Method for operating an air-conditioning system of a motor vehicle

Abstract

A method for operating an air-conditioning system of a motor vehicle, wherein the air-conditioning system comprises a refrigerant circulation and a water circulation which are thermally coupled with one another across a condenser/gas cooler. Water circulation flows through the condenser/gas cooler at a low volumetric rate of flow and a high temperature difference so the water circulation transfers heat in the heating heat exchanger to the air in a similar temperature range. Refrigerant circulation cools from 65° C. to 70° C. to −10° C. to +30° C. and water circulation raises to a temperature of 55° C. to 65° C. and that an adaptation of the temperature profile of the water circulation to the temperature profile of the refrigerant circulation takes place in the condenser/gas cooler utilizing a temperature glide of the refrigerant. The refrigerant is significantly cooled.

Claims

1. A method for operating an air-conditioning system of a motor vehicle, wherein the air-conditioning system comprises a refrigerant circulation and a water circulation which are thermally coupled with one another across a condenser/gas cooler and the water circulation comprises, in addition to a pump, a heating heat exchanger for heating the air for the passenger compartment of a motor vehicle and the refrigerant circulation comprises a compressor, an expansion element and an evaporator, comprising the steps of flowing the water circulation through the condenser/gas cooler at a volumetric rate of flow and a temperature difference such that the water circulation transfers heat in the heating heat exchanger to the air in a temperature range, cooling the refrigerant circulation from 65° C. to 70° C. to −10° C. to +30° C., and raising the water circulation to a temperature of 55° C. to 65° C., and adapting the temperature of the water circulation to the temperature of the refrigerant circulation, wherein the adapting is executed by a controller to cool the refrigerant in the condenser/gas cooler utilizing a temperature glide of the refrigerant, wherein the controller controls a volumetric air flow rate V.sup.dot.sub.air a rotational speed n.sub.V of the compressor and a rotational speed n.sub.P of the pump based on an ambient temperature t.sub.U, a specified target temperature t.sub.nominal, an evaporation temperature t.sub.1 after the expansion element in the refrigerant circulation, a coolant water temperature t.sub.2 after the condenser/gas cooler in the water circulation and an air temperature t.sub.out in the passenger compartment; wherein the evaporation temperature t.sub.1 is measured after the expansion element in the refrigerant circulation system, and wherein the cooling water temperature t.sub.2 is measured after the condenser or gas cooler in the water circulation system.

2. A method according to claim 1, wherein at the heating heat exchanger air is conveyed over several serially connected heat exchanger segments.

3. A method according to claim 1, wherein the pressure as well as the volumetric rate of flow of the water is utilized as a setting parameter for the capacity of the heat pumps with respect to heating as well as also heat source capacity.

4. A method according to claim 1, wherein the refrigerant circulation is operated with an internal heat exchanger, several compressors or several condensers/gas coolers, or a combination thereof.

5. A method according to claim 4, wherein the flow through the heating heat exchanger and/or the several condensers/gas coolers takes place in counter-flow or cross-flow.

6. A method according to claim 1, wherein the water circulation is operated with a mixture of water and glycol.

7. A method according to claim 6, wherein the refrigerant circulation is operated with an internal heat exchanger.

8. A method according to claim 1, wherein the refrigerant circulation is operated with a refrigerant mass flow of 10 to 300 kg/hr with the refrigerant R744.

9. A method according to claim 8, wherein the refrigerant circulation is operated with several compressors.

10. A method according to claim 8, wherein the water circulation is operated with a mixture of water and glycol.

11. A method according to claim 1, wherein the refrigerant circulation is operated with the refrigerant R744 in super- as well as also sub-critical.

12. A method according to claim 11, wherein the refrigerant circulation is operated with several condensers/gas coolers.

13. A method according to claim 11, wherein the water circulation is operated with a mixture of water and glycol.

14. A method according to claim 1, wherein the water circulation is operated at a flow rate of 1 kg/hr to 540 kg/hr.

15. A method according to claim 14, wherein the refrigerant circulation is operated with the refrigerant R1234yf in super- as well as also sub-critical state.

16. A method according to claim 14, wherein the refrigerant circulation is operated with an internal heat exchanger.

17. A method according to claim 14, wherein the water circulation is operated with a mixture of water and glycol.

18. A method according to claim 14, wherein the flow through the heating heat exchanger and/or the condenser/gas cooler takes place in counter-flow or cross-flow.

