Device for using the waste heat of flue gas pipes

Abstract

The invention relates to a device for utilizing the waste heat from flue gas pipes of solid fuel-fired appliances, wherein the device comprises an air heat exchanger with a cold air inlet and a warm air outlet, as well as at least one thermally conductive inner component that is at least partially connected to the outer casing of the flue pipe (1) by a metallic thermal conductor. According to the invention, the air heat exchanger consists of a double-walled, fully enclosed hollow body (2), the inner casing (4) of which, in the assembled state, rests against the outer casing of the flue gas pipe (1), and whose warm air outlet is connected to an air duct of a warm air heating system. This has the advantage that the device can be attached to conventional flue gas pipes without the assistance of an installer and without significant effort, and the room air heated within it can be fed directly into a duct or distribution system of a warm air heating system. This cools the flue gas, i.e., reduces its heat output.i.e., the heating energy of the fuel used in the fireplace is better utilized and the heat energy gained is used to heat other rooms.

Description

State of the art

[0001] The invention relates to a device for utilising the waste heat from flue gas pipes of fireplaces heated with solid fuels, for example stoves and fireplaces according to the preamble of claim 1.

[0002] Devices for utilizing waste heat from flue gas pipes of solid fuel-fired fireplaces are available in a wide variety of designs and for a variety of applications. Such devices are typically heat exchangers located in or on the flue pipe of stoves or fireplaces to recover heat from the flue gases. In order to comply with legal fire protection requirements and the Combustion Ordinance, these heat exchangers are generally not allowed to interfere with the flue system of the fireplaces, so that with such devices, the waste heat can be transferred solely via a metallic, heat-conducting connection between the outer wall of the flue pipe and the heat transfer system.It is also advantageous if such devices can be easily retrofitted by non-specialists to the exhaust system, for example the stove pipe of a stove or fireplace fired with solid fuels.

[0003] One well-known use of waste heat from wood-burning stoves is to operate a warm-air heating system. This is advantageous in two ways. Firstly, heat is extracted from a room that is usually overheated by a wood-burning stove, thus preventing overheating of that room. At the same time, this heat is fed into the warm-air heating system via a pressure or suction device connected to the heat exchanger to heat one or more additional rooms.

[0004] For example, a device for the indirect exchange of heat between a stovepipe and the surrounding air is known. The stovepipe is surrounded by strand-shaped profile ribs made of a thermally conductive material arranged radially around it. The outer narrow sides of these profile ribs are attached to at least one clamp, for example, a quick-release fastener, at a distance from each other, while their inner, free narrow sides are in frictional contact with the outer wall of the stovepipe (EP 0 083 379 A1).

[0005] A heat exchanger for stoves is also known to improve their heating performance, which consists of two half-circuits that engage around the stove pipe and are attached to it by clamping means, to which in turn several vertical fins arranged at a distance from one another are attached, between which the room air flows through due to its own buoyancy or is possibly guided through with the help of a fan (DE 20 2006 014 424 U1).

[0006] A device for utilizing the waste heat from fireplace stove exhaust pipes is also known. It consists of a cylindrical body that is open at the top and bottom and is formed by a plurality of interconnected plate segments and is designed in two parts in the form of two half-shells. Angled sheet metal supports are arranged on the inside of the plate segments, which hold the plate segments at a distance from the exhaust pipe, so that an annular flow channel is formed around the exhaust pipe. The two half-shells of the device are connected to one another using known connecting means, such as hinge-like joints or connecting screws, and are placed around the exhaust pipe of the fireplace stove like a sleeve and clamped to it. Room air flows upwards through the annular flow channel, the flow velocity of which can be influenced by additional fittings. Fittings that constrict the flow channel increase the flow velocity.The plate segments, which have a specific thickness, can be made of a heat-storing material, such as gray cast iron or ceramic. The air rising from the exhaust pipe, which rises along their inner surface, heats them up, and the stored heat is released into the room via their outer surfaces (DE 20 2017 000 457 U1).

