GB2071878A - Flue damper control system - Google Patents

Abstract

A flue damper is mechanically driven through a sensor control to change the physical position of a damper within a flue associated with a furnace or other combustion device. After the demand for ignition of the furnace, the flue damper is rotated slowly into the full open position whereupon ignition of the furnace is permitted. After the demand has been satisfied, the ignition is ceased and at a predetermined time thereafter the damper is slowly moved to the closed position whereby to inhibit completely, in the cases of oil fired devices, and to a substantial degree (a maximum of 90%), in gas fired devices, the orifice size of the exhaust flue thereby preserving the residual heat within the boiler or fire box which would otherwise escape through the flue into the atmosphere. Such device decreases, in excess of 15%, the amount of energy consumed by reducing the cool-down effects of the fire box or boiler. <IMAGE>

Description

SPECIFICATION Energy saving flue damper This invention relates to a damper mechanism for opening and closing the orifice size of an exhaust flue associated with a heating device such as a furnace, whether gas or oil fired.

There are a number of automatic flue dampers located in the vent stack for commercial or household furnaces or other apparatus which are designed to close the vent stack during times when combustion within the furnace does not occur, and to open during times when the combustion is occuring in the apparatus. Normally, the open position is controlled by a damper spring. In case of default of electric energy the damper itself is moved to its open from closed position; otherwise, by a direct current solenoid associatedly connected to interface with the temperature sensing device which operates the vent-to close it.

Such device moves, quickly, the damper from its open to close position as a result of the solenoid action and this is not desirable on at least two counts; firstly, extra associated noise with the damper reaching its limit position from its closed to open or open to the closed position, and secondly, the increased mechanical structure necessary in order to stop the inertia of the quick moving damper.

in another automatic stack damper an electric motor is used to rotate the damper within the stack from its open to its closed position and from the closed to its open position either with or without a bias means that operates the vent. Such device is clearly indicated in U.S.A. Patent #4, 0 3 9, 1 2 3, entitled AUTO MATIC STACK DAMPER to Seymour Frankel, issued 2 August 1977. It suffers from a number of disadvantages which include the requirement that the motor operated vent be connected to a thermal sensing device such as a thermostat located in the vent. It is the vent thermostat which activates and deactivates the electric motor associated with the Frankel device. Thus the response of the damper is immediate upon the demand of the thermostat to call heat and at shut-off period.The requirement of Frankel causes the damper to shut when the thermostat, which senses the temperature in the room to be heated, goes off only after the thermo-sensor, which is physically located in the exhaust flue of the furnace, crosses below a cool-down threshold temperature which in most instances is fixed at 400"F, aPproximately 1 70 C.

Particularly, an oil fired furnace, where the oil fired furnace is not "tuned" and incomplete combustion normally takes place, soot or carbon particles are generated by the fire of the oil fired furnace, and move out into the exhaust flue and normally, because they also contain residual oil particles thereon, adhere to the flue. This causes the temperature sensor in the flue of Frankelto be coated with temperature insulating carbon particles.

Hence, the sensitivity of the sensor may become immune due to the carbon particle coating, in which case, the flue temperature is substantially higher than the 400"F minimum threshold and this causes improper operation of the Frankel device.

In instances where the ignition fuel is oil, there is a tendency therefore to prematurely close the damper while still hot escaping flue gases emanate from the fire box since there is still oil in the fire box. Hence, carbon monoxide has a tendency to dangerously accumulate.

Further, such devices, because they operate to close after a fairly long sustained period of time, their ability to preserve the temperature in the fire box, or more accurately in the boiler of the furnace, is decreased because of the extremely long period of time that elapses after de-ignition of the furnace and closing of the vent as will hereinafter be noted.

Although, in one sense, the Frankel thermosensor in the exhaust flue may be perceived as a time delay mechanism, this is inaccurate since the temperature sensor creates an apparent time delay whose elapsed time is variable and unpredictable. This is unacceptable from two divergent points of view; firstly, the vent may be closed too soon whereupon dangerous flue gases are trapped in the furnace fire box; or secondly the vent may not close soon enough whereupon great heat loss escapes up the exhaust flue between the duration of deignition of the furnace and the closing off of the vent. Lack of energy preservation after deignition of the furnace is highly significant, in the latter case, and may even result in undisclosed inutility in such device.The latter aspect becomes even more acute when there is a large cross-sectional area of the flue vent and with a greater height of the flue stack since, as those skilled in the art will know, a greater volume of air passes through a vent stack because of greater draw when the crosssectional area of the vent stack is larger and its height is higher.

