Accurate method for judging defrosting of variable frequency heat pump water heaters for heating

Abstract

The present invention relates to a defrosting accurate judgment method for a variable frequency heat pump water heater for heating, characterized in that the defrosting judgment steps are as follows: (a) when the variable frequency heat pump is running and the outdoor heat exchanger has not started to frost, a relationship formula I is established in the controller for the change of the frost-free opening S1 of the electronic expansion valve with the outdoor ambient temperature Tw and the operating frequency f of the variable frequency compressor; (b) after the variable frequency heat pump has been running for a period of time, a frost layer begins to form on the surface of the fin of the outdoor heat exchanger, and a relationship formula II is established in the controller for the change of the defrosting opening S2 of the electronic expansion valve with the outdoor ambient temperature Tw and the operating frequency f of the variable frequency compressor; (c) during a start-stop operation cycle of the variable frequency heat pump, the controller records the refrigerant superheat ΔT of the outdoor heat exchanger at this time, starts to judge whether to defrost, and operates according to step (d); (d) the frequency f of the variable frequency compressor is kept unchanged, and the real-time opening S of the electronic expansion valve is reduced to S2, etc. for defrosting judgment. It does not need to add an additional frost layer thickness detection component and a control component, thereby improving the accuracy of defrosting judgment.

Description

Technical Field

[0001] The invention relates to a method for accurately judging defrosting of a variable frequency heat pump water heater for heating, and in particular to a method for judging defrosting of a variable frequency heat pump water heater for heating which adopts throttling of an electronic expansion valve. Background Art

[0002] As a highly efficient and energy-saving hot water product, variable frequency heat pump water heaters are widely used for winter heating. However, when operating in winter, the outdoor heat exchanger needs to be defrosted from time to time. Determining when defrosting is needed is a key technical issue for variable frequency heat pump water heaters.

[0003] At present, the most commonly used method is timed defrosting, that is, the variable frequency heat pump compressor starts to defrost after a fixed period of operation; due to the large changes in the relative humidity of the outdoor environment, this fixed operation time defrosting method may have the problem of defrosting when there is no frost, when there is little frost, or when the frost layer is very thick. There is also a defrosting method that directly or indirectly measures the thickness of the frost layer. This defrosting method requires the variable frequency heat pump system to add some necessary frost thickness detection devices, which increases the equipment cost, and the reliability of frost thickness judgment needs to be improved; therefore, it is necessary to invent a simple and reliable defrosting judgment method. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for accurately judging the defrosting of a variable frequency heat pump water heater for heating. The method can accurately judge the time when the variable frequency heat pump system starts to enter the defrosting state, and does not require additional frost layer thickness detection components and control components, thereby improving the accuracy of defrost judgment.

[0005] In order to achieve the above-mentioned object, the present invention is implemented as follows: it is a defrosting accurate judgment method for a variable frequency heat pump water heater for heating, characterized in that the variable frequency heat pump water heater includes a variable frequency compressor, a heating heat exchanger, an electronic expansion valve, an inlet temperature sensor, an outdoor heat exchanger, an outdoor ambient temperature sensor, a controller and an outlet temperature sensor; the inlet temperature sensor is arranged at the refrigerant inlet of the outdoor heat exchanger, and the temperature detected by the inlet temperature sensor is the refrigerant inlet temperature Tj of the outdoor heat exchanger; the outlet temperature sensor is arranged at the refrigerant outlet of the outdoor heat exchanger, and the temperature detected by the outlet temperature sensor is the refrigerant outlet temperature Tc of the outdoor heat exchanger; the temperature detected by the outdoor ambient temperature sensor is the outdoor ambient temperature Tw;

[0006] The defrost judgment steps are as follows:

[0007] (a) When the variable frequency heat pump is running and the outdoor heat exchanger has not started to frost, the test method is used to test the outdoor heat exchanger at different outdoor ambient temperatures T wUnder different operating frequencies f of the variable frequency compressor, the corresponding frost-free opening S1 of the electronic expansion valve is obtained, and the relationship between the frost-free opening S1 of the electronic expansion valve and the outdoor ambient temperature Tw and the operating frequency f of the variable frequency compressor is established in the controller: S1=g(Tw,f)

[0008] (b) After the variable frequency heat pump has been running for a period of time, frost begins to form on the surface of the outdoor heat exchanger fins. When the frost layer on the surface of the outdoor heat exchanger fins reaches the set thickness and needs to be defrosted, the test method is used to test the frost layer at different outdoor ambient temperatures T w Under different operating frequencies f of the variable frequency compressor (1), the corresponding defrost opening S2 of the electronic expansion valve is obtained, and a relation II between the defrost opening S2 of the electronic expansion valve and the outdoor ambient temperature Tw and the operating frequency f of the variable frequency compressor is established in the controller: S2=h(Tw,f);

