A control method for a fixed air conditioning and a fixed air conditioning

Abstract

The application provides a control method and fixed air conditioner for cooling, heating, air conditioning simultaneously, and relates to the technical field of air conditioners. The method first realizes the function of cooling and heating simultaneously. In the operation condition, the outer ring temperature Tw of an outdoor unit is obtained. When the outer ring temperature Tw is less than the preset outer ring temperature T1, it indicates that there is a risk of frosting of the indoor unit heat exchanger at this time. At this time, the opening degree of the low-pressure expansion valve and the inner expansion valve of the indoor unit upstream and downstream can be adjusted. The low-pressure expansion valve and the inner expansion valve are adjusted as a whole as a hypothetical expansion valve, so that the evaporation temperature of the outdoor heat exchanger and the evaporation temperature of the indoor heat exchanger change, and then the evaporation temperature of the indoor unit in the refrigeration mode is greater than the frosting critical temperature T2, which can avoid the frosting phenomenon of the heat exchanger of the indoor unit, thereby ensuring the air volume and avoiding the condensation of the surface of the indoor unit, and also avoiding the noise problem caused by the condensation dripping.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, and more specifically, to a control method for a fixed air conditioner that can simultaneously provide cooling and heating, and to a fixed air conditioner that can simultaneously provide cooling and heating. Background Technology

[0002] In the residential air conditioning market, installation has gradually shifted from one unit per household to one unit per room, and now it's common for each household to have four or five air conditioners. Correspondingly, centered in cities, there is a growing demand for fixed-type air conditioners that can share outdoor units and reduce installation space. Additionally, in specific markets, such as small and medium-sized hotels where space for outdoor unit installation is limited, there is also a demand for fixed-type air conditioners. Among these demands, many users are further requesting fixed-type air conditioners with separate cooling and heating settings for both cooling and heating functions.

[0003] The inventors' research revealed that when achieving simultaneous heating and cooling functions, the evaporation temperature of the outdoor heat exchanger becomes the baseline when the outside air temperature is low, such as below 0°C. However, the evaporation temperature of the indoor heat exchanger during cooling operation can sometimes reach below 0°C. When the evaporation temperature of the indoor heat exchanger is below 0°C, frost will form on the heat exchanger, affecting airflow and potentially causing air to stop flowing altogether. After the indoor unit cools down, condensation will appear on its surface, leading to water droplets dripping down. Summary of the Invention

[0004] The problem solved by this invention is how to prevent frost formation on indoor heat exchangers when heating and cooling are operating simultaneously at low external temperatures.

[0005] To solve the above problems, the present invention adopts the following technical solution.

[0006] In one aspect, embodiments of the present invention provide a control method for a fixed simultaneous cooling and heating air conditioner, applicable to such air conditioners, wherein the fixed simultaneous cooling and heating air conditioner includes an outdoor unit and multiple indoor units connected to the outdoor unit simultaneously, and the control method includes: At least one of the indoor units is set to heating mode, at least one of the indoor units is set to cooling mode, and the compressor assembly in the outdoor unit is located on the heating operation side; Obtain the outer ring temperature Tw of the outdoor unit; When the outer ring temperature Tw is less than the preset outer ring temperature T1, the opening degree of the inner expansion valve and low-pressure expansion valve of the indoor unit in the cooling mode is controlled so that the evaporation temperature of the indoor unit is greater than the frosting critical temperature T2. The internal expansion valve is located on the liquid distribution pipe upstream of the indoor unit in the cooling mode, and the low-pressure expansion valve is located on the low-pressure gas distribution pipe downstream of the indoor unit in the cooling mode.

[0007] The control method for a fixed air conditioner that simultaneously provides heating and cooling, provided in this embodiment of the invention, firstly achieves simultaneous heating and cooling functionality by setting at least one indoor unit to heating mode and at least one indoor unit to cooling mode simultaneously. The compressor assembly in the outdoor unit is located on the heating operation side, thus ensuring that most indoor units are in heating mode and a few are in cooling mode. Under this operating condition, the outer ring temperature Tw of the outdoor unit is obtained. When the outer ring temperature Tw is less than the preset outer ring temperature T1, it indicates a risk of frosting on the indoor unit's heat exchanger. In this case, the opening of the low-pressure expansion valve and the internal expansion valve upstream and downstream of the indoor unit can be adjusted. The low-pressure expansion valve and the internal expansion valve are treated as a hypothetical expansion valve and adjusted accordingly. This causes a change in the evaporation temperature of the outdoor and indoor heat exchangers, resulting in the evaporation temperature of the indoor unit in cooling mode being greater than the frosting critical temperature T2, thereby preventing frosting on the indoor unit's heat exchanger. Compared to existing technologies, this invention adjusts the opening of the low-pressure expansion valve and the internal expansion valve, enabling the evaporation temperature of the indoor unit in cooling mode to be greater than the frosting critical temperature T2. This prevents the heat exchanger of the indoor unit from frosting, thus ensuring airflow while preventing condensation on the surface of the indoor unit and avoiding noise problems caused by condensation dripping.

