United States Patent
`Borgeson et al.
`
`[19]
`
`[11] Patent Number:
`5,590,642
`Jan. 7, 1997
`[45] Date of Patent:
`
`|lllllIlllIlll|||I|I|||||||||||||||I||||||Illll|||II|||||IIIIIIIIIIIIIIIIII
`US005590642A
`
`[54] CONTROL METHODS AND APPARATUS
`FOR GAS-FIRED COMBUSTORS
`
`[75]
`
`Inventors: Robert A. Borgeson, Cleveland
`'
`Heights, Ohio; Robert M. Russ, Los
`Altos Hills, Calif.; Larry A. Lincoln,
`Milpitas, Calif.; Thomas L. Webster,
`Piedmont, Calif.; Nir Merry, Albany,
`Ca1if.; William W. Bassett, Wheaton,
`Ill.
`
`[73] Assignee: Gas Research Institute, Chicago, Ill.
`
`[21] Appl. No.: 378,516
`
`[22] Filed:
`
`Jan. 26, 1995
`
`Int. C1.6 ........................................................ F24H 3/00
`[51]
`[52] us. Cl.
`................................... 126/116 A; 126/110 R;
`236/11
`
`[58] Field of Search ............................ 126/116 A, 110 R,
`126/110 A, 110 E; 236/10, 11
`
`[56]
`
`References Cited
`
`U.s. PATENT DOCUMENTS
`
`4,192,641
`4,334,855
`4,445,638
`
`3/1980 Nakagawa et a1.
`................_. ...... 431/15
`6/1982 Nelson ...................... 431/20
`
`......................... 237/8 R
`5/1984 Connell et a1.
`
`8/1985 Nelson ...................................... 431/20
`4,533,315
`4,547,150 1011985 Vereecke .....
`431/1
`4,583,936
`4/1986 Kriegger .....
`
`.. 431/78
`4,588,372
`5/1986 Torborg
`6/1987 Foley ................ 431/12
`4,676,734
`
`126/116 A
`4,688,547
`8/1987 Ballard et a1.
`11/1987 Thompson et a1.
`..
`4,707,646
`318/332
`
`4,729,207
`3/1988 Dempsey et a1.
`126/112
`3/1991 Matsumoto et a1.
`.
`.. 364/426.02
`5,001,640
`
`7/1991 Lynch ..............
`126/116 A
`5,027,789
`8/1991 Clark ................. 431/12
`5,037,291
`
`5,112,217
`5/1992 Ripka et al.
`..... 431/12
`
`5,123,080
`6/1992 Gillett et a1.
`388/934
`
`..
`5,206,566
`4/1993 Yoshida et a1.
`318568.22
`
`5,248,083
`9/1993 Adams et a1.
`..... 236/11
`............................ 236/11
`5,307,990
`5/1994 Adams et a1.
`
`Primary Examiner—Carroll B. Dority
`Attorney, Agent, or Firm—Dick and Harris
`
`[57]
`
`ABSTRACT
`
`A control system for a fluid—fuel burner, such as a furnace for
`an HVAC system. The furnace has a variable flow of fuel
`into the burner. In addition, the circulating air blower is also
`variable. The furnace heat exchanger plenum is maintained
`at a substantially constant temperature, as a means for
`providing substantially constant
`temperature air to the
`spaces to be heated.
`
`17 Claims, 4 Drawing Sheets
`
`SUPPLY AIR
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`
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`
`RETURN
`AIR
`
`
`HONEYWELL - EXHIBIT 1001
`
`HONEYWELL - EXHIBIT 1001
`
`

`

`US. Patent
`
`Jan. 7, 1997
`
`Sheet 1 of 4
`
`5,590,642
`
`
`
`

`

`US. Patent
`
`Jan. 7, 1997
`
`Sheet 2 of 4
`
`5,590,642
`
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`US. Patent
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`Jan. 7, 1997
`
`Sheet 3 of 4
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`US. Patent
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`Jan. 7, 1997
`
`Sheet 4 of 4
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`5,590,642
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`

