Device and method for icing prevention regulation for heat pump evaporators

Abstract

The invention relates to a device and a method for icing prevention regulation for a heat pump evaporator (3) in air conditioning systems of vehicles, composed of a subsection (1) of a refrigerant circuit which can be operated both as a heat pump and also as an air conditioning system. The device comprises the heat pump evaporator (3), an electrical or mechanical refrigerant compressor (4), a cooler fan (9) which is attached to the heat pump evaporator (3) and which draws ambient air (11) upstream from and through the heat pump evaporator (3) at an adjustable flow speed, and which thus permits a permanent flow of ambient air (11) over the heat pump evaporator surface, a first temperature sensor (6) in or on the refrigerant line (5, 5a) upstream from the heat pump evaporator (3) with respect to the heat pump operating direction, and a control and regulating unit (8). The control and regulating unit (8) is connected via signal lines (10, 10a, 10b, 10c, 10e) at least to the first temperature sensor (6), to further sensors, in particular for detecting the ambient air temperature (Tu) and the vehicle speed (V.sub.F), to the expansion valve (2), to the cooler fan (9) and to the refrigerant compressor (4) for the direct or indirect regulation of the flow cross section of the expansion valve (2) and the rotational speed of the electric refrigerant compressor (4) or of the regulating valve of the mechanical refrigerant compressor (4) and for the actuation of the cooler fan (9) of the vehicle during heat pump operation.

Claims

1. A device in an air conditioning system for a vehicle for regulation of a surface temperature level and icing prevention regulation for a heat pump evaporator, comprising: the heat pump evaporator which functions during an air conditioning system operation in an air conditioning system operating direction as an air conditioning system condenser, an externally regulatable expansion valve for opening and closing, a refrigerant compressor, refrigerant lines between the externally regulatable expansion valve and the heat pump evaporator and between the heat pump evaporator and the refrigerant compressor, a cooler fan attached to the heat pump evaporator which draws ambient air upstream from and through the heat pump evaporator at an adjustable flow speed, and thereby permits a flow of the ambient air over a heat pump evaporator surface, a first temperature sensor arranged at the inlet of the heat pump evaporator, for detecting the refrigerant temperature upstream from the heat pump evaporator with respect to a heat pump operating direction, and a controller for storing a pressure drop characteristic map, the pressure drop characteristic map corresponding to a pressure drop of the heat pump evaporator, the pressure drop determining the Tout of the heat pump evaporator, the controller being directly connected to the externally regulatable expansion valve, the controller being connected to the externally regulatable expansion valve via signal lines, the controller being further connected at least to the first temperature sensor, additional sensors, measurement signal emitters or processing units with calculated values for detecting the ambient air temperature (Tu) and a vehicle speed (VF), the cooler fan, and the refrigerant compressor, wherein the heat pump evaporator operates counter to the air conditioning operation direction during icing prevention regulation; wherein the heat pump function is continuously maintained at below 0 C. ambient air temperature; wherein the controller is adapted to control the externally regulated expansion valve such that the inlet temperature of the refrigerant at an inlet of the heat pump evaporator lies below the ambient air temperature being below 0 C.; wherein the controller is adapted to prompt the cooler fan at below 0 C. ambient air temperature; wherein the device is a subsection of a refrigerant circuit operable both as a heat pump system and the air conditioning system, the heat pump system having a heat pump operating direction, the air conditioning system having the air conditioning system operating direction, the heat pump operating direction being opposing to the air conditioning system operating direction.

2. The device according to claim 1, further comprising an ambient moisture sensor for determining the ambient moisture and/or a rain sensor which detects rain or snow fall.

3. The device according to claim 1, wherein a pressure sensor is provided in order to regulate an outlet temperature (T.sub.out) of the refrigerant from the heat pump evaporator, and a second sensor connected to the control and regulating unit via the another signal line is provided in the refrigerant line downstream from the outlet of the heat pump evaporator on the path to the refrigerant compressor, with respect to the heat pump operating direction.

4. The device according to claim 1, wherein potential pressure drops in the refrigerant line placed between the heat pump evaporator outlet and a pressure sensor for regulating the outlet temperature (T.sub.out) of the refrigerant from the heat pump evaporator are stored per the pressure drop characteristic map in the control and regulating unit.

5. The device according to claim 1, wherein a maximum rotational speed of the compressor when using the electric refrigerant compressor, or a maximum control current of the regulating valve when using the mechanical refrigerant compressor being estimated with the aid of the ambient temperature (T.sub.U).

6. The device according to claim 1, wherein the refrigerant compressor is an electrical or a mechanical compressor, and the signal lines connect the control and regulation unit to the refrigerant compressor if the electric refrigerant compressor is used or to a regulating valve of the mechanical refrigerant compressor if the mechanical refrigerant compressor is used.