[0008] Further, the step of controlling the opening degree of the internal expansion valve and low-pressure expansion valve corresponding to the indoor unit in cooling mode includes: Obtain the target total opening Pm, wherein the target total opening Pm is the sum of the first target opening P1 of the internal expansion valve and the second target opening P2 of the low-pressure expansion valve; Obtain the high pressure value Pg, low pressure value Pd, and target indoor evaporation pressure Ps of the indoor unit in cooling mode; The first target opening P1 and the second target opening P2 are calculated based on the pipeline high pressure value Pg, the pipeline low pressure value Pd, the target indoor evaporation pressure Ps, and the target total opening Pm. Adjust the internal expansion valve to the first target opening P1, and adjust the low-pressure expansion valve to the second target opening P2.

[0009] The fixed-function air conditioner with simultaneous cooling and heating provided in this embodiment of the invention determines the fluid resistance of the entire refrigeration flow path by determining the target total opening degree Pm. This enables the internal expansion valve and the low-pressure expansion valve to achieve coordinated adjustment, avoiding mutual interference between the valves and causing flow path instability. At the same time, a target indoor evaporation pressure Ps is set, which typically indicates that the indoor unit will not frost under this evaporation pressure. The target indoor evaporation pressure Ps can be determined based on experience or simulation experiments. Combined with the measured or calculated high-pressure value Pg and low-pressure value Pd of the pipeline, the first target opening degree P1 and the second target opening degree P2 can be calculated. Based on this, the opening degree of the internal expansion valve and the low-pressure expansion valve can be adjusted to further ensure that the evaporation temperature of the indoor unit in the cooling mode is greater than the frosting critical temperature T2.

[0010] Furthermore, the first target opening P1 and the second target opening P2 satisfy the following formula: P1=Pm*(Pg-Ps) / {Pg-Ps+α(Ps-Pd)}; P2 = Pm - P1; Where α is the pressure loss ratio of liquid refrigerant and gaseous refrigerant.

[0011] The control method for a fixed air conditioner that can simultaneously provide cooling and heating, provided in this embodiment of the invention, determines the opening of the internal expansion valve and the low-pressure expansion valve by setting calculation formulas for the first target opening degree P1 and the second target opening degree P2, and by correcting them based on the pressure loss ratio of the liquid refrigerant and the gaseous refrigerant. This further prevents interference between the action lines of each valve, which could cause instability, and thus provides stable operation while adjusting the evaporation pressure of the indoor unit.

[0012] Furthermore, the pressure loss ratio α between liquid and gaseous refrigerants is between 5 and 10.

[0013] Furthermore, the steps to obtain the target total opening Pm include: Obtain the current total opening degree Pq, wherein the current total opening degree Pq is the sum of the current opening degree of the internal expansion valve and the current opening degree of the low-pressure expansion valve; Obtain the superheat difference Ts between the current superheat Sd and the target superheat Sm; The differential separation δP is calculated based on the superheat difference Ts. The target total opening Pm is calculated based on the current total opening Pq and the differential opening δP.

[0014] The control method for a fixed air conditioner that simultaneously provides cooling and heating, provided in this embodiment of the invention, calculates the target total opening degree Pm based on the superheat and the opening degree of the previous cycle. This ensures the rationality of the target total opening degree Pm and further determines the linkage total opening degree of the internal expansion valve and the low-pressure expansion valve, determines their adjustment range, and provides favorable conditions for subsequent accurate determination of the opening degree of the internal expansion valve and the low-pressure expansion valve.

[0015] Furthermore, the target total opening Pm satisfies the following formula: Pm = Pq + δP; δP=A{ Ts(n) + B×(Ts(n) - Ts(n-1))}; Ts = Sd - Sm; Where Ts(n) is the superheat difference in the current cycle, Ts(n-1) is the superheat difference in the previous cycle, A is the first calculation constant, and B is the second calculation constant.

[0016] The control method for a fixed air conditioner that simultaneously provides cooling and heating, provided in this embodiment of the invention, derives the differential opening degree δP from the opening degree and superheat degree of the previous cycle, achieves accurate calculation of the target total opening degree Pm, and determines the adjustment range of the internal expansion valve and the low-pressure expansion valve.

[0017] Furthermore, the first calculation constant A is between 0.6 and 0.8, and the second calculation constant B is between 1 and 3.

[0018] Furthermore, the current superheat Sd is the difference between the refrigerant temperature Tm of the outdoor unit and the heat exchange temperature Th of the indoor unit, and the target superheat is between 2-4℃.

[0019] The control method for a fixed air conditioner that provides both cooling and heating in this invention provides a reasonable setting of the target superheat, which ensures that the pipe temperatures of the indoor and outdoor units are different, thereby achieving different evaporation pressures and further preventing frost formation on the indoor unit.

