Furnace control using induced draft blower, exhaust gas flow rate sensing and density compensation
First Claim
1. In a heating system of the type having a combustion chamber with a fuel burner, an inlet for combustion air, and an exhaust stack for exhaust gas, the improvement comprising:
- a blower connected to the exhaust stack for inducing exhaust gas flow through the exhaust stack and for drawing combustion air into the combustion chamber;
means for variably controlling the volume delivery rate of the blower such that volume flow of exhaust gas through the exhaust stack and of combustion air into the combustion chamber are simultaneously regulated;
variable fuel supply control means responsive to the volume flow of exhaust gas through the exhaust stack for supplying fuel to the burner at a rate linearly proportional to the volume flow of exhaust gas and combustion air such that the furnace can operate at higher and lower firing rates; and
compensation means cooperating with the fuel supply control means and responsive to the density of the exhaust gas for modifying the rate of supplying fuel for a given volume flow of exhaust gas and combustion air when the exhaust gas density changes, whereby excess combustion air relative to fuel supplied at lower firing rates can be reduced.
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Accused Products
Abstract
An induced draft combustion apparatus and its associated control system has a blower located in the exhaust stack or vent which is used to induce the movement of air and combustion products into, through and out of the combustion chamber. A flow-restricting orifice in the exhaust stack near the blower causes a region of higher pressure to exist upstream from the orifice with a region of lower pressure downstream from the orifice. An exhaust gas pressure signal representative of the exhaust gas volume flow rate is sensed on one side of the orifice and is fed back to a modulating gas valve which controls the outlet gas flow from the valve to be proportional to the magnitude of the exhaust gas volume flow rate. By controlling blower speeds and exhaust gas volume flow capacities as related to a selected orifice size, various firing rates for the furnace can be selected, from the design maximum down to various derated levels. Temperature-sensitive devices cooperating with the stack orifice or with the modulating gas valve are employed to compensate for changes in the density of the exhaust gas which accompany startup and changes in firing rate.
94 Citations
18 Claims
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1. In a heating system of the type having a combustion chamber with a fuel burner, an inlet for combustion air, and an exhaust stack for exhaust gas, the improvement comprising:
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a blower connected to the exhaust stack for inducing exhaust gas flow through the exhaust stack and for drawing combustion air into the combustion chamber; means for variably controlling the volume delivery rate of the blower such that volume flow of exhaust gas through the exhaust stack and of combustion air into the combustion chamber are simultaneously regulated; variable fuel supply control means responsive to the volume flow of exhaust gas through the exhaust stack for supplying fuel to the burner at a rate linearly proportional to the volume flow of exhaust gas and combustion air such that the furnace can operate at higher and lower firing rates; and compensation means cooperating with the fuel supply control means and responsive to the density of the exhaust gas for modifying the rate of supplying fuel for a given volume flow of exhaust gas and combustion air when the exhaust gas density changes, whereby excess combustion air relative to fuel supplied at lower firing rates can be reduced. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. In a heating system of the type having a combustion chamber with a fuel burner, an inlet for combustion air, and an exhaust stack for exhaust gas, the improvement comprising:
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a blower connected to the exhaust stack for inducing exhaust gas flow through the exhaust stack and for drawing combustion air into the combustion chamber; means for variably controlling the volume delivery rate of the blower such that volume flow of exhaust gas through the exhaust stack and of combustion air into the combustion chamber are simultaneously regulated; variable fuel supply control means responsive to the volume flow of exhaust gas through the exhaust stack for supplying fuel to the burner at a rate linearly proportional to the volume flow of exhaust gas and combustion air such that the furnace can operate at higher and lower firing rates; compensation means cooperating with the fuel supply control means and responsive to the density of the exhaust gas for modifying the rate of supplying fuel for a given volume flow of exhaust gas and combustion air when the exhaust gas density changes, whereby excess combustion air relative to fuel supplied at lower firing rates can be reduced, wherein the fuel burner is a gas burner;
wherein the fuel supply control means comprises means for communicating a feedback pressure signal and a servoregulator valve which supplies fuel gas at a pressure level which is linearly proportional to a feedback pressure signal representative of the rate of flow of exhaust gas, which signal is communicated to the valve; and
wherein the means for modifying the rate of supplying fuel comprises means for modifying the effect of the feedback pressure signal in the valve;wherein the servoregulator valve includes a servoregulator chamber divided by a spring-balanced diaphragm into two chambers, to one of which the feedback pressure signal is communicated, and wherein the means for modifying the effect of the feedback pressure signal comprises means for modifying the spring balance of the diaphragm; wherein the means for modifying the effect of the pressure feedback signal comprises movable bimetal means to which one of the diaphragm balancing springs is connected, and heating means responsive to the temperature of the exhaust gas and connected with said bimetal means, said heating means causing said bimetal means to move so as to modify the force exerted by said one spring on the diaphragm. - View Dependent Claims (9, 10, 11, 12, 13)
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14. In a heating system of the type having a combustion chamber with a fuel burner, an inlet for combustion air, and an exhaust stack for exhaust gas, the improvement comprising:
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a blower connected to the exhaust stack for inducing exhaust gas flow through the exhaust stack and for drawing combustion air into the combustion chamber; means for variably controlling the volume delivery rate of the blower such that volume flow of exhaust gas through the exhaust stack and of combustion air into the combustion chamber are simultaneously regulated; variable fuel supply control means responsive to the volume flow of exhaust gas through the exhaust stack for supplying fuel to the burner at a rate linearly proportional to the volume flow of exhaust gas and combustion air such that the furnace can operate at higher and lower firing rates; and compensation means cooperating with the fuel supply control means and responsive to the temperature of the exhaust gas for modifying the rate of supplying fuel for a given volume flow of exhaust gas and combustion air when the exhaust gas temperature changes whereby excess combustion air relative to fuel supplied at lower firing rates can be reduced. - View Dependent Claims (15, 16, 17)
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18. A control system for a heating system having a combustion chamber with a fuel burner, an inlet for combustion air and an exhaust stack for exhaust gas from the combustion chamber comprising:
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means connected to the exhaust stack for inducing exhaust gas flow through the exhaust stack and for drawing combustion air through the inlet into the combustion chamber; flow sensing means for sensing the flow of exhaust gas through the exhaust stack;
regulating means for regulating the rate of fuel supply to the fuel burner;first means connecting said flow sensing means to said regulating means for regulating the rate of fuel supply to the burner in response to the flow of exhaust gas out of the exhaust stack; density sensing means for sensing a parameter indicative of the density of the exhaust gas; and
second means connecting said density sensing means to said regulating means for regulating the rate of fuel supply to compensate for changes in exhaust gas density as these affect the ratio of combustion air to fuel supplied to the fuel burner.
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Specification