The invention relates to a heat exchanger intended for a central heating boiler, which heat exchanger is manufactured as a monocasting from substantially aluminum, the heat exchanger comprising a number of walls which bound on one side a water-carrying channel and on the other a burner space.
A central heating boiler comprising such heat exchanger is known from practice and is for instance marketed by applicant under the type indications W21c ECO and W28c ECO. The principle of the W21c ECO is shown in a brochure of applicant dated February 1996. The maximal output of the known boiler is 21 kW and 28 kW respectively. A particular advantage of the known boiler is that it is particularly compact. The built-in depth of the known boiler is for instance 350 mm. Another advantage of the heat exchanger of the known boiler is that it is designed as a monoblock casting, as a result of which the manufacture thereof is relatively simple.
The output of a central heating boiler is inter alia determined by the size of the burner that is used. In the known boiler, the burner, which is substantially of cylindrical design, is cantilevered at one end face thereof. When a greater output is required, the length of the burner could be increased. However, this leads to problems with regard to the one-sided suspension of the burner. Moreover, as a consequence hereof, the built-in depth of the central heating boiler becomes too great.
Another possibility for increasing the output of the known boiler is enlarging the diameter of the burner. Although this is in itself possible, the amount of flue gas to be discharged will then form a problem. The known boiler comprises a single flue gas draft. In this single flue gas draft the temperature of the flue gases must be reduced as far as possible, so that as much heat as possible is transferred from the flue gases to the water to be heated. In order to arrive at a proper heat transfer, pins increasing the heat-transferring surface extend in the flue gas draft. To enable the larger amount of flue gas to be discharged, the section of the flue gas draft would have to be enlarged. This means that for a proper heat transfer to be maintained, the pins increasing the heat-transferring surface would have to be of a longer design. However, this is not possible, because during the casting of the heat exchanger, the molten aluminum flowing into the cavities for forming the pins has already solidified before the end of the cavity is reached. Consequently, the further elongation of the pins is not possible due to problems in terms of casting technique. Due to the above-described problems, it is not possible to merely increase the diameter of the burner for increasing the output of the central heating boiler.
The object of the invention is to provide a heat exchanger intended for a central heating boiler having a greater output than the known central heating boiler, the intended heat exchanger being particularly compact and hence suitable for a central heating boiler which, like the known boiler, has a slight built-in depth.
To this end the heat exchanger according to the invention is manufactured as a monocasting from substantially aluminum, the heat exchanger comprising the features of claim 1.
The heat exchanger being manufactured as a monocasting, it can be manufactured in a relatively quick and efficient manner. The presence of more than one flue gas draft enables discharging a greater amount of flue gas, while the section of the flue gas drafts can remain small, so that relative to the flow-through section, a relatively large heat-transferring surface is nevertheless obtained. Due to the greater amount of flue gas that can be discharged, a larger burner having a greater output can be used. Outputs up to about 30 kW per flue gas draft are possible in the heat exchanger according to the invention. Because the heat exchanger according to the invention now involves parallel flue gas drafts, preferably located side by side, the slight built-in depth of the known central heating boiler can be maintained. Hence, with the heat exchanger according to the invention, a central heating boiler can be provided having a greater output than the known central heating boiler while the same degree of compactness is achieved, in particular with regard to the built-in depth. As the walls which bound the burner space and the flue gas drafts are water-cooled, an optimal heat-transfer to the water to be heated is obtained, while, moreover, the heat exchanger is cooled in an efficient manner, so that it nowhere becomes overheated. The one-piece core renders the manufacture of the core and the positioning of the core in the mold relatively simple, so that the manufacture of the heat exchanger is relatively simple as well and, accordingly, can take place in an economically favorable manner.
According to a further elaboration of the invention, intended for increasing the efficiency of a central heating boiler, comprising a heat exchanger according to the invention, each flue gas draft of the heat exchanger may comprise two opposite walls having pins extending substantially perpendicularly thereto, which pins enlarge the heat-transferring surface and extend into the relevant flue gas draft.
The invention also relates to a central heating boiler comprising a heat exchanger according to the invention. It is a matter of course that such central heating boiler has the advantages mentioned hereinabove in respect of the heat exchanger.
It should be noted that DE-A-34 27 957 discloses a central heating boiler comprising a heat exchanger, which heat exchanger seems to be designed as two castings which are manufactured separately and subsequently connected to each other. The known heat exchanger comprises a single flue gas draft. The problems of such a single flue gas draft are described above in relation to the W21c ECO and W28 c ECO devices. The walls of the known heat exchanger bound on one side a water-carrying channel and on the other a burner space and the said single flue gas draft.
Further elaborations of the invention are described in the subclaims and will hereinafter be specified on the basis of an exemplary embodiment, with reference to the accompanying drawings.
Fig. 1 shows an exemplary embodiment of the heat exchanger 1 according to the invention. As is clearly visible, the heat exchanger 1 is manufactured as a monocasting substantially from aluminum. The heat exchanger comprises a number of walls 2, 3, 4, which walls bound on one side a water-carrying channel 5 and on the other a burner space 6 and two parallel flue gas drafts 7, 8. The flue gas drafts 7, 8 extend from the burner space 6. The burner space 6 is intended for accommodating a burner. The walls 2, 3, 4 bounding the burner space 6 and the flue gas drafts 7, 8 are water-cooled in that the water-carrying channel 5 extends therealong. The water-carrying channel 5 is of such design that it is formed with a single, one-piece core 9, shown in Fig. 3. Each flue gas draft 7, 8 comprises two opposite walls 2, 3 having pins 10 extending substantially perpendicularly thereto, which pins enlarge the heat-exchanging surface and extend into the relevant flue gas draft 7, 8. The flow system of the water-carrying channel can be considered to be a series connection of a number of parallel channel parts. In explanation thereof, I refer to Fig. 3, which, it is true, shows the core by means of which the water-carrying channel is formed, but which can also be considered to be a representation of the water-carrying channel itself. Water coming from a central heating pipe system enters the heat exchanger adjacent its bottom side at the location of arrow R. From there, it continues its path in a feed-in part 5a of the water-carrying channel 5. Adjacent the rear of the heat exchanger 1, the channel 5a divides into two separate channel parts 5b, 5c. Such division is clearly shown in Fig. 2. Located in channel 5b is a partition 11 which forces the hot water to flow forwards again to subsequently rise again and flow back towards the rear again. From the rear, the water then flows in a common channel part 5d which separates the two flue gas drafts 7, 8 from each other. In the channel 5d, too, a partition 12 is located, which provides that the water first flows forwards and then upwards, to subsequently flow to the rear again, enabling the water to divide again from there and flow to two following separate subchannels 5b' and 5c'. This process repeats itself again, after which the water flows, via 5b''' and 5c''', into a common channel 5E, whence the water flows to the inlet A of the central heating pipe system. With such embodiment of the water-carrying channel 5, it is effected that all walls of the flue gas drafts and the burner space are water-cooled, so that an optimal efficiency is obtained and all parts of the heat exchanger remain sufficiently cooled. To effect an easy cleaning of the flue gas drafts and a proper accessibility of the burner space 6, this burner space 6 and the flue gas drafts 7, 8 are accessible from at least one side S. The side S is clearly indicated in Fig. 2. Fig. 2 also clearly shows that the water-carrying channel 5 has a substantially m-shaped section, viewed in a direction perpendicular to a horizontal cross-sectional plane II-II located at the level of the flue gas drafts 7, 8.
The heat exchanger may comprise three or more flue gas drafts, and instead of a cylindrical burner room 6, a burner space having a different shape may be used.