IE50936B1 - Fume scavenging hood with air supply - Google Patents

Abstract

1. Vapour extraction hood with an elongate suction chamber (8) with at least one air draw-off channel and at least one air supply channel (1) for the supply of air, whereby in the suction chamber (8) a recuperator is disposed, the heat exchange elements (tubes 13, exchange plates 13') of which consist of metal and whereby under the heat exchange elements (13, 13') there is provided at least one catching surface (17, 18) for dropping oil and grease impurities, characterized in that the tubes (13) or the exchange plates (13') of the heat exchanger extend between an air supply receiver chamber (11) and an air supply collecting chamber (14) and are capable of being flowed through by the air supply which is heatable in the heat exchange with the exhaust air.

Description

Price 90p This invention relates to a vapour extraction hood with an elongate suction chamber with at least one air extraction channel and at least one air supply channel for the supply air, wherein in the suction chamber a recuperator is dis5 posed, the heat exchange elements (tubes and exchange plates) of which consist of metal and wherein under the heat exchange elements there is provided at least one catching surface for dropping oil and grease impurities.

Vapour exhaust hoods such as these are particularly well known for large kitchens. They consist of an extended housing which is mounted over the range generating the vapour, etc. Over essentially the entire length of the hood there is a suction chamber, usually closed-off by a grid, to which at least one extract duct is connected at the top. A header is visualized above the suction chamber for supply air delivered from the surroundings via a special supply-air duct which normally has openings fitted with diffusors above the suction chamber. In this way, within an area essentially covering the range or similar vapour is extracted above the suction chamber and conveyed away, while supply air is delivered correspondingly, approximately parallel to the room ceiling, on the upper side of the hood. - 2 50936 With a freely suspended, symmetrically arranged vapour extraction hood above a free-standing range there is a flow of supply air on both sides of the hood, parallel to the ceiling, towards the sides of tie room, where it drops and passes into the suction flow, towards the middle suction chamber, so that on both sides of the freely suspended hood there are, to a certain extent flow patterns with horizontal axes within the Kitchen, which ensure a satisfactory collection of the vapour generated and its transfer into the suction chamber. The same flow ensues when the hood is located on a side wall, but the symmetry does not exist, there is only one flow pattern.

There are no problems when the outside air temperature is appropriately hign, because then the supply air flows into the room or, for example, the large kitchen at a temperature at least corresponding to that of the spice. However, in regions with definitely cold seasons the case in frequently experienced where very cola supply air is drawn in so that having regard to the relatively large quantities of air being circulated a rapid and unpleasant cooling of the space results, for this reason it is Known to preneat the supply air by means of preheater supplied with heat from an external source of energy and located at a suitable point in supply duct, towards the hood. The preheater must be dimensioned so that even on the expected extremely cold days sufficient energy is available to ensure that the supply air is heated to a prescribed minimum temperature. This requires, particularly in regions experiencing severe spells of cold weather, an adequately dimensioned preheater, with associated high installation costs. In addition to this, the preheater also operates when the supply air is only moderately cold, with correspondingly lower efficiency, below its rated output and with a relatively high specific energy consumption, while on extremely cold -3days the energy consumption is correspondingly great owing to heavy preheat requirement.

Since, at the same time, the air extracted is thrown away at a comparably high temperature, the thought is encouraged to try to recover at least part of the preheat energy by heat exchange with the extract air. To this end the supplyand extract-air ducts can be run together in close proximity, so as to meet in a conventional platten heat exchanger or similar, in which the warm extract air and the cool supply air are separated from each other by the plates. It has, however, been demonstrated that because of the fat and oil particles carried along with the extract air a heat exchange such as this gets very quickly dirty so that the exchange of heat and particularly the flow of air are lastingly hindered. Fouling of this kind is, moreover, difficult to eradicate, because supply and extract ducts are usually mounted behind false ceilings, so that access to the heat exchanger is frequently only gained by considerable effort.

In addition, as a rule the required cleaning calls for skilled people from the contractor, it cannot be undertaken by the kitchen staff without difficulty, because dismantling and reerection has to be carried out by skilled people.

