WO2006101568A1

WO2006101568A1 - Transcritical refrigeration system with suction line heat exchanger

Info

Publication number: WO2006101568A1
Application number: PCT/US2005/047530
Authority: WO
Inventors: Tobias H. Sienel; Yu Chen; Parmesh Verma; Hans-Joachim Huff
Original assignee: Carrier Comercial Refrigeration Inc
Current assignee: Taylor Commercial FoodService LLC
Priority date: 2005-03-18
Filing date: 2005-12-30
Publication date: 2006-09-28
Anticipated expiration: 2007-09-18

Abstract

A bottle cooler system includes means (64) for heat exchange between a first portion (66) of the flowpath upstream of the expansion device and a second portion (68) of the flowpath downstream of the low temperature heat exchanger.

Description

TRANSCRITICA'iL-RBPRIGERATION SYSTEM WITH SUCTION LINE HEAT

EXCHANGER

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] Benefit is claimed of US Patent Application Ser. No. 60/663,958, entitled "TRANSCRITICAL REFRIGERATION SYSTEM WITH SUCTION LINE HEAT EXCHANGER" and filed March 18, 2005. Copending application docket 05-258-WO, entitled HIGH SIDE PRESSURE REGULATION FOR TRANSCRITICAL VAPOR COMPRESSION SYSTEM and filed on even date herewith, discloses prior art and inventive cooler systems. The present application discloses possible modifications to such systems. The disclosures of said applications are incorporated by reference herein as if set forth at length.

BACKGROUND OF THE INVENTION [0002] The invention relates to refrigeration. More particularly, the invention relates to beverage coolers.

[0003] FIG. 1 schematically shows transcritical vapor compression system 20 utilizing CO₂ as working fluid. The system comprises a compressor 22, a gas cooler 24, an expansion device 26, and an evaporator 28. The exemplary gas cooler and evaporator may each take the form of a refrigerant-to-air heat exchanger. Airflows across one or both of these heat exchangers may be forced. For example, one or more fans 30 and 32 may drive respective airflows 34 and 36 across the two heat exchangers. A refrigerant flow path 40 includes a suction line extending from an outlet of the evaporator 28 to an inlet 42 of the compressor 22. A discharge line extends from an outlet 44 of the compressor to an inlet of the gas cooler. Additional lines connect the gas cooler outlet to expansion device inlet and expansion device outlet to evaporator inlet.

[0004] The major difference between transcritical and conventional operation is that heat rejection in the gas cooler is in the supercritical region because the critical temperature for CO₂ is 87.8° F. Consequently, pressure is not solely dependent on temperature and this opens additional control and optimization issues for system operation. [0005] For a fixed gas cooler discharge temperature, as the high side pressure is increased, the exit enthalpy of the refrigerant decreases, yielding a higher differential enthalpy through the gas cooler. The capacity of the gas cooler is a function of the mass flowrate of refrigerant and the enthalpy difference across the gas cooler. For a beverage cooler, the evaporator may be essentially at the cooler interior temperature. It is typically αesired ϊo maintain' this teffiptTrature in a very narrow range regardless of external condition.

For example, it may be desired to maintain the interior very close to 37° F. This temperature essentially fixes the steady state compressor suction pressure.

[0006] For a fixed compressor suction pressure, as the high side pressure increases, the amount of energy used by the compressor increases, and the volumetric efficiency of the compressor decreases. When the volumetric efficiency of the compressor decreases, the flowrate through the system decreases. The balance of these two counteracting effects is typically an increase in gas cooler capacity as the high side pressure is increased. However, above a certain pressure the amount of capacity increase becomes very small. Because the expansion device is usually isenthalpic, the evaporator capacity will also typically increase as the high side pressure increases.

[0007] The energy efficiency of a vapor compression system, the coefficient of performance (COP), is usually expressed as a ratio of the system capacity to the energy consumed. Because an increase in pressure typically produces both a higher capacity and a higher energy consumption, the balance between the two will dictate the overall COP. Therefore, there is typically an optimal pressure which yields the highest possible performance.

[0008] An electronic expansion valve is usually used as the device 26 to control the high side pressure to optimize the COP of the CO₂ vapor compression system. An electronic expansion valve typically comprises a stepper motor attached to a needle valve to vary the effective valve opening or flow capacity to a large number of possible positions (typically over one hundred). This provides good control of the high side pressure over a large range of operating conditions. The opening of the valve is electronically controlled by a controller 50 to match the actual high side pressure to the desired set point. The controller 50 is coupled to a sensor 52 for measuring the high side pressure.