`1
`CONTROL METHODS AND APPARATUS
`FOR GAS-FIRED COMBUSTORS
`
`5,590,642
`
`2
`
`BACKGROUND OF THE INVENTION
`
`1. Technical Field
`
`The present invention is directed to control systems for
`burner devices for fluid (liquid and gaseous) fuels, and in
`particular,
`to burners used for HVAC systems, such as
`gas—fired burners for furnaces, boilers, heat pumps and the
`like.
`2. The Prior Art
`
`A variety of control systems have been developed for
`regulating the operation of burners which utilize fluid fuels.
`Control systems for HVAC systems, in particular, have been
`the subject of considerable development.
`One approach has been to develop a control system which
`has, as its goal, absolute maximum combustion efliciency.
`Such a system is disclosed in Foley, U.S. Pat. No. 4,676,734.
`The Foley ’734 apparatus, which can also be used in ovens
`or stoves, as well as furnaces and boilers, involves the
`constant alteration of the amount of input air introduced into
`the combustion process. The combustion output is then
`monitored, and used as feedback, for the next alteration of
`input air. Foley ’734 further teaches a furnace configuration
`in which input air and input fuel appear to be varied, in a
`limited sense, and which has a fixed temperature output of
`conditioned air.
`
`Another prior art burner control system is disclosed in
`Krieger, U.S. Pat. No. 4,583,936. The control in Krieger
`appears to be accomplished through variation of the duty
`cycle of the burner. Although the flow rate of fuel into each
`burner is fixed, the amount of time the burner is “on” is
`varied, in order to vary the thermal input. Air flow into the
`burner appears variable.
`A characteristic which is corrrmon to such control systems
`is that of the various controllable “independent variables,”
`such as gas input rate, combustion air input rate, circulation
`air rate (for forced air HVAC systems), at most one of these
`variables is provided with a control capable of operation in
`other than fixed modes or settings, or are capable of minute
`variations, in response to changes in operating conditions,
`such as changes in building load, room damper or vent
`configuration, etc.
`It is desirable to provide a general control system for
`gas-fired burner apparatus, such as may be used in gas-fired
`furnaces, boilers, and the like, the separate components of
`which are capable of operation in more that just a few fixed
`settings and so are capable of more responsive operation
`relative to such changes in building load or other operating
`conditions and requirements.
`
`SUMMARY OF THE INVENTION
`
`, The present invention comprises, in part, an apparatus for
`causing a circulating heat transfer medium to transfer heat.
`In particular, the apparatus comprises a burner for fluid
`fuels, operably connected to a source of fluid fuel; means for
`modulating the flow of fluid fuel from the source to the
`burner; means for enabling the transfer of heat from the
`burner to the heat transfer medium, operably associated with
`the burner; means for circulating the heat transfer medium
`from the means for enabling transfer of heat, to a position
`remote from the burner, for transfer of at least some of the
`heat from the heat transfer medium, at the remote position,
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`4o
`
`45
`
`50
`
`55
`
`60
`
`65
`
`and for circulating the heat transfer medium back to the
`means for enabling transfer of heat; and means for modu-
`lating the operation of the means for circulating the heat
`transfer medium, for varying the amount of heat transferred
`from the heat transfer medium.
`
`The apparatus may firrther comprise means for controlling
`the means for modulating the flow of fluid fuel and the
`means for circulating the heat transfer medium.
`In a preferred embodiment, the means for modulating the
`flow of fluid fuels from the source to the burner comprises
`a modulating gas valve. The modulating gas valve is con-
`templated to be controlled by a pulse width modulated
`control signal—although other control signals could be used
`for operable modulation, including direct current and multi-
`step functioning valves.
`The aforementioned apparatus may also comprise means
`for supplying combustion air to the burner in amounts
`substantially in excess of the stoichiometric ratio appropriate
`for the fluid fuel employed. The means for supplying com-
`bustion air to the burner may be operably configured to
`supply air in a fully modulable manner. Alternatively, the
`means for supplying combustion air to the burner may be
`operably configured to supply air in a modulable manner
`within one of two or more, substantially non-overlapping
`ranges of flow rate. In a still further alternative, the means
`for supplying combustion air to the burner may be operably
`configured to supply air at two fixed rates of flow.
`The invention also comprises, in part, an apparatus for
`controlling operation of a burner for fluid fuels, for heating
`a heat transfer medium to a desired temperature. In particu-
`lar, the apparatus is operably connected to a source of fuel
`and comprises a burner; means for modulating the flow rate
`of fuel from the source to the burner; a flow path for a heat
`transfer medium; means for exchanging heat, released in the
`burner from combustion of the fuel, into the heat transfer
`medium; means for modulably transporting the heat transfer
`medium along the flow path; means for monitoring the
`temperature of the means for exchanging heat; means for
`monitoring the temperature of the heat transfer medium at a
`position remote from the means for exchanging heat; control
`means, operably associated with the temperature monitoring
`means, the means for variably regulating fuel flow rate, and
`the means for modulably transporting the heat
`transfer
`medium,
`for substantially simultaneously actuating the
`means for variably regulating fuel flow rate, and the means
`for modulably transporting the heat transfer medium, so as
`to maintain the temperature of the means for exchanging
`heat within a range of predetermined temperature values.
`In the aforementioned embodiment, the flow path for the
`heat
`transfer medium directs the heat
`transfer medium
`through one or more zones which require temperature con-
`trol, and a return air plenum is provided to enable circulation
`of the heat transfer medium from the heat exchanger means
`to the zones and back to the heat exchanger. The means for
`monitoring the temperature of the heat transfer medium at a
`position remote from the heat exchanger comprises tem—
`perature sensor means operably disposed in the return heat
`transfer conduit.
`
`The present invention also comprises a method for con~
`trolling the operation of an apparatus for causing a circu-
`lating heat transfer medium to transfer heat.
`The method comprises the steps of:
`providing a burner for fluid fuel, operably connected to a
`source of fluid fuel;
`modulating the flow of fluid fuel from the source to the
`burner;
`
`

