Reversible air conditioning device for a motor vehicle and method for operating such a device

Description

[0001] The present invention claims priority from French application 2102628 filed on March 16, 2021.

[0002] The invention relates to the field of air conditioning of motor vehicles in general, and in particular of motor vehicles with electric motors and / or those with thermal motors, such as hybrid thermal / electric propulsion vehicles.

[0003] Air conditioning is a comfort feature increasingly common in motor vehicles. Typically, a vehicle air conditioning system consists of four main components: a compressor, a condenser, an expansion valve, and an evaporator. These four components are arranged within a closed circuit through which a refrigerant (or heat transfer fluid) circulates. Some vehicles have systems that provide both air conditioning (or cooling) and heating for the passenger compartment. In these systems, certain components have a dual function. For example, they might include two heat exchangers that alternately act as condensers or evaporators depending on whether the system is operating in air conditioning or heating mode.

[0004] For example, document FR3079919 describes a reversible air conditioning system that reduces fuel consumption due to a mechanical compressor in the case of an internal combustion engine and range loss in the case of an electric or hybrid vehicle, and which is capable of operating, in the case of a vehicle equipped with an internal combustion engine, even when the engine is momentarily switched off. This system also provides excellent results but generates significant equipment costs for the vehicle that receives it.

[0005] US document 2012 / 117993 describes a method for managing a reversible vehicle air conditioning device, the device being configured to operate in either cooling or heating mode.

[0006] It is common in reversible air conditioning systems for the refrigerant to circulate in two separate loops or sub-circuits, sharing common components but with different directions of flow depending on whether it circulates in the heating sub-circuit (or loop) or the cooling sub-circuit (or loop). One of the problems encountered is protecting the compressor from the ingestion of liquid refrigerant.

[0007] The invention aims to address at least one of the advantages and disadvantages encountered in the prior art by proposing a reversible air conditioning device and a method for implementing such a device in which the compressor is protected from the ingestion of refrigerant in liquid form during the switch from one operating mode to another.

[0008] To this end, and according to a first aspect, the invention relates to a method for managing a reversible air conditioning system for a motor vehicle, the system being configured to operate alternately in a cooling mode in which a refrigerant flows in a given direction in a cooling sub-circuit or in a heating mode in which a refrigerant flows in the opposite direction in a heating sub-circuit, the system comprising an external heat exchanger, an internal heat exchanger, at least one compressor and at least one expansion valve mounted between the external heat exchanger and the internal heat exchanger; the method being remarkable in that, in response to a command to activate the system in at least one of the operating modes, it comprises the following steps: a compressor activation step; a closing step of the expansion valve(s);and a step of measuring the superheat of the refrigerant fluid at the compressor inlet and comparing the measured value to a target superheat value and opening said at least one expansion valve when the measured superheat value is greater than or equal to the target superheat value.

[0009] As can be understood from the definition just given, the invention consists of incorporating a latency period between the moment the device is activated in a given mode (for example, in heating mode) and the moment the compressor starts. This latency period is chosen to be sufficient for the refrigerant in the reservoir corresponding to the sub-circuit of the other operating mode (for example, the first reservoir) to be completely evaporated, that is, in gaseous form. This latency period is determined by calculating the superheat measured at the compressor inlet. The compressor is thus protected against liquid ingestion.

[0010] Preferably, the process is implemented in response to a command to activate the device in heating mode. The invention is remarkable because it allows the compressor to be protected without adding any components to the circuit; for example, without adding a valve at the outlet of the first reservoir. Indeed, when the reversible air conditioning unit is activated with a command to operate in heating mode, the refrigerant, in liquid form and contained in the first reservoir located in the cooling sub-circuit, is drawn into the compressor. It is important that this refrigerant be in gaseous form before entering the compressor.

[0011] According to a preferred embodiment, the process further includes a step of activating a fan capable of creating an additional airflow at the heat exchanger located upstream of the compressor according to the direction of refrigerant flow associated with the activated operating mode.

[0012] For example, the process is implemented in response to a command to activate the device in heating mode and the activated fan is a motor-fan unit located at the front of the vehicle.

[0013] Preferably, the fan activation step is carried out before the compressor activation step; and / or the fan activation step is carried out when the vehicle is traveling at a speed lower than a predetermined speed.

