EXCHANGER

Field of the invention

This invention relates to a heat exchanger having both heat-exchanging and air-cleaning functions, said heat exchanger comprising a set of tubular casings which are accommodated in a housing and extend between inlets and outlets in outer boundary walls thereof and which are arranged each to receive at least one air filter of the type comprising an air-permeable tube whose one end is closed and whose opposite end is open to allow free passage of air, either in the form of air conducted into the filter tube through the open end and caused to pass through the tube wall from inside and outwards during filtration, e.g. particle separation, or in the form of air which is caused to pass through the tube wall from outside and inwards during filtration, e.g. gas separa- tion, the filter being mountable in the surrounding casing with an air gap formed between this and the filter tube. Background of the invention

WO91/03689 discloses a heat exchanger comprising a set of tubular casings, made of e.g. thin metal sheet, each accommodating at least one air filter of the above- mentioned type. For high-efficiency air filtering plants, it is in practice preferred to mount two filters in each casing, viz. a particle separating filter and a gas sepa¬ rating filter. The particle separating filter may consist of a tube composed of different layers of fibrous, macro- porous as well as microporous structure, and a plurality of movable strips are arranged inside the tube. Polluted air passes through this filter, for example air supplied to a building from outside, from inside and out through the tube wall during separation, of the solid particles of the air in the interior of the filter tube, in which they are retained by the strips. Also the gas separating filter

is tubular, but the tube wall is composed of two concen- trical, spaced-apart layers of air-permeable material, between which a layer of adsorbing and/or absorbing material is inserted, e.g. active carbon or porous granules, capable of collecting and retaining noxious gases, such as CO, N0„, SO,, etc. Air passes through this filter from outside and in through the tube wall. If bot a particle separating and a gas separating filter are mounted in each casing, they are arranged one after the other along the longitudinal axis of the casing, more precisely the particle separating filter is mounted adjacent the casing inlet and the gas separating filter connection with the casing outlet. The unfiltered, in mo cases comparatively cold outdoor air or supply air will taken in via the open inlet end of the particle separati filter, pass out through the filter tube wall during sep ration of its particle contents and, subsequently, be forced further through the cylindrical gap between the outside of the filter tube and the inside of the casing be caused in the next step to pass through the tube wall of the gas separating filter from outside and inwards, an finally be evacuated via the outlet of the gas separating filter, after removal of noxious, gaseous components. As the air passes through said gap, heat exchange occurs wit a gaseous medium flowing around the outside of the indivi dual casing. Such heat exchange can be either heating or cooling. In the heating case, the heat exchanging medium flowing around may advantageously be comparatively warm, consumed exhaust air which by heat transition via the casing heats the incoming, colder supply air, and in the other, cooling case, the medium may be comparatively cold possibly moist air which cools the incoming, warm supply air.

Although a heat exchanger of this type is advanta- geous in so far as it is capable of both cleaning air and exchanging heat in a single compact unit instead of in tw separate bulky units, the known construction has, however

3 appeared to have a heat-exchanging effect that did not reach the desired level. This is primarily caused by the fact that the rate of flow of the air passing the gap between the casing and the filter is uneven, seen along the longitudinal extension of the casing. More precisely the rate of flow is comparatively low at the inlet end o the particle separating filter and successively increase in the direction of the closed end of the filter, at the same time as the rate of flow in the gap is comparativel high in the vicinity of the closed end of the gas sepa¬ rating filter and is successively reduced to a very low level at the outlet end of this filter. This means that acceptable heat-exchanging effect is achieved only in th vicinity of the centre of the casing, whereas the effect in the area of the two casing ends is unsatisfactory. Objects of the invention

The object of the present invention is to obviate t above-mentioned drawback of the prior art heat exchanger and, in general, provide a higher degree of efficiency i the heat exchange between the respective media. Accordin to a first aspect of the invention, the object is to pro vide this improved degree of efficiency by taking specia steps within each casing. According to a second aspect, the invention aims at providing the improved degree of efficiency by taking special steps on the outside of the casing. According to a third aspect, the invention aims providing the improved degree of efficiency by further developing the actual filter within the casing. Accordin to all three aspects, the main object is, however, to provide an improved degree of efficiency, while main¬ taining at least the same high air-cleaning effect as in the prior art construction. Brief description of the inventive idea

According to the invention, the above-mentioned ob- jects are achieved by means of the heat exchanger stated in the accompanying claims 1-8 and by the air filter stated in claims 9 and 10.

