GB2100407A

GB2100407A - Space heater

Info

Publication number: GB2100407A
Application number: GB8212945A
Authority: GB
Original assignee: SCRUTTON BRIAN JOHN
Current assignee: SCRUTTON BRIAN JOHN
Priority date: 1981-05-05
Filing date: 1982-05-05
Publication date: 1982-12-22

Abstract

A space heater comprises a combustion chamber 11 and heat exchanger boxes 12 which are formed from flat metal plates and interconnected by pipes 14. Air is forced by a fan 5 over the lower surfaces of the combustion chamber 11 and then between the combustion chamber 11 and the heat exchanger boxes 12 and between the heat exchanger boxes 12 and deflecting plates 6 before emerging through outlets 7. The combustion gases travel along the combustion chamber 11 in a first direction away from a burner mounting 11a. The gases then travel in a second direction opposite to the first and then travel along the heat exchange boxes 12 in the first direction. In one embodiment the travel in the second direction is along the heat exchange boxes 12 which are divided into two portions by internal baffles 15. In another embodiment the travel in the second direction is along the combustion chamber 11. The gases exit through a flue 10. <IMAGE>

Description

SPECIFICATION Space heater This invention relates to a space heater.

The use of space heaters using a fan to pass air over the heated surface of a burner chamber is well known. A typical use of space heaters is to provide ducted hot air heating in car repair workshops and car showrooms. Such a heater would burn waste lubricating oil obtained from the work carried out in the workshop. Generally such heaters comprise a cabinet provided with an air intake, a fan, a burner chamber situated within the cabinet and an air outlet. The burner chamber is heated internally usually by means of a gas, oil or waste oil burner and the air passed through the cabinet and over the outer surface of the chamber is thus heated and is subsequently passed out of the cabinet via the air outlet.The burner chamber in such heaters is formed from metal sheet and is either in the form of a drum or a series of interconnected chambers which enable the air to be heated to come into contact with a greater surface area of the burner chamber. The provision of interconnected chambers also enables the heat from the burner flue gases to be utilised more efficiently.

An example of this type of space heater is shown in GB 1,284,450.

However such space heaters have a number of problems in use.

In the case of burner chambers involving curved surfaces deposits have been found to build up quickly and are difficult to remove. In contrast it has been found that the use of flat plates in the construction of the chambers for the combustion gases results in such deposits easily flaking off, often spontaneously, and the build up of deposits at the bottom of these chambers can be severe if waste oil is burned. It is necessary to clean out the burner chamber from time to time and prior art burner chambers whilst attempting to provide a chamber that provides an efficient transfer of heat have neglected this requirement resulting in burner chambers which are difficult to clean as access to the places where the deposits collect is restricted if not impossible.Furthermore prior art burner chambers made from flat sheet have involved a large number of bends and welds and do not combine simplicity in construction with efficient transfer of heat.

In the prior art the combustion gases are often passed through a large number of narrow tubes during heat exchange with the air being heated.

This provides a large surface area for the heat exchange, but when waste oil is burnt the narrow tubes tend to become blocked by deposits. Such a heater is shown in UK Patent Specification 929,987. Another design which allows a large surface area for heat exchange includes a series of closely-spaced plates defining narrow spaces between them Air to be heated and hot combustion gases are passed through respective alternate spaces. These narrow spaces also tend to become blocked.

A large surface area for heat exchange is not the only factor relevant to the efficiency of the heat exchange in the heater. A tortuous and long path for the combustion gases as they flow from the burner to the flue result in a long residence time in the heater for the combustion gases. This is very important for good heat exchange, since the longer the gases are in the heater the more time they have to give up their heat.

Consequently, many designs of space heater include a "double reversal" or "triple pass" path for the combustion gases. In such a design the burner fires into the combustion chamber in a first direction, in which the gases make a first pass.

Then the path makes a first reversal and runs in a direction opposite to the first, providing the second pass. A second reversal turns the path back into the first direction which provides the third pass, leading to the flue.

