DE102021201378A1 - Method of operating a heat pump - Google Patents

Abstract

In order to create a method (80) for operating a heat pump (10) in a motor vehicle (100), with an ambient heat exchanger (20) and an interior heat exchanger (30), which are connected to one another via a refrigerant circuit (40), which increases efficiency, it is proposed that when the motor vehicle (100) starts driving, the humidity of a vehicle environment (U) should be determined and if the determined humidity falls below (85) a threshold value, the heat pump (10) be used to cover a future heating requirement of a vehicle interior (101 ) of the motor vehicle (100) to operate.

Description

The invention relates to a method for operating a heat pump in a motor vehicle, with an ambient heat exchanger and an interior heat exchanger, which are connected to one another via a refrigerant circuit. Furthermore, the invention relates to a motor vehicle with a heat pump.

In electrically powered vehicles, heat pumps are often used to heat the vehicle interior. Here, the heat required to heat the vehicle interior is extracted from the vehicle environment and supplied to the vehicle interior. In this process, a heat exchanger that is thermally coupled to the vehicle environment cools down in such a way that the air in the vehicle environment falls below the dew point and frost forms on the surface of the heat exchanger.

The surface of the heat exchanger becomes increasingly iced up due to the formation of frost and thus prevents efficient operation of the heat pump. In order to allow air to flow through the heat exchanger again, defrosting cycles or defrosting processes are necessary, in which the iced-up heat exchanger is heated. As a result, the ice melts and air can flow through the heat exchanger again. However, such defrost cycles affect the efficiency and performance of the heat pump.

Methods for carrying out defrosting cycles are already known, which initiate the defrosting process of an evaporator after a predefined operating time has elapsed. Methods are also known which measure a suction pressure of the air passing through the evaporator in order to initiate a defrosting process when the suction pressure decreases.

The problem with the known methods for performing defrosting cycles, however, is that with relatively low humidity when the vehicle starts driving, a high heating output is required for heating the vehicle interior from the heat pump for a short time, so that the evaporator ices up as soon as the vehicle starts driving. This reduces the air mass flow that passes through the evaporator until the next defrosting process. Due to the comparatively dry air, however, the layer of ice on the evaporator increases only slightly, so that the next defrosting process is only carried out after a longer period of time. The efficiency of a heat pump controlled in this way is therefore insufficient.

The object of the invention is to provide a method for operating a heat pump with increased efficiency. This object is achieved by the features specified in claim 1. Further advantageous configurations of the invention are described in the dependent claims.

According to one aspect of the invention, a method for operating a heat pump in a motor vehicle is provided. The heat pump is equipped with an ambient heat exchanger and an indoor heat exchanger, which are connected to each other via a refrigerant circuit. In this case, a compressor or a compressor is provided in order to convey a refrigerant through the refrigerant circuit and thus bring about an expansion and compression of the refrigerant.

At the start of a journey of the motor vehicle, an air humidity of a vehicle environment is determined. In a subsequent step, it is checked whether the humidity determined falls below a threshold value. If the determined air humidity falls below the threshold value, the heat pump is operated to cover a future heating requirement, instead of a current heating requirement, of a vehicle interior of the motor vehicle.

As a result, an icing prevention mode of the heat pump can be implemented, which suppresses the briefly increased heating output at the start of the journey and prevents the ambient heat exchanger, which acts as an evaporator, from suddenly icing up. This means that the stationary heating capacity requirement can be used as an orientation based on an upper limit for the relative outside humidity in relation to the temperature.

In an icing prevention mode, the evaporation temperature in the ambient heat exchanger is regulated in such a way that it does not fall below the dew point of the ambient air and icing of the ambient heat exchanger is avoided.

The stationary heating power requirement occurs when the vehicle interior has been heated to a predefined temperature level. The temperature level preferably corresponds to a desired temperature and is set by a user or driver of the motor vehicle. The energy requirement of stationary operation depends on the outside temperature and the desired temperature and can be determined in advance and stored on a data carrier of a control device in the motor vehicle. If in stationary operation the icing prevention of the ambient heat transfer gers is the most efficient operation of the heat pump, icing of the ambient heat exchanger is also avoided when starting the journey.