[0014] According to a preferred embodiment of the invention, in response to an activation command of the device according to at least one of the operating modes, the method includes a preliminary measurement of the superheat of the refrigerant fluid at the inlet of the compressor and controls the closing step of the expansion valve(s) if the superheat value is less than the target superheat value.

[0015] Preferably, the target overheat value is at least 4 K, more preferably equal to or greater than 5 K.

[0016] Advantageously, the process is implemented in response to an activation command for the device in at least one of the operating modes if said activation command corresponds to a change of operating mode from cooling to heating or from heating to cooling. In other words, a person skilled in the art will have a particular advantage in implementing the process in the event of a reversal of the refrigerant flow direction.

[0017] According to a second aspect, the invention relates to a motor vehicle remarkable in that it comprises a reversible air conditioning device configured to operate alternately in a cooling mode in which a refrigerant flows in a given direction in a cooling sub-circuit or in a heating mode in which a refrigerant flows in the opposite direction and in a heating sub-circuit, the device comprising an external heat exchanger, an internal heat exchanger, at least one compressor and at least one expansion valve mounted between the external heat exchanger and the internal heat exchanger; and further comprises an electronic control unit associated with said device and configured to implement the method according to the first aspect.

[0018] Preferably, the vehicle also includes a human-machine interface that can be used by the vehicle user to control the activation of the reversible air conditioning system according to one of its operating modes.

[0019] In one embodiment, the reversible air conditioning unit includes a refrigerant storage tank located between one or more expansion valves and the outdoor heat exchanger. Preferably, the unit includes two expansion valves mounted in parallel between the outdoor and indoor heat exchangers; a first expansion valve arranged for use when the unit operates in cooling mode and a second expansion valve arranged for use when the unit operates in heating mode; and the unit includes a tank located between the first expansion valve and the outdoor heat exchanger.

[0020] In one embodiment, the reversible air conditioning unit includes a refrigerant storage tank located between one or more expansion valves and the indoor heat exchanger. Preferably, the unit includes two expansion valves mounted in parallel between the outdoor and indoor heat exchangers; a first expansion valve arranged for use when the unit operates in cooling mode and a second expansion valve arranged for use when the unit operates in heating mode; and the unit includes a tank located between the second expansion valve and the indoor heat exchanger.

[0021] According to one embodiment, the reversible air conditioning system comprises a single compressor associated with four pipes, each equipped with a valve so as to define a cooling sub-circuit and a heating sub-circuit; and / or in that it comprises a single expansion valve that can be used in both directions of refrigerant flow and said expansion valve being common to the heating sub-circuit and the cooling sub-circuit.

[0022] The invention will be well understood and other aspects and advantages will become clear upon reading the following description given with reference to the attached drawing plate on which: [ Fig. 1 ] there figure 1 is a schematic representation of a reversible air conditioning unit operating in cooling mode. Fig. 2 ] there figure 2 is a schematic representation of a reversible air conditioning unit operating in heating mode. Fig. 3 ] there figure 3 is a time diagram illustrating the different steps that follow one another when the reversible air conditioning device is activated in heating mode.

[0023] In the following description, the term "include" is synonymous with "include" and is not restrictive in that it permits the presence of other elements or means in the device or vehicle to which it relates, or other steps in the process under consideration. It is understood that the term "include" includes the terms "consist of." Similarly, the terms "interior," "exterior," "front," and "rear" shall be understood in relation to the general orientation of the vehicle as viewed in its normal direction of travel. In the various figures, the same reference numerals designate identical or similar elements.

[0024] In the following description, the method of managing a reversible air conditioning device, the reversible air conditioning device and the vehicle comprising such a device and implementing such a method will be described jointly.

[0025] According to one aspect, the invention relates to a motor vehicle remarkable in that it comprises a reversible air conditioning device configured to operate alternately in a cooling mode in which a refrigerant flows in a given direction in a cooling sub-circuit or in a heating mode in which a refrigerant flows in the opposite direction and in a heating sub-circuit, the device comprising an external heat exchanger, an internal heat exchanger, at least one compressor and at least one expansion valve mounted between the external heat exchanger and the internal heat exchanger; and further comprises an electronic control unit associated with said device and configured to implement the method according to the invention.

