A heat pump intermediate heat exchanger air supplement system and a control method thereof

Abstract

The present application relates to heat pump system technical field, specifically to a kind of heat pump intermediate heat exchanger air supplement system and its control method, according to the evaporation pressure of heat pump unit operation, condensing pressure, the frequency of compressor, refrigerating capacity and other parameters, reference REFPROP function obtains the state parameters of entire two-stage compression process of unit compressor, such as primary compression end pressure, enthalpy, density, intermediate chamber enthalpy and mixed density, determine the air supplement amount of heat pump unit main loop according to the deviation value range of compressor optimum intermediate pressure ratio and main loop circulating air supplement ratio.The opening of auxiliary road electronic expansion valve is adjusted, and the outlet pressure value of unit is close to the optimum intermediate pressure of compressor.By air supplement control, it can be controlled according to the deviation value of heat pump system air supplement ratio and compressor intermediate pressure ratio to control the opening of auxiliary road electronic expansion valve during the operation of unit, so that the air supplement pressure of unit is the optimum intermediate pressure, thereby realizing the optimal heating performance of unit.

Description

Technical Field

[0001] This invention relates to the field of heat pump system technology, specifically to a gas supply system for an intermediate heat exchanger in a heat pump and its control method. Background Technology

[0002] Air source heat pumps now mostly employ intermediate heat exchangers (i.e., economizers) to achieve stable operation of the unit in ultra-low temperature environments. The principle is to draw in a portion of intermediate-pressure gas through the intermediate-pressure suction port of the vapor injection enthalpy-increasing compressor, mix it with partially compressed refrigerant, and then compress it again. This achieves the effect of two-stage compression with a single compressor, increasing the refrigerant flow rate in the water-side heat exchanger, increasing the enthalpy difference of the main circulation loop, and widening the operating range of the heat pump unit. Simultaneously, it addresses to some extent the problem of excessively high exhaust temperatures when the compressor operates under high pressure ratio conditions with low ambient temperature and high water temperature.

[0003] However, air-source heat pump units that use an economizer to achieve enthalpy enhancement through gas replenishment typically adjust the valve opening of their auxiliary electronic expansion valve based on the temperature difference between the refrigerant entering and exiting the economizer in the gas replenishment circuit (i.e., auxiliary circuit superheat) and the deviation from the target superheat setpoint of the auxiliary circuit. This adjusts the amount of gas replenishment entering the compressor. While this method can achieve enthalpy enhancement to some extent, adjusting the gas replenishment amount solely based on the auxiliary circuit superheat cannot ensure that the compressor's gas replenishment pressure is at the optimal intermediate pressure, achieving the optimal gas replenishment ratio. Consequently, it cannot fully utilize the compressor's optimal heating performance at low ambient temperatures. Furthermore, under the same gas replenishment pressure, the superheat of the gas replenishment has a relatively small impact on the cooling capacity and coefficient of performance (COP). Summary of the Invention

[0004] To address the problems mentioned in the background art, this invention provides a heat pump intermediate heat exchanger gas supply system and its control method based on existing technology. This system ensures that during unit operation, the opening of the auxiliary electronic expansion valve is controlled by calculating the deviation between the gas supply ratio of the heat pump system and the intermediate pressure ratio of the compressor, so that the gas supply pressure of the unit reaches the optimal intermediate pressure, thereby achieving the optimal heating performance of the unit.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a heat pump intermediate heat exchanger gas replenishment system, comprising a main circulation loop and a gas replenishment auxiliary loop. The main circulation loop sequentially includes a compressor, a water-side heat exchanger, an intermediate heat exchanger, an air-side heat exchanger, and a gas-liquid separator. The main inlets of the water-side heat exchanger and the intermediate heat exchanger are connected, and the main outlet of the intermediate heat exchanger is connected to the liquid distributor of the air-side heat exchanger. A main loop filter and a main loop expansion valve are provided between the main outlet of the intermediate heat exchanger and the liquid distributor. This system improves heat exchange efficiency between the water-side heat exchanger and the intermediate heat exchanger, effectively reducing energy loss and enhancing heat recovery capacity. The gas-liquid separator effectively separates gas and liquid in the system, reducing the impact of air bubbles on the pump and heat exchangers. Precise adjustment of the fluid flow rate and pressure in the main circulation loop ensures that each heat exchanger operates under optimal conditions.

