A heating unit and a defrosting control method thereof

Abstract

The present application relates to a heating unit and a defrost control method thereof. The method comprises obtaining a heat medium temperature Tr in a refrigerant-liquid heat medium heat exchanger when defrosting is determined to be necessary; determining whether there is a risk of freezing of the refrigerant-liquid heat medium heat exchanger during the defrost process based on the relationship between the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger and the heat medium freezing temperature Trf, and / or the relationship between the temperature Tc of the refrigerant in the outdoor heat exchanger and the heat medium freezing temperature Trf; and if it is determined that there is a risk of freezing during defrost, entering a pre-defrost mode. The above scheme can select whether to perform a pre-defrost operation based on the defrost operation status during actual use of the heating unit, thereby preventing the refrigerant-liquid heat medium heat exchanger from freezing and being damaged during the defrost operation.

Description

Technical Field

[0001] The present invention relates to the technical field of air source heat pump heating units, and in particular to a heating unit and a defrosting control method thereof. Background Art

[0002] The heating scheme that uses the air source heat pump heating unit based on the reverse Carnot cycle principle as the heat source and liquid heat medium as the heat transfer medium has been widely used in people's daily work and life.

[0003] When the outdoor ambient temperature is low, there is a possibility of frost on the outdoor heat exchanger. When the thickness of the frost layer on the outdoor heat exchanger reaches a certain condition, the operating efficiency of the outdoor heat exchanger drops sharply. At this time, the outdoor heat exchanger needs to be defrosted.

[0004] Existing heat pump heating units mainly directly change the operating state of the four-way reversing valve when defrosting begins, so that the outdoor heat exchanger originally used as an evaporator to absorb heat from the outdoor side is switched to be used as a condenser, and the high-temperature refrigerant discharged by the compressor is used to melt the frost attached to the outdoor heat exchanger.

[0005] However, in some cases, directly switching the four-way reversing valve and changing the flow direction of the refrigerant in the outdoor heat exchanger may cause the refrigerant with a lower temperature originally staying in the outdoor heat exchanger to be transported to the refrigerant-liquid heat medium heat exchanger. The liquid heat medium may change from liquid to solid, and the heat medium may expand, thereby causing damage to the refrigerant-liquid heat medium heat exchanger. Summary of the Invention

[0006] To address the aforementioned issues, the present invention provides a defrost control method for a heating unit that can select whether to perform a pre-defrost operation based on the defrost operation during actual use of the heating unit. When the heat medium temperature is close to the freezing point of the heat medium or the refrigerant temperature in the outdoor heat exchanger is low, performing a pre-defrost operation on the unit before normal defrosting can effectively improve the unit's reliability during defrost operation and prevent freezing damage to the refrigerant-liquid heat medium heat exchanger during defrost operation.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0008] A defrost control method for a heating unit is provided, the heating unit comprising a four-way reversing valve, the four-way reversing valve being switchable between a first conduction direction and a second conduction direction. When the four-way reversing valve is conducted in the first conduction direction, the refrigerant is heated by an outdoor heat exchanger, then heated and pressurized by a compressor, and then enters a refrigerant-liquid heat medium heat exchanger for heat exchange; when the four-way reversing valve is conducted in the second conduction direction, the higher-temperature refrigerant flowing out of the refrigerant-liquid heat medium heat exchanger is heated and pressurized by the compressor, then enters the outdoor heat exchanger for heat exchange. The method comprises:

[0009] In the heating mode, obtaining the temperature Tc of the refrigerant in the outdoor heat exchanger, and determining whether the outdoor heat exchanger needs to be defrosted according to the temperature Tc of the refrigerant in the outdoor heat exchanger;

[0010] When it is determined that defrosting is required, the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger is obtained, and based on the relationship between the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger and the heat medium freezing temperature Trf, and / or the relationship between the refrigerant temperature Tc in the outdoor heat exchanger and the heat medium freezing temperature Trf, it is determined whether there is a risk of freezing of the refrigerant-liquid heat medium heat exchanger during the defrost process;

[0011] If it is determined that there is no freezing risk during defrosting, the system enters normal defrosting mode, and the four-way valve is turned on in the second conduction direction.

