An air conditioning unit using a low-GWP, weakly flammable refrigerant

Abstract

This invention provides an air conditioning unit using a low-GWP, weakly flammable refrigerant, comprising an indoor cavity and an outdoor cavity. The outdoor cavity houses a compressor and a condenser, while the indoor cavity houses an evaporator. The indoor and outdoor cavities are arranged side-by-side. The compressor, condenser, and evaporator are sealed together via piping to form a refrigeration circuit. This refrigeration circuit is filled with a unidirectionally flowing low-GWP, weakly flammable refrigerant. The compressor is located on the side of the outdoor cavity closest to the indoor cavity, and the evaporator is located on the side of the indoor cavity closest to the outdoor cavity. A heating element, which independently executes the air conditioning unit's heating mode, is located on the side of the indoor cavity furthest from the compressor. This invention provides an air conditioning unit using a low-GWP, weakly flammable refrigerant. By filling a closed refrigeration circuit with this refrigerant, unidirectional flow refrigeration is achieved, and the heating element provides heating. The use of a microchannel condenser reduces the refrigerant charge, lowers costs, and reduces energy consumption.

Description

Technical Field

[0001] This utility model relates to the field of air conditioning unit technology, and in particular to an air conditioning unit using a low-GWP, weakly flammable refrigerant. Background Technology

[0002] With the ecological impact of global warming, the European Union has banned the use of refrigerant R134a in newly approved vehicles since January 1, 2013. Greenhouse gas emissions are to be reduced to 40% by 2030, and emissions of fluorinated greenhouse gases need to be reduced by 90% by 2050 compared to 2015. Therefore, the use of low-GWP refrigerants in tram air conditioning units is imperative.

[0003] For air conditioning units with the same cooling capacity, traditional air conditioning units require more than 30% higher refrigerant charge than the standard recommended charge. Since the refrigerant charge cannot be reduced further, secondary heat exchange technology is needed, leading to a significant increase in cost and energy consumption.

[0004] The air conditioning unit involved in this utility model can effectively solve the above-mentioned defects while meeting environmental protection requirements. Utility Model Content

[0005] To address the problems existing in the prior art, this utility model provides an air conditioning unit that uses a low-GWP, weakly flammable refrigerant. By charging a low-GWP, weakly flammable refrigerant into a closed refrigeration circuit, unidirectional flow refrigeration is achieved, and heating elements provide heating, thereby reducing costs and energy consumption and improving the environmental friendliness of the product.

[0006] To solve the above-mentioned technical problems, this utility model provides an air conditioning unit using a low-GWP, weakly flammable refrigerant, employing the following technical solution:

[0007] An air conditioning unit using a low-GWP weakly flammable refrigerant includes an indoor cavity and an outdoor cavity. The outdoor cavity is equipped with a compressor and a condenser, and the indoor cavity is equipped with an evaporator. The indoor cavity and the outdoor cavity are arranged side by side. The compressor, condenser and evaporator are sealed and connected by a pipeline to form a refrigeration circuit. The refrigeration circuit is filled with a unidirectionally flowing low-GWP weakly flammable refrigerant.

[0008] The compressor is located on the side of the outdoor cavity closer to the indoor cavity, and the evaporator is located on the side of the indoor cavity closer to the outdoor cavity;

[0009] A heating element that independently executes the air conditioning unit's heating mode is provided on the side of the indoor cavity away from the compressor.

[0010] Furthermore, the indoor cavity is located above the air inlet.

[0011] Furthermore, the condenser is a microchannel heat exchanger with a flat tube structure, and the equivalent diameter of the microchannel is in the range of 10-1000 μm.

[0012] Furthermore, there are at least two sets of condensers, arranged parallel to each other on both sides of the compressor.

[0013] Furthermore, an indoor fan is also provided inside the indoor cavity, and the evaporator, heating element, and indoor fan are arranged parallel to each other in the indoor cavity.

[0014] Furthermore, the evaporator has a copper tube and aluminum fin structure, including multiple pipes, each with a length ranging from 3 to 10 meters.

[0015] Furthermore, the length of each pipe in the evaporator is less than or equal to 5m.

[0016] Furthermore, it also includes an electrical control box, which is located at the return air vent on the indoor cavity side.