[0006] The auxiliary gas supply circuit includes an auxiliary inlet pipe and an auxiliary outlet pipe. The auxiliary inlet pipe connects to the main circulation loop between the water-side heat exchanger and the intermediate heat exchanger. The other end of the auxiliary inlet pipe connects to the auxiliary inlet of the intermediate heat exchanger. An auxiliary filter and an auxiliary expansion valve are installed on the auxiliary inlet pipe. The auxiliary outlet of the intermediate heat exchanger and the compressor's gas supply port are connected via the auxiliary outlet pipe. The auxiliary filter in the auxiliary gas supply circuit 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 pressure instability. The design of the auxiliary gas supply circuit allows for flexible gas replenishment when needed, maintaining the system's optimal operating condition and ensuring long-term stable operation.

[0007] As a further aspect of the invention, a high-pressure sensor and a high-pressure switch are sequentially installed along the exhaust direction in the main circulation loop between the compressor exhaust port and the water-side heat exchanger inlet. The high-pressure sensor monitors the pressure changes in the main circulation loop in real time, ensuring that the system operates within a predetermined pressure range. This allows for the timely detection of potential faults or abnormalities, enhancing the system's safety and reliability.

[0008] As a further embodiment of the present invention, a main inlet temperature sensor is provided at the main inlet of the intermediate heat exchanger to detect the main inlet temperature, a main outlet temperature sensor is provided at the main outlet of the intermediate heat exchanger to detect the main outlet temperature, an auxiliary inlet temperature sensor is provided at the inlet of the auxiliary outlet of the intermediate heat exchanger to detect the auxiliary inlet temperature, and an auxiliary outlet temperature sensor is provided at the outlet of the auxiliary outlet of the intermediate heat exchanger to detect the auxiliary outlet temperature. A gas supply pressure sensor is also provided on the liquid outlet pipe of the auxiliary outlet. Each temperature sensor can monitor the temperature changes of each fluid channel in real time, providing important data support for the system's operating status, achieving precise temperature control, and improving heat exchange efficiency.

[0009] By monitoring the temperatures of the main and auxiliary circuits, the operating parameters of the heat exchanger can be adjusted in a timely manner to optimize the heat exchange process. Based on the difference between the inlet and outlet temperatures, the fluid flow rate can be adjusted to improve heat exchange efficiency.

[0010] As a further embodiment 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, providing system operating status information, promptly detecting abnormalities, and ensuring system stability and safety. The low-pressure switch automatically shuts off the system or issues an alarm when the pressure drops to a set threshold, preventing gas backflow, compressor damage, or system malfunctions caused by low pressure, thereby enhancing the system's protection capabilities.

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

[0013] As a further embodiment of the present invention, an inlet water temperature sensor is provided at the heat exchange inlet of the water-side heat exchanger, and an outlet water temperature sensor is provided at the heat exchange outlet of the water-side heat exchanger. Real-time monitoring of the inlet and outlet water temperatures of the heat exchanger ensures the visualization of system operating parameters, facilitating effective management by operators. Real-time temperature data is used to calculate the heat exchange efficiency of the heat exchanger, adjust flow rate and other operating parameters, improve overall heat exchange efficiency, and save energy. The automated control system collects temperature data to achieve precise closed-loop control, adjusting flow rate and pump speed in real time to adapt to different operating conditions and enhance the system's intelligence level.

[0014] As a further embodiment of the present invention, the intermediate heat exchanger gas supply system of the heat pump is also equipped 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 embodiment of the present invention, a control method for a gas supply system for an intermediate heat exchanger of a heat pump is provided. The gas supply system for an intermediate heat exchanger of a heat pump includes a control module. The control module includes a preset control program. The control program is coded with a temperature function, a density function, an enthalpy function, and an entropy function. The control module captures initial information parameters and obtains the theoretical gas supply ratio a and the system gas supply ratio a' by calling the temperature function, density function, enthalpy function, and entropy function in the REFPROP function. The optimal intermediate pressure value to be achieved by the evaporation pressure of the auxiliary gas supply path of the intermediate heat exchanger is preset, and the intermediate pressure value range is [Pmin, Pmax].

