A variable frequency direct expansion machine

Abstract

The present invention discloses a variable frequency direct expansion machine, comprising: a fixed frequency indoor unit and a variable frequency outdoor unit connected by a connection pipe, and a control device. The fixed frequency indoor unit comprises: an evaporator, a first one-way valve, a thermal expansion valve, a temperature sensing bag and a first liquid pipe, the evaporator is connected to the liquid pipe, the first one-way valve is arranged on the liquid pipe and connected in parallel with the thermal expansion valve, the temperature sensing bag is electrically connected to the thermal expansion valve, and the temperature sensing bag is located near the inlet of the first liquid pipe; the variable frequency outdoor unit comprises: a condensing operating valve, a second one-way valve, an electronic expansion valve and a second liquid pipe, the condensing operating valve and the second one-way valve are both connected in series with the second liquid pipe, and the two ends of the electronic expansion valve are connected in parallel to the input end of the condensing operating valve and the output end of the second one-way valve; the control device is used to control the condensing operating valve to be in a closed state, and throttling control is performed by the electronic expansion valve during cooling and heating.

Description

Technical Field

[0001] The invention relates to a variable frequency direct expansion machine which is transformed and upgraded from a fixed frequency direct expansion machine to a variable frequency machine, and belongs to the technical field of air conditioning. Background Art

[0002] The direct expansion air conditioning unit (abbreviated as DX unit) is a unit with its own compressor. The liquid refrigerant in its refrigeration system directly evaporates (expands) in its evaporator coil, absorbing heat from the air outside the coil (that is, the air inside the air conditioner room) to cool it. At present, DX units have been widely used in production and life. However, old DX units are basically fixed-frequency outdoor units. They generally have disadvantages such as high energy consumption, narrow application range, and uncomfortable air output.

[0003] Since the compressor load of a fixed-frequency direct expansion machine cannot be changed, the air outlet temperature cannot be controlled. Fixed-frequency direct expansion machines generally use thermal expansion valves to manage the superheat of the refrigerant. This control mode can control the superheat more accurately when the fixed-frequency direct expansion machine continues to output at a high load. However, depending on the environment and user needs, the frequency of a variable-frequency direct expansion machine may sometimes be only 20% of the rated frequency. At this time, the thermal expansion valve cannot control the superheat of the refrigerant well. As a result, a large amount of liquid refrigerant returns to the compressor, causing liquid compression and damage to the compressor. In addition, many old fixed-frequency direct expansion machines use R22 refrigerant, and the original thermal expansion valve cannot be used with the currently commonly used R410A refrigerant. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a variable frequency direct expansion machine. The variable frequency direct expansion machine is upgraded from a fixed frequency direct expansion machine by frequency conversion, and can achieve accurate superheat control of the refrigerant.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] According to a first aspect of an embodiment of the present invention, there is provided a variable frequency direct expansion machine, comprising a fixed frequency indoor unit and a variable frequency outdoor unit connected by a connection pipe, and a control device;

[0007] The fixed-frequency indoor unit comprises: an evaporator, a first one-way valve, a thermal expansion valve, a temperature-sensing package and a first liquid pipe, wherein the evaporator is connected to the first liquid pipe, the first one-way valve is arranged on the first liquid pipe and connected in parallel with the thermal expansion valve, the temperature-sensing package is connected to the thermal expansion valve, and the temperature-sensing package is located near the inlet of the first liquid pipe;

[0008] The variable frequency outdoor unit comprises: a condensing operating valve, a second one-way valve, an electronic expansion valve and a second liquid pipe, the condensing operating valve and the second one-way valve are both connected in series with the second liquid pipe, and two ends of the electronic expansion valve are connected in parallel to the input end of the condensing operating valve and the output end of the second one-way valve;

[0009] The control device is used to send an opening instruction to the electronic expansion valve control board to control the opening change of the electronic expansion valve to ensure that the return air superheat is stable in the target temperature range.

[0010] Preferably, the variable frequency outdoor unit further includes a first temperature sensor and a low pressure sensor;

[0011] The control device is connected to the first temperature sensor and the low pressure sensor, and is used to obtain the return air superheat by subtracting the saturation temperature corresponding to the low pressure detected by the low pressure sensor from the measured value of the first temperature sensor.

