US2155642A - Control for heating systems - Google Patents

Description

- April 25, 1939..

R. P. DEWEY CONTROL FOR HEATING SYSTEMS Filed.Feb. 23, 1935 3 Sheets-Sheet l INVENTOR Ritchie P, Dew

ATTORNEYS April25, 1939. R. P. DEWEY 2,155,642

CONTROL FOR HEATI NG SYSTEMS Filed Feb. 23, 1935 5 Sheet-Sheet 2 7 [I v v I //4- 8 To LINE INVENTOR Rit'chie P. Dewey BY I F aw W -M ATTORN EY5 April 25, 1939. R. P. DEWEY CONTROL FOR HEATING SYSTEMS 3 Sheets-Sheet 5 Filed Feb. 23, 1935 INVENTOR Ritchie P Dew BY ATTORNEYS Patented Apr. 25, 1939 UNITED STATES PATENT OFFICE 2,155,642 CONTROL FOR (HEATING SYSTEMS Application February 23, 1935, Serial No. 7,885

12 Claims.

This invention relates generally to the control of the furnaces of heating systems and more particularly to those wherein heat is supplied intermittently by operation of a burner using liquid or gaseous fuel. In systems of this character, considerable available heat supplied by the burner is lost by circulation of the heated gases out of the furnace during the periods of idleness of the burner.

Theprimary object of the present invention is to provide for more efficient utilization of the heat delivered by the furnace burner in heating systems of the above character While at the same time insuring safety in the operation of the burner. In carrying out this object, the invention aims to provide a valve for controlling the flow of air through the combustion chamber of the furnace and a novel mechanism for coordinating the operation of the valve with the operation of the burner so as to prevent the escape of heated gases up the furnace stack while the burner is idle.

The invention also resides in the novel manner of interlocking the burner and valve controls so as to provide for optimum safety in the operation of the burner.

Another object is to provide a novel control which, in addition to opening and closing a valve for the above purpose, may be utilized for maintaining a constant draft for the furnace during operation of the burner.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which Figure 1 is a schematic view and wiring diagram of a heating system and the controls therefor embodying the features of the present invention. g

Figs. 2 and 3 are schematic views and wiring diagrams of modified forms of the control.

The invention is shown for purposes of illustration as applied to a heating system in which heating fluid to be circulated to different parts of a building is heated by an oil burner I by which combustion is produced within the fire box 2 during operation of an electric motor 3 which causes liquid fuel and air for combustion to be supplied to the burner proper. In the present instance, the means for preventing circulation of air through the combustion chamber when the burner is idle comprises a damper 6 interposed in the usual stack duct 5 leading from the combustion chamber to the chimney flue 4. When the damper is disposed in the substantially closed position shown, the furnace is closed against the escape of heated gases up the chimney. The stack duct is fully open when the damper is disposed in the position shown in dotted outline. As is common in oil burner controls, the motor 3 is energized by closure of a switch 8 actuated by the armature 9 of a magnet or relay l0 having a winding l l. Closure of the switch 8 causes the motor 3 to be energized from a source of alternating current through a circuit including the usual safety switch mechanism indicated generally at l2.

Generally stated, the present invention contemplates maintenance of the damper 6 in substantially closed position while the burner is idle, movement of the damper toward open position in response to a call for heat by control means such as a room thermostat, starting of the burner only after the damper has reached a predetermined open position, and closure of the damper automatically as an incident to stopping of the burner when the control means ceases to call for heat,

While the damper may be actuated in various ways, it is desirable for a purpose which will appear later to employ an electric power operator of the reversing or modulating type as shown in Fig. 1. To this end, an electric motor I3 is connected by suitable reduction gearing to a shaft lit by which the damper is oscillated back and forth between open and closed positions in which limit switches l6 and I! are opened respectively by cams I8 and I9 on the shaft l5. The motor shown is of the shaded pole induction type with a main winding 20 constantly energized from a loW voltage source M of alternating current. The field member provides two poles defining a recess for a squirrel cage rotor 2| and having thereon sets of shading coils 22 and 23 adapted to be short-circuited selectively to cause rotation of the rotor in one direction or the other and movements of the damper 6 toward open and closed positions respectively.

