METHOD FOR OPERATING AN AIR CONDITIONING SYSTEM FOR A VEHICLE

Description

[0001] The invention relates to a method for operating an air conditioning system for a vehicle, a control unit and a vehicle.

[0002] Heat exchangers are used in a variety of applications in vehicles, such as motor vehicles, for example, for air conditioning. In this function, heat exchangers are commonly used as part of a heat pump, which extracts heat from the outside air to provide air conditioning. This concept is particularly well-suited to electric vehicles, increasing their range compared to electric heating.

[0003] However, such heat pumps have the problem that at low outside temperatures, such as -4 °C or below, the heat exchanger is prone to icing, as it must be very cold to achieve the temperature difference necessary for heat transfer. As a result, the heat exchanger must be defrosted after some time, which can be very energy-intensive. However, this is necessary in conventional systems to remove the accumulated ice, which impairs the efficiency of heat transfer.

[0004] DE 10 2012 109 483 A1 discloses a method for controlling an energy supply system. This involves determining which of a set of control variables enable more energy-efficient control of a heat transfer medium. A heat exchange process is then controlled initially based on the control variable determined to be more energy-efficient. The control variable determined to be less energy-efficient is only used to control the heat exchange if the control objective cannot be achieved with the control variable determined to be more energy-efficient alone.

[0005] US 2014 / 0 069 123 A1, FR 3 026 172 A1, and DE 10 2010 020 321 A1 each disclose methods for operating an air conditioning system for a vehicle, in which an attempt is made to prevent icing of an outside air heat transfer medium. It is mentioned that the heat pump can be operated at a fluid temperature at which the dew point is not undershot.

[0006] DE 10 2017 206 135 A1, DE 10 2017 104 646 A1, DE 11 2016 003 261 T5 and US 2011 / 0 016 896 A1 disclose methods for operating a temperature control system for a vehicle, in which it is addressed to operate a heat pump with a fluid temperature at which the dew point is undershot.

[0007] The invention is based on the object of finding a technical solution that avoids air conditioning of a vehicle in inefficient operating conditions.

[0008] The object is solved by the subject matter of independent patent claims 1, 8 and 9. Further preferred embodiments of the invention emerge from the remaining features mentioned in the subclaims.

[0009] A first aspect of the invention relates to a method for operating an air conditioning system for a vehicle, the air conditioning system comprising: a heat pump with an outside air heat exchanger; and a further heating source for an interior of the vehicle; The method comprises the following steps: determining a heating power requirement for air conditioning the vehicle; determining a required heat output at the outside air heat exchanger; determining an outside air condition; determining a fluid temperature required in the outside air heat exchanger for the required heat output; determining whether a dew point of the outside air at the outside air heat exchanger is undershot at the required fluid temperature;and then selecting an operating strategy for the air conditioning system based on criteria that include at least the coverage of the heating power requirement, the outside air temperature and an overall energy efficiency of the air conditioning system, by means of a control unit of the vehicle from a group that includes at least the following operating strategies: b) partial coverage of the heating power requirement by operating the heat pump with a fluid temperature at which the dew point is not undershot, and additional coverage of the heating power requirement by operating the additional heating heat source; c) temporary partial coverage of the heating power requirement by operating the heat pump with a fluid temperature at which the dew point is undershot, and additional coverage of the heating power requirement by operating the additional heating heat source, followed by a defrosting phase of the outside air heat exchanger;d) temporarily meeting the heating demand by operating the heat pump at a fluid temperature below the dew point, followed by a defrosting phase of the outdoor air heat exchanger; whereby the operating strategy with the greatest overall efficiency that meets the heating demand is selected.

[0010] In other words, the overall energy efficiencies for the operating strategies included in the group are determined and the operating strategy with the highest overall efficiency that covers the heating power demand is selected.

[0011] Selecting the operating strategy in this way advantageously ensures that the heating demand is met, and by coordinating the use of the available heat sources—namely, the outside air and the additional heat source—the air conditioning system always operates at its highest efficiency. This is achieved, in particular, by allowing combinations, such as the operation of the heat pump under icing conditions with the operation of an electric heating source, which, viewed in isolation, may be unfavorable in terms of efficiency. It is important that these combinations balance each other out with regard to overall efficiency over the course of the process.Thus, under certain conditions, an overall efficiency can be achieved that is higher than the overall efficiency that could be achieved if, for example, only the heat pump or only the additional heating source were used to cover the heating output requirement.