[0017] Furthermore, the electrical control box is equipped with an arc-extinguishing device.

[0018] Furthermore, the heating element includes at least two separately controllable heating circuits, each of which is equipped with a PTC electric heater;

[0019] Alternatively, each heating circuit may have at least two PTC electric heaters connected in parallel, and the heating power of each PTC electric heater may be controlled separately.

[0020] In summary, the air conditioning unit with low GWP and weakly flammable refrigerant provided by this utility model has the following advantages compared with the prior art:

[0021] Reduce the refrigerant charge in the following ways:

[0022] 1. Microchannel condensers consist of flat tubes with an equivalent diameter of 10-1000μm, resulting in high heat exchange efficiency and a smaller internal volume. Compared with traditional tube-fin condensers, the refrigerant capacity of the condenser can be reduced by 20%-50%.

[0023] 2. The refrigerant pressure drop of the copper tube aluminum fin evaporator is limited to within 30 kPa, including multiple pipelines, each with a length of 3-10 m. In this project, the length of each pipeline is controlled within 5 m, reducing the refrigerant charge by 5%-10%.

[0024] 3. By rationally arranging components, the length of the refrigerant pipeline can be reduced, and unnecessary refrigeration components, such as liquid receivers and gas-liquid separators, can be eliminated, thereby reducing the refrigerant charge by 5%-15%.

[0025] 4. While meeting noise requirements, appropriately increase the air supply volume and condensing air volume, and reduce the heat exchange area of ​​the evaporator and microchannel condenser. Increase the air supply volume by 8-15% and the condensing air volume by 10%-30%.

[0026] Through the above methods, the refrigerant charge is significantly reduced by more than 30%, meeting the refrigerant charge limit required by the EN378 standard, and greatly reducing the manufacturing cost of the unit.

[0027] By using the following components and appropriate control logic, the temperature inside the refrigerant is reduced to prevent it from exceeding the refrigerant's ignition point, thus improving safety:

[0028] Circuit breakers, contactors, and other components are all integrated into the electrical control box. The contactors and other components are equipped with arc-extinguishing devices, and the electrical control box has an IP66 protection rating.

[0029] By employing the above methods, the source of ignition is prevented from being generated, and the indoor temperature is reduced, greatly improving the safety of the air conditioning unit.

[0030] The specific embodiments of this utility model will be described in further detail below with reference to the accompanying drawings. Attached Figure Description

[0031] The accompanying drawings, as part of this utility model, are used to provide a further understanding of the present utility model. The illustrative embodiments and descriptions of the present utility model are used to explain the present utility model, but do not constitute an undue limitation of the present utility model. Obviously, the drawings described below are merely some embodiments; those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0032] In the attached diagram:

[0033] Figure 1 This is a schematic diagram of the layout structure of the air conditioning unit of this utility model;

[0034] Figure 2 This is a schematic diagram of the control logic of the air conditioning unit of this utility model;

[0035] In the picture:

[0036] 1. Housing; 2. Outdoor fan; 3. Compressor; 4. Electrical control box; 5. Evaporator; 6. PTC electric heater; 7. Indoor fan; 8. Fresh air filter; 9. Fresh air valve; 10. Mixing air filter; 11. Microchannel condenser; 12. Return air temperature sensor.

[0037] It should be noted that the accompanying drawings and text description are not intended to limit the scope of the present invention in any way, but rather to illustrate the concept of the present invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate this utility model, but are not intended to limit the scope of this utility model.

[0039] In the description of this utility model, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0040] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0041] This utility model provides an air conditioning unit using a low-GWP weakly flammable refrigerant, including an indoor cavity and an outdoor cavity. The outdoor cavity is equipped with a compressor 3 and a condenser, and the indoor cavity is equipped with an evaporator 5. The indoor cavity and the outdoor cavity are arranged in parallel. The compressor 3, the condenser and the evaporator 5 are connected by a sealed pipeline to form a refrigeration circuit. The refrigeration circuit is filled with a unidirectionally flowing low-GWP weakly flammable refrigerant.

[0042] The compressor 3 is located on the outdoor cavity side near the indoor cavity, and the evaporator 5 is located on the indoor cavity side near the outdoor cavity.

