Low water temperature starting method for steam heat pump, control device thereof and steam heat pump

Abstract

The application discloses a low-water-temperature starting method of a steam heat pump, a control device thereof and the steam heat pump. The low-water-temperature starting method comprises the following steps: detecting the current water temperature of a condenser, opening a second control valve, and discharging water in the condenser; closing the second control valve and then opening a unit; detecting the current refrigerant pressure of the condenser, and calculating the current saturation temperature of the refrigerant; and according to requirements, supplementing water into the condenser. The low-water-temperature starting method can empty the water level of the condenser, so that the refrigerant in the heat exchange coil is not soaked in water before the unit is started, and the condensation temperature and pressure can be rapidly increased without increasing a large cost. After the unit is started, the refrigerant on the condenser side has enough pressure difference to pass through the expansion valve and then enter the next cycle, so that the unit can be successfully started. During the starting process, water is supplemented into the condenser according to the refrigerant pressure and saturation temperature, so that the condenser can return to normal control and operation in the later period.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat pump, in particular to a low water temperature starting method of steam heat pump, a control device thereof and the steam heat pump. BACKGROUND

[0002] A heat pump is a high-efficiency energy-saving device that makes full use of low-grade heat. Heat can spontaneously transfer from a high-temperature object to a low-temperature object, but not spontaneously in the opposite direction. The working principle of a heat pump is to force heat to flow from a low-temperature object to a high-temperature object in a reverse cycle, which only consumes a small amount of net work in a reverse cycle to obtain a larger heat supply, and can effectively utilize low-grade heat that is difficult to apply to achieve energy-saving purposes.

[0003] Generally, a heat pump includes a compressor, a condenser, an expansion valve and an evaporator connected in series. After being compressed by the compressor, the refrigerant forms a gaseous high-temperature refrigerant. The gaseous high-temperature refrigerant is then passed through the condenser to exchange heat, and the heat is condensed and released in the condenser to heat the water on the other side to achieve heating. The subsequent liquid low-temperature refrigerant is then throttled and expanded by the expansion valve and enters the evaporator to vaporize and absorb heat, obtaining gaseous refrigerant, which is then pressurized by the compressor to form a pressure difference cycle, and the operation is repeated in this way.

[0004] Currently, in a shell-and-tube condenser, cooling water usually flows in the tube (i.e. through each tube), and refrigerant flows in the shell (i.e. through the shell space outside the tubes), the cooling water absorbs the heat of the refrigerant through the tubes to condense the refrigerant into liquid, i.e. the water heat exchange tube is immersed in the refrigerant. In a new type of condenser integrated with condensation + vaporization integrated structure, the tube of the condenser is connected to the refrigerant, and the shell is connected to the water (softened water), i.e. the refrigerant heat exchange tube is immersed in the water. In the above-mentioned structure of the condenser, when the heat pump uses high-pressure refrigerant, the initial water temperature is lower than 50℃, such as the initial water temperature is only 10℃, the refrigerant pressure on the condenser side is about 7 kgf (relative pressure), which makes the refrigerant in the condenser have enough pressure difference to pass through the expansion valve and then enter the evaporator to vaporize and absorb heat, so that the cycle can proceed smoothly. However, when the heat pump uses low-pressure refrigerant (this case is equivalent to the equipment being placed for a long time, and a large amount of liquid refrigerant is accumulated in the refrigerant pipeline on the condenser side), the initial water temperature is lower than 10℃ (the water temperature includes the case of 10℃), and the refrigerant pressure on the condenser side is only 0 kgf (relative pressure), which causes the refrigerant to have insufficient pressure difference to pass through the expansion valve and then enter the evaporator and other equipment, so that after the compressor runs for a period of time, all the refrigerant coming out of the compressor exists in the condenser, and the cycle does not work in the whole system, resulting in no refrigerant entering the inlet of the compressor, and finally the compressor automatically shuts down, resulting in the failure of the heat pump to start.

