Patent Application
20190024956
The present invention relates to a single-circuit refrigerator with two temperature zones, which are cooled by evaporators connected in series one after the other in a refrigerant circuit.
If the two evaporators are connected in the refrigerant circuit without appreciable flow resistance between them, approximately equal pressures and evaporation temperatures corresponding in each case to these pressures occur in both. These evaporation temperatures must be lower than the temperature of the respective coldest temperature zone. The difference in temperature between the evaporators and the warmer of the two temperature zones is correspondingly great.
A single-circuit refrigerator is known from DE 10 2013 223 737 AI, wherein a throttle section, which ensures different pressures and consequently also different evaporation temperatures in the two evaporators, is inserted between first and second evaporators in a refrigerant circuit. By controlling the evaporation temperatures the cooling performance can be distributed according to the refrigeration requirement over both evaporators, and the compressor can run continuously. Stop-start losses and unnecessary temperature fluctuations can thus be avoided, thereby improving the energy efficiency of the refrigeration.
A generally widespread measure for improving the energy efficiency of a refrigerator is to connect a capillary, which extends from the condenser to the evaporator, and an intake line, which leads from the outlet of the evaporator to the compressor, to a heat exchanger, so that the refrigerant flowing in the capillary to the evaporator is cooled, and the refrigerant vapor extracted from the evaporator is heated up.
If a heat exchanger such as the one in the refrigerator known from DE 10 2013 223 737 AI is provided in the refrigerator, the refrigerant vapor has the temperature of the second, colder evaporator upon entering the heat exchanger, with the result that the refrigerant from the capillary, upon entering the first evaporator, may have a temperature below the evaporation temperature of the first evaporator. If this is the case, then any evaporation of refrigerant in the capillary before it reaches the first heat exchanger is precluded. Without the delaying effect of vapor bubbles, the mass throughput of the capillary is higher than that of the compressor, with the result that liquid refrigerant accumulated in front of the capillary drains off faster than it can be reproduced in the condenser. If it has drained off and only refrigerant vapor can still flow from the condenser into the capillary, the mass throughput thereof decreases greatly, and the pressure in the condenser rises so that more liquid refrigerant is reproduced and at once flows through the capillary again with high mass throughput. The constant alternation between liquid refrigerant and vapor or between high and low mass throughput in the capillary results in annoying operating noises.
Even though excessive cooling of the refrigerant at the outlet of the capillary can easily be prevented if the heat exchanger were shortened or otherwise less efficiently constructed, this would, however, result in a loss of energy efficiency.
The object of the invention is to create a single-circuit refrigerator with evaporators that can operate at different pressures, in which the noise emission is reduced without negatively affecting energy efficiency.
The object is achieved wherein, in a single-circuit refrigerator with a refrigerant circuit, in which the following are connected in series one after the other between a pressure port and an intake port of a compressor:
a downstream section of the intake line is connected with the first throttle section to a first heat exchanger, and an upstream section of the intake line is connected with the second throttle section to a second heat exchanger. Therefore, when the refrigerant vapor in the intake line reaches the downstream section thereof, it has already been preheated by the second heat exchanger to a temperature that is at most slightly below the evaporation temperature in the first evaporator. Any cooling of the refrigerant in the first throttle section to a temperature below the evaporation temperature of the first evaporator can thus be precluded. A partial evaporation of the refrigerant therefore remains possible in the first throttle section, and if the vapor produced in the first throttle section constantly limits its mass throughput, noise-intensive fluctuations such as described above can be prevented.
In order to form the second heat exchanger, the second throttle section can comprise a line section, which is connected with the upstream section of the intake line by an adhesive, in particular by an adhesive tape.
Consequently, in an alternative embodiment, the second throttle section may comprise a line section, which is run inside the upstream section of the intake line.
Consequently, in a yet further alternative, the second throttle section comprises a line section, which is coiled around the upstream section of the intake line.
To achieve an efficient transfer of heat in the second heat exchanger, it is helpful if the lines to be formed in the heat exchanger are narrow in diameter. In particular, the line section of the second throttle section may be designed as a capillary.
Furthermore, it is expedient if the second throttle section has an adjustable conductance, by which variable pressure differences and therefore also variable temperature conditions can be set between first and second evaporator.
In particular, the second throttle section may comprise a controllable expansion valve for adjusting the conductance.
The expansion valve may essentially be solely responsible for the drop in pressure between first and second evaporator; however, it may also be connected in series with a capillary, so that the drop in pressure comprises a fixed amount from the capillary and a variable amount from the expansion valve.
