Heat pump intermediate heat exchanger air supply system and control method thereof

Abstract

The invention relates to the technical field of heat pump systems, in particular to a heat pump intermediate heat exchanger air supply system and a control method thereof.A REFPROP function is introduced according to the evaporation pressure, the condensation pressure, the compressor frequency, the refrigerating capacity and other parameters of operation of a heat pump unit to obtain all state parameters of the whole two-stage compression process of a unit compressor, such as the primary compression end pressure and the enthalpy value; and according to the deviation value range of the optimal intermediate pressure ratio of the compressor and the air supply ratio of the main path circulation, the air supply amount of the main path circulation of the heat pump unit is determined. By adjusting the opening degree of the auxiliary path electronic expansion valve, the auxiliary path outlet pressure value of the unit is close to the optimal middle pressure of the compressor. By means of air supply control, it is guaranteed that in the operation process of the unit, the opening degree of the auxiliary electronic expansion valve can be controlled according to the calculated deviation value of the air supply ratio of the heat pump system and the intermediate pressure ratio of the compressor, the air supply pressure of the unit is the optimal intermediate pressure, and therefore the optimal heating performance of the unit is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of heat pump systems, and in particular to an air supply system for an intermediate heat exchanger of a heat pump and a control method thereof. Background Art

[0002] Air source heat pumps now mostly use intermediate heat exchangers (i.e. economizers) to achieve stable operation of the unit in ultra-low temperature environments. The principle is to inhale a portion of the intermediate pressure gas through the intermediate pressure suction hole of the jet enthalpy increase compressor, mix it with the partially compressed refrigerant and then compress it, so as to achieve the effect of completing two-stage compression with a single compressor, increase the refrigerant flow in the water-side heat exchanger, increase the enthalpy difference of the main circulation loop, and expand the operating range of the heat pump unit. At the same time, it solves the problem of excessively high exhaust temperature when the compressor is running under high pressure ratio conditions with low ambient temperature and high water temperature to a certain extent.

[0003] However, for air source heat pump units that use economizers to achieve the effect of air replenishment and enthalpy increase, the control method of the auxiliary circuit electronic expansion valve is generally to adjust the valve opening according to the temperature difference between the refrigerant entering and leaving the economizer in the air replenishment circuit (i.e., the auxiliary circuit superheat) and the deviation value of the auxiliary circuit target superheat setting value, so as to adjust the amount of air replenishment entering the compressor. Although this adjustment method can achieve the effect of air replenishment and enthalpy increase of the unit to a certain extent, adjusting the air replenishment volume only according to the auxiliary circuit superheat cannot ensure that the compressor's air replenishment pressure is the optimal intermediate pressure and achieve the optimal air replenishment ratio, thereby failing to give full play to the compressor's optimal heating effect under low ambient temperature. Moreover, under the same air replenishment pressure, the air replenishment superheat has little effect on the cooling capacity and the superheat of the refrigeration performance coefficient. Summary of the invention

[0004] In order to solve the problems raised in the above background technology, the present invention provides a heat pump intermediate heat exchanger air supply system and its control method based on the prior art, which ensures that when the unit is running, the opening of the auxiliary electronic expansion valve is controlled by calculating the deviation value between the heat pump system air supply ratio and the compressor intermediate pressure ratio, so that the unit's air supply pressure reaches the optimal intermediate pressure and achieves the unit's optimal heating performance.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: a heat pump intermediate heat exchanger air supply system, including a main circulation loop and an air supply auxiliary circuit, the main circulation loop is provided with a compressor, a water side heat exchanger, an intermediate heat exchanger, a wind side heat exchanger and a gas-liquid separator in sequence, the water side heat exchanger is connected to the main road inlet of the intermediate heat exchanger, the main road outlet of the intermediate heat exchanger is connected to the liquid separation head of the wind side heat exchanger, and the main circulation loop between the main road outlet of the intermediate heat exchanger and the liquid separation head is provided with a main road filter and a main road expansion valve; the heat exchange between the water side heat exchanger and the intermediate heat exchanger is more efficient, which can effectively reduce energy loss and improve heat recovery capacity. The setting of the gas-liquid separator effectively separates the gas and liquid in the system and reduces the influence of bubbles on the pump and the heat exchanger. The fluid flow and pressure in the main circulation loop are accurately adjusted to ensure that each heat exchanger can operate under optimal conditions.

[0006] The auxiliary gas supply line includes an auxiliary liquid inlet pipe and an auxiliary liquid outlet pipe. The auxiliary liquid inlet pipe is connected to the main circulation loop between the water side heat exchanger and the intermediate heat exchanger. The other end of the auxiliary liquid inlet pipe is connected to the auxiliary inlet of the intermediate heat exchanger. The auxiliary liquid inlet pipe is provided with an auxiliary filter and an auxiliary expansion valve. The auxiliary outlet of the intermediate heat exchanger and the compressor gas supply port are connected through the auxiliary liquid outlet pipe. The auxiliary filter of the auxiliary gas supply line prevents impurities from entering the intermediate heat exchanger, effectively preventing pressure fluctuations caused by gas mixing in the main circulation loop, improving the stability of the entire system, and avoiding potential risks caused by unstable pressure. The design of the auxiliary gas supply line allows flexible gas replenishment when the system needs it, maintaining the best working state of the system and ensuring long-term stable operation.

