DE102020104742A1 - Control of a heat pump in variable operating conditions - Google Patents

Abstract

In order to create a method for operating a heat pump (10), in particular in a motor vehicle (100), with an ambient heat exchanger (20) and an interior heat exchanger (40), which are connected to one another via a refrigerant circuit (50), which has a degree of icing of the Ambient heat exchanger (20) can determine without the use of additional sensors, it is proposed to determine a degree of icing (V) as the operating parameter of the heat pump (10) by calculation, with a defrosting process when a limit value (G) of the determined degree of icing (V) is exceeded or reached (A) of the ambient heat exchanger (20) is initiated.

Description

The invention 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. The invention also relates to a motor vehicle with a heat pump.

In electrically powered vehicles, heat pumps are often used to heat the passenger compartment. Here, the heat required to heat the passenger compartment is extracted from the vehicle environment and fed to the passenger compartment. In this process, a heat exchanger 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 is formed on the surface of the heat exchanger.

Due to the formation of frost, the surface of the heat exchanger is increasingly icing up 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 up. As a result, the ice melts and air can flow through the heat exchanger again. However, such defrosting cycles impair the efficiency and performance of the heat pump.

Methods for performing defrosting cycles are already known, which initiate the defrosting process of an evaporator after a predefined operating time has elapsed. In the case of heat pumps with changing operating states, such time-controlled defrosting cycles can additionally reduce the efficiency of the heat pump, since the duration is usually optimized for a specific operating state or forms a compromise between several operating states.

In stationary refrigeration machines, sensors that can measure the degree of icing of evaporators are used to determine the need to carry out a defrosting process. For mobile applications, such as in the case of vehicle-mounted heat pumps, no sensors for determining the degree of icing are known to date. Furthermore, such sensors can increase the installation effort of the heat pump and require evaluation electronics, which increases the costs of the heat pump.

The invention is based on the object of creating a method for determining the degree of icing in evaporators without the use of additional sensors. This object is achieved by the features specified in claim 1. Further advantageous refinements of the invention are described in the subclaims.

According to one aspect of the invention, 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 heat exchanger, which are connected to one another via a refrigerant circuit. A refrigerant can be conveyed through the refrigerant circuit by means of a compressor or a pump. For example, the ambient heat exchanger and the interior heat exchanger can perform a function of a heat pump via the refrigerant circuit.

According to the invention, a degree of icing is determined by calculation as an operating parameter of the heat pump. If a limit value of the determined degree of icing is exceeded or reached, a defrosting process of the ambient heat exchanger is initiated.

The calculation of the degree of icing and the control of defrosting processes can be implemented by a control device which can be connected to the heat pump for data transmission. Optionally, the control device can be connected to at least one sensor for data transmission in order to receive, for example, operating parameters such as temperature of the ambient heat exchanger, air temperature, operating state of the heat pump, speed of the refrigerant compressor and the like.

The process can be used to define the operating parameter “degree of icing” and to use it to regulate operating states and defrosting processes of the heat pump. This operating parameter characterizes the icing condition of the ambient heat exchanger or an evaporator. The degree of icing can be used across all operating states.

In particular, the degree of icing can be calculated without the use of sensors. The degree of icing can preferably be determined mathematically as a function of an operating time and as a function of the environmental conditions, such as, for example, air temperature, air humidity and weather data. In addition, other factors, such as the flow rate of the refrigerant and the area of the ambient heat exchanger, can be included in the calculation of the degree of icing.

The degree of icing can be determined particularly precisely if it is proportional to a mass of a layer of frost on the ambient heat exchanger and / or to a Pressure loss coefficient of the ambient heat exchanger and / or a thermal insulation effect of the layer of frost on the ambient heat exchanger is determined. In this way, further factors which influence the thermodynamic interaction between the ambient heat exchanger of a layer of frost or ice and the ambient air can be taken into account when calculating the degree of icing.