[0012] If it is determined that there is a risk of freezing during defrosting, the four-way valve maintains conduction in the first conduction direction, and adjusts the compressor operating frequency Fc and the throttling degree of the throttling mechanism to the pre-defrost mode until it is determined that there is no risk of freezing during defrosting and enters the normal defrost mode;

[0013] The frequency of the compressor in the pre-defrost mode is lower than that in the heating mode, and the throttling degree of the throttle valve in the pre-defrost mode is lower than that in the heating mode.

[0014] Preferably, the determining whether the outdoor heat exchanger needs to be defrosted according to the temperature Tc of the refrigerant in the outdoor heat exchanger includes:

[0015] The temperature Tc of the refrigerant in the outdoor heat exchanger is compared with a preset defrost temperature. When the temperature Tc of the refrigerant in the outdoor heat exchanger reaches the preset defrost temperature, it is determined that defrosting is required.

[0016] Preferably, the determining whether there is a freezing risk during defrosting based on the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger includes:

[0017] The heat medium freezing temperature Trf is obtained. When the difference between the heat medium temperature Tr and the heat medium freezing temperature Trf in the refrigerant-liquid heat medium heat exchanger reaches a preset value, or when the difference between the refrigerant temperature Tc and the heat medium freezing temperature Trf in the outdoor heat exchanger reaches a preset value, it is determined that there is a freezing risk during defrosting.

[0018] Preferably, in the pre-defrost mode, the throttling degree of the throttling mechanism is adjusted to a minimum throttling degree.

[0019] Preferably, in the heating mode, the compressor frequency is adjusted according to a preset mode. When switching from the heating mode to the pre-defrost mode, the compressor frequency of the switched pre-defrost mode is lower than the compressor frequency at the current moment in the heating mode at the time of switching.

[0020] Preferably, the method further includes, after the unit operates in normal defrosting mode, determining whether the unit has completed defrosting; if it is determined that defrosting is completed, adjusting the four-way valve to conduct in the first conducting direction, and the unit operates in heating mode.

[0021] The present invention also provides a heating unit, which is applied with any of the above methods.

[0022] The present invention adopts the above-mentioned technical solution, taking into account the refrigerant-liquid heat medium heat exchanger situation that may occur during the defrosting process of the outdoor heat exchanger. When the heat medium temperature in the refrigerant-liquid heat medium heat exchanger is close to the heat medium freezing temperature, or the refrigerant temperature in the outdoor heat exchanger is close to the heat medium freezing temperature, that is, the refrigerant temperature is low, it is determined that there is a risk of freezing of the refrigerant-liquid heat medium heat exchanger during the normal defrosting process. When it is determined that there is a risk of freezing of the refrigerant-liquid heat medium heat exchanger during the normal defrosting process, the pre-defrost mode is entered in advance to increase the temperature of the refrigerant in the heat exchanger and the temperature of the heat medium in the refrigerant-water heat exchanger to prevent freezing during the subsequent normal defrosting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the heating system structure in this application;

[0024] Figure 2 This is a schematic diagram of the refrigerant flow in the heating mode of the heating unit;

[0025] Figure 3 This is a schematic diagram of the refrigerant flow in the defrost mode of the heating unit;

[0026] Figure 4 This is the defrost operation control logic diagram of the heating unit in this application;

[0027] Figure 5 This is the defrost control timing diagram a of the heating unit in this application;

[0028] Figure 6 This is the defrost control timing diagram b of the heating unit in this application. DETAILED DESCRIPTION

[0029] The embodiments of the present invention are described in detail below.

[0030] First, the symbols involved in this application are explained:

[0031] Tc: refrigerant temperature in the outdoor heat exchanger;

[0032] Tr: heating medium temperature;

[0033] Trf: Heat medium freezing temperature

[0034] Fc: compressor operating frequency;

[0035] Pv: throttling degree of throttling mechanism;

[0036] g: shutdown signal recording parameters;

[0037] y: Enter pre-defrost mode to record parameters.

[0038] like Figure 1 The heating system shown includes a heating unit 1 and a heat user 2. The heating unit 1 includes a compressor 11, a four-way reversing valve 12, an outdoor heat exchanger 13, a refrigerant temperature sensor 14 for the outdoor heat exchanger, a throttling mechanism 15, an outdoor fan 16, a refrigerant-liquid heat medium heat exchanger 17, a liquid heat medium temperature sensor 18, and a control mechanism 19. The control mechanism 19 is used to switch the operating mode of the heating unit and control the conduction direction of the four-way reversing valve 12, the operating frequency of the compressor 11, and the opening of the throttling mechanism 15 in the corresponding mode.