[0007] As a further solution of the present invention, a high-pressure sensor and a high-pressure switch are sequentially arranged in the main circulation loop between the compressor exhaust port and the water-side heat exchanger inlet along the exhaust direction. The high-pressure sensor monitors the pressure change of the main circulation loop in real time to ensure that the system operates within a predetermined pressure range. Potential faults or abnormal conditions are discovered in a timely manner to enhance the safety and reliability of the system.

[0008] As a further solution of the present invention, a main inlet temperature sensor is provided at the inlet of the main road of the intermediate heat exchanger, and the main inlet temperature is obtained by detecting the main inlet temperature; a main outlet temperature sensor is provided at the outlet of the main road of the intermediate heat exchanger, and the main outlet temperature is obtained by detecting the main outlet temperature; an auxiliary inlet temperature sensor is provided at the inlet of the auxiliary road of the intermediate heat exchanger, and the auxiliary inlet temperature is obtained by detecting the auxiliary inlet temperature; an auxiliary outlet temperature sensor is provided at the outlet of the auxiliary road of the intermediate heat exchanger, and the auxiliary outlet temperature sensor is provided, and the auxiliary outlet temperature is obtained by detecting the auxiliary outlet temperature; and a gas replenishment pressure sensor is also provided on the auxiliary road liquid outlet pipe. Each temperature sensor can monitor the temperature change of each fluid channel in real time, provide important data support for the operating status of the system, realize accurate temperature control, and improve heat exchange efficiency.

[0009] By monitoring the temperature of the main and auxiliary circuits, the operating parameters of the heat exchanger can be adjusted in time to optimize the heat exchange process. According to the difference in inlet and outlet temperatures, the fluid flow rate can be adjusted to improve the heat exchange efficiency.

[0010] As a further solution of the present invention, a low-pressure sensor and a low-pressure switch are provided on the main circulation loop between the gas-liquid separator and the compressor.

[0011] The low-pressure sensor monitors the low-pressure status in the main circulation loop in real time, provides system operation status information, detects abnormal conditions in time, and ensures the stability and safety of the system. The low-pressure switch will automatically cut off the system or sound an alarm when the pressure drops to the set threshold, preventing gas backflow, compressor damage or system failure caused by low pressure, thereby enhancing the protection capability of the system.

[0012] As a further solution of the present invention, an intake temperature sensor is provided at the intake port of the compressor, and an exhaust temperature sensor is provided at the exhaust port of the compressor to monitor the intake and exhaust temperatures of the compressor in real time, collect temperature data, and ensure that the compressor operates within a safe and efficient temperature range.

[0013] As a further solution of the present invention, a water inlet temperature sensor is provided at the heat exchange inlet of the water side heat exchanger, and a water outlet temperature sensor is provided at the heat exchange outlet of the water side heat exchanger. The inlet and outlet temperatures of the heat exchanger are monitored in real time to ensure that the operating parameters of the system are visualized, which is convenient for operators to effectively manage. Real-time temperature data is used to calculate the heat exchange efficiency of the heat exchanger, adjust the flow rate and other operating parameters, improve the overall heat exchange efficiency, and save energy. The automated control system collects temperature data, realizes precise closed-loop control, and adjusts the flow rate and pump speed in real time to adapt to different working conditions and improve the intelligence level of the system.

[0014] As a further solution of the present invention, the heat pump intermediate heat exchanger air supply system is also provided with an ambient temperature sensor, which detects the ambient temperature. The main expansion valve is an EEV electronic expansion valve, and the auxiliary expansion valve is an EVI electronic expansion valve.

[0015] As a further solution of the present invention, a control method for a heat pump intermediate heat exchanger air supply system, a heat pump intermediate heat exchanger air supply system, including a control module, the control module including a preset control program, the control program encoding is provided with a temperature function, a density function, an enthalpy function and an entropy function, the control module captures initial information parameters, and obtains a theoretical air supply ratio a and a system air supply ratio a' by calling the temperature function, density function, enthalpy function and entropy function in the REFPROP function, and presets the optimal intermediate pressure value reached by the evaporation pressure of the intermediate heat exchanger air supply auxiliary circuit, and the intermediate pressure value range [Pmin, Pmax].

