EP0024376A1

EP0024376A1 - Heating apparatus

Info

Publication number: EP0024376A1
Application number: EP80302818A
Authority: EP
Inventors: Archibald Watson Kidd
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-08-17
Filing date: 1980-08-15
Publication date: 1981-03-04

Abstract

In a domestic or small commercial heating boiler the combustion air which is supplied by a fan (38) to the burner (32) is shut off by draught control means (48) when the fan (38) is not running. This prevents loss of heat while the burner is not firing. Preferably the draft control means is a gravity biassed flap (48) in the path of combustion air to the burner.

To reduce the need for cleaning, an air inlet (44) to the boiler is provided with a filter (70) to clean the air wich enters.

Description

This invention relates to oil or gas fired heating apparatus used ,to heat a fluid medium. It is applicable both to water heating boilers and to heating apparatus used to heat air for ducted warm air heating systems. The invention is particularly applicable to domestic and small commercial heating apparatus, which may have a heat output in the range 60,000 to 200,000 B.Th.U. (approx 60,000 - 200,000 kilojoules), although the invention is not necessarily restricted to this range.
Domestic and small commercial heating apparatus, particularly oil fired water heating boilers, lose a great deal of valuable heat during the time when the burner is not actually firing. Since the "off-time" tends to be a good deal more than the "on-time" the total loss of heat in a year can be alarmingly high. This heat loss is caused by the draught produced by the chimney. Once the chimney warms up it produces a suction at the outlet flue and this draws cold air into the boiler or other apparatus. Normally the air chiefly enters through the burner. Air which is drawn in while the burner is not actually firing, passes through the combustion space and the whole of the heating space and then out into the chimney taking with it a great deal of heat. In other words, the boiler or other apparatus when not in use acts like an inverted radiator dissipating heat to the environment outside the building.
This problem appears to have gone substantially unrecognised in the case of domestic or small commercial size apparatus.
It is an object of this invention to provide an economiser device which will prevent or at any rate very largely reduce this flow of cold air through the boiler when it is not actually firing. The device can be of extremely simple constructions and therefore of modest cost.
Broadly in this invention there is provided a heating apparatus for a fluid medium having a burner for the combustion of one of the fluid fuels, i.e. gas or oil, and a fan to convey combustion air to the burner, characterised by the interposition of draught control means in the path of combustion air to the burner, the draught control means being movable between an open position permitting flow of air to the burner and a closed position blocking said flow, the draught control means being arranged to open while the fan is running and to close automatically when the fan is inoperative thereby to block convective air flow through the boiler.
The fan may be incorporated within a burner unit, and such a burner unit may be a conventional unit which is already in commercial production.
It is preferred that the draught control means is biassed to its,closed position and urged open when the fan is running by the pressure of the air stream generated by the fan. The draught control means may in particular be a flap pivoted about a horizontal axis offset from its centre of gravity, the weight of the flap biassing it to a closed position, and air pressure generated by the fan, when running, urging it open. This is a particularly simple and convenient arrangement which is economical in manufacture.
It is appropriate for the boiler to have, as is conventional, a casing with an inlet for combustion air, piping for the supply of gas or oil to the burner and in the case of an oil fired boiler, a pump for the oil, a motor to drive the fan and the oil pump (if any), an outlet for flue gases, and heat exchange means exposed to the heat of combustion with an inlet and an outlet each connected to the said heat exchange means to permit a flow therethrough.
The heat exchange means may comprise a tank or pipework for the fluid medium to be heated and in a preferred arrangement the heat exchange means is a tank inside which there is a casing defining the combustion space into which the burner discharges, a plurality of tubes conveying the hot flue gases from the combustion space through the tank to the outlet for flue gases. Preferably the, combustion space is so positioned in the tank that the fluid medium to be heated surrounds the combustion space almost completely.
An embodiment of the invention will now be illustrated with reference to the accompanying drawings, in which:

Fig. 1 is a side view of a domestic water-heating boiler embodying the invention; and
Fig. 2 is a front view of the same boiler but showing a possible modification in phantom.

