Combustion blower control for modulating furnace
First Claim
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1. A method of operating a combustion appliance that includes a variable speed combustion blower and a pressure switch, the method comprising:
- determining an expected combustion blower speed at which the pressure switch is expected to change state, including the steps of;
increasing the blower speed until the pressure switch changes state; and
once the pressure switch changes state, decreasing the blower speed until the pressure switch changes state again;
detecting, during operation of a combustion cycle, that the pressure switch does not change state at the expected combustion blower speed;
after detecting that the pressure switch does not change state at the expected combustion blower speed, temporarily adjusting the expected combustion blower speed to a temporary combustion blower speed at which the pressure switch changes state;
operating the combustion appliance using the temporary combustion blower speed; and
repeating the detecting, temporary adjusting and operating steps during a subsequent combustion cycle of the combustion appliance as necessary to respond to transient changes in one or more operating conditions of the combustion appliance.
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Abstract
A furnace includes a combustion blower and one or more pressure switches. In some cases, the one or more pressure switches may be used to calculate one or more operating points for the combustion blower. Additional operating points may be calculated by interpolation and/or extrapolation, as appropriate. The furnace may temporarily alter these operating points as necessary to keep the furnace safely operating in response to minor and/or transient changes in the operating conditions of the furnace.
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Citations
14 Claims
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1. A method of operating a combustion appliance that includes a variable speed combustion blower and a pressure switch, the method comprising:
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determining an expected combustion blower speed at which the pressure switch is expected to change state, including the steps of; increasing the blower speed until the pressure switch changes state; and once the pressure switch changes state, decreasing the blower speed until the pressure switch changes state again; detecting, during operation of a combustion cycle, that the pressure switch does not change state at the expected combustion blower speed; after detecting that the pressure switch does not change state at the expected combustion blower speed, temporarily adjusting the expected combustion blower speed to a temporary combustion blower speed at which the pressure switch changes state; operating the combustion appliance using the temporary combustion blower speed; and repeating the detecting, temporary adjusting and operating steps during a subsequent combustion cycle of the combustion appliance as necessary to respond to transient changes in one or more operating conditions of the combustion appliance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of operating a combustion appliance that includes a variable speed combustion blower and a pressure switch, the method comprising:
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determining an expected combustion blower speed at which the pressure switch is expected to change state; detecting, during operation of a combustion cycle, that the pressure switch does not change state at the expected combustion blower speed; temporarily adjusting the expected combustion blower speed to a temporary combustion blower speed at which the pressure switch changes state; operating the combustion appliance using the temporary combustion blower speed; and starting a subsequent combustion cycle using the temporary combustion blower speed, followed by decreasing the temporary combustion blower speed.
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13. A controller configured to control a combustion appliance that includes a burner, a gas valve configured to provide gas to the burner, a low pressure switch and a high pressure switch, the low and high pressure switches, and a combustion blower, the controller configured to:
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calibrate the combustion blower by altering a speed of the combustion blower to determine blower speeds at which the low and high pressure switches open and close; after the calibrate step, determine during combustion cycle, via the low pressure switch and/or the high pressure switch, when operating conditions have changed such that the low pressure switch and/or the high pressure switch do not close at expected combustion blower speeds; temporarily change the speed of the combustion blower to a temporary combustion blower speed so that the low and/or high pressure switch, as appropriate, close during the combustion cycle; start a subsequent combustion cycle using the temporary combustion blower speed; and decrease the temporary combustion blower speed. - View Dependent Claims (14)
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Specification