System and method of detection of low gas supply pressure in gas appliances

Abstract

A combustion control system is provided, the system comprising: a fuel inlet; an air inlet; a burner into which a mixture of fuel and air is supplied, to be burned to produce heat; a controller; a combustion sensor configured to measure the composition of the combustion gases; wherein the controller is configured to: determine, using the output of the combustion sensor, the composition of the combustion gases; determine the speed of supplying the fuel / air mixture into the burner; correlate the speed of supplying the fuel / air mixture into the burner and the composition of the fuel / air mixture; and determine whether the curve representing the correlation differs from a constant by more than a threshold.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to detection of low gas supply pressure for gas appliances such as boilers, e.g. boilers for producing hot water, in particular boilers for use in a home heating or HVAC system.BACKGROUND OF THE INVENTION

[0002] In a gas appliance such as a boiler (e.g. a boiler run in a home for producing hot water), gas is used as fuel which is combusted (burned) to produce heat. Prior to entering a combustion chamber of the appliance, gas is mixed with air. The gas / air ratio of such mixture of air and gas depends on many factors.

[0003] To facilitate the flow of gas into the combustion chamber and / or to adjust the gas / air ratio, several features may be provided. Among these features may be valves, a fan etc. In particular, the fan can be operated in different speeds. For example, in normal operation, the speed of the fan influences the amount of gas / air mixture supplied into the combustion chamber. In conventional boilers, the fan speed is used by a processing unit to determine the heat input of the boiler (i.e. the amount of gas that enters the combustion chamber and is then transformed by combustion into heat). This determination depends on the gas pressure being sufficient to keep a steady gas / air ratio in the gas / air mixture. In certain situations, however, the gas pressure may be not sufficient to supply enough gas to keep the gas / air ratio even in higher fan speeds. This may be a result of e.g. supply chain problems. This negatively influences the gas / air ratio (e.g., the gas / air mixture is too lean and / or the heat output of the boiler is insufficient).

[0004] There is therefore a need for improvements in conventional boilers.SUMMARY OF THE INVENTION

[0005] In a first aspect, a combustion control system is provided. The system comprises a fuel inlet; an air inlet; a burner into which a mixture of fuel and air is supplied, to be burned to produce heat; a controller; a combustion sensor configured to measure the composition of the combustion gases; wherein the controller is configured to: determine, using the output of the combustion sensor, the composition of the combustion gases; determine the speed of supplying fuel / air mixture into the burner; correlate the speed of supplying the fuel / air mixture into the burner and the composition of the combustion gases; and determine whether the curve representing the correlation differs from a constant by more than a threshold.

[0006] In embodiments of the combustion control system, one or more of the following features may be used.

[0007] The the controller may be further configured to: in response to determination that the curve representing the correlation differs from a constant by more than a threshold, determine the maximum speed of supplying the fuel / air mixture into the burner for which the curve representing the correlation differs from a constant by less than a threshold.

[0008] In response to determination of the maximum speed of supplying the fuel / air mixture into the burner for which the curve representing the correlation differs from a constant by less than a threshold, the controller may be further configured to adjust the speed of supplying the fuel / air mixture into the burner such that the speed is below the maximum speed.

[0009] The controller may be further configured to: in response to determination that the curve representing the correlation differs from a constant by more than a threshold, determine the pressure of fuel supplied into the fuel / air mixture is lower than 10 mbar.

[0010] The controller, in response to determination that the curve representing the correlation differs from a constant by more than a threshold, may be further configured to output a message for a user. The message may be a warning for a user that gas supply pressure is low and / or a request for the user to check or adjust the gas supply pressure.

[0011] The controller, in response to determination that the curve representing the correlation differs from a constant by more than a threshold, may be further configured to shut off the supply of gas into the burner.

[0012] The system may further comprise a fan positioned upstream of the burner and wherein the speed of supplying the fuel / air mixture into the burner may be adjusted by adjusting the speed of the fan.

[0013] The combustion sensor may be an oxygen sensor. The combustion sensor may be positioned upstream of the burner.

[0014] In a second aspect, a method of operating a combustion control system is provided. The system comprises: a fuel inlet; an air inlet; a burner into which a mixture of fuel and air is supplied, to be burned to produce heat; a controller; and a combustion sensor configured to measure the composition of combustion gases; the method comprises: determining, by the controller, using the output of the combustion sensor, the composition of the combustion gases; determining, by the controller, the speed of supplying the fuel / air mixture into the burner; correlating, by the controller, the speed of supplying the fuel / air mixture into the burner and the composition of the combustion gases; and determining, by the controller, whether the curve representing the correlation differs from a constant by more than a threshold.

