Heat pump air conditioning system

Abstract

The present invention provides a heat pump air-conditioning system comprising: a refrigerant circuit in which a compressor, an outdoor heat exchanger, a throttling element, and an indoor heat exchanger are sequentially connected so that a refrigerant circulates therein; the control part can control the compressor to operate according to the oil return frequency so as to enable the lubricating oil in the refrigerant loop to flow back to the compressor; the calculation part is configured to obtain the corresponding suction density rho G based on the compressor suction pressure Ps and the compressor suction temperature Ts in the refrigeration mode; acquiring the lubricating oil density rho L; based on the refrigerant volume flow qG and the lubricating oil volume flow qL corresponding to the actual operation frequency H of the compressor, the oil return frequency Ho, # imgabs0 # is calculated, a and b are constants, and when the compressor operates according to the oil return frequency Ho, the Foroude number Fr2 of the air suction side of the compressor is larger than or equal to 1. The oil return control execution condition and the executed oil return frequency are controlled according to the system operation parameters, the oil return frequency is reduced, the oil return frequency is reduced, and the user comfort and the unit reliability are improved.

Description

Technical Field

[0001] The invention relates to the technical field of air conditioning, and in particular to a heat pump air conditioning system. Background Art

[0002] The compressor, the core component of the heat pump air conditioning system, requires sufficient lubricating oil to ensure that there is no wear between its relatively moving parts. However, the working process of the compressor requires the absorption and discharge of refrigerant. When the refrigerant is discharged, a small amount of lubricating oil is often carried with it. If the lubricating oil discharged by the compressor cannot return to the compressor in time, the amount of oil in the compressor will continue to decrease, while the amount of oil flowing in the refrigeration cycle will continue to increase. This causes the lubrication reliability of the compressor to continue to decrease on the one hand, and on the other hand, a layer of oil film will adhere to the refrigerant layer of the heat exchanger. The thicker the oil film, the greater the thermal resistance, causing the capacity and energy efficiency of the heat pump air conditioning system to continue to decline. The oil film on the pipe wall in the refrigeration cycle pipeline is as follows: Figure 1 shown.

[0003] In the prior art, the above-mentioned problem is solved by adding oil separators, oil return bypass lines and other designs, but in fact, lubricating oil will still accumulate in the refrigeration cycle. If the amount of oil sucked in and discharged by the compressor can be basically equal, the oil cycle of the refrigeration system can also achieve balance. When the compressor frequency is low, the Froed number Fr is small, the refrigerant flows slowly, gravity plays a dominant role, and lubricating oil is more likely to accumulate in the system. Based on this principle, a relatively high oil return frequency is set in the prior art. After the compressor has been running for a certain period of time at an operating frequency lower than the oil return frequency, the compressor is forced to control the compressor to run at the oil return frequency for a period of time, and the stored oil in the refrigeration cycle is recovered to the compressor. The control process in the prior art is as follows: Figure 2 shown.

[0004] Heat pump air conditioning systems are usually designed to operate within a certain range. Most heat pump air conditioning systems can operate effectively at outdoor temperatures between -18°C and 40°C. Some heat pump air conditioning systems with better performance can have a wider operating temperature range and can operate under more extreme temperature conditions. This makes the calculation of the oil return frequency often set according to the most severe operating conditions, such as extremely low temperature heating. This method causes the oil return frequency to be higher than most operating conditions. When the heat pump air conditioning system operates according to the oil return frequency, the actual operating frequency required by the unit is much lower than the oil return frequency, resulting in the energy provided to the indoor unit being much higher than the actual energy required. The excessive capacity of the indoor unit causes a decrease in user comfort, and even the evaporation temperature drops below 0°C, causing the heat pump air conditioning system to shut down to prevent freezing. Summary of the invention

[0005] In view of the problem in the prior art that the oil return frequency is set according to the most severe working condition, resulting in the energy supplied to the indoor unit being much higher than the actually required energy, the first aspect of the present invention designs and provides a heat pump air conditioning system.

[0006] The heat pump air conditioning system includes a refrigerant circuit, which sequentially connects a compressor, an outdoor heat exchanger, a throttling element and an indoor heat exchanger so that the refrigerant circulates therein. The heat pump air conditioning system also includes a control unit, which can control the compressor to operate according to the oil return frequency so that the lubricating oil in the refrigerant circuit flows back to the compressor.

[0007] In one or more embodiments of the present application, the heat pump air conditioning system further includes a calculation unit configured to calculate the compressor suction pressure P in the cooling mode. s and compressor suction temperature T s Get the corresponding suction density ρ G ; Get the density of lubricating oil ρ L ; Refrigerant volume flow q corresponding to the actual operating frequency H of the compressor G Estimated lubricating oil volume flow rate q L , based on the lubricating oil density ρ L , Lubricating oil volume flow q L and the air density ρ G Calculate the oil return frequency H o , Where a and b are constants and satisfy the condition that when the compressor returns to the oil frequency H o During operation, the Froude number on the suction side of the compressor satisfies F r 2 ≥1.

