Gas water heater

Abstract

The utility model discloses a gas water heater which comprises a heat exchanger, a control structure and a main water outlet pipeline, one end of the main water outlet pipeline is connected with the heat exchanger, and the other end of the main water outlet pipeline is connected with a first inner water outlet pipeline and a second inner water outlet pipeline in a branched mode. The inner pipe diameter of the first inner water outlet pipeline is smaller than that of the second inner water outlet pipeline; the second inner water outlet pipeline is connected with the first inner branch pipeline and the second inner branch pipeline in a forked mode through a control structure, and the control structure controls one of the first inner branch pipeline and the second inner branch pipeline to be communicated with the second inner water outlet pipeline. The gas water heater has an external circulation state and an internal circulation state; in an outer circulation state, the second inner branch pipeline is communicated with the second inner water outlet pipeline; in an inner circulation state, the first inner branch pipeline is communicated with the second inner water outlet pipeline. The internal circulation time can be shortened, it is guaranteed that a user uses boiled water at any time, fuel gas can be saved, and meanwhile due to the fact that the fuel gas water heater further has the external circulation state, the original zero-cold-water function is reserved.

Description

Technical Field

[0001] The utility model relates to the technical field of water heaters, in particular to a gas water heater. Background Art

[0002] There are two common problems in the existing gas water heaters: one is that after stopping the use of water, when the water is turned on again in a short period of time, a period of high-temperature water will appear because the water in the heat exchange tube absorbs the preheating of the heat exchange plate, which is called the water temperature rise in the industry; the other is that when the second ignition is turned on for heating, cold water that has not been heated in time will flow to the water outlet, which is called the secondary water temperature drop in the industry. Both problems are inherent problems caused by the structure of the water heater.

[0003] In order to solve these two problems, a "zero cold water gas water heater" has appeared in the prior art. In this water heater, the water pump, the internal pipeline of the water heater, and the operation of the water pump are designed so that when the ignition and the flame are turned off, hot water is appropriately introduced into the water inlet pipeline to form an internal circulation inside the water heater (the direction of water flow is as follows: Figure 1 In the direction indicated by the solid arrow in the middle), the temperature fluctuation of hot water can be reduced and the experience of using hot water can be optimized.

[0004] However, users also have cold water needs when using zero cold water gas water heaters, such as Figure 1 As shown, the water heater is also connected to an external circulation (the direction of water flow is as follows Figure 1 When the internal circulation is started, the external circulation will inevitably be followed, which will prolong the internal circulation time. The purpose of setting the internal circulation of the water heater is to preheat the cold water in front of the heat exchanger so that the water can maintain a suitable temperature when the water is turned on for the second time. However, due to the existence of the external circulation, the hot water is diverted to the external circulation, and the water in front of the heat exchanger heats up more slowly, which wastes gas.

[0005] Therefore, it is necessary to design a new gas water heater to overcome the above-mentioned disadvantages. Utility Model Content

[0006] Therefore, the technical problem to be solved by the present invention is that in the existing gas water heaters with both internal and external circulations, the hot water heated by the internal circulation will be diverted to the external circulation, causing the water on the front side of the heat exchanger to heat up more slowly and waste gas, thereby providing a gas water heater.

[0007] In order to solve the above technical problems, the technical solution of the utility model is as follows:

[0008] A gas water heater comprises a heat exchanger, a control structure, and a main water outlet pipeline, wherein one end of the main water outlet pipeline is connected to the water outlet of the heat exchanger, and the other end is forked to connect a first internal water outlet pipeline and a second internal water outlet pipeline; the inner pipe diameter of the first internal water outlet pipeline is smaller than the inner pipe diameter of the second internal water outlet pipeline, so that the first internal water outlet pipeline is a flow limiting pipeline; one end of the second internal water outlet pipeline away from the main water outlet pipeline is forked to connect a first internal branch pipeline and a second internal branch pipeline through the control structure, the water in the first internal water outlet pipeline and the second internal branch pipeline merge and flow out of the gas water heater, and the control structure controls the first internal branch pipeline and the second internal branch pipeline to selectively connect to the second internal water outlet pipeline; in the external circulation state, the second internal branch pipeline is connected to the second internal water outlet pipeline; in the internal circulation state, the first internal branch pipeline is connected to the second internal water outlet pipeline.