[0005] In the prior art, an electric heating is built inside the condenser or an external circulating heating device is connected, before the unit is started, the water temperature is heated to 50 DEG C or above, then the unit is started, at this time, the refrigerant pressure on the condenser side can reach about 3 kg, so that the refrigerant has enough pressure difference to pass through the expansion valve and then enter the evaporator to perform the next heat exchange cycle, so that the unit is successfully started, but the above method needs to improve the condenser, increase the equipment, and thus increase the overall cost. SUMMARY

[0006] In order to overcome the shortcomings of the prior art, one of the purposes of the present application is to provide a low water temperature starting method of a steam heat pump, which solves the above-mentioned traditional problems.

[0007] The second purpose of the present application is to provide a control device using the low water temperature starting method.

[0008] The third purpose of the present application is to provide a steam heat pump using the low water temperature starting method.

[0009] One of the purposes of the present application is achieved by using the following technical scheme:

[0010] A low water temperature starting method of a steam heat pump, the steam heat pump comprising a compressor, a condenser, an expansion valve and an evaporator, the condenser comprising a shell, a heat exchange coil arranged in the shell, a water inlet pipe arranged on the shell, a steam outlet pipe, a refrigerant inlet pipe, a refrigerant outlet pipe, a refrigerant pressure detector, a liquid level detector, a water temperature detector and a drain pipe, a first control valve being installed on the water inlet pipe, a second control valve being installed on the drain pipe, the liquid level detector being provided with A detection point, B detection point, C detection point and D detection point arranged from bottom to top, the low water temperature starting method of the steam heat pump comprising the following steps:

[0011] S1: detecting the current water temperature T1 of the condenser, when T1≤ water set temperature T2, opening the second control valve to drain the water in the condenser;

[0012] S2: detecting the water level L1 of the condenser, when L1 is less than the lowest liquid level of the liquid level detector and the duration is greater than the drain duration set time threshold t1, closing the second control valve and then starting the unit;

[0013] S3: detecting the current refrigerant pressure P1 of the condenser, calculating the current saturation temperature T3 of the refrigerant according to the property table of the refrigerant, when the second set temperature threshold T5>T3≥ the first set temperature threshold T4 and the A detection point of the liquid level detector is continuously disconnected for the first set time threshold t2, opening the first control valve to supply water to the condenser, and the water supply is stopped when the A detection point is continuously closed for the second set time threshold t3, then entering the next step S4;

[0014] S4: detecting the current refrigerant pressure P2 of the condenser, calculating the current saturation temperature T6 of the refrigerant according to the property table of the refrigerant; when T6 is greater than or equal to the second set temperature threshold T5 and the C detection point of the liquid level detector is continuously disconnected for a third set time threshold t3, the first control valve is opened to supply water to the condenser, and the water supply is performed to the C detection point which is continuously closed for a fourth set time threshold t4, the low water temperature control is exited, and the normal control of the unit is performed.

[0015] Preferably, in step S1, T2 is 30-50 DEG C.

[0016] Preferably, in step S2, t1 is 10-30 min.

[0017] Preferably, in step S3, the refrigerant is one of R1233zd, R245fa, R515B and R142b.

[0018] Preferably, in step S3, the first set temperature threshold T4 is 68-75 DEG C, the second set temperature threshold T5 is 78-85 DEG C, the first set time threshold t2 is 3-6 s, and the second set time threshold t3 is 3-6 s.

[0019] Preferably, in step S4, the third set time threshold t3 is 3-6 s, and the fourth set time threshold t4 is 3-6 s.

