EP3918258A1

EP3918258A1 - Refrigeration device having parallel vaporisers and operating method therefor

Info

Publication number: EP3918258A1
Application number: EP20702978.6A
Authority: EP
Inventors: Lars Mack; Hans Ihle; Achim Paulduro
Original assignee: BSH Hausgeraete GmbH
Current assignee: BSH Hausgeraete GmbH
Priority date: 2019-02-01
Filing date: 2020-01-27
Publication date: 2021-12-08
Also published as: US20220099339A1; US11959682B2; CN113366269B; WO2020157010A1; CN113366269A; DE102019201291A1

Abstract

The invention relates to a refrigeration device having at least one warm storage compartment and one cold storage compartment (1, 2) and a refrigerator, in which at least two vaporisers (8, 10) that are parallel to one another are connected in series with a compressor (4), a condenser (5), and a shut-off valve (15) arranged between the condenser and the vaporisers to form a refrigerant circuit in order for each vaporiser (8, 10) to cool one of the storage compartments (1, 2). An operating method for this refrigeration device comprises the steps a) deciding whether a need for cooling has newly occurred in the warm storage compartment (1), and, if yes, b) operating the compressor (4) while the shut-off valve (15) is closed in order to cause refrigerant to back up in the condenser (5), c) opening the shut-off valve (15) and supplying the vaporiser (8) of the warm storage compartment (1) with the backed up refrigerant, characterised in that in step b) the mass flow rate through the compressor (4) is estimated and the time for carrying out the step c) is determined by means of the estimated mass flow rate.

Description

Refrigerator with parallel evaporators and operating procedures therefor

The present invention relates to a refrigerator with parallel evaporators and a method for operating such a refrigerator.

In refrigeration devices with several storage compartments for different temperatures, in which each storage compartment is assigned its own evaporator, the evaporators can be connected in series or in parallel in a refrigerant circuit. Evaporators connected in series have the disadvantage that it is only possible to selectively cool the storage compartments to a very limited extent, since the evaporators can only be supplied with refrigerant either together or not at all. Refrigerators with parallel evaporators have a more complicated structure because valves are required for a selective supply of the evaporators, which allow one or the other evaporator to be selectively cut off from the refrigerant supply.

If an evaporator is separated from the remaining refrigerant circuit by such a valve, the liquid refrigerant contained in the evaporator no longer participates in the circulation through this remaining refrigerant circuit, so that the amount of refrigerant circulating in the remaining refrigerant circuit can vary, depending on how much liquid refrigerant is just stored in the separated evaporator. However, insufficient refrigerant circuit filling leads to inefficient operation. To remedy this problem, e.g. known from EP 1106943 B1, a valve between the outlet of the

To close the condenser and the evaporators and to operate the compressor in order to pump refrigerant from the evaporator of the colder storage compartment into the condenser and thus have a sufficient amount of refrigerant available for the subsequent cooling operation of the warmer compartment.

According to EP 1106943 B1, the amount of the refrigerant to be recovered in this way should be determined as a function of the ambient temperature, in particular if the ambient temperature is low, the period in which the compressor operates when the valve is closed should be selected longer than when the valve is high. It can be achieved in this way that the amount of the refrigerant circulating when the warmer compartment is cooled is greater in the long-term time average at a low ambient temperature than at a high one; Individual case fluctuations, which result from the fact that when the need for cooling occurs in the warmer compartment, different amounts of liquid refrigerant can be contained in the evaporator of the colder compartment and, accordingly, the amounts of liquid refrigerant still contained therein after pumping can vary from case to case. cannot be prevented in this way.

It is therefore an object of the invention to provide a refrigeration device or an operating method for it, with which it can be reliably ensured that an appropriate amount of circulating refrigerant is always available for operating the warmer evaporator.

