Regulation of heat pump in variable operating states

Abstract

The invention relates to the regulation of a heat pump in a variable operating state. In order to provide a method for operating a heat pump (10), in particular in a motor vehicle (100), having an ambient heat exchanger (20) and an interior heat exchanger (40), which are connected to one another via a refrigerant circuit (50), the freezing degree of the ambient heat exchanger (20) can be determined without using additional sensors, according to the invention, the icing degree (V) is calculated as an operating parameter of the heat pump (10), and a defrosting process (A) of the ambient heat exchanger (20) is introduced when a limit value (G) of the determined icing degree (V) is exceeded or reached.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for operating a heat pump, in particular 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 present application relates to a motor vehicle with a heat pump. BACKGROUND

[0002] In electrically driven vehicles, a heat pump is often used for heating the passenger compartment. Here, the heat required for heating the passenger compartment is drawn from the vehicle surroundings and delivered to the passenger compartment. In the process, the heat exchanger, which is in thermal connection with the vehicle surroundings, cools down such that the dew point of the air below the vehicle surroundings and frost is formed on the surface of the heat exchanger.

[0003] Due to the formation of frost, the surface of the heat exchanger is increasingly iced up and thus inhibits the efficient operation of the heat pump. In order to enable the air flow through the heat exchanger again, a defrosting cycle or defrosting process is required, in which the iced-up heat exchanger is heated. The ice thus melts and the air flow through the heat exchanger can be achieved again. However, such a defrosting cycle impairs the efficiency and the performance of the heat pump.

[0004] Methods for carrying out a defrosting cycle are already known, which introduce a defrosting process of the evaporator after the end of a predefined operating duration. In a heat pump with changing operating states, such a time-controlled defrosting cycle can additionally reduce the efficiency of the heat pump, since the duration is usually optimized for a specific operating state or is formed as a compromise between a plurality of operating states.

[0005] In order to determine the need for carrying out a defrosting process, in stationary refrigerators sensors are used which measure the icing degree of the evaporator. For mobile applications, for example in a heat pump on the vehicle side, no sensors for determining the icing degree are currently known. Furthermore, such sensors can increase the assembly effort of the heat pump and require evaluation electronics, whereby the costs of the heat pump increase. SUMMARY

[0006] The object of the present application is to provide a method for determining the icing degree of an evaporator without using additional sensors. This object is achieved by the features specified in the present application. Further advantageous embodiments of the present application are specified in the description.

[0007] According to an aspect of the present application, a method for operating a heat pump, in particular in a motor vehicle, is provided. The heat pump has an ambient heat exchanger and an interior space heat exchanger, which are connected to one another via a refrigerant circuit. The refrigerant can be conveyed through the refrigerant circuit by means of a compressor or a pump. The ambient heat exchanger and the interior space heat exchanger can implement the function of the heat pump via the refrigerant circuit, for example.

[0008] According to the present application, the icing degree is determined computationally as an operating parameter of the heat pump. A defrosting process of the ambient heat exchanger is introduced when a limit value of the determined icing degree is exceeded or reached.

[0009] The computation of the icing degree and the control of the defrosting process can be implemented by means of a controller, which can be connected to the heat pump in data transmission. Alternatively, the controller can be connected to at least one sensor in data transmission in order to receive operating parameters, for example the temperature of the ambient heat exchanger, the air temperature, the operating state of the heat pump, the rotational speed of the refrigerant compressor, etc.

[0010] The operating parameter "icing degree" can be defined by means of the method and applied in the operating state of the heat pump and in the regulation of the defrosting process. Here, the operating parameter characterizes the icing state of the ambient heat exchanger or the evaporator. The icing degree can be applied comprehensively in the operating state here.

[0011] In particular, the icing degree can be computed without the use of sensors. Preferably, the icing degree can be determined computationally from the operating time and from environmental conditions, for example the air temperature, the air humidity and weather data. In addition, further factors such as the flow rate of the refrigerant and the area of the ambient heat exchanger can be incorporated into the computation of the icing degree.

[0012] If the icing degree is determined in proportion to the mass of the frost layer on the ambient heat exchanger and / or to the pressure loss coefficient of the ambient heat exchanger and / or to the thermal insulation effect of the frost layer on the ambient heat exchanger, the icing degree can be determined particularly precisely. Thereby, further factors can be taken into account in the computation of the icing degree, which influence the thermodynamic interaction between the ambient heat exchanger and the ambient air of the frost or ice layer.

[0013] According to a further embodiment, the icing degree of the ambient heat exchanger is increased computationally from an initial value of the icing degree during the operation of the heat pump up to a limit value or beyond. During the operation of the heat pump, the icing of the ambient heat exchanger increases continuously depending on the operating state of the heat pump and the ambient conditions. In particular, the icing of the ambient heat exchanger and thus the icing degree increases with the progress of the operating time. By means of the computation of the icing degree, the real icing or frost layer can be computationally imitated or simulated. The initial value of the icing degree can for example have the value 0, since at the end of the defrosting process or at the start of the vehicle journey, there is no icing of the ambient heat exchanger.