[0020] Furthermore, the preset outer ring temperature T1 is between 8-12℃; the frosting critical temperature T2 is between -1℃ and 3℃.

[0021] The control method for a fixed air conditioner that simultaneously provides heating and cooling, provided by this invention, enables the control to be activated when the indoor unit may experience frosting by limiting the temperature of the control conditions, while maintaining the original control under other conditions to ensure its heating / cooling effect. Simultaneously, the frosting critical temperature is used to characterize the temperature at which frosting may occur. When the indoor unit's temperature exceeds this critical temperature, frosting can be avoided, further ensuring the normal operation of the indoor unit.

[0022] In another aspect, embodiments of the present invention provide a fixed-function air conditioner that simultaneously provides cooling and heating, applicable to the aforementioned control method for such a fixed-function air conditioner, wherein the fixed-function air conditioner includes: Multiple indoor units; The outdoor unit includes an outdoor heat exchanger, a compressor assembly, a high-pressure gas collection pipe, a low-pressure gas collection pipe, and a liquid distributor. The liquid distributor is connected to multiple indoor units via multiple liquid distribution pipes. The outdoor heat exchanger is connected to the liquid distributor via a pipe. The compressor assembly is connected to the outdoor heat exchanger via a pipe. The high-pressure gas collection pipe is connected to the compressor assembly via a pipe and is also connected to multiple indoor units via multiple high-pressure gas distribution pipes. The low-pressure gas collection pipe is connected to the compressor assembly via a pipe and is also connected to multiple indoor units via multiple low-pressure gas distribution pipes. The compressor assembly is used to compress the refrigerant and adjust its flow direction. Each liquid distribution pipe is equipped with an internal expansion valve, and each high-pressure gas distribution pipe is equipped with a high-pressure solenoid valve. The high-pressure solenoid valve is used to open in heating mode so that the refrigerant flows from the high-pressure gas collection pipe to the corresponding indoor unit. Each low-pressure gas distribution pipe is equipped with a low-pressure expansion valve, which is used to open in cooling mode so that the refrigerant flows from the corresponding indoor unit to the low-pressure gas collection pipe. Attached Figure Description

[0023] Figure 1 This is a diagram of the refrigeration circulation piping for a fixed cooling and heating unit in the existing technology. Figure 2 The pressure-enthalpy curve of the refrigeration cycle of a fixed cooling and heating unit in the prior art; Figure 3 This is a schematic diagram of a fixed air conditioner that provides simultaneous cooling and heating according to an embodiment of the present invention; Figure 4 A flowchart illustrating the steps of a control method for a fixed-type air conditioner with cooling and heating provided in an embodiment of the present invention; Figure 5 This is a refrigeration circulation pipeline diagram of a fixed air conditioner that provides simultaneous cooling and heating, as provided in an embodiment of the present invention. Figure 6 This is a pressure-enthalpy curve of the refrigeration cycle of a fixed air conditioner that provides simultaneous cooling and heating, as provided in an embodiment of the present invention. Figure 7 for Figure 4 The detailed flowchart of step S3.

[0024] Explanation of reference numerals in the attached figures: 100 - Fixed air conditioner with simultaneous cooling and heating; 110 - Outdoor unit; 111 - Outdoor heat exchanger; 112 - Compressor assembly; 113 - High-pressure manifold; 114 - Low-pressure manifold; 115 - Liquid distributor; 116 - Liquid distributor pipe; 117 - High-pressure distributor pipe; 118 - Low-pressure distributor pipe; 120 - Indoor unit; 130 - Internal expansion valve; 140 - High-pressure solenoid valve; 150 - Low-pressure expansion valve. Detailed Implementation

[0025] As disclosed in the background section, in existing air conditioning systems that simultaneously provide heating and cooling, one indoor unit can operate in cooling mode while the other is in heating mode. This allows for simultaneous operation of both heating and cooling functions by circulating refrigerant. In other words, most indoor units can operate in heating mode, while a smaller portion can operate in cooling mode. However, in this scenario, when the outside air temperature is low, such as 0°C or below, the evaporation temperature of the outdoor heat exchanger becomes the baseline. This can cause the evaporation temperature of the indoor heat exchanger during cooling operation to sometimes drop below 0°C, leading to problems such as frosting, reduced airflow, and condensation.

[0026] Furthermore, under normal circumstances, the evaporation temperature of the indoor heat exchanger is typically controlled at around 10°C to avoid frost formation. However, when a fixed split-type unit simultaneously provides heating and cooling, as mentioned earlier, during the heating cycle, both the outdoor and indoor heat exchangers function as evaporators. When the outside air temperature is below 0°C, the outdoor heat exchanger needs to maintain its evaporation temperature below 0°C to absorb heat from the surrounding air. In the cooling cycle, the evaporation temperature of the indoor heat exchanger is the same as that of the outdoor heat exchanger. Figure 1 and Figure 2 As shown, in conventional air conditioning piping control, when the pressure loss between points b and c is negligible, the pressures at points b and c are equal. Therefore, the evaporation temperatures (evaporation pressures) of the outdoor and indoor heat exchangers are the same, resulting in frost formation.

