NL2011063C2

NL2011063C2 - Air heater.

Info

Publication number: NL2011063C2
Application number: NL2011063A
Authority: NL
Inventors: Arend Ferdinandus Vries
Original assignee: Thermobile Ind B V
Priority date: 2013-06-28
Filing date: 2013-06-28
Publication date: 2015-01-05
Also published as: WO2014209111A1; EP3014193B1; EP3014193A1

Abstract

The invention pertains to an air heater, which air heater comprises: -a combustion chamber, -a burner, -a sleeve-shaped heat exchanger, wherein the sleeve-shaped heat exchanger is arranged coaxially with the combustion chamber, -a first annular air passage for heated air, which extends between the combustion chamber and inner wall of the sleeve-shaped heat exchanger, -a housing, in which the heating unit is arranged, in which housing a second air passage for heated air is present between the housing and the sleeve-shaped heat exchanger, -a fan for drawing air into the housing -an air distribution chamber for providing air to the first annular air passage and the second air passage, wherein the front wall of the sleeve-shaped heat exchanger has a frusto-conical shape that converges in the direction away from the fan.

Description

P31671NL00/NBL Air heater

The invention pertains to an air heater. Air heaters of the type to which the invention pertains are suitable for heating a space, for example a room in a building, a storage space, a stable, or a greenhouse.

Air heaters that comprise a combustion chamber for burning fuel are known. It is also known to use hot flue gas that is produced by such burning of fuel to heat air, in particular by means of a heat exchanger that has the hot flue gas on the warm side and the air to be heated on the cool side. Such heated air can be used to heat a space.

It is an object of the invention to provide an air heater that is energy efficient.

This object is achieved with the air heater of claim 1.

The air heater according to the invention comprises a heating unit. In this heating unit, a tubular combustion chamber with a burner is present. The tubular combustion chamber optionally has a cylindrical shape, for example with a circular cross section. Alternatively, other shapes of the combustion chamber are possible, for example a cylindrical shape with a square or hexagonal cross section.

The burner is provided with a fuel inlet that allows fuel to be supplied to the burner. The fuel can be any suitable combustion fuel, preferably in liquid or gaseous form. Examples of suitable fuels are propane gas, natural gas, butane gas, oil, waste oil, rapeseed oil, kerosene, paraffin oil, diesel, gasoline.

Preferably, the fuel inlet of the burner is connected to a fuel reservoir, for example a gas tank or oil tank, so that a continuous flow of fuel can be supplied to the burner. Optionally, the flow rate of the fuel to the burner can be controlled, for example by a control valve and/or by an active or passive flow regulator. Such a control valve or flow regulator is not necessary.

The combustion chamber is provided with a combustion air inlet for providing oxygen to the burning process. The combustion air inlet can be provided in a wall of the combustion chamber and/or in the burner. Furthermore, the combustion chamber has a flue gas outlet for discharging the flue gas that is produced by the process of burning fuel from the combustion chamber.

The burning process of the fuel generates heat, which heat heats the walls of the combustion chamber.

The heating unit of the air heater according to the invention further comprises a sleeveshaped heat exchanger, that is arranged coaxially with the combustion chamber. The combustion chamber and the sleeve-shaped heat exchanger are radially spaced apart, which makes that an annular space is present between the combustion chamber and the sleeveshaped heat exchanger.

The sleeve-shaped heat exchanger has an inner wall, an outer wall and a front wall and preferably also a rear wall. In case no rear wall is present, the inner wall and outer wall are directly connected to each other at side opposite of the front wall.

The sleeve-shaped heat exchanger has a flue gas inlet and a flue gas outlet. The flue gas inlet of the sleeve-shaped heat exchanger receives flue gas for the flue gas outlet of the combustion chamber. To that end, the flue gas outlet of the combustion chamber is in fluid communication with the flue gas inlet of the sleeve-shaped heat exchanger. This fluid communication can for example be provided by providing a tube or pipe that extends from the flue gas outlet of the combustion chamber to the flue gas inlet of the sleeve-shaped heat exchanger. Via the flue gas inlet, the flue gas is introduced into the sleeve-shaped heat exchanger.

