Patent Publication Number: US-10309687-B2

Title: Combustion control system of gas water heater or wall-hanging boiler and control method thereof

Description:
TECHNICAL FIELD 
     The present application relates to the field of water heater, in particular relates to a combustion control system of a gas water heater or wall-hanging boiler, and a control method thereof. 
     BACKGROUND TECHNOLOGY 
     In the prior art, there are different requirements for thermal loads of the combustor of a gas water heater or a wall-hanging boiler according to different demands for the amount and temperature of hot water. For example, when there is a need for a large amount of hot water, the combustor needs to have a larger thermal load, and when a small amount of hot water is desired, the combustor may only have a smaller thermal load. 
     Currently, the thermal load of a combustor is controlled mainly by controlling currents of a proportional valve and a fan. To be specific, when a larger thermal load is needed, a larger current will be supplied to the proportional valve, so that the proportional valve can have a larger opening, thereby more fuel gas will be allowed to pass through the proportional valve and reach the combustor for combustion; meanwhile, a larger current will also be supplied to the fan to provide it with a larger rotation speed to increase the flow of combustion air, so that the fuel gas can be better combusted in the combustor, and thereby the combustor will have a larger thermal load. 
     Under ideal conditions, the currents of the proportional valve and the fan are in correspondence relationship with each other, i.e., a determined current allows the proportional valve to have a determined opening. In general, the flow of fuel gas that passes through the proportional valve is in correspondence relationship with the opening of the proportional valve, and, since the flow of fuel gas is also in correspondence relationship with the flow of combustion air required for combustion, the current of the proportional valve and the flow of combustion air are also in correspondence relationship with each other. Furthermore, the flow of combustion air is formed in correspondence relationship with both of the demanded rotation speed and current of the fan, so that the current of the proportional valve and the current of the fan are also in correspondence relationship with each other. Due to the above correspondence relationships, the gas water heater and wall-hanging boiler in the prior art mostly apply a method of controlling thermal loads of the combustor by correspondingly controlling the currents of the proportional valve and the fan. 
     However, in real life, the operation environments for most gas water heaters or wall-hanging boilers are not ideal. In a case where there is wind in the operating environment, a reverse wind pressure may be generated at the exhaust channel of the gas water heater or wall-hanging boiler, blocking the exhaust of the gas water heater or wall-hanging boiler. When a reverse wind pressure occurs, the rotational resistance of the fan is increased, so that the current of the fan is decreased. At this point, this may lead to a reduction of the flow of combustion air, causing deterioration of the combustion condition and even flameout. In order to prevent the above situations from happening, a current compensation mechanism is provided for the fan, which will compensate the current of the fan when the current of the fan is decreased, so as to recover the rotational speed of the fan. Please further refer to  FIG. 1 . The existing compensation mechanisms mostly employ a method of sectional compensating the current of the fan. For example, when the reduction of current of the fan is less than 7%, no compensation or rotational speed increasing is performed for the current of the fan; when the reduction of current of the fan is 7%-13%, the fan is compensated by increasing its rotational speed to 500 rpm; when the reduction of current of the fan is 13%-25%, the fan is compensated by increasing the rotational speed to 700 rpm; and when the reduction of current of the fan is larger than 25%, a failure is reported. As such, when the reduction of current is smaller than a threshold value, no compensation will be performed for the current of the fan, at this point, the flow of combustion air is reduced, which influences the combustion condition and thereby reduces the thermal load of the combustor. Besides, due to the existence of the reverse wind pressure, even if the rotational speed of the fan is increased, the matching of the flow of combustion air is still inaccurate, and the flow of combustion air is still smaller than that in a state free of reverse wind pressure. It can be seen from the above that after the rotational speed of the fan is compensated, since the flow of combustion air is relatively small, the thermal load of the water heater is still low and is hard to satisfy the demands for the amount and temperature of hot water. 
     SUMMARY 
     The purpose of the embodiments of the present application is to provide a combustion control system of a gas water heater or wall-hanging boiler with good wind resistance capability, and a control method thereof. 
