Method for operating a refrigeration system for a vehicle with a refrigerant circuit having a heat pump function

Abstract

Method for operating a refrigeration system (10) for a vehicle with a refrigerant circuit (1) having a heat pump function, wherein the refrigerant circuit (1) comprises the following components: - a refrigerant compressor (4) with a high-pressure outlet and an inlet side, - an external heat exchanger (5) which can be operated either as a condenser or gas cooler for refrigeration operation or as a heat pump evaporator for heat pump operation by means of a heat pump expansion device (AE3) and can be directly connected to the high-pressure outlet of the refrigerant compressor (4) by means of a shut-off device (A4), - an evaporator branch (2.1) with an evaporator (2) and an evaporator expansion element (AE2), wherein the evaporator branch (2.1) can be connected on the low-pressure side to the inlet side of the refrigerant compressor (4) and on the high-pressure side to the external heat exchanger (5), and - a heating branch (8.1) with a heating condenser (8) or hot gas cooler (8) that directly or indirectly heats an air supply flow (L) for the vehicle interior, wherein the heating branch (8.1) can be connected upstream to the high-pressure outlet of the refrigerant compressor (4) by means of a shut-off device (A3) and downstream to the heat pump expansion device (AE3) for the purpose of carrying out heat pump operation, and wherein the external heat exchanger (5) is defrosted after heat pump operation - the external heat exchanger (5) is connected in series with the heating condenser (8) or hot gas cooler (8) at the high pressure generated by the refrigerant compressor (4) or at a medium pressure lower than the high pressure, - the refrigerant heated by means of the refrigerant compressor (4) is first pre-cooled at the heating condenser (8) or hot gas cooler (8) and then the residual heat remaining in the refrigerant is released in the external heat exchanger (5), and - the refrigerant exiting the external heat exchanger (5) is expanded to a low pressure by means of a defrost expansion device (AE, AE5) and fed to the refrigerant compressor (4) on the inlet side.

Description

[0001] The invention relates to a method for operating a refrigeration system for a vehicle with a refrigerant circuit having a heat pump function.

[0002] Such refrigeration systems are known that can be operated both in heat pump mode for heating a vehicle interior and in refrigeration system mode for cooling the vehicle interior. In heat pump mode, the supply air to the vehicle interior is conditioned and heated by the heat provided by the heat pump.

[0003] When using ambient air as a heat source, an external heat exchanger of a refrigerant circuit is used in conjunction with a heat pump expansion unit as the heat pump evaporator. In this process, heat is extracted from the ambient air, causing the refrigerant in the external heat exchanger to evaporate and potentially warm or even superheat. Simultaneously, the external heat exchanger cools on its surface due to the evaporation temperature of the refrigerant. This cooling of the external heat exchanger can lead to frost formation and ultimately icing of the heat exchanger because the evaporation temperature drops below the ambient temperature. This occurs when moisture in the ambient air condenses on the surface of the external heat exchanger. Depending on the weather conditions, moisture can also directly impact the surface of the external heat exchanger and freeze.

[0004] Due to increasing frost and icing on the surface of the external heat exchanger, the potential for refrigerant evaporation decreases, and consequently, so does the heating capacity, as the heat-transferring surface area, and thus the potential of the refrigerant to absorb heat, decreases over the operating period of the heat pump.

[0005] A refrigeration system with a refrigerant circuit for operating in heat pump and defrost modes is known from FR 3 025 299 A1. This refrigerant circuit comprises a two-part external heat exchanger and a two-stage refrigerant compressor, which generates an intermediate pressure level in addition to a high-pressure level. In heat pump mode, the refrigerant, compressed to high pressure, is expanded via a heating coil and a heat pump expansion device into a series connection of the two sections of the external heat exchanger.

[0006] To perform an initial defrost cycle, the first section of the external heat exchanger is connected to the first stage of the refrigerant compressor, so that this first section is pressurized and thus heated, while the second section of the external heat exchanger continues the heat pump operation. This second section is connected to the high-pressure outlet of the refrigerant compressor via an expansion valve. In this operating mode, the external heat exchanger is partially defrosted by means of the first section.

[0007] To perform a second defrost cycle, the second section of the external heat exchanger is connected to the high-pressure outlet of the refrigerant compressor evaporator via the heat pump expansion valve and a heating coil, with the heat pump expansion valve fully open. The refrigerant flowing from the second section of the external heat exchanger is expanded into the first section of the external heat exchanger by means of another expansion valve and then fed to the inlet side of the refrigerant compressor. In this operating mode, the second section of the external heat exchanger is defrosted.

[0008] From JP 2019-1244 A, a refrigeration system with a refrigerant circuit having a heat pump function is known, which has the following components: - a refrigerant compressor, - an external heat exchanger that can be operated either as a condenser or as a heat pump evaporator and an expansion element that can be used for the heat pump function, - a heating condenser that can be directly connected to the high-pressure outlet of the refrigerant compressor, which can be connected in series with the external heat exchanger and serves to heat an intake air stream supplied to the vehicle interior, - an evaporator with an expansion element, - a chiller with an expansion element for cooling a heat-generating component of the vehicle, - an internal intermediate heat exchanger for use as a heat source by means of a further heat pump process, and - a defrosting branch, with which the high-pressure outlet of the refrigerant compressor can be directly connected to the condenser for defrosting.

[0009] In both refrigeration and heating operation of this known refrigeration system, the external heat exchanger is directly or indirectly connected downstream of the heating condenser, whereby in heating operation the refrigerant from the heating condenser first flows via the intermediate heat exchanger and is then expanded into the external heat exchanger as a heat pump evaporator by means of the expansion device.

[0010] To dehumidify (reheat) the supply air stream introduced into the vehicle interior, heat is extracted from the supply air stream by means of the evaporator and then transferred back to the supply air stream via the heating condenser. During defrosting, the refrigerant compressed by the refrigerant compressor is fed directly to the defrost circuit. This defrosting operation can be carried out in parallel with dehumidification (reheat) or heating operation. If heating and dehumidification are carried out in parallel, the external heat exchanger serves as the heat pump evaporator, and the intermediate heat exchanger and chiller serve as heat sources. In defrosting operation, only the intermediate heat exchanger and the chiller are used as heat sources. The latter also applies when heating and defrosting are carried out in parallel.