`

`5,590,642
`
`3
`enabling the transfer of heat from the burner to the heat
`transfer medium, by conducting the heat
`transfer
`medium in a heat transfer relationship to the burner;
`circulating the heat transfer medium, from the means for
`enabling transfer of heat, to a position remote from the
`burner, for transfer of at least some of the heat, from the
`heat transfer medium, at the remote position;
`circulating the heat transfer medium back to the means for
`enabling transfer of heat; and
`modulating the circulation of the heat transfer medium,
`for varying the amount of heat transferred from the heat
`transfer medium. Accordingly, it is contemplated that
`such a method be applicable for the operation of
`various HVAC and related equipment, such as furnaces,
`boilers and hydronic systems, among others.
`The step of modulating the flow of fluid fuel from the
`source to the burner is preferably accomplished with a
`modulating gas valve. In addition, the step of modulating the
`flow of fluid fuel further comprises the step of controlling
`the modulating gas valve with a pulse-width modulated
`control signal—although other types of modulating control
`signals, such as direct current, and even multi—step (e.g.
`greater than 2 steps) functioning valves are also contem-
`plated for use.
`The aforementioned method further comprises the step of:
`supplying combustion air to the burner in amounts sub-
`stantially in excess of the stoichiometric ratio appro-
`priate for the fluid fuel employed.
`The step of supplying combustion air further comprises
`the step of supplying the combustion air at one or more fixed
`flow rates. Alternatively, the step of supplying combustion
`air further comprises the step of supplying the combustion
`air in a modulable manner within one or more substantially
`non—overlapping ranges of flow rate. In a still further alter-
`native, the step of supplying combustion air further com—
`prises the step of supplying the combustion air in a fully
`modulable manner.
`
`The present invention also comprises a method for con-
`trolling operation of a burner for fluid fuels, for heating a
`heat transfer medium to a desired temperature. The method
`comprises the steps of:
`providing an initial amount of fuel to the burner and
`igniting the fuel to begin burner operation;
`supplying further fuel to the burner at a predetermined
`initial flow rate;
`transferring heat from the burner to the heat transfer
`medium by passing the heat transfer medium through a
`heat exchanger heated by the burner;
`circulating the heated heat transfer medium along a pre-
`determined flow path;
`monitoring the temperature of the heat transfer medium at
`the heat exchanger, at which heat from the bumer is
`transferred to the circulating heat transfer medium;
`monitoring the temperature of the heat transfer medium at
`a position remote from the heat exchanger;
`substantially simultaneously modulating the rate of sup—
`ply of the fuel to the burner, and modulating the rate of
`circulation of the heat transfer medium along the pre—
`determined flow path, so as to control the temperature
`of the heat transfer medium to a predetermined tem—
`perature condition.
`In the aforementioned method, the step of monitoring the
`temperature of the heat transfer medium at a position remote
`from the means for exchanging heat further comprises the
`step of:
`
`10
`
`15
`
`20
`
`25
`
`3O
`
`35
`
`4o
`
`45
`
`SO
`
`55
`
`60
`
`65
`
`4
`
`monitoring the temperature of the heat transfer medium in
`a return air plenum, after the heat transfer medium has
`. been directed through one or more spaces to be tem-
`perature controlled.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic representation of a simplified HVAC
`control system according to the present invention;
`FIG. 2 is a block diagram indicating the respective
`orientation of FIGS. 2A and 2B;
`
`FIG. 2A is a portion of a schematic representation of the
`control system for a three zone HVAC system; and
`FIG. 2B is another portion of a schematic representation
`of the control system for a three zone HVAC system.
`FIG. 3 is a further schematic representation of the furnace
`component portion of the simplified modulating gas furnace
`system according to FIG. 1.
`
`BEST MODE FOR PRACTICING THE
`INVENTION
`
`While the present invention is susceptible to embodiment
`in many different forms, there is shown in the drawings and
`will be described herein in detail, several embodiments, with ,
`the understanding that the present disclosure is to be con-
`sidered as an exemplification of the principles of the inven—
`tion, and is not
`intended to limit the invention to the
`embodiments illustrated.
`
`Although the present invention is disclosed in the embodi-
`ment of an HVAC system for use, for example,
`in a
`residential occupied space, the method and apparatus dis-
`closed herein can also be used in many other applications in
`which a bumer, of fluid fuel, is used to heat a circulating
`fluid medium.
`
`An apparatus for heating a circulating fluid medium,
`which employs a gas—fired burner, has numerous principal
`sources of input which may govern its operation. One such
`input is the rate at which fuel gas is supplied to the burner.
`Another is the rate at which combustion air is supplied to the
`burner. Still another is the rate at which the fluid medium is
`circulated. The present invention seeks to attain an improved
`control and performance from such apparatus, by enabling
`each of these, and other inputs to be controlled through the
`use of continuous, real-time modulation,
`in response to
`exchanging external loads, among other possible factors, as
`opposed to continuous operation, in which most of these
`sources of input are fixed or limited to operations at, at most,
`a few set levels.
`
`For the purposes of the present invention, these principles
`will be discussed in the environment of a gas-fired, forced
`air HVAC system, although they are equally applicable to
`other forms of the apparatus described, such as gas-fired
`boilers, etc. The concept of modulation, at its core,
`is
`employed so that an HVAC system, for example, may act to
`constantly balance the output of the furnace (or the like) with
`the average load on the space being conditioned, in response
`to various varying environmental conditions.
`A residential HVAC system (or commercial system) may
`' be provided with a zone type control system, in which a
`single furnace/air conditioner and blower supply heated/
`chilled/untreated air to several spaces through a plurality of
`ducts. The exit of each duct opening in to each space, may
`be closed, in isolation with respect to the rest of the system,
`by an automatic damper operating system, in response to the
`
`

