US20130035029A1

US20130035029A1 - Supply Air Unit

Info

Publication number: US20130035029A1
Application number: US13/515,911
Authority: US
Inventors: Mika Ruponen; Panu Mustakallio; Risto Kosonen; Maija Virta; Harri Itkonen
Original assignee: Halton Oy
Current assignee: Halton Oy
Priority date: 2009-12-18
Filing date: 2010-12-16
Publication date: 2013-02-07
Also published as: FI20096350A0; PL2513567T3; WO2011073525A1; EP2513567B1; FI122953B; EP2513567A1; FI20096350A

Abstract

The supply air unit (100) comprises a supply air chamber (10), at least one mixing chamber (20 a , 20 b), which opens into the air-conditioned room space, nozzles (60 a , 60 b), through which a fresh airflow (L1) is conducted from the supply air chamber (10) into the mixing chamber, a first heat-transfer unit (A), which comprises at least one heat exchanger (30 a , 30 b), through which a circulated airflow (L2) is conducted from the room space into the mixing chamber. The supply air unit also comprises a second heat-transfer unit (B), which is formed by at least one radiating element (50), which has a radiating surface (51), to which heat is transferred from the air-conditioned room space for cooling or from which heat is transferred into the air-conditioned room space for heating, and which radiating surface also comprises openings, whereby the radiating surface becomes sound-absorbing.

Description

FIELD OF INVENTION

The invention concerns a supply air unit in accordance with the preamble to claim 1.

PRIOR ART

Supply air units or air-conditioning beams usually comprise a supply air chamber, a mixing chamber and a heat exchanger. A flow of fresh air is brought from the supply air chamber into the mixing chamber, in which the flow of fresh air is mixed together with a circulated airflow, whereupon the combined airflow is conducted into a room space. The circulated airflow is conducted into the mixing chamber through a heat exchanger, in which the circulated airflow can be either heated or cooled. The flow of fresh air induces the circulated airflow to flow from the room through the heat exchanger into the mixing chamber.
Patent application FI 20060035 presents a supply air unit and a method for controlling the airflow rate. The supply air unit comprises a supply air chamber, a heat exchanger and a mixing chamber. From the supply air chamber the flow of fresh air is conducted through nozzles into the mixing chamber, in which the supply airflow induces a circulated airflow to flow from the room through the heat exchanger into the mixing chamber. In the mixing chamber, the combined fresh airflow and circulated airflow are conducted from the mixing chamber's outlet opening into the air-conditioned room space. The supply air unit also comprises a separate additional air opening, which is equipped with a controller, which can be used for controlling the rate of fresh airflow supplied from the supply air chamber past the nozzles and into the room space. The additional air opening may lead from the supply air chamber either directly into the air-conditioned room space or into the mixing chamber.
Patent application FI 20075213 presents a supply and exhaust air unit, which comprises a supply air chamber and a mixing chamber. In this solution the supply and exhaust air unit also comprises a separate additional air opening, which is equipped with a controller and which can be used for controlling the rate of fresh airflow supplied from the supply air chamber past the nozzles and into the room space. The supply and exhaust air unit also comprises an exhaust air opening, which is equipped with a controller and which can be used for controlling the rate of air exhausted from the room space.
Patents FI 117682 B, 118236 B present supply air units, which comprise a supply air chamber, a heat exchanger and a mixing chamber. A fresh airflow is conducted from the supply air chamber through nozzles into the mixing chamber, in which the supply airflow induces a circulated airflow to flow from the room through the heat exchanger and into the mixing chamber. In the mixing chamber, the combined fresh airflow and circulated airflow are conducted from the mixing chamber's outlet opening into the air-conditioned room space. The publications present various systems for controlling the induction ratio and for controlling either the rate of fresh airflow supplied into the mixing chamber or the rate of circulated airflow conducted from the air-conditioned room space into the mixing chamber.
Patent EP 0 365 586 B1 presents a ventilation device, which comprises an elongated supply air chamber, which is located in connection with the ceiling surface in the air-conditioned room space, and located beside it an elongated panel. The panel is heated or cooled by tubes, which are fitted in connection with the panel's top surface and in which a heat carrier flows. In the supply air chamber there is a supply air passage, from which air is blown in the horizontal direction along the horizontal bottom surface of said panel, whereby the airflow blown inside is in thermal interaction with the panel. On the panel's top surface there is a heat-insulating material, which also covers the tubes transporting the heat carrier. Thus, the aim here is to boost the transfer of heat from the radiating surface into the air-conditioned room space by using forced convection, which is brought about by blowing the supply airflow along the panel's bottom surface, that is, the radiating surface. This again raises the temperature of the radiating surface and in this way reduces the radiation. The increase in efficiency achieved by blowing is considerably smaller than the increase in efficiency achieved by heat exchangers.
In the air-conditioned room space the air is stratified in such a way that the lighter warm air rises up towards the room's ceiling surface, whereas the heavier cool air sinks down towards the room's floor surface. In the heat transfer taking place by convection only, heating and cooling take place through the air moving through the heat exchanger. Efficient heat transfer would thus require that the air circulates at a high velocity in the room space, but a high velocity again will cause draught. In the heat transfer taking place by radiation only, heating and cooling take place as radiation between the heat transferring surface and the room surfaces. A person will feel both the temperature of the room surfaces and the temperature of the air in the room.

