A control method for exhaust temperature of a low-temperature heat pump system

Abstract

The application provides a control method suitable for exhaust temperature of a low-temperature heat pump system, relates to the technical field of heat pump unit control, and aims to improve the heating efficiency of the heat pump under low ambient temperature and prevent the exhaust temperature from being too high when a large pressure ratio is operated, so as to ensure the reliability of the system. The method is divided into three exhaust temperature control stages: low, medium and high exhaust temperature stages. In the low-temperature stage, the exhaust temperature is controlled by fixing the opening degree of the air supplementing expansion valve. In the medium-temperature stage, a plurality of control intervals are divided according to the evaporation temperature, the target exhaust superheat degree of each interval is calculated, and the opening degree of the air supplementing expansion valve is adjusted accordingly. In the high-temperature stage, the air supplementing expansion valve is fully opened, and the direction and opening degree of the liquid injection electric regulating valve are adjusted according to the exhaust temperature variation trend. By collecting the outlet water temperature of the shell-and-tube heat exchanger, the compressor exhaust temperature and the suction pressure, the system accurately adjusts the action of each control valve and improves the performance of the system under low temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat pump unit control, in particular to a control method for exhaust temperature of a low-temperature heat pump system. BACKGROUND

[0002] With the development of air source heat pump technology, further expanding the application range of air source heat pump, improving energy conversion efficiency is the trend and challenge of future development. In recent years, the use of air source heat pump gradually spreads to the cold northern region. In the area with low ambient temperature, the heat absorbed by the air source heat pump from the environment will decrease with the temperature, resulting in the decrease of evaporation temperature and pressure. In order to ensure the necessary outlet water temperature, the compressor needs to run at high compression ratio, which causes the problem of high exhaust temperature and low heating capacity.

[0003] To solve the above problems, the low-temperature air source heat pump generally adopts the air supplementing and enthalpy increasing system. The system effectively reduces the exhaust temperature, and improves the heating capacity and overall operating efficiency of the unit. The air supplementing and enthalpy increasing system includes air supplementing and enthalpy increasing compressor, air supplementing expansion valve and economizer, etc. The air supplementing amount of the system is realized by controlling the opening degree of the air supplementing expansion valve.

[0004] At present, the air supplementing expansion valve of most heat pump manufacturers mainly depends on the fixed superheat degree or exhaust temperature of the inlet and outlet of the economizer for control. This method limits the flexibility of the air supplementing control range, and it is difficult to ensure the rationality of the air supplementing amount, and thus the efficiency of the system in the whole operating range cannot be guaranteed.

[0005] In addition, the control method of the liquid injection valve is also mainly the simple on-off control, that is, the liquid injection is started when the exhaust temperature exceeds the set value, and stopped when the set value is lower. This control method easily causes the exhaust temperature to fluctuate sharply, which affects the stable operation of the system and reduces the energy efficiency. SUMMARY

[0006] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a control method for exhaust temperature of a low-temperature heat pump system, which improves the heating capacity of the air source heat pump unit under low ambient temperature operation.

[0007] To achieve the above purpose, the present application provides the following scheme:

[0008] A control method suitable for the exhaust temperature of a low-temperature heat pump system, the low-temperature heat pump system comprising: a supplementary gas enthalpy increasing compressor, an electronic expansion valve, a shell-and-tube heat exchanger, a fin heat exchanger, an economizer, a gas-liquid separator, a four-way valve, a supplementary gas expansion valve, and a liquid injection electric regulating valve, wherein one end of the supplementary gas enthalpy increasing compressor is connected with a port of one side of the four-way valve; three ports of the other side of the four-way valve are connected with one end of the shell-and-tube heat exchanger, one end of the fin heat exchanger, and one end of the gas-liquid separator, respectively; the other end of the fin heat exchanger is connected with one end of one side of the economizer, one end of the supplementary gas expansion valve, and one end of the liquid injection electric regulating valve through the electronic expansion valve, respectively; the other end of the shell-and-tube heat exchanger is connected with the other end of one side of the economizer; the other end of the supplementary gas enthalpy increasing compressor is connected with the other end of the gas-liquid separator; one end of the other side of the economizer is connected with the other end of the supplementary gas enthalpy increasing compressor and the other end of the liquid injection electric regulating valve, respectively; the other end of the other side of the economizer is connected with the other end of the supplementary gas expansion valve; and the control method comprises:

[0009] When the supplementary gas enthalpy increasing compressor is in a working state under a heating model, an exhaust temperature of an outlet of the supplementary gas enthalpy increasing compressor, an outlet water temperature of the shell-and-tube heat exchanger, and a suction pressure of an inlet of the supplementary gas enthalpy increasing compressor are acquired.