[0026] The vehicle and the reversible air conditioning system will first be described with reference to figures 1 And 2in which the cooling mode is illustrated in figure 1 and the heating mode is illustrated in figure 2 In both figures, the elements not used by the operating mode considered (air conditioning or heating) are represented by dotted lines.

[0027] There figure 1 This illustrates the system operating in passenger compartment cooling mode. The compressor 13 circulates the refrigerant in the circuit by drawing in the gaseous fluid from the internal heat exchanger 9, compressing it, and sending it to the external heat exchanger 3, located at the front of the vehicle, which here acts as the condenser. The fluid arrives at the condenser as a high-pressure, high-temperature gas. The condenser is a heat exchanger in which the refrigerant changes from a gaseous to a liquid state, a stage during which the fluid releases some of its heat, before passing through the expansion valve 7 (here called the first expansion valve 7 because the circuit shown includes two). The role of the expansion valve 7 is to reduce the pressure, and therefore the temperature, of the refrigerant. A first storage tank 5 is located upstream of the first expansion valve 7.The role of the first reservoir 5 (intended to be used in cooling mode) is to supply the first expansion valve 7 with refrigerant in liquid form in a homogeneous manner and thus to maintain constant performance of the cooling sub-circuit by damping any variations in refrigerant supply.

[0028] After passing through the first expansion valve 7, the fluid is carried to the internal heat exchanger 9 located in the vehicle's passenger compartment, which here functions as an evaporator. The evaporator changes the refrigerant from a liquid to a gaseous state. During this phase change, the refrigerant absorbs heat from the air passing through the evaporator. The cooled air is then distributed to the passenger compartment via a ventilation system. At the evaporator outlet, the refrigerant is in a gaseous state and is drawn into the compressor 13 to begin a new cycle.

[0029] When the device is operating in heating mode, as illustrated in figure 2 The direction of refrigerant flow is reversed compared to the cooling mode. This is made possible by the presence, for example, of a set of four ON / OFF valves (11, 15, 17, 19) arranged at the inlet and outlet of the compressor. Thus, two ON / OFF valves are located at the outlet of compressor 13: a first ON / OFF outlet valve 15 that connects the outlet of compressor 13 to the external heat exchanger 3, and a second ON / OFF outlet valve 19 that connects the outlet of compressor 13 to the internal heat exchanger 9. Two additional ON / OFF valves are located at the inlet of compressor 13: a first ON / OFF inlet valve 11 that connects the internal heat exchanger 9 to the inlet of compressor 13, and a second ON / OFF inlet valve 17 that connects the external heat exchanger 3 to the inlet of compressor 13. When the circuit operates in cooling mode as illustrated in figure 1 The first inlet valve 11 and outlet valve 15 are opened so that the refrigerant is directed to the external heat exchanger 3 after passing through the compressor 13, and the first expansion valve 7 is actuated. When the circuit operates in heating mode as illustrated in figure 2 , the first valves are closed and the second inlet valve 17 and outlet valve 19 are opened so that the refrigerant is directed to the internal heat exchanger 9 after passing through the compressor 13 and the second expansion valve 23 and actuated.

[0030] When the system is used in heating mode, the refrigerant is sent in a compressed, high-temperature gaseous state to the internal heat exchanger 9, which acts as a condenser. The condenser heats the air blown into the passenger compartment by heat exchange, causing the refrigerant to change from a gaseous to a liquid state. The fluid is then drawn to the second expansion valve 23, which is mounted in parallel with the first expansion valve 7. It should be understood that when the second expansion valve 23 is in use, the first expansion valve 7 is closed (or not used), and vice versa. A second storage tank 21 is located upstream of the second expansion valve 23. The second expansion valve 23 reduces the pressure, and therefore the temperature, of the refrigerant. The fluid is then drawn to the external heat exchanger 3, located in the vehicle's passenger compartment, which acts as an evaporator.The evaporator changes the refrigerant from a liquid to a gaseous state. During this phase change, the refrigerant absorbs heat from the air passing through the evaporator. At the evaporator outlet, the gaseous refrigerant is drawn into the compressor 13, thus beginning a new cycle. One of the roles of the second reservoir 21 is to store the refrigerant in liquid form, minimizing the amount of subcooled liquid remaining in the internal heat exchanger 9. This configuration ensures a uniform temperature of the refrigerant in the internal heat exchanger 9, and consequently, a uniform temperature of the air blown into the passenger compartment.