[0043] A heating element that independently executes the air conditioning unit's heating mode is installed on the side of the indoor cavity away from the compressor 3.

[0044] This utility model provides an air conditioning unit using a low-GWP, weakly flammable refrigerant, comprising a housing 1, wherein the housing 1 is divided into an indoor cavity and an outdoor cavity by a partition, such as... Figure 1As shown, in this embodiment, the indoor and outdoor cavities are an integrated structure, separated internally by a partition, and arranged parallel to each other. The housing 1 houses a compressor 3, an evaporator 5, and a condenser, all connected in a fully enclosed manner via refrigeration piping. In this embodiment, the condenser is a microchannel condenser 11. The compressor 3, microchannel condenser 11, and evaporator 5 are welded together by copper pipes (refrigeration piping). This fully sealed connection eliminates the risk of leakage in the entire refrigeration circuit, avoiding the risk of refrigerant leakage and combustion in high-temperature or heating modes.

[0045] The compressor 3 and condenser are located inside the outdoor cavity. An outdoor fan 2 is installed on the top wall of the outdoor cavity (the side wall that communicates with the outside) to provide ventilation and heat dissipation for the compressor 3 and condenser. The compressor 3 is located near the partition in the outdoor cavity, meaning it is located on the same side of the outdoor cavity as it is near the indoor cavity. There are at least two sets of condensers, arranged parallel to each other on both sides of the compressor 3. The refrigerant inlets of the two condensers are close to the compressor 3 to reduce the number of connecting pipes between the compressor 3 and the condenser.

[0046] Evaporator 5 is installed inside the indoor cavity, which is connected to the outside. It supplies heat-exchanged air to the inside and regulates the indoor temperature. Preferably, evaporator 5 is located above the indoor air inlet. On the side of evaporator 5, preferably away from the outdoor cavity, an indoor fan 7 is installed. The air outlet of the indoor cavity (air conditioning unit) is located below the indoor fan 7. The heat-exchanged air is directly supplied to the indoor (car compartment) through the air outlet to regulate the indoor temperature and achieve indoor temperature comfort.

[0047] The indoor air supply outlet is set on any side wall of the indoor cavity. A fresh air inlet is provided at the fresh air inlet, and a fresh air filter 8 and a fresh air valve 9 are provided at the fresh air inlet. The outside fresh air entering from the fresh air inlet enters the static pressure chamber (not shown in the figure), mixes with the indoor return air, is filtered by the mixing air filter 10, passes through the evaporator 5, and is sent into the room by the indoor fan 7.

[0048] The refrigeration circuit includes components such as compressor 3, microchannel condenser 11, and evaporator 5, which are connected together by copper pipe welding. Refrigerant R1234yf flows unidirectionally through the refrigeration circuit and its components, exchanging heat through forced convection with the indoor fan 7 and outdoor fan 2 to achieve the cooling function of the air conditioning unit and provide cool air to the vehicle interior. In this application, the refrigeration circuit is a fully enclosed system, greatly reducing the risk of refrigerant leakage.

[0049] The refrigeration circuit includes two or more independent refrigeration systems, with at least one refrigeration system serving as a backup system. When any system fails, the other system can continue to operate normally, thus achieving redundancy design.

[0050] In this embodiment, the refrigeration circuit is charged with R1234yf refrigerant, and the refrigerant charge is reduced through the following technical solution, thereby reducing the cost and improving refrigeration efficiency:

[0051] The microchannel condenser 11 has a flat tube structure, composed of flat tubes with an equivalent diameter of 10-1000μm. It has high heat exchange efficiency and a smaller internal volume of heat exchanger. Compared with the traditional tube-fin type, the refrigerant capacity of the condenser can be reduced by 20%-50%. The equivalent diameter of the flat tubes of the microchannel condenser 1111 is determined according to the rated power of the air conditioning unit.

[0052] Evaporator 5 adopts a copper tube aluminum fin evaporator, and the refrigerant pressure drop is limited to within 30 kPa during the operation of the air conditioning unit. The copper tubes are bent to form multiple parallel pipes, and the length of each pipe can be selected from 3 to 10 m. Similarly, the length of each pipe is determined according to the rated power of the air conditioning unit and the internal volume of the indoor cavity. In this embodiment, the length of each pipe is controlled within 5 m, that is, the pipe length is less than or equal to 5 m, which can reduce the refrigerant charge by 5%-10% compared with evaporators with longer pipe lengths.