The object is achieved, on the one hand, in a method for operating a refrigeration device with at least one warm and one cold storage compartment and a refrigeration machine, in which at least two evaporators, which are parallel to one another, for cooling each of the storage compartments with a compressor, a condenser and an intermediate one the condenser valve and the evaporators are connected in series to form a refrigerant circuit, with the steps

a) Decide whether new cooling requirements have arisen in the warm storage compartment, and if so,

b) operating the compressor with the shut-off valve closed in order to accumulate refrigerant in the condenser,

c) opening the shut-off valve and charging the evaporator of the warm storage compartment with the jammed refrigerant,

in step b) the mass flow through the compressor is estimated and the point in time for carrying out step c) is determined on the basis of the estimated mass flow.

In order to prevent the amount of circulating refrigerant from becoming too large, it should in particular be avoided that if there is twice a cooling requirement in the warmer compartment without the evaporator of the colder compartment being refilled in between, the latter is pumped out again. Therefore step b) is preferably only then carried out if the storage compartment last supplied before the time of step a) is the cold storage compartment.

Since the mass flow also decreases as the evaporator of the colder compartment empties during the pumping, the amount of the refrigerant remaining in the evaporator or the accumulated in the condenser can be inferred from the latter, and the duration of the pumping can be are controlled in such a way that in each individual case, after pumping over, a quantity of circulating refrigerant suitable for operating the evaporator in the warmer compartment is available.

The mass flow can be estimated with little effort on the basis of the power consumption and / or the speed of the compressor.

It can be assumed that the mass flow is linearly proportional to the power consumption of the compressor.

To simplify matters, the mass flow can be estimated on the assumption that the temperature of the refrigerant at a suction port of the compressor

Evaporation temperature of the refrigerant in the evaporator of the cold storage compartment is. This results in the density of the refrigerant at the suction connection, and by multiplying this by the volume flow, the mass flow can be calculated.

In practice, the refrigerant absorbs ambient heat on the way from the evaporator to the suction connection. In order to enable a more realistic estimate of the mass flow rate, a temperature sensor for detecting the

Temperature of the suctioned refrigerant can be provided.

It is less expensive than a dedicated temperature sensor at the suction connection if a temperature sensor that is conventionally already present can be used for the present invention. One way to do this is to

To use the ambient temperature sensor and to assume that the temperature of the refrigerant vapor on the way from the evaporator to the compressor approaches the ambient temperature measured by the ambient temperature sensor to a fixed differential value, ie the mass flow can be estimated on the assumption that the temperature of the refrigerant at a suction connection of the compressor is below the ambient temperature by a fixed difference.

This first difference is typically 2-5 ° C, preferably about 4 ° C.

In particular, if the speed of the compressor is known, the volume throughput can be estimated from this and a known suction-side stroke volume of the compressor and the mass flow can be estimated by multiplying it by the density corresponding to the assumed temperature at the suction connection.

Analogously, it can be assumed that when the compressor is operating at a fixed speed, the temperature in the condenser is around a second fixed

Difference value is above the ambient temperature. Consequently, the mass flow can be estimated on the assumption that the pressure at a pressure connection of the

Compressor corresponds to the saturation vapor pressure of the refrigerant at the ambient temperature increased by the differential value.

In particular, with a known speed of the compressor and a known pressure-side stroke volume, the volume throughput at the pressure connection of the compressor can be calculated as the product of both and the mass flow as product of the volume throughput and the density of the refrigerant corresponding to the assumed temperature.

In order to improve the quality of an estimate of the amount of refrigerant contained in the evaporator of the colder compartment or of the compressor runtime required for pumping out the amount of refrigerant required in each case, the step can also be carried out before step b

Compartment temperature of the colder compartment are rated to be one of the normal

different refrigerant distribution, e.g. shortly after super operation, based on an excessively low compartment temperature or the opening of a door or storage of warm refrigerated goods based on an excessively high compartment temperature

consider. In general, a compartment temperature that is too low will lengthen step b), and a compartment temperature that is too high will shorten it.

