GB2102116A - Solid fuel-fired heating appliance and control means therefor - Google Patents

Abstract

A solid fuel-fired heating appliance includes a casing (2) housing a grate for supporting a fire, and air control means (10) for controlling the supply of combustion air to the fire and movable to provide different, predetermined heating conditions from the appliance. A flue (8) for the exhaust gases projects from the casing (2), a temperature sensitive device (14) being positioned in the flue (8), and interconnected with air control means (10) such that, if the temperature within the flue (8) as sensed by the device (14) moves outside a predetermined range associated with the preset heating condition of the appliance, the air control means are actuated to bring said temperature back within said range. A further temperature sensitive device for sensing the room temperature may also be interconnected with the air control means. <IMAGE>

Description

SPECIFICATION Solid fuel-fired heating appliance and control means therefor This invention relates to heating appliances fired by solid fuel, such as coal coke or wood, and particularly to means for controlling the temperature in flues associated with room-sealed heating appliances located in domestic residences and burning smokeiess fuels.

Such appliances are vented to atmosphere through associated chimneys or flues which must be capable of withstanding the conditions created by the appliances. Flues are commonly of stainless steel and have a preferred operating temperature range of 1 000C to 5400C, although they can withstand temperature of up to 7600C for shorter periods.

There are two major problems with which the flues of current appliances have to cope extended firing of the appliance resulting in temperatures in the flue well in excess of 8000C for prolonged periods which in turn causes high temperature oxidation and reduction of the metal flues; prolonged idling of the appliance whereby the temperature in the flue does not rise above the acid due point and the flue gases are not burned off, resulting in acid corrosion of the metal of the flue and the formation of thick layers of soot in the flue.

These problems result primarily from the fact that combustion in the appliance is under the control of a manually-operated damper which can be incorrectly used.

According to the present invention there is provided a solid fuel-fired heating appliance comprising a casing containing a grate for supporting a fire and, preferably, a boiler assembly, means for controlling the ingress of combustion air to the casing and movable to any one of a number of preset positions to provide different predetermined heating conditions from the appliance, said casing being adapted for attachment thereto of a flue to receive exhaust gases from the fire, the appliance further comprising a temperature-sensitive device for location in said flue and interconnected with said air control means in such a manner that, during operation of the appliance to provide a predetermined heating condition therefrom, said air control means are actuated in accordance with the temperature in the flue to maintain said temperature between predetermined minimum and maximum values associated with said predetermined heating condition.

Thus it will be appreciated that such an arrangement can over-ride a preset condition of the air control means if the temperature in the flue moves outside a predetermined temperature range associated with said preset condition of the air control means. This facility is particularly useful at the upper and lower ends of the permitted temperature range that can be accommodated by a flue.

A preferred appliance includes a further temperature sensitive device for location in a room containing the appliance to sense the ambient temperature in said room, the further device being interconnected with the air control means in such a manner that, during operation of the appliance to provide predetermined heating conditions therefrom, said air control means are actuated in accordance with the temperature in the room to maintain said temperature at a predetermined value.

Such a further tmperature sensitive device is particularly useful when the appliance is idling with a view to conserving fuel, said further device ensuring that combustion air to the fire is increased if the ambient temperature drops.

By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawings of which: Fig. 1 is a schematic illustration of an appliance according to the invention, and Fig. 2 is a schematic illustration of the means for controlling the flow of combustion air to the fire in the appliance of Fig. 1.

Referring to the drawings the illustrated roomsealed smokeless fuel appliance includes an outer casing 2 housing a boiler assembly (not shown) and grate (not-shown) for receiving thereon the solid fuel. A door 4 closes the open front of said casing, while the front of a removable ash pit is shown at 6. A conventional stainless steel twinwalled flue 8 extends from the upper regions of the casing 2 to vent to atmosphere.

Located within the lower regions of the casing 2 is an air control means 10, for example a pivotal flap, which can be located into any one of a number of preset positions corresponding to particular operating conditions of the appliance.

