A method of and an equipment for providing ventilation in a processing space

Abstract: A method of providing ventilation for a processing space (1) with an access opening (3) from the surroundings, the space being separated from the surroundings by blowing treated supply air (A) into it to form an air curtain (5) at the opening in order to prevent the entrance of surrounding air. To enable an efficient separation of the space even with a great temperature difference between the supply air and the surrounding air, the supply air is blown to form a free circulation flow (A') in the space. The direction of the circulation flow at the opening is opposite to the direction of convection flows (B) of surrounding air created by the temperature difference, and the flow rate at the opening is greater than that of the convection flows. In an equipment for realizing the method, devices (6, 7) for introducing supply air are mounted to create a free circulation flow (A') in the processing space (1), forming an air curtain at the opening.

Description: This invention relates to a method of and an equipment for providing ventilation for a production line or other similar processing space which is separated from the surroundings and into which an access opening positioned above the floor level leads from the surroundings, wherein the processing space is separated from the surroundings by blowing treated supply air into the processing space so that an air curtain preventing the entrance of surrounding air is formed in the area of the open access opening of the processing space. Special requirements are set on the temperature, purity or other properties of air in the food industry, electronics industry, etc. In the food industry, for example, a product should be handled below 10°C to ensure its preservation and for hygienic reasons in general. This requires extremely high cooling powers and causes health hazards to the workers. In the electronics industry, work stages that require high purity are performed in processing spaces, so-called laminar cabinets, separated from the rest of the factory space. The worker stays outside the cabinet and the workpiece is in the cabinet, which is open at the front and into which air filtered to a very high degree of purity is introduced usually through its ceiling. The work can thus be performed in extremely pure conditions without having to filter the air in the entire factory space to such a high degree of purity. In the small cabinet, the air change rate can be kept on a very high level with reasonable costs, usually at several hundreds of times per hour, and so the flow conditions are easy to control if the purity of air is the only requirement. German Offenlegungsschrift 2 030 565 discloses a system for controlling the purity of air in laminar cabinets used widely in clean room techniques. The laminar cabinet comprises two zones, one with a vertical flow of air and the other with a horizontal flow of air. One aims at keeping the flow laminar, so that even a minor temperature difference between the cabinet and the surrounding air destroys the flow field completely. Laminar cabinets thus operate appropriately only when the temperature of the supply air and also that of the cabinet is equal to the temperature of air surrounding the cabinet. If the temperature of the supply air and that of the surrounding air differ from each other, convection flows occur due to the density differences of the air and totally change the flows within and around the cabinet. The flow in the laminar cabinet changes substantially even when the supply air of the cabinet is only 2 to 3 degrees colder than the surroundings. The supply air, which is thus heavier than the surrounding air, "drops" to the bottom of the cabinet and flows therefrom over the open front edge and drops further to the floor level, where it causes so-called floor draught. At the same time, warmer room air flows into the cabinet at the upper edge of the access opening, and mixes with the supply air and deteriorates its purity, being less thoroughly filtered. If the temperature of the cabinet is higher than that of the surroundings, the direction of flow is the opposite, that is, into the cabinet from below and out of the cabinet at the top. Laminar cabinets are unsuitable for air having a temperature clearly above or below the surrounding air temperature. It is also previously known to separate the processing space from the surroundings by providing an air curtain in the access opening. German Offenlegungsschrift 2 245 265 suggests that the air jet providing the air curtain should be divided between two nozzles, which can be directed. Due to induction, the jets, however, join rapidly, whereafter the two jets are no longer of any use. In place of several expected small induction flow turbulences, one large turbulence is created on both sides of the jet. Due to the temperature differences, the air tends to flow outward from the upper portion of the door and inward from its lower portion, so that the system, in fact, increases the influence of convection flows instead of decreasing it. German Offenlegungsschrift 2 359 218 also relates to air curtain blowing. Also in this arrangement the blow strengthens the convection flows. The air in the jet mixes with the outdoor air and is thus colder than the room air, and so it cannot possibly start rising upward under the influence of a mere recess. The cold air flows along the floor into the entire room space, and the warm room air flows out along the ceiling. The described nozzle blowing technique strengthens the convection flow of the warm air. To be able to control the system, the floor grate should be heated or a strong blow should be directed upward from its inner edge so as to enable the formation of the desired flow field. European Patent Application 0 139 128 describes a laminar cabinet, which, however, does not comprise two zones but an air curtain in which the air is blown downward or sideward in parallel with the laminar flow. The basic idea is that instead of the air circulating in the cabinet and possibly containing poisonous gases, the surrounding air containing no such gases