[0008] In one or more embodiments of the present application, the heat pump air conditioning system further includes a determination unit configured to determine the air intake density ρ G , the lubricating oil density ρ L , the refrigerant volume flow rate q G and the lubricating oil volume flow q L When the constant a does not satisfy the following formula, it is presumed that the oil return operation is performed:

[0009]

[0010] The control unit controls the compressor to operate according to the oil return frequency so that the lubricating oil in the refrigerant circuit flows back to the compressor when the determination unit estimates that the oil return operation is to be performed. When the Froude number on the suction side of the compressor satisfies F r 2 ≥1.

[0011] In one or more embodiments of the present application, the constant a is generated according to the pipe diameter D on the suction side of the compressor.

[0012] In one or more embodiments of the present application, the constant b is generated according to the displacement C of the compressor.

[0013] In one or more embodiments of the present application, the heat pump air conditioning system further includes a generating unit configured to generate an oil return frequency H based on the oil return frequency H calculated by the calculating unit. o The frequency difference ΔH from the actual operating frequency H generates the duration for executing the oil return operation. The larger the frequency difference is, the shorter the duration for controlling the compressor to operate according to the oil return frequency is.

[0014] A second aspect of the present invention provides a heat pump air conditioning system, the heat pump air conditioning system includes a refrigerant circuit, which sequentially connects a compressor, an outdoor heat exchanger, a throttling element, and an indoor heat exchanger so that the refrigerant circulates therein. The heat pump air conditioning system also includes a control unit, which can control the compressor to operate according to the oil return frequency when performing oil return operation so that the lubricating oil in the refrigerant circuit flows back to the compressor.

[0015] In one or more embodiments of the present application, the heat pump air conditioning system further includes a determination unit configured to determine the compressor suction pressure P in the cooling mode based on the compressor suction pressure P s and compressor suction temperature T s Get the corresponding suction density ρ G ; Get the density of lubricating oil ρ L ; Refrigerant volume flow q corresponding to the actual operating frequency H of the compressor G Estimated lubricating oil volume flow rate q L , and at the suction density ρ G , the lubricating oil density ρ L , the refrigerant volume flow rate q G and the lubricating oil volume flow q L When the constant a does not satisfy the following formula, it is presumed that the oil return operation is performed:

[0016]

[0017] When the above formula is satisfied, the Froude number on the suction side of the compressor satisfies F r 2 ≥1.

[0018] A third aspect of the present invention provides a heat pump air conditioning system, the heat pump air conditioning system includes a refrigerant circuit, which sequentially connects a compressor, an outdoor heat exchanger, a throttling element, and an indoor heat exchanger so that the refrigerant circulates therein. The heat pump air conditioning system also includes a control unit, which can control the compressor to operate according to the oil return frequency when performing oil return operation so that the lubricating oil in the refrigerant circuit flows back to the compressor.

[0019] In one or more embodiments of the present application, the heat pump air conditioning system further includes an estimating unit configured to estimate the suction pressure P of the compressor when the suction superheat is higher than the set superheat threshold. s Call and compressor suction pressure P s The corresponding oil return frequency, where the compressor suction pressure P s The lower it is, the higher the oil return frequency.

[0020] In one or more embodiments of the present application, the heat pump air conditioning system further includes a determination unit configured to determine the compressor suction pressure P in the cooling mode based on the compressor suction pressure P s and compressor suction temperature T s Get the corresponding suction density ρ G ; Get the density of lubricating oil ρ L ; Refrigerant volume flow q corresponding to the actual operating frequency H of the compressor G Estimated lubricating oil volume flow rate q L , and at the suction density ρ G , the lubricating oil density ρ L , the refrigerant volume flow rate q G and the lubricating oil volume flow q L When the constant a does not satisfy the following formula, it is presumed that the oil return operation is performed:

[0021]

[0022] When the above formula is satisfied, the Froude number on the suction side of the compressor satisfies F r 2 ≥1.

[0023] In one or more embodiments of the present application, the heat pump air conditioning system also includes a generating unit, which is configured to generate a duration for executing the oil return operation based on a frequency difference between the oil return frequency estimated by the estimating unit and the actual operating frequency. The larger the frequency difference, the shorter the duration for controlling the compressor to operate according to the oil return frequency.

[0024] The present invention controls the execution conditions and the executed oil return frequency of the oil return control according to the system operation parameters, reduces the number of oil returns, reduces the oil return frequency, and improves the user comfort and the reliability of the unit.

[0025] After reading the specific embodiments of the present invention in conjunction with the accompanying drawings, other features and advantages of the present invention will become more clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0027] Figure 1 It is a schematic diagram of the oil film on the pipe wall in the refrigeration cycle pipeline of the existing heat pump air conditioning system;

[0028] Figure 2 It is a control flow chart in the prior art;

[0029] Figure 3 A schematic diagram of the structure of a heat pump air conditioning system provided by one or more embodiments of the present application;

[0030] Figure 4 A schematic diagram of the structure of a heat pump air conditioning system provided by one or more embodiments of the present application;

[0031] Figure 5 A schematic diagram of the structure of a heat pump air conditioning system provided by one or more embodiments of the present application;

[0032] Figure 6 A flow chart of a heat pump air conditioning system provided for one or more embodiments of the present application;