[0007] The disadvantage of these heat exchanger devices is that the additional heat gained through the targeted use of waste heat from the flue gases, in addition to the heat directly radiated by the stove or fireplace, remains in the room, so that the room is usually overheated. Experience has shown that stoves and fireplaces without their own means of heat storage have the unpleasant habit of overheating the room, despite economical fuel consumption, especially if the room is relatively small. Even the use of an air circulation pump or fans can only remedy this disadvantage to a limited extent.

[0008] Also known is a two- or multi-part chimney fitting consisting of a load-bearing outer casing, a flue gas pipe attached to it by webs, and a pipe system carrying a heat medium. Insulation is provided between the outer casing and the flue gas pipe to prevent the heat emanating from the hot flue gases rising in the flue gas pipe from escaping. To prevent excessive cooling of the flue gases, the pipe system carrying the heat medium is arranged in the insulation or in corner areas of the flue pipe remote from the cylindrical inner circumference of the flue gas pipe. The pipe system can be connected to a heat transfer circuit (DE 27 31 835 A1). The disadvantage of this chimney fitting is that, due to its intended use for mounting a chimney, it is not suitable for retrofitting to exhaust pipes of fireplaces installed in living spaces.

[0009] State-of-the-art warm-air heating systems also include systems in which the air heated by an energy source is circulated via an air duct system within the room itself or into other rooms of the building using air suction or pressure devices. A known example of this is an air heat exchanger, preferably located on the rear wall of a fireplace, in which an air blower or air pump draws or pushes the warm air directly from the fireplace room through a hose or duct system (DE 20 2010 014 475 U1). However, this easily retrofittable warm-air heating system has the disadvantage that the air heat exchanger, which is directly connected to the fireplace, must be relatively large to achieve high heat output and therefore requires a lot of space.

[0010] More effective warm air heating systems, such as those described in the utility model documents DE G 81 14 795.3 U1 or DE 202 04 993 U1, require the air heat exchanger to be arranged directly in the combustion chamber of the fireplace or stove, which in turn has the disadvantage of interfering with the combustion chamber and thus resulting in a complex retrofitting that can usually only be carried out by specialists.

[0011] A recuperator for utilizing the flue gas heat from stoves, ovens, and / or fireplaces is also known. It consists of an outer casing surrounding the flue gas pipe, which, together with the outer casing of the flue gas pipe and an upper and lower cover, forms a hollow body closed on all sides. The air flow pipe has an air inlet and an air outlet. A fan creates forced circulation of the air through an air flow pipe. Air guiding devices are arranged between the flue gas pipe and the air flow pipe (DE G 85 05 894 U1). The disadvantage of this recuperator is that, with the integrated flue gas pipe, it forms a compact exhaust system and therefore cannot be mounted on existing flue gas pipes.

[0012] Finally, a building ventilation system is known that uses a chimney as part of the ventilation system. The chimney has a firebox and a flue connected to the firebox to discharge the gases from the firebox to the outside environment. A ventilation duct directs the outside air into the building. A motor-driven draught regulator is connected to the flue duct to direct the flue gases to the outside. A motor-driven fan drives the air flow through the duct to replace the air lost inside the building due to the flue gases (CA 2 494 239 A1).

[0013] The invention is therefore based on the object of modifying the known devices for utilising the waste heat from flue gas pipes of fireplaces heated with solid fuels in such a way that they can be easily retrofitted to the flue gas pipe, enable effective heat transfer and targeted distribution of the heated room air.

