Treatment system and method for treating workpieces

Abstract

In order to provide a treatment system (100) for treating workpieces (102) that is of simple and compact instruction and allows efficient treatment of workpieces, the treatment system (100) comprises the following: a treatment space (110) which serves to receive one or more workpieces (102) and in which a treatment operation can be performed; and one or more air recirculation units (118) by means of which a recirculating air flow can be generated which is conducted through the treatment space (110), wherein the one or more air recirculation units (118) each comprise one or more electric heating devices (122).

Description

[0001] Treatment plant and method for treating workpieces

[0002] The present invention relates to a treatment system for treating workpieces, in particular a dryer for drying coated vehicle bodies. The treatment system is thus particularly a component of a painting system for painting vehicle bodies.

[0003] Dryers are currently mostly centrally heated. Burner systems, gas turbines, or other gas-fired systems are particularly suitable for this. For gas-fired systems, central heating is often the preferred solution due to its flexibility, controllability, pre-assembly of fan units, and savings in electricity consumption. However, it can also pose disadvantages when it comes to installing external supply units and connecting them via gas ducts.

[0004] The present invention is based on the object of providing a treatment plant which is simple and compact in design and enables efficient operation.

[0005] This object is achieved according to the invention by a treatment plant according to claim 1.

[0006] The treatment system is used to treat workpieces. Specifically, the treatment system is a dryer for drying vehicle bodies.

[0007] The treatment system preferably comprises the following: a treatment chamber, which serves to accommodate one or more workpieces and in which a treatment process can be carried out; and one or more recirculation units, by means of which a recirculation flow can be generated through the treatment chamber, wherein the one or more recirculation units each comprise one or more electrical heating devices.

[0008] Because the treatment system preferably comprises one or more recirculation units, each with one or more electric heaters, the treatment system can preferably be designed in a simple and compact manner. In particular, compared to centrally gas-heated systems, complex duct systems can be eliminated.

[0009] The treatment system preferably comprises several electrical heating devices, which serve in particular to heat different treatment chamber sections. The treatment system thus preferably comprises a decentralized heating system. This allows interfaces and thus complexity in engineering and on the construction site to be minimized.

[0010] Preferably, the one or more heating devices each comprise one or more electric heating registers. This allows the one or more heating devices to be quickly controllable and to exhibit low pressure loss.

[0011] It can be advantageous if the treatment room comprises several treatment room sections, with each treatment room section being assigned a separate recirculation unit.

[0012] The treatment system preferably comprises a conveying device by means of which the workpieces can be conveyed along a conveying direction through the treatment chamber.

[0013] The treatment chamber sections are preferably arranged successively along the conveying direction of the conveying device of the treatment plant.

[0014] The workpieces can preferably be conveyed through the treatment chamber in a transverse orientation, wherein in the transverse orientation a longitudinal axis, in particular a vehicle longitudinal axis, of the workpieces is aligned transversely, in particular at least approximately perpendicularly, to the conveying direction and / or at least approximately horizontally.

[0015] It may be advantageous if each recirculation unit comprises the following: a fan for driving the recirculation air flow in the respective recirculation unit; an electric heating device for heating the recirculation air flow; one or more supply devices for supplying the heated recirculation air flow to the treatment room; one or more return ducts for returning the recirculation air flow from the treatment room to the fan.

[0016] By means of the fan, the circulating air flow can preferably be driven in such a way that it flows successively through the electric heating device, a distribution chamber, a treatment chamber section of the treatment chamber, a return duct and an intake chamber, in particular in this order, before reaching the fan again.

[0017] The electric heating device is preferably arranged downstream of the fan and / or upstream of a distribution chamber with respect to the flow direction of the circulating air flow. The distribution chamber, for example, is directly adjacent to the treatment chamber and serves to distribute the circulating air flow to several supply devices, in particular nozzles. The supply devices, in particular nozzles, preferably direct the circulating air flow into the treatment chamber.

[0018] It may be advantageous if each recirculation unit comprises a fan for driving the recirculation air flow in the respective recirculation unit and an electric heating device for heating the recirculation air flow, wherein an intake space is preferably provided upstream of the fan.

[0019] It may be advantageous if the intake chamber extends in a horizontal transverse direction of the treatment plant, which is in particular perpendicular to a conveying direction, over at least approximately 50%, in particular at least approximately 100%, preferably at least approximately 200%, of a horizontal extent of an impeller of the fan.