Short circuiting of the coils 22 to open the stack damper when the burner controlling device, which may be the room thermostat 24, calls for heat is effected in the present instance through the medium of a magnet or relay 25. The thermostat shown comprises a thermo-sensitive element 40c arranged to move a tongue H11 in opposite directions in response to temperature changes in the space heated by the system, the switch 28 being closed when the space temperature falls below the value desired to be maintained. Means such as a magnetic detent 12 may be provided for causing movement of the tongue between the stationary contacts with a snap action.

The magnet 25 has a winding 26 in a circuit which extends from the power lead 21 through the switch 28 of the thermostat, a conductor, -a normally closed switch 36 of a relay 3|, a conductor 32, the winding 26 and a conductor 33 leading to the other power lead 34. when the winding 26 is energized, the magnet armature 35 is raised closing a switch 36. This establishes a short circuit for the coils 22 extending from the coils through the limit switch l6, a conductor 33, a switch 39 which is closed when the relay I6 is deenergized, a conductor 46, the switch 36, conductor 4| and the conductor 34 which leads to the common terminal of the two sets of shading coils.

To insure movement of the damper to a substantially open position before combustion can be started, while at the same time placing the magnet under the control of the thermostat 24 in so far as stopping of the burner is concerned, the initial energization of the winding II is governed by a switch 43 which is closed when the ma et 25 is energized and also by a normally open switch 44 which is closed by a cam 45 on the shaft |5 as the damper approaches open position. The circuit for the winding extends from the power line 34 through the conductor 4| the switch 43, conductor 41, the winding II, the switch 44, and

a conductor 46 extending to the power lead 21.

For a purpose which will appear later, a locking circuit for the relay coil II is provided. This extends from the power line 34 through the conductor 4|, the switch 43, the conductor 41, the winding I, a switch 48 which is closed when the relay I0 is energized, and a conductor 49 leading through the conductor 46 to the power line 21 and having interposed therein a switch I63 actuated by a cam I04 on the shaft l5.

Operation of the burner is interrupted by the breaking of the energizing circuit for the relay 25 which occurs when the thermostat ceases to call for heat as evidenced by opening of the switch 26. Deenergization of the relay 25 results in opening of the switch 43 which interrupts the energizing circuit of the relay I0. As an incident to this, a short circuit is established for the shading coils 23 causing the motor to run in a direction to close the stack damper 6. This circuit extends from the coils 23 through a conductor 50, the limit switch H, a conductor 5|, a switch 52 which is closed when the relay 25 is deenergized, and the conductors 4| and 34. When this circuit is closed, the motor I3v operates until the damper 6 has been moved to the closed position shown in which the limit switch I! is opened by the cam IS, the motor and its associated gearing serving to hold the damper in closed position.

To provide for restoration of all of the parts of the control mechanism above described to normal burner starting position as an incident to stopping of the motor 3 by the safety control switching mechanism I2, the winding 53 of the relay 3| is connected to the power leads from the current source through the medium of conductors 54 and 55, the former being joined to the power lead between the switches 6 and I2 so that energization of the winding 53 is conditioned upon closure of the switches 8 and I2. Whenever the relay 3| is deenergized by interruption of its circuit by the switch mechanism I2, the circuit for the magnet 25 will be interrupted by opening of the switch 36.

With the motor operator and the control arranged as above described, the damper is operated quietly and reliably and its movements are properly coordinated with the operation of the burner so that under no conditions can the burner be started until the damper has been moved to open position. Moreover, the controls are so interlocked that the burner, after being stoppedthrough abnormal causes, cannot be restarted without recycling the damper operator to again move the damper to open position. By controlling the damper operator and burner magnet I0 indirectly through the medium of the electromagnet 25, it will be observed that stopping of the burner is effected by opening rather than closing of a circuit. Optimum safety is thus obtained in operation of the burner.

