System structure and control method of high-drop multi-connection

Abstract

The application discloses a system structure and a control method of a high-drop multi-connected system, and belongs to the technical field of multi-connected air conditioners. The system outdoor unit is provided with a liquid accumulator and a plate heat exchanger, the outlet of the liquid accumulator is connected in parallel with a subcooling circulation loop, the loop is provided with an EEVSC and a THO-H, a main circuit is connected in series with a PSH2, a pressure reduction assembly composed of an SV10 and an EEVD connected in parallel is arranged downstream of the PSH2, and a thrombolytic pressure relief bypass is arranged in the liquid accumulator. The unit is matched with a PSH1 and a PSL multi-point pressure sensor. The application distinguishes two installation forms, i.e., an indoor unit higher than an outdoor unit and an outdoor unit higher than an indoor unit, forms four special control working conditions in combination with refrigeration and heating, and respectively implements differentiated collaborative regulation and control on an electronic expansion valve, a solenoid valve and a compressor according to temperature and pressure signals. The independent subcooling loop offsets the gravity loss of the high-drop refrigerant, the parallel pressure reduction assembly cooperates with the thrombolytic structure to realize multi-stage pressure protection, and the application can be adapted to 30-100m vertical height difference scenes.

Description

Technical Field

[0001] This invention belongs to the field of central air conditioning multi-split system technology, specifically involving the refrigerant circulation system of air-cooled multi-split systems with ultra-high drop installation conditions of 30-100m and intelligent pressure and flow coordinated control technology for different operating conditions. It is suitable for multi-split air conditioning installation scenarios with large vertical height difference between indoor and outdoor units and long piping, such as high-rise buildings and mountainous buildings. Background Technology

[0002] A standard multi-split air conditioning system consists of one outdoor unit connected in parallel with multiple indoor units. The refrigerant completes the cooling and heating cycle through the compressor, four-way valve, outdoor heat exchanger, main electronic expansion valve, and indoor units. Standard models are only suitable for installations with a vertical height difference of ≤30m between the indoor and outdoor units, and do not have a dedicated high-drop pressure balancing and subcooling regulation branch.

[0003] When the vertical height difference between the indoor and outdoor units reaches 30-100m, the refrigerant liquid column generates enormous static pressure. Combined with the pressure loss along the long piping, this leads to two major defects: 1) Significant reduction in cooling / heating output: Under high vertical differences, the refrigerant is affected by gravity, resulting in a larger refrigerant mass flow rate through the indoor unit. This significantly increases the gravitational potential energy loss MGH (M is the refrigerant mass, G=9.8m / s², H is the vertical height difference); insufficient system liquid enthalpy difference leads to inadequate evaporation / heat exchange, resulting in a significant decrease in cooling and heating capacity and large fluctuations in indoor temperature. 2) High risk of system overpressure damage: When the outdoor unit is in heating or cooling mode, the static pressure of the refrigerant in the liquid pipe, combined with the high pressure of the compressor, can easily cause the instantaneous system pressure to exceed the pressure resistance thresholds of the copper pipes, filters, and electronic expansion valves, leading to pipe bursts, valve damage, and refrigerant leakage. Conventional units lack graded pressure detection and active pressure relief branches, relying solely on a single high-pressure protection shutdown, which frequently causes the unit to operate unstablely.

[0004] Existing high-drop multi-split air conditioners simply increase the compressor's rated frequency and thicken the pipe walls, without setting up an independent subcooling circulation branch, dual high-pressure staged pressure detection, or a parallel pressure-reducing component consisting of solenoid valves and electronic expansion valves. Furthermore, they do not differentiate control strategies for the four operating conditions: outdoor unit below indoor unit, outdoor unit above indoor unit, and cooling / heating. This results in the following inherent shortcomings: ① No independent EEVSC subcooling branch, unable to actively reduce the refrigerant mass flow rate on the indoor side, gravity losses cannot be offset, and heat exchange efficiency is poor under high-low drop conditions; ② Only a single-point high-pressure detection cannot predict local overpressure in the branch, and there is no active pressure-reducing circuit, leading to a high risk of component damage; ③ A unified compressor frequency control logic does not differentiate target high and low pressures based on the static pressure loss differences of the four operating conditions, causing the system to deviate from its optimal operating range for extended periods, resulting in low energy efficiency and frequent protection shutdowns; ④ No liquid receiver with a thrombus-based pressure relief structure, leaving no bypass pressure relief channel when system pressure rises suddenly, with pressure shocks directly acting on valves and pipes. Summary of the Invention