As an alternative or in addition, it can also be assessed how long the last one

Specialist supply time of the colder subject took the duration of step b) adjust accordingly. This means that the longer this specialist supply time has taken, the greater the amount of liquid refrigerant to be expected in the evaporator of the colder compartment, and the longer the pumping phase of step b) takes.

In principle, a one-off, e.g. at the beginning of pumping

made estimate how long the pumping phase should last, i.e. how long to wait before performing step c).

Alternatively, the mass flow can be repeatedly estimated during the pumping and step c) can be carried out if the estimate has given a value of the mass flow below a threshold.

The object is further achieved by using a refrigeration device, in particular a

Household refrigeration device, with at least one warm and one cold storage compartment, a refrigeration machine in which at least two parallel evaporators for cooling each of the storage compartments with a compressor, a condenser and a shut-off valve arranged between the condenser and the evaporators are connected in series to form a refrigerant circuit are, and with a control unit for controlling the operation of the compressor, the control unit is set up, in particular programmed, to carry out the method described above.

The invention also relates to a computer program product with program code means which enable a computer to carry out the method described above or to function as a control unit in a refrigerator as described above.

Further features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. Show it:

1 shows a block diagram of a refrigeration device according to the invention;

2 shows a flowchart of an operating method of the refrigeration device;

3 shows a detail of the method;

4 shows a variant of the detail. Fig. 1 shows schematically a household refrigerator with at least one warm storage compartment 1 and a cold storage compartment 2, which are surrounded by a common heat-insulating housing 3. The warm storage compartment 1 can, for example, be a normal cooling compartment and the cold storage compartment 2 can be a freezer compartment. A refrigerant circuit includes one

speed-controlled, operable at various non-disappearing speeds

Compressor 4, one connected to a pressure connection of the compressor 4

Condenser 5, a valve assembly 6 with an input connected to the condenser 5 and two outputs, a first throttle point 7, typically a capillary, which is connected to a first output of the valve assembly 6, a first evaporator 8 connected to an output of the throttle point 7 Cooling the warm storage compartment 1, a second throttle point 9, which at the second output of the

Valve assembly 6 is connected, a second evaporator 10 connected to an outlet of the throttle point 9 for cooling the cold storage compartment 2

Check valve 11 at an outlet of the second evaporator 10, a T-piece 12, which connects an outlet of the first evaporator 8 with an outlet of the check valve 11, and a suction line 13, which connects an outlet of the T-piece 12 with a suction connection of the compressor 4 connects.

The valve assembly 6 supports a first state in which it connects its input to the first output, a second state in which it connects the input to the second output, and a third state in which the input and both outputs are separated. For this purpose, it can have a directional control valve 14 in series with a shut-off valve 15.

A fan 16, 17 can be provided in each of the two storage compartments 1, 2 in order to drive an air flow via the evaporator 8, 10 of the relevant compartment and thus influence the cooling capacity of the relevant evaporator 8, 10.

In order to control the operation of the compressor 4 and the valve assembly 6, one is

Control circuit 18, preferably a microprocessor or microcontroller, with

Temperature sensors 19, 20 connected, which are arranged on the storage compartments 1, 2 to detect their temperatures. The control circuit 18 can also have an ambient temperature sensor 21, a temperature sensor 19 for detecting the temperature of the evaporator 8 of the warmer compartment 1, and a current intensity sensor 23 for detecting a supply current of the compressor 4 and / or one

Speed sensor 24 to be connected to detect the speed of the compressor 4.

2 shows a flowchart of one executed by the control circuit 18

Operating procedures. The description of the method begins at a point in time when there is no cooling requirement in either of the compartments 1, 2 and the compressor 4 is therefore switched off. The valve assembly 6 is in the third state, the

Check valve 11 is closed. The temperatures of the two evaporators 8, 10 correspond approximately to those of the compartments 1, 2 cooled by them; the pressures in the evaporators 8, 10 are the vapor pressures of the refrigerant corresponding to these temperatures. A pressure equalization between the evaporators 8, 10 is by the

Check valve 11 and the valve assembly 6 prevented.