Referring to the drawings, the boiler has an outer casing 26 within which there is a tank 10 to contain water 12 to be heated. Inside this tank there is located a further casing 14 which provides the space 15 in which combustion takes place. The hot gases produced by the combustion pass up tubes 16 extending through the tank 10 and transfer their heat to the water 12 in the tank 10. The casing 14 is almost entirely surrounded by water in the tank 10 so that heat passing out through the casing 14 is given up to water rather than being wastefully dissipated. At one side of the boiler there are an inlet 18 to the tank 10 and an outlet 20 from it. These carry returning cold water and outflowing hot water respectively. The hot gases which pass up the tubes 16 are collected together in a manifold space 22 and leave the boiler up, the outlet 24 which is connected to a chimney. Within the tubes 16 conventional spiral metal "retarders" (not shown) may be fitted to cause swirling of the hot gases and to improve the transfer of heat to water in the tank 12.
Over the top, sides and back of the tank 10, heat insulation 28, consisting for example of glass fibre, is provided. Low down at the front there is an opening through the tank 10 into the casing 14 for purposes of cleaning. This opening is normally maintained closed by means of a closure member 30 inserted in it.
In the air space between the front of the tank 10 and the outer casing 26 there are accommodatd a burner unit 32, an oil pump 34 and a motor 36 which drives them both. These components are conventional in themselves and are shown in outline only. The burner unit 32 incorporates a fan 38 which draws air in axially at the side face 40 of the burner unit (this is the side face which is visible in Fig. 1) and blows this air into the combustion space 15 as an air stream surrounding a spray of finely divided oil droplets which it also discharges into the combustion space 15 from its nozzle 42. The burner unit 32 is provided with conventional high 1 electrodes (not shown) for ignition.
The outer casing 26 provides a reasonably airtight enclosure so that air for combustion can enter only through an inlet 44. At this inlet there is a short duct 46 through which the incoming air passes and in this duct there is a draught control flap or plate 48 pivoted around a horizontal axis -50 which is slightly offset from the centre of gravity of the flap so that the flap is partially balanced. The closed position of the flap 48, to which its weight biasses it, is upright and in this position it substantially blocks the duct 46. The flap opens by turning around its pivot 50 (in a clockwise direction as seen in Fig. 1) and this enables air to enter through the duct 46. Operation of the fan 38 in the burner unit 32, causes a suction effect so that the flap 48 is urged open against its own weight and so air can enter the casing 26 and hence pass through the burner unit 32 into the combustion space 15. However, it is arranged that the fan 38 stops while the burner is not firing so that then the.only suction to which the flap 48 is subjected is the natural convective draught through the boiler and up the chimney, this latter producing much less suction than does the fan 38. The flap 48 is sufficiently heavy to close against the convective draught when the fan 38 is not running and so flow of air through the boiler and comcomitant dissipation of heat is, in accordance with the invention, prevented while the boiler is not firing.
A screw threaded stop 52, screwed through a bracket 54 so that its position is adjustable, limits the extent to which the flap 48 can open so that when the burner unit 32 is firing the flap 48 is only allowed to open the requisite amount to admit the proper quantity of combustion air.
To ensure that the boiler works satisfactorily under varying conditions it may be found advisable to provide a draught stabilizer 56 at the chimney connection 24 of the boiler or alternatively at the base of the chimney proper. This draught stabilizer 56 may be similar in construction to the above described duct 46 and draught control flap 48 at the inlet 44, except that its flap 58 is more lightly set so as to open to allow air to pass up the chimney at a lower suction pressure than the flap 48. This makes sure that the flap 48 will always remain closed despite variations in chimney suction until such time as the fan 38 of _the burner unit 32 is operated.
Alternative constructions to the one described above are possible to control the inlet air to the burner unit 32. One possibility is shown in phantom in Fig. 2. With this modification, no draught control means would be provided at the inlet 44, but instead an inlet duct 60 is fitted to the burner unit 32 so that all air drawn in by the fan 38 must enter through this duct. Within this duct 60 a flap 62 partially balanced around pivot axis 63 in exactly analogous manner to the flap 48 is provided and it is arranged to be opened by the suction of the fan 38 but to close against- the natural convective draught when the fan is not running. A stop 64 adjustable by a screw thread is again provided to limit opening of the flap.
With the arrangement shown in phantom in Fig. 2 it is necessary that air should be able to enter the combustion space 15 only through the burner unit 32. This can be achieved by ensuring that the burner unit is a reasonably close fit in the aperture in the tank 10 through which it projects into the space 15.
Boilers tend to have their air inlet at a low level, and dust which is ingested with the combustion air collects in the burner unit (where there is generally a film of leaked oil on most surfaces). Dust collecting on the fan impairs its efficiency and hence the efficiency of combustion, and dust on the igniting electrodes can eventually prevent ignition.
In the boiler shown, the air inlet 44 to the casing 26 is placed at a high level. This is found advantageous in that a raised inlet generally leads to less dust being sucked into the burner unit with a consequent reduction in the frequency with which the burner unit 32 needs to be cleaned, and increasing the efficiency of combustion. Additionally, the inlet 44 is so provided with a simple air filter element 70 which can take the form of a piece of cloth mounted in a frame slidable in guides (not shown in detail) at the sides of the inlet 44, and readily removable for cleaning or renewal. By this simple expedient it is arranged that the combustion air remains relatively clean, also further reducing the frequency with which cleaning of the burner unit is necessary.
Modifications to the boiler shown are of course possible. Other means may be employed for biassing the draught control means to a closed position: for example in place of a gravity-biassed flap 48 or 62 a spring loaded vane could be employed. The burner unit 32 for oil firing could be replaced by a generally similar burner unit for gas. Moreover, the draught control arrangement could be applied in accordance with this invention also in a heating apparatus where the fluid medium heated was not water but was air for a ducted warmed air heating system.