     In order to solve the above problem, the present application provides a combustion control system of a gas water heater or a wall-hanging boiler, comprising: a flue gas channel consisted of a combustor, a heat exchanger and a stepless speed regulating fan and a smoke tube which are connected sequentially; a control unit connected to a signal input end of the stepless speed regulating fan; a wind pressure sensor assembly that detects a pressure signal upstream of an impeller of the stepless speed regulating fan, a signal output end of the wind pressure sensor assembly being connected to the control unit; the control unit comprising a storage storing a correspondence relationship between the pressure signal upstream of the impeller of the stepless speed regulating fan and a thermal load of the combustor, and a controller that controls operation of the stepless speed regulating fan according to the correspondence relationship. 
     The present application also provides a control method for the above mentioned combustion control system of a gas water heater or a wall-hanging boiler, comprising steps as follows: the controller obtains a thermal load of the combustor according to a operation condition of the gas water heater or wall-hanging boiler, and obtains a pressure signal upstream of the stepless speed regulating fan corresponding to the thermal load based on the correspondence relationship in the storage, and uses the pressure signal as a target pressure signal; the controller obtains a current pressure signal upstream of the stepless speed regulating fan measured by the wind pressure sensor; the controller controls a rotational speed of the stepless speed regulating fan, and adjusts the current pressure signal to approach the target pressure signal. 
     As is clear from the above technical solutions provided by the embodiments of the present application, the control system and control method provided by the present application regulate the rotational speed of the stepless speed regulating fan by detecting a pressure upstream of the impeller of the stepless speed regulating fan, thus, in a case where a reverse wind pressure occurs, the pressure upstream of the stepless wind-regulating fan can be maintained by increasing the rotational speed of the stepless wind-regulating fan, thereby the flow of combustion air in the gas water heater as well as the combustion stability can be maintained. Compared to the prior art, the present application enables the matching between the wind quantity provided by the fan and the combustion condition to be more accurate by maintaining stability of the pressure upstream of the stepless speed regulating fan; meanwhile, it also greatly improves the wind pressure resistance capability of the gas water heater or wall-hanging boiler; in particular, the above control system is combined with a wind-proof cap that has an area larger than the smoke tube outlet, which wind-proof cap can realize balances at different angles under different internal and external pressure differences, providing better buffering and protection for the internal combustion, and in case of mutation of the reverse wind pressure, keeping good combustion conditions and providing stable thermal loads. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to explain more clearly the embodiments in the present application or the technical solutions in the prior art, the following will briefly introduce the figures needed in the description of the embodiments or the prior art. Obviously, figures in the following description are only some embodiments of the present application, and for an ordinary person skilled in the art, other figures may also be obtained based on these figures without paying creative efforts. 
         FIG. 1  is a diagram of relation between the control of motor rotational speed and the wind pressure in the prior art; 
         FIG. 2  is a structural diagram of the gas water heater provided by one embodiment of the present application; 
         FIG. 3  is a module diagram of the gas water heater provided by one embodiment of the present application; 
         FIG. 4  is a stereogram of the smoke tube in  FIG. 2 . 
         FIG. 5  is a front view of the smoke tube in  FIG. 4 ; 
         FIG. 6  is a section view of the smoke tube in  FIG. 5  along line A-A; 
         FIG. 7  is a top view of the wind-proof cap in  FIG. 6 ; 
         FIG. 8  is a stereogram of the fan mounting member and part of the piezometer tube in  FIG. 2 . 
         FIG. 9  is a stereogram of the fan mounting member and part of the piezometer tube in  FIG. 2 . 
         FIG. 10  is a stereogram of part of the piezometer tube in  FIG. 8  or  FIG. 9 ; 
         FIG. 11 a    is a schematic diagram of the piezometer tube provided by one embodiment of the present application; 
         FIG. 11 b    is a section view of the piezometer tube in  FIG. 11 a    along line B-B; 
         FIG. 12  is a stereogram of the wind pressure sensor provided by one embodiment of the present application; 
         FIG. 13  is a diagram of relation between the thermal load and the wind pressure signal provided by one embodiment of the present application; 
         FIG. 14  is a flow chart of the control method provided by one embodiment of the present application; 
         FIG. 15  is a diagram of the section view of the stepless speed regulating fan and part of the piezometer tube provided by one embodiment of the present application along a motor shaft of the stepless speed regulating fan. 
     