[0039] The four-way reversing valve 12 can switch between a first conducting direction and a second conducting direction. When the four-way reversing valve 12 is conducted in the first conducting direction, the refrigerant is heated by the outdoor heat exchanger 13 and then heated and pressurized by the compressor 11 before entering the refrigerant-liquid heat medium heat exchanger 17 for heat exchange; when the four-way reversing valve is conducted in the second conducting direction, the higher temperature refrigerant flowing out of the refrigerant-liquid heat medium heat exchanger is heated and pressurized by the compressor and then flows into the outdoor heat exchanger for heat exchange.

[0040] In this embodiment, the control mechanism 19 can control the heating unit 1 to operate in the heating mode, the defrost mode and the pre-defrost mode. In the heating mode and the pre-defrost mode, the four-way reversing valve 12 is turned on in the first conduction direction, and the refrigerant on the heating unit side flows in the direction of Figure 2 The arrow in the middle points to the flow; in the defrost mode, the four-way reversing valve 12 is turned on in the second conduction direction, and the refrigerant flow direction on the heating unit side is Figure 3 The middle arrow points to the circulation.

[0041] This embodiment provides a defrost control method for a heating unit to prevent damage to the refrigerant-liquid heat medium heat exchanger caused by low-temperature refrigerant circulating through it during the initial defrost operation of the heating unit, resulting in a phase change from liquid heat medium to solid. This method adds a pre-defrost mode to the conventional heating mode and normal defrost mode of the heating unit. If the heating unit detects a potential freezing risk in the refrigerant-liquid heat medium heat exchanger during normal defrost operation, the pre-defrost mode is used to increase the temperature of the refrigerant in the outdoor heat exchanger and the temperature of the heat medium in the refrigerant-water heat exchanger. The system then returns to normal defrost mode to prevent subsequent freezing.

[0042] The overall concept of the defrost control method of the above heating unit is as follows:

[0043] Before the heating unit defrosts its outdoor heat exchanger, a determination is made as to whether there is a possibility of freezing of the refrigerant-liquid heat medium heat exchanger during the defrost operation. If there is a possibility of freezing of the refrigerant-liquid heat medium heat exchanger during the defrost operation, a pre-defrost process is performed before normal defrost operation. If there is no possibility of freezing of the refrigerant-liquid heat medium heat exchanger during the defrost operation, the unit is directly defrosted. The greater the possibility of freezing of the refrigerant-liquid heat medium heat exchanger during the defrost operation, the closer the heat medium temperature is to the freezing temperature of the heat medium before defrosting begins; and / or the greater the possibility of freezing of the refrigerant-liquid heat medium heat exchanger during the defrost operation, the closer the refrigerant temperature is to the freezing temperature of the heat medium. Heating units also have two criteria for determining whether the refrigerant-liquid heat exchanger may freeze during defrost operation. The criteria differ between those that have entered pre-defrost mode and those that have not. Under the same heat medium temperature conditions, a higher refrigerant temperature during pre-defrost operation than during non-pre-defrost operation is required to determine whether the refrigerant-liquid heat exchanger is likely to freeze during defrost operation. Furthermore, after entering pre-defrost operation, the compressor's operating frequency is lower than before, and the throttling mechanism is reduced. The four-way reversing valve remains in heating mode. By reducing the compressor frequency and the throttling valve, the compressor suction pressure is increased, raising the refrigerant pressure in the refrigerant-water heat exchanger, and thus the refrigerant temperature in the refrigerant-water heat exchanger. Ultimately, this increases the heat medium temperature in the refrigerant-water heat exchanger, achieving the pre-defrost effect. After the heating unit enters normal defrosting operation, the throttling degree of its throttling mechanism is adjusted to the minimum, and the four-way reversing valve is adjusted to the defrosting operation state.

[0044] The defrost control method of the heating unit is described in detail below.