[0010] An actual exhaust superheat degree is determined according to the outlet water temperature and the exhaust temperature, and an evaporation temperature is determined according to the suction pressure.

[0011] A plurality of temperature control stages are determined according to the exhaust temperature; the temperature control stages comprise a low exhaust temperature control stage, a medium exhaust temperature control stage, and a high exhaust temperature control stage.

[0012] In the low exhaust temperature control stage, the opening degrees of the liquid injection electric regulating valve and the supplementary gas expansion valve are controlled according to the exhaust temperature.

[0013] In the medium exhaust temperature control stage, a plurality of control intervals are determined according to the evaporation temperature, and a target exhaust superheat degree in each control interval is calculated, so as to control the opening degree of the supplementary gas expansion valve according to the target exhaust superheat degree and the actual exhaust superheat degree.

[0014] In the high exhaust temperature control stage, the opening degree of the liquid injection electric regulating valve is controlled according to the variation trend of the exhaust temperature.

[0015] Preferably, determining the actual exhaust superheat degree according to the outlet water temperature and the exhaust temperature comprises:

[0016] The outlet water temperature is added with a preset temperature to calculate a condensation temperature.

[0017] The actual exhaust gas superheat degree is obtained by subtracting the calculated condensing temperature from the exhaust gas temperature.

[0018] Preferably, determining the evaporation temperature according to the suction gas pressure comprises:

[0019] Determining the saturation temperature corresponding to the suction gas pressure as the evaporation temperature.

[0020] Preferably, determining a plurality of temperature control stages according to the exhaust gas temperature comprises:

[0021] When the exhaust gas temperature meets the condition of T 排气 <T1, the current temperature control stage is determined as the low exhaust gas temperature control stage;

[0022] When the exhaust gas temperature meets the condition of T1≤T 排气 <T2, the current temperature control stage is determined as the medium exhaust gas temperature control stage;

[0023] When the exhaust gas temperature meets the condition of T 排气 ≥T2, the current temperature control stage is determined as the high exhaust gas temperature control stage; wherein, T 排气 is the exhaust gas temperature; T1 is a first temperature control stage threshold temperature, and T2 is a second temperature control stage threshold temperature.

[0024] Preferably, in the low exhaust gas temperature control stage, the opening degrees of the liquid injection electric regulating valve and the air supplement expansion valve are controlled according to the exhaust gas temperature, comprising:

[0025] Adjusting the working state of the liquid injection electric regulating valve to a closed state, and at the same time setting an initial opening degree for the air supplement expansion valve, and setting the initial opening degree as a fixed opening degree.

[0026] Preferably, the calculation process of the target exhaust gas superheat degree comprises:

[0027] Through pre-set experiments, the value of the exhaust gas superheat degree corresponding to the optimal refrigeration coefficient at different condensing temperatures in each control interval is measured;

[0028] Fitting the relationship between the exhaust gas superheat degree and the condensing temperature according to the value of the exhaust gas superheat degree;

[0029] Determining each target exhaust gas superheat degree according to the relationship between the exhaust gas superheat degree and the condensing temperature.

[0030] Preferably, controlling the opening degree of the air supplement expansion valve according to the target exhaust gas superheat degree and the actual exhaust gas superheat degree comprises:

[0031] When the actual exhaust gas superheat is greater than the target exhaust gas superheat, the opening of the air supplement expansion valve is controlled to increase by a PID control mode;

[0032] When the actual exhaust gas superheat is less than the target exhaust gas superheat, the opening of the air supplement expansion valve is controlled to decrease by a PID control mode.

[0033] Preferably, in the high exhaust gas temperature control stage, the opening of the liquid injection electric regulating valve is controlled according to the change trend of the exhaust gas temperature, comprising:

[0034] When the temperature difference of the exhaust gas temperature read in two adjacent detection periods is greater than a preset first temperature difference trend threshold, it is determined that the liquid injection electric regulating valve enters a fast regulating stage, and the regulating amplitude of each regulating period is A%;

[0035] When the temperature difference of the exhaust gas temperature read in two adjacent detection periods is less than a preset second temperature difference trend threshold, it is determined that the liquid injection electric regulating valve enters a slow regulating stage, and the regulating amplitude of each regulating period is B%; wherein A is a first preset regulating amplitude, B is a second preset regulating amplitude, and A>B.

