EP2706312B1 - Method for operating a cooler and cooler - Google Patents

Description

The present invention relates to a method of operating a refrigerator, e.g. a refrigeration system, air conditioner or heat pump, comprising a refrigerant having a closed circuit in which an evaporator, a first compressor and at least one parallel connected second compressor, a condenser, a subcooler and a first expansion valve are arranged successively.

Cooling machines of this type and methods for operating the same are known in principle, wherein cooling machines generally produce a cooling effect on their evaporator and a heating effect on their condenser. For example, heat pumps are used to convert heat stored in the soil, groundwater or air into thermal heat. Ideally, the thermal heat or heat energy generated thereby exceeds a necessary for operating the heat pump electrical energy by a multiple. Heat pumps thus represent a resource-saving option for supplying heat. Further examples of refrigerating machines are refrigerators, freezers or chests or air conditioning systems.

In order to be able to react variably to different load requirements, some chillers are equipped with several compressors in parallel, whereby one or more compressors are operated simultaneously depending on the required heat or cooling capacity. For example two parallel compressors available, so is also spoken by a tandem compressor.

The compressors compress the refrigerant evaporated in the evaporator and discharge the compressed refrigerant at its outputs as so-called pressurized gas having an increased pressure and an elevated temperature. If the compressors are operated at the limit of their capacity, the temperature of the compressed gas may exceed allowable limits and damage the compressors.

For cooling the compressor, it is therefore known to supply these via specially provided injection ports expanded refrigerant, which has a lower temperature than the compressed gas. In this case, liquid refrigerant is branched off from the circuit for each compressor, fed to an expansion valve associated with the respective compressor, expanded therein, vaporized in a subcooler and then injected into the compressor. If so-called scroll compressors are used, the injection can take place directly into the scroll spiral.

This form of compressor cooling is disadvantageous in that a separate according to its operating state controlled expansion valve is provided for each compressor. With regard to control effort and production costs, a refrigeration machine having such a compressor cooling is correspondingly complicated and expensive.

A method according to the preamble of claim 1 is known from FR 2 598 788 A1 known. Similar methods are further in the US 2005/0235689 A1 . WO 2008/082408 A1 and WO 2008/130359 A1 described.

The invention has for its object to provide a simpler method of operating a chiller of the type mentioned, which is accompanied at the same time with lower investment costs for the chiller and contributes to avoiding damage to the compressors and increasing their life.

The solution of this object is achieved by a method having the features of claim 1.

The inventive method provides that liquid refrigerant branched off from the circuit between the condenser and the subcooler, expanded by means of a second expansion valve, at least partially evaporated by the subcooler and then supplied to the first and / or second compressor for cooling.

In other words, only a single expansion valve is provided for expansion of the branched off for the cooling of multiple compressor refrigerant, namely the second expansion valve. A branching of the cooling path to the individual compressors takes place according to the invention only after the at least partial evaporation of the refrigerant expanded by the common second expansion valve.

On further, individual compressors associated expansion valves can therefore be dispensed with, which not only components and thus costs can be saved in the production of the refrigerator, but in the case of using a controlled expansion valve and the regulatory burden is considerably simplified.

Advantageous embodiments of the invention are set forth in the subclaims, the description and the drawing.

According to one embodiment, the second expansion valve is regulated by means of a control unit. In other words, the second expansion valve is a regulated expansion valve, with the help of which, for example, the overheating of the diverted, expanded and vaporized refrigerant can be regulated. Thus, only a single control unit is needed for the cooling of several and preferably all compressors. Also required for an overheating control sensors for detecting pressure and temperature of the branched, expanded and vaporized refrigerant need to be provided only simply. It can be saved in this way so even more costs.

Preferably, the second expansion valve is controlled in response to overheating of the refrigerant evaporated by the subcooler. The second expansion valve is in this case controlled such that the refrigerant is not only evaporated by the subcooler, but also overheated. Overheating of the refrigerant ensures that the refrigerant has completely evaporated, i. exclusively in gaseous form. Typically, overheating is regulated to a value between 0K and 10K.

In order to carry out an overheating control of the second expansion valve, the pressure and the temperature of the diverted refrigerant are advantageously detected after the subcooler, since the overheating of the refrigerant can be determined particularly reliably from these values.

According to the invention, a compressed gas temperature of the or each compressor in operation is detected, for example by means of a temperature sensor arranged in the region of the compressor outlet. In this way, an impermissibly high pressure gas temperature of a compressor can be detected in good time and a corresponding cooling of the compressor can be initiated.