[0015] In embodiments of the seconf aspect, the combustion control system is as described in connection with the first aspect. In embodiments of the second aspect, the method implemented by the controller may correspond to the steps executed by the controller from the first aspect.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figures 1a and 1b are schematic views of a boiler fitted with arrangement for detection of low gas supply pressure; Figure 2 is an illustration of how net heat input and oxygen percentage can be used for detection of low gas supply pressure; Figure 3 is a flow chart of a method for controlling a boiler. DETAILED DESCRIPTION

[0017] The below description is for illustration only and is not intended to be limiting. Various elements of embodiments described below may be combined into new embodiments not explicitly described herein, as appropriate.

[0018] Fig 1 shows a schematic view of an example gas appliance 100. The appliance may be a boiler (a water heater) which combusts fuel (e.g. natural gas) to produce heat.

[0019] In the example shown in Fig 1, the appliance 100 comprises a controller 101, which is connected to various components of the appliance 100 and controls the various processes performed by these components. The controller 101 may be connected, among other components, to an igniter 102 and a fan 104. Not all connections between the controller 101 and the components of the appliance 100 are shown in Fig 1.

[0020] The appliance 100 comprises a combustion chamber 103. The combustion chamber 103 is a space into which fuel (e.g. natural gas mixed with air) is supplied and in which heat is produced by combusting the fuel. The combustion of the fuel is initiated in the combustion chamber 103 by the igniter 102, which is connected to and controlled by the controller 101. The combustion chamber 103 further comprises a burner 109 and a heat exchanger 110.

[0021] The appliance 100 further comprises the fan 104, a mixer 105 which serves to mix air and fuel prior to the mixture entering the fan 104 (e.g., a Venturi) and a valve 107. The fan 104 serves to supply the mixture of air and fuel from a mixer 105 to the combustion chamber 103 and more particularly to the burner 109. In the description below, it is referred primarily to "gas", but it will be understood that such references may also mean "fuel".

[0022] The valve 107 (which may in principle comprise several components) may be a gas valve which serves to regulate the input of gas into the mixer 105. The mixer 105 is upstream of the fan 104.

[0023] The fan 104 is connected to the controller 101, which monitors the speed of the fan 104. In normal operation, based on the fan speed, the controller 101 may determine the heat input of the boiler 100 (i.e. the amount of gas in the gas / air mixture supplied to the burner 109 and therefore burned to produce heat).

[0024] In some embodiments, the boiler 100 may comprise pressure feedback 108, shown schematically between the valve 107 and the mixer 105. In normal operation, the pressure feedback 108 is provided to enable the valve 107 to control the amount of gas supplied in response to the supplied air. In other words, supplied air pressure is fed back to the valve 107 and based on its value, the valve 107 allows or restricts the flow of gas into the mixer 105 to keep the gas / air ratio approximately level.

[0025] If the gas supply pressure (i.e. the pressure of the gas supplied to the boiler 100 from an external source, e.g. mains) is low (e.g. lower than 10 mbar) may have adverse effects on the heat input, the fuel / air mixture composition and / or on functioning of the boiler 100. The adverse effects on functioning of the boiler 100 may range from a nuisance (e.g. unusually loud ignition or running of the boiler 100) to more substantial matters (e.g. the boiler 100 running inefficiently, the boiler shutting down unexpectedly, etc.).

[0026] A particular way to detect low gas supply pressure and subsequently mitigate its effects is described below.

[0027] In the example embodiment of Fig 1, the boiler 100 is provided with a combustion sensor 106. Two example locations for the combustion sensor 106 are shown in Figs 1a and 1b. In the example of Fig 1a, the combustion sensor 106a is shown positioned within the combustion chamber 109. In the example of Fig 1b, the combustion sensor 106b is shown in the flue gas exhaust 111. It will be understood that these two locations are provided as example only. More than one combustion sensor 106 may be provided.

[0028] The combustion sensor 106 may be e.g. oxygen sensor, CO 2 sensor, or any other appropriate sensor capable of measuring the composition of the gases in the combustion chamber 109 and / or the flue gas exhaust 111. In Fig 1a, the sensor 106a measures the composition of the gases in the combustion chamber 109. In Fig 1b, the sensor 106b measures the composition of the flue gases. The composition of the gases in the combustion chamber 109 and / or in the flue gas exhaust 111 may be indicative of excess air in the gas / air mixture (i.e. air which is not used in combustion).

[0029] For example, if the sensor 106 is an oxygen sensor, the percentage of oxygen in the combustion chamber 109 and / or in the flue gas exhaust 111 may be indicative of excess air in the gas / air mixture (i.e. air which is not used in combustion) as follows. It will be understood that if the combustion sensor 106 is a different type of sensor (e.g. a CO 2 sensor), the described mechanism would work analogously.