[0014] The object is achieved according to the invention by a device for utilizing the waste heat from flue gas pipes having the features according to claim 1. The invention and its advantages

[0015] The device according to the invention has the advantage that it can be attached to conventional flue gas pipes without the assistance of an installer and without great effort, and the room air heated by it can be fed directly into a duct or duct system of a warm-air heating system. This cools the flue gas, meaning the heat energy of the fuel used in the fireplace is more effectively utilized, and the generated heat energy is used to heat other rooms. At the same time, overheating of the air in the room in which the fireplace is located is also avoided.This is achieved by the heat exchanger consisting of a double-walled, fully enclosed hollow body with a cold air inlet and a warm air outlet. When installed, the inner casing of the heat exchanger rests against the outer casing of the flue gas pipe, creating a metallic, heat-conducting connection between the flue gas pipe and the heat exchanger. The warm air outlet is connected to an air duct of a warm air heating system. The heat exchanger can be firmly connected to the flue gas pipe as a compact component or retrofitted to an already installed flue gas pipe using clamping devices.

[0016] In an advantageous embodiment of the invention, the double-walled, fully enclosed hollow body is designed to be split along a plane of its longitudinal axis to allow it to be subsequently connected to an already installed flue gas pipe. In this case, at least one fastening element is arranged on the hollow body, with which it can be attached to the flue gas pipe and removed again. Clamping elements such as screws, clamps, or tensioning straps can be used as fastening elements. Magnetic fastening elements are also possible.

[0017] According to an advantageous embodiment of the invention in this regard, a longitudinal division of the outer shell of the hollow body is designed as a hinge. This has the advantage that the hollow body remains one piece, i.e., for installation on the flue gas pipe, it simply needs to be opened up, placed around it, and screwed together at the seam. Another variant involves designing a longitudinal division of the outer shell of the hollow body as a detachable seamed joint, so that the heat exchanger is in two parts.

[0018] Another advantageous embodiment of the invention consists in designing the double-walled, all-round, closed hollow body as a three-quarter hollow cylinder. However, the flue gas pipe is then not completely enclosed by the heat exchanger. The free quarter can accommodate, for example, the inlet connection for drawing in cold air and the outlet connection for warm air for connecting to the air duct of the warm air heating system, as well as the fastening means for the heat exchanger. The three-quarter hollow cylinder can then be arranged so that the free quarter faces a wall, so that the connections and fastening means are not visible from the front.

[0019] To remove the heated air from the heat exchanger as quickly as possible and supply it to the additional room(s) to be heated, it is advantageous to draw the cold air into the heat exchanger using a fan. The same effect can be achieved by connecting the warm air outlet of the heat exchanger to the intake side of a fan, and the air duct of the warm air heating system to the discharge side of a fan.

[0020] According to an additional advantageous embodiment of the invention, air baffles are arranged in the hollow body, which ensure forced air flow in the heat exchanger, thereby better utilizing the waste heat from the flue gas pipe. Depending on the desired flow pattern, the air baffles can be arranged longitudinally and / or horizontally in several planes of the hollow body. Additionally, ribs can be arranged in the hollow body, at least one of whose edges is in heat-conducting contact with the flue gas pipe and / or the air baffles.

[0021] In another advantageous embodiment of the invention, a ventilation flap is arranged near the warm air outlet of the double-walled hollow body, via which an additional regulation of the warm air flow in the room in which the stove or fireplace is located and thus also of the warm air flow passed on to the warm air heating system is possible.

[0022] Further advantages and advantageous embodiments of the invention can be found in the following description, the claims and the drawings. drawing

[0023] Preferred embodiments of the subject matter according to the invention are illustrated in the drawings and are explained in more detail below. Fig. 1 a spatial representation of a device according to the invention, Fig. 2 a spatial representation of a second variant of a device according to the invention, Fig. 3 a spatial representation of the second variant of Fig. 2 in the unfolded state, Fig. 4 a plan view of the device Fig. 2 , Fig. 5 a longitudinal section through the device from Fig. 2 , Fig. 6 a cross section through the device from Fig. 2 and Fig. 7 a spatial representation of an embodiment of a horizontal air baffle. Description of the embodiments

[0024] Since warm air heating systems are known in themselves, they have not been shown in the drawings and only the air heat exchanger to be connected to it, including the flue gas pipe, has been shown.