Devices, such as Frankel, is Canada have been banned by the Canadian Standards Association precisely for the reasons hereinbefore enumerated.

The present invention overcomes the major failing of Frankel by having a time dependent or time elapse delay system immune from temperature and other factors, so that the heating cycle ignition and de-ignition points are precisely maintained. Also a synchronous motor is provided for slowly moving the vent from its open to closed position.

The present invention therefore contemplates an improvement to a heating system that includes a furnace for generating heat, and that passes exhaust by-product up a vent ing stack, the furnace having a furnace control circuit to turn off and on the furnace, the improvement comprising: (a) a damper having a pivoting vane in said venting stack, the vane pivoting between an opened and a closed position; (b) an actuator attached to the pivoting vane for pivoting said vane to the open and to the closed positions, said actuator including; (i) a synchronous motor coupled to a shaft and to said vane for pivoting said vane; (ii) a time dependent delay means including first switch means for making electrical connection with the motor whereby to energize the motor into rotation whereby the vane rotates;; (iii) second switch means for making electrical contact and adapted to be connected in series with the furnace control circuit and to energize the furnace control circuit when the second switch means is closed so as to cause the furnace to go on; (iv) means carried by the shaft for closing the second switching means when the shaft is at a predetermined relative position;; (v) relay means including first and second contact pairs, the relay means responsive to and adapted for serial connection to a thermostat whereby on closing of the thermostat, in response to the minimum ambient temperature selected, the relay means is energized to open one of said contact pairs and to close the other of said contact pairs, the first said contact pair in series with the motor whereby to de-energize the motor whereupon the vent rotates open and when fully open means (iv) closes the switch means (iii) whereby the furnace control circuit is closed and the furnace turns on, the second of said contact pairs being in series with said second switch means and the furnace control circuit.

This invention also contemplates an improved method of preserving heat within an environment that utilizes a furnace for generating heat, whether by gas or oil fired burner, and that passes, as exhaust, by-products up a venting stack the furnace having a control circuit which turns it off, the improved method including the steps of:: (a) positioning in the venting stack, in close proximity to the furnace a damper having an operative pivoting vane therein for opening and closing the cross-sectional area of the damper and hence, the venting stack; (b) operating the damper to close the venting stack after a predetermined time when the furnace is not consuming fuel to create heat; (c) sensing the ambient temperature of an environment to be heated and establishing therefore, a maximum and minimum ambient temperature; (d) activating the damper to open when the minimum ambient temperature is sensed by said sensing step; (e) igniting the combustionable fuels in said furnace so that said furnace creates heat and conveying the heat to said environment: (f) closing the supply of fuel to the furnace when the maximum ambient temperature is reached; and (g) waiting a predetermined period, after step (e) and then closing the vent in the exhaust flue stack thereby preserving the remaining heat contained in the furnace for distribution to the environment.

Embodiments of the invention will now be described way of example with reference to the accompanying drawings in which: Figure 1 is a perspective view of the mechanical device.

Figures 2 and 3 are side elevations respectively, of the device of Fig. 1.

Figure 4 is a location diagram of the vent in use.

Figure 5 is a top view of a full closure vent preferred for oil fired application, as is shown in side elevations in Figs. 2 and 3.

Figure 6 is an electrical circuit diagram.

Figure 7 is an alternative embodiment of a damper, top view as in Fig. 2, but possessing a vane of reduced area to show continuous venting in the closed position, as preferred for gas fired application.