[0020] Alternatively or additionally, the intake chamber can be arranged between the treatment chamber and the fan, in particular with respect to a horizontal transverse direction of the treatment system running perpendicular to a conveying direction. Furthermore, alternatively or additionally, the intake chamber can be arranged at least approximately at the same height in the vertical direction as an impeller of the fan.

[0021] In a further embodiment or development of the invention, it can be provided alternatively or additionally that each recirculation unit comprises a fan for driving the recirculation air flow in the respective recirculation unit and an electric heating device for heating the recirculation air flow, wherein an ejection area and / or a homogenization area are preferably provided downstream of the fan.

[0022] It may be advantageous if the ejection region and / or the equalization region extend in the vertical direction over at least approximately 50%, in particular at least approximately 100%, preferably at least approximately 200%, of a vertical extent of an impeller of the fan (120).

[0023] Alternatively or in addition to this, it may be advantageous if the discharge area and / or the equalization area are arranged directly above the fan and / or an intake chamber.

[0024] Furthermore, alternatively or additionally, it can be provided that the ejection area and / or the equalization area are arranged in the horizontal direction at least approximately at the same height as the one or more electrical heating devices.

[0025] It is preferably provided that the fan is a radial fan, wherein a rotational axis of an impeller of the radial fan is preferably aligned at least approximately horizontally and / or at least approximately perpendicularly to a conveying direction of the treatment plant.

[0026] It can be provided that the one or more return channels run below the treatment chamber, in particular in a floor wall of the treatment system that delimits the treatment chamber at the bottom.

[0027] It may be advantageous if one or more of the recirculating air units each have one or more supply ducts, by means of which recirculating air, which has been heated by means of the electric heating device, can be guided from one side of the treatment room, on which the electric heating device is arranged, to another side of the treatment room and can be introduced into the treatment room there.

[0028] One or more supply channels can, for example, fluidically connect a distribution chamber arranged immediately downstream of the electric heating device with another distribution chamber arranged on an opposite side of the treatment chamber.

[0029] Alternatively or additionally, one or more supply channels can be provided to fluidically connect, for example, a distribution chamber located directly downstream of the electric heating device with one or more supply devices, in particular nozzles, in a floor wall of the treatment system. This allows, in particular, sill areas or other heavy-duty parts of the workpieces to be targeted with circulating air.

[0030] In one embodiment of the invention, it can be provided that one or more of the recirculation units each comprise several electrical heating devices.

[0031] It may be particularly advantageous if the one or more electrical heating devices are the only devices that serve, in particular, primarily to heat the circulating air flow.

[0032] It may be advantageous if the one or more recirculation units, especially all of the recirculation units, are arranged laterally adjacent to the treatment room. In particular, scaffolding for elevated installation is then preferably unnecessary.

[0033] Preferably, the one or more recirculation units are fully accessible at ground level, in particular for assembly and / or maintenance work.

[0034] The treatment plant then preferably does not require a complex scaffolding structure.

[0035] The present invention is further based on the object of providing a method that enables efficient operation of a treatment plant using a simple and compact design. This object is achieved according to the invention by a method according to the independent method claim.

[0036] The method is in particular a method for treating workpieces, in particular for drying vehicle bodies.

[0037] Preferably, the method comprises the following:

[0038] Feeding one or more workpieces to a treatment room of a treatment system, in particular a treatment system according to the invention;

[0039] Heating the one or more workpieces by means of one or more circulating air streams, wherein the one or more circulating air streams are generated by means of one or more circulating air units;

[0040] Heating the one or more circulating air streams by means of one or more electrical heating devices.

[0041] The method preferably has one or more of the features and / or advantages described in connection with the treatment plant.

[0042] Preferably, the treatment plant further comprises one or more of the features and / or advantages described in connection with the method.

[0043] It can be beneficial if conditioned fresh air is supplied to the treatment room and this fresh air is then circulated as a recirculation air flow in one or more recirculation units, with heat being supplied in the recirculation units exclusively by electrical heating.

[0044] The conditioned fresh air is supplied via one or two locks at one or both ends of the treatment room.

[0045] The treatment plant preferably further comprises an exhaust device for removing exhaust air. The exhaust air is removed, in particular, from a treatment chamber section arranged centrally with respect to the conveying direction, for example. It may be advantageous if the exhaust air is fed to a purification device, for example, a regenerative thermal oxidizer (RTO), to remove contaminants contained in the exhaust air. The purification device is preferably located outside a building in which the treatment plant is installed.

