US2084880A - Control apparatus for heating systems - Google Patents

Description

June 22, 1937.

G. H. WOTRING 2,084,880

CONTROL APPARATUS FOR HEATING SYSTEMS Filed Nov. 19, 1955 Gaglor'd H. \A/ tri'hg, by 5. 9

His Attorney.

Patented June 22, 1937 UNITED STATES CONTROL APPARATUS FOR HEATING SYSTEMS Gaylord H. Wotring, West Caldwell, N. J.,. assignor to General Electric Company, a corporation of New York Application November 19, 1935, Serial No. 50,526

10 Claims.

My invention relates to automatic control apparatus for heating systems. An object of my invention is to provide a heating system employing an automatically controlled burner with a special automatic safety control means to periodically out off the supply of fuel frequently for relatively brief intervals so as to prevent the accumulation of fuel in the furnace v in case of failure of the automatic flame detector or other automatic safety control parts of the usual control system.

A further object of my invention is to provide a heating system of the type employing a burner controlled by the sequential operation of athermal responsiveelement positioned in the space to be heated and a safety device responsive to the presence of flame within the burner with an additional safety meansilwhich periodically cuts off the supply of fuel a plurality of times each day for brief intervals to cause the aforesaid thermal and flame responsive means to go through their predetermined sequence of operation. Due to this additional safety means if the normal safety control devices do not follow their predetermined sequence of operation due to mechanical failure, or for any other reason, the heating system will not function except for a very limited period until they are repaired.

My invention is of particular importance with respect to unattended burners of the fluid fuel type having automatic control devices which go through a definite cycle of operations upon the initiation of combustion-in response to a call for heat from a thermostat located within the zone to be heated. In heating systems of this type, there is-usually employed an automatic safety device responsive to the presence of flame or proper combustion within the furnace for controlling the system. This flame'detecto'r is commonly of 'the type which provides a limited time within which proper combustion may take place and if the flame does not appear within this time, the control system will beplaced in its initial condition. The system will then recycle a definite number of times after which, if proper combustion does not occur, manual control means must be operated to have thesystem function. Flame detectors of the type usually utilized have a start and run position so that if the flame detector is in its initial or start position and for the burner motor is established and, in some control systems, the ignition system is de-energized.

Under most conditions the initiation of combustion takes place with very little trouble, the flame being fairly steady throughout the starting period. However, in cold weather it frequently happens that during starting with a cold furnace the flame fails momentarily. Normally this causes the flame detector to operate causing the 10 oil valve to close, but, if the flame detector failed in its run position, the oil valve would remain open and oil would be sprayed into the combus-r tion chamber. If the furnace had been running and the bricks were hot, the oil might reignite, 15 but with a cold furnace this would not occur. Under these conditions, the unit might continue to run indefinitely until someone detected the odor of oil or for some other reason inspected the furnace. 20

While the possibility of a dual failure of the flame detector and the flame is somewhat remote, yet it is a condition that is likely to occur and which should be guarded against. Therefore, it is an object of my invention to do this in a simple manner by periodically de-energizing the control system at frequent intervals of about thirty minutes or one hour. This would shut the unit down temporarily but under normalconditions it would recycle and start. Thus, under the worst 30 possible set of conditions in which the normal safety control might fail, oil could be sprayed into the boiler but for thirty minutes or one hour or for any interval as fixed by the period of interruption. 35

A more detailed understanding of the manner in which the above outlined objects are attained may be had from the following description taken in conjunction with the accompanying drawing in which:

Fig. 1 is a schematic diagram showing an elevation, partiallyin section, of the heating system employing my invention.

Fig. 2 is a schematic wiring diagram showing f the electrical and thermostatic control for the 45 system.

