EP3004756B1

EP3004756B1 - Refrigeration circuit

Info

Publication number: EP3004756B1
Application number: EP13726194.7A
Authority: EP
Inventors: Rainer Schrey; Joerg KURZAY
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2013-05-29
Filing date: 2013-05-29
Publication date: 2018-04-11
Anticipated expiration: 2033-05-29
Also published as: EP3004756A1; WO2014191035A1; CN105431692B; CN105431692A; US20160109170A1

Description

The invention relates to a refrigeration circuit, and in particular a refrigeration circuit comprising means for leak detection.
Refrigeration circuits comprising in the direction of flow of a circulating refrigerant a compressor unit for compressing the refrigerant, at least one condenser and at least one evaporator having a expansion device connected upstream thereof are well known in the art.
For allowing efficient operation of the refrigeration circuit an optimum refrigerant charge is needed. This optimum charge varies with ambient conditions as e.g. the ambient temperature, and the cooling capacity, e.g. the number of cooling cabinets/coldrooms, to be supplied. To secure the respective optimum charge under all possible ambient conditions, typically a refrigerant receiver (or buffer) is provided. Said refrigerant receiver stores excessive liquid refrigerant which is currently not needed for optimum operation of the system, and releases liquid refrigerant back to the system if more refrigerant is needed or if the system has lost refrigerant due to a leak. Said receiver typically is equipped with a device, e.g. a liquid level sensor, for detecting the level of liquid stored within the receiver. In case of refrigerant being lost due to leakage, the liquid level sensor provides an alarm signal as soon as the level of refrigerant stored within the receiver falls below the predetermined minimum liquid level. However, since the system usually comprises an amount of refrigerant which is considerably larger than the amount of refrigerant which is needed under most operation conditions, the system may lose a large amount of refrigerant before the predetermined minimum refrigerant level is reached and the alarm is set off.
It therefore would be beneficial to provide a refrigeration circuit comprising improved leak detection means allowing to detect even small leaks of the refrigeration circuit at an early stage of the leakage.
According to US 2007/125102 A1 the refrigerant charge adequacy of an air conditioning system is determined by the sensing of two temperatures in the system, one being at a midpoint in a condenser coil and the other being the temperature in the liquid line of the condenser discharge, with the difference then being indicative of the degree of subcooling, which, in turn, may be indicative of refrigerant charge condition. The method is refined by measuring a third temperature at the compressor discharge, with the three temperature values then being used to calculate a pair of residual values which provide an indication of whether the two temperature approach is useful in determining charge adequacy under the existing conditions and if not, whether the system is overcharged or undercharged
It further would be beneficial to provide a refrigeration circuit which may be produced and operated at low costs and which does occupy only little space.
A refrigeration circuit according to exemplary embodiments of the invention comprises in the direction of flow of a circulating refrigerant: a compressor unit for compressing the refrigerant; a condenser; and at least one evaporator having an expansion device connected upstream thereof; the refrigeration circuit further comprising a subcooling temperature sensor located at an outlet of the condenser for measuring the temperature of refrigerant leaving the condenser; a control unit functionally connected to the subcooling temperature sensor and configured for detecting a leak in the refrigeration circuit based on the refrigerant temperature measured by the subcooling temperature sensor, wherein the condenser comprises a liquefying portion configured for at least partially liquefying the refrigerant and a subsequent subcooling portion configured for subcooling and storing liquefied refrigerant; wherein the outlet of the condenser, particularly the outlet of the subcooling portion, is connected to the expansion device of the at least one evaporator through a receiver-free connection line. The subcooling portion is connected either directly to the liquefying portion, i.e. without an additional device arranged between the liquefying portion and the subcooling portion, or only by means of a gas-liquid-separator as it will be described in detail with reference to Fig. 3.
A method for detecting a leak in a refrigeration circuit according to further exemplary embodiments of the invention comprises the steps of compressing the refrigerant; at least partially liquefying the refrigerant in a liquefying portion of a condenser; flowing the at least partially liquefied refrigerant from the liquefying portion to a subsequent subcooling portion of the condenser; subcooling the refrigerant in the subcooling portion of the condenser; leading the refrigerant from the outlet of the condenser, particularly the outlet of the subcooling portion, to an expansion device of at least one evaporator in a direct, receiver-free manner, and evaporating the refrigerant; the method further comprising the steps of measuring the temperature of the liquid refrigerant leaving the subcooling portion of the condenser; and detecting a leak in the refrigeration circuit based on the liquid temperature measured by the subcooling temperature sensor. The at least partially liquefied refrigerant is lead to the liquefying portion either directly, i.e. without an additional device arranged between the liquefying portion and the subcooling portion, or by means of a gas-liquid-separator separating the gaseous portion from the liquid portion as it will be described in detail with reference to Fig. 3.
Exemplary embodiments of the invention are described in detail below with reference to the figures, wherein:

Fig. 1 shows a schematic view of a refrigeration circuit according to a first exemplary embodiment of the invention.
Fig. 2 shows a schematic view of a refrigeration circuit according to a second exemplary embodiment of the invention.
Fig. 3 shows a schematic view of a refrigeration circuit according to a third exemplary embodiment of the invention.
Fig. 1 shows a schematic view of a refrigeration circuit 1a according to a first exemplary embodiment of the invention.