[0033] Figure 7 A schematic diagram of the structure of a heat pump air conditioning system provided by one or more embodiments of the present application;

[0034] Figure 8 A schematic diagram of the structure of a heat pump air conditioning system provided by one or more embodiments of the present application;

[0035] Fig. 9 A schematic diagram of the structure of a heat pump air conditioning system provided by one or more embodiments of the present application;

[0036] Fig.10 A schematic diagram of the structure of a heat pump air conditioning system provided by one or more embodiments of the present application;

[0037] Fig.11 A flow chart of a heat pump air conditioning system provided for one or more embodiments of the present application;

[0038] Fig.12 A schematic diagram of the corresponding relationship between the oil return frequency and the suction pressure in the heat pump air conditioning system provided by one or more embodiments of the present application;

[0039] Fig.13A schematic diagram of the structure of a heat pump air conditioning system provided by one or more embodiments of the present application;

[0040] Fig.14 A schematic diagram of the structure of a heat pump air conditioning system provided by one or more embodiments of the present application;

[0041] In the figure: 100, heat pump air conditioning system; 10, outdoor unit; 11, indoor unit 101, compressor; 102, outdoor heat exchanger; 103, outdoor throttling element; 104a, indoor throttling element; 104b, indoor throttling element; 105, indoor heat exchanger; 105a, indoor heat exchanger; 105b, indoor heat exchanger; 106, outdoor fan; 107, water tank; 108, gas-liquid separator; 109, gas side shut-off valve; 110, liquid side shut-off valve; 111, indoor controller; 111a, indoor controller; 111b, indoor controller; 112, liquid side connecting pipe; 113, gas side connecting pipe; 114, switching valve; 115, fan coil; 116, heating equipment; 20, calculation unit; 21, control unit; 22, determination unit; 23, generation unit; 30, estimation unit. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0043] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0044] The terms "first", "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0045] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0046] In the present invention, unless otherwise clearly stipulated and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0047] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific examples of processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0048] A heat pump air conditioning system is a system that uses heat pump technology for air conditioning and heating. It uses the heat pump cycle principle to adjust the indoor temperature by absorbing heat from a low-temperature heat source and releasing it to a high-temperature heat source. The heat pump air conditioning system can provide efficient air conditioning and heating functions during the cooling and heating seasons. Compared with traditional air conditioning systems, heat pump air conditioning systems have higher energy efficiency because they use the heat energy existing in nature for energy transfer instead of relying entirely on electricity to produce cooling or heating effects. They also have less impact on the environment and do not produce direct exhaust emissions. Heat pump air conditioning systems have become one of the important technologies for sustainable energy utilization, helping to reduce energy consumption and environmental pollution.

[0049] The embodiments of the heat pump air conditioning system provided in the present application are described with reference to the accompanying drawings.

[0050] The heat pump air conditioning system 100 is installed in buildings such as apartments, hotels, office buildings, and residences. The heat pump air conditioning system 100 can independently perform refrigeration operation or independently perform heating operation.

[0051] As Figure 3 shown, the heat pump air conditioning system 100 includes an outdoor unit 10, and a liquid-side communication pipe 112 and a gas-side communication pipe 113 connecting the outdoor unit 10 and the indoor unit 11 to form a vapor compression refrigeration cycle. As Figure 3 shown, the refrigeration cycle is mainly realized by a refrigerant circuit, and components such as a compressor 101, a condenser, a throttling element, and an evaporator are used in the refrigerant circuit. The refrigeration cycle includes a series of processes involving compression, condensation, expansion, and evaporation to cool or heat the indoor space.

[0052] From a principle perspective, a low-temperature and low-pressure refrigerant enters the compressor 101, and the compressor 101 compresses the refrigerant gas into a high-temperature and high-pressure state and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and heat is released to the high-temperature heat source through the condensation process.

[0053] The throttling element expands the high-temperature and high-pressure liquid-phase refrigerant formed by condensation in the condenser into a low-pressure liquid-phase refrigerant. The evaporator evaporates the refrigerant expanded in the throttling device and returns the refrigerant gas in a low-temperature and low-pressure state to the compressor 101. The evaporator can absorb the heat of the low-temperature heat source (air, water, or soil) by using the latent heat of evaporation of the refrigerant. Throughout the cycle, the heat pump air conditioning system 100 can adjust the temperature of the indoor space.

[0054] The following introduces the outdoor unit 10. The outdoor unit 10 is installed in the outdoor natural environment and includes a compressor 101, a switching valve 114 (usually a four-way valve), an outdoor heat exchanger 102, an outdoor throttling element 103 (usually an electronic expansion valve), a liquid-side cut-off valve 110, and a gas-side cut-off valve 109 in the refrigeration cycle. The outdoor unit 10 can perform heating operation or refrigeration operation on the outdoor side to provide energy for increasing the indoor temperature or reducing the indoor temperature to the indoor unit 11.