Referring, in part to all the drawings, the principal embodiments of the invention include, in summary, an improved heating system that includes a furnace, referred to as reference 30, for generating heat, whether as a gas fired or oil fired or otherwise fired unit, and that passes exhaust by-products as a result of combustion up a venting stack, referenced 32. The furnace has a furnace control circuit (not shown), but those skilled in the art will be familiar with it, to turn the furnace off and on; the improvement comprises; a damper, generally illustrated as 1, having a pivoting vane, either 1 5 or 15', in said venting stack 2, the vane pivoting between a closed (the solid position in Fig. 1) and an open position (the phantom position in Fig. 1); an actuator attached to the pivoting vane for pivoting said vane to the open or to the closed positions. The said actuator includes a synchronous motor 6 coupled to a shaft 7 and to said vane 1 5 for pivoting said vane; a time dependent delay means 9 including a first switch means, 9" for making electrical connection with the motor 6 whereby to energize the motor 6 into rotation whereby the vane 1 5 rotates. A second switch means referenced 11 for making electrical contact and adapted to be connected in series which the furnace control circuit and to energize the furnace control circuit when the second switch means is closed so as to cause the furnace to go on.

Means (the projection of lever arm 4) carried by the shaft 7 for closing the second switch means when the shaft 7 and hence, lever 4 is in a predetermined position. A relay means 1 9 includes first and second contact pairs as illustrated, the relay means 1 9 responsive to and adapted for serial connection to a thermostat, referenced 43, whereby on closing of the thermostat, in response to the minimum ambient temperature selected for the heated environment, the relay means 9 is energized to open one of said contact pairs and to close the other of said contact pairs, the first of said contact pairs connected in series to the synchronous motor 6 whereby to de-energize the motor whereupon the vent 1 5 rotates open under the force of a biasing spring 14, and when fully open the projection of shaft 4 closes the switch means 11, which in the preferred embodiment is a micro-switch. The furnace control circuit is thus closed and the furnace 30 turns on, the second of said contact pairs being connected in series with said second switch means 11 and the furnace control circuit.

After the thermostat reaches and senses the maximum ambient temperature selected, it opens and this opens the relay means which reverses the two contact pairs which, in one circuit, immediately opens the furnace control circuit so that the furnace is turned off, and in the other circuit energizes the time dependent delay means 9 whereupon after the predetermined delay of time, the coil 9' thereof, causes the switch 9" to close activating the synchronous motor 6 into the counterclockwise direction to close the vane 1 5.

Referring to Figs. 1 and 4 a damper assembly 1 is positioned in the exhaust flue venting stream downstream from a furnace or other heating device 30 to which it is attached.

More particularly, the damper 1 is positioned in the vent stack 32 just downstream of a barometric damper 33 that is disposed between furnace 30 and damper 1.

Referring to Figs. 1 through 5 the damper assembly 1 includes outer sheet metal tubing 2, preferably of aluminized steel to resist rust and to withstand 1 200*F (650"C) and a diametrically positioned shaft 7 which projects into outside bearing members 1 6 mounted in the walls of the tubing 2. A circular sheet member 1 5 is affixed to the shaft 7 as a vane and is pivoted by the rotational position of the shaft whereby to open and close the internal diameter and to change the effective cross sectional area of the sleeve 2. One end of the damper shaft 7 extends to a coupling 8 which attaches itself, as by conventional means, to a synchronous motor 6 that is secured by bolts 6' through standoffs or spcers 6" onto a circumferential housing 20.Through coupling 8 is mounted a lever arm 4 acts as a lever that can mechanically move or pivot the vane 1 5 from open to closed or closed to open position. The vane is shown in Fig. 1, in phantom, in a more open position than in solid and the position of the lever arm 4 in the phantom position is that which correspondingly represents the more open position in phantom. A return coil spring 14 embraces the lever 4 and biasingly urges the shaft 7 counterclockwise, when referring to Fig. 2, so that the vane is fully opened. When the electric synchronous motor 6 is energized, it urges against the bias of the spring 14 to close the vane and to hold the vane in the closed position, that of Fig. 5.

Referring to the electrical circuit diagram Fig. 6 it includes a terminal block 35 for the interconnection of various wires and circuits associated with the time delay mechanism 9 the relay mechanism 1 8 housing first and second contact pairs and other switches. Wire pair 40 is to be connected to a 24 volt transformer which supplies the energy to the complete system. Wire pair 42 interconnect to a room thermostat 43 which, when closed, calls for heat. The heat cycle commences. In reality the thermostat 43 energizes relay 1 8 to make contacts of the first contact pair and break the contacts of the second contact pair.