[0012] In the context of the invention, the overall energy efficiency is the ratio of the electrical energy absorbed by a compressor of the heat pump to the energy absorbed by the other heat source, for example electrical energy.

[0013] The heating power requirement for air conditioning, for example, is determined in the usual way based on a target and actual temperature in the vehicle. Depending on the desired accuracy, other factors can also be taken into account, such as the vehicle's air capacity or the heat capacity of the air.

[0014] To determine the outside air condition, for example, the temperature and humidity of the outside air are measured in a known manner, and a dew point is derived from this. The relevance of the dew point in the method according to the invention lies in particular in that it indicates whether or not ice is forming on the outside air heat exchanger.

[0015] With regard to the required fluid temperature in the outside air heat exchanger, the person skilled in the art will recognize, based on the teaching disclosed here, that, for example, an inflow temperature of the fluid into the outside air heat exchanger represents a suitable reference and its flow velocity must be taken into account.

[0016] The defrosting phase of the outside air heat exchanger can be achieved, for example, by reversing the heat pump process or by actively or passively supplying heat, which will be discussed in more detail later.

[0017] Preferably, the additional heat source used comprises an electric heat source. Electric heat sources are known to be among the less efficient heat sources, but this is advantageously compensated for and even overcompensated for in the process according to the invention by the described synergy effects.

[0018] The air conditioning system used is preferably intended for an electric vehicle, as the increased energy efficiency has a particularly beneficial effect on the range.

[0019] In a preferred embodiment of the method of the invention, the group comprises as a further operating strategy: a) Covering the heating power requirement by operating the heat pump with a fluid temperature at which the dew point is not undercut.

[0020] Under suitable conditions, the heat pump can also be operated alone without any risk of icing.

[0021] In a further preferred embodiment of the method of the invention, it is provided that the group comprises as a further operating strategy: c) temporary partial coverage of the heating power requirement by operating the heat pump with a fluid temperature below the dew point, and additional coverage of the heating power requirement by operating the further heating heat source, followed by a defrosting phase of the outside air heat exchanger.

[0022] In this way, the icing of the outside air heat exchanger can be slowed down and the need for a defrost phase can be delayed.

[0023] In a further preferred embodiment of the method of the invention, it is provided that in operating strategy c) or d) in the defrosting phase, the heating power requirement is covered by operating the additional heating heat source.

[0024] In this way, the defrosting phase is advantageously bridged and loss of comfort is avoided.

[0025] In a further preferred embodiment of the method of the invention, it is provided that heat from the further heating source is used for defrosting the outside air heat exchanger.

[0026] In this way, defrosting can advantageously be performed without reversing the heat pump process. If the heat pump process is also reversed, the heat from the additional heating source can advantageously counteract the resulting cooling effect of reversing the heat pump process, thus avoiding noticeable fluctuations in the vehicle's air conditioning.

[0027] According to the invention, in operating strategy c) a simulation, a predictive control or the use of a characteristic map is carried out on the basis of user information and an icing model, whereby it is determined when the heating power requirement is eliminated and then a partial coverage of the heating power requirement takes place by operating the heat pump with a fluid temperature at which the dew point is undershot, and a supplementary coverage of the heating power requirement takes place by operating the further heating heat source, so that this operating strategy leads to a maximization of the overall efficiency until the heating power requirement is eliminated.

[0028] The user information can, for example, be navigation information about the duration of the heating requirement, e.g., in the form of a distance to be covered by the vehicle, or it can also include an air conditioning setting. The simulation can then determine, for example, when the vehicle should be parked and thus air conditioning is no longer required. Based on this, the simulation can determine, for example, how much heating power can be provided by the heat pump under icing conditions until the heating requirement is no longer met, and how much must be supplemented by the additional heating source until the entire heating requirement is met, so that the highest possible overall efficiency is achieved, for example, until the destination is reached.

[0029] Defrosting of the outside air heat exchanger can thus be shifted to a time when air conditioning is not required. This allows defrosting to be performed passively, for example, by scheduling a rest period for the air conditioning system after use. This advantageously slows down the icing of the outside air heat exchanger while the air conditioning system is in operation, for example, while driving, but is generally permitted.

[0030] In a further preferred embodiment of the method of the invention, it is provided that in operating strategy c) or d) a simulation is carried out on the basis of user information and an icing model as to when the heating power requirement is eliminated and the heating power requirement is covered until the heating power requirement is eliminated by operating the heat pump with a fluid temperature at which the dew point is undershot.