`

`5,590,642
`
`5
`
`command of a central control system, relative to the output
`of, among other things, temperature sensors in that space.
`When changes in the flow configuration, such as the
`closing of dampers in a zoned HVAC system, take place, the
`air flow through the system, and the rate of heat transfer
`from the furnace plenum, to the circulating air, for example,
`are also effected. It is a goal of many HVAC systems, to
`assure that the temperature in the plenum is held constant,
`since this will help assure that the discharge temperatures at
`the exits of the ducts are likewise held constant, so that a
`desired comfort level, once attained, can be maintained.
`The present invention includes a method and apparatus
`for controlling the operation of a gas-fired HVAC system. In
`a preferred embodiment, the system comprises a gas—fired
`furnace for a forced-air heating and cooling system. FIG. 1
`illustrates a schematic diagram of the control system 10, and
`the furnace shown in such an example is of the condensing
`type—although use of non-condensing furnaces, as well as
`other gas-fired apparatus, are likewise contemplated.
`The concept of modulation, as applied to a condensing
`furnace, forced-air system is as follows: a) the induced draft
`fan speed (if present) is set to a rate which ensures normal
`combustion and excess air levels at the maximum fuel input
`rate (as discussed hereinbelow); b) the induced draft fan
`speed is kept constant while the fuel input rate is modulated
`downward, according to changing load on the space being
`conditioned; c) the circulating air blower is modulated, in
`order to obtain a balance between plenum air temperature
`rise, supply air temperature and overall system efiiciency.
`In system 10 (FIG. 1 and FIG. 2), control of the combus-
`tion process is accomplished by the operation of modulating
`gas valve 22. The heat from combustion is supplied to
`plenum heat exchanger 24 (as shown in FIG. 3). In or
`adjacent to the plenum heat exchanger 24, a sensor 26 is
`provided which supplies an input to controller 25 (FIG. 3),
`which is processed with plenum temperature controls using
`conventionally known fuzzy logic algorithm 28 techniques.
`The output of the processing of the information from sensor
`26, via algorithm 28, is employed to regulate the operation
`of the modulating gas valve 22.
`The heat from plenum heat exchanger 24 is transferred via
`ducting 27 to the circulating air medium to the space 30 to
`be heated. Space temperature sensor 32 monitors the tem-
`perature in space 30, and the information obtained is pro—
`cessed in the controller via plenum static pressure control
`algorithm 34. However, it is contemplated that, if desired,
`for example, in a single zoned system (as opposed to a
`multi-zoned system) that plenum static pressure control
`algorithm 34 not be relied upon. Instead, it may be desirable
`to merely measure the temperature in space 30 directly.
`From algorithm 34 is obtained information necessary to
`regulate the operation of indoor blower motor 36, in par-
`ticular, the desired plenum static pressure which is to be
`maintained by the blower 36 (and which is sensed by
`suitably provided pressure sensors in the plenum). In a
`preferred embodiment, it is contemplated that the algorithm
`further calculates and, in turn, controls both modulating gas
`valve 22 and induced draft blower motor 40 to obtain the
`desired stoichiometric ratio 38. To enable the speed of the
`circulating air blower 36 to be varied in a substantially
`infinitely adjustable manner, the motor for the blower must