The method allows a gain in efficiency to be achieved with minimal application effort. The current energy requirement for heating the vehicle interior is not taken into account in order to avoid short-term icing of the ambient heat exchanger.

According to one exemplary embodiment, the future heating demand is configured as a heating demand of the vehicle interior in a stationary regulated operation of the heat pump after an initial heating-up phase of the vehicle interior. The heat pump is preferably operated after a period of 3 to 15 minutes from the start of the motor vehicle's journey to provide a heating output to cover future heating requirements. As a result of this measure, the anti-icing mode of the heat pump can be implemented in a technically particularly simple manner with the aid of a time delay. After the time delay has elapsed, which starts when the journey begins, the heat pump can be started or continued in operation.

The future heating requirement of the vehicle interior can be determined particularly precisely if this is determined as a function of an outside temperature and an adjustable desired temperature of the vehicle interior. In particular, the future heating requirement can be determined by a control unit of the motor vehicle. The control unit can also regulate and control the heat pump. In addition, the control unit is connected to sensors and can establish a communication connection to an external unit in order to receive or send data. The control device can include an internal or external memory in order to store data at least temporarily.

According to a further embodiment, if the determined air humidity exceeds a threshold value, the heat pump is operated to cover a current heating requirement of the vehicle interior of the motor vehicle. The air humidity determined corresponds to a relative air humidity of the vehicle environment. If the relative humidity is very high, an anti-icing mode cannot be implemented in a sensible manner. In this respect, a "conventional" regulation of the heat pump by the control unit can be used in such a scenario, which takes into account the current heating requirement of the vehicle interior.

Only when the relative humidity drops, such as 60% at 0°C or 50% at -10°C, can the stationary operation of the heat pump and thus the future heating requirements of the vehicle interior be taken into account.

A preliminary decision can be made on the basis of the current humidity, according to which a strategy (current heating requirement or future heating requirement of steady-state operation) is selected for operating the heat pump and the heat pump is controlled.

According to a further exemplary embodiment, the threshold value for the air humidity is defined as a function of a temperature. The threshold value can be stored in the memory of the control unit in the form of a characteristic curve or a comparison table. The threshold value can preferably take into account all possible operating temperatures, for example -10° C. to +80° C., of the motor vehicle.

The efficiency of the heat pump can be further increased if a software model of the heat pump is created parallel to the operation of the heat pump and, based on the software model, it is checked whether a defrosting process of the ambient heat exchanger and operation to cover the future heating requirement of the vehicle interior compared to operation of the heat pump for Cover the current heating needs of the vehicle interior is more energy efficient. Based on the result of the test, the operation of the heat pump is maintained or changed. The operation of the heat pump can be switched over or maintained in particular to cover the current heating requirement or to cover the future heating requirement. Here, on the basis of the software model of the heat pump, a check is made as to whether it is possible to switch to the anti-icing mode in the heat pump's icing and de-icing mode. If this is the case, it makes sense to first defrost the heat exchanger and then switch it to anti-icing mode.

In a further embodiment, data of a planned route is received, based on the received data an air volume flowing through the ambient heat exchanger along the planned route is determined and the heat pump is operated depending on the air volume to cover the future heating requirement or to cover the current heating requirement of the vehicle interior . With this measure, a predicted value of the flow through the heat exchanger can be used for the operation of the heat pump. It can be less for a city trip and a cross-country When driving or driving on the motorway, an increased air volume can be assumed. An increased volume of air flowing through the ambient heat exchanger results in a lower driving temperature difference in the heat transfer between the ambient air and the refrigerant of the ambient heat exchanger. This reduces the risk of falling below the dew point of the ambient air.

The control unit can set the operating mode of the heat pump precisely when the air humidity in the vehicle environment is determined directly by a sensor, indirectly by a temperature sensor and/or a pressure sensor and/or by receiving data from an external unit. In addition to the direct measurement of the humidity, the control unit can receive weather data from the external unit and then evaluate it. The external unit can be designed as a backend or a weather service.