SUMMARY OF INVENTION

The supply air unit according to the invention is characterised by the features presented in the characterising part of claim 1.
The supply air unit comprises a supply air chamber, at least one mixing chamber, which opens into the air-conditioned room space, nozzles or a nozzle gap, through which a fresh airflow is conducted from the supply air chamber into said at least one mixing chamber, a first heat transfer unit, which is formed by at least one heat exchanger, through which a circulated airflow is conducted from the air-conditioned room space into said at least one mixing chamber, and in which the circulated airflow is cooled or heated. The combined airflow formed from said at least one mixing chamber by the fresh airflow and the circulated airflow is conducted into the air-conditioned room space. The supply air unit also comprises a second heat transfer unit, which is located in its lower part and which is formed by at least one radiating element, which has a radiating surface, to which heat is transferred from the air-conditioned room space for cooling or from which heat is transferred into the air-conditioned room space for heating. The radiating surface also comprises a perforation, which makes it sound-absorbing. The perforation reduces the reflection of sound taking place in the radiating surface, whereby the acoustic characteristics of the room space are improved.
The supply air unit has a first heat transfer unit transferring heat by convection and a second heat transfer unit transferring heat by radiation. In the first heat transfer unit, heat is transferred from a heat-carrying liquid travelling in tubing to the heat exchanger's heat transfer surfaces and further from these into a circulated airflow travelling between the heat transfer surfaces. In the second heat transfer unit, heat is transferred from a heat-carrying liquid travelling in tubing to the radiating surface and further from this as radiation to the room surfaces.
The tubes of the heat exchangers and the radiating element can be dimensioned in such a way that the flow characteristics in the tubes are different. When only a low cooling power is required in the air-conditioned room space, the flow is kept turbulent in the radiating element's tubing and laminar in the heat exchanger s' tubes. A high turbulence of the flow in the radiating element's tubing leads to a high heat transfer coefficient between the heat-carrying liquid and the tube, whereby the heat transfer from the heat-carrying liquid to the tube becomes more efficient. A laminar flow in the heat exchangers' tubes will for its part produce a low heat-transfer coefficient and thus lower heat transfer from the heat-carrying liquid to the tube. A major part of the cooling power is thus obtained from the radiating element, whereby the sense of draught caused by the cool moving airflow can be minimized.
When more cooling is needed, the flow velocity of the heat-carrying liquid is increased, so that the flow will become turbulent also in the heat exchangers, whereby the cooling power of the heat exchangers increases. In this state, a larger part of the need for cooling in the room space is transferred through the moving air.
With the solution according to the invention, cooling capacity is delivered in a cooling situation into the air-conditioned room space both by convection and by radiation, whereby the thermal comfort can be improved in the room space as a result of reduced movement of air. Thanks to the radiation, the supply air unit also in a shorter time will affect the sense of warmth of a person staying in the air-conditioned room space.
The invention will be described in the following by referring to some advantageous embodiments of the invention, which are shown in the figures of the appended drawings, but there is no intention to restrict the invention to these alone.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a schematic cross-sectional view of a supply air unit according to the invention.

FIG. 2 is a schematic cross-sectional view of another supply air unit according to the invention.

FIG. 3 is a schematic cross-sectional view of a third supply air unit according to the invention.