    
    
     DETAILED DESCRIPTION 
     In order to enable the persons skilled in the art to better understand the technical solutions of the present application, a clear and comprehensive description will be made to the technical solutions in the embodiments of the present application in the following in combination with the figures in the embodiments of the present application, obviously, the embodiments described herein are only part of the embodiments of the present application rather than the entire embodiments of the application. Based on the embodiments of the present application, all other embodiments obtained by ordinary skilled persons in the field without paying creative efforts should pertain to the extent of protection of the present application. 
     Please refer to  FIGS. 2, 3 and 15  together, which illustrate a gas water heater  10  provided by one embodiment of the present application. The gas water heater  10  comprises: a flue gas channel  18  consisted of a combustor  12 , a heat exchanger  14  and a stepless speed regulating fan  16  and a smoke tube  17  which are connected sequentially; a control unit  20  electrically connected to a signal input end of the stepless speed regulating fan  16 ; a wind pressure sensor assembly  22  that detects a pressure signal upstream of an impeller  49  of the stepless speed regulating fan  16 , a signal output end of the wind pressure sensor assembly  22  being connected to the control unit  20 ; the control unit  20  comprising a storage  24  for storing a correspondence relationship between the pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16  and a thermal load of the combustor  12 , and a controller  26  that controls operation of the stepless speed regulating fan  16  according to the correspondence relationship. 
     The gas water heater  10  provided by the embodiment of the present application further regulates the rotational speed of the stepless speed regulating fan  16  by detecting a pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16 . Thus, in a case where a reverse wind pressure occurs, the pressure upstream of the stepless wind-regulating fan  16  can be maintained by increasing the rotational speed of the stepless wind-regulating fan  16 , thereby the flow of combustion air in the gas water heater  10  as well as the thermal load of the combustor  12  can be maintained. The pressure signal is a signal obtained by detection of the wind pressure sensor assembly  22 , and is used to represent pressure. The upstream of the impeller  49  of the stepless speed regulating fan  16  may be an upstream of the overall flow direction of air flow inside the gas water heater  10 . 
     In operation process of the gas water heater  10 , the impeller  49  of the stepless speed regulating fan  16  rotates rapidly to cause flow of the air flow, so that fuel gas is combusted on the combustor  12 . During rotation of the impeller  49  of the stepless speed regulating fan  16 , a negative pressure will be formed upstream of the impeller  49  of the stepless speed regulating fan  16 . Due to the existence of the negative pressure, the gas in the heat exchanger  14  and combustor  12  will be driven to flow towards the stepless speed regulating fan  16 , thereby realizing the flow of air flow inside the gas water heater  10 . Seen as such, the formation of negative pressure is realized by setting the stepless speed regulating fan  16 , while the negative pressure further leads to the flow of air flow. Therefore, it is clear that as long as the negative pressure is maintained, the heat exchanger  14  and the combustor  12  will be maintained with a certain combustion air flow, and thus the combustor  12  can be maintained at a stable thermal load. The present application detects a pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16  by setting a wind pressure sensor assembly  22 , thereby achieves to detect pressure in a negative pressure state formed by the stepless speed regulating fan  16 , and further controls rotation of the stepless speed regulating fan  16  according to the pressure signal. 
     In a specific embodiment, for example: when the gas water heater is operated, a thermal load can be calculated based on the set temperature, actual water flow and inflow water temperature etc. of the gas water heater or wall-hanging boiler, and a target pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16  under that thermal load can thus be obtained according to the correspondence relationship stored in the storage  24 , then, the controller  26  controls the stepless speed regulating fan  16  to rotate so as to allow a current pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16  to reach the target pressure signal. 
     Furthermore, when the current pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16  is larger than the target pressure signal, the controller  26  can control the stepless speed regulating fan  16  to increase its rotational speed so as to decrease the current pressure signal to the target pressure signal; when the current pressure signal is smaller than the target pressure signal, the controller  26  can control the stepless speed regulating fan  16  to decrease its rotational speed so as to increase the current pressure signal to the target pressure signal. 
     In a specific embodiment, the thermal load of the combustor  14  can be calculated by the following formula:
 