[0045] like Figure 4 As shown, the defrost control method of the heating unit includes: in the heating mode, obtaining the temperature Tc of the refrigerant in the outdoor heat exchanger, and judging whether the outdoor heat exchanger needs to be defrosted according to the temperature Tc of the refrigerant in the outdoor heat exchanger;

[0046] When it is determined that defrosting is required, the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger is obtained, and based on the relationship between the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger and the heat medium freezing temperature Trf, and / or the relationship between the refrigerant temperature Tc in the outdoor heat exchanger and the heat medium freezing temperature Trf, it is determined whether there is a risk of freezing of the refrigerant-liquid heat medium heat exchanger during the defrost process;

[0047] If it is determined that there is no freezing risk during defrosting, the system enters normal defrosting mode, and the four-way valve is turned on in the second conduction direction.

[0048] If it is determined that there is a risk of freezing during defrosting, the four-way valve maintains conduction in the first conduction direction, and adjusts the compressor operating frequency Fc and the throttling degree of the throttling mechanism to the pre-defrost mode until it is determined that there is no risk of freezing during defrosting and enters the normal defrost mode.

[0049] The frequency of the compressor in the pre-defrost mode is lower than that in the heating mode, and the throttling degree of the throttle valve in the pre-defrost mode is lower than that in the heating mode.

[0050] The above method increases the compressor suction pressure and the pressure of the refrigerant in the refrigerant-water heat exchanger by reducing the compressor frequency and the throttling degree of the throttle valve, thereby increasing the refrigerant temperature in the refrigerant-water heat exchanger, and finally achieving the purpose of increasing the temperature of the heat medium in the refrigerant-water heat exchanger and achieving a pre-defrosting effect.

[0051] In the above method, determining whether the outdoor heat exchanger requires defrosting based on the refrigerant temperature Tc in the outdoor heat exchanger includes comparing the refrigerant temperature Tc in the outdoor heat exchanger with a preset defrost temperature, and determining that defrosting is necessary when the refrigerant temperature Tc in the outdoor heat exchanger reaches the preset defrost temperature. In this embodiment, the refrigerant temperature in the outdoor heat exchanger is obtained by an outdoor heat exchanger refrigerant temperature sensor 14. The preset defrost temperature can be a point value or a temperature range, and its specific value can be determined in advance through experiments.

[0052] In the above method, determining whether there is a risk of freezing in the refrigerant-liquid heat medium heat exchanger during the defrost operation based on the relationship between the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger and the heat medium freezing temperature Trf, and / or the relationship between the refrigerant temperature Tc in the outdoor heat exchanger and the heat medium freezing temperature Trf, includes obtaining the heat medium freezing temperature Trf and determining that there is a risk of freezing during the defrost operation when the difference between the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger and the heat medium freezing temperature Trf reaches a preset value, or when the difference between the refrigerant temperature Tc in the outdoor heat exchanger and the heat medium freezing temperature Trf reaches a preset value. The greater the likelihood of freezing in the refrigerant-liquid heat medium heat exchanger during the defrost operation, the closer the heat medium temperature is to the heat medium freezing temperature before the defrost operation begins. The greater the likelihood of freezing in the refrigerant-liquid heat medium heat exchanger during the defrost operation, the closer the refrigerant temperature is to the heat medium freezing temperature before the defrost operation begins. Therefore, the difference between Tr and Trf, or the difference between Tc and Trf, can be used to determine the likelihood of freezing in the refrigerant-liquid heat medium heat exchanger during a defrost process. Based on this information, the heating unit can be controlled to determine whether to enter pre-defrost mode before normal defrost operation. The difference between Tr and Trf, or the difference between Tc and Trf, can be a specific point value or a range of values. In the embodiments, the specific value can be determined through experimentation.

[0053] In this embodiment, the corresponding relationship between determining whether there is a freezing risk during the defrost process and the difference between Tr and Trf or the difference between Tc and Trf is shown in Table 1:

[0054]

[0055] Table 1

[0056] Wherein, y represents the parameter recorded when entering the pre-defrost mode. y=0 means that the pre-defrost mode has not been entered before in this operation; y=1 means that the pre-defrost mode has been entered before in this operation.