[0036] According to the specific embodiments of the present application, the following technical effects are provided:

[0037] The application provides a control method suitable for exhaust temperature of a low-temperature heat pump system, and the low-temperature heat pump system comprises a supplementary air enthalpy compressor, an electronic expansion valve, a shell-and-tube heat exchanger, a fin heat exchanger, an economizer, a gas-liquid separator, a four-way valve, a supplementary air expansion valve and a liquid injection electric regulating valve, wherein one end of the supplementary air enthalpy compressor is connected with a port of one side of the four-way valve; three ports of the other side of the four-way valve are connected with one end of the shell-and-tube heat exchanger, one end of the fin heat exchanger and one end of the gas-liquid separator respectively; the other end of the fin heat exchanger is connected with one end of one side of the economizer, one end of the supplementary air expansion valve and one end of the liquid injection electric regulating valve through the electronic expansion valve respectively; the other end of the shell-and-tube heat exchanger is connected with the other end of one side of the economizer; the other end of the supplementary air enthalpy compressor is connected with the other end of the gas-liquid separator; one end of the other side of the economizer is connected with the other end of the supplementary air enthalpy compressor and the other end of the liquid injection electric regulating valve respectively; the other end of the other side of the economizer is connected with the other end of the supplementary air expansion valve; the control method comprises the following steps: when the supplementary air enthalpy compressor is in a working state in a heating model, the exhaust temperature of one end of the supplementary air enthalpy compressor, the water outlet temperature of the shell-and-tube heat exchanger and the suction pressure of the other end of the supplementary air enthalpy compressor are obtained; the actual exhaust superheat degree is determined according to the water outlet temperature and the exhaust temperature, and the evaporation temperature is determined according to the suction pressure; a plurality of temperature control stages are determined according to the exhaust temperature; the temperature control stages comprise a low exhaust temperature control stage, a medium exhaust temperature control stage and a high exhaust temperature control stage; in the low exhaust temperature control stage, the opening degrees of the liquid injection electric regulating valve and the supplementary air expansion valve are controlled according to the exhaust temperature; in the medium exhaust temperature control stage, a plurality of control intervals are determined according to the evaporation temperature, the target exhaust superheat degrees in the control intervals are calculated, and the opening degree of the supplementary air expansion valve is controlled according to the target exhaust superheat degrees and the actual exhaust superheat degree; in the high exhaust temperature control stage, the opening degree of the liquid injection electric regulating valve is controlled according to the change trend of the exhaust temperature. The application improves the heating capacity of an air source heat pump unit under low ambient temperature operation, effectively controls the problem of excessively high exhaust temperature when the unit operates under large pressure ratio, and ensures reliable operation of the unit. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0039] Figure 1A low-temperature heat pump system structure schematic diagram provided by the embodiment of the present application is shown in the figure.

[0040] Figure 2 A method flow chart provided by the embodiment of the present application is shown in the figure.

[0041] Reference numerals are explained as follows:

[0042] 1 - outlet water temperature; 2 - exhaust temperature; 3 - suction pressure; 4 - air supplement expansion valve; 5 - liquid injection electric regulating valve. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0044] The purpose of the present application is to provide a control method suitable for the exhaust temperature of a low-temperature heat pump system, to control the opening of an air supplement electronic expansion valve according to the exhaust superheat, to ensure the reasonable liquid supply requirement on the air supplement side, and to ensure the refrigerant at the outlet of the economizer on the air supplement side to be saturated vapor in the ideal state; and to adjust a liquid injection electric regulating valve according to the exhaust temperature, to ensure the exhaust temperature of the system to be within a reasonable range.