[0005] To address the shortcomings of existing multi-split air conditioners installed in scenarios with a height difference of 30-100m, such as large refrigerant gravity loss, reduced cooling and heating output, easy damage to components due to system overpressure, uncompensated pressure loss from long piping, and frequent high-pressure protection shutdowns, this paper proposes a system structure and operating condition-specific control method for high-drop multi-split air conditioners. This method enables precise control of refrigerant flow and system pressure under ultra-high height differences, improves cooling and heating performance, and completely eliminates the risk of overpressure damage.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a high-drop multi-split air conditioning system, including an outdoor unit and multiple indoor units connected in parallel. The outdoor unit contains a compressor, an oil separator, a four-way valve, an outdoor heat exchanger, a liquid receiver, and a gas-liquid separator. The outdoor heat exchanger is connected to the indoor units via a main liquid pipe and a main gas pipe. The liquid receiver outlet is divided into two paths: one is the main liquid supply line, and the other is a subcooling circulation loop. The main liquid supply line is sequentially connected to the condenser side channel of the plate heat exchanger, a high-pressure sensor PSH2, and a pressure reducing assembly. The pressure reducing assembly is connected to the main liquid pipe. An electronic expansion valve EE is installed on the subcooling circulation loop. VSC, the subcooling loop is connected to the evaporator side channel of the plate heat exchanger; the evaporator side outlet pipe of the plate heat exchanger is equipped with a temperature sensor THO-H, and the end of the subcooling loop is connected to the gas-liquid separator; the high pressure sensor PSH2 is located between the condenser side outlet of the plate heat exchanger and the pressure reducing assembly; the pressure reducing assembly includes a solenoid valve SV10 and an electronic expansion valve EEVD connected in parallel; the liquid receiver is equipped with a thrombus-type pressure relief bypass structure; the compressor exhaust end is equipped with a high pressure sensor PSH1, and the compressor return end is equipped with a low pressure sensor PSL.

[0007] Preferably, the bore diameter of the solenoid valve SV10 is the same as that of the electronic expansion valve EEVD.

[0008] This invention also provides a control method for the high-drop multi-split air conditioning system, including four high-drop dedicated control conditions. When the unit simultaneously meets the condition that the compressor shutdown time is greater than 3 minutes, the corresponding control condition is switched on. When the condition is not met, the high-drop control is exited, EEVSC and EEVD are reset to step 0, the solenoid valve SV10 is de-energized and closed, and the system switches to the conventional multi-split air conditioning control logic. The specific control methods for the four conditions are as follows. The four operating condition control methods are as follows: Operating Condition 1: Indoor unit temperature is higher than outdoor unit temperature. Cooling mode: The control target is a refrigerant saturation temperature difference of 25°C between the first high-pressure sensor PSH1 and the second high-pressure sensor PSH2. The opening of the electronic expansion valve EEVSC in the subcooling loop is continuously adjusted using a PID algorithm. The electronic expansion valve EEVD in the pressure reducing branch is kept fully open for 470 steps, and the solenoid valve SV10 is energized. The detection pressure of the low-pressure sensor PSL is collected in real time, and the compressor frequency is adjusted to a target value of 0.6MPa. Operating Condition 2: Outdoor unit temperature is higher than indoor unit temperature. Cooling mode: The outdoor unit reads the actual temperature measured by the temperature sensor THO-H and calculates the corresponding refrigerant saturated evaporation temperature by combining it with the pressure detected by the low-pressure sensor PSL. A PID algorithm is used to adjust the opening of the electronic expansion valve EEVSC, aiming for a temperature difference of 10℃. The opening of the electronic expansion valve EEVD is adjusted in a closed loop, with the pressure measured by the second high-pressure sensor PSH2 at 3.0MPa as the pressure stabilization target. The solenoid valve SV10 is de-energized and closed. The compressor uses the low-pressure sensor PSL pressure of 0.5MPa as the reference pressure for frequency increase / decrease control. Operating Condition 3: Indoor unit is higher than outdoor unit, heating mode: the subcooling loop electronic expansion valve EEVSC is completely closed; the second high pressure sensor PSH2 collects a pressure of 3.0MPa as the adjustment target, the closed-loop control of the electronic expansion valve EEVD opening is used, and the solenoid valve SV10 is kept closed; based on the detection value of the first high pressure sensor PSH1, the compressor frequency is increased or decreased with a target high pressure of 3.2MPa. Operating Condition 4: Outdoor unit is higher than indoor unit. Heating mode: Electronic expansion valve EEVSC of subcooling circulation loop is completely closed; electronic expansion valve EEVD is fixed at 470 steps and fully open; solenoid valve SV10 is energized and conducting; the first high pressure sensor PSH1 collects the high pressure and completes the compressor frequency regulation with 2.5MPa as the target pressure.

