Combination heating apparatus

AREA OF INVENTION

The present invention relates to a heater for providing central heating and hot water (tap water) in a caravan, house car, camping boat or similar.

PRIOR ART

In the Swedish Patent Specification No. 7804976-4, there is described a heater for caravans or similar moveable housing. The hot combustion gases from a LP-burner or similar is adapted to pass a heat exchanger in the shape of a tube with radial flanges. The flanges extend outside the surface of the tube, where a heat medium is positioned enclosed inside a second concentric tube. The heat medium is used for central heating and is fed to radiators of the caravan. Outside the second tube, there may be a spiral comprising further heat medium which is used for hot tap water. This equipment is positioned in a housing with relatively small cross-sectional area but a large height. In this manner a relatively compact equipment is formed.

In the French Patent Specification No. 1460368 there is described a heater intended for a small house or other larger permanent housing. The heater comprises a laying tap water cylinder with a volume of for example 1200 litres. A burner is positioned inside a second cylindrical tube, which is positioned eccentrically at the lower part of the tap water cylinder. The tube of the burner is provided with radial flanges for taking up heat energy from the burner. A third tube is positioned concentric outside the burner tube and encloses a heat medium for central heating used for heating the housing via radiators etc. The third tube is provided with flanges extending out in the tap water cylinder for improving the heat transfer.

GB-A-2 257 242 discloses a water and air heating apparatus which conductively heats air and water simultaneously by means of a hollow heat exchanger disposed in a tank and controls the relative rates of heating of the air and water by means of a control system which controls a fan impelling the air through the heat exchanger. The heat is provided by a burner positioned in a burner tube with radial flanges transmitting heat to a second concentric space for heating air therein.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a heating apparatus which is specifically adapted for caravans and similar mobile housings with small spacings and thus is very compact. Another object of the invention is to provide a heating apparatus for heating air for central heating as well as water for tap water supply.

Thus, there is provided a heating apparatus for heating tap water and for central heating of a mobile house such as a caravan, comprising a burner as a heat source, the burner being positioned in a burner tube; a second tube surrounding said burner tube and forming a ring-shaped space between the burner tube and the second tube, said ring-shaped space containing air for central heating and a tap water vessel surrounding said ring-shaped space. The burner tube comprising radial flanges extending from the interior of the burner tube and through the surface thereof to the ring-shaped space for heat exchange with and heating of the air for central heating. According to the invention, the tap water vessel and the second tube are lying cylinders and the second tube is provided with a heat transferring plate covering a predetermined part of the lower portion of the second tube, the flanges of the burner tube being in contact with said heat transferring plate.

Thus, the lower flanges of the burner tube contact the heat transferring plate and rest thereon, but do not reach the surface of the second tube at the portions not covered by the heat transferring plate. In this way, the heat energy is transmitted directly from the lower flanges via the heat transferring plate to the tap water vessel, whereby the flanges can have a higher temperature without the tap water being overheated, as is explained in more details below.

According to the invention, the tap water vessel, the second tube and the burner tube are all lying cylinders which are eccentrically placed inside each other so that the second tube is eccentric in the tap water vessel and the burner tube is eccentric in the second tube. Preferably, the burner tube is closed in one end and is provided with a baffle dividing the tube in an upper portion in which the very burner is positioned and a lower portion for returning the combustion gases.

SHORT DESCRIPTION OF THE DRAWINGS

Herein below, the invention will be described in more details with reference to preferred embodiments of the invention and with reference to the appended drawings, in which:

• Fig. 1 is a cross-sectional view of the heater according to the invention;
• Fig. 2 is a longitudinal section through the heater according to Fig. 1;
• Fig. 3 is a cross-sectional view similar to Fig. 1 but with an insert for air-supported central heating;
• Fig. 4 is a longitudinal sectional view with a cover for the burner put in place;
• Fig. 5 is a cross-sectional view showing the burner and fan and lines in connection therewith.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In Fig. 1 there is shown the heater 1 according to the invention in cross-section. As appears from the figure, the heater comprises in principle three horizontal, in each other positioned eccentric tubes forming spaces there between intended to enclose the heat medium.

