 in a forward direction beneath the lamp 83 to absorb heat and to support the air wall to prevent turbulence and intermixture of ambient air therewith. The air flow through the passage 81 also insulates the upper shelf 58 from the heat of the lamp 83, and this air is deiiected downwardly by the `bafie 82 toward the return flue 43.

The second stream of air from the rear duct 54 is discharged through upper openings 72 into the upper display area 56 above the upper shelf 58, and the remaining or uppermost stream of air is deiiected by batiie 73' into the forwardly extending top duct 84. The latter stream is further divided, a portion thereof passing through apertures 86 in a forwardly directed path along the top panel 60 toward the discharge ue 87, and the remainder of A the low temperature primary air stream being discharged through the angularly positioned discharge iiue 87 and forming a wall of low temperature air in front of the

shelves

57 and 58. The air passing in front of the shelves is directed downwardly toward the return duct 43 in the front wall of the display case 10 and is returned to the primary system for further refrigeration and recirculation.

The forward flow of air beneath each

shelf

57 and 58 and the top wall 23 has a velocity that will cause the air to move substantially parallel to the shelves and top wall until these air streams merge with the downwardly moving primary air wall. Inasmuch as low ternperature air will naturally tend to fall, the forwardly moving path of air is provided beneath each shelf to produce a plenum effect and prevent the front wall of air from being drawn inwardly or rearwardly at these areas thereby causing a turbulence that would cause intermixture of ambient air with the cold front wall of the case 10.

The primary air streams ow through the display area 39 and pick up heat and moisture and are returned through the return grill 44 to the front flue 43 for recirculation. The low temperature of this primary air and the saturated condition thereof is such that contact with the return grill 44 or front

iiue walls

19 and 42 may cause condensation of moisture and consequent freezing. Therefore, the return grill heater 44 keeps the grill 44 in a warmed condition to prevent frost formations on the grill 44, and the slight rise in return air temperature tends to prevent moisture condensation in the return iiue 43 and minimizes frost formation or snow therein.

In the operation of the secondary system, refrigerated air is drawn into the front iiue 20, across the bottom iiue 18 and upwardly in the rear iiue 22 to the refrigeration chamber 24. This air is pushed by the fan 33 through the evaporator coil 37 and outwardly and downwardly through the discharge chamber 28. The secondary air `is highly turbulent moving into this chamber 28, but the honeycomb grid 28' has a plurality of vertical passages which straighten the flow of air into a nonturbulent vertically moving body of air. lt will be noted that the wall of low temperature 4air expelled from the discharge passage 87 flows at an `angle to vertical toward the return grill 44, and that an unrestricted vertical discharge of the secondary air wall through the plate 31 (as shown in copending application Serial No. 68,308) causes this secondary air lwall to impinge against the primary low temperature wall at a point substantially half way to the shelf 58. It has been found that the discharge of these two air walls at optimum velocities, in order to minimize turbulence and moisture pick-up and maintain the air curtain direction across the open front toward the return grills 38 and 44, actually produces turbulence yby the force of the secondary wall impinging against the primary wall and these walls were not formed in as non-turbulent parallel liow paths as had been indicated in earlier tests. Accordingly, the air restrictor 32 is provided to act as a control grid having two important functions; iirst it creates a further plenum effect on the `inner l-ayer of secondary air whereby it is diffused in a manner that appreciably reduces the velocity of this inner layer, and second, the air restricting action of the grid '32 tends to redirect the outer portion of secondary air to by-pass the grid and in this manner ilow angularly through the plate 31 toward the return grill 38. The reduced velocity of the inner layer of secondary air forms a buffer zone and reduces to a minimum the interference of the secondary air wall `with the primary low temperature air wall.

Copending application Serial No. 68,308 discloses the use iof La. secondary air wall that is relatively dry and within the high refrigeration temperature range in order to have a greater moisture holding capacity for minimizing moisture migration into the primary system. Even though this secondary wall was at high refrigeration temperatures at its discharge point, its temperature dropped during liow across the open front into the medial refrigeration temperature range approaching the low temperatures of the primary air system by the time the secondary air was taken into the return duct 20. Accordingly, frost formation on the grill 38 and other moisture problems were only partially understood and met by this earlier case.

It has been discovered that the temperature of the secondary air wall may be lowered into the medial or low temperature ranges by providing a larger evaporator coil 37 and refrigeration system therefor, and at these lower temperatures etiieient operation may still be provided. Although the secondary air wall cannot hold as much total moisture as an air wall at higher temperatures, more moisture from the -return air is removed and deposited on the coil 37 so that total moisture pick-up by a medial or low refrigeration temperature air curtain is substantial. Furthermore, the evaporator coil 37 may be rapidly defrosted by heater 92 and at periods intermediate to the main refrigeration system defrost whereby long periods of operation of the main system are provided to minimize temperature variations of the product in the display area.

It will be noted that the heat load of the

lamps

71 and 83 and of the

grill heaters

38 and 44 are taken on by the air circulation on the return portion of the cycle so that this heat load is not imposed on the food products in the display area. This additional heat `load is easily absorbed by the evaporator means 48, 53 and 37 and is import-ant in keeping the air return .grills and passages open during operation as well as facilitating rapid case defrosts of the main evaporator means 48 and 53.

From the foregoing, it will be understood that substantial improvements in air circulation and in temperature Iand moisture control have been provided in a two system open front display case.

It i s to `be understood that the foregoing description and accompanying drawing have been given only by way of illustration and example, `and that changes and modifications in the present disclosure, which will be readily app-arent to all skilled in the art, are contemplated as within the scope of the present invention, which is limited only by the claims which follow.