The purpose of the invention is to make use of the heat energy in the extract air for preheating, particularly the supply air, without service by skilled personnel being necessary at disturbingly short intervals.

The invention accordingly provides a vapour extraction hood with an elongate suction chamber with at least one air extraction channel and at least one air supply channel for the supply of air, wherein in the suction chamber a recuperator is disposed, the heat exchange elements (tubes and exchange plates) of which consist of metal and wherein under the heat exchange elements there is provided at least one catching surface for dropping oil and grease impurities, characterized in that the tubes or the exchange plates of the heat exchanger extend between an air supply receiver chamber and an air supply collecting chamber and are capable - 4 50936 of being flowed through by the air supply which is heatable in the heat exchange with the exhaust air.

With that, a heat exchanger in the form of a recuperator will first be located directly in the sucticn chanfcer of the hood, that is, in an area where the extract air is still hot and therefore the fat and oil particles carried with the extract air are in liquid form. In this way the hardening of fat deposits, etc. in the region of the heat exchanger is avoided so, too, is the disadvantageous Influence on heat transfer and air flow. Moreover, such carbohydrate impurities in liquid form are either drawn through the recuperator with the extract air, or can drip-off the heat-exchanger elements. With this arrangement the recuperator calls neither for additional space nor far fundamental dimension changes to the vapour extract tood, because in the sucticn chanter of custcnery hoods there is space available in any case, which can be utilized for the installation of heat-exchange elements of the recuperator. Ctoing to the location of the heat exchanger elements between a supply-air receiving chamber in the vicinity of erne end of the extended hood and a supply-air collecting chanter in the vicinity of the other end, the supply air is conveyed along a carparitively long route in the path of the hot extract air, so that intensive exchange of heat and lasting preheating can be achieved.

Preferably the heat exchange elements are rectilinear txtes, having for 2 preference a cross-secticnal surface of at least 10cm each. Preferably the tubes are of round cross-secticn, and they are preferably fabricated fran copper or aluminium. ftn application of tubes as heat exchange elements according to claims 2 to 5 also produces pronounced turbulence of the hot extract air and thereby a good transfer of heat, ftn application in particular of Tauscher plat ten, according to claims 6 to 10, arranged vertically, parallel to each other, produces, conversely, a reduction in the turbulence losses in the flow, but, in spite of this, good heat transfer through the large heat-exchange surface and in many applications therefore is to be pxefered to a recuperator having a nest of tubes. By conveying water in seme of the tubes or in tubes in pockets within the Tauscher platten it is possible in every case, with or without simultaneous preheating of the supply air, to recover sane of the heat frcm the extract air in the farm of warm water which can be heated directly, while flowing through, depending upon the tapping, or via an inter- 5 -mediate storage vessel.

Further details, characteristics and advantages are provided by the following description of arrangements, with the aid of the drawing.

Fig. 1 Section, schematically simplified, through a vapour exhaust hood according to the invention, on lines 1-1, Fig.2, Fig, 2 a section on lines 11-11 Fig. 1, Fig. 3 a different arrangement, corresponding to the representation in Fig. 1, of a vapour exhaust hood according to the invention, on lines ill-III, Fig. h, Fig. 4 a section on lines IV—IV, Fig. 3 and Fig, 5 an enlargement of detail V encircled in Fig. 3. fhe vipour exhaust hood has a supply air duct 1 leading from the surroundings and, in the case of the example, two extract ducts 2 leading to the surroundings and in tne region of rhe extract ducts 2, not shown on the drawing, there is an extract fan, arranged in the recognizee manner, which maintains the flow of air for tne supply air and the extract air; this flow is indicated in the first case with arrows 3 and in the latter with arrow3 4. The actual vapour exhaust hood has a housing 5 which is suspended from a kitchen ceilint in a manner which is not detailed in the case of the present example. The housing p is subdivided in the actually well-known manner, into an upper header 6 for supply nir which flows into the inner space through discharge openingsYfitted with diffusors in an appro30 priate manner, and 8 a suction Chamber, which is also closed ty grilles, for example, of expanded metal. -b50936 In accordance •ith the arro-..s shown 4 the air is drawn from the interior of a room, move i ringe or similar piece oi equipment, UiiOugh grid 9 into the suction chamber a and is conveyed away through the extract air . duct. Between the suction chamber 8 and the supply-air header b there is a partition 10 to which the extract air ducts 2 are attached; these, sealed, pass through the flattened header 6 adjoining header 10.