According to the present invention there is provided a space heater comprising a combustion box containing a combustion chamber, a burner which fires into the combustion chamber in a first direction, one or more heat-exchange boxes whose interior or interiors are connected to said combustion chamber for flow of combustion gases through the heat-exchange boxes towards a flue outlet, and means for passing air over the exterior surfaces of said combustion box and said heat-exchange box or boxes so that the air is heated, the heat-exchange box or boxes and the combustion chamber being constructed from flat sheet material and being so designed and the connection or connections between their interiors being so disposed that, in use, combustion gases travel from the burner along the combustion chamber in the said first direction, then travel in a second direction substantially opposed to the first along either (i) the combustion chamber or (ii) the heat-exchange box or boxes and then travel in the said first direction along the heat exchange box or boxes.

If the second pass is to be along the heat exchange box or boxes, the connection or connections with the combustion chamber should be at the end of the combustion chamber remote from the point where the burner fires into the chamber and the heat exchange box or boxes should each have a longitudinal baffle arranged so that the combustion gases make the second pass on one side of the baffle, pass around the end of it, and make the third pass on the other side of the baffle. If the second pass is to be along the combustion chamber, the connection or connections with the heat exchange box or boxes should be at the end of the combustion chamber from which the burner fires into the chamber.In this case no baffles are necessary because the firing of the burner into the combustion chamber propels the combustion gases along the chamber in the first direction and the gases have to make the first reversal and second pass along the combustion chamber in order to reach the connection or connections to the heat exchange box or boxes. No baffles are necessary in the heat exchange box or boxes when there is only one pass along them.

Embodiments of the present invention, given by way of examples, will now be described with reference to the accompanying drawings in which: Fig. 1 is an end view of a space heater according to a preferred embodiment of the present invention, from which an end panel and the burner unit have been removed; Fig. 2 is a plan view of the combustion box, chamber, heat-exchange boxes and flue box shown in Fig. 1; Fig. 3 is a simplified view corresponding to Fig.

1 of an alternative embodiment; Fig. 4 is a side view of the inside of the combustion chamber of the embodiment of Fig. 3; and Fig. 5 is a view corresponding to Fig. 2 of the embodiment of Fig. 3.

The space heater shown in Figs. 1 and 2 of the drawings comprises an outer casing 1 having a lower compartment 2 and an upper compartment 3. The lower compartment is provided with air inlet louvres 4 and a centrifugal fan 5 which draws air into the lower compartment and then forces the air into the upper compartment 3. The upper compartment 3 is provided with air deflector plates 6, air outlets 7 and combustion box support rails 8 which are mounted on supports 9 provided at either end of the upper compartment.

A flue 10 is provided to conduct the burner exhaust gases outside the building or space to be heated. The burner chamber 11 is freely carried on the support rails 8 and is formed from flat mild steel plate through other suitable materials (such as stainless steel) may be used. The box 11 is substantially rectangular and has a burner mounting 1 a provided at one end.Rectangular heat-exchange boxes 12 are provided mounted on but spaced from each of the uppermost faces of the burner chamber which is mounted with one of its edges pointing towards the fan outlet from the lower chamber 2 so as to provide good contact and flow of the air from the fan over the hot outer surface of the box 1 The boxes 12 are mounted on supports 1 3 so that an air flow gap is left between the header boxes and the burner chamber, the opposed walls of each box 12 and the burner chamber being substantially parallel.

Connecting pipes 14 are provided between the boxes 12 and combustion box 11 at the opposite end of the burner chamber to the burner unit mounting 11 a. The header boxes 12 may also be constructed from flat mild steel plate or other suitable material. A conventional burner (which may be suitable for burning gas, fuel oil, waste oil or mixtures of fuel oil and waste oil) is mounted on the burner mounting, but is not shown in the drawing.

The rectangular shape of the box 11 and the boxes 1 2 has the advantage that their construction is both considerably cheaper and easier than that of prior art burner boxes which involve the use of curved surfaces or complicated shapes involving a variety of bends and welds.

The box 11 and heat exchange boxes 12 are mounted in the upper compartment 3 in such a way that the deflector plates 6 are situated parallel to the outer face of each header box with an air flow gap between them. Air from the fan 5 is thus forced over the combustion chambers lower surfaces and then passes between the boxes 12 and the chamber 11 or between the deflector plates 6 and the boxes 12 before leaving the upper compartment via outlets 7.