[0020] Preferably, the steam heat pump further comprises a water supply device, the water supply device comprises a water storage tank, a water outlet pipe, a water return pipe and a water pump, the third control valve is arranged on the water outlet pipe, the fourth control valve is arranged on the water return pipe, the water inlet of the water pump is connected with the drain pipe and the water outlet pipe respectively, and the water outlet of the water pump is connected with the water return pipe and the water inlet pipe respectively; when the condenser needs to drain water, the first control valve and the third control valve are closed, the second control valve and the fourth control valve are opened, the drain pipe, the water pump and the water return pipe are communicated, and the water in the condenser is pumped into the water storage tank; when the condenser needs to supply water, the second control valve and the fourth control valve are closed, the first control valve and the third control valve are opened, the water outlet pipe, the water pump and the water inlet pipe are communicated, and the water in the condenser is supplied.

[0021] Preferably, the volume ratio between the heat exchange cavity and the steam cavity of the condenser is 1: (0.8-1.2).

[0022] The second purpose of the application is achieved by the following technical scheme:

[0023] A control device comprises the low water temperature starting method.

[0024] The third purpose of the application is achieved by the following technical scheme:

[0025] A steam heat pump comprising the low water temperature starting method.

[0026] Compared with the prior art, the application has the beneficial effects that:

[0027] The low water temperature starting method of the application can make the refrigerant in the heat exchange coil not soak in water before the unit starts by emptying the water level of the condenser, and can achieve the purpose of quickly increasing the condensing temperature and pressure without increasing large costs, so that the refrigerant on the condenser side can have enough pressure difference to pass through the expansion valve after the unit starts, and then enter the next cycle, so that the unit can start successfully. During the starting process, water is supplied to the condenser according to the refrigerant pressure and saturation temperature, so that the condenser can return to normal control and operation in the later period. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A process flow chart of the steam heat pump of the application;

[0029] Figure 2 A structural schematic view of the condenser of the application;

[0030] Figure 3 A sectional view of the condenser shown in the figure; Figure 2

[0031] Figure 4 A logic control chart of the low water temperature control of the application.

[0032] In the figure: 10, compressor; 20, condenser; 30, expansion valve; 40, evaporator; 50, shell; 51, heat exchange coil; 52, water inlet pipe; 53, steam outlet pipe; 54, refrigerant inlet pipe; 55, refrigerant outlet pipe; 56, liquid level detector; 57, drain pipe; 58, liquid baffle; 60, water storage tank; 61, water outlet pipe; 62, water return pipe; 63, water pump. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned purposes, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth in order to provide a thorough understanding of the application. However, the application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the application, so the application is not limited to the specific embodiments disclosed below.

[0034] ​In the description of the present application, it needs to be understood that the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise explicitly and specifically limited.

[0035] In the description of the present application, it needs to be understood that when an element is considered to be "connected" to another element, it can be directly connected to another element or there can be an intermediate element. In contrast, when an element is referred to as "directly" connected to another element, there is no intermediate element.

