Refrigeration unit

Abstract

Refrigeration appliance, in particular a household refrigeration appliance, with a condenser (4), at least one first evaporator (7) cooling a first storage compartment (23), a throttle point (6) connecting an outlet of the condenser (4) to an inlet of the first evaporator (7), a collecting container (8, 30) for liquid refrigerant overflowing from the first evaporator (7), which is connected to an outlet of the first evaporator (7) and is arranged in a warmer environment than the environment of the first evaporator (7), wherein a temperature sensor (20) is assigned to the collecting container (8, 30) and the throttle point (6) comprises a controllable expansion valve (14) which is controlled based on the temperature detected by the temperature sensor (20), characterized in that the controllable expansion valve (14) is designed to control small mass flows and a capillary (15) is connected upstream of the controllable expansion valve (14).

Description

[0001] The present invention relates to a refrigeration appliance, in particular a household refrigeration appliance such as a refrigerator or freezer or a combination appliance with several storage compartments maintained at different operating temperatures.

[0002] In addition to energy efficiency, low or unobtrusive operating noise is a key quality feature of household refrigeration appliances. A key cause of operating noise is the circulation of the refrigerant within such an appliance. While the compressor and, if present, fans in a refrigeration appliance are not silent, they can be controlled and operated at a constant speed, so that the noise they generate is barely noticeable due to its uniformity.

[0003] For cost reasons, household refrigeration appliances typically use a capillary tube as a throttling point for expanding the refrigerant. The capillary tube cannot be actively controlled; its mass flow is high as long as high-density liquid refrigerant is present at the capillary inlet. Once this has flowed out through the capillary, refrigerant vapor penetrates the capillary. Due to the low density of the vapor, this leads to a reduction in the mass flow, so that refrigerant condenses again in front of the capillary. On the other hand, the vapor flows through the capillary at a higher speed than the liquid refrigerant, and the resulting velocity fluctuations lead to clearly perceptible fluctuations in operating noise.

[0004] Thermostatic expansion valves, which allow active control of the mass flow, are common in commercial refrigeration systems. These are typically located downstream of a receiver large enough to allow clean separation of vapor and liquid and to supply the expansion valve exclusively with liquid refrigerant, as long as the receiver contains a sufficient amount. To ensure this, the mass flow through the expansion valve is controlled using a pressure sensor. By keeping gaseous refrigerant away from the expansion valve, efficiency losses can be avoided. These losses would occur if vapor were compressed using energy and then allowed to expand again in the expansion valve without the energy being utilized.

[0005] Installing a pressure sensor is complex, as the pressure sensor must communicate directly with the refrigerant being measured and be suitably sealed. This, combined with the cost of the existing controllable expansion valves and the fact that expansion valves suitable for the small mass flows to be controlled in household refrigeration appliances were scarce, has long hindered their use in household refrigeration appliances. Only in recent years have household refrigeration appliances been developed that use controllable expansion valves.

[0006] DE 10 2015 215 491 A1 discloses a household refrigeration appliance in which a controllable expansion valve is connected in series between two evaporators. This allows the pressure difference between the evaporators to be varied, thus variably adjusting the operating temperatures of the storage compartments cooled by the evaporators. Since refrigerant evaporated in the upstream evaporator can only flow through the expansion valve, liquid and vapor refrigerant must alternate in the expansion valve, and quiet operation is not possible.

[0007] The object of the present invention is to create a highly efficient and yet cost-effective refrigeration appliance, in particular a household refrigeration appliance.

[0008] The object is achieved in that, in a refrigeration device, in particular a household refrigeration device, with a condenser, at least one first evaporator cooling a first storage compartment, a throttle point which connects an outlet of the condenser to an inlet of the first evaporator, a collecting container for liquid refrigerant overflowing from the first evaporator, which is connected to an outlet of the first evaporator and is arranged in a warmer environment than the environment of the first evaporator, a temperature sensor is assigned to the collecting container and the throttle point comprises a controllable expansion valve which is controlled on the basis of the temperature detected by the temperature sensor.

[0009] The collection tank creates a buffer whose filling level with liquid refrigerant can be estimated based on the measured temperature. By controlling the mass flow through the expansion valve based on this temperature, it can be ensured that there is always enough liquid refrigerant available upstream of the throttle point when the compressor is running to keep vapor away from the expansion valve. At the same time, it is possible to completely flood the first evaporator with liquid refrigerant and thus provide a high cooling capacity, which is required, for example, to quickly cool freshly loaded refrigerated goods. By installing the collection tank in a warmer environment than the first evaporator, it can be ensured that liquid refrigerant that overflows from the first evaporator into the collection tank does not collect there, but rather evaporates quickly.