[0016] As a further embodiment of the present invention, a control method for a heat pump intermediate heat exchanger makeup gas system includes the following steps:

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

[0018] Step 2: Based on Step 1, a preset intermediate pressure value is obtained. Based on the intermediate pressure value, the enthalpy function and energy function are called again to calculate the isentropic enthalpy value of the compressor during initial compression, the actual enthalpy value of the compressor during initial compression, the internal energy of the compressor during initial compression, the internal energy of the intermediate cavity after gas mixing, the enthalpy value of the intermediate cavity, the entropy value of the second-stage compressor, the theoretical enthalpy value at the end of compression, the actual enthalpy value at the end of compression, and the compressor exhaust temperature.

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

[0020] The theoretical gas replenishment ratio α is calculated using the formula: α = ρ1 / ρ3 - 1;

[0021] Step 4: Based on the preset intermediate pressure value, given the condensing pressure, pressure drop of the auxiliary gas supply line, superheat of the auxiliary gas supply line, and subcooling of the main circulation loop, obtain the pressure and temperature before and after the EVI electronic expansion valve of the auxiliary gas supply line of the intermediate heat exchanger, the outlet temperature and pressure of the auxiliary gas supply line, and the outlet pressure and temperature of the main circulation loop. Then, call the enthalpy function to obtain the enthalpy h5 at the inlet of the main gas supply line of the intermediate heat exchanger, the enthalpy h6 at the outlet of the main gas supply line of the intermediate heat exchanger, and the enthalpy h8 at the outlet of the auxiliary gas supply line of the intermediate heat exchanger. Calculate the ratio of the refrigerant flow rate of the auxiliary gas supply line to the refrigerant flow rate of the main circulation loop, i.e., the system gas supply ratio a'.

[0022] According to the law of conservation of energy, the formula for calculating the system's gas replenishment 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. Use the intermediate pressure 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, when the actual gas supply pressure is greater than Pmax or when the actual gas supply pressure is less than Pmin;

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

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

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

[0029]

[0030]

[0031] Wherein, δ1 and δ2 both represent the opening control quantity of the EVI electronic expansion valve in the supplementary air path;

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

[0033] θ2 represents the difference between the actual pressure of the supplementary air path 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 auxiliary gas supply pressure is in the optimal intermediate pressure range [Pmin,Pmax]. The high-pressure sensor at the compressor exhaust port detects the system's exhaust pressure value in real time, and the exhaust pressure value is converted into a high-pressure saturation temperature value. The exhaust temperature sensor at the compressor exhaust port detects the system's exhaust temperature value in real time. Based on 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 provides a preset value for the target exhaust superheat. The difference between the actual exhaust superheat and the target exhaust superheat is calculated. The opening control amount of the auxiliary electronic expansion valve is then calculated according to the formula to ensure that the actual exhaust superheat reaches the target exhaust superheat. The formula for calculating the opening of the auxiliary electronic expansion valve is as follows:

[0037]

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

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows: This system calculates the various state parameters of the entire two-stage compression process of the unit compressor based on parameters such as the evaporation pressure, condensation pressure, compressor frequency, and cooling capacity of the heat pump unit, using the REFPROP function. These parameters include the primary compression final pressure, enthalpy, density, intermediate cavity enthalpy, and mixed density. The amount of gas supplied to the main circulation of the heat pump unit is determined based on the deviation range between the optimal intermediate pressure ratio of the compressor and the main circulation gas supply ratio.