As will be seen particularly from Fig, 2, the supply . air, in accordance with arrows 3 is next delivered from supply-air duct 1 via a lateral section of distribution neater b into a supply-air receiving space 11 on whose sidewall 12 next to the suction space 8 a large number of tubes 13 enter; the supply air, in accordance with 1>. arrow 5, enters these tubes from the supply-air receiving space 11. Sealed, with the supply air inside them, the tubes 13 traverse the length of suction chamber 8 and on the side opposite this suction cha ber 8 the air is delivered from the tubes 1i into the supply air collecting chamber 14 whose sidewall 15, next to the tubes 13, matches sidewall 12 with openings for tubes 13. From the supply air collecting chamber 14 the supply air Is deliver-d via an after heater 16, whose function will be explained in more detail later, to the header . 6, on the side opposite supply air duct 1 and from there is delivered laterally, approximately parallel to the ceiling, via diffusors 7, as shown particularly in Fig, 1.

The hot extract air drawn from the room and through grid 9 thus passes over the bundle of tubes 13 at right angles to the direction of the axes of the individual tubes 13; in the case of the example these axes are parallel to each other ano. straight. 50836 In the example the tubes have a circular cross section which offers minimal resistance to flow to the extract air flowing in the direction of arrows 4. In the interests of heat transfer the walls of tubes 13 are as thin as possible; they can, if necessary, be supported additionally from sidewalls 12 and 13 in order to prevent bending. These supports are not dedailed. Ihe heat transfer is particularly good if the tube walls are of copper or aluminium. To achieve a not too high resistance to flow a comparatively small number of individual tubes 13 is visualized; for eximple, approximately 10 to 30 tubes 13 on each side of the symmetrical plane as shown in Fig. 1, section lines II-J.I; the tubes must have a cross sectional area of at least 10 cr/ in order to convey the required qumtity of supply air from the supplyair receiving space 11 to the supply air collecting room 1a, It is specially important that the tube 13 spacing is J not too small, the spacing should not be less than approximately 5 cm. On the one hand, this spacing is important because of the resistance to flow, since a small number of larger tubes, with a distinct space between each presents far less resistance to flow to the extract air flowing at right angles to the tube bundle than a closely packed bundle of smaller tubes having the same total cross-sectional area, particularly however, 0 ing to the tube spacing, unlike the arrangement shown in Fig. 1, the tubes cm -also be alternately displaced vertically with respect to each other providing the possibility for the liquid fat and oil particles settling on pipes 13 to run off. The total tube bundle in the hot extract air stream acts in fact, to a cert tin extent, also as a filter because the liquid fit or oil particles contained in the stream of extrace sir are centrifuged out and deposited onto the tubes 1 by local, small turbulences; they drip off with appropriate agglomeration. If in spite of this larger impurities still remain, possibly as a result -850936 of curried-over and gradually agglomerating hard substances, the tubes 13 can be cleaned by the kitchen staff relatively easily because, owing to the relatively large spaces a large proportion of the tube surfaces remain readily accessible. Nevertheless, particularly with the method illustrated in Fig. 1, the tube 1j5 arrangement is such that essentially the entire cross section of the extract air stream is encompassed, so that regardless of the position of the stream cross section, the extract air must flow over a multiplicity of tubes 13· To catch the oil or liquid fat dripping from the tubes 13, trays 17 are visualized on both sides of the tube bundle and one in the middle 18 formed directly from the wail of housing 5. Together, these ensure that oil or fat cannot drip down from housing 5. The side trays 17 in the form of guide plates within suction space 8 guide the liquid impurities towards the centre and cooling down is avoided because the plates which form the trays are also located in the hot extract air stream. In the middle area of the central tray 18 there can be a further conveyance to a collection vessel if the gutter-shaped arrangement of tray 18 is not adequate. This additional collection vessel is not illustrated.