According to a further aspect of the invention, a motor vehicle is provided which has a heat pump with an ambient heat exchanger and an interior heat exchanger. The ambient heat exchanger and the interior heat exchanger are connected to one another via a refrigerant circuit. The motor vehicle is set up to carry out the method according to the invention. As a result, when the motor vehicle starts driving due to an initially high heating demand of the vehicle interior, the risk of icing of the ambient heat exchanger can be reduced and the efficiency of the heat pump can be increased.

• 1 eine schematische Darstellung eines erfindungsgemäßen Kraftfahrzeugs mit einer Wärmepumpe gemäß einer Ausführungsform, und
• 2 ein schematisches Ablaufdiagramm zum Veranschaulichen des erfindungsgemäßen Verfahrens gemäß einer Ausführungsform.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. Show it:

• 1 a schematic representation of a motor vehicle according to the invention with a heat pump according to one embodiment, and
• 2 a schematic flowchart to illustrate the method according to the invention according to one embodiment.

In the figures, the same structural elements each have the same reference numbers.

the 1 10 shows a schematic side view of a motor vehicle 100 with a heat pump 10 for air treatment according to an embodiment. The heat pump 10 is used, for example, to set a temperature in a vehicle interior 101 of the motor vehicle 100. In particular, the heat pump can be used to heat or cool the vehicle interior 101. Motor vehicle 100 is designed as a passenger car. The heat pump 10 can be used analogously in any motor vehicle 100, such as trucks, buses, agricultural vehicles and the like.

The heat pump 10 has an ambient heat exchanger 20 which is thermally coupled to a vehicle environment U or ambient air. As a result, the ambient heat exchanger 20 can withdraw heat from the vehicle environment U during heating operation of the heat pump 10 . The ambient heat exchanger 20 can be designed, for example, as an evaporator in the heating mode of the heat pump 10 .

Furthermore, the heat pump 10 has an interior heat exchanger 30 . The interior heat exchanger 30 is thermally connected to the vehicle interior 101 in order to heat or cool the vehicle interior 101 depending on the operating state of the heat pump 10 .

The ambient heat exchanger 20 and the interior heat exchanger 30 are connected to one another in a fluid-carrying manner via a refrigerant circuit 40 . A refrigerant can be conveyed through the refrigerant circuit 40 by means of a refrigerant compressor 41 in order to enable heat to be extracted from the environment U and heat to be supplied to the vehicle interior 101 .

By extracting heat from the environment U, the ambient heat exchanger 20 can ice up and thus lose its efficiency. At the start of the journey in particular, the ambient heat exchanger 20 can ice up particularly quickly if there is a correspondingly high heating requirement in the vehicle interior 101 .

A controller 50 may be connected to the refrigerant compressor 41 and configured to control the heat pump 10 . In particular, the control device 50 can implement requirements for a heating capacity or cooling capacity of the heat pump 10 in the form of an adjustment of an operating state of the heat pump 10 .

The control unit 50 is also connected to a sensor 60 in a data-conducting manner. The control unit 50 can receive and evaluate data on a relative humidity of the vehicle environment U from the sensor 60 . In addition, the controller 50 can establish a wireless communication link 51 to receive data from an external unit 70 .

The external unit 70 can be designed as a weather service and a current or provide predicted humidity at the motor vehicle 100 location.

The control device 50 also has a memory 52 . Threshold values for the relative air humidity as a function of a temperature can be stored in the memory 52 . For example, such threshold values can be stored in memory 52 in the form of a characteristic curve.

In the 2 a schematic flow diagram for illustrating the method 80 according to an embodiment is shown. The method 80 serves to operate the heat pump 10 and can be carried out by the motor vehicle 100 .

In a first step, the relative humidity of the vehicle environment U is determined. The relative humidity can, for example, be measured 81 directly by a sensor 60 or humidity sensor and/or received 82 from an external unit 70 . The control unit 50 can receive and evaluate the corresponding data in digital or analog form 83.