[0027] To address the aforementioned problems, this invention provides a novel control method and air conditioner for a fixed-type simultaneous cooling and heating system. This system allows for adjustments to the opening of the low-pressure expansion valve between the cooling and heating elements (CD) to change the evaporation temperatures of the outdoor and indoor heat exchangers. Therefore, even when the outside air temperature is below 0°C, the evaporation temperature of the indoor heat exchanger can be controlled to prevent freezing. To make the above-mentioned objectives, features, and advantages of this invention more apparent, specific embodiments of the invention are described in detail below with reference to the accompanying drawings. Specific Implementation See also Figure 3 and Figure 4This embodiment provides a control method for a fixed-mode air conditioner 100 that can simultaneously provide cooling and heating. The fixed-mode air conditioner 100 can simultaneously provide cooling and heating functions. By adjusting the opening of the expansion valve on the pipeline, the evaporation temperature of the indoor unit 120 can be adjusted to avoid frost formation on the indoor heat exchanger when the cooling and heating are operating simultaneously at low external temperatures. This ensures airflow while preventing condensation on the surface of the indoor unit 120 and also avoids noise problems caused by condensation dripping.

[0029] See Figure 3 The fixed air conditioner 100 with simultaneous cooling and heating provided in this embodiment includes an outdoor unit 110 and multiple indoor units 120 connected to the outdoor unit 110. The outdoor unit 110 includes an outdoor heat exchanger 111, a compressor assembly 112, a high-pressure gas collection pipe 113, a low-pressure gas collection pipe 114, and a distributor 115. The distributor 115 is connected to the multiple indoor units 120 through multiple distributor pipes 116. The outdoor heat exchanger 111 is connected to the distributor 115 through a pipe. The compressor assembly 112 is connected to the outdoor heat exchanger 111 through a pipe. The high-pressure gas collection pipe 113 is connected to the compressor assembly 112 through a pipe and is connected to the multiple indoor units 120 through multiple high-pressure gas distribution pipes 117. The low-pressure gas collection pipe 114 is connected to the compressor assembly 112 via a pipe, and is also connected to multiple indoor units 120 via multiple low-pressure gas distribution pipes 118. The compressor assembly 112 is used to compress the refrigerant and adjust the refrigerant flow direction. Each liquid distribution pipe 116 is equipped with an internal expansion valve 130, and each high-pressure gas distribution pipe 117 is equipped with a high-pressure solenoid valve 140. The high-pressure solenoid valve 140 is used to open in the heating state so that the refrigerant flows from the high-pressure gas collection pipe to the corresponding indoor unit 120. Each low-pressure gas distribution pipe 118 is equipped with a low-pressure expansion valve 150, which is used to open in the cooling state so that the refrigerant flows from the corresponding indoor unit 120 to the low-pressure gas collection pipe 114.

[0030] In this embodiment, see Figure 3 When cooling is achieved using the heating element, one indoor unit 120 is in cooling mode, while the remaining indoor units 120 are in heating mode. The refrigerant flow is shown in the diagram. In the heating circuit, the internal expansion valve 130 and the high-pressure solenoid valve 140 are open, while the low-pressure expansion valve 150 is closed. In the cooling circuit, the internal expansion valve 130 and the low-pressure expansion valve 150 are open, while the high-pressure solenoid valve 140 is closed. Simultaneously, the four-way valve in the compressor assembly 112 operates on the heating side. In this embodiment, the main focus is on controlling the opening degree of the internal expansion valve 130 and the low-pressure expansion valve 150 in the cooling circuit, while maintaining the original opening degree control in the heating circuit, ensuring that the heating circuit is not affected.

[0031] Please see Figure 4The control method for the fixed cooling and heating air conditioner 100 provided in this embodiment includes the following steps: S1: At least one indoor unit 120 is set to heating mode, at least one indoor unit 120 is set to cooling mode, and the compressor assembly 112 in the outdoor unit 110 is located on the heating operation side.

[0032] Specifically, to achieve simultaneous heating and cooling functions, the internal expansion valve 130 and high-pressure solenoid valve 140 in the heating circuit are opened, while the low-pressure expansion valve 150 is closed. Similarly, the internal expansion valve 130 and low-pressure expansion valve 150 in the cooling circuit are opened, while the high-pressure solenoid valve 140 is closed. The number of indoor units 120 in heating mode should be greater than the number in cooling mode, thus ensuring that the four-way valve in the compressor assembly 112 of the outdoor unit 110 operates on the heating side. This embodiment uses one indoor unit 120 in cooling mode as an example. However, as the number of indoor units 120 in cooling mode increases, their control methods become relatively independent and can be implemented using the control method described in this embodiment.

[0033] S2: Obtain the outer ring temperature Tw of the outdoor unit 110.