By locating the damper 6 within the outlet duct 5 and by employing a power operator of the reversing or throttling type, the same operator may be utilized to advantage to regulate the position of the damperi and maintain a predetermined draft on the combustion chamber during operation of the burner, so that uniform operating conditions will be maintained at all times. This additional function may be performed simply and conveniently through the provision of a switching mechanism responsive to the pressure within the stack duct 5 at apoint between the furnace and the damper and arranged to be placed in active control of the shading coils 22 and 23 as an incident to starting of the burner.

In the form shown, the draft gauge comprises a casing 56 closed at one end by a diaphragm 51 and communicating with the interior of the stack duct 5 through the medium of a pipe 53. The diaphragm is connected to a lever 53 cooperating with two contacts to form control switches 6| and 62. The contacts of the switches are connected draft pressure rises above the value for which the gauge is set, the switch 62 will be closed and the shading coils 23 will be short circuited causing movement of the damper toward closed position. In this way, the damper will oscillate back and forth to maintain a draft determined by the setting of the draft gauge.

To render the draft gauge effective only during operation of the burner, the switch arm 59 is connected to the shading coils 22 and 23 through the medium of a conductor 66, a switch 61 which is closed when the relay I6 is energized, the conductor 40, the switch 36 and the conductors 4| and 34. Thus, the draft gauge will be rendered ineffectual when either of the relays Ill and 25 is deenergized. The locking circuit above described through the switches 43 and 43 prevents the relay l0 from being deenergized in the event that the damper is moved under the control of the draft gauge toward closed position a distance suilicient to cause the switch 44 to be opened.

To insure against complete closure of the damper 6 in the event that the draft gauge should fail to function properly, a switch 65 is interposed in the conductor 5| and arranged to be may be obtained by shaping the cam I04 to allow the switch I03 to open when the position of safe minimum closure is reached under the control of the draft gauge. Opening of the switch breaks the locking circuit for the winding ll thereby causing the operation of the burner to be interrupted.

For installations where control of the furnace draft is not desired, coordination of the damper movements and the burner operation may be effected and a simplification in the mechanism obtained by utilizing the arrangements shown in Figs. 2 and 3. In these modifications, the damper is arranged to be actuated by a power operator adapted to execute cycles of fixed length initiated by the thermostat 24, the operator serving as a relay for starting the burner only after the damper has been opened.

The operator comprises an electric motor 18 and suitable gearing operating to'drive a shaft ll connected to the damper 6 by a crank mechanism I2 which, in successive half revolutions of the shaft, alternately opens and closes the damper. The motor has a main winding 13 adapted to be energized from the source M of alternating current by closure of parallel starting circuits through switches I4 and 15 which are closed by cams 18 and 11 when the shaft is in damper open and closed positions respectively. One circuit extends from the winding 13 through a conductor 18, the switch 15, a conductor 19, a switch 80 which is closed when the thermostat is calling for heat, a conductor 8| to the ungrounded side of the current source. Closure of this circuit initiates a cycle of the operator to move the damper to open position during which the switch 15 is opened and a switch 82 closed by a cam 83 to establish a circuit for maintaining energization of the motor until the damper has reached open position whereupon the switch 82 is allowed to open. The circuit for initiatingthe damper closing cycle extends from the conductor 18 through the switch H, a conductor 84 and a switch 85 which is closed when the thermostat ceases to call for heat. This cycle is also terminated when the cam 83 allows the maintaining switch 82 to open.