[0057] As shown in the table above, preferably, the determination of whether there is a risk of freezing of the refrigerant-liquid heat medium heat exchanger during the defrost process based on the relationship between the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger and the heat medium freezing temperature Trf, and / or the relationship between the refrigerant temperature Tc in the outdoor heat exchanger and the heat medium freezing temperature Trf, further includes determining whether the pre-defrost mode has been entered during the current operation. If so, determining whether there is a risk of freezing based on the first set of Tr-Trf values ​​and / or Tc-Trf; if not, determining whether there is a risk of freezing based on the second set of Tr-Trf values ​​and / or Tc-Trf. The first set of differences and the second set of differences are different. Generally speaking, if the pre-defrost mode has been entered during the current operation, the pre-defrost mode is entered when the difference between Tr-Trf and / or Tc-Trf is large; if the pre-defrost mode has not been entered during the current operation, the pre-defrost mode is entered when the difference between Tr-Trf and / or Tc-Trf is relatively small. By setting the above difference, since the pre-defrost mode has already been entered, it is considered that according to the current temperature of the refrigerant, the risk of freezing of the refrigerant-liquid heat medium heat exchanger during the subsequent normal defrost process is higher. Therefore, by selecting different difference ranges to control it to enter the pre-defrost mode in advance, the reliability is higher.

[0058] like Figure 4 As shown, the defrost operation control logic of the heating unit in this embodiment consists of 20 steps from S0 to S19. The following is a detailed description of each step:

[0059] Step S0: Heating operation starts, then enters step S1;

[0060] Step S1: operate in normal heating mode, then proceed to step S2;

[0061] Step S2: The compressor frequency Fc and the throttle mechanism throttling degree Pv operate in normal mode, and then proceed to step S3;

[0062] Step S3: Detect the refrigerant temperature in the outdoor heat exchanger, and then proceed to step S4;

[0063] Step S4: Detect whether the outdoor heat exchanger needs to be defrosted. If the outdoor heat exchanger needs to be defrosted, proceed to step S5; otherwise, proceed to step S6;

[0064] Step S5: Detect the heat medium temperature Tr, and then proceed to step S7;

[0065] Step S6: Determine whether the unit has received a shutdown signal. If so, proceed to step S17; otherwise, proceed to step S1.

[0066] Step S7: Determine whether there is a risk of freezing of the refrigerant-liquid heat medium heat exchanger during the unit defrosting process. If there is a risk of freezing, proceed to step S8; otherwise, proceed to step S10.

[0067] Step S8: The unit operates in the pre-defrost mode, and then enters step S9;

[0068] Step S9: Adjust the compressor operating frequency Fc and the throttling degree Pv of the throttling mechanism according to the pre-defrost mode, and then enter step S7; in step S9, by reducing the compressor frequency and the throttling degree of the throttle valve, the compressor suction pressure is increased, the pressure of the refrigerant in the refrigerant-water heat exchanger is increased, and then the refrigerant temperature in the refrigerant-water heat exchanger is increased, and finally the purpose of increasing the temperature of the heat medium in the refrigerant-water heat exchanger is achieved, thereby achieving the pre-defrost effect.

[0069] Step S10: The unit operates in normal defrosting mode, and then proceeds to step S11;

[0070] Step S11: Adjust the compressor operating frequency Fc and the throttling degree Pv of the throttling mechanism according to the normal defrosting mode, and then enter step S12:

[0071] Step S12: Determine whether the unit has completed the defrosting operation. If the defrosting operation is completed, proceed to step S16; otherwise, proceed to step S13;

[0072] Step S13: Determine whether the unit has received a shutdown signal. If so, proceed to step SS14; otherwise, proceed to step S15.

[0073] Step S14: Shutdown signal recording parameter g=1, then proceed to step S10;

[0074] Step S15: Shutdown signal recording parameter g=0, then go to step S10;

[0075] Step S17: Determine whether the shutdown signal recording parameter g is equal to 1. If g=1, proceed to step S18; otherwise, proceed to step S1.

[0076] Step S18: The unit is shut down, and then the process goes to step S19;

[0077] Step S19: End the program.

[0078] Figure 5 This is the defrost control timing diagram a of the heating unit involved in the present invention. When the unit does not need to enter the pre-defrost stage during the defrost process, it is in accordance with Figure 5 Controlled by the timing diagram in .

[0079] like Figure 5As shown in the figure, the entire control process includes 5 time nodes: t0, t1, t2, t3, and t4.