[0010] In order to ensure different ambient temperatures for the first evaporator and the collection container, the collection container can be separated from the first storage compartment by a thermal insulation layer.

[0011] To enable precise control of small mass flows through the expansion valve, it can be helpful to connect the expansion valve in series with a capillary so that part of the pressure difference between the condenser and the first evaporator drops at the capillary and the rest at the expansion valve.

[0012] In order to avoid evaporation starting in the capillary shortly before its downstream end and noises being generated by the alternating vapor and liquid refrigerant at the capillary outlet, the capillary should be located upstream of the expansion valve and the pressure difference across it should be small enough to prevent evaporation of refrigerant before reaching the expansion valve.

[0013] Typically, the capillary should be sized to have a smaller pressure drop than the controllable expansion valve.

[0014] A vapor separator can be installed upstream of the controllable expansion valve (and, if applicable, the capillary).

[0015] The vapor separator separates not only refrigerant vapor but also non-condensable residual gas that remains in the refrigerant circuit cavities during assembly from the liquid refrigerant. By dimensioning the vapor separator sufficiently, a larger amount of residual gas can be neutralized than is currently typically left behind during the evacuation of the refrigerant circuit. The additional effort associated with installing the vapor separator can therefore be at least partially offset by shortening the evacuation time.

[0016] In the simplest case, the vapor separator is a widened portion or chamber with a cross-section large enough to allow the flow of refrigerant to slow sufficiently to allow vapor bubbles to rise from the liquid refrigerant. Such a separation chamber preferably has a maximum horizontal cross-sectional dimension of at least 8 mm between an upper inlet and a lower outlet, or a maximum horizontal cross-sectional area of ​​at least 0.5 cm. 2The separation chamber can contain internals that prevent swirling in the liquid refrigerant, such as partition walls or a bed of particles. The effectiveness of the vapor separator can also be based on a large volume and a correspondingly long residence time of the refrigerant, which gives the phases time to separate from one another. This capacity should preferably be sufficient to provide space for at least half of the total refrigerant in the liquid state in the refrigeration unit. To ensure bubble-free discharge of the refrigerant even at increased compressor capacity, for example during rapid cooling operation, the capacity of the vapor separator can be designed for up to 90% of the quantity of refrigerant in the liquid state. The vapor separator and the first evaporator can be designed together to provide space for the entire refrigerant in the liquid state.

[0017] The condenser outlet should be connected to the throttle point without the need for an additional evaporator.

[0018] According to a particularly preferred embodiment, the collecting container is a second evaporator. This can be of the same design as the first evaporator, e.g., a roll-bond, ToS, or finned evaporator.

[0019] The second evaporator is conveniently used to cool a second storage compartment.

[0020] Since the second evaporator only receives liquid refrigerant when the first overflows, the operating temperature of the second storage compartment should be higher than that of the first.

[0021] The evaporators can be arranged in direct thermal contact with the storage compartments cooled by them, ie the above-mentioned environments of the first evaporator and the collecting container or second evaporator can be these storage compartments themselves.

[0022] A compartment temperature sensor in the second storage compartment can then serve as the aforementioned temperature sensor controlling the expansion valve. This avoids the costs associated with installing an additional sensor.

[0023] To avoid unnecessarily restricting the space available for the evaporator(s), the controllable expansion valve can be housed in a partition wall between the storage compartments. This leaves one of the storage compartments completely accessible for mounting one of the evaporators.

[0024] The aforementioned thermal insulation layer can be part of the partition wall. Since the expansion valve cools down during operation, in this case, a recess in the thermal insulation layer that accommodates the expansion valve should be open at least toward the cooler compartment, i.e., generally the first storage compartment.

[0025] To reliably prevent overflow of the recovery tank or second evaporator, its capacity should be large enough to accommodate at least half of the refrigerant in liquid form. This may not be sufficient for the entire refrigerant, as liquid refrigerant generally only reaches the recovery tank once the first evaporator is full.

[0026] A control circuit should be configured to set a high mass flow through the controllable expansion valve when the detected temperature is high and a low mass flow when the detected temperature is low.

[0027] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. They show: Fig. 1 a block diagram of a refrigeration device according to a first embodiment; Fig. 2 a schematic section through the refrigeration device Fig. 1; Fig. 3 is a block diagram of a refrigeration device according to a second embodiment of the invention; and Fig. 4 a schematic section through the refrigeration device Fig. 3.

