STORAGE BATTERY SYSTEM

Abstract

A control device of a storage battery system may determine a degree of deterioration of each of the first storage battery modules and the second storage battery modules. Further, the control device may issue a notification of at least one replacement between a predetermined first storage battery module and a predetermined second storage battery module and a change of storage positions of the predetermined first storage battery module and the predetermined second storage battery module in accordance with the degree of deterioration of each of the first storage battery modules and the second storage battery modules.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe invention relates to a storage battery system.2. Description of the Prior ArtJapanese Unexamined Patent Application No. 2019-164915 discloses the invention concerning a storage battery device. The storage battery device includes a plurality of storage battery modules and a control unit disposed in a case of the storage battery device. The control unit comprises an expansion plug to which an expansion storage battery module can be connected.SUMMARY OF THE INVENTIONIncidentally, in the above-described related art, when a battery module is added, the extension storage battery module is disposed in the case, and a cover of the case is replaced together with it. Therefore, it is considered that addition of a battery module becomes complicated.Further, the battery module is deteriorated or the like in accordance with the number of charging and discharging operations, but the above-described prior art literature does not mention a countermeasure or the like against the deterioration of the battery module.The invention has been made in consideration of the above-mentioned fact, and an object thereof is to provide a storage battery system in which influence by deterioration of a battery module can be reduced without complicated addition of a battery module.A storage battery system according to a first aspect includes: a main power storage device including a first housing unit, a plurality of first storage battery modules accommodated in the first housing unit, a cooling unit accommodated in the first housing unit and configured to cool the inside of the first housing unit, and a control unit accommodated in the first housing unit and configured to control charging and discharging of the first storage battery modules; and an extension power storage device including a second housing unit, and a plurality of second storage battery modules housed in the second housing unit, the second storage battery modules being electrically connectable to the first storage battery modules and replaceable with the first storage battery modules, the second storage battery modules being charged and discharged under the control of the control unit, the control unit being configured to determine a degree of deterioration of each of the first storage battery modules and the second storage battery modules, and to output a notification of at least one of a replacement between a predetermined one of the first storage battery modules and a predetermined one of the second storage battery modules and a change in storage positions of the predetermined one of the first storage battery modules and the predetermined one of the second storage battery modules in accordance with the degree of deterioration.According to the storage battery system of the first aspect, the main power storage device is provided, and the main power storage device includes the first housing unit and the plurality of first storage battery modules and the control unit accommodated in the first housing unit. Further, the control unit may control charging and discharging of the first storage battery modules, and in this aspect, may charge the first storage battery modules by an external power supply or supply electric power from the first storage battery modules to a load.Further, the cooling unit capable of cooling the inside of the first housing unit is accommodated in the first housing unit, and the cooling unit can cool the first storage battery modules to reduce the deterioration of the first storage battery modules.When the supply of electric power to the load by the main power storage device alone is insufficient, an extension storage battery module needs to be prepared. When a configuration is adopted in which the extension storage battery module is disposed in the first housing unit, a change of a part of the first housing unit is required, and it is considered that the installation of the extension storage battery module becomes complicated.In this aspect, the extension power storage device is provided, and the extension power storage device includes the second housing unit and the plurality of second storage battery modules accommodated in the second housing unit. Further, the second storage battery modules may be electrically connected to the first storage battery modules and may be charged and discharged under the control of the control unit.Therefore, in this aspect, when the supply of the electric power to the load by the main power storage device alone is insufficient, electric power can be supplied from the extension power storage device to the main power storage device. That is, in this aspect, the storage battery module may be added to the main power storage device without an extension storage battery module being provided in the first housing unit.Incidentally, the deterioration of the first storage battery module and the second storage battery module varies with the number of charging and discharging operations or the like, but the degree of the deterioration varies depending on the first storage battery module and the second storage battery module. Further, since the first storage battery module and the second storage battery module are used during