Enclosable evaporator/defroster unit for a refrigerated display case

Abstract

The invention is for an enclosable evaporator/defroster unit for a refrigerated display case. The refrigerated display case has a cabinet with a floor, a ceiling, a front wall, a rear wall, and side walls. There is an access opening in one of the front wall, the rear wall and the side walls. An air duct extends around the cabinet for conducting a current of air. The air duct forms a substantially closed conduit. There is a gap in the conduit that coincides with the access opening in the cabinet. A fan circulates air in the air duct. An evaporator coil is positioned in the air duct to cool the circulating air. A defroster unit is also positioned near the evaporator coils to melt the condensation on the evaporator coil. The defroster unit has a heater, dampers, and an actuator for moving the dampers between an open and a closed position.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to refrigerated display cases and, more particularly but not by way of limitation, to evaporator coil defrosters associated with such display cases.

[0003] 2. Discussion

[0004] Retailers use refrigerated display cases predominantly for merchandising of food, but also for other perishable items, such as flowers. Frozen food refrigerated display cases are maintained at low temperatures at about 0° F. Ice cream refrigerated display cases are maintained in the range of −15° F. to −10° F. Because of the relatively high refrigeration demand for frozen foods and ice cream, retailers commonly keep these items in glass-door, reach-in coolers. However, for display purposes, some retailers find the open front, multi-deck display cases to be preferable. In the medium temperature range of 20° F. to 40° F., retailers prefer to use glass-door display cases for freshly cut meats, cheeses and other delicatessen items, while they prefer to use open front display cases for packaged meats and dairy products.

[0005] There are certain features required for all type of refrigerated display cases. First, all refrigerated display cases have a refrigeration system that cools the product. This is typically done by positioning an evaporator coil in a conduit and circulating air through the conduit. The evaporator coil contains cold refrigerant flowing through it and exchanges heat with the warmer circulating air in the conduit. The conduit surrounds a cabinet that holds the refrigerated objects.

[0006] A second feature that all refrigerated display cases have is an apparatus for defrosting the evaporator coils. Moisture in the conduit air condenses on the cold evaporator coils and interferes with the heat transfer between the cold refrigerant in the evaporator coils and the conduit air. This in turn causes an increased need for energy input into the refrigeration system. As a result, all refrigerated display cases have defroster heaters, usually electric or hot gas, to melt the frozen condensation on the evaporator coils.

[0007] Refrigerated display cases generally have two cycles of operation: a refrigeration cycle and a defrost cycle. During the refrigeration cycle, the refrigeration system operates and the defrost heater is idle. During the defrost cycle, the refrigeration system shuts down and the defroster heater operates. Many systems also have an idle, non-operational mode in which neither the refrigeration system nor the defroster system operates.

[0008] For an ideally designed system in the absence of any defrosting requirements, a refrigeration system operates at its maximum efficiency when it runs all the time to maintain a design air temperature at some point in the system. The refrigeration system will lose efficiency every time it has to cycle between an idle mode to an operating mode to maintain the air design temperature. It will also lose efficiency the longer the time it is in the idle mode. As a result, when a refrigeration system has to shut down to defrost the evaporator coil, the refrigeration system will be less efficient the longer it has to remain idle. Thus, it is desirable to minimize the time of the defrost cycle. For a long defrost cycle, there is also a greater likelihood for spoilage of product, especially for frozen foods.

[0009] There have been many inventions directed to improving the operation of refrigerated display cases with defrosters. For example U.S. Pat. No. 4,239,518 issued to Steelman discloses a refrigerated case with a movable fan that draws ambient air past the evaporator coil.

[0010] U.S. Pat. No. 5,669,222 issued to Jaster et al. discloses a defroster system in which an evaporator coil is heated by the condensation of the refrigerant supplied by a compressor used in the refrigeration process.

[0011] U.S. Pat. No. 4,312,190 issued to Ibrahim et al. (Ibrahim '190) discloses a refrigerated glass door merchandiser for which a heat trap prevents heat generated during a defrost cycle from flowing back into the refrigerated display section. The heat trap is a labyrinth structure that, during the defrost cycle, prevents air in a conduit from flowing back through a fan for circulating air through the conduit.