In order to recognize whether cooling demand has occurred in one of the compartments 1, 2, step S1 of comparing those measured by the temperature sensors 19, 20 is carried out

Compartment temperatures T1, T2 are repeated until one of them has a

Switch-on threshold T1ein or T2ein has risen. If the exceeded

Switch-on threshold T2 is on, i.e. if there is a need for cold in the colder compartment 2, the compressor 4 is switched on (S2). The refrigerant then sucked in by the compressor 4 originates primarily from the warmer evaporator 8 as long as it contains liquid refrigerant. The valve assembly 6 is immediately switched to the second state (S3) in order to compress and liquefy the condenser 5

Supply refrigerant to the evaporator 10. The operating state achieved in this way is maintained until the compartment temperature T2 falls below a switch-off threshold T2out (S4).

If the switch-on threshold T1 exceeded in step S1 is on, the compressor 4 is also switched on (S5), but the speed selected for the compressor 4 in this case can differ from the speed set in step S2. If the evaporator supplied in an immediately preceding operating phase of the compressor 4 was the evaporator 8, then it can be assumed that refrigerant has already been pumped out of the evaporator 10 and the quantity in circulation is sufficient for efficient operation of the evaporator 8. In this case, the method immediately jumps to step S7 described below. Otherwise, the valve assembly 6 remains in the third state, so that the pump 4 promotes Refrigerant jams in the condenser 5. Since thus no fresh refrigerant reaches the evaporator 8, the pressure in the suction line 13 decreases until the pressure in the evaporator 10 falls below, the check valve 11 opens and refrigerant from the

Evaporator 10 is suctioned off.

If a condition which is explained in more detail below is fulfilled in step S6, the control circuit 18 sets the valve assembly 6 into the first state (S7), the refrigerant that has accumulated in the condenser flows out to the first evaporator 8, and the latter starts to cool the compartment 1 . Since the temperature of compartment 1 is higher than that of compartment 2, this is also the pressure of the one flowing out of evaporator 8

Refrigerant vapor higher than the pressure in the evaporator 10. As a result, the check valve 11 closes, so that the evaporator 10 is decoupled both at its inlet and at the outlet from the rest of the refrigerant circuit and the amount of the refrigerant circulating between the compressor 4, the condenser 5 and the evaporator 8 does not change more changes.

The efficiency with which compartment 1 is cooled depends on the amount of this circulating refrigerant. If this is too low, then a large part of the refrigerant must be in the

The condenser must be concentrated so that a pressure suitable for liquefaction can be built up, and there is little refrigerant available for evaporation

Available that evaporates at low pressure and correspondingly low temperature. If it is too high, a high compressor output is required in order to maintain a suitable pressure in the evaporator 8 and to feed the refrigerant drawn off into the condenser 5, which is under high pressure. For efficient cooling operation, it is therefore important to choose the time for switching the valve assembly 6 to the first state such that, regardless of how much refrigerant is contained in the second evaporator at the time of step S5, the distribution of the refrigerant to the evaporator 10 on the one hand and on the remaining refrigerant circuit on the other hand at step S7 is essentially the same each time the method is repeated.

This is achieved in step S6 by estimating the mass flow of the refrigerant drawn off from the evaporator 10. This mass flow is greater, the greater the amount of refrigerant currently contained in the evaporator 10; simplifying it can be assumed that the amount of vapor drawn off per unit of time is directly proportional to the amount of liquid refrigerant in the evaporator 10. The mass flow also corresponds to the volume flow rate of the compressor 4 on the suction side, multiplied by the density of the drawn-in refrigerant. The former is the product of the constant and known stroke volume of the compressor 4 and that of that

Speed sensor measured speed, the latter can be derived from the temperature of the evaporator 10 detected by the temperature sensor 22 using the vapor pressure curve of the refrigerant. I.e. the control circuit 18 measures that as shown in FIG

Evaporator temperature (S31), determines the pressure p in the evaporator 10 (S32) and multiplies this by the volume flow rate Q of the compressor 4 (S33) in order to obtain the mass flow m. As soon as this mass flow falls below a predetermined limit value in the course of repeated measurements of the rotational speed and the evaporator temperature (S34), the condition of step S6 is fulfilled and the control unit switches the valve assembly 6 into the first state.