 Q   thermal =( T   set   −T   inlet )* Q   flow  
 
     wherein, Q thermal  represents the thermal load, T set  represents the set temperature, T inlet  represents the inflow water temperature, and Q flow  represents an actual water flow. 
     A further example is: when a reverse wind pressure occurs, the wind quantity of the stepless speed regulating fan  16  will be decreased under the influence of the reverse wind pressure, which will lead to an increase in a current pressure upstream of the stepless speed regulating fan  16 , and the wind pressure sensor assembly  22  will detect the current pressure signal. The controller  26  can compare the current pressure signal with the target pressure signal to find that the current pressure signal is larger than the target pressure signal, and then controls the stepless speed regulating fan  16  to increase its rotational speed to decrease the current pressure signal to the target pressure signal so as to achieve to maintain the thermal load of the combustor. It is clear that the gas water heater  10  has a good wind resistance performance. 
     Of course, the embodiments of the present application are not limited to gas water heater, but are also applicable in a wall-hanging boiler. The wall-hanging boiler comprises the combustor, heat exchanger, stepless speed regulating fan, control unit and wind pressure sensor assembly described in the present application. To be specific, the structures and operation modes of these components are the same as that depicted in the present application documents, so detailed descriptions thereof will be omitted here. 
     The combustor  12  can be connected to a fuel gas pipeline on which a proportional valve may be provided, by which proportional valve the flow of combustion air entering the combustor  12  is controlled. Fuel gas can be combusted in the combustor  12  to release energy. The thermal load of the combustor  12  may be heat released per unit time during combustion of the combustion air in the combustor  12 . 
     The heat exchanger  14  is connected to the combustor  12 , and can absorb heat released by the combustor  12  and transfer the heat to the water to be heated. Along flue gas flow direction, the heat exchanger  14  is provided downstream of the combustor  12 , so that heat exchanges can be performed to the high temperature flue gas produced after combustion in the combustor  12  in the heat exchanger  14 . In this embodiment, the heat exchanger  14  may be a finned tube heat exchanger. 
     The stepless speed regulating fan  16  is provided downstream of the heat exchanger  14  and provides a driving force for the flow of flue gas flow. Thus the fuel gas in the fuel gas pipeline can reach the combustor  12  for combustion via the proportional valve, and the high temperature flue gas after combustion can reach the heat exchanger  14 . Furthermore, the stepless speed regulating fan  16  drives the flue gas subjected to heat exchange in the heat exchanger  14  to exit the gas water heater through a flue gas channel  18 . A signal input end of the stepless speed regulating fan  16  is electrically connected to the control unit  20 , so that the controller  26  can control the rotational speed of the stepless speed regulating fan  16 . The stepless speed regulating fan  16  has an air inlet and an air outlet. In this embodiment, the air inlet corresponds to the heat exchanger  14 , so that the flue gas through the heat exchanger  14  can enter the stepless speed regulating fan  16  through the air inlet and flow out from the air outlet; the air outlet is connected to a smoke tube  17  such that the flue gas flowing out from the air outlet can be expelled from the smoke tube  17 . The stepless speed regulating fan  16  comprises: a fan shell  47  with the air inlet  45  and air outlet, a motor  43 , and the impeller  49  driven to rotate by the motor  43 . The impeller  49  is provided inside the fan shell  47 . The motor  43  drives the impeller  49  to rotate so that air flow enters the fan shell  47  from the air inlet  45  and flow out of the fan shell  47  from the air outlet. 
     Please refer to  FIGS. 2, 4, 5 and 6  together. In one embodiment, a smoke tube outlet  28  of the smoke tube  17  is provided with a wind-proof cap  30  that opens and closes along with a change of pressure inside and outside the smoke tube outlet  28 . 
     In this embodiment, the smoke tube outlet  28  is provided with a wind-proof cap  30  to achieve the effect that when a reverse air flow occurs at the smoke tube outlet  28  the wind-proof cap  30  can stop the reverse air flow from entering the inside of the gas water heater  10 , thereby reducing a reverse wind pressure applied to the stepless speed regulating fan  16 . To be specific, the wind-proof cap  30  is in rotational connection with the smoke tube  17 . 
     Please refer to  FIGS. 6 and 7  together. Furthermore, the wind-proof cap  30  has an area larger than an area of the smoke tube outlet  28 . Thus, in some circumstances when stronger reverse air flows occur, the wind-proof cap  30  can cover the smoke tube outlet  28  to prevent the strong reverse air flow from directly striking the stepless speed regulating fan  16 . Besides, the air flow driven by the stepless speed regulating fan  16  flows along the smoke tube  17  and can push the wind-proof cap  30  to open, so that the inside flue gas can be expelled from the smoke tube outlet  28 . 
