WO2009052368A1

WO2009052368A1 - A medium- and low-temperature integrated refrigerating/freezing system

Info

Publication number: WO2009052368A1
Application number: PCT/US2008/080297
Authority: WO
Inventors: Zhong GU; Zhiwei He; Chuanxue Duan
Original assignee: Carrier Corporation
Priority date: 2007-10-17
Filing date: 2008-10-17
Publication date: 2009-04-23
Also published as: EP2198211A1; CN101413738A; US20100212350A1; EP2198211A4

Abstract

A medium- and low-temperature integrated refrigerating/freezing system (40) comprises an integrated unit (41), a medium-temperature refrigerating cabinet (43), a low-temperature freezing cabinet (42) and corresponding connecting pipes (44). The integrated unit (41) further comprises a common condenser (54) for condensing the high-temperature and high-pressure gaseous refrigerant in the medium-temperature refrigerating system and the low-temperature freezing system, a common reservoir (55) for the storage of the high- temperature and high-pressure liquid refrigerant in the medium-temperature refrigerating system and the low-temperature freezing system, a subcooling adjusting mechanism (56, 57) for adjusting the subcooling degree in the low-temperature freezing system and a suction temperature adjusting mechanism (431, 432, 58) for adjusting the suction temperature of the low-temperature freezing system.

Description

A MEDIUM- AND LOW-TEMPERATURE INTEGRATED REFRIGERATING/FREEZING

SYSTEM

BACKGROUND [0001] The present disclosure relates to a medium- and low-temperature integrated refrigerating/freezing system, and in particular to an integrated system for providing medium-temperature refrigerating and low-temperature freezing for foods and cold drinks, etc. in supermarkets and convenience stores.

[0002] In real life, various freezing display cabinets are provided in supermarkets or convenience stores for providing a freezing environment for preservation and freezing of foods, beverage and cold drinks when the ambient temperature is relatively higher. Generally different products have different requirements to the temperature of freezing and preservation. Usually, freezing systems are classified as low-temperature freezing systems and medium-temperature refrigeration systems. Low-temperature freezing systems usually provide an evaporator temperature of about 30-35 degrees centigrade below zero, mainly for products such as ice cream or other frozen food. Medium-temperature refrigerating systems usually provide an evaporator temperature of about 8-10 degrees centigrade below zero for products such as milk, drinks, produce, meat, and other perishable foods. Currently, a low-temperature freezing system and a medium-temperature refrigerating system are two independent systems without mutual interference, because the compression ratios of the two systems are different, so are the energy efficiencies of these systems. Fig. 1 is a schematic diagram of the structure of a medium-temperature refrigerating system which comprises a compressor 1, a condenser 2, an expansion valve 4, a reservoir 3, an evaporator 5 connected with a medium-temperature refrigerating cabinet and refrigerant pipes 6 correspondingly connecting the devices and forming a closed circulation loop. In operation, low-temperature and low-pressure gaseous refrigerant is changed into high-temperature and high-pressure gas after having been compressed by the compressor 1. After entering into the condenser 2, the high-temperature and high-pressure gaseous refrigerant releases its heat to the ambient, transforms into a high-temperature and high-pressure liquid and flows into the expansion valve 4 via the reservoir 3. The expansion valve 4 reduces the pressure of the refrigerant and adjusts the flow rate of the refrigerant, so as to enable the high-temperature and high-pressure liquid refrigerant to change into low-temperature and low-pressure two-phase liquid and gas and to flow into the evaporator 5. A fan (not shown) is also provided near the evaporator inside the refrigerating cabinet for blowing air towards the surface of the coiled pipes of the evaporator in order to have heat exchange between the low-temperature and low-pressure liquid refrigerant in the coiled pipes of the evaporator 5 and the air flowing through the surface of the coiled pipes of the evaporator, so as to generate cold air for preservation and storage of various foods in the refrigerating cabinet. The refrigerant changes into a low-temperature and low-pressure gas after absorbing heat and flows back to the compressor 1, completing a complete and closed cycle by the refrigerant.