A problem with this estimation of the mass flow can arise from the fact that the refrigerant is pumped out of the evaporator 10

Evaporation temperature of the refrigerant in the evaporator 10 decreases, but the measured evaporator temperature follows this actual evaporation temperature only with a delay. On the other hand, it can be assumed that both temperatures still correspond to one another when the compressor 4 is started up. This fact can be exploited in that, according to a variant shown in FIG. 4, the mass flow m only immediately after the start of the compressor 4 on the basis of its stationary speed n reached shortly after the start and the temperature T20 of the compartment 2 or T22 measured at this time of the evaporator 10 is estimated (S41). Since the mass flow m, as stated above, can be assumed to be proportional to the mass m of the refrigerant contained in the evaporator 10, knowledge of the mass flow m is sufficient to estimate the mass m still contained in the evaporator 10 itself and subsequently an operating time At of the compressor 4 (S42) required to reduce this mass m to a predetermined value. As soon as this operating time At has passed (S43), the valve arrangement is set to the first state in step S7. io

According to a further development, it can be useful to take into account a temperature detected in the storage compartment 2 by the sensor 22. If this is below the switch-off threshold, this suggests that the super operation was just recently and therefore a relatively large amount of liquid refrigerant in the evaporator 10, so that in this case the

Operating time At is estimated higher in step S42 than if a compartment temperature between the switch-on and switch-off value is measured. Conversely, a compartment temperature above the switch-on value can indicate that a large amount of fresh, warm refrigerated goods have been loaded into the compartment 2 shortly before and the liquid refrigerant of the evaporator 10 is therefore largely used up; in this case, the operating time At is estimated in step S42 to be lower than at a normal compartment temperature between the switch-on and switch-off values.

According to a further development, it can be taken into account that the temperature at which the refrigerant reaches the compressor 4 is no longer the evaporator temperature, but rather approaches the ambient temperature on the way through the suction line 12. Unless a temperature sensor is provided directly at the suction connection of the compressor 4 in order to measure the temperature of the refrigerant arriving there, it can be assumed in a simplified manner that this temperature is around a constant value of e.g. 4-5 ° C lower than the ambient temperature measured by sensor 21. The mass flow is thus estimated in that the volume throughput of the compressor 4 is not multiplied by the density at the evaporator temperature as described above, but by the density at the measured or estimated temperature at the suction port of the compressor 4.

Another variation suggests that the temperature of the

Condenser 5 during the operation of the compressor 4 by a constant value in the range 10-20 ° C, e.g. approx. 15 ° C, is higher than the ambient temperature. This enables the control circuit 18 to derive the pressure both at the suction and at the pressure connection of the compressor 4 from the measured value of the ambient temperature. The mechanical power (isentropic power) provided by the compressor 4 for compressing the refrigerant is proportional to the product of the pressure difference and

Volume flow. At the same time, it is a design-dependent fixed percentage

(typically about 70%) of the electrical power consumed by the compressor. This means that the mass flow is a product of volume flow and density is proportional to the electrical power of the compressor 4, and that a limit value of the mass flow is undershot when the electrical power of the compressor 4 falls below a limit value. Since the supply voltage can be assumed to be constant, it is sufficient in this case that the control circuit

The supply current of the compressor 4 is monitored and step S6 is carried out as soon as it falls below a limit value which depends on the ambient temperature.

The relationship between the limit value of the electrical power and the ambient temperature can be determined empirically and stored in a memory

Control circuit 18 can be stored.

