Method to operate a climatization device at low ambient temperatures

Abstract

A present disclosure relates to a method to operate an air conditioning system (10) of a motor vehicle under very low ambient temperature conditions and an indication that the vehicle is planned to be parked. A first inlet (12A) of an air conduit (11A) is adapted to receive ambient air and a second inlet (12B) is adapted to receive air from a vehicle compartment (15) in a recirculation mode. The method is characterized in that the air conditioning system (10) is operated in a special after-run mode after being parked, wherein the airflow is operated in a recirculation mode, a first valve arrangement (28C) associated and in series with an evaporator (24A) is opened or kept open and a compressor (21) and a first blower (14B) are continued to be operated on pre-determined operational speeds for a pre-determined first time span after a determination of a permanent parking condition.

Description

METHOD TO OPERATE A CLIMATIZATION DEVICE AT LOW AMBIENT TEMPERATURESCross Reference

[0001] The present application is based on and claims the benefit of priority from German Patent Application No.102025103297.1 filed in Germany filed on January 29, 2025, the entire disclosure of the above application is incorporated herein by reference.

[0002] The present invention relates to a method to operate a climatization device at low ambient temperatures. The main application of the invention is for vehicle climatization but not limited thereto.

[0003] Conventional vehicles with an internal combustion engine provide enough engine waste heat to heat the passenger cabin in cold ambient temperatures. On the other hand, in battery electric vehicles (BEV), the passenger cabin needs to be heated by a heat pump system and supplemented by electric high voltage heater. The use of electric high voltage heaters results in high costs and additional development challenges like packaging constraints. The elimination of a high voltage electric heater is desirable from packaging perspective. But since the heat pump system must operate at very cold ambient temperatures like -30°C (minus 30 degrees Celsius), this brings additional challenges to heat pump development.

[0004] Present heat pump systems, in particular within the automotive field, have to deal with many challenges such as high system performance in a very wide operational range while keeping system costs as low as possible. When used for electrical vehicles, energy efficiency is very important since this has a direct impact to the driving range of the vehicle.

[0005] Present heat pump systems, in particular within the automotive field, have to deal with many challenges such as high system performance in a very wide operational range while keeping system costs as low as possible. When used for electrical vehicles, energy efficiency is very important since this has a direct impact to the driving range of the vehicle.Summary

[0006] The majority of such heat pump systems use an accumulator in front of the compressor. The use of an accumulator results in higher pressure drops at the compressor inlet and hence resulting in reduced system cooling performance especially during fast charging scenario. The use of a receiver at the high-pressure side (instead of an accumulator) may have some drawbacks for the suction side upstream of the compressor such as lack of lubrication or liquid refrigerant reaching the compressor.

[0007] Related air conditioning systems of a motor vehicle typically comprise an air conduit with two inlets, at least one outlet, and an associated first blower to provide climatized air for a vehicle compartment through that at least one outlet. They further generically comprise a refrigerant cycle with a compressor, a first heat exchanger for heating and an evaporator for cooling / dehumidification, whereas both heat exchangers are disposed within the air conduit, and an outside heat exchanger. The first inlet of the air conduit is adapted to receive ambient air and a second inlet is adapted to receive air from the vehicle compartment in a recirculation mode.

[0008] The use of a receiver on the high-pressure side of the system offers higher cooling performance of the system but absence of an accumulator in front of the compressor results in problems like the risk of liquid refrigerant passing to compressor and the lack of lubrication of the compressor, especially during system start-up. In particular for automotive applications, heat pump systems may need to be operated or even started until very low ambient temperatures like -30°C. Since at system stop the operational requirements are different than at the next system start, refrigerant may become maldistributed over the system and may be located in voluminous components such as heat exchangers. The local amount and concentration of associated lubricant (oil) may be critically low such to cause damage to the compressor. Therefore, refrigerant and oil management is very critical at low ambient temperature.

[0009] It is an object of the present invention to find alternative ways to support a safe and efficient system start up at low ambient temperatures while maintaining a defined climatization performance target and keeping system costs down.

[0010] This object is solved by a method to operate an air conditioning system of a motor vehicle with the features of claim 1. Advantageous variants and embodiments are defined in the dependent claims.