[0046] In one embodiment of the invention, it can be provided that the one or more recirculating air flows are supplied in at least approximately horizontal direction to one or more fans of the one or more recirculating air units.

[0047] Alternatively or additionally, it can be provided that the one or more recirculating air flows are discharged upwards from the one or more fans in at least an approximately vertical direction.

[0048] Furthermore, alternatively or additionally, it can be provided that the one or more circulating air flows are deflected in a spatial area arranged above the one or more fans and / or, in particular in at least approximately horizontal direction, are fed to the one or more electrical heating devices.

[0049] Furthermore, the treatment plant and / or the method may preferably have one or more of the features and / or advantages described below:

[0050] Optionally, it can be provided that in a room area directly adjacent to a fan, which in particular opens into a heating device, one or more guide elements for targeted flow guidance and / or flow influence are arranged.

[0051] By means of one or more guide elements, an at least approximately homogeneous flow to the heating device can preferably be achieved.

[0052] Furthermore, alternatively or additionally, one or more cover elements can be provided that partially cover an inflow cross-sectional area of ​​the heating device. This can also serve to achieve a more homogeneous flow. One or more cover elements can, for example, be designed as perforated plates to locally throttle the flow.

[0053] The one or more cover elements are therefore preferably throttle elements.

[0054] It may be advantageous if the one or more heating devices, in particular heating registers, are dimensioned in such a way that they can be removed from a receptacle for the respective heating device in a direction running at least approximately parallel to the conveying direction, in particular without the need to dismantle other components of the treatment plant.

[0055] For example, it can be provided that each recirculation unit is assigned to several treatment room sections, but extends only over one of the treatment room sections, so that one or more adjacently arranged treatment room sections, starting from the heating device along the conveying direction, allow a free space for maintenance and / or repair of the heating device.

[0056] In particular, one or more electric heating registers are dimensioned such that their insertion depth is less than the length of a treatment chamber along the conveying direction. The arrangement of the heating devices is selected in particular so that, in addition to each heating device, at least one adjacent treatment chamber section is not occupied by a heating device. Removal can then take place in or against the conveying direction (dryer flow direction). This preferably reduces the required space reserve perpendicular to the conveying direction to the removal space for the fan.

[0057] Heat exchangers, for example, can be provided to recover heat dissipated via the exhaust air. These transfer the heat, for example, to a fresh air stream being supplied. In particular, this can preferably achieve partial preheating of the fresh air stream.

[0058] Alternatively, heat recovery can preferably be achieved via waste heat boilers. The one or more recirculation units can preferably be pre-assembled together with the associated one or more treatment room sections and transported as a unit to a final assembly location. This preferably eliminates the need for media interfaces; only a power connection is then required.

[0059] Preferably, one or more, in particular all, electrically operated heating components, such as fresh air heat exchangers and / or fresh air heaters, can be supplied with a medium voltage of, for example, at least approximately 3 kV and / or at most approximately 8 kV, in particular 4160 V to 6600 V, in particular instead of the usual 400 V. For this purpose, for example, one or more medium-voltage heating elements can be provided. This may require special heating elements with corresponding additional costs, but offers great savings potential, preferably in the periphery, i.e. with regard to connections, cables, etc. In addition, this preferably requires a significantly lower voltage transformation factor from the supply network, which, among other things, reduces the size of the transformer station in favor of lower investment costs and saves space.The connection to an electrically operated heating component with such a medium voltage also preferably results in significantly smaller cable diameters.

[0060] Further preferred features and / or advantages of the invention are the subject of the following description and the drawings of exemplary embodiments.

[0061] The figures show:

[0062] Fig. 1 is a schematic vertical cross-section through an embodiment of a treatment plant;

[0063] Fig. 2 is an enlarged view of a recirculation unit of the treatment plant from Fig. 1;

[0064] Fig. 3 is a schematic perspective view of a heating device of the recirculation unit of the treatment plant from Fig. 1; and Fig. 4 is a vertical cross-section through a region of a treatment room facing away from the recirculation unit of an alternative embodiment of a treatment plant.

[0065] Identical or functionally equivalent elements are provided with the same reference numerals in all figures.

[0066] An embodiment of a treatment system designated as a whole by 100, shown in Figs. 1 to 3, serves to treat workpieces 102, in particular vehicle bodies 104. The treatment system 100 is in particular a dryer 106 for drying previously coated vehicle bodies 104.