Further features and advantages of the invention will emerge from the description which follows of exemplary embodiments, with reference to the attached diagrams. In these:
The refrigerant circuit shown in
As can be seen more clearly in the schematic section in
With reference again to
The line section 18 designed as a capillary is preferably long enough to ensure a drop in pressure between the evaporators 8, 10, which corresponds to a difference in the evaporation temperatures of the evaporators 8, 10 of several ° C., even if the expansion valve 22 is fully open. Therefore, within the adjustment range of the expansion valve 22, it is possible for the difference in pressure between the evaporators 8, 10 to be controlled more precisely than if this difference in pressure had to be maintained by the expansion valve 22 alone.
An upstream section 12 of the intake line 11 is thermally bonded with the second throttle section 9 to form a heat exchanger 14; a downstream section 13 of the intake line 11 forms a further heat exchanger 15 together with the first throttle section 6.
A temperature sensor 19 or 20 is disposed on each of the compartments 16, 17. The temperature sensors 19, 20 are connected to a control unit 21, which controls the rotation speed of the compressor 1 and the degree of opening of the expansion valve 22 by comparing the temperatures reported by the temperature sensors 19, 20 with target temperatures for the compartments 16, 17 that are set by a user. If, for example, the temperature sensor 19 indicates a cooling requirement in the normal cooling compartment 16, i.e. if the temperature in the normal cooling compartment 16 is at the upper end of a tolerance interval around the target temperature set by the user, then the control unit 21 checks the temperature of the freezer compartment 17. If this is in the upper section of a tolerance interval around the set target value of the latter, the control unit 21 increments the rotation speed of the compressor 1 so that both compartments 16, 17 are cooled more intensively; if, on the other hand, the temperature of the freezer compartment 17 is in the lower section of the tolerance interval, so that more intensive cooling would result in the tolerance interval being exceeded at the lower end, then the control unit increments the degree of opening of the second throttle section 9, so that the pressure in the evaporator 8 is reduced. The overall cooling performance remains essentially unchanged as a result, but the share of overall cooling performance increases in relation to the normal cooling compartment 16, so that it can be cooled without at the same time causing excessive cooling in the freezer compartment 17.
Accordingly, if the temperature in the freezer compartment 17 reaches the upper end of the tolerance range, the control unit 21 determines, on the basis of the temperature of the normal cooling compartment 16, whether the rotation speed of the compressor 1 is incremented in order to cool both compartments 16, 17 more intensively, or whether the degree of opening of the second throttle section 9 is reduced in order to increase the share of overall cooling performance relating to the freezer compartment.
If the temperature of the normal cooling compartment 16 reaches the lower end of the tolerance range, on the basis of the freezer compartment temperature it is determined whether the rotation speed of the compressor 1 decrements or the degree of opening of the second throttle section 9 is decremented, and in the event that the freezer compartment reaches the lower end of the tolerance range, a decision must be made between decrementing the compressor rotation speed and incrementing the degree of opening of the second throttle section 9.
A control unit equivalent to the one described above for the compressor 1 and the expansion valve 22 can also be implemented by means of a PID module.
The series connection of the two heat exchangers 14, 15 along the intake line 11 causes the refrigerant vapor extracted from the evaporator 10 of the freezer compartment 17, on reaching the heat exchanger 15, to already have a temperature that corresponds approximately to the evaporation temperature in the evaporator 8. The evaporation in the capillary 7 of the first throttle section 6 is therefore not completely suppressed, so that a small quantity of vapor is constantly present in the capillary 7 and limits the mass throughput thereof. In this way, noise-intensive oscillations of the mass throughput, which may occur in particular if the capillary 7 is free of vapor and its mass throughput exceeds that of the compressor 1 until a supply of liquid refrigerant in the condenser is expended and only refrigerant vapor can flow back into the capillary, are avoided.
To establish a close thermal contact between the line section 18 and the upstream section 12 of the intake line 11, the two can be surrounded by an adhesive tape 23, preferably an aluminum adhesive tape with good thermal conductivity, as outlined in
In another embodiment of the heat exchanger 14, the line section 18 extends within the interior of the intake line 11, as shown in
Consequently, in a further alternative, as shown in in
The expansion valve 22 may, according to a variant that is not shown, be formed by a directional valve and a number of capillary sections of different lengths, one of which in each case is linked into the refrigerant circuit by the directional valve.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 215 491.2 | Aug 2015 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/066852 | 7/15/2016 | WO | 00 |