According to a further exemplary embodiment, the degree of icing of the ambient heat exchanger is mathematically increased starting from an initial value of the degree of icing up to the limit value being exceeded or reached during the operation of the heat pump. During the operation of the heat pump, the icing of the ambient heat exchanger increases steadily depending on the operating state of the heat pump and the environmental conditions. In particular, the icing and thus the degree of icing of the ambient heat exchanger increase with the advancing operating time. By calculating the degree of icing, the real icing or layer of frost can be computationally reproduced or simulated. The initial value of the degree of icing can have a value of 0, for example, since there is no icing of the ambient heat exchanger after a completed defrosting process or when the motor vehicle starts to drive.

The operating mode and the required output of the heat pump can be mapped particularly precisely by the degree of icing of the ambient heat exchanger if it is increased as a function of at least one operating state and / or an operating time of the operation of the heat pump. The degree of icing can be increased iteratively or continuously with the operating time. As the heat output of the heat pump at the interior heat exchanger increases, the ambient heat exchanger is cooled more so that the ambient heat exchanger freezes more quickly and the degree of freezing increases more quickly.

The operating states of the heat pump can in particular be set as a function of parameters such as the outside air temperature, ambient air humidity and the heating output of the heat pump. These parameters can change while the motor vehicle is in motion. As a result, the regulation or defrost control of the heat pump must be adapted to the changed parameters. The change in the operating state of the heat pump also changes the rate or speed at which the degree of icing increases.

According to a further embodiment, the degree of icing of the ambient heat exchanger is reset to the initial value after a completed defrosting process of the ambient heat exchanger and / or when the motor vehicle starts to drive. This measure enables the degree of icing to be reliably determined from a constant initial value. A corresponding calculation of the degree of icing can take place, for example, via an integral and can thus be implemented in a particularly simple manner from a technical point of view.

By changing the operating states of the heat pump as a reaction to changing environmental conditions or performance requirements of the heat pump, the degree of icing can easily be transferred between the operating states if the degree of icing of the ambient heat exchanger is at least temporarily stored and when the operating state of the heat pump changes from a first operating state to at least a second operating state the heat pump is continuously increased. A value of the degree of icing in the first operating state preferably increases at different rates over the operating time compared to a value of the degree of icing in the second operating state. As a result, the degree of icing can be used as an operating parameter even when the operating states of the heat pump change and can represent a reliable measure for the icing of the ambient heat exchanger.

According to one embodiment, the degree of icing of the ambient heat exchanger is calculated using an integral over the operating time. $$V=r_0+{\displaystyle {\int }_0^t{m}_{de}{}_{sub}^{.}}dt$$

In this case, a time integral of an increase in mass due to the formation of the frost layer on a surface of the ambient heat exchanger for determining the degree of icing is formed with the unit of a mass.

The increase in mass due to the formation of the frost layer on the surface of the ambient heat exchanger depends on various parameters, in particular environmental variables. $$m_{de}{}_{sub}^{.}=\beta \cdot \mathrm{F.}\cdot {\rho }_{{}_{\mathrm{L.}uft}}\cdot \left(X_{\mathrm{L.}uft}\left(T\right)-X{\text{'}}_{\mathrm{L.}uft}\left(T\right)\right)$$

In particular, an area of the ambient heat exchanger, a water content in the air, a saturation content of the air, a mass transfer coefficient and a maximum water storage capacity of the ambient heat exchanger can be used to calculate the mass increase.

Such a computational determination of the degree of icing by integral calculation is robust and technically easy to implement. This allows the icing to be determined based on the operating conditions since the last defrost and based on the current degree of icing. This corresponds to a relative calculation of an increase or decrease in the degree of icing on the basis of the initial value or a previous value of the degree of icing.