At relatively high supply-air temperature preheating by the tube heat exchanger is not only unnecessary, it is undesirable if the room temper ture is not to be unduly increased. For this event a control element has been visualized which in the example takes the form of .1 swivel damper 19, located between supply—air duct 1 and the supply-air receiving space 11. In the position illustrated in Fig. 2 this swivel damper covers the neighbouring opening 20 of header duct 6, -950936 however, in a position 90° to the left with respect to fig. 2, the opening 21 of the supply-air receiving space 11, is covered. In this position, with opening 21 covered, the entry of supply 11 is prevented; j instead, iccording to arrow 3 shown dotted, the supply lir enters directly from the side of supply-air duct 1 into header duct fa and from there is discharged through the outlets, without preheating. The position of swivel damper 19, which could also be adjusted by hand according to the resulting temperature, is adjustable by meins of a schematically indicated servo motor as, for example, in electric motor, which is controlled according to the temperature. For this purpose a temperature sensor 2' is located in the supely-air stream, according to arrows 3, behind the supply-air collecting chamber 14, where it measures the supplylir temperature after passing through the tube heat exchanger ana, in the case of the example, the after heater 1b. With a thermostatic circuit not shown a maximum temperature can be selected up to which the swivel damper 19 is held in tr.e position according to Fig. 2, therefore preheating of the entire supplyair qurntity takes pi ice. Above this maximum temperature of, for example, 17°C a control command is given to the setting motor 22 to readjust the swivel damper 19, in an infinitely variable manner or in small steps, in such ι wiy that some of the supply air is diverted from supp.y-jir duct 1, according to dotted arrow 3, directly into header duct fa, while another part con10 tinues to flow through the tubes. If by this operation no adequate lowering of the temperature below the maxi..1 a. t;:..per iture of 17°C is achieved, damper 19 gnduilly closes opening 21 of the supply-air receiving .'.nice 11 completely, so that the entire supply-;ir quantity is aisenarged straight into the room through discharge opening 7, from header duct fa, -.ithout prehe iting. -1050936 In the example, in addition to terperature sensor 23 a further tempera l ure sensor 24 is visualized which also measures the temperature of the supply air in the stream, behind the after heater 16, and is connected to another thermostatic control device which is not shown in greater detail. Naturally, if the control circuit were appropriately adapted, sensors 23 and 24 could also be combined in a single sensor, since it only depends upon the control, via the control cir1 i cuitry, of the once-measured circuit. In the case of the example, in the control circuit which backs up the temperature sensor the minimum temperature is preset, for example, at 1b°C and no external energy is supplied to the after heater 16 until the temperature i'·11s below this value, in the example after heater 1b is supplied with hot water from pipe connections 2>, of course it would be possible to visualize an electrically heated after heater. If the temperature of the supply air still falls below the temperature set at temperature sensor 2n, in spite oi. tne enforced preheating of the total supply-air quantity in the tubes 13, brought about by the swivel setting controlled by temperature sensor 23, then supplementary heat is admitted to after heater 1b, until the supply air has been heated up to the selected minimum temperature or until the entire energy available per time unit in the after heater 1b has been released. In this way apart from extreme exceptions, a constant supply-air temperature of, for example, 17°C is achieved automatically at all times at the discharge openings 7. With this arrangement, a required heating of the supply air first takes place in tne tube heat exchanger and for this purpose toe neat energy of the exhaust air is used. Preheating in after heater 16, by means of an external energy source, only takes place when this heat energy is not longer adequate to achieve the desired temperature. It is, of course, possible for the minimum temperature selected at temperature sensor 24 to be below the maximum temperature also for an extended period in order to delay the use of external energy as long as possible and only to release this if the supply-air temperature drops below an acceptable level, in spite of preheating in the tubes 13.

