GB2102940A - Thermostatically controlled solid fuel appliances - Google Patents

Abstract

Apparatus (10) for controlling the transfer of heat from a combustion chamber to a given locus, for example an oven (11), in a solid fuel combustion appliance in which said locus is spaced-apart from the combustion chamber. The apparatus (10) comprises an air chamber (12) surrounding the oven (11) and by means of which heat is transferred from the combustion chamber to the oven (11). The air chamber (12) has an inlet (13) and an outlet (17) and a thermostat (16) which controls the admission of ambient air to the air chamber (12) through the inlet (13) by controlling the operation of a flap or shutter (15) associated with the inlet (13). The thermostat (16) used is suitably a bellows-type thermostat which includes an ether heat sensing capsule (24) located within the oven (11). <IMAGE>

Description

SPECIFICATION Thermostatically controlled solid fuel appliances This invention relates to apparatus for controlling the temperature of solid fuel-fired appliances. in particular, the invention relates to apparatus for controlling the temperature of an oven of a solid fuel-fired combustion appliance.

When an oven is heated by means of a solid fuel fire it has not hitherto been possible to apply any form of rapid-acting thermostatic control to insure that the particular temperature is not exceeded. Great inconvenience and wastage of prepared food may result from uncontrolled and unpredictable overheating of the oven.

There are several known methods of applying heat in a reasonably well distributed manner to a solid fuel-fired oven and it contents. One such method is known as external convection heating wherein an oven is surrounded by a closed air chamber which allows an even transfer of heat to the oven.

A typical arrangement of an oven employing external convection heating is depicted in Fig. 1 of the drawings. The oven of Fig. 1 is surrounded on its two sides, top, bottom and optionally the back, by a closed air chamber. The effect of the application of heat, by radiation and conduction from an associated solid fuel combustion chamber or by transfer from heated gases, is to promote an air circulation in the sealed chamber partially surrounding the oven, thereby, distributing internal heat in the oven more evenly than would be the case if external heat had been applied in the same way without the intervening convection chamber. This means of controlling heat transfer to an oven is slow to respond to changes in heat output from the combustion chamber and has not been widely used in practice.

It is an object of the present invention to provide apparatus which ensures rapid-acting thermostatic control of solid fuel combustion appliances and, in particular, the oven of such appliances.

The invention provides apparatus for controlling the transfer of heat from a combustion chamber to a given locus in a solid fuel combustion appliance in which said locus is spaced-apart from said combustion chamber, said apparatus comprising an air chamber surrounding said locus and by means of which heat is transferred from the combustion chamber to said locus, said air chamber having an inlet and an outlet, and the apparatus being provided with thermostat means to control a supply of ambient air to said air chamber, thereby controlling the supply of heat to said locus by controlling the admission of air to the air chamber.

Preferably, the given locus is an oven.

The air chamber may include a plurality of inlets for the admission of ambient air, said inlets suitably comprising a number of slots or apertures disposed in a wall of said air chamber.

Further, preferably, the thermostat means is of the type which includes a flat or shutter device for controlling the size of an opening and which is used in the present apparatus in association with either the inlet or the outlet of the air chamber and, thereby, controls the supply of air to said chamber depending on the heat of the oven.

A number of proprietary brands of thermostat may be used in the apparatus of the present invention.

One suitable type of thermostat is a bellowstype thermostat wherein one end of the bellows is connected via a system of levers to a flap or shutter device which controls the opening and closing of either the inlet or outlet of the air chamber and which is connected at its other end to a control lever having a control knob which is located externally of the apparatus, the bellows being connected by a thin capillary tube to a heat sensing capsule which may be located either within the oven or the air chamber.

Alternatively, the bellows may be substituted by a Bourdon tube.

Other suitable heat sensing means which may be employed in the thermostat include a conventional bimetallic strip.