`be capable of substantially infinite speed adjustment.
`Accordingly, an electrically commutated motor (ECM), as
`are presently known in the art, would, among other com-
`mercially available motors, comprise an acceptable motor
`for use.
`
`10
`
`IS
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`Modulating gas valve 22 is shown in FIG. 2 and FIG. 3
`as being controlled in a relationship based upon the speed of
`the indoor blower motor 36, and the feedback information
`supplied by plenum temperature sensor 26. The results of
`algorithms 28 and 38 are combined (at 20; FIG. 2) to provide
`control of the modulating gas valve. The modulating gas
`valve 22 is coupled to indoor blower motor 36 via a feed
`forward loop 35 (FIG. 2). A fuzzy logic control loop, using
`conventionally known fuzzy logic programming techniques,
`biases the valve output based on feedback from the plenum
`temperature sensor 26.
`'
`The gas valve feed forward equation (within feed forward
`loop 35) is defined as:
`GAS FF %=GV MIN+(GV MAX~—-GV M]N)X((IBM
`OUTPUT—IBM MIN)/(IBM MAX—IBM MIN», in
`which:
`.
`
`FF % is the valve setting in % of full opening;
`GV MIN is a minimum gas valve setting (computation
`based on furnace size and valve manufacturer data);
`GV MAX is a maximum gas valve setting (computa-
`tion based on furnace size and valve manufacturer
`data);
`IBM OUTPUT is the sensed indoor blower motor
`speed;
`IBM MAX is the maximum indoor blower motor
`
`speed;
`IBM MIN is the minimum indoor blower motor speed.
`The gas valve output is the sum of the feed forward
`equation and an offset provided by the fuzzy logic, which, in
`a preferred embodiment, may be i10%. The gas valve
`output equation therefore is:
`GAS OUTPUT %=GV FF%+GV FUZZY.
`
`The actual valve which will be used for gas modulation
`may be a solenoid-operated valve of known design of the
`type in which the percentage of opening is proportional to
`the DC voltage applied to the solenoid coil. The present
`invention, in part, may utilize a solenoid-type gas valve, in
`which the DC modulating coil is governed through the use
`of a Pulse Width Modulated signal. In a modulating gas
`valve, the output gas pressure is varied in direct relation to
`the current passing through the modulating coil. In prior art
`gas valves, such a valve is driven by varying an analog
`voltage across the modulating coil,
`typically requiring
`elaborate digital-to-analog circuitry. The present invention
`requires no analog circuitry, has comparable control, and
`more linear operation with less hysteresis, as compared to
`the prior art method.
`Although other valve specifications may be employed, it
`is contemplated that,
`in a preferred embodiment of the
`invention, and for example, in furnaces operating in the
`range of 75-120K BTU, a valve operating in the pressure
`ranges of 2.5"—5.0" water column (W.C.), and 5.0"—12.0"
`W.C. may be utilized. Indeed, it is contemplated that an
`appropriate commercially available valve, such as from
`White Rodgers of Missouri (a division of Emerson Electric),
`will have an output gas pressure which will be proportional
`to an average DC. voltage applied to its modulating coil.
`Furthermore, the voltage applied to the modulating coil of
`the valve may be a constant frequency pulse-width—modu—
`lated (PWM) rectangular waveform, having a duty cycle
`modulated between 0%—on and 100%-on, wherein the fre-
`quency of the waveform may be 1200 Hz i5%—although as
`will be understood to those, having ordinary skill in the art,
`valves having modulating coils with other operating speci-
`fications are likewise contemplated for use. In a preferred
`
`

