DE102019131879A1 - Procedure for defrosting an ambient heat exchanger - Google Patents

Abstract

A method is disclosed for carrying out a defrosting process of an air conditioning device (100), in particular a vehicle-side air conditioning device which has a refrigerant circuit (21), a refrigerant being used by a compressor (12) in the refrigerant circuit (21) to heat an ambient heat exchanger (25) against a Working direction (A) of the refrigerant is promoted, the temperature of the refrigerant being set before flowing into the ambient heat exchanger (25). An air conditioning device (100) is also disclosed.

Description

The invention relates to a method for performing a defrosting process of an air conditioning device, in particular a vehicle-side air conditioning device which has a refrigerant circuit. The invention also relates to an air conditioning device.

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. To reduce the time required for a defrosting process, the melt water must drain off the heat exchanger as quickly as possible.

During the defrosting process, the vehicle can only be heated to a limited extent by the heat pump. Instead, the vehicle cabin can be heated by an electrical auxiliary heater. Compared to the heat pump, however, the electrical auxiliary heater is inefficient. In addition to the use of an additional heater, the heat pump can be operated against a working direction or by reversing the process. The process reversal enables the heat exchanger to be defrosted quickly by reaching high temperatures of the refrigerant when it enters the heat exchanger. During this process, however, the melt water can evaporate, which is energy-intensive.

The invention is based on the object of creating a method for the controlled defrosting of a heat exchanger and for avoiding evaporation of melt water during the defrosting process. 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 performing a defrosting process of an air conditioning device is provided. The air-conditioning device can be, for example, a vehicle-mounted or a stationary air-conditioning device which has a refrigerant circuit and at least one coolant circuit thermally coupled to the refrigerant circuit.

A refrigerant is conveyed by a compressor in the refrigerant circuit for heating an ambient heat exchanger against a working direction of the refrigerant, the temperature of the refrigerant being set before it flows into the ambient heat exchanger.

The ambient heat exchanger is operated as an evaporator in the working direction of the refrigerant and thus cools or extracts heat from the ambient air. An interior heat exchanger is arranged in the refrigerant circuit and is flowed through in the working direction of the refrigerant as a condenser in order to give off heat to an air flow which heats an interior. Analogously to this, the air conditioning device can be operated against the working direction in order to cool the air flow into the interior.

The interior space can be, for example, a vehicle interior, a cargo hold, a building, a server room and the like.

According to a further aspect of the invention, an air conditioning device is provided for air conditioning an interior space by means of an interior heat exchanger, the air conditioning device being set up to carry out the method according to the invention. The air conditioning device can preferably have an interior heat exchanger and an ambient heat exchanger, which are connected to one another by a refrigerant circuit. A compressor is used to convey the refrigerant in the working direction or against the working direction. Furthermore, the refrigerant circuit can be thermally coupled to other coolant circuits by means of heat exchangers. The air conditioning device can perform an operation or a defrosting operation. In one work process, the interior heat exchanger and the ambient heat exchanger are coupled to one another in a fluid-conducting manner by the refrigerant. The refrigerant is conveyed by a compressor in the refrigerant circuit, creating a bidirectional heat pump.

During the defrosting process, the interior heat exchanger can be bridged in order to prevent the interior from cooling down unintentionally, or it can be used as a heat source. The ambient heat exchanger is heated during the defrosting process in order to melt any icing.

Experimental investigations on vehicle heat pumps have shown that excessively high inlet temperatures of the refrigerant in the icy ambient heat exchanger lead to partial evaporation of the melt water and convective heat dissipation to the environment. Evaporation of the melt water should be avoided, however, since the evaporation process requires a high expenditure of energy and thereby lowers the overall efficiency of the air conditioning device. The defrosting process should preferably melt the ice rather than evaporate it.

The ability to set the temperature of the refrigerant before it enters the ambient heat exchanger means that a controlled defrosting process of the ambient heat exchanger can take place, which avoids evaporation of melt water during the defrosting process. The defrosting process is preferably carried out by reversing the process of the refrigerant conveyed, in which the ambient heat exchanger functions as an evaporator. The layer of frost or the layer of ice on the ambient heat exchanger serves as a heat sink during the defrosting process. The set temperature of the refrigerant can preferably depend on ambient conditions, such as, for example, air temperature, air pressure, relative humidity and the like.