[0011] In a refrigeration system for a hybrid vehicle, as described in US Patent 2011 / 0016896 A1, which incorporates a refrigerant circuit with a heat pump function, the refrigerant, compressed to high pressure by a refrigerant compressor, is always fed directly to a heating condenser first in all operating modes. During refrigeration operation (AC operation), the refrigerant absorbs heat from the supply air flowing into the vehicle interior via an evaporator. The refrigerant is then compressed by the refrigerant compressor, fed through the heating condenser into an external condenser, where the heat absorbed by the evaporator is dissipated to the ambient air before the refrigerant is expanded through an expansion device into the evaporator. If icing of the external condenser is detected, AC operation is initiated.To prevent a drop in the temperature of the vehicle interior, the supply air flow is heated by means of an electric heating element or with the waste heat from the combustion engine of the hybrid vehicle.

[0012] Furthermore, a refrigeration system with a refrigerant circuit having a heat pump function is known from DE 11 2012 000 758 T5, in which frost formation on an evaporator arranged in an air conditioning unit during heating and dehumidification operation is avoided by preventing a refrigerant supply to the evaporator.

[0013] Furthermore, JP H07-19675 A discloses a refrigeration system for an electric vehicle with a refrigerant circuit incorporating a heat pump function. Defrosting of the external heat exchanger is prevented during operation of the electric vehicle and is only carried out when the vehicle is at a charging station. To perform the defrosting operation, the refrigerant from the high-pressure outlet of the refrigerant compressor is first fed to a heating condenser and then to the external heat exchanger to perform the defrosting function. From the external heat exchanger, the refrigerant is fed via a throttling point into an evaporator to absorb heat from an airflow supplied to the vehicle interior of the electric vehicle before returning to the refrigerant compressor.

[0014] DE 695 03 822 T2 describes an improved refrigeration system for dehumidification operation, featuring a refrigerant circuit with a heat pump function. A fan control system for a condenser fan, as described therein, incorporates a switching hysteresis to prevent rapid changes in operating mode. For defrosting, the refrigerant from the high-pressure outlet of the refrigerant compressor is first fed to a heating condenser and then to the external heat exchanger to perform the defrosting function. From the external heat exchanger, the refrigerant is fed via a throttling point into an evaporator to absorb heat from an airflow supplied to the passenger compartment of the electric vehicle before returning to the refrigerant compressor.

[0015] From DE 10 2007 028 252 A1, a refrigerant circuit with two evaporators and an ejector pump is known, which functions as a refrigerant decompression device and refrigerant circulation device. If frost formation occurs in one of the two evaporators during refrigeration system operation, the ejector pump is shut down, so that a high-temperature refrigerant discharged by the refrigerant compressor flows through a bypass channel section and a channel section branching off from it, so that the hot gas refrigerant is introduced into both evaporators and thereby defrosts them.

[0016] US Patent 2014 / 0020415 A1 describes a method for operating a heat distribution device in a hybrid vehicle. This device comprises an engine cooling circuit and a refrigerant circuit designed for combined operation in refrigeration and heat pump modes, as well as for a post-heating mode. The refrigerant circuit includes an evaporator, a compressor, a heat exchanger for transferring heat from the refrigerant to the air being conditioned in a vehicle interior, and a heat exchanger for transferring heat between the refrigerant of the refrigeration circuit and the coolant of the engine cooling circuit. This heat exchanger can be operated both as a heat pump evaporator for transferring heat from the coolant to the refrigerant and as a condenser for transferring heat from the refrigerant to the coolant.In heat pump mode, after passing through a heat exchanger that absorbs heat energy from the combustion engine or ambient air, the refrigerant is routed via a bypass line past the evaporator and an internal heat exchanger to the compressor of the refrigerant circuit. If the combustion engine is used as the heat source in heat pump mode, the heat exchanger of the refrigerant circuit, which absorbs heat energy from the ambient air, is bypassed, preventing any heat energy from being absorbed from the ambient air.

[0017] The object of the invention is to provide a method for operating a refrigeration system for a vehicle with a refrigerant circuit having a heat pump function, with which improved and, in particular, efficient operation can be achieved with regard to defrosting operation.

[0018] This problem is solved by a method having the features of claim 1.

[0019] This method for operating a refrigeration system for a vehicle with a refrigerant circuit that has a heat pump function and includes the following components: - a refrigerant compressor with a high-pressure outlet and an inlet side, - an external heat exchanger, which can be operated either as a condenser or gas cooler for refrigeration operation or as a heat pump evaporator for heat pump operation by means of a heat pump expansion device and can be directly connected to the high-pressure outlet of the refrigerant compressor by means of a shut-off device, - an evaporator branch with an evaporator and an evaporator expansion element, wherein the evaporator branch can be connected on the low-pressure side to the inlet side of the refrigerant compressor and on the high-pressure side to the external heat exchanger, and - a heating branch with a heating condenser or hot gas cooler that directly or indirectly heats an air supply flow for the vehicle interior, wherein the heating branch can be connected upstream to the high-pressure outlet of the refrigerant compressor by means of a shut-off device and downstream to the heat pump expansion device for the purpose of carrying out heat pump operation, and whereby the external heat exchanger is defrosted after heat pump operation - the external heat exchanger is connected in series with the heating condenser or hot gas cooler at the high-pressure level generated by the refrigerant compressor or at a lower intermediate pressure compared to the high pressure, - the refrigerant, heated by the refrigerant compressor, is first pre-cooled at the heating condenser or hot gas cooler, and then the residual heat remaining in the refrigerant is released in the external heat exchanger, and - the refrigerant exiting the external heat exchanger is expanded to a low pressure by means of a defrost expansion device and fed to the refrigerant compressor on the inlet side.

[0020] In this process, the heating condenser or hot gas cooler remains active when switching from air-source heat pump operation to defrosting mode, so that a partial heat flow continues to be transferred to the supply air flow into the vehicle interior. The external heat exchanger to be defrosted is supplied with moderately tempered waste heat from the refrigerant exiting, for example, the heating coil, thus ensuring the continuation of heating operation via the refrigerant circuit. Furthermore, unlike direct exposure to hot gas from the refrigerant compressor, which can ultimately also result in a reversal of the refrigerant flow direction, the external heat exchanger is not subjected to high temperature stress.

[0021] A defrost cycle is initiated when the heating output decreases due to a reduced evaporation potential at the external heat exchanger. This condition can be detected using various parameters, such as the compressor power consumption and / or the high pressure at the refrigerant compressor outlet.

[0022] According to an advantageous further development of the invention, - the defrost expansion device is arranged in a defrost branch, with which the external heat exchanger is connected to the inlet side of the refrigerant compressor for carrying out the defrosting operation, - to carry out the defrosting operation, the external heat exchanger is connected to the heating condenser or flue gas cooler via the heat pump expansion device, wherein the heat pump expansion device is either controlled to an open state or is controlled such that the external heat exchanger operates at a medium pressure lower than the high pressure, and - the refrigerant is depressurized to low pressure by means of the defrost expansion device.