The flue gas flows through the heat exchanger from the flue gas inlet to the flue gas outlet of the sleeve-shaped heat exchanger. While the flue gas flows through the sleeveshaped heat exchanger, the flue gas heats at least the inner wall and the outer wall of the sleeve-shaped heat exchanger. Optionally, also the front wall and/or the rear wall of the sleeve-shaped heat exchanger is heated by the flue gas. When the front wall and preferably also the rear wall of the sleeve-shaped heat exchanger are heated by the flue gas, this increases the efficiency of the air heater.

The most straightforward way to make that the flue gas heats the inner wall, the outer wall and optionally also the front wall and/or the rear wall of the sleeve-shaped heat exchanger is making that the flue gas is in contact with these walls while it flows through the sleeve-shaped heat exchanger. Alternatively, it is for example possible that the flue gas flows through a tube of thermally conductive material, thereby heating the tube. This tube is in thermal contact with for example the inner wall, outer wall and/or front wall of the sleeveshaped heat exchanger, and in turn heats the wall of the sleeve-shaped heat exchanger with which it is in contact.

Preferably, the sleeve-shaped heat exchanger comprises a flue gas chamber that is arranged between the flue gas inlet and the flue gas outlet. So, the flue gas passes through the flue gas chamber as is flows through the sleeve-shaped heat exchanger from the flue gas inlet of the sleeve-shaped heat exchanger to the flue gas outlet thereof. Optionally, a plurality of flue gas chambers is present, being arranged either in series with each other or parallel to each other.

Preferably, the flue gas chamber or at least one of the flue gas chambers is at least partly delimited by the front wall, the inner wall and/or the outer wall of the sleeve-shaped heat exchanger.

Optionally, the sleeve-shaped heat exchanger comprises a flue gas flow path that extends between the flue gas inlet and the flue gas outlet. Such a flue gas flow path can for example be defined by flow direction elements which are arranged inside the flue gas chamber. Such flow direction elements can for example be partition walls with one or more flow through openings therein, which partition walls are arranged in the flue gas chamber of the sleeve-shaped heat exchanger. The flow direction elements force the flue gas to follow a particular route through the sleeve-shaped heat exchanger. A gas flow path can for example have a serpentine shape.

The heating unit of the air heater according to the invention further comprises a first annular air passage for heated air. This first annular air passed is formed by the space that is present between the circumferential wall of the combustion chamber and the inner wall of the sleeve-shaped heat exchanger. Air flowing through the first annular air passage is heated by the circumferential wall of the combustion chamber and the inner wall of the sleeve-shaped heat exchanger.

The air heater according to the invention further comprises a housing. The heating unit as described above is arranged inside this housing. The housing comprises a circumferential wall, which extends around the heating unit at a distance in radial direction from the heating unit. Due to this distance, a second air passage is present between the circumferential wall of the housing and the outer wall of the sleeve-shaped heat exchanger. Optionally, this second air passage has an annular shape.

The housing further comprises a heated air outlet for discharging heated air from the housing. This “heated air outlet” is an outlet for heated air; the outlet is not heated itself by any dedicated heating means. The heated air outlet is in fluid communication with the first annular air passage and the second air passage. Air flowing through the first annular air passage and air flowing through the second air passage will be discharged from the housing via the heated air outlet.

The housing further comprises a combined air inlet. Through this combined air inlet, air is introduced into the housing from the environment of the air heater, for example from the space in which the air heater is arranged. Air that enters the housing via the combined air inlet can be heated in the first annular air passage or in the second annular air passage and will be discharged again from the housing as heated air. Optionally, some of the air that enters the housing via the combined air inlet is used as combustion air, and introduced into the combustion chamber via the combustion air inlet.

Optionally, multiple combined air inlets are present.

The air heater according to the invention is further provided with a fan for drawing air into the housing through the combined air inlet. The fan is arranged inside the housing. It can be driven by any suitable driver, for example an electromotor.

The air heater according to the invention is further provided with an air distribution chamber. The air distribution chamber is located inside the housing, downstream of the fan and upstream of the heating unit (“downstream” and “upstream” as seen in the direction of the air flow from the combined air inlet to the heated air outlet of the housing). The air distribution chamber is in fluid communication with first annular air passage and the second air passage.