[0009] In transcritical vapor compression systems, the high pressure in the system is above the critical point of the fluid is thus semi-independent of the temperature of the heat sink fluid. A pressure which yields the highest efficiency is often chosen to optimize the system performance. For transcritical vapor compression systems, it is important to minimize the temperature of the refrigerant entering the expansion valve in order to maximize the system efficiency.

SUMMARY OF THE INVENTION [OOlKJ] A bottle cooler "System includes means for heat exchange between a first portion of the flowpath upstream of the expansion device and a second portion of the flowpath downstream of the low temperature heat exchanger.

[0011] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a schematic of a baseline refrigeration system. [0013] FIG. 2 is a schematic of a CO₂ bottle cooler refrigeration system with a suction line heat exchanger (SLHX).

[0014] FIG. 3 is a graph of capacity for the system of FIG. 2 and the baseline system.

[0015] FIG. 4 is a graph of coefficient of performance for the system of FIG. 2 and the baseline system. [0016] FIG. 5 is a partial view of an integrated expansion device and SLHX.

[0017] FIG. 6 is a side schematic view of a display case including a refrigeration and air management cassette.

[0018] FIG. 7 is a view of a refrigeration and air management cassette.

[0019] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0020] A suction line heat exchanger (SLHX) is an internal heat exchanger which transfers heat from the refrigerant before it enters the expansion valve to before the entrance to the compressor. FIG. 2 shows a system 60 formed as a modification of the prior art system 20 to include an SLHX 64 along the refrigerant flowpath 62. The SLHX is a refrigerant-to-refrigerant heat exchanger having a first leg 66 along the flowpath downstream of the first heat exchanger 24 and upstream of the expansion device 26. The SLHX has a second leg 68 in heat exchange relation with the first leg 66 and located downstream of the second heat exchanger 28 but upstream of the compressor (i.e., along the suction line). [0021] The effect of the SLHX on the efficiency and capacity of the system at a certain operating condition are shown in FIGS. 3and 4. FIGS. 3 and 4 respectively show capacity and COP against gas cooler pressure with traces 100 and 120 representing the baseline system and traces 102 and 122 representing the addition of the SLHX. From these, it can be seen that the SLHX improves both capacity and efficiency by about 10% in a middle pressure range near 1600psi with yet better performance at lower pressure..

[0022] The increased low pressure performance is particularly significant when simple expansion devices are used (e.g., fixed orifices rather than electronic expansion valves) which do not optimize the high pressure in the system to achieve peak efficiency. In operation, pressure may vary around the optimal point for the system. If the pressure is significantly below the optimal point, the system without the SLHX will be more compromised in efficiency than the one with the SLHX. Thus, the addition of the SLHX permits a low cost system (e.g., without an expensive EEV) to have performance more competitive with an expensive system. [0023] For simple, small systems, a low cost SLHX can consist of wrapping a first portion 66 (FIG. 5) of the refrigerant line (or the expansion device itself, e.g., if it is a capillary tube), around a second portion of the refrigerant line 68. FIG. 5 also shows exemplary directions of a refrigerant flow 70. A similar result can be achieved in an economical manner by forming the leg 66 integrally within the discharge header or tube of the evaporator (thereby acting as the leg 68). The integration can be carried one step further by integrating the discharge header, SLHX, and expansion device into one body. This invention is particularly useful for transcritical vapor compression systems, generally, and particularly small systems such as those used in refrigerators or bottle coolers. [0024] FIG. 6 shows an exemplary bottle cooler 200 having a removable cassette 202 containing the refrigerant and air handling systems. The exemplary cassette 202 is mounted in a compartment ol a base 2U4 ot a housing. The housing has an interior volume 206 between left and right side walls, a rear wall/duct 216, a top wall/duct 218, a front door 220, and the base compartment. The interior contains a vertical array of shelves 222 holding beverage containers 224. [0025] The exemplary cassette 202 draws the air flow 34 through a front grille in the base 224 and discharges the air flow 34 from a rear of the base. The cassette may be extractable through the base front by removing or opening the grille. The exemplary cassette drives the air flow 36 on a recirculating flow path through the interior 206 via the rear duct 210 and top duct 218. [0026] FIG. 7 shows further details of an exemplary cassette 202. The heat exchanger 28 is positioned in a well 240 defined by an insulated wall 242. The wall 242 separates a cold section of the system (the well and case above) from a hot section (an air duct 256 passing the flow 34 through the heat exchanger 24. The heat exchanger 28 is shown positioned mostly in an upper rear quadrant of the cassette and oriented to pass the air flow 36 generally rearwardly, with an upturn after exiting the heat exchanger so as to discharge from a rear portion o the cassette upper end.