There is an outer first tap water tube 2 and an inside thereof positioned second tube 3, which there between define a space 4 for tap water. The space 4 is closed at its both ends by gables 5, 6, see Fig. 2. The second tube 3 is eccentrically positioned in the tap water tube 2, so that a narrow portion is formed in the lower portion of the space 4 and a larger portion at the upper portion (seen according to Fig. 1). Thus, the largest portion of the volume of the space 4 will be positioned at the upper portion above the second tube 2.

An inlet 7 to the space 4 is positioned at the bottom and an outlet 8 is positioned at the upper portion of the space 4. The inflow of tap water takes place in two expanding channels 9, 10 defined by the second tube 3 and the tap water tube 2, as clearly appears from Fig. 1. This entails that the velocity of the water is decreased smoothly and that stratification in the tap water space 4 will be disturbed in as small extent as possible. It might be suitable to adapt two inlets (and two outlets) along the length of the tap water tube 2 so that the axial flow also will be minimised.

In the preferred embodiment of the invention, the volume of the space 4 is about 8,4 litres.

A third burner tube 11 is positioned eccentrically in the second tube 3 and delimits a ring-shaped space 12 with the same shape as the tap water space 4, but smaller. This ring-shaped space 12 is intended for a heat medium to be used in the central heating system of the caravan, usually a mixture of water and glycol.

The burner tube 11 is shorter than the second tube 3 and its inner end is closed by a gable or bottom 13. In the embodiment of the invention shown, there are two inlets 15 and one outlet 14 to the ring-shaped space 12, which are positioned in the gable 5 closing the second tube 3. A circulation pump (not shown) circulates the heat medium to radiators positioned in the space to be heated by the central heating system.

In the preferred embodiment of the invention, the volume of the ring-shaped space 12 is about 4,1 litres.

Thus, the burner tube 11 forms a cup-shaped space 16 delimited by the burner tube 11 and the gable bottom 13 of this tube. This cup-shaped space 16 is provided with several radial and axially extending flanges 17 extending inwards from the shell surface of the tube 11. Inside the flanges there is adapted a baffle 18. The baffle 18 is composed of a tube with the cross-section shown in Fig. 1. The baffle 18 is shorter than the burner tube 11 so that a distance is formed between the inner end of the baffle and the bottom 13 of the burner tube 11. Moreover, there is a bottom in the baffle so that the baffle is closed at the inner end.

In the cup-shaped space 16 above the baffle, there is positioned a LP-gas burner (not shown). The burner is of a construction known per se and delivers a flame in the space 16 above the baffle. Air is supplied to the flame and the space 16 from a specific inlet and via a pump so that the air flows axially and parallel with the flanges 17. Thus, the hot combustion gases deliver heat energy to the flanges 17 and preferably to the flanges positioned in the upper portion of the space 16.

When the combustion gases reach the inner end of the space 16, they pass axially back below the baffle 11 and emit their remaining heat energy to the flanges 17 at the lower portion of the burner tube 11. Finally, the combustion gases pass out to the surroundings via a line as is described closer below.

The LPG-burner and the pump are attached to the lower end of the tube 11 with a flange and several screw connections. Moreover, the joint is provided with a suitable sealing. Thus, the LP-gas and the combustion gases are positioned inside the tube 11 and can never reach the area inside the caravan.

The outer shell surface of the burner tube 11 will be heavily heated by the LPG-burner while the heat is transmitted to the shell surface by the flanges 17. The heat energy is then transmitted to the heat medium in the ring-shaped space 12. In this space 12 there is a thermostatic body 19 which senses the temperature of the heat medium.

The heat energy is then further transmitted from the heat medium in the ring-shaped space 12 to the tap water in space 4.

The operation of the heating apparatus according to the invention is the following: When the thermostatic body 19 senses that the temperature of the heat medium is below a predetermined value, for example 70°C, the LPG-burner is started by known means. The burner heats the flanges 17, which deliver heat energy to the heat medium, which is positioned in the ring-shaped space 12, whereby the temperature rises. When the temperature exceeds a predetermined second temperature, for example 80°C, the LPG-burner is shut off. However, there is a comparatively large mass in the flanges 17, which thus will carry a relatively large amount of heat energy. This entails that the burner will be activated during relatively long periods and with relatively long pauses there between.

The heat demand in the caravan is in turn sensed by a room thermostat and this thermostat controls a circulation pump which circulates the hot heat medium from the ring-shaped space 12 and to radiators positioned in the caravan.