cooling, the deterioration of the first storage battery module and the second storage battery module can be delayed, and therefore, the use of a first storage battery module or a second storage battery module having a high degree of deterioration while the first storage battery module or the second storage battery module is cooled allows the life of the entire storage battery system to be secured.In this aspect, the control unit may determine the degree of deterioration of each of the first storage battery modules and the second storage battery modules. Further, the control unit may output a notification of at least one of a replacement between a predetermined one of the first storage battery modules and a predetermined one of the second storage battery modules and a change in storage positions of the predetermined first storage battery module and the predetermined second storage battery module in accordance with the degree of deterioration of each of the first storage battery modules and the second storage battery modules.Therefore, the control unit can issue a notification of, for example, the exchange between a second storage battery module having a relatively large degree of deterioration housed in the second housing unit and a first storage battery module having a relatively small degree of deterioration housed in the first housing unit.As a result, an operator or the like that has received the notification can replace the second storage battery module having a relatively high degree of deterioration and the first storage battery module having a relatively low degree of deterioration. Thus, the second storage battery module is brought into a coolable state, and thus the deterioration of the second storage battery module can be reduced.Further, the control unit may issue a notification of, for example, the change in the position of the first storage battery module with a relatively large degree of deterioration accommodated in the first housing unit.As a result, the operator or the like that has received the notification can arrange, inside the first housing unit, a first storage battery module having a relatively high degree of deterioration at a position that can be easily cooled by the cooling unit, and arrange a first storage battery module having a relatively low degree of deterioration at a position that can be hardly cooled by the cooling unit. Thus, the deterioration degrees of the first storage battery modules in the first housing unit can be averaged.As a storage battery system according to a second aspect, in the storage battery system according to the first aspect, the first storage battery modules and the second storage battery modules may be installed in a vehicle and are configured to supply electric power to the vehicle.According to the storage battery system of the second aspect, the first storage battery modules and the second storage battery modules may be installed in a vehicle and supply the vehicle with electric power.Therefore, for example, at the time of replacement or the like of the first storage battery module or the second storage battery module mounted on the vehicle, when the deterioration degrees of the first storage battery module and the second storage battery module are smaller than that of the first storage battery module mounted on the first housing unit or that of the second storage battery module mounted on the second housing unit, the first storage battery module or the second storage battery module mounted on the vehicle can be reused as part of the main power storage device or as part of the extension power storage device.As a storage battery system according to a third aspect, in the storage battery system according to the first aspect or the second aspect, the main power storage device and the extension power storage device are installed at predetermined locations.According to the storage battery system of the third aspect, the main power storage device and the extension power storage device are installed at predetermined locations, and the main power storage device and the extension power storage device can supply electric power to a load in a building or the like, for example.As a storage battery system according to a fourth aspect, in the storage battery system according to any one of the first aspect to the third aspect, the cooling unit is air-cooled, and the first housing unit and the second housing unit are connected to each other.According to the storage battery system of the fourth aspect, the cooling unit accommodated in the first housing unit is air-cooled, so that the first storage battery module in the first housing unit can be cooled by the cold air generated by the cooling unit, so that the deterioration of the first storage battery module can be reduced.Further, in this aspect, the first housing unit and the second housing unit are connected to each other. Thus, the second storage battery module in the second housing unit can be cooled by the cold air generated by the cooling unit, so that the deterioration of the second storage battery module can be reduced.As described above, the storage battery system according to the present invention has the excellent effect that the influence by the deterioration of the battery module can be reduced while the work of adding the battery module does not become complicated.BRIEF DESCRIPTION OF THE DRAWINGSHereinafter, features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: FIG. 1A is a block diagram schematically showing a configuration and operation of a storage battery system according to this embodiment, and a first state; FIG. 1B is a block diagram schematically showing a configuration and operation of the storage battery system according to this embodiment, and a second state; FIG. 2 is a schematic view schematically showing the configuration of the storage battery system according to this