In one embodiment, the temperature of the refrigerant is set before it flows into the ambient heat exchanger by regulating a speed of the compressor and / or by regulating an opening of at least one expansion valve. The at least one expansion valve is preferably integrated into the refrigerant circuit and can therefore act on the refrigerant. By controlling a speed of the compressor or compressor, the pressure or the flow rate of the refrigerant through the evaporator and the condenser and thus the temperature of the refrigerant can be varied.

For example, when the speed of the compressor is reduced, a lower temperature of the refrigerant and thus of the ambient heat exchanger can be set during the defrosting process.

The temperature of the refrigerant can also be influenced by varying the opening of the expansion valve. By reducing the opening of the expansion valve, a higher pressure of the refrigerant and thus a higher temperature can be achieved. Enlarging the valve opening thus leads to a decrease in temperature of the refrigerant.

According to a further exemplary embodiment, the temperature of the refrigerant is set before it flows into the ambient heat exchanger by a hot gas desuperheater or an air-side condenser inserted into the refrigerant circuit in a fluid-conducting manner. The hot gas desuperheater is preferably designed as a first heat exchanger, which thermally couples a heating heat exchanger for heating an interior space to the refrigerant circuit via a first coolant circuit. The first heat exchanger or the air-side condenser is set up to heat or cool an air flow into an interior space generated by an interior fan. The first heat exchanger can be designed, for example, as a water-refrigerant heat exchanger and can be arranged upstream of the ambient heat exchanger in the flow direction of the refrigerant during the defrosting process. By using the first heat exchanger, the heat can be taken from the refrigerant at a high temperature level and used to heat the interior during the defrosting process. The heating heat exchanger can preferably be arranged in series or parallel to the interior heat exchanger.

The heat removed from the refrigerant by the first heat exchanger can be set particularly precisely if the coolant of the first coolant circuit is conveyed by a first pump, the mass flow of the first pump and / or an air flow generated by the interior fan being regulated to set the temperature of the refrigerant become. The amount of heat dissipated from the refrigerant can be controlled by cleverly regulating a coolant volume by the hot gas desuperheater. An air mass flow, which cools the heating heat exchanger, can also influence the heat transfer of the first heat exchanger or the hot gas desuperheater. In particular, an increase in the coolant flow and / or the air volume flow can result in greater cooling of the refrigerant.

The air-side condenser can be designed as a refrigerant-air heat exchanger, which can give off the heat of the refrigerant directly to ambient air and preferably to an air flow directed into the interior. As a result of this measure, the use of the first coolant circuit can be dispensed with.

For example, water or an aqueous solution can be used as the coolant.

According to a further embodiment, an internal heat exchanger is arranged in the refrigerant circuit in the working direction upstream of the hot gas de-heater, the refrigerant after passing through the hot gas de-heater and before flowing into the ambient heat exchanger is passed through the internal heat exchanger. By using the internal heat exchanger, a further heat sink can be created for the refrigerant in order to prevent overheating of the ambient heat exchanger and evaporation of melt water during the defrosting process. The internal heat exchanger forms a loop in the refrigerant circuit, through which the refrigerant is thermally coupled to the refrigerant upstream of the first heat exchanger and thus precooled after it has passed the hot gas de-heater or the first heat exchanger.

In an alternative embodiment, the internal heat exchanger can be used in connection with the air-side condenser.

The effect of the internal heat exchanger on the refrigerant can be controlled particularly precisely if an inflow of the refrigerant to the internal heat exchanger is opened or closed by at least one valve and / or a bypass line. This measure can in particular enable the internal heat exchanger to be switched on as required, for example by means of a shut-off valve, a three-way valve and the like. In this case, the refrigerant can be routed completely or partially via the internal heat exchanger if a lowering of the temperature of the refrigerant is required before it enters the ambient heat exchanger.

The mentioned options for setting the temperature of the refrigerant during the defrosting process can be implemented individually or in combination with one another.