Description

(1) Further details, characteristics and advantages of embodiments of the invention are evident in the following description of embodiment examples with reference to the associated drawing. In the drawing depict:

(2) FIG. 1: a simplified diagram of an air-conditioning system according to the invention,

(3) FIG. 2a: log(p)—[enthalpy] h diagram of a conventional refrigeration process with R744 as the refrigerant in transcritical process control,

(4) FIG. 2b: log(p)—h diagram according to the method according to the invention with R744 as the refrigerant in transcritical process control,

(5) FIG. 3: simplified diagram of a multifunctional air-conditioning system,

(6) FIG. 4a: log(p)—h diagram for R744,

(7) FIG. 4b: T-S diagram for the refrigerant R744,

(8) FIG. 5a: log(p)—h diagram for the refrigerant R1234yf,

(9) FIG. 5b: T-S diagram for the refrigerant R1234yf,

(10) FIG. 6: simplified diagram of an embodiment of an air-conditioning system,

(11) FIG. 7: control and regulation arrangement for an air-conditioning system.

(12) FIG. 1 shows an air-conditioning system substantially built of two main components, the refrigerant circulation 2 and the water circulation 3.

(13) The refrigerant circulation 2 comprises at least one compressor 4, one condenser/gas cooler 5, one expansion element 6 as well as one evaporator 7 as basic components of the circuit, as is customary and known in prior art. In addition, depending on the refrigerant employed and optionally additional requirements, several compressors 4, expansion elements 6 or also evaporators 7 can in principle be utilized and supplemented, wherein the gas cooler/condenser 5 in terms of function represents the thermal coupling to the water circulation 3.

(14) The water circulation 3 comprises a pump 8 for the circulation of the circuit and the heating heat exchanger 9 which is integrated into the ventilation system of the motor vehicle and via which the heating of the air 10 of the passenger compartment takes place. The thermal coupling of the refrigerant circulation 2 and the water circulation 3 takes place across a heat exchanger which, according to its function in the refrigerant circulation 2, is referred to as condenser/gas cooler 5. The heat from the refrigerant circulation 2 is output via the condenser/gas cooler 5 to the water circulation 3, whereupon the heated water transfers in the heating heat exchanger 9 the heat to the air 10 for heating the passenger compartment of the motor vehicle.

(15) The refrigerant circulation indicates by the measurement point with the reference number 11 the refrigerant suction status before the compression, by the reference number 12 the refrigerant compression final state after the compression of the refrigerant, by the reference number 13 the refrigerant high-pressure state before the expansion and by the reference number 14 the refrigerant low-pressure state after the expansion. As will be explained in the following in further Figures, these points are points of state in the state diagrams for the refrigerant.

(16) FIG. 2a depicts a log(p)—h diagram for R744 as the refrigerant and a transcritical method according to prior art and will be described in the following with reference to FIG. 1. The isothermal curve of t=50° C. extends through point 13, the refrigerant high-pressure state before expansion. This means that the refrigerant after the gas cooler 5 has a temperature of 50° C. and is expanded to low pressure from 90 to 20 bars at point 14, the refrigerant low-pressure state after the expansion. In the evaporator 7 and with minimal overheating the refrigerant absorbs energy under evaporation and is lastly from point 11, the refrigerant suction state before the compression, to point 12, the refrigerant compression final state after the compression, compressed to high pressure in compressor 4.

(17) As a comparison of the process controls, in FIG. 2b is shown schematically a (log(p), h) diagram according to the invention. In order to be able to compare the processes, the pressure level is selected to be the same as in the method from FIG. 2a. Through the modifications in the process control according to the invention, the state points for the temperatures, however, differ from prior art. In particular point 13, the high-pressure state of the refrigerant before expansion, thus the state of the refrigerant after the gas cooler 5, is decreased from the temperature to 30° C. The expansion takes place as before after point 14, the refrigerant low-pressure state after the expansion. Since point 14 in the process is located further to the left in comparison to FIG. 2a, an increase of the enthalpy difference can be noticed from point 14 to point 11 in the state diagram. This means that the usable cooling capacity increases. The compression from point 11 to point 12 takes place analogously to the method according to prior art up to a final compression temperature which, in the example for the refrigerant R744, is up to approximately 120° C.

(18) In FIG. 3 is shown schematically a somewhat more complex implementation of a circuit, wherein the basic concept is realized in the same manner. The air-conditioning system 1 is again analogously comprised of the refrigerant circulation 2 and the water circulation 3 that are thermally coupled across the condenser/gas cooler 5 of the refrigerant circulation 2. The refrigerant circulation 2 is expanded to the effect that evaporation takes place in parallel on different pressure planes. For this purpose, expansion elements 6 are assigned to evaporators 7, 16, 17 that are referred to as evaporator 7, as battery cooler 16 and as cooler 17. The cooler 17 is integrated into the water circulation 3 by a loop of the latter and, in the depicted embodiment, the air-conditioning system 1 can heat the water circulation 3, depending on the requirements, across the condenser/gas cooler 5 or cool it across the cooler 17. Pumps 8 are provided for this purpose for the water circulation 2 [sic:3]. In addition to the condenser/gas cooler 5, in the water circulation 3 are provided the heating heat exchanger 9 and additionally a heat exchanger as charge-air cooler 19, for example in hybrid motor vehicles. The water circulation 3 is complemented by a low-temperature heat exchanger 15 via which not required waste heat in particular operating states can be discharged to the surrounding. The integration of the various heat exchangers 5, 9, 15, 19 of the water circulation 3 takes place across changeover valves 18.

