US 5,865,611 AGranted

Fuel-fired modulating furnace calibration apparatus and methods

AssigneeRheem Manufacturing Company

InventorDennis R. Maiello

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Abstract

A gas-fired air heating furnace has a modulatable supply air blower and a modulatable gas valve operatively connected to the combustion air heat exchanger burner. A calibration sequence of a microprocessor-based control system is utilized to automatically determine the precise relationship between the gas valve setting and the actual heat transferred by the heat exchanger to air flowing through the furnace by measuring the actual air temperature rise across the heat exchanger obtained using initial calibration settings of the blower and gas valve. The microprocessor uses the results of its calibration sequence to establish an adjustment correlation between the blower and gas valve settings which the microprocessor subsequently utilizes to adjust the flow rates of the blower and the gas valve in a manner maintaining a predetermined, generally constant air temperature rise across the heat exchanger while the furnace alters its overall air heating output rate in response to changing heating demands from the conditioned space served by the furnace.

Claims13

Dependent claims

Heat transfer apparatus subjectable to a variable heat transfer demand load and comprising:

recirculating means for recirculating a fluid medium through a flow path;
first adjustment means associated with said recirculating means and operable to selectively vary the mass flow rate of the fluid medium through said flow path;
a heat exchanger interposed in said flow path to be traversed by fluid medium flowing therethrough;
fuel-fired means, connected to said heat exchanger, for receiving fluid fuel from a source thereof and utilizing the received fuel to create a heat exchange between said heat exchanger and the fluid medium traversing said heat exchanger and a corresponding temperature change in the fluid medium traversing said heat exchanger;
second adjustment means associated with said fuel-fired means and operable to selectively vary the amount of fluid fuel received by said fuel-fired means;
and
calibration and control means for automatically adjusting each of said first and second adjustment means to accommodate changes in said variable heat transfer demand load, said calibration and control means being operative to:
set one of said first and second adjustment means to a predetermined calibration setting thereof,
calculate a theoretical setting for the other of said first and second adjustment means based on an assumed relationship between the setting of said second adjustment means and the resulting magnitude of heat transfer between said heat exchanger and the recirculating fluid medium,
adjust said other of said first and second adjustment means to said theoretical setting,
determine the actual fluid medium temperature differential resulting from said calibration and theoretical settings,
change the determined actual fluid medium temperature differential to a desired fluid medium temperature differential magnitude by adjusting one of said first and second adjustment means to a second setting thereof,
use the settings of said first and second adjustment means with the fluid medium temperature differential at said desired magnitude thereof to determine the actual relationship between the setting of said second adjustment means and the resulting magnitude of heat transfer between said heat exchanger and the recirculating fluid medium,
utilize the determined actual relationship between the setting of said second adjustment means and the resulting magnitude of heat transfer between said heat exchanger and the recirculating fluid medium to establish a correlation between the settings of said first and second adjustment means which will maintain the desired fluid medium temperature differential magnitude,
alter the setting of one of said first and second adjustment means in response to a change in heat transfer demand load for said heat transfer apparatus, and
alter the setting of the other of said first and second adjustment means in accordance with the established correlation between the settings of said first and second adjustment means.

13 more elements

For use in conjunction with a heat transfer apparatus subjectable to a variable heat transfer demand load and including recirculating means for recirculating a fluid medium through a flow path, first adjustment means associated with said recirculating means and operable to selectively vary the mass flow rate of the fluid medium through said flow path, a heat exchanger interposed in said flow path to therethrough, by fluid medium flowing therethrough, fuel-fired means, connected to said heat exchanger, for receiving fluid fuel from a source thereof and utilizing the received fuel to create a heat exchange between said heat exchanger and the fluid medium traversing said heat exchanger and a corresponding temperature change in the fluid medium traversing said heat exchanger, and second adjustment means associated with said fuel-fired means and operable to selectively vary the amount of fluid fuel received by said fuel-fired means, a method of controlling the operation of said heat transfer apparatus, said method comprising the steps of:

