The present invention relates to a device for heating a first liquid present in a boiler, wherein a flue gas housing with a burner disposed therein is provided in said boiler, which housing is connected to a flue duct which extends from said housing through the boiler and which is connected via a pipe to a flue gas discharge channel outside the boiler, and wherein said first heated liquid is in contact with a heat exchanger for heating a second liquid.

A device of this kind is known from FR-A-2 714 719, which device consists of a boiler with a burner disposed therein, which delivers flue gases to a flue gas housing. A flue duct is spirally wound round the flue gas housing. The heat emitted by the flue gases heats a first liquid. Said first liquid delivers parts of the heat to a second liquid which is being supplied, possibly via a coil, to the upper side of the boiler and which is discharged in a reasonably heated condition.

It has become apparent that the efficiency of such a device can be enhanced by making improvements in such a device.

A device of the above kind is furthermore known from Dutch patent application No. 9101501 in the name of the present applicant.

The discharge pipe of the boiler known therefrom, which is connected to the housing defining a combustion chamber for the purpose of discharging combustion gases, extends from said combustion chamber through the boiler to the underside of the boiler. Said discharge pipe is connected outside the boiler to an upwardly extending flue via a pipe section which includes an angle of less than 90 with the horizontal. A significant drawback of this boiler is its relatively high energy consumption. Moreover, the temperature of the liquid to be heated cannot be controlled with great accuracy, so that the capacity of the boiler constitutes a limitation in case of a varying demand, for example for hot water. In addition, it has become apparent in practice that the use of a device of this kind leads to inadequate utilization of the heat which is generated on combustion.

After all, it is desirable for the temperature of the combustion gases to be as low as possible upon exiting the boiler, which means that the energy contained in the combustion gases has been utilized practically completely for heating the liquid present in the boiler.

Accordingly, it is an object of the present invention to provide a device which comprises a boiler which has a high energy efficiency. Another object is to obtain an improved (simple) device with a high heating efficiency and a high yearly efficiency.

A further object of the present invention is to provide a device which comprises a boiler in which a heating facility for hot water, so-called sanitary and household water, as well as a facility for so-called CH water is incorporated.

Furthermore it is an object of the present invention to provide a boiler which is easy to install and which is readily accessible in case of repairs.

The present invention as referred to in the introduction is according to the invention characterized in that the flue gas housing (5) extends over the burner (6), that the flue duct (7) extends spirally through at least part of the boiler (1), and that the heat exchanger (17) is disposed outside the boiler (1) and separately therefrom.

In the present device heating of the liquid which is present in the boiler, preferably sanitary water (hereinafter called"the first liquid"), thus takes place via the boiler and the transport of the hot combustion gases through the flue duct, which flue duct is disposed in the first liquid that is present in the boiler. The flue duct preferably consists of a pipe which is smooth on the outside so as to prevent undesirable elements, such as lime, from adhering thereto. Such elements have an adverse influence on the heat-transmitting capacity of the flue duct. In addition, the energy content of the first liquid thus heated in the boiler is used advantageously for heating a medium (the second liquid), preferably water, which is used as so-called CH water. Thus the combustion gases are used for heating the first liquid that is present in the boiler, which liquid in turn functions as a heat-transmitting medium for the second liquid.

According to a special embodiment of the present invention the heat exchanger, which functions to heat the second liquid, is a plate heat exchanger, which plate heat exchanger is disposed outside the boiler and which comprises a supply pipe and a discharge pipe for the first liquid and a supply pipe and a discharge pipe for the second liquid.

The selection of the position of the supply pipe for the first liquid is not particularly critical, but it is preferable to select the position so that the heat exchange in the heat exchanger takes place in counterflow.

The use of a plate heat exchanger outside the boiler is in particular advantageous because repairs can easily be carried out in a construction of this kind. Another advantage of the use of the plate heat exchanger is the fact that it makes it possible to transfer a capacity equal to that whi ch i s del i vered by the burner. Furthermore the heat losses are minimized when a plate heat exchanger is used.

In a special embodiment it is furthermore preferable for the flue gas housing to be disposed at a point located between three quarters of the height of the elongated, vertically disposed boiler and the upper end thereof, wherein the flue duct that springs from the flue gas housing extends downwards through the boiler and is connected to the flue gas discharge channel at a point located between the lower end of the boiler and one quarter of the height thereof. Since the flue duct extends downwards through the boiler it is possible to cool down the flue gases produced on combustion to approximately the temperature of the inflowing cold first water, so that such a construction leads to an optimum utilization of the energy contained in the combustion gases.