[0016] As a further solution of the present invention, a control method for an air supply system of a heat pump intermediate heat exchanger comprises the following steps:

[0017] Step 1: Given the compressor isentropic efficiency, the compressor suction pipe temperature drop and pressure drop and the exhaust pipe temperature drop and pressure drop, the water-side heat exchanger side subcooling value, the air-side heat exchanger side superheat value, obtain the compressor operating frequency, evaporation pressure, condensation pressure in real time, call the temperature function, enthalpy function and entropy function, and calculate the evaporation temperature, condensation temperature, compressor suction enthalpy value and primary compression isentropic value of the system operation respectively;

[0018] Step 2: Based on step 1, an intermediate pressure value is preset and according to the intermediate pressure value, the enthalpy function and the energy function are called again to respectively calculate the isentropic enthalpy value of the initial compression of the compressor, the actual enthalpy value of the initial compression, the internal energy of the initial compression, the internal energy of the intermediate cavity after the air supplement and mixing, the enthalpy value of the intermediate cavity, the entropy value of the secondary compressor, the theoretical enthalpy value at the end of compression, the actual enthalpy value at the end of compression and the exhaust temperature of the compressor;

[0019] Step 3: Using the data obtained in step 1 and step 2, call the density function to obtain the initial compression working fluid density ρ1 of the compressor and the working fluid density after air replenishment ρ3, and calculate the theoretical air replenishment ratio a.

[0020] The calculation formula of the theoretical air supply ratio α is: α=ρ1 / ρ3-1;

[0021] Step 4: According to the preset intermediate pressure value, given the condensing pressure, the pressure drop of the auxiliary air supply line, the superheat of the auxiliary air supply line and the subcooling of the main circulation loop, the front and rear pressures and temperatures of the EVI electronic expansion valve of the auxiliary air supply line of the intermediate heat exchanger, the outlet temperature and outlet pressure of the auxiliary air supply line, the outlet pressure of the main circulation loop and the outlet temperature of the main circulation loop are obtained, and then the enthalpy function is called to obtain the inlet enthalpy value h5 of the main road of the intermediate heat exchanger, the outlet enthalpy value h6 of the main road of the intermediate heat exchanger and the outlet enthalpy value h8 of the auxiliary air supply line of the intermediate heat exchanger, and the ratio of the refrigerant flow rate of the auxiliary air supply line to the refrigerant flow rate of the main circulation loop is calculated, that is, the system air supply ratio a'.

[0022] According to the law of conservation of energy, the calculation formula of the system gas supply ratio a' is:

[0023] α'=(h5-h6) / (h8-h5);

[0024] Step 5: Compare the theoretical air supply ratio α obtained in step 3 with the system air supply ratio a' obtained in step 4, and use the intermediate pressure value range [Pmin, Pmax] when a / a'≤±1% as the target parameter to control the opening of the auxiliary EVI electronic expansion valve, so that the auxiliary air supply pressure reaches the optimal intermediate pressure range;

[0025] Step 6: When a / a'>1%, that is, the actual gas injection pressure is greater than Pmax or the actual gas injection pressure is less than Pmin;

[0026] When the actual air supply pressure is greater than Pmax, take the difference between Pmax and the actual air supply pressure, and then calculate the EVI electronic expansion valve opening control amount of the air supply auxiliary circuit according to the calculation formula, and control the auxiliary circuit electronic expansion valve to the valve opening control amount calculated by the calculation formula, so that the auxiliary circuit air supply pressure reaches the middle pressure value range [Pmin, Pmax];

[0027] When the actual air supply pressure is less than Pmin, take the difference between the actual air supply pressure and Pmin, and then calculate the EVI electronic expansion valve opening control amount of the air supply auxiliary circuit according to the calculation formula, and control the auxiliary circuit electronic expansion valve to the valve opening control amount calculated by the calculation formula, so that the auxiliary circuit air supply pressure reaches the middle pressure value range [Pmin, Pmax];

[0028] Step 7: In step 6, the auxiliary electronic expansion valve is controlled to a valve opening control amount calculated by a calculation formula, and the calculation formula is as follows:

[0029]

[0030]

[0031] Among them, δ1 and δ2 both represent the opening control amount of the EVI electronic expansion valve in the air supply auxiliary circuit;

[0032] θ1 represents the difference between the actual pressure of the air supply auxiliary circuit and the upper limit Pmax of the optimal intermediate pressure value;

[0033] θ2 represents the difference between the actual pressure of the air supply auxiliary circuit and the lower limit of the optimal intermediate pressure value Pmin;

[0034] Kp represents the proportional coefficient; Ki represents the integral coefficient; Kd represents the differential coefficient;

[0035] Step 8: When a / a'≤±1%, the pressure of the air supply auxiliary line is in the optimal intermediate pressure range [Pmin, Pmax]. The high-pressure sensor at the compressor exhaust port detects the exhaust pressure value of the system in real time. The exhaust pressure value is converted into a high-pressure saturation temperature value. The exhaust temperature sensor at the compressor exhaust port detects the exhaust temperature value of the system in real time. According to the exhaust temperature value and the high-pressure saturation temperature value, the actual exhaust superheat of the heat pump system can be calculated.