Further, the second expansion valve is controlled in dependence on the pressure gas temperature of a compressor when the pressure gas temperature of at least one compressor exceeds a predetermined threshold. Normally, for example, an overheating control of the second expansion valve, so it is switched to a pressure gas temperature control of the expansion valve as soon as the pressure gas temperature of at least one compressor is unacceptably high. In the pressurized gas temperature control mode, the expansion valve is controlled so that the discharge gas temperature again becomes an allowable value. To this end, the overheating of the refrigerant is reduced as much as necessary to a waiver of overheating, i. Avoid complete evaporation of the refrigerant. If necessary, the refrigerant may also only partially evaporate, i. So with a certain amount of liquid, are introduced into the compressor. In this way damage to the compressors can be effectively avoided and their life can be increased.

To further reduce the control effort, the second expansion valve according to the invention is controlled as a function of the respective highest compressed gas temperature of all compressors in operation. The condition of the compressor with the highest pressure gas temperature can be said to be most critical to the function of the refrigerator. This compressor must therefore be primarily cooled. The regulation of the second expansion valve is therefore dependent on this reason performed by the discharge gas temperature of the compressor with the highest pressure gas temperature. The other compressors in operation are cooled accordingly for easier control, even if not or at least not absolutely necessary.

According to a further embodiment, the supply of the refrigerant evaporated by the subcooler is controlled to the first compressor by means of a first shut-off valve and to the second compressor by means of a second shut-off valve, wherein the respective valve associated with the shut-off valve is opened as soon as it starts its operation. In other words, a compressor is only supplied with branched-off refrigerant for cooling when it is actually in operation. If a compressor is in operation, it is continuously supplied with refrigerant for cooling. The check valves may for example be designed as solenoid valves.

Another object of the invention is a refrigerator with the features of claim 6.

The refrigerator according to the invention makes it possible to carry out the method according to the invention, so that the advantages described above can be achieved accordingly.

Fig. 1

eine schematische Ansicht einer erfindungsgemäßen Kältemaschine.

The invention will be described purely by way of example with reference to a possible embodiment with reference to the accompanying drawings. It shows:

Fig. 1

a schematic view of a refrigerator according to the invention.

In Fig. 1 a chiller in the form of a heat pump 10 is shown. The heat pump 10 comprises a main circuit 11 having a refrigerant, the refrigerant flowing through the heat pump 10 in normal operation in a direction indicated by arrows.

For the compression of gaseous refrigerant, a first compressor 12 and a second compressor 14 connected in parallel therewith are provided which, if necessary, can operate either individually or both at the same time.

The compressed by the compressors gaseous refrigerant, also referred to as compressed gas, is liquefied in a condenser 16 and thereby cooled. The liquefied refrigerant is then supplied to a majority through a subcooler 18 through a first expansion valve 20, through which the liquid refrigerant is expanded. The expanded refrigerant is then vaporized in an evaporator 22 and then fed back to the compressors 12, 14.

A smaller portion of the refrigerant liquefied in the condenser 16 is diverted from the main circuit 11 between the condenser 16 and the subcooler 18 and supplied to a second expansion valve 24. The branched refrigerant is expanded in the second expansion valve 24 and then exchanges heat in the subcooler 18 with the liquid refrigerant of the main circuit 11, at least partially evaporating it. The liquid refrigerant guided in the main circuit 11 through the subcooler 18 is further cooled by the heat exchange with the branched and expanded refrigerant.

The branched refrigerant evaporated in the subcooler is supplied to both the first compressor 12 and the second compressor 14 via injection ports 26 for cooling. In this case, the cooling refrigerant is always supplied to a compressor 12, 14 when it is in operation. Only when a compressor 12, 14 is stopped, the cooling refrigerant supply is interrupted by means of a respective compressor 12, 14 associated solenoid valve 28a, 28b.

The control of the second expansion valve 24 is performed by a control unit 30 which is connected to temperature sensors 32a, 32b, which detect the temperatures of the compressed gas at the outputs of the compressors 12, 14. Furthermore, the control unit 30 is connected to a temperature sensor 34 and a pressure sensor 36, which detect the temperature and the pressure of the diverted in the subcooler 18 branched refrigerant downstream of the subcooler 18. From the temperature and pressure values detected by the temperature sensor 34 and the pressure sensor 36, the control unit 30 can calculate the overheating of the evaporated refrigerant.

As long as the pressure gas temperatures detected by the temperature sensors 32a, 32b at the outputs of the compressors 12, 14 are below a predetermined threshold value, the control unit 30 performs overheating control. That the second expansion valve 24 is controlled so as to maintain a desired value of the superheat of the branched refrigerant evaporated by the subcooler 18.

If by means of the temperature sensors 32a, 32b on one of the compressors 12, 14 a pressure gas temperature above the predetermined threshold value is detected, the control unit 30 switches to compressed gas temperature control and increases the flow of refrigerant through the second expansion valve 24 so as to increase the cooling of the compressors 12, 14 and thus achieve a reduction in the compressed gas temperature below the predetermined threshold.