     In one embodiment, the wind-proof cap  30  has a turn-up  32  that covers part of the smoke tube  17 . In this embodiment, an edge of the wind-proof cap  30  is extended in a direction for covering the outer lateral wall of the smoke tube  17 , forming the turn-up  32 . As such, when a reverse air flow pushes the wind-proof cap  30  to cover the smoke tube outlet  28 , the turn-up  32  can effectively diminish the reverse air flow entering the smoke tube  17  from a gap between the wind-proof cap  30  and the smoke tube outlet  28 , thereby further decreases a reverse wind pressure suffered by the stepless speed regulating fan  16 . 
     Please refer to  FIGS. 4, 5 and 6  together. In one embodiment, the flue gas channel  18  also comprises an outer surface close to the smoke tube outlet  28  to which a transitional smoke tube  34  that accommodates the wind-proof cap  30  is connected. The transitional smoke tube  34  accommodates the wind-proof cap  30  so that the wind-proof cap  30  and the smoke tube outlet  28  are not directly exposed to the external environment, furthermore, the transitional smoke tube  34  will have an influence to air flow in the external environment. The external environment may be an environment of the natural world where the air flow direction varies a lot. If the wind-proof cap  30  and the smoke tube outlet  28  are directly exposed in the external environment, due to the varied air flow directions, the wind-proof cap  30  may be opened to a relative large angle such that when a reverse air flow towards the inside of the smoke tube  17  occurs, it may be hard for the wind-proof cap  30  to restore and thus loses its efficacy. In this embodiment, by setting the transitional smoke tube  34 , the air flow flowing only towards the transitional smoke tube  34  can reach the wind-proof cap  30 , i.e., the transitional smoke tube  34  blocks air flows of other directions to prevent the wind-proof cap  30  from being opened to a relative large angle. And since the air flow that reaches the wind-proof cap  30  flows in a direction towards the inside of the smoke tube  17 , it will push the wind-proof cap  30  to move in a direction for covering the smoke tube outlet  28 , thereby blocking a reverse air flow from entering the smoke tube  17  and reducing a reverse wind pressure suffered by the stepless speed regulating fan  16 . 
     Please refer to  FIGS. 2 and 8  together. A fan mounting member  36  is provided between the heat exchanger  14  and the stepless speed regulating fan  16 . The fan mounting member  36  can be fixedly connected to a housing of the gas water heater  10 , and can further be fixedly connected to the fan shell of the stepless speed regulating fan  16 , thereby a position limitation of the stepless speed regulating fan  16  is realized. The fan mounting member  36  is located upstream of the stepless speed regulating fan  16  in an air flow direction, the fan mounting member  36  is provided with an opening corresponding to the air inlet of the stepless speed regulating fan  16 , so that the flue gas of the heat exchanger  14  can reach the air inlet through the opening. 
     In one embodiment, the wind pressure sensor assembly  22  measures a pressure at a position upstream of the stepless speed regulating fan  16  and close to the air inlet. Since this part of pressure changes significantly with the rotational speed of the stepless speed regulating fan  16 , the controller  26  can rapidly control the rotational speed of the stepless speed regulating fan  16  according to a current pressure signal detected by the wind pressure sensor assembly  22 . 
     Please refer to  FIGS. 2, 8, 9 and 10 . In one embodiment, the wind pressure sensor assembly  22  comprises a piezometer tube  38  and a wind pressure sensor  40 ; one end of the piezometer tube  38  is connected to the wind pressure sensor  40 , while the other end thereof is a pressure measuring end  42 . The wind pressure sensor  40  is provided at a position outside the flue gas channel  18  and higher than a positon of the pressure measuring end  42 . In this embodiment, the pressure measuring end of the piezometer tube  38  can be provided upstream of the stepless speed regulating fan  16 , so that an interior of the piezometer tube  38  is in communication with the upstream of the stepless speed regulating fan  16 . At this point, a gas pressure inside the piezometer tube  38  is equal to a gas pressure upstream of the stepless speed regulating fan  16 , thus a gas pressure signal in the piezometer tube  38  can be detected by means of the wind pressure sensor  40 , thereby obtaining a pressure signal upstream of the stepless speed regulating fan  16 . Since the upstream of the stepless speed regulating fan  16  is in communication with the heat exchanger  14 , the gas flowing into the stepless speed regulating fan  16  is the flue gas through the heat exchanger  14 . Since the temperature of the flue gas is relatively high, if the wind pressure sensor  40  is directly provided upstream of the stepless speed regulating fan  16 , the heat of the flue gas will greatly shorten the service life of the wind pressure sensor  40 . In this embodiment, by setting the piezometer tube  38  and placing the pressure measuring end  42  of the piezometer tube  38  between the stepless speed regulating fan  16  and the combustor  12 , the wind pressure sensor  40  can be provided at a position relatively far away from the flue gas, i.e., outside the flue gas channel  18 , and, a pressure upstream of the stepless speed regulating fan  16  can also be measured by the piezometer tube  38 , thereby prolonging the service life of the wind pressure sensor  40 . To be specific, a part of the piezometer tube  38  close to the pressure measuring end  42  is fixedly connected to the fan mounting member, realizing the position limitation of the pressure measuring end  42 . 