In my preferred embodiment I have shown a zone, room, group of rooms, building or the like Lthe temperature of which is to be maintained within certain predetermined limits. The heat- 50 ing medium is supplied to the zone from a furnace 8 of the type employing liquid fuel by means of an inlet conduit 9 leading to a heat exchange device, such as a radiator I0, located within the zone. In a closed steam heatingsystem, such as I have chosen for my preferred embodiment, the condensate is led back to the furnace boiler through a conduit ii. Manually operable means (not shown) may be provided to cut off-a particular heat exchange deviceif desired. A

The furnace is provided with a combustion chamber l2 having a lining l3 of fire brick or the like and a flue'M for the escape of combustion gases. The flame is directed downwardly into the combustion chamber from a burner 'head l5 provided with an air and fuel nozzle l6 and ignition electrodes ll. Air and fuel are supplied to the burner head by means of a burner motor l8 energized through lines i9 and 26 from a main control 2i which may be of the type disclosed in the 'copending'application of John Eaton, Serial No. 735,103, filed July 14, 1934. Details of the control which I have chosen in order to fully describe my invention will be described at greater length in connection with Fig. 2. When the mo; tor is energized, it supplies the burner head with air through a conduit 22 and with fuel through a fuel inlet conduit 23, the, fuel being obtained from a source of fuel supply 2E through a conduit 25 leading to the fuel pump. In my preferred embodiment, I have illustrated the fuel as being of the liquid type but it is obvious to those skilled .in the art that my invention is equally applicable to systems using a gaseous fuel, the continued feeding of which, in the absence of combustion, is likely to cause disastrous consequences. An electrically operated solenoid 26 and its associated valve, indicated schematically in Fig. 1, are adapted to control the flow of fuel. The valve is shown mounted adjacent the burner motor l8, but it may be positioned, at any suitable place, as for example, in the burner head I5. The valve operating solenoid is energized through lines 27 and 23 which lead to the main control 2! mentioned above.

The furnace is provided with a flame responsive device 36 of any conventional type having a response to temperature. variations in the zone I by means of a combined time and temperature control device 31 within which is provided a conventional contact carrying thermal responsive element 38, which I have shown .asa bimetallic member. This thermal responsive element initiates operation of the furnace when it engages a starting contact 39, which it does when a predetermined low temperature obtains within the zone, and shutsdown the furnace when it engages stopping contact 40 when the temperature within the zone has attained a predetermined high value. The thermal element 38 and contacts 39 and 40 are connected to the main control 2| by meansof electrical connections M, 42, and 43, respectively.

In order to periodically cut ofi the supply of fuel to the burner, I have provided means for establishing a circuit across the thermal element and the stop contact 40, thus, in effect, cutting out or rendering ineffective the thermal responsive element, and this I have done by means of a clock mechanism 44 adapted to rotate a cam afosasao adapted to close a circuit across electrical connections it and t3 by means of connections 68 and 69, respectively, and thus close the stop cir-' cuit.

In Fig. 2, I have disclosed a, burner control system in which my invention is incorporated and in the following description of the circuit I have utilized corresponding reference numerals to indicate like parts of both figures. The

burner motor l8, referring now to Fig. 2, is energized from any suitable source of power 5i and 52, the motor circuit having in it a pair of normally open contacts and bridging member as indicated by reference numeral 53. When these contacts are closed, the motorcircuit is completed through electrical connections 19 and 26. The control is energized at a suitable voltage by means of a transformer 54 having a primary winding 55 and a secondary winding 56. One side of the secondary is connected to the run contact 33 of the flame responsive device through electrical connection 36 while the remaining side of the secondary winding is connected to the stop contact of the thermostat through electrical connection 51 which is connected to electrical connection 43. I have provided the control system with a main operating solenoid 58 provided with a co-operating extended armature 59. One side of the solenoid is connected to the secondary of the transformer through electrical connections 60 and 6'! while the other side of the solenoid is connected to the thermal responsive element 38 of the room thermostat through electrical connection M.

motor circuit and also to establish a holding circuit for itself through contacts 6! and electrical connections 62 and 63. This holding circuit is adapted to cut out the room thermostat and the flame responsive device as may be noted by an inspection of the figure. Both of the contacts 53 and 65 are actuated to their closed position by movement of the extended armature member 59 and this same member is also adapted to open the aforesaid holding circuit for the main operating solenoid 58 by actuation of the normally closed contacts 64 after a brief time delay. The above mentioned holding circuit leads from contacts 6i through electrical connections 63 and 34 to the contacts 64, electrical connection 65, normally closed contacts 66, and electrical connection 61 to one side of the secondary winding. The contacts 64 remain closed after the energization of solenoid 58 for a length of time determined by the characteristics of a time delay mechanism, illustrated as a dash pot 68. The purpose of this time delay in the opening of the holding circuit after the energization of the main operating solenoid is to provide .a combustion initiating period of a predetermined length during which fuel is supplied to the burner. If the flame responsive device 30 has not moved to its proper runningposition at the termination of this period, the fuel supply is cut on and the system will recycle. To prevent continued recycling I have provided a pair of normally closed contacts which are arranged to be opened after This main operating solenoid is adapted when energized to close contacts 53 in the 'each operation of the main operating solenoid 'ating solenoid 58.