[0036] Step 9: Based on step 8, the system gives a preset value of the target exhaust superheat, subtracts the actual exhaust superheat from the target exhaust superheat, and calculates the opening control amount of the auxiliary electronic expansion valve according to the calculation formula, so that the actual exhaust superheat reaches the target exhaust superheat. The calculation formula for controlling the opening of the auxiliary electronic expansion valve is as follows:

[0037]

[0038] δ3 represents the opening control amount of the EVI electronic expansion valve in the air supplementary circuit; θ3 represents the difference between the actual exhaust superheat and the target exhaust superheat in the air supplementary circuit; Kp is the proportional coefficient; Ki is the integral coefficient; and Kd is the differential coefficient.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows: the system refers to the REFPROP function according to the evaporation pressure, condensing pressure, frequency of the compressor, refrigeration capacity and other parameters of the heat pump unit, calculates the various state parameters of the entire secondary compression process of the unit compressor, including the final pressure of the primary compression, enthalpy value, density, intermediate cavity enthalpy value and mixed density, and determines the air supply volume of the main circulation of the heat pump unit according to the deviation range of the optimal intermediate pressure ratio of the compressor and the main circulation air supply ratio.

[0040] By adjusting the opening of the auxiliary electronic expansion valve, the auxiliary outlet pressure value of the unit (i.e., the air supply pressure) is made close to the optimal intermediate pressure of the compressor. When the air supply reaches the optimal intermediate pressure, the heating capacity and performance coefficient of the heat pump unit are greatly improved. Through the air supply control method, the opening of the auxiliary electronic expansion valve is controlled by calculating the deviation between the air supply ratio of the heat pump system and the intermediate pressure ratio of the compressor to ensure that the air supply pressure of the unit is the optimal intermediate pressure, thereby achieving the optimal heating performance of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the principle of the air supply system of the heat pump intermediate heat exchanger of the present invention;

[0042] Figure 2 The pressure-enthalpy diagram of the air supply system of the heat pump intermediate heat exchanger of the present invention;

[0043] Figure 3 This is a control logic flow chart of the heat pump intermediate heat exchanger air replenishment system of the present invention.

[0044] In the figure: 1-gas-liquid separator, 2-main circulation loop, 201-main expansion valve, 202-main filter, 203-main inlet temperature sensor, 204-main outlet temperature sensor, 205-high pressure switch, 206-high pressure sensor, 207-exhaust temperature sensor, 208-intake temperature sensor, 209-low pressure switch, 210-low pressure sensor, 3-air side heat exchanger, 4-intermediate heat exchanger, 5-air supply auxiliary line, 501-air supply pressure sensor, 502-auxiliary outlet temperature sensor, 503-auxiliary inlet temperature sensor, 504-auxiliary expansion valve, 505-auxiliary filter, 6-water side heat exchanger, 601-water inlet temperature sensor, 602-water outlet temperature sensor, 7-compressor. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below through embodiments and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0046] The serial numbers of the components herein, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The "connection" and "coupling" mentioned in this application, unless otherwise specified, include direct and indirect connections (couplings). In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc. are based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0047] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature means that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or 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" or "below" a second feature means that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0048] Example 1

[0049] like Figure 1As shown, a heat pump intermediate heat exchanger air replenishment system includes a main circulation loop 2 and an air replenishment auxiliary circuit 5. The main circulation loop is provided with a compressor 7, a water side heat exchanger 6, an intermediate heat exchanger 4, an air side heat exchanger 3 and a gas-liquid separator 1 in sequence. The water side heat exchanger is connected to the main inlet of the intermediate heat exchanger. A main inlet temperature sensor 203 is provided at the main inlet of the intermediate heat exchanger, and the main inlet temperature sensor detects the main inlet temperature. A main outlet temperature sensor 204 is provided at the main outlet of the intermediate heat exchanger, and the main outlet temperature sensor detects the main outlet temperature. An auxiliary inlet temperature sensor 503 is provided at the inlet of the auxiliary circuit of the intermediate heat exchanger, and the auxiliary inlet temperature sensor detects the auxiliary inlet temperature. An auxiliary outlet temperature sensor 502 is provided at the outlet of the auxiliary circuit of the intermediate heat exchanger, and the auxiliary outlet temperature sensor detects the auxiliary outlet temperature. A gas replenishment pressure sensor 501 is also provided on the auxiliary outlet pipe. Each temperature sensor can monitor the temperature changes of each fluid channel in real time, provide important data support for the operating status of the system, realize precise temperature control, and timely adjust the operating parameters of the heat exchanger by monitoring the temperature of the main and auxiliary channels.

[0050] The main outlet of the intermediate heat exchanger is connected to the liquid separation head of the wind side heat exchanger. A main filter 202 and a main expansion valve 201 are provided on the main circulation loop between the main outlet of the intermediate heat exchanger and the liquid separation head.