7. The device according to claim 6, wherein the control and regulation unit has technical programming measures for regulation of a rotational speed of the electric refrigerant compressor or of the regulating valve of the mechanical refrigerant compressor.

8. The device according to claim 1, wherein a valve element of the externally regulatable expansion valve opens or closes a flow cross-section of the externally regulatable expansion valve, a regulating valve of the refrigerant compressor opens or closes the refrigerant compressor and a motor of the cooler fan adjusts a rotational speed of the cooler fan of the vehicle during heat pump operation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a refrigerant circuit of a heat pump according to the prior art;

(2) FIG. 2 shows a diagram with the temperature curve of the refrigerant over the flow length from the inlet to the outlet of a heat pump evaporator compared with the ambient air temperature T.sub.U due to pressure drops, prior art;

(3) FIG. 3a shows a diagram with the temperature curve of the refrigerant over the flow length from the inlet to the outlet of the heat pump evaporator with refrigerant temperatures below the ambient air temperature T.sub.U;

(4) FIG. 3b shows a diagram with the temperature curve of the refrigerant over the flow length from the inlet to the outlet of the heat pump evaporator compared with air ambient temperature T.sub.U when the temperature is regulated;

(5) FIG. 4 shows a subsection of a refrigerant circuit including sensors and actuators for the air heat pump having pressure and temperature sensors upstream and downstream from the heat pump evaporator; and

(6) FIG. 5 shows a subsection of a refrigerant circuit including sensors and actuators for the air heat pump without pressure and temperature sensors downstream from the heat pump evaporator.

DETAILED DESCRIPTION

(7) A prior art heat pump 100 from WO 2009/094691 A1 depicted in FIG. 1 comprises a refrigerant circuit having a heat pump evaporator 170, a compressor 150, a condenser 140 and an expansion valve 130, which is situated between the outlet of the condenser 140 and the inlet of the heat pump evaporator 170. The connection between the heat pump evaporator 170, the compressor 150, the condenser 140, the expansion valve 130 and, in turn, the heat pump evaporator 170 are provided by refrigerant lines 190 for the refrigerant flow. In the heat pump evaporator 170, the refrigerant liquid absorbs the heat from the ambient air 180 and evaporates to form refrigerant vapor. The compressor 150 compresses the refrigerant vapor using mechanical energy and increases temperature of the refrigerant vapor as a result. In the condenser 140, the refrigerant vapor transfers its heat to the heating circuit 145, the refrigerant vapor condenses and once again becomes refrigerant liquid. In the expansion valve 130, the pressure of the refrigerant liquid is reduced by opening the expansion valve 130 and the refrigerant liquid again passes to the heat pump evaporator 170, in which refrigerant vapor again forms as a result of absorption from the heat of the ambient air 180, and thus, the circulatory function is repeated. Attached to the heat pump evaporator 170 is a fan 160, which is connected to a control unit 120 which, in turn, is in signal connection with the compressor 150 and a temperature sensor 110. The heat pump 100 includes a refrigerant flow through the heat pump evaporator 170, which may be regularly or temporarily interrupted by the control unit 120. During normal operation, the fan 160 draws ambient air 180 over one side 172 of the heat pump evaporator 170, as a result of which the ambient air 180 is conducted over the heat pump evaporator surface, and refrigerant vapor is produced through absorption of heat from the ambient air 180. In the case of an icing of the heat pump evaporator 170, the very low temperatures in the icing region being indicated by the temperature sensor 110, the refrigerant flow in the compressor 150 is stopped by the control unit 120. Subsequently, the air direction of the fan 160 is reversed by the control unit 120, i.e., with the aid of the fan 160, the direction 480 of the air flow is diverted from the side 174 to the evaporator surface, such that warmer air is conducted onto the evaporator surface and the heat pump evaporator 170 is de-iced.

(8) FIG. 2 illustrates the disadvantages of the prior art with reference to a diagram. The diagram depicts the temperature curve of the refrigerant over the flow length from the inlet to the outlet of a heat pump evaporator as compared to the ambient air temperature T.sub.U based on the pressure drops, with an inlet temperature T.sub.in and an outlet temperature T.sub.out. Because of the pressure drops in the heat pump evaporator, regulating the outlet temperature level, in particular when using the refrigerants R134a and R1234yf, may cause a refrigerant temperature T.sub.in to occur having a temperature difference of T.sub.in above the ambient air temperature T.sub.U, as shown in FIG. 2. This results in heat dissipating into the environment or in a reduction in the surface utilized for heat absorption, and thus to reduced efficiency of the heat pump.