[0023] In this method according to the invention, the defrosting process and the coupled and continuous indoor air conditioning operate on the basis of a triangular process. No additional heat source is used, apart from the heat supplied by the compressor.

[0024] Furthermore, in this method according to the invention, the main flow path of the refrigerant remains unchanged when switching from heat pump operation to defrost operation; only the opening cross-sections of the expansion devices need to be changed. In this case, the heat pump expansion device is fully opened. It is also possible to throttle the refrigerant flow only slightly with this heat pump expansion device so that the external heat exchanger operates at a lower pressure level, a so-called intermediate pressure level, and thus at a temperature level at which the risk of thermal shock is greatly reduced and at which the refrigerant flows through the heat exchanger at a temperature level above the freezing point of water.

[0025] According to another advantageous embodiment of the invention, it is provided that - the refrigerant circuit is designed with a chiller branch comprising a chiller and a chiller expansion device, which can be connected in parallel to the evaporator branch, - to carry out a reheat operation by means of a reheat branch having a reheat expansion device, the heating condenser or hot gas cooler is connected downstream to the external heat exchanger, - to carry out the defrosting operation, the reheat operation is carried out, whereby the reheat expansion device is either controlled to an open state or is controlled in such a way that the external heat exchanger operates at a lower intermediate pressure than the high pressure, and - the refrigerant is expanded to low pressure by means of the chiller expansion device as a defrost expansion device.

[0026] Preferably, with the reheat expansion element open, an identical pressure level is set in the outer heat exchanger as in the heating condenser or hot gas cooler, or with the reheat expansion element throttled, a third pressure level is set between the high pressure level in the heating condenser or hot gas cooler and the low pressure level in the chiller.

[0027] In this further development of the invention, the refrigerant from the heating condenser or hot gas cooler is fed to the external heat exchanger via a reheat branch with a reheat expansion element. The refrigerant exiting the external heat exchanger is fed to the chiller branch before being returned to the inlet side of the refrigerant compressor. The chiller expansion element reduces the pressure to low pressure while the chiller's refrigerant circuit is stationary. It is also possible to operate this defrosting process as a closed loop with flowing refrigerant in the chiller, thus activating an additional heat source for defrosting and potentially eliminating or reducing the need for additional electrical power.

[0028] Furthermore, in this defrosting process and the coupled and continued indoor air conditioning, either a triangular process is used, in which no additional heat source besides the heat supplied by the compressor is utilized, or alternatively, a closed-loop process with a water-source heat pump system implemented via the chiller. In this case, in addition to the heat supplied by the compressor, the heat contained in the chiller's cooling medium is also utilized.

[0029] Since the external heat exchanger is traversed in the same direction as in refrigeration system operation, only minor flow and pressure losses occur.

[0030] According to a particularly advantageous further development of the invention, - the external heat exchanger is designed for flow with outside air with a controllable arrangement, wherein at least part of the surface of the external heat exchanger can be closed off to the airflow by means of this arrangement, and - to carry out the defrosting operation, the assembly is completely closed.

[0031] Such an arrangement, for example an air damper or louver arrangement, prevents the defrosting process from actually starting when a cold airflow occurs at the required high or medium pressure, thus preventing icing from immediately re-starting or prolonging the defrosting process. In particular, for the defrosting process to begin, it must be ensured that a condensation pressure is established in the external heat exchanger with a corresponding condensation temperature of at least 1°C, which is just above the freezing point of water at 0°C, in order to actually dissolve the frost and ice layer.

[0032] According to a further preferred embodiment of the invention, the defrosting operation is terminated when the outlet temperature of the refrigerant exiting the external heat exchanger reaches a predetermined positive temperature threshold, which is, for example, 3 °C. This outlet temperature should then remain permanently stable at, for example, 3 °C.

[0033] Furthermore, it is particularly advantageous if, according to further training, the pressure value in the external heat exchanger is set to a condensation pressure corresponding to a condensation temperature greater than 0 °C by means of the air heat pump or reheat expansion device in conjunction with the defrost expansion device or the chiller expansion device for the purpose of carrying out the defrosting operation.

[0034] Furthermore, it is particularly advantageous to use a pressure-temperature sensor to adjust and monitor the mean pressure for the AC and heat pump circuits with the external heat exchanger and the defrost expansion device, in order to achieve a condensation pressure level in the refrigerant above the freezing point of water (0 °C). Individual sensors can also be used instead of a combined pressure and temperature sensor.

[0035] Similarly, it is particularly advantageous to use a pressure-temperature sensor to monitor the intermediate pressure setting for the reheat branch with the external heat exchanger up to the chiller expansion unit (which also acts as a defrost expansion unit), in order to achieve a condensation pressure level in the refrigerant above the freezing point of water (0 °C). Instead of a combined pressure and temperature sensor, individual sensors can also be used.

[0036] Should a reduction in comfort during the defrosting process occur despite an active heat pump system, an electric heating element can be used to cover a heating deficit.

[0037] Finally, according to a particularly preferred further development, it is advantageous if, after the defrosting operation has ended, the liquid condensate generated at the external heat exchanger is driven off by means of a fan arrangement assigned to the external heat exchanger.

[0038] Further advantages and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. These show: Fig. 1 a circuit diagram of a refrigeration system to illustrate a first embodiment of the method according to the invention, and Fig. 2 a circuit diagram of a refrigeration system to illustrate a second embodiment of the method according to the invention.

[0039] Before explaining the exemplary embodiments of the method according to the invention using the refrigeration systems 10 as described below, Fig. 1 and Fig. 2. These will initially be described together due to their identical basic structure.

[0040] The refrigerant circuit 1 of the refrigeration system 10 according to Fig. 1 and Fig. 2 can be operated in both a refrigeration or cooling operation (called AC operation for short) and in a heat pump mode and has two evaporators, namely an evaporator 2 and a chiller 3, which is thermally coupled to a refrigerant circuit 3.0 for cooling, e.g. a high-voltage battery.