[0003] Fig. 2 is a schematic diagram of the structure of a low-temperature freezing system, of which the working principle is essentially the same as that of the medium-temperature refrigerating system. Since the low-temperature freezing system is required for generating relatively lower temperature, the system has a relatively high compression ratio, and in order to protect the low-temperature compressor it is needed to lower the exhaust temperature of the low-temperature compressor 1. In comparison with a medium-temperature refrigerating system, therefore, in the structure of the low-temperature freezing system, the refrigerant flowing out of the reservoir 3 flows into a branch as well as directly into the evaporator 5. In the branch, the high-temperature and high-pressure liquid refrigerant from the reservoir 3 flows via an injection valve 7, expands, absorbs heat and changes into a low-temperature and low-pressure gas which is provided directly to the compressor 1. The refrigerant in the branch lowers the suction temperature of the compressor 1, thereby the exhaust temperature of the compressor 1 being lowered and the compressor 1 being effectively protected.

[0004] The two currently available independent systems are capable of providing supermarkets and convenience stores with a low-temperature freezing system and a medium-temperature refrigerating system respectively, and meeting the requirements for the storage of various foods at medium-temperature and low-temperature. However, since two independent systems are employed in this case, machine rooms are needed in the supermarkets and convenience stores for accommodating the compressors and condensers of the two systems, which not only wastes space in supermarkets and convenience stores, but also adds complexity of site installation. Meanwhile, the repetitive use of the condensers and the reservoirs by the two independent systems wastes raw materials and increases the hardware costs of the systems, both being disadvantageous to energy saving and cost reduction.

SUMMARY [0005] In one aspect, a medium- and low-temperature integrated refrigerating/freezing system may provide medium temperature refrigeration for storing foods, etc. and low temperature freeze for storing cold drinks, etc. The system may comprise an integrated unit, a (group of) medium-temperature refrigerating cabinet(s), a (group of) low-temperature freezing cabinet(s) and corresponding connecting pipes. The integrated unit may further comprise: a common condenser for condensing high- temperature and high-pressure gaseous refrigerant in the medium-temperature refrigerating system and the low-temperature freezing system; a common reservoir for storing the high-temperature and high-pressure liquid refrigerant in the medium-temperature refrigerating system and the low-temperature freezing system; a subcooling adjusting mechanism for adjusting the subcooling of the low-temperature freezing system; and a suction temperature adjusting mechanism for adjusting intake temperature of the low-temperature freezing system.

[0006] The system may have compact structure and energy saving as well as easy installation and relatively high energy utilization efficiency.

[0007] The system may provide a medium- and low-temperature integrated refrigerating/freezing system, in which the integrated unit further comprises a (group of) medium-temperature compressor(s) and a (group of) low-temperature compressor(s).

[0008] The system may provide a medium- and low-temperature integrated refrigerating/freezing system, in which the medium-temperature refrigerating cabinet and the low-temperature freezing cabinet comprise respectively an evaporator, an expansion valve and a product cabinet for food placement. [0009] The system may provide a medium- and low-temperature integrated refrigerating/freezing system, in which the suction ends of the (group of) medium-temperature compressor(s) and the (group of) low-temperature compressor(s) are respectively connected to the evaporators of the medium-temperature refrigerating cabinet and the low-temperature freezing cabinet, and the exhaust ends thereof are jointly connected to the inlet end of the common condenser.

[0010] The system may provide a medium- and low-temperature integrated refrigerating/freezing system, in which the outlet end of the common condenser is connected to the inlet end of the reservoir.

[0011] The system may provide a medium- and low-temperature integrated refrigerating/freezing system, in which the expansion valve in the integrated unit, an intermediate heat exchanger and the corresponding connecting pipes form the subcooling adjusting mechanism.

[0012] The system may provide a medium- and low-temperature integrated refrigerating/freezing system, in which a first inlet end of the intermediate heat exchanger of the subcooling adjusting mechanism is directly connected to the reservoir, and a second inlet end of the intermediate heat exchanger of the subcooling adjusting mechanism is connected to the reservoir via the expansion valve.

[0013] The system may provide a medium- and low-temperature integrated refrigerating/freezing system, in which a first outlet end of the intermediate heat exchanger is connected to the inlet end of the low-temperature freezing cabinet.

[0014] The system may provide a medium- and low-temperature integrated refrigerating/freezing system, in which the suction temperature adjusting mechanism comprises a first branch connecting the second outlet end of the intermediate heat exchanger with the suction end of the medium-temperature compressor, and a second branch connecting the second outlet end of the intermediate heat exchanger with the suction end of the low-temperature compressor, wherein the second branch contains an adjustment valve.