[0036] Please refer to Figures 1-4 The low water temperature starting method of the steam heat pump of a preferred embodiment of the present application is used to improve the successful starting of the heat pump unit under the condition of low water temperature, wherein the steam heat pump comprises a compressor 10, a condenser 20, an expansion valve 30, an evaporator 40 and a control device. The compressor 10, the condenser 20, the expansion valve 30 and the evaporator 40 are connected in series to form a refrigerant heating cycle. The condenser 20 directly produces high-temperature steam by absorbing the temperature of the high-temperature refrigerant compressed by the compressor 10. The condenser 20 is of a shell-and-tube structure. The tube passage of the condenser 20 is connected to the refrigerant, and the shell passage is connected to water (softened water). In one embodiment, as shown in Figure 2 and Figure 3As shown, the condenser 20 comprises a shell 50, a heat exchange coil 51 arranged in the shell 50, a water inlet pipe 52 arranged on the shell 50, a steam outlet pipe 53, a refrigerant inlet pipe 54, a refrigerant outlet pipe 55, a refrigerant pressure detector, a liquid level detector 56, a water temperature detector, and a drain pipe 57. The water inlet pipe 52 is located at the bottom of the shell 50, and the steam outlet pipe 53 is located at the top of the shell 50. The water inlet pipe 52 and the steam outlet pipe 53 are both in communication with the shell 50. The refrigerant inlet pipe 54 is in communication with one end of the heat exchange coil 51, and the refrigerant outlet pipe 55 is in communication with the other end of the heat exchange coil 51. The refrigerant pressure detector is used to detect the refrigerant pressure of the condenser 20, and can be arranged in the heat exchange coil 51 or on the refrigerant outlet pipe 55. The liquid level detector 56 is arranged on one side of the shell 50 and is used to detect the water level in the shell 50. The water temperature detector is used to detect the temperature of the water in the shell 50. The drain pipe 57 is arranged at the bottom of the shell 50. A first control valve is arranged on the water inlet pipe 52, and a second control valve is arranged on the drain pipe 57. A control device is used to control the entire system, and the control device comprises the low water temperature starting method. The liquid level detector 56 is provided with A, B, C and D detection points arranged from bottom to top. That is, the detection liquid level of the A detection point is the lowest, and the detection liquid level of the D detection point is the highest. The B and C detection points are located between the A and D detection points.

[0037] Specifically, as shown in the figure, the low water temperature starting method comprises the following steps: Figure 4

[0038] S1: detecting the current water temperature T1 of the condenser 20. When T1≤water set temperature T2, the second control valve is opened to drain the water in the condenser 20, otherwise, the process returns.

[0039] In the step, when the system detects that the water temperature of the condenser 20 is low, the low water temperature protection is started, and a low water temperature warning mark appears. At this time, the low water temperature starting button needs to be pressed to start the low water temperature starting method of the present application, so as to improve the safety of the system. In this embodiment, the water set temperature T2 is 30-50°C, such as 30°C, 35°C, 40°C, 45°C or 50°C, and preferably T2 is 40°C. The draining time of the condenser 20 is related to the capacity of the condenser 20, and therefore is not described one by one.

[0040] S2: detecting the water level L1 of the condenser 20. When L1 is less than the lowest liquid level of the liquid level detector 56 and the duration is greater than the draining duration set time threshold t1, the second control valve is closed, and then the compressor 10 of the unit is started. Otherwise, the process returns.

[0041] ​In this step, the water in the condenser 20 is gradually exposed to the water surface during the discharge, and the heat exchange coil 51 is not submerged in the water, so that the temperature of the refrigerant in the heat exchange coil 51 gradually rises, or the refrigerant gradually changes from a liquid to a gaseous state, so that the pressure of the refrigerant in the condenser 20 gradually rises. When the pressure of the refrigerant reaches a certain pressure, there is enough pressure difference through the expansion valve 30 after the unit is started. Before the compressor 10 is started, the starting requirements of the unit except the water level of the condenser 20 must be met to start.

[0042] The drainage time is determined according to the specific volume of the condenser 20 and the size of the drain pipe 57, and the drainage duration threshold t1 below the lowest liquid level of the liquid level detector 56 can be set according to experience. In one embodiment, the drainage duration threshold t1 is 10-30 min, such as 10 min, 15 min, 20 min, 25 min, 30 min, etc.

[0043] S3: Detect the current refrigerant pressure P1 of the condenser 20, and calculate the current saturation temperature T3 of the refrigerant according to the refrigerant property table; when the second set temperature threshold T5 > T3 ≥ the first set temperature threshold T4, and the A detection point of the liquid level detector 56 is continuously disconnected for the first set time threshold t2, then the first control valve is opened, and water is supplied to the condenser 20, and the water is supplied to the A detection point continuously closed for the second set time threshold t3, and then enters the next step S4, otherwise returns.