[0055] The compressor 101 is used to suck in low-pressure gas refrigerant and compress it into high-pressure gas refrigerant, and then discharge it. The compressor 101 can use a screw compressor, which is efficient and reliable, can provide a large cooling capacity, and is suitable for large spaces or applications that require high cooling / heating capabilities, such as large commercial buildings, industrial facilities, and large residential buildings. The compressor 101 can also use, for example, a rolling rotor compressor, and the form of the compressor 101 is not further restricted here. The compressor 101 is driven by a motor, and the speed of the motor can be variably controlled by a frequency converter. The frequency converter is usually equipped with a closed-loop control system, which can monitor the parameters of the motor through sensors, and dynamically adjust the output frequency and voltage based on feedback information, so that the motor driving the compressor 101 is always in the best working condition.

[0056] The switching valve 114 is used to switch the flow direction of the refrigerant between the cooling mode and the heating mode.

[0057] The outdoor heat exchanger 102 is configured to be used as a condenser in cooling operation and as an evaporator in heating operation. The outdoor heat exchanger 102 can exchange heat with the heat in the outdoor air guided by the outdoor fan 106. Through the heat of the outdoor air, the heat pump air conditioning system can absorb heat from the external environment or release heat to the outdoor air to achieve cooling or heating of the indoor space. The outdoor heat exchanger 102 can also use the heat in the water source for heat exchange. For example, it can be configured to exchange heat with groundwater, a well, a water body or other water sources, and perform heat exchange through the geothermal heat in the water source, thereby achieving the cooling or heating function of the heat pump air conditioning system.

[0058] The outdoor throttling element 103 (electronic expansion valve) is used to reduce the pressure of the high-pressure refrigerant in the cooling mode and the heating mode.

[0059] The liquid-side shutoff valve 110 and the gas-side shutoff valve 109 are located at the interface connecting the external equipment and the pipeline.

[0060] The outdoor unit 10 is also provided with a gas-liquid separator 108 (liquid storage device). The gas-liquid separator 108 is provided on the suction side of the compressor 101 and is a shell-shaped component for separating and storing the refrigerant into gas and liquid. The gas-liquid separator 108 can store excess refrigerant.

[0061] In the heating mode, a refrigerant circuit for heating operation can be formed in the outdoor unit 10, which is referred to as a heating cycle. The outdoor throttling element 103, the outdoor heat exchanger 102, the switching valve 114 (one path in the four-way valve), the gas-liquid separator 108, the compressor 101 and the switching valve 114 (the other path in the four-way valve) are connected in sequence from the liquid-side connecting pipe 112 to the gas-side connecting pipe 113.

[0062] In the cooling mode, a refrigerant circuit for cooling operation can be formed in the outdoor unit 10, which is referred to as a refrigeration cycle. The direction from the gas-side connecting pipe 113 to the liquid-side connecting pipe 112 is connected in sequence with a switching valve 114 (one path in the four-way valve), a gas-liquid separator 108, a compressor 101, a switching valve 114 (another path in the four-way valve), an outdoor heat exchanger 102 and an outdoor throttling element 103.

[0063] The entire outdoor unit 10 is controlled by an outdoor controller, which is arranged in an electrical box with good sealing performance and heat dissipation function. The outdoor controller includes components such as a processor, a storage unit, an input / output interface, and a communication interface. The processor can be a dedicated processor, a central processing unit (CPU), etc. The processor can access the storage unit to execute instructions or applications stored in the storage unit to realize related functions. The storage unit can include a volatile memory and / or a non-volatile memory. The input / output interface can be connected to various sensors arranged in the outdoor unit 10 to receive the detection values ​​of various sensors arranged in the outdoor unit 10. The input / output interface can also be connected to devices such as a frequency converter, a compressor 101, an outdoor fan 106, a switching valve 114, and an outdoor throttling element 103 to output control instructions generated by the processor to them. The communication interface can support different wireless communication protocols, such as Wi-Fi, Bluetooth, near-field communication, NB-IoT, etc., to communicate with other electronic devices, including but not limited to cloud servers, computers (host computers), smart phones, tablets, PDAs, smart control tools, wearable devices and vehicle-mounted equipment, etc.

[0064] The indoor unit 11 is described below. The indoor unit 11 performs a cooling operation or a heating operation using the energy generated by the outdoor unit 10 to increase the indoor temperature or the energy to decrease the indoor temperature.

[0065] In one or more embodiments of the present application, the indoor unit 11 includes a water tank 107. The water tank 107 is usually installed in a basement, a storage room, or an equipment room. In one or more embodiments of the present application, the water tank 107 can also be arranged outdoors, such as on a roof or a courtyard.

[0066] The indoor heat exchanger 105 is connected to the water tank 107 through a water circulation pipeline. The indoor heat exchanger 105 is used as a condenser in heating operation and as an evaporator in cooling operation. The indoor heat exchanger 105 absorbs heat from the water tank or releases heat through the water circulation system.

[0067] The water tank 107 is further connected to the heating equipment 116 (such as floor heating, radiator) and the fan coil 115 through a pipeline system. The heat pump air conditioning system transfers heat from the water tank to the heating equipment and the fan coil through water circulation, thereby realizing the heating function of the indoor space.