[0014] If the icing degree is increased depending on at least one operating state of the operation of the heat pump and / or the operating time, the operating pattern of the heat pump and the required power can be depicted particularly precisely by means of the icing degree of the ambient heat exchanger. Here, the icing degree can be increased iteratively or continuously with the operating time. With an increasing thermal power of the heat pump at the interior space heat exchanger, the ambient heat exchanger is cooled more strongly, so that the ambient heat exchanger ices more quickly and the icing degree increases more quickly.

[0015] The operating state of the heat pump can be adjusted in particular depending on parameters such as the outside air temperature, the ambient air humidity and the heating power of the heat pump. During the journey of the vehicle, these parameters can change. The regulation or defrosting control of the heat pump must therefore be adapted to the changing parameters. Due to the change in the operating state of the heat pump, the rate or speed of the increase in the icing degree also changes.

[0016] According to a further embodiment, the icing degree of the ambient heat exchanger is reset to the initial value after the end of the defrosting process of the ambient heat exchanger and / or at the start of the vehicle journey. By this measure, the icing degree can be reliably determined from a constant initial value. The corresponding computation of the icing degree can for example be carried out via integration and can thus be technically particularly simple to implement.

[0017] If the icing degree of the ambient heat exchanger is at least temporarily stored and increased uninterruptedly in the operating state transformation of the heat pump from a first operating state of the heat pump to at least one second operating state, the icing degree can be technically simply transferred between the operating states by means of the operating state transformation of the heat pump as a reaction to changing ambient conditions or power requirements of the heat pump. Preferably, the value of the icing degree in the first operating state is not increased as quickly with respect to the operating time as the value of the icing degree in the second operating state. Thus, the icing degree can be used as an operating parameter and depict a reliable measure for the icing of the ambient heat exchanger even at the operating state transformation of the heat pump.

[0018] According to an embodiment, the icing degree of the ambient heat exchanger is computed as an integral with respect to the operating time.

[0019] Here, the integral over time of the increase in mass of the frost layer formed on the surface of the ambient heat exchanger is used to determine the icing degree in units of mass.

[0020] The increase in mass of the frost layer formed on the surface of the ambient heat exchanger here depends on different parameters, in particular environmental variables (Umweltgroesse), In particular, the area of the ambient heat exchanger, the water content in the air, the saturation content of the air (Saettigungsgehalt), the substance transfer coefficient (Stoffuebergangskoeffizient) and the maximum water storage capacity of the ambient heat exchanger can be used for the calculation of the increase in mass.

[0021] The determination of the icing degree by integral calculation (Integralrechnung) is thus robust and technically simple to implement. The icing can thus be determined on the basis of the operating conditions since the last defrosting and on the basis of the current icing degree. This corresponds to a relative calculation of the increase or decrease in the icing degree from the initial value or the previous value of the icing degree.

[0022] Alternatively or additionally, a situation-dependent or absolute calculation of the icing degree can also be calculated from the current operating state.

[0023] According to a further aspect of the application, a motor vehicle having a heat pump for carrying out the method according to the application is provided. The interior space heat exchanger of the heat pump can here be used to cool or heat the interior space of the motor vehicle. In the heating operation of the interior space, the ambient heat exchanger, which is coupled to the interior space heat exchanger via the refrigerant circuit, is cooled. Here, frost can build up over time on the surface of the ambient heat exchanger. Due to the frost layer on the surface of the ambient heat exchanger, the efficiency of the heat pump is reduced and the heating power of the interior space or passenger compartment is impaired.

[0024] The icing degree of the ambient heat exchanger can be estimated or simulated by the method and used to effectively carry out the defrosting process. Here, if the value of the icing degree reaches or exceeds a limit value, the defrosting process can be introduced.

[0025] The limit value of the icing degree can be designed constantly or variably depending on the operating state of the heat pump. BRIEF DESCRIPTION OF DRAWINGS

[0026] Embodiments of the application are explained in detail below with reference to the drawings, in which: Figure 1 A schematic view of a motor vehicle according to the application with a heat pump according to an embodiment is shown, and Figure 2a and Figure 2bA diagrammatic chart showing the pressure loss coefficient of the air side of an ambient heat exchanger and the determined icing degree for illustrating the method according to the application is shown.

