US2509334A - Heater control - Google Patents

Description

May 30, 1950 A. R. COLLINS HEATER CONTROL Filed Feb. 27. 1946 atentedl til 195a fllrihur ltt. Collins, Parts Midge, lill, assignor to Stewart-Warner worporation, tlhicago, till, a corporation oil Virginia application ltehruary 2t, wit, serial l lo. stucco it illaims. Wt. Eddth} l The present invention relates to heater controls and is, more particularly, directed to a control system adapted for use with a heater oi the general type disclosed in the patents to 'iheodore it. Korsgren 2,482,552, issued Septernher 2d, liittl,

and Frank A. Ryder 2,502,345, issued March 28. I

195a. It will be appreciated, however, that at though the control system of the present inven tion is particularly adapted for use with heaters oi this type, it is not limited to such use hut is or more general application.

"it is an object of the present invention to pro vide a control system for a heater which will modulate the output of the heater according to demand conditions.

An additional object of the present invention is to provide a novel heater control circuit and mechanism which operates the heater at a low rate of heat output unless greater heat output is necessary to satisfy the prevailing conditions.

Yet another object of the present invention is to provide an improved heater control arrangement which prevents the heater from cycling on and on excepting under extremely mild weather conditions.

Still another object of the present invention is to accomplish all of the above with a mechanism or low cost and which is safe and reliable in operation.

Other objects and advantages will become apparent from the following description of a preferred embodiment of my invention which is 11 lustrated in the accompanying drawings.

lnthe drawings, in which similar characters of reference are used to indicate similar parts in tooth the figures:

Fig. l is a diagrammatic representation oi a heater oi the type disclosed in the previously re ierred to copending applications; while Fig. 2 is a diagrammatic representation oi the control system for use therewith which illustrates the present invention, including both mechanical and electrical components.

As explained in the previously referred to co pending applications, the heating system with which the control arrangement of the present in vention is particularly adapted for use is comprised of a variable speed electric motor it which drives a ventilating air hlower it and a combustion air hlower it. The combustion air hlower receives its air through a duct it which leads preferably to the outside of the building to be heated. The ventilating air blower it receives its air through an opening it which map he in the space to he heated. Air from these two hill hit

tth

- at sources, that is, the ventilating air blower ill and the combustion air hlower it, is passed into the heater proper Ht where the ventilating air circalates over a heat exchanger it and leaves the heater at an appropriate opening so as to pass into the space to be heated. Within the heater, the combustion air is mixed with a gaseous fuel delivered through a pipe it and this mixture is ignited by a spar-it plug it which receives en ergy irorn an ignition transformer hi. Products at commotion, after passing through the heat exchanger it, are exhausted to the atmosphere remote from the space to he heated through the exhaust pipe liy means or" a modulating control valve lit, the pressure on the fuel passing through the pipe it to the heater varies depending upon the rate oi combustion air flow from the blower i This is accomplished by means of a static pressure tap t l connected to the combustion air conduit and a low pressure tap 36 connected to the throat oi? a venturi it located in the same conduit. It is apparent that these connections are such that the greater the rate of flow of comhustion air, the greater the pressure difierential existing between the taps it and 3B. This pressure difierence is communicated to the valve ti and as is explained in the previously referred to copending application of Frank A. Ryder, this pressure acts to vary the pressure upon the fuel supplied to the heater, such that the mixture ratio in the heater is kept comparatively constant regardless of the rate oi flow of combustion air. Thus, the heat output of the heater depends upon the voltage across the variable speed motor ill. The higher this voltage, the higher the speed of rotation of the motor and blowers, and thus the greater the heat output. The converse is, oi course. also true.

The control arrangement particularly adapted, but not limited, to use with a heater of this type and which forms the subject matter oi the present invention comprises a heat motor it made up of a cylindrical container it having an inturned annular flange til at its open end sealed to the open endoi a corrugated metal bellows at. at its upper or opposite end, the container wall is spaced from the closed end as of the bellows sutflciently to provide room for an electric heating element W. The space within the container ti and around the bellows M is filled with a liquid which expands when heated. Acetone has been found satisfactory for this purpose.

.dt its upper end it, the inside surf-ace of the hollows is connected to a linlrti which extends out through the open end thereof and is connected by means oi a pivot pin ht with an intermediate point of an arm 58 pivoted at one nd to a stationary portion of the structure at 68. The opposite end of this arm is prowlcled with a yoke 60. The spacing from the yoke 69 to the pin 54 is great as compared to the spacing be-= tween the points 54 and to, so that the yoke moves in the same direction as the link. 52 but to a considerably greater extent.