[0040] By adjusting the opening of the auxiliary circuit electronic expansion valve, the auxiliary circuit outlet pressure (i.e., the make-up gas pressure) of the unit is brought close to the compressor's optimal intermediate pressure. When the make-up gas volume reaches the optimal intermediate pressure, the heat pump unit's heating capacity and coefficient of performance are greatly improved. Through the make-up gas control method, the opening of the auxiliary circuit electronic expansion valve is controlled by calculating the deviation between the heat pump system's make-up gas ratio and the compressor's intermediate pressure during unit operation, ensuring that the unit's make-up gas pressure is at the optimal intermediate pressure, thereby achieving the unit's optimal heating performance. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the gas supply system for the intermediate heat exchanger of the heat pump according to the present invention.

[0042] Figure 2 This is the pressure-enthalpy diagram of the gas supply system for the intermediate heat exchanger of the heat pump in this invention;

[0043] Figure 3 This is a flowchart of the control logic for the gas supply system of the intermediate heat exchanger of the heat pump in this invention.

[0044] In the diagram: 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-Maintenance air auxiliary circuit, 501-Maintenance air 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-Inlet water temperature sensor, 602-Outlet water temperature sensor, 7-Compressor. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be 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 merely illustrative of the invention and are not intended to limit the invention.

[0046] The serial numbers assigned to components in this document, such as "first," "second," etc., are merely used to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages). In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0047] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature means that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "below" of the second feature means that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0048] Example 1

[0049] like Figure 1As shown, a heat pump intermediate heat exchanger gas supply system includes a main circulation loop 2 and a gas supply auxiliary loop 5. The main circulation loop is sequentially equipped 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. The water-side heat exchanger and the main loop inlet of the intermediate heat exchanger are connected. A main inlet temperature sensor 203 is installed at the main loop inlet of the intermediate heat exchanger to detect the main inlet temperature. A main outlet temperature sensor 204 is installed at the main loop outlet of the intermediate heat exchanger to detect the main outlet temperature. An auxiliary inlet temperature sensor 503 is installed at the inlet of the auxiliary loop of the intermediate heat exchanger to detect the auxiliary inlet temperature. An auxiliary outlet temperature sensor 502 is installed at the outlet of the auxiliary loop of the intermediate heat exchanger to detect the auxiliary outlet temperature. A gas supply pressure sensor 501 is also installed on the liquid outlet pipe of the auxiliary loop. Each temperature sensor can monitor the temperature changes of each fluid channel in real time, providing important data support for the system's operating status and enabling precise temperature control. By monitoring the temperature of the main and auxiliary channels, the operating parameters of the heat exchanger can be adjusted in a timely manner.

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

[0051] The auxiliary gas 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 filter 505 and an auxiliary expansion valve 504 are installed on the auxiliary liquid inlet pipe. The auxiliary outlet of the intermediate heat exchanger and the compressor gas supply port are connected through the auxiliary liquid outlet pipe.

[0052] A low-pressure sensor 210 and a low-pressure switch 209 are installed on the main circulation loop between the gas-liquid separator 1 and the compressor 7. These are used to detect the low-pressure side pressure value and to set up low-pressure protection to prevent the system from operating at excessively low pressure.

[0053] The compressor suction port is equipped with a suction temperature sensor 208, and the compressor discharge port is equipped with a discharge temperature sensor 207. The water-side heat exchanger has an inlet water temperature sensor 601 at its heat exchange inlet and an outlet water temperature sensor 602 at its heat exchange outlet. The heat pump intermediate heat exchanger makeup system is also equipped with an ambient temperature sensor to detect 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 loop and the auxiliary air supply loop are equipped with circulating refrigerant.

[0055] After being compressed by the compressor, the refrigerant forms a high-temperature, high-pressure gaseous refrigerant. This gaseous refrigerant enters the water-side heat exchanger 6 through the compressor's exhaust port. After exchanging heat with water in the water-side heat exchanger, the gaseous refrigerant condenses into a high-pressure liquid refrigerant. A high-pressure sensor 206 and a high-pressure switch 205 are sequentially installed along the exhaust direction in the main circulation loop between the compressor's exhaust port and the water-side heat exchanger inlet. The high-pressure side pressure is measured in real time. The high-pressure liquid refrigerant from the water-side heat exchanger outlet enters both the main circulation loop and the auxiliary gas supply loop.