[0012] Preferably, the fixed-frequency indoor unit further includes a second temperature sensor, and the second temperature sensor is used to detect the outlet air temperature; the variable-frequency outdoor unit further includes a compressor;

[0013] The control device is connected to the compressor and the second temperature sensor respectively, and is also used to control the compressor to increase or decrease gears when the air outlet temperature exceeds the corresponding temperature range.

[0014] Preferably, the control device is specifically used for:

[0015] After the stable operation time of the compressor reaches a first time, the outlet air temperature is obtained. When the outlet air temperature exceeds the upper limit of the set temperature range by 1°C, the operating frequency of the compressor is controlled to increase by one level; when the outlet air temperature is 1°C lower than the lower limit of the set temperature range, the operating frequency of the compressor is controlled to decrease by one level.

[0016] Preferably, the control device is also used for:

[0017] When the compressor is in the minimum working gear for a second time period, and the air outlet temperature is less than or equal to the difference between the lower limit of the set temperature range and 1° C. for a third time period, controlling to shut down all compressors;

[0018] Among them, the first duration and the second duration are greater than the third duration.

[0019] According to a second aspect of an embodiment of the present invention, there is provided a variable frequency direct expansion machine, comprising: a fixed frequency indoor unit and a variable frequency outdoor unit connected by a connection pipe, and a control device;

[0020] The fixed-frequency indoor unit comprises: an evaporator, a first one-way valve, a thermal expansion valve, a temperature-sensing package and a first liquid pipe, wherein the evaporator is connected to the first liquid pipe, the first one-way valve is arranged on the first liquid pipe and connected in parallel with the thermal expansion valve, the temperature-sensing package is connected to the thermal expansion valve, and the temperature-sensing package is located near the inlet of the first liquid pipe;

[0021] An external expansion valve box is connected in series on the online pipe connected to the liquid pipe, the external expansion valve box is arranged near the fixed-frequency indoor unit, the external expansion valve box has a built-in electronic expansion valve control board and a third one-way valve, the third one-way valve is connected in series on the online pipe connected to the first liquid pipe and is connected in parallel with the electronic expansion valve control board, and the electronic expansion valve control board is communicatively connected with the main control board of the variable-frequency outdoor unit;

[0022] The variable frequency outdoor unit is provided with an electronic expansion valve, a second one-way valve and a second liquid pipe, the second one-way valve is connected in series with the second liquid pipe, and the electronic expansion valve is connected in parallel with the second one-way valve;

[0023] The control device is used to control the return air superheat of the electronic expansion valve control board and the electronic expansion valve.

[0024] Preferably, the control device is specifically used for:

[0025] During cooling, the refrigerant is controlled not to pass through the electronic expansion valve of the variable frequency outdoor unit, but to directly reach the external expansion valve box through the third one-way valve;

[0026] During heating, the refrigerant is controlled not to pass through the electronic expansion valve control board of the external expansion valve box, but to directly reach the electronic expansion valve of the variable frequency outdoor unit through the second one-way valve.

[0027] Preferably, the electronic expansion valve control board is connected to the main control board of the variable frequency outdoor unit.

[0028] Preferably, the electronic expansion valve of the variable frequency outdoor unit and the electronic expansion valve control board of the external expansion valve box operate synchronously.

[0029] Preferably, the control target of the return air superheat control is 5°C to 7°C.

[0030] Preferably, the variable frequency outdoor unit further includes a first temperature sensor and a low pressure sensor;

[0031] The control device is connected to the first temperature sensor and the low pressure sensor, and is used to obtain the return air superheat by subtracting the saturation temperature corresponding to the low pressure detected by the low pressure sensor from the measured value of the first temperature sensor.

[0032] Preferably, the fixed-frequency indoor unit further includes a second temperature sensor, and the second temperature sensor is used to detect the outlet air temperature; the variable-frequency outdoor unit further includes a compressor;

[0033] The control device is connected to the compressor and the second temperature sensor respectively, and is also used to control the compressor to increase or decrease gears when the air outlet temperature exceeds the corresponding temperature range.

[0034] Preferably, the control device is specifically used for:

[0035] After the stable operation time of the compressor reaches a first time, the outlet air temperature is obtained. When the outlet air temperature exceeds the upper limit of the set temperature range by 1°C, the operating frequency of the compressor is controlled to increase by one level; when the outlet air temperature is 1°C lower than the lower limit of the set temperature range, the operating frequency of the compressor is controlled to decrease by one level.