Brief description of the accompanying drawings

In the drawings, Fig. 1 is a simplified perspective view of the funda¬ mental design of a heat exchanger according to WO91/03689 in a first embodiment (this figure corresponds to Fig. 1 in WO91/03689), Fig. 2 is an enlarged and simplified longitudinal view o an individual casing included in the heat ex¬ changer, according to an alternative, further developed embodiment (this figure corresponds to Fig. 5 in W091/03689), Fig. 3 is a longitudinal view corresponding to Fig. 2 bu seen from above, illustrating a heat exchanger designed according to the present invention, and Fig. 4 is an enlarged cross-sectional view of the indivi dual casing illustrated in Fig. 3. Brief description of the construction according to WO91/03689

In Fig. 1 illustrating a heat exchanger having a particle separating filter only, a filter housing general ly designated 1 is built in or included in a main tube 2 for supplying the supply air taken in from outside, to different rooms in a building. The supply air passes through the tube 2 in the direction of the arrows A. The housing 1 comprises two end walls 3, 4, two side walls 5, 6, a roof 7 and a bottom 8. In the front end wall 3 there are formed a plurality of holes 9 which serve as inlets for the incoming air and in which a number of particle separating filters generally designated 10 are mounted. These filters are in the form of tubes whose one end is closed by means of a bottom plate 11 and whose opposite end has an opening 12 forming an inlet of the filter, thereby allowing the supply air to flow from inside and out through the filter. A set of strips 13 are arranged i the cavity defined by the tube wall.

Reference is now also made to Fig. 2 which illus¬ trates a further developed embodiment in which not only number of particle separating filters 10 are arranged, b also a corresponding number of gas separating filters 10' As shown in this Figure, the filters are accommodated in pairs in a common casing 14 of a material which is imper meable or at least difficult for the air to permeate. Th casing is suitably cylindrical or, in some other manner, tubular and is of a greater diameter than the two filter 10, 10' such that a gap 15 of annular cross-section is formed between the filters and the casing. The casing extends between the two end walls 3, 4 of the housing 1, in which end walls openings 16 form inlets of the casing and openings 17 form outlets thereof. The individual gas separating filter 10' is composed of two concentrical layers 18, 19 of an air-permeable material, e.g. perfo¬ rated metal sheet of different diameters, between which layer 20 of a gas-adsorbing or gas-absorbing material is arranged. One end of the filter is closed by means of a bottom plate 21 and its opposite end is formed with an opening 22.

The. walls 3, 4, 5, 6 shown in Fig. 1 define, togeth with the roof 7, the bottom 8 and the casings 14, a pas¬ sage generally designated 23 through which e.g. exhaust air can pass in the direction of the arrows B. The exhau air is normally warmer than the supply air passing throu the casings 14, whereby the exhaust air will heat the supply air by heat exchange via the casings 14. As men¬ tioned by way of introduction, comparatively cold air ca be used instead of warm exhaust air as heat-exchanging medium for the purpose of cooling the incoming supply ai According to the embodiment shown in Fig. 2, the in coming supply air will first pass the particle separatin filters 10, more precisely from inside and out there- through, is then conducted further via the gap 15 to the gap separating filters 10' through which it passes from outside and inwards to be finally evacuated via the

openings 22 in these filters. The drawback of this embod ment is, as mentioned by way of introduction, that the rate of flow through the filter 10 will be low in the vicinity of the open end of the filter, and subsequently successively increases in the direction of the closed en 11. Analogously, the rate of flow is comparatively high the closed end 21 of the filter 10', whereupon it de¬ creases in the direction of the open end 22. This means that a maximum heat-exchanging effect is obtained only i the area midway between the end walls 3, 4, whereas the effect is fairly mediocre in the vicinity of the opposit ends of the housing 14. Detailed description of the inventive idea