[0011] The disclosure in this specification employs a method to operate an air conditioning system (10) of a motor vehicle. The method is performed on an air conditioning system (10) comprising: an air conduit (11A) with two inlets (12A, 12B), at least one outlet (13A - 13C), and an associated first blower (14B) to provide climatized air for a vehicle compartment (15) through that at least one outlet (13A - 13C); and a refrigerant cycle (20) with a compressor (21), a first heat exchanger (22) for heating and an evaporator (24A) for cooling / dehumidification both being disposed within the air conduit (11A), and an outside heat exchanger (23), whereas a first inlet (12A) of the air conduit (11A) is adapted to receive ambient air and a second inlet (12B) is adapted to receive air from the vehicle compartment (15) in a recirculation mode, whereas an indication is received that the vehicle is planned to be parked..

[0012] The method is characterized in that the air conditioning system (10) is operated in a special after-run mode, wherein an indication for a Low-Ambient-Temperature condition (“LAT”-condition) is received, the airflow is operated in a recirculation mode, a first valve arrangement (28C) associated and in series with the evaporator (24A) is opened or kept open and the compressor (21) and the first blower (14B) are continued to be operated on pre-determined operational speeds for a pre-determined first time span after the determination of a permanent parking condition (“PP”-condition).

[0013] The invention will now be described with embodiments and with reference to the figures:Figure 1 displays a schematic layout of an air conditioning system which may benefit from the method according to an embodiment of the invention;Figure 2 displays a partial view of the layout according to Figure 1 with an additional air channel;Figure 3 displays a generic view of the vehicle compartment with respect to the various air inlets and outlets as general background; andFigure 4 displays a flow chart of the method to operate an air conditioning system according to an embodiment of the invention.

[0014] The method to operate an air conditioning system of a motor vehicle according to the present disclosure is designed for Low-Ambient-Temperature conditions, hereinafter abbreviated as “LAT” condition in combination with a permanent parking condition, hereinafter abbreviated as “PP” condition.

[0015] After reception of an indication that the vehicle is planned to be parked, the method is characterized in that the air conditioning system is operated in a special after-run mode with the following features: An indication for a “LAT” condition is received, the airflow is operated in a recirculation mode, a first valve arrangement associated and in series with the evaporator is opened or kept open and the compressor and the first blower are continued to be operated on pre-determined operational speeds for a pre-determined first time span after the determination of a “PP” condition. The special after-run mode has the effect that refrigerant and oil residing within the evaporator at determination of the “PP” condition will be immediately flushed out of the evaporator such to be available for restart at the compressor suction side. The operation of the first blower and the recirculated air will ensure that thermal energy of the still warm air from the vehicle compartment can ensure that the pressure level within the evaporator is still high - which otherwise at very low ambient temperature at restart may not be possible to guarantee without an additional electric air side heater. Thus, with the inventive concept, an electric heater may be dispensed with.

[0016] The various method steps can occur in any appropriate order, i.e. the “LAT” condition can be received when the first valve arrangement is already open and the airflow is already in recirculation mode, or alternatively, the valve opening and / or the recirculation is adapted only after reception of the “LAT” condition. A recirculation mode includes any suitable air flow where at least a partial airflow is recirculated through the second air inlet. The pre-determined operational speeds of the compressor and the first blower are typically pre-calibrated by simulations or system tests and are adapted to the specific vehicle and climatization device.

[0017] An indication that the vehicle is planned to be parked is a pre-event to the “PP” condition itself. A plan to park the vehicle can be derived by one or more inputs from the various systems of the vehicle such as the drive system, the navigation system or historic onboard data, including indicators such as switching off the ignition key of the vehicle (and equivalent means to stop the operation of the vehicle), arriving at or approaching a regular destination where the vehicle is known to be parked regularly (e.g. via historic data), reaching a parking area or a destination programmed by a navigation system and applying a permanent break. The determination of a “PP” condition can be based on one or more of the above indicators including the definitive shut off and vacating of the vehicle. The determination of a “PP” condition may involve a time offset having lapsed after the one or more indicators to ensure the vehicle definitely has been parked as may be easily defined in typical scenarios and as it will appear apparent to a person skilled in the art.

[0018] An indication of a ”LAT” condition can include one or more factors selected from a present ambient temperature below a first temperature threshold or a predicted ambient temperature below a second temperature threshold for a future point in time. The future point in time may be derived by historic data (e.g. typical hour of the day when the vehicle is started), a stored starting time (e.g. by a navigation system) and / or an arbitrary time during a preset time interval (e.g. one week). The first and second temperature thresholds can be same or different and are typically in the range of -10°C to -20°C (the range between minus 10 degrees Celsius and minus 20 degrees Celsius).