[0009] Preferably, if the PSH2 detection pressure exceeds the 3.0MPa threshold during operation, the solenoid valve SV10 is fully opened and the electronic expansion valve EEVD is fully opened to perform active pressure relief; the thrombus-type pressure relief bypass structure of the reservoir serves as a secondary safety pressure relief mechanism to buffer the system from high-pressure impact.

[0010] Preferably, the method is suitable for installation conditions where the vertical height difference between the indoor and outdoor units is 30m to 100m.

[0011] Compared with the prior art, the beneficial effects of the present invention are: Adaptable to installation scenarios with large vertical height differences, improving heat exchange performance: This invention sets up an independent subcooling circulation loop, which can actively adjust the degree of refrigerant subcooling, effectively offsetting the refrigerant gravitational potential energy loss caused by high height differences, balancing the refrigerant flow distribution in the pipeline, avoiding insufficient liquid supply under high height difference conditions, stabilizing indoor heat exchange effect, and improving the basic output capacity of the unit for cooling and heating.

[0012] The graded pressure regulation combined with multiple pressure relief structures significantly improves system operational safety: This invention uses dual high-pressure detection elements to monitor pipeline pressure in real time, and works in conjunction with an adjustable pressure reducing component consisting of a solenoid valve and an electronic expansion valve connected in parallel. This allows for proactive adjustment of pipeline flow resistance and dynamic balancing of system pressure based on different installation height differences and hot / cold operating modes. At the same time, the built-in thrombus-type pressure relief bypass in the liquid receiver serves as a secondary safety protection, buffering pressure surges and preventing damage to pipelines, valves, and other components due to system overpressure, thus reducing the risk of refrigerant leakage.

[0013] Differentiated control logic for different operating conditions to adapt to different high and low position installation and operation modes: For two installation forms, namely outdoor unit low position and indoor unit high position, and outdoor unit high position and indoor unit low position, dedicated valves and compressor collaborative control strategies are designed to match four types of operating conditions for cooling and heating. The optimal adjustment scheme can be automatically matched according to the actual operating status of the unit to compensate for the pressure loss caused by long piping and vertical height difference. The unit's operating conditions are more stable and less likely to trigger high pressure or low pressure abnormal protection shutdown.

[0014] The system operates in a manner that better matches the optimal working range, optimizing the overall performance of the unit: By setting corresponding pressure control targets based on different working conditions, and with the fine-tuning of the subcooling branch using PID, the compressor and throttling components are always kept in the working range that is suitable for the current high differential load, reducing ineffective energy consumption and improving the long-term operational stability and overall economic efficiency of the unit.

[0015] Adaptive control with high degree of automation and ease of use: The unit automatically identifies the operating mode and pipeline pressure and temperature status by relying on built-in sensors. It can automatically switch to the high drop exclusive control logic as long as the compressor shutdown delay condition is met, without the need for manual on-site debugging and parameter modification; The exit condition is clear and specific, and it can seamlessly switch to the conventional control mode, adapting to various high and low drop installation scenarios, making it more versatile. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the high-drop multi-unit air conditioning system of the present invention.