(19) FIGS. 4a, 4b and 5a, 5b depict qualitative state diagrams of R744 and of R1234yf. Diagrams 4a and 4b show the transcritical process for the refrigerant R744, wherein in the diagrammatic component plan of the cooling system, the heat exchanger for the discharge of the heat from the refrigerant circulation 2 is functionally utilized as gas cooler 5 from the process state 12, the refrigerant final compression state after the compression, to the refrigerant high-pressure state before the expansion 13. In contrast thereto, in FIGS. 5a and 5b the refrigerant R1234yf is depicted qualitatively, in which the heat exchanger for the discharge of heat to the water circulation 3 operates as condenser 5 with reference to the FIGS. 1 and 3.

(20) FIG. 4b depicts a T-S diagram which shows the utilization of the temperature glide for the refrigerant in the heat transfer from the refrigerant to the water circulation in the condenser/gas cooler 5. The condenser/gas cooler 5 is herein connected in counterflow such that the heating of the water in the heat exchanger to temperatures above the refrigerant output temperature takes place. Analogously, in FIG. 5b is shown the utilization of the temperature glide with minor restrictions through the temperature plateau within the two-phase region for the refrigerant R1234yf.

(21) In FIG. 6 is depicted in part a [fluid] circuit diagram wherein are shown the refrigerant circulation 2 and the water circulation 3, wherein, as a parameter for the regulation of the method according to the concept, the compressor 4 is supplemented via the rotational speed n.sub.V of the compressor of the refrigerant circulation and the pump 8 with the rotational speed n.sub.P of the pump of the water circulation. Furthermore are depicted the temperatures t.sub.1, the evaporator temperature after the expansion element 6 in the refrigerant circulation 2, and the coolant water temperature after the heating, denoted by t.sub.2, within the water circulation 3 after the condenser/gas cooler 5. The air 10 is herein first cooled in evaporator 7, for example for the purpose of dehumidification, and subsequently its temperature is raised across the heating heat exchanger 9 to the temperature of the ambient air in the passenger compartment.

(22) FIG. 7 depicts a control and regulation arrangement 20 which implements the regulation strategy in the air-conditioning system, wherein, as the input variables the ambient temperature t.sub.U as well as the specified target temperature t.sub.nominal are regulated through a balance via the evaporation temperature t.sub.1, the coolant water temperature t.sub.2 and the regulation of the air temperature in the passenger compartment t.sub.out with the regulation of the volumetric air flow rate V.sup.dot.sub.air as well as the rotational speed compressor refrigerant circulation n.sub.V and the rotational speed pump water circulation n.sub.P.

(23) Depending on the ambient temperature and the required set temperature of the passengers, a heating capacity results as well as the minimum starting temperature of the water to be reached. At the start of travelling in the extreme case, by assumption, no residual heat will be available in the motor vehicle. Thus, during heat pump operation an appropriate heating capacity must be absorbed at a low temperature level. With the aid of the high pressure of the refrigerant circulation and of the volumetric rate of flow of the water, the heating of the passenger compartment as well as also the capacity of the heat source to be additionally taken up, can be set. The heat source is most frequently limited thereby that the heat exchanger may freeze up. It is significant that the previously known water circulation always had a constant temperature of 55 to 60° C. between forward and return flow. This is a significant difference from the operating mode according to the invention.

LIST OF REFERENCE NUMBERS

(24) 1 Air-Conditioning system

(25) 2 Refrigerant circulation

(26) 3 Water circulation

(27) 4 Compressor

(28) 5 Condenser/gas cooler

(29) 6 Expansion element

(30) 7 Evaporator

(31) 8 Pump

(32) 9 Heating heat exchanger

(33) 10 Air

(34) 11 Refrigerant suction state before compression

(35) 12 Refrigerant compression end state after compression

(36) 13 Refrigerant high-pressure state before expansion

(37) 14 Refrigerant low-pressure state after expansion

(38) 15 Low temperature heat exchanger

(39) 16 Battery cooler

(40) 17 Cooler

(41) 18 Changeover valves

(42) 19 Charge-Air cooler

(43) 20 Control and regulation arrangement

(44) t.sub.U Ambient temperature

(45) t.sub.nominal Target temperature

(46) t.sub.1 Evaporation temperature

(47) t.sub.2 Coolant water temperature

(48) t.sub.out Air temperature passenger compartment

(49) n.sub.V Rotational speed compressor refrigerant circulation

(50) n.sub.P Rotational speed pump water circulation