[0031] In contrast to the previously described embodiment of the method, defrosting takes place outside of the vehicle's operation, for example, and can thus be carried out very slowly and efficiently, or even with the help of energy provided by a charging station. In this embodiment, for example, it is checked whether icing of the outside air heat exchanger can be permitted under given conditions if this still leads to the highest possible overall efficiency, for example, until the end of the journey.

[0032] Efficient heat pump operation can cover the heating demand alone. Here, too, defrosting can be shifted to a time when air conditioning is no longer required.

[0033] In a further preferred embodiment of the method of the invention, it is provided that the required heat power consumption is updated several times and the selection of the operating strategy is adapted.

[0034] It may turn out that the previously selected operating strategy permanently meets the criteria. Otherwise, the operating strategy can be changed. It should also be noted that naming the operating strategies a) to d) does not imply any order or ranking; rather, the operating strategies are always compared, and the currently most suitable operating strategy is selected based on the stated criteria.

[0035] Thus, the method of the invention allows the best operating strategy to always be used, even under changing conditions.

[0036] A second aspect of the invention relates to a control device configured to carry out a method according to the preceding description.

[0037] A third aspect of the invention relates to a vehicle comprising an air conditioning system with a heat pump, an outside air heat exchanger and a further heating heat source for an interior of the vehicle and comprising a control unit according to the preceding description.

[0038] In particular, the vehicle can comprise the technical means described in connection with the method of the invention and can take on the forms disclosed in connection with the method of the invention. The control unit can be configured accordingly and comprise control software designed for the method of the invention.

[0039] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

[0040] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show: Figure 1 shows an air conditioning system and a control unit according to the invention in a vehicle according to the invention; and Figure 2 shows a schematic representation of an application of criteria for selecting an operating strategy.

[0041] Figure 1 shows in the upper part an exemplary embodiment of a vehicle 10 according to the invention with an air conditioning system 12 and a control unit 14 according to the invention. The vehicle 10 here is an electric vehicle 16.

[0042] In the lower part of Figure 1 the air conditioning system 12 is shown in principle.

[0043] The air conditioning system 12 of the electric vehicle 16 includes a heat pump 18. The heat pump 18 has an outside air heat exchanger 20 that can be operated as an evaporator.

[0044] This is arranged in an engine compartment 22 of the electric vehicle 16 behind a radiator grille 24. Furthermore, the heat pump 18 includes an internal air heat exchanger 26, which can be operated as a condenser / gas cooler.

[0045] The indoor air heat exchanger 26 is arranged in an outflow duct 28. A further heating source 30, which in this case comprises an electrical heating source 32, is also provided in the outflow duct 28.

[0046] Air 34, which has previously been sucked in as supply air 40 from the environment or the interior 36 of the electric vehicle 16, can flow into an interior 36 of the electric vehicle 16 through the outflow channel 28.

[0047] Outside air 38 flows through the radiator grille 24 into the engine compartment 22 and is guided along the outside air heat exchanger 20.

[0048] Heat stored in the outside air 38 can enter the heat pump 18 via the outside air heat exchanger 20 and be transferred as heat output to the supply air 40 via the inside air heat exchanger 26. Furthermore, the electrical heating source 32 can generate electrical heat and also transfer it to the supply air 40.

[0049] The control unit 14 in the electric vehicle 16 is configured to operate the air conditioning system 12 in the manner according to the invention.

[0050] In this context, Figure 2 a schematic representation of an application of criteria for selecting an operating strategy for the air conditioning system 12.

[0051] The vertical axis represents an outside air temperature of 42. The horizontal axis represents a heating power requirement of 44.

[0052] For simplification, a target temperature in the interior 36 of the vehicle 10 is considered constant. The outside air humidity and the flow velocity of a fluid in the outside air heat exchanger 20 are also assumed to be constant.

[0053] The diagram now shows qualitatively how different operating strategies a), b), c), d) can be selected as examples in order to cover the heating power requirement 44 with the greatest possible overall efficiency of the air conditioning system 12.

[0054] For example, in the method of the invention it can be determined that these criteria in the area of ​​operating strategies a) can be met by pure heat pump operation without the outside air heat exchanger 20 icing up.