     In this embodiment, during operation process of the wind pressure sensor assembly  22 , since the flue gas will be condensed in the piezometer tube  38  and produce a small amount of liquid, the wind pressure sensor  40  is provided at a position higher than the position of the pressure measuring end  42  to make it hard for the condensed liquid in the piezometer tube  38  to reach the wind pressure sensor  40 , thereby avoiding damages to the wind pressure sensor  40 . Furthermore, please refer to  FIGS. 11 a  and 11 b   . A cavity  44  lower than the pressure measuring end  42  is connected between the piezometer tube  38  and the wind pressure sensor  40 , and a cross sectional area of the cavity  44  is larger than that of the piezometer tube  38 . By setting in such way, the condensed liquid in the piezometer tube  38  can flow into the cavity  44 , which further reduces the influence of the condensed liquid to the wind pressure sensor assembly  22 , and can also reduce outflow of the condensed liquid from the pressure measuring end  42  to prevent other elements from being damaged. 
     Please refer to  FIGS. 2 and 15  together. In one embodiment, the pressure measuring end  42  extends from the air inlet  45  of the stepless speed regulating fan  16  into the inside of the fan shell  47  of the stepless speed regulating fan  16 . In this embodiment, the motor  43  is located outside the fan shell  16  and can drive the impeller  49  to rotate. The impeller  49  is provided in the fan shell  47 , and can cause air flow to enter the fan shell  47  from the air inlet  45  and flow out of the fan shell  47  from the air outlet. The pressure measuring end  42  extends into the inside of the fan shell  47  and is still located upstream of the impeller  49  of the stepless speed regulating fan  16 . In this embodiment, the stepless speed regulating fan  16  is a centrifugal fan, i.e., the impeller  49  is a centrifugal impeller. When the impeller  49  rotates, it will drive the air flow to move towards a circumferential direction of the impeller  49  from an axial direction of the impeller  49 . The pressure measuring end  42  can extend into the stepless speed regulating fan  16  along an axial direction of the impeller  49  from the air inlet  45 , at this point, the pressure measuring end  42  is still located upstream of the impeller  49  in the direction of the air flow, so that the wind pressure sensor assembly  22  can measure a pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16 . 
     Please refer to  FIGS. 2 and 12  together. In one embodiment, in order to further reduce the influence of thermal radiation of flue gas to the wind pressure sensor  40 , a thermal insulating apparatus  46  is provided between the wind pressure sensor  40  and the flue gas channel  18 . In this embodiment, the thermal insulating apparatus  46  may be a partition board placed between the wind pressure sensor  40  and the flue gas channel  18 , by which the thermal radiation of the flue gas channel  18  to the wind pressure sensor  40  is reduced. The material of the thermal insulating apparatus  46  may be stainless steel, ceramic, fiberglass, asbestos, rock cotton and silicate, etc. Of course, the material of the thermal insulating apparatus  46  is not limited to the above examples. In this embodiment, the wind pressure sensor  40  is fixedly connected to the housing of the gas water heater  10  by means of a mounting plate  48 , and the thermal insulating apparatus  46  is fixedly connected to the mounting plate  48 . 
     Please refer to  FIGS. 2 and 3  together. The control unit  20  controls the rotational speed of the stepless speed regulating fan  16  based on the pressure signal measured by the wind pressure sensor assembly  22 . The storage  24  stores a correspondence relationship between the pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16  and the thermal load, which correspondence relationship can realize the correspondence of the two by functional operation, and it can also store the correspondence relationship having numerical values of the two by using a data table. 
     In a specific embodiment, the correspondence relationship may be f=kQ+b, wherein f is the pressure signal upstream of the stepless speed regulating fan  16 , Q is the thermal load of the combustor  12 , k is sensitivity of the wind pressure sensor  40 , and b is a reference value of the wind pressure sensor  40 . A more specific example should be: the correspondence relationship may be f=0.5Q−194, based on which the trajectory line in  FIG. 13  (wherein the pressure signal f is represented by the unit Hz output by the wind pressure sensor) can be obtained. 
     In a specific embodiment, the correspondence relationship may also be stored in the storage  24  in the form of a data table that records data of the pressure signal and the thermal load correspondingly. To be specific, the data table can be seen in the following table 1. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Number 
                 Pressure signal (Hz) 
                 Thermal load (L/min*C. °) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 172 
                 672 
               