[0015] The system may provide a medium- and low-temperature integrated refrigerating/freezing system, in which the integrated unit is connected to the medium-temperature refrigerating cabinet and the low-temperature freezing cabinet in a plug-and-play manner.

[0016] In another aspect, a refrigerating system comprises: at least one medium-temperature refrigerating device comprising at least one medium-temperature evaporator; at least one low-temperature freezing device comprising at least one low-temperature evaporator; an integrated unit comprising: at least one medium-temperature compressor connected to the medium-temperature evaporator; at least one low-temperature compressor connected to the low-temperature evaporator; a condenser connected to the exhaust ends of the at least one medium-temperature compressor and the at least one low-temperature compressor for condensing the high-temperature and high-pressure gaseous refrigerant exhausted from the exhaust ends of the at least one medium-temperature compressor and the at least one low-temperature compressor; a reservoir connected to the condenser for storing the high-temperature and high-pressure liquid refrigerant exhausted from the condenser; a subcooling adjusting mechanism connected with the reservoir and to the low-temperature evaporator for adjusting the subcooling of the low-temperature freezing circulation system; a suction temperature adjusting mechanism connected with the reservoir and respectively to the low-temperature compressor and the medium-temperature compressor for adjusting the suction temperature of the low- temperature freezing circulation system; and a medium-temperature connecting pipeline connected to the reservoir and the medium-temperature evaporator.

[0017] The system may provide a refrigerating system, in which the subcooling adjusting mechanism comprises an intermediate heat exchanger connected to the low-temperature evaporator, a first inlet end of the intermediate heat exchanger is directly connected to the reservoir, and a second inlet end thereof is connected to the reservoir via an expansion valve. [0018] The system may provide a refrigerating system, in which the first outlet end of the intermediate heat exchanger is connected to the low- temperature evaporator of the low-temperature freezing device.

[0019] The system may provide a refrigerating system, in which the suction temperature adjusting mechanism comprises a first branch connecting the second outlet end of the intermediate heat exchanger with the suction end of the medium-temperature compressor, and a second branch connecting the second outlet end of the intermediate heat exchanger with the suction end of the low-temperature compressor, wherein the second branch contains an adjustment valve.

[0020] The system may be implemented to effectively reduce installation space for the freezing system. A plug-and-play connection may be employed to facilitate the system's site installation and later adjustments and maintenance. The integrated design may optimize the layout of the pipelines. The whole system may offer simplified hardware structure and high performance.

[0021] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of the structure of a prior art medium-temperature refrigerating system.

[0023] Figure 2 is a schematic diagram of the structure of a prior art low-temperature freezing system.

[0024] Figure 3 is a schematic diagram of the structure of an embodiment of the present medium- and low-temperature integrated refrigerating/freezing system. [0025] Figure 4 is a schematic diagram of the structure of the medium- and low-temperature refrigerating/freezing cabinet of the system of Figure 3.

[0026] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0027] It is easily understood that according to the technical solutions of the present disclosure, those skilled in the art would be able to propose other embodiments of the medium- and low-temperature integrated refrigerating/freezing system of the present invention without departing from the real spirit of the present invention; therefore, the following embodiments and drawings are merely illustrative examples of the technical solutions of the present disclosure and they are not to be deemed as the whole of the present disclosure or be deemed as limiting or defining the technical solutions of the present disclosure.

[0028] In Fig. 3, an embodiment of a medium- and low-temperature integrated refrigerating/freezing system 40 mainly comprises an integrated unit 41, a low-temperature freezing cabinet 42, a medium-temperature refrigerating cabinet 43 and connecting pipes 44. The integrated unit 41 has two inlet ends (inlets) 102, 104 and two outlet ends (outlets) 101, 103. The housing of the low-temperature freezing cabinet 42 is provided with an inlet end and an outlet end. The housing of the medium- temperature refrigerating cabinet 43 is provided with an inlet end and an outlet end.