[0068] An indoor controller 111 is provided in the indoor unit 11. The indoor controller 111 includes components such as a processor, a storage unit, an input / output interface, and a communication interface. The processor may be a dedicated processor, a central processing unit (CPU), etc. The processor may access the storage unit to execute instructions or applications stored in the storage unit to implement related functions. The storage unit may include a volatile memory and / or a non-volatile memory. The input / output interface may be communicatively connected to various sensors provided in the indoor unit 11 to receive detection values ​​of various sensors provided in the indoor unit 11. The communication interface may support different wireless communication protocols, such as Wi-Fi, Bluetooth, etc.

[0069] The indoor controller 111 is communicatively connected to a control terminal, which may be a remote controller, a wired controller, or other mobile terminals such as a smart phone, a tablet computer, a computer, a wearable device, and the like.

[0070] The number of indoor heat exchangers in the indoor unit can be one or more, for example Figure 4 As shown, an indoor heat exchanger 105a and an indoor heat exchanger 105b are provided, and indoor throttling elements (such as Figure 4 The indoor throttling element is configured to reduce the pressure of the refrigerant and expand it, and the opening of the indoor throttling element is adjustable, for example, an electronic expansion valve can be selected.

[0071] In a heat pump air conditioning system, the core component compressor requires sufficient lubricating oil to ensure that there is no wear between its relatively moving parts. In one or more embodiments of the present application, the heat pump air conditioning system further includes a control unit 21, which can control the compressor to operate according to the oil return frequency so that the lubricating oil in the refrigerant circuit flows back to the compressor, and by increasing the frequency of the compressor, the Froude number Fr is increased, so that the lubricating oil is not easily accumulated in the refrigeration system.

[0072] In one or more embodiments of the present application, in order to obtain a more accurate oil return frequency and avoid the problem that the energy provided to the indoor unit is much higher than the actually required energy, resulting in excessive capacity of the indoor unit and reduced user comfort, in one or more implementations of the present application, Figure 5 As shown, a calculation unit 20 is also provided in the heat pump air conditioning system.

[0073] The calculation unit 20 is configured to perform the following Figure 6 The multiple steps shown:

[0074] Step S101: In cooling mode, based on the compressor suction pressure P s and compressor suction temperature T s Get the corresponding suction density ρ G .

[0075] Step S102: Obtaining the density ρ of lubricating oil (also called refrigeration oil) L .

[0076] Step S103: Based on the refrigerant volume flow rate q corresponding to the actual operating frequency H of the compressor G Estimated lubricating oil volume flow rate q L .

[0077] Step S104: Based on the lubricating oil density ρ L , Lubricating oil volume flow q L and the air density ρ G Calculate the oil return frequency H o ,

[0078] The calculated oil return frequency H o When the compressor returns to the oil frequency H o During operation, the Froude number on the suction side of the compressor satisfies F r 2 ≥1.

[0079] The following is an introduction to the calculated oil return frequency H from a principle perspective: o .

[0080] In fluid mechanics, the Froude number is a dimensionless physical quantity used to describe the characteristics of a fluid under the action of external forces, especially the stability of fluid flow. It is defined as:

[0081]

[0082] Where V is the velocity of the fluid, g is the acceleration of gravity, and L is the characteristic length, which usually refers to a specific linear dimension in the direction of fluid flow. The Froude number is used to determine the stability of fluid motion. When the Froude number is less than 1, the fluid flow is stable. When the Froude number is greater than or equal to 1, the fluid flow may become unstable.

[0083] Further expanding on the definition of Froude number, the constraint condition is further set as F r 2≥1. In physical terms, this means that the ratio of the square of the velocity of the fluid to the square of the ratio of gravity to the characteristic length is greater than 1, which also means that the inertial force of the fluid is greater than the gravity, but the constraint condition is set to F r 2 ≥1, which will more directly reflect the influence of the kinetic energy of the mixed fluid of refrigerant and lubricating oil on gravity, that is, whether the flowing mixed fluid of refrigerant and lubricating oil can overcome the influence of gravity and return to the compressor.

[0084] Furthermore, the constraints can be written as:

[0085]

[0086] Among them, U 2 U represents the square of the velocity of the entire mixed fluid (refrigerant and lubricant oil), and the flow of the gas and liquid mixture is estimated using the Smith formula in the classic literature. 2 It can be expressed as:

[0087]

[0088] Among them, U G is the flow rate of gaseous refrigerant when the tube is full, U L is the flow rate of lubricating oil when the pipe is full, ρ G is the refrigerant density, ρ L is the density of lubricating oil. 2 In the expression, the numerator represents the sum of the kinetic energy of the gas and the liquid, and the denominator represents the density of the liquid in the mixed fluid. In this equation, if the velocity components of the gas and liquid are larger, they will contribute more to the overall velocity of the mixed fluid. On the contrary, if the velocity of one phase is smaller, its contribution to the overall velocity is relatively small. Through this expression, the mixing effect of the velocities of each phase in the multiphase fluid can be described, that is, whether the current kinetic energy is sufficient to drive the flow of lubricating oil.