embodiment; FIG. 3 is a block diagram showing a functional configuration of a control device constituting a part of the storage battery system according to this embodiment; FIG. 4 is a flowchart for illustrating a control flow related to management of a deterioration degree of a storage battery module in the storage battery system according to this embodiment; FIG. 5 is a flowchart showing a control flow related to the management of supplied electric power in the storage battery system according to this embodiment; FIG. 6A is a block diagram schematically illustrating a configuration and operation of a storage battery system according to a modification example of this embodiment and showing a first state; and FIG. 6B is a block diagram schematically illustrating a configuration and operation of the storage battery system according to the modification example of this embodiment, and showing a second state.DETAILED DESCRIPTION OF EMBODIMENTSNext, referring to FIGS. 1 to 6, an exemplary embodiment of an electric power management system according to the present invention will be described. As shown in FIGS. 1A, 1B, and 2, a "storage battery system 10" according to this embodiment includes a "main power storage device 14" disposed at a predetermined location within a site of a building 12 and an "extension power storage device 16" electrically connectable to the main power storage device 14.As shown in FIG. 1A, the main power storage device 14 includes a "case 22" serving as a first housing unit, "storage battery modules 24" accommodated as a plurality of first storage battery modules in the case 22, a "cooling device 26" serving as a cooling unit, and a "control device 28" serving as a control unit.Specifically, the case 22 includes a door (not shown) that can be opened and closed, and the storage battery module 24 can be inserted and removed in a state where the door is opened.The storage battery module 24 is configured of a plurality of lithium ion battery cells (not shown), and a plurality of storage battery modules 24 are continuously arranged in a height direction of the case 22. The storage battery modules 24 are electrically connected to a connection portion (not shown) in the case 22, and an electric current can be supplied to various loads connected to the main power storage device 14 via the connection portion.Further, the storage battery module 24 may also be used as a vehicle battery by being mounted on a vehicle, and electric power may be supplied to various loads provided in the vehicle.The cooling device 26 uses a water-cooled system and can cool the storage battery module 24. Specifically, the cooling device 26 includes a pipe (not shown) that runs along arrangement portions of the storage battery module 24 in the case 22 and through which a coolant (water) can flow, a pump (not shown) that pumps the coolant, and a radiator (not shown) that cools the coolant. Note that the cooling device 26 is operated based on the control of the control device 28, as described below.The control device 28 includes a central processing unit (CPU) 28A, a read only memory (ROM) 28B, a random access memory (RAM) 28C, a memory 28D, a communication interface (I / F) 28E, and an input / output I / F 28F. Further, the CPU 28A, the ROM 28B, the RAM 28C, the memory 28D, the communication I / F 28E, and the input / output I / F 28F are connected to each other via a bus 28G to enable communication therebetween.The CPU 28A is a central processing unit and controls various devices by executing various programs, and performs control with respect to the main power storage device 14 and the extension power storage device 16. Specifically, the CPU 28A may read a program from the ROM 28B and execute the program using the RAM 28C as a work area. Further, the control device 28 may perform various functions with an execution program stored in the ROM 28B read out and executed by the CPU 28A, as described later.The memory 28D includes a hard disk drive (HDD) or a solid state drive (SSD), and stores various kinds of data and various programs including an operating system. Further, the memory 28D stores measurement results obtained by various measurement devices as described below.The communication I / F 28E is an interface used for connection between the control device 28 and a network N, and can communicate with a monitor 18 installed in the building 12 and a mobile terminal 20 or the like used by a resident of the building 12. The interface uses a communication standard such as Ethernet (registered trademark), FDDI, or Wi-Fi (registered trademark). Further, the communication I / F 28E may include a wireless device.The input / output I / F 28F is an interface through which the control device 28 can communicate with the cooling device 26, a thermometer 30 installed in the case 22, and a resistance meter 32 in the storage battery module 24, or the like.The extension power storage device 16 includes a "case 34" serving as a second housing unit and "storage battery modules 36" serving as a plurality of second storage battery modules accommodated in the case 34.Specifically, the case 34 is configured similarly to the case 22, and allows the storage battery module 36 to be inserted and removed. Further, the storage battery module 36 is referred to as the storage battery module 36 for convenience, but has the same configuration as the storage battery module 24. Note that the storage battery module 36 also includes the resistance meter 32, similar to the storage battery module 24.Further, the extension power storage device 16 may be electrically connected to the main power storage device 14 via a wire harness 38. When the main power storage device 14 and the extension power storage device 16 are connected to each other through the wire harness 38, the storage battery modules 24 and the storage battery modules 36 are brought into a state of