The invention will be understood from the following description of embodiments thereof given by way of example only with reference to Figs. 2 and 3 of the accompanying drawings in which: Fig. 2 is a schematic representation of one embodiment of apparatus according to the invention; and Fig. 3 is a schematic representation of a second embodiment of apparatus according to the invention.

Referring to Fig. 2 there is illustrated apparatus, indicated generally at 10, for controlling the application of heat to an oven 11 forming part of a solid fuel combustion appliance (not shown). The apparatus 10 includes an air chamber 12 in which a convection circulation is set up when the appliance is in use. The convection chamber 12 has an inlet 13 situated at a low point 14 in said chamber 12. Opening and closing of the inlet 13 is controlled by a flap or shutter 1 5 which forms part of a conventional thermostat, indicated generally at 16, and which thermostat 1 6 is described in greater detail below. The flap or shutter 1 5 is hinged to the inlet 13 in conventional manner.

When the inlet 13 is opened, as illustrated in Fig. 2, ambient air is admitted into the chamber 1 2. Consequently there is a loss of heated air via a permanently open outlet 1 7 situated at a high point 1 8 in the chamber 12 and which outlet 17 is continuous with a duct or channel 19. Air from the air chamber 12 eventually discharges into the room in which the appliance is located. The construction of the channel 1 9 is such that it ensures an evenly distributed air flow within the chamber 12.

The thermostat 16, which is housed in a chamber 20 beneath the oven 11 and the chamber 12, consists of a bellows 21 which is connected at 22 by means of a capillary tube 23 to an ether heat sensing capsule 24 located within the oven 11. At one end 25 the bellows 21 is connected to a rod 26 which is disposed at right angles to the longitudinal axis of the bellows 21. One end of the rod 26 is connected to one end of a lever 27 which is at right angles to said rod 26 and the other end of said lever 27 is pivotally connected at 29 to a projection 28 associated with the hinged end of the flap 1 5.

The bellows 21 is connected at its other end 30 to a control lever 31 having a control knob 32 which is located externally of the chamber 20.

The control knob 32 acts as a manual regulator for the thermostat 1 6 in conventional manner.

In use, the regulator is set to the required temperature and provided the fire is producing sufficient heat, the oven 11 will reach the required temperature. As soon as the required temperature is reached, the ether in the capsule 24 expands resulting in expansion of the bellows 21 and the opening of the inlet 13, thereby admitting air to ambient temperature into the chamber 1 2 from the chamber 20. Air enters the chamber 20 through an opening in the front wall 33 thereof.

It will be appreciated that as the bellows 21 expands, the rod 26 and the lever 27 move in the drection of the arrow in Fig. 2 and the projection 28 moves in a clockwise direction causing the flap 1 5 to be pulled downwards and the inlet 13 to open.

As the temperature in the oven falls, the ether in the capsule 24 contracts resulting in contraction of the bellows 21 and shutting of the inlet 1 3 by the flap 1 5 by a reverse sequence of actions to those described in the preceding paragraphs.

Accordingly, the apparatus depicted in Fig. 2 of the drawings permits the oven temperature of a solid fuel combustion appliance to be maintained at, but not to exceed, any desired temperature normally employed in cooking. The apparatus of Fig. 2 achieves this control by admitting air at ambient temperature into the chamber 12 under the control of the thermostat 16.

In the embodiment described above only one air outlet and channel is employed. However, more than one outlet which is continuous with a respective channel may be used.

In an alternative arragement, the air outlet or outlets may discharge directly into the main flue.

Such an arrangement would accelerate air flow through the air chambers since the pressure difference of the flue rather than the buoyancy of the air within the air chamber would provide the necessary energy to promote air movement.

Furthermore, the admission of air from the air chamber directly into the main flue, more specifically the admission of air between the combustion chamber and the main flue or chimney, reduces the draught available to pull air through said combustion chamber resulting in a decrease in the rate of combustion which augments the cooling effect of the ambient air in the air chamber.

