Cascade refrigeration system

Abstract

The utility model discloses a cascade refrigerating system which comprises a high-temperature-stage refrigerating unit and a low-temperature-stage refrigerating unit. The high-temperature-stage refrigerating unit comprises a high-temperature-stage compressor, a high-temperature-stage condenser and a cascade heat exchanger serving as a high-temperature-stage evaporator. The low-temperature-stage refrigerating unit comprises a low-temperature-stage compressor, a low-temperature-stage evaporator and the cascade heat exchanger serving as a low-temperature-stage condenser in the low-temperature-stage refrigerating unit. A pre-cooling heat exchanger is arranged on a pipeline between the low-temperature-stage compressor and the cascade heat exchanger and arranged on one side of the high-temperature-stage condenser, and the pre-cooling heat exchanger and the high-temperature-stage condenser share a condensation fan. High-temperature and high-pressure gas exhausted by the low-temperature-stage compressor is primarily cooled through the pre-cooling assembly and then is further cooled through the cascade heat exchanger, and the refrigerating capacity of the high-temperature-stage compressor is effectively reduced.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of cascade refrigeration system, especially to a cascade refrigeration system that can improve energy efficiency. BACKGROUND

[0002] Cascade refrigeration system is a kind of high-efficiency refrigeration system, mainly used to realize the refrigeration demand of ultra-low temperature environment, such as in chemical industry, medicine, biological sample preservation and gas liquefaction etc. It realizes extremely low evaporation temperature by the combination of multiple refrigeration cycles, and the characteristics of different working medium in different temperature intervals are brought to the extreme.

[0003] Cascade refrigeration system is usually composed of two or more independent refrigeration circuits, and these circuits are connected with each other through a heat exchanger (usually called cascade heat exchanger, intermediate heat exchanger).

[0004] Typical cascade refrigeration system is divided into high-temperature level circuit and low-temperature level circuit. The main function of high-temperature level circuit is to absorb heat from the evaporator of low-temperature level circuit and discharge it to the environment. High-temperature level circuit includes high-temperature compressor, high-temperature condenser (condensing high-temperature level working medium), high-temperature expansion valve and high-temperature evaporator (acting as cascade heat exchanger of low-temperature level circuit).

[0005] The main function of low-temperature level circuit is to provide extremely low evaporation temperature to meet the final refrigeration demand. Low-temperature level circuit includes low-temperature compressor, low-temperature condenser (i.e. cascade heat exchanger, cascading with high-temperature evaporator), low-temperature expansion valve and low-temperature evaporator (directly absorbing heat of the cooled object).

[0006] Cascade heat exchanger is the core component connecting high-temperature level and low-temperature level circuits, which is both the evaporator of high-temperature circuit and the condenser of low-temperature circuit. Therefore, the heat exchange efficiency of cascade heat exchanger directly determines the performance of cascade refrigeration system.

[0007] Therefore, how to provide a cascade refrigeration system with higher energy efficiency is a technical problem to be solved. UTILITY MODEL CONTENT

[0008] The utility model discloses a cascade refrigeration system to solve the technical problem that the performance of the cascade refrigeration system in the prior art depends entirely on the cascade heat exchanger.

[0009] The cascade refrigeration system provided by the utility model includes high-temperature level refrigeration unit and low-temperature level refrigeration unit.

[0010] The high-temperature level refrigeration unit includes high-temperature level compressor, high-temperature level condenser and cascade heat exchanger as high-temperature level evaporator.

[0011] The low-temperature stage compressor, the low-temperature stage evaporator, and the cascade heat exchanger serving as a low-temperature stage condenser of the low-temperature stage refrigeration unit;

[0012] A precooling heat exchanger is arranged on a pipeline between the low-temperature stage compressor and the cascade heat exchanger, and the precooling heat exchanger is arranged on the high-temperature stage condenser side and shares a condensing fan with the high-temperature stage condenser.

[0013] Further, the distance between the condensing fan and the precooling heat exchanger is less than the distance between the condensing fan and the high-temperature stage condenser.

[0014] Further, the cascade refrigeration system comprises a timer for timing the shutdown duration of the low-temperature stage compressor, and the control module of the cascade refrigeration system receives the signal of the timer when the set temperature is greater than the preset temperature and sends a shutdown instruction to the condensing fan.