a predetermined number of recycling operations by any of the devices customarily used. In the drawing I have illustrated such a device only schematically and consisting of a ratchetmechanism 69. The mechanism may be spring biased by spring S in order that it return to its initial position upon the occurrence of proper combustion and'it may be prevented from returning to its initial position until combustion occurs by an electromagnetically controlled pawl P. Upon 58 the ratchet mechanism 69 is moved one step in a clockwise direction by means of latch 18 on armature 59. The ratchet mechanism 69 may be provided with a projection 7| arranged to cooperate with a pivoted arm 12 carrying one of the aforesaid normally closed contacts 66. Upon actuation of arm 12 by engagement with a member H, the normally closed contacts 86 are opened and are held in open position by latch 13 until the latter is manually released.

The fuel supply, as previously stated, is controlled by a valve operating solenoid 26 which is energized simultaneously with the main operating solenoid 58. In my preferred embodiment, the simultaneous energization is obtained by connecting solenoid 26 in parallel with solenoid 58 as I have done by means of electrical connections 21 and 28.

Proper ignition may be obtained by the use of any of the conventional and well known ignition systems. One system that might be used is the constantly energized type comprising a transformer and its associated spark electrodes. Such an ignition system might be energized only when the burner motor is energized by merely adding another pair of normally open contacts to be actuated by operation of solenoid 58, or the system might be arranged so that it will remain energized for but a predetermined time.

The room thermostat is connected to the circuit thus far described by means of electrical connections 4|, 42, and 43, of which electrical connection 8| has been previously described. Electrical connection 42 interconnects the start contacts on the flame responsive device of the room thermostat and electrical connection 83 leads from the stop contact of the room thermostat to one side of the secondary winding of the transformer 58. The means I have provided for periodically cutting off the fuel supply has been previously described and the connections are the same described in connection with Fig. 1. It will be noted fromFig. 2 that each time the circuit across connections 88 and 49 is closed by member 81, a short circuit is placed across the valve operating solenoid 26 and the main oper- Consequently, these solenoid coils are deenergized to periodically cut off the fuel supply for brief intervals and to cause the system to recycle, as brought out more fully in the following description of the operation of the system as a whole.

When the room thermostat is in its intermediateor stop position, the burner motor l8 will remain de-energized and the main solenoid controlled contacts 53, BI, and 64 will be in the positions indicated in Fig. 2. In addition, the flame responsive device 38 within the boiler will have been moved to its starting or normally closed position due to the absence of a flame.

Assume that the temperature within the zone 8 decreases to such a value that the bimetallic element 38, moving ina counterclockwise direction, engages starting contact 39 to initially energize the fuel valve operating solenoid and the main operating solenoid. The energizing circuit for the main operating solenoid 58 ,is as follows: From the secondary winding 56 of the transformer through electrical connections 51 and 68 to the main operating solenoid 58, and

from thence to the other side of the secondary .to open the fuel valve as it is connected in parallel to main operating solenoid 58 by means of connections 21 and 28. The burner motor is energized by the closing of normally open contacts 53 controlled by the main operating solenoid so that operation of the burner will be initiated. The normally open contacts 8| in the holding circuit for relay 58 are also closed at the same time that the motor circuit is energized to maintain solenoid 58 energized while element 3| of the flame responsive device is actuated from its start to run position. This holding circuit consists of connection 62, contacts 6| and connection 63-the remainder of the circuit being the same as the starting circuit previously described. An inspection of Fig. 2 will disclose the fact that the holding circuit cuts the flame responsive device and room thermostat from the circuit. However, there is but a temporary elimination of these control devices from the circuit because of the actuation of the normally closed contacts 66 to their open position after a time delay, as will be described in the succeeding paragraph.