Claims

1. A heating apparatus comprising a casing (26) with an inlet (44) for combustion air, a burner (32) in the casing for the combustion of gas or oil, a fan (38) within the casing to convey combustion air into the casing and to the burner, and heat exchange means (10) exposed to the heat of combustion for the heating of a fluid medium (12) characterized in that draught control means (48,62) are provided within the casing (26) in the path of combustion air to the burner (32), and movable between an open position permitting flow of air and a closed position blocking said flow, the draught control means (48,62) being arranged to be urged open by a stream of air generated by the fan while it is running, and to close automatically when the fan is inoperative, thereby blocking convective air flow through the heating apparatus.

2. Apparatus according to Claim 1 wherein said draught control means comprises a pivotally mounted flap (48,62) disposed within a duct (46,60) for combustion air, the flap (48,62) being biassed to a closed position blocking the duct, and the fan (38), when running, generating a sufficiently forceful air stream to displace the flap against the bias to a position enabling air flow through the duct.

3. Apparatus according to Claim 2 wherein the flap (48,62) is only partially balanced about its pivot axis so that it is biassed by its own weight into an upright position in which it blocks the flow of air through said duct (46,60).

4. Apparatus according to Claim 2 or Claim 3 wherein said duct (46) is contiguous with the inlet (44) to the casing.

5. Apparatus according to Claim 2 or Claim 3 wherein said duct (60) is immediately upstream of the fan (38).

6. Apparatus according to any one of Claims 2 to 5 provided with an adjustable stop (52,64) to limit opening movement of the flap.

7. Apparatus according to any one of the preceding claims wherein the heat exchange means is a tank (10) for the fluid medium (12) to be heated, the apparatus having a plurality of tubes (16) for leading hot flue gases through the tank (10) from a combustion space (15) into which the burner (32) is arranged to discharge.

8. Apparatus according to Claim 7 wherein the combustion space (15) is substantially surrounded by the fluid medium (12) to be heated.

9. Apparatus according to any one of the preceding claims wherein the air inlet (44) is provided with a filter (70) for air drawn in through it.

10. Apparatus according to any one of the preceding claims which is a water heating boiler and the said heat exchange means is a tank (10) for water (12) to be heated.