A method for controlling oil return in a heat pump system

Abstract

An oil return control method of a heat pump system, when operating, comprising the following steps: step one, the air conditioning system is powered on and runs, and enters step two; step two, the central controller judges whether the current running mode is a defrosting mode, when it is yes, enters step thirteen, and when it is no, enters step three; step three, the central controller calculates the current compression ratio Pcr, and has Pcr=(Hp+A) / (Lp+A), and enters step four; Hp is the current high pressure value of the compressor obtained through a high pressure sensor, and the unit is kgf; Lp is the current low pressure value of the compressor obtained through a low pressure sensor, and the unit is kgf; A is a constant, A=1 kgf; step four, the central controller judges whether Pcr<2.2 is established, when it is yes, enters step five, and when it is no, enters step nine; step five, the central controller detects and obtains T0, T1 and T3, and enters step six.

Description

TECHNICAL FIELD

[0001] The application relates to an oil return control method of a heat pump system. BACKGROUND

[0002] A heat recovery air-cooled heat pump cold and hot water machine is disclosed in Chinese patent document No. CN 104913556 A, which is published on September 16, 2015, and the heat recovery air-cooled heat pump cold and hot water machine comprises a hot water side heat exchanger, an air side heat exchanger, an air conditioner side heat exchanger and a compressor. The oil return control method comprises the following steps: judging whether the heat recovery air-cooled heat pump cold and hot water machine meets an oil return condition; if it is judged that the heat recovery air-cooled heat pump cold and hot water machine meets the oil return condition, obtaining a current operation mode of the heat recovery air-cooled heat pump cold and hot water machine; and controlling the heat recovery air-cooled heat pump cold and hot water machine to perform an oil return action according to the current operation mode of the heat recovery air-cooled heat pump cold and hot water machine. When the heat recovery air-cooled heat pump cold and hot water machine meets any one of the following conditions, it is judged that the heat recovery air-cooled heat pump cold and hot water machine meets the oil return condition: 1) the heat recovery air-cooled heat pump cold and hot water machine is powered on for the first time and the heat recovery air-cooled heat pump cold and hot water machine accumulatively operates for a first preset time; 2) the compressor continuously operates for a second preset time; 3) the heat recovery air-cooled heat pump cold and hot water machine accumulatively operates for a third preset time; and 4) the cumulative start-up times of the compressor reach a preset number of times. The oil return control method is not ideal and needs to be improved. SUMMARY

[0003] The purpose of the present application is to provide a safe and reliable oil return control method of a heat pump system to overcome the shortcomings in the prior art.

[0004] An oil return control method of a heat pump system is designed according to the purpose, which is characterized by comprising a variable frequency compressor, a water side heat exchanger, a tube-fin heat exchanger and a variable frequency fan. The high pressure outlet and the low pressure outlet of the variable frequency compressor are connected to the water side heat exchanger and the tube-fin heat exchanger through an electromagnetic four-way valve respectively. The water side heat exchanger is connected to the tube-fin heat exchanger through a throttling device. The high pressure outlet of the variable frequency compressor is provided with a high pressure sensor. The low pressure outlet of the variable frequency compressor is provided with a low pressure sensor. The water inlet pipe of the water side heat exchanger is provided with a water inlet temperature sensor. The water outlet pipe of the water side heat exchanger is provided with a water outlet temperature sensor. The tube-fin heat exchanger is provided with a refrigerant temperature sensor. The central controller of the heat pump system is electrically connected to the variable frequency fan, the variable frequency compressor, the refrigerant temperature sensor, the high pressure sensor and the low pressure sensor. The operation comprises the following steps:

[0005] Step 1: the air conditioning system is powered on and operated, and step 2 is entered.

[0006] Step two, the central controller judges whether the current running mode is defrosting mode, when it is yes, step thirteen is entered, when it is no, step three is entered;

[0007] Step three, the central controller calculates the current compression ratio Pcr, Pcr=(Hp+A) / (Lp+A), step four is entered; Hp is the current high pressure value of the compressor obtained by the high pressure sensor, unit is kgf, Lp is the current low pressure value of the compressor obtained by the low pressure sensor, unit is kgf; A is a constant, A=1 kgf;

[0008] Step four, the central controller judges whether Pcr<2.2 is true, when it is yes, step five is entered, when it is no, step nine is entered;

[0009] Step five, the central controller detects and obtains T0, T1 and T3, step six is entered; wherein, T0 is the current outlet water temperature of the water side heat exchanger obtained by the outlet water temperature sensor, T1 is the current inlet water temperature of the water side heat exchanger obtained by the inlet water temperature sensor, T3 is the current refrigerant temperature of the tube-fin heat exchanger obtained by the refrigerant temperature sensor;