being connected in parallel.Next, a functional configuration of the control device 28 will be described with reference to FIG. 3. With the CPU 28A that reads out the execution program stored in the ROM 28B and executes the execution program, the control device 28 functions as a connection of a communication unit 40, a charge / discharge control unit 42, a cooling control unit 44, a storage battery information acquisition unit 43, a deterioration degree determination unit 46, and a storage battery management unit 48.The communication unit 40 can communicate with various devices via the network N and, as shown in FIG. 2, can transmit and receive various items of information to and from the monitor 18 and the mobile terminal 20.When the charge / discharge control unit 42 receives an electric power supply signal as an input signal from a switch provided in the control device 28 or a predetermined terminal, the charge / discharge control unit 42 supplies the electric power stored in the storage battery modules 24 or the storage battery modules 36 to a load connected to the main power storage device 14.Further, when the charge / discharge control unit 42 receives a charge start signal as input from the switch or the terminal, the charge / discharge control unit 42 charges the storage battery modules 24 or the storage battery modules 36 with electric power supplied from an external power supply connected to the main power storage device 14.The storage battery information acquisition unit 43 may store information on a temperature detected by the thermometer 30 in the box 22 and information on an internal resistance value detected by the resistance meter 32 of each of the storage battery modules 24 and the storage battery modules 36, and transmit these pieces of information to the cooling control unit 44, the deterioration degree determination unit 46, and the storage battery management unit 48.The cooling control unit 44 may control the cooling device 26 based on the information on the temperature in the box 22. Specifically, the cooling control unit 44 operates the cooling device 26 when the temperature in the box 22 is equal to or higher than a threshold value, and stops the cooling device 26 when the temperature in the box 22 is lower than the threshold value.The deterioration degree determination unit 46 may determine a deterioration degree of each of the storage battery modules 24 and the storage battery modules 36 based on the information acquired by the storage battery information acquisition unit 43. Specifically, the deterioration degree determination unit 46 in each of the storage battery modules 24 and the storage battery modules 36 compares an internal resistance value at the time of start of use and a current internal resistance value to determine that the storage battery module 24 or the storage battery module 36 is deteriorated when an increase rate of the internal resistance value becomes equal to or higher than a threshold value. That is, in this embodiment, the increase rate of the internal resistance value with respect to the internal resistance value of an initial state of each of the storage battery modules 24 and the storage battery modules 36 is evaluated as the degree of deterioration of each of the storage battery modules 24 and the storage battery modules 36.Further, the deterioration degree determination unit 46 notifies the monitor 18 and the mobile terminal 20 of management information of the deteriorated storage battery module 24 or storage battery module 36, for example, a serial number or the like of the deteriorated storage battery module 24 or storage battery module 36.Further, the deterioration degree determination unit 46 sets optimum storage positions with respect to the box 22 and the box 34 of the storage battery module 24 and the storage battery module 36 based on the deterioration degree of each of the storage battery modules 24 and the storage battery modules 36, and notifies the monitor 18 and the mobile terminal 20 of the storage positions of the storage battery module 24 and the storage battery module 36 based on the storage positions as management information.The storage battery management unit 48 decides which electric power of the main power storage device 14 or the extension power storage device 16 is preferentially used based on the information on the temperature in the box 22.Specifically, the storage battery management unit 48 preferentially uses the electric energy of the main power storage device 14 when the temperature in the box 22 is equal to or higher than a threshold value, and preferentially uses the electric energy of the extension power storage device 16 when the temperature in the box 22 is lower than the threshold value.Actions and Effects of this EmbodimentNext, the actions and effects of this embodiment will be described.As shown in FIG. 1A, the main power storage device 14 is provided, and the main power storage device 14 includes the case 22, the plurality of storage battery modules 24, and the control device 28 housed in the case 22. Further, the control device 28 may control charging and discharging of the storage battery modules 24, and in this embodiment, may charge the storage battery modules 24 to a load by an external power supply or supply electric power from the storage battery modules 24.Further, the case 22 includes the cooling device 26 that can cool the inside of the case 22, and the cooling device 26 can cool the storage battery module 24 to prevent deterioration of the storage battery module 24.When the supply of electric power to the load by the main power storage device 14 alone is insufficient, an extension storage battery module needs to be provided. At this time, when a configuration is used in which the extension storage battery module is disposed in the case 22, work for replacing a part of the case 22 is required, and