is used in the air jet. In this way, the escape of the gases is prevented. The purpose of the laminar flow in the cabinet in this case as well as in laminar cabinets in general is to keep the particles of the surrounding air away from the cabinet. Thus no circulation flow is created, and one attempts to avoid its creation. Finnish Patent Specification 80778 describes a flow field created in a free space by an air jet technique. In an attempt to avoid circulation flows, the air is blown at an angle of 90° from nozzles positioned in two rows. One does not attempt to affect the convection flows. The object is an even, downwardly directed "air bed", in which mixing with the surrounding air is insignificant. Depending on the temperature and flow rate ratios, an air flow blown downward drops if the air in the flow is clearly colder than the air contained in the large room space. If it is clearly warmer, the flow remains on the ceiling level, turns 90° on reaching the wall of the room space and passes further along the ceiling in the direction of the room. If the temperature of the air flow is substantially equal to that of the air contained in the room space, the flow is divided into two branches, turns 90° in the horizontal plane already before reaching the wall of the room space and simultaneously turns 90° in the vertical plane. The end result is that the air flow passes downward at the corners of the air supply means. The air distribution device has no noticeable effect on the thermal flows in the large room space. German Offenlegungsschrifts 2 305 101 and 2 359 218 describe methods of providing air curtains in large access openings, such as door openings on the floor level in large production spaces and other similar room spaces to prevent the escape of warm room air. In these methods the air is blown outward from the room space and the blowing and the circulation flow are parallel with the convection flows. DE-B-1 120 104 discloses the separation of a processing space from the surroundings by means of an air curtain which is formed between a blow duct and a suction duct. The air curtain entrains some of the air in the processing space, thus driving a recirculating flow within the space, but also extracting air from the space and lowering the pressure therein. Thus supply air is sucked rather than blown into the space The object of the present invention is to provide a method which avoids the above-mentioned disadvantages and enables a processing space to be separated efficiently by means of an air curtain even when the temperature difference between the supply air and the surroundings is as great as 10° and even more. This object is achieved by means of a method according to claim 1, and equipment according to claim 5. The method according to the invention enables cooled and heated areas to be separated from a large production space, a room or other such space in accordance with the requirements of the production process. As the entire production space need not be cooled or heated to a temperature required for a specific work stage, the demand of cooling or heating energy decreases and the investments required for producing the energy are decisively reduced. If required, air within the cooled or heated area can also be kept extremely clean without filtering the entire air flow required for air-conditioning the production space. In addition, air impurities possibly formed in the production space are not able to enter the production line. The product hygiene can thus be decisively improved with low costs. The system also eliminates the health hazards of the workers and the working conditions are considerably improved, which improves the productivity of work considerably. The basic idea of the invention is simple. Processing spaces which are colder or warmer than normal are separated as efficiently as possible from the rest of the production space by means of light-structure walls or curtains, which as such is known in the prior art. It is, however, necessary for the work that at least one of the walls is left open or at least provided with large openings, through which the air colder or warmer than the surroundings would escape as a convection flow from within the cabinet if nothing else would be done. Convection flows and leakages of cold/warm air caused by such flows are prevented by creating a circulation flow in the separated processing space, the direction of which is against the convection flows and the flow rate is greater than that of the convection flows. The flow is obtained by shaping the separated space so that a circulation flow is able to develop efficiently and by blowing the supply air into the space through a narrow continuous nozzle having the same width as the opening or wall or through small nozzles or openings positioned close to each other in one or more rows, so that a circulation flow is achieved. The invention also relates to an equipment according to claim 5 for applying the method described above. In the following the invention will be described in more detail with reference to the attached drawings, in which Figure 1 a schematic vertical sectional view of a processing space in which an air flow arrangement known in the prior art is applied; Figure 2 is a schematic view of a processing space in which ventilation according to one embodiment of the method according to the invention is applied; Figures 3 to 5 are similar views of a processing space in which ventilation is provided according to alternative embodiments of the invention; and Figures 3A and 3B are enlarged views of details of the structure shown in Figure 3. Figure 1 illustrates a known ventilation arrangement. A processing space 1 is surrounded by a cabinet 2 having an access opening 3 on one side. Cooled supply air A is blown through nozzles 4 provided at the ceiling of the cabinet in order to form an air curtain 5 within the area of the opening. A desired flow of the supply air at the opening of the processing space is shown by arrows A'' drawn by broken lines. However, surrounding warmer room air flows into the cabinet at the upper edge of the opening as convection flows B, and mixes with the supply