[0080] like Figure 5 As shown, the stage from t0 to t1 is the heating operation stage, the stage from t1 to t4 is the normal defrosting operation stage, and the stage after t4 is the heating operation stage.

[0081] like Figure 5 As shown, the normal defrost operation stage from t1 to t4 includes four time nodes, namely t1, t2, t3 and t4. The stage from t1 to t2 is the transition stage from the heating operation stage to the normal defrost operation stage, and the stage from t3 to t4 is the transition stage from the normal defrost operation stage to the normal heating operation stage.

[0082] like Figure 5 As shown in the figure, the control method of the compressor operating frequency is:

[0083] The stage from t0 to t1 and the stage after t4 are controlled according to the heating operation mode;

[0084] The stages t1 to t2 and t3 to t4 are controlled according to the defrost switching control mode, and the compressor frequency can be directly shut down or switched to a lower operating frequency;

[0085] The stages t2 to t3 are controlled according to the normal defrosting operation mode.

[0086] like Figure 3 As shown, the control mode of the throttling mechanism is:

[0087] The stage from t0 to t1 and the stage after t4 are controlled according to the heating operation mode;

[0088] The operation from t1 to t4 is in normal defrosting mode.

[0089] like Figure 5 As shown, the control mode of the four-way reversing valve is:

[0090] The stages from t0 to t2 and after t3 are controlled according to the heating operation mode;

[0091] The t2~t3 stages are controlled according to the normal defrosting operation mode, and the throttling degree is adjusted to the minimum.

[0092] Figure 6 This is the defrost control timing diagram b of the heating unit involved in the present invention. When the unit needs to enter the pre-defrost stage during the defrost process, it is in accordance with Figure 6 Controlled by the timing diagram in .

[0093] like Figure 6 As shown in the figure, the entire control process includes 6 time nodes: t0, t1, t2, t3, t4, and t5.

[0094] like Figure 6 As shown, the stage from t0 to t1 is the heating operation stage, the stage from t0 to t2 is the pre-defrosting operation stage, the stage from t2 to t5 is the normal defrosting operation stage, and the stage after time point t5 is the heating operation stage.

[0095] like Figure 6 As shown, the normal defrost operation stage from t2 to t5 includes four time nodes, namely t2, t3, t4 and t5. The stage from t2 to t3 is the transition stage from the heating operation stage to the normal defrost operation stage, and the stage from t4 to t5 is the transition stage from the normal defrost operation stage to the normal heating operation stage.

[0096] like Figure 6 As shown in the figure, the control method of the compressor operating frequency is:

[0097] The stage from t0 to t1 and the stage after t5 are controlled according to the heating operation mode;

[0098] The stage t1 to t2 is controlled according to the pre-defrost control mode, and its compressor frequency is lower than that of the stage t0 to t1;

[0099] The stages t2 to t3 and t4 to t5 are controlled according to the defrost switching control mode, and the compressor frequency can be directly shut down or switched to a lower operating frequency;

[0100] The stages t3 to t4 are controlled according to the normal defrosting operation mode.

[0101] like Figure 6 As shown, the control mode of the throttling mechanism is:

[0102] The stage from t0 to t1 and the stage after t5 are controlled according to the heating operation mode;

[0103] During the t1 to t5 stages, the machine operates in the normal defrosting mode and the throttling degree is adjusted to the minimum.

[0104] like Figure 6 As shown, the control mode of the four-way reversing valve is:

[0105] The stages from t0 to t3 and after t4 are controlled in heating mode;

[0106] The stages t3 to t4 are controlled according to the normal defrosting operation mode.

[0107] The above method can select whether to perform a pre-defrost operation based on the actual defrost operation of the heating unit during use. When the heating medium temperature is close to the freezing point of the heating medium or the refrigerant temperature in the outdoor heat exchanger is low, performing a pre-defrost operation on the unit before normal defrosting can effectively improve the unit's reliability during defrost operation and prevent the refrigerant-liquid heating medium heat exchanger from freezing and damaging during defrost operation.