it is considered that the installation of the extension storage battery module becomes complicated.In this embodiment, the extension power storage device 16 is provided, and the extension power storage device 16 includes the case 34 and the plurality of storage battery modules 36 accommodated in the case 34.Therefore, in this embodiment, when the supply of the electric power to the load by the main power storage device 14 alone is insufficient, the main power storage device 14 can be supplied with electric power from the extension power storage device 16. That is, in this embodiment, the storage battery module may be added to the main power storage device 14 without providing an extension storage battery module in the case 22.Incidentally, the storage battery module 24 and the storage battery module 36 are deteriorated according to the number of charging and discharging operations or the like, and the degree of deterioration varies depending on the storage battery module 24 and the storage battery module 36. Further, deterioration of the storage battery module 24 and the storage battery module 36 can be delayed because the storage battery module 24 and the storage battery module 36 are used while being cooled, so that by using a storage battery module 24 or a storage battery module 36 having a high degree of deterioration while the storage battery module 24 or the storage battery module 36 is cooled, the life of the entire storage battery system 10 can be secured.In this embodiment, the control device 28 may determine the degree of degradation of each of the storage battery modules 24 and the storage battery modules 36. Further, the control device 28 may issue a notification of at least one of replacement between a predetermined storage battery module 24 and a predetermined storage battery module 36 and change of storage positions of the predetermined storage battery module 24 and the predetermined storage battery module 36 in accordance with the degree of deterioration of each of the storage battery modules 24 and the storage battery modules 36.Next, with reference to substantially the flowchart of FIG. 4, a control flow related to the processing executed by the control device 28 at the time of managing the deterioration degree of the storage battery module will be described. The control flow is started when the CPU 28A of the control device 28 receives a predetermined control signal at predetermined time intervals.When this control flow is started in step S 100, the CPU 28A functions as the storage battery information acquisition unit 43 to acquire the information on the internal resistance value of each of the storage battery modules 24 and the storage battery modules 36, and then proceeds to step S 101.In step S 101, the CPU 28A functions as the deterioration degree determination unit 46 to evaluate the degree of deterioration of each of the storage battery modules 24 and the storage battery modules 36 based on the information obtained from the storage battery information acquisition unit 43. When it is determined that there is a storage battery module 24 or a storage battery module 36 having a degree of deterioration equal to or greater than a threshold (step S 101: YES), the process proceeds to step S 102. On the other hand, when it is determined that there is no storage battery module 24 or storage battery module 36 having a degree of deterioration equal to or higher than the threshold (step S 101: NO), the process returns to step S 100.In step S 102, the CPU 28A functions as the deterioration degree determination unit 46 to inform the monitor 18 and the mobile terminal 20 of the management information of the storage battery module 24 and the storage battery module 36, and ends the control flow. Specifically, the CPU 28A transmits, to the monitor 18 and the mobile terminal 20, information such as a serial number for identifying the deteriorated storage battery module 24 or storage battery module 36, and information on optimum storage positions with respect to the box 22 and the box 34 of the storage battery module 24 and the storage battery module 36 on the basis of the degrees of deterioration of the storage battery module 24 and the storage battery module 36.Therefore, for example, the control device 28 may notify the exchange between a storage battery module 36 having a relatively high degree of deterioration in the box 34 and a storage battery module 24 having a relatively low degree of deterioration in the box 22.As a result, an operator or the like who has received the notification can replace the storage battery module 36 having a relatively high degree of deterioration and the storage battery module 24 having a relatively small degree of deterioration, as shown in FIG. 1B. Thus, the storage battery module 36 is brought into a coolable state, and thus the deterioration of the storage battery module 36 can be reduced.Further, the controller 28 may provide a notification of, for example, the change in position of the storage battery module 24 stored in the box 22 with a relatively high degree of degradation.As a result, the operator or the like who has obtained the notification can arrange, within the box 22, a storage battery module 24 having a relatively high degree of deterioration at a position that is easily cooled by the cooling device 26, and a storage battery module 24 having a relatively low degree of deterioration at a position that is difficult to be cooled by the cooling device 26. Thus, the degradation level of the storage battery module 24 may be averaged in box 22.Further, in this embodiment, the control device 28 may set whether it uses one of the main power storage device 14 and the extension power storage device 16 to supply the load with electric power. Next, with reference to substantially the flowchart of FIG. 5, a control flow according to the processing executed