[0045] In order to make the above-mentioned purpose, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0046] Figure 1 A low-temperature heat pump system structure schematic diagram provided by the embodiment of the present application is shown in the figure. Figure 1As shown, the low-temperature heat pump system of this embodiment includes: a gas-injecting enthalpy-increasing compressor, an electronic expansion valve, a shell-and-tube heat exchanger, a finned heat exchanger, an economizer, a gas-liquid separator, a four-way valve, a gas-injecting expansion valve 4, and a liquid-injecting electric regulating valve 5. One end of the gas-injecting enthalpy-increasing compressor is connected to one port of the four-way valve; the other three ports of the four-way valve are respectively connected to one end of the shell-and-tube heat exchanger, one end of the finned heat exchanger, and one end of the gas-liquid separator; the other end of the finned heat exchanger is connected to the electronic expansion valve 5. The expansion valve is connected to one end of one side of the economizer, one end of the gas-injection expansion valve 4, and one end of the liquid-injection electric regulating valve 5, respectively; the other end of the shell-and-tube heat exchanger is connected to the other end of one side of the economizer; the other end of the gas-injection enthalpy-increasing compressor is connected to the other end of the gas-liquid separator; one end of the other side of the economizer is connected to another end of the gas-injection enthalpy-increasing compressor and the other end of the liquid-injection electric regulating valve 5, respectively; the other end of the other side of the economizer is connected to the other end of the gas-injection expansion valve 4. The shell-and-tube heat exchanger also has one end for water outlet, and in this embodiment, its outlet water temperature 1 is obtained through this end. In this embodiment, the suction pressure 3 is also collected at the inlet of the gas-injection enthalpy-increasing compressor.

[0047] As an example, the electric regulating valve 5 of this embodiment is electrically regulated, and the valve opening and closing size and direction are controlled according to the trend and magnitude of the change in exhaust temperature 2.

[0048] Specifically, this embodiment also includes a gas replenishment and liquid injection control system, which includes: a heating condenser outlet water temperature sensor, a suction pressure sensor, an exhaust temperature sensor, and a unit controller that outputs two 0-10V analog signals to control the opening of the gas replenishment expansion valve and the liquid injection electric regulating valve, respectively.

[0049] like Figure 2 As shown, the control method in this embodiment includes:

[0050] Step 100: When the gas-injection enthalpy-increasing compressor is in the working state under the heating model, obtain the discharge temperature at the outlet of the gas-injection enthalpy-increasing compressor, the water outlet temperature of the shell and tube heat exchanger, and the suction pressure at the inlet of the gas-injection enthalpy-increasing compressor.

[0051] Step 200: Determine the actual exhaust superheat based on the outlet water temperature and exhaust temperature, and determine the evaporation temperature based on the suction pressure;

[0052] Step 300: Determine multiple temperature control stages based on exhaust temperature; the temperature control stages include low exhaust temperature control stage, medium exhaust temperature control stage, and high exhaust temperature control stage;

[0053] Step 400: During the low exhaust temperature control stage, control the opening degree of the liquid injection electric regulating valve and the gas replenishment expansion valve according to the exhaust temperature.

[0054] Step 500: In the medium exhaust temperature control stage, a plurality of control intervals are determined according to the evaporation temperature, and a target exhaust gas superheat degree in each control interval is calculated to control the opening degree of the supplementary gas expansion valve according to the target exhaust gas superheat degree and the actual exhaust gas superheat degree;

[0055] Step 600: In the high exhaust temperature control stage, the opening degree of the liquid injection electric regulating valve is controlled according to the change trend of the exhaust temperature.

[0056] Optionally, the algorithm of the exhaust gas superheat degree is that the condensation temperature is calculated by the condenser outlet water temperature plus ΔT, and the exhaust gas superheat degree is obtained by subtracting the calculated condensation temperature from the exhaust temperature. Demonstratively, ΔT is the heat exchange end difference, which is fixed at 5 degrees, and can be adjusted according to the actual heat exchanger heat exchange condition.

[0057] Specifically, the evaporation temperature algorithm is the saturation temperature corresponding to the suction pressure; the suction pressure of the embodiment is a measured value, that is, the suction pressure is obtained by measurement.

[0058] Further, the system of the embodiment adds the control of the supplementary gas expansion valve and the liquid injection electric regulating valve when the compressor is in the working state.

[0059] Further, the specific control idea of the embodiment is as follows:

[0060] Firstly, the temperature control system is divided into three control stages according to the exhaust temperature, i.e. the low exhaust temperature control stage T 排气 <T1; the medium exhaust temperature control stage T 排气 <T2; and the high exhaust temperature control stage T 排气 ≥T2. Demonstratively, T1 and T2 are obtained by experiment, and in the embodiment, they can be taken as fixed values, i.e. T1=90℃; T2=105℃ can be adjusted according to the actual operation condition.

[0061] (1) Low exhaust temperature control stage:

[0062] When the system is started, the system is in the low exhaust temperature control range T 排气 <T1, the liquid injection electric regulating valve is in the closed state, at this time an initial opening degree is given to the supplementary gas expansion valve, and the opening degree is a fixed opening degree.