[0031] It is understood that in such a system the refrigerant will circulate in two separate loops or sub-circuits containing the common elements. Indeed, the reversal of the direction of circulation by the compressor associated with expansion valves (7, 23) mounted in parallel defines, within the same closed circuit, a heating sub-circuit (or loop) and a cooling sub-circuit (or loop).

[0032] The reversible air conditioning unit is shown on the figures 1 And 2According to one embodiment, it comprises two expansion valves (7, 23) mounted in parallel between the external heat exchanger 3 and the internal heat exchanger 9. In this embodiment, a first expansion valve 7 is arranged for use when the device operates in cooling mode, and a second expansion valve 23 is arranged for use when the device operates in heating mode. However, other embodiments are possible. For example, in another embodiment shown, it comprises a single expansion valve that can be used in both directions of refrigerant flow.

[0033] For example, in the reversible air conditioning device according to the invention, the maximum condensation pressure in the device operating in heating mode is between 12 and 15 absolute bars (where zero corresponds to a perfect vacuum); and the minimum evaporation pressure in the device operating in heating mode is about 1 absolute bar.

[0034] Finally, the vehicle also includes an electronic control unit (ECU) associated with said device 1 and configured to implement the process described below. As a reminder, an electronic control unit (ECU) is an integrated electronic device that reads signals from sensors located in various places and components of the car and, based on this information, can control or monitor different onboard components. In this case, as we will see, the electronic control unit will read signals from at least one temperature sensor located at the compressor inlet and will calculate a superheat temperature, which it will then compare to a target or threshold value. Depending on the result of this comparison, the electronic control unit will activate or not activate one or more of the expansion valves of the reversible air conditioning system.

[0035] The control functions of the reversible air conditioning system (for example, the activation function of one or more expansion valves) are implemented by sending instructions from the electronic control unit to the various components of the device 1, for example, via a multiplexed network onboard the vehicle, or through a control device specific to said device 1. The electronic control unit will typically include at least one memory and at least one computer. The vehicle according to the invention will therefore include an electronic system comprising a "body domain" subsystem encompassing the body and comfort electronics, of which the air conditioning and heating system is a part.

[0036] It should be noted that multiplexed networks are digital communication networks that allow electrical equipment or subsets of electrical equipment to communicate with each other using a reduced number of wires. The implementation of such multiplexed networks in a vehicle is known to those skilled in the art and will not be described in further detail. For example, the invention can implement a CAN (Controller Area Network), LIN (Local Interconnect Network), MOST (Media Oriented System Transport), SWC (Single-wire CAN), HS-CAN (High-Speed ​​CAN), Flexray, Safe-by-wire, or other types of multiplexed networks.

[0037] The functions of the reversible air conditioning system, in heating and cooling modes, can be automated and / or operated manually by the vehicle user via a manual control button on the dashboard or a human-machine interface. This interface typically includes a display that allows the user to control and / or configure the system. Various types of displays can be used, such as voice-activated displays or touchscreens.

[0038] According to the invention, the method for managing a reversible air conditioning device for a motor vehicle is implemented automatically in response to an activation command for the device according to at least one of the operating modes, whether this activation command is automatic or is subject to intervention by one of the vehicle's occupants via the human-machine interface.

[0039] The method according to the invention advantageously comprises the following steps: a step of activating the compressor or at least one of the compressors; a step of closing the expansion valve(s); and a step of measuring the superheat of the refrigerant fluid at the inlet of the compressor and comparing the measured value to a target superheat value and opening the expansion valve associated with the operating mode considered when the measured superheat value is greater than or equal to the target superheat value.

[0040] According to one embodiment of the invention, the steps of activating the compressor or at least one of the compressors and closing the expansion valve(s) are carried out successively. According to another embodiment of the invention, the steps of activating the compressor or at least one of the compressors and closing the expansion valve(s) are carried out simultaneously.

[0041] According to a preferred embodiment, the process is implemented in response to an activation command of the device in heating mode and / or in cooling mode; preferably in heating mode.