[0034] Specifically, the outdoor temperature can be detected by a temperature sensor installed in the outdoor unit 110 to obtain the outer ring temperature Tw. Generally speaking, since the main mode is heating, the outdoor heat exchanger 111 of the outdoor unit 110 usually needs to control the evaporation temperature below the outer ring temperature Tw in order to absorb heat from the surrounding air.

[0035] When the outer ring temperature Tw is less than the preset outer ring temperature T1, step S3 is executed: control the opening degree of the internal expansion valve 130 and the low-pressure expansion valve 150 corresponding to the indoor unit 120 in the cooling mode, so that the evaporation temperature of the indoor unit 120 is greater than the frosting critical temperature T2.

[0036] Specifically, the internal expansion valve 130 is located on the liquid distribution pipe 116 upstream of the indoor unit 120 in cooling mode, and the low-pressure expansion valve 150 is located on the low-pressure gas distribution pipe 118 downstream of the indoor unit 120 in cooling mode. For specific location relationships, please refer to... Figure 2 And as described above.

[0037] Specifically, the preheating outer ring temperature is between 8-12℃, preferably 10℃, while the frosting critical temperature T2 is between -1℃ and 3℃, preferably 0℃. When the external ambient temperature is below 10℃, for example, when the external ambient temperature is 0℃ or below, the outdoor heat exchanger 111 of the outdoor unit 110 needs to control its evaporation temperature below 0℃ in order to absorb heat from the surrounding air. At this time, the evaporation temperature of the heat exchanger of the indoor unit 120 will also be affected, and there is a risk of frosting. However, by adjusting the opening of the internal expansion valve 130 and the low-pressure expansion valve 150, the evaporation temperatures of the outdoor and indoor heat exchangers can be changed, increasing the evaporation temperature of the heat exchanger of the indoor unit 120, for example, to 2℃, at which point frosting will not occur. Therefore, even when the external air temperature is below 0℃, the evaporation temperature of the heat exchanger of the indoor unit 120 can be controlled to prevent freezing. Furthermore, by limiting the temperature of the control conditions, this control can be activated when there is a possibility of frost formation on the indoor unit, while maintaining the original control under other conditions to ensure its heating / cooling effect. At the same time, the frost critical temperature is used to characterize the temperature at which frost may occur. When the indoor unit 120 exceeds this temperature, frost formation can be avoided, further ensuring the normal operation of the indoor unit 120.

[0038] It should be noted that, in conjunction with the above, Figure 5 and Figure 6 , Figure 5 This is a simplified diagram of the indoor cooling cycle. Figure 6 This is a pressure-enthalpy curve. In this embodiment, superheat control can be used to control the opening of the internal expansion valve 130 and the low-pressure expansion valve 150, and the evaporation pressure of the indoor unit 120 can be adjusted by the pressure loss ratio of the pipelines containing the internal expansion valve 130 and the low-pressure expansion valve 150. Specifically, by adjusting the opening of the low-pressure expansion valve 150 between c and d, the evaporation temperature of the outdoor heat exchanger 111 on the outdoor side and the evaporation temperature of the indoor heat exchanger can be changed. Therefore, even if the outside air temperature is below 0°C, the indoor heat exchanger can be prevented from freezing.

[0039] The control method provided in this embodiment first achieves simultaneous heating and cooling functions by setting at least one indoor unit 120 to heating mode and at least one indoor unit 120 to cooling mode. The compressor assembly 112 in the outdoor unit 110 is located on the heating operation side, thus ensuring that most indoor units 120 are in heating mode and a few are in cooling mode. Under this operating condition, the outer ring temperature Tw of the outdoor unit 110 is obtained. When the outer ring temperature Tw is less than the preset outer ring temperature T1, it indicates a risk of frost formation on the heat exchanger of the indoor unit 120. At this time, the opening of the low-pressure expansion valve 150 and the inner expansion valve 130 upstream and downstream of the indoor unit 120 can be adjusted. The low-pressure expansion valve 150 and the inner expansion valve 130 are treated as a hypothetical expansion valve and adjusted accordingly. This causes a change in the evaporation temperature of the outdoor heat exchanger and the evaporation temperature of the indoor heat exchanger, thereby ensuring that the evaporation temperature of the indoor unit 120 in cooling mode is greater than the frost critical temperature T2, thus preventing frost formation on the heat exchanger of the indoor unit 120. Specifically, by adjusting the opening of the low-pressure expansion valve 150 and the internal expansion valve 130, the evaporation temperature of the indoor unit 120 in cooling mode can be made greater than the frosting critical temperature T2, thus preventing the heat exchanger of the indoor unit 120 from frosting. This ensures airflow while preventing condensation on the surface of the indoor unit 120 and also avoids noise problems caused by condensation dripping.

[0040] The following section discusses step S3, combining... Figure 7 The specific control methods for the opening degrees of the internal expansion valve 130 and the low-pressure expansion valve 150 are described in detail. Specifically, step S3 includes the following sub-steps: S31: Obtain the target total opening Pm.