[0027] In the figures, identical structural elements correspondingly have identical reference numerals. DETAILED DESCRIPTION

[0028] Figure 1 A diagrammatic side view of a motor vehicle 100 with a heat pump 10 for air treatment according to an embodiment is shown. The heat pump 10 is exemplarily designed as a roof air conditioning device in a flat construction type, which is fitted on a motor vehicle 100 designed as a bus. The heat pump 10 can be similarly applied on any motor vehicle (e.g. passenger car, truck, agricultural vehicle, etc.) 100.

[0029] The heat pump 10 has an ambient heat exchanger 20, which is supplied with a surrounding environment U or ambient air via an optional ventilator 30. Thereby, the ambient heat exchanger 20 can extract heat from the surrounding environment U in a heating operation of the heat pump 10. The ambient heat exchanger 20 can for example be designed as an evaporator in a heating operation of the heat pump 10.

[0030] Furthermore, the heat pump 10 has an interior space heat exchanger 40. The interior space heat exchanger 40 is arranged in a passenger compartment or vehicle interior space 101 for heating or cooling the passenger compartment 101.

[0031] The ambient heat exchanger 20 and the interior space heat exchanger 40 are fluidically connected to each other via a refrigerant circuit 50. By means of the refrigerant circuit 50, a refrigerant can be conveyed by means of a refrigerant pump 51 or a refrigerant compressor, so that heat can be extracted from the surrounding environment U and conveyed to the passenger compartment 101.

[0032] Due to the extraction of heat from the surrounding environment U, the ambient heat exchanger 20 can ice up and thus lose its efficiency. In order to perform a defrosting process, the ambient heat exchanger 20 can be deiced by means of a defrosting process in the shown embodiment. To this end, the heat pump 10 can be operated for example in the opposite direction to the heating operation, in order to briefly heat the ambient heat exchanger 20.

[0033] A controller 60 can be connected with the refrigerant pump 51 and set up to control the heat pump 10. In particular, the controller 60 can enable a demand of a heating or cooling power of the heat pump 10 in the form of an adaptation of an operating state of the heat pump 10. In adapting the operating state of the heat pump 10, for example the rotational speed of the refrigerant pump 51, the flow rate of the refrigerant, the actuation of valves, etc. can be changed.

[0034] In Figure 2a and Figure 2bIn the diagram shown in Fig. 1 an exemplary pressure loss coefficient ζ of the air side of the ambient heat exchanger 20 is shown, which changes over time or operating time t. In the diagram shown in Fig. 1 the determined icing degree V is shown, which likewise depends on the operating time t of the heat pump 10. Figure 2a In the diagram shown in Fig. 1 an exemplary pressure loss coefficient ζ of the air side of the ambient heat exchanger 20 is shown, which changes over time or operating time t. In the diagram shown in Fig. 1 the determined icing degree V is shown, which likewise depends on the operating time t of the heat pump 10. Figure 2b In the diagram shown in Fig. 1 an exemplary pressure loss coefficient ζ of the air side of the ambient heat exchanger 20 is shown, which changes over time or operating time t. In the diagram shown in Fig. 1 the determined icing degree V is shown, which likewise depends on the operating time t of the heat pump 10.

[0035] The pressure loss coefficient ζ of the air side of the ambient heat exchanger 20 is a dimensionless measure for the pressure loss at the ambient heat exchanger 20 and serves to illustrate the consequences of icing. As icing increases, the ambient heat exchanger 20 can extract less heat from the surroundings U and thus reduce the efficiency of the heat pump 10. In order to remove the icing of the ambient heat exchanger 20, a defrosting process A is introduced. By means of the defrosting process A the icing of the ambient heat exchanger 20 can be removed, so that the pressure loss coefficient ζ of the air side rises again.

[0036] In the diagram shown in Fig. 1 an exemplary pressure loss coefficient ζ of the air side of the ambient heat exchanger 20 is shown, which changes over time or operating time t. In the diagram shown in Fig. 1 the determined icing degree V is shown, which likewise depends on the operating time t of the heat pump 10. Figure 2a In the diagram shown in Fig. 1 an exemplary pressure loss coefficient ζ of the air side of the ambient heat exchanger 20 is shown, which changes over time or operating time t. In the diagram shown in Fig. 1 the determined icing degree V is shown, which likewise depends on the operating time t of the heat pump 10.

[0037] In the second operating state 80 the heat pump 10 is operated with less power, so that the icing of the ambient heat exchanger 20 proceeds more slowly.

[0038] In the diagram shown in Fig. 1 an exemplary pressure loss coefficient ζ of the air side of the ambient heat exchanger 20 is shown, which changes over time or operating time t. In the diagram shown in Fig. 1 the determined icing degree V is shown, which likewise depends on the operating time t of the heat pump 10. Figure 2b In the diagram shown in Fig. 1 an exemplary pressure loss coefficient ζ of the air side of the ambient heat exchanger 20 is shown, which changes over time or operating time t. In the diagram shown in Fig. 1 the determined icing degree V is shown, which likewise depends on the operating time t of the heat pump 10.