The yok 60 straddles a pin '52 at the end of a variable resistor slider arm bt pivoted at a point 66 adjacent the pin 52. The opposite end or the arm 64 is equipped with a slider tit which is in contact with a coil type resistance element 70, one end of which is connected by way of a wire 12 to the blower motor it, the op osite side of the motor being connected r supply by a lead it. As the slider a high resistance end of the elemen end in the illustration, slider operates to open a switch t: connected between the slider arr other side of the power the resistance element it'll causes the within the container to expand, th the upper end of the bellows 3161 This movement, operating through swings the arm 56 downwardly arou point 58 so that the yolre til, by us pin 62, swings the slider t8 toward the motor, thereby decreasing the the motor circuit and increasing the s blowers i2 and it. Whenever the electric heater 50 is tie-energized a sufficient length or time to permit the bellows 56 to elongate a predetermined amount, the slider 68 will be swung almost completely to the high resistance end of the resistor 10, at which point the motor it is operating at the lowest speed consistent with efucient heater combustion. If under these conditions the heat output of the heating system is still more than is required, the slider -58 will move a slight additional amount, whereupon the projection it opens the switch it, thus interrupting the motor circuit so as to discontinue heater operation until such time as heat is required.

The controller for the electric heating element 50 of the heat motor it comprises a bridge circuit made up of fixed resistors A and B which may be identical and are so connected that one end of each is common, as indicated at this end being connected to one end of the heating ele ment Ell by a wire 82. The opposite end to of the resistor A is connected to the main line through a rectifier be which may be of th well known copper oxide type and which permits electric energy to flow from the line toward the resistance element A but not in the opposite direction.

Similarly, the opposite end to of resistor B is connected to the other side of the power supply by way of a line 86. From the terminal til of resistor B, the line 86 also leads to one end of a resistance element D1, the other side of this latter resistor being connected by a wire to one end of a fourth resistance element Dz. At its opposite end, resistor D2 is connected to a wire 94 which leads to a variable resistor C connected on its other side to a line 95 leading to the power supply end =88 of the resistor A. The electric heater 50, previously mentioned as being connected on one side to the lead 82, is. connected at its opposite end by a wire Qt to a second rectiher 98, while from the opposite side or the rectiresistance.

her a line I00 leads to a point [0| upon the wire 94 which connects resistors D: and 0.

Of these resistors, A and B are of fixed value and have a. low temperature coemcient of resistance. In other words, changes in temperature have littl or no appreciable effect upon their Also, the variable resistor C has a. low temperature coefllcient of resistivity. 0n the other hand, the resistors D1 and D: have a high temperature coeilicient of resistance, such that an increase in the temperature of these units increases their resistanc considerably. The resistance element D1 is located within a cas M2 at some point along the inlet air duct iii. The case is equipped withan air inlet tube I04 which extends into the air duct i6 and has its open end facing upstream. A second tube H16 leads from the case ltt and extends into the duct 16 so as to face downstream therein. Thus, whenever air is flowing through the duct ii, a portion thereof will be diverted into the box 402 so as to circulate around the resistor D1 and then return to the duct. The resistance element D1 is, therefore, maintained at the temperature of the air outside of the building to be heated with the result that its resistance increases whenever the outside air temperature increases. The resistor D2 is positioned within a case i138 located within the room to be heated so that it s maintained at substantially the temperature of the air therein.

Inspection of the circuit just described will disclose that the resistors A, B, and C form three sides of a bridge while the resistors D1 and D: in series form the fourth side. Inasmuch as the resistance of A and B is constant, it follows that whenever the resistance of D1 and D2 together is less than the resistance 6, the bridge will be unbalanced so as to cause current to flow through the heating element 50. On the other hand, if the resistors D1 and D2 together are at a high enough temperature so that their resistance is greater than the resistor C, no current will flow through the heating element 50 because the rectifier 38 prevents current transmission in the reverse direction.

The additional rectifier 84 is used because the circuit is shown as connected to an alternating current source. If a direct current source is used, this rectifier 8t is unnecessary.