(9) According to the invention, the surface temperature level and the refrigerant temperature in the entire heat pump evaporator are adjusted to a predefined temperature level. The diagram from FIG. 3a shows a simplified, linearly decreasing temperature curve of the refrigerant over the refrigerant flow length from inlet to outlet of the heat pump evaporator having refrigerant temperatures below the ambient air temperature T.sub.U at a temperature difference T.sub.in at the inlet and a difference T.sub.out at the outlet. This temperature change is caused by the pressure drop on the refrigerant side in the 2-phase region. The diagram from FIG. 3b shows a temperature curve of the refrigerant when regulating the temperature with a changing rise over the refrigerant flow length from inlet to outlet of the heat pump evaporator, compared with ambient temperature T.sub.U. In this example, the refrigerant is fully evaporated and superheated in the region of the temperature rise.

(10) The refrigerant temperature T.sub.in at the inlet of the heat pump evaporator, as shown in FIGS. 3a and 3b, with a temperature difference T.sub.in of, for example, 1 K, lies slightly below the ambient air temperature T.sub.U, respectively, below the air inlet temperature into the heat pump evaporator. The outlet temperature T.sub.out of the refrigerant is largely determined by the pressure drop and, therefore, the mass flow of the refrigerant. For this purpose, the compressor rotational speed of an electric refrigerant compressor or the regulating valve of a mechanical refrigerant compressor is regulated, such that the saturation pressure of the refrigerant associated with the outlet pressure exhibits a certain difference T.sub.max relative to ambient air temperature T.sub.U, namely a difference between 2 to 10 K, preferably 2 to 5 K, as shown in FIG. 3b. In the case of a temperature curve, as is shown in FIG. 3b, the difference T.sub.out between the outlet temperature T.sub.out and the ambient air temperature T.sub.U is calculated based on the sum of difference T.sub.max and the superheating of the refrigerant.

(11) FIG. 4 shows a subsection 1 of a refrigerant circuit of an air conditioning system as a device for icing prevention regulation for a heat pump evaporator. The device 1 comprises a preferably externally regulatable expansion valve 2 having an air conditioning condenser 3 (AC condenser), which functions during heat pump operation as a heat pump evaporator 3 and is perfused during heat pump operation preferably counter to the air conditioning operating direction (AC operating direction) on the refrigerant side, a refrigerant compressor 4 and refrigerant lines 5 between expansion valve 2 and heat pump evaporator 3, and between heat pump evaporator 3 and refrigerant compressor 4. According to FIG. 4, a first temperature sensor 6 is arranged in or on a section 5a of the refrigerant line 5 upstream from the heat pump evaporator 3 and a combined pressure-temperature sensor 7 is arranged in a section 5b of the refrigerant line 5b downstream from heat pump evaporator 3, in each case relative to the heat pump operating direction. The measurement signals from the sensors, from the first temperature sensor 6 and the combined pressure-temperature sensor 7 are processed by a control and regulating unit 8, which, in addition to processing other sensors present in the vehicle, for example the ambient air temperature T.sub.U, the vehicle speed v.sub.F, etc., for the heat pump, actuates the cooler fan 9 of the vehicle shown in FIG. 4 and regulates directly or indirectly the flow cross-section of the expansion valve 2 and the rotational speed of an electric refrigerant compressor 4 or the regulator valve of a mechanical refrigerant compressor 4. Optionally, still other sensors may be used for determining the dew point or the condition of the ambient air such as, for example, rain sensor or an ambient moisture sensor. For this purpose, the control and regulating unit 8 is connected via at least one signal line 10, 10a to the external regulator of the expansion valve 2, via at least one signal line 10, 10b to the first temperature sensor 6, via at least one signal line 10, 10c to the cooler fan 9, via at least one signal line 10, 10d to the combined pressure-temperature sensor 7, and via at least one signal line 10, 10e to the refrigerant compressor or, respectively, a regulator for the refrigerant compressor 4.

(12) The cooler fan 9 attached to the heat pump evaporator 3 draws ambient air 11 at an adjustable flow speed upstream from and through the heat pump evaporator 3, and thus permits a permanent flow of ambient air (11) over the heat pump evaporator surface. Unlike the pure air conditioning system operation (AC operation), the cooler fan 9 is also prompted at temperatures below 0 C. ambient air temperature T.sub.U by the air conditioning system (heat pump), preferably as a function of the travelling speed v.sub.F. The expansion valve 2 is used to regulate the inlet temperature T.sub.in into the heat pump evaporator 3. In the process, the expansion valve 2 is closed far enough that the refrigerant temperature T.sub.in at the inlet of the heat pump evaporator 3 lies slightly, for example, 1 K, below the ambient air temperature T.sub.U, respectively, below the air inlet temperature into the heat pump evaporator 3. If the expansion valve 2 is opened to wide, the inlet temperature T.sub.in rises above the ambient air temperature T.sub.U because of the pressure drop in the heat pump evaporator 3. In this case, a portion of the heat exchange surface is used not for evaporating, but, if necessary, even for condensing the refrigerant. As a result, the efficiency of the air heat pump is negatively impacted.