[0017] The attached diagram is labeled as follows: 1. Compressor; 2. Oil separator; 3. Four-way valve; 4. Outdoor heat exchanger; 5. Liquid receiver; 6. Gas-liquid separator; 7. Main liquid pipe; 8. Main gas pipe; 9. Plate heat exchanger. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below through examples.

[0019] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0020] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0021] This invention is designed for multi-split air conditioning installation scenarios with a vertical height difference of 30m to 100m between indoor and outdoor units. Through an independent subcooling circulation loop, parallel pressure reducing components, and a multi-point pressure and temperature acquisition structure, combined with four types of differentiated operating condition control logic, it achieves adaptive adjustment of refrigerant flow and system pressure under high height difference conditions. The implementation process of this invention will be fully described below in conjunction with different installation height differences and operating modes.

[0022] A high-drop multi-split air conditioning system includes an outdoor unit and multiple indoor units connected in parallel. The outdoor unit houses a compressor 1, an oil separator 2, a four-way valve 3, an outdoor heat exchanger 4, a liquid receiver 5, and a gas-liquid separator 6. The outdoor heat exchanger 4 is connected to the indoor units via a main liquid pipe 7 and a main gas pipe 8. The liquid receiver 5 has two outlets: one is a main liquid supply line, and the other is a subcooling circulation loop. The main liquid supply line is sequentially connected to the condenser side channel of a plate heat exchanger 9, a high-pressure sensor PSH2, and a pressure reducing assembly. The pressure reducing assembly is connected to the main liquid pipe 7. An electronic expansion valve EE is installed on the subcooling circulation loop. VSC, the subcooling circulation loop is connected to the evaporator side channel of plate heat exchanger 9; the evaporator side outlet pipe of plate heat exchanger 9 is equipped with a temperature sensor THO-H, and the end of the subcooling circulation loop is connected to gas-liquid separator 6; the high pressure sensor PSH2 is located between the condenser side outlet of plate heat exchanger 9 and the pressure reducing assembly; the pressure reducing assembly includes a solenoid valve SV10 and an electronic expansion valve EEVD connected in parallel; the liquid receiver 5 is equipped with a thrombus-type pressure relief bypass structure, the compressor 1 exhaust end is equipped with a high pressure sensor PSH1, and the compressor 1 return end is equipped with a low pressure sensor PSL.

[0023] In a preferred embodiment of this invention, the solenoid valve SV10 has the same diameter as the electronic expansion valve EEVD, both being 3mm.

[0024] Example 1: Indoor unit is higher than outdoor unit, cooling operation. After the unit completes shutdown and resting, if the compressor has been off for more than 3 minutes, the system recognizes that the indoor unit is installed higher than the outdoor unit and is currently running in cooling mode, and automatically switches to the dedicated control logic for operating condition one. The liquid refrigerant output from the receiver is divided into two paths: one path enters the subcooled side of the plate heat exchanger to supply refrigerant to the main liquid supply line, and the other path enters the evaporator side of the plate heat exchanger via EEVSC to form a subcooling cycle; the controller reads the refrigerant saturation temperatures corresponding to PSH1 and PSH2 in real time, and performs PID adjustment of EEVSC with a target temperature difference of 25℃, dynamically adjusting the refrigerant flow in the subcooled branch to enhance the subcooling effect of the main refrigerant and offset the gravity loss caused by the vertical height difference. In the pressure reducing branch, EEVD maintains a fixed opening of 470 steps, and solenoid valve SV10 remains conductive to reduce the overall flow resistance of the liquid supply line; the controller continuously collects the low-pressure PSL and uses this as a benchmark to dynamically adjust the compressor operating frequency to compensate for the pressure loss caused by long piping and high height difference, ensuring sufficient refrigerant supply to the indoor unit and stable cooling and heat exchange conditions. If the pipeline pressure rises abnormally during operation, the PSH2 monitors the high pressure in the branch in real time and uses the built-in thrombus-type pressure relief bypass structure in the liquid receiver to buffer the impact pressure and prevent damage to components due to pressure. When the unit is shut down for less than 3 minutes or when switching to heating mode, the system exits the control of this operating condition, EEVSC and EEVD are reset to step 0, solenoid valve SV10 is closed, and the system switches to the conventional multi-split unit control logic.