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

[0057] At the same time, the refrigerant in the auxiliary gas supply circuit absorbs the heat of the refrigerant in the main circulation circuit and becomes superheated vapor refrigerant. The superheated vapor refrigerant enters the compressor 7 from the compressor gas supply port.

[0058] Example 2

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

[0060] The control method for the gas supply system of the intermediate heat exchanger of the heat pump includes the following steps:

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

[0062] Step 2: Based on Step 1, a preset intermediate pressure value is obtained. Based on the intermediate pressure value, the enthalpy function and energy function are called again to calculate the isentropic enthalpy value of the compressor during initial compression, the actual enthalpy value of the compressor during initial compression, the internal energy of the compressor during initial compression, the internal energy of the intermediate cavity after gas mixing, the enthalpy value of the intermediate cavity, the entropy value of the second-stage compressor, the theoretical enthalpy value at the end of compression, the actual enthalpy value at the end of compression, and the compressor exhaust temperature.

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

[0064] The theoretical gas replenishment ratio α is calculated using the formula: α = ρ1 / ρ3 - 1;

[0065] Step 4: Based on the preset intermediate pressure value, given the condensing pressure, pressure drop of the auxiliary gas supply line, superheat of the auxiliary gas supply line, and subcooling of the main circulation loop, obtain the pressure and temperature before and after the EVI electronic expansion valve of the auxiliary gas supply line of the intermediate heat exchanger, the outlet temperature and pressure of the auxiliary gas supply line, and the outlet pressure and temperature of the main circulation loop. Then, call the enthalpy function to obtain the enthalpy h5 at the inlet of the main gas supply line of the intermediate heat exchanger, the enthalpy h6 at the outlet of the main gas supply line of the intermediate heat exchanger, and the enthalpy h8 at the outlet of the auxiliary gas supply line of the intermediate heat exchanger. Calculate the ratio of the refrigerant flow rate of the auxiliary gas supply line to the refrigerant flow rate of the main circulation loop, i.e., the system gas supply ratio a'.

[0066] According to the law of conservation of energy, the formula for calculating the system's gas replenishment 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. Use the intermediate pressure 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, when the actual gas supply pressure is greater than Pmax or when the actual gas supply pressure is less than Pmin;

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

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

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

[0073]

[0074]

[0075] Wherein, δ1 and δ2 both represent the opening control quantity of the EVI electronic expansion valve in the supplementary air path;

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

[0077] θ2 represents the difference between the actual pressure of the supplementary air path 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 auxiliary gas supply pressure is in the optimal intermediate pressure range [Pmin,Pmax]. The high-pressure sensor at the compressor exhaust port detects the system's exhaust pressure value in real time, and the exhaust pressure value is converted into the high-pressure saturation temperature value. The exhaust temperature sensor at the compressor exhaust port detects the system's exhaust temperature value in real time. Based on 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 provides a preset value for the target exhaust superheat. The difference between the actual exhaust superheat and the target exhaust superheat is calculated. The opening control amount of the auxiliary electronic expansion valve is then calculated according to the formula to ensure that the actual exhaust superheat reaches the target exhaust superheat. The formula for calculating the opening of the auxiliary electronic expansion valve is as follows:

[0081]

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

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

[0084] In the description of this specification, the terms "connection", "installation", "fixing", "setting", etc. are interpreted broadly. For example, "connection" means a fixed connection or an indirect connection through an intermediate component without affecting the relationship between components and the technical effect. It can also mean an integral connection or a partial connection. For those skilled in the art, the specific meaning of the above terms in this invention or invention can be understood according to the specific circumstances.