[0012] The heat trap of Ibrahim '190 partially addresses the need to isolate the heat and vapor generated by a defroster heater from the display section of the refrigerated merchandiser. However, the refrigerated display case of Ibrahim '190 allows warm ambient air to infiltrate the refrigeration system because it shuts off the fan during a defrost cycle.

[0013] Thus, there is a continuing need for a providing a defroster system for a refrigerated display case that lowers the energy requirements of the refrigeration system while meeting all the requirements of the refrigeration system for preserving food and other perishable items.

SUMMARY OF THE INVENTION

[0014] The advantages and features of the present invention will be apparent from the following description when read in conjunction with the accompanying drawings and appended claims.

[0015] The invention is for a refrigerated display case with a display section for displaying refrigerated objects. The refrigerated display case has a cabinet with a floor, a ceiling, a front wall, side walls and an access opening to access refrigerated objects. There is an air duct extending around the cabinet for conducting a current of air that circulates in the air duct. The air duct forms a substantially closed conduit, but has a conduit gap substantially coincident with the access opening. The air duct has an inlet and an outlet on opposed sides of the conduit gap. A fan is positioned in the air duct near the air inlet for circulating the air through the conduit. A cold evaporator coil of a refrigeration system is positioned in the air duct. When the warmer air circulates past the evaporator coils, there is an exchange of heat between cold refrigerant in the coils and the air.

[0016] A defroster unit is positioned in the air duct near the coils. The defroster heater melts frozen condensate from the coils during a defrost cycle. During the defrost cycle, an actuator closes dampers to enclose a defroster heater and the evaporator coil. The closing of the dampers retards heat transfer from the space near the evaporator coil, which reduces a heat gain by the refrigerated objects in the refrigerated display case. Thus, there is a net reduction of energy required to refrigerate the display case and a reduction in the amount of lost refrigeration product due to heating.

[0017] The advantages, and features of the present invention will be apparent from the description below when read in conjunction with the drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a side view of a refrigerated display case of the present invention.

[0019] FIG. 2 is a side view of a refrigerated display case of the present invention.

[0020] FIG. 3 is a side view of a refrigerated display case of the present invention.

[0021] FIG. 4 is a schematic representation of a refrigeration unit as embodied by the present invention.

[0022] FIG. 5 is a side view of one embodiment of an evaporator enclosure for containing evaporator coil and a defroster heater.

[0023] FIG. 6 is a front view of one embodiment of an evaporator enclosure for containing evaporator coil and a defroster heater.

[0024] FIG. 7 is a side view of one embodiment of an evaporator enclosure for containing evaporator coil and a defroster heater.

[0025] FIG. 8 is a front view of one embodiment of an evaporator enclosure for containing evaporator coil and a defroster heater.

DESCRIPTION

[0026] Referring to FIG. 1, a refrigerated display case 10 has a cabinet 12, about which refrigerated air circulates to refrigerate the cabinet 12. A layer of thermal insulation 13 is positioned on the periphery of the cabinet 12. The refrigerated air flows through an air duet 14 that forms a substantially closed circular path. The cabinet 12 has an access opening 16 for a person to access refrigerated objects displayed in the case 10. The cabinet also has a floor 18, a ceiling 20, a r ear interior wall 22, and side walls (not shown in FIG. 1). In some embodiments, a glass door may cover the access opening 16. Refrigerated objects, such as meat, milk or ice cream, are placed in a display section 24 of the case 10.

[0027] During a refrigeration cycle, air is drawn into the air duct 14 at inlet opening 26 by the electric fan 28. Hinged dampers 30 and 32 are in an open position so that air moves through an evaporator unit 34. Actuators 36 and 38 move the dampers 30 and 32, respectively, from an open position to a closed position (as shown in FIG. 2 below). As air moves past a cold evaporator coil 40 in the evaporator unit 34, a heat exchange occurs between the relative warm air and cold refrigerant in the evaporator coil 40. During the refrigeration cycle, a defroster heater 42 does not operate and air does not enter the lower space 44 of the air duct 14. The lower space 44 should have a height of at least 3 inches in order to ensure sufficient space for flow of air through the air duct 14.