[0036] Preferably, the control device is also used for:

[0037] When the compressor is in the minimum working gear for a second time period, and the return air temperature is less than or equal to the difference between the lower limit of the set temperature range and 1° C. for a third time period, shut down all compressors;

[0038] Among them, the first duration and the second duration are greater than the third duration.

[0039] Preferably, the set temperature interval includes: a set cooling temperature interval and a set heating temperature interval;

[0040] The set refrigeration temperature range includes any one of the following three refrigeration temperature ranges:

[0041] The first-stage refrigeration temperature range is 18℃~22℃, the second-stage refrigeration temperature range is 22℃~25℃, and the third-stage refrigeration temperature range is 25℃~28℃;

[0042] The set heating temperature range includes any one of the following three heating temperature ranges:

[0043] The first-level heating temperature range is 20℃~24℃, the second-level heating temperature range is 24℃~28℃, and the third-level heating temperature range is 28℃~32℃;

[0044] The first duration and the second duration are 6 minutes, and the third duration is 5 seconds.

[0045] Compared with the prior art, the present invention can upgrade the fixed-frequency outdoor unit to a variable-frequency outdoor unit when the fixed-frequency outdoor unit reaches the end of its service life and the fixed-frequency indoor unit still needs to be used, thereby reducing the cost of transformation and reducing energy consumption. In addition, the present invention can also control the expansion valve when the indoor and outdoor units are short-distance after replacing the variable-frequency direct expansion machine; and control the expansion valve after adding an expansion valve box over a long distance after replacing the variable-frequency direct expansion machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of the overall structure of a variable frequency direct expansion machine in the first embodiment of the present invention;

[0047] Figure 2 It is a schematic diagram of the layout of the temperature sensing package in the fixed-frequency indoor unit of the prior art;

[0048] Figure 3 This is a schematic diagram of the layout of the temperature sensing package in the first embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of the overall structure of a variable frequency direct expansion machine in the second embodiment of the present invention;

[0050] Description of Figure Numbers:

[0051] 10. Fixed frequency indoor unit; 101. Evaporator; 102. First check valve; 103. Thermal expansion valve; 104. Temperature sensing package; 105. First liquid pipe; 106. First return air pipe;

[0052] 20. Inverter outdoor unit;

[0053] 201, second air return pipe;

[0054] 202, air return pipe operating valve;

[0055] 203, four-way valve;

[0056] 204, suction air temperature sensor;

[0057] 205. High pressure sensor;

[0058] 206, first maintenance valve;

[0059] 207. High voltage switch;

[0060] 208. Oil separator;

[0061] 209. Filter;

[0062] 210, exhaust temperature sensor;

[0063] 211. Compressor;

[0064] 212, capillary;

[0065] 213. Gas-liquid separator;

[0066] 214, second maintenance valve;

[0067] 215. Low pressure sensor;

[0068] 216. Condenser;

[0069] 217. Outside air temperature sensor;

[0070] 218. Condensation operating valve;

[0071] 219, second one-way valve;

[0072] 220, electronic expansion valve;

[0073] 221, Liquid pipe operating valve;

[0074] 222, second liquid pipe;

[0075] 30. Online pipe;

[0076] 40. External expansion valve box;

[0077] 401, third one-way valve;

[0078] 402. Electronic expansion valve control board. DETAILED DESCRIPTION

[0079] The technical content of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0080] After in-depth research, the inventor found that as long as the old direct expansion indoor unit has the ability to accurately control the return air superheat, the original direct expansion indoor unit can be transformed and upgraded into a variable frequency direct expansion machine. After upgrading to a variable frequency direct expansion machine, the outlet air temperature control function can be added to control the outlet air temperature very well. When the fixed frequency outdoor unit reaches the end of its service life and the fixed frequency indoor unit still needs to be used, it is a good choice to transform and upgrade the fixed frequency outdoor unit into a variable frequency outdoor unit when replacing the fixed frequency outdoor unit. Below, the specific implementation steps of the above technical ideas are described in detail.