[0044] In this step, the refrigerant pressure P1 is the saturation pressure of the refrigerant, and the corresponding saturation temperature can be found by interpolation according to the property table. The property table is input into the system in advance to facilitate program searching. Continuous disconnection means that the water level does not reach the A detection point, and continuous closure means that the water level reaches the A detection point. The instantaneous signal may be caused by sensor fluctuations, and may appear as a false value. In order to improve the accuracy of the data, the received signal is continuously received to exclude the false judgment caused by the fluctuations of the instrument. In one embodiment, the refrigerant is one of R1233zd, R245fa, R515B, and R142b. The first set temperature threshold T4 is 68-75°C, and the second set temperature threshold T5 is 78-85°C; the first set time threshold t2 is 3s-6s, and the second set time threshold t3 is 3s-6s. Preferably, the first set temperature threshold T4 is 70°C, the second set temperature threshold T5 is 80°C, the first set time threshold t2 is 5s, and the second set time threshold t3 is 5s.

[0045] S4: detecting the current refrigerant pressure P2 of the condenser 20, calculating the current saturation temperature T6 of the refrigerant according to the refrigerant property table; when T6≥the second set temperature threshold T5, and the C detection point of the liquid level detector 56 is continuously disconnected for the third set time threshold t3, then the first control valve is opened, and water is added to the condenser 20, and the water is added to the condenser 20 until the C detection point is continuously connected for the fourth set time threshold t4, the low water temperature control is exited, and the normal control of the unit is performed, otherwise, it is returned.

[0046] In this step, when the water is added to the C detection point, the water level in the condenser 20 has submerged the heat exchange coil 51 or slightly exposed the heat exchange coil 51, and the unit can be normally operated, and the program needs to be exited, and then the normal PID control of the unit is returned. In one embodiment, the third set time threshold t3 is 3s-6s, the fourth set time threshold t4 is 3s-6s, preferably, the third set time threshold t3 is 5s, and the fourth set time threshold t4 is 5s.

[0047] The tube passage of the condenser 20 of the present application is connected to the refrigerant, and the shell passage is connected to the water (softened water), and the condenser 20 is integrated with the gasification structure, the water level in the condenser 20 is in the middle and lower part of the heat exchange coil 51 in the normal operation, all the heat exchange tubes are submerged in the water to achieve the best heat exchange effect, so as to reduce the condensation temperature and pressure. When starting, the water in the condenser 20 is completely emptied to quickly increase the condensation temperature and pressure, so that even if the water temperature is at a lower temperature, the refrigerant pressure on the condenser 20 side can also meet the requirements, and there is enough pressure difference to make the refrigerant pass through the expansion valve 30 into the evaporator 40 to circulate, so that the unit starts successfully.

[0048] In other embodiments, as shown in Figure 1 The steam heat pump further includes a water adding device, the water adding device includes a water storage tank 60, a water outlet pipe 61, a water return pipe 62 and a water pump 63, the third control valve is arranged on the water outlet pipe 61, the fourth control valve is arranged on the water return pipe 62, the water inlet of the water pump 63 is connected with the drain pipe 57 and the water outlet pipe 61 respectively, and the water outlet of the water pump 63 is connected with the water return pipe 62 and the water inlet pipe 52 respectively. When the condenser 20 needs to drain water, the first control valve and the third control valve are closed, the second control valve and the fourth control valve are opened, the drain pipe 57, the water pump 63 and the water return pipe 62 are communicated, and the water in the condenser 20 is pumped into the water storage tank 60; when the condenser 20 needs to add water, the second control valve and the fourth control valve are closed, the first control valve and the third control valve are opened, the water outlet pipe 61, the water pump 63 and the water inlet pipe 52 are communicated, and the water in the condenser 20 is added. The water in the water storage tank 60 is softened water. The embodiment is to avoid waste of water resources, and the discharged water is introduced into the water storage tank 60 for subsequent use.