REFERENCES

1 (warm) storage compartment

2 (cold) storage compartment

3 housing

4 compressors

5 condensers

6 valve assembly

7 (first) throttle point

8 (first) evaporator

9 (second) throttle point

10 (second) evaporators

11 check valve

12 T piece

13 suction line

14 way valve

15 shut-off valve

16 fan

17 fan

18 control circuit

19 temperature sensor

20 temperature sensor

21 temperature sensor

22 temperature sensor

23 current sensor

24 speed sensor

Claims

PATENT CLAIMS

1. A method for operating a refrigeration device with at least one warm and one cold storage compartment (1, 2) and a refrigeration machine, in which at least two mutually parallel evaporators (8, 10) for cooling each of the storage compartments (1, 2) with one Compressor (4) .A condenser (5) and a shut-off valve (15) arranged between the condenser and the evaporators are connected in series to form a refrigerant circuit, with the steps

a) Decide whether cooling needs have arisen in the warm storage compartment (1), and if so,

b) operating the compressor (4) with the shut-off valve (15) closed in order to accumulate refrigerant in the condenser (5),

c) opening the shut-off valve (15) and charging the evaporator (8) of the warm storage compartment (1) with the jammed refrigerant,

characterized in that

in step b) the mass flow through the compressor (4) is estimated and the time for carrying out step c) is based on the estimated

Mass flow is set.

2. The method according to claim 1, characterized in that step b) is carried out only if the storage compartment last supplied before the time of step a) is the cold storage compartment (2).

3. The method according to claim 1 or 2, characterized in that the

Mass flow is estimated based on the power consumption of the compressor (4).

4. The method according to claim 3, characterized in that the mass flow

linearly proportional to the power consumption of the compressor (4) is estimated.

5. The method according to any one of the preceding claims, characterized in that the mass flow is estimated on the basis of the speed of the compressor (4).

6. The method according to any one of claims 1 to 5, characterized in that the mass flow is estimated on the assumption that the temperature of the refrigerant at a suction port of the compressor (4)

Evaporation temperature of the refrigerant in the evaporator (10) of the cold storage compartment (2).

7. The method according to any one of claims 1 to 5, characterized in that an ambient temperature is measured and the mass flow is estimated on the assumption that the temperature of the refrigerant at a suction port of the compressor (4) by a fixed difference below

Ambient temperature.

8. The method according to any one of the preceding claims, characterized in that an ambient temperature is measured and the mass flow is estimated on the assumption that the pressure at a pressure connection of the compressor (4) corresponds to the saturation vapor pressure of the refrigerant at the ambient temperature increased by a fixed differential value.

9. The method according to any one of claims 6 to 8, characterized in that the temperature of the refrigerant at the pressure port of the compressor (4) is derived from the temperature of the refrigerant at the suction port of the compressor assuming an isentropic change in state in the compressor.

10. The method according to any one of claims 1 to 9, characterized in that based on an estimate of the mass flow a waiting time until

Implementation of step c) is determined.

11. The method according to any one of claims 1 to 9, characterized in that the mass flow is repeatedly estimated in the course of an operating phase of the compressor (4) and step c) is carried out when the estimate has given a value of the mass flow below a threshold.

12. Refrigeration device, in particular household refrigeration device, with at least one warm and one cold storage compartment (1, 2), a refrigeration machine in which at least two evaporators (8, 10) which are parallel to one another for cooling each of the Storage compartments (1, 2) with a compressor (4), a condenser (5) and a shut-off valve (15) arranged between the condenser and the evaporators are connected in series to form a refrigerant circuit, and with a control unit (18) for controlling the operation of the compressor (4), characterized in that the control unit (18) is set up, in particular programmed, in order to carry out the method according to one of claims 1 to 10.

13. Computer program product with program code means that enable a computer to carry out the method according to one of claims 1 to 11 or to work as a control unit (18) in a refrigerator according to claim 12.