air, the flow of which is shown by arrows A' drawn by solid lines. This air flows along the bottom of the cabinet and over the open front edge and further down to the floor level. The known arrangements usually comprise a perforated top plate or a filter cell or some other similar planar air distribution device, through which air flows at a low rate so as to obtain a laminar flow. The object is to achieve an even, slow flow over the entire cross-sectional area of the opening. The air flow rate is low, e.g. 0.05 to 0.4 m/s. In the arrangement shown in Figure 2, a supply duct 6 is provided adjacent to a lower edge 2a of the opening 3 of the cabinet. The duct 6 is provided with nozzles 7 directed in parallel with a bottom 2b of the cabinet. Cooled supply air A is blown into the processing space through the nozzles at a high rate. A supply air flow A' passes from below via a back wall 2c of the cabinet up to a ceiling 2d and along it to a front wall 2e and further downward across the opening of the cabinet as a natural flow (cold air flows downward). The initial flow rate of the supply air is so high that the circulation flow described above remains in the cabinet, and no warmer room air enters the cabinet as a convection flow B at the upper edge of the opening, unlike in Figure 1. This requires that the flow rate of the circulation flow is still higher than the flow rate of the convection flow of the room air at the upper edge 2f of the opening. The flow A', which otherwise would tend to escape from the cabinet, is forced to turn back into the cabinet by the nozzles 6. The circulation flow takes place at the upper edge of the opening 3 in a direction opposite to or greatly deviating from the direction of the convection flows. The height of the cabinet and the opening should not be considerably greater than the width, as otherwise two superimposed circulation flows easily result, of which the upper flow is open so that warm air flows into the cabinet at the upper edge of the opening while cold air flows out in the middle. This can be prevented by means of a duct 8 positioned at the upper edge of the opening and having nozzles 9 through which air is blown downward, as shown in Figure 3. In this way, it is possible to control even relatively high openings. In this specific case, in order that the supply air flow to be cooled would not increase excessively, the air blown through the nozzles 9 is circulation air C sucked into a duct 10 provided at the back 2c of the cabinet and returned through the duct 8 into the circulation flow A'. A relatively reliable way of preventing the splitting of the circulation flow A' into two is to position a duct 11 at the top of the cabinet, as shown in Figure 4, and introduce supply air through small nozzles 12 positioned in several rows. A double turbulence A', A'' is thus formed within the cabinet, as shown in Figure 4, in which air flows downward on both sides and upward in the middle. The circulation flow can be ensured by blowing air in parallel with the bottom of the cabinet while taking circulation air C through the duct 10. Neither one of the last-mentioned functions is needed in all cases. This way of ventilation as well as that shown in Figure 5 is especially suitable for use when both side walls of the cabinet or production line are open. The nozzles 6 thereby blow against each other from the opposite sides of the cabinet or the production line, and the duct 10 is positioned in the middle of the cabinet or production line. Figure 5 shows an embodiment in which supply air is blown through the duct 11 provided at the top of the cabinet in two directions through nozzles 12 positioned in several rows. This arrangement is particularly suitable for use in large processing spaces, since the jets remain strong on the surface of the cabinet for a long time due to the so-called Coanda phenomenon. Figure 3A is an enlarged view of an alternative structure for the air supply arrangement shown in Figure 2. In Figure 3A, the same reference numerals as in Figure 2 are used. Figure 3B is an enlarged view of an alternative structure for the additional air circulation arrangement shown in Figure 2. In Figure 3B, the same reference numerals as in Figure 2 are used. In order to promote the circulation flow A', A'', guide plates 2g to 2m for guiding the flow may be provided in the processing space 1. The guide plates 2g to 2m can be positioned close to the walls of the processing space. They may also be formed by portions of the walls or the ducts. The drawings and the description related to them are only intended to illustrate the idea of the invention. In their details, the method and the equipment according to the invention may vary within the scope of the claims. The cabinet of the processing space may comprise plates or other means accelerating or directing the circulation flow of supply air and directing or preventing the convection flow of surrounding air at points where the convection flow tends to enter the circulation flow. It is also possible to provide nozzle blows at various points of the cabinet; in Figure 3, for instance, the duct 8 can thus be positioned at the top of the cabinet, so that the nozzles 9 blow along the front wall 2e. In the embodiment of Figure 2, a further duct having nozzles blowing upward along the wall 2c can be provided in the lower portion of the back wall 2c. In the embodiment of Figure 4, the duct 8 shown in Figure 3 can be added, or a duct having nozzles blowing upward can be provided centrally below the duct 11, etc. Even though the invention has been described above in connection with a stationary processing space, such as a laboratory cabinet, it can also be applied to a processing space positioned e.g. within a desired area of a continuous production line. In such a case, the opening(s) to be closed by an air curtain may be the access opening(s) of a moving conveyor. The supply air can be kept colder, warmer, cleaner or in a condition otherwise deviating from the surrounding air, and blown as a circulation flow according to the invention. Reference signs in the claims are intended for better understanding and shall not limit the scope.