[0028] Fig. Figure 1 illustrates the principle of the invention using a block diagram that essentially shows components of a refrigerant circuit of a household refrigeration appliance. The refrigerant circuit comprises, in a conventional manner, a compressor 1, from whose pressure connection 2 a pressure line 3 extends via a condenser 4 and a receiver 5 or dryer to a throttling point 6. In a low-pressure section of the refrigerant circuit adjoining the throttling point 6, an evaporator 7 and an evaporator 8 follow one another. A suction pipe 9 extending from the evaporator 8 carries the refrigerant back to a suction connection 10 of the compressor 1.

[0029] At the collector 5, the pressure line 3 is locally widened to form a chamber 11 acting as a vapor separator, with an inlet 12 at the top and an outlet 13 at the bottom. A mixture of liquid refrigerant and vapor from the condenser 4 enters the collector 5 via the inlet 12. Since the free cross-section of the collector 5 is larger than that of the pressure line 3 before and after it, the flow velocity of the refrigerant is reduced in the collector, and both phases of the refrigerant have the opportunity to separate from each other. To ensure that this can occur without being hindered by capillary effects, the free cross-section of the collector 5 should, at least locally, have an area of ​​at least 0.5 cm 2or the diameter must reach a value of at least 8 mm. A sufficient residence time of the refrigerant for phase separation is achieved by a large volume of the chamber; this is preferably dimensioned to accommodate at least half of the total refrigerant present in the device in liquid state, ie with a refrigerant filling quantity of e.g. 50 or 100 g and a density of 0.5 g / cm 3 The capacity of the chamber should be at least 50 or 100 cm 3 In order to prevent the liquid refrigerant in the collector from being subjected to a swirling motion when the refrigerant flows out via the outlet 13, thereby preventing vapor bubbles from reaching the outlet 13, a bed of granulate, in particular of a drying material that binds residual water in the refrigerant, can also be accommodated in a region of the collector 5 near the outlet.

[0030] The throttle point 6 comprises at least one controllable expansion valve 14. In Fig. 1, a capillary 15 is also provided between the collector 5 and the expansion valve 14. The capillary 15 is dimensioned to generate only the smaller part of the pressure drop between the condenser 4 and the evaporator 7, the larger part being generated at the controllable expansion valve 14. In particular, the nitrogen flow through the capillary can be 500-800 l / h at a pressure drop of 6 bar. The series connection with the capillary 15 enables the expansion valve 14 to precisely control smaller mass flows for a given pressure difference than if the expansion valve were exposed to the pressure of the refrigerant alone. Furthermore, since the capillary 15 is arranged upstream of the expansion valve 14, the pressure in the capillary 15 is high enough along its entire length to prevent evaporation of refrigerant in the capillary 15.Since the capillary is thus not cooled by internal evaporation, residual heat of the liquid refrigerant can be efficiently transferred to the vapor flowing back to the compressor 1 in an internal heat exchanger 16, in which the capillary 15 runs in close contact with the suction pipe 9.

[0031] The evaporator 8 is connected to the evaporator 7 in such a way that liquid refrigerant only enters the evaporator 8 when the evaporator 7 is full. For this purpose, the evaporator 7 can, for example, be equipped with a refrigerant pipe 17 that continuously rises from an inlet 18 to an outlet 19 of the evaporator 7, so that vapor generated in the evaporator 7 flows toward the outlet 19, but liquid refrigerant can flow past the rising vapor toward the inlet 18.

[0032] A temperature sensor 20 can be attached to the evaporator 8; preferably, it is arranged without direct contact with the evaporator 8 in a storage compartment 21 cooled by the latter (see Fig. 2), typically mounted in a normal refrigeration compartment of the refrigeration appliance, to measure the temperature of the storage compartment 21. This indicates, with a delay and averaged over time, the amount of liquid refrigerant entering the evaporator 8.

[0033] A control circuit 22 is connected to the temperature sensor 20 and the expansion valve 14 in order to control the latter based on measured values ​​from the temperature sensor 20. It can also be connected to the compressor 1 in order to also control its speed based on these measured values ​​and, if applicable, a temperature in a storage compartment 23 cooled by the evaporator 7 (see Fig. 2) to control the measured temperature.