[0010] Step six, the central controller judges whether the current running mode is refrigeration mode, when it is yes, step seven is entered, when it is no, step fifteen is entered;

[0011] Step seven, the central controller judges whether T0>T1 and T3 decreases with the increase of frequency are true, when it is yes, step eight is entered, when it is no, step fourteen is entered;

[0012] Step eight, the central controller judges the electromagnetic four-way valve fault, the central controller issues a stop command;

[0013] Step nine, the central controller judges whether Pcr>14 is true, when it is yes, step ten is entered, when it is no, step thirteen is entered;

[0014] Step ten, the central controller controls the variable frequency fan to increase the speed, step eleven is entered; the variable frequency fan controlled by the central controller increases the speed in the range of 80-150 rpm each time;

[0015] Step eleven, the central controller judges whether the current speed of the variable frequency fan is the highest speed, when it is yes, step twelve is entered, when it is no, step fourteen is entered;

[0016] Step twelve, the central controller controls the variable frequency compressor to decrease the frequency, step fourteen is entered; the variable frequency compressor controlled by the central controller decreases the frequency in the range of 3-10 Hz each time;

[0017] Step thirteen, the current running state is maintained, step two is entered;

[0018] Step fourteen, through an energy adjustment cycle, enter step two; the energy adjustment cycle is in the range of 30-60 seconds;

[0019] Step fifteen, the central controller judges whether the current operation mode is the heating mode, when it is yes, enter step sixteen, when it is no, enter step seventeen;

[0020] Step sixteen, the central controller judges whether T0 < T1 and T3 increases with the frequency rise is true, when it is no, enter step fourteen, when it is yes, enter step eight;

[0021] Step seventeen, the central controller controls the variable frequency fan to reduce the speed, enter step eighteen; the central controller controls the variable frequency fan to reduce the speed in the range of 80-150 rpm each time;

[0022] Step eighteen, the central controller judges whether the current speed of the variable frequency fan is the lowest speed, when it is yes, enter step nineteen, when it is no, enter step fourteen;

[0023] Step nineteen, the central controller controls the variable frequency compressor to increase the frequency, enter step fourteen; the central controller controls the variable frequency compressor to increase the frequency in the range of 3-10 Hz each time.

[0024] The technical scheme of the present application can effectively avoid the influence of the system oil return defect on the normal lubrication requirement of the variable frequency compressor, and ensure the normal operation of the variable frequency compressor.

[0025] The present application increases the oil return control of the system from the control of the compression ratio of the variable frequency compressor of the control system and the failure warning of the electromagnetic four-way valve, fills the gap of the existing oil return scheme, and can better ensure the normal operation of the system.

[0026] In summary, the present application has the characteristics of reliable oil return and stable operation. BRIEF DESCRIPTION OF DRAWINGS

[0027] Fig. 1 It is a structural schematic diagram of an embodiment of the present application.

[0028] Fig. 2 It is a control block diagram of the present application.

[0029] In the figure: 1 is a variable frequency compressor, 2 is an electromagnetic four-way valve, 3 is a water-side heat exchanger, 4 is a tube-fin heat exchanger, and 5 is a throttling device. DETAILED DESCRIPTION

[0030] The present application will be further described below in combination with the drawings and embodiments.

[0031] Reference Figs. 1-2The application discloses an oil return control method of a heat pump system, and relates to the technical field of heat pump systems.

[0032] The operation comprises the following steps:

[0033] Step one, the air conditioning system is powered on and runs, and step two is entered;

[0034] Step two, the central controller judges whether the current running mode is a defrosting mode, when the answer is yes, step thirteen is entered, and when the answer is no, step three is entered;

[0035] Step three, the central controller calculates the current compression ratio Pcr, and step four is entered; the compression ratio Pcr=(Hp+A) / (Lp+A), Hp is the current high-pressure value of the compressor obtained through the high-pressure sensor, the unit is kgf, Lp is the current low-pressure value of the compressor obtained through the low-pressure sensor, the unit is kgf, and A is a constant, A=1 kgf.

[0036] When working, the heat pump system controls the compression ratio Pcr in real time, the reasonable range value of the compression ratio Pcr is Pcr=2.2-14, the reasonable range value of the compression ratio Pcr is different for different compressors, and the parameters can be set respectively.

[0037] When the compression ratio Pcr is less than 2.2, the heat pump system will have oil return problems, and oil shortage will occur; when the compression ratio Pcr is greater than 14, the heat pump system will be in an over-limit running state, which is an unsafe running state, and the heat pump system will be damaged.