[0049] Further as shown in Figure 2 andFigure 3 As shown, the shell 50 has an air inlet cavity, a heat exchange cavity, a steam cavity, a transfer cavity and a liquid outlet cavity. The heat exchange coil 51 is arranged in the heat exchange cavity. The steam cavity is arranged at the upper portion of the heat exchange cavity (the steam cavity and the heat exchange cavity are divided by the water level). The heat exchange coil 51 is divided into an upper coil and a lower coil. The refrigerant inlet pipe 54, the air inlet cavity, the upper coil, the transfer cavity, the lower coil, the liquid outlet cavity and the refrigerant outlet pipe 55 are sequentially connected to form a refrigerant heat dissipation channel. The refrigerant inlet pipe 54 is connected to the outlet of the compressor 10 to introduce high-temperature gaseous refrigerant. The refrigerant outlet pipe 55 is connected to the inlet of the expansion valve 30 to output low-temperature liquid refrigerant. The water inlet pipe 52 is connected to the heat exchange cavity. The steam outlet pipe 53 is connected to the steam cavity.

[0050] In one embodiment, the volume ratio between the heat exchange cavity and the steam cavity is 1:(0.8-1.2), such as 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2. Preferably, the volume ratio between the heat exchange cavity and the steam cavity is 1:1.1. The volume ratio is determined according to the steam output and heat storage.

[0051] In this embodiment, a partition plate is arranged between the air inlet cavity and the liquid outlet cavity. That is, the shell 50 is divided into the air inlet cavity and the liquid outlet cavity by the partition plate. The refrigerant inlet pipe 54 and the refrigerant outlet pipe 55 are arranged at the side of the shell 50. The refrigerant inlet pipe 54 is arranged at the end of the air inlet cavity away from the partition plate, that is, slightly upward. The refrigerant inlet pipe 54 does not directly collide with the heat exchange coil 51, which is beneficial to the flow of the refrigerant. The refrigerant outlet pipe 55 is arranged at the end of the liquid outlet cavity close to the partition plate, that is, slightly upward. The arrangement of the refrigerant outlet pipe 55 is beneficial to the heat exchange time of the refrigerant in the heat exchange coil 51.

[0052] In one embodiment, the total heat exchange area of the upper coil is greater than the total heat exchange area of the lower coil, so as to improve the heat exchange effect of the upper portion. Preferably, the total heat exchange area of the upper coil is 1.1-2.2 times the total heat exchange area of the lower coil.

[0053] Optionally, a liquid blocking plate 58 is arranged in the shell 50. The liquid blocking plate 58 is arranged at the upper portion of the steam cavity and below the steam outlet. The liquid blocking plate 58 and the steam outlet have a flow gap therebetween. An electric control valve is arranged at the steam outlet. The saturation temperature and pressure of the steam outlet are controlled by adjusting the opening degree of the electric control valve.

[0054] The above embodiment optimizes and improves the shell 50 by dividing the interior of the shell 50 into a heat exchange cavity and a steam cavity, placing the heat exchange coil 51 in the heat exchange cavity, passing the high-temperature refrigerant into the upper heat exchange coil 51, transferring most of the heat to the system water in the upper part of the heat exchange cavity to heat it, and then passing the heat-exchanged refrigerant out of the lower heat exchange coil 51 to preheat the remaining heat to the system water in the lower part of the heat exchange cavity. The system water in the heat exchange cavity is heated continuously, and the steam formed by the system water flows into the steam cavity and is then output from the steam outlet, so that the condensation and gasification are integrated into one structure, and the direct steam output effect is realized in the same tank, which not only saves a flash device and reduces the investment in equipment, but also reduces the maintenance cost in the later period.

[0055] The technical features of the above embodiments can be combined arbitrarily, and to make the description simple, all possible combinations of the technical features in the above embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present application.