               
                 2 
                 207 
                 739 
               
               
                 3 
                 243 
                 806 
               
               
                 4 
                 279 
                 873 
               
               
                 5 
                 315 
                 940 
               
               
                 6 
                 351 
                 1008 
               
               
                 7 
                 387 
                 1075 
               
               
                 8 
                 423 
                 1142 
               
               
                 9 
                 459 
                 1209 
               
               
                 10 
                 495 
                 1276 
               
               
                 11 
                 530 
                 1343 
               
               
                   
               
            
           
         
       
     
     Please refer to  FIG. 14 , the embodiments of the present application also provide a control method for the above mentioned combustion control system of a gas water heater or a wall-hanging boiler. The control method comprises steps as follows: 
     step S 10 : the controller  26  obtains a thermal load of the combustor  14  according to a operation condition of the gas water heater or wall-hanging boiler, and obtains a pressure signal corresponding to the thermal load based on the correspondence relationship in the storage, and uses the pressure signal as a target pressure signal. 
     In this embodiment, the operation condition includes set temperature, actual water flow and inflow water temperature, wherein the set temperature may be a temperature set by a user operating the gas water heater or wall-hanging boiler according to actual needs; the actual water flow may be the flow of water flowing into the gas water heater or wall-hanging boiler when operated; and the inflow water temperature may be a water temperature at a water inlet or a pipeline connected to the water inlet of the gas water heater or wall-hanging boiler. 
     In a specific embodiment, the thermal load of the combustor  14  can be calculated by the following formula:
 