[0019] The first valve arrangement may have any suitable combination of expansion and shut-off function. It may be an electric expansion valve which can be fully opened and closed. In a specific embodiment, the first valve arrangement comprises a closable thermostatic expansion valve which automatically adjusts the opening degree on basis of a thermal response associated with the evaporator. By utilizing the special after-run mode, the thermostatic expansion valve will be operable on the response of the sufficiently warm compartment recirculation air guided through the evaporator such that the thermal load will support its automatic opening which otherwise at very low ambient temperatures may no longer be responsive or able to open at all. Thus, an electric expansion valve may be dispensed with, and a more cost-effective thermostatic expansion valve can be used.

[0020] In rare conditions the special after-run mode may not be possible and other strategies for start-up at very low temperatures may need to be employed. In order to avoid an ineffective after-run, the compartment air temperature is determined, and the after-run mode is only engaged if the determined compartment temperature is above a pre-defined threshold. Such threshold needs to be determined by simulations or system tests depending on the specific vehicle configuration. In typical configurations the threshold is typically higher than 10°C (10 degrees Celsius) and more preferably higher than 15°C (15 degrees Celsius). In case the special after-run mode cannot be employed, the flushing of the evaporator may be deferred to the re-start (where the “LAT” condition may no longer be present or less favourable countermeasure may be employed).

[0021] In typical systems, the air conduit comprises several outlets including a foot outlet. In a preferred embodiment, the foot outlet is opened or kept open and the other outlets are closed when the special after-run mode is operated. In case passengers are still within the vehicle the use of the foot outlet is least disturbing.

[0022] Preferably, only the first heat exchanger for heating is switched within the high-pressure side of the refrigerant cycle and the outside heat exchanger is cut off from the active part of the refrigerant cycle. In cold ambient conditions the pressure level at the outside heat exchanger is reduced such that the pressure difference to the low-pressure side is reduced at system stop. An automatically adjusting thermostatic expansion valve upstream of the evaporator may not easily react upon such reduced pressure difference. Hence, with the outside heat exchanger cut off, the evaporator flushing is more effective.

[0023] For air conditioning systems with more than one evaporator, such as for multi-zone and / or front / rear air conditioning, typically as known in the art, a first evaporator is disposed in a first air channel of the air conduit, a second evaporator is disposed in a second air channel of the air conduit and the first evaporator and the second evaporator are arranged in parallel with each other within the refrigerant cycle. In such configurations, preferably the special after-run mode is carried out consecutively for the first evaporator and the second evaporator. When using thermostatic expansion valves associated with the evaporators, it is easier to calculate the refrigerant mass flow if the flushing is carried out consecutively. A certain preciseness of such calculation is important to make sure that a minimum level of refrigerant mass flow is achieved in order to guarantee an effective oil / refrigerant flush.

[0024] The required system parameters for the special after-run mode (e.g. the evaporator blower airflow, the compressor speed and the timing) can be determined for each specific vehicle configuration.

[0025] In typical passenger vehicle configurations such airflow is typically in the range between 50kg / h(kilogram per hour) - 200kg / h (the range between 50kg / h and 200kg / h), preferable 100kg / h - 150kg / h (the range between 100kg / h and 150kg / h). A minimum airflow reliably achievable in typical configurations is about 50kg / h - 80kg / h (the range between 50kg / h and 80kg / h), so that the blower operation for the special after-run mode is towards the lower operational range. In typical configurations, the compressor speed is controlled in such a way that a mass flow of the refrigerant in the range between 20kg / h - 50kg / h (the range between 20kg / h and 50kg / h) is maintained.

[0026] The pre-determined first time span is typically in the range of 10s - 60s (the range between 10 seconds and 60 seconds), preferably 15s - 30s (the range between 15 seconds and 30 seconds), whereas the first valve, the compressor and the first blower are shut down after the pre-determined first time span has lapsed. Preferably, a second blower associated with the outside heat exchanger is operated for a pre-determined second time span after the compressor and / or the first blower is switched off. Such second time span lies preferably in the range of 30s - 120s (the range between 30 seconds and 120 seconds).

[0027] The general background to the present disclosure is shown with reference to Figures 1 to 3. Figure 1 shows a schematic layout of an air conditioning system 10 which may benefit from the method according to an embodiment of the invention which will be explained in more detail with reference to Figure 4.