[0041] The target total opening Pm is the sum of the first target opening P1 of the internal expansion valve 130 and the second target opening P2 of the low-pressure expansion valve 150. Here, the internal expansion valve 130 and the low-pressure expansion valve 150 are treated as a hypothetical expansion valve for superheat control. The fluid resistance of the entire path on the indoor unit 120 side can be determined by the superheat control scheme, that is, the opening of the hypothetical expansion valve can be determined. The sum of the opening of the internal expansion valve 130 and the opening of the low-pressure expansion valve 150 is the opening of the hypothetical expansion valve.

[0042] When actually obtaining the target total opening degree Pm, it can be calculated based on the current opening degree and differential opening degree, combined with the superheat control method. Specifically, firstly, the current total opening degree Pq can be obtained, that is, the current opening degree of the hypothetical expansion valve. The current total opening degree Pq is the sum of the current opening degree of the internal expansion valve 130 and the current opening degree of the low-pressure expansion valve 150, which can be read directly. Then, the superheat difference Ts between the current superheat degree Sd and the target superheat degree Sm is obtained. The current superheat degree Sd can be the difference between the temperature of the refrigerant pipe of the outdoor unit 110 and the temperature of the heat exchanger of the indoor unit 120 in the refrigeration cycle. The target superheat degree Sm can be set and obtained. This value can be an empirical value or a simulation result value. After obtaining the superheat difference Ts, the differential opening degree δP can be calculated based on the superheat difference Ts. Finally, the target total opening degree Pm is calculated based on the current total opening degree Pq and the differential opening degree δP.

[0043] In this embodiment, the current superheat Sd is the difference between the refrigerant temperature Tm of the outdoor unit 110 and the heat exchange temperature Th of the indoor unit 120. Both the refrigerant temperature Tm and the heat exchange temperature Th can be measured values, and the target superheat is between 2-4℃, preferably 3℃. The target total opening Pm is calculated based on the superheat and the opening of the previous cycle, ensuring the rationality of the target total opening Pm. This further determines the linkage total opening of the internal expansion valve 130 and the low-pressure expansion valve 150, defines their adjustment range, and provides favorable conditions for accurately determining the opening of the internal expansion valve 130 and the low-pressure expansion valve 150 subsequently. A reasonable setting of the target superheat ensures different pipe temperatures between the indoor unit 120 and the outdoor unit 110, thereby achieving different evaporation pressures and further preventing frost formation on the indoor unit 120.

[0044] Furthermore, the target total opening Pm satisfies the following formula: Pm = Pq + δP; δP=A{ Ts(n) + B×(Ts(n) - Ts(n-1))}; Ts = Sd - Sm; Where Ts(n) is the superheat difference in the current cycle, Ts(n-1) is the superheat difference in the previous cycle, A is the first calculation constant, and B is the second calculation constant. Specifically, the first calculation constant A is between 0.6 and 0.8, and the second calculation constant B is between 1 and 3. The first and second calculation constants will vary depending on the machine model and the type of expansion valve, and are usually empirical values. By deriving the differential opening δP from the opening and superheat of the previous cycle, the target total opening Pm is accurately calculated, and the adjustment range of the internal expansion valve 130 and the low-pressure expansion valve 150 is determined.

[0045] S32: Obtain the high pressure value Pg, low pressure value Pd, and target indoor evaporation pressure Ps of the indoor unit 120 in cooling mode.

[0046] Specifically, when this model is equipped with a high-pressure sensor, the pipeline high-pressure value Pg is the value measured by that sensor. When no high-pressure sensor is installed, the pipeline high-pressure value Pg can be the average condensing pressure (condensing temperature) calculated based on the temperature of the heat exchanger of the indoor unit 120 during heating operation. Similarly, when this model is equipped with a low-pressure sensor, the pipeline low-pressure value Pd is the value measured by that sensor. When no low-pressure sensor is installed, the pipeline low-pressure value Pd can be the evaporating pressure (evaporating temperature) calculated based on the temperature of the outdoor heat exchanger 111 of the outdoor unit 110. The target indoor evaporating pressure is a set value. The target indoor evaporating pressure Ps typically indicates that the indoor unit 120 will not experience frost formation at that evaporating pressure, and can be determined based on experience or simulation experiments.

[0047] S33: The first target opening P1 and the second target opening P2 are calculated based on the pipeline high pressure value Pg, the pipeline low pressure value Pd, the target indoor evaporation pressure Ps, and the target total opening Pm.

[0048] Specifically, the first target opening P1 and the second target opening P2 satisfy the following formula: P1=Pm*(Pg-Ps) / {Pg-Ps+α(Ps-Pd)}; P2 = Pm - P1; Wherein, α is the pressure loss ratio of liquid refrigerant and gaseous refrigerant. In this embodiment, the pressure loss ratio α of liquid refrigerant and gaseous refrigerant is between 5 and 10, preferably 6.8. The opening of the two valves is determined by the pressure loss ratio of the internal expansion valve 130 and the low-pressure expansion valve 150 to prevent the valves from interfering with each other.