[0067] The treatment system 100 comprises a housing 108 surrounding a treatment chamber 110. The treatment chamber 110 serves to accommodate workpieces 102 for treatment thereof.

[0068] The workpieces 102 can be conveyed in particular by means of a conveying device 112 (shown only in Fig. 4) of the treatment system 100 along a conveying direction 114 through the treatment chamber 110 and can be exposed to heated circulating air.

[0069] The treatment system 100 comprises an air duct 116, which in particular comprises one or more recirculation units 118. By means of the one or more recirculation units 118, a recirculation volume flow can be passed through the treatment chamber 110 several times.

[0070] Each recirculation unit 118 preferably comprises a fan 120 for driving the recirculated air flow, an electric heating device 122 for heating the recirculated air flow, and one or more supply devices 126, designed, for example, as nozzles 124, for supplying the recirculated air flow to the treatment chamber 110, and one or more return ducts 128 for discharging the recirculated air flow from the treatment chamber 110.

[0071] A distribution chamber 130 is preferably arranged between the heating device 122 and one of the plurality of supply devices 126, which serves to distribute the heated circulating air flow to the supply devices 126. The distribution chamber 130 is preferably accessible to persons and also serves as a maintenance area 132 for performing cleaning and / or maintenance work within the respective recirculation unit 118.

[0072] The fan 120 is preferably a free-running built-in fan.

[0073] Preferably, the fan 120 is a radial fan. Alternatively, in an embodiment not shown, the fan 120 can also be a longitudinal flow fan (axial fan).

[0074] Upstream of the fan 120, an intake chamber 134 is preferably provided, which extends in particular transversely, preferably perpendicularly, to the conveying direction 114 over a depth that corresponds at least approximately to the diameter of an impeller of the fan 120. This enables efficient intake perpendicular to the conveying direction 114.

[0075] The suction chamber 134 is preferably arranged between the treatment chamber 110 and the fan 120, in particular with respect to a horizontal transverse direction of the treatment system 100 running perpendicular to the conveying direction 114.

[0076] An ejection area 136 of the fan 120 is preferably formed above the fan 120. The fan 120 thus preferably sucks in a horizontal direction and ejects upwards in a vertical direction.

[0077] The ejection area 136 is preferably followed by a homogenization area 138, which serves to supply the circulating air flow to the heating device 122 as homogeneously as possible. As can be seen in particular from Figs. 2 and 3, one or more guide elements 140, one or more cover elements 142 and / or one or more throttle elements 144 can be provided for further homogenization of the flow to the heating device 122, for example frame elements, perforated plates or other components that contribute to a uniform flow to and / or through the heating device 120.

[0078] The one or more guide elements 140, the one or more cover elements 142, and / or the one or more throttle elements 144 can, for example, be screwed or otherwise secured to support elements or other components of the air guide 116. In particular, a replaceable attachment can be provided to allow the element(s) to be replaced for further optimization or maintenance.

[0079] The heating device 120 is or comprises in particular a heating register 146 through which the circulating air flow can flow, wherein in particular electrical resistance heating elements of the heating device 120 generate heat and release it to the circulating air flow.

[0080] One or more filter elements 148 are preferably arranged downstream of the heating device 120, in particular in the distribution chamber 130 or adjacent thereto, for example, directly upstream of the one or more supply devices 126. The one or more filter elements 148 serve in particular to separate contaminants from the circulating air stream before it is fed to the treatment chamber 110.

[0081] The one or more return ducts 128 are arranged, in particular integrated, for example, in a bottom wall 150 of the housing 108 of the treatment system 100. Preferably, the one or more return ducts 128 extend over more than half the width of the treatment chamber, so that, in particular, the recirculating air is extracted at least approximately on a side of the treatment chamber 110 opposite the supply devices 126.

[0082] The embodiment of a treatment plant 100 shown in Figs. 1 to 3 functions as follows:

[0083] First, one or more workpieces 102 are introduced into the treatment chamber 110 by means of the conveying device 112 along the conveying direction 114. The workpieces 102 are then exposed to heated circulating air from the one or more circulating air units 118 and are thereby dried, for example.