[0108] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0109] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A defrost control method for a heating unit, for use in a heating unit, wherein the heating unit includes a four-way valve, which can be switched between a first conduction direction and a second conduction direction. When the four-way valve is switched in the first conduction direction, the refrigerant is heated by an outdoor heat exchanger and then heated and pressurized by a compressor before entering the refrigerant-liquid heat medium heat exchanger for heat exchange; when the four-way valve is switched in the second conduction direction, the higher-temperature refrigerant flowing out of the refrigerant-liquid heat medium heat exchanger is heated and pressurized by the compressor before flowing into the outdoor heat exchanger for heat exchange; characterized in that: The method comprises: In the heating mode, obtaining the temperature Tc of the refrigerant in the outdoor heat exchanger, and determining whether the outdoor heat exchanger needs to be defrosted according to the temperature Tc of the refrigerant in the outdoor heat exchanger; When it is determined that defrosting is required, the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger is obtained, and based on the relationship between the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger and the heat medium freezing temperature Trf, and / or the relationship between the refrigerant temperature Tc in the outdoor heat exchanger and the heat medium freezing temperature Trf, it is determined whether there is a risk of freezing of the refrigerant-liquid heat medium heat exchanger during the defrost process; If it is determined that there is no freezing risk during defrosting, the system enters normal defrosting mode, and the four-way valve is turned on in the second conduction direction. If it is determined that there is a risk of freezing during defrosting, the four-way valve maintains conduction in the first conduction direction, and adjusts the compressor operating frequency Fc and the throttling degree of the throttling mechanism to the pre-defrost mode until it is determined that there is no risk of freezing during defrosting and enters the normal defrost mode; The frequency of the compressor in the pre-defrost mode is lower than that in the heating mode, and the throttling degree of the throttle valve in the pre-defrost mode is lower than that in the heating mode.

2. The defrost control method for a heating unit according to claim 1, characterized in that: The determining whether the outdoor heat exchanger needs to be defrosted according to the temperature Tc of the refrigerant in the outdoor heat exchanger includes: The temperature Tc of the refrigerant in the outdoor heat exchanger is compared with a preset defrost temperature. When the temperature Tc of the refrigerant in the outdoor heat exchanger reaches the preset defrost temperature, it is determined that defrosting is required.

3. The defrosting control method for a heating unit according to claim 1, characterized in that: The determining whether there is a freezing risk of the refrigerant-liquid heat medium heat exchanger during the defrost process based on the relationship between the heat medium temperature Tr in the refrigerant-liquid heat medium heat exchanger and the heat medium freezing temperature Trf, and / or the relationship between the refrigerant temperature Tc in the outdoor heat exchanger and the heat medium freezing temperature Trf, includes: The heat medium freezing temperature Trf is obtained. When the difference between the heat medium temperature Tr and the heat medium freezing temperature Trf in the refrigerant-liquid heat medium heat exchanger reaches a preset value, and / or the difference between the refrigerant temperature Tc and the heat medium freezing temperature Trf in the outdoor heat exchanger reaches a preset value, it is determined that there is a freezing risk during defrosting.

4. The defrost control method for a heating unit according to claim 3, characterized in that: It also includes determining whether the pre-defrost mode has been entered during this operation. If so, determining whether there is a freezing risk based on the first group of Tr-Trf values ​​and / or Tc-Trf; if not, determining whether there is a freezing risk based on the second group of Tr-Trf values ​​and / or Tc-Trf.

5. The defrost control method for a heating unit according to claim 1, characterized in that: In the pre-defrost mode, the throttling degree of the throttling mechanism is adjusted to the minimum throttling degree.

6. The defrost control method for a heating unit according to claim 1, characterized in that: In the heating mode, the compressor frequency is adjusted according to a preset mode. When switching from the heating mode to the pre-defrost mode, the compressor frequency of the switched pre-defrost mode is lower than the compressor frequency of the current moment in the heating mode at the time of switching.

7. The defrost control method for a heating unit according to claim 1, characterized in that: The method further includes, after the unit operates in a normal defrost mode, determining whether the unit has completed defrosting; if it is determined that defrosting is completed, adjusting the four-way valve to conduct in a first conduction direction, and the unit operates in a heating mode.

8. A heating unit, characterized in that: The method according to any one of claims 1 to 7 is applied.

9. The heating unit according to claim 8, characterized in that: It includes a refrigerant temperature sensor for detecting the refrigerant temperature of the outdoor heat exchanger, and a heat medium temperature sensor for detecting the heat medium temperature in the refrigerant-liquid heat medium heat exchanger.

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