Such settings are conveniently achieved by appropriate manual operation of a dial or like device on a main electronic control unit 12 linked to the air control means 10. The dial is preferably graduated with a scale corresponding with the temperature in the flue at the particular operating conditions, typically: Temperature in flue Setting above ambient OFF O"C 0 1000C MINIMUM 1 2000C 2 3000C 3 4O0CC 4 5000C 5 5400CMAXIMUM A temperature sensitive device 14 is positioned in the lower regions of the flue 8 to monitor the temperatureof the exhaust gases in said flue. This device 14 forms part of an over-riding arrangement built into the control unit 12.This over-riding arrangement is such that, if the temperature in the flue 8 as sensed by the device 14 differs by more than L200C from the expected temperature, the control unit 12 comes into operation to actuate the air control means 10 to increase or decrease the air flow to the fire as necessary to achieve the correct temperature within the flue.

The minimum setting of the scale, position '0', is chosen to ensure that the temperature in the flue does not fall below that at which the harmful acids and chlorides in the exhaust gases become active, this position being termed the 'slumber' position.

The maximum setting that can be achieved manually by a user is setting '5' which corresponds with the maximum permissible temperature in the flue under normal operating conditions of the appliance.

In the event of a chimney fire whereby temperature in the chimney exceed 5400 C, the electronics of the control unit are such as to operate it at setting equivalent to '6' and above.

In the event of a power failure, the air control means would be arranged to remain in an open position equivalent to a preselected temperature in the flue, for example 4000C above ambient, thus ensuring that the appliance would continue to operate at an acceptable level of safety.

When the appliance is switched off, the air control means are initially closed while the temperature in the flue 8 falls to ambient. The air control means is then returned to the position it would adopt at setting '3' - i.e. 4000C above ambient - to provide air supply to the flue to vent said flue and to dry out any condensation which may have formed during the cooling cycle.

In certain conditions it may be possible to provide a flue enclosure duct surrounding the flue 8 and to direct air pre-heated by contact with the exterior surface of the flue 8 from said enclosure duct to the top surface of the appliance and to the combustion air supply point of the appliance, thus allowing the appliance to become independent of room air.

It may prove desirable to provide a further temperature sensitive device 1 6 located in the room housing the appliance and interconnected with the control unit in such a manner that, when the temperature in the room differs by more than a predetermined amount from the expected temperature, the air control means 10 is actuated to obtain the expected temperature in the room.

This facility may prove useful in the 'slumber' or idling condition of the appliance where it is desired to conserve fuel and where room temperature may therefore fall below a desired level.

Claims (5)

1. A solid fuel-fired heating appliance comprising a casing containing a grate for supporting a fire, and means for controlling the ingress of combustion air to the casing and movable to any one of a number of preset positions to provide different predetermined heating conditions from the appliance, said casing being adapted for attachment thereto of a flue to receive exhaust gases from the fire, the appliance further comprising a temperature sensitive device for location in said flue and interconnected with said air control means in such a manner that, during operation of the appliance to provide a predetermined heating condition therefrom, said air control means are actuated in accordance with the temperature in the flue to maintain said temperature between predetermined minimum and maximum values associated with said predetermined heating condition.

2. A heating appliance as claimed in claim 1 and comprising a further temperature sensitive device for location in a room containing the appliance to sense the ambient temperature in said room, the further device being interconnected with the air control means in such a manner that, during operation of the appliance to provide predetermined heating conditions therefrom, said air control means are actuated in accordance with the temperature in the room to maintain said temperature at a predetermined value.

3. A heating appliance as claimed in claim 1 or claim 2 in which the or each temperature sensitive device is interconnected with, to actuate, the air control means, said control unit being manually operable to provide any one of said different predetermined heating conditions from the appliance, the arrangement being such that, if the temperature in the flue as sensed by that temperature sensitive device therein differs from that normally associated with the manual setting of the control unit by more than a predetermined amount, the control unit is actuated to over-ride the manual setting and to move the air control means to a position to regain the associated flue temperature.

4. A heating appliance as claimed in any one of claims 1 to 3 in which the flue is enclosed within a duct, air preheated by contact with the exterior surface of the flue directed from the annular space between the flue and said duct to the appliance to comprise or supplement the combustion air thereto.

5. A solid fuel-fired heating appliance substantially as described with reference to and as illustrated by the accompanying drawings.