[0084] For this purpose, the circulating air is circulated by means of the fan 120 and, starting from the fan 120, flows successively through the homogenization area 138, the heating device 122, the distribution chamber 130, optionally one or more filter elements 148, the one or more feed devices 126, the treatment chamber 110, and the one or more return ducts 128. Finally, the circulating air returns to the fan 120 via the intake chamber 134. The heat required to carry out the treatment process is generated by the heating device 122. For this purpose, the heating device 122 is or comprises an electrical heating register 146, which releases electrically generated heat to the circulating air flow as it flows through the same.

[0085] The heating device 122 thus generates heat where it is needed. An additional heat source located outside the respective recirculation unit 118, which would otherwise take up too much space, is thus preferably unnecessary. The recirculation unit 118 can thus be designed particularly compactly. In particular, complex piping for heating gas or other heat transfer media is eliminated.

[0086] It may be provided that each recirculation unit 118 comprises a single heating device 122.

[0087] Alternatively, each recirculation unit 118 may comprise a plurality of heating devices 122.

[0088] As can be seen in particular from Fig. 4, it can be provided that the circulating air flow is not supplied entirely on one side to the treatment chamber 110, but that, for example, a distribution chamber 130 is arranged on each side. The supply of heated circulating air then takes place in particular on the one hand, as in the embodiment according to Figs. 1 to 3, and on the other hand, according to Fig. 4, on the opposite side of the treatment chamber 110. For this purpose, the opposite distribution chamber 130 is preferably supplied with heated circulating air by means of a supply duct 156.

[0089] In further alternative embodiments of treatment systems 100, one or more feed channels 156 can additionally or supplementarily be arranged in the floor wall 150 and, for example, lead to feed devices 126, which serve to apply pressure to heavy-duty components of the workpieces 102, for example, sills or supporting structures of a vehicle body 104. For example, it can be provided that one or more feed devices 126 are arranged in the region of a dryer rear wall and / or in the floor area and extend, for example, along two vehicle sills of the workpiece 102.

[0090] As a result, a more uniform heating of the workpiece 102 can preferably be realized overall, wherein the one or more electrical heating devices 122 can result in a compact design and efficient system operation.

[0091] List of reference symbols

[0092] Workpiece treatment system

[0093] Vehicle body dryer housing

[0094] Treatment room Conveyor device Conveyor direction Air flow Recirculation unit Fan

[0095] Heating device nozzle

[0096] Feeding device Return channel Distribution room Maintenance area Suction area Ejection area

[0097] Uniformity area Guide element Cover element Throttle element Heating register Filter element Bottom wall Feed channel