[0029] The integrated unit 41 comprises a housing 51 , a low-temperature compressor 52, a medium-temperature compressor 53, a heat rejection heat exchanger (condenser) 54, a reservoir 55, an intermediate heat exchanger 56, an expansion device (e.g., valve) 17, an adjustment valve 58, and the associated connecting pipes 44. The housing 51 of the integrated unit 41 can be a sealed box, and it can also have doors or other similar structures for installing/removing/accessing the low-temperature compressor 52, the medium-temperature compressor 53, the condenser 54, the reservoir 55, the intermediate heat exchanger 56 and the associated connecting pipes 44. The housing 51 may have shock absorption feet (not shown), and the housing 51 can be designed into a shock-proof and noise-proof structure for improving system performance of the integrated unit 41 and for increasing system stability. Inside the housing 51, each of the elements may be arranged for convenient connection between the elements and for laying out the connecting pipes 44. The integrated unit may be a roof-mounted or other remote unit. Although shown connected to a single medium temperature evaporator and cabinet and a single low temperature evaporator and cabinet, a given integrated unit may be connected to multiple such medium temperature evaporators and/or cabinets and/or multiple low temperature evaporators and/or cabinets. Also, each integrated unit may have multiple such medium temperature compressors and/or low temperature compressors in respective compressor sets.

[0030] The low-temperature freezing cabinet 42 may be similar to the medium-temperature refrigerating cabinet 43. Each cabinet 42, 43 (FIG. 4) comprises a product cabinet 61 and a refrigerating device area 62. The product cabinet 61 can be designed into a structure suitable for storage of foods and convenient for people to access, such as an open structure or a compartment structure having one or more doors 65. The refrigerating device area 62 is used for providing refrigerating air to the product cabinet 61. The refrigerating device area 62 includes an expansion device (e.g., valve) 63, heat absorption heat exchanger (e.g., evaporator) 64 and associated connecting pipes 44. A fan (not shown) may also be provided to drive an airflow across the evaporator 64 and through the product cabinet 61. The cabinets may be rooms of a building or separate display or storage cases.

[0031] The connection of the whole medium- and low-temperature integrated refrigerating/freezing system 40 is shown in Fig. 3, in which the outlet end 101 of the integrated unit 41 is connected to the inlet end of the low-temperature freezing cabinet 42 via the associated connecting pipes 44, the outlet end of the low- temperature freezing cabinet 42 is connected to the inlet end 102 of the of the integrated unit 41 via the connecting pipes 44. The outlet end 103 of the integrated unit 41 is connected to the inlet end of the medium- temperature refrigerating cabinet 43 via the associated connecting pipes 44, and the outlet end of the medium- temperature refrigerating cabinet 43 is connected to the inlet end 104 of the of the integrated unit 41 via the associated connecting pipes 44. The integrated unit 41 may be connected in a plug-and-play manner to the medium-temperature refrigerating cabinet 43 and the low-temperature freezing cabinet 42 to facilitate site installation and operation.

[0032] In the integrated system 41, the suction (inlet/intake/low pressure) end of the low-temperature compressor 52 is connected to the inlet end 102 of the of the integrated unit 41 via the associated connecting pipes 44, the suction end of the medium- temperature compressor 53 is connected to the inlet end 104 of the of the integrated unit 41 via the associated connecting pipes 44, thereby providing the respective connections of the medium- temperature compressor 53 and the low-temperature compressor 52 to the evaporators 64 within the medium-temperature refrigerating cabinet 43 and the low-temperature freezing cabinet 42. The exhaust (outlet/discharge/high pressure) end of the low-temperature compressor 52 merges with the exhaust end of the medium- temperature compressor 53 via the associated connecting pipes 44 and is connected to the inlet end of the condenser 54 via the associated connecting pipes 44. The outlet end of the condenser 54 is connected to the inlet end of the reservoir 55 via the connecting pipes 44.