Fig. 3 to i show a modified arrangement of the invention which is sometimes preferred because the tubes 13 emnloyed as hnat exchange elements as shown in Fig. 1 and 2 ire repiiced by heat exchange plates 13' which, as will be immediately seen by comparing Fig. 1 and 3, are arranged in rows so that slits 13d are formed on both side of the plates through which the extract air cm ris- in quiet laminar flow. In this way a considerable reduction in the turbulence is achieved and ilso tre resistance to flow, as a result of the recuperitor io med from exchange plites. With the plates 13' constructed fro correspondingly thin-wall material irid p : rticul irly bearing in mind tue increased exchange surf-ce on bofn sides of the slits 13Λ there is very good h it tr ins''·τ so that, excellent heat recovery can .iso tike pi ice. The use of V2a steel enables nli tea 1'-'' ta be m in if actured with extremely thin silent met il w lLls, ns Fi~. j shows, two m^til sheets 131 and 132 can he used ,,ere, identically shaped, each with i fold 133 at one am md arranged for insertion 134 at the other; the ends or edges in the area of fold 133 or insertion 134 ire fol With mis method a ;late 13' is produced with the simplest possible min.if icturing method. -1250936 In the rise oi the example a heat exchange tube 135 is ins· rted it both ends of exchange plate 13'; water can be warmed in these with heat from the exhaust air.

A food transfer of heat is achieved when copper is us'-d for the manufacture of heat exchange tubes 135, uioreov· r, the circumference of heat exchan e tube 135 is selected so that it rests snugly in the bend n"'ir both of plate 15'. In addition, the sheets 131 and 132 can be crimped on both sides at the inner side of heat exchange tube 173, this treatment not only secures the heat exchange tubes 155 against movement towards each other, but also reduces ti.eir area of contact with the cold supply air inside the exchange plate 13' mu, conversely, increases the heat transfer from the hot extract air. It would, of course, also be possible, j articularly in the centre are: of the recuperator with comparatively wide e/change plates 13' to provide a larger number of heat exchange tubes 135 for warming water, and also with the arrangement shown in Fig. 1 and 2 some of the tubes 13 shown there can be connected to water as required to provide process or domestic hot water.

As Fig. 4 shows in scheraaticdlly simplified form it is possible to visualize on one side of the vapour exhaust hood flow 26 and return 27 connections for water in the heat exchange tubes 133, with suitable headers 28 and 29 arr i.·.· d in such a way at both ends of exchanger plates 13' that, in accordance -ith the arrangement drawn, the cold . iter is delivered to the heat exchange tubes 135 vii flow 26 and a receiving header 281, flowing through and receiving preheat, the water is deflected by the collector which acts as a header 29, on the opposite side, into the lo.er tubes 135 and there is led back into a aischirge collector 282 which is located on the same side as the receiving header 281 and from where discharge vii dr lin 27 tikes place. The drain can either lead direct to .. capping, so that heating of the Water takes slice according to the tapping, as a con-1350936 tinuous he iter, or then, with the water circulating continuously between return 27 and flow 26, an intermediate storage vessel is connected, from which warmed water with little temperature fluctuation can be tapped. p It is of considerable importance that the water can be heated in every case, regardless of preheating the supply air because, in fact, heating is increased if at high outdoor temperatures the supply air does not flow through the exchanger plates 13'. In this way part utilization of the heat in the warm extract air is achieved in every case. With the arrangement according to Fig. 1 and 2 it is also possible, depending on local climitic conditions, to consider the possibilities for mounting collectors 28 mu 29 in the neighbourhood of sidewalls 12 and 1> and, for instance, during the summer · months, with a once-only changeover, fundamentally to employ the entire exhaust air quantity as a massive heat-.-r for water, with water flowing through the tubes 13 instead ol supply air.

Fig. h, again scnematicaliy simplified, visualizes a mouiiied irran _om‘'nt for controlling the supply air, either througn the recuperator or directly into hinder duct b. Here two swivel dumpers 19' and 19 ue dinned, these are actuated parillel to each other by linkage 22' and in the case of the example are pivoted centrally in such a way that when damper 19' □' ••ns the ot .er 19 closes -and vice versa. In this way the control is technically simpler, because the distribution of the supply air to the header duct 6 on the one hind and to the supply air receiving spice 11 on the oth’r is essentially proportional to the adjusting path and in xhe manner shown the two rigidly connected swivel aimpeps 191 and 19 in their final positions alternately almost completely close or completely open the appropri ate openings 20 and 21.