[0042] The invention is remarkable because it protects the compressor without adding any components to the circuit; for example, without adding a valve at the outlet of the first reservoir. Indeed, when the reversible air conditioning unit is operated in heating mode, the refrigerant in liquid form, contained in the first reservoir located in the cooling sub-circuit, is drawn into the compressor. It is important that this refrigerant be in gaseous form before entering the compressor. The invention is remarkable in that it facilitates the transition of the refrigerant to a gaseous state by closing the expansion valve(s) so that the external heat exchanger 3 is, during this lag time, entirely dedicated to vaporizing the fluid contained in said reservoir.On the other hand, and preferentially, it promotes the passage of the refrigerant into gaseous form by including a step of activating a fan capable of creating an additional airflow at the heat exchanger located upstream of the compressor according to the direction of circulation of the refrigerant associated with the activated operating mode.

[0043] Thus, when the process is implemented in response to a command to activate the device in heating mode, and the activated fan is a motor-fan unit located at the front of the vehicle, preferably the fan activation step is performed before the compressor activation step; and / or the fan activation step is performed when the vehicle is traveling at a speed lower than a predetermined speed, i.e., when the airflow generated by the vehicle's speed is insufficient.

[0044] Superheating represents an increase in the temperature of the fluid drawn in at the evaporator outlet without a corresponding increase in pressure. It also determines the proper fluid supply to the evaporator. Superheating is the difference between the temperature measured at the expansion valve and the evaporation temperature at the compressor inlet. The temperature can be measured using any method known to those skilled in the art, such as a thermometer or probe.

[0045] Preferably, the target superheat value is at least 4 K (or 4°C), more preferably equal to or greater than 5 K (or 5°C). For example, the target superheat value is between 4 and 10 K (or 4 and 10°C), preferably between 5 and 8 K (or 5 and 8°C). In the context of the invention, the increase in measured superheat is indicative of the evaporator's fluid supply. When the reservoir upstream of the evaporator is empty because all the fluid has been drawn off, the evaporator is no longer sufficiently supplied with fluid, and the superheat value increases. It is time to open the expansion valve.

[0046] Advantageously, the process is implemented in response to an activation command for the device in at least one of the operating modes if said activation command corresponds to a change of operating mode from cooling to heating or from heating to cooling. In other words, a person skilled in the art will have a particular advantage in implementing the process in the event of a reversal of the refrigerant flow direction.

[0047] In a preferred embodiment of the invention, in response to a command to activate the device according to at least one of the operating modes, the method includes a preliminary measurement of the refrigerant superheat at the compressor inlet and triggers the closing of the expansion valve(s) (7, 23) if the superheat value is below the target superheat value, for example, below 5K (or 5°C). This configuration allows for the detection of the appropriateness of implementing a delay time at the start of the process. In other words, the presence of fluid in liquid form in the reservoir upstream of the heat exchanger acting as an evaporator is detected by a lower than normal superheat, such that the expansion valve must be temporarily closed to mitigate this problem and protect the compressor from liquid ingestion.

[0048] Thus, according to one embodiment of the invention, the process comprises the following steps: a step of activating the device in heating mode; an optional step of activating the motor-fan unit; a step of activating the compressor; and a step of measuring the superheat of the refrigerant fluid at the compressor inlet and comparing the measured value to a target superheat value and opening the expansion valve associated with the operating mode considered when the measured superheat value is greater than or equal to the target superheat value.

[0049] Thus, according to another embodiment of the invention, the method comprises the following steps: a step of activating the device in heating mode; an optional step of activating the motor-fan unit; a step of activating the compressor; a step of measuring the superheat at the compressor inlet and comparing the measured value to a target superheat value and controlling the closing of the expansion valve(s) while the compressor is activated when the measured superheat value is less than the target superheat value; and a further step of measuring the superheat of the refrigerant at the compressor inlet and comparing the measured value to a target superheat value and opening the expansion valve associated with the operating mode considered when the measured superheat value is greater than or equal to the target superheat value.

[0050] There figure 3illustrates the different steps that take place when the reversible air conditioning system is activated in heating mode.

[0051] Initially, the compressor is stopped and the expansion valve(s) are open. The pressure is uniform throughout the circuit. The first reservoir is still filled with liquid refrigerant because, before the system was shut down, it was operating in cooling mode.

[0052] Initially (first step), the motor-fan unit (GMV) is activated to create an outside airflow through the external heat exchanger in addition to the airflow created by the vehicle's speed.

[0053] In a second step, the compressor is activated while the expansion valve(s) are closed in order to dry the first tank by sucking up the fluid which evaporates by passing through the evaporator.