[0033] The outlet end of the reservoir 55 is branched into three flow paths/branches (formed by associated components including the connecting pipes 44) 71, 72, and 73. In the flow path 71, the outlet end of the reservoir 55 is directly connected to the inlet end of the medium- temperature refrigerating cabinet 43 via the associated connecting pipes 44, thereby realizing connection of the outlet end of the reservoir 55 with the expansion valve 63 within the medium-temperature refrigerating cabinet 43. In the flow path 72, the outlet end of the reservoir 55 is connected with the first inlet end of the intermediate heat exchanger 56, and is connected with the inlet end of the low-temperature freezing cabinet via the associated connecting pipes 44 at the first outlet end of the intermediate heat exchanger 56, thereby realizing the connection of the outlet end of the reservoir 55 with the expansion valve 63 within the medium-temperature refrigerating cabinet 43 via the first branch/segment 75 of the intermediate heat exchanger 56. In the flow path 73, the outlet end of the reservoir 55 is connected to the inlet end of the expansion valve 57 via the associated connecting pipes 44, and is connected with the second inlet end of the intermediate heat exchanger 56 via the associated connecting pipes 44 at the outlet end of the expansion valve 57. The flow path 73 continues through the second branch/segment 76 of the intermediate heat exchanger 56. The second branch/segment 76 is in heat exchange relation with the first branch/segment 75. The second outlet end of the intermediate heat exchanger 56 is divided into two branches 431, 432. In the first branch 431 the second outlet end of the intermediate heat exchanger 56 merges with the outlet end of the refrigerating cabinet 43 via the associated connecting pipes 44 and is directly connected to the suction end of the medium-temperature compressor 53. In the second branch 432, the second outlet end of the intermediate heat exchanger 56 is first connected to the adjustment valve 58 via the associated connecting pipes 44, and then merges with the outlet end of the low-temperature freezing cabinet 42 via the connecting pipes 44 for connecting to the suction end of the low-temperature compressor 52.

[0034] When the system starts up, the low-temperature and low-pressure gaseous refrigerant flowing out of the outlet ends of the medium-temperature refrigerating cabinet 43 and the low-temperature freezing cabinet 42 flows into the medium-temperature compressor 53 and the low-temperature compressor 52 respectively, and they are compressed into high-temperature and high-pressure gas, and then merge together and flow together into the condenser 54. In the condenser 54, the high-temperature and high-pressure gaseous refrigerant becomes high- temperature and high-pressure liquid refrigerant after having released heat to the ambient and flows into the reservoir 55. In the flow path 71 at the outlet end of the reservoir 55, the high-temperature and high-pressure liquid refrigerant flows into the expansion valve 63 within the medium-temperature refrigerating cabinet 43 via the associated connecting pipes 44, changes into a low-temperature and low-pressure liquid after throttling and pressure decreasing through the expansion valve 63, flows through the coiled pipes in the evaporator 64 within the medium-temperature refrigerating cabinet 43 and exchanges heat with the air on the surface of the coiled pipes to generate medium-temperature cold air in order to transform the low-temperature and low-pressure liquid refrigerant into low-temperature and low-pressure gaseous refrigerant, and to flow back into the medium-temperature compressor 53, thus forming a circulating loop of the medium-temperature system. In the flow path 72, the high- temperature and high-pressure liquid refrigerant at the outlet end of the reservoir 55 flows through the intermediate heat exchanger 56. In the flow path 73, the high-temperature and high-pressure liquid refrigerant at the outlet end of the reservoir 55 is first changed into the low-temperature and low-pressure liquid refrigerant via pressure-deceasing throttling via the expansion valve, and then flows through the intermediate heat exchanger 56. The two refrigerant flows in the flow paths 72, 73 at different temperatures exchange heat in the intermediate heat exchanger 56. The high-temperature and high-pressure liquid refrigerant in the flow path 72 releases heat in the intermediate heat exchanger 56, making the high-temperature and high-pressure liquid refrigerant pre-cooled before flowing into the low-temperature freezing cabinet 42, thereby effectively adjusting the subcooling of the low-temperature freezing system so as to improve refrigerating effects and performance of the low-temperature freezing system. The pre-cooled refrigerant enters into the expansion valve 63 of the low-temperature freezing cabinet 42 for throttling to change into the low-temperature and low-pressure liquid refrigerant, flows into the coiled pipes within the evaporator 64 and exchanges heat with the ambient air to supply low-temperature cold air. The heat-absorbed gaseous refrigerant flows back into the low-temperature compressor 52 to form a circulating loop of the low-temperature freezing system. The low-temperature and low-pressure liquid refrigerant in the flow path 73 absorbs heat within the intermediate heat exchanger 56 to change into the low-temperature and low-pressure gaseous refrigerant. There are two branches 431 and 432 for the refrigerant flowing out of the intermediate heat exchanger 56. In the first branch 431 , the low- temperature and low-pressure gaseous refrigerant merges directly with the low-temperature and low-pressure gaseous refrigerant flowing out of the medium-temperature refrigerating cabinet 43 and flows into the medium-temperature compressor 53. In the second branch 432, the low-temperature and low-pressure gaseous refrigerant first flows through the adjustment valve 58, merges with the low-temperature and low-pressure gaseous refrigerant flowing out of the low-temperature freezing cabinet 42 and then flows into the low-temperature compressor 52, thereby effectively adjusting the suction temperature of the low-temperature compressor via the adjustment valve 58 and protecting the low-temperature compressor 42. Control may be automatic via a controller (e.g., an electronic control system such as a microcontroller) responsive to sensor (not shown) input and any user-set or user-input parameters or commands.