Wire pair 41 in interconnected to the heating device 30 and for example is connected directly to either a gas solenoid which operates the gas valve of a gas fired furnace, or in the case of an oil burner, to the electrical motor of the oil burner of an oil fired furnace. Hence, this pair 41 is connected to the furnace on/off control circuit. Access to this circuit is obtained by disconnecting the boiler or furnace high limit control and placing this wire pair in series therewith so that the boiler or furnace is activated ON when the micro-switch 11 closes. From the terminals of the terminal block 35, the wire pair 41 is in series with the micro-switch 11 and with the second contact pair (normally open) of relay 1 8. When relay 1 8 is energized this second contact pair is closed.

Assuming, now, that the motor 6 is energized to hold the vane 1 5 in the closed position of Fig. 5, in that instance, the time delay relay 9 will be closed as in the solid position of Fig. 1. When the room thermostat 43 closes and the call of heat therefore is made, control relay 1 8 is energized thereby and the contacts of relay 1 8 are therefore moved from the solid to the phantom position, of both contact pairs. Contacts of the time delay 9 are opened from the phantom position to the solid position and the motor 6 is de-energized. On de-energization, the return coil spring 14 moves the vane 1 5 to the open position, the phantom position of Fig. 1 and when the open position is fully achieved, (see Fig. 3) the projection of the lever 4 through the shaft 7 strikes the leverage arm 49 of the micro-switch 11 to close the same thereby completing the furnace control circuit through the second contact pair of relay 1 8. The furnace goes on and heating begins.

When the heat level required is reached, the thermostat 43 opens thereby de-energizing the relay coil 1 8 moving the contact pairs thereof into the solid position shown in Fig. 6.

The furnace goes off since the second contact pair of relay 1 8 is opened thereby. The time delay coil 9' is energized but will not activate the switch thereof until the given time delay period of the time delay switch is reached; typically two minutes. When the time delay period has elapsed, the switch 9" closes and the synchronous motor 6 is activated to return the vane 1 5 (15') to the closed position. A typical time delay mechanism preferred, is a mechanical time delay mechanism that is preferably temperature compensated. That manufactured by the Paragon Electric Company, a division of AMF of the United States of America with a two minute delay, namely, model number t903 mechanical time delay mechanism is satisfactory.

For servicing or for other reasons where it is desirable to override the electrical function of the vent as hereinbefore described and hence to cause the vane 1 5 to be located and fixed in the open position, the lever arm 4 may be moved by hand from the solid position to the phantom position, as shown in Fig. 1, and the dead bolt 50 indexed there to cross and to hold the lever arm 4 in the vertical phantom position. This mechanical override permits maintainance of the device 1 and the furnace while at the same time, since the longitudinal axis of the lever arm is mounted in the same plane as that of the vane 15, the lever arm 4 is a visual indicator of the actual position of the vane 1 5 in the damper 1.

In order to keep the actuator component as "cool" as possible and thereby to eliminate the transfer of heat from the stack 2 to the housing 20 and its cover 20' they are mounted on an extension bracket 25 and if desirable, the extention bracket 25 may be composed of material other than metal so that to inhibit, as much as possible, the conduction of heat from the sleeve to the housing 20 and its components. Mounting of the bracket 25 to the stack 2 is simplistically done by sheet metal screws, shown in Fig. 1 but not referenced.

Referring to Fig. 5 and another embodiment of vane 15' the same has its peripheral margins parallel and truncated so that the vane 15' displays an area as when in the closed position of Fig. 5 of about 90% of the actual cross sectional area of the sleeve 2.

This, leaves, on the two diametrically opposed marginal sides of the vane 15' space area 1 9 for flue gases to pass by the vane 15' even when in the fully closed position. This feature is desirable when the damper assembly 1 is used in gas fired furnaces, with pilot lights, so as to not inhibit the flow of exhaust biproducts generated in the fire box by the pilot light during furnace de-ignition.