[0039] By means of the change of the operating states 70, 80 of the heat pump 10 as a reaction to changing environmental conditions or power requirements of the heat pump 10, the icing degree V can be shifted between the operating modes 70, 80. For this purpose, the controller 60 can at least temporarily store the icing degree V of the ambient heat exchanger 20 and calculate without interruption in the operating state change 90 of the heat pump 10 from the first operating state 70 to the second operating state 80 of the heat pump 10. Here, the value of the icing degree V in the first operating state 70 rises less quickly with respect to the value of the icing degree V in the second operating state 80 with regard to the operating time t. By means of the slower rise of the icing degree V in the second operating state 80 the defrosting process A is activated at a later operating time point, since the limit value G of the icing degree V is reached more slowly.

[0040] The icing degree V of the ambient heat exchanger 20 is calculated as an integral with respect to the operating time t.

[0041] Here, the integral over time of the mass increase due to the formation of a frost layer on the surface of the ambient heat exchanger 20 is used to determine the icing degree V in units of mass.

[0042] The mass increase due to the formation of a frost layer on the surface of the ambient heat exchanger 20 is calculated according to the following formula: where F is the surface area of the ambient heat exchanger 20, X is the water content of the air at the ambient temperature T, X' is the saturation water content of the air, β is the mass transfer coefficient, r0 is the maximum water storage capacity of the ambient heat exchanger 20 and is the air density.

[0043] The icing degree V of the ambient heat exchanger 20 thus depends on the ambient conditions that favor the formation of a frost layer on the ambient heat exchanger 20.

[0044] After the defrosting process A of the ambient heat exchanger 20 is completed and / or at the start of the journey of the motor vehicle 100, the icing degree V is reset to the initial value V0 of the icing degree V.

[0045] List of reference signs 100 motor vehicle 101 passenger compartment 10 heat pump 20 ambient heat exchanger 30 ventilator 40 interior space heat exchanger 50 refrigerant circuit 51 refrigerant pump / refrigerant compressor 60 controller 70 first operating state 80 second operating state 90 operating state change ζ pressure loss coefficient on the air side air density A defrosting process β mass transfer coefficient F surface area of the ambient heat exchanger G limit value of the icing degree r0 maximum water storage capacity of the ambient heat exchanger t operating time T ambient temperature U ambient environment V icing degree V0 initial value of the icing degree X water content of the air X' saturated water content of the air.

Claims

1. A method for operating a heat pump (10) in a motor vehicle (100) having an ambient heat exchanger (20) and an interior heat exchanger (40) connected to one another via a refrigerant circuit (50), characterized in that A degree of freezing (V) is determined computationally as an operating parameter of the heat pump (10), wherein a defrosting process (A) of the ambient heat exchanger (20) is initiated when a limit value (G) of the determined degree of freezing (V) is exceeded or reached, wherein the degree of freezing (V) of the ambient heat exchanger (20) is computationally increased from an initial value (V0) of the degree of freezing (V) until the limit value (G) is exceeded or reached during operation of the heat pump (10) and is calculated relative to a pressure loss coefficient (ζ) of the ambient heat exchanger (20). ), wherein the freezing degree (V) of the ambient heat exchanger (20) is at least temporarily stored and continuously increased during an operating state change (90) of the heat pump (10) from a first operating state (70) to at least one second operating state (80), wherein the value of the freezing degree (V) in the first operating state (70) increases not as quickly as the value of the freezing degree (V) in the second operating state (80) with respect to the operating time (t).

2. The method according to claim 1, wherein The degree of icing (V) is determined in proportion to the mass of the frost layer on the ambient heat exchanger (20) and / or the thermal insulation effect of the frost layer on the ambient heat exchanger (20).

3. The method according to claim 1, wherein The icing degree (V) of the ambient heat exchanger (20) is increased as a function of at least one operating state (70, 80) and / or an operating time (t) of the operation of the heat pump (10).

4. The method according to claim 1, wherein The degree of freezing (V) of the ambient heat exchanger (20) is reset to an initial value (V0) after a defrosting process (A) of the ambient heat exchanger (20) is completed and / or when the method is used for operating a heat pump (10) in a motor vehicle (100) at the start of driving the motor vehicle (100).

5. The method according to any one of claims 1 to 4, wherein The degree of icing (V) of the ambient heat exchanger (20) is calculated as the integral over the operating time (t): in, in, F is the surface area of ​​the ambient heat exchanger, X is the water content of air at ambient temperature T, X' is the saturation content of air, β is the mass transfer coefficient, r0 is the maximum water storage capacity of the ambient heat exchanger.

6. A motor vehicle (100) having a heat pump (10) for carrying out the method according to any one of claims 1 to 5.

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