Reference is now made to Figs 3 and 4 which illus- trate the present invention. As is apparent from these Figures, each of the filters 10, 10' is, when mounted in the heat exchanger, accommodated in jackets 24 and 25, respectively, of which the first-mentioned has an open e 24* and a closed end 24", and the latter also has an ope end 25' and a closed end 25". In this embodiment, the jackets 24, 25 are parts or sections of a single conti¬ nuous tube 26 which is common to the two filters and whos central area has a transverse partition 27 forming a closed end of the respective jacket. The diameter of the tube 26 is greater than the diameter of the filters 10, 10' and smaller than the diameter of the casing 14. Con¬ sequently, the tube 7 divides the gap 15 into two section or ducts, viz. an inner duct 15' in each of the jackets 24, 25, and an outer through duct 15". The tube 26 is slightly shorter than the casing 14 and mounted with its two opposite open ends at a certain distance inside the end walls 3, 4, thereby forming open passages 28, 29 between the ducts 15' and 15". In case the filters 10, 10 are of such a length that they extend with their closed ends up to the area adjacent the partition 27, the two jackets 24, 24' are slightly shorter than the actual filters. In practice, the tube 26 can be selected to have

7 a diameter adapted such that the cross-sectional area of the outer air duct 15" is essentially of the same size a that of the duct 15' between the tube and the respective filter. This means that the tube wall 26 will be posi- 5 tioned somewhat closer to the housing 14 than the outsid of each filter.

As shown in Fig. 4, the casing 14 is advantageously folded or wave-shaped in cross-section for the purpose o providing a casing surface which is enlarged as compared

10 with an entirely circular or cylindrical shape. In prac¬ tice, the casing can be made of an extruded material, su as aluminium or plastics. Also the jacket tube 26 can advantageously be made of extruded aluminium or plastics To keep the tube 26 in place in a centred position insid

15 the casing 14, the outside of the tube is formed with at least three spacers 30, 31, 32 which are suitably equi¬ distantly spaced from each other. Most suitably, these spacers are in the form of elongate ribs or rib-like members extending along the entire length of the tube 26

20 by being extruded together with the tube as such. The fr edges of the ribs are suitably formed with a rounded end 33.

Also the inside of the jacket tube 26 is formed wit spacers 34, 35, 36 which, like the external spacers, are

25 suitably three in number and are equidistantly spaced fr each other along the circumference of the jacket tube. A illustrated in Fig. 4, each of these spacers may compris a pair of beads 38, 39 which define a cavity 40 for re¬ ceiving fastening means, e.g. nail- or screw-like member

30 (not shown), by means of which the jacket tube 26 is fix in relation to annual flanges 41, 42 (see Fig. 3) which close the casing 14 and have holes for receiving the filters.

In the embodiment shown in Fig. 4, the filter 10 ha

35 an external wall of folded paper which at the closed end of the filter is connected, for example by gluing, with cup-shaped end closing wall corresponding to the end wal

11 in the prior art embodiment according to Fig. 1. This end closure is in the form of an essentially flat end wal which at its circumference passes into an annular flange encircling the end portion of the folded filter wall. In Fig. 4, this flange is indicated by the circle line 43. Owing to the presence of the internal spacers 34, 35, 36, the filter 10 will be centered at its closed inner end by the annual flange 43 of the end closure abutting the spacers. Simultaneously, the open end of the filter is centered in the central opening in the cover plate 41. Th gas separating filter 10' is centred and kept in position correspondingly.

The heat exchanger according to the invention func¬ tions as follows. The outdoor air, which in most cases is cold and polluted to a varying degree, which should pass the filters 10, 10' , is supplied via the open end of the particle separating filter 10 and passes through the filt from inside and outwards, as indicated by the arrows in Fig. 3. Having passed the filter, the air encounters the external jacket 24 which forces the air back in the direc tion of the open end of the filter and the passage 28. No until at this passage, the flow of air can again be de¬ flected back to its original direction of motion and from then on pass through the outer duct 15" up to the passage 29. At this passage, the air flow is again deflected through 180° and is forced into the internal duct 15' in the jacket 25 so as to finally pass through the gas sepa¬ rating filter 10' from outside and inwards and be evacuat via the open end 22 in this filter. According to the basi inventive idea, essentially all the air is thus forced to pass from the passage 28 positioned at one end of the casing to the passage 29 positioned at the opposite end, which means that heat exchange between the incoming suppl air and the heat-exchanging medium outside the casing 14, e.g. warm exhaust air from the building in question, will take place along the entire length of the casing, while accomplishing a maximally efficient heat transfer.