[0081] <First Embodiment>

[0082] like Figure 1 As shown, the first embodiment of the present invention discloses a variable frequency direct expansion machine, which at least comprises: a fixed frequency indoor unit (i.e., an indoor unit of an existing fixed frequency direct expansion machine) 10 and a variable frequency outdoor unit 20 connected by a connection pipe 30, and a control device;

[0083] The fixed-frequency indoor unit 10 includes: an evaporator 101, a first one-way valve 102, a thermal expansion valve 103, a temperature-sensing package 104 and a first liquid pipe 105. The evaporator 101 is connected to the first liquid pipe 105. The first one-way valve 102 is arranged on the first liquid pipe 105 and connected in parallel with the thermal expansion valve 103. The temperature-sensing package 104 is connected to the thermal expansion valve 103. The position of the temperature-sensing package 104 is changed to be arranged near the inlet of the first liquid pipe 105.

[0084] The variable frequency outdoor unit 20 includes: a condensing operating valve 218, a second one-way valve 219, an electronic expansion valve 220 and a second liquid pipe 222. The condensing operating valve 218 and the second one-way valve 219 are connected in series with the second liquid pipe 222, and both ends of the electronic expansion valve 220 are connected in parallel to the input end of the condensing operating valve 218 and the output end of the second one-way valve 219.

[0085] The control device is used to control the condensing operating valve 218 to be in a closed state, and to perform throttling control through the electronic expansion valve 220 during cooling and heating.

[0086] In addition, the variable frequency outdoor unit 20 further includes: a first temperature sensor and a low pressure sensor 215;

[0087] The control device is electrically connected to the first temperature sensor and the low pressure sensor 215, and is used to obtain the return air superheat by subtracting the saturation temperature Ts corresponding to the low pressure detected by the low pressure sensor 215 from the measured value of the first temperature sensor.

[0088] The fixed-frequency indoor unit also includes a second temperature sensor, namely, an outlet air temperature sensor, which is used to detect the outlet air temperature; the variable-frequency outdoor unit also includes a compressor 211;

[0089] The control device is electrically connected to the compressor 211 and the second temperature sensor, respectively, and is also used to control the compressor 211 to increase or decrease gears when the air outlet temperature exceeds the corresponding temperature range.

[0090] In some embodiments, the fixed frequency indoor unit is further provided with a first return air pipe 106. The variable frequency outdoor unit may further include the following components: a second return air pipe 201; a return air pipe operating valve 202; a four-way valve 203; an air intake temperature sensor 204; a high pressure sensor 205; a first maintenance valve 206; a high pressure switch 207; an oil separator 208; a filter 209; an exhaust temperature sensor 210; a compressor 211; a capillary tube 212; a gas-liquid separator 213; a second maintenance valve 214; a low pressure sensor 215; a condenser 216; an outdoor air temperature sensor 217; and a liquid pipe operating valve 221.

[0091] like Figure 2 and Figure 3As shown, the embodiment of the present invention changes the position of the temperature-sensing package 104 of the original direct expansion machine from the outlet of the evaporator 101 to the inlet of the first liquid pipe 105 arranged at the fixed-frequency indoor unit 10, so that the thermal expansion valve 103 will have a relatively large opening at any time. This is conducive to shielding the control ability of the thermal expansion valve 103 of the old indoor unit on the refrigerant flow.

[0092] The embodiment of the present invention also replaces the sensor head of the indoor temperature sensor to facilitate monitoring of the outlet air temperature and prepare for controlling the outlet air temperature.

[0093] The following is a detailed description of the situation where the connection pipe 30 between the indoor unit and the variable frequency outdoor unit does not exceed 20m:

[0094] Since the distance of the connection pipe 30 is not long, the pressure loss effect of the two-phase transport in the connection pipe 30 is within an acceptable range. At this time, the indoor unit only needs to change the position of the temperature sensing package 104 of the thermal expansion valve 103, and the pipeline does not need to be changed.

[0095] The outdoor unit closes the condensing operating valve 218, and keeps the one-way valve circuit closed. At this time, both cooling and heating are throttled by the electronic expansion valve 220EEVH1. The low pressure detected by the low pressure sensor 215 is subtracted from the suction temperature sensor 204 (Tho-S), and the saturation temperature Ts corresponding to the R410A refrigerant at this pressure is calculated through the physical property table to obtain the return air superheat. The return air superheat control target is 5℃~7℃.

