US20090084125A1

US20090084125A1 - Refrigerated merchandiser system

Info

Publication number: US20090084125A1
Application number: US12/238,048
Authority: US
Inventors: Kwok Kwong Fung
Original assignee: Carrier Corp
Current assignee: Hill Phoenix Inc
Priority date: 2007-09-28
Filing date: 2008-09-25
Publication date: 2009-04-02
Also published as: CA2639852A1

Abstract

A refrigerated display case includes a heat exchanger with circuits that route secondary fluid in a counterflow direction with respect to the airflow through the heat exchanger. At least one circuit directs secondary fluid from the entrance end to the exit end of the heat exchanger to exchange heat with air exiting the heat exchanger. The higher fluid temperature raises the air dry bulb and lowers the air relative humidity to improve the capability of the air to absorb moisture in the display case.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority from provisional application Ser. No. 60/995,921, filed Sep. 28, 2007.

BACKGROUND

The function of food and beverage merchandisers is to keep product cool and to present product to customers in an appealing way. To cool product, a heat exchanger coil with incoming cold fluid is used to maintain air temperature requirement at the case. A fan system coupled with the coil will generate airflow through the coil so that the air will drop to a desired temperature, which then continues to circulate through the ductwork of the case. In open cases, the air will discharge through a discharge grille to form an air curtain. The air curtain will chill merchandise that is displayed on shelves or racks. The air then flows through a return grille into a ductwork and into the fan system, completing the air circulation cycle.
In some applications where a high efficiency heat exchanger is used, the air exiting the coil approaches the coil fluid temperature. This is particularly true in winter, when some supermarkets allow their store inside condition to be lowered to reduce the heating cost. As a result, the loading on the coil can be reduced significantly that the coil is well oversized. In such instances, the relative humidity of the air exiting the coil approaches 100%. This air exiting the coil will be distributed throughout the display case and will chill the merchandise on display effectively.
However, in supermarkets, there are many occasions that case set up and merchandise on display are not as specified in case application guidelines. Merchandise protruding into the air curtain, overloading of boxes in well area can cause disruption and deflection of the air curtain. All such instances result in warm store ambient air migrating into the merchandise display area. This outside air dew point is normally significantly higher than the temperature maintained inside the display case. The outside air after migration into the case interior will drop in temperature to below its dew point when mixed with the cold air inside the display case. Due to the air inside the case just coming off the coil is already close to saturation, there is little capacity in the case air to absorb the moisture separated out of the outside air when its temperature drops below the dew point, and localized condensation can occur on the neighboring interior surface (shelf and merchandise) of the case. Some of the merchandise is packaged in paper cartons. The paper cartons may absorb the moisture condensed onto their surfaces and become soggy over time. This can cause the packages to lose structural integrity and break down when being handled by shoppers.

SUMMARY

A refrigerated merchandiser system includes an insulated cabinet defining a product display area and a compartment, a heat exchanger within the compartment that circulates chilled secondary fluid from a chiller, and an air circulating fan for circulating air from the product display area through the compartment. The heat exchanger includes a plurality of heat exchanger tubes through which the secondary fluid is routed. The tubes are connected to form at least one circuit having a plurality of passes that circulate secondary fluid in a counterflow direction toward the upstream end of the heat exchanger in order to cool the air. The heat exchanger also includes at least one circuit having passes that include a counterflow section for cooling the air passing through the heat exchanger, followed by a pass adjacent a downstream end of the heat exchanger for heating air exiting the heat exchanger.
The system utilizes heat content in the return air to modify secondary fluid temperature in the coil circuitry to control the relative humidity of the air exiting the evaporator. This improves the case interior air moisture absorption capability, and thus prevents localized condensation onto the merchandise surfaces when additional moisture is being introduced into the display case interior by outside air migrating into the display case as a result of misuse or overloading of merchandise beyond the display case capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a refrigerated merchandiser system in which secondary coolant from a chiller system is used to cool air within display cases.

FIG. 2 is a sectional view of a refrigerated display case.

FIGS. 3A and 3B are a perspective view and a top view, respectively, showing a portion of the heat exchanger within the display case.

FIG. 4 is a diagram illustrating the flow of secondary fluid through circuits of the heat exchanger.