[0009] In the utility model, the control structure can control the first internal branch pipeline and the second internal branch pipeline to selectively connect to the second internal water outlet pipeline. When the gas water heater is in the internal circulation state, the first internal branch pipeline is connected to the second internal water outlet pipeline. Since the first internal water outlet pipeline is a flow limiting pipeline, the amount of water diverted by the first internal water outlet pipeline is very small. Therefore, most of the water from the main water outlet pipeline enters the water inlet pipeline through the second internal water outlet pipeline and the first internal branch pipeline, and then enters the heat exchanger for preheating. Only a small amount of water flows out through the first internal water outlet pipeline, thereby improving the efficiency of the internal circulation, so that when the user uses water for the second time in a short time, the water temperature fluctuation is minimized to the greatest extent possible, avoiding the user from perceiving the obvious temperature rise when the water is stopped and the temperature drop when the water is turned on, thereby greatly optimizing the use experience of the water heater and saving gas. At the same time, the control structure can also control the second internal branch pipeline to connect to the second water outlet pipeline and the gas water heater to enter the external circulation state, thereby not affecting the original external circulation zero cold water function.

[0010] Further, the control structure is a two-position three-way valve, which includes a valve body, and a first flow hole, a second flow hole and a third flow hole are provided on the valve body. The first flow hole is connected to the second internal water outlet pipe, the second flow hole is connected to the first internal branch pipe, and the third flow hole is connected to the second internal branch pipe.

[0011] Furthermore, the two-position three-way valve also includes a valve core, which includes a valve stem, a first valve and a second valve, the first valve and the second valve are respectively fixed to the first end and the second end of the valve stem, and are respectively used to control the on-off of the third flow hole and the second flow hole; when the gas water heater is in an external circulation state, the first valve is opened and the second valve is closed; when the gas water heater is in an internal circulation state, the first valve is closed and the second valve is opened.

[0012] Furthermore, the two-position three-way valve also includes an elastic reset member and an electromagnetic control valve, the end face of the first end and the end face of the second end respectively form a first pressure-bearing surface and a second pressure-bearing surface, the area of ​​the first pressure-bearing surface is larger than the area of ​​the second pressure-bearing surface, and a first pilot passage, a second pilot passage and a pilot hole are opened in the valve body; the first pilot passage and the second pilot passage are respectively connected to the first flow hole, and are respectively arranged corresponding to the first pressure-bearing surface and the second pressure-bearing surface; the pilot hole is connected to the second pilot passage, and the electromagnetic control valve controls the on-off of the pilot hole; when the gas water heater is in the internal circulation state, the pilot hole is opened, and when the gas water heater is in the internal circulation state, the pilot hole is closed; the elastic reset member pushes the valve core to reset.

[0013] Furthermore, the two-position three-way valve comprises a driving gear, a worm section is provided on the valve stem, and the driving gear meshes with teeth on the worm section.

[0014] Furthermore, a first pilot solenoid valve is provided in the valve body corresponding to the third flow hole, for controlling the on-off of the third flow hole; a second pilot solenoid valve is provided in the valve body corresponding to the second flow hole, for controlling the on-off of the second flow hole; when the gas water heater is in an external circulation state, the first pilot solenoid valve is opened and the second pilot solenoid valve is closed; when the gas water heater is in an internal circulation state, the first pilot solenoid valve is closed and the second pilot solenoid valve is opened.

[0015] Furthermore, the flow rate of the first internal water outlet pipeline is 1 L / min to 2 L / min.

[0016] Furthermore, it also includes a water inlet pipeline. When the gas water heater is in the internal circulation state, the second internal water outlet pipeline is connected to the first internal branch pipeline and the water inlet pipeline in sequence via the control structure.

[0017] Furthermore, it also includes an external water pipeline, the first internal water outlet pipeline is connected to the external water pipeline, and when the gas water heater is in the external circulation state, the second internal water outlet pipeline is connected to the second internal branch pipeline and the external water pipeline in sequence via the control structure, and the external water pipeline is forked to connect the hot water pipeline and the cold water pipeline, the hot water pipeline is suitable for connecting water-using equipment, and the outlet end of the cold water pipeline is connected to the water inlet pipeline.