When the system is in use, the variable resistor E, which may be located within the same case I08 as the resistor D2, is adjusted to the temperature desired. If the temperature setting called for is such that the resistance of the portion of the resistor C remaining in circuit is less than the resistors D1 and D2 together, no current will flow through the heating element 59. Since the bellows 48 is not heated, it will drop toward room temperature and will expand so as to swing the slider 68 downwardly until the switch '56 has been opened. The heater is, therefore, in the off position.

If, under the above conditions, the temperature within the room drops, or if the temperature outside the space to be heated decreases, the resistance of the elements 102 or D1, respectively, will be decreased. Whenever the decrease in the resistance of either becomes sufficient so that the resistance of the two in series is less than that of the resistor C, the bridge becomes unbalanced I and current is caused to flow through the heating element 50, thereby raising the temperature of the liquid filling within the case 42 so as to 5 close the switch I8 and start the heater. If the temperature of the room is well below a desirable level, or if the temperature outside has dropped considerably, it is apparent that the resistance of the elements D2 or D1, or both, will drop sufficiently so that the greater bridge unbalance will .cause a greater heating eifect in the element 50,

thereby causing the slider 68 to move so as to take still more resistance out of the motor circuit and increase the heater output still more.

From the above it is apparent that the bridge circuit always operates to provide heat whenever the temperature of the room is below a satisfactory level and that as the temperature of the room approaches the satisfactory level, the heater is gradually modulated so as to reduce the heat 1 output. It is also apparent that this effect is influenced by the anticipating unit D1 which is located so that it can sense the temperature of the outside air. Thus, any sudden drop or rise in the outside air temperature causes the heater to produce more or less heat, respectively, even though the temperature within the space to be heated has not changed. This permits the heater to increase the heat output to the room so as to keep up with the increased heat loss from the room to the outside.

If it is desired that the room controller unit D: have a more pronouced eflect in influencing heater operation than the unit D1, this can easily be accomplished. For instance, merely,by decreasing'the resistance of the unit D1 relative to D2, so that changes in the temperature of the unit I): will have a greater eflect upon the total resistance in that leg of the bridge than will changes in the temperature of the resistor D1,

, the desired result is achieved.

, sistor comprised of the coil in and slider 68. it

will be appreciated that, if desired, this unit may comprise a variable reactance of the inductive type or may be a variable transformer.

Having described my invention. what I claim as new and useful and desire to secure by Letters Patent of the United States is:

1. In a device of the type described, a motor speed controller, a heat responsive device con hosted for operation of said controller, an electric heating element for operating said heat responsive device, a first resistor having a high temperature coeflicient of resistance and arranged to be sensitive to the temperature of the space to be heated, a second resistor having ,a high temperature coeiiicient of resistance arranged to be sensitive to the temperature of the ambient air, a variable resistor having a low temperature coemcient of resistance, said resistors being electrically connected so that both of said resistors having a high temperature coeflicient of resistance form one leg of a bridge circuit, said variable resistor forming a second leg of said bridge circuit, other resistor; having a low temperature coeiilcient of resistance forming the other legs of said bridge circuit. circuit means connecting said bridge to a power source and a bridging wire for said bridge containing said heating element, said bridging wire including a rectifier for preventing energization of said heating element by said bridge when said bridge is unbalanced in one direction but for causing continuous energization of said heating element when said bridge is unbalanced in the other direction.

2. In a device of the type described, a variable reactor. an electric heating element, means responsive to the heat output of said heating element for operating said reactor, a pair of resistors each having a high temperature coeflicient of resistance, said resistors being connected togather and forming one leg of a bridge circuit and being arranged to be sensitive to different temperature conditions, a variable resistor'having a low temperature coefficient of resistance forming another leg of said bridge, other circuit elements forming the other leg of said bridge, circuit means connecting said bridge to. a power source and a bridging wire for said bridge containing said heating element, said bridging wire including a rectifier for preventing energization of said heating element by said bridge when said bridge is unbalanced in one direction but for causing continuous energization of said heating element when said bridge is unbalanced in the other direction.

3. In a device of the type described, a variable reactor, an electric heating element responsive to an electric current for operating said reactor, a bridge circuit for energizing said current responsive means when said bridge is unbalanced, said bridge including temperature responsive resistors arranged to be sensitive to the temperature of the space to be heated and of the ambient air and a bridging wire containing said electric heating element. and means to prevent current flowing from said bridge to said electric heating element when said bridge is unbalanced in one direction. I

ARTHUR R. COLLINS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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