[0015] Further, the condensing fan has at least one high gear and at least one low gear.

[0016] Further, the high-temperature stage condenser has a heat dissipation fan and a condensing temperature sensor for detecting the condensing temperature of the high-temperature stage condenser, and the control module of the cascade refrigeration system controls the heat dissipation fan to start and stop when receiving different detection signals of the condensing temperature sensor.

[0017] Further, a filter and a throttling device are arranged between the high-temperature stage condenser and the cascade heat exchanger.

[0018] Further, a filter and a throttling device are arranged between the cascade heat exchanger and the low-temperature stage evaporator.

[0019] Further, the throttling device is a capillary tube.

[0020] Further, a pressure switch is arranged between the precooling heat exchanger and the cascade heat exchanger.

[0021] The precooling assembly further improves the performance of the cascade refrigeration system, and avoids that the cascade refrigeration system simply relies on the heat exchange efficiency of the cascade heat exchanger. BRIEF DESCRIPTION OF DRAWINGS

[0022] The utility model will be described in detail below in combination with embodiments and drawings, in which:

[0023] Figure 1 is the system structure schematic diagram of one embodiment of the utility model.

[0024] Figure 2 is a system structure schematic diagram of another embodiment of the utility model.

[0025] Figure 3 is a condensing fan control flow chart of an embodiment of the utility model.

[0026] Figure 4 is a refrigerant flow direction schematic diagram of another embodiment of the utility model.

[0027] Mark explanation:

[0028] 1, high temperature level compressor;2, high temperature level condenser;3, complex superimposed heat exchanger;4, gas-liquid separator;5, condensing fan;6, high temperature level throttling device;7, high temperature level filter;8, low temperature level compressor;9, precooling assembly;10, low temperature level evaporator;11, low temperature level throttling device;12, low temperature level filter;13, pressure switch. Specific implementation

[0029] In order to make the technical problem, technical scheme and beneficial effect of the utility model to be solved more clear and obvious, the utility model is further described in detail below by combining with the drawings and examples.It should be understood that the specific examples described here are only used to explain the utility model, and are not used to limit the utility model.

[0030] Therefore, one feature indicated in the specification will be used to explain one feature of one embodiment of the utility model, and it is not suggested that each embodiment of the utility model must have the explained feature.In addition, it should be noted that the specification describes many features.Although certain features can be combined together to show possible system design, these features can also be used in other combinations which are not explicitly explained.Therefore, unless otherwise explained, the explained combination is not intended to limit.

[0031] The utility model proposes a new complex superimposed refrigeration system in view of the problem that the performance of complex superimposed refrigeration system completely depends on complex superimposed heat exchanger.

[0032] As shown in Figure 1 The utility model discloses complex superimposed refrigeration system, including high temperature level refrigerating unit and low temperature level refrigerating unit.

[0033] High temperature level refrigerating unit includes high temperature level compressor 1, high temperature level condenser 2, complex superimposed heat exchanger 3 as high temperature level evaporator, gas-liquid separator 4 arranged before the suction port of high temperature level compressor 1, and condensing fan 5 arranged at high temperature level condenser 2.

[0034] Low temperature level refrigerating unit includes low temperature level compressor 8, low temperature level evaporator 10 and the above-mentioned complex superimposed heat exchanger 3 as low temperature level condenser in low temperature level refrigerating unit.

[0035] A pre-cooling assembly 9 (pre-cooling heat exchanger) is arranged on the pipeline between the low-temperature stage compressor 8 and the above-mentioned cascade heat exchanger, and the pre-cooling assembly 9 is arranged on the side of the high-temperature stage condenser 2 and shares the condensing fan 5 with the high-temperature stage condenser 2.

[0036] The pre-cooling assembly is added in the low-temperature stage refrigerating unit, and the pre-cooling assembly is arranged together with the high-temperature stage condenser, the high-temperature and high-pressure gas discharged by the low-temperature stage compressor can be preliminarily cooled through the pre-cooling assembly, and then further cooled through the cascade heat exchanger, so that the refrigerating capacity of the high-temperature stage compressor is reduced, and the performance of the whole cascade refrigerating system is improved.