[0018] Furthermore, it also includes a water flow sensor, a water inlet temperature sensor and a water outlet temperature sensor, the water flow sensor and the water inlet temperature sensor are both installed on the water inlet pipeline, and the water outlet temperature sensor is installed on the main water outlet pipeline and adjacent to the water outlet of the heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation methods of the utility model or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a structural schematic diagram of an existing gas water heater;

[0021] Figure 2 This is a schematic diagram of the structure of the gas water heater of the utility model;

[0022] Figure 3 It is a schematic diagram of the flow path in the shunt pipeline when the gas water heater is in the external circulation state in the first embodiment of the utility model;

[0023] Figure 4 It is a schematic diagram of the flow path in the shunt pipeline when the gas water heater is in the internal circulation state in the first embodiment of the utility model;

[0024] Figure 5 It is a schematic diagram of the flow path in the shunt pipeline when the gas water heater is in the external circulation state in the second embodiment of the utility model;

[0025] Figure 6 It is a schematic diagram of the flow path in the shunt pipeline when the gas water heater is in the internal circulation state in the second embodiment of the utility model;

[0026] Figure 7 It is a schematic diagram of the flow path in the shunt pipeline when the gas water heater is in the external circulation state in the third embodiment of the utility model;

[0027] Figure 8 It is a schematic diagram of the flow path in the bypass pipeline when the gas water heater is in the internal circulation state in the third embodiment of the utility model.

[0028] Description of reference numerals:

[0029] 1. Heat exchanger;

[0030] 2. Water inlet pipeline; 21. Water pump; 22. Water flow sensor; 23. Insulated water tank; 231. Water inlet temperature sensor;

[0031] 30. Main water outlet pipeline; 300. Water outlet temperature sensor; 31. First internal water outlet pipeline; 32. Second internal water outlet pipeline; 33. First internal branch pipeline; 34. Second internal branch pipeline; 35. External water outlet pipeline; 36. Hot water pipeline; 37. Cold water pipeline; 371. One-way valve;

[0032] 4. Control structure; 40. Motor; 41. Valve body; 411. First pilot passage; 412. Second pilot passage; 413. Pilot hole; 414. Mounting groove; 42. Valve core; 420. Valve stem; 421. First valve; 422. Second valve; 423. Worm section; 424. First pressure-bearing surface; 425. Second pressure-bearing surface; 43. Elastic reset member; 44. Solenoid control valve; 45. Solenoid valve coil; 46. Driving gear; 47. First pilot solenoid valve; 48. Second pilot solenoid valve;

[0033] 7. Water use equipment;

[0034] A. Connection node; B. Diversion pipeline; C. First flow hole; D. Second flow hole; E. Third flow hole. DETAILED DESCRIPTION

[0035] The technical solution of the utility model will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0036] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0037] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Before introducing the gas water heater of the utility model, the accompanying drawings are described first: Figures 3 to 8 Both Figure 2 Schematic diagram of the flow path inside the bypass pipeline B where the square frame portion is located.

[0040] like Figures 2 to 8 As shown, the utility model provides a gas water heater, including a burner (not shown), a heat exchanger 1, a water pump 21, a water inlet pipeline 2, a water outlet pipeline and a control structure 4 (as shown in the figure). Since the burner, the heat exchanger 1 and the water pump 21 are conventional components of a gas water heater, they are not improved in the utility model, so they are not described here.

[0041] like Figure 2 As shown, the water inlet pipeline 2 is connected to the water inlet of the heat exchanger 1 for supplying water to the heat exchanger 1. In the water inlet direction, a water pump 21, a water flow sensor 22 and a heat preservation water tank 23 are sequentially installed on the water inlet pipeline 2. A water inlet temperature sensor 231 is arranged in the heat preservation water tank 23.

[0042] like Figure 2 As shown, the water outlet pipeline includes a main water outlet pipeline 30 , a first internal water outlet pipeline 31 , a second internal water outlet pipeline 32 , a first internal branch pipeline 33 , a second internal branch pipeline 34 , an external water outlet pipeline 35 , a hot water pipeline 36 and a cold water pipeline 37 .

