ES2664417T3 - Water heating device with air pressure switch - Google Patents

Abstract

An apparatus (1) for heating water with gas comprising: a housing (10); a burner (104) arranged in the housing to generate heat; a heat exchanger (107) for absorbing heat and transferring heat to the water that passes through it; an air supply fan (105) arranged in the housing to supply air to the burner; characterized by an air pressure switch (30) having a negative pressure port (301) and a positive pressure port (302), said negative pressure port being connected to the air supply fan through a first tube (31) and said positive pressure port being connected to the atmosphere through a second tube (33); and because the housing defines an air inlet (111) in a lower portion thereof; wherein the second tube (33) has an air intake end (331), and said air intake end is located adjacent to the air inlet to receive air passing through the air inlet; said air inlet (111) is arranged in a front plate (11) of the housing, and said front plate is provided with a screen plate (112) having a lower edge that forms an upper edge of the air inlet; wherein the air intake end (331) is disposed behind the screen plate (112).

Description

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DESCRIPTION

Water heating apparatus with air pressure switch Field of the invention

The present invention relates to a gas water heating apparatus that uses an air pressure switch that is not affected by adverse wind.

Background of the invention

Gas water heating devices generally include gas water heaters and gas boilers. A typical gas water heater can provide domestic hot water for domestic use, such as use in the kitchen, in the washing machine and in the bathroom. The water heater can include a gas burner for the combustion of a mixture of gas and air, heat exchange coils to heat water as it flows through them, and hydraulic pipes connected to external sanitary facilities to supply hot water . A typical gas boiler works to heat water that is pumped around a boiler circuit. The boiler circuit is normally connected, by means of appropriate valves, to space heaters, such as radiators or to an underfloor heating circuit, so that the heat output from the boiler can be used for central heating purposes . Such a gas water heating apparatus according to the preamble of claim 1 can be found in the publication of German patent application DE 41 34 230 A1, with the same applicant as that of the present invention.

The appliances are often equipped with air supply fans and combustion hoods. The air supply fan provides air to the burner and forces the combustion gas generated by the burner to flow into the flue gas hood to be discharged outside. When the appliance is operated for the first time, the air supply fan works first to check if the gas leak is working properly and, if the result is affirmative, the appliance will be put into operation. An air pressure switch is used to verify the situation of the gas leak and, in addition, it can activate the shutdown of the appliance in case there is a blockage of the gas leak.

The air pressure switch normally has a positive pressure port or opening and a negative pressure port or opening that are connected, respectively, to a positive pressure chamber and a negative pressure chamber separated by a membrane. When there is a pressure change, the membrane will be pushed by the pressure difference to activate a switch on or off (on or off). Usually, the air pressure switch causes the negative pressure port to be connected to the air supply fan to detect the negative pressure generated by the fan.

When the appliance is started up, if the air supply fan operates properly, the air pressure switch will detect a pressure value in its negative pressure port that is less than the preset threshold. However, if the combustion gas leak is blocked, the air pressure switch will detect a pressure value that is greater than the preset threshold, and then the appliance will not start. For an external gas water heating apparatus, the apparatus may be subjected to an adverse wind that exerts a wind pressure through the combustion hood on the air supply fan, so that it is detected by the air pressure switch a higher pressure value, which means that the device cannot be started or the operation of the device has to be stopped. Obviously, this is not desired by the designers because the combustion gas exhaust block must not occur and the combustion gas must still be discharged.

The Chinese Utility Model CN2913943Y describes an outdoor gas water heater that is capable of functioning properly even if it encounters an adverse wind. A temperature sensing switch is used therein to replace the air pressure switch. For example, when the combustion gas leak is blocked, the temperature inside the water heater inevitably increases and, once the temperature exceeds a predetermined threshold, the switch will detect it and activate the stop of the water heater. However, the temperature rise inside the water heater may result from a loss of different factors, in other words, the apparatus may be stopped due to malfunction.

Compendium of the invention

It is an object of the present invention to provide a gas water heating apparatus that employs an air pressure switch that is not affected by an adverse wind, thereby ensuring that the apparatus functions properly even if it encounters an adverse wind.