[0034] If the temperature detected by the temperature sensor 20 while the compressor 1 is running exceeds a setpoint, the expansion valve 14 is opened further. This occurs gradually, i.e., as long as the setpoint is exceeded, the control circuit 22 increases the degree of opening of the expansion valve 14 continuously or in regular small steps to ensure that the increase in the degree of opening does not lead to the collector 5 temporarily drying out and the entry of vapor into the throttle point 6. The likelihood of this happening is further reduced by the large volume of the collector 5 and the fact that if the setpoint is exceeded, it can be expected that the evaporator 8 will contain little to no liquid refrigerant and accordingly a large amount must be stored in the collector 5.The increasing supply of liquid refrigerant to the evaporator 7 due to the increase in the degree of opening eventually causes the evaporator 8 to overflow, and refrigerant penetrating into the evaporator 8 leads to a decrease in the temperature detected by the temperature sensor 20, so that the setpoint is reached or undershot and the control circuit 22 no longer increases the degree of opening of the expansion valve 14.

[0035] Conversely, as long as the temperature detected by temperature sensor 20 while compressor 1 is running is below a second setpoint, which may be identical to or lower than the aforementioned setpoint, the degree of opening of expansion valve 14 is gradually reduced. This reduces the amount of liquid refrigerant reaching evaporator 8, and the temperature of storage compartment 21 detected by temperature sensor 20 gradually increases. The cooling capacity available at evaporator 7 does not change as long as liquid refrigerant still reaches evaporator 8. Only when this no longer happens and evaporator 7 is only partially filled with liquid refrigerant does its cooling capacity decrease.

[0036] In order to adapt the latter to the respective demand, it can be provided that the control circuit 22 further controls the speed of the evaporator 1 based on the cooling requirement of the storage compartment 23. If the measured temperature in the latter exceeds a setpoint, the speed of the compressor 1 is gradually increased. If the opening degree of the expansion valve 14 is not changed at the same time, this leads to increased evaporation in the evaporator 8 and a corresponding increase in the amount of liquid refrigerant in the receiver 5. The increased evaporation causes the temperature in the storage compartment 23 to drop, which, according to the principles explained in the previous paragraph, leads to the opening degree of the expansion valve 14 being reduced, less liquid refrigerant reaching the evaporator 8, and the additional cooling capacity remaining essentially concentrated on the evaporator 7. Conversely, if the temperature falls below the setpoint, the speed can be reduced.

[0037] Fig. 2 shows a schematic cross section through a body 24 of the refrigeration device of Fig. 1. The cooler storage compartment 23 is located below the warmer one 21 and separated from the latter by a partition wall 25. Like the rest of the body 24, the partition wall 25 is designed as a hollow body with outer walls 26, the interior of which is foamed with an insulating material 27. The suction pipe 9 runs downward in a rear wall of the body 24 along both storage compartments 23, 21; along part of its length, the capillary 15 runs inside it or in contact with its outer wall to form the internal heat exchanger 16.

[0038] A recess 28 in the layer of insulating material 27 is provided to accommodate the expansion valve 14. Since the latter cools during operation, the recess 28 is open toward the storage compartment 23 to allow heat to flow from there to the expansion valve 14. The recess can be closed by a cover 29 with low heat insulation, which is removable to allow for repairs to the expansion valve 14 if necessary.

[0039] Fig. 3 shows a second embodiment of the refrigeration device in a Fig. 1 analog representation. Components of the refrigerant circuit that are similar to those already described above are given the same reference numerals and will not be described again. The second evaporator 8 is replaced here by a collecting container 30, which does not necessarily cool a storage compartment. Instead, the collecting container 30 can be arranged in an evaporator chamber 31 of a no-frost refrigeration device upstream of the evaporator 7 with respect to the direction of circulation of an air flow circulating between the evaporator chamber 31 and the storage compartment 21 or 23, as shown by way of example in Fig. 4 shown.