[0056] The above embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A method for starting a steam heat pump at low water temperature, characterized in that, The steam heat pump includes a compressor, a condenser, an expansion valve, and an evaporator. The condenser includes a shell, a heat exchange coil inside the shell, a water inlet pipe, a steam outlet pipe, a refrigerant inlet pipe, a refrigerant liquid outlet pipe, a refrigerant pressure detector, a liquid level detector, a water temperature detector, and a drain pipe. A first control valve is installed on the water inlet pipe, and a second control valve is installed on the drain pipe. The liquid level detector has detection points A, B, C, and D arranged from bottom to top. The low water temperature start-up method of the steam heat pump includes the following steps: S1: Detect the current water temperature T1 of the condenser. When T1 ≤ water set temperature T2, open the second control valve to drain the water in the condenser. S2: Detect the water level L1 in the condenser. When L1 is less than the lowest level of the level detector and the duration is greater than the drainage continuous set time threshold t1, close the second control valve and then start the unit. S3: Detect the current refrigerant pressure P1 of the condenser, and calculate the current saturation temperature T3 of the refrigerant according to the refrigerant property table; when the second set temperature threshold T5 > T3 ≥ the first set temperature threshold T4, and the A detection point of the liquid level detector is continuously disconnected for the first set time threshold t2, then open the first control valve to replenish water into the condenser until the A detection point is continuously closed for the second set time threshold t3, and then proceed to the next step S4; S4: Detect the current refrigerant pressure P2 of the condenser, and calculate the current saturation temperature T6 of the refrigerant according to the refrigerant property table; when T6 ≥ the second set temperature threshold T5, and the C detection point of the liquid level detector is continuously disconnected for the third set time threshold t3, the first control valve is opened to replenish water into the condenser. Water is replenished until the C detection point is continuously closed for the fourth set time threshold t4, then the low water temperature control is exited and the normal control of the unit is carried out.

2. The low-water-temperature start-up method for a steam heat pump according to claim 1, characterized in that, In step S1, T2 is 30℃-50℃.

3. The low-water-temperature start-up method for a steam heat pump according to claim 1, characterized in that, In step S2, t1 is 10 min - 30 min.

4. The low-water-temperature start-up method for a steam heat pump according to claim 1, characterized in that, In step S3, the refrigerant is one of R1233zd, R245fa, R515B, or R142b.

5. The low-water-temperature start-up method for a steam heat pump according to claim 4, characterized in that, In step S3, the first set temperature threshold T4 is 68-75℃, the second set temperature threshold T5 is 78-85℃; the first set time threshold t2 is 3s-6s, and the second set time threshold t3 is 3s-6s.

6. The low-water-temperature start-up method for a steam heat pump according to claim 1, characterized in that, In step S4, the third set time threshold t3 is 3s - 6s, and the fourth set time threshold t4 is 3s - 6s.

7. The low-water-temperature start-up method for a steam heat pump according to claim 1, characterized in that, The steam heat pump also includes a water replenishment device, which includes a water storage tank, an outlet pipe, a return pipe, and a water pump. A third control valve is installed on the outlet pipe, and a fourth control valve is installed on the return pipe. The inlet of the water pump is connected to both the drain pipe and the outlet pipe, and the outlet of the water pump is connected to both the return pipe and the inlet pipe. When the condenser needs to drain, the first and third control valves are closed, and the second and fourth control valves are opened, connecting the drain pipe, the water pump, and the return pipe to pump water from the condenser into the water storage tank. When the condenser needs to replenish water, the second and fourth control valves are closed, and the first and third control valves are opened, connecting the outlet pipe, the water pump, and the inlet pipe to replenish water to the condenser.

8. The low-water-temperature start-up method for a steam heat pump according to claim 1, characterized in that, The volume ratio between the heat exchange chamber and the steam chamber of the condenser is 1:(0.8-1.2).

9. A control device, characterized in that, Including the low water temperature start-up method as described in any one of claims 1-8.

10. A steam heat pump, characterized in that, Including the low water temperature start-up method as described in any one of claims 1-8.

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