In accordance with one aspect of the present invention, a gas water heating apparatus is provided which includes a housing, a burner, a heat exchanger, an air supply fan and an air pressure switch. The burner is arranged in the housing to generate heat. The heat exchanger is adapted to absorb heat and transfer heat to the water that passes through it. The air supply fan is arranged in the housing to supply air to the burner. Pressure switch

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of air has a negative pressure port and a positive pressure port; wherein the negative pressure port is connected to the air supply fan by means of a first tube, and the positive pressure port is connected to the atmosphere by means of a second tube. The housing has an air inlet in a lower portion thereof; wherein the second tube has an air intake end, and the air intake end is located adjacent to the air inlet to receive the air that passes through the air inlet. The air inlet is located on a front plate of the housing, and the front plate is provided with a screen or protection plate having a lower edge that forms an upper edge of the air inlet; in which the air intake end is disposed behind the screen plate.

Preferably, the air intake end is disposed in a position lower than that of the positive pressure port of the air pressure switch along the vertical direction.

Preferably, the air intake end is disposed in the middle zone of the air inlet along a lateral direction.

Preferably, the screen plate is formed with a baffle that extends horizontally inward, and the air intake end is disposed below the baffle.

Preferably, the apparatus further includes a flue gas hood arranged inside the housing to receive the gas resulting from the combustion generated by the burner, the flue gas hood having a leading end having a gas exhaust port therein. to discharge combustion gas abroad.

In an alternative embodiment, which is not within the scope of claim 1, a first air intake port is disposed at the front end of the flue gas hood, and the second tube is connected between the positive pressure port and the first air intake hole.

Preferably, in said alternative embodiment that does not fall within the scope of claim 1, a second air intake orifice is disposed at the front end of the flue gas hood and above the first air intake orifice; the second tube comprising a connecting tube section connected between the first and second air intake holes and an extension tube section extending from the connecting tube section and connected to the positive pressure port, and the said extension tube section located, at least partially, above the second air intake port.

Preferably, the second tube defines a vent in its body.

Since the pressure exerted by the adverse wind can also be detected in the positive pressure port, the pressure change in the negative pressure port is counteracted by the pressure change in the positive port, and therefore the pressure switch of air would not be affected by adverse wind, and the malfunction of the apparatus by adverse wind can be avoided.

In the foregoing, the characteristics and technical advantages of the present invention have been outlined in general terms so that the following detailed description of the invention can be better understood. Additional features and advantages of the invention will be described below, which are the subject of the claims of the invention.

Brief description of the drawings

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the description that follows taken together with the accompanying drawings, in which:

Figure 1 is a flat view showing a gas water heating apparatus according to an embodiment that is not within the scope of claim 1;

Figure 2 is a perspective view showing the apparatus of Figure 1 from which a front plate is removed;

Figure 3 is a plan view showing the apparatus of Figure 1 from which a side plate is removed;

Figure 4 is a perspective view showing a flue gas hood according to an embodiment that is not within the scope of claim 1;

Figure 5 is a front view showing the flue gas hood of Figure 4;

Figures 6A to 6C are cross-sectional views taken along line AA of Figure 5, with Figures 6A, 6B, 6C respectively showing a first position, a second position and a third position of a movable bell deflector for flue gas.

Figure 7 is a perspective view showing a rain screen of the apparatus of Figure 1;

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Figure 8 is a top view of the rain screen of Figure 7;

Figure 9 is a side view of the rain screen of Figure 7;

Figure 10 is similar to Figure 5, showing a flue gas hood according to another embodiment that is not within the scope of claim 1;

Figure 11 is similar to Figure 6A, which is a cross-sectional view of the flue gas hood of Figure 10;

Figure 12 is a perspective view showing a gas water heating apparatus according to an embodiment of the present invention, in which the front plate together with the side plate and the rain screen are removed;

Figure 13 is a front view showing the apparatus of Figure 12 in which the rain screen has been added;

Figure 14 is a side view showing the apparatus of Figure 13.

Detailed description of the preferred embodiments

Reference will now be made to the figures of the drawings to describe in detail the preferred embodiments. However, the embodiments cannot be used to limit the present invention. Also protected by the present invention, defined by claim 1, are changes such as structure, method and function, evidently made by the ordinary person skilled in the art.

Gas water heaters and gas boilers can be operated with combustible gas, such as natural gas, city gas, liquefied petroleum gas, methane, etc., thereby supplying hot water and / or heating a living space. for domestic sanitary and heating purposes. The embodiments to be described in the following take a gas water heater as an example, but the present invention is not limited to this and can also be applied to gas boilers.

Referring first to Figures 1 to 3, a gas water heating apparatus is adapted to be mounted outdoors, which includes a housing 10, a hood 20 for flue gas, a heat exchanger 107, a burner 104 , an air supply fan 105, an air pressure switch 30, and an inlet tube 101, an outlet tube 102, a gas supply pipe 103 extending out of the housing 10.