In order to increase the efficiency of the heatexchanger boxes they are provided with internal longitudinal baffles 1 5. The flue gases from the burner must thus pass from the far end of the combustion box 11 from the burner via the connecting pipes 14 into the boxes 12 then along the boxes 12 first towards the burner and then back towards the flue 10 to which both boxes 12 are connected by a flue box 1 6. The burner chamber and header boxes thus form a three pass system. In order to facilitate cleaning of the header boxes, cleaning ports 17 fitted with removable inspection covers are provided at the ends of the boxes 12 remote from the burner and at the end of the box 11 remote from the burner.

Cleaning is thus not impeded by the baffles 15.

Figures 3, 4 and 5 show an alternative embodiment in which the combustion gases make two passes in the combustion chamber 11 and only one in the heat exchange boxes 12. In this embodiment the connecting pipes 14 are at the same end of the combustion chamber 11 as the burner mounting 1 a (see Fig. 4) and the heat exchange boxes 12 have no baffles (see Fig. 5).

Because the burner fires into the combustion chamber 11 with considerable force the combustion gases travel right across it in the direction from left to right in Figure 4. However, the only exits from the combustion chamber 11 are the pipes 14, which are at the same end of the chamber 11 as the burner mounting 11 a.

Consequently the combustion gases follow the path shown by the arrows in Figure 4.

On entering the heat exchange boxes 12 the combustion gases pass along it once and leave to enter the flue 10, following the path shown by the arrows in Figure 5.

Both embodiments are simple and economical to construct, are efficient at heating air passed through them, and avoid the use of long narrow passages or ducts for the combustion gases. The path followed by the combustion gases has a greatly reduced tendency to block, and is relatively easy to clean.

Claims

1. A space heater comprising a combustion box containing a combustion chamber, a burner which fires into the combustion chamber in a first direction, one or more heat-exchange boxes whose interior or interiors are connected to said combustion chamber for flow of combustion gases through the heat-exchange boxes towards a flue outlet, and means for passing air over the exterior surfaces of said combustion box and said heat-exchange box or boxes so that the air is heated, the heat-exchange box or boxes and the combustion chamber being constructed from flat sheet material and being so designed and the connection or connections between their interiors being so disposed that, in use, combustion gases travel from the burner along the combustion chamber in the said first direction, then travel in a second direction substantially opposed to the first along either (i) the combustion chamber or (ii) the heat-exchange box or boxes and then travel in the said first direction along the heat exchange box or boxes.

2. A space heater according to claim 1 in which the said travel of the combustion gases in the second direction is along the heat exchange box or boxes and in which the heat exchange box or boxes each contain a longitudinal baffle so arranged that, in use, the combustion gases travel along the heat exchange box or boxes in the second direction on one side of the baffle and then travel along the heat exchange box or boxes in the first direction along the other side of the baffle.

3. A space heater according to claim 1 or claim 2 wherein said heat-exchanger box or boxes are located on the downstream side of the combustion box with respect to the air flow past the combustion box, and have a surface opposed to and spaced from a surface of the combustion box so as to provide a passage between them for flow of the air being heated.

4. A space heater according to claim 3 wherein said adjacent heat-exchange box and combustion box surfaces are substantially parallel.

5. A space heater according to claim 3 or claim 4 having two of said heat-exchange boxes and wherein said adjacent heat-exchange box surfaces slope inwardly towards each other in the direction of said airflow.

6. A space heater according to any one of the preceding claims wherein said combustion box and the or each heat-exchange box are substantially rectangular as seen in cross-section perpendicular to said first direction.

7. A space heater according to any one of the preceding claims wherein the or each heatexchange box is provided with one or more removable inspection covers at one longitudinal end thereof.

8. A space heater according to any one of the preceding claims wherein the combustion box has the burner at one end and a removable inspection cover at the opposite end.

9. A space heater according to any one of claims 1 to 8 wherein said combustion box is freely supported on rails allowing longitudinal thermal expansion of the box.

10. A space heater substantially as described herein with reference to and as shown in Figures 1 and 2 or Figures 3 to 5 of the accompanying drawings.