[0053] By rationally arranging components, the length of connecting pipes can be reduced, thereby improving cooling efficiency. For example... Figure 1 As shown, there are two sets of microchannel condensers 11, which are respectively set on both sides of the outdoor fan 2. The compressor 2 is set between the two sets of condensers 11 on the side closer to the indoor cavity. The electrical control box 4 is set on the side of the indoor cavity closer to the outdoor cavity and at the return air vent of the indoor cavity. The evaporator 5 is set between the electrical control box 4 and the indoor fan 7. This layout reduces the length of the refrigeration pipe through which the refrigerant flows and reduces unnecessary refrigeration components, such as liquid receivers and gas-liquid separators. Compared with the connection method or layout of traditional refrigeration circuits, the refrigerant charge can be reduced by 5%-15%.

[0054] While meeting noise and heat exchange requirements, appropriately increasing the air supply and condensing air volume can reduce the heat exchange area of ​​the evaporator 5 and the microchannel condenser 11. Through numerous experiments, it has been found that by combining different tube lengths of the evaporator 5 and different equivalent diameters of the microchannel condenser 11, the air supply volume of the indoor fan 7 can be increased by 8-15%, and the air volume of the outdoor fan 2 can be increased by 10%-30%.

[0055] By using the above methods, the refrigerant charge can be significantly reduced. With all factors combined, the refrigerant charge is reduced by more than 30% compared to the same specifications of compressor air conditioning units, meeting the refrigerant charge limit required by EN378 standard. This satisfies the refrigeration demand while greatly reducing the manufacturing cost of the unit.

[0056] On the side of the indoor cavity closest to the outdoor cavity, there is a control unit, which is located in the electrical control box 4. The electrical components of the control unit, such as circuit breakers and contactors, are integrated in the electrical control box 4. Based on the real-time temperature inside and outside the vehicle, the control unit controls the operation and shutdown of the electrical components of the air conditioning unit to realize the control of the cooling and heating functions of the air conditioning unit.

[0057] The electrical control box 4 has an IP66 protection rating and is equipped with an arc-extinguishing device inside. Preferably, the circuit breaker, contactor and other electrical control components are also equipped with arc-extinguishing devices. The electrical control box 4 is located above the return air vent of the air conditioning unit, and the return air is used to dissipate heat from the electrical control box 4. The indoor cavity is located above the return air and supply air vents, thereby preventing the occurrence of ignition sources from the source and reducing the temperature of the indoor cavity to prevent the temperature of the indoor cavity from exceeding the ignition point temperature of R1234fy refrigerant, thus improving safety.

[0058] R1234fy refrigerant flows in one direction in the refrigeration circuit, and there is no four-way valve in the refrigeration circuit. Therefore, the refrigeration circuit of the air conditioning unit can only realize the cooling function, while the heating function is realized through the heating element.

[0059] In this embodiment, the heating element includes at least two separately controllable heating circuits. Each heating circuit is equipped with a PTC electric heater 6, or at least two PTC electric heaters 6 are connected in parallel on the control circuit. Each PTC electric heater 6 can be controlled separately to achieve the regulation of heating amount and the power of the PTC electric heater 6 can be controlled separately, such as full heating, half heating, or even 1 / 3 or 1 / 4 heating.

[0060] The heating function of the air conditioning unit is achieved by the PTC electric heater 6. When heating is required, the refrigerant in the refrigeration circuit stops rotating and does not perform heat exchange. However, the indoor fan 7 runs to deliver the heat generated by the PTC electric heater into the room.

[0061] like Figure 1 As shown, in this embodiment, the PTC electric heater 6 is disposed between the evaporator 5 and the indoor fan 7. The evaporator 5, the PTC electric heater 6, and the indoor fan 7 are arranged parallel to each other in the indoor cavity. The indoor fan 7 delivers the heat generated by the PTC electric heater 6 into the room. As the temperature of the PTC electric heater 6 increases, the heat exchange capacity of the PTC decreases. During the fault protection test, unlike the rapid temperature rise of tubular resistance wire electric heating, the temperature rise of the PTC electric heater 6 is not significant, but rather slow, far below the limit temperature requirement of A2L refrigerant, thus ensuring the heating demand of the air conditioning unit.