Claims: A method of providing ventilation for a production line or other similar processing space (1) which is separated from the surroundings and into which an access opening (3) positioned above the floor level leads from the surroundings, wherein the processing space is separated from the surroundings by blowing treated supply air (A) into the processing space so that an air curtain (5) preventing the entrance of surrounding air is formed in the area of the open access opening of the processing space, characterized in that the supply air (A) is blown into the processing space (1) such that it flows along a closed wall of the processing space, and such that a free circulation flow (A') is created in the processing space comprising the supply air; the direction of the free circulation flow (A') at the access opening (3) is substantially from a top portion to a bottom portion of the access opening (3) and is substantially opposite to the direction of convection flows (B) of surrounding air created by a temperature difference between the introduced supply air and the surrounding air, and the flow rate of the circulation flow (A') being greater than the flow rate of the convection flows at the access opening. A method according to claim 1 , characterized in that the supply air (A) is blown into the processing space (1) at a front edge (2a) of its access opening (3) parallel with the bottom (2b) of the processing space and then passes along the back side (2c) of the processing space to its top portion (2d) and further downward from an upper edge (2f) of the access opening towards the bottom of the processing space. A method according to claim 1, characterized in that the supply air is blown into the processing space within the area of the circulation flow and substantially in a direction parallel with the circulation flow. A method according to claim 1, characterized in that additional supply air (C) is blown into the processing space (1) at its top portion so that it passes downward from the upper edge (2f) of the access opening (3) towards the bottom (2b) of the processing space and further to the top portion of the processing space. An equipment for providing ventilation for a production line or other similar processing space (1) which is separated from the surroundings and into which an access opening (3) positioned above the floor level leads from the surroundings, the equipment comprising means (6, 7; 11, 12) for blowing treated supply air (A) into the processing space so that the supply air forms an air curtain (5) preventing the entrance of surrounding air at the access opening (3) of the processing space, characterized in that the means (6, 7; 11, 12) for introducing the supply air (A) are positioned in the processing space (1) in such a way that the supply air is blown into the processing space such that it flows along a closed wall thereof and then flows in the processing space as a free circulation flow (A'; A', A'') having at the access opening (3) a direction substantially from a top portion to a bottom portion of the access opening (3) and substantially opposite to the direction of convection flows (B) of surrounding air caused by temperature differences between the supply air and the surrounding air, and having a flow rate greater than the flow rate of the convection flows of the surrounding air at a lower edge of the access opening. An equipment according to claim 5, in which the processing space (1) is formed by a cabinet having an access opening (3) on one side, characterized in that the means (6, 7) for introducing supply air (A) are mounted at the lower edge (2a) of the opening (3), and that the means blow the supply air in a direction parallel with the bottom (2b) of the cabinet towards the back side (2c) of the cabinet so that the supply air passes along the back side and the ceiling (2d) and then forms an air curtain (5) at the opening. An equipment according to claim 6, characterized in that means (8, 9) are mounted at the upper edge (2f) of the opening (3) of the cabinet (2) for blowing additional air (C) in a direction parallel with the opening toward the lower edge (2a). An equipment according to claim 7, characterized in that the means (8, 9) for blowing additional air (C) are connected to the processing space (1) for sucking additional air from the circulation flow (A') of the supply air (A). An equipment according to claim 5, characterized in that the means (11, 12) for introducing supply air (A) are mounted at the top of the processing space for blowing supply air towards and along the ceiling (2d) of the processing space in such a way that the supply air flows in two diverging circulation flows (A', A''), one (A') flowing downward in parallel with the opening (3) and the other (A'') flowing downward along the back side (2c) of the processing space and both (A', A'') upward in the middle of the processing space. An equipment according to claim 5, characterized in that the means (11, 12) for introducing supply air (A) are mounted at the top of the processing space (1) for blowing supply air in opposite directions towards the opening (3) and towards the back side (2c) of the processing space, respectively, so that the supply air flows in two circulation flows (A', A''), one (A') downward in parallel with the opening (3) and the other (A'') downward along the backside (2d) of the processing space and both (A', A'') upward in the middle of the processing space. An equipment according to claim 9 or claim 10, characterized in that guide plates (2g to 2m) are provided in or close to the walls of the processing space (1) for guiding the flow of air and promoting the circulation flow (A', A'').

Inventors: LESKINEN SEPPO, LESKINEN, SEPPO
Applicants: FLAEKT OY, ABB FLAEKT OY
Application year: 1992
Main classification: F24F9
IPC codes: F24F9, F24F3