[0028] The air conditioning system 10 comprises an air conduit with at least a first air channel 11A, air inlets 12A, 12B, air outlets 13A - 13C and a refrigerant cycle 20. The refrigerant cycle 20 has a compressor 21, a condenser 22 as first heat exchanger for heating and at least one evaporator 24A for cooling / dehumidification. A first blower 14B as well as the condenser 22 and the evaporator 24A are disposed within the first air channel 11A for delivering air from the air inlets 12A, 12B into a vehicle compartment 15 to be climatized. An outside heat exchanger 23 with an associated second blower 14A is typically located at the front part of a vehicle (not shown).

[0029] Recently, air conditioning systems have become rather complex due to various performance, cost and other requirements. Therefore, for completeness of the present disclosure, typically further heat exchangers are provided, such as a chiller 25 to transfer heat between the refrigerant cycle 20 and coolant cycles for cooling components such as a battery or inverter, and an internal heat exchanger 26 as well known in the art. The system further comprises a receiver 27 at the high-pressure side, several expansion valves 28A - 28C, valves 29A - 29F, fixed orifice throttles 29G, 29H, sensors 30A - 30C and a control unit 31. Sensors 30A, 30B are combined temperature / pressure sensors for general control strategies of the main refrigerant cycle 20 and sensor 30C is a temperature sensor used for the control of the superheat downstream of the chiller 25. The other valves 29A - 29F are used for various purposes to operate the refrigerant cycle 20 in different operational modes such as one or more cooling modes, heating modes or re-heating modes known as such in the art.

[0030] Expansion valves 28A - 28C may be of any appropriate type. For more robust control they can be fully openable and closable electric expansion valves. Due to cost reasons, expansion valve 28C may be a closable thermostatic expansion valve which automatically adjusts the opening degree on basis of a thermal response associated with the first evaporator 24A. Instead of a closable thermostatic expansion valve 28C, there could be a valve arrangement of two separate components of a thermostatic valve and a shut-off valve in series (not shown). A check valve 29D downstream of the evaporator 24A prevents a backflow of refrigerant from the suction side of the compressor 21. The method to operate the refrigerant cycle 20 within the meaning of the present disclosure provides a problem solution for very low temperature operation in particular if for valve 28C a closable thermostatic expansion valve is used, as will be explained further below in more detail.

[0031] Figure 2 shows a partial view of the layout around the first evaporator 24A according to Figure 1. An additional second evaporator 24B is arranged within an additional second air channel 11B. Within the refrigerant cycle 20, upstream of the second evaporator 24B a second closable thermostatic expansion valve 28D (along with a shut-off function) is provided in order to control the pressure step on basis of a thermal response associated with the second evaporator 24B. Both evaporators 24A, 24B are arranged in parallel with each other within the refrigerant cycle 20. A check valve 29D is located downstream of the evaporator 24B to avoid back-flow from the suction side of the compressor 21.

[0032] Turning to Figure 3, as example of a generic view of the vehicle compartment 15, a passenger compartment with a front and a rear air conditioner is shown in relation to the various air inlets 12A, 12B and outlets 13A - 13E. As known in the art, a first inlet 12A is adapted to receive ambient air and a second inlet 12B is adapted to receive air from the vehicle compartment 15 in a recirculation mode (whereas the exact positioning of the exit point from the vehicle compartment 15 is not important here). Air having passed the first air channel 11A can exist through various air outlets such as the face outlet 13A, the defrost outlet 13B or the foot outlet 13C. Air having passed the second air channel 11B can exit through further outlets such as a rear face outlet 13D and a rear foot outlet 13E. The second air channel 11B may have any reasonable relation to the first air channel 11A, e.g. branching off at a point between the air inlets 12A, 12B and the outlets 13A - 13C. In such case, no additional blower would be required. Alternatively, both air channels 11A, 11B well could be independent with separate blowers (not shown).

[0033] The method disclosed in this specification is performed by the air conditioning system under a control of the control unit 31. The control unit 31 includes a computer system that has at least one hardware processor to perform the control to implement the method. The hardware processor is configured to perform steps defined in the method. The hardware processor may be provided by (i) a processor and a memory storing program for performing the method, when executed by the processor, and / or (ii) a hardware logic circuit configured to perform the method.