According to another preferred embodiment, the flue gas housing extends upwards through the boiler from the bottom side thereof, wherein the flue duct of the flue gas housing which is present near the upper end of the boiler extends in the direction of the lower end thereof and is connected to the flue gas discharge channel at the bottom side of the boiler.

Since the flue duct, in which the combustion gases are present, extends along a large part of the boiler, it is thus possible to realise an enhanced utilization and control of the entire heat content of the boiler. In addition it is possible, by providing a number of temperature measuring points at various points in the boiler, for the capacity of the burner disposed in the flue gas housing to be adjusted thereto. Furthermore it is possible to have the first liquid to be heated circulate over the plate heat exchanger disposed outside the boiler.

In the present boiler the flue gases condensate in the flue duct which is connected to the housing. In order to prevent undesirable corrosion on the inside of the flue duct, it is desirable to coat the inside thereof with a corrosion resistant protective layer.

The present invention will be explained in more detail hereafter with reference to the drawing. In the drawing:

Figure 1 shows a boiler whose principle is known from FR-A-2 714 719, in which boiler the heat exchanger for heating the second liquid is disposed in the upper part of the boiler; Figure 2 is a representation of an embodiment of the boiler according to the invention, in which boiler the heat exchanger for heating the second liquid is in the form of a plate heat exchanger, which is disposed outside the boiler; Figure 3 is a representation of a special embodiment of a boiler according to the invention, wherein the flue gas housing extends upwards through the boiler from the bottom side thereof; and Figure 4 shows a device according to Figure 3, wherein only one flue duct springs from the upper side of the flue gas housing, however.

Figure 1 shows a device of the type which is known from FR-A-2 714 719. In order to provide a clear explanation of the device according to the invention as described with reference to Figures 2-4, the device according to Figure 1 is shown in a form which is comparable to that of Figures 2-4. Accordingly, like numerals relate to comparable parts of the device. Boiler 1 is mounted at a suitable location, using a mounting element 2. The necessary pumps, control systems and the like have been left out for easy reference. Present in boiler 1 is an amount of water (first liquid), which is preferably used for sanitary purposes.

The supply of said sanitary water takes place via pipe 3 at the bottom side of the boiler 1, and the water exits the boiler 1 at the upper side via pipe 4. The first liquid present in boiler 1 is heated through the use of a flue gas housing 5, in which a burner 6 is disposed. The combustion gases produced on combustion exit housing 5 via a flue duct 7, which extends downwards in boiler 1. The flue duct extends up to connecting point 8 of boiler 1, and it is connected to a flue gas discharge channel (not shown) via pipe 12. Furthermore present in boiler 1 is a spiral-shaped heat exchanger 9, which heat exchanger 9 functions to heat the second liquid, preferably heating water or CH water. The supply of the second liquid to the heat exchanger 9 takes place via pipe 10. The discharge of the CH water thus heated takes place via pipe 11. It is also possible, however, to reverse the direction of flow in heat exchanger 9.

The spiral heat exchanger 9 is disposed in the upper end of the elongated, vertically disposed boiler 1.

The boiler 1 shown in Figure 2 comprises a flue gas housing 5, in which a burner 6 disposed in housing 5 is provided. Housing 5 is connected to a flue duct 7 which extends downwards from housing 5 through boiler 1 and which is connected outside the boiler 1, via connecting point 8, to a pipe 12 which is connected to a flue gas discharge channel (not shown). Present in boiler 1 is an amount of first liquid, in particular sanitary water. The supply of sanitary water to boiler 1 takes place via pipe 3, and the water exits boiler 1 at the upper side thereof via pipe 4. The first liquid is heated by means of the combustion gases that are released on combustion, which gases are led through flue duct 7 and which are subsequently discharged via pipe 12. In this embodiment boiler 1 is provided with a pipe 13 on the upper side, via which the already heated first water is supplied to a plate-shaped heat exchanger 17 disposed outside boiler 1. It is also possible, however, to connect pipe 4 to pipe 13, so that it is not necessary to provide a draining point on boiler 1. The discharge of sanitary water from heat exchanger 17 takes place via pipe 14, which pipe 14 is also connected to boiler 1. Thus circulation of sanitary water takes place via pipe 13, heat exchanger 17 and pipe 14. When it is decided not to discharge the first liquid directly via pipe 4 in the embodiment of Figure 2, a partial discharge of heated first liquid must take place outside the device via a draining point (not shown) at pipe 14. The heat exchanger 17 also comprises an inlet 15 for heating a medium (the second liquid), in particular so-called CH water.