[0038] Step four, the central controller judges whether Pcr<2.2 is true, when the answer is yes, step five is entered, and when the answer is no, step nine is entered;

[0039] Step five, the central controller detects and obtains T0, T1 and T3, and step six is entered; wherein T0 is the current water outlet temperature of the water-side heat exchanger 3 obtained through the water outlet temperature sensor, T1 is the current water inlet temperature of the water-side heat exchanger 3 obtained through the water inlet temperature sensor, and T3 is the current refrigerant temperature of the tube-fin heat exchanger 4 obtained through the refrigerant temperature sensor;

[0040] Step six, the central controller determines whether the current operating mode is the refrigeration mode, when it is yes, step seven is entered, when it is no, step fifteen is entered;

[0041] Step seven, the central controller determines whether T0>T1 and T3 decreases with the increase of the frequency, when it is yes, step eight is entered, when it is no, step fourteen is entered;

[0042] In the determination of whether T3 decreases with the increase of the frequency, two T3 corresponding to the current frequency of the variable frequency compressor in the previous and subsequent energy adjustment periods are recorded, and then the relationship between the two T3 and the frequency is compared. For example, in the previous energy adjustment period, the current frequency of the variable frequency compressor is 45 Hz, and the corresponding T3 is 62℃. In the previous energy adjustment period, the current frequency of the variable frequency compressor is 52 Hz, and the corresponding T3 is 64℃. Therefore, from 45 Hz to 52 Hz, 62℃<64℃ increases with the increase of the frequency, and thus T3 is not decreased, and thus it is not established. The same calculation is also performed in step sixteen.

[0043] In the refrigeration mode, the central controller detects that the compression ratio Pcr<2.2, and satisfies 1) TO>T1; 2) T3 decreases with the increase of the frequency of the compressor, and then the central controller determines that the electromagnetic four-way valve has failed, the heat pump system reports the corresponding fault and stops.

[0044] Step eight, the central controller determines the failure of the electromagnetic four-way valve, and the central controller issues a stop command;

[0045] Step nine, the central controller determines whether Pcr>14 is established, when it is yes, step ten is entered, when it is no, step thirteen is entered;

[0046] Step ten, the central controller controls the variable frequency fan to increase the speed, and step eleven is entered. The central controller controls the variable frequency fan to increase the speed by a range of 80-150 rpm each time.

[0047] When the compression ratio Pcr of the heat pump system is greater than 14, the central controller controls the variable frequency fan to increase the speed by an energy adjustment period as a regulation period, and by a range of 80-150 rpm, so as to reduce the Pcr value, so that the heat pump system satisfies Pcr<14.

[0048] Step eleven, the central controller determines whether the current speed of the variable frequency fan is the highest speed, when it is yes, step twelve is entered, when it is no, step fourteen is entered;

[0049] Step twelve, the central controller controls the variable frequency compressor to decrease the frequency, and step fourteen is entered. The central controller controls the variable frequency compressor to decrease the frequency by a range of 3-10 Hz each time.

[0050] When the current rotating speed of the variable frequency fan is increased to the highest rotating speed, and the Pcr requirement of the heat pump system cannot be met, the central controller starts to start the variable frequency compressor to perform the frequency reduction action. That is, the energy regulation period is taken as a regulation period, and the frequency is reduced by 3-10 Hz to meet the oil return requirement of the heat pump system.

[0051] The actual operating frequency of the variable frequency compressor after frequency reduction cannot be lower than the minimum operating frequency of the heat pump system.

[0052] In practice, the frequency reduction can be performed by 5 Hz.

[0053] Step thirteen, keep the current operating state, and enter step two.

[0054] When the compression ratio of the heat pump system is 2.2≤Pcr≤14, the heat pump system keeps the current operating state and does not perform additional control.

[0055] Step fourteen, after an energy regulation period, enter step two; the energy regulation period is 30-60 seconds.

[0056] Step fifteen, the central controller determines whether the current operating mode is the heating mode, when it is yes, enter step sixteen, and when it is no, enter step seventeen.

[0057] Step sixteen, the central controller determines whether T0

[0058] In the heating mode, the central controller detects that the compression ratio Pcr is less than 2.2, and meets 1) TO

[0059] Step seventeen, the central controller controls the variable frequency fan to reduce the rotating speed, and enters step eighteen; the central controller controls the variable frequency fan to reduce the rotating speed by 80-150 rpm each time.

[0060] The heat pump system controls the variable frequency fan to reduce the speed by 80-150 rpm in an energy regulation period to increase the Pcr value, so that the heat pump system can meet Pcr>2.2.

[0061] Step eighteen, the central controller determines whether the current rotating speed of the variable frequency fan is the minimum rotating speed, when it is yes, enter step nineteen, and when it is no, enter step fourteen.

[0062] When the current rotating speed of the variable frequency fan is reduced to the minimum rotating speed, and the Pcr requirement of the heat pump system cannot be met, the central controller starts to start the variable frequency compressor to perform the frequency increasing action.

[0063] Step nineteen, the central controller controls the variable frequency compressor to perform frequency increasing, and enters step fourteen.

