WO1981000609A1

WO1981000609A1 - Flue control

Info

Publication number: WO1981000609A1
Application number: PCT/AU1980/000050
Authority: WO
Inventors: A Homewood
Original assignee: Boral Gas Pty Ltd; A Homewood
Priority date: 1979-08-24
Filing date: 1980-08-25
Publication date: 1981-03-05
Also published as: EP0034160A1; JPS56501060A; EP0034160A4

Abstract

A flue control for fluid fuelled heaters, to minimise heat losses through the flue when the burner is not operating, comprising a pressure or electric solenoid operated damper or baffle, operable, upon the sensing of a predetermined temperature or pressure condition within the heater, to selectively open or close the damper or baffle thereby optimising fluid fuel consumption. The pressure or electric solenoid operated damper or baffle is responsive to changes in pressure of fluid fuel entering a burner for combustion.

Description

FLUE CONTROL

THIS INVENTION is concerned with a flue control for combustion heated apparatus utilizing a fluid fuel.

In conventional fluid fuelled combustion heated apparatus such as a gas or oil fuelled hot water system, steam generator or any other furnace, various forms of combustion control are available. For example, thermostatic or pressurestatic- control means are usually provided to regulate a supply of fluid fuel to a combustion chamber to control the quantity of heat generated therefrom. The thermostatic control means may be adapted to be operable by a predetermined flue gas temperature or the temperature of a medium to be heated by the apparatus. In a similar manner, a pressurestatic device may be adapted to be operable by the internal pressure within the medium to be heated or by the combustion gas pressure within a lue. In a conventional hot water system, such a control means usually comprises a thermostat adapted to reduce or shut off a fluid fuel supply to the combustion chamber when the stored water reaches a desired temperature. The thermostat will then increase or re-commence fuel supply when the temperature of the stored water falls below a predetermined level.

In conventional fluid fuelled combustion heaters a pilot flame or electrically operated ignition means is usually provided to re-ignite the fluid fuel upon actuation of the thermostatic or pressurestatic control means to increase or re-commence the fuel supply. Where the combustion gas exhaust flue of such heaters is in thermal communication with a means for storing heat, the exhaust flue acts as a heat exchanger to transfer heat from combustion gases to the heat storage medium. Heat storing combustion heaters of the above- mentioned type suffer the disadvantage that upon reaching a desired operating temperature, the thermostatic or pressure¬ static control means operates to reduce the fluid fuel supply to a minimum level where a pilot flame remains alight or, where an electrically operated re-ignition means is provided, the fuel supply may be cut off completely. Under these conditions , air at ambient temperature enters the flue and is heated either by the pilot flame or by a transfer of heat from the heat storage medium thus creating an updraught. It will be readily apparent to a skilled addressee that such an updraught of relatively cool air is effective in removing a substantial quantity of heat from the heat storage medium before normal combustion is re-commenced.

The present invention aims to alleviate the above- mentioned thermal inefficiency of prior art combustion heaters and to provide means for controlling a fluid fuel combustion heater to achieve greater thermal efficiency.

According to one aspect of the invention there is provided a flue control means for a fluid fuelled heater comprising; means for restricting the flow of gas in a flue; sensing means to sense a predetermined condition in a combustion heater, and; control means operatively connected to said restricting means, whereby in use, on sensing of a pre¬ determined condition in said heater, said control means is caused to actuate said flue restricting means.

In a preferred embodiment of the invention, the means for restricting the flow of gas comprises a damper, baffle or the like, capable of substantially blocking the bore of a lue .

In another preferred embodiment of the invention, the sensing means comprises a thermostat or pressurestat.

In a further preferred embodiment, the control means comprises an electrically operated solenoid.

In a most preferred embodiment of the invention the control means is operable by fluid fuel pressure.

One preferred embodiment of the invention will now be described with reference to the accompanying drawings in which: FIG. 1 illustrates a gas or oil heated hot water system with a flue control according to the invention;

FIG. 2 illustrates an enlarged view of the encircled area of FIG. 1. FIG. 3 illustrates one embodiment of the flue gas restricting means connected to one embodiment of the control means.

FIG. k illustrates an alternative embodiment of the flue gas restricting means. FIGS. 5 and 6 illustrate alternative embodiments of the control means .

In FIG. 1 a gas or oil heated hot water system 1 is provided with a combustion chamber 2 and an exhaust gas flue 3« Gas burner k is situated within the combustion chamber and is connected to a thermostatically controlled valve 5 . Valve 5 is controlled by a conventional water temperature thermostat 6, preferably of the "snap-action" type. A pilot burner or electric ignition device 7 is provided adjacent burner k . A combustion chamber control 8 comprising a thermocouple or an electrical device such as a thermistor is connected to valve 5 via a known fusible link « Situated above flue 3 is a damper or baffle plate 10 connected to a diaphragm valve 11 which in turn is operatively connected to one end of gas or oil conduit 12. The other end of conduit 12 is connected, by a suitable junction, to burner fuel feed conduit 13•

In the course of a normal heating cycle of, for example , a gas heated hot water system the gas pressure in eed conduit 13 and conduit 12 is sufficient to maintain diaphragm valve 11 in a retracted state such that damper or baffle plate 10 is in a fully opened condition offering no resistance to the passage of combustion gases through the flue 3- As the water in the system 1 reaches the desired temperature, thermostat 6 operates to cause valve 5 to restrict the flow of gas to burner h such that only a pilot flame 7 - -

remains alight.