[0025] Fig. 1shows the simplest embodiment of the device according to the invention, in which a separate air heat exchanger is pushed onto a chimney pipe 1. The air heat exchanger consists of a double-walled hollow cylinder 2, closed at the top and bottom, which has an outer shell 3 and an inner shell 4, wherein the outer shell 3 and the inner shell 4 are each hermetically connected to one another at their upper edge by an upper cover 5 and at their lower edge by a lower cover 6. In its lower region, near the lower cover 6, the outer shell has an inlet nozzle 7 for the cold air and in its upper region, near the upper cover 5, an outlet nozzle 8 for the warm air. To regulate the flow of warm air, the upper cover 5 is provided with a ventilation flap 9.

[0026] The inner diameter of the inner shell 4 of the hollow cylinder 2 is slightly larger than the outer diameter of the chimney pipe 1 in order to easily slide the air heat exchanger over the chimney pipe 1 or, conversely, to easily insert the chimney pipe 1 into the air heat exchanger. This fit must also be selected to ensure sufficient surface contact between the chimney pipe 1 and the inner shell 4 of the hollow cylinder 2 for intensive heat transfer from the chimney pipe 1 to the air heat exchanger. It goes without saying that the inner shell must always be adapted to the shape of the chimney pipe 1. If the chimney pipe 1 has a shape other than circular, for example, a polygonal cross-section, the inner shell 4 of the hollow cylinder 2 must have a corresponding polygonal cross-section.

[0027] A significantly more intensive heat transfer is achieved by creating a metallic press fit between the chimney pipe 1 and the inner shell 4 of the hollow cylinder 2. According to the invention, this is achieved by dividing the hollow cylinder 2 and connecting the two halves together in an articulated manner. The two halves are pressed together using conventional clamping devices, thereby creating a metallic, heat-conducting connection between the chimney pipe 1 and the hollow cylinder 2 of the air heat exchanger.

[0028] In Fig. 2Such a split air heat exchanger is shown in a perspective top view. The special feature of this design is that this air heat exchanger is designed as a split three-quarter hollow cylinder 10, the exposed vertical dividing surfaces of which are each hermetically sealed by a vertical cover 11. The dividing surfaces that adjoin one another when closed are open. In this area, the two halves of the three-quarter hollow cylinder 10 are connected to one another by a vertical hinge 12. In the present example, the inlet nozzle 7 for the cold air and the outlet nozzle 8 for the warm air are inserted into one vertical cover 11.The two halves of the three-quarter hollow cylinder 10 can be connected to one another by means of two tensioning bands 13 arranged in its upper and lower area, which can be tensioned by means of tensioning screws 14 according to the principle of a hose clamp and at the same time press the two halves of the three-quarter hollow cylinder 10 against the chimney pipe 1.

[0029] Fig. 3shows the split air heat exchanger in the unfolded state, with one half already attached to the chimney pipe 1. The air heat exchanger can also be attached to the chimney pipe 1 in any other way. For example, it is also possible to guide the two free ends of the clamping bands through a threaded bushing, through which a clamping screw is turned. The clamping screw has a pressure plate adapted to the shape of the chimney pipe at its free shaft end. By tightening the clamping screw, which is supported on the chimney pipe via the pressure plate, the clamping band is tightened, thus pressing the two halves of the air heat exchanger against the chimney pipe.