[0049] The first target opening degree P1 and the second target opening degree P2 are calculated using the above formulas. The opening degree of the internal expansion valve 130 and the low-pressure expansion valve 150 is determined by correcting the pressure loss ratio α of the liquid refrigerant and the gaseous refrigerant, thus preventing interference between the action lines of each valve and causing instability. This ensures stable operation while adjusting the evaporation pressure of the indoor unit 120.

[0050] S34: Adjust the internal expansion valve 130 to the first target opening P1, and adjust the low-pressure expansion valve 150 to the second target opening P2.

[0051] Specifically, after the results of the first target opening P1 and the second target opening P2 are calculated, the internal expansion valve 130 and the low-pressure expansion valve 150 can be directly adjusted to the corresponding openings to complete the control.

[0052] In this embodiment, the fluid resistance of the entire refrigeration flow path is determined by setting the target total opening degree Pm, thereby enabling the internal expansion valve 130 and the low-pressure expansion valve 150 to achieve linkage adjustment, avoiding mutual interference between the actions of each valve and causing instability in the flow path. At the same time, a target indoor evaporation pressure is set. This target indoor evaporation pressure Ps can usually characterize the phenomenon that the indoor unit 120 will not frost under this evaporation pressure. The target indoor evaporation pressure Ps can be determined based on experience or simulation experiments. Combined with the measured or calculated high pressure value Pg and low pressure value Pd of the pipeline, the first target opening degree P1 and the second target opening degree P2 can be calculated, and the opening degree of the internal expansion valve 130 and the low-pressure expansion valve 150 can be adjusted accordingly to further ensure that the evaporation temperature of the indoor unit 120 in the cooling mode is greater than the frosting critical temperature T2.

[0053] It should be noted that this embodiment uses superheat control to determine the fluid resistance of the entire path on the indoor unit 120 side, that is, to determine the target total opening Pm of the hypothetical expansion valve. The valve opening of each valve is then determined by the pressure loss ratio of the internal expansion valve 130 and the low-pressure expansion valve 150, preventing interference and instability in the operation of each valve. Furthermore, when the number of indoor units 120 operating in cooling mode increases, superheat control is also used to distribute the refrigerant flow in each path, and the indoor evaporation pressure is adjusted by the pressure loss ratio of the internal expansion valve 130 and the low-pressure expansion valve 150 upstream of each path.

[0054] In summary, this embodiment provides a fixed air conditioner 100 that can simultaneously provide both heating and cooling, and its control method. First, it achieves the function of simultaneous heating and cooling by setting at least one indoor unit 120 to heating mode and at least one indoor unit 120 to cooling mode. The compressor assembly 112 in the outdoor unit 110 is located on the heating operation side, thereby ensuring that most indoor units 120 are in heating mode and a few indoor units 120 are in cooling mode. Under this operating condition, the outer ring temperature Tw of the outdoor unit 110 is obtained. When the outer ring temperature Tw is lower than the preset outer ring temperature T1, it indicates a risk of frost formation on the heat exchanger of the indoor unit 120. This can be addressed by adjusting the opening of the low-pressure expansion valve 150 and the internal expansion valve 130 upstream and downstream of the indoor unit 120. By treating the low-pressure expansion valve 150 and the internal expansion valve 130 as a single, hypothetical expansion valve, the evaporation temperatures of the outdoor and indoor heat exchangers change. This ensures that the evaporation temperature of the indoor unit 120 in cooling mode is greater than the frost critical temperature T2, thus preventing frost formation on the heat exchanger of the indoor unit 120. Specifically, by adjusting the opening of the low-pressure expansion valve 150 and the internal expansion valve 130, the evaporation temperature of the indoor unit 120 in cooling mode is made greater than the frost critical temperature T2, preventing frost formation on the heat exchanger of the indoor unit 120. This ensures airflow while preventing condensation on the surface of the indoor unit 120 and avoiding noise problems caused by condensation dripping.