[0037] As shown in FIG. Figure 2 In a preferred embodiment, the distance between the condensing fan and the pre-cooling heat exchanger is less than the distance between the condensing fan and the high-temperature stage condenser.

[0038] The pre-cooling assembly of the low-temperature stage refrigerating unit is close to the condensing fan, the condensing fan can simultaneously dissipate heat for the high-temperature stage condenser and the low-temperature stage pre-cooling assembly, so that the high-temperature and high-pressure gas discharged by the low-temperature stage compressor can be better preliminarily cooled through the pre-cooling assembly, and then further cooled through the cascade heat exchanger, thereby effectively reducing the refrigerating capacity of the high-temperature stage compressor.

[0039] In an embodiment, the cascade refrigerating system of the utility model comprises a timer for timing the shutdown duration of the low-temperature stage compressor, and the control module of the cascade refrigerating system receives the signal of the timer when the set temperature is greater than the preset temperature, and sends a shutdown instruction to the condensing fan.

[0040] When the cascade refrigerating system is started, the condensing fan is generally in an open state, but when the set temperature is greater than the preset temperature, that is, the refrigeration requirement is not so high, the condensing fan can also be controlled to be shut down when the shutdown duration of the low-temperature stage compressor reaches a certain duration, thereby improving the energy efficiency of the system.

[0041] In an embodiment, the condensing fan has at least one high gear and at least one low gear. Those skilled in the art can select the corresponding high gear and low gear by setting the temperature and the condensing temperature of the high-temperature stage condenser as a reference, so as to meet the refrigeration requirement and save energy consumption.

[0042] Figure 3 An embodiment is shown for adjusting by setting the temperature and the condensing temperature of the high-temperature stage condenser, in which the condensing fan has two gears, one of which is a high gear and the other of which is a low gear.

[0043] When the set temperature minus the indoor temperature is greater than or equal to 5 degrees Celsius, the condensing fan operates at a high gear.

[0044] If the set temperature minus the temperature in the tank is less than 5 degrees Celsius, further determination of the condensing temperature of the high-temperature stage condenser is needed. If the condensing temperature of the high-temperature stage condenser is greater than or equal to 40 degrees Celsius, the condensing fan is still operated at the high gear. If the condensing temperature of the high-temperature stage condenser is less than 40 degrees Celsius, it is determined whether the condensing temperature of the high-temperature stage condenser is less than or equal to 38 degrees Celsius. If yes, the condensing fan is operated at the low gear. If the condensing temperature of the high-temperature stage condenser is greater than 38 degrees Celsius, that is, the condensing temperature of the high-temperature stage condenser is in the interval range of (38, 40), the gear of the condensing level is kept unchanged at this time.

[0045] When the condensing fan is operated at the low gear, if the set temperature is greater than the preset temperature and the low-temperature stage compressor has been stopped for 2 minutes, the condensing fan is stopped.

[0046] The specific temperatures, times, etc. in this embodiment are only examples and do not limit the protection scope of the utility model. Those skilled in the art can adjust them according to needs.

[0047] In one embodiment, the high-temperature stage condenser has a heat dissipation fan and a condensing temperature sensor for detecting the condensing temperature of the high-temperature stage condenser.

[0048] The control module of the cascade refrigeration system controls the heat dissipation fan to start and stop when receiving different detection signals of the condensing temperature sensor.

[0049] For example, when the condensing temperature of the high-temperature stage condenser is greater than a condensing threshold, the heat dissipation fan is controlled to start, and when the condensing temperature of the high-temperature stage condenser is less than or equal to a condensing threshold, the heat dissipation fan is controlled to stop.

[0050] In one embodiment, a filter and a throttling device are arranged between the high-temperature stage condenser and the cascade heat exchanger.

[0051] In one embodiment, a filter and a throttling device are arranged between the cascade heat exchanger and the low-temperature stage evaporator.

[0052] The throttling device in the above embodiment can be a capillary tube or other throttling devices such as an electronic expansion valve.

[0053] The filter is usually installed in front of the cascade heat exchanger of the low-temperature stage refrigeration unit and the high-temperature stage refrigeration unit, and is used to filter impurities in the refrigerant to ensure the cleanliness and normal operation of the system pipeline and core components. For example, before the working medium of the low-temperature stage condenser flows to the cascade heat exchanger, the filter can capture solid particles in the working medium to prevent these particles from entering the cascade heat exchanger and causing blockage or reducing the heat exchange efficiency.