FIG. 4 is a schematic cross-sectional view of a fourth supply air unit according to the invention.

FIG. 5 is a schematic cross-sectional view of a fifth supply air unit according to the invention.

FIG. 6 is a schematic cross-sectional view of a sixth supply air unit according to the invention.

FIG. 7 is a schematic cross-sectional view of a seventh supply air unit according to the invention.

FIG. 8 is a schematic view of a heat-transfer circuit suitable for the supply air unit shown in FIG. 1.

DESCRIPTION OF ADVANTAGEOUS EMBODIMENTS

FIG. 1 is a cross-sectional view of a supply air unit according to the invention.
The supply air unit 100 comprises a supply air chamber 10, whose cross-section is essentially rectangular comprising in its lower part triangular bracket sections 10 a, 10 b. In the roof surface of the left-hand bracket section 10 a there is a first row of nozzles 60 a or a nozzle gap. In the roof surface of the right-hand bracket section 10 b there is a second row of nozzles 60 b or a nozzle gap. At a distance from the supply air chamber's 10 left-hand vertical side wall 11 a there is a first heat exchanger 30 a with a rectangular cross-sectional shape. At a distance from the supply air chamber's 10 right-hand vertical side wall 11 b there is a second heat exchanger 30 b with a rectangular cross-sectional shape. A first mixing chamber 20 a is formed in a space between the supply air chamber's 10 left-hand vertical side wall 11 a and the first heat exchanger 30 a. A second mixing chamber 20 b is formed in a space between the supply air chamber's 10 right-hand vertical side wall 11 b and the second heat exchanger 30 b.
In the first mixing chamber's 20 a top part a first outlet opening 25 a is formed, and in the second mixing chamber's 20 b top part a second outlet opening 25 b is formed. Both outlet openings 25 a, 25 b are formed in such a way that the airflow LA leaving the supply air unit 100 is guided from the mixing chamber 20 a, 20 b in the air-conditioned room space to the side essentially in the direction of the room's ceiling surface K.
A first suction chamber 40 a is formed outside the outer surface of the first heat exchanger 30 a, and a second suction chamber 40 b is formed outside the outer surface of the second heat exchanger. The bottom surface of each suction chamber 40 a, 40 b has openings 41 a, 41 b, from which the circulated air L2 taken from the room space can enter the suction chamber 40 a, 40 b. Suction chambers 40 a, 40 b are not needed for the supply air unit's 100 operation, so they can also be omitted. Their function is mostly aesthetic. In a supply air unit 100 without suction chambers 40 a, 40 b, the circulated airflow L2 arrives directly at the outer side surface of the heat exchangers 30 a, 30 b.
A fresh supply airflow L1 is conducted by a blowing fan into the supply air chamber 10, for example, by way of a tube fitting (not shown in the figure) located in its end surface, and further through the supply air chamber's 10 first row of nozzles 60 a into the first mixing chamber 20 a and through the second row of nozzles 60 b into the second mixing chamber 20 b. In the mixing chambers 20 a, 20 b a fresh airflow L1, which is directed vertically upwards, induces the circulated airflow L2 from the air-conditioned room space to travel through the suction chambers 40 a, 40 b and the heat exchanger 30 a, 30 b into the mixing chambers 20 a, 20 b. The circulated airflow L2 can be cooled or heated in the heat exchangers 30 a, 30 b. In the mixing chambers 20 a, 20 b, the fresh airflow L1 directed upwards travels tangentially in relation to the heat exchanger's 30 a, 30 b surface, which opens into the mixing chamber 20 a, 20 b.
The combined airflow LA formed of the fresh airflow L1 and the circulated airflow L2 in the first mixing chamber 20 a is conducted from the first outlet opening 25 a along ceiling surface K to the left in the figure, and the combined airflow LA formed in the second mixing chamber 20 b is conducted from the second outlet opening 25 b along ceiling surface K to the right in the figure.
The supply air unit 100 is symmetrical in relation to the vertical central axis Y-Y and it is preferably formed by an elongated body. The supply air unit 100 is suspended at the supply air chamber's 10 roof wall 11 d with suitable suspension fasteners to the ceiling K of the air-conditioned room space in such a way that the supply air chamber's 10 roof wall 11 d remains at a distance from the ceiling surface K.
The heat exchangers 30 a, 30 b here form a first heat-transfer unit A, in which heat is transferred by convection into the circulated airflow L2 flowing through the heat exchangers 30 a, 30 b.
To the supply air chamber's 10 bottom wall 11 c is supported a radiating element 50, which comprises a horizontal, planar radiating surface 51, tubes 52, which are located above radiating surface 51 in connection with it and in which a heat carrier circulates, and a heat insulation 53, which prevents the heating or cooling effect of the heat carrier flowing in tubes 52 from being transferred upwards from the radiating element 50 to the supply air chamber's 10 bottom wall 11 c.