 Q   thermal =( T   set   −T   inlet )* Q   flow  
 
     wherein, Q thermal  represents the thermal load, T set  represents the set temperature, T inlet  represents the inflow water temperature, and Q flow  represents the actual water flow. 
     In this embodiment, after obtaining the thermal load of the combustor  14 , the controller  26  can obtain a target pressure signal upstream of the stepless speed regulating fan  16  according to the correspondence relationship, i.e., when the upstream of the stepless speed regulating fan is maintained at the target pressure signal, the actual thermal load of the combustor  14  can reach the mentioned thermal load. 
     Step S 20 : the controller  26  obtains a current pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16  detected by the wind pressure sensor  40 . 
     Step S 30 : the controller  26  controls by a rotational speed of the stepless speed regulating fan  16 , and adjusts the current pressure signal to approach the target pressure signal. 
     In this embodiment, when the current pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16  is larger than the target pressure signal, the controller  26  can control the stepless speed regulating fan  16  to increase its rotational speed so as to decrease the current pressure signal to the target pressure signal; when the current pressure signal is smaller than the target pressure signal, the controller  26  can control the stepless speed regulating fan  16  to decrease its rotational speed so as to increase the current pressure signal to the target pressure signal. 
     A further example is: when a reverse wind pressure occurs, the wind quantity of the stepless speed regulating fan  16  will be decreased under the influence of the reverse wind pressure, which will lead to an increase in a current pressure upstream of the stepless speed regulating fan  16 , and the wind pressure sensor assembly  22  will detect the current pressure signal; the controller  26  can compare the current pressure signal with a target pressure signal to find that the current pressure signal is larger than the target pressure signal, and then controls the stepless speed regulating fan  16  to increase its rotational speed to decrease the current pressure signal to the target pressure signal so as to maintain the thermal load of the combustor. It is thus clear that the gas water heater  10  has a good wind resistance performance. 
     In one embodiment, when the wind-proof cap  30  tends to close or is closed, the controller  26  controls the stepless speed regulating fan to increase its rotational speed. In this embodiment, when a reverse air flow occurs in the flue gas channel  18 , the reverse air flow will push the wind-proof cap  30  to cover the smoke tube outlet  28 , so that air flow in the smoke tube  17  is blocked, the resistance to the stepless speed regulating fan  16  is increased and the rotational speed of the stepless speed regulating fan  16  is decreased, resulting in an increased current pressure upstream of the impeller  49  of the stepless speed regulating fan  16 . As such, the controller  26  controls the stepless speed regulating fan  16  to increase its rotational speed so as to reduce the current pressure upstream of the impeller  49  of the stepless speed regulating fan  16  and increase the flow velocity of air flow in the smoke tube  17 , thereby pushing the wind-proof cap  30  to resist the external reverse air flow. 
     In one embodiment, the correspondence relationship between the pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16  and the thermal load of the combustor  12  is |Δf|∝|ΔQ|, wherein Δf is an amount of change of the pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16 , and ΔQ is an amount of change of the thermal load of the combustor  12 . Thus, the amount of change of the pressure signal is in direct proportional relationship with that of the thermal load, and the controller  26  controls the rotational speed of the stepless speed regulating fan  16  based on this rule to maintain the thermal load of the combustor  12 . As a specific example, the correspondence relationship may be f=kQ+b, wherein f is the pressure signal upstream of the impeller  49  of the stepless speed regulating fan  16 , Q is the thermal load of the combustor  12 , k is sensitivity of the wind pressure sensor  40 , and b is a reference value of the wind pressure sensor  40 . A more specific example should be: the correspondence relationship may be f=0.5Q−194, based on which the trajectory line in  FIG. 13  (wherein the pressure signal f is represented by the unit Hz output by the wind pressure sensor) can be obtained. 
     In one embodiment, the correspondence relationship includes a predefined function that expresses a logical relationship between the pressure signal and the thermal load, the predefined function has a predefined parameter which represents a reference value of the wind pressure sensor  40 ; the wind-proof cap  30  covers the smoke tube outlet  28  before the stepless speed regulating fan  16  is operated, and the controller  26  obtains the current pressure signal detected by the wind pressure sensor assembly  22  as the reference value of the pressure signal upstream of the stepless speed regulating fan in the correspondence relationship. 
     In this embodiment, the predefined function may be a linear function, a quadratic function or a higher order function. To be specific, as exemplified before, the correspondence relationship may be f=kQ+b. The predefined function has a predefined parameter, which may be a part of the predefined function or an input variable. The predefined parameter represents a reference value of the wind pressure sensor  40  and can be understood in such a way that the predefined function conducts calculation by using the reference value of the wind pressure sensor  40  as a parameter. The reference value of the wind pressure sensor  40  can be understood as an output value of the wind pressure sensor  40  in a state free of outside interference or where the outside interference can be ignored. 
     In this embodiment, after the wind pressure sensor  40  has been used for a long time, due to aging of the wind pressure sensor  40 , the phenomenon of zero drift may occur thus the detected pressure signal cannot accurately reflect the pressure upstream of the stepless speed regulating fan  16 , and as a result the control of the rotational speed of the stepless speed regulating fan according to the detected pressure signal is also inaccurate. In this embodiment, the problem of inaccurate measurement caused by zero drift has been overcome by using the current pressure signal measured by the wind pressure sensor assembly  22  as the reference value in the stored correspondence relationship in a state where the stepless speed regulating fan  16  is not operated. That is to say, in this embodiment, the reference value of the pressure signal in the correspondence relationship can be dynamically adjusted according to the state of aging of the wind pressure sensor  40 , thereby the measured current pressure signal can accurately reflect the pressure upstream of the stepless speed regulating fan  16 . 
     As is clear from the above technical solutions provided by the embodiments of the present application, the control system and control method provided by the present application regulate the rotational speed of the stepless speed regulating fan by detecting a pressure upstream of the impeller of the stepless speed regulating fan, thus, in a case where a reverse wind pressure occurs, they can maintain the pressure upstream of the stepless wind-regulating fan by increasing the rotational speed of the stepless wind-regulating fan, thereby the flow of combustion air in the gas water heater as well as the combustion stability can be maintained. Compared to the prior art, the present application enables the matching between the wind quantity provided by the fan and the combustion condition to be more accurate by maintaining stability of the pressure upstream of the stepless speed regulating fan; meanwhile, the wind pressure resistance capability of the gas water heater or wall-hanging boiler is also greatly improved; in particular, the above control system is combined with a wind-proof cap that has an area larger than the smoke tube outlet, which wind-proof cap can realize balances at different angles under different internal and external pressure differences, providing better buffering and protection for the internal combustion, keeping good combustion conditions and providing stable thermal loads in case of mutation of reverse wind pressure. 
     Although the present application has been depicted by the embodiments, under the inspiration of the technical essence of the present application, skilled persons in the art may combine the above embodiments, and may also make changes to the embodiments of the present application, but these should all be covered within the protection scope of the present application as long as the functions and effects achieved thereby are identical or similar to the present application.