[0025] Example 2: Outdoor unit is higher than indoor unit, cooling operation. If the unit's shutdown time meets the condition that the compressor has been shut down for more than 3 minutes, the system determines that the outdoor unit is installed at a higher position and is operating in cooling mode, switching to the second control strategy. The EEVSC in the subcooling loop uses PID control based on the THO-H collected temperature and the refrigerant saturation temperature difference calculated from PSL to stabilize the heat exchanger's heat exchange capacity. It continuously performs secondary subcooling of the downward-facing high-pressure liquid refrigerant, reducing the liquid column pressure rise effect caused by the high position of the outdoor unit. At this time, the solenoid valve SV10 remains closed, and the refrigerant can only flow through the EEVD. The controller uses the PSH2 detected pressure as a reference to adjust the EEVD opening in a closed loop, stabilizing the liquid supply branch pressure within a safe range and avoiding the overpressure risk caused by the high drop. The compressor uses the low-pressure collected from PSL as the adjustment reference to increase and decrease the frequency, adapting to the pressure loss of the long downward pipeline and ensuring stable evaporation of the indoor evaporator. Once the PSH2 monitored pressure exceeds the safe range, the pressure reducing branch simultaneously increases its throttling and pressure relief capacity. The liquid receiver's throttling bypass structure serves as a backup pressure relief channel, providing double protection against high-pressure damage to the system's pipelines and valves.

[0026] Example 3: Indoor unit is higher than outdoor unit, heating mode If the compressor stops for more than 3 minutes, the unit is identified as operating in heating mode and the indoor unit is installed at a higher height, entering operating mode three control. The subcooling branch EEVSC is completely closed, and the subcooling circulation loop stops working; the system relies on the pressure reducing branch to achieve pressure regulation, the solenoid valve SV10 remains closed, the controller reads the PSH2 pipeline pressure and adjusts the EEVD opening in a closed loop to continuously balance the system high pressure and prevent damage to components from continuous high pressure rise during heating mode. The controller collects the high pressure signal from the compressor discharge end PSH1 and adjusts the compressor operating frequency based on the set target pressure to offset the pressure loss caused by the vertical height difference and long piping, ensuring stable refrigerant circulation in the heating cycle and uniform indoor heat exchange. When operating conditions change and no longer meet the requirements for entering this operating mode, all valves reset and close, exiting the high-drop dedicated control.

[0027] Example 4: Outdoor unit is higher than indoor unit, heating mode After the unit has been shut down and allowed to stand still for 3 minutes, the system identifies the outdoor unit as being in high-level heating mode and initiates the four-stage control logic. The EEVSC remains completely closed, and the subcooling circulation branch does not participate in operation. The pressure-reducing branch EEVD maintains a fixed opening of 470 steps, and the solenoid valve SV10 is open, allowing refrigerant to flow simultaneously in both paths. This significantly reduces pipe flow resistance and alleviates the problem of excessively high system pressure during high-level heating of the outdoor unit. The controller uses the exhaust pressure collected by PSH1 to control the compressor's frequency adjustment, matching the pipe pressure loss under the current elevation difference to stabilize the overall heating cycle. Throughout the entire process, the system monitors the operating status in real time through multiple pressure sensors (PSH1, PSH2, PSL), and with the liquid receiver's thrombus-relieving structure, it avoids overpressure faults and ensures continuous and stable heating of the unit.

[0028] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-drop multi-split air conditioning system, comprising an outdoor unit and multiple indoor units connected in parallel, wherein the outdoor unit is equipped with a compressor, an oil separator, a four-way valve, an outdoor heat exchanger, a liquid receiver, and a gas-liquid separator, and the outdoor heat exchanger is connected to the indoor units via a main liquid pipe and a main gas pipe, characterized in that: The liquid receiver outlet is divided into two paths: one is the main liquid supply line, and the other is the subcooling circulation loop. The main liquid supply line is sequentially connected to the condenser side channel of the plate heat exchanger, the high-pressure sensor PSH2, and the pressure reducing assembly. The pressure reducing assembly is connected to the main liquid pipe. The subcooling circulation loop is equipped with an electronic expansion valve EEVSC and is connected to the evaporator side channel of the plate heat exchanger. The evaporator side outlet pipe of the plate heat exchanger is equipped with a temperature sensor THO-H, and the end of the subcooling circulation loop is connected to the gas-liquid separator. The high-pressure sensor PSH2 is located between the condenser side outlet of the plate heat exchanger and the pressure reducing assembly. The pressure reducing assembly includes a solenoid valve SV10 and an electronic expansion valve EEVD connected in parallel. The liquid receiver is equipped with a thrombus-type pressure relief bypass structure. The compressor exhaust end is equipped with a high-pressure sensor PSH1, and the compressor return end is equipped with a low-pressure sensor PSL.