[0034] With reference to the flowchart shown in Figure 4, an embodiment of the method to operate an air conditioning system 10 will be described in greater detail. As well known in the art, after system start in step 10 it is checked in step 20, if a heating and / or cooling demand for the vehicle compartment 15 or for the coolant cycle connected to the chiller 25 (e.g. for the vehicle battery) is requested. Such demand may be based on user input, sensor data or otherwise pre-programmed information. In step 30 the operation mode and the target system parameters will be decided in any appropriate way. The selection of the operational method may include to select a cooling, a heating or a re-heating mode associated with specific settings of the compressor and blower speeds and valve and air door opening degrees as this will be apparent to a skilled person in the art.

[0035] Before setting the decided operational mode and parameters, in step 40 it is checked whether the ambient temperature is below a threshold temperature T1. Threshold temperature T1 is predetermined such that below T1 the thermostatic expansion valve 28C will not sufficiently open upon thermal feedback from the evaporator 24A. Under these conditions a flushing of the evaporator 24A will not work automatically with a thermostatic expansion valve 28C (the same applies to rear evaporator 24B and thermostatic expansion valve 28D). For typical components and configurations T1 is about -15°C.

[0036] If the ambient temperature is above T1, the system will start with the flushing of the front evaporator 24A with step 110 and optionally with the rear evaporator 24B in step 120 within a normal flushing operation. In step 70 the normal operation is then initiated as decided in step 30.

[0037] If the ambient temperature is below T1, in step 50 it will be determined that the evaporator flushing cannot be safely activated. The system will either start slowly or take other measures to compensate for potentially trapped refrigerant and oil within the evaporator (which is out of scope of this disclosure) and then resume with step 70

[0038] In step 60 is will be continuously checked if the vehicle is planned to be parked. If this is not the case, the system will return with normal operation with step 70. Indications that the vehicle is planned to be parked may comprise a variety of factors such as the entering of a designated parking area or reaching a navigation destination.

[0039] If an indication is received that the vehicle is planned to be parked, the system can prepare for a permanent parking condition (“PP” condition, e.g. vehicle stationary, ignition off).

[0040] In step 200 it is checked if a Low-Ambient-Temperature condition (“LAT” condition) exists and if the air temperature in the vehicle compartment 15 is above a second threshold temperature T2, typically set to be about T2=15°C.

[0041] If one of the conditions is not met, the system will be shut down normally in step 300, i.e. without a special after-run mode to flush the evaporators 24A, 24B. In the embodiment, the “LAT” condition is met if the ambient temperature is expected to drop at least once below the pre-determined threshold value T1 for the next 72 hours. More sophisticated embodiments may take into account other patterns, such as a predicted next start of the vehicle (e.g. by regular or programmed operational schedules).

[0042] If a “LAT” condition was identified and the temperature of the vehicle compartment 15 is above T2, the air conditioning system is prepared to be operated in a special after-run mode in steps 210 to 230 once the “PP” condition is met. In step 210, the airflow is operated in full recirculation mode (i.e. inlet 12A is fully closed and inlet 12B is fully open) and only the foot outlet 13C is open, the other air outlets in the vehicle compartment 15 are fully closed. Moreover, the refrigerant cycle 20 will be operated in reheat mode, i.e. the outside heat exchanger 23 is cut off and only the condenser 22 is operated on the high-pressure side of the refrigerant cycle 20. For this operational mode, valve 29A is fully closed and valve 29B is fully open as this is represented by the bold lines within Figure 1.

[0043] In step 210, first the front evaporator 24A will be flushed. For that purpose, valve 28C is open (it may have been open already, but typically it has been closed before, if the present ambient temperature is <0°C (if the present ambient temperature is smaller than zero degree Celsius)), valve 28D is closed. After a pre-determined time offset t0 after reaching the “PP” condition, e.g. t0=20 seconds, the speeds of the first blower 14B will be set to the lowest possible level (e.g. 80kg / h) and the compressor 21 will be set to reach 30kg / h refrigerant mass flow for a first time span t1=20 seconds.

[0044] Next, in step 220, valve 28C will be closed and valve 28D will be opened such to continue with the flushing of the rear evaporator 24B in the same manner as the front evaporator 24A. The speeds of the blower 14B and the compressor 21 can be kept. After the first time span t1 has passed again, the compressor 21 and the blower 14B will be stopped and valve 28D will be closed.

[0045] In step 230, the second blower 14A associated with the outside heat exchanger 23 will now be operated for a pre-determined second time span t2=60 seconds in a low-speed setting. Once the second blower 14A is stopped, the system can conclude the shut-down with step 300.