The air distribution chamber receives air that has been drawn into the housing by the fan and provides this air to the first annular air passage and the second air passage.

As air flows from the air distribution chamber to the heated air outlet of the housing via the first annular air passage, this air is heated by the circumferential wall of the combustion chamber and by the inner wall of the sleeve-shaped heat exchanger. The air that flows from the air distribution chamber to the heated air outlet of the housing via the second air passage is heated by the outer wall of the sleeve-shaped heat exchanger.

Optionally, the air flow from the first annular air passage is combined with the air flow from the second air passage before the air flows leave the housing via the heated air outlet.

Optionally, the housing comprises multiple heated air outlets. In that case, it is possible that the air flow from the first annular air passage is not combined with the air flow from the second air passage before the air flows leave the housing. In such an embodiment, the first annular air passage is connected to one or more dedicated heated air outlets and the second air passage is connected to one or more different dedicated heated air outlets.

In the air heater according to the invention, the front wall of the sleeve-shaped has a frusto-conical shape that converges in the direction away from the fan. The frusto-conical shape makes that a larger portion of the air from the air distribution chamber passes through the first annular air passage instead of through the second air passage, in comparison with a design where the front wall of the sleeve-shaped heat exchanger is at a right angle to the inner wall and outer wall of the sleeve-shaped heat exchanger. As the air in the first annular air passage is heated by both the circumferential wall of the combustion chamber and the inner wall of the sleeve-shaped heat exchanger, the air in the first annular air passage is heated more effectively that the air in the second air passage, where it is only heated on one side, by the outer wall of the sleeve-shaped heat exchanger.

Furthermore, the frusto-conical shape of the front wall of the sleeve-shaped heat exchanger provides a smooth flow path for the air to the first annular air passage. This makes that the flow resistance for the flow path via the first annular air passage to the heated air outlet is relatively low. This also causes a larger portion of the air from the air distribution chamber to pass through the first annular air passage instead of through the second air passage as compared with a design where the front wall of the sleeve-shaped heat exchanger is at a right angle to the inner wall and outer wall of the sleeve-shaped heat exchanger.

In addition, due to the lower flow resistance, the fan consumes less power for making the air flow through the housing of the air heater according to the invention as compared to a design where the front wall of the sleeve-shaped heat exchanger is at a right angle to the inner wall and outer wall of the sleeve-shaped heat exchanger.

The frusto-conical shape of the front wall of the sleeve-shaped heat exchanger makes that less power is consumed by the fan and that a larger portion of the air passes through the air passage that provides the most effective heating of the air flowing through it. Both effects contribute to the air heater being energy efficient.

Energy efficiency can be defined as the ratio between the total energy input and the energy output of the heated air that leaves the heated air outlet of the housing. A further advantage of the air heater according to the invention is that it is easy and cheap to manufacture. No special or dedicated tools are necessary in the production process. Known air heaters often require the use of specially designed tools to provide components that are to be welded with the proper shape for welding seam, but such tools are not necessary for producing the air heater according to the invention.

In a possible embodiment, the air heater according to the invention comprises one or more third air passages, which extend between the air distribution chamber and the heated air outlet. These third air passages can be formed as tubes or pipes that extend at least partially through the sleeve-shaped heat exchanger, in particular through the flue gas chamber thereof. The flue gas in the sleeve-shaped heat exchanger heats the walls of the tube or pipe that forms the third air passage, which walls in turn heat the air flowing through the third air passage. Optionally, these third air passages extend between the front wall and the rear wall of the sleeve-shaped heat exchanger. This way, the surface area that is active in the heat transfer in the air heater is increased.

Optionally, flow directing elements are provided in the first annular air passage and/or in the second air passage in order to force the flow of air to follow a particular flow path. However, care should be taken to introduce as little increase in flow resistance for the air flow as possible.

In general, it is advantageous to design the air heater in such a way that the flow resistance of the air passing through the first annular air passage is low enough to obtain a significant flow of air through the first annular air passage.

