EP2382423B1

EP2382423B1 - Induction unit for uniting air flows

Info

Publication number: EP2382423B1
Application number: EP09838971.1A
Authority: EP
Inventors: Per Åke LARSSON
Original assignee: Swegon AB
Current assignee: Swegon Operations AB
Priority date: 2009-01-26
Filing date: 2009-12-23
Publication date: 2018-10-24
Anticipated expiration: 2029-12-23
Also published as: AU2009338225A1; SE0950029A1; EP2382423A1; CN102292600A; CN102292600B; NZ594194A; SE533440C2; WO2010085194A1; EP2382423A4; US20120015600A1

Description

The present invention relates to an induction unit for uniting air flows, comprising at least one induction duct coordinated with a primary air duct of the type specified in the preamble to patent claim 1 below.
Induction units, in which air flowing out of nozzles, slits or the like creates an induction (the ejector effect), which causes ambient air (circulated air) to circulate through a heat exchanger etc are already known. Examples are the nozzles formed as so-called ducted primary air nozzles directly in the wall of a primary air duct, which is connected to a fresh air fan. Extending from the duct wall with primary air nozzles and parallel to the outlet flow direction thereof is an induction duct, which in its duct wall adjoining the primary air nozzles has an inlet opening for circulated air, leading to a common outlet for the air mixture. The inlet opening for circulated air is arranged transversely to the outlet flow direction of the primary air nozzles.
By means of its fan pressure the fresh air fan produces jets through the nozzles, which in turn generate a static negative pressure over the inlet opening, which may be connected to a heat exchanger. The circulated air, also referred to as secondary air, is thereby drawn in through the inlet opening oriented transversely to the outlet flow direction of the primary air nozzles and through the heat exchanger, where the air is either cooled or heated, whereupon the secondary air is forced to change direction by approximately 90 degrees during mixing with the primary air, before the air mixture is returned to the surrounding air through a common outlet.
One problem with induction units of this type is the flow losses occurring, which are associated with the change in the direction of the secondary air as it is drawn in and mixed with the primary air.
Another problem is that the efficiency of the heat exchanger becomes irregular and poorly optimized in that the static negative pressure generated by the primary air nozzles over the inlet opening connected to the heat exchanger varies over different parts of its area. Thus the static negative pressure is almost 100% in the part of the inlet opening area closest to the duct wall with the primary air nozzles, whereas the static negative pressure drops towards 0% in the part of the inlet opening area situated furthest away from this duct wall. Previously known induction units (figure 1) therefore have a curved flow path for the secondary air, which in combination with an uneven static pressure over the heat exchanger surface means that the air cannot be evenly distributed over the heat exchanger surface.
WO 2004/085930 discloses an induction unit upon which the preamble of appending claim 1 is based. An object of the invention is to provide an improved induction unit, which is not impaired by the problems and disadvantages inherent in hitherto known technical solutions of this type that have been described above.
This object is achieved by an induction unit according to the invention, which has the characteristic features in the independent patent claim 1. Advantageous developments and enhancements of the invention are set forth in the dependent patent claims, in the description and in the drawing.
Experiments with computer simulation (so-called CFD simulation) which have been carried out with the induction unit according to the invention have shown that the velocity distribution becomes very even over the secondary air intake.
With the construction according to the invention the flow paths through the induction unit run straight from the secondary air intake to the outlet with as low a flow resistance as possible in order to maximize the secondary air flow. Where applicable, the flow through a connected heat exchanger then becomes uniform, which leads to an optimum utilization of the heat exchanger surface.
The invention is described in more detail below with reference to a schematic drawing attached. In the drawing figure 1 shows a cross section through one embodiment of an induction unit of conventional type, figure 2 shows a cross section through an induction unit according to the invention having one induction duct, figure 3a shows a cross section through a further embodiment provided with a partition wall and two induction ducts, figures 3b and 3c are perspective sketch views, which show how the induction unit in figure 3a can be formed in sections, figure 4 shows a variant of the induction unit in figure 3 having three induction ducts and figure 5 shows a further enhanced embodiment of the induction unit in figure 3.
In the drawings the same reference numerals have been assigned to identical parts and parts having the same function.