DETAILED DESCRIPTION

FIG. 1 is a diagram of refrigerated merchandiser system 10, which includes chiller system 12 located within a machine room area of a store, and display cases 14 located in the area of a store accessible to customers (the store floor). Chiller system 12 includes compressor 20, condenser 22, expansion valve 24, heat exchanger 26, and pump 28, which are connected in a closed refrigerant circuit via refrigerant lines 30, 32, 34, and 36. Heat exchanger 26, pump 28, and display cases 14 are connected in a closed secondary coolant circuit by heat exchanger output line 38, secondary coolant supply line 40, and secondary coolant return line 42. Each display case 14 includes control valve 50 and heat exchanger 52, which are connected in the secondary coolant circuit.
The outlet or high pressure side of compressor 20 is connected via refrigerant line 30 to the inlet of condenser 22. The outlet of condenser 22 is connected through refrigerant line 32 to expansion valve 24. The outlet of expansion valve 24 is connected through refrigerant line 34 to heat exchanger 26. Suction line 36 returns the refrigerant that flows through heat exchanger 26 to the inlet of compressor 20. The refrigerant circulated through the closed refrigerant loop can be any commercially used refrigerant, such as R-22.
The refrigerant flowing through heat exchanger 26 is used to chill secondary coolant that has been returned to heat exchanger 26 from display cases 14 through return line 42. The chilled secondary coolant from heat exchanger 26 is supplied through heat exchanger output line 38 to the inlet of pump 28, and is pumped under pressure through secondary coolant supply line 40 to flow control valves 50 of display cases 14. Flow control valves 50 are typically thermostatically controlled to maintain a desired temperature within display cases 14. additional manual or sensor controlled flow valves may also be provided on either the supply or the return side of heat exchanger 52. When flow control valve 50 is open, secondary coolant flows through flow control valve 50 and through the coils of heat exchanger 52, and then to return line 42 and back to chiller system 12. Secondary coolant may be, for example, propylene glycol, a brine, or any other fluid having suitable for heat transfer in heat exchangers 26 and 52.
FIG. 2 shows a sectional view of display case 14, which is an open front insulated cabinet that defines front opening 62 and product display area 64. Shelves 66 are mounted in display area 64 to support products that require refrigeration. Lower inner wall 68, rear inner wall 70, and top inner wall 72 are spaced from the outer wall of cabinet 60 to define an air circulation compartment made up of air return duct 74, rear air duct 76, and air discharge duct 78. Discharge grille 80 is located at the outlet end of discharge duct 78, and return grille 82 is located at the inlet end of return duct 74. Located within return duct 74 are air circulation fan system 84, and heat exchanger 52.
Fan system 84 takes air that has been received through return grille 82 and forces the air through heat exchanger 52 into rear duct 76. Rear wall 70 has holes through which some of the air in rear duct 76 diffuses into product display area 74. The remainder of the air moves upward through rear duct 76 to discharge duct 78. The chilled air is discharged through discharge grille 80 generally downward across opening 62 of cabinet 60. This forms an air curtain that separates the interior volume of display area 64 from the ambient air external to display case 14. As a result, merchandise on display within display case 14 can be chilled to and maintained at a desired temperature that is lower than ambient temperature with the store, even though the front of case 14 is open.
The present invention addresses a problem that can occur with refrigerated display cases when outside air migrates into the interior of the display case. This can occur, for example, as a result of merchandise protruding into the air curtain, so that the air curtain is disrupted, thereby creating a path for ambient air into the case interior. The ambient air typically has a dew point that is significantly higher than the temperature maintained within the display case. The air that is being circulated within the display case may have little capacity to absorb moisture because the air exiting the heat exchanger may be close to saturation. The result could be localized condensation on surfaces within the display case, such as the packaging of the merchandise being displayed.
The invention uses heat content which has been transferred from the air flowing through heat exchanger 52 to reheat air exiting heat exchanger 52, which controls the relative humidity of the air exiting heat exchanger 52 and entering rear duct 76. As a result, the air being circulated through rear duct 76 and into product display area 64 has greater capability to absorb moisture, and thus has more capacity to remove moisture on surfaces within the display area 64.
FIGS. 3A and 3B are partial views showing one embodiment of heat exchanger 52 positioned within cabinet 60. Heat exchanger 52 is a coil type heat exchanger having an array of parallel heat exchanger tubes 90 that are connected to form a number of flow circuits through which secondary fluid flows. As described in more detail in conjunction with FIG. 4, the flow circuits of heat exchanger 52 include circuits that provide counterflow of secondary fluid in a direction opposite the direction of airflow, as well as circuits that provide counterflow followed by flow through a tube near the downstream or exit end of heat exchanger 52 to reheat cooled air as it enters rear duct 76.