[0055] Furthermore, for example, it can be determined in the method of the invention that these criteria in the area of ​​operating strategy c) can be met by a heat pump operation in combination with an operation of the electric heating source 32, whereby the outside air heat exchanger 20 freezes. Operating strategy c) is in Figure 2 shown in two areas of the diagram. In the front area, closer to the vertical axis, i.e., with a lower heating power requirement 44, the defrosting phase occurs passively after the air conditioning requirement has been eliminated. In the rear area, further away from the vertical axis, i.e., with a higher heating power requirement 44, the defrosting phase occurs by reversing the heat pump process, supplementing the heating power requirement 44 with the electric heat source 32. List of reference symbols

[0056] 10Vehicle 12Air conditioning system 14Control unit 16Electric vehicle 18Heat pump 20Outside air heat exchanger 22Engine compartment 24Radiator grille 26Inside air heat exchanger 28Outlet duct 30Additional heating source 32Electric heating source 34Air 36Interior 38Outside air 40Supply air 42Outside air temperature 44Heating power requirement

Claims

1. Method for operating a climate control system (12) for a vehicle (10), wherein the climate control system (12) comprises: - a heat pump (18) having an outside air heat exchanger (20); and - a further heating source (30) for an interior (36) of the vehicle (10); wherein the method comprises the following steps: - determining a heating power requirement (44) for the climate control of the vehicle (10); - determining a required thermal power input at the outside air heat exchanger (20); - determining an outside air condition; - determining a fluid temperature in the outside air heat exchanger (20) that is necessary for the required thermal power input; - determining whether the outside air (38) at the outside air heat exchanger (20) falls below a dew point at the necessary fluid temperature; and then - selecting an operating strategy for the climate control system (12) on the basis of criteria which include at least meeting the heating power requirement (44), the outside air temperature (42) and an overall energy efficiency of the climate control system (12), by means of a control unit (14) of the vehicle (10) from a group which includes at least the following operating strategies: b) meeting part of the heating power requirement (44) by operating the heat pump (18) at a fluid temperature which does not fall below the dew point, and meeting the rest of the heating power requirement (44) by operating the further heating source (30); c) temporarily meeting part of the heating power requirement (44) by operating the heat pump (18) at a fluid temperature which falls below the dew point, and meeting the rest of the heating power requirement (44) by operating the further heating source (30), followed by a thawing phase of the outside air heat exchanger (20); d) temporarily meeting the heating power requirement (44) by operating the heat pump (18) at a fluid temperature which falls below the dew point, followed by a thawing phase of the outside air heat exchanger (20); - wherein the operating strategy having the greatest overall energy efficiency that meets the heating power requirement is selected.

2. Method according to claim 1, characterized in that the group comprises as a further operating strategy: a) meeting the heating power requirement (44) by operating the heat pump (18) at a fluid temperature which does not fall below the dew point.

3. Method according to either claim 1 or claim 2, characterized in that in operating strategy c) or d), in the thawing phase, the heating power requirement (44) is met by operating the further heating source (30) and heat from the further heating source (30) is used for thawing the outside air heat exchanger (20), and in that, in addition, a heat pump process of the heat pump (18) is reversed, heat from the further heating source (30) counteracting the cooling effect which results from the reversal of the heat pump process.

4. Method according to any of the preceding claims, characterized in that in operating strategy c), a simulation, a predictive control or the use of a characteristic map is carried out on the basis of user information and an icing model, it being determined when the heating power requirement (44) no longer applies, and then part of the heating power requirement (44) is met by operating the heat pump (18) at a fluid temperature which falls below the dew point and the rest of the heating power requirement (44) is met by operating the further heating source (30), so that this operating strategy leads to a maximization of the overall efficiency until the heating power requirement (44) no longer applies.

5. Method according to claim 1, characterized in that in operating strategy c) or d), a simulation is carried out on the basis of user information and an icing model when the heating power requirement (44) no longer applies, and the heating power requirement (44) is met until the heating power requirement (44) no longer applies by operating the heat pump (18) at a fluid temperature which falls below the dew point.

6. Method according to any of the preceding claims, characterized in that the further heating source (30) used comprises an electric heating source (32).

7. Method according to any of the preceding claims, characterized in that the climate control system (12) used is provided for an electric vehicle (16).

8. Control unit (14) designed to carry out a method according to any of claims 1 to 7.

9. Vehicle (10), comprising a climate control system (12) having a heat pump (18), an outside air heat exchanger (20) and a further heating source (30) for an interior (36) of the vehicle (10), and comprising a control unit (14) according to claim 8.