[0043] like Figure 2 As shown, a water outlet temperature sensor 300 is installed on the main water outlet pipeline 30. The water outlet temperature sensor 300 is close to the water outlet of the heat exchanger 1. The inlet end of the main water outlet pipeline 30 is connected to the water outlet of the heat exchanger 1.

[0044] like Figure 2 As shown, the outlet end of the main water outlet pipeline 30 is bifurcated to connect the first inner water outlet pipeline 31 and the second inner water outlet pipeline 32. The end of the second inner water outlet pipeline 32 away from the main water outlet pipeline 30 is bifurcated to connect the first inner branch pipeline 33 and the second inner branch pipeline 34 through the control structure 4. The first inner branch pipeline 33 is connected to the water inlet pipeline 2, and the connection node is A. The water in the first inner water outlet pipeline 31 and the second inner branch pipeline 34 merge and flow out of the gas water heater into the outer water outlet pipeline 35. The inner pipe diameter of the first inner water outlet pipeline 31 is significantly smaller than that of the second inner water outlet pipeline 32, so that the water flow resistance in the first inner water outlet pipeline 31 is relatively large and becomes a flow limiting pipeline. The flow rate of the first inner water outlet pipeline 31 is 1L / min to 2L / min.

[0045] One end of the outgoing water pipe 35 away from the main water outlet pipe 30 is bifurcated to connect the hot water pipe 36 and the cold water pipe 37. The hot water pipe 36 is connected to the water-using equipment 7. The outlet end of the cold water pipe 37 is connected to the water inlet pipe 2. A one-way valve 371 is installed on the cold water pipe 37, so that water only flows along the cold water pipe 37 to the water inlet pipe 2.

[0046] The aforementioned control structure 4 controls the first inner branch pipeline 33 and the second inner branch pipeline 34 to selectively connect to the second inner water outlet pipeline 32, and the first inner branch pipeline 33 is a normally disconnected pipeline, and the second inner branch pipeline 34 is a normally connected pipeline. The gas water heater has an external circulation state (which is the default state) and an internal circulation state. In the external circulation state, the control structure 4 controls the second inner branch pipeline 34 to connect to the second inner water outlet pipeline 32, and the first inner branch pipeline 33 is disconnected from the connection with the second inner water outlet pipeline 32. In the internal circulation state, the control structure 4 controls the first inner branch pipeline 33 to connect to the second inner water outlet pipeline 32, and the second inner branch pipeline 34 is disconnected from the connection with the second inner water outlet pipeline 32.

[0047] The specific structures of three control structures 4 are described below. Of course, the control structure 4 can also be in other forms, which are not specifically limited here and can be selected according to actual needs.

[0048] like Figure 3 and Figure 4 As shown in the figure, as a first embodiment, the control structure 4 is a two-position three-way pilot solenoid valve, which includes a motor 40 , a valve body 41 , a valve core 42 , a first pilot passage 411 , a second pilot passage 412 , a pilot hole 413 , a solenoid control valve 44 , and a solenoid valve coil 45 .

[0049] The valve body 41 is provided with a first flow hole C, a second flow hole D, and a third flow hole E. The first flow hole C is connected to the aforementioned second internal water outlet pipe 32, the second flow hole D is connected to the aforementioned first internal branch pipe 33, and the third flow hole E is connected to the aforementioned second internal branch pipe 34. The valve body 41 is provided with a first pilot passage 411, a second pilot passage 412, and a pilot hole 413. The first pilot passage 411 and the second pilot passage 412 are connected to the first flow hole C respectively. A mounting groove 414 is provided at the root of the first pilot passage 411 away from the first flow hole C, and an elastic reset member 43 is installed in the mounting groove 414. The axis of the elastic reset member 43 is parallel to the length direction of the valve stem 420. When the gas water heater switches from the internal circulation state to the external circulation state, the elastic reset member 43 is used to push the valve stem 420 to reset.