To initiate operation of the burner after the damper 6 has been moved to fully open position, the winding H of the burner control magnet is, in the form shown in Fig. 2, arranged to be energized by closure of a circuit extending from the power source l4 through a conductor 86, the winding II, a conductor 81, a switch 88 actuated by a cam 89 on the shaft H and a conductor 90. The cam 89 has a lobe 9| which, in the damper open position of the shaft H, maintains the switch 88 closed, the switch being open in all other positions. Thus, it will be seen that while the switch 88 is closed, as will "be the condition whenever the damper is in open position, the winding II will be energized and the burner will operate, provided the circuit of the burner motor may be completed through the safety controls 12. When the switch 88 opens as it will in the initial movement of the damper toward closed position in response to closure of the thermostat switch 85, the winding H will be deenergized and operation of the burner thereby interrupted. The operation of the burner is thus interlocked with the movements of the damper so that movement of the damper to open position is a condition precedent to starting of the burner.

If desired, the control shown in Fig. 2 may be modified as shown in Fig. 3 for the purpose of cuit for the magnet winding I I not only through the cam operated switch 88 but also through the switch 88 of the thermostat which is closed when the space temperature falls below the desired value and which also serves to initiate the damper opening cycle of the power operator. To this end, one contact of the switch 88 is connected to the conductor 81 and the other joined by a conductor 92-to the conductor 19.

With this arrangement, the power operator is started and the damper moved toward open position when the thermostat switch 80 is closed which also prepares the circuit for the magnet winding II for closure by the switch 88. This occurs as the damper reaches. fully open position, the magnet l being thereby energized and the burner started. Operation of the burner continues until the heating requirements of the space are satisfied causing the switch 88 to be opened and the switch 85 to be closed. Opening of the former switch deenergizes the magnet and stops the burner, while closure of the switch 85 initiates a cycle of the motor operator to close the damper 6. Thus, while the starting of the burner results from closure of a switch, the burner is stopped by opening of the switch 85.

I claim as my invention:

1. In a heating system, the combination of a furnace having a burner and a stack outlet duct, a damper in said duct for opening and closing the same, electric motor driving means arranged to actuate said damper, an electromagnet adapted when energized to start and maintain the operation of said burner, a second electromagnet adapted when energized to initiate operation of said motor driving means to move said damper toward open position, switching means operating upon deenergization of said first magnet to initiate operation of said motor driving means and cause movement of said damper to substantially closed position, a switch adapted to be closed when said second magnet is energized, a second switch adapted to be closed upon movement of said damper to a predetermined open position,

an energizing circuit for the winding of said first mentioned magnet extending through said switches whereby to cause deenergization of said first magnet upon deenergization of the second -magnet, and switching means, such as a room thermostat, controlling the energization of said second mentioned magnet.

2. In a heating system, the combination of a furnace having a burner, a damper adapted when in closed position to prevent the circulation of air through the combustion chamber of said furnace, an electric actuator for said damper, an electromagnet adapted when energized to start and maintain the operation of said burner, a second electromagnet adapted when energized to control said actuator and cause movement of said damper toward open position, switching means operating upon deenergization of said first. magnet to control said actuator and cause movement of said damper to substantially closed position, a switch adapted to be closed when said second magnet is energized, a second switch adapted to be closed upon movement of said damper to a predetermined open position, an energizing circuit for the winding of said first mentioned magnet extending through said switches whereby to cause deenergization of said first magnet upon deenergization of the second magnet, and a thermostatic switch controlling the energization of said said second mentioned magnet in response to temperatures in the space heated by said system.

3. The combination with a heating furnace having a motor driven fluid burner of a damper controlling a passageway through the combustion chamber of said furnace, a motor driven operator arranged to move said damper between open and closed positions in said duct, a magnet adapted when energized to initiate and maintain operation of the burner motor, switching means actuated by said magnet and controlling said operator to cause movement of the damper thereby to closed position when said magnet is deenergized. thermostatic switching means responsive to temperature changes in the space to which heat supplied by said burner is delivered and adapted, when calling for heat, to initiate operation of said operator and cause movement of said damper toward open position, and switching means actuated in the movement of said damper to a predetermined open position to effect energization of said magnet.