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

According to a further aspect of the invention, a motor vehicle is provided which has a heat pump for carrying out a method according to the invention. An interior heat exchanger of the heat pump can serve to cool or heat the interior of the motor vehicle. When the interior is heated, an ambient heat exchanger coupled to the interior heat exchanger via a refrigerant circuit is cooled. Over time, frost can form on the surface of the ambient heat exchanger. Due to the layer of frost on the surface of the ambient heat exchanger, the efficiency of the heat pump is reduced and the heating output of the interior or passenger compartment is impaired.

The method allows the degree of icing of the ambient heat exchanger to be estimated or simulated and used for efficient implementation of defrosting processes. A defrosting process can be initiated if the value of the degree of icing reaches or exceeds a limit value.

Depending on the operating state of the heat pump, the limit value for the degree of icing can be configured to be constant or variable.

• 1 eine schematische Darstellung eines erfindungsgemäßen Kraftfahrzeugs mit einer Wärmepumpe gemäß einer Ausführungsform, und
• 2a und 2b schematische Diagramme eines luftseitigen Druckverlustbeiwerts eines Umgebungswärmeübertragers und eines ermittelten Vereisungsgrads zum Veranschaulichen eines erfindungsgemäßen Verfahrens.

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
• 2a and 2 B schematic diagrams of an air-side pressure loss coefficient of an ambient heat exchanger and a determined degree of icing to illustrate a method according to the invention.

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

the 1 shows a schematic side view of a motor vehicle 100 with a heat pump 10 for air treatment according to one embodiment. The heat pump 10 is designed, for example, as a roof air conditioning system in flat construction, which is mounted on a motor vehicle designed as a bus 100 is mounted. The heat pump 10 can be used analogously in any motor vehicle 100 such as passenger cars, trucks, agricultural vehicles and the like can be used.

The heat pump 10 has an ambient heat exchanger 20th on, which has an optional fan 30th with an environment U or ambient air is supplied. This allows the ambient heat exchanger 20th when the heat pump is in heating mode 10 Warmth of the environment U revoke. The ambient heat exchanger 20th can, for example, be used as an evaporator in the heating mode of the heat pump 10 be designed.

Furthermore, the heat pump 10 an indoor heat exchanger 40 on. The indoor heat exchanger 40 is in a passenger compartment or vehicle interior 101 arranged to the passenger compartment 101 to heat or cool.

The ambient heat exchanger 20th and the indoor heat exchanger 40 are via a refrigerant circuit 50 fluidly connected to each other. Through the refrigerant circuit 50 can a refrigerant by means of a refrigerant pump 51 or a refrigerant compressor to remove heat from the environment U and supplying heat to the passenger compartment 101 to enable.

By removing heat from the environment U can the ambient heat exchanger 20th freeze and thus lose its efficiency. To carry out a defrosting process, the ambient heat exchanger can be used in the illustrated embodiment 20th be defrosted by a defrosting process. For example, the heat pump 10 be operated in a direction opposite to the heating mode to the ambient heat exchanger 20th to be heated briefly.

A control unit 60 can with the refrigerant pump 51 be connected and set up to the heat pump 10 to control. In particular, the control unit 60 Requirements for a heating capacity or cooling capacity of the heat pump 10 in the form of an adaptation of an operating state of the heat pump 10 realize. When adapting the operating status of the heat pump 10 can for example be a speed of the refrigerant pump 51 , a flow rate of the refrigerant, a control of valves and the like can be changed.

In the 2a and 2 B schematic diagrams are shown to illustrate a method according to the invention. the 2a shows an exemplary air-side pressure loss coefficient ζ of the ambient heat exchanger 20th which changes over time or operating time t changes. In the 2 B is a determined degree of icing V shown which also depends on the operating time t the heat pump 10 depends.