[0030] At the Fig. 4In the top view of the device according to the invention shown in Figure 1, the upper cover 5 is shown partially open, so that the interior of the air heat exchanger is visible. This shows that there are vertical and horizontal fittings in the interior. These all have the task of intensifying the heat transfer from the chimney pipe 1 to the cold air flowing in from below via the inlet nozzle 7. These fittings are described below in conjunction with the Fig. 5 shown longitudinal section and the one in Fig. 6illustrated cross-section through the three-quarter hollow cylinder 10. As can be seen from the figures mentioned, the interior of the three-quarter hollow cylinder 10 is divided into individual chambers by vertical guide plates 15, whereby in the present example, in each half of the three-quarter hollow cylinder 10, three chambers are formed by two vertical guide plates 15, of which the chambers adjoining the division plane form a common larger chamber. As can be seen from Fig. 5 As can be seen, the vertical guide plates 15 are all designed in their length and are each attached with a longitudinal edge to the inner casing 4 of the three-quarter hollow cylinder 10 in such a way that they alternately allow the air flow to pass past the lower cover 4 and then past the upper cover 5, ie they cause the air flow to meander within the three-quarter hollow cylinder 10. As can be seen from the Fig. 4 and 6As can be seen, the vertical baffles end just before the outer shell 3 of the three-quarter hollow cylinder 10 so that they are not cooled by it. The meandering guides the air flow over a longer distance near the chimney pipe 1, thereby intensifying the heat exchange. Additional heat exchange occurs via the vertical baffles 15 themselves, which heat up due to their metallic connection to the inner shell 4, which in turn is metallically connected to the chimney pipe 1 in a heat-conducting manner.

[0031] An additional intensification of the heat transfer to the air flow is achieved, as can be seen in particular from the Fig. 4 and 6 can be seen, is achieved by the arrangement of horizontal guide plates 16 which are arranged on the inner wall 4 of the three-quarter hollow cylinder 10. Fig. 5shows that the guide plates 16 are arranged at different heights in the individual chambers. The guide plates 16 can be designed, for example, as flat or angled plates. The vertical guide plates 16 used in the present embodiment are, as can be seen from Fig. 7 As can be seen, it is additionally provided with a recess 17 and a baffle plate 18 arranged above it. Such a baffle plate 16 can, as shown in the present example, be manufactured in one piece, for example by punching out and bending the baffle plate 18. At such a horizontal baffle plate 16, the air flow is divided into two and redirected, thereby further intensifying the heat exchange.

[0032] All features presented here can be essential to the invention both individually and in any combination. Reference number list

[0033] 1Chimney pipe 2Hollow cylinder 3Outer casing 4Inner casing 5Upper cover 6Lower cover 7Inlet nozzle 8Outlet nozzle 9Ventilation flap 10Three-quarter hollow cylinder 11Vertical cover 12Hinge 13Clamping band 14Clamping screw 15Vertical baffle 16Horizontal baffle 17Recess 18Baffle plate

Claims

1. A device for utilising the waste heat from flue gas pipes of solid fuel-fired fireplaces, the device comprising an air heat exchanger with a cold air inlet and a warm air outlet and at least one thermally conductive inner component which is at least partially connected to the outer casing of the flue pipe (1) in a metallically heat-conducting manner, characterized by that the air heat exchanger consists of a double-walled hollow body (2) closed on all sides, the inner casing (4) of which, when assembled, rests against the outer casing of the flue gas pipe (1) and the warm air outlet of which is connected to an air duct of a warm air heating system.

2. Device according to claim 1, characterized by that the double-walled hollow body (2) closed on all sides is divided in a plane of its longitudinal axis and is fastened to the flue gas pipe (1) by means of at least one clamping means (13, 14).

3. Device according to claim 2, characterized by that a longitudinal division of the outer shell (3) of the hollow body (2) is designed as a hinge (12).

4. Device according to claim 2, characterized by that a longitudinal division of the outer shell (3) of the hollow body (2) is designed as a detachable folded connection.

5. Device according to one of claims 1 to 4, characterized by that the double-walled hollow body (2) closed on all sides is a three-quarter hollow cylinder (10).

6. Device according to claim 1, characterized by that the cold air inlet is connected to the pressure side of a fan of the warm air heating system.

7. Device according to claim 1, characterized by that the warm air outlet is connected to the suction side of a fan of the warm air heater.

8. Device according to one of claims 1 to 7, characterized by that in the hollow body (2) air baffles (15, 16) are arranged.

9. Device according to one of claims 1 to 7, characterized by that ribs connected to the flue gas pipe (1) and / or the air baffles (15, 16) are arranged in the hollow body (2).

10. Device according to one of claims 1 to 9, characterized by that a ventilation flap (9) is arranged near the warm air outlet of the double-walled hollow body (2).

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