From that point of view, in a design where the front wall of the sleeve-shaped heat exchanger has an outer rim and an inner rim and the outer rim has a larger diameter than the inner rim, and in which the combustion chamber has a front wall that faces the air distribution chamber, it can be advantageous if the front wall of the combustion chamber is arranged downstream of the outer rim of the front wall of the sleeve-shaped heat exchanger (“downstream” as seen in the direction of the air flow from the combined air inlet to the heated air outlet of the housing). This allows a smooth flow of the air into the first annular air passage. Optionally, the front wall of the combustion chamber is even arranged downstream of the inner rim of the front wall of the sleeve-shaped heat exchanger

The invention will be described in more detail below under reference to the drawing, in which in a non-limiting manner exemplary embodiments of the invention will be shown.

The drawing shows in:

Fig. 1 : a schematic representation of an embodiment of an air heater according to the invention, in cross section,

Fig. 2 : a schematic representation of a flue gas chamber with flow direction elements,

Fig. 3: a front view of the heating unit,

Fig. 4: a front view of the heating unit arranged in the housing,

Fig. 5: an air heater according to the invention mounted on a trolley.

Fig. 1 shows an embodiment of an air heater according to the invention, in cross section.

The air heater according to the invention comprises a heating unit 1, a housing 2, a fan 3 and an air distribution chamber 4.

The heating unit 1 comprises a tubular combustion chamber 10. The combustion chamber 10 has a longitudinal axis 11, a circumferential wall 12, a front wall 13 and a rear wall 14.

The combustion chamber 10 is provided with a burner 16. This burner burns fuel that is supplied to it via the fuel inlet 17. In the embodiment shown in fig. 1, the fuel inlet is connected to a fuel reservoir 18 via fuel line 19. A flow regulator 20 or a control valve can provided in fuel line 19 so that the flow rate of the fuel from the fuel reservoir 18 to the burner 16 can be controlled, but the presence of such a flow regulator or control valve is not necessary.

The combustion chamber 10 is provided with a combustion air inlet 15. In the example of fig. 1, the combustion air inlet 15 is located in the burner, but alternatively it can be provided in the front wall 13 of the combustion chamber 10, or in the circumferential wall 12 or even the rear wall 14.

Optionally, the combustion air inlet 15 is connected to one or more combustion air inlet tubes (which are not shown in the figure for reasons of clarity, but can be seen in fig. 4) which extend into the air distribution chamber 4, optionally to a location in the air distribution chamber 4 close to the housing 2, for guiding air from the air distribution chamber 4 into the combustion chamber 10.

The burning of the fuel by burner 16 causes generates heat. This results in a heating of the circumferential wall 12, the front wall 13 and the rear wall 14 of the combustion chamber. The burning of the fuel by burner 16 also generates flue gas, which is generally quite hot.

The flue gas is discharged from the combustion chamber 10 via flue gas outlet 21.

In operation, two separate flows pass through the air heater: the flue gas flow and the (heated) air flow. These are separate flows, they do not mix inside the air heater according to the invention.

The heating unit 1 further comprises a sleeve-shaped heat exchanger 30. The sleeveshaped heat exchanger 30 has a longitudinal axis 35, a front wall 31, an inner wall 32, an outer wall 33 and a rear wall 34. In the embodiment of fig. 1, the front wall 31, inner wall 32, outer wall 33 and rear wall 34 together define a flue gas chamber 39. In the embodiment of fig. 1, the flue gas chamber 39 has a generally annular shape.

The sleeve-shaped heat exchanger 30 is arranged coaxially with the combustion chamber 10. The diameter of the circumferential wall 12 of the combustion chamber 10 is smaller than the diameter of the inner wall 32 of the sleeve-shaped heat exchanger 30. So, an annular space 40 is present between the combustion chamber 10 and the sleeve-shaped heat exchanger 30.

The front wall 31 of the sleeve-shaped heat exchanger 30 has a frusto-conical shape, which converges in the direction towards the combustion chamber and away from the air distribution chamber 4 and the fan 3. The front wall 31 of the sleeve-shaped heat exchanger 30 has an outer rim 41 and an inner rim 42. In the embodiment of fig. 1, the flue gas chamber 39 extends to the outer rim 41 of the front wall 31.

When the flue gas is discharged from the combustion chamber 10 via the flue gas outlet 21 of the combustion chamber, it is transferred via tube 22 to flue gas inlet 36 of the sleeveshaped heat exchanger 30. From the flue gas inlet 36 of the sleeve-shaped heat exchanger 30, the hot flue gas enters the flue gas chamber 39 of the sleeve-shaped heat exchanger 30.