After this initial operation there are two possible things which may happen, one being the proper initiation of combustion and consequent movement of the flame responsive element to its run position, the second being improper combustion, that is, failure of the flame responsive device to move to its run position within a predetermined time limit, as fixed by the opening of the normally closed contacts 84. Assuming first that proper combustion takes place and that element 3| is moved so as to engage the run contact 33 of the flame responsive device within a predetermined time, a second holding circuit for the relay 58 is completed as follows: From one side of the transformer secondary winding through electrical connections 57 and 68 to main operating solenoid 58 and from thence to the other side of the secondary winding through electrical connection 62, the now closed normally open contacts 8|; electrical connection 63, element 3| of the flame responsive device and its cooperating run contact 33 and electrical connection 38. After the establishment of this holding circuit, the contacts 64 will open within a specified time to de-energize a part of the starting circuit. It may be noted also that once this holding circuit is established, the room thermostat will not exert a control again until bimetallic element 38 reaches its stop contact, at which time a short circuit is placed across the main operating solenoid 58 and the fuel valve operating solenoid 26, but, before this happens, the oil burner has been placed into operation and operates until such a time as determined by the movement of bimetallic element 38 of the room thermostat or until the lapse of a predetermined time interval, as

determined by the operation of the timing mechanism 44 and its associated cam as. If the room thermostat has not moved to its stop position when one of the projections 48 actuates-member d! into its circuit closing position, then the closure of this circuit effects the same result as does the operation of the room thermostat to its stop position because of the fact that a short circuit is placed across the two snlenoids. Thus the fuel valve is closed and relay 58 de-energized and with the de-energization of the latter, the burner motor circuit is opened at 53. The holding circuit for relay 58 is opened at 6| and the normally closed contacts 66 are closed placing the control system into the position indicated in Fig. 2.

After a brief interval, the short circuit across the operating relays is removed and the system will repeat the operation outlined above if the room thermostat has remained in or regained its starting position and if the flame detector in response to the disappearance of the flame has returned to its start position. It is obvious that if the flame responsive element has failed and remains in its run position'during the initiation of combustion the system will not start again as there will be no proper starting circuit. Furthermore, it is evident that in case of such failure of the flame responsive device during the operative period and before the closing of contact er, oil

will not be supplied to the burner for a greater period than that determined by the operation of the time controlled cam mechanism id and. $5.

I shall now describe briefly the operation of my system in the event the flame responsive element 3! does not reach its run position within the propere' time as determined by the opening of the contacts 6d. The initial energization of solenoids 58 and 26 when the flame responsive device 30 is in its start position and the room thermostat is in its start position has already been described but, briefly, the energizing circuit for solenoid 58 is as follows: From one side of the secondary winding 56 through electrical connections 57 and 60 to solenoid winding 58 and from thence to the other side of the secondary as follows: Electric connection M, the room thermostat in its start position, electrical connection d2, flame responsive device in its start position, electrical connection 36, normallyclosed contacts 661, electrical connection 65, normally closed contacts 66 and electrical connection 61. Upon the energization of the relay 58 a holding circuit therefor is established through electrical connection 62, contact 6i, and electrical connection 63. It

is obvious from the circuit diagram and from the preceding description that the room thermostat will exert no controlling function thereafter and neither will the flame responsive device unless the latter has reached its run position, but, i asmuch as it has been assumed that the :flame responsive device did not reach its run position within a predetermined time, the holding circuit will be de-energized by the opening of contacts 64. The opening of the holding circuit causes de-energization of relay 58, closing of the fuel valve, and a movement of ratchet device 69 which is engaged by projection ID as the latter moves upward. Ratchet device 69 is held bypawl P in the advance position to which it is moved by occurred. It having been assumed that the flame responsive device does not reach its run position prior to the opening of the initial holding circuit by time delay switch 6d then the device will remain either in its start position or return to that position after a certain time delay depending upon the characteristics of the flame responsive device. In either event engagement of the flame responsive device with its associated start contact, with the room thermostat remaining in a position calling for additional heat, will again result in the energization of the relay 58, the closing of a holding circuit, and the consequent opening of contact 6 3 upon failure of the flame responsive device to move to its run position will again, occur. After three such operations without combustion occurring, the fatchet mech-. anism ts will have moved to an extent such that the projection it will cause an opening of the normally closed contacts ft. The latter will thereafter be maintained in its open position by means of latch 73 until the latter is manually reset.