[0096] In the embodiment of the present invention, the control process of the air outlet temperature is as follows:

[0097] The frequency of the compressor 211 is divided into the following ten gears:

[0098] 30Hz, 40Hz, 50Hz, 60Hz, 70Hz, 80Hz, 90Hz, 100Hz, 110Hz, 120Hz;

[0099] The outlet air temperature is detected by the outlet air temperature sensor of the indoor unit (not shown in the figure).

[0100] Since most direct expansion machines are fresh air units, the external environment has a great influence on the outlet air temperature. In order to avoid frequent large-scale fluctuations in the frequency of the compressor 211, the PID (proportional, integral and differential) control and the ±1°C temperature difference start-stop control used by most air conditioners are not used here. The embodiment of the present invention adopts a temperature range control method, which is specifically described as follows:

[0101] When cooling, the temperature range is divided into three levels: Level 1 is 18℃~22℃, and the corresponding wire controller setting is <22℃; Level 2 is 22℃~25℃, and the corresponding wire controller setting is 22℃~25℃; Level 3 is 25℃~28℃, and the corresponding wire controller setting is >25℃. The factory default is Level 1.

[0102] When heating, the temperature range is divided into three levels: Level 1 is 20℃~24℃, and the corresponding wire controller setting is <23℃; Level 2 is 24℃~28℃, and the corresponding wire controller setting is 23℃~28℃; Level 3 is 28℃~32℃, and the corresponding wire controller setting is >28℃. The factory default is Level 2.

[0103] When the air outlet temperature exceeds the corresponding temperature range, it is necessary to increase or decrease the gear of the compressor 211. The air outlet temperature is detected every 3 minutes, and the average is taken for 10 seconds.

[0104] After the compressor 211 runs stably for 6 minutes, the level is increased or decreased according to the temperature range of the level set by the wired controller (the outlet temperature increases by 1 level when it exceeds the upper limit by 1°C, and decreases by 1 level when it is lower than the lower limit by 1°C). The above judgment and corresponding operation are performed every 2 minutes thereafter. If the minimum energy level lasts for 6 minutes and the outlet temperature is <= set value - 1°C for 5 seconds, all compressors 211 are turned off. Since the compressor is already running at the lowest speed, the outlet temperature detection of the indoor unit still needs to reduce the speed, and the compressor needs to be stopped at this time.

[0105] <Second Embodiment>

[0106] like Figure 4 As shown, the second embodiment of the present invention also provides another variable frequency direct expansion machine, which includes: a fixed frequency indoor unit 10 and a variable frequency outdoor unit 20 connected by a connecting pipe 30, and a control device.

[0107] Among them, the fixed-frequency indoor unit 10 includes: an evaporator 101, a first one-way valve 102, a thermal expansion valve 103, a temperature sensing package 104 and a first liquid pipe 105. The evaporator 101 is connected to the first liquid pipe 105. The first one-way valve 102 is arranged on the first liquid pipe 105 and is connected in parallel with the thermal expansion valve 103. The temperature sensing package 104 is connected to the thermal expansion valve 103, and the temperature sensing package 104 is located near the entrance of the first liquid pipe 105.

[0108] An external expansion valve box 40 is connected in series to the online pipe 30 connected to the first liquid pipe 105. The external expansion valve box 40 is arranged near the fixed-frequency indoor unit 10. The external expansion valve box 40 has an electronic expansion valve control board (EEV control board) 402 and a third one-way valve 401 built in. The third one-way valve 401 is on the online pipe 30 connected to the first liquid pipe 105 and is connected in parallel to the electronic expansion valve control board 402. The electronic expansion valve control board 402 is communicatively connected to the main control board of the variable-frequency outdoor unit.

[0109] The variable frequency outdoor unit 20 is provided with an electronic expansion valve 220, a second one-way valve 219 and a second liquid pipe 222, the second one-way valve 219 and the second liquid pipe 222 are connected in series, and the electronic expansion valve 220 and the third one-way valve 401 are connected in parallel;

[0110] The control device is used to send an opening instruction to the EEV electronic expansion valve control board 402 to control the opening change of the electronic expansion valve 220 to ensure that the return air superheat is stable in the target temperature range, such as 5°C to 7°C.