The reduced gas pressure in conduit 13 (and thus conduit 12) permits diaphragm valve 11 to return to its normal state whereby damper or baffle plate 10 substantially closes the outlet of flue 3- In this manner, the flow of cool gas upwardly through flue 3 is essentially eliminated thus assisting retention of heat in the water contained in system 1.

Damper or baffle plate 10 may be provided with a smal perforation to permit the passage therethrough of the combustion gases of the pilot flame but the perforation is sufficiently small as to substantially prevent an updraught of additional cool air through flue 3. In this manner it is believed that at least part of the heat of combustion of the pilot flame may be contributed to the system 1 rather than being permitted to go to waste as in prior art devices of this type.

As a safety measure in the event of a failure of diaphragm valve 11 or a flue blockage, an additional thermostat 8 may be provided in the combustion chamber 2. The thermostat may be chosen to have an operating temperature effective to cause gas control valve 5 to cut off the supply of gas to the burner in the event that the temperature in the combustion chamber exceeds a predetermined level. As a further safety measure, a fusible link of known type may be placed in the circuit connecting thermostat 8 and gas control valve 5 . If a blockage or restriction occurs in flue 3_. backflowing combustion gases cause the link 9 to fuse thus disabling control valve 5 until the fusible link is replaced. FIG. 3 illustrates an embodiment of the invention wherein the damper or baffle plate 10 is an essentially flat disc and the control means comprises a diaphragm valve 11 of known type.

FIG. k illustrates an alternative embodiment of damper or baffle plate 10 wherein the damper or baffle plate is pivotally mounted within the flue. - 5 ^"

FIG. 5 illustrates an alternative embodiment of a control means suitable to control the damper or baffle plate of an oil fired combustion heater. The apparatus of FIG. 5 operates in a similar manner to the diaphragm valve of FIG. 3 except that it is operated by oil pressure and the flexible diaphragm is replaced by piston 14 which is compressed against a spring 15.

FIG. 6 illustrates yet a further embodiment of the control means comprising an electric solenoid 16 for operating the damper or baffle plate. In a combustion heating apparatus with an electrically operated combustion ignition system, it may be most advantageous to employ an electric solenoid to operate the damper or baffle plate. EXAMPLE The following comparative example is illustrative of the advantages of the present invention.

Two essentially identical "Vulcan 80" fast recovery gas hot water systems of 80 litre capacity and a rated thermal input of 26.4 Megajoule/hr were employed. One of the systems was fitted with a control system as generally illustrated in FIGS. 1-3.

Over a seven day test period, hot water was drawn from both systems for the first five days at a rate of 227 litres per day (comprising five portions, each of 5- litres, at intervals of one and a half hours). No water was drawn from either system for the remaining two days. The fuel employed for the test was town gas having a thermal capacity of 19 Megajoule/metre and the following observations were recorded:

* Similar results were obtained with Natural Gas and LP Gas.

It can be clearly seen that considerable savings in energy consumption may be realized according to the present invention. In a domestic hot water system, to which the present invention is particularly suited, a 10^ overall saving in energy consumption is contemplated when a flue control according to the invention is fitted.

It is envisaged that a flue control according to the invention may be retro-fitted to existing fluid fuel heating devices by incorporating the damper or baffle plate and control means therefor in a downdraught prevention cowl on the heater flue assembly.

It will be apparent that many modifications or variations may be possible without departing from the spirit or scope of the invention.

Claims

1. A flue control means or a fluid fuelled heater comprising; means for restricting the flow of gas in a flue; sensing means to sense a predetermined condition in a combustion heater, and; control means operatively connected to said restricting means; whereby, in use, on sensing of a predetermined condition in said heater, said control means is caused to actuate said flue restricting means.

2. A device as claimed in claim 1 wherein the means for restricting the flow of gas in a flue comprises a. damper, baffle or the like, capable of substantially blocking the bore of the flue.

3- A device as claimed in claim 1 or claim 2 wherein the sensing means comprises a thermostat or pressurestat .

4. A device as claimed in any preceding claim wherein the control means is a fluid pressure operated diaphragm or piston.

5. A device as claimed in claim 4 wherein said fluid pressure is derived from a fluid fuel.

6. A device as claimed in any one of claims 1-4 wherein the control means is an electrically operated solenoid.

7« device as claimed in any preceding claim wherein the fluid fuelled heater comprises a hot water system.

8. A device as claimed in any preceding claim wherein the fluid fuel is gaseous.

9. device as claimed in any one of claims 1-7 wherein the fluid fuel is a liquid hydrocarbon.

10. A device as claimed in any preceding claim wherein there is further provided a fusible link in an electrical circuit between a thermostatically controlled fuel supply valve and a combustion chamber thermostat, said fusible link being situated adjacent an entry to said combustion chamber.

11. A device as claimed in any preceding claim wherein the control means is attached to a downdraught preventer cowl .

12. A fluid fuelled heater wherever provided with a flue control device according to any one of the preceding claims.