[0009] (c) In a start-stop operation cycle of the variable frequency heat pump, the controller calculates the frost-free opening S1 and defrost opening S2 of the electronic expansion valve corresponding to the outdoor ambient temperature Tw and the variable frequency compressor operating frequency f according to the relationship formula I and the relationship formula II. When the real-time opening S of the electronic expansion valve is 0.1 (S1- S2) + S2≤S≤0.2 (S1- S2) + S2, the controller records the refrigerant superheat ΔT of the outdoor heat exchanger at this time, that is, ΔT=Tc-Tj, and starts to judge whether to defrost, and operates according to step (d);

[0010] (d) Keep the frequency f of the variable frequency compressor unchanged and reduce the real-time opening S of the electronic expansion valve to S2. If the real-time superheat of the refrigerant in the outdoor heat exchanger ΔT2 ≥ ΔT + 2°C, it indicates that the controller's defrost judgment is correct. The opening control mode of the electronic expansion valve is restored to the control mode before the defrost judgment is started and continues to operate. When the actual opening S of the electronic expansion valve is the same as the defrost opening S2 calculated by equation II, the heat pump system starts to defrost. If the real-time superheat of the refrigerant in the outdoor heat exchanger ΔT2 < ΔT + 2°C, the variable frequency heat pump system defrosts according to the conventional timed defrost mode.

[0011] In the technical solution, the frost layer in step (b) is set to have a thickness value ranging from 0.2 to 1.2 mm.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] (1) It can accurately judge the time when the variable frequency heat pump system starts to enter the defrosting state, and the performance of the variable frequency heat pump system is improved;

[0014] (2) The variable frequency heat pump system does not require additional frost thickness detection components and control components, and its structure is simpler. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural principle diagram of the heat pump system implemented by the present invention. DETAILED DESCRIPTION

[0016] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0017] like Figure 1 As shown, it is a defrosting accurate judgment method for a variable frequency heat pump water heater for heating, the variable frequency heat pump water heater comprises a variable frequency compressor 1, a heating heat exchanger 2, an electronic expansion valve 3, an inlet temperature sensor 4, an outdoor heat exchanger 5, an outdoor environment temperature sensor 6, a controller 7 and an outlet temperature sensor 8; the inlet temperature sensor 4 is arranged at the refrigerant inlet of the outdoor heat exchanger 5, and the temperature detected by the inlet temperature sensor 4 is the refrigerant inlet temperature Tj of the outdoor heat exchanger 5; the outlet temperature sensor 8 is arranged at the refrigerant outlet of the outdoor heat exchanger 5, and the temperature detected by the outlet temperature sensor 8 is the refrigerant outlet temperature Tc of the outdoor heat exchanger 5; the temperature detected by the outdoor environment temperature sensor 6 is the outdoor environment temperature Tw;

[0018] The defrost judgment steps are as follows:

[0019] (a) When the variable frequency heat pump is running but the outdoor heat exchanger 5 has not started to frost, the outdoor environment temperature T w Under different operating frequencies f of the variable frequency compressor 1, the corresponding frost-free opening S1 of the electronic expansion valve 3 is obtained, and the relationship between the frost-free opening S1 of the electronic expansion valve 3 and the outdoor ambient temperature Tw and the operating frequency f of the variable frequency compressor 1 is established in the controller 7: S1=g(Tw,f)

[0020] (b) After the variable frequency heat pump has been running for a period of time, frost begins to form on the surface of the fins of the outdoor heat exchanger 5. Through the test method, when the frost layer on the surface of the fins of the outdoor heat exchanger 5 reaches a set thickness and needs to be defrosted, the corresponding defrost opening S2 of the electronic expansion valve 3 is obtained, and a relationship II is established in the controller 7 to show that the defrost opening S2 of the electronic expansion valve 3 changes with the outdoor ambient temperature Tw and the operating frequency f of the variable frequency compressor 1: S2=h(Tw,f); in actual application, the manufacturer sets the defrost thickness of the fin surface of the outdoor heat exchanger 5 according to the performance of the variable frequency heat pump. The set thickness value of the frost layer can be selected within the range of 0.2 to 1.2 mm, and the optimal frost layer thickness is 0.7 mm.