[0030] The sensor 106 detects a percentage of oxygen in the combustion chamber 109 and / or in the flue gas exhaust 111. The oxygen percentage thus obtained may be plotted by the controller 101 against the speed of the fan 104 (measured and / or controlled by the controller 101), with example resulting curves shown in Fig 2. In Fig 2, the horizontal axis represents the heat input (which, in normal operation, is equivalent to the speed of the fan 104) and the vertical axis represents the percentage of oxygen in the combustion chamber 109 and / or in the flue gas exhaust 111.

[0031] The resulting curve, also known as lambda curve, depends on the gas supply pressure, as illustrated in Fig 2: If the gas supply pressure is nominal (where nominal gas supply pressure may depend on factors such as the size of the boiler 100, its maximum heat capacity etc. and in many applications may be e.g. 10 mbar or higher), the lambda curve is flat, as shown by curve 201. A flat curve in this context means that the lambda curve 201 resembles a constant or nearly constant function. In other words, in this context, a flat curve means that the deviation of the lambda curve 201 from a constant may be less than a threshold. The threshold may depend on various parameters such as the size of the boiler 100, the maximum heat capacity of the boiler 100, and other factors. The threshold may be e.g. 1%. The threshold may be less than 1%. The threshold may be e.g. 0.5% or 0.2%.

[0032] If the gas supply pressure is low (e.g. lower than 10 mbar), the lambda curve deviates from a flat curve (as defined above) by more than a threshold. The threshold may be e.g. 0.2%, 0.5% or 1%. In some embodiments and applications, the threshold may be higher than 1%, e.g. 2%, 3% or 5%. Two examples are shown in Fig 2, which shows a lambda curve for gas pressure 10 mbar 201 (which fulfils the definition of a flat curve in the current context), a lambda curve for gas supply pressure 5 mbar 202 and a lambda curve for gas supply pressure 3 mbar 203 (where the curves 202 and 203 are not flat curves in the current context).

[0033] The shape of the lambda curve and / or the deviation of the lambda curve from the state shown by curve 201 (where the gas pressure is nominal, e.g. 10 mbar or more) indicates the difference between the nominal gas pressure and the real gas pressure. In particular, lower gas supply pressure means greater deviation of the curve from the state shown by curve 201, which is illustrated by curve 202 (5 mbar) deviating less from a flat curve (e.g. curve 201) than curve 203 (3 mbar).

[0034] Once a point is detected in which the lambda curve starts deviating from the flat curve by more than a threshold (illustrated by points 202A for curve 202 (5 mbar) and 203A for curve 203 (3 mbar)), the controller 101 may take an action. The threshold may be e.g. as discussed above in connection to flat curve. The threshold may be e.g. 2%, 1%, 0.5% or 0.2%, generally depending on factors such as size of the boiler 100, its heat capacity, the nominal gas supply pressure etc. The action taken by the controller 100 may be aimed at mitigating the effects of low gas supply pressure.

[0035] Example actions aimed at mitigating the effects of low gas supply pressure may be: assessing the gas supply pressure, e.g. based on the shape and deviation of the respective lambda curve; determining that the gas supply pressure is low (e.g. lower than 10 mbar); shutting the boiler off; displaying a message for a user and / or transmitting a message to a user device (e.g. a mobile phone), where the message may be e.g. a warning for a user that gas supply pressure is low, a request for the user to check or adjust the gas supply pressure and the like; adjusting (e.g. limiting or restricting) the speed of the fan 104 and thus the gas / air mixture supply into the burner 109 (i.e., adjusting the capacity of the boiler) such that the boiler 100 returns to a point prior to a state before the lambda curve started deviating from a flat curve by more than a threshold (i.e., to a state where the lambda curve behaviour is normal); any combination of the above.

[0036] These actions may be achieved e.g. by closing the gas supply valve 107 and / or by adjusting the speed of the fan 104, as appropriate.

[0037] As a particular example, the controller 101 may display a warning for the user about low gas supply pressure and limit the heat capacity of the boiler 100 and / or limit the boiler 100 to the highest speed of gas / air mixture supply into the burner 109 for which the lambda curve does not deviate from a flat curve by more than a threshold. This may be achieved by adjusting (e.g. lowering) the speed of the fan 104.

[0038] As another example, the controller 101 may display a warning for the user about low gas supply pressure and shut the boiler 100 off. This may be achieved by closing the valve 107 (cutting off the gas supply).

[0039] The above-described actions may be taken simultaneously or in succession. Other actions may be taken by the controller 101 in response to the lambda curve deviating from a flat curve by more than a threshold.

[0040] Among the advantages of the above-described arrangement is a safer and / or more efficient operation of the boiler 100 and negligible additional costs, and improved maintenance of the boiler 100.

[0041] The boiler 100 may be controlled as follows.