[0051] The auxiliary air supply line 5 includes an auxiliary liquid inlet pipe and an auxiliary liquid outlet pipe. The auxiliary liquid inlet pipe is connected to the main circulation loop between the water side heat exchanger and the intermediate heat exchanger. The other end of the auxiliary liquid inlet pipe is connected to the auxiliary inlet of the intermediate heat exchanger. An auxiliary liquid inlet pipe is provided with an auxiliary filter 505 and an auxiliary expansion valve 504. The auxiliary outlet of the intermediate heat exchanger and the air supply port of the compressor are connected through the auxiliary liquid outlet pipe.

[0052] A low pressure sensor 210 and a low pressure switch 209 are provided on the main circulation loop between the gas-liquid separator 1 and the compressor 7. They are used to detect the pressure value on the low pressure side and set low pressure protection to avoid excessive low pressure when the system is running.

[0053] An intake temperature sensor 208 is provided at the compressor intake port, and an exhaust temperature sensor 207 is provided at the compressor exhaust port. A water inlet temperature sensor 601 is provided at the heat exchange inlet of the water side heat exchanger, and a water outlet temperature sensor 602 is provided at the heat exchange outlet of the water side heat exchanger. An ambient temperature sensor is also provided on the air supply system of the heat pump intermediate heat exchanger, and the ambient temperature sensor detects the ambient temperature. The main expansion valve 201 is an EEV electronic expansion valve, and the auxiliary expansion valve 504 is an EVI electronic expansion valve.

[0054] Both the main circulation circuit and the air supply auxiliary circuit are provided with circulating refrigerant.

[0055] After the refrigerant is compressed by the compressor, a high-temperature and high-pressure gaseous refrigerant is formed. The high-temperature and high-pressure gaseous refrigerant enters the water-side heat exchanger 6 from the compressor exhaust port. The high-temperature and high-pressure gaseous refrigerant is condensed into a high-pressure liquid refrigerant after heat exchange with water in the water-side heat exchanger. The main circulation loop between the compressor exhaust port and the water-side heat exchanger inlet is provided with a high-pressure sensor 206 and a high-pressure switch 205 in sequence along the exhaust direction. The high-pressure side pressure value is measured in real time, and the high-pressure liquid refrigerant at the outlet of the water-side heat exchanger enters the main circulation loop and the air supply auxiliary circuit respectively.

[0056] The refrigerant in the main circulation loop is throttled and reduced in pressure by the EVI electronic expansion valve in the intermediate heat exchanger and the air supply auxiliary line to form a low-temperature medium-pressure refrigerant for heat exchange. The low-temperature medium-pressure refrigerant is throttled and reduced in pressure by the EEV electronic expansion valve to become a low-temperature, low-pressure wet steam refrigerant. The low-temperature, low-pressure wet steam refrigerant then enters the air-side heat exchanger to absorb ambient heat and become a low-temperature, low-pressure gaseous refrigerant. It passes through the gas-liquid separator in turn and enters the compressor along the compressor suction port.

[0057] At the same time, the refrigerant in the air supply auxiliary circuit absorbs the heat of the refrigerant in the main circulation loop to become a superheated vapor refrigerant, and the superheated vapor refrigerant enters the compressor 7 from the compressor air supply port.

[0058] Example 2

[0059] like Figure 2 and Figure 3 As shown, a control method for a heat pump intermediate heat exchanger air supply system includes a control module, the control module includes a preset control program, the control program code is provided with a temperature function, a density function, an enthalpy function and an entropy function, the control module captures initial information parameters, and obtains a theoretical air supply ratio a and a system air supply ratio a' by calling the temperature function, density function, enthalpy function and entropy function in the REFPROP function, and presets the optimal intermediate pressure value reached by the evaporation pressure of the intermediate heat exchanger air supply auxiliary circuit, and the intermediate pressure value range [Pmin, Pmax].

[0060] The control method of the air supply system of the heat pump intermediate heat exchanger comprises the following steps:

[0061] Step 1: Given the compressor isentropic efficiency, the compressor suction pipe temperature drop and pressure drop and the exhaust pipe temperature drop and pressure drop, the water-side heat exchanger side subcooling value, the air-side heat exchanger side superheat value, obtain the compressor operating frequency, evaporation pressure, condensation pressure in real time, call the temperature function, enthalpy function and entropy function, and calculate the evaporation temperature, condensation temperature, compressor suction enthalpy value and primary compression isentropic value of the system operation respectively;

[0062] Step 2: Based on step 1, an intermediate pressure value is preset and according to the intermediate pressure value, the enthalpy function and the energy function are called again to respectively calculate the isentropic enthalpy value of the initial compression of the compressor, the actual enthalpy value of the initial compression, the internal energy of the initial compression, the internal energy of the intermediate cavity after the air supplement and mixing, the enthalpy value of the intermediate cavity, the entropy value of the secondary compressor, the theoretical enthalpy value at the end of compression, the actual enthalpy value at the end of compression and the exhaust temperature of the compressor;

[0063] Step 3: Using the data obtained in step 1 and step 2, call the density function to obtain the initial compression working fluid density ρ1 of the compressor and the working fluid density after air replenishment ρ3, and calculate the theoretical air replenishment ratio a.