[0028] The cold air from the evaporator unit 34 rises in the air duct 14 behind the rear wall 22, passes through the air duct 14 above the ceiling 20, and exits the air duct 14 at the outlet opening 46. The cold air in the air duct 14 refrigerates the floor 18, the rear wall 22, the ceiling 20 and, in turn, the display section 24. Air exiting the outlet opening 46 forms an air curtain 48 in an air duct gap 50 because of the vacuum pressure created by the fan 28 at the inlet 26.

[0029] For the present embodiment, the air duct gap 50 coincides with the access opening 16. However, it is contemplated that for various embodiments, the air duct gap 50 would not necessarily coincide with the access opening 16. Under normal conditions, the flow in the air curtain 48 is not too strong, so that a person may comfortably access refrigerated objects in the refrigerated display case 10. However, the air flow should be sufficiently strong to prevent too much warm ambient air from entering the inlet 26.

[0030] FIGS. 2 shows the same embodiment of the refrigerated display case 10 as in FIG. 1 at a different time of operation. FIG. 2 shows the refrigerated display case 10 just after a refrigeration cycle has ended and just before a defrost cycle has begun. As shown in FIG. 2, the actuators 36 and 38 are moving the dampers 30 and 32, respectively, from the open position to a closed position. The electric fan 28 continues to turn because the air in the air duct 14 is protected from heat gain, as described below. Although not shown in FIG. 2, refrigerant has stopped circulating through the evaporator coil 40.

[0031] FIG. 3 shows the same embodiment of a refrigerated display case 10 as in FIGS. 1 and 2 during a defrost cycle. As shown in FIG. 3, the actuators 36 and 38 have moved the dampers 30 and 32, respectively, from the open position to the closed position. The electric fan 28 continues to turn because the air in the air duct 14 is protected from heat gain, as described below. Although not shown in FIG. 3, refrigerant has stopped circulating through the evaporator coil 40. The defroster heater 42 has now activated.

[0032] The defroster heater 42 may be an electric heater or a hot gas heater. It is positioned near the evaporator coil 40 to melt any frozen condensation that has accumulated during the refrigeration cycle. A reflective material 52 is applied to an inside surface of the generally box-like evaporator enclosure 54 of the evaporator unit 34 to inwardly reflect radiation emanating from the defroster heater 42. The reflective material 52 may be a reflective paint, reflective tape or a separate piece made from a reflective substance, such as aluminum or stainless steel. Furthermore, an insulating material 56 (best seen in FIGS. 5-8) is applied to the outside of the evaporator enclosure 54 to retard heat transfer from the evaporator enclosure 54 by both heat conduction and heat convection. Water produced by the defrosting of the evaporator coil 40 drains through a drain (not shown).

[0033] It is important to note that providing the evaporator enclosure 54 around the evaporator unit 34 reduces the amount of energy required to melt the frozen condensation from the evaporator coil 40. This results, in part, from the retention of heat by the evaporator enclosure 54 because of the use of the reflective material 52 and the insulating material 56. This reduction of required energy is also due in part to the closing of the dampers 30 and 32, which prevents air flow and heat convection away from the evaporator coil 40.

[0034] It is also important that the defroster heater 42 is located close to the evaporator coil 40 and that the defroster heater 42 is enclosed in the evaporator enclosure 54. This allows the defroster heater 42 to melt the condensation on the evaporator coil 40 by a combination of radiative heat transfer, free convective heat transfer and, to a small degree, conduction heat transfer. Free convection relies on the thermal currents generated by the heat from the defroster heater 42 to move the air within the evaporator enclosure 54. As a result, it is not necessary to generate secondary air currents flowing through the evaporator enclosure 54 to melt the frozen condensation by forced convection. The time required to defrost the evaporator coil 40 is greatly reduced when compared to the time required for defroster systems without an evaporator enclosure 54.