The flue gas flows through the flue gas chamber 39 of the sleeve-shaped heat exchanger 30 to the flue gas outlet 37 of the sleeve-shaped heat exchanger 30, where it is discharged via tube 38. Preferably, the tube 38 is connected to a chimney or other type of vent located outside of the space to be heated. This avoids the presence of undesired contaminants in the space in which the air is heated.

While the flue gas flows through the sleeve-shaped heat exchanger 30, the flue gas is in contact with the front wall 31, inner wall 32 and outer wall 33 of the sleeve-shaped heat exchanger 30. This results in a heating of these walls 31,32, 33 of the sleeve-shaped heat exchanger 30.

Optionally, in flow direction elements 43 such as partition walls are present in the flue gas chamber 39. These flow partition elements 43 are not shown in fig. 1 for reasons of clarity, but they are shown schematically in fig. 2. The flow direction elements 43 guide the flue gas through the sleeve-shaped heat exchanger 30 along a desired flow path, for example a serpentine shaped flow path as indicated by the arrows 44 in fig. 2. The flow direction elements can help to obtain a uniform heating of the front wall 31, inner wall 32 and outer wall 33 of the sleeve-shaped heat exchanger 30.

The other flow through the air heater according to the invention is the flow of air, which air is heated during its passage through the air heater.

The housing 2 comprises a combined air inlet 50 at the upstream end of the air heater (“upstream” as seen in the direction of the flow of (heated) air through the air heater) and a heated air outlet 43 at the downstream end of the air heater (“downstream” as seen in the direction of the flow of (heated) air through the air heater).

Fan 3, which is arranged in housing 2 downstream of the combined air inlet 50 draws air from the environment of the air heater into the housing 2. Fan 3 is driven by driver 54.

The air that is drawn in by the fan 3 arrives in the air distribution chamber 4. As can be seen in fig. 1, the front wall 31 of the sleeve-shaped heat exchanger 30 delimits the air distribution chamber 4 on the downstream side.

From the air distribution chamber 4, the air flows either into first annular air passage 51, second air passage 52 or combustion air inlet 15. Air that flows into the combustion air inlet 15 is used for burning the fuel in the combustion chamber 10.

Air that flows into the first annular air passage 51 is heated by the circumferential wall 12 of the combustion chamber and the inner wall 32 of the sleeve-shaped heat exchanger 30 while the air flows through this first annular air passage 51. After that, it is discharged as heated air through heated air outlet 53.

Air that flows into the second air passage 52 is heated by the outer wall 33 of the sleeve-shaped heat exchanger 30 while the air flows through this second air passage 52. After that, it is discharged as heated air through heated air outlet 53.

In the embodiment of fig. 1, a third air passage 57 is present, which extends between the air distribution chamber and the heated air outlet. This third air passage 57 can be formed as a tube or a pipe that extends at least partially through the flue gas chamber 39 of the sleeve-shaped heat exchanger 30.

As can be seen in fig. 1, the front wall 31 of the sleeve-shaped 30 has a frusto-conical shape that converges in the direction away from the fan 3. The frusto-conical shape makes that a larger portion of the air from the air distribution chamber 4 passes through the first annular air passage 51 instead of through the second air passage 52, in comparison with a design where the front wall of the sleeve-shaped heat exchanger is at a right angle to the inner wall and outer wall of the sleeve-shaped heat exchanger.

As the air in the first annular air passage 51 is heated by both the circumferential wall 12 of the combustion chamber 10 and the inner wall 32 of the sleeve-shaped heat exchanger 30, the air in the first annular air passage 51 is heated more effectively that the air in the second air passage 52. In the second air passage 52, the air is only heated from one side, by the outer wall 33 of the sleeve-shaped heat exchanger 30.

Furthermore, the frusto-conical shape of the front wall 31 of the sleeve-shaped heat exchanger 30 provides a smooth flow path for the air to the first annular air passage 51. This makes that the flow resistance for the flow path via the first annular air passage 51 to the heated air outlet 53 is relatively low. This also causes a larger portion of the air from the air distribution chamber 4 to pass through the first annular air passage 51 instead of through the second air passage 52 as compared with a design where the front wall of the sleeve-shaped heat exchanger is at a right angle to the inner wall and outer wall of the sleeve-shaped heat exchanger.