[0050] The valve core 42 includes a valve stem 420, a first valve 421 and a second valve 422. The first valve 421 and the second valve 422 are connected to the first end and the second end of the valve stem 420, respectively. The first valve 421 and the second valve 422 move synchronously with the valve stem 420. The first valve 421 and the second valve 422 control the opening and closing of the third flow hole E and the second flow hole D, respectively. The end surface of the first end and the end surface of the second end form a first pressure-bearing surface 424 and a second pressure-bearing surface 425, respectively. The area of ​​the second pressure-bearing surface 425 is larger than the area of ​​the first pressure-bearing surface 424.

[0051] like Figure 3 As shown, when the gas water heater is in the external circulation state, the electromagnetic control valve 44 controls the pilot hole 413 to be closed, and the water outlet of the heat exchanger 1 enters the control structure 4 through the main water outlet pipeline 30, the second internal water outlet pipeline 32, and the first flow hole C in sequence; then enters the first pilot passage 411 to reach the first pressure-bearing surface 424, and the first pressure-bearing surface 424 is pressurized. Since the pilot hole 413 is closed, the water entering the second pilot passage 412 cannot reach the first pressure-bearing surface 424 through the pilot hole 413. The second pressure-bearing surface 425, the second pressure-bearing surface 425 of the valve stem 420 is not subjected to water pressure, and the pressure difference between the first pressure-bearing surface 424 and the second pressure-bearing surface 425 drives the valve stem 420 to move rightward, thereby opening the first valve 421 and closing the second valve 422. In this way, the water in the valve body 41 enters the outgoing water pipeline 35 through the third flow hole E and the second internal branch pipeline 34 in turn. At the same time, the water flow from the first internal water outlet pipeline 31 also converges into the outgoing water pipeline 35.

[0052] like Figure 4 As shown, when the gas water heater is in the internal circulation state, the electromagnetic control valve 44 controls the pilot hole 413 to open, and the water from the second pilot passage 412 reaches the second pressure-bearing surface 425 through the pilot hole 413. Since the second water pressure borne by the second bearing surface 425 is greater than the first water pressure borne by the first bearing surface 424, the difference between the second water pressure and the first water pressure drives the valve stem 420 to move to the left, so that the first valve 421 is closed and the second valve 422 is opened. The water entering the second internal water outlet pipeline 32 from the main water outlet pipeline 30 enters the heat exchanger 1 from the second flow hole D of the valve body 41 through the first internal branch pipeline 33 and the water inlet pipeline 2 for preheating, thereby avoiding the water outlet being cold water when the water is boiled for the second time, thereby improving the user experience.

[0053] like Figure 5 and Figure 6 As shown in FIG. 1 , as a second embodiment, the control structure 4 is a two-position three-way servo motor valve. The second embodiment differs from the first embodiment in that the driving method of the valve stem 420 is different. Figure 5From the perspective, the right end of the valve stem 420 is provided with a worm section 423, and the teeth on the worm section 423 mesh with the driving gear 46, and the driving gear 46 is driven by the motor 40 to rotate, thereby driving the valve stem 420 to move left and right. Of course, the worm section 423 can also be provided at the left end of the valve stem 420.

[0054] When the gas water heater is in external circulation state, Figure 5 As shown, the valve stem 420 moves to the right, the first valve 421 opens, and the second valve 422 closes. The water in the valve body 41 enters the outgoing water pipeline 35 through the third flow hole E and the second internal branch pipeline 34 in turn. At the same time, the water flow from the first internal water outlet pipeline 31 also converges into the outgoing water pipeline 35.

[0055] When the gas water heater is in the internal circulation state, Figure 6 As shown, the valve stem 420 moves to the left, the first valve 421 is closed, and the second valve 422 is opened. The water in the valve body 41 enters the heat exchanger 1 through the second flow hole D, the first internal branch pipe 33 and the water inlet pipe 2 for preheating, avoiding cold water when the water is turned on for the second time, thereby improving the user experience.

[0056] In the first and second embodiments, the first valve 421 and the second valve 422 are controlled in linkage.

[0057] like Figure 7 and Figure 8 As shown, as a third embodiment, the control structure 4 includes a first pilot solenoid valve 47 and a second pilot solenoid valve 48. The first pilot solenoid valve 47 is a normally open pilot solenoid valve. The second pilot solenoid valve 48 is a normally closed pilot solenoid valve. The second pilot solenoid valve 48 is used to control the on-off of the second flow hole D. The first pilot solenoid valve 47 is used to control the on-off of the third flow hole E. The first pilot solenoid valve 47 and the second pilot solenoid valve 48 are independent of each other and are controlled separately.