The housing 10 may be composed of a number of plates, such as a front plate 11, a rear plate, an upper plate, a lower plate 12 and a pair of side plates. In this embodiment, the back plate and the bottom plate 12 are formed integral in a first piece, and the front plate 11, the upper plate and the pair of side plates are formed integral in a second piece. In the course of assembling the apparatus, the components can be mounted first on the first piece, and then the second piece is mounted on the first piece to complete the assembly. That way, assembly can be easier. When the apparatus is installed on a wall, the rear plate faces the wall, and an air inlet is arranged on the different plates from the rear plate. The air inlet may be arranged in the front plate 11, in the side plate or even in the lower plate 12 and, in this embodiment, the air inlet 111 is defined in a lower portion of the front plate 11.

Burner 104 has a box and a number of burner blades (not shown) arranged side by side in the box. Each burner vane generally has a passage for the gas-air mixture therein for mixing the fuel gas supplied from the gas supply line and combustion air 103 supplied by the air supply fan 105, and supplying the mixture. of gas-air to the top of it to be ignited and burned. Since the configuration and arrangement of the burner blades are well known in the art, a detailed description is omitted for purposes of brevity and simplification.

The heat exchanger 107 is located above the burner 104. The heat exchanger 107 may include multiple heat absorption fins and a heat absorption pipe that passes through the multiple heat absorption fins. The heat absorbing pipe is connected to an upstream water supply channel and a downstream hot water supply channel. The water that passes through the inlet pipe 101 and the upstream water supply channel is then heated in the heat exchanger 107 by heat exchange with the combustion exhaust gas of the burner 104. The heated hot water is fed to the hot water supply channel downstream and also passes through the outlet pipe 102 for domestic sanitary use, such as for drinking, showering or bathing.

In this embodiment, the air supply fan 105 is disposed below the burner 104, which is operated to supply outside air to the burner 104 as combustion air, and also forces the combustion gas to flow into the gas hood 20 combustion and then discharged to the outside.

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The combustion gas hood 20 is mounted on the heat exchanger 107 to collect the combustion gas containing carbon monoxide and nitric oxides and expel it to the outside. With reference to Figure 4, Figure 5 and Figures 6A to 6C, the flue gas hood 20 has an envelope, in this embodiment along the exhaust direction of the combustion gas, the part sequentially including a part rear 23, a front part 21 and an projecting part 22 extending from the front part 21. When the combustion gas hood 20 is mounted in the housing 10, the projecting part 22 is exposed to the outside of the housing 10.

The rear part 23 is retained in the upper part of the heat exchanger 107, and its lower part is open to define a gas inlet port 231. The projecting part 22 has a gas exhaust port 221 at the front end thereof, and a number of drain holes 222 are located at the bottom of the front end. The hood 20 for combustion gas defines therein a channel 232 for combustion gas between the gas inlet port 231 and the gas exhaust port 221. The front part 21 has a bottom wall that extends between the port of gas intake 231 and the gas exhaust port 221, and at least a part of the lower wall extends obliquely upwardly from the gas exhaust port 201, which can prevent outside wind and rain from entering the apparatus through the gas exhaust port 221 in some way. Even if the outside rain passes through the gas exhaust port 221 and enters the flue gas hood, the oblique bottom wall can conduct rain downstream and exit through the drain holes 222.

A movable baffle 242 is arranged in the channel 232 for flue gas in order to change the opening size in the cross section of the flue gas channel. In this embodiment, the movable baffle 242 is pivotally arranged at the rear 23, and includes a vertical portion 2421 and a bending portion 2422 that bends from the top of the vertical portion 2421. A fixed plate 241 is mounted in channel 232 for combustion gas. The fixed plate 241 has a horizontal section 2411 fixedly mounted on the upper wall of the flue gas channel 232 by welding or riveting, and a vertical section 2412 perpendicular to the horizontal section 2411 that provides a pivot 243 at a distal end of the same. The pivot 243 is connected to the movable deflector 242 at a junction of the vertical portion 2421 and the bending portion 2422, so that the movable deflector 242 can pivot on this pivot 243.

In this embodiment, the movable baffle 242 is coupled with the fixed plate 241 to change the opening size in the cross section of the flue gas channel 232. The fixed plate 241 and the movable baffle 242 together occupy the cross section of the flue gas channel 232 where they are located. To ensure that the movable baffle can move freely, there may be a clearance between the side sides of the fixed plate 241 and the movable baffle 242 and the side walls of the flue gas channel 232, and the clearance dimension may be the same or less than 1 mm. In the course of a pivoting movement of the movable baffle 242, there is a gap between the bottom of the movable baffle 242 and the bottom wall of the channel 232 for combustion gas, and this gap can define the opening in the section cross channel 232 for flue gas.