setting one of said first and second adjustment means to a predetermined calibration setting thereof,
calculating a theoretical setting for the other of said first and second adjustment means based on an assumed relationship between the setting of said second adjustment means and the resulting magnitude of heat transfer between said heat exchanger and the recirculating fluid medium,
adjusting said other of said first and second adjustment means to said theoretical setting,
determining the actual fluid medium temperature differential resulting from said calibration and theoretical settings,
changing the determined actual fluid medium temperature differential to a desired fluid medium temperature differential magnitude by adjusting one of said first and second adjustment means to a second setting thereof,
using the settings of said first and second adjustment means with the fluid medium temperature differential at said desired magnitude thereof to determine the actual relationship between the setting of said second adjustment means and the resulting magnitude of heat transfer between said heat exchanger and the recirculating fluid medium,
utilizing the determined actual relationship between the setting of said second adjustment means and the resulting magnitude of heat transfer between said heat exchanger and the recirculating fluid medium to establish a correlation between the settings of said first and second adjustment means which will maintain the desired fluid medium temperature differential magnitude,
altering the setting of one of said first and second adjustment means in response to a change in heat transfer demand load for said heat transfer apparatus, and
altering the setting of the other of said first and second adjustment means in accordance with the established correlation between the settings of said first and second adjustment means.

6 more elements

A fuel fired air heating furnace comprising:

a modulatable supply air blower adjustable to recirculate a selectively variable flow of air to and from a conditioned space served by the furnace;
a fuel fired heat exchanger positioned in the path of the recirculating air;
a fuel burner connected to said heat exchanger and operative to receive fuel from a source thereof and responsively flow a flame and resulting hot combustion gases into said heat exchanger;
a modulatable fuel supply valve operatively connected to said fuel burner and being adjustable to permit a selectively variable fuel inflow rate to said fuel burner;
and
a control system for modulating said supply air blower and said fuel supply valve in a correlated manner maintaining the air temperature rise across said heat exchanger at a predetermined, generally constant magnitude, said control system including calibration means operable to establish the necessary correlation between the settings of said supply air blower and said fuel supply valve, said calibration means including:
means for adjusting the flow rates of said supply air blower and said fuel supply valve to initial calibration settings thereof,
means for measuring the resulting steady state air temperature rise across said heat exchanger,
means for utilizing the measured steady state air temperature rise to establish the relationship between the fuel supply valve setting and the actual heat transferred to the air by said heat exchanger, and
means for using said established relationship to determine said necessary correlation between the settings of said supply air blower and said fuel supply valve.

7 more elements

A method of operating a fuel fired air heating furnace having a modulatable supply air blower adjustable to recirculate a selectively variable flow of air to and from a conditioned space served by the furnace, a fuel fired heat exchanger positioned in the path of the recirculating air, a fuel burner connected to said heat exchanger and operative to receive fuel from a source thereof and responsively flow a flame and resulting hot combustion gases into said heat exchanger, and a modulatable fuel supply valve operatively connected to said fuel burner and being adjustable to permit a selectively variable fuel inflow rate to said fuel burner, said method comprising the steps of:

adjusting the flow rates of said supply air blower and said fuel supply valve to initial calibration settings thereof,
measuring the resulting steady state air temperature rise across said heat exchanger;
utilizing the measured steady state air temperature rise to establish the relationship between the fuel supply valve setting and the actual heat transferred to the air by said heat exchanger;
using said established relationship to determine a correlation between the settings of said supply air blower and said fuel supply valve necessary to maintain a predetermined, generally constant air temperature rise across said heat exchanger for each setting of either of said supply air blower and said fuel supply valve;
and
modulating said supply air blower and said fuel supply valve, in accordance with said correlation, in response to a change in heating demand from a conditioned space served by said fuel fired air heating furnace,
said steps of adjusting the flow rates, measuring the resulting steady state air temperature rise, and utilizing the measured steady state air temperature rise being performed by:
adjusting the flow rate of one of said supply air blower and said fuel supply valve to a calibration setting,
adjusting the flow rate of the other of said supply air blower and said fuel supply valve to a calibration setting based on a thermodynamic equilibrium relationship among the adjusted flow rate of said one of said supply air blower and said fuel supply valve, a desired air temperature rise across said heat exchanger, and the adjusted flow rate of said other of said supply air blower and said fuel supply valve,
measuring the actual resulting steady state air temperature rise across said heat exchanger,
changing the adjusted flow rate calibration setting of one of said supply air blower and said fuel supply valve to change the actual air temperature rise across said heat exchanger to the desired air temperature rise across said heat exchanger, and
utilizing the relationship between the calibration settings of said supply air blower and said fuel supply valve, while the air temperature rise across said heat exchanger is equal to the desired air temperature rise, to determine the correlation between the calibration setting of said fuel supply valve and the actual heat transferred to the air by said heat exchanger.

9 more elements

Dependencies are inferred from the claim text.