by the control device 28 at the time of management of supplied electric power of the storage battery module will be described. The control flow is started when the CPU 28A of the control device 28 receives a predetermined control signal at predetermined time intervals.When the control flow is started, the CPU 28A functions as the storage battery management unit 48 to determine whether or not the temperature in the box 22 is equal to or higher than a threshold in step S 200. When it is determined that the temperature in the box 22 is equal to or higher than the threshold (step S 200: YES), the process proceeds to step S 201. On the other hand, when it is determined that the temperature in the box 22 is lower than the threshold (step S 200: NO), the process proceeds to step S 202.In step S 201, the CPU 28A functions as the storage battery management unit 48 to set a circuit such that the electric power from the storage battery module 24 is supplied to the main power storage device 14 of the load, and ends the control flow.In step S 202, the CPU 28A functions as the storage battery management unit 48 to set the circuit so that the electric power from the storage battery module 36 of the extension power storage device 16 is supplied to the load, and ends the control flow.Further, in this embodiment, the storage battery modules 24 and the storage battery modules 36 may be mounted on a vehicle and supply the vehicle with electric power.Therefore, for example, in the replacement or the like of the vehicle-mounted storage battery modules 24 and 36, when the degrees of deterioration of the storage battery module 24 and the storage battery module 36 are smaller than that of the storage battery module 24 housed in the case 22 or the storage battery module 36 housed in the case 34, the storage battery module 24 or the storage battery module 36 that has been mounted in the vehicle can be reused as a part of the main power storage device 14 or as a part of the extension power storage device 16.Further, in this embodiment, the main power storage device 14 and the extension power storage device 16 are installed at predetermined locations, and the main power storage device 14 and the extension power storage device 16 can supply electric power to a load in the building 12 or the like.As described above, in this embodiment, the influence by the deterioration of the battery module can be reduced while preventing the additional work of installing battery modules from becoming complicated.Modification Example of this EmbodimentNext, with reference to FIGS. 6A and 6B, a modification example of this embodiment will be described.In this modification example, the case 22 of the main power storage device 14 and the case 34 of the extension power storage device 16 are connected to each other through a communication portion 50, and the cooling device 26 is air-cooled by an air blower or the like, as shown in FIG. 6A.With such a configuration, the storage battery module 24 in the case 22 can be cooled by the cold air generated by the cooling device 26, so that the deterioration of the storage battery module 24 can be reduced.Further, in this embodiment, the case 22 and the case 34 are connected to each other. Thus, in the case 34, the storage battery module 36 can be cooled by the cold air generated from the cooling device 26, so that the deterioration of the storage battery module 36 can be reduced. Further, also in this modification, a storage battery module 36 having a relatively high degree of deterioration and a storage battery module 24 having a relatively low degree of deterioration may be replaced as shown in FIG. 6B. Thus, the storage battery module 36 can be brought into a more coolable state, and thus the deterioration of the storage battery module 36 can be reduced.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 2019-164915

[0002]

Claims

A storage battery system comprising: a main power storage device including: a first housing unit; a plurality of first storage battery modules accommodated in the first housing unit; a cooling unit accommodated in the first housing unit and configured to cool the inside of the first housing unit; and a control unit accommodated in the first housing unit and configured to control charging and discharging of the first storage battery modules; and an extension power storage device comprising: a second housing unit; and a plurality of second storage battery modules housed in the second housing unit, the second storage battery modules being electrically connectable to the first storage battery modules and replaceable with the first storage battery modules, the second storage battery modules being charged and discharged under the control of the control unit, the control unit being configured to determine a degree of deterioration of each of the first storage battery modules and the second storage battery modules, and to output a notification of at least one of a replacement between a predetermined one of the first storage battery modules and a predetermined one of the second storage battery modules and a change in storage positions of the predetermined one of the first storage battery modules and the predetermined one of the second storage battery modules in accordance with the degree of deterioration.The storage battery system of claim 1, wherein the first storage battery modules and the second storage battery modules are installed in a vehicle and configured to provide the vehicle with electrical power.The storage battery system according to claim 1, wherein the main power storage device and the extension power storage device are installed at predetermined locations.The storage battery system of claim 1, wherein: the cooling unit is air cooled; and the first housing unit and the second housing unit are connected to each other.

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