Figures 6A-6C show the movable baffle 242 when it is located in a first position, in a second position and in a third position, respectively. As shown in Figure 6A, when there is no exhaust of combustion gas, and there is no external wind and / or rain input, the movable deflector 242 is located in a first position in which it is in a suspended state. At this time, the vertical portion 2421 of the movable deflector is in the same plane as the erect section 2412 of the fixed plate, and the bending portion 2422 of the movable deflector and the vertical section 2412 of the fixed plate form an angle to each other. In the first position, the opening in the cross-section of the flue gas channel 232 has the smallest size, and the lower part of the movable deflector 242 is precisely in contact with the bottom wall of the flue gas channel 232. Preferably, in this position, there is a first gap between the bottom of the movable baffle 242 and the bottom wall of the flue gas channel 232, and the distance d1 of the first gap is about 1.2 mm. In this way, once the outside rain reaches the movable deflector 242 in the cold weather, the rain can flow over the bottom wall of the flue gas channel 232 and drain out or, otherwise, ice could form between the bottom of the movable baffle 242 and the bottom wall of the channel 232 for combustion gas and causing a blockage of the channel 232 for combustion gas.

As indicated by the arrows shown in Figure 6B, when there is an exhaust or exhaust of combustion gas, or there is both an exhaust of combustion gas and an outside wind inlet and the thrust of the combustion gas is stronger than that of the outer wind, the movable baffle 242 is pushed into the second position by the gas flow. In this position, each of the vertical portion 2421 and the bending portion 2422 forms an angle with respect to the vertical section 2412 of the fixed plate, and a second separation space is defined between the bottom of the movable deflector 242 and the bottom wall of channel 232 for combustion gas. The second separation space has a separation distance d2 which is greater than the first separation distance d1, in other words, in this position, the opening in the cross section of the flue gas channel 232 is greater than in the first position , and the size of the distance of the second separation depends on the force exerted by the gas flow.

As indicated by the arrows shown in Figure 6C, when there is an outside wind inlet, or there is

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both an exhaust of combustion gas and an outside wind inlet and the thrust of the outside wind is stronger than that of the combustion gas, the movable deflector 242 is pushed into the third position by the outside wind. The third position and the second position are located on opposite sides of the first position. In the third position, a third gap between the lower part of the movable baffle 242 and the lower wall of the channel 232 for combustion gas is defined. In most cases, the third separation space has a separation distance d3 that is greater than the first separation distance d1 but less than the second separation distance d2; in other words, in this position, the opening in the cross-section of the flue gas channel 232 is larger than that of the first position but smaller than that of the second position, and the size of the third separation distance depends on the force exerted by the outside wind. The embodiment of Figure 6C shows a maximum size of the third separation distance and, at this time, the bending portion 2422 of the movable deflector rests against the vertical section 2412 of the fixed plate, and the vertical portion 2421 of the movable deflector and the vertical section 2412 of the fixed plate form an angle to each other. Thus, there is even a combustion gas leak as well as an outside wind inlet and the external wind thrust is stronger than that of the gas flow, and the combustion gas can still be discharged out through the third separation space.

Like the embodiments shown above, when there is an entry of wind and / or outside rain, the movable deflector is able to engage with the fixed plate to limit the opening size in the cross section of the flue gas channel, thereby resisting wind and / or the rain; on the other hand, when there is exhaust of combustion gas, the movable baffle can be pushed by the gas flow to increase the opening size in the cross section of the flue gas channel, to allow the combustion gas to be discharged into out gently. In addition, since the movable deflector uses a bending portion, even if the wind entering and the flue gas discharged both exist and the wind is stronger than the gas flow, the opening in the cross section of the gas channel of Combustion is still small in size to ensure that combustion gas can be discharged out. It would be apparent to those skilled in the art that the bending portion of the movable deflector can be omitted and, in that case, the movable deflector does not have the third position. In addition, the movement of the movable deflector is not limited to a pivoting movement, being able to move along a linear direction in other embodiments. For example, the movable baffle can be arranged in the oblique part 221 of the bottom wall of the flue gas channel 232, and the opening in the cross section is defined by an upper part of the movable baffle and the top wall of the channel 232 for flue gas, the size of which can be adjusted by a linear movement of the movable baffle on the oblique part 221 of the lower wall.