The thermostat used in the apparatus of Fig. 2 and which has an integral flap or shutter may be replaced by a thermo-statically-controlled air shutter associated with the air inlet. Whilst the location of the thermostat or the thermostaticallycontrolled air shutter is preferably located at theinlet to the air chamber, it would work equally well if located in the path of air exiting via the air outlet or outlets.

Referring to Fig. 3 of the drawings, there is illustrated apparatus, indicated generally at 40, for controlling the application of heat to an oven 41 forming part of a solid fuel combustion appliance (not shown). The apparatus 40 includes an air chamber 42 in which a convection circulation is set up when the appliance is in use.

The air chamber 42 has a pair of slots 43, 44 contiguous with walls 45, 46, respectively, of the air chamber 42 and which are formed in a plate 47 defining bottom 48 of said air chamber 42.

The slots 43, 44 ensure an even distribution in terms of temperature of incoming ambient air within the chamber 42. The ambient air enters a chamber 49 situated below the air chamber 42 through a circular inlet 50 situated in a wall 51 of said chamber 49 and passes through said slots 43, 44 into the convection chamber 42.

Admission of ambient air through the inlet 50 is controlled by a thermostat (not shown). Incoming ambient air displaces heated air within the chamber 42 which exits through an outlet 52 in a top plate 53 of the convection chamber 42 and passes into the main flue (not shown) of the appliance.

The modus operandi of the apparatus 40 under control of the thermostat is essentially similar to the modus operandiof the apparatus of Fig. 2 described above.

It will be appreciated that the apparatus according to the invention allows the temperature of an oven of a solid fuel combustion appliance to be regulated more quickly and effectively than has hitherto been possible.

The apparatus according to the invention is particularly suitable for use in the solid fuel appliances of our Patent Nos. 1 526524 and 1 588433.

Claims (12)

Claims

1. Apparatus for controlling the transfer of heat from a combustion chamber to a given locus in a solid fuel combustion appliance in which said locus is spaced apart from said combustion chamber, said apparatus comprising an air chamber surrounding said locus and by means of which heat is transferred from the combustion chamber to said locus, said air chamber having an inlet and an outlet, and the apparatus being provided with thermostat means to control a supply of ambient air to said air chamber, thereby controlling the supply of heat to said locus by controlling the admission of air to the air chamber.

2. Apparatus according to claim 1, wherein the locus is an oven.

3. Apparatus according to claim 1 or claim 2, wherein the air chamber includes a plurality of inlets for the admission of ambient air, said inlets comprising slots or apertures disposed in a wall of said air chamber.

4. Apparatus according to any one of claims 1 to 3, wherein the thermostat means includes a flap or shutter mechanism for controlling the opening of the or each inlet of the air chamber, thereby controlling the supply of ambient air to the air chamber.

5. Apparatus according to any one of claims 1 to 3, wherein the thermostat means controls the opening of an inlet in a chamber communicating with the air chamber for the admission of ambient air thereto through one or more slots or apertures in a wall of said air chamber.

6. Apparatus according to claim 4 or claim 5, wherein the thermostat is a bellows-type thermostat and wherein contraction and expansion of the bellows controls the operation of said flap or shutter.

7. Apparatus according to claim 4 or claim 5, wherien the thermostat includes a Bourdon tube which controls the operation of said flap or shutter.

8. Apparatus according to any one of claims 1 to 7, wherein the heat sensing element of the thermostat is a heat sensing capsule.

9. Apparatus according to any one of claims 1 to 7, wherein the heat sensing element of the thermostat is a conventional bimetallic strip.

10. Apparatus according to any one of the preceding claims, wherein the or each outlet of the air chamber is continuous with an integral channel or duct which contributes to an even air flow within the air chamber.

11. Apparatus according to any one of the preceding claims, wherein the or each outlet discharges directly into the main flue of the appliance.

12. Apparatus according to claim 1, substantially as hereinbefore described with reference to and as illustrated in Figs. 2 and 3 of the accompanying drawings.