According to a further exemplary embodiment, the refrigerant for performing the defrosting process is conveyed through the ambient heat exchanger against the working direction, an interior heat exchanger being bridged during the defrosting process and the refrigerant being conveyed via a second heat exchanger to remove heat from a second coolant circuit. This measure makes it possible to avoid unintentional cooling of the interior heat exchanger and thus the air flow directed into the interior. Depending on the heat capacity of the interior heat exchanger, it can continue to warm the air flow at least temporarily. A series connection of the heating heat exchanger or the air-side condenser can compensate for a decrease in heat output by the interior heat exchanger during the defrosting process of the ambient heat exchanger. The second coolant circuit can provide waste heat from drive components or power electronics, for example.

In an alternative embodiment, the interior heat exchanger can serve as a heat source, so that the second coolant circuit or a thermal coupling of the coolant circuit with the second coolant circuit can be dispensed with. Furthermore, operation without the use of a heat source, for example as a triangular process, is possible.

The efficiency of the air conditioning device during the defrosting process can be increased if an absolute temperature of the refrigerant before flowing into the ambient heat exchanger is limited to 40 ° C, 60 ° C or 100 ° C against the working direction. By limiting the temperature of the refrigerant, evaporation of the melt water during the defrosting process can be prevented by technically simple means. A corresponding temperature limit can preferably be set depending on the ambient conditions.

The efficiency of the air conditioning device can be further increased if a temperature difference between the refrigerant before it flows into the ambient heat exchanger and an ambient temperature is set by regulating the temperature of the refrigerant, the temperature difference being set to 5 K, 10 K or 20 K. By controlling the temperature of the refrigerant as a function of the ambient temperature, unnecessary heating of the refrigerant can be avoided and the heat loss can be minimized.

The setting of the opening of the expansion valve, the speed of the compressor, the speed of the first pump and / or the control of the bridging or connection of the internal heat exchanger can be done by control commands from a central control unit, which determines the ambient conditions and appropriate control commands for setting the temperature of the Generated refrigerant.

• 1 einen Schaltplan einer Klimatisierungsvorrichtung im Betrieb gemäß einer Ausführungsform,
• 2 ein Druck-Enthalpie-Diagramm zum Illustrieren eines Abtauvorgangs mit der in 1 gezeigten Kl imatisieru ngsvorrichtu ng,
• 3 einen Schaltplan der Klimatisierungsvorrichtung während eines Abtauvorgangs zum Veranschaulichen eines Verfahrens gemäß einer ersten Ausführungsform,
• 4 einen Schaltplan der Klimatisierungsvorrichtung während eines Abtauvorgangs zum Veranschaulichen eines Verfahrens gemäß einer zweiten Ausführungsform, und
• 5 einen Schaltplan der Klimatisierungsvorrichtung während eines Abtauvorgangs zum Veranschaulichen eines Verfahrens gemäß einer dritten Ausführungsform.

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

• 1 a circuit diagram of an air conditioning device in operation according to an embodiment,
• 2 a pressure-enthalpy diagram to illustrate a defrosting process with the in 1 air conditioning device shown,
• 3rd a circuit diagram of the air conditioning device during a defrosting process for Illustrating a method according to a first embodiment,
• 4th a circuit diagram of the air conditioning device during a defrosting process to illustrate a method according to a second embodiment, and
• 5 a circuit diagram of the air conditioning device during a defrosting process to illustrate a method according to a third embodiment.

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

The 1 Fig. 13 shows a circuit diagram of an air conditioning device 100 in operation according to one embodiment. The air conditioning device 100 is operated in the illustrated embodiment in heating mode, in which an interior 10 by a stream of air L. is warmed.

The air flow is through an indoor fan 11 generated. The airflow L. penetrates an interior heat exchanger 20th and an optional heat exchanger 30th and absorbs heat, which in the interior 10 is transported.

The indoor heat exchanger 20th is fluid-conducting with a refrigerant circuit 21 connected, which via two expansion valves 22nd , 23 and via an ambient heat exchanger 25th leads. One in the refrigerant circuit 21 introduced hot gas desuperheater or first heat exchanger 31 can be used to regulate a temperature of a refrigerant which is in the refrigerant circuit 21 is located.

The first heat exchanger 31 is in the working direction A. of the refrigerant upstream of the ambient heat exchanger 25th arranged and can thus regulate a refrigerant inlet temperature. The first heat exchanger couples for this purpose 31 the refrigerant circuit 21 thermal with a first coolant circuit 32 .