[0035] It is easily understood that the medium- and low-temperature integrated refrigerating/freezing system of the present invention comprises the integrated unit 41, the (group of) medium-temperature refrigerating cabinet(s) 42, the (group of) low-temperature freezing cabinet(s) 43 and the connecting pipes 44. In the integrated unit 41 the medium- and low-temperature freezing systems share one condenser 54 and the reservoir 55; the expansion valve 57, the intermediate heat exchanger 56 and the corresponding connecting pipes 44 form the subcooling adjusting mechanism of the low-temperature freezing system for adjusting subcooling of the low-temperature freezing system and improving the overall performance and the stability of the low-temperature freezing system; the expansion valve 57, the intermediate heat exchanger 56, the adjustment valve 58 and the corresponding connecting pipes 44 further form an suction temperature adjusting mechanism for the low-temperature freezing system for lowering the suction temperature of the low-temperature freezing system in order to better protect the low-temperature compressor 52.

[0036] By using such a medium- and low-temperature integrated refrigerating/freezing system, it can effectively reduce the installation space for the system, and the integrated unit can be directly installed outdoors, such as on a roof. The costs of the whole system are significantly less than that of two independent medium-temperature and low-temperature systems. The optimization of the pipelines within the integrated unit and the plug-and-play connection between the integrated unit and the medium-temperature and low-temperature freezing cabinets facilitate site installation and daily maintenance of the devices. The performance of the whole system, in particular of the low-temperature system, has very high stability.

[0037] Although an embodiment is described above in detail, such description is not intended for limiting the scope of the present disclosure. It will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, when implemented in the reengineering of an existing container configuration, details of the existing configuration may influence or dictate details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.

Claims

CLAIMSWhat is claimed is:

1. A medium- and low-temperature integrated refrigerating/freezing system (40) for providing refrigerating medium temperature for food storage, etc. and freezing-low temperature for cold drink storage, etc., which comprising an integrated unit (41), a (group of) medium-temperature refrigerating cabinet(s) (43), a (group of) low-temperature freezing cabinet(s) (42) and corresponding connecting pipes (44), wherein said integrated unit comprises: a common condenser (54) for condensing high-temperature and high-pressure gaseous refrigerant in the medium-temperature refrigerating system and the low-temperature freezing system; a common reservoir (55) for storing the high-temperature and high-pressure liquid refrigerant in the medium-temperature refrigerating system and the low-temperature freezing system; a subcooling adjusting mechanism (56, 57) for adjusting the subcooling in the low-temperature freezing system; and a suction temperature adjusting mechanism (431, 432, 58) for adjusting the suction temperature of the low- temperature freezing system.

2. The medium- and low-temperature integrated refrigerating/freezing system as claimed in claim 1 , wherein said integrated unit further comprises a (group of) medium-temperature compressor(s) (53) and a (group of) low-temperature compressor(s) (52).

3. The medium- and low-temperature integrated refrigerating/freezing system as claimed in claim 2, wherein said medium-temperature refrigerating cabinet(s) and said low-temperature freezing cabinet(s) comprise respectively an evaporator (64), an expansion valve (63) and a product cabinet (61) for food placement.

4. The medium- and low-temperature integrated refrigerating/freezing system as claimed in claim 3, wherein the suction end(s) of said medium-temperature compressor(s) and low-temperature compressor(s) are respectively connected to the evaporators of the medium-temperature refrigerating cabinet(s) and the low-temperature freezing cabinet(s), and the exhaust ends thereof are jointly connected to the inlet end of said common condenser.

5. The medium- and low-temperature integrated refrigerating/freezing system as claimed in claim 4, wherein the outlet end of the common condenser (54) is connected to the inlet end of the reservoir (55).