Referring again to Figure 2, an air pressure switch 30 is mounted in the housing 10, and has a negative pressure port 301 and a positive pressure port 302. The negative pressure port 301 is connected to the fan of supply of air 105 through a first tube 31 to detect the negative pressure generated by the fan 105, and the positive pressure port 302 is connected to the atmosphere through a second tube 32. In the state of the art, when Adverse wind enters the apparatus through the gas exhaust port 221 of the combustion hood 20, the pressure switch 30 will detect the negative pressure changes caused by fan speed changes 405, which can give place to stop the device. However, in this embodiment, since the pressure exerted by the adverse wind can also be detected in the positive pressure port 302, the change in pressure of the negative pressure port 301 is counteracted by the change in pressure in the port of positive pressure 302, so that the air pressure switch 30 would not be affected by adverse wind, and the malfunction of the apparatus, caused by adverse wind, can be avoided.

With reference to Figures 4, 5 and 6A at 6C, in order to ensure that the pressure detected in the positive pressure port 301 is as close as possible to the pressure exerted by the adverse wind, a first inlet port 223 of air is disposed next to the gas exhaust port 221, and the second tube 32 is connected between the first air intake port 223 and the positive pressure port 301. By means of this, the adverse wind that passes through the gas exhaust port 221 can reach the positive pressure port 301 through the first air intake hole 223 and the second tube 32. In a preferred embodiment, the first air intake hole 223 is defined at the front end of the projecting part 22 of the hood 20 for combustion gas.

In the aforementioned embodiments, when it reaches the hood 20 for combustion gas through the gas exhaust port 221, rain can flow into the second tube 32 through the first air intake hole 223 and reach the positive pressure port 302, which can cause damage to the air pressure switch if the rain comes in contact with electronic parts. Figures 10 and 11 illustrate a further embodiment, in which a second air intake port 224 is disposed adjacent to the gas exhaust port 221; preferably, the air intake orifice 224 is defined at the leading end of the projecting portion 22, and is located above the first air intake orifice 223. The second tube 32 includes a connection tube section 322 connected between the first and second air intake holes 223, 224, and an extension tube section 323 is connected between the connection tube section 322 and the pressure port positive 302 of the air pressure switch. In this arrangement, the connection tube section 322 is U-shaped and the extension tube section 323 is located, at least partially, above

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of the second air intake hole 224.

Thus, when outside rain enters the connection tube section 322 through the first air intake hole 223 and / or the second air intake hole 224, the rain will not enter the extension tube section 323 because the extension tube section 323 is located, at least partially, above the second air intake hole 224, and then the rain drains out through the first air intake hole 223. When outside wind enters the connecting tube part 322 through the first hole 223 and the second hole 224, the two wind flows converge and enter the extension tube part 323. Referring to Fig. 4, in a preferred embodiment, a vent hole 321 is arranged in the extension tube section 323, in order to make the positive pressure port 302 communicate with the atmosphere in case they get stuck the first and second air intake holes 223, 224. Of course, in other embodiments, the first and second air inlet holes 223, 224 can be replaced by the vent hole 321 to establish the air connection between the positive pressure port 302 and the atmosphere.

Referring again to Figure 2, together with Figure 7 to Figure 9, a rain screen 40 is arranged in the housing 10 and adjacent to the air inlet 111 to prevent rain from entering the apparatus. The rain screen 40 includes a main panel 41, an upper panel 411, a lower panel 412 and a pair of side panels 42, 43.

The main panel 41 is turned towards the air inlet 111. The upper panel 411 is bent from the top of the front panel 41, and extends obliquely downwards, towards the air inlet 111. The lower panel 412 is bent perpendicularly from the lower part of the main panel 41 and also extends towards the air inlet 111. The pair of side panels 42, 43 are bent perpendicularly from opposite sides of the main panel 41 and extend in the direction away from the air inlet 111 At least one of the side plates is provided with a certain number of openings and, in a preferred embodiment, the two side panels 42, 43 have the openings 421,431. Due to this, the rain that arrives at the apparatus through the air inlet 111 can be retained mainly by the main panel 41, and the openings 421, 431 defined in the side panels allow air to enter the apparatus in order of producing combustion.