2. The high-drop multi-split air conditioning system according to claim 1, characterized in that: The solenoid valve SV10 has the same bore diameter as the electronic expansion valve EEVD.

3. A control method for a high-altitude multi-unit air conditioning system based on any one of claims 1 to 2, characterized in that, It includes four special control conditions for high drop. When the unit simultaneously meets the condition that the compressor shutdown time is greater than 3 minutes, it switches to the corresponding control condition. If the condition is not met, it exits the high drop control, EEVSC and EEVD are reset to step 0, the solenoid valve SV10 is de-energized and closed, and it switches to the conventional multi-split unit control logic. The specific control methods for the four conditions are as follows. The four operating condition control methods are as follows: Operating Condition 1: Indoor unit temperature is higher than outdoor unit temperature. Cooling mode: The control target is a refrigerant saturation temperature difference of 25°C between the first high-pressure sensor PSH1 and the second high-pressure sensor PSH2. The opening of the electronic expansion valve EEVSC in the subcooling loop is continuously adjusted using a PID algorithm. The electronic expansion valve EEVD in the pressure reducing branch is kept fully open for 470 steps, and the solenoid valve SV10 is energized. The detection pressure of the low-pressure sensor PSL is collected in real time, and the compressor frequency is adjusted to a target value of 0.6MPa. Operating Condition 2: Outdoor unit temperature is higher than indoor unit temperature. Cooling mode: The outdoor unit reads the actual temperature measured by the temperature sensor THO-H and calculates the corresponding refrigerant saturated evaporation temperature by combining it with the pressure detected by the low-pressure sensor PSL. A PID algorithm is used to adjust the opening of the electronic expansion valve EEVSC, aiming for a temperature difference of 10℃. The opening of the electronic expansion valve EEVD is adjusted in a closed loop, with the pressure measured by the second high-pressure sensor PSH2 at 3.0MPa as the pressure stabilization target. The solenoid valve SV10 is de-energized and closed. The compressor uses the low-pressure sensor PSL pressure of 0.5MPa as the reference pressure for frequency increase / decrease control. Operating Condition 3: Indoor unit is higher than outdoor unit, heating mode: the subcooling loop electronic expansion valve EEVSC is completely closed; the second high pressure sensor PSH2 collects a pressure of 3.0MPa as the adjustment target, the closed-loop control of the electronic expansion valve EEVD opening is used, and the solenoid valve SV10 is kept closed; based on the detection value of the first high pressure sensor PSH1, the compressor frequency is increased or decreased with a target high pressure of 3.2MPa. Operating Condition 4: Outdoor unit is higher than indoor unit. Heating mode: Electronic expansion valve EEVSC of subcooling circulation loop is completely closed; electronic expansion valve EEVD is fixed at 470 steps and fully open; solenoid valve SV10 is energized and conducting; the first high pressure sensor PSH1 collects the high pressure and completes the compressor frequency regulation with 2.5MPa as the target pressure.

4. The method according to claim 3, characterized in that: If the pressure detected by PSH2 exceeds the 3.0MPa threshold during operation, the solenoid valve SV10 is fully opened and the electronic expansion valve EEVD is fully opened to perform active pressure relief; the thrombus-type pressure relief bypass structure of the reservoir serves as a secondary safety pressure relief mechanism to buffer the system from high-pressure impact.

5. The method according to claim 3, characterized in that: The method is suitable for installation conditions where the vertical height difference between indoor and outdoor units is 30m to 100m.

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