The air-side pressure loss coefficient ζ of the ambient heat exchanger 20th is a dimensionless measure for the pressure loss at the ambient heat exchanger 20th and serves to illustrate the consequences of icing. As the ice builds up, the ambient heat exchanger 20th less heat from the environment U withdraw and thus reduce the efficiency of the heat pump 10 . About the icing of the ambient heat exchanger 20th to eliminate defrosts A. initiated. Through a defrosting process A. the surrounding heat exchanger can be iced up 20th can be eliminated so that the air-side pressure loss coefficient ζ increases again.

In the 2a is the course of the air-side pressure loss coefficient ζ with defrosting processes carried out A. in two different operating states or operating modes 70 , 80 shown. This is where the heat pump 10 in a first operating state 70 through the control unit 60 operated and at a change of operating state 90 through the control unit 60 in a second operating state 80 switched.

In the second operating state 80 becomes the heat pump 10 operated with a lower output, so that the ambient heat exchanger freezes 20th runs slower.

In the 2 B is the one in operation of the heat pump 10 , for example by the control unit 60 , calculated degree of icing V illustrated. The degree of icing V is used as the operating parameter of the heat pump 10 calculated. When a limit value is exceeded or reached G the determined degree of icing V becomes a defrosting process A. of the ambient heat exchanger 20th initiated. This can also be done by the control unit 60 technically implemented.

By changing the operating status 70 , 80 the heat pump 10 as reactions to changing environmental conditions or performance requirements of the heat pump 10 can be the degree of icing V between the operating states 70 , 80 be handed over. The control unit can do this 60 the degree of icing V of the ambient heat exchanger 20th save at least temporarily and when there is a change in operating mode 90 the heat pump 10 from the first operating state 70 in the second operating state 80 the heat pump 10 continuously calculated. A value of the degree of icing increases V in the first operating state 70 versus a value of the degree of icing V in the second operating state 80 over the operating time t at different speeds. Due to a slower increase in the degree of icing V in the second operating state 80 the defrosting process A. activated at a later time because the limit value G the degree of icing V is reached more slowly.

The degree of icing V of the ambient heat exchanger 20th is based on an integral over the operating time t calculated. $$V=r_0+{\displaystyle {\int }_0^t{m}_{de}{}_{sub}^{.}}dt$$

durch die Bildung der Reifschicht auf einer Oberfläche des Umgebungswärmeübertragers 20 zum Ermitteln des Vereisungsgrads V mit der Einheit einer Masse gebildet.Thereby a time integral of a mass increase becomes $m_{de}{}_{sub}^{.}$

by the formation of the frost layer on a surface of the ambient heat exchanger 20th to determine the degree of icing V formed with the unity of a mass.

durch die Bildung der Reifschicht auf der Oberfläche des Umgebungswärmeübertragers 20 wird gemäß der folgenden Formel berechnet $$m_{de}{}_{sub}^{.}=\beta \cdot F\cdot {\rho }_{{}_{Luft}}\cdot \left(X_{Luft}\left(T\right)-X{\text{'}}_{Luft}\left(T\right)\right)$$

mit F einer Oberfläche des Umgebungswärmeübertragers 20, X einem Wassergehalt der Luft bei einer Umgebungstemperatur T, X' einem Sättigungsgehalt der Luft, β einem Stoffübergangskoeffizient, r0 einer maximalen Wasserspeicherfähigkeit des Umgebungswärmeübertragers 20 und ρ_Luft der Luftdichte.The increase in mass $m_{de}{}_{sub}^{.}$

by the formation of the frost layer on the surface of the ambient heat exchanger 20th is calculated according to the following formula $$m_{de}{}_{sub}^{.}=\beta \cdot \mathrm{F.}\cdot {\rho }_{{}_{\mathrm{L.}uft}}\cdot \left(X_{\mathrm{L.}uft}\left(T\right)-X{\text{'}}_{\mathrm{L.}uft}\left(T\right)\right)$$

with F a surface of the ambient heat exchanger 20th , X a water content of the air at an ambient temperature T , X ' a saturation level of the air, β a mass transfer coefficient, r0 a maximum water storage capacity of the ambient heat exchanger 20th and ρ _air the air density.