The radiating element 50 forms a second heat-transfer unit B, in which heat is transferred from the planar radiating surface 51 as radiation to the planar surfaces of the room space.
FIG. 2 shows a schematic cross-section of another supply air unit according to the invention. In this embodiment, the supply air unit comprises a supply air chamber 10 supported against the ceiling K, a first heat-transfer unit A supported against the bottom surface of supply air chamber 10, and a second heat-transfer unit B located below the first heat-transfer unit A, at a distance from the first heat-transfer unit A. In this embodiment, the first heat-transfer unit A is formed by one heat exchanger 30. A fresh airflow L1 is blown from the supply air chamber's 10 nozzles 60 a, 60 b in a horizontal direction to the sides and into the mixing chambers 20 a, 20 b. A circulated airflow L2 is conducted from the room space through a space between the second heat-transfer unit B and the heat exchanger 30 through heat exchanger 30 into mixing chambers 20 a, 20 b, from which the combined airflow LA is blown in a horizontal plane to the sides into the air-conditioned room space. The second heat-transfer unit B is entirely similar to the second heat-transfer unit B shown in FIG. 1.
FIG. 3 shows a schematic cross-section of a third supply air unit according to the invention. This embodiment differs from the embodiment shown in FIG. 2 in that the supply air chamber 10 and the first heat-transfer unit A, that is, the heat exchanger 30, are turned through 180 degrees. Heat exchanger 30 is at a distance from ceiling K, and the second heat-transfer unit B is mounted to the supply air chamber's 10 bottom wall. A circulated airflow L2 is conducted from the room space through a space between the heat exchanger 30 and ceiling K through heat exchanger 30 and into mixing chambers 20 a, 20 b, from which the combined airflow LA is blown in a horizontal plane to the sides into the air-conditioned room space. The second heat-transfer unit B is entirely similar to the second heat-transfer unit B shown in FIG. 1.
FIG. 4 shows a schematic cross-section of a fourth supply air unit according to the invention. This embodiment differs from the embodiment shown in FIG. 2 as regards the second heat-transfer unit B. The second heat-transfer unit B is here formed by a radiating element 50, the radiating surface 51 of which forms a broken line. In other respects the second heat-transfer unit B is similar to the second heat-transfer unit B shown in FIG. 1.
FIG. 5 shows a schematic cross-section of a fifth supply air unit according to the invention. This embodiment differs from the embodiment shown in FIG. 2 as regards the second heat-transfer unit B. The second heat-transfer unit B is here formed by a radiating element 50, the radiating surface 51 of which forms a wave line. In other respects the second heat-transfer unit B is similar to the second heat-transfer unit B shown in FIG. 1.
With the solutions shown in FIGS. 4 and 5 it is possible to increase the radiating surface's 51 surface area in relation to the space required by the radiating surface 51 in the horizontal direction. Hereby, the surface area absorbing sound will also grow. A solution of this kind also increases the radiation effect on the side surfaces of the air-conditioned room space.
FIG. 6 shows a schematic cross-section of a sixth supply air unit according to the invention. This embodiment differs from the embodiment shown in FIG. 1 in that the first heat-transfer circuit A is here formed by one heat exchanger 30 only, whereby the structure becomes asymmetrical.
FIG. 7 shows a schematic cross-section of a seventh supply air unit according to the invention. This embodiment differs from the embodiment shown in FIG. 6 in that the second heat-transfer unit B is here mounted at a certain angle α in relation to the horizontal plane. The supply air unit may be mounted to the ceiling near a wall of the room or in a corner, whereby the radiating surface's 51 inclination will direct the radiation to the desired place in the air-conditioned room space, for example, towards the mid-point in the room space.
FIG. 8 is a schematic view of a heat-transfer circuit suitable for the supply air unit shown in FIG. 1. The heat-transfer circuit is here formed by the radiating element's 50 heat-transfer tubing 52, by the first heat exchanger's 30 a heat-transfer tubing 32 a and by the second heat exchanger's 30 b heat-transfer tubing 32 b. The radiating element's 50 heat-transfer tubing 52 is connected in series with the second heat exchanger's 30 b heat-transfer tubing 32 b. The second heat exchanger's 30 b heat-transfer tubes 32 b are for their part connected in series with the first heat exchanger's 30 a heat-transfer tubing 32 a. A control unit 60 located in the supply circuit is used to control the velocity of the heat-carrying liquid supplied into the heat-transfer circuit.