[0055] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A control method for a fixed-function air conditioner that provides both cooling and heating, applicable to such air conditioners, wherein the fixed-function air conditioner includes an outdoor unit (110) and multiple indoor units (120) simultaneously connected to the outdoor unit (110), characterized in that... The control method includes: At least one of the indoor units (120) is set to heating mode, at least one of the indoor units (120) is set to cooling mode, and the compressor assembly (112) in the outdoor unit (110) is located on the heating operation side; Obtain the outer ring temperature Tw of the outdoor unit (110); When the outer ring temperature Tw is less than the preset outer ring temperature T1, the opening degree of the inner expansion valve (130) and low pressure expansion valve (150) corresponding to the indoor unit (120) in the cooling mode is controlled so that the evaporation temperature of the indoor unit (120) in the cooling mode is greater than the frosting critical temperature T2. The internal expansion valve (130) is located on the liquid distribution pipe (116) upstream of the indoor unit (120) in the cooling mode, and the low-pressure expansion valve (150) is located on the low-pressure gas distribution pipe (118) downstream of the indoor unit (120) in the cooling mode. The step of controlling the opening degree of the internal expansion valve (130) and the low-pressure expansion valve (150) corresponding to the indoor unit (120) in cooling mode includes: Obtain the target total opening Pm, wherein the target total opening Pm is the sum of the first target opening P1 of the internal expansion valve (130) and the second target opening P2 of the low-pressure expansion valve (150); Obtain the high pressure value Pg, low pressure value Pd, and target indoor evaporation pressure Ps of the indoor unit (120) in cooling mode; The first target opening P1 and the second target opening P2 are calculated based on the pipeline high pressure value Pg, the pipeline low pressure value Pd, the target indoor evaporation pressure Ps, and the target total opening Pm. Adjust the internal expansion valve (130) to the first target opening P1, and adjust the low-pressure expansion valve (150) to the second target opening P2; Wherein, the first target opening P1 and the second target opening P2 satisfy the following formula: P1=Pm*(Pg-Ps) / {Pg-Ps+α(Ps-Pd)}; P2 = Pm - P1; Where α is the pressure loss ratio of liquid refrigerant and gaseous refrigerant; In cooling mode, the evaporation temperature of the indoor unit (120) is greater than that of the outdoor unit (110), the preset outer ring temperature T1 is between 8-12℃, and the frosting critical temperature T2 is between -1℃ and 3℃.

2. The control method for a fixed air conditioner with simultaneous cooling and heating according to claim 1, characterized in that, The pressure loss ratio α between liquid and gaseous refrigerants is between 5 and 10.

3. The control method for a fixed air conditioner with simultaneous cooling and heating according to claim 1, characterized in that, The steps to obtain the target total aperture Pm include: Obtain the current total opening degree Pq, wherein the current total opening degree Pq is the sum of the current opening degree of the internal expansion valve (130) and the current opening degree of the low-pressure expansion valve (150); Obtain the superheat difference Ts between the current superheat Sd and the target superheat Sm; The differential separation δP is calculated based on the superheat difference Ts. The target total opening Pm is calculated based on the current total opening Pq and the differential opening δP.

4. The control method for a fixed air conditioner with simultaneous cooling and heating according to claim 3, characterized in that, The target total opening Pm satisfies the following formula: Pm = Pq + δP; δP=A{ Ts (n) + B×(Ts (n) - Ts (n-1) )}; Ts = Sd - Sm; Among them, Ts (n) Ts represents the difference in superheat during the current cycle. (n-1) The difference in superheat from the previous cycle is represented by A, which is the first calculation constant, and B is the second calculation constant.

5. The control method for a fixed air conditioner with simultaneous cooling and heating according to claim 4, characterized in that, The first calculation constant A is between 0.6 and 0.8, and the second calculation constant B is between 1 and 3.

6. The control method for a fixed air conditioner with simultaneous cooling and heating according to claim 4, characterized in that, The current superheat Sd is the difference between the refrigerant temperature Tm of the outdoor unit (110) and the heat exchange temperature Th of the indoor unit (120), and the target superheat is between 2-4℃.

7. A fixed air conditioner that simultaneously provides cooling and heating, characterized in that, The control method applicable to the fixed-split air conditioner with simultaneous cooling and heating as described in any one of claims 1-6, wherein the fixed-split air conditioner with simultaneous cooling and heating comprises: Multiple indoor units (120); An outdoor unit (110) includes an outdoor heat exchanger (111), a compressor assembly (112), a high-pressure gas collection pipe (113), a low-pressure gas collection pipe (114), and a distributor (115). The distributor (115) is connected to multiple indoor units (120) via multiple distributor pipes (116). The outdoor heat exchanger (111) is connected to the distributor (115) via a pipe. The compressor assembly (112) is connected to the outdoor heat exchanger (111) via a pipe. The high-pressure gas collection pipe (113) is connected to the compressor assembly (112) via a pipe and is connected to multiple indoor units (120) via multiple high-pressure gas distribution pipes (117). The low-pressure gas collection pipe (114) is connected to the compressor assembly (112) via a pipe and is connected to multiple indoor units (120) via multiple low-pressure gas distribution pipes (118). The compressor assembly (112) is used to compress the refrigerant and adjust the refrigerant flow direction. Each liquid distribution pipe (116) is provided with an internal expansion valve (130), and each high-pressure gas distribution pipe (117) is provided with a high-pressure solenoid valve (140). The high-pressure solenoid valve (140) is used to open in the heating state so that the refrigerant flows from the high-pressure gas collection pipe (113) to the corresponding indoor unit (120). Each low-pressure gas distribution pipe (118) is provided with a low-pressure expansion valve (150). The low-pressure expansion valve (150) is used to open in the cooling state so that the refrigerant flows from the corresponding indoor unit (120) to the low-pressure gas collection pipe (114).

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