In a further step 84, a check is made as to whether the determined air humidity falls below a threshold value.

If the determined air humidity falls below the threshold value 85 , the heat pump 10 is operated to cover a future heating requirement of the vehicle interior 101 of the motor vehicle 100 . As a result, a stationary heating requirement during operation of the heat pump 10 in icing mode is taken into account instead of the current or present heating requirement of the vehicle interior 101. This can be implemented, for example, by a delayed activation of the heat pump 10. A corresponding time delay can be between 3 and 15 minutes, for example, depending on the desired temperature and boundary conditions.

Alternatively, the heat pump 10 can already be operated at the start of the journey with a reduced or adjusted output, which is required for stationary operation or the heating requirement of the vehicle interior 101 .

If the determined air humidity exceeds a threshold value 86 , the heat pump 10 is operated by the control unit 50 to cover a current heating requirement of the vehicle interior 101 of the motor vehicle 100 .

Reference List

100

motor vehicle

101

vehicle interior

10

heat pump

20

ambient heat exchanger

30

indoor heat exchanger

40

Refrigerant circulation

41

refrigerant compressor

50

control unit

51

communication link

52

Storage

60

Sensor for measuring humidity

70

external unit

80

procedure

81

Measuring relative humidity

82

Obtaining relative humidity from external unit

83

Receiving and processing data

84

Comparison of humidity with threshold value

85

Measure if the threshold value is not reached

86

Measure if the threshold is exceeded

u

Vehicle environment / ambient air

Claims (9)

Method (80) for operating a heat pump (10) in a motor vehicle (100), with an ambient heat exchanger (20) and an interior heat exchanger (30), which are connected to one another via a refrigerant circuit (40), wherein when the motor vehicle (100 ) an air humidity of a vehicle environment (U) is determined, characterized in that when the determined air humidity falls below (85) a threshold value, the heat pump (10) is operated to cover a future heating requirement of a vehicle interior (101) of the motor vehicle (100). procedure after claim 1 , wherein the future heating requirement is designed as a heating requirement of the vehicle interior (101) in a steady-state regulated operation of the heat pump after an initial heating phase of the vehicle interior (101), the heat pump (10) ready for provide a heating output to cover the future heating requirement after a period of 3 to 15 minutes from the start of the motor vehicle (100) is operated. procedure after claim 1 or 2 , The future heating requirement of the vehicle interior (101) depending on an outside temperature and an adjustable desired temperature of the vehicle interior (101) is determined. Procedure according to one of Claims 1 until 3 , wherein the threshold value for the humidity is determined as a function of a temperature, in particular 60% at 0°C or 50% at -10°C. Procedure according to one of Claims 1 until 4 , wherein when the determined air humidity exceeds (86) a threshold value, the heat pump (10) is operated to cover a current heating requirement of the vehicle interior (101) of the motor vehicle (100). procedure after claim 5 , wherein a software model of the heat pump (10) is created parallel to the operation of the heat pump (10), based on the software model is checked whether a defrosting process of the ambient heat exchanger (20) and an operation to cover the future heating requirement of the vehicle interior (101) compared operation of the heat pump (10) to cover the current heating requirement of the vehicle interior (101) is more energy-efficient, the operation of the heat pump (10) being maintained or converted based on the result of the test. Procedure according to one of Claims 1 until 6 , wherein data of a planned route are received, based on the received data a volume of air flowing through the ambient heat exchanger (20) along the planned route is determined and the heat pump (10) depending on the air volume to cover the future heating requirement or to cover the current heating requirement of the vehicle interior (101) is operated. Procedure according to one of Claims 1 until 7 , The air humidity of the vehicle environment (U) being determined directly by a sensor (60), indirectly by a temperature sensor and/or a pressure sensor and/or by receiving data from an external unit (70). Motor vehicle (100), which has a heat pump (10) with an ambient heat exchanger (20) and an interior heat exchanger (30), which are connected to one another via a refrigerant circuit (40), the motor vehicle (100) being set up to implement the method (80 ) according to any one of the preceding claims.

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