FIGS. 3A and 3B also show a portion of secondary coolant supply line 40, flow control valve 50, inlet header 92, outlet header 94, manual shutoff valve 96, flow control valve 98, and a portion of secondary coolant return line 42. Air enters heat exchanger 52 at inlet or upstream end 100 and exits into rear duct 76 at exit or downstream end 102.
FIG. 4 is a diagram illustrating the connection of tubes 90 to form flow circuits 110, 112, 114, 116, 118, 120, 122, and 124. In the embodiment shown in FIG. 4, a total of fifty parallel tubes T1-T50 are shown. Tubes T45-T50 are not used in any of circuits 110-124, but in other embodiments having different circuit configurations, those tubes may be used as well to provide greater cooling capacity.
In the diagram shown in FIG. 4, connections between tubes of a circuit at the side closest to the viewer are shown in solid lines, while connections between tubes made at the opposite side of heat exchanger 52 are shown in dotted lines. An X within the circle representing a tube signifies where secondary fluid from inlet header 92 enters a circuit. A dot in the center of a circle representing a tube indicates where secondary fluid flows out of the circuit to outlet header 94.
Circuit 110 is formed by tubes T1, T2, T3, and T4. Secondary fluid from inlet header 92 enters tube T1, flows the length of T1, and crosses over to tube T2. The secondary fluid flows through tube T2, crosses over to tube T3 and flows the length of tube T3. It then crosses over at the opposite side of heat exchanger 52 and flows down tube T4, where it exits to outlet header 94. The general direction of flow of secondary fluid through circuit 110 is in a counterflow direction, opposite to the direction of air flow. In other words, in FIG. 4, the counterflow direction of secondary fluid is from left-to-right, while air flow is from right-to-left.
Circuit 112 includes tubes T5-T8. Secondary fluid enters tube T5 and exits at tube T8. The direction of flow of secondary fluid through circuit 112 is in the counterflow direction.
Circuit 114 includes tubes T9-T12. Flow of secondary fluid through circuit 114 is in the counterflow direction, with secondary fluid entering at tube T9 and exiting at tube T12.
Circuit 116 includes tubes T13-T22. A first portion of circuit 116 formed by tubes T13-T21 provides counterflow, with secondary fluid entering at tube T13 and moving generally in a counterflow direction until it reaches tubes T20 and T21 at the upstream or entrance end of heat exchanger 52. A connection is then provided from tube T21 to tube T22, which is positioned near the upper exit or downstream end of heat exchanger 52. As a result, secondary fluid that has been heated as a result of counterflow movement from tube T13 to tube T21 is delivered to tube T22, where the air passing through heat exchanger 52 is the coolest. The higher fluid temperature of secondary fluid flowing through tube T22 is used to reheat the air exiting heat exchanger 52. By exchanging heat with the cooler air, tube T22 raises the air dry bulb and lowers the air relative humidity. This dryer air has increased capacity to remove moisture that may have deposited within display area 64.
Circuit 118 is formed by tubes T23-T26. Secondary fluid enters tube T23 and exits at T26. The flow of secondary fluid is in the counterflow direction.
Circuit 120 includes tubes T27-T30. Flow of secondary fluid is in the counterflow direction. Secondary fluid enters at tube T27 and exits at tube T30.
Circuit 122 includes tubes T31-T40. Secondary fluid flows in a counterflow direction from an entrance at tube T31 to tube T38. A secondary fluid then makes an additional pass at the upstream end of heat exchanger 52 through tube T39, and then is routed to a final pass at tube T40. Tube T40 is located near the upper downstream end or exit end of heat exchanger 52. The function of tube T40 is similar to the function of tube T22 in exchanging heat with cold air that is about to exit heat exchanger 52. The heating supplied by tube T40 (as well as tube T22) helps to raise air dry bulb and lower air relative humidity as the air enters rear duct 76.
Circuit 124 includes tubes T41-T44. Secondary fluid enters circuit 124 at tube T41 and exits at tube T44. The flow of secondary fluid is in the counterflow direction with respect to air flow through heat exchanger 52.
In the embodiment shown in FIG. 4, most of the circuits (i.e., circuits 110, 112, 114, 118, 120, and 124) have secondary fluid flowing in a rear to front counterflow direction with respect to air flow. The other two circuits 116 and 122 feature a larger number of passes and a counterflow of secondary fluid to the front or upstream end of heat exchanger 52. The secondary fluid is then routed from the second to last pass to a final pass located near the rear or downstream end of heat exchanger 52. The final passes for circuits 116 and 122 are at tubes T22 and T40, respectively. The higher fluid temperature passing through tubes T22 and T44 reheats the cold air that is about to exit heat exchanger 52 and enter rear duct 76. This reheating of the air raises the air dry bulb and lowers air relative humidity, so that the air has a greater capacity to remove moisture that has been deposited inside product display area 64.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, although two circuits 116 and 122 are shown in FIG. 4 as providing the reheating feature, other embodiments may use only one circuit, or more than two circuits to provide reheating. Similarly, the number of circuits that provide counterflow of secondary fluid with routing the fluid for reheating air may also vary in number. The number of tubes in each circuit, and the total number of tubes and circuits will also vary depending on the display case and the operating conditions under which it will be used.
adjacent to a downstream end of the heat exchanger to heat air exiting the heat exchanger.