[0085] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A control method of a heat pump intermediate heat exchanger air supplement system, the heat pump intermediate heat exchanger air supplement system comprising a main circulation loop (2) and an air supplement auxiliary loop (5), the main circulation loop being sequentially 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), the water side heat exchanger and the intermediate heat exchanger being connected, the intermediate heat exchanger being connected with a distribution head of the air side heat exchanger, and a main loop filter (202) and a main loop expansion valve (201) being arranged on the main circulation loop between the intermediate heat exchanger and the distribution head; the air supplement auxiliary loop (5) comprising an auxiliary loop liquid inlet pipe and an auxiliary loop liquid outlet pipe, the auxiliary loop liquid inlet pipe being connected with the main circulation loop between the water side heat exchanger and the intermediate heat exchanger, the other end of the auxiliary loop liquid inlet pipe being connected with an auxiliary loop inlet of the intermediate heat exchanger, and an auxiliary loop filter (505) and an auxiliary loop expansion valve (504) being arranged on the auxiliary loop liquid inlet pipe, the auxiliary loop outlet of the intermediate heat exchanger being connected with a compressor air supplement port through the auxiliary loop liquid outlet pipe; the control method comprising a control module, the control module comprising a preset control program, the control program being encoded with a temperature function, a density function, an enthalpy function and an entropy function, the control module capturing initial information parameters, obtaining a theoretical air supplement ratio a and a system air supplement ratio a' by calling the temperature function, the density function, the enthalpy function and the entropy function in the REFPROP function, and presetting an optimal intermediate pressure value of an evaporation pressure of the intermediate heat exchanger air supplement auxiliary loop, the intermediate pressure value being in a range [Pmin, Pmax]; and the control method comprising the following steps: Step 1: given a compressor isentropic efficiency, compressor suction pipe temperature drop and pressure drop and exhaust pipe temperature drop and pressure drop, water side heat exchanger side subcooling degree value, air side heat exchanger side superheating degree value, real-time acquisition of compressor operating frequency, evaporation pressure, condensation pressure, calling of the temperature function, the enthalpy function and the entropy function, and calculation of evaporation temperature, condensation temperature, compressor suction enthalpy value and primary compression isentropic value of system operation; Step 2: on the basis of Step 1, presetting an intermediate pressure value and calling the enthalpy function and the energy function again according to the intermediate pressure value, and calculating compressor primary compression isentropic enthalpy value, primary compression actual enthalpy value, primary compression internal energy, internal energy of the intermediate cavity after air supplement mixing, intermediate cavity enthalpy value, secondary compressor entropy value, theoretical enthalpy value of the compression end, actual enthalpy value of the compression end and compressor exhaust temperature; and Step 3: calling the density function by using data obtained in Step 1 and Step 2, obtaining compressor primary compression working medium density p1 and working medium density p3 after air supplement, and calculating a theoretical air supplement ratio a, a' = (p3-p1) / p1. ​ characterized in that ​ ​ ​ ​ ​ The theoretical air supplement ratio a calculation formula is: ; Step 4: According to the preset intermediate pressure value, the given condensing pressure, the pressure drop of the supplementary gas auxiliary path, the superheat of the supplementary gas auxiliary path and the subcooling of the main circulating loop, the front and rear pressures and temperatures of the EVI electronic expansion valve of the intermediate heat exchanger supplementary gas auxiliary path, the outlet temperature and pressure of the supplementary gas auxiliary path, the outlet pressure of the main circulating loop and the outlet temperature of the main circulating loop are obtained, and the enthalpy function is called to obtain the inlet enthalpy value h5 of the main path of the intermediate heat exchanger, the outlet enthalpy value h6 of the main path of the intermediate heat exchanger and the outlet enthalpy value h8 of the auxiliary path of the intermediate heat exchanger, and the ratio of the refrigerant flow rate of the supplementary gas auxiliary path to the refrigerant flow rate of the main circulating loop, i.e. the system supplementary gas ratio a', is calculated, According to the law of conservation of energy, the system gas supplement ratio a' calculation formula is: ; Step 5: The theoretical supplementary gas ratio a obtained in step 3 and the system supplementary gas ratio a' obtained in step 4 are compared, and the intermediate pressure value range [Pmin, Pmax] when a / a'≤±1% is taken as the target parameter to control the opening of the auxiliary path EVI electronic expansion valve, so that the auxiliary path supplementary gas pressure reaches the optimal intermediate pressure range; Step 6: When a / a' > 1%, i.e. when the actual supplementary gas pressure is greater than Pmax or the actual supplementary gas pressure is less than Pmin; When the actual supplementary gas pressure is greater than Pmax, the difference between Pmax and the actual supplementary gas pressure is taken, and the opening control amount of the EVI electronic expansion valve of the supplementary gas auxiliary path is calculated according to the calculation formula, and the auxiliary path electronic expansion valve is controlled to the valve opening control amount calculated by the calculation formula, so that the auxiliary path supplementary gas pressure reaches the intermediate pressure value range [Pmin, Pmax]; When the actual supplementary gas pressure is less than Pmin, the difference between the actual supplementary gas pressure and Pmin is taken, and the opening control amount of the EVI electronic expansion valve of the supplementary gas auxiliary path is calculated according to the calculation formula, and the auxiliary path electronic expansion valve is controlled to the valve opening control amount calculated by the calculation formula, so that the auxiliary path supplementary gas pressure reaches the intermediate pressure value range [Pmin, Pmax]; Step 7: In step 6, the auxiliary path electronic expansion valve is controlled to the valve opening control amount calculated by the calculation formula, and the calculation formula is as follows: ； Wherein, δ1 and δ2 both represent the opening control amount of the EVI electronic expansion valve of the supplementary gas auxiliary path; θ1 represents the difference between the actual pressure of the supplementary gas auxiliary path and the upper limit Pmax of the optimal intermediate pressure value; θ2 represents the difference between the actual pressure of the supplementary gas auxiliary path and the lower limit Pmin of the optimal intermediate pressure value; Kp represents the proportional coefficient; Ki represents the integral coefficient; Kd represents the differential coefficient; Step 8: When a / a'≤±1%, the supplementary gas auxiliary path pressure is in the optimal intermediate pressure value 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, and the actual exhaust superheat of the heat pump system is calculated according to the exhaust temperature value and the high-pressure saturation temperature value; Step 9: On the basis of step 8, the system is given a preset value of a target exhaust gas superheat, the actual exhaust gas superheat is subtracted from the target exhaust gas superheat, and the opening control amount of the auxiliary path electronic expansion valve is calculated according to the calculation formula, so that the actual exhaust gas superheat reaches the target exhaust gas superheat. The calculation formula of the opening of the auxiliary path electronic expansion valve is as follows: ; δ3 represents the opening control amount of the EVI electronic expansion valve of the supplementary gas auxiliary path; θ3 represents the difference between the actual exhaust superheat of the supplementary gas auxiliary path and the target exhaust superheat; Kp is the proportional coefficient; Ki is the integral coefficient; Kd is the differential coefficient.