[0111] In the embodiment of the present invention, the position of the temperature-sensing package 104 of the original direct expansion machine is changed from the outlet of the evaporator 101 to the inlet of the first liquid pipe 105, so that the thermal expansion valve 103 will have a relatively large opening at any time. The thermal expansion valve 103 loses the ability to control the refrigerant flow. In addition, in the embodiment of the present invention, an indoor air outlet temperature sensor will be added to facilitate monitoring of the air outlet temperature and prepare for controlling the air outlet temperature.

[0112] In some embodiments, the control device is specifically configured to:

[0113] During cooling, the refrigerant is controlled not to pass through the electronic expansion valve 220, but to directly reach the external expansion valve box 40 through the third one-way valve 401;

[0114] During heating, the refrigerant is controlled not to pass through the electronic expansion valve control board 402 of the external expansion valve box 40, but to directly reach the electronic expansion valve 220 of the variable frequency outdoor unit through the second one-way valve 219.

[0115] Preferably, the electronic expansion valve control board 402 is communicatively connected with the main control board of the variable frequency outdoor unit.

[0116] In some embodiments, the electronic expansion valve 220 of the outdoor unit and the electronic expansion valve control board 402 of the external expansion valve box 40 act synchronously. Synchronous action is conducive to more convenient control and is conducive to ensuring the return air superheat. The specific implementation process of synchronous control may include: there are two EEV control interfaces on the outdoor substrate, and when there is a change in the EEV control, the same opening instruction can be directly sent.

[0117] In some embodiments, the control target of the return air superheat control is 5°C to 7°C.

[0118] In some embodiments, the variable frequency outdoor unit further includes: a first temperature sensor and a low pressure sensor 215;

[0119] The control device is electrically connected to the first temperature sensor and the low pressure sensor 215, and is used to obtain the return air superheat by subtracting the saturation temperature Ts corresponding to the low pressure detected by the low pressure sensor 215 from the measured value of the first temperature sensor.

[0120] In some embodiments, the variable frequency outdoor unit further includes a compressor 211 and a second temperature sensor, and the second temperature sensor is used to detect the outlet air temperature;

[0121] The control device is electrically connected to the compressor 211 and the second temperature sensor, respectively, and is also used to control the compressor 211 to increase or decrease gears when the air outlet temperature exceeds the corresponding temperature range.

[0122] The following is a detailed description of the situation where the connection pipe 30 between the indoor unit and the outdoor unit exceeds 20m and does not exceed 70m:

[0123] Since the connection pipe 30 is too long, if only the outdoor expansion valve is used for throttling, the refrigerant will have a large pressure loss in the connection pipe 30, which may affect the performance. When cooling, the outdoor unit electronic expansion valve 220 cannot be used for control, and an external expansion valve box 40 needs to be added next to the indoor unit to throttle the refrigerant.

[0124] The external expansion valve box 40 has an EEV control board built in, and is connected to the outdoor unit main control board through, for example, a 485 communication line. The outdoor unit's electronic expansion valve 220EEVH and the EEV of the external expansion valve box 40 operate synchronously. Both expansion valves are controlled by the return air superheat. The return air superheat control target is 5°C to 7°C.

[0125] During cooling, the refrigerant does not pass through the electronic expansion valve 220EEVH1, but directly reaches the external expansion valve box 40 through the non-return valve next to it. At this time, the EEV in the external expansion valve box 40 plays a throttling role.

[0126] During heating, the refrigerant does not pass through the EEV of the external expansion valve box 40, but directly reaches the electronic expansion valve 220EEVH of the outdoor unit through the one-way valve next to it. At this time, the electronic expansion valve 220EEVH of the outdoor unit plays a throttling role.

[0127] In this way, the electronic expansion valve 220 is located very close to the heat exchanger, which can effectively reduce flow loss.

[0128] In the embodiment of the present invention, the control process of the air outlet temperature is as follows:

[0129] The frequency of compressor 211 is divided into the following ten gears:

[0130] 30Hz, 40Hz, 50Hz, 60Hz, 70Hz, 80Hz, 90Hz, 100Hz, 110Hz, 120Hz;

[0131] The outlet air temperature is detected by the outlet air temperature sensor of the indoor unit.