[0063] (2) Medium exhaust temperature control stage:

[0064] When the system is in the medium exhaust temperature control stage T 排气 <T2, the system enters the supplementary gas expansion valve regulating control stage, in which the system can correspond to different target exhaust gas superheat degrees according to different evaporation temperature intervals, and the interval division is as follows

[0065] Evaporation temperature control interval 1: T蒸发 <T setp01 Target exhaust gas superheat 1;

[0066] Evaporation temperature control interval 2: T setp01 ≤T 蒸发 <T setp02 Target exhaust gas superheat 2;

[0067] Evaporation temperature control interval 3: T setp02 ≤T 蒸发 <T setp03 Target exhaust gas superheat 3;

[0068] Evaporation temperature control interval 4: T 蒸发 >T setp03 Target exhaust gas superheat 4;

[0069] Specifically, the present embodiment is according to the experimentally measured value of the exhaust gas superheat corresponding to the evaporation temperature under the optimal COP, and the corresponding curve and polynomial are fitted according to the test data, and the inflection point of the curve is the basis for segmentation. In the present embodiment, it can be set to a fixed value, i.e. T setp01 =-17.5℃; T setp02 =-12.5℃; T setp03 =-2.5℃.

[0070] According to different evaporation temperatures, the exhaust gas superheat is divided into different control intervals, each control interval corresponds to different target superheat setting values, the actual exhaust gas superheat of each section is taken as a control variable, and the opening degree of the air supplementing expansion valve is adjusted through the PID control mode, and the control signal is a voltage signal of 0-10V.

[0071] The algorithm of the target superheat: through experiments, the value of the exhaust gas superheat corresponding to the optimal COP under different condensing temperatures in each evaporation temperature interval is measured, and thus the relationship between the exhaust gas superheat and the condensing temperature is fitted.

[0072] The actual control value of the exhaust gas superheat in each evaporation temperature control interval, i.e. the target exhaust gas superheat, can be calculated through the relationship. When the actual exhaust gas superheat > target exhaust gas superheat, the air supplementing expansion valve is opened, and when the actual exhaust gas superheat < target exhaust gas superheat, the air supplementing expansion valve is closed.

[0073] The following describes the algorithm of the target exhaust gas superheat in the exhaust gas temperature control stage through an example.

[0074] Through experiments, it is found that:

[0075] Evaporation temperature control interval 1: T 蒸发 <-17.5, 30℃≤T 冷凝The value of the exhaust gas superheat degree corresponding to different condensing temperatures under the optimal COP measured in the interval of ≤50.0℃ is fitted to obtain a calculation formula of the optimal superheat degree corresponding to the evaporation temperature: y=0.008x 2 +0.08x+36.9.

[0076] Evaporation temperature control interval 2: -17.5℃≤T 蒸发 <-12.5℃, at 30℃≤T 冷凝 The value of the exhaust gas superheat degree corresponding to different condensing temperatures under the optimal COP measured in the interval of ≤50.0℃ is fitted to obtain a calculation formula of the optimal superheat degree corresponding to the evaporation temperature: y=0.008x 2 +0.198x+29.57.

[0077] Evaporation temperature control interval 3: -7.5℃≤T 蒸发 <-2.5℃, at 30℃≤T 冷凝 The value of the exhaust gas superheat degree corresponding to different condensing temperatures under the optimal COP measured in the interval of ≤50.0℃ is fitted to obtain a calculation formula of the optimal superheat degree corresponding to the evaporation temperature: y=0.008x 2 +0.43x+19.

[0078] Evaporation temperature control interval 4: T 蒸发 ≥-2.5℃, at 30℃≤T 冷凝 The value of the exhaust gas superheat degree corresponding to different condensing temperatures under the optimal COP measured in the interval of ≤50.0℃ is fitted to obtain a calculation formula of the optimal superheat degree corresponding to the evaporation temperature: y=0.008x

[0079] In the above formula, x is the evaporation temperature, and y is the exhaust gas superheat degree.

[0080] (3) High exhaust temperature control stage

[0081] When the system is in the high exhaust temperature control stage T 排气 >T2, the system enters the control stage of the liquid injection electric regulating valve.