[0040] The Fig.Figure 4 shows a section through a partition wall 32 of a no-frost refrigeration appliance. The evaporator chamber 31 is separated from the cold storage compartment 23 below by a thin partition wall 33 and from the warmer storage compartment 21 above by a wall filled with insulating material 27. A fan 34 is arranged in a conventional manner downstream of the evaporator 7, which is designed as a finned evaporator, to draw air from each of the compartments 21, 23 via an inlet 35. The compartment from which the air is drawn is determined by the position of a flap 36. Regardless of the position of the flap 36, the drawn-in air upstream of the evaporator 7 is always warmer than downstream of it. By mounting the collection vessel 30 in the evaporator chamber 31 upstream of the evaporator 7, it is located in a warmer environment than the latter, and refrigerant that overflows from the evaporator 7 into the collection vessel 30 can still evaporate therein.By ensuring that the combined capacity of the evaporator 7 and the collecting tank 30 is sufficient to hold all of the refrigerant present in the refrigerant circuit in liquid form, overflow of the collecting tank 30 into the suction pipe 9 can be prevented. REFERENCE SYMBOL 1 compressor 2 pressure connection 3 pressure line 4 condensers 5 collectors 6 throttle point 7 evaporators 8 evaporators 9 intake manifold 10 Suction connection 11 Chamber 12 Entrance 13 Outlet 14 Expansion valve 15 capillaries 16 heat exchangers 17 Refrigerant pipe 18 Entrance 19 Outlet 20 Temperature sensor 21 storage compartment 22 Control circuit 23 storage compartment 24 Corpus 25 Partition wall 26 Exterior wall 27 Insulation material 28 recess 29 lids 30 collection containers 31 Evaporator chamber 32 Partition wall 33 Partition wall 34 Fan 35 Entrance 36 flap

Claims

[1] Refrigeration appliance, in particular a household refrigeration appliance, comprising a condenser (4), at least one first evaporator (7) cooling a first storage compartment (23), a throttle point (6) connecting an outlet of the condenser (4) to an inlet of the first evaporator (7), a collecting container (8, 30) for liquid refrigerant overflowing from the first evaporator (7), which container is connected to an outlet of the first evaporator (7) and is arranged in a warmer environment than the environment of the first evaporator (7), wherein the collecting container (8, 30) is assigned a temperature sensor (20) and the throttle point (6) comprises a controllable expansion valve (14) which is controlled on the basis of the temperature detected by the temperature sensor (20), characterized by that the controllable expansion valve (14) is designed to control small mass flows and a capillary (15) is connected upstream of the controllable expansion valve (14). [2] Refrigeration device according to claim 1, characterized by that the collecting container (8) is separated from the first storage compartment (23) by a layer of insulating material (27). [3] Refrigeration appliance according to claim 1 or 2, characterized by that the refrigeration device has an internal heat exchanger (16) in which the capillary (15) runs in close contact with the suction pipe (9). [4] Refrigerating appliance according to claim 1, 2 or 3, characterized by that the capillary (15) is dimensioned to have a smaller pressure drop than the controllable expansion valve (14). [5] Refrigeration device according to one of the preceding claims, characterized by that a steam separator (5) is connected upstream of the controllable expansion valve (14). [6] Refrigeration device according to claim 5, characterized bythat the steam separator (5) has a separation chamber (11) with an upper inlet (12), a lower outlet (13) and a horizontal cross-sectional dimension which between inlet and outlet (12, 13) at least locally exceeds 8 mm, and / or a horizontal cross-sectional area which between inlet and outlet (12, 13) at least locally exceeds 0.5 cm 2 and / or has a capacity sufficient to accommodate at least half, preferably 90%, of the refrigerant in liquid state. [7] Refrigeration device according to one of the preceding claims, characterized by that the outlet of the condenser (4) is connected to the throttle point (6) without the interposition of another evaporator. [8] Refrigeration device according to one of the preceding claims, characterized by that the collecting container (8) is a second evaporator (8). [9] Refrigeration device according to claim 8, characterized bya second storage compartment (21) cooled by the second evaporator (8). [10] Refrigeration device according to claim 9, characterized by that the operating temperature of the second storage compartment is higher (21) than that of the first storage compartment (23). [11] Refrigeration appliance according to claim 9 or 10, characterized by that the temperature sensor (20) is a compartment temperature sensor of the second storage compartment (21). [12] Refrigerating appliance according to claim 9, 10 or 11, characterized by that the controllable expansion valve (14) is accommodated in an intermediate wall (25) between the storage compartments (21, 23). [13] Refrigeration device according to claim 12, characterized by that the intermediate wall (25) contains a thermal insulation layer (27) and the expansion valve (14) is accommodated in a recess (28) of the thermal insulation layer (27) which is open towards the first storage compartment (23). [14] Refrigeration device according to one of the preceding claims, characterized bythat the capacity of the collecting container (8, 30) is dimensioned to accommodate at least half of the refrigerant in liquid state. [15] Refrigeration device according to one of the preceding claims, characterized by in that a control circuit (22) is arranged to set a high mass flow through the controllable expansion valve (14) at a high detected temperature and a low mass flow at a low detected temperature.

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