US 5,993,195 AGranted

Combustion air regulating apparatus for use with induced draft furnaces

AssigneeCarrier Corporation

InventorKevin D. Thompson

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Abstract

A combustion air regulating apparatus which is adapted for use with two stage induced draft furnaces and which allows such furnaces to be used with low cost AC inducer motors of the type having one or a small number of nominally fixed operating speeds. A flow restrictor assembly is disposed in fluidic series with the air intake and the exhaust vent to controllably restrict the flow of air through the burner box when the inducer motor operates at its low speed. A pressure sensing assembly is connected to sense a pressure approximately equal to that across the heat exchanger, and to control the flow resistance of the flow restrictor assembly to maintain a sufficient level of excess air when the furnace operates in its low stage. A solenoid valve responsive to the establishment of high stage furnace operation causes the flow restrictor assembly to establish and maintain its minimum flow resistance during operation in that stage.

Claims30

Dependent claims

A combustion air regulating apparatus for use in an induced draft gas furnace which includes a combustion air intake, an exhaust vent, a burner box, a heat exchanger, and an inducer blower, and which has a first, low firing rate and a second, high firing rate, said combustion air regulating apparatus including, in combination:

an inducer motor for driving said inducer blower, said motor having a first, nominally fixed low speed and a second, nominally fixed high speed, and being of the type which has greater load-related speed fluctuations when it operates at said low speed than when it operates at said high speed;
a flow restrictor assembly disposed in fluidic series between the air intake and the exhaust vent for controllably restricting the flow of air through said burner box when the inducer motor operates at said low speed;
a pressure sensing assembly including a movable diaphragm having first and second sides and first and second pressure inputs that are in fluidic communication with respective ones of said sides;
first means for connecting said first pressure input to a part of the furnace which is at a pressure approximately equal to the pressure at an outlet end of the heat exchanger;
second means for connecting said second pressure input to a part of the furnace which is at a pressure approximately equal to the pressure at an inlet end of the heat exchanger;
and
a connecting member, coupled between said movable diaphragm and said flow restrictor assembly, for controllably restricting the flow of air between the air intake and the exhaust vent to maintain an approximately constant pressure drop across said heat exchanger when said motor operates at said low speed.

4 more elements

A combustion air regulating apparatus for use in an induced draft gas furnace which includes a combustion air intake, an exhaust vent, a burner box, a heat exchanger, and an inducer blower, and which has one or more firing rates, said combustion air regulating apparatus including, in combination:

an inducer motor for driving said inducer blower, said motor having one or more nominally fixed operating speeds which correspond to said one or more firing rates, and being of a type which operates at a speed that is relatively poorly regulated when said motor operates at at least its lowest operating speed;
flow control means located in fluidic series between said combustion air intake and said exhaust vent for controllably varying the rate of flow of combustion air through said burner box when said motor operates at at least its lowest operating speed;
pressure responsive means for controlling said flow control means in accordance with the pressure at at least an outlet end of the heat exchanger, said pressure responsive means having at least one inlet and a movable diaphragm having a first side that is in fluidic communication with said at least one inlet;
means for connecting said at least one inlet to a location within the furnace which is at a pressure that approximates the pressure at the outlet end of the heat exchanger;
and
a coupling member, connected between said diaphragm and said flow control means, to assure that variations in the pressure across the heat exchanger cause said flow control means to vary said rate of flow and thereby maintain an excess air level within the burner box at an approximately constant value when said motor operates at at least its lowest operating speed.

3 more elements

Dependencies are inferred from the claim text.