[0041] Refrigerant circuit 1 according to Fig. 1 and Fig. 2 consists of the following components: - a refrigerant compressor 4, - an external heat exchanger 5 designed as a condenser or gas cooler with a heat pump expansion device AE3 assigned to it in its function as a heat pump evaporator for heating operation, - an internal heat exchanger 6, - a low-pressure side accumulator 7, - an interior evaporator branch 2.1 with the evaporator 2 designed as a front evaporator and an upstream evaporator expansion device AE2, - a check valve R1 downstream of the evaporator 2, which is fluidly connected to the inlet side of the refrigerant compressor 4 via the accumulator 7 and the low-pressure side section of the internal heat exchanger 6, - a chiller branch 3.1 with the chiller 3, a chiller expansion device AE1 upstream of it, wherein the chiller 3 is used not only for cooling, e.g., an electrical component of the vehicle, but also for realizing a water heat pump function by utilizing the waste heat of at least one electrical component, - an AC and heat pump branch 5.1 with the external heat exchanger 5 and the heat pump expansion device AE3, wherein in heating mode the AC and heat pump branch 5.1 is fluidly connectable upstream via the heat pump expansion device AE3 to the indoor evaporator branch 2.1 forming a first branch point Ab1 and downstream via a defrost expansion device AE5 according to Fig. 1 or via a shut-off device A2 according to Fig. 2 is fluidly connectable to the inlet side of the refrigerant compressor 4, while in AC operation the AC and heat pump branch 5.1 is fluidly connectable upstream via a shut-off device A4 to the high-pressure outlet of the refrigerant compressor 4, - a heating branch 8.1 with a heating condenser 8 or hot gas cooler 8 which directly or indirectly heats a supply air flow L for the vehicle interior, wherein the heating branch 8.1 is fluidly connectable upstream via a shut-off device A3 to the high-pressure outlet of the refrigerant compressor 4 and downstream via a shut-off device A1 to the first branch point Ab1 and thus to the interior evaporator branch 2.1, - a reheat branch 5.2 with a reheat expansion element AE4 designed as an expansion valve, wherein the reheat branch 5.2 is fluidly connected downstream to the outer heat exchanger 5 forming a second branch point Ab2 and upstream to the heating condenser 8 or hot gas cooler 8, - a defrost branch 5.4 with a lockable defrost expansion device AE5 and a non-return valve R2 according to Fig. 1, wherein the defrosting branch 5.4 can be fluid-connected upstream via the second branch point Ab2 to the outer heat exchanger 5 and downstream to the accumulator 7, - a heat pump return branch 5.4 with a shut-off device A2 and a check valve R2 according to Fig. 2, wherein the heat pump return branch 5.4 can be fluid-connected upstream via the second branch point Ab2 to the external heat exchanger 5 and downstream to the accumulator 7, - a suction branch 5.5 with a shut-off device A5, wherein the suction branch 5.5 connects upstream to the heating condenser 8 or hot gas cooler 8 and downstream via a third branch point Ab3 to the defrost expansion device AE5 (see Fig. 1) or with the shut-off device A2 (see Fig. 2) and the non-return valve R2 of the defrosting branch 5.3 (see Fig. 1) or of the heat pump return branch 5.4 (see Fig. 2) is fluid-connected, and - an electric heating element 9, e.g. designed as a high-voltage PTC heating element, as an auxiliary heater for an air supply L directed into the vehicle interior, which is located together with the heating condenser 8 or hot gas cooler 8 and the evaporator 2 in an air conditioning unit 1.1 and is connected downstream of the heating condenser 8 or hot gas cooler 8 and thus also the evaporator 2 on the air side.

[0042] The sensors in refrigerant circuit 1 are as follows: Fig. 1 and Fig. 2. Several pressure and temperature sensors are provided for controlling and regulating the system.

[0043] Thus, a first pressure-temperature sensor pT1 is assigned to the refrigerant compressor 4 at the high-pressure outlet, furthermore a second pressure-temperature sensor pT2 at the outlet of the accumulator 7, a third pressure-temperature sensor pT3 at the outlet of the external heat exchanger 5, a fourth pressure-temperature sensor pT4 at the outlet of the heating condenser 8 or hot gas cooler 8 and finally a fifth pressure-temperature sensor pT5 at the low-pressure side outlet of the chiller 3.

[0044] With the two shut-off devices A3 and A4 according to the Fig. 1 and Fig. 2. Depending on the state of these two shut-off devices, the refrigerant flow from the high-pressure side of the refrigerant compressor 4 is directed either into the external heat exchanger 5 for AC mode with shut-off device A4 open and shut-off device A3 closed, or into the heating branch 8.1 for heating or reheat mode with shut-off device A3 open and shut-off device A4 closed.

[0045] The following describes the heating operation of refrigerant circuit 1 according to Fig. 1. will be described.

[0046] In heating mode of refrigerant circuit 1, when using the external heat exchanger 5 as a heat pump evaporator to implement an air source heat pump or when using the chiller 3 to implement a water source heat pump, the shut-off valve A4 is closed and the shut-off valve A3 is opened, so that hot refrigerant, such as R744, can flow into the heating branch 8.1. Furthermore, combined operation between water source and air source heat pumps is also possible.

[0047] To perform the heating function using the external heat exchanger 5 as a heat pump evaporator, the refrigerant, compressed by the refrigerant compressor 4, flows through the open shut-off valve A3 to transfer heat to the supply air stream L directed into the passenger compartment and into the heating condenser 8 or hot gas cooler 8. It is then expanded through the open shut-off valve A1 via the heat pump expansion valve AE3 into the external heat exchanger 5 to absorb heat from the ambient air. Finally, with the defrost expansion valve AE5 fully open, it flows back to the refrigerant compressor 4 via the defrost branch 5.4. The expansion valves AE1, AE2, and AE4 remain closed, as does the shut-off valve A5.

[0048] In this air-source heat pump operation using the external heat exchanger 5, heat is extracted from the airflow L1 passing over this external heat exchanger 5 and transferred to the refrigerant, thereby cooling the surface of the external heat exchanger. Due to this cooling of the external heat exchanger, frost and icing can occur on the heat exchanger 5 because condensate from the surroundings precipitates onto its surface, resulting from an evaporation temperature below the ambient temperature.

[0049] If the surface of the outer heat exchanger 5 becomes covered with a layer of material relevant to the comfort of the vehicle interior, resulting in a decreasing potential for refrigerant evaporation and thus a decreasing heating capacity, detectable via a decreasing compressor delivery volume flow, i.e. reduced power consumption of the refrigerant compressor 4 and / or via the decreasing high pressure of the refrigerant at the outlet of the refrigerant compressor 4, the air heat pump operation is interrupted and a defrosting operation is initiated.

[0050] To prevent further icing on the outer heat exchanger 5 and excessive cooling of the refrigerant flowing through the outer heat exchanger 5, the air supply to the outer heat exchanger 5 is blocked during defrosting by means of a controllable arrangement 5.6. Such an arrangement 5.6 is designed as a controllable air damper arrangement or as a controllable louver arrangement and can be completely closed. Thus, during defrosting, the air damper arrangement or louver arrangement is completely closed.