Fig. 2 shows a schematic representation of a flue gas chamber 39. In the flue gas chamber 39, flow direction elements 43 are arranged. These flow direction elements 43 guide the flow of flue gas along a desired path, e.g. a path with a serpentine shape.

The shape of the desired flow path is preferably chosen such that a desired distribution of heat of the inner wall 32, outer wall 33 and/or front wall 31 of the sleeve-shaped heat exchanger 30 is obtained, for example a uniform heat distribution or a heat distribution with a desired gradient.

Fig. 3 shows a front view of the heating unit 1. It shows the sleeve-shaped heat exchanger 30, and in particular the frusto-conical front wall 31 of the sleeve-shaped heat exchanger 30. Also, the combustion chamber 10 and the first annular air passage 51 are shown. Supports 55 make sure that the relative position of the combustion chamber 10 and the sleeve-shaped heat exchanger 30 are maintained, while obstructing the air flow through the first annular air chamber as little as possible.

Fig. 4 shows a front view of the heating unit 1 arranged in the housing 2. In order to obtain this view, the housing 2 at the location of the air distribution chamber 4 has been removed. Fig. 4 shows the sleeve-shaped heat exchanger 30, and in particular the frusto-conical front wall 31 of the sleeve-shaped heat exchanger 30. Also, the combustion chamber 10 and the first annular air passage 51, as well as the second air passage 52 between the outer wall 33 of the sleeve-shaped heat exchanger 30 and the housing 2 are shown. In the lower front of fig. 4, a part of the drive 54 for the fan is visible.

Fig. 4 further shows combustion air inlet tubes 56 that guide air from the air distribution chamber to the combustion air inlet 15 of the combustion chamber.

Fig. 5 shows an air heater according to the invention mounted on a trolley 70. As air heaters of the type according to the invention are often used temporarily and at different locations, they are optionally mounted on a trolley or other structure that makes them easy to move from one place to the other.

In this example, the trolley comprises wheels 71 and a pushbar 72. A fuel reservoir 17 is integrated into the trolley and an electrical switchbox 60 for the control of the air heater is mounted onto the trolley 70 as well.

The housing 2 in the vicinity of the air distribution chamber 4 has been removed to show the location of the heating unit inside the housing 2. In use, of course, the housing 2 extends over the air distribution chamber 4 as well.

Claims

An air heater, which air heater comprises: a heating unit, which heating unit comprises: - a tubular combustion chamber, which combustion chamber has a circumferential wall and is provided with an air inlet for combustion air and a flue gas outlet, which combustion chamber is further provided with a burner for burning fuel in a heating chamber and thereby producing flue gas, which burner has a fuel inlet, - a sleeve-shaped heat exchanger, the sleeve-shaped heat exchanger being arranged coaxially with the combustion chamber, which sleeve-shaped heat exchanger comprises a flue gas inlet and a flue gas outlet, which flue gas inlet is connected to the flue gas outlet of the combustion chamber for receiving flue gas from the combustion chamber and introducing the flue gas into the sleeve-shaped heat exchanger, which sleeve-shaped heat exchanger has an inner wall, an outer wall and a front wall with at least the inner The wall and the outer wall are adapted to be heated by the flue gas, - a first annular air passage for heated air, which extends between the peripheral wall of the combustion chamber and the inner wall of the sleeve-shaped heat exchanger, - a housing in which the heating unit is provided, which housing comprises a peripheral wall, a combined air inlet for introducing air into the housing and a heated air outlet for discharging heated air from the housing, which heated air outlet is in fluid communication with the first annular air passage, in which housing a second air passage is present between the peripheral wall of the housing and the outer wall of the sleeve-shaped heat exchanger, which second air passage is in fluid communication with the heated air outlet of the housing, a fan for inward drawing air into the housing through the combined air inlet, which fan is arranged in the housing, an air distribution chamber for receiving air drawn into the housing by the fan and for supplying this air to the first annular air passage and the second air passage, which air distribution chamber is present in the housing downstream of the fan and upstream of the heating unit, which air distribution chamber is in fluid communication with the first annular air passage and the second air passage, the front wall of the sleeve-shaped heat exchanger having the shape of a truncated cone converging in the direction away from the fan.