[0064] The actual operating frequency of the heat pump system after frequency increasing cannot be greater than the maximum operating frequency of the heat pump system.

[0065] Based on the above control logic design optimization, the present application can better handle problems that cannot be solved by conventional logic, and can solve the problem of lack of oil return of the variable frequency compressor of the heat pump system as much as possible.

[0066] In the description of the present application, it should be understood that the orientations or positional relationships indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application, and 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 technical features indicated.

[0067] The basic principles and main features of the present application and the advantages of the present application have been shown and described above. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application, and various changes and improvements can be made to the present application without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for controlling the oil return of a heat pump system, characterized in that: The system includes a variable frequency compressor (1), a water-side heat exchanger (3), a tube-fin heat exchanger (4), and a variable frequency fan. The high-pressure outlet and low-pressure outlet of the variable frequency compressor (1) are connected to the water-side heat exchanger (3) and the tube-fin heat exchanger (4) respectively through an electromagnetic four-way valve (2). The water-side heat exchanger (3) is connected to the tube-fin heat exchanger (4) through a throttle (5). A high-pressure sensor is installed at the high-pressure outlet of the variable frequency compressor (1), and a low-pressure sensor is installed at the low-pressure outlet of the variable frequency compressor (1). An inlet water temperature sensor is installed on the inlet pipe of the water-side heat exchanger (3), and an outlet water temperature sensor is installed on the outlet pipe of the water-side heat exchanger (3). A refrigerant temperature sensor is installed on the tube-fin heat exchanger (4). The central controller of the heat pump system is electrically connected to the variable frequency fan, the variable frequency compressor (1), the refrigerant temperature sensor, the high-pressure sensor, and the low-pressure sensor respectively. The operation includes the following steps: Step 1: Power on and run the air conditioning system; proceed to Step 2. Step 2: The central controller determines whether the current operating mode is defrosting mode. If it is, proceed to step thirteen; if it is not, proceed to step 3. Step 3: The central controller calculates the current compression ratio Pcr, which is Pcr = (Hp + A) / (Lp + A), and then proceeds to step 4; Hp is the current high pressure value of the compressor obtained by the high pressure sensor, in kgf; Lp is the current low pressure value of the compressor obtained by the low pressure sensor, in kgf; A is a constant, A = 1 kgf; Step 4: The central controller determines whether Pcr < 2.2 is true. If it is true, proceed to step 5; if it is false, proceed to step 9. Step 5: The central controller detects and obtains T0, T1 and T3, and proceeds to step 6; where T0 is the current outlet water temperature of the water-side heat exchanger (3) obtained by the outlet water temperature sensor, T1 is the current inlet water temperature of the water-side heat exchanger (3) obtained by the inlet water temperature sensor, and T3 is the current refrigerant temperature of the tube-fin heat exchanger (4) obtained by the refrigerant temperature sensor. Step 6: The central controller determines whether the current operating mode is cooling mode. If it is, proceed to step 7; if it is not, proceed to step 15. Step 7: The central controller determines whether T0 > T1 and T3 decreases as the frequency increases. If it is true, proceed to step 8; if it is not true, proceed to step 14. Step 8: The central controller determines that the solenoid four-way valve is faulty and issues a stop command. Step 9: The central controller determines whether Pcr > 14 is true. If it is true, proceed to step 10; if it is false, proceed to step 13. Step 10: The central controller controls the variable frequency fan to increase its speed, proceeding to step 11; the central controller controls the variable frequency fan to increase its speed by 80-150 rpm each time. Step 11: The central controller determines whether the current speed of the variable frequency fan is the maximum speed. If it is, proceed to step 12; if it is not, proceed to step 14. Step 12: The central controller controls the variable frequency compressor to reduce its frequency, proceeding to step 14; the range of frequency reduction for each step is 3-10Hz. Step 13: Maintain the current running state and proceed to Step 2; Step fourteen: After one energy regulation cycle, proceed to step two; the energy regulation cycle ranges from 30 to 60 seconds. Step 15: The central controller determines whether the current operating mode is heating mode. If it is, proceed to step 16; if it is not, proceed to step 17. Step 16: The central controller determines whether the condition T0 < T1 and T3 increases with increasing frequency is true. If it is not true, proceed to step 14; if it is true, proceed to step 8. Step 17: The central controller controls the variable frequency fan to reduce its speed, proceeding to step 18; the range of speed reduction for each variable frequency fan controlled by the central controller is 80-150 rpm. Step 18: The central controller determines whether the current speed of the variable frequency fan is the minimum speed. If it is, proceed to step 19; if it is not, proceed to step 14. Step 19: The central controller controls the variable frequency compressor to increase its frequency, proceeding to step 14; the central controller controls the variable frequency compressor to increase its frequency in a range of 3 to 10 Hz each time.

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