[0082] T 排气 =T2, the air injection expansion valve is in a fully open state, and the liquid injection electric regulating valve is in a fully closed state. To avoid the jump of the exhaust temperature, which leads to unstable system operation, the liquid injection electric valve adopts proportional regulation, that is, when T 排气 >T2, the system judges the change of the exhaust temperature once in each detection cycle (which can be set), and controls the direction of the opening and closing of the liquid injection electric regulating valve according to the temperature change trend; at the same time, the size of the opening and closing of the liquid injection electric regulating valve is adjusted according to the amplitude of the exhaust temperature change.

[0083] The specific operation method is as follows: when the temperature difference of the exhaust gas temperature read in two adjacent detection periods is greater than T Dset , it is determined that the liquid injection electric regulating valve needs to enter the fast regulating stage, and the regulating range of each regulating period is A%; when the temperature difference of the exhaust gas temperature read in two adjacent detection periods is less than T Dset -T Diff , it is determined that the liquid injection electric regulating valve needs to enter the slow regulating stage, and the regulating range of each regulating period is B%. Exemplarily, T Dset is a fixed value obtained through tests, which can be adjusted according to actual operation, and in this embodiment, T Dset = 5℃; the values of A and B are obtained through tests, and in order to prevent the exhaust gas temperature from continuously rising after the liquid injection regulating valve participates in the regulation, the values of A and B can be adjusted according to actual operation, and in this embodiment, A = 8% and B = 3%; T Diff is adjusted according to actual operation, in order to prevent the control value from jumping at a fixed temperature, and in this embodiment, T Diff is a fixed value, T Diff = 3℃.

[0084] Specifically, the entire control system of this embodiment is divided into three control stages according to the exhaust gas temperature, different system devices are regulated, the purpose of air supplementing and enthalpy increasing is achieved, and the exhaust gas temperature of the system is controlled in a safe range; the control stage of air supplementing and enthalpy increasing increases the algorithm of the exhaust gas superheat degree corresponding to the optimal COP, and is a multi-stage control; and in the high exhaust gas temperature control stage, the liquid injection valve adopts an electric regulating valve, and a proportional regulating mode is adopted. In addition, the system divides the control of the liquid injection electric regulating valve into fast and slow regulating modes by judging the range of the change of the exhaust gas temperature, effectively avoids the exhaust gas temperature jump caused by the traditional on-off control, and causes the system to run unstably.

[0085] The beneficial effects of the present application are as follows:

[0086] (1) The present application improves the heating capacity of the air source heat pump unit under low ambient temperature operation;

[0087] (2) When the unit operates under high pressure ratio, the present application can effectively control the problem of excessively high exhaust gas temperature, and ensure the reliable operation of the unit.

[0088] In the specification, each embodiment is described in a progressive manner, and each embodiment focuses on the difference from other embodiments, and the same or similar parts of each embodiment can be referred to each other.

[0089] The principles and implementation manners of the present application are described by using specific examples in the present application, and the above examples are only used to help understand the method of the present application and its core idea; meanwhile, for the general technical personnel in the art, the specific implementation manners and application ranges will be changed according to the idea of the present application. In conclusion, the content of the present specification should not be understood as the limitation of the present application.