[0058] When the gas water heater is in external circulation state, Figure 7 As shown, the first pilot solenoid valve 47 is opened and the second pilot solenoid valve 48 is closed, and the water in the valve body 41 enters the outgoing water pipeline 35 through the third flow hole E and the second internal branch pipeline 34 in turn. At the same time, the water flow from the first internal water outlet pipeline 31 also converges into the outgoing water pipeline 35.

[0059] When the gas water heater is in the internal circulation state, Figure 8 As shown, the first pilot solenoid valve 47 is closed and the second pilot solenoid valve 48 is opened, and the water in the valve body 41 enters the heat exchanger 1 through the second flow hole D, the first internal branch pipe 33 and the water inlet pipe 2 for preheating, avoiding cold water when the water is turned on for the second time, thereby improving the user experience.

[0060] In the present invention, since the control structure 4 can control the first inner branch pipeline 33 and the second inner branch pipeline 34 to select one to connect to the second inner water outlet pipeline 32, when the gas water heater is in the inner circulation state, the first inner branch pipeline 33 is connected to the second inner water outlet pipeline 32, and since the first inner water outlet pipeline 31 is a flow limiting pipeline, the amount of water diverted by the first inner water outlet pipeline 31 is very small, so most of the water from the main water outlet pipeline 30 enters the water inlet pipeline 2 through the second inner water outlet pipeline 32 and the first inner branch pipeline 33, and then The water enters the heat exchanger 1 for preheating, and only a small amount of water flows out through the first inner water outlet pipe 31, thereby improving the efficiency of the inner circulation, so that when the user uses water for a short time, the water temperature fluctuation is minimized to the maximum extent, and the user is prevented from feeling the obvious temperature rise when the water is stopped and the temperature drop when the water is turned on, thereby greatly optimizing the use experience of the water heater and saving gas. At the same time, the control structure 4 can also control the second inner branch pipe 32 to connect to the second water outlet pipe 34, and the gas water heater enters the outer circulation state, so as not to affect the original outer circulation zero cold water function.

[0061] In addition, in the internal circulation state, although the water flow of the first internal water outlet pipe 31 is relatively small, when the user turns on the water-using device, water will still flow out from the water-using device 7. The gas water heater can detect the user's water use and immediately switch back to the default state of the external circulation, so that the gas water heater can realize the switching between the internal circulation state and the external circulation state in time.

[0062] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other changes or modifications in different forms can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention of the utility model.

Claims

1. A gas water heater, characterized in that: The invention comprises a heat exchanger (1), a control structure (4), and a main water outlet pipeline (30); one end of the main water outlet pipeline (30) is connected to the water outlet of the heat exchanger (1), and the other end is bifurcated to connect a first internal water outlet pipeline (31) and a second internal water outlet pipeline (32); the inner diameter of the first internal water outlet pipeline (31) is smaller than the inner diameter of the second internal water outlet pipeline (32), so that the first internal water outlet pipeline (31) is a flow-limiting pipeline; the end of the second internal water outlet pipeline (32) away from the main water outlet pipeline (30) is bifurcated to connect a first internal branch pipeline (33) and a second internal branch pipeline (32) through the control structure (4). Two internal branch pipelines (34), water in the first internal water outlet pipeline (31) and the second internal branch pipeline (34) merge and flow out of the gas water heater, and the control structure (4) controls the first internal branch pipeline (33) and the second internal branch pipeline (34) to selectively connect to the second internal water outlet pipeline (32); the gas water heater has an external circulation state and an internal circulation state; in the external circulation state, the second internal branch pipeline (34) connects to the second internal water outlet pipeline (32); in the internal circulation state, the first internal branch pipeline (33) connects to the second internal water outlet pipeline (32).

2. The gas water heater according to claim 1, characterized in that: The control structure (4) is a two-position three-way valve, comprising a valve body (41), the valve body (41) being provided with a first flow hole (C), a second flow hole (D) and a third flow hole (E), the first flow hole (C) being connected to the second internal water outlet pipeline (32), the second flow hole (D) being connected to the first internal branch pipeline (33), and the third flow hole (E) being connected to the second internal branch pipeline (34).