[0054] In the third stage, the superheat threshold TS1, which guarantees the absence of liquid in the tank, is reached. This threshold can be determined experimentally, or a value of at least 4 or 5°C is chosen. The expansion valve associated with the heating sub-circuit is opened (marked "opening D2" on the diagram), and the device operates normally; the superheat threshold returns to its normal value TS2.

Claims

1. Method of managing a reversible air conditioning system device (1) for a motor vehicle, the device being configured to operate alternately in a cooling mode in which a refrigerant circulates in a given direction in a cooling sub-circuit or in a heating mode in which a refrigerant circulates in a reverse direction and in a heating sub-circuit, the device (1) comprising an exterior heat exchanger (3), an interior heat exchanger (9), at least one compressor (13) and at least one pressure reducer (7, 23) mounted between the exterior heat exchanger (3) and the interior heat exchanger (9); the method being characterised in that in response to an activation order of the device in at least one of the operating modes, it comprises the steps of: an activation step of the compressor a step of closing the compressor steps of the compressor the steps of the steps of the steps of the steps of the steps of the steps of the device; pressure reducers (7, 23); and a step of measuring the overheating of the refrigerant at the entry of the compressor and comparing the measured value with a target overheating value and opening said at least one pressure reducer when the measured overheating value is greater than or equal to the target overheating value.

2. Method according to claim 1, wherein it is implemented in response to an activation order of the device in heating mode.

3. Method according to either of Claims 1 and 2, further comprising a step of activation of a fan capable of generating an additional air flow at the level of the heat exchanger arranged upstream to the compressor according to the direction of circulation of the refrigerant associated with the activated operating mode; preferably; the method is implemented in response to an activation order of the device in heating mode and the activated fan is a motor-driven fan unit arranged at the level of the front face of the vehicle.

4. Method according to Claim 3, wherein the step of activation of a fan is realised before the step of activation of the compressor (13); and / or wherein the step of activation of a fan is realised when the vehicle is travelling at a speed lower than a predetermined speed.

5. Method according to one of Claims 1 to 4, characterised in that, in response to an activation order of the device according to at least one of the operating modes, the method comprises a preliminary measurement of the overheating of the refrigerant fluid at the entry of the compressor and orders the step of closing the pressure reducer or reducers (7, 23) if the overheating value is lower than the target overheating value.

6. Process according to one of Claims 1 to 5, characterised in that the target value of overheating is at least 4 K, more preferably equal to or greater than 5 K.

7. Method according to one of Claims 1 to 6, characterised in that it is implemented in response to an activation order of the device according to at least one of the operating modes if said activation order corresponds to a change in operating mode from the cooling mode to the heating mode.

8. Motor vehicle comprising a reversible air conditioning system device (1) configured to operate alternately according to a cooling mode in which a refrigerant circulates according to a given direction in a cooling subcircuit or according to a heating mode in which a refrigerant circulates in reverse direction and in a heating subcircuit, the device (1) comprising an exterior heat exchanger (3), an interior heat exchanger (9), at least one compressor (13) and at least one pressure reducer (7, 23) mounted between the exterior heat exchanger (3) and the interior heat exchanger (9); and in that it further comprises an electronic control unit associated with said device (1) and configured to implement the method according to one of Claims 1 to 7.

9. Vehicle according to Claim 8, wherein the reversible air conditioning system device (1) comprises an accumulation tank (5) for refrigerant fluid arranged between the one or more pressure regulators (7, 23) and the outer heat exchanger (3); preferably, the device comprises two pressure regulators (7, 23) mounted in parallel between the outer heat exchanger (3) and the inner heat exchanger (9); a first pressure regulator (7) being arranged to be used when the device is operating in cooling mode and a second pressure regulator (23) being arranged to be used when the device is operating in heating mode; and wherein the device (1) comprises a tank (5) arranged between the first pressure regulator (7) and the outer heat exchanger (3)10. Vehicle according to Claim 8 or 9, wherein the reversible air conditioning system device comprises a single compressor associated with four pipes each being provided with a valve so as to define a cooling subcircuit and a heating subcircuit and / or wherein it comprises a single pressure reducer which can be used in the two directions of circulation of the refrigerant fluid and said pressure reducer being common to the heating subcircuit and to the cooling subcircuit.