Inside the heat exchanger 17, heat contained in the first liquid supplied via pipe 13 is transferred to the CH water that is supplied via inlet 15.

The heated CH water is discharged via pipe 16 while being heated in heat exchanger 17 in accordance with the counterflow principle. It is preferable to use a plate heat exchanger 17 in view of the fact that its heat transfer capacity is advantageous for the device and the use according to the invention.

Figure 3 schematically shows another preferred embodiment of boiler 1. In general, the device according to Figure 3 corresponds to the device which is shown in Figure 2, in particular as regards the use of the plate-shaped heat exchanger 17 which is disposed outside boiler 1. Present in boiler 1 is the first liquid, in particular sanitary water, which is supplied to boiler 1 at the bottom side thereof via pipe 3 and which subsequently exits the boiler 1 at the upper side thereof via pipe 4. The heating of the first liquid in boiler 1 takes place

through the use of a new flue gas housing 5. Said housing 5 extends upwards through the boiler from the bottom side thereof, wherein a flue duct 7 connected to housing 5 near the upper end of boiler 1 extends in downward direction and is connected to a pipe 12 at the bottom side of boiler 1, via connecting point 8, which pipe 12 is connected to a flue gas discharge channel (not shown). Disposed in the upper part of boiler 1 is a pipe 13, which supplies the heated first liquid that is present in boiler 1 to the heat exchanger 17. Under circumstances yet to be defined it is possible to connect pipe 4 to pipe 13, so that the use of a draining point on boiler 1 is not necessary. The discharge of the heated first liquid from heat exchanger 17 takes place via discharge pipe 14, which pipe 14 is connected to boiler 1. When a construction of this kind is used, circulation of the first liquid takes place via pipe 13, heat exchanger 17 and pipe 14 back into boiler 1. The heat exchanger 17 also comprises a supply pipe 15 and a discharge pipe 16 for the second liquid to be heated, preferably water which is used for central heating purposes. The special construction of the flue duct 7 enables an adequate heat transfer of the heat contained in the combustion gases to the first liquid to be heated, which liquid is subsequently used for heating another medium, namely the second liquid. The construction of flue duct 17 according to Figure 3 is special in that the duct springs from several places on the upper side of flue gas housing 5.

Figure 4 shows an embodiment of the device according to the invention which can be considered to be a variant of the device which is shown in Figure 3. The main difference between the embodiment which is shown in Figure 4 and that which is shown in Figure 3 is that the flue duct 7 of Figure 4 springs from only one place at the upper side of the flue gas housing 5, and that the flue duct 7 of Figure 4 has a larger diameter than that of Figure 3. This means also, however, that in Figure 4 fewer coils 7 of the flue duct are disposed round the flue gas housing 5 than in Figure 3. The embodiment according to Figure 4 is of simpler construction than that of Figure 3.

Using the above-described three special embodiments according to the invention as shown in Figures 2-4, it has become apparent that the energy efficiency of the device according to the invention is higher than that of the devices which are known from the prior art. This is due in particular to a combination of factors such as the fact that the first liquid (sanitary water or drinking water) is heated

directly by means of the flue gases, and that heat storage takes place in the first liquid. The burner 6 is of a type which enables a large modulation range, viz. between 8-40 kWatt or, put differently, a range of 1 to 5. Thus a high heating efficiency, viz. higher than 104% in comparison with the bottom value, is possible as well as a high yearly efficiency, viz. higher than 60%.

Moreover, the ratio between the maximum burner capacity and the boiler capacity is relatively high, which means that the ratio is higher than 0.20 kW/1. With the device according to the invention control can take place on the basis of the heat capacity of the boiler, which means that the control not only takes place on the basis of the temperatures prevailing in boiler 1, but that said temperatures are rel ated to imaginary volume parts of boiler 1, so that it is a matter of heat content or heat capacity. The heat capacity thus determined is compared with the heat capacity that is required at a particular point in time, and on the basis of this information an optimum control of the device according to the invention is set.