In this case, the control unit 30 regulates the second expansion valve 24 as a function of the respectively highest pressure gas temperature detected by the temperature sensors 32a, 32b. When both compressors 12, 14 are actually operating and the pressurized gas temperature of only one of the compressors 12, 14 is above the predetermined threshold, both compressors 12, 14 are similarly cooled, i. also the respective other compressor 12, 14 undergoes a stronger cooling.

When the compressed gas temperature of the hottest compressor 12, 14 drops below a predetermined threshold again, the control unit 30 switches back to overheating control, which then takes place again on the basis of the measured values detected by the temperature sensor 34 and the pressure sensor 36.

LIST OF REFERENCE NUMBERS

10

heat pump

11

Main circuit

12

first compressor

14

second compressor

16

condenser

18

subcooler

20

first expansion valve

22

Evaporator

24

second expansion valve

26

Injection ports

28a, 28b

magnetic valve

30

control unit

32a, 32b

temperature sensor

34

temperature sensor

36

pressure sensor

Claims (9)

1. A method of operating a refrigerating machine which comprises a closed circuit (11) which has a refrigerant and in which an evaporator (22); a first compressor (12) and at least one second compressor (14) connected in parallel therewith; a condenser (16); a subcooler (18); and a first expansion valve (20) are arranged after one another,
   wherein liquid refrigerant is branched off from the circuit (11) between the condenser (16) and the subcooler (18), is expanded by means of a second expansion valve (24), is at least partly evaporated by the subcooler (18) and is supplied to the first and/or second compressor (12, 14) for cooling,
   characterized in that
   a compressed gas temperature of the or each compressor (12, 14) in operation is detected by means of a temperature sensor (32a, 32b) arranged in the region of the respective compressor outlet; and
   in that the second expansion valve (24) is regulated in dependence on the respective highest compressed gas temperature of all the compressors (12, 14) in operation when the compressed gas temperature of at least one compressor (12, 14) exceeds a predetermined threshold value.
2. A method in accordance with claim 1,
   characterized in that
   the second expansion valve (24) is regulated by means of a regulation unit (30).
3. A method in accordance with claim 1 or claim 2,
   characterized in that
   the second expansion valve (24) is regulated in dependence on an overheating of the refrigerant evaporated by the subcooler (18).
4. A method in accordance with any one of the preceding claims,
   characterized in that
   the pressure and the temperature of the branched-off refrigerant are detected after the subcooler (18) to carry out an overheating regulation of the second expansion valve (24).
5. A method in accordance with any one of the preceding claims,
   characterized in that
   the supply of the refrigerant evaporated by the subcooler (18) to the first compressor (12) is controlled by means of a first shut-off valve (28a) and the supply of the refrigerant evaporated by the subcooler (18) to the second compressor (14) is controlled by means of a second shut-off valve (28b), with the shut-off valve (28a, 28b) associated with the respective compressor (12, 14) being opened when the latter starts its operation.
6. A refrigerating machine comprising a closed circuit (11) which has a refrigerant and in which an evaporator (22); a first compressor (12) and at least one second compressor (14) connected in parallel therewith; a condenser (16); a subcooler (18); and a first expansion valve (20) are arranged after one another,
   wherein a branch path branches off from the circuit (11) between the condenser (16) and the subcooler (18), said branch path having a second expansion valve (24), being in a heat exchange relationship with the subcooler (18) and being connected to the compressors (12, 14) to expand liquid refrigerant, to evaporate it at least partly and to supply it to the first and/or second compressor (12, 14) for cooling,
   characterized in that
   a regulation unit (30) for regulating the second expansion valve (24) is connected to temperature sensors (32a, 32b) in the region of the outlets of the compressors (12, 14) and is configured to regulate the second expansion valve (24) in dependence on the respective highest compressed gas temperature of all the compressors (12, 14) in operation when the compressed gas temperature of at least one compressor (12, 14) exceeds a predetermined threshold value.
7. A refrigerating machine (10) in accordance with claim 6,
   characterized in that
   the regulation unit (30) is connected to a pressure sensor (36) and to a temperature sensor (34) which are arranged after the subcooler (18) at the branch path.
8. A refrigerating machine (10) in accordance with claim 6 or claim 7,
   characterized in that
   the regulation unit (30) is configured to regulate the second expansion valve (24) in dependence on an overheating of the refrigerant evaporated by the subcooler (18) in the branch path.
9. A refrigerating machine (10) in accordance with any one of the claims 6 to 8,
   characterized in that
   the supply of the refrigerant evaporated by the subcooler (18) to the first compressor (12) can be shut off by means of a first shut-off valve (28a) and the supply of the refrigerant evaporated by the subcooler (18) to the second compressor (14) can be shut off by means of a second shut-off valve (28b).

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