[0064] The calculation formula of the theoretical air supply ratio α is: α=ρ1 / ρ3-1;

[0065] Step 4: According to the preset intermediate pressure value, given the condensing pressure, the pressure drop of the auxiliary air supply line, the superheat of the auxiliary air supply line and the subcooling of the main circulation loop, the front and rear pressures and temperatures of the EVI electronic expansion valve of the auxiliary air supply line of the intermediate heat exchanger, the outlet temperature and outlet pressure of the auxiliary air supply line, the outlet pressure of the main circulation loop and the outlet temperature of the main circulation loop are obtained, and then the enthalpy function is called to obtain the inlet enthalpy value h5 of the main road of the intermediate heat exchanger, the outlet enthalpy value h6 of the main road of the intermediate heat exchanger and the outlet enthalpy value h8 of the auxiliary air supply line of the intermediate heat exchanger, and the ratio of the refrigerant flow rate of the auxiliary air supply line to the refrigerant flow rate of the main circulation loop is calculated, that is, the system air supply ratio a'.

[0066] According to the law of conservation of energy, the calculation formula of the system gas supply ratio a' is:

[0067] α'=(h5-h6) / (h8-h5);

[0068] Step 5: Compare the theoretical air supply ratio α obtained in step 3 with the system air supply ratio a' obtained in step 4, and use the intermediate pressure value range [Pmin, Pmax] when a / a'≤±1% as the target parameter to control the opening of the auxiliary EVI electronic expansion valve, so that the auxiliary air supply pressure reaches the optimal intermediate pressure range;

[0069] Step 6: When a / a'>1%, that is, the actual gas injection pressure is greater than Pmax or the actual gas injection pressure is less than Pmin;

[0070] When the actual air supply pressure is greater than Pmax, take the difference between Pmax and the actual air supply pressure, and then calculate the EVI electronic expansion valve opening control amount of the air supply auxiliary circuit according to the calculation formula, and control the auxiliary circuit electronic expansion valve to the valve opening control amount calculated by the calculation formula, so that the auxiliary circuit air supply pressure reaches the middle pressure value range [Pmin, Pmax];

[0071] When the actual air supply pressure is less than Pmin, take the difference between the actual air supply pressure and Pmin, and then calculate the EVI electronic expansion valve opening control amount of the air supply auxiliary circuit according to the calculation formula, and control the auxiliary circuit electronic expansion valve to the valve opening control amount calculated by the calculation formula, so that the auxiliary circuit air supply pressure reaches the middle pressure value range [Pmin, Pmax];

[0072] Step 7: In step 6, the auxiliary electronic expansion valve is controlled to a valve opening control amount calculated by a calculation formula, and the calculation formula is as follows:

[0073]

[0074]

[0075] Among them, δ1 and δ2 both represent the opening control amount of the EVI electronic expansion valve in the air supply auxiliary circuit;

[0076] θ1 represents the difference between the actual pressure of the air supply auxiliary circuit and the upper limit Pmax of the optimal intermediate pressure value;

[0077] θ2 represents the difference between the actual pressure of the air supply auxiliary circuit and the lower limit of the optimal intermediate pressure value Pmin;

[0078] Kp represents the proportional coefficient; Ki represents the integral coefficient; Kd represents the differential coefficient;

[0079] Step 8: When a / a'≤±1%, the pressure of the air supply auxiliary line is in the optimal intermediate pressure range [Pmin, Pmax]. The high-pressure sensor at the compressor exhaust port detects the exhaust pressure value of the system in real time. The exhaust pressure value is converted into a high-pressure saturation temperature value. The exhaust temperature sensor at the compressor exhaust port detects the exhaust temperature value of the system in real time. According to the exhaust temperature value and the high-pressure saturation temperature value, the actual exhaust superheat of the heat pump system is calculated;

[0080] Step 9: Based on step 8, the system gives a preset value of the target exhaust superheat, subtracts the actual exhaust superheat from the target exhaust superheat, and calculates the opening control amount of the auxiliary electronic expansion valve according to the calculation formula, so that the actual exhaust superheat reaches the target exhaust superheat. The calculation formula for controlling the opening of the auxiliary electronic expansion valve is as follows:

[0081]

[0082] δ3 represents the opening control amount of the EVI electronic expansion valve in the air supplementary circuit; θ3 represents the difference between the actual exhaust superheat and the target exhaust superheat in the air supplementary circuit; Kp is the proportional coefficient; Ki is the integral coefficient; and Kd is the differential coefficient.

[0083] The electrical components mentioned in this article are all connected to an external main controller and 380V commercial power, and the main controller can be a conventional known device for control such as a computer.

[0084] In the description of this specification, the terms "connect", "install", "fix", "set", etc. are understood in a broad sense. For example, "connection" is a fixed connection or an indirect connection through an intermediate component without affecting the relationship between components and the technical effect. It can also be an integral connection or a partial connection. As in this example, for ordinary technicians in this field, the specific meanings of the above terms in the present invention or invention can be understood according to the specific circumstances.