Claims

1. A method for controlling the discharge temperature of a low temperature heat pump system, characterized by, The low-temperature heat pump system includes: a gas-injecting enthalpy-increasing compressor, an electronic expansion valve, a shell-and-tube heat exchanger, a finned heat exchanger, an economizer, a gas-liquid separator, a four-way valve, a gas-injecting expansion valve, and a liquid-injection electric regulating valve. One end of the gas-injecting enthalpy-increasing compressor is connected to one port of the four-way valve; the other three ports of the four-way valve are respectively connected to one end of the shell-and-tube heat exchanger, one end of the finned heat exchanger, and one end of the gas-liquid separator; the other end of the finned heat exchanger is connected via the electronic expansion valve to one end of the economizer, one end of the gas-injecting expansion valve, and one end of the liquid-injection electric regulating valve; the other end of the shell-and-tube heat exchanger is connected to the other end of one side of the economizer; the other end of the gas-injecting enthalpy-increasing compressor is connected to the other end of the gas-liquid separator; one end of the other side of the economizer is connected to the other end of the gas-injecting enthalpy-increasing compressor and the other end of the liquid-injection electric regulating valve; the other end of the other side of the economizer is connected to the other end of the gas-injecting expansion valve. The control method includes: When the gas-injecting enthalpy-increasing compressor is in the working state under the heating model, the exhaust temperature of the outlet of the gas-injecting enthalpy-increasing compressor, the water outlet temperature of the shell and tube heat exchanger, and the suction pressure of the inlet of the gas-injecting enthalpy-increasing compressor are obtained. The actual exhaust superheat is determined based on the outlet water temperature and the exhaust temperature, and the evaporation temperature is determined based on the intake pressure. Multiple temperature control stages are determined based on the exhaust temperature; the temperature control stages include a low exhaust temperature control stage, a medium exhaust temperature control stage, and a high exhaust temperature control stage; During the low exhaust temperature control phase, the opening degree of the liquid injection electric regulating valve and the gas replenishment expansion valve is controlled according to the exhaust temperature. During the exhaust temperature control stage, multiple control intervals are determined based on the evaporation temperature, and the target exhaust superheat in each control interval is calculated to control the opening of the gas replenishment expansion valve based on the target exhaust superheat and the actual exhaust superheat. During the high exhaust temperature control phase, the opening degree of the liquid injection electric regulating valve is controlled according to the changing trend of the exhaust temperature. Multiple temperature control stages are determined based on the exhaust temperature, including: When the exhaust temperature meets the condition T exhaust < T1, the current temperature control stage is determined as the low exhaust temperature control stage. When the exhaust temperature meets the condition T1≤T_exhaust<T2, the current temperature control stage is determined as the intermediate exhaust temperature control stage; When the exhaust temperature meets the condition T_exhaust ≥ T2, the current temperature control stage is determined as the high exhaust temperature control stage; where T_exhaust is the exhaust temperature; T1 is the threshold temperature of the first temperature control stage, and T2 is the threshold temperature of the second temperature control stage. During the high exhaust temperature control phase, controlling the opening degree of the liquid injection electric regulating valve according to the changing trend of the exhaust temperature includes: When the temperature difference of the exhaust temperature read in two adjacent detection periods is greater than a preset first temperature difference trend threshold, it is determined that the liquid injection electric regulating valve enters a fast regulating stage, and the regulating amplitude of each regulating period is A%; When the temperature difference of the exhaust temperature read in two adjacent detection periods is less than a preset second temperature difference trend threshold, it is determined that the liquid injection electric regulating valve enters a slow regulating stage, and the regulating amplitude of each regulating period is B%; wherein A is a first preset regulating amplitude, B is a second preset regulating amplitude, and A>B.

2. The control method for low temperature heat pump system discharge temperature according to claim 1, wherein, The actual exhaust superheat degree is determined according to the outlet water temperature and the exhaust temperature, and the method comprises: The condensing temperature is calculated by adding the outlet water temperature to a preset temperature; The actual exhaust superheat degree is obtained by subtracting the calculated condensing temperature from the exhaust temperature.

3. The control method for low temperature heat pump system discharge temperature according to claim 1, wherein, The evaporation temperature is determined according to the suction pressure, and the method comprises: The evaporation temperature is determined as the saturation temperature corresponding to the suction pressure.

4. The control method for low temperature heat pump system discharge temperature according to claim 1, wherein, In the low exhaust temperature control stage, the opening degree of the liquid injection electric regulating valve and the air supplement expansion valve is controlled according to the exhaust temperature, and the method comprises: The working state of the liquid injection electric regulating valve is adjusted to a closed state, and an initial opening degree is set for the air supplement expansion valve at the same time, and the initial opening degree is set as a fixed opening degree.

5. The control method for low temperature heat pump system discharge temperature according to claim 1, wherein, The calculation process of the target exhaust superheat degree comprises: The value of the exhaust superheat degree corresponding to the optimal refrigeration coefficient at different condensing temperatures in each control interval is measured through a preset experiment; A relationship between the exhaust superheat degree and the condensing temperature is fitted according to the value of the exhaust superheat degree; The target exhaust superheat degree is determined according to the relationship between the exhaust superheat degree and the condensing temperature.

6. The control method for low temperature heat pump system discharge temperature according to claim 1, wherein, The opening degree of the air supplement expansion valve is controlled according to the target exhaust superheat degree and the actual exhaust superheat degree, and the method comprises: When the actual exhaust superheat degree is greater than the target exhaust superheat degree, the opening degree of the air supplement expansion valve is increased through a PID control mode; When the actual exhaust superheat degree is less than the target exhaust superheat degree, the opening degree of the air supplement expansion valve is decreased through a PID control mode.

Images