[0051] To carry out such a defrosting operation, the airflow L1 to the external heat exchanger 5 as part of the radiator package is therefore first interrupted by means of arrangement 5.6 - if the vehicle-side boundary conditions allow it - and the heat pump expansion element AE3 is fully opened, whereby both the heating condenser 8 or hot gas cooler 8 and the external heat exchanger 5 are operated at the same high pressure level generated by the refrigerant compressor 4, with the refrigerant compressor 4 being used as the sole heat source for this defrosting operation.In this system, the heating condenser 8 or hot gas cooler 8 and the external heat exchanger 5 are connected in series with respect to the refrigerant and are operated as heat sinks, so that the refrigerant heated by the refrigerant compressor 4 is first pre-cooled at the heating condenser 8 or hot gas cooler 8, in order to then release the residual heat remaining in the refrigerant in the external heat exchanger 5, in order to defrost the frost or ice on the surface of the external heat exchanger 5.

[0052] The refrigerant exiting the outer heat exchanger 5 enters the defrosting branch 5.4 via the branch point Ab2, where it is expanded to low pressure by means of the defrosting expansion device AE5. The refrigerant is then returned to the inlet side of the refrigerant compressor 4 via the check valve R2, the accumulator 7, and the low-pressure section of the inner heat exchanger 6.

[0053] If, during this defrosting operation, the heating condenser 8 or flue gas cooler 8 does not release any heat, or if its high-pressure level and thus its temperature level are reduced too much, i.e., for example, by a minimum amount greater than 5 bar (chemical refrigerant) or 10 bar (R744), depending on the refrigerant used, the heat pump expansion device AE3 can also be throttled in stages. This allows the external heat exchanger 5 to operate at a low pressure level, namely at a medium pressure level compared to the pressure level of the heating condenser 8 or flue gas cooler 8, and thus at a temperature level at which a temperature shock is avoided, as would otherwise be the case if the heat generated by the refrigerant compressor 4 were to impinge completely and directly on the external heat exchanger 5 via the open shut-off device A4.

[0054] To carry out the defrosting operation, the high or medium pressure in the outer heat exchanger 5 is adjusted by means of the defrost expansion device AE5 to a condensation pressure corresponding to a condensation temperature greater than 0 °C, e.g., 5 °C. This ensures that a sufficient temperature difference is achieved between the refrigerant and the frosted surface, thus enabling rapid defrosting.

[0055] During this defrosting operation, the refrigerant compressor 5 can be controlled to a maximum refrigerant volume flow rate in order to provide a maximum amount of heat for the defrosting process. The refrigerant compressor 4 is designed as either a mechanical or an electric compressor.

[0056] During defrosting, any heating deficit that may occur in the vehicle interior can be compensated for, for example, by switching on the electric heating element 9, which additionally heats the supply air flow L.

[0057] The defrosting operation is terminated when the outlet temperature at the outlet of the outer heat exchanger 5, as measured by a temperature sensor T, reaches a positive temperature threshold permanently and stably, e.g. 3°C.

[0058] Furthermore, the pressure value measured by the third pressure-temperature sensor pT3 can be used as a reference value for the condensation pressure level detected and present at the outer heat exchanger 5. If both values ​​are directly compared in a further step, it can be ensured that the refrigerant flowing through the outer heat exchanger 5 either does not superheat throughout the entire component or, in the case of superheat, that the refrigerant has a higher temperature level throughout the entire surface of the outer heat exchanger 5 than the freezing point of water at 0°C to ensure complete defrosting.

[0059] After the defrost cycle has finished, a fan arrangement assigned to the outer heat exchanger can be activated (in Fig. (1 not shown) the liquid condensate generated at the outer heat exchanger 5 is driven off. This drying process by driving off the condensate prevents short-term and renewed icing at the outer heat exchanger 5.

[0060] Once the defrost cycle is complete, and after opening assembly 5.6, the system can return to air-source heat pump operation via the external heat exchanger 5 by resetting the relevant operating points. This involves fully opening the defrost expansion valve AE5 and resetting the heat pump expansion valve AE3 to its corresponding expansion function. If necessary, the electric heating element 9 is also switched off or its heating power reduced.

[0061] If waste heat is present in the refrigerant circuit 3.0, defrosting via the AC and heat pump branch 5.1 and the defrost branch 5.4 can also be carried out in such a way that the refrigerant flow, after passing through the heating condenser 8 or hot gas cooler 8 and the open shut-off valve A1, is split into a partial flow flowing through the heat pump expansion device AE3 and the external heat exchanger 5, and a partial flow flowing into the chiller branch 3.1. This latter partial flow is used for water-source heat pump operation by expanding the refrigerant in this partial flow into the chiller 3 via the chiller expansion device AE1. This additionally supports the heating of the supply air flow L and the defrosting of the external heat exchanger 5. During this defrosting operation, the external heat exchanger 5 and the chiller 3 are supplied with refrigerant in parallel.

[0062] The following describes heating operation using the chiller 3 as a heat source.

[0063] To perform the heating function using the chiller 3, the refrigerant, compressed by the refrigerant compressor 4, flows through the open shut-off valve A3 to transfer heat to an intake air stream L directed into the vehicle interior, then into the heating condenser 8 or hot gas cooler 8. Subsequently, it expands through the open shut-off valve A1 and the first branch point Ab1 via the chiller expansion valve AE1 into the chiller 3 to absorb waste heat from the electrical and / or electronic components located in the coolant circuit 3.0. During this heating function, the expansion valves AE3 and AE4, as well as the shut-off valve A5, are closed, and the shut-off valve A2 is fully open. In water-heat pump operation, any refrigerant extracted from the AC and heat pump branch 5.1 is drawn off via the shut-off valve A2 and fed to the accumulator 7 via the check valve R2.

[0064] An indirect delta connection is achieved by opening shut-off valve A1 and allowing the refrigerant compressed by refrigerant compressor 4 to expand into chiller 3 via chiller expansion valve AE1. Simultaneously, no mass flow is generated on the refrigerant side, i.e., in coolant circuit 3.0. For example, the water used as a coolant remains stationary on the coolant side of chiller 3, and chiller 3 is not actively circulated with coolant. Expansion valves AE2, AE3, and AE4 remain closed in this configuration.

[0065] In a reheat operation, the supply air stream L supplied to the vehicle interior is first cooled and thus dehumidified by means of the evaporator 2, in order to then at least partially reheat the supply air stream L with the heat extracted from the supply air stream L and the heat supplied to the refrigerant via the refrigerant compressor 4 by means of the heating condenser 8 or the hot gas cooler 8.

[0066] A reheat operation of the refrigerant circuit 1.1 is carried out in different ways depending on the heat balance.