The radiating element's 50 heat-transfer tubing 52 and the heat exchangers' 30 a, 30 b heat- transfer tubes 32 a, 32 b can be dimensioned so that the flow characteristics in the heat- transfer tubes 52, 32 a, 32 b are different. When only a low cooling power is needed in the air-conditioned room space, the flow in the radiating element's 50 heat-transfer tubing 52 is turbulent, while in the heat exchangers' 30 a, 30 b heat- transfer tubes 32 a, 32 b the flow is laminar. A high turbulence in the flow in the radiating element's 50 heat-transfer tubes 52 leads to a high heat-transfer coefficient between the heat-carrying liquid and the tube, whereby the heat transfer from the heat-carrying liquid to the tube becomes more efficient. On the other hand, a laminar flow in the heat exchanger's 30 a, 30 b heat- transfer tubes 32 a, 32 b produces a low heat-transfer coefficient and thus a lower heat transfer from the heat-carrying liquid to the tube. A major part of the cooling power is hereby obtained from the radiating element 50. When more cooling is required, the flow velocity of the heat-carrying liquid is increased, so that the flow becomes turbulent also in the heat exchangers 30 a, 30 b, whereby the cooling power of the heat exchangers 30 a, 30 b will increase.
Different turbulence in the radiating element's 50 tubing 52 and in the heat exchangers' 30 a, 30 b heat- transfer tubes 32 a, 32 b can be achieved, for example, by the choice of tube dimensions or by distributing the flow of the heat-carrying liquid into one or more circuits after the radiating element 50. When the heat-carrying liquid is conducted into a tube having a larger flow cross-section area, its flow velocity will drop, and the other way round. When the heat-carrying liquid's flow is branched off from the first heat-transfer tube into two heat-transfer tubes, its flow velocity will drop, if the totalled flow cross-section area of these two heat-transfer tubes exceeds the flow cross-section area of the first heat-transfer tube.
The circuit shown in FIG. 8 forms a simple control circuit. The heat exchangers' 30 a, 30 b heat- transfer tubes 32, 32 b and the radiating element's 50 heat-transfer tubing 52 can also be supplied by their own supply circuits and they can be controlled by separate control devices.
In the embodiments shown in the figure, the second heat-transfer unit B is formed by one radiating element 50, but when required the supply air unit 100 may of course comprise several radiating elements 50. The supply air unit 100 could, for example, comprise two or more parallel radiating elements 50.
The radiating surface 51 of the radiating element 50 shown in the figures may be formed by a metal sheet, which has openings and which is made, for example, of aluminium or steel. The cross-section of the openings in radiating surface 51 can be, for example, round, rectangular, polygonal, elliptic, oval, etc. The radiating element's 50 heat insulation 53 may for its part be formed by mineral wool, glass wool, expanded polystyrene, polyurethane or by some other such material which insulates heat. By forming the radiating surface 51 from a perforated sheet the structure is made sound-absorbing. Sound will travel from the radiating surface's 51 openings into the heat insulation 53 located above radiating surface 51 and it will be absorbed there. The radiating element 50 can also be constructed in such a way that radiating surface 51, heat-transfer tubes 52 and heat insulation 53 are cast together to form a whole. Radiating surface 51 and heat-transfer tubes 52 are located in a mould and then, for example, fluid ceramics are poured on them. When the ceramics solidifies, a radiating element 50 will result which forms a whole.
The invention is not limited to the cross-sectional forms shown in the figure. The cross-sectional forms of supply air chamber 10, mixing chambers 20 a, 20 b and heat exchangers 30 a, 30 b may be rectangular but also, for example, triangular, polygonal, key-stone shapes or their combinations.
In the embodiments shown in the figures, radiating element 50 is the supply air unit's lowest component, and no supply air flow L1 is directed against the radiating element's 50 radiating surface 51. Thus, radiating surface 51 functions as a pure radiator, from which a cooling or heating effect is transferred to surfaces in the room space. Thus, the air in between radiating surface 51 and the surfaces in the room space will hardly be cooled or heated at all by the radiating element's 50 effect.
The above was only a presentation of some advantageous embodiments of the invention, and it is obvious to a person skilled in the art that numerous modifications can be made to these within the scope defined in the appended claims.