`

`5,590,642
`
`7
`
`embodiment of the invention, the modulation range of the
`signal controlling the coil may be 50%—100% PWM.
`In such an embodiment,
`the instantaneous on-period
`voltage and steady-state 100%-on duty cycle voltage is
`contemplated to be 18 VDC; wherein the gas valve will be
`configured to be fully open at 16.2 VDC or greater, con-
`tinuously applied, while full closing of the valve will take
`place if the voltage falls below 3.00 VDC continuous.
`However, it will be understood that other voltages and/or
`current for opening and closing the valve are contem-
`plated——depending on, for example, the particular valve so
`utilized.
`
`The furnace may include two firing modes: a low~fire
`mode, and a modulating mode. During the low-fire mode,
`the gas valve is held at its lowest operating point. Low—fire
`operation is used when, for example, the heating mode is in
`effect (as opposed to cooling) and the temperature of the
`space (e.g., room) to be heated is close to, but just below, the
`set point temperature, for a specified period of time; if the
`furnace is in a minimum modulation mode, and the room
`temperature only just exceeds the set point temperature, the
`fumace may be configured to switch over to low-fire opera-
`tion. When the valve is held at its lowest operating point
`(i.e., low-fire), it may, for example, have an output pressure
`of 0.50i0.03" W,C. Alternatively, if the room temperature is
`substantially above the set point temperature, or maintains a
`predetermined value for a specified time, the furnace may
`shut off entirely.
`The modulating mode may be used, or engaged, when the
`room temperature drops a certain value below the set point
`temperature, or maintains a certain value below the set point
`temperature for a specified time period. The criteria for
`causing switch—over from one mode of operation, to another,
`may be determined based upon the season, climate, thermal
`characteristics of the structure and space to be heated!
`cooled, and the personal preferences of the occupants, as
`well as efficiency considerations based upon the operating
`characteristics of the HVAC components being used.
`In a preferred embodiment of the invention, from a
`“fumace-ofl” state, the furnace may not proceed directly to
`a “low-fire” mode, but will proceed to “furnace modula-
`tion”. From the modulation mode, the furnace may switch to
`off or to low-fire. From the low-fire mode, the furnace may
`switch to off or modulation.
`Also in a preferred embodiment of the invention, the
`supply of combustion air to the furnace may be regulated by
`operation of the induced draft blower 40 at one (or more)
`speeds: a high speed (e.g., 100% of IBM MAX), set if the
`gas valve setting is greater than a specific value, e.g. 45%;
`and a lower speed for all gas valve settings below the
`predetermined specific value. The operation of the blower, in
`a preferred embodiment of the invention, will be otherwise
`fixed, once established at the high or low speed.
`In any of the embodiments, the possible air—to-fuel mix-
`tures of which the system is capable are intended to be
`configured so as to provide for an air-rich combustion
`mixture. Although not the best possible efficiency, an air—rich
`mixture may be preferred for several reasons,
`including
`more complete combustion, far less pollutants; less likeli-
`hood of explosion hazard; less likelihood of toxic fume
`hazard. For example, during high firing rates, the percentage
`of excess air may be in the order of 30%, while during
`“low—fire” operations, the percentage of excess air will be
`substantially higher.
`A schematic representation of a more complex system, is
`shown in FIG. 2 wherein the system includes three zones
`101—103 (zone 1, zone 2, and zone 3, respectively), wherein
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`the zones may be temperature controlled substantially inde-
`pendently of each other. For ease in illustration and under-
`standing, elements in the system of FIG. 2 which are the
`same as or similar to elements in the system of FIG. 1 and
`FIG. 3 have been given like reference numerals.
`Each of zones 1, 2 and 3 have their own damper 52, 54,
`56, respectively, which may serve to isolate that particular
`zone from the flow coming from supply air plenum 50. A
`return air flow temperature sensor 58 provides a portion of