[0062] The heating element includes at least two PTC electric heaters 6, each of which can be individually controlled to meet different temperature requirements. Using PTC electric heaters also reduces the temperature of the evaporator chamber, lowers the risk of combustion of flammable refrigerant, and improves the safety of the air conditioning unit.

[0063] The controller contains control logic for the heating element to control its operating state. In this embodiment, the heating unit includes a semi-heating mode and a full-heating mode, specifically, as follows: Figure 2 As shown, the heating element is configured as follows:

[0064] When the return air temperature (detected by a return air temperature sensor 12 installed at the return air inlet) exceeds (or is greater than or equal to) the first set temperature a, the heating element enters a semi-heating mode, meaning that the heating element's heat output is controlled to be only half of its rated heat output. For example, only one PTC electric heater 6 (assuming the heating element includes two PTC electric heaters 6) can be controlled to enter heating mode, while the other PTC electric heater 6 stops working; or both PTC electric heaters 6 can be controlled to heat at only 50% of their rated power. Semi-heating control is a conventional control method in this field and will not be elaborated upon. Any existing or future control method is applicable to this application.

[0065] When the return air temperature exceeds the second temperature b, the temperature at the PTC electric heater 6 is close to and / or exceeds the ignition point of R1234fy refrigerant. Continued heating may cause the residual R1234fy refrigerant in the refrigeration circuit to burn. At this time, both sets of PTC electric heaters 6 stop working to improve heating safety.

[0066] When both sets of PTC electric heaters 6 stop working for a predetermined time, such as 1 minute, the PTC electric heaters 6 resume normal control. "Resuming normal control" means restoring the original heating state; for example, if it was in a semi-warm mode before stopping heating, it will return to semi-warm control after the predetermined time; if it was in full-heat mode before stopping heating, it will return to full-heat control.

[0067] When the return air temperature drops to the third control temperature c (less than or equal to the third control temperature c), the PTC electric heater 6 enters the full heat mode control.

[0068] Once the indoor temperature reaches the set temperature, the air conditioning unit stops heating. The indoor fan 7 continues to run for a predetermined time, such as 3 minutes, before stopping to prevent heat buildup on the PTC heater 6.

[0069] The first set temperature a is taken in the range of 53-57℃, the second set temperature b is taken in the range of 59-62℃, and the third set temperature c is taken in the range of 47-50℃.

[0070] It should be noted that the preset times for the PTC electric heater 6 to stop heating midway and for the air conditioning unit to stop heating are different, but both can be set according to the heating and cooling rates of the PTC electric heater 6 to avoid fluctuations in indoor temperature.

[0071] The control box 4 is located at the return air vent, and the return air cools the control box 4. The control box 4 is equipped with an arc extinguishing device to prevent the generation of electric arcs / sparks. A PTC electric heater 6 is installed, and the PTC electric heater 6 is configured with corresponding control logic for half-heating, full-heating, and intermittent stopping heating. This avoids the occurrence of ignition sources from the source and reduces the temperature of the indoor cavity. Even if the refrigerant leaks, it cannot cause combustion, which greatly improves the safety of the air conditioning unit.

[0072] In summary, the air conditioning unit with low GWP and weakly flammable refrigerant provided by this utility model has the following advantages compared with the prior art:

[0073] Reduce the refrigerant charge in the following ways:

[0074] 1. Microchannel condensers consist of flat tubes with an equivalent diameter of 10-1000μm, resulting in high heat exchange efficiency and a smaller internal volume. Compared with traditional tube-fin condensers, the refrigerant capacity of the condenser can be reduced by 20%-50%.

[0075] 2. The refrigerant side pressure drop of the copper tube aluminum fin evaporator is limited to within 30 kPa, and the length of each pipe is 3-10 m. In this project, the length of each pipe is controlled within 5 m, reducing the refrigerant charge by 5%-10%.