In the first coolant circuit 32 is the heat exchanger 30th , the first heat exchanger 31 and a first pump 33 arranged. The first pump 33 conveys a coolant via the first heat exchanger 31 and thus extracts heat from the refrigerant. The heat extracted from the refrigerant is then transferred to the heat exchanger 30th and given to the air stream Lab.

The ambient heat exchanger 25th can heat from an environment in working mode or heating mode U remove. The extracted heat is transferred through the refrigerant circuit 21 to the interior heat exchanger 20th which transfer the heat to the air flow L. and thus to the interior 10 gives.

In the heating mode of the air conditioning device 100 are a first shut-off valve 26th and a second shut-off valve 27 closed. A third shut-off valve 28 and a fourth shut-off valve 29 are open and allow the refrigerant to flow through the ambient heat exchanger 25th in working direction A. . A second heat exchanger is used here 40 and a third expansion valve 24 bridged.

The refrigerant can be used by a compressor 12th be conveyed or circulated in the refrigerant circuit.

The second heat exchanger 40 couples the refrigerant circuit 21 thermal with a second coolant circuit 41 . The second coolant circuit 41 can be one or more components 42 , such as traction components, which generate heat. A second pump 43 can the coolant of the second coolant circuit 41 promote and if necessary the heat of the component 42 via the second heat exchanger 40 to the refrigerant circuit 21 transport.

By removing heat from the environment U can the ambient heat exchanger 25th freeze and lose efficiency. To do this, it is necessary to carry out a defrosting process in order to increase the efficiency of the air-conditioning device 100 restore.

In 2 FIG. 13 is a pressure-enthalpy diagram for illustrating a defrosting process with the one in FIG 1 air conditioning device shown 100 shown. It is in particular a pressure p and an enthalpy h of the melt water 50 shown during different thermodynamic steps. The meltwater 50 absorbs the heat of the refrigerant in the ambient heat exchanger 25th on. The diagram consists of three sections in which the meltwater is in a liquid state of aggregation 51 , in a gaseous state 53 or as wet steam 52 is present. An excess 54 the heat of the refrigerant, which brings the melt water to the boil, has to pass through the first heat exchanger, for example 31 be discharged.

Due to the steep course of the isotherms in the gas area 53 The diagram shows a high temperature difference between the refrigerant or the melt water and the environment U . Due to the high temperature difference between the refrigerant in the gas area 53 and the environment U can cause high losses to the environment U due to the high driving temperature difference. These losses can be reduced by adjusting the temperature of the refrigerant, since only the heat of fusion required for melting 55 the ambient heat exchanger 25th is fed.

The 3rd Fig. 13 shows a circuit diagram of the air conditioning device 100 during a defrosting process to illustrate a method according to a first embodiment. The first shut-off valve 26th , the third shut-off valve 28 and the fourth shut-off valve 29 are closed here. The refrigerant can thus pass through the second shut-off valve 27 to the ambient heat exchanger 25th are transported with the refrigerant against the working direction A. through the ambient heat exchanger 25th flows through.

During the defrosting process, the interior heat exchanger 20th bridged so that the second heat exchanger 40 and the second coolant circuit 41 serve as a heat source and the components 42 cool.

This keeps the temperature of the refrigerant as it enters the ambient heat exchanger 25th is throttled or adjusted, the temperature of the refrigerant is regulated by the first heat exchanger 31 .

In the 4th Fig. 3 is a circuit diagram of the air conditioning device 100 shown during a defrosting process to illustrate a method according to a second embodiment. In contrast to the exemplary embodiments already described, the refrigerant circuit 21 an internal heat exchanger 60 on. The internal heat exchanger 60 has an inflow 61 on which the first heat exchanger 31 is downstream. The internal heat exchanger 60 is before the first heat exchanger 31 arranged, whereby the in the first heat exchanger 31 refrigerant flowing in through the internal heat exchanger 60 is pre-cooled.

The 5 Fig. 13 shows a circuit diagram of the air conditioning device 100 during a defrosting process to illustrate a method according to a third embodiment. In particular, there is a defrosting operation of the ambient heat exchanger 25th with traction components 42 as a heat source and the internal heat exchanger 60 as an additional heat sink for the refrigerant in addition to the first heat exchanger 31 made clear.