[0054] In one embodiment, a pressure switch is arranged between the precooling heat exchanger and the cascade heat exchanger.

[0055] The pressure switch is a pressure monitoring and protection device that detects the pressure of the low-temperature stage circuit and activates a protection mechanism in abnormal situations. If the pressure of the low-temperature stage refrigeration unit is too high (such as an abnormally high condensing pressure) or too low (such as insufficient working medium or excessive throttling), the pressure switch will cut off the compressor circuit to prevent the low-temperature stage compressor from being damaged by overloading or dry running. For example, if the low-temperature stage condensing pressure (the pressure in the cascade heat exchanger) exceeds the set value, the pressure switch will stop the low-temperature compressor from running to protect the cascade heat exchanger and other components from damage caused by excessive pressure.

[0056] As shown in Figure 4 The refrigerant circulation process of the cascade refrigeration system of the utility model is as follows.

[0057] Figure 4 In the high-temperature stage refrigeration unit, a high-temperature stage compressor 1, a high-temperature stage condenser 2, a high-temperature stage filter 7, a high-temperature stage throttling device 6, a cascade heat exchanger 3, and a gas-liquid separator 4 are provided on the circulation loop.

[0058] In the low-temperature stage refrigeration unit, a low-temperature stage compressor 8, a pre-cooling component 9, a pressure switch 13, a cascade heat exchanger 3, a low-temperature stage filter 12, a low-temperature stage throttling device 11, and a low-temperature stage evaporator 10 are provided on the circulation loop.

[0059] The refrigerant circulation process of the high-temperature stage refrigeration unit is as follows.

[0060] The high-temperature stage compressor compresses the low-pressure high-temperature stage refrigerant gas into a high-pressure high-temperature gas. The high-pressure high-temperature gas exchanges heat with the environment air or cooling water through the high-temperature stage condenser, releases heat, and condenses into a high-pressure liquid. The high-pressure liquid is throttled and reduced in pressure by the throttling device and then enters the cascade heat exchanger. In the cascade heat exchanger, the refrigerant in the high-temperature stage circuit absorbs the heat released by the refrigerant in the low-temperature stage circuit, evaporates into a low-pressure gas, and returns to the high-temperature stage compressor.

[0061] The refrigerant circulation process of the low-temperature stage refrigeration unit is as follows.

[0062] The low-temperature stage compressor compresses the low-pressure low-temperature stage refrigerant gas into a high-pressure high-temperature gas. The high-pressure high-temperature gas is pre-cooled in the pre-cooling component and then enters the cascade heat exchanger to exchange heat with the evaporated refrigerant in the high-temperature stage circuit, releases heat, and condenses into a high-pressure liquid. The high-pressure liquid is throttled and reduced in pressure by the throttling device and then enters the low-temperature stage evaporator. In the low-temperature stage evaporator, the low-temperature stage refrigerant absorbs the heat of the cooled object, evaporates into a low-pressure gas, and returns to the low-temperature stage compressor.

[0063] The principle of the cascade refrigeration system is based on the Carnot cycle and heat exchange of two refrigeration cycles. The high-temperature stage refrigeration unit is responsible for working in a higher temperature range to provide a condensing environment for the low-temperature stage refrigeration unit; the low-temperature stage refrigeration unit is operated in a lower temperature range to directly provide refrigeration for the final load.

[0064] The heat flow path of the cascade refrigeration system is: heat of the cooled object→low-temperature stage evaporator→low-temperature stage compressor→low-temperature stage condenser (cascade heat exchanger)→high-temperature stage evaporator→high-temperature stage compressor→high-temperature stage condenser→environment.

[0065] The cascade heat exchanger is the core component of the entire system, which takes away the heat of the low-temperature stage refrigerant through the high-temperature stage refrigerant, and realizes heat transfer and cascade operation of the two independent refrigeration cycles.

[0066] The cascade operation mode of the cascade refrigeration system enables the system to select refrigerants with optimal thermodynamic characteristics in different evaporation temperature and condensation temperature ranges, greatly improving the overall system energy efficiency ratio (COP).