An air heater according to any one of the preceding claims, wherein the front wall of the sleeve-shaped heat exchanger is adapted to be heated by the flue gas.

An air heater according to any one of the preceding claims, wherein the front wall of the sleeve-shaped heat exchanger partially defines the air distribution chamber.

Air heater according to any of the preceding claims, wherein the front wall of the sleeve-shaped heat exchanger has an outer edge and an inner edge, the outer edge having a larger diameter than the inner edge, and wherein the combustion chamber has a front wall that faces is to the air distribution chamber, the front wall of the combustion chamber being arranged downstream of the outer edge of the front wall of the sleeve-shaped heat exchanger.

An air heater according to claim 4, wherein the front wall of the combustion chamber is arranged downstream of the inner edge of the front wall of the sleeve-shaped heat exchanger.

6. An air heater according to any one of the preceding claims, wherein the sleeve-shaped heat exchanger comprises a flue gas chamber arranged between the flue gas inlet and the flue gas outlet, which flue gas chamber is at least partially bounded by the front wall, the inner wall, and / or the outer wall of the sleeve-shaped heat exchanger, optionally through the front wall, the inner wall, the outer wall and / or rear wall of the sleeve-shaped heat exchanger.

The air heater according to claim 6, wherein the flue gas chamber has an annular shape.

An air heater according to claim 6 or 7, wherein the sleeve-shaped heat exchanger comprises a flue gas path extending between the flue gas inlet and the flue gas outlet, which flue gas path is defined by flow direction elements arranged in the flue gas chamber.

The air heater of claim 8, wherein the flue gas path has a twisted shape.

An air heater according to any one of the preceding claims, wherein the combustion chamber is cylindrical, preferably cylindrical with a circular cross section.

An air heater according to any one of the preceding claims, wherein the air distribution chamber is in fluid communication with the combustion air inlet of the combustion chamber.

The air heater according to any of the preceding claims, wherein the air heater further comprises a third air passage extending between the air distribution chamber and the heated air outlet, which view optionally extends at least partially through the sleeve-shaped heat exchanger.

A method of heating a room in which an air heater is used according to any of the preceding claims, which method comprises the following steps: - supplying fuel and air to the burner of the combustion chamber, burning fuel in the combustion chamber, thereby heating the peripheral wall of the combustion chamber and producing flue gas, - removing the flue gas from the combustion chamber via the flue gas outlet of the combustion chamber and introducing the flue gas into the sleeve-shaped heat exchanger via the flue gas inlet of the heat exchanger, the flue gas from the flue gas inlet of the sleeve-shaped heat exchanger to the flue gas outlet of the sleeve-shaped heat exchanger, thereby heating at least the inner wall and the outer wall of the sleeve-shaped heat exchanger, introducing air into the housing via the combined air inlet of the housing through the Let it turn of the fan, introducing this air into the air distribution chamber, generating a first air flow from the air distribution chamber to the heated air outlet of the housing via the first annular air passage, in which first annular air passage the first air flow is heated by the circumferential wall of the combustion chamber and through the inner wall of the sleeve-shaped heat exchanger, generating a second air flow from the air distribution chamber to the heated air outlet of the housing via the second air passage, in which second air passage the second air flow is heated by the outer wall of the sleeve-shaped heat exchanger, - delivering the thus heated first air stream and the thus heated second air stream from the housing via the heated air outlet of the housing.

The method of claim 13, wherein the front wall of the sleeve-shaped heat exchanger is heated by the flue gas.

The method of claim 14, wherein the air in the air distribution chamber and / or the first annular air passage is heated by the front wall of the sleeve-shaped heat exchanger.

An air heating system, comprising: - a cart with at least one wheel, - an air heater according to any of claims 1-12, wherein the air heater is mounted on the cart.

The system of claim 16, wherein the system further comprises a fuel reservoir and / or a switch cabinet, which fuel reservoir and / or switch cabinet are preferably mounted on or integrated into the cart.