A certain number of rain retention fins 422, 432 are disposed near the openings 421, 431 in the side panels 42, 43. Each rain retention fin 422, 432 has an inclined portion 4221,4321 which extends obliquely from an edge of the opening 421, 431, and a parallel portion 4222, 4322 extending from the inclined portion and in parallel with the side panels 42, 43. This configuration is capable of further preventing the sprinkling of rain into the interior of the apparatus.

For rain screen 40 it is mounted in the housing 10 by means of its lower panel 412 which is connected to the lower plate 12 by means of screws. The lower panel 412 of the rain screen 40 defines a certain number of drain openings 4121 therein, and the lower plate 12 of the housing 10 is provided with a number of drain slots 122 corresponding to the drain openings 4121. in this way, the rain that the main panel 41 opposes can drain out of the apparatus through the drain openings 4121 and the drain slots 122. In addition, the bottom plate 12 is provided with a step 121 located adjacent to a mounting position of the screen 40 for rain on the bottom plate 12, and this step can act as an obstruction to prevent the rain that the main panel 41 opposes from entering the mounting position.

Figures 12 to 14 show an embodiment of the gas water heating apparatus according to the present invention, and the main difference from the previous embodiments is the position of the second tube. In the present embodiment, the second tube 33 has one end connected to the positive pressure port 302 of the air pressure switch 30, and the other end, namely the air intake end 331, located adjacent to the air inlet 111. The air intake end 331 is disposed in a position lower than that of the positive pressure port 302 around the vertical direction lake. By this, even if the outside rain passes in or condensation water forms in the second tube 33, the fluid would not circulate towards the air pressure switch 30. In addition, the air intake end 331 is disposed in the middle zone of the air inlet 111 along a lateral direction, which can ensure that the positive pressure port detects the adverse wind that arrives from the air inlet directly.

Referring to FIG. 14, the front plate 11 is provided with a screen plate 112 having a lower edge defining an upper edge of the air inlet 111. The air intake end 331 of the second tube is disposed behind screen plate 112, and this arrangement can prevent outside rain from spreading into the second tube 33 through the air intake end 331. In addition, the screen plate 112 is provided with a baffle 1121 that extends horizontally inwards, and the air intake end 331 is disposed below the baffle 1121. In this way, the adverse wind can be driven into the second tube 33 so that the pressure detected in the positive pressure port 302 is as close as possible to the wind pressure at the air inlet 111.

Similar to the previous embodiments, the second tube 33 has a vent hole 322 to cause the positive pressure port 302 to communicate with the atmosphere in case the air intake end 331 of the second tube 33 is stuck.

It is to be understood, however, that even though numerous features and advantages of the present invention have been set forth in the preceding description, together with details of the structure and function of the invention, the description is only illustrative, and can be made changes of detail, especially in matters of number, shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broadest general meaning of the thermal in which the appended claims have been expressed.

Claims (6)

5 10 fifteen twenty 25 30 1. A gas water heating apparatus (1) comprising: a housing (10); a burner (104) arranged in the housing to generate heat; a heat exchanger (107) to absorb heat and transfer heat to the water that passes through it; an air supply fan (105) arranged in the housing to supply air to the burner; characterized by an air pressure switch (30) having a negative pressure port (301) and a positive pressure port (302), said negative pressure port being connected to the air supply fan through a first tube ( 31) and said positive pressure port being connected to the atmosphere through a second tube (33); Y why the housing defines an air inlet (111) in a lower portion thereof; wherein the second tube (33) has an air intake end (331), and said air intake end is located adjacent to the air inlet to receive air passing through the air inlet; said air inlet (111) is arranged in a front plate (11) of the housing, and said front plate is provided with a screen plate (112) having a lower edge that forms an upper edge of the air inlet; wherein the air intake end (331) is disposed behind the screen plate (112). 2. A gas water heating apparatus according to claim 1, wherein said air intake end (331) is disposed in a position lower than that of the positive pressure port (332) of the air switch air pressure along a vertical direction. 3. A gas water heating apparatus according to claim 1, wherein said air intake end (331) is disposed in the middle area of the air inlet (111) along a direction side. 4. A gas water heating apparatus according to claim 1, wherein said screen plate (112) is formed with a deflector (1121) extending horizontally inward, and the intake end (331) of air is arranged below the baffle. 5. A gas water heating apparatus according to claim 1, further comprising a hood (20) for combustion gas arranged in the housing to receive the generator combustion gas by the burner, wherein said hood for flue gas it has a front end that defines a gas exhaust port (221) therein, to discharge the flue gas to the outside. 6. A gas water heating apparatus according to claim 1, wherein said second tube (33) defines a ventilation hole (321,332) in its body.