Since the temperature of the heat medium in the ring-shaped space 12 varies only to a small extent between 70°C and 80°C, the tap water in the vessel 2 will achieve a temperature in this range. Any specific control of the temperature of the tap water will, thus be superfluous. However, there is an excess temperature sensor of the tap water, which prevents activation of the LPG-burner if the temperature of the tap water exceeds for example 98°C, which indicates a malfunction.

As an alternative heat source, there are two electric heaters which are positioned in the ring-shaped space and heat the heat medium therein. The exact position is not critical and can be varied in dependence of the desired design.

At certain occasions, water-supported heat energy is not used in caravans and similar mobile housings, but it is instead desired to use air-supported central heating in which air is used as heat source, i.e. hot air is introduced into the caravan. The heating apparatus according to the invention can be adapted to such air-supported heating.

Such an embodiment is shown in more details in Fig. 3. As appears therefrom, the burner tube has been modified so that the radial flanges extend beyond the shell surface and into the ring-shaped space 12. The flanges 20 extend almost up to the inner surface of the second tube 3, which means that the burner tube 21 is almost concentric with the second tube 3.

The ring-shaped space 22 between the second tube 3 and the burner tube 21 comprises the air to be heated in this embodiment. The air is heated against the outer portions of the flanges 20 and thus, has a large are for heat transfer. However, in this embodiment the flanges are considerably hotter than in the first embodiment and must as a rule exceed 100°C for that sufficient heating of the air should be able to take place.

By this high temperature of the flanges, there is a risk that the tap water will be heated to above 100°C. Thus, specific measures must be undertaken.

Thus, the burner tube 21 and its flanges 20 are adapted so that the outer diameter of the flanges is somewhat smaller than the inner diameter of the second tube 3 so that the flanges 20 never reach up to the inner surface of the second tube 3. However, at the lower portion of the tube 3 there is a heat transferring plate 23 against which the radial flanges 20 abut. Thus, heat energy is transmitted directly from the lower flanges 20 and to the heat transferring plate 23 and thence to the lower portion of the tap water space 4 in the vicinity of the inlet 7 for cold water.

The heat transferring plate 23 is so dimensioned that the right balance is obtained between the heat energy transferred to the circulating air and the energy transmitted to the tap water. For making more easy the heat transfer, a heat transmitting paste is positioned between the heat transferring plate and the second tube. In this way, the heat transfer coefficient between the plate and the tube is minimised.

Since the flanges at the upper portion do not touch the second tube, the heat transfer from the flanges to the tube will be rather small and essentially consisting of convection heat transfer via the air which should be heated. However, this air is rather cold and thus, any effective heat transfer does not take place this way. If however, the air circulation ceases, for example by the fact that the air circulation fan stops, the heat transfer between the flanges and the second tube can be considerable and entail overheating of the tap water.

In order to decrease the risk for such overheating of the tap water, there is one further measure undertaken. As is shown in Fig. 4, the entire heating apparatus is positioned in a cover 24. The air which should be heated is sucked inside the heater through openings 25 positioned in the front portion of the cover 24 above the first tube 2 according to arrows 26 and 27 and thus cools the upper warmest outer surface of the tap water vessel 2 at the same time as the air is preheated. The air then passes along the entire tube 2 and thence radially inwards to the end of the tube 21 according to arrow 28, and thence into several openings 29 according to arrows 30. Suitably, there are several openings 29 along the periphery of the ring-shaped space 22 so that the air passes beyond all flanges and takes up heat energy from the flanges. Finally, the air passes out through an outlet 31 and via suitable lines and nozzles to the interior of the caravan to be heated.

In this embodiment, it is also of importance that the flanges have a large mass, which accumulates a relatively large amount of heat.

In this embodiment, there is an excess temperature sensor preventing the operation of the heat source if the temperature of the tap water exceeds for example 98°C. Electric cartridges used as alternative heat source are preferably places adjacent the flanges.

As appears from that stated above, the heat transferring plate can be dimensioned so that right balance is achieved between air-supported central heating and tap water.

It is suitable to make the second tube and its flanges through extrusion in aluminum. At the same time, the surfaces of the flanges can be profiled so that the surface areas thereof increase still further, which is especially important at air-supported central heating.