Figure 1 shows a previously known induction unit 2, which has so-called ducted primary air nozzles 4 formed directly in the wall of a primary air duct 6, which is connected to a fresh air fan (not shown). Extending from the duct wall with the primary air nozzles 4 and parallel to the outlet flow direction thereof is an induction duct 8, which in its duct wall adjoining the primary air nozzles 4 has a secondary air intake 12, connected via a heat exchanger 10, leading to a common outlet 14 for the air mixture. The secondary air intake 12 is situated transversely to the outlet flow direction of the primary air nozzles 4. By means of its fan pressure the fresh air fan produces jets through the nozzles 4, which in turn generate a static negative pressure over the secondary air intake 12 and the heat exchanger 10 connected thereto. The secondary air is thereby drawn in through the secondary air intake 12 and through the heat exchanger 10, where the air is either cooled or heated, whereupon the secondary air is forced to change direction by approximately 90 degrees during mixing with the primary air, before the air mixture is returned to the surrounding air through the common outlet 14. As previously stated, the static negative pressure generated by the primary air nozzles over the inlet opening connected to the heat exchanger thereby varies over different parts of its area. Thus the static negative pressure is almost 100% in the part of the inlet opening area closest to the duct wall with the primary air nozzles 4, whereas the static negative pressure drops towards 0% in the part of the inlet opening area situated furthest away from this duct wall.
Figure 2 shows a cross section through a basic embodiment of an induction unit 20 according to the invention, having one induction duct 21, which by contrast extends substantially straight from an upstream end with a secondary air intake 22 to a downstream end with an outlet 24 and has a straight reference line A passing through the ends. The flow paths from the upstream end with the secondary air intake 22 to the downstream end with the outlet 24 are thereby straight and parallel to the reference line A, which compared to the state of the art gives a substantially lower flow resistance and hence a maximized secondary air flow. Owing to the straight flow paths through the induction unit, when a heat exchanger 26 is connected to the secondary air intake 22 this moreover also advantageously affords a uniform flow through the heat exchanger 26, which leads to an optimum utilization of the entire heat exchanger surface. The variations in the static negative pressure are therefore very small and close to 100% over the entire area of the inlet opening 22.
The induction unit 20 according to the invention is likewise provided with primary air nozzles in the form of ducted first openings 28, which are formed directly in a first duct wall 29 between the induction duct 21 and a first primary air duct 30, which is likewise connected to a fresh air fan (not shown). According to the invention, the first duct wall 29 has been profiled into a substantially z-like shape with a waist 32 running transversely to the reference line A, in which each first opening 28 is made and through which a primary air flow F1 directed with concurrent flow can be introduced into the induction duct 21 at a relatively small angle α of approximately 0-10° to the reference line A. The waist 32 is suitably situated at approximately 1/3 of the distance between the secondary air intake 22 and the outlet 24. A first leg of the first duct wall 29, diverging from an opposing second duct wall 34 towards the secondary air intake 22, extends from the waist 32 and is bounded by its attachment to an outer wall 36 of the first primary air duct 30. The second duct wall 34 constitutes the opposite boundary of the secondary air intake 22, so that the entire cross section of the secondary air intake 22 is open to the induction duct. From the waist 32 a second leg of the first duct wall 29, converging with the second duct wall 36 towards the outlet 24, extends a further 1/3 of the distance in such a way as to produce a cross section which is less than half of the cross section of the secondary air intake and which has a substantially constant cross section over the remaining 1/3 towards the outlet 24. The reference line A extends centrally in the part of the induction duct of constant cross-section. The second duct wall 36 of the induction duct 21 may be of an extent corresponding to this cross section. The secondary air intake 22 thereby has an area which is at least twice as large as the outlet 24, thereby forming a venturi 38, the venturi effect of which contributes to a greater suction effect in the secondary air intake 22.
Figure 3a shows a further enhanced embodiment similar to that in figure 2, with a two-duct induction unit 20' formed by two laterally inverted induction units 20 having a first induction duct 21' and a second induction duct 21", each having its associated primary air duct, a first primary air duct 30' and a second primary air duct 30" with associated first openings 28'. Every second duct wall 34 here has been replaced by a partition wall 38, which separates the first induction duct 21' from the second induction duct 21". The partition wall 38 makes it possible to distribute various air flows to the induction ducts, for example by fitting the first primary air duct 30' and the second primary air duct 30" with first openings 28' of different sizes. Alternatively each first opening 28', or a group of first openings 28' blowing into each induction duct, may be closable in a manner known in the art, in order to allow the first induction duct 21', for example, to be shut off whilst the second induction duct 21" continues to operate, or vice-versa. The regulation of the primary air between the primary air ducts may also be controlled in some other way, for example by throttle control of the inflow to each primary air duct or by using different fans, which are individually controllable, in order to create the intended effect. One example may be to use the first primary air duct 30' for a basic flow and to use the second primary air duct 30" and/or further primary air ducts, which will be described later with reference to figure 4, for one or more forced-air flows. When operating with different primary air flows in each induction duct, the partition wall 38 results in separate air paths for each duct and hence an optimum induction. The partition wall may also be of moveable design, that is to say if the first primary air duct 30' has most primary air, the first induction duct 21' must also be larger, which can be achieved in a manner known in the art by displacing the partition wall 38 towards the second induction duct 21".