[0035] As a result, the efficiency losses associated with having to shut the refrigeration system down during a longer defrost cycle are also reduced. Thus, the energy savings are much greater than the energy that would be saved just by running the defrost heater a shorter period of time.

[0036] Another important feature of the embodiment shown in FIGS. 1-3 is that, during either the defrost mode or in the refrigeration mode, the air current in the air duct 14 is maintained in a single continuous circulatory path. That is, it is not necessary to divert the flow into multiple currents to melt the condensation on the evaporator coil 40. This helps to maintain the flow without the use of additional fans needed to circulate the air through multiple paths.

[0037] In FIG. 4, a schematic representation is shown of the operation of the mechanical components of the refrigeration system used to cool the refrigerated display case 1 0. Gaseous refrigerant is compressed in a compressor 60. The refrigerant passes then through a condenser coil 62, over which a fan 64 blows cool ambient air, to remove heat. The removal of heat from the refrigerant causes it to condense into a liquid.

[0038] The liquid refrigerant then flows through a metering device 68 where it expands to a gas and moves through the evaporator coil 40. The refrigerant absorbs heat in changing from a liquid to a gas, causing the air that is blown over the coil 40 by the fan 28 to cool. The expanded gas exits the evaporator coil 40 and through a solenoid valve 66 that shuts off the flow of refrigerant during a defrost cycle. The expanded gas refrigerant returns to the compressor 60 to begin the refrigeration cycle again.

[0039] FIGS. 5 and 6 show the evaporator enclosure 54 that surrounds the evaporator unit 34. The evaporator enclosure 54 is normally open and the dampers 30 and 32 are in an open position during a refrigeration cycle. As shown in FIGS. 5 and 6, the dampers 30 and 32 are in the closed position. All of the interior walls of the evaporator enclosure 54 are covered with reflective material 52. All of the exterior walls of the evaporator enclosure 54 are covered with an insulating material 56, including the dampers 30 and 32. Two electric motors 36A and 38A act as actuators to move the dampers 30 and 32 between the open and closed position, respectively. Although two electric motors 36A and 38A are shown in FIGS. 5 and 6, the actuators 36 and 38 could be hydraulic motors, or a single electric motor combined with a mechanical linkage.

[0040] As shown in FIG. 6, the damper 30 is rigidly attached to an axle 55. The electric motor 36A has a drive shaft 37 coupled to the axle 55. Rotation of the motor drive shaft 37 causes the axle 55 to also rotate and causes the damper 30 to move to an open or closed position. In one embodiment, the non-hinged ends of the dampers 30 and 32 engage a compressible material in closing and form a tight seal to prevent leakage of heat by convection.

[0041] FIGS. 7 and 8 show an alternative embodiment of the evaporator enclosure 54 that surrounds the evaporator unit 34. The evaporator enclosure 54 is normally open and the dampers 30 and 32 are in an open position during a refrigeration cycle. As shown in FIG. 7, the damper 32 is in the closed position. In FIG. 7, the damper 30 is in a partially open position merely for purposes of illustrating the movement of the dampers 30 and 32. All of the interior walls of the evaporator enclosure 54 are covered with reflective material 52. All of the exterior walls of the evaporator enclosure 54 are covered with an insulating material 56, including the dampers 30 and 32.

[0042] Bimetal coil actuators 36B and 38B move the dampers 30 and 32, respectively, from an open position and a closed position. The bimetal coil actuators have the property of expanding and contracting their spiral coil in response to temperature changes. As seen in FIG. 8, at an interior end, the coil 36B is connected to a first pin 37B, which is in turn rigidly connected to the bottom of the enclosure. At an exterior end, the coil 36B is connected to a second pin 39B, which in turn is rigidly connected to the damper 30. An internal, electric heating element (not shown) heats the bimetal coil 36B causing it to expand and move the damper 30 to the open position. Shutting off electrical power to the internal heating element causes the bimetal coil 36B to cool and retract the damper 30 to the closed position.

[0043] For purposes of the claims that follow, a defroster unit is defined to be the defroster heater 42, the hinged dampers 30 and 32, and the actuators 36 and 38 that move the dampers 30 and 32.