Claims (9)

1. An improvement to a heating system that includes a furnace for generating heat, and that passes exhaust by-products up a venting stack, the furnace having a furnace control circuit to turn off and on the furnace, the improvement comprising: (a) a damper having a pivoting vane in said venting stack, the vane pivoting between an opened and a closed position; (b) an actuator attached to the pivoting vane for pivoting said vane to the open and to the closed positions, said actuator including; (i) a synchronous motor coupled to a shaft and to said vane for pivoting said vane; (ii) a time depenent delay means including first switch means for making electrical connection with the motor whereby to energize the motor into rotation whereby the vane rotates;; (iii) second switch means for making electrical contact and adapted to be connected in series with the furnace control circuit and to energize the furnace control circuit when the second switch means is closed so as to cause the furnace to go on; (iv) means carried by the shaft for closing the second switch means when the shaft is at a predetermined relative position;; (v) relay means including first and second contact pairs, the relay means responsive to and adapted for serial connection to a thermostat whereby on closing of the thermostat, in response to the minimum ambient temperature selected, the relay means is energized to open one of said contact pairs and to close the other of said contact pairs, the first said contact pair in series with the motor whereby to de-energize the motor whereupon the vent rotates open and when fully open means (iv) closes the switch means (iii) whereby the furnace control circuit is closed and the furnace turns on, the second of said contact pairs being in series with said second switch means and the furnace control circuit.

2. The improvement as claimed in claim 1 including biasing means for holding the pivoting vane open when the motor is de-energized.

3. The improvement as claimed in claim 2 wherein means (iv) is a longitudinal member which is attached to said shaft and is rotated thereby about an axis orthogonal to its own longitudinal axis, one end of said member adapted to strike said switch means and to close it.

4. The improvement as claimed in claim 1 wherein said second switch means is a microswitch.

5. The improvement as claimed in claims 2, 3 or 4 wherein the thermostat, in response to the maximum ambient temperature, opens and thus deactivates the relay causing the second contact pair to open whereby the furnace control circuit is opened, and to close said first contact pair thereby to activate the time dependent delay means, which after its predetermined time, closes and powers into rotation the synchronous motor so as to rotate the vent to close.

6. The improvement as claimed in claim 2, 3 or 4 wherein the thermostat, in response to the maximum ambient temperature, opens and thus deactivates the relay causing the second contact pair to open whereby the furnace control circuit is opened, and to close said first contact pair thereby to activate the time dependent delay means, which after its predetermined time, closes and powers into rotation the synchronous motor so as to rotate the vent to close and the time dependent delay means closes to activate the motor after only two minutes of activation by the relay means.

7. The improvement as claimed in claims 2, 3 or 4 wherein the thermostat, in response to the maximum ambient temperature, opens and thus deactivates the relay causing the second contact pair to open whereby the furnace control circuit is opened, and to close said first contact pair thereby to activate the time dependent delay means, which after its predetermined time, closes and powers into rotation the synchronous motor so as to rotate the vent to close and the time dependent delay means is a mechanical time delay mechanism.

8. An improved method of preserving heat within an environment that utilizes a furnace for generating heat, whether by gas or oil fired burner, and that passes, as exhaust, byproducts up a venting stack the furnace having a control circuit which turns it off, the improved method including the steps of:: (a) positioning in the venting stack, in close proximity to the furnace a damper having an operative pivoting vane therein for opening and closing the cross-sectional area of the damper and hence, the venting stack and biasing the damper open; (b) operating the damper to urge against the said biasing and to close the venting stack after a predetermined time when the furnace is not consuming fuel to create heat; (c) sensing the ambient temperature of an environment to be heated and establishing therefore, a maximum and minimum ambient temperature; (d) releasing the damper to open under said biasing when the minimum ambient temperature is sensed by said sensing step; (e) igniting the combustionable fuels in said furnace so that said furnace creates heat and conveying the heat to said environment; ; (f) closing the supply of fuel to the furnace when the maximum ambient temperature is reached; and (g) waiting a predetermined period, after step (e) and then repeating step (b).

9. An automatic flue damper assembly for a furnace substantially as described with reference to Figs. 1 to 6 of the accompanying drawings, or as modified according to Fig. 7.