[0132] Since most direct expansion machines are fresh air units, the external environment has a great influence on the outlet air temperature. In order to avoid frequent large-scale fluctuations in the frequency of the compressor 211, the PID (proportional integral differential) control and ±1°C temperature difference start-stop control used by most air conditioners are not used here. The temperature range control method is adopted in the embodiment of the present invention, which is described in detail as follows.

[0133] When cooling, the temperature range is divided into three levels: Level 1 is 18℃~22℃, corresponding to the upper wire controller setting (user setting) <22℃; Level 2 is 22℃~25℃, corresponding to the upper wire controller setting of 22℃~25℃; Level 3 is 25℃~28℃, corresponding to the upper wire controller setting >25℃. The factory default is Level 1.

[0134] When heating, the temperature range is divided into three levels: Level 1 is 20℃~24℃, corresponding to the upper line controller setting <23℃; Level 2 is 24℃~28℃, corresponding to the upper line controller setting 23℃~28℃; Level 3 is 28℃~32℃, corresponding to the upper line controller setting >28℃. The factory default is Level 2.

[0135] When the air outlet temperature exceeds the corresponding temperature range, it is necessary to increase or decrease the gear of the compressor 211. The air outlet temperature is detected every 3 minutes, and the average is taken for 10 seconds.

[0136] After the compressor 211 runs stably for 6 minutes, the level is increased or decreased according to the temperature range of the level set by the wired controller (the outlet temperature increases by 1 level when it exceeds the upper limit by 1°C, and decreases by 1 level when it is lower than the lower limit by 1°C). The above judgment and corresponding operation are performed every 2 minutes thereafter. If the minimum energy level lasts for 6 minutes and the outlet temperature is <= set value - 1°C for 5 seconds, all compressors 211 are turned off and the state is temperature control OFF.

[0137] For example, the return air temperature is 18℃, the target temperature is set to 19.5℃, and the compressor is continuously required to reduce the frequency. However, the compressor is already running at the lowest frequency, and the compressor has been running at the lowest frequency for 6 minutes, and the return air temperature is still lower than 18.5℃. Therefore, the control device controls the only running variable frequency compressor to stop.

[0138] Compared with the prior art, the present invention can upgrade the fixed-frequency outdoor unit to a variable-frequency outdoor unit when the fixed-frequency outdoor unit reaches the end of its service life and the fixed-frequency indoor unit still needs to be used. During the upgrading process, the original indoor unit and the online pipe can be retained, and only the outdoor unit is replaced, thereby reducing the cost of upgrading and reducing energy consumption.

[0139] On the other hand, the technical solution provided by the present invention is conducive to controlling the expansion valve when the distance between the internal and external machines is short after replacing the variable frequency direct expansion machine; and controlling the expansion valve after adding an expansion valve box over a long distance after replacing the variable frequency direct expansion machine.

[0140] The variable frequency direct expansion machine provided by the present invention, which is upgraded from a fixed frequency direct expansion machine to a variable frequency machine, is described in detail above. For a person skilled in the art, any obvious changes made to it without departing from the essence of the present invention will constitute an infringement of the patent right of the present invention and will bear corresponding legal liabilities.

Claims

1. A variable frequency direct expansion machine, characterized in that include: Fixed-frequency indoor units and variable-frequency outdoor units connected by online pipes, as well as control equipment; The fixed-frequency indoor unit comprises: an evaporator, a first one-way valve, a thermal expansion valve, a temperature-sensing bag and a first liquid pipe, wherein the evaporator is connected to the first liquid pipe, the first one-way valve is arranged on the first liquid pipe and connected in parallel with the thermal expansion valve, the temperature-sensing bag is electrically connected to the thermal expansion valve, and the temperature-sensing bag is located near the inlet of the first liquid pipe; The variable frequency outdoor unit comprises: a condensing operating valve, a second one-way valve, an electronic expansion valve and a second liquid pipe, the condensing operating valve and the second one-way valve are both connected in series with the second liquid pipe, and two ends of the electronic expansion valve are connected in parallel to the input end of the condensing operating valve and the output end of the second one-way valve; The control device is used to control the condensing operating valve to be in a closed state, and to perform throttling control through the electronic expansion valve during cooling and heating.

2. The variable frequency direct expansion machine according to claim 1, characterized in that The variable frequency outdoor unit also includes: a first temperature sensor and a low pressure sensor; The control device is electrically connected to the first temperature sensor and the low pressure sensor, and is used to obtain the return air superheat by subtracting the saturation temperature corresponding to the low pressure detected by the low pressure sensor from the measured value of the first temperature sensor.