It is realised that the combustion gases passing beyond the lower flanges already are cooled and thus, the lower flanges will always be colder than the upper flanges. This fact is used automatically according to the invention, since cold water is supplied at the lower flanges, whereby still a large temperature differential exists, and thus and effective heat transfer. In the embodiment with air-supported central heating, the lower flanges are similarly used for heating the tap water, which has a lower temperature, while the upper flanges with high temperature are used for heat exchange with the air, in which a high temperature difference is necessary.

The air for the combustion in the burner is supplied by means of a fan 32 from an inlet 33 positioned at the roof 34 of the caravan, see Fig. 5. From the inlet 33 there is a suction line 35 to the fan 32 positioned adjacent the burner 36 and then to the nozzle of the burner. LP-gas is supplied to the nozzle via a separate line (note shown). At the nozzle there are electrodes which upon activation delivers a spark igniting the LP-gas. A monitor device of a type known per se controls if ignition takes place and cuts off the supply of LP-gas at no flame.

The combustion gases are taken out from the lower portion of the burner tube to an exhaust tube 37, which runs concentric inside the inlet line 35 to a chimney 38 at the roof of the caravan. Thus, there is obtained a balanced inlet of combustion air and exhaust of combustion gases in a manner known per se. The flow directions are shown with arrows 39 and 40.

At the lowest point of the inlet line 35, there is a first hole 41 for letting out possible condensate water. The hole is connected to a hose 42 leading down below the caravan. Opposite said first hole 41, there is a second hole 43 on the exhaust tube 37, which lets out possible water from the inlet line 35 and further through the first hole 41 and the hose 42.

By this arrangement, there is automatically obtained an outflow of condensate water. The pressure in the inlet line 35 at the first hole 41 is a small negative pressure, which makes sure that no exhaust gases can pass out through the hose 42 but an air flow in the opposite direction is achieved. The pressure in the exhaust tube at the second hole 43 is a small over pressure, but this second hole leads to the inlet line and the combustion gases can therefor not pass out through the hose. Instead, these are re-circulated to the burner.

Herein above have been described two embodiments of the invention with reference to the appended drawings. However, it is realised that the invention is not limited to the solutions shown on the drawings but can be modified within certain limits. Such for a skilled person obvious modifications should of course be included within the scope of the invention.

It is specifically remarked that in Fig. 3 several inlet openings 29 are shown, but it is realised that the lower inlet openings very well can be left out, specially those in connection with the heat transferring plate.

In Fig. 4 there is shown two inlets for tap water, but it is realised that more than two inlets can be used. It is also advantageous to use several tap water outlets.

Moreover, there is shown in Fig. 2 that the inlet 15 and the outlet 14 for the heat medium is positioned at the same gable 5, whereby the heat medium will spool over the outer surface of the burner tube 11 in an arc and turn back to the outlet. It is however realised that it also can be suitable to arrange inlet at one end and outlet at the other end.

The tap water vessel 2 and the second tube 3 are shown as cylindrical vessels, which is suitable since they should be able to withstand a relatively high pressure. However, it is also possible to adapt the tap water vessel with another shape, which can be suitable, such as partly rectangular shape. In the last-mentioned case, the volume of the vessel can be used still better for obtaining a compact heater with a large volume of hot tap water.

By using lying cylinders, the ability of the water to form layers is better used, which is of great importance in connection with the tap water vessel. By the expanding channels 9 and 10, there is obtained an effective breaking of the incoming water jet and the movement energy is transmitted to pressure in a smooth transition. The inlet 7 also opens to the shell surface of the second tube, which entails redirection and spreads the water flow. The hot water can undisturbed rise to the upper part of the tap water vessel. Such an effective stratification cannot be obtained at standing cylinders, which is almost the only version at heaters for mobile housings.

By adapting the burner tube eccentrically inside the second tube, the advantage is obtained that the lower flanges can transmit the heat energy thereof almost directly to the tap water, while the upper flanges transmit the energy thereof essentially to the heat medium. By adapting the number of upper and lower flanges and the size of the baffle and the placing thereof, the ratio between the heat transfer to the tap water and to the heat medium can be influenced upon and balanced at construction. Moreover, the counter-current principle is used so that the colder combustion gases act against the cool incoming tap water.

It has been stated above that the burner is a LP-gas burner, but it is realised that also other types of burners can be used, such as burners for diesel oil etc.