Claims

Claims Treatment plant (100) for the treatment of workpieces (102), in particular for drying vehicle bodies, wherein the treatment plant (100) comprises the following: - a treatment room (110) which serves to accommodate one or more workpieces (102) and in which a treatment process can be carried out; - one or more recirculation units (118) by means of which a recirculated airflow can be generated through the treatment room (110), wherein the one or more recirculation units (118) each comprise one or more electric heating devices (122). Treatment system (100) according to claim 1, characterized in that the treatment room (110) comprises several treatment room sections, each treatment room section being assigned a separate recirculation unit (118). Treatment system (100) according to one of claims 1 or 2, characterized in that each recirculation unit (118) comprises the following: - a fan (120) to drive the recirculated air flow in the respective recirculation unit (118); - an electric heating device (122) for heating the circulating air stream; - one or more supply devices (126) for supplying the heated recirculated air stream to the treatment room (110); - one or more return channels (128) for returning the recirculated air flow from the treatment chamber (110) to the fan (120). Treatment system (100) according to claim 3, characterized in that the electric heating device (122) is arranged downstream of the fan (120) and upstream of a distribution chamber (130) with respect to a flow direction of the recirculated air flow, wherein the distribution chamber (130) adjoins the treatment chamber (110) and serves to distribute the recirculated air flow to several supply devices (126), in particular nozzles (124). Treatment system (100) according to one of claims 1 to 4, characterized in that each recirculation unit (118) comprises a fan (120) for driving the recirculation flow in the respective recirculation unit (118) and an electric heating device (122) for heating the recirculation flow, wherein an intake chamber (134) is provided upstream of the fan (120), wherein a) the intake chamber (134) extends in a horizontal transverse direction of the treatment system (100), which is in particular perpendicular to a conveying direction (114), over at least approximately 50%, in particular at least approximately 100%, preferably at least approximately 200% of a horizontal extension of an impeller of the fan (120); and / or b) the intake chamber (134) is arranged between the treatment chamber (110) and the fan (120), in particular with respect to a horizontal transverse direction of the treatment system (100) perpendicular to a conveying direction (114);and / or c) the intake chamber (134) is arranged in the vertical direction at least approximately at the same height as an impeller of the fan (120). Treatment system (100) according to one of claims 1 to 5, characterized in that each recirculation unit (118) comprises a fan (120) for driving the recirculation flow in the respective recirculation unit (118) and an electric heating device (122) for heating the recirculation flow, wherein downstream of the fan (120) a discharge area (136) and / or a homogenization area (138) are provided, wherein a) the discharge area (136) and / or the homogenization area (138) extend in the vertical direction over at least approximately 50%, in particular at least approximately 100%, preferably at least approximately 200% of a vertical extent of an impeller of the fan (120);and / or b) the discharge area (136) and / or the equalization area (138) are arranged directly above the fan (120) and / or an intake chamber (134); and / or c) the discharge area (136) and / or the equalization area (138) are arranged in a horizontal direction at least approximately at the same height as the one or more electric heating devices (122). Treatment system (100) according to any one of claims 1 to 6, characterized in that the fan (120) is a radial fan, wherein an axis of rotation of an impeller of the radial fan is oriented at least approximately horizontally and / or at least approximately perpendicular to a conveying direction (114) of the treatment system (100). Treatment system (100) according to any one of claims 1 to 7, characterized in that each recirculation unit (118) comprises the following: - a fan (120) to drive the recirculated air flow in the respective recirculation unit (118); - an electric heating device (122) for heating the circulating air stream; - one or more supply devices (126) for supplying the heated recirculated air stream to the treatment room (110); - one or more return channels (128) for returning the recirculated air flow from the treatment chamber (110) to the fan (120); and that the one or more return channels (128) run below the treatment chamber (110), in particular in a floor wall (150) of the treatment system (110) that bounds the treatment chamber (110) downwards. Treatment system (100) according to one of claims 1 to 8, characterized in that each recirculated air unit (118) comprises the following: - a fan (120) to drive the recirculated air flow in the respective recirculation unit (118); - an electric heating device (122) for heating the circulating air stream; - one or more supply devices (126) for supplying the heated recirculated air stream to the treatment room (110); - one or more return channels (128) for returning the recirculated air flow from the treatment room (110) to the fan (120); and that one or more of the recirculated air units (118) each have one or more supply channels (156) by means of which recirculated air, which has been heated by means of the electric heating device (122), can be guided from one side of the treatment room (110), on which the electric heating device (122) is arranged, to another side of the treatment room (110) and introduced there into the treatment room (110). Treatment system (100) according to claim 9, characterized in that one or more of the supply channels (156) connect a distribution chamber (130) arranged directly downstream of the electric heating device (122) with a further distribution chamber (130) arranged on an opposite side of the treatment chamber (110) via a fluid flow. Treatment system (100) according to any one of claims 1 to 10, characterized in that the one or more electric heating devices (122) are the only devices for heating the recirculated air stream. Treatment system (100) according to any one of claims 1 to 11, characterized in that the one or more recirculated air units (118) are arranged laterally adjacent to the treatment chamber (110) and / or are fully accessible at ground level, particularly for assembly and / or maintenance work.Method for treating workpieces (102), in particular for drying vehicle bodies (104), wherein the method comprises:. - Feeding one or more workpieces (102) to a treatment room (110) of a treatment system (100), in particular a treatment system (100) according to one of claims 1 to 12; - Heating one or more workpieces (102) by means of one or more recirculating air streams, wherein the one or more recirculating air streams are generated by means of one or more recirculating air units (118); - Heating one or more recirculated air streams by means of one or more electric heating devices (122). Method according to claim 13, characterized in that conditioned fresh air is supplied to the treatment room (110) and this fresh air is subsequently circulated as a recirculated air stream in one or more recirculation units (118), wherein heat is supplied to the recirculation units (118) exclusively by means of electric heating. Method according to one of claims 13 or 14, characterized in that the one or more recirculated air streams a) are supplied in an at least approximately horizontal direction to one or more fans (120) of the one or more recirculated air units (118); and / or b) are discharged upwards from the one or more fans in an at least approximately vertical direction; and / or c) are deflected in a space area arranged above the one or more fans (120) and are supplied in an at least approximately horizontal direction to the one or more electric heating devices (122).

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