4. In a heating system, the combination with a furnace having a burner and stack outlet duct, a damper in said duct for opening and closing the same, reversible electric motor driving means having two windings selectively operable to cause movement of said damper in opposite directions, an electromagnet adapted when energized to initiate and maintain operation of said burner, a second electromagnet adapted when energized to establish a circuit through one of said windings causing movement of said damper toward open position, thermostatic control means governing the energization of said second magnet, switching means operated by said motor and acting as an incident to movement of the damper to a predetermined open position to energize said first mentioned magnet and thereby initiate operation of the burner, a draft gauge adapted to control said windings and operable to determine the direction and extent of movement of said damper whereby to maintain a predetermined draft for said furnace, switching means operated by said second magnet and acting upon energization of the latter to place said gauge in active control of said windings, and a locking circuit for maintaining energization of said first magnet including two switches respectively closed when said first and second mentioned magnets are energized.

5. The combination with a furnace having a burner and a damper controlling a stack duct leading from said furnace, reversible electric motor driving means for actuating said damper, control means such as a room thermostat. means responsive to said control means to initiate operation of said motor in a direction to move said damper toward open position, means responsive to movement of said damper to a predetermined open postion to initiate operation of said burner, and means rendered operative as an incident to starting of 'said burner and acting during operation thereof in response to draft fluctuations to control the direction and extent of operation of said motor whereby to maintain a predetermined draft for said furnace.

6. The combination with a furnace having a burner and a damper controlling a stack outlet from said furnace, of a power operator arranged to move said damper varying distances back and forth between open and closed positions in said duct, a device responsive to the pressure in said duct between said damper and said furnace and controlling the direction and extent of movement of said damper by said operator so as to maintain a substantially constant draft pressure, means operating automatically to withdraw said device from and place the same in control of said operator as incidents to stopping and starting of said burner, means operating as an incident to stopping of said burner to control said operator and causemovement of said damper to a predetermined closed position, and means actuated by movement of said damper to a predetermined open position to initiate operation of said burner.

"I. The combination with a furnace having a burner and a damper controlling a stack outlet from said furnace, of a power operator arranged to move said damper varying distances back and forth between open and closed positions in said duct, a device responsive to the pressure in said duct between said damper and said furnace and controlling the direction and extentof movement of said damper by said operator so as-to maintain a substantially constant draft pressure, and means operating automatically to withdraw said device from and place the same in control of said operator as incidents to stopping and starting of said burner.

8. The combination with a furnace having a burner anda damper controlling a stack outlet from said furnace, of a power operator arranged to move said damper varying distances back and forth between open and closed positions in said duct, a device responsive to the pressure in said duct between said damper and said furnace and controlling the direction and extent of movement of said damper by said operator so as to maintain a substantially constant draft pressure, and means operating automatically to withdraw said device from the control of said operator when said damper moves to a predetermined partially closed position in closing and when the operation of said burner is interrupted.

9. The combination with a 'fumace having a burner and a damper controlling a stack outlet from said furnace, of a power operator arranged to move said damper varying distances back and forth between open and closed positions in said duct, a draft gauge controlling said operator to determine the direction and extent of movement of said damper thereby whereby to maintain a substantially constant draft, an electromagnet adapted when energized and deenergized to start and stop said burner, means operating as an incident to deenergization of said magnet to control' said operator and initiate movement of said damper toward closed position, a second electromagnet adapted when energized to initiate the operation of said operator to cause movement of said damper toward open position, and

means operating automatically to render said operation of said operator and cause a predetermined iurnace draft to be maintained.

,12. The combination with a was having a burner and a damper controlling a stack outlet from said furnace, of a power operator arranged to move said damper varying distances back and forth between open and closed positions in said duct, a device responsive to the pressure in said duct between said damper and said mrnace and controlling the direction and extent of movement of said damper by said operator so as to maintain a substantially constant draft pressure, and means operating automatically to render said operator ineflectual when said damper has been moved under the control of said device to a predetermined partially closed position.

RITCHIE P. DEWEY.

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