In contrast to the in 4th embodiment shown can be the inflow 61 to the internal heat exchanger 60 via a valve 62 and / or a bypass line 63 controlled or bridged.

List of reference symbols

100

Air conditioning device

10

inner space

11

Interior fan

12th

compressor

20th

Indoor heat exchanger

21

Refrigerant circuit

22nd

first expansion valve

23

second expansion valve

24

third expansion valve

25th

Ambient heat exchanger

26th

first shut-off valve

27

second shut-off valve

28

third shut-off valve

29

fourth shut-off valve

30th

Heat exchanger

31

first heat exchanger / hot gas desuperheater

32

first coolant circuit

33

first pump

40

second heat exchanger

41

second coolant circuit

42

Component / traction components

43

second pump

50

Meltwater

51

the liquid state of the melt water

52

Melt water in the form of wet steam

53

gaseous state of the melt water

54

Excess heat

55

Heat of fusion

60

internal heat exchanger

61

Inflow to the internal heat exchanger

62

Valve at the inflow

63

Internal heat exchanger bypass line

A.

Working direction

L.

Airflow

U

Surroundings

Claims (10)

A method for carrying out a defrosting process of an air conditioning device (100), in particular a vehicle-side air conditioning device which has a refrigerant circuit (21), a refrigerant being used by a compressor (12) in the refrigerant circuit (21) to heat an ambient heat exchanger (25) against a working direction (A ) of the refrigerant is conveyed, characterized in that the temperature of the refrigerant is set before it flows into the ambient heat exchanger (25). Procedure according to Claim 1 , the temperature of the refrigerant being set before it flows into the ambient heat exchanger (25) by regulating a speed of the compressor (12) and / or by regulating an opening of at least one expansion valve (22, 23, 24). Procedure according to Claim 1 or 2 , the temperature of the refrigerant being set before it flows into the ambient heat exchanger (25) by a hot gas desuperheater (31) or an air-side condenser inserted in a fluid-conducting manner into the refrigerant circuit (21), the hot-gas desuperheater or the air-side condenser as a first heat exchanger (31) is designed, which thermally couples a heating heat exchanger (30) for heating an interior (10) via a first coolant circuit (32) with the refrigerant circuit (21) and wherein the first heat exchanger (32) or the air-side condenser is set up to pass one through Interior fan (11) generated air flow (L) to warm up or cool in an interior (10). Procedure according to Claim 3 , the coolant of the first coolant circuit (32) being conveyed by a first pump (33), the mass flow of the first pump (33) and / or an air flow (L) generated by the interior fan (11) for setting the temperature of the refrigerant be managed. Procedure according to Claim 3 or 4th , an internal heat exchanger (60) being arranged in the refrigerant circuit in a working direction (A) upstream of the hot gas de-heater (31), the refrigerant through the internal heat exchanger after passing through the hot gas de-heater (31) and before flowing into the ambient heat exchanger (25) (60) is performed. Procedure according to Claim 5 , wherein an inflow (61) of the refrigerant to the internal heat exchanger is opened or closed by at least one valve (62) and / or a bypass line (63). Method according to one of the Claims 1 to 6th , whereby the refrigerant for performing the defrosting process is conveyed through the ambient heat exchanger (25) counter to the working direction (A), an interior heat exchanger (20) being bridged during the defrosting process and the refrigerant being bridged via a second heat exchanger (40) for removing heat from a second Coolant circuit (41) is promoted. Method according to one of the Claims 1 to 7th , wherein an absolute temperature of the refrigerant before flowing into the ambient heat exchanger (25) against the working direction (A) is limited to 40 ° C, 60 ° C or 100 ° C. Method according to one of the Claims 1 to 8th , wherein a temperature difference between the refrigerant before flowing into the ambient heat exchanger (25) and an ambient temperature is set by regulating the temperature of the refrigerant, the temperature difference being set to 5 K, 10 K or 20 K. Air-conditioning device (100) for air-conditioning an interior (10), in particular a vehicle interior, by means of an interior heat exchanger (20), the air-conditioning device (100) being set up to carry out a method according to one of the preceding claims.

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