[0089] In one or more embodiments of the present application, for a two-phase mixture flowing in a pipeline, the characteristic length L is the inner diameter D of the pipeline, and U 2 Substitute D into the constraint F r 2 ≥1, the constraint can be rewritten as:

[0090]

[0091] Furthermore, the volume flow rate of the refrigerant q G It can be expressed as:

[0092] Similarly, the volume flow rate of the lubricating oil q L It can be expressed as:

[0093] According to the volume flow rate q of the refrigerant G and the volume flow rate of the lubricating oil q L The constraint condition can be further rewritten as:

[0094]

[0095] The inequality

[0096]

[0097] Simplifying, we can get:

[0098]

[0099] Further transform the above formula:

[0100]

[0101]

[0102]

[0103]

[0104] Thus, the minimum value of the refrigerant volume flow rate can be obtained, that is, The oil return frequency can be obtained based on the ratio of the refrigerant volume flow rate and the compressor displacement C, that is:

[0105]

[0106] In the above formula, is a constant related only to the pipe diameter, and C is a constant related only to the compressor displacement, so the oil return frequency H can be simplified to obtain o The expression Constants a and b can be measured under experimental conditions and written in advance for easy access, where constant a can be equal to The calculation result may be further rounded or truncated, or further symbolically processed, merged or decomposed, or further functionally processed.

[0107] In one or more optional embodiments of the present application, the value range of a is 3×10 -5 ~2×10 -3 , the value range of b is 2×10 -5 ~1×10 -4 .

[0108] like Figure 7As shown, based on the above derivation process, the heat pump air conditioning system provided in the present application is further provided with a determination unit 22.

[0109] The determination unit 22 is configured to determine the air density ρ G , the lubricating oil density ρ L , the refrigerant volume flow rate q G and the lubricating oil volume flow q L When the constant a does not satisfy the following formula, it is presumed that the oil return operation is performed:

[0110]

[0111] When the determining unit 22 estimates that the oil return operation is to be performed, the control unit 21 controls the compressor to operate according to the oil return frequency so that the lubricating oil in the refrigerant circuit flows back to the compressor.

[0112] In satisfying

[0113]

[0114] When the Froude number F on the suction side of the compressor is r 2 ≥1.

[0115] According to the above derivation, it can be concluded that when the following formula is satisfied

[0116]

[0117] The kinetic energy of the current mixed fluid is sufficient to drive the flow of the lubricating oil, that is, it meets the oil return requirement. When the above formula is not satisfied, it means that the kinetic energy of the mixed fluid is insufficient to drive the flow of the liquid. The control unit 21 is further used to control the compressor to operate according to the oil return frequency so that the lubricating oil in the refrigerant circuit can flow back to the compressor.

[0118] In one or more embodiments of the present application, when it is estimated that the above formula is not satisfied, the control unit 21 starts timing, and when the timing reaches a set time, the control unit 21 controls the compressor to operate according to the oil return frequency so that the lubricating oil in the refrigerant circuit flows back to the compressor.

[0119] The following is an introduction to the parameter acquisition process.

[0120] First, once the temperature and pressure of a single-phase substance are determined, its state point can be determined, and further all parameters including density can be obtained. s and compressor suction temperature T s Then the corresponding suction density ρ can be obtained G For example, a heat pump air conditioning system can have a built-in density meter, which can be used to obtain the compressor suction pressure P by looking up the table. sand compressor suction temperature T s Then the corresponding suction density ρ is obtained G ; It can also be calculated based on the ideal gas state equation, for example

[0121]

[0122] R is the gas constant.

[0123] Secondly, based on the actual operating frequency H of the compressor, the corresponding refrigerant volume flow rate q can be calculated G , with refrigerant volume flow q G Equal to q G =H×C, that is, the refrigerant volume flow rate q G It is equal to the product of the actual operating frequency H of the compressor and the compressor displacement C.

[0124] q L The oiling rate and refrigerant volume flow rate q obtained from the previous test of the compressor can be G For example, the oiling rate can be 0.02, then q L , = 0.02 × q G .

[0125] Density of lubricating oil ρ L It is the performance parameter of the lubricant itself, usually provided by the lubricant manufacturer, usually: 500kg / m 3 Up to 1000kg / m 3 .

[0126] like Figure 8 As shown, in one or more embodiments of the present application, the heat pump air conditioning system further includes a generating unit 23. The generating unit 23 is configured to generate an oil return frequency H calculated by the calculating unit 20 based on the oil return frequency H calculated by the calculating unit 20. o The frequency difference ΔH from the actual operating frequency H generates the duration for executing the oil return operation. The larger the frequency difference is, the shorter the duration for controlling the compressor to operate according to the oil return frequency is.

[0127] For example, the duration of controlling the compressor to operate according to the oil return frequency may be 1 hour to 5 hours. o When -H≥10Hz, the compressor is controlled to run for a cumulative time of 2 hours according to the oil return frequency; when the frequency difference 10Hz≥ΔH≥1Hz, the compressor is controlled to run for a cumulative time of 4 hours according to the oil return frequency to ensure the load balance of the system.