[0042] In step 301, the controller 101 determines a speed of the fan 104. More generally, the controller 101 may determine the speed of supplying the gas / air mixture into the burner 109.

[0043] In step 302, the sensor 106 measures the composition of the gases in the combustion chamber 109 and / or in the flue gas exhaust 111. The sensor 106 may measure e.g. the oxygen percentage in the gases.

[0044] In step 303, the controller 101 correlates the speed of the fan 104 and the composition of gases measured by the sensor 106 (e.g. oxygen percentage). More generally, the controller 101 may correlate the speed of supplying the gas / air mixture into the burner 109 and the composition of the gases in the combustion chamber 109 and / or in the flue gas exhaust 111.

[0045] In step 304, based on the result of the correlation from step 303, the controller 101 determines one or more of the following: the value of gas supply pressure (e.g. in mbar); that the gas supply pressure is low (e.g. lower than 10 mbar); the maximum heat input level (e.g. fan speed or the speed of supplying the gas / air mixture into the burner 109) of the burner 109 for which the available gas supply pressure is capable of achieving the correct fuel / air mixture.

[0046] Additionally, in response to the determination outlined above, the controller 101 may take one or more of the following actions: shut the boiler off; display and / or transmit a message for a user, e.g. a warning for a user that gas supply pressure is low, a request for the user to check or adjust the gas supply pressure and the like; adjust and / or limit (restrict) the speed of the fan 104 to adjust and / or limit gas / air mixture supplied into the burner 109 (i.e. the capacity of the boiler) such that the boiler 100 returns to a point prior to a state before the lambda curve started deviating from a flat curve by more than a threshold (i.e., a state where the lambda curve behaviour is normal); any combination of the above.

[0047] The boiler 100 described above may in particular be a home-based appliance, to be used in a home heating system, home HVAC system and the like.

Claims

1. A combustion control system comprising: a fuel inlet; an air inlet; a burner into which a mixture of fuel and air is supplied, to be burned to produce heat; a controller; a combustion sensor configured to measure the composition of the combustion gases; wherein the controller is configured to: determine, using the output of the combustion sensor, the composition of the combustion gases; determine the speed of supplying fuel / air mixture into the burner; correlate the speed of supplying the fuel / air mixture into the burner and the composition of the combustion gases; and determine whether the curve representing the correlation differs from a constant by more than a threshold.

2. The combustion control system of claim 1, wherein the controller is further configured to: in response to determination that the curve representing the correlation differs from a constant by more than a threshold, determine the maximum speed of supplying the fuel / air mixture into the burner for which the curve representing the correlation differs from a constant by less than a threshold.

3. The combustion control system of claim 2, wherein in response to determination of the maximum speed of supplying the fuel / air mixture into the burner for which the curve representing the correlation differs from a constant by less than a threshold, the controller is further configured to adjust the speed of supplying the fuel / air mixture into the burner such that the speed is below the maximum speed.

4. The combustion control system of any one of preceding claims, wherein the controller is further configured to: in response to determination that the curve representing the correlation differs from a constant by more than a threshold, determine the pressure of fuel supplied into the fuel / air mixture is lower than 10 mbar.

5. The combustion control system of any one of preceding claims, wherein the controller, in response to determination that the curve representing the correlation differs from a constant by more than a threshold, is further configured to output a message for a user.

6. The combustion control system of claim 5, wherein the message is a warning for a user that gas supply pressure is low and / or a request for the user to check or adjust the gas supply pressure.

7. The combustion control system of any one of preceding claims, wherein the controller, in response to determination that the curve representing the correlation differs from a constant by more than a threshold, is further configured to shut off the supply of gas into the burner.

8. The combustion control system of any one of the preceding claims, wherein the system further comprises a fan positioned upstream of the burner and wherein the speed of supplying the fuel / air mixture into the burner is adjusted by adjusting the speed of the fan.

9. The combustion control system of any one of the preceding claims, wherein the combustion sensor is an oxygen sensor.

10. The combustion control system of any one of the preceding claims, wherein the combustion sensor is positioned upstream of the burner.

11. A method of operating a combustion control system, the system comprising: a fuel inlet; an air inlet; a burner into which a mixture of fuel and air is supplied, to be burned to produce heat; a controller; a combustion sensor configured to measure the composition of combustion gases; wherein the method comprises: determining, by the controller, using the output of the combustion sensor, the composition of the combustion gases; determining, by the controller, the speed of supplying the fuel / air mixture into the burner; correlating, by the controller, the speed of supplying the fuel / air mixture into the burner and the composition of the combustion gases; and determining, by the controller, whether the curve representing the correlation differs from a constant by more than a threshold.

12. A method of claim 11, wherein the combustion control system is as described in any one of claims 2 to 10.

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