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

3. The control method of the heat pump intermediate heat exchanger air supplement system according to claim 2, characterized in that: The intermediate heat exchanger main path inlet is provided with a main inlet temperature sensor (203) for detecting the main inlet temperature, the intermediate heat exchanger main path outlet is provided with a main outlet temperature sensor (204) for detecting the main outlet temperature, the intermediate heat exchanger auxiliary path inlet is provided with an auxiliary inlet temperature sensor (503) for detecting the auxiliary inlet temperature, the intermediate heat exchanger auxiliary path outlet is provided with an auxiliary outlet temperature sensor (502) for detecting the auxiliary outlet temperature, and the auxiliary path outlet liquid pipe is further provided with a gas supplement pressure sensor (501).

4. The control method of the heat pump intermediate heat exchanger air injection system according to claim 3, characterized in that: The main circulation loop between the gas-liquid separator and the compressor is provided with a low pressure sensor (210) and a low pressure switch (209).

5. The control method of the heat pump intermediate heat exchanger air supplement system according to claim 4, characterized in that: The compressor suction port is provided with a suction temperature sensor (208), and the compressor exhaust port is provided with an exhaust temperature sensor (207).

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

7. The control method of the heat pump intermediate heat exchanger air supplement system according to claim 6, characterized in that: The heat pump intermediate heat exchanger gas supplement system is further provided with an environment temperature sensor for detecting the environment temperature, the main path expansion valve (201) is an EEV electronic expansion valve, and the auxiliary path expansion valve (504) is an EVI electronic expansion valve.

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