[0085] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A heat pump intermediate heat exchanger air supply system, characterized in that: The invention comprises a main circulation loop (2) and an air supply auxiliary circuit (5), wherein a compressor (7), a water-side heat exchanger (6), an intermediate heat exchanger (4), an air-side heat exchanger (3) and a gas-liquid separator (1) are arranged in sequence on the main circulation loop, the water-side heat exchanger is connected to the main inlet of the intermediate heat exchanger, the main outlet of the intermediate heat exchanger is connected to the liquid separation head of the air-side heat exchanger, and a main filter (202) and a main expansion valve (201) are arranged on the main circulation loop between the main outlet of the intermediate heat exchanger and the liquid separation head; The auxiliary air supply line (5) comprises an auxiliary line liquid inlet pipe and an auxiliary line liquid outlet pipe. The auxiliary line liquid inlet pipe is connected to the main circulation loop between the water side heat exchanger and the intermediate heat exchanger. The other end of the auxiliary line liquid inlet pipe is connected to the auxiliary line inlet of the intermediate heat exchanger. An auxiliary line filter (505) and an auxiliary line expansion valve (504) are provided on the auxiliary line liquid inlet pipe. The auxiliary line outlet of the intermediate heat exchanger and the air supply port of the compressor are connected via the auxiliary line liquid outlet pipe.

2. The heat pump intermediate heat exchanger air supply system according to claim 1, characterized in that: A main circulation loop between the compressor exhaust port and the water-side heat exchanger inlet is provided with a high-pressure sensor (206) and a high-pressure switch (205) in sequence along the exhaust direction.

3. The heat pump intermediate heat exchanger air supply system according to claim 2, characterized in that: A main inlet temperature sensor (203) is provided at the inlet of the main path of the intermediate heat exchanger, and the main inlet temperature is obtained by the main inlet temperature sensor. A main outlet temperature sensor (204) is provided at the outlet of the main path of the intermediate heat exchanger, and the main outlet temperature is obtained by the main outlet temperature. An auxiliary inlet temperature sensor (503) is provided at the inlet of the auxiliary path of the intermediate heat exchanger, and the auxiliary inlet temperature is obtained by the auxiliary inlet temperature sensor. An auxiliary outlet temperature sensor (502) is provided at the outlet of the auxiliary path of the intermediate heat exchanger, and the auxiliary outlet temperature is obtained by the auxiliary outlet temperature. A gas replenishment pressure sensor (501) is also provided on the auxiliary liquid outlet pipe.

4. A heat pump intermediate heat exchanger air supply system according to claim 3, characterized in that: A low pressure sensor (210) and a low pressure switch (209) are provided on the main circulation loop between the gas-liquid separator and the compressor.

5. The heat pump intermediate heat exchanger air supply system according to claim 4, characterized in that: An intake temperature sensor (208) is provided at the intake port of the compressor, and an exhaust temperature sensor (207) is provided at the exhaust port of the compressor.

6. The heat pump intermediate heat exchanger air supply system according to claim 5, characterized in that: A water inlet temperature sensor (601) is provided at the heat exchange inlet of the water side heat exchanger, and a water outlet temperature sensor (602) is provided at the heat exchange outlet of the water side heat exchanger.

7. The heat pump intermediate heat exchanger air supply system according to claim 6, characterized in that: The heat pump intermediate heat exchanger air supply system is also provided with an ambient temperature sensor, which detects the ambient temperature. The main expansion valve (201) is an EEV electronic expansion valve, and the auxiliary expansion valve (504) is an EVI electronic expansion valve.

8. A control method for a heat pump intermediate heat exchanger air supply system, using the heat pump intermediate heat exchanger air supply system according to claim 7, characterized in that: The control module includes a control module which includes a preset control program. The control program code is provided with a temperature function, a density function, an enthalpy function and an entropy function. The control module captures initial information parameters, obtains a theoretical air supply ratio a and a system air supply ratio a' by calling the temperature function, the density function, the enthalpy function and the entropy function in the REFPROP function, and presets the optimal intermediate pressure value reached by the evaporation pressure of the intermediate heat exchanger air supply auxiliary circuit, and the intermediate pressure value range [Pmin, Pmax].