The degree of icing of the ambient heat exchanger 20th is therefore dependent on the ambient conditions, which cause the formation of a layer of frost on the ambient heat exchanger 20th favor.

After a completed defrosting process A. of the ambient heat exchanger 20th and / or when the motor vehicle starts to travel 100 becomes the degree of icing V to an initial value Vo of the degree of icing V reset.

List of reference symbols

100

Motor vehicle

101

Passenger compartment

10

Heat pump

20th

Ambient heat exchanger

30th

fan

40

Indoor heat exchanger

50

Refrigerant circuit

51

Refrigerant pump / refrigerant compressor

60

Control unit

70

first operating status

80

second operating state

90

Change of operating status

ζ

air-side pressure loss coefficient

ρair

Airtightness

A.

Defrosting

β

Mass transfer coefficient

F.

Surface of the ambient heat exchanger

G

Limit value of the degree of icing

r0

maximum water storage capacity of the ambient heat exchanger

t

Operating time

T

Ambient temperature

U

Surroundings

V

Degree of icing

V0

Initial value of the degree of icing

X

Water content of the air

X '

Saturation content of the air

Claims (8)

Method for operating a heat pump (10), in particular in a motor vehicle (100), with an ambient heat exchanger (20) and an interior heat exchanger (40), which are connected to one another via a refrigerant circuit (50), characterized in that a degree of icing (V) is calculated as the operating parameter of the heat pump (10), with a defrosting process (A) of the ambient heat exchanger (20) being initiated when a limit value (G) of the determined degree of icing (V) is exceeded or reached. Procedure according to Claim 1 , the degree of icing (V) being determined proportionally to a mass of a layer of frost on the ambient heat exchanger (20) and / or to a pressure loss coefficient (ζ) of the ambient heat exchanger (20) and / or to a thermal insulation effect of the layer of frost on the ambient heat exchanger (20) . Procedure according to Claim 1 or 2 , the degree of icing (V) of the ambient heat exchanger (20) being mathematically increased starting from an initial value (Vo) of the degree of icing (V) until the limit value (G) is exceeded or reached during operation of the heat pump (10). Procedure according to Claim 3 , the degree of icing (V) of the ambient heat exchanger (20) being 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). Procedure according to Claim 3 or 4th , the degree of icing (V) of the ambient heat exchanger (20) being reset to an initial value (Vo) after a completed defrosting process (A) of the ambient heat exchanger (20) and / or when the motor vehicle (100) starts to drive. Method according to one of the Claims 1 until 5 , the degree of icing (V) of the ambient heat exchanger (20) being stored at least temporarily and continuously increased in the event of an operating state change (90) of the heat pump (10) from a first operating state (70) to at least a second operating state (80) of the heat pump (10) , wherein a value of the degree of icing (V) in the first operating state (70) increases at different rates over the operating time (t) compared to a value of the degree of icing (V) in the second operating state (80). Method according to one of the Claims 1 until 6th , where the degree of icing (V) of the ambient heat exchanger (20) is calculated using an integral over the operating time (t): $$V=r_0+{\displaystyle {\int }_0^t{m}_{de}{}_{sub}^{.}}dt$$

with $$m_{de}{}_{sub}^{.}=\beta \cdot \mathrm{F.}\cdot {\rho }_{{}_{\mathrm{L.}uft}}\cdot \left(X_{\mathrm{L.}uft}\left(T\right)-X{\text{'}}_{\mathrm{L.}uft}\left(T\right)\right)$$

and with F, a surface of the ambient heat exchanger X, a water content of the air at an ambient temperature T X ', a saturation content of the air β, a mass transfer coefficient r0, a maximum water storage capacity of the ambient heat exchanger Motor vehicle (100) which has a heat pump (10) for carrying out a method according to one of the preceding claims.

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