`the input for the fuzzy logic circuit 28,
`instead of the
`individual space sensor 32 used in the system of FIG. 1.
`In prior art zoned systems employing a furnace, the speed
`of the-circulating air fan was not modulated, but was kept
`constant at full speed. Indeed,
`the bypass damper was
`utilized to divert a portion of the heated circulating air back
`toward the filmace plenum, or, for example, simply dumped
`to an unused room, instead of being delivered to any of the
`heated zones. Indeed, during periods of reduced zone loads,
`the damper was operated so as to put more of the heated air
`into the unused room.
`In the embodiment of the present invention, however,
`non-condensing furnaces can also benefit from modulation,
`through the installation of a modulating gas valve, and
`through the installation of an appropriate ECM for driving
`the circulating air blower. Furthermore, in such foregoing
`embodiments, the induced draft blower, supplying combus—
`tion air to the furnace, has been disclosed as being at one of
`two fixed rates, selected to ensure that air substantially in
`excess of the appropriate stoichiometric ratio, for the fuel
`being used,
`is always present.
`In a further alternative
`embodiment of the invention, variable operation of the
`induced draft blower is also provided.
`An advantage of having an at least somewhat variable
`induced draft motor, is that it can exert some control over the
`amount of excess air. While some excess air is always to be
`present, for the previously mentioned reasons, it is desirable
`to control the amount of air, since it is well known that
`excess air negatively impacts the overall efficiency of the
`furnace, and can also be detrimental to the furnace structure
`itself. These same principles can also be applied, according
`to the present invention, to furnaces which employ, instead
`of an inducer, a power burner. In a still further preferred
`embodiment, the induced air blower can be configured and
`suitably controlled so as to be fully modulated over a full
`range of volumetric flow rates between IBM MAX and IBM
`MIN.
`
`It will also be understood to those with ordinary skill in
`the HVAC art, that, although the present invention has been
`described primarily with respect to various “heating” opera-
`tions, the invention is also capable of operating in a “cool-
`ing” operation (e.g. gas-fired air conditioner).
`The foregoing description and drawings merely explain
`and illustrate the invention and the invention is not limited
`thereto except insofar as the appended claims are so limited,
`as those skilled in the art who have the disclosure before
`them will be able to make modifications and variations
`therein without departing from the scope of the invention.
`We claim:
`
`1. An apparatus for causing a circulating heat transfer
`medium to transfer heat and for delivering such heat to a
`space in response to a heating load being imposed on the
`space, comprising:
`a burner for fluid firels, operably connected to a source of
`fluid fuel;
`means for modulating the flow of fluid fuel from the
`source to the burner;
`means for enabling the transfer of heat from the burner to
`the heat transfer medium, operably associated with the
`burner;
`
`

`

`5,590,642
`
`9
`means for circulating the heat transfer medium from the
`means for enabling transfer of heat, to a position remote
`from the burner, for transfer of at least some of the heat
`from the heat transfer medium, at the remote position,
`and for circulating the heat transfer medium back to the
`means for enabling transfer of heat; and
`means for modulating the operation of the means for
`circulating the heat transfer medium, for varying the
`amount of heat
`transferred from the heat
`transfer
`medium,
`the modulation of the fuel flow and the modulation of the
`circulation of the heat transfer medium each being of
`operably controlled by control means, between at least
`three respective rates of operation, other than a zero
`flow rate,
`the modulation of the fuel flow and the circulation of the
`heat transfer medium further being controlled so as to
`be capable of occurring during a single heating cycle
`towards a continuous balancing of heat being supplied
`to the space with heating loads being imposed on the
`space.
`2. The apparatus according to claim 1, wherein the means
`for modulating the flow of fluid fuels from