[0067] With sufficient heating capacity in refrigerant circuit 1, only the evaporator 2 is supplied with refrigerant. This is achieved by connecting the heating condenser 8 or hot gas cooler 8 downstream to the evaporator 2 via the evaporator expansion element AE2 through the open shut-off valve A1, while the chiller expansion element AE1 remains closed. From the evaporator 2, the refrigerant flows back to the refrigerant compressor 4 via the check valve R1, the accumulator 7, and the internal heat exchanger 6. The heat absorbed in the evaporator 2, together with the heat flow introduced by the refrigerant compressor 4, is then transferred via the heating condenser 8 or hot gas cooler 8 to the supply air flow L into the vehicle interior. The expansion elements AE1, AE3, and AE4 are completely closed during this process.

[0068] In the event of a heat deficiency in the refrigerant circuit 1.1, in addition to the evaporator 2, the chiller 3 is also included in the reheating process by selectively and as required opening of the chiller expansion element AE1 and / or the external heat exchanger 5 by similarly selectively and as required opening of the heat pump expansion element AE3.

[0069] In the event of excess heat during reheat operation, in addition to heat being transferred to the passenger compartment's supply air stream L via the heating condenser 8 or hot gas cooler 8, heat is also transferred to the vehicle's surroundings via the external heat exchanger 5 before the refrigerant flows back to the refrigerant compressor 4 via the evaporator 2. For this purpose, the refrigerant is expanded to an intermediate pressure above the evaporation pressure by means of the reheat expansion element AE4 of the reheat branch 5.2 for condensation and then expanded to low pressure in the evaporator 2 by means of the evaporator expansion element AE2.

[0070] A defrost cycle is initiated via this reheat branch 5.2 if, during air-source heat pump operation, the external heat exchanger 5 detects a build-up of condensation relevant to interior comfort, which reduces the potential for refrigerant evaporation and thus the heating capacity. This detection is based on a decreasing compressor delivery volume flow, i.e., the power input of the refrigerant compressor 4, and / or on the profile, i.e., the decreasing high pressure of the refrigerant at the outlet of the refrigerant compressor 4.

[0071] In this case, the air source heat pump operation is interrupted and then the defrosting operation is initiated.

[0072] This defrosting operation using the reheat branch 5.2 is carried out using the refrigeration system 10 with the refrigerant circuit 1 according to Fig. 2 explained.

[0073] During this defrosting operation, the refrigerant produced by the refrigerant compressor 4 is fed to the heating condenser 8 or hot gas cooler 8 via the open shut-off valve A3 and then, with the shut-off valve A1 closed and the reheat expansion valve AE4 fully open, directed to the external heat exchanger 5, whereby the shut-off valve A2 of the heat pump return branch 5.4 and the shut-off valve A4 are closed.

[0074] This ensures that both the heating condenser 8 or hot gas cooler 8 and the external heat exchanger 5 operate at the same high-pressure level generated by the refrigerant compressor 4, with the refrigerant compressor 4 serving as the sole heat source for this defrosting operation. The heating condenser 8 or hot gas cooler 8 and the external heat exchanger 5 are connected in series with respect to the refrigerant and operate as heat sinks. The refrigerant, heated by the refrigerant compressor 4, is first pre-cooled at the heating condenser 8 or hot gas cooler 8. The remaining heat in the refrigerant is then transferred to the external heat exchanger 5, thereby defrosting any frost or ice buildup on the surface of the external heat exchanger 5.

[0075] The refrigerant exiting the external heat exchanger 5 is fed to the chiller branch 3.1 via the AC and heat pump branch 5.1 with the heat pump expansion valve AE3 fully open. In this chiller branch 3.1, the chiller expansion valve AE1, acting as a defrost expansion valve AE, reduces the refrigerant to low pressure before it is returned to the refrigerant compressor 4 via the accumulator 7 and the internal heat exchanger 6. The chiller expansion valve AE1 reduces the pressure from high pressure to low pressure. The high pressure level must be set to a value greater than 0°C, e.g., 5°C. To maintain a heating effect for the cabin supply air flow L, this value should be significantly higher. This ensures a sufficient temperature difference between the refrigerant and the iced surface, which in turn enables rapid defrosting.

[0076] This defrosting operation can be implemented as an indirect delta circuit, in which no volume flow is generated on the coolant side via chiller 3, i.e., in coolant circuit 3.0. For example, the water-glycol mixture used as coolant remains stationary on the coolant side of chiller 3, or chiller 3 is not actively circulated with coolant. Alternatively, the defrosting operation can also be carried out as a closed-loop process with chiller 3 active, in which the coolant in coolant circuit 3.0 is circulated and the refrigerant flowing through it is simultaneously evaporated. In this case, additional heat can be absorbed from the coolant circuit to support the heating of the supply air flow L and the defrosting of the external heat exchanger 5.

[0077] In this defrosting operation using the AC and heat pump branch 5.1 and the chiller branch 3.1, the refrigerant compressor 4 can be controlled to a maximum refrigerant volume flow at the maximum possible pressure ratio in order to provide a maximum amount of heat for the defrosting operation. The refrigerant compressor 4 is designed as either a mechanical or an electric compressor.

[0078] If, during this defrosting operation, the heating condenser 8 or hot gas cooler 8 does not release any heat, or if the pressure level in the heating coil and thus its temperature level is reduced too much, i.e., for example, by a minimum amount greater than 5 bar (chemical refrigerant) or 10 bar (R744), depending on the refrigerant used, the reheat expansion device AE4 can also be throttled down to such an extent that the external heat exchanger 5 is operated at a lower pressure level, namely an intermediate pressure compared to the pressure level of the heating condenser 8 or hot gas cooler 8, and thus at a temperature level at which a temperature shock is avoided, as would otherwise be the case if the heat generated by the refrigerant compressor 4 were to impinge completely and directly on the external heat exchanger 5 via the open shut-off device A4.Even in the case of intermediate pressure operation, the requirement remains that the condensation intermediate pressure level, and thus the condensation temperature, must be set above 0°C using the defrost expansion device AE (i.e., the chiller expansion device AE1) and the reheat expansion device AE4. Pressure monitoring can be achieved via a pressure or pressure-temperature sensor provided in the reheat branch 5.2.

[0079] To prevent the icing from progressing on the outer heat exchanger 5 and the refrigerant flowing through the outer heat exchanger 5 from cooling down too much and the associated drop in pressure level, an air supply to the outer heat exchanger 5 is prevented during defrosting operation by means of a controllable arrangement 5.6.