[0128] like Fig. 9As shown, in one or more embodiments of the present application, when the computing power of the heat pump air conditioning system is limited, or when the data to be processed in a short time is close to the upper limit of the processor, the oil return control can also be performed when the critical condition is reached, and the compressor operation is controlled by the oil return frequency calculated in the prior art. Exemplarily, the heat pump air conditioning system includes a determination unit 22, which is configured to determine the compressor suction pressure P in the cooling mode based on the compressor suction pressure P s and compressor suction temperature T s Get the corresponding suction density ρ G ; Get the density of lubricating oil ρ L ; Refrigerant volume flow q based on the actual operating frequency of the compressor G and lubricating oil volume flow q L , and at the suction density ρ G , the lubricating oil density ρ L , the refrigerant volume flow rate q G and the lubricating oil volume flow q L When the constant a does not satisfy the following formula, it is presumed that the oil return operation is performed:

[0129]

[0130] When the above formula is satisfied, the Froude number F on the suction side of the compressor is r 2 ≥1, constant a is generated based on the pipe diameter D on the suction side of the compressor; constant b is generated based on the compressor displacement C.

[0131] The estimation process of the above formula refers to the detailed description of the first embodiment, which will not be repeated here.

[0132] like Figures 10 to 12 As shown, in one or more embodiments of the present application, the heat pump air conditioning system further includes an estimating unit 30, which is configured to estimate the suction pressure P of the compressor when the suction superheat is higher than the superheat threshold. s Call and compressor suction pressure P s The corresponding oil return frequency, where the compressor suction pressure P s The lower it is, the higher the oil return frequency. When the suction superheat is higher than the superheat threshold, it means that the liquid component in the gas has evaporated and the liquid component is relatively small, which further leads to a small amount of lubricating oil returning to the compressor. When the suction superheat is not higher than the superheat threshold, it means that the refrigerant and the lubricating oil are well soluble, and the liquid refrigerant in the two-phase mixed fluid can directly bring the lubricating oil back to the compressor without the need for oil return control.

[0133] Further, according to the compressor suction pressure P s Call and compressor suction pressure P s Corresponding oil return frequency, compressor suction pressure Ps The lower it is, the higher the oil return frequency.

[0134] In one or more embodiments of the present application, the compressor suction pressure P s It is linearly related to the oil return frequency, such as Fig.12 shown.

[0135] Specifically, the heat pump air conditioning system performs as follows Fig.11 Multiple steps shown.

[0136] Step S201: Obtain the compressor suction pressure P s , suction temperature T s And the actual operating frequency H.

[0137] Step S202: Calculate the suction air superheat

[0138] Using the compressor suction pressure P s Find the corresponding saturated steam temperature T sat , for example, by looking up a table (refrigerant property table), the suction superheat T s SH=T s -T sat .

[0139] Step S203: Determine whether the suction air superheat is higher than a set threshold. For example, determine whether the suction air superheat is higher than 1, that is, whether there is a T s SH>1.

[0140] Step S204: If the suction superheat is higher than the set threshold, the oil return frequency corresponding to the compressor suction pressure is called based on the compressor suction pressure, that is, based on the following example: Fig.12 The corresponding relationship shown in the figure is to call the oil return frequency according to the compressor suction pressure; if the suction superheat is not higher than the set threshold, normal operation is performed (such as Fig.11 (as shown in step S207).

[0141] Step S205: Execute the oil return operation, that is, control the compressor to operate according to the oil return frequency so that the lubricating oil in the refrigerant circuit flows back to the compressor.

[0142] Step S206: Determine whether a shutdown signal is received; if a shutdown signal is received, execute shutdown control.

[0143] like Fig.13 As shown, in one or more embodiments of the present application, oil return control can also be performed when a critical condition is reached, and the compressor operation can be controlled at the oil return frequency called in the above embodiment. Exemplarily, the heat pump air conditioning system includes a determination unit 22, which is configured to determine the compressor suction pressure P in the cooling mode based on the compressor suction pressure P s and compressor suction temperature Ts Get the corresponding suction density ρ G ; Get the density of lubricating oil ρ L ; Refrigerant volume flow q corresponding to the actual operating frequency H of the compressor G Estimated lubricating oil volume flow rate q L , and at the suction density ρ G , the lubricating oil density ρ L , the refrigerant volume flow rate q G and the lubricating oil volume flow q L When the constant a does not satisfy the following formula, it is presumed that the oil return operation is performed:

[0144]

[0145] When the above formula is satisfied, the Froude number F on the suction side of the compressor is r 2 ≥1, oil return control is not required.

[0146] The calculation process of the above inequality and the derivation process of constants a and b refer to the detailed description of the above embodiment, which will not be repeated here.

[0147] like Fig.14 As shown, in one or more embodiments of the present application, the heat pump air conditioning system further includes a generating unit 23. The generating unit 23 is configured to generate a duration for executing the oil return operation based on a frequency difference between the oil return frequency estimated by the estimating unit 30 and the actual operating frequency, and the greater the frequency difference, the shorter the duration for controlling the compressor to operate according to the oil return frequency.

[0148] For example, the duration of controlling the compressor to operate according to the oil return frequency may be 1 hour to 5 hours. o When -H≥10Hz, the compressor is controlled to run for a cumulative time of 2 hours according to the oil return frequency; when the frequency difference 10Hz≥ΔH≥1Hz, the compressor is controlled to run for a cumulative time of 4 hours according to the oil return frequency to ensure the load balance of the system.