[0027] The exemplary SHLX 64 is shown within the hot section. It may be positioned there for packaging efficiency. When a portion of the SLHX is placed in the hot section, it is preferred to avoid heat loss to the hot section air, and in this regard it is preferred to insulate the SLHX and adjacent line from exposure to the air flow 34. Similarly, if in the cold section, insulation may be desirable to avoid heating of the air flow 36. [0028] One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, when implemented as a remanufacturing of an existing system or reengineering of an existing system configuration, details of the existing configuration may influence details of the implementation. Accordingly, other embodiments are within the scope of the following claims.

Claims

What is claimed is: 1. A cooler system comprising: a compressor (22) for driving a carbon dioxide based refrigerant along a flow path (62) in at least a first mode of system operation; a first heat exchanger (24) along the flow path downstream of the compressor in the first mode; a second heat exchanger (28) along the flow path upstream of the compressor in the first mode to cool contents of an interior volume (206) of the system; an expansion device (26); and means (64) for heat exchange between a first portion (66) of the flowpath at or upstream of the expansion device and a second portion (68) of the flowpath at or downstream of second heat exchanger.

2. The system of claim 1 wherein the means (64) comprises: a wrapping of a refrigerant line along at least one of the first and second portions.

3. The system of claim 1 wherein the means (64) comprises: a double helix interwrapping of a refrigerant line along the first and. second portions.

4. The system of claim 1 wherein the means (64) comprises: a wrapping of a refrigerant line along one of the first and second portions around the other of the first and second portions.

5. The system of claim 1 wherein the means (64) comprises: a wrapping of a refrigerant line along the first portion and around the second portion.

6. The system of claim 1 wherein the means (64) comprises: a wrapping of a refrigerant line along the second portion around the expansion device, the expansion device being a capillary tube device.

7. The system of claim 1 wherein the means (64) comprises: a wrapping of a capillary tube of the expansion device around a refrigerant line along the second portion.

8. The system of claim 1 wherein the means (64) comprises: an integrating of a refrigerant line along the first into a discharge header or tube of the second heat exchanger.

9. The system of claim 1 wherein the means (64) comprises: an integrating of a discharge header, SLHX, and expansion device into one body.

10. The system of claim 1 being a self-contained externally electrically powered beverage cooler (200), positioned outdoors.

11. The system of claim 1 wherein: the first and second heat exchangers are refrigerant-air heat exchangers.

12. The system of claim 11 wherein: the means 64 is positioned within an air flow path of the first heat exchanger and is insulated.

13. The system of claim 1 wherein: the refrigerant consists essentially of CO₂; and the first and second heat exchangers are refrigerant-air heat exchangers each having an associated fan (30, 32), an air flow (34) across the first heat exchanger (24) being an external to external flow and an air flow (36) across the second heat exchanger (28)being a recirculating internal flow.

14. The system of claim 1 in combination with said contents which include: a plurality of beverage containers (224) in a 0.3-4.0 liter size range.

15. The system of claim 14 being selected from the group consisting of: a cash-operated vending machine; a transparent door front, closed back, display case; and a top access cooler chest.

16. A system comprising: a compressor (2^"2)^' for driving a carbon dioxide based refrigerant along a flow path

(62) in at least a first mode of system operation; a first heat exchanger (24) along the flow path downstream of the compressor in the first mode; a second heat exchanger (28) along the flow path upstream of the compressor in the first mode; an expansion device (26); and a SLHX (64) for heat exchange between a first portion (66) of the flowpath at or upstream of the expansion device and a second portion (68) of the flowpath at or downstream of second heat exchanger.

17. The system of claim 16 wherein: the second heat exchanger is positioned to cool an air flow (36).

18. A method for operating a refrigeration system, the method comprising: compressing and driving a carbon dioxide based refrigerant along a flow path (62) in at least a first mode of system operation; rejecting heat from the refrigerant along the flow path downstream of the compressing in the first mode; receiving heat to the refrigerant along the flow path upstream of the compressing in the first mode; expanding the refrigerant between the rejecting and the receiving; and exchanging heat from the refrigerant between rejecting and the expanding to the refrigerant between the receiving and the compressing.

19. The method of claim 18 wherein: the rejecting is to a first air flow; and the receiving is from a second air flow.

20. A method for manufacturing a refrigeration system or reengineering a configuration of said system from a baseline, the method comprising: adding a suction line heat exchanger, where the baseline lacked such a suction line heat exchanger. L i Trie method'of claim 20 further comprising: adding a fixed expansion device in place of an electronic expansion valve.