[0080] Such an arrangement 5.6 is designed as a controllable air damper arrangement or as a controllable louver arrangement and can be completely closed. Thus, during defrosting operation, the air damper arrangement or louver arrangement is completely closed.

[0081] In this defrosting operation, carried out using the AC and heat pump branch 5.1 and the chiller branch 3.1, the chiller 3 can advantageously be used as an additional heat source to reduce the duration of the defrosting operation. A further advantage is that the refrigerant flow direction in this defrosting operation corresponds to the refrigerant flow direction in AC operation, resulting in low flow and pressure losses. Because the refrigerant is pre-cooled by the heating condenser 8 or hot gas cooler 8, the residual heat released at the external heat exchanger 5 prevents any temperature shock from occurring there.

[0082] During defrosting, any heating deficit that occurs in the vehicle interior can be compensated for, for example, by switching on the electric heating element 9 to heat the supply air flow L.

[0083] The defrosting operation is terminated when the outlet temperature at the outlet of the outer heat exchanger 5, as measured by the pressure-temperature sensor pT3, reaches a positive temperature threshold permanently and stably, e.g. 3°C.

[0084] Furthermore, the pressure value measured via the third pressure-temperature sensor pT3 can be used as a reference value for the condensation pressure level detected and present at the outer heat exchanger 5. If both values ​​are directly related to each other in a further step, it can be ensured that the refrigerant flowing through the outer heat exchanger 5 either does not superheat throughout the entire component or, in the case of superheat, that the refrigerant has a higher temperature level throughout the entire surface of the outer heat exchanger 5 than the freezing point of water at 0°C to ensure complete defrosting.

[0085] After the defrosting cycle has finished, a fan arrangement assigned to the outer heat exchanger 5 can be activated (in Fig. (2 not shown) the liquid condensate accumulated on the outer heat exchanger 5 is driven off. This drying process by driving off the condensate is intended to prevent short-term and renewed icing on the outer heat exchanger 5.

[0086] Once the defrost cycle is complete, the system can return to air-source heat pump operation via the external heat exchanger 5 by first opening the assembly 5.6 and then resetting the corresponding operating points. This involves fully opening the shut-off valve A2 and, with the shut-off valve A1 open and the reheat expansion valve AE4 closed, resetting the heat pump expansion valve AE3 to its corresponding expansion function. If necessary, the electric heating element 9 is also switched off or its heating power reduced.

[0087] If a shut-off valve A2 is used in the heat pump return line 5.4 of the refrigerant circuit 1 of the refrigeration system 10, the defrosting process can only be carried out fully via the reheat line 5.2 and the reheat expansion valve AE4 if the heating condenser 8 or the hot gas cooler 8 remains active. If a defrost expansion valve AE5 is used instead of the shut-off valve A2 (see...). Fig. 1), a defrosting process of the external heat exchanger 5 can take place either via the reheat branch 5.2 and the reheat expansion element AE4 or alternatively via the AC and heat pump branch 5.1 and the associated heat pump expansion element AE3 according to the embodiment shown in the illustration. Fig. 1.

[0088] It is also possible that, if sufficient waste heat is present in the fluid of coolant circuit 3.0, the system does not switch back to air-source heat pump operation after defrosting, but instead switches from the direct or indirect triangular process during defrosting to water-source heat pump operation. After the defrosting and drying process is complete, interior heating then continues via a pure water-source heat pump operation.

[0089] For the sake of completeness, the AC operation of refrigerant circuit 1 of refrigeration system 10 is also described according to the Fig. 1 and Fig. 2 explained.

[0090] In AC operation, the heating branch 8.1 is shut off by means of the shut-off valve A3, so that hot refrigerant, such as R744, cannot flow through the heating condenser 8 or the hot gas cooler 8. However, to retrieve refrigerant from the inactive heating branch 8.1, the shut-off valve A5 of the extraction branch 5.5 is opened, and the refrigerant can flow back through the shut-off valve A5 and the check valve R2, while the defrost expansion valve AE5 is simultaneously closed (see diagram). Fig. 1) or when shut-off device A2 is closed at the same time (see below). Fig. 2) flow in the direction of accumulator 7.

[0091] In AC operation of refrigerant circuit 1 according to Fig. 1 and Fig. 2. The refrigerant, compressed to high pressure, flows from the refrigerant compressor 4, with shut-off valve A4 open, into the outer heat exchanger 5, the high-pressure section of the inner heat exchanger 6, via the fully open heat pump expansion valve AE3 and the first branch point Ab1 into the evaporator branch 2.1 and / or into the chiller branch 3.1. From the chiller branch 3.1, the refrigerant flows back to the refrigerant compressor 4 via the accumulator 7 and the low-pressure section of the inner heat exchanger 6, while the refrigerant from the evaporator branch 2.1 flows through the check valve R1 and can then also flow back to the refrigerant compressor 4 via the accumulator 7 and the low-pressure section of the inner heat exchanger 6.

[0092] The first pressure-temperature sensor pT1 of the refrigerant circuit 1 serves to determine the refrigerant temperature and the high pressure of the compressed medium at the outlet of the refrigerant compressor 4. Monitoring these two parameters serves to monitor the maximum permissible mechanical and thermal loads on the refrigeration system, specifically at the outlet of the refrigerant compressor 4, and, if necessary, to limit system operation by means of control measures requested by a control unit, e.g., an air conditioning control unit, in order not to exceed the permissible maximum values.

[0093] The second pressure-temperature sensor pT2 of the refrigerant circuit 1 serves, especially in refrigeration systems with a refrigerant storage unit located on the low-pressure side, for underfill detection, but also for setting and monitoring a required low pressure.

[0094] The third pressure-temperature sensor pT3 of the refrigerant circuit 1, provided at the outlet side of the external heat exchanger 5, primarily serves to adjust or monitor the system operating parameters “optimal high pressure” during supercritical system operation or “subcooling after the external heat exchanger 5” during subcritical system operation.

[0095] In a further function, this third pressure-temperature sensor pT3 monitors the mean pressure level set in the outer heat exchanger 5 during defrosting operation. Depending on the position of the pressure sensor component pT3 before or after the outer heat exchanger 5, the resulting pressure level before or after the outer heat exchanger 5 can be determined using characteristic curves.

[0096] The one according to the refrigerant circuit 1 after Fig. 1 and Fig.The fourth pressure-temperature sensor pT4, arranged downstream of the heating condenser 8 or hot gas cooler 8, serves to control, but also to monitor the different operating modes of the refrigerant circuit 1, especially in heat pump mode with active flow through the heating condenser 8 or hot gas cooler 8 by a control unit, e.g. an air conditioning control unit.