[0046] 10 Air conditioning system, 11A, 11B Air channels, 12A, 12B Air inlets, 13A - 13E Air outlets, 14A, 14B Blowers, 15 Vehicle compartment, 20 Refrigerant cycle, 21 Compressor, 22 Condenser, 23 Outside heat exchanger, 24A, 24B Evaporator, 25 Chiller, 26 Internal heat exchanger, 27 Receiver, 28A - 28D Expansion valves, 29A - 29H Valves, 30A - 30C Sensors, 31 Control unit

Claims

1.

1. A method to operate an air conditioning system (10) of a motor vehicle, the air conditioning system (10) comprising: an air conduit (11A) with two inlets (12A, 12B), at least one outlet (13A - 13C), and an associated first blower (14B) to provide climatized air for a vehicle compartment (15) through that at least one outlet (13A - 13C), and a refrigerant cycle (20) with a compressor (21), a first heat exchanger (22) for heating and an evaporator (24A) for cooling / dehumidification both being disposed within the air conduit (11A), and an outside heat exchanger (23), whereas a first inlet (12A) of the air conduit (11A) is adapted to receive ambient air and a second inlet (12B) is adapted to receive air from the vehicle compartment (15) in a recirculation mode, whereas an indication is received that the vehicle is planned to be parked, characterized in that the air conditioning system (10) is operated in a special after-run mode, wherein an indication for a Low-Ambient-Temperature condition (“LAT”-condition) is received, airflow is operated in the recirculation mode, a first valve arrangement (28C) associated and in series with the evaporator (24A) is opened or kept open and the compressor (21) and the first blower (14B) are continued to be operated on pre-determined operational speeds for a pre-determined first time span after a determination of a permanent parking condition (“PP”-condition).

2.

2. The method to operate an air conditioning system (10) according to claim 1, characterized in that the first valve arrangement (28C) comprises a closable thermostatic expansion valve (28C) which automatically adjusts an opening degree on basis of a thermal response associated with the evaporator (24A).

3.

3. The method to operate an air conditioning system (10) according to claim 1 or 2, characterized in that a compartment air temperature is determined and the after-run mode is only engaged if a determined compartment air temperature is above a pre-defined threshold, preferably higher than 10°C, more preferably higher than 15°C.

4.

4. The method to operate an air conditioning system (10) according to any one of claims 1 to 3, characterized in that the air conduit (11A) comprises several outlets (13A - 13C) including a foot outlet (13C) and the foot outlet (13C) is opened or kept open and the other outlets (13A, 13B) are closed.

5.

5. The method to operate an air conditioning system (10) according to any one of claims 1 to 4, characterized in that only the first heat exchanger (22) for heating is switched within a high-pressure side of the refrigerant cycle (20) and the outside heat exchanger (23) is cut off from an active part of the refrigerant cycle (20).

6.

6. The method to operate an air conditioning system (10) according to any one of claims 1 to 5, characterized in that a first evaporator (24A) is disposed in a first air channel (11A) of the air conduit (11A, 11B), a second evaporator (24B) is disposed in a second air channel (11B) of the air conduit (11A, 11B), the first evaporator (24A) and the second evaporator (24B) are arranged in parallel with each other within the refrigerant cycle (20) and the special after-run mode is carried out consecutively for the first evaporator (24A) and the second evaporator (24B).

7.

7. The method to operate an air conditioning system (10) according to any one of claims 1 to 6, characterized in that the airflow of the first blower (14B) associated with the evaporator (24A) is in the range between 50kg / h - 200kg / h, preferable 100kg / h - 150kg / h.

8.

8. The method to operate an air conditioning system (10) according to any one of claims 1 to 7, characterized in that a compressor speed is controlled in such a way that a refrigerant mass flow in the range between 20kg / h - 50kg / h is maintained.

9.

9. The method to operate an air conditioning system (10) according to any one of claims 1 to 8, characterized in that the pre-determined first time span is in the range of 10s - 60s, preferably 15s - 30s and a first expansion valve (28C), the compressor (21) and the first blower (14B) are shut down after the pre-determined first time span has lapsed.

10.

10. The method to operate an air conditioning system (10) according to claim 9, characterized in that a second blower (14A) associated with the outside heat exchanger (23) is operated for a pre-determined second time span after the compressor (21) and / or the first blower (14B) is switched off, preferably in the range of 30s - 120s.

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