[0021] (c) In a start-stop operation cycle of the variable frequency heat pump, the controller 7 calculates the frost-free opening S1 and defrost opening S2 of the electronic expansion valve 3 corresponding to the outdoor ambient temperature Tw and the operating frequency f of the variable frequency compressor 1 according to the relationship formula I and the relationship formula II. When the real-time opening S of the electronic expansion valve 3 is 0.1 (S1- S2) + S2≤S≤0.2 (S1- S2) + S2, the controller 7 records the refrigerant superheat ΔT = Tc-Tj of the outdoor heat exchanger 5 at this time, starts to judge whether to defrost, and operates according to step (d);

[0022] (d) Keep the frequency f of the variable frequency compressor 1 unchanged, and reduce the real-time opening S of the electronic expansion valve 3 to the defrosting opening S2. If the real-time superheat of the refrigerant in the outdoor heat exchanger 5 ΔT2 ≥ ΔT + 2°C, it means that the defrosting judgment of the controller 7 is correct. The opening control mode of the electronic expansion valve 3 is restored to the control mode before the defrosting judgment is started and continues to operate. When the actual opening S of the electronic expansion valve 3 is the same as the defrosting opening S2 calculated according to the relationship II, the heat pump system starts to defrost; if the real-time superheat of the refrigerant in the outdoor heat exchanger 5 ΔT2 < ΔT + 2°C, the heat pump system defrosts according to the conventional timed defrosting mode. The control method of the timed defrosting mode is determined by the manufacturer.

[0023] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for accurately judging defrosting of a variable frequency heat pump water heater for heating, characterized in that The variable frequency heat pump water heater comprises a variable frequency compressor (1), a heating heat exchanger (2), an electronic expansion valve (3), an inlet temperature sensor (4), an outdoor heat exchanger (5), an outdoor ambient temperature sensor (6), a controller (7) and an outlet temperature sensor (8); the inlet temperature sensor (4) is arranged at the refrigerant inlet of the outdoor heat exchanger (5), and the temperature detected by the inlet temperature sensor (4) is the refrigerant inlet temperature Tj of the outdoor heat exchanger (5); the outlet temperature sensor (8) is arranged at the refrigerant outlet of the outdoor heat exchanger (5), and the temperature detected by the outlet temperature sensor (8) is the refrigerant outlet temperature Tc of the outdoor heat exchanger (5); the temperature detected by the outdoor ambient temperature sensor (6) is the outdoor ambient temperature Tw; The defrost judgment steps are as follows: (a) When the variable frequency heat pump is running and the outdoor heat exchanger (4) has not yet started to frost, the test method is used to test the outdoor heat exchanger at different outdoor ambient temperatures T w Under different operating frequencies f of the variable frequency compressor (1), the corresponding frost-free opening S1 of the electronic expansion valve (3) is obtained, and a relationship I is established in the controller (7) between the frost-free opening S1 of the electronic expansion valve (3) and the outdoor ambient temperature Tw and the operating frequency f of the variable frequency compressor (1): S1=g(Tw,f) (b) After the variable frequency heat pump has been running for a period of time, frost begins to form on the surface of the fins of the outdoor heat exchanger (5). When the frost on the surface of the fins of the outdoor heat exchanger (4) reaches a set thickness and needs to be defrosted, the test method is used to test the frost at different outdoor ambient temperatures T w Under different operating frequencies f of the variable frequency compressor (1), the corresponding defrost opening S2 of the electronic expansion valve (3) is obtained, and a relationship II is established in the controller (7) showing that the defrost opening S2 of the electronic expansion valve (3) varies with the outdoor ambient temperature Tw and the operating frequency f of the variable frequency compressor (1): S2=h(Tw,f); (c) During an on-off operation cycle of the variable frequency heat pump, the controller (7) calculates the outdoor ambient temperature Tw at this moment and the frost-free opening S1 and defrost opening S2 of the electronic expansion valve (3) corresponding to the operating frequency f of the variable frequency compressor (1) according to the relational expressions I and II. When the real-time opening S of the electronic expansion valve (3) is 0.1 (S1-S2) + S2≤S≤0.2 (S1-S2) + S2, the controller (7) records the refrigerant superheat ΔT of the outdoor heat exchanger (5) at this moment, i.e. ΔT=Tc-Tj, and starts to judge whether to defrost, and operates according to step (d); (d) The frequency f of the variable frequency compressor (1) is kept constant, and the real-time opening S of the electronic expansion valve (3) is reduced to S2. If at this time the real-time superheat ΔT2 of the refrigerant in the outdoor heat exchanger (5) is ≥ ΔT + 2°C, it indicates that the defrosting judgment of the controller (7) is correct. The opening control mode of the electronic expansion valve (3) is restored to the control mode before the defrosting judgment is started and continues to operate. When the actual opening S of the electronic expansion valve (3) is the same as the defrosting opening S2 calculated by the relationship II, the heat pump system starts to defrost. If the real-time superheat ΔT2 of the refrigerant in the outdoor heat exchanger (5) is less than ΔT + 2°C, the variable frequency heat pump system defrosts according to the conventional timed defrosting mode.

2. The defrosting accurate judgment method of the variable frequency heat pump water heater for heating according to claim 1 is characterized in that The frost layer thickness setting value range in step (b) is 0.2 to 1.2 mm.

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