6. The medium- and low-temperature integrated refrigerating/freezing system as claimed in claim 5, wherein said expansion valve (57), said intermediate heat exchanger (56) and said corresponding connecting pipes in said integrated unit form said subcooling adjusting mechanism.

7. The medium- and low-temperature integrated refrigerating/freezing system as claimed in claim 6, wherein a first inlet end of the intermediate heat exchanger of said subcooling adjusting mechanism is directly connected to said reservoir, and a second inlet end is connected to said reservoir via said expansion valve.

8. The medium- and low-temperature integrated refrigerating/freezing system as claimed in claim 7, wherein a first outlet end of said intermediate heat exchanger is connected to an inlet end of said low-temperature freezing cabinet.

9. The medium- and low-temperature integrated refrigerating/freezing system as claimed in claim 8, wherein said suction temperature adjusting mechanism comprises a first branch (431) connecting a second outlet end of said intermediate heat exchanger (56) with the suction end of said medium-temperature compressor (53), and a second branch (432) connecting the second outlet end of said intermediate heat exchanger with the suction end of said low-temperature (52) compressor, wherein said second branch contains an adjustment valve (58).

10. The medium- and low-temperature integrated refrigerating/freezing system as claimed in claim 1 , wherein the integrated unit is connected to said medium-temperature refrigerating cabinet and said low-temperature freezing cabinet in a plug-and-play manner.

11. A refrigerating system (40) comprising: at least one medium-temperature refrigerating device (43) comprising at least one medium-temperature evaporator; at least one low-temperature freezing device (42) comprising at least one low-temperature evaporator; and an integrated unit (41) comprising: at least one medium-temperature compressor (53) connected to said medium-temperature evaporator; at least one low-temperature compressor (52) connected to said low-temperature evaporator; a condenser (54) connected to the exhaust ends of said at least one medium-temperature compressor and the at least one low-temperature compressor, for condensing the high-temperature and high-pressure gaseous refrigerant exhausted from the exhaust ends of said at least one medium-temperature compressor and the at least one low-temperature compressor; a reservoir (55) connected to said condenser for storing the high-temperature and high-pressure liquid refrigerant exhausted from the condenser; a subcooling adjusting mechanism (56, 57) connected with said reservoir and to said low-temperature evaporator for adjusting the subcooling of a low-temperature freezing circulation system; a suction temperature adjusting mechanism (431 , 432, 58) connected with said reservoir and respectively to said low-temperature compressor and said medium-temperature compressor, for adjusting the suction temperature of the low-temperature freezing circulation system; and a medium-temperature connecting pipeline (71) connected to said reservoir and the medium-temperature evaporator.

12. The refrigerating system as claimed in claim 11 , wherein said subcooling adjusting mechanism comprises an intermediate heat exchanger (56) connected to said low-temperature evaporator, a first inlet end thereof is directly connected to said reservoir, and a second inlet end thereof is connected to said reservoir via an expansion valve.

13. The refrigerating system as claimed in claim 12, wherein a first outlet end of said intermediate heat exchanger is connected to the low-temperature evaporator of said low-temperature freezing device.

14. The refrigerating system as claimed in claim 13, wherein said suction temperature adjusting mechanism comprises a first branch connecting the second outlet end of said intermediate heat exchanger with the suction end of said medium-temperature compressor, and a second branch connecting the second outlet end of said intermediate heat exchanger with the suction end of said low-temperature compressor, wherein said second branch contains an adjustment valve.

15. A refrigeration system (40) comprising: a first compartment (42); a second compartment (43); at least one compressor (52, 53) for compressing refrigerant; a condenser (54) for condensing compressed refrigerant from the at least one compressor; a reservoir for storing condensed refrigerant; a first expansion device and a first evaporator in a flow path associated with the first compartment (72) for expanding refrigerant and cooling the first compartment; and a second expansion device and second evaporator in a flow path (71) associated with the second compartment for expanding the condensed refrigerant and cooling the second compartment, further characterized by: means (56, 57, 58, 431, 432) for adjusting a degree of overcooling and adjusting a suction temperature of refrigerant associated with the first compartment.

16. The system of claim 15 wherein: the condenser (54) and the reservoir (55) are common to the flow path (72) associated with the first compartment and the flow path (71) associated with the second compartment.

17. A method for operating the system of claim 15, comprising: under automated control, using said means for adjusting to adjust the degree of subcooling and the suction temperature of refrigerant associated with the first compartment.