Figures 3b and 3c are perspective sketch views, which show how the induction unit 20' in figure 3a can be formed in sections, where each section 40 is box-shaped of a height H, depth D and length L and comprises the two primary air ducts 30'; 30" and the two induction ducts 21'; 21". As can be seen from figure 3b, the profiled waist 32" of the first duct wall 29", for example, may be provided with a group of three first openings 28', which connect each primary air duct to the associated induction duct. Thus, as shown in figure 3c, an induction unit 20" may thereby be constructed in modular form from one or more sections 40, depending on the required capacity in the particular case. The modular construction in sections 40 allows an induction unit 20" of height H, depth D and length n x L to be assembled from a suitable number n of sections 40 in accordance with the particular ventilation and/or air conditioning requirement.
Figure 4 shows a variant of the induction unit having three induction ducts. In this variant an induction unit 20 according to the basic embodiment in figure 2 has been combined with an induction unit 20' according to the embodiment in figure 3, creating a three-duct induction unit 20"'. This three-duct variant therefore has a first induction duct 21', a second induction duct 21" and a third induction duct 21"', each comprising its own associated primary air duct, a first primary air duct 30', a second primary air duct 30" and a third primary air duct 30"' with associated first openings 28'. The function of each duct in this variant is equivalent to the preceding embodiments and will therefore not be described in more detail here. It is pointed out that for special requirements it is obviously also possible to combine a plurality of single-duct and/or two-duct and/or three-duct modules with one another, in order to obtain an induction unit that fulfills the high requirements placed on adjustability by means of a plurality of different flows.
In particular, there is almost unlimited scope here not only for adjusting individual or groups of first openings 28', but also for guiding the primary air between the various primary air ducts, for example through throttle control of the inlet flow to each primary air duct or through the use of different fans, which are individually adjustable in order to create the intended effect. One example may be the use of the first primary air duct 30' for a basic flow and use of the second primary air duct 30" for a forced-air flow to a first level and the third primary air duct 30"' for a forced-air flow to a second level and any further primary air ducts to further boost the forced-air flows. When operating with different primary air flows in each induction duct, the partition wall 38"' or equivalent partition walls result in separate air paths for each duct and hence an optimum induction. Alternatively the basic flow can be ensured by means of two or three primary air ducts, after which forced-air flows can be produced by means of an optional further number of primary air ducts.
Figure 5 shows a further enhanced embodiment 20"" of the induction unit in figures 3a-c. Here the design of each induction duct has been further improved in that the z-profiled first duct wall 29 has been replaced by a plane wall, to reduce the flow resistance further and to improve the efficiency. A third induction duct 42 and a fourth induction duct 42' are therefore formed each with their own plane third wall 44 or fourth wall 44' on either side of an associated, likewise plane partition wall, which for the sake of clarity has here been termed a dividing wall 46. From the secondary air intake 48 each plane third wall 44 and plane fourth wall 44' converges to a position situated at substantially 2/3 of the distance to the outlet 50 and extends with a substantially constant cross section over the remaining 1/3 of the distance to outlet.
The first duct wall 29, profiled to a substantially z-like shape, with a waist 32 which runs transversely to the reference line A and which partially encroaches on the cross sectional area of each induction duct, and in which each first opening 28 is made, has therefore in each case been replaced by a plane third wall 44 or fourth wall 44'. Each first opening 28 in previous embodiments according to figures 2-4 has then been replaced by a second primary air nozzle 52 embodied as a bent pipe, which in place of the waist 32 projects a distance into each induction duct 42, 42' and which may be configured in such a way that the primary air flow can be directed parallel to the dividing wall 46 and the reference line A. Every second primary air nozzle 52, or group of second primary air nozzles 52 blowing into each induction duct, may also be closed in a manner known in the art, in order to allow the third induction duct 42, for example, to be shut off whilst the fourth induction duct 42' continues to operate, or vice-versa.
The construction according to the enhanced embodiment 20"" means that, because only the second primary air nozzles 52 project into the third and fourth induction ducts 42, 42' through isolated points in the plane third wall 44 and fourth wall 44' respectively, the second primary air nozzles 52 affect the flow resistance in each of the induction ducts 42, 42' to a substantially lesser degree than the waist 32 running transversely to the reference line A in preceding embodiments.
Even though the induction unit in the various embodiments has been described in conjunction with a heat exchanger, the heat exchanger may, where appropriate, as shown by the dashed defining lines of the heat exchanger across the upstream end, be omitted and the induction unit used, for example, for mixing circulated air with fresh air in specific proportions.