The embodiment of the invention illustrated and described herein has been selected for the purpose of clearly setting forth the principles involved. It will be apparent, however, that the invention is susceptible of being modified to meet different conditions in its use, and I, therefore, aim to cover by the appended claims all modifications within the true spirit and scope of my invention.

What I claim as new anddesire to secure by Letters Patent of the United States is:

1. In a heating system, the combination including a furnace,- means for supplying fuel thereto, control means normally operable for starting and stopping operation of said fuel supply means, and timing means operable a plurality of times each day for periodically stopping operation of said fuel supply means for a relatively brief interval to detect failure of said control means. 4 I L 2. In a heating system, the combination including a furnace, means for supplying fuel thereto, control means including a thermal responsive device and a safety device normally operable for controlling said fuel supply means,,

timing device operable a plurality of times each day for periodicallycutting ofi the supply of fuel to said furnace for relatively short lengths of time for rendering the system inoperative upon failure of said safety device.

4. In a heating system, the combination ineluding a zone to be heated, a source of supply of a heating medium therefor including a furnace of the type employing fluid fuel, a source of fuel supply, means for controlling the supply of fuel to said furnace in response to temperature variations within said zone, said means including a thermal responsive device located within said zone operable between start and stop positions and a flame detector located within said furnace operable from start to "run positionsv inresponse to the presence of flame, and. means including an independent timing device operable a plurality of times each day for periodically cutting off said fuel supply for relatively brief intervals irrespective of the positions of said thermal responsive device and flame detector.

5. In a heating system, the combination including a zone to be heated, a source of supply of a heating medium therefor including a furnace of the type employing fluid fuel, a source of fuel supply, thermal responsive means for controlling the supply of fuel to said furnace in response to temperature changes within said zone, said meansfurnace for supplying said zone with a heating medium, means for supplying said furnace with fuel,.control means including a safety device for normally controlling the fuel supply in response to temperature variations within said zone, and means including a timing device operable a plurality of times each day for rendering said control means ineffective and cutting off the supply of fuel for a brief interval at substantially frequent recurring periods to render the system inoperative upon failure of said safety device.

7. In a thermal control system, the combination including a thermal responsive device comprising a thermal element operable between two circuit making positions in response to temperature variations, and means separate from said thermal element and including timing means operable a plurality of times each day for render ing said thermal responsive device ineffective to exert control for recurring intervals of relatively brief duration irrespective of the position of the said thermal element. I

8. In combination, a source of electric power,

an electrically operated fuel burner mechanism including means controlling the fuel supply, a. control system for said mechanism, said system including a thermal responsive device for initially energizing said control system, a safety device responsive to the presence of flame for maintaining said control system energized upon the occurrence of proper combustion and means including a timing device operable a plurality of times each day for periodically de-energizing said control system for brief intervals to cut off the supply of fuel whereby said system is rendered inoperative upon failure of said safety device.

9. In an automatic control system for a burner having an electrically operated fuel supplying means, the combination comprising means adapted to energize said fuel supplying means for initiating fuel feed to the burner upon a demand for heat, means including switching mechanisms subject to failure for deenergizing said fuel supplying means if combustion is not established within a, predetermined time interval and for maintaining said fuel supplying means energized until the demand for heat has been satisfied upon occurrence of combustion within said time interval, and means operable a plurality of times each day independently of said first mentioned means periodically deenergizing said fuel supplying means for terminating fuel feed to the burner.

10. In acontrol system for fluid fuelburners, an electrically operated fuel supply means, a control circuit for operating said supply means, said circuit being of the recycling type including switching mechanism requiring a starting circuit for said fuel supply means and thereafter a running circuit established by said starting circuit, said switching mechanism including a combustion responsive safety switchsubject to failure but normally operable to deenergize the running circuit in the event of combustion failure and, upon cooling, to reestablish said starting circuit, in combination with means to momentarily deenergize the running circuit a multiplicity of times each day whereby to normally cause the system to recycle and, in the event of failure of the switching mechanism to normally establish the starting circuit, to prevent a prolonged supply 0 unconsumed fuel to the furnace.

GAYLORD H. WO'I'RING.

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