Claims

1. A refrigerated merchandiser system comprising:

a chiller for cooling a fluid; and

a display case comprising:

a product display area;

an air circulation compartment in air flow communication with the product display area;

an air circulation fan system for circulating air returned from the product display area through the air circulation compartment to the product display area, wherein the air has a relative humidity; and

a heat exchanger connected in fluid communication with the chiller, the heat exchanger including a plurality of tubes for circulating fluid from the chiller to exchange heat with air passing from an upstream end to a downstream end through the heat exchanger, wherein the tubes are connected to form at least a first circuit and a second circuit, the first circuit circulating fluid in a counterflow direction toward the upstream end to cool the air, and the second circuit having a first portion for circulating fluid in a counterflow direction toward the upstream end followed by a portion for circulating fluid toward the downstream end to reheat the air as it exits the heat exchanger and lower the relative humidity of the air.

2-3. (canceled)

4. A refrigerated merchandiser including a cabinet defining a product display area, an air circulation compartment in air flow communication with the product display area, an air circulation fan, and a heat exchanger whereby air flow passes from the air circulation fan through the heat exchanger in heat exchange relationship with chilled fluid passing through the heat exchanger, characterized in that the heat exchanger comprises:

a first circuit in which the chilled fluid passes in counterflow relationship to the air flow; and

a second circuit in which chilled fluid first passes in counterflow relationship with the air flow to an upstream end of the heat exchanger, and then passes towards a downstream end of the heat exchanger to heat air exiting the heat exchanger.

5. The system of claim 1, the chiller further comprising:

a compressor;

a condenser connected to the compressor;

an expansion valve connected to the condenser;

a chiller heat exchanger connected to the expansion valve and to the compressor; and

a pump for passing coolant from the chiller heat exchanger to the display case.

6. The system of claim 1, wherein the heat exchanger is a coil-type heat exchanger.

7. The system of claim 1, wherein the air circulation compartment is defined by a lower inner wall, a rear inner wall, a top inner wall, and an outer wall of the display case.

8. The system of claim 1, wherein the air circulation compartment further comprises:

a return duct for receiving air from the product display area;

a rear duct connected to the return duct; and

a discharge duct connected to the return duct, wherein at least a portion of the air is discharged back into the product display area.

9. The system of claim 8, wherein the air circulation fan system is located within the return duct.

10. The system of claim 8, wherein the heat exchanger is located within the return duct.

11. The system of claim 1, further comprising:

a supply line for passing fluid from the chiller to the heat exchanger; and

a return line for passing fluid from the heat exchanger to the chiller.

12. The system of claim 11, further comprising:

an inlet header connecting the supply line to the heat exchanger; and

an outlet header connecting the return line to the heat exchanger.

13. The system of claim 11, wherein the supply line has a flow control valve.

14. The system of claim 1, wherein the fluid is selected from the group consisting of propylene glycol, brines, and other fluids suitable for heat transfer.

15. A refrigeration merchandiser system comprising:

a chiller system having a first heat exchanger; and

a display case comprising:

an air circulation circuit having a return duct and a discharge duct;

a fan system for circulating air from the return duct to the discharge duct; and

a second heat exchanger in communication with the air circulation circuit and the chiller system, the heat exchanger having a first circuit, a second circuit, an upstream end, and a downstream end, wherein the fan system passes air through the heat exchanger from an upstream end of the heat exchanger to a downstream end of the heat exchanger, the first circuit passes coolant from the chiller system from the downstream end towards the upstream end, and the second circuit passes coolant from the downstream end towards the upstream end and back towards the downstream end to dry the air.

16. The system of claim 15, wherein the second heat exchanger is located in the return duct of the display case.

17. The system of claim 15, wherein the coolant is selected from the group consisting of propylene glycol, brines, and other fluids suitable for heat transfer.

18. The system of claim 15, wherein the first circuit and the second circuit are each comprised of multiple tubes.

19. The system of claim 15, wherein the chiller system further comprises:

a compressor connected to the first heat exchanger;

a condenser connected to the compressor;

an expansion valve connected to the condenser and the first heat exchanger; and

a pump for passing coolant from the first heat exchanger of the chiller to the display case.

20. The system of claim 19, further comprising:

a flow control valve between the pump and the second heat exchanger to control flow of coolant to the second heat exchanger.

21. A method for circulating air in a refrigerated merchandiser system comprising:

circulating air from a product display area through a heat exchanger;

passing coolant through a first section of the heat exchanger from a downstream end of the heat exchanger towards an upstream end of the heat exchanger;

passing coolant through a second section of the heat exchanger from the downstream end of the heat exchanger towards the upstream end of the heat exchanger and back towards the downstream end of the heat exchanger to form dry air;

circulating dry air from the heat exchanger back to the product display area.

22. The method of claim 21, and further comprising:

pumping coolant from a chiller system to the heat exchanger through a supply line; and

pumping coolant from the heat exchanger back to the chiller system through a return line.