3. The variable frequency direct expansion machine according to claim 2, characterized in that The fixed-frequency indoor unit also includes a second temperature sensor, which is used to detect the outlet air temperature; The variable frequency outdoor unit also includes a compressor; The control device is electrically connected to the compressor and the second temperature sensor, respectively, and is also used to control the compressor to increase or decrease gears when the air outlet temperature exceeds the corresponding temperature range.

4. A variable frequency direct expansion machine, characterized in that include: Fixed-frequency indoor units and variable-frequency outdoor units connected by online pipes, as well as control equipment; The fixed-frequency indoor unit comprises: an evaporator, a first one-way valve, a thermal expansion valve, a temperature-sensing bag and a first liquid pipe, wherein the evaporator is connected to the first liquid pipe, the first one-way valve is arranged on the first liquid pipe and connected in parallel with the thermal expansion valve, the temperature-sensing bag is electrically connected to the thermal expansion valve, and the temperature-sensing bag is located near the inlet of the first liquid pipe; An external expansion valve box is connected in series on the online pipe connected to the first liquid pipe, the external expansion valve box is arranged near the fixed-frequency indoor unit, the external expansion valve box has an electronic expansion valve control board and a third one-way valve built in, the third one-way valve is connected in series on the online pipe connected to the first liquid pipe and is connected in parallel with the electronic expansion valve control board, and the electronic expansion valve control board is communicatively connected to the main control board of the variable-frequency outdoor unit; The variable frequency outdoor unit is provided with an electronic expansion valve, a second one-way valve and a second liquid pipe, the second one-way valve is connected in series with the second liquid pipe, and the electronic expansion valve is connected in parallel with the second one-way valve; The control device is used to send an opening instruction to the electronic expansion valve control board to control the opening change of the electronic expansion valve to ensure that the return air superheat is stable in the target temperature range.

5. The variable frequency direct expansion machine according to claim 4, characterized in that The control device is specifically used for: During refrigeration, the refrigerant does not pass through the electronic expansion valve, but directly reaches the external expansion valve box through the third one-way valve; During heating, the refrigerant is controlled not to pass through the electronic expansion valve control board of the external expansion valve box, but to directly reach the electronic expansion valve of the variable frequency outdoor unit through the second one-way valve.

6. The variable frequency direct expansion machine according to claim 4, characterized in that: The electronic expansion valve control board is connected to the main control board of the variable frequency outdoor unit; the electronic expansion valve of the variable frequency outdoor unit and the electronic expansion valve control board of the external expansion valve box act synchronously.

7. The variable frequency direct expansion machine according to claim 4, characterized in that The variable frequency outdoor unit also includes: a first temperature sensor and a low pressure sensor; The control device is electrically connected to the first temperature sensor and the low pressure sensor, and is used to obtain the return air superheat by subtracting the saturation temperature corresponding to the low pressure detected by the low pressure sensor from the measured value of the first temperature sensor.

8. The variable frequency direct expansion machine according to claim 7, characterized in that The variable frequency outdoor unit also includes a compressor, and the fixed frequency indoor unit is also provided with a second temperature sensor, the second temperature sensor is used to detect the outlet air temperature; The control device is electrically connected to the compressor and the second temperature sensor, respectively, and is also used to control the compressor to increase or decrease gears when the air outlet temperature exceeds the corresponding temperature range.

9. The variable frequency direct expansion machine according to claim 8, characterized in that The control device is specifically used for: After the stable operation time of the compressor reaches a first time, the outlet air temperature is obtained. When the outlet air temperature exceeds the upper limit of the set temperature range by 1°C, the operating frequency of the compressor is controlled to increase by one level; when the outlet air temperature is 1°C lower than the lower limit of the set temperature range, the operating frequency of the compressor is controlled to decrease by one level.

10. The variable frequency direct expansion machine according to claim 9, characterized in that The control device is also used for: When the compressor is in the minimum working gear for a second time period, and the air outlet temperature is less than or equal to the difference between the lower limit of the set temperature range and 1° C. for a third time period, turning off all compressors; Among them, the first duration and the second duration are greater than the third duration.

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