That stated above regarding the jacket tube 26 constitutes a first aspect of the invention, viz. in the form of an internal improvement of the heat-exchanging properties. According to a second aspect described below, the invention also aims at accomplishing an external im¬ provement of the heat-exchanging properties.

According to the embodiment disclosed in WO91/03689 (see Figs 1 and 2), the passage 23 for the transverse flo of exhaust air is laterally defined by the end walls 3, 4 only. The distance between these walls is comparatively great at the same time as the spaces between the individu housings are ample. This implies that the warm exhaust ai whose caloric content is to be transferred to the incomin cold supply air, will pass through the passage 23 at a fairly low velocity. In this manner, merely a limited portion of the caloric content of the air will be trans¬ ferred to the supply air.

To remedy this, the present invention provides for t arrangement of one or more partitions 44, 44' (see Fig. 3 in the passage 23, viz. in parallel with the end walls 3, and spaced therefrom and from each other. As a result, separate partial passages or ducts 45, 45', 45" will be formed inside the passage 23, through which partial ducts the exhaust air will be forced to pass so as to flow arou the casings two or more times, as indicated by the arrows in Fig. 3. While assuming that the filter housing contain two partitions, as indicated in Fig. 3, the warm exhaust air can thus be taken into a first partial duct 45, be deflected through 180° in the second partial duct 45' and subsequently once more be deflected through 180° before passing to the exhaust air outlet via the third partial duct 45".

Since the warm exhaust air is, in this manner, force to flow around the casings two or more times (however, around different sections thereof), the residence time of the exhaust air in the filter housing will be longer than according to the prior art embodiment, whereby the heat-

transferring effect will be further improved.

According to the embodiment shown in Figs 3 and 4, t invention is carried into effect by the mounting of a stationary jacket tube in each casing, each jacket 24, 25 being adapted to receive a standard-type filter. However, it is also possible to carry the inventive idea into effe by modifying the filter in question and, consequently, ob viate the need of mounting a particular jacket tube insid the casing. According to a third aspect, the invention th relates to a filter which, already when delivered or at least before mounting thereof, comprises a jacket mounted on the outside of the filter tube, the jacket length bein slightly smaller than the length of the filter tube, ther by forming a passage between one end of the jacket and th open end of the filter tube, said passage corresponding t the passages 28, 29 according to the embodiment shown in Fig. 3. Such a jacket mounted directly on the filter may either have a greater diameter than the filter tube or ev essentially the same diameter as the filter tube, viz. wh the outer wall of the filter tube consists of folded pape In the latter case, a cylindrical jacket may thus be mounted on the outside of the outer ridges of the folds, whereby individual return air ducts are formed between th jacket and the folds. Irrespective of the design, the jacket in question m advantageously be made of a material which is entirely impermeable to air, for example metal or plastics. Within the scope of the invention, this is, however, not absolut ly necessary since the desired effect can be achieved eve if the material of the jacket is slightly permeable to ai Thus, the only essential thing is that the material of th jacket is more difficult for air to permeate than the material of the respective filter. This means, for exampl that a jacket mounted directly on a filter can be made of inexpensive paper, provided that this paper is more diffi¬ cult for air to permeate than the paper material of the filter tube wall.

Possible modifications of the invention

Of course, the invention is not restricted merely to the embodiments described above. The invention thus is applicable also to such heat exchangers as contain a sing type of filter, e.g. a particle separating filter, only o filter being arranged in each casing instead of two, as illustrated in Fig. 3. In this context, it should also be mentioned that it is possible to mount in each casing two separate jackets for each filter, i.e. jackets that do no constitute sections of a common tube.