Claims

1. Supply air unit (100), which comprises:

a supply air chamber (10),

at least one mixing chamber (20, 20 a, 20 b), which opens into the air-conditioned room space,

nozzles (60, 60 a, 60 b) or a nozzle gap, through which a fresh airflow (L1) is conducted from the supply air chamber (10) into said at least one mixing chamber (20 a, 20 b),

a first heat-transfer unit (A), which is formed by at least one heat exchanger (30, 30 a, 30 b), through which a circulated airflow (L2) is conducted from the air-conditioned room space into said at least one mixing chamber (20, 20 a, 20 b), whereby the circulated airflow (L2) is heated or cooled in said at least one heat exchanger (30, 30 a, 30 b),

characterised in that the supply air unit also comprises:

a second heat-transfer unit (B), which is formed by at least one radiating element (50), which is located in the lower part of the supply air unit (100) and in which there is a radiating surface (51), to which heat is transferred from the air-conditioned room space for cooling, or from which heat is transferred into the air-conditioned room space for heating, which radiating surface (51) also comprises openings, whereby the radiating surface (51) becomes sound-absorbing.

2. Supply air unit (100) according to claim 1, characterised in that the first heat-transfer unit (A) comprises a first heat-transfer tubing (32 a, 32 b) and the second heat-transfer unit (B) comprises a second heat-transfer tubing (52), which are connected together in series.

3. Supply air unit (100) according to claim 2, characterised in that the first heat-transfer unit's (A) heat-transfer tubing (32 a, 32 b) and the second heat-transfer unit's (B) heat-transfer tubing (52) are mutually dimensioned in such a way that the heat-carrying liquid's flow velocity is higher in the second heat-transfer unit's (B) heat-transfer circuit (52) in comparison with the heat-carrying liquid's flow velocity in the first heat-transfer unit's (A) heat-transfer circuit (32 a, 32 b).

4. Supply air unit (100) according to any of claims 1-3, characterised in that the radiating element (50) comprises heat-transfer tubes (52) located above the radiating surface (51) and an insulation (53), which prevents the cooling or heating effect of the heat-transfer tubes (52) from moving upwards from the radiating element (50).

5. Supply air unit (100) according to any of claims 1-4, characterised in that, thus, the radiating element's (50) radiating surface (51) is formed by a horizontal planar surface.

6. Supply air unit (100) according to any of claims 1-5, characterised in that the supply air unit (100) is mounted at its top part to the ceiling, and the second heat-transfer unit (B) is mounted into the lower part of supply air unit (100).

7. Supply air unit (100) according to any of claims 1-6, characterised in that the supply air unit (100) comprises:

a supply air chamber (10), wherein there are vertical side walls (11 a, 11 b), a bottom wall (11 c) and a roof wall (11 d), at which the supply air chamber (10) is suspended from the ceiling (K),

two heat exchangers (30 a, 30 b),

two mixing chambers (20 a, 20 b), which are formed in a space between the supply air chamber's (10) side walls (11 a, 11 b) and the heat exchangers (30 a, 30 b) located at a distance from them,

a row of nozzles (60 a, 60 b) or a nozzle gap in the lower part of each mixing chamber (20 a, 20 b), whereby a fresh airflow (L1) is conducted from the supply air chamber (10) through the row of nozzles (60 a, 60 b) or the nozzle gap into the mixing chambers (20 a, 20 b) upwards in the vertical direction,

a radiating element (50), which is mounted to the supply air chamber's (10) bottom wall (11 c).

8. Supply air unit (100) according to claim 7, characterised in that in the top part of the mixing chambers (20 a, 20 b) there are outlet openings (25 a, 25 b), which are formed in such a way that the combined airflow (LA) discharging from the mixing chambers (20 a, 20 b) is directed horizontally in the direction of the ceiling surface.