[0076] 3. By rationally arranging components, the length of the refrigerant pipeline can be reduced, and unnecessary refrigeration components, such as liquid receivers and gas-liquid separators, can be eliminated, thereby reducing the refrigerant charge by 5%-15%.

[0077] 4. While meeting noise requirements, appropriately increase the air supply volume and condensing air volume, and reduce the heat exchange area of ​​the evaporator and microchannel condenser. Increase the air supply volume by 8-15% and the condensing air volume by 10%-30%.

[0078] Through the above methods, the refrigerant charge is significantly reduced by more than 30%, meeting the refrigerant charge limit required by the EN378 standard, and greatly reducing the manufacturing cost of the unit.

[0079] By using the following components and appropriate control logic, the temperature inside the refrigerant is reduced to prevent it from exceeding the refrigerant's ignition point, thus improving safety:

[0080] Circuit breakers, contactors, and other components are all integrated into the electrical control box. The contactors and other components are equipped with arc-extinguishing devices, and the electrical control box has an IP66 protection rating.

[0081] By employing the above methods, the source of ignition is prevented from being generated, and the indoor temperature is reduced, greatly improving the safety of the air conditioning unit.

[0082] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any way. Although the present utility model has been disclosed above with reference to a preferred embodiment, it is not intended to limit the present utility model. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present utility model. The implementation schemes in the above embodiments can be further combined or replaced. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present utility model without departing from the scope of the present utility model shall still fall within the scope of the present utility model.

Claims

1. An air conditioning unit employing a low GWP weakly flammable refrigerant, comprising an indoor chamber and an outdoor chamber, a compressor and a condenser are arranged in the outdoor chamber, and an evaporator is arranged in the indoor chamber, characterized in that: The indoor cavity and the outdoor cavity are arranged side by side, the compressor, the condenser and the evaporator are connected by pipelines to form a refrigeration circuit, the refrigeration circuit is filled with low-GWP weakly flammable refrigerant which flows in one direction; the compressor is arranged on the side of the outdoor cavity close to the indoor cavity, and the evaporator is arranged on the side of the indoor cavity close to the outdoor cavity. The indoor cavity is provided with a heating element which independently performs a heating mode of the air conditioning unit on the side away from the compressor.

2. The air conditioning unit employing a low GWP weakly flammable refrigerant as claimed in claim 1, wherein: The indoor cavity is arranged above the air inlet.

3. The air conditioning unit employing a low GWP weakly flammable refrigerant as claimed in claim 1, wherein: The condenser is a micro-channel heat exchanger with a flat tube structure, and the equivalent diameter of the micro-channel is in the range of 10-1000 μm.

4. The air conditioning unit employing a low GWP weakly flammable refrigerant as claimed in claim 3, wherein: The condenser is at least two groups, which are arranged in parallel on both sides of the compressor.

5. The air conditioning unit employing a low GWP weakly flammable refrigerant as claimed in claim 1, wherein: The indoor cavity is further provided with an indoor fan, and the evaporator, the heating element and the indoor fan are arranged in parallel in the indoor cavity.

6. The air conditioning unit employing a low GWP weakly flammable refrigerant as claimed in claim 1, wherein: The evaporator is a copper tube aluminum fin structure, which includes multiple pipelines, and the length of each pipeline is in the range of 3-10 m.

7. An air conditioning unit employing a low GWP weakly flammable refrigerant as claimed in claim 6 wherein: The length of each pipeline of the evaporator is less than or equal to 5 m.

8. The air conditioning unit employing a low GWP weakly flammable refrigerant as claimed in claim 1, wherein: Further comprising an electric control box, which is arranged at the return air inlet on the side of the indoor cavity.

9. The air conditioning unit employing a low GWP weakly flammable refrigerant as claimed in claim 8, wherein: An arc extinguishing device is arranged in the electric control box.

10. An air conditioning unit employing a low GWP weakly flammable refrigerant as claimed in any one of claims 1 to 9, characterized in that: The heating element includes at least two heating circuits which can be controlled respectively, and a PTC electric heater is arranged on each heating circuit. Or at least two PTC electric heaters are arranged in parallel on each heating circuit, and each PTC electric heater can control the heating power thereof.

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