[0067] In the description of the utility model, it is understood that the orientation words such as "front, back, up, down, left, right", "transverse, vertical, perpendicular, horizontal" and "top, bottom" and the like indicated orientation or position relationship usually based on the orientation or position relationship shown in the drawings, just for the convenience of describing the utility model and simplifying the description, in the absence of the opposite statement, these orientation words do not indicate and imply that the indicated device or element must have a particular orientation or be constructed and operated in a particular orientation, therefore it can not be understood as the limitation of the protection scope of the utility model. The orientation words "inner, outer" refer to the inner and outer of the contour of each component itself.

[0068] For the convenience of description, spatial relative terms such as "on", "above", "upper surface", "upper" and the like can be used here to describe the spatial position relationship of one device or feature with other devices or features as shown in the drawings. It should be understood that the spatial relative terms are intended to include different orientations in use or operation in addition to the orientation of the device described in the drawings. For example, if the device in the drawing is inverted, the device described as "above" or "on" other devices or structures will be positioned "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below" orientations. The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used here are interpreted accordingly.

[0069] In addition, it needs to be explained that the use of "first", "second" and the like to limit the parts, only for the convenience of the corresponding parts for the distinction, such as no further declaration, the above words have no special meaning, therefore can not be understood as the limit of the scope of the utility model.

[0070] Unless specifically stated otherwise, the relative arrangement of components and steps, numerical expressions, and values stated in these embodiments do not limit the scope of the utility model. At the same time, it should be understood that in order to facilitate the description, the size of each part shown in the drawings is not drawn according to the actual proportional relationship. The technology, method and equipment known to those skilled in the related art can not be discussed in detail, but under appropriate circumstances, the technology, method and equipment should be regarded as part of the authorized description. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary, not as a limitation. Therefore, other examples of exemplary embodiments can have different values. It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0071] The above is only the preferred embodiment of the utility model, and does not limit the utility model, any modification, equivalent replacement and improvement within the spirit and principle of the utility model should be included in the protection scope of the utility model.

Claims

1. A cascade refrigeration system characterized by, The high-temperature stage refrigeration unit and the low-temperature stage refrigeration unit; The high-temperature stage refrigeration unit comprises a high-temperature stage compressor, a high-temperature stage condenser, and a cascade heat exchanger as a high-temperature stage evaporator; The low-temperature stage refrigeration unit comprises a low-temperature stage compressor, a low-temperature stage evaporator, and the cascade heat exchanger as a low-temperature stage condenser; A precooling heat exchanger is arranged between the low-temperature stage compressor and the cascade heat exchanger, and the precooling heat exchanger is arranged on the side of the high-temperature stage condenser and shares a condensing fan with the high-temperature stage condenser.

2. The cascade refrigeration system of claim 1, wherein, The distance between the condensing fan and the precooling heat exchanger is less than the distance between the condensing fan and the high-temperature stage condenser.

3. The cascade refrigeration system of claim 1, wherein, The cascade refrigeration system comprises a timer for timing the length of time when the low-temperature stage compressor is stopped, and the control module of the cascade refrigeration system receives the signal of the timer when the set temperature is greater than the preset temperature and sends a stop command to the condensing fan.

4. The cascade refrigeration system of claim 1, wherein, The condensing fan has at least one high gear and at least one low gear.

5. The cascade refrigeration system of claim 1, wherein, The high-temperature stage condenser has a cooling fan and a condensing temperature sensor for detecting the condensing temperature of the high-temperature stage condenser, and the control module of the cascade refrigeration system controls the cooling fan to start and stop when receiving different detection signals of the condensing temperature sensor.

6. The cascade refrigeration system of claim 1, wherein, A filter and a throttling device are arranged between the high-temperature stage condenser and the cascade heat exchanger.

7. The cascade refrigeration system of claim 1, wherein, A filter and a throttling device are arranged between the cascade heat exchanger and the low-temperature stage evaporator.

8. The cascade refrigeration system of claim 6 or 7, wherein, The throttling device is a capillary tube.

9. The cascade refrigeration system of claim 1, wherein, A pressure switch is arranged between the precooling heat exchanger and the cascade heat exchanger.

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