(13) The outlet temperature of the refrigerant is determined largely by the pressure drop and, thus, the flow mass of the refrigerant. For this purpose, the compressor rotational speed of an electric refrigerant compressor 4 is regulated or, respectively, the regulating current of a regulator for a mechanical refrigerant compressor 4 is adjusted so that the saturation temperature of the refrigerant associated with the outlet pressure lies below the ambient air temperature T.sub.U, and thereby maintains a certain difference relative to this ambient air temperature T.sub.U (preferably 5 to 10 K). In this case, the saturation temperature of the refrigerant is determined according to FIG. 4 based on the pressure signal p detected by the combined pressure-temperature sensor 7, with the aid of characteristic curves, polynomial functions stored in the control and regulating unit 8, or by access to libraries having detailed property data functions.

(14) There is also the possibility of storing a pressure drop characteristics map for the heat pump evaporator 3 and to estimate the maximum possible compressor rotational speed or the maximum possible regulating current with the aid of the ambient air temperature T.sub.U, below which the saturation temperature of the refrigerant associated with the outlet pressure lies, while maintaining a specific difference T.sub.max relative to this ambient air temperature T.sub.U, namely of preferably 5 to 10 K. In this case, the potentially combined pressure and temperature sensors downstream from the heat pump evaporators 3 may be eliminated, as shown by the device 1 in FIG. 5. Thus, the device 1 for icing prevention regulation for a heat pump evaporator 3 according to the representation in FIG. 5 lacks, in contrast to FIG. 4, a pressure-temperature sensor 7 downstream from the heat pump evaporator 3, with respect to the heat pump operating direction, and a corresponding signal line 10d from the pressure-temperature sensor 7 to the control and regulating unit 8.

LIST OF REFERENCE NUMERALS

(15) 1 Device, subsection of a refrigerant circuit of an air conditioning system 2 Expansion valve 3 Heat pump evaporator, air conditioning system condenser, (AC-condenser) 4 Refrigerant compressor 5 Refrigerant line 5a Section of the refrigerant line (upstream from the heat pump evaporator 3) 5b Section of the refrigerant line (downstream from the heat pump evaporator 3) 6 (First) temperature sensor 7 (combined Pressure-temperature sensor 8 Control and regulating unit 9 Cooler fan 10 Signal lines 10a Signal line (between control and regulating unit 8 and expansion valve 2) 10b Signal line (between control and regulating unit 8 and (first) temperature sensor 6) 10c Signal line (between control and regulating unit 8 and cooler fan 9) 10d Signal line (between control and regulating unit 8 and pressure-temperature sensor 7) 10e) Signal line (between control and regulating unit 8 and refrigerant compressor 4) 11 Ambient air T.sub.U Ambient air temperature T.sub.in Inlet temperature (of the refrigerant in the heat pump evaporator 3), refrigerant temperature at the inlet into the heat pump evaporator 3 T.sub.out Outlet temperature (of the refrigerant exiting the heat pump evaporator 3) T.sub.in Difference of the inlet temperature of the refrigerant entering the heat pump evaporator relative to the air ambient temperature T.sub.U T.sub.out Difference of the outlet temperature of the refrigerant relative to the environment T.sub.max Difference of the saturation temperature of the refrigerant associated with the refrigerant at the outlet of the heat pump evaporator relative to the environment V.sub.F Driving speed, vehicle speed p Pressure, pressure signal 100 Heat pump (prior art) 110 Temperature sensor (in heat pump 100 according to the prior art) 120 Control unit (in heat pump 100 according to the prior art) 130 Expansion valve (in heat pump 100 according to the prior art) 140 Condenser (in heat pump 100 according to the prior art) 145 Heating circuit (in heat pump 100 according to the prior art) 150 Compressor (in heat pump 100 according to the prior art) 160 Fan (in heat pump 100 according to the prior art) 170 Evaporator (in heat pump 100 according to the prior art) 172 Side of the evaporator 170 (in heat pump 100 according to the prior art) 174 Side of the evaporator 170 (in heat pump 100 according to the prior art) 180 Ambient air 190 Refrigerant lines (in heat pump 100 according to the prior art) 480 Direction of the air flow (in heat pump 100 according to the prior art)