[0044] It is clear that the present invention is well adapted to carry out the objects and to attain the ends and advantages mentioned as well as those inherent therein. While presently preferred embodiments of the invention have been described in varying detail for purposes of the disclosure, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed within the spirit of the invention disclosed and as defined in the above text and in the accompanying drawings.

Claims

1. A refrigerated display case with a display section for displaying refrigerated objects, comprising:

(a) a cabinet having a floor, a ceiling, a front wall, a rear wall, side walls and an access opening in one of the front wall, the rear wall, and the side walls, wherein the access opening provides access to the refrigerated objects;

(b) an air duct extending around the cabinet for conducting a current of air, wherein:

(i) the air duct forms a substantially closed conduit with a conduit gap substantially coincident with the access opening in the cabinet; and

(ii) the air duct has an inlet opening and an outlet opening at opposed sides of the conduit gap;

(c) a fan for circulating air through the duct, such that an air curtain is established between the inlet opening and the outlet opening;

(d) an evaporator coil positioned in the air duct, wherein, during a refrigeration cycle, a refrigerant expands in the evaporator coil and the fan causes air to flow over the evaporator coil resulting in an exchange of heat between the air in the duct and the cold refrigerant; and

(e) a defroster unit comprising:

(i) a heater for melting condensation on an outside of the evaporator coil;

(ii) hinged dampers; and

(iii) an actuator for moving the dampers from an open position during the refrigeration cycle to a closed position during a defrost cycle.

2. The refrigerated display case of claim 1 wherein moving the dampers from the open position to the closed position provides an evaporator enclosure and retards heat transfer from the space near the evaporator coil.

3. The refrigerated display case of claim 1 wherein the actuator to move the dampers is an electric motor.

4. The refrigerated display case of claim 1 wherein the actuator to move the dampers is a bimetal coil.

5. The refrigerated display case of claim 2 further comprising a reflective material to cover the interior walls of the evaporator enclosure.

6. The refrigerated display case of claim 2 further comprising an insulating material to cover the exterior walls of the evaporator enclosure.

7. The refrigerated display case of claim 1 wherein, during the refrigeration cycle and the defrost cycle, the current of air in the air duct forms a single continuous circulatory path.

8. A defroster unit for a refrigerated display case with an evaporator coil positioned in an air duct, the defroster unit comprising:

(a) a heater for heating an outside of the evaporator coil to melt frozen condensation accumulated thereon;

(b) a pair of dampers positioned inside the air duct; and

(c) an actuator for moving the dampers from an open position during a refrigeration cycle to a closed position during a defrost cycle.

9. The defroster unit of claim 8 wherein moving the dampers from the open position to the closed position provides an evaporator enclosure for the evaporator unit and the defroster heater and wherein the evaporator enclosure retards heat transfer from the space near the evaporator coil.

10. The defroster unit of claim 8 wherein the actuator is an electric motor.

11. The defroster unit of claim 8 wherein the actuator is a bimetal coil.

12. The defroster unit of claim 9 further comprising a reflective material to cover the interior walls of the evaporator enclosure.

13. The defroster unit of claim 9 further comprising an insulating material to cover the exterior walls of the evaporator enclosure.

14. In a refrigerated display case having air circulating in an air duct with an evaporator coil located in the air duct and having a defrost heater located near the evaporator coil, a method for preventing the heat generated during a defrost cycle from causing food spoilage, the method comprising:

(a) positioning the evaporator coil and the defrost heater in an evaporator enclosure within the air duct wherein the evaporator enclosure can be opened or closed by moving dampers to an open or closed position;

(b) moving the dampers to an open position during a refrigeration cycle of operation of the refrigerated display case; and

(c) moving the dampers to a closed position during a defrost cycle of operation of the refrigerated display case.

15. The method of claim 14 wherein an actuator moves the dampers to an open position or a closed position.

16. The method of claim 15 wherein the actuator is an electric motor.

17. The method of claim 15 wherein the actuator is a bimetal coil.

18. The method of claim 15 wherein the actuator is a hydraulic motor.