3. The gas water heater according to claim 2, characterized in that: The two-position three-way valve also includes a valve core (42), and the valve core (42) includes a valve stem (420), a first valve (421) and a second valve (422); the first valve (421) and the second valve (422) are respectively fixed to the first end and the second end of the valve stem (420), and are respectively used to control the on-off of the third flow hole (E) and the second flow hole (D); when the gas water heater is in an external circulation state, the first valve (421) is opened and the second valve (422) is closed; when the gas water heater is in an internal circulation state, the first valve (421) is closed and the second valve (422) is opened.

4. The gas water heater according to claim 3, characterized in that: The two-position three-way valve further comprises an elastic reset member (43) and an electromagnetic control valve (44); the end surface of the first end and the end surface of the second end respectively form a first pressure-bearing surface (424) and a second pressure-bearing surface (425); the area of ​​the first pressure-bearing surface (424) is larger than the area of ​​the second pressure-bearing surface (425); a first pilot passage (411), a second pilot passage (412) and a pilot hole (413) are provided in the valve body (41); the first pilot passage (411) and the second pilot passage (412) are respectively connected to the first pilot passage (411) and the second pilot passage (412); The first flow hole (C) is connected to the first pressure-bearing surface (424) and the second pressure-bearing surface (425), respectively; the pilot hole (413) is connected to the second pilot passage (412), and the electromagnetic control valve (44) controls the on-off of the pilot hole (413); when the gas water heater is in an internal circulation state, the pilot hole (413) is opened, and when the gas water heater is in an internal circulation state, the pilot hole (413) is closed; the elastic reset member (43) pushes the valve core (42) to reset.

5. The gas water heater according to claim 3, characterized in that: The two-position three-way valve comprises a driving gear (46), a worm section (423) is provided on the valve stem (420), and the driving gear (46) meshes with teeth on the worm section (423).

6. The gas water heater according to claim 2, characterized in that: A first pilot solenoid valve (47) is provided in the valve body (41) corresponding to the third flow hole (E) for controlling the on-off of the third flow hole (E); a second pilot solenoid valve (48) is provided in the valve body (41) corresponding to the second flow hole (D) for controlling the on-off of the second flow hole (D); when the gas water heater is in an external circulation state, the first pilot solenoid valve (47) is opened and the second pilot solenoid valve (48) is closed; when the gas water heater is in an internal circulation state, the first pilot solenoid valve (47) is closed and the second pilot solenoid valve (48) is opened.

7. The gas water heater according to any one of claims 1 to 6, characterized in that: The flow rate of the first internal water outlet pipeline (31) is 1 L / min to 2 L / min.

8. The gas water heater according to any one of claims 1 to 6, characterized in that: It also includes a water inlet pipeline (2). When the gas water heater is in the internal circulation state, the second internal water outlet pipeline (32) is connected to the first internal branch pipeline (33) and the water inlet pipeline (2) in sequence via the control structure (4).

9. The gas water heater according to claim 8, characterized in that: It also comprises an outgoing water pipeline (35), wherein the first inner water outlet pipeline (31) is connected to the outgoing water pipeline (35), and when the gas water heater is in the outer circulation state, the second inner water outlet pipeline (32) is connected to the second inner branch pipeline (34) and the outgoing water pipeline (35) in sequence via the control structure (4), and the outgoing water pipeline (35) is bifurcated to connect a hot water pipeline (36) and a cold water pipeline (37), wherein the hot water pipeline (36) is suitable for connecting to a water-using device (7), and the outlet end of the cold water pipeline (37) is connected to the water inlet pipeline (2).

10. The gas water heater according to claim 8, characterized in that: It also includes a water flow sensor (22), a water inlet temperature sensor (231) and a water outlet temperature sensor (300), wherein the water flow sensor (22) and the water inlet temperature sensor (231) are both installed on the water inlet pipeline (2), and the water outlet temperature sensor (300) is installed on the main water outlet pipeline (30) and adjacent to the water outlet of the heat exchanger (1).

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