Claims (22)

1. Vapour extraction hood with an elongate suction chamber with at least one air extraction channel and at least one air supply channel for the supply of air, wherein in the suction chamber a recuperator is disposed, the heat exchange elements (tubes and exchange plates) of which consist of metal and wherein under the heat exchange elements there is provided at least one catching surface for dropping oil and grease impurities, characterized in that the tubes or the exchange plates of the heat exchanger extend between an air supply receiver chamber and an air supply collecting chamber and are capable of being flowed through by the air supply which is heatable In the heat exchange with the exhaust air.

2. Vapour extraction hood according to claim 1, characterized in that the heat exchange elements are rectilinear tubes.

3. Vapour extraction hood according to claim 2, characterized in that the tubes have a cross-sectional surface of at least 10cm each.

4. Vapour extraction hood according to claim 2 or 3, characterized in that the tubes are of round cross-section.

5. Vapour extraction hood according to one of claims 2 to 4, characterized in that the tubes consist of copper or aluminium.

6. Vapour extraction hood according to claim 1, characterized in that the heat exchange elements are formed as exchange plates bounding flow slots between one another and standing vertically parallel to one another.

7. Vapour extraction hood according to claim 6, characterized in that the walls of the exchange plates consist of V2A steel-plate and that two identical sheet metal plates are connected to one another in opposite arrangement by edge folds. - 15 50936

8. Vapour extraction hood according to claim 6 or 7, characterized in that there are provided in the upper and lower end areas of the exchanger plates heat exchanger tubes for the passage of water to be heated. 5

9. Vapour extraction hood according to claim 8, characterized in that the heat exchanger tubes are surrounded by grooves over a large portion of their peripheral surface close to the wall of the exchange plate.

10. Vapour extraction hood according to claim 8 or 9, 10 characterized in that the heat exchange tubes consist of copper.

11. Vapour extraction hood according to one of claims 6 to 10, characterized in that each exchange plate extends in the area of its arrangement substantially over the whole 15 height of the recuperator.

12. Vapour extraction hood according to one of claims 1 to 11, characterized in that the heat exchange elements have a mutual distance apart of several centimeters, preferably at least 5 cm. 20

13. Vapour extraction hood according to one of claims 1 to 12, characterized in that the heat exchange elements occupy, distributed approximately uniformly, the cross-section of the exhaust air flow.

14. Vapour extraction hood according to one of the claims 25 I to 13, characterized in that at least a few of the heat exchange elements (tubes and heat exchange tubes) are connected to a feed and discharge for water.

15. Vapour extraction hood according to one of the claims 1 to 14, characterized in that there is provided between the 30 air supply channel and the air supply receiver chamber a flow control member (swivel valve or valves or rods) which controls the distribution of the air - 16 50936 supply flow to the recuperator and (by by-passing the recuperator) directly into a distributor channel to the blower apertures.

16. Vapour extraction hood according to claim 15, characterized in that the flow control member has at least one swivel valve which in one position covers at least approximately completely the cross-section of the mouth of the air supply receiver chamber and in the other position covers the cross-section of the mouth of the distributor channel.

17. Vapour extraction hood according to claim 15 or 16, character ized in that the control position of the flow control member (swivel valve or valves or rods) is adjustable by means of (in particular) an electric adjusting motor.

18. Vapour extraction hood according to claim 17, characterized in that the adjusting motor is controllable thermostatically by means of a temperature sensor disposed in the air supply flow behind the recuperator which temperature sensor produces, above a pre-adjustable maximum temperature of the heated air supply, a control signal for the increasing diversion of the air supply in the distributor channel.

19. Vapour extraction hood according to one of the claims 1 to 18, characterized in that an extraneous energy fed reheater is provided in the air supply flow behind the air supply collecting chamber.

20. Vapour extraction hood according to claim 19, characterized in that for the control of the energy supply to the reheater a temperature sensor, disposed in the air supply flow behind the reheater is provided which temperature sensor below a pre-adjustable minimum temperature produces a control signal for increasing the energy supply to the reheater. - 17 50936

21. Vapour extraction hood according to claims 18 and 20, characterized in that the maximum temperature for the control of the flow control member (swivel valve or valves or rods) is at least slightly higher than the minimum 5 temperature for the control of the energy supply to the reheater.

22. A vapour extraction hood substantially as herein described with reference to and as illustrated in the accompanying drawings.