What is claimed is:

1. A refrigerated display case having a display area with an open front side and at least one shelf therein, lamp means mounted below and Iadjacent to the front of said shelf for lighting the display area below said shelf, first means for cooling a primary air stream to low refrigeration temperatures and -circulating said primary stream through said display area to cool products therein, second means receiving air from said first means and forming a wall of primary air across said open front `side, said rst means including duct means below said shelf and extending toward said lamp means, land means for discharging primary air out of said duct ymeans into circumscribing relation with said lamp means.

2. The display `case according to claim 1 in which said duct means has a bottom forming wall with a plurality of perforated vertical steps through which said primary air is discharged into the display area in a surface wiping direction with the `adjacent surface of said bottom forming wall.

3. A refrigerated display case having a display area with an open front side and at least one shelf therein, lamp means mounted below and adjacent to the front of said shelf for lighting the display area below said self, rst means for cooling a primary air stream to low refrigeration temperatures and circulating said primary air through said display area to cool :products therein, said first means forming a wall of primary air across said open front side, said first means including duct means below said shelf extending toward said lamp means, and air passage means in communication with said duct means and formed between said lamp means and said shelf.

4. The display case according to claim 3 in which baffle means are provided on the front of said shelf and form a downwardly sloping surface spaced forwardly from said lamp means, and said air passage means includes an air channeling guide having a discharge opening behind said baffle means.

5. The display case according to claim 4 including return duct means for receiving said primary air from said display area :and said wall of air land recirculating said returning air to said rst means, and said baffle means defiects air from said `ai-r passage means downwardly toward said return duct means.

6. A refrigerated display case having a display area with an open front side and at least one shelf therein, first means for cooling `a primary air stream to low refrigeration temperatures and for circulating said primary stream through said display area to cool products therein, said first means forming a wall of primary air across said open front side, return duct means for returning said primary air from said display area and wall of air to said first means for recirculation, lamp means mounted below and adjacent to the front of said shelf, delivery duct means below said shelf extending toward said lamp means, air

guide means in communication with said delivery duct means and forming an `air passage between said lamp means and said shelf, baffle means secured to the front of said shelf and being angularly positioned to deflect primary air from said air passage toward said return duct means.

7. A refrigerated display case having a display area with an open front side, first means for cooling a primary air stream to low refrigeration temperatures and for circulating said primary air through said display area and forming a rst wall Vof primary air across the open front side, a return flue for returning said primary air from said 4display `area and said first wall to said first means for recirculation, second means forming a second wall of secondary air across said open front side between said rst wall and ambient air, said second means including a vertical discharge chamber in which secondary air is moved toward said first wall, and means in said discharge chamber for reducing the velocity of a layer of secondary air on the side of the second wall adjacent to said first wall.

8. The display case according to claim 7 including an air directionalizing grid in said discharge chamber to eliminate turbulence of said secondary air and form it into a vertically moving body.

9. The display case according to claim '7 in which said discharge chamber has an enlarged discharge opening, a first perforated grill covering said opening, and said last mentioned means comprises a second perforated grill intersecting said first grill to form a restrictor for the inner layer of secondary air in said discharge chamber and to deflect the outer portion of air angularly outwardly into a predetermined flow path.

10. The display case according to claim 7 in which said second means includes an evaporator for cooling said secondary air to refrigerated temperatures at least as low as within a medial temperature range between yabout 10 F. and 30 F.

lll. A refrigerated display case having a display area with an open front side and at least one shelf therein, first means for normally cooling a primary air stream to low refrigeration temperatures and circulating said primary air to cool products in said display area, said first means forming a wall of primary air across said open front side, duct means receiving primary air from said display area and wall of air and delivering it to said rst means for recirculation, defrost means for defrosting said first means, a lamp mounted on the front of said shelf, and a portion of said primary air being circulated around said lamp and heated thereby in the return portion of the circulation cycle of said primary air to dissipate such lamp heat away from the shelf.

References Cited by the Examiner UNITED STATES PATENTS 2,822,672 2/1958 Dickson 62-256 3,063,252 l1/1962 Lamb 62-256 3,082,612 3/1963 Beckwith 62-256 3,128,609 4/1964 Beckwith 6.2.-256

WILLIAM J. WYE, Primary Examiner.

Claims

1. A REFRIGERATED DISPLAY CASE HAVING A DISPLAY AREA WITH AN OPEN FRONT SIDE AND AT LEAST ONE SHELF THEREIN, LAMP MEANS MOUNTED BELOW AND ADJACENT TO THE FRONT OF SAID SHELF FOR LIGHTING THE DISPLAY AREA BELOW SAID SHELF, FIRST MEANS FOR COOLING A PRIMARY AIR STREAM TO LOW REFRIGERATION TEMPERATURES AND CIRCULATING SAID PRIMARY STREAM THROUGH SAID DISPLAY AREA TO COOL PRODUCTS THEREIN, SECOND MEANS RECEIVING AIR FROM SAID FIRST MEANS AND FORMING A WALL OF PRIMARY AIR ACROSS SAID OPEN FRONT SIDE SAID FIRST MEANS INCLUDING DUCT MEANS BELOW SAID SHELF AND EXTENDING TOWARD SAID LAMP MEANS, AND MEANS FOR DISCHARGING PRIMARY AIR OUT OF SAID DUCT MEANS INTO CIRCUMSCRIBING RELATION WITH SAID LAMP MEANS.