Claims

An induction unit for uniting air flows, comprising at least one induction duct (21) coordinated with a primary air duct (30) and having an upstream end and a downstream end and a straight reference line (A) passing through the ends, and at least one first opening (28) for a primary air flow (F1), connected to the primary air duct (30) and opening with concurrent flow into the induction duct (21), at least one secondary air intake (22) for the intake of a secondary air flow (F2) to the induction duct (21) from a space surrounding the induction unit, and at least one outlet (24) designed to return an air flow (F3) resulting from the primary air flow and the secondary air flow to the space surrounding the induction unit, and that the secondary air intake (22) is arranged at the upstream end of the induction duct (21), characterized in that the at least one first opening (28) for the primary air flow (F1) is formed directly in a first duct wall (29) between the induction duct (21) and a first primary air duct (30), wherein the first duct wall (29) has been profiled into a substantially z-like shape with a waist (32) running transversely to the reference line A, in which each first opening (28) is made and through which a primary air flow F1 directed with concurrent flow can be introduced into the induction duct 21 at a relatively small angle α to the reference line A and wherein the waist (32) is suitably situated at approximately 1/3 of the distance between the secondary air intake (22) and the outlet (24) so that both the primary air flow (F1) itself and the secondary air flow (F2) generated thereby, and the resulting air flow (F3) are directed substantially parallel to the reference line (A) of the induction duct.
The induction unit as claimed in claim 1, characterized in that each first opening (28) is arranged in such a way that both the primary air flow (F1) itself and the secondary air flow (F2) generated thereby, and the resulting air flow (F3) are directed substantially parallel to the center line (A) of the induction duct.
The induction unit as claimed in claim 1 or 2, characterized in that a longitudinal partition wall (38) is arranged in the induction duct in such a way that a first induction duct (21') is formed on one side of the partition wall and a second induction duct (21") is formed on the other side of the partition wall.
The induction unit as claimed in claim 3, characterized in that each induction duct (21', 21") has its own primary air duct (30', 30") with associated first openings (28') for the primary air.
The induction unit as claimed in claim 4, characterized in that the first primary air duct (30') and the second primary air duct (30") have openings (28') of different sizes.
The induction unit as claimed in claim 4, characterized in that the partition wall (38) is moveable.
The induction unit as claimed in one of the preceding claims, characterized in that at least one induction duct (21') can be shut off whilst at least one induction duct (21") continues in operation and/or that at least one induction duct (21') can be set in operation whilst at least one induction duct (21") is in operation and/or that the resulting flow (F3) in each induction duct (21', 21") is individually variable, depending on the primary air flow through the associated primary air duct (30', 30").
The induction unit as claimed in one of the preceding claims, characterized in that the secondary air intake (22) has an area which is at least twice as large as the area of the outlet (24).
The induction unit as claimed in one of the preceding claims, characterized in that a heat exchanger (26) is connected in series to the secondary air intake.
The induction unit as claimed in one of the preceding claims, characterized in that the outlet (24) is arranged at the downstream end of the induction duct and is oriented substantially axially with its center line (A).