[0097] The fifth pressure-temperature sensor pT5 of the refrigerant circuit 1 serves to monitor and control the degree of superheat at the outlet of the chiller 3.

[0098] It should also be mentioned that all sensors can be designed as combination sensors or as individual sensors for recording the state variables of the refrigerant circuit. REFERENCE MARK 1 Refrigerant circuit of the refrigeration system 10 1.1 Air conditioner 2 evaporators 2.1 Interior evaporator branch 3 Chiller 3.0 Coolant circuit of the chiller 3 3.1 Chiller branch 4 refrigerant compressors 5 external heat exchangers 5.1 AC and heat pump branch 5.2 Reheat branch 5.4 Defrosting branch or heat pump return branch 5.5 Extraction branch 5.6 Arrangement of the external heat exchanger 5 6 internal heat exchanger 7 Accumulator 8 internal heating condenser or hot gas cooler 8.1 Heating branch 9 electric heating element 10 Refrigeration system A1 Shut-off device A2 shut-off device A3 shut-off device A4 shut-off device A5 shut-off device From junction 1 Ab2 Junction Ab3 Junction AE Defrost Expansion Organ AE1 Chiller Expansion Organ AE2 evaporator expansion unit AE3 Heat Pump Expansion Valve AE4 Reheat Expansion Organ AE5 Defrost Expansion Unit L Supply air flow L1 Airflow pT1 first pressure-temperature sensor pT2 second pressure-temperature sensor pT3 third pressure-temperature sensor pT4 fourth pressure-temperature sensor pT5 fifth pressure-temperature sensor R1 check valve R2 check valve T temperature sensor

Claims

[1] Method for operating a refrigeration system (10) for a vehicle with a refrigerant circuit (1) having a heat pump function, wherein the refrigerant circuit (1) comprises the following components: - a refrigerant compressor (4) with a high-pressure outlet and an inlet side, - an external heat exchanger (5) which can be operated either as a condenser or gas cooler for refrigeration operation or as a heat pump evaporator for heat pump operation by means of a heat pump expansion device (AE3) and can be directly connected to the high-pressure outlet of the refrigerant compressor (4) by means of a shut-off device (A4), - an evaporator branch (2.1) with an evaporator (2) and an evaporator expansion element (AE2), wherein the evaporator branch (2.1) can be connected on the low-pressure side to the inlet side of the refrigerant compressor (4) and on the high-pressure side to the external heat exchanger (5), and - a heating branch (8.1) with a heating condenser (8) or hot gas cooler (8) that directly or indirectly heats an air supply flow (L) for the vehicle interior, wherein the heating branch (8.1) can be connected upstream to the high-pressure outlet of the refrigerant compressor (4) by means of a shut-off device (A3) and downstream to the heat pump expansion device (AE3) for the purpose of carrying out heat pump operation, and wherein the external heat exchanger (5) is defrosted after heat pump operation - the external heat exchanger (5) is connected in series with the heating condenser (8) or hot gas cooler (8) at the high pressure generated by the refrigerant compressor (4) or at a lower intermediate pressure than the high pressure, - the refrigerant heated by means of the refrigerant compressor (4) is first pre-cooled at the heating condenser (8) or hot gas cooler (8) and then the residual heat remaining in the refrigerant is released in the external heat exchanger (5), and - the refrigerant exiting the external heat exchanger (5) is expanded to a low pressure by means of a defrost expansion device (AE, AE5) and fed to the refrigerant compressor (4) on the inlet side. [2] The method of claim 1, wherein - the defrost expansion device (AE5) is arranged in a defrost branch (5.4) to which the external heat exchanger (5) is connected to the inlet side of the refrigerant compressor (4) for the purpose of carrying out the defrosting operation, - to carry out the defrosting operation, the external heat exchanger (5) is connected to the heating condenser (8) or hot gas cooler (8) via the heat pump expansion device (AE3), wherein the heat pump expansion device (AE3) is either controlled to an open state or is controlled such that the external heat exchanger (5) operates at a medium pressure lower than the high pressure, and - the refrigerant is expanded to low pressure by means of the defrost expansion device (AE5). [3] The method of claim 1, wherein - the refrigerant circuit (1) is formed with a chiller branch (3.1) comprising a chiller (3) and a chiller expansion element (AE1), which can be connected in parallel to the evaporator branch (2.1), - to carry out a reheat operation by means of a reheat branch (5.2) having a reheat expansion device (AE4) the inner heating condenser (8) or hot gas cooler (8) is connected downstream to the outer heat exchanger (5), - to carry out the defrosting operation, the reheat operation is carried out, wherein the reheat expansion device (AE4) is either controlled to an open state or is controlled such that the external heat exchanger (5) operates at a lower intermediate pressure than the high pressure, and - the refrigerant is expanded to low pressure by means of the chiller expansion device (AE1) as a defrost expansion device (AE). [4] Method according to any one of the preceding claims, wherein - the external heat exchanger (5) is designed for flow with outside air with a controllable arrangement (5.6), wherein at least a part of the surface of the external heat exchanger (5) can be closed off for air flow by means of this arrangement (5.6), and - the arrangement (5.6) is closed to carry out the defrosting operation. [5] Method according to any of the preceding claims, wherein the defrosting operation is terminated when the outlet temperature of the refrigerant exiting the external heat exchanger (5) reaches a predetermined positive temperature threshold. [6] Method according to one of the preceding claims, in which, for the purpose of carrying out the defrosting operation, the pressure value in the outer heat exchanger (5) is adjusted to a condensation pressure which corresponds to a condensation temperature of greater than 0 °C by means of the defrosting expansion device (AE, AE5) or by means of the defrosting expansion device (AE, AE5) and the heat pump expansion device (AE3) or by means of the defrosting expansion device (AE, AE5) and the reheat expansion device (AE4). [7] Method according to any of the preceding claims, excluding claim 3, wherein a pressure-temperature sensor (pT3) is used to adjust and monitor the mean pressure for the AC and heat pump branch (5.1) with the external heat exchanger (5) and the defrost expansion device (AE5) to achieve a condensation pressure level in the refrigerant above the freezing point of water at 0°C. [8] Method according to one of the preceding claims, excluding claim 2, wherein a pressure-temperature sensor (pT3) is used to monitor and adjust the mean pressure for the reheat branch (5.2) with the external heat exchanger (5) up to the chiller expansion device (AE1) as a defrost expansion device (AE) to achieve a condensation pressure level in the refrigerant above the freezing point of water at 0 °C. [9] Method according to one of the preceding claims, in which, after the defrosting operation has ended, the liquid condensate produced at the outer heat exchanger (5) is driven off by means of a fan arrangement associated with the outer heat exchanger (5).

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