[0149] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0150] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. Heat pump air conditioning system, include: a refrigerant circuit which sequentially connects the compressor, the outdoor heat exchanger, the throttling element, and the indoor heat exchanger so that the refrigerant circulates therein; and a control unit, which can control the compressor to operate according to the oil return frequency so that the lubricating oil in the refrigerant circuit flows back to the compressor; It is characterized by further comprising: The calculation unit is configured to calculate the compressor suction pressure P in the cooling mode based on the compressor suction pressure P s and compressor suction temperature T s Get the corresponding suction density ρ G ; Get the density of lubricating oil ρ L ; Refrigerant volume flow q corresponding to the actual operating frequency H of the compressor G Estimated lubricating oil volume flow rate q L ; Based on the lubricating oil density ρ L , Lubricating oil volume flow q L and the air density ρ G Calculate the oil return frequency H o , Where a and b are constants and satisfy the condition that when the compressor returns to the oil frequency H o During operation, the Froude number on the suction side of the compressor satisfies F r 2 ≥1.

2. The heat pump air conditioning system according to claim 1, It is characterized in that Also includes: A determination unit configured to determine the air density ρ G , the lubricating oil density ρ L , the refrigerant volume flow rate q G and the lubricating oil volume flow q L When the constant a does not satisfy the following formula, it is presumed that the oil return operation is performed: The control unit controls the compressor to operate at an oil return frequency so that the lubricating oil in the refrigerant circuit flows back to the compressor when the determination unit estimates that the oil return operation is to be performed. In satisfying When the Froude number on the suction side of the compressor satisfies F r 2 ≥1.

3. The heat pump air conditioning system according to claim 1 or 2, It is characterized in that The constant a is generated based on the pipe diameter D on the suction side of the compressor; The constant b is generated according to the compressor displacement C.

4. The heat pump air conditioning system according to claim 1 or 2, It is characterized in that Also includes: A generating unit configured to generate an oil return frequency H based on the oil return frequency H calculated by the calculating unit. o The frequency difference ΔH from the actual operating frequency H generates the duration for executing the oil return operation. The larger the frequency difference is, the shorter the duration for controlling the compressor to operate according to the oil return frequency is.

5. Heat pump air conditioning system, include: a refrigerant circuit which sequentially connects the compressor, the outdoor heat exchanger, the throttling element, and the indoor heat exchanger so that the refrigerant circulates therein; and a control unit, which can control the compressor to operate according to the oil return frequency when performing the oil return operation so that the lubricating oil in the refrigerant circuit flows back to the compressor; It is characterized by further comprising: The determining unit is configured to determine the compressor suction pressure P in the cooling mode based on the compressor suction pressure P s and compressor suction temperature T s Get the corresponding suction density ρ G ; Get the density of lubricating oil ρ L ; Refrigerant volume flow q corresponding to the actual operating frequency H of the compressor G Estimated lubricating oil volume flow rate q L , and at the suction density ρ G , the lubricating oil density ρ L , the refrigerant volume flow rate q G and the lubricating oil volume flow q L When the constant a does not satisfy the following formula, it is presumed that the oil return operation is performed: When the above formula is satisfied, the Froude number on the suction side of the compressor satisfies F r 2 ≥1.

6. The heat pump air conditioning system according to claim 5, It is characterized in that The constant a is generated based on the pipe diameter D on the suction side of the compressor; The constant b is generated according to the compressor displacement C.

7. Heat pump air conditioning system, include: a refrigerant circuit which sequentially connects the compressor, the outdoor heat exchanger, the throttling element, and the indoor heat exchanger so that the refrigerant circulates therein; and a control unit, which can control the compressor to operate according to the oil return frequency so that the lubricating oil in the refrigerant circuit returns to the compressor; It is characterized by further comprising: The estimating unit is configured to estimate the suction air superheat degree based on the compressor suction pressure P when the suction air superheat degree is higher than the set superheat degree threshold value. s Call and compressor suction pressure P s The corresponding oil return frequency, where the compressor suction pressure P s The lower it is, the higher the oil return frequency.

8. The heat pump air conditioning system according to claim 7, further comprising: include: The determining unit is configured to determine the compressor suction pressure P in the cooling mode based on the compressor suction pressure P s and compressor suction temperature T s Get the corresponding suction density ρ G ; Get the density of lubricating oil ρ L ; Refrigerant volume flow q corresponding to the actual operating frequency H of the compressor G Estimated lubricating oil volume flow rate q L , and at the suction density ρ G , the lubricating oil density ρ L , the refrigerant volume flow rate q G and the lubricating oil volume flow q L When the constant a does not satisfy the following formula, it is presumed that the oil return operation is performed: When the above formula is satisfied, the Froude number on the suction side of the compressor satisfies F r 2 ≥1.

9. The heat pump air conditioning system according to claim 8, It is characterized in that The constant a is generated based on the pipe diameter D on the suction side of the compressor; The constant b is generated according to the compressor displacement C.

10. The heat pump air conditioning system according to any one of claims 7 to 9, It is characterized in that Also includes: The generating unit is configured to generate a duration for executing the oil return operation based on a frequency difference between the oil return frequency estimated by the estimating unit and an actual operating frequency, wherein the larger the frequency difference is, the shorter the duration for controlling the compressor to operate according to the oil return frequency is.

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