9. A control method for an air supply system of a heat pump intermediate heat exchanger according to claim 8, characterized in that: The steps include: Step 1: Given the compressor isentropic efficiency, the compressor suction pipe temperature drop and pressure drop and the exhaust pipe temperature drop and pressure drop, the water-side heat exchanger side subcooling value, the air-side heat exchanger side superheat value, obtain the compressor operating frequency, evaporation pressure, condensation pressure in real time, call the temperature function, enthalpy function and entropy function, and calculate the evaporation temperature, condensation temperature, compressor suction enthalpy value and primary compression isentropic value of the system operation respectively; Step 2: Based on step 1, an intermediate pressure value is preset and according to the intermediate pressure value, the enthalpy function and the energy function are called again to respectively calculate the isentropic enthalpy value of the initial compression of the compressor, the actual enthalpy value of the initial compression, the internal energy of the initial compression, the internal energy of the intermediate cavity after the air supplement and mixing, the enthalpy value of the intermediate cavity, the entropy value of the secondary compressor, the theoretical enthalpy value at the end of compression, the actual enthalpy value at the end of compression and the exhaust temperature of the compressor; Step 3: Using the data obtained in step 1 and step 2, call the density function to obtain the initial compression working fluid density ρ1 of the compressor and the working fluid density after air replenishment ρ3, and calculate the theoretical air replenishment ratio a. The calculation formula of the theoretical air supply ratio α is: α=ρ1 / ρ3-1; Step 4: According to the preset intermediate pressure value, given the condensing pressure, the pressure drop of the auxiliary air supply line, the superheat of the auxiliary air supply line and the subcooling of the main circulation loop, the front and rear pressures and temperatures of the EVI electronic expansion valve of the auxiliary air supply line of the intermediate heat exchanger, the outlet temperature and outlet pressure of the auxiliary air supply line, the outlet pressure of the main circulation loop and the outlet temperature of the main circulation loop are obtained, and then the enthalpy function is called to obtain the inlet enthalpy value h5 of the main road of the intermediate heat exchanger, the outlet enthalpy value h6 of the main road of the intermediate heat exchanger and the outlet enthalpy value h8 of the auxiliary air supply line of the intermediate heat exchanger, and the ratio of the refrigerant flow rate of the auxiliary air supply line to the refrigerant flow rate of the main circulation loop is calculated, that is, the system air supply ratio a'. According to the law of conservation of energy, the calculation formula of the system gas supply ratio a' is: α'=(h5-h6) / (h8-h5); Step 5: Compare the theoretical air supply ratio α obtained in step 3 with the system air supply ratio a' obtained in step 4, and use the intermediate pressure value range [Pmin, Pmax] when a / a'≤±1% as the target parameter to control the opening of the auxiliary EVI electronic expansion valve, so that the auxiliary air supply pressure reaches the optimal intermediate pressure range; Step 6: When a / a'>1%, that is, the actual gas injection pressure is greater than Pmax or the actual gas injection pressure is less than Pmin; When the actual air supply pressure is greater than Pmax, take the difference between Pmax and the actual air supply pressure, and then calculate the EVI electronic expansion valve opening control amount of the air supply auxiliary circuit according to the calculation formula, and control the auxiliary circuit electronic expansion valve to the valve opening control amount calculated by the calculation formula, so that the auxiliary circuit air supply pressure reaches the intermediate pressure value range [Pmin,Pmax]; When the actual air supply pressure is less than Pmin, take the difference between the actual air supply pressure and Pmin, and then calculate the EVI electronic expansion valve opening control amount of the air supply auxiliary circuit according to the calculation formula, and control the auxiliary circuit electronic expansion valve to the valve opening control amount calculated by the calculation formula, so that the auxiliary circuit air supply pressure reaches the intermediate pressure value range [Pmin,Pmax]; Step 7: In step 6, the auxiliary electronic expansion valve is controlled to the valve opening control amount calculated by the calculation formula, and the calculation formula is as follows: Among them, δ1 and δ2 both represent the opening control amount of the EVI electronic expansion valve in the air supply auxiliary circuit; θ1 represents the difference between the actual pressure of the air supply auxiliary circuit and the upper limit Pmax of the optimal intermediate pressure value; θ2 represents the difference between the actual pressure of the air supply auxiliary circuit and the lower limit of the optimal intermediate pressure value Pmin; Kp represents the proportional coefficient; Ki represents the integral coefficient; Kd represents the differential coefficient; Step 8: When a / a'≤±1%, the pressure of the air supply auxiliary line is in the optimal intermediate pressure range [Pmin, Pmax]. The high-pressure sensor at the compressor exhaust port detects the exhaust pressure value of the system in real time. The exhaust pressure value is converted into a high-pressure saturation temperature value. The exhaust temperature sensor at the compressor exhaust port detects the exhaust temperature value of the system in real time. According to the exhaust temperature value and the high-pressure saturation temperature value, the actual exhaust superheat of the heat pump system is calculated; Step 9: Based on step 8, the system gives a preset value of the target exhaust superheat, subtracts the actual exhaust superheat from the target exhaust superheat, and calculates the opening control amount of the auxiliary electronic expansion valve according to the calculation formula, so that the actual exhaust superheat reaches the target exhaust superheat. The calculation formula for controlling the opening of the auxiliary electronic expansion valve is as follows: δ3 represents the opening control amount of the EVI electronic expansion valve in the air supplementary circuit; θ3 represents the difference between the actual exhaust superheat and the target exhaust superheat in the air supplementary circuit; Kp is the proportional coefficient; Ki is the integral coefficient; and Kd is the differential coefficient.

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