The refrigeration circuit 1a comprises in the direction of flow of a circulating refrigerant, which is indicated by arrow A, a compressor unit comprising at least one compressor 2 for compressing the refrigerant; at least one condenser 4 and at least one evaporator 10 having a corresponding expansion device 8 connected upstream thereof.
The at least one condenser 4 comprises an upstream-side liquefying portion 4a fluidly connected to an outlet of the compressor 2 and configured for at least partially liquefying the refrigerant supplied by the compressor 2, and a subsequent downstream-side subcooling portion 4b, which is configured for subcooling and storing the refrigerant, which has been liquefied by the liquefying portion 4a of the condenser 4. An outlet of the liquefying portion 4a is connected directly to the liquefying portion 4b, i.e. the liquefying portion 4a and the subcooling portion 4b are either formed integrally with each other and/or are connected by means of a receiver-free connection line, so that the refrigerant, which has been liquefied within the liquefying portion 4a flows directly from the liquefying portion 4a into the subcooling portion 4b. The outlet of the condenser 4, in particular the outlet of the subcooling portion 4b, is fluidly connected to the expansion device 8 of the at least one evaporator 10 by means of a receiver-free connection line 7, so that the liquefied and subcooled refrigerant flows directly, i.e. without passing a receiver, from the subcooling portion 4b into the expansion device 8 without passing another device, in particular without passing a receiver.
The subcooling portion 4b of the condenser 4 is not only configured for subcooling the liquefied refrigerant, but also for storing any excessive liquid refrigerant, which is not needed for the operation of the refrigeration circuit 1a under the current ambient conditions in order to fulfill the actual cooling demands. As a result, contrary to the prior art, there is no need to provide an additional receiver for storing the excessive refrigerant.
A subcooling temperature sensor 6 is provided a the outlet of the subcooling portion 4b of the condenser 4 in order to measure the temperature of the liquefied and subcooled refrigerant leaving the condenser 4.
An expansion device 8 for expanding the liquefied and subcooled refrigerant is provided downstream of the subcooling temperature sensor 6. The expanded refrigerant leaving the expansion device 8 is delivered to at least one evaporator 10 fluidly connected between an outlet of the expansion device 8 and an inlet of the at least one compressor 2. In said at least one evaporator 10 the refrigerant is evaporated thereby providing the desired cooling capacity of the refrigeration circuit 1a.
In the exemplary embodiment shown in Figure 1, only a single compressor 2, a single condenser 4, a single expansion device 8 and a single evaporator 10 are respectively shown; the skilled person, however, will easily understand that a plurality of each of said devices 2, 4, 8, 10 may be provided if necessary or desired. E.g. a plurality of evaporators 10 respectively comprising an associated expansion device 8 may be provided in order to provide a plurality of heat sinks, which are e.g. installed in a number of refrigerated goods presentation furnitures provided in a supermarket.
The subcooling temperature sensor 6 is functionally, e.g. electrically, connected to a control unit 12, which is configured for operating as leakage detection system by monitoring the temperature signal provided by the subcooling temperature sensor 6. In particular, the control unit 12 may be configured to compare the actual temperature signal provided by the subcooling temperature sensor 6 with a predetermined temperature, which is calculated and/or stored by means of a calculation and/or storage unit 14 provided within the control unit 12.
If the control unit 12 detects a leakage of refrigerant from the refrigeration circuit 1a, it sets off an alarm, e.g. an optical and/or an acoustical alarm, by means of at least one appropriate alarm device 16, 18 functionally connected to the control unit 12. Additionally or alternatively, the control unit 12 may stop the operation of the compressor(s) 2, in order to avoid a further loss of refrigerant. Alternatively, the compressor(s) 2 may be operated at reduced speed in order to provide at least partial refrigeration capacity without loosing to much refrigerant.
The calculation and/or storage unit 14 may calculate the predetermined temperature or select the predetermined temperature to be compared with the measured temperature from a plurality of stored values based on temperatures measured by at least on additional temperature sensor 20, 22, 24, 26 including e.g. an ambient air temperature sensor 20 and/or refrigerant temperature sensors 22, 24, 26 which are provided at further positions of the refrigeration circuit 1a for measuring the temperature of the refrigerant circulating within the refrigeration circuit 1a.
The calculation and/or selection of the predetermined temperature may also be based on an external value, e.g. a desired cooling capacity, which has been input by an operator by means of an input device 28 connected to the control unit 12.
Example calculations for a refrigeration circuit, in which the evaporating temperature, the superheating at the evaporator 10 and the cooling capacity have been kept constant, have been carried out:

Evaporating Temperature -10°C

Superheat Evaporator 10K

Cooling Capacity 100kW
In a first step, the influence of ambient temperature on the subcooling with constant refrigerant charge has been examined:

1. Initial charge:

Input:

Refrigerant Charge	23,4 kg
Ambient temperature T_amb	35 °C

Output:

Subcooling temperature T_sub

3K

2. Change of Ambient Temperature:

Input:

Refrigerant Charge	23,4 kg
Ambient temperature T_amb	25 °C

Output:

Subcooling temperature T_sub

4,7 K

I.e. a decrease of the ambient temperature T_amb of ΔT_amb = -10 °C results in an increase of the subcooling temperature T_sub measured by the temperature sensor 6 of ΔT_sub = + 1,7 K (from 3 K to 4,7 K).
In a second step, the influence of charge loss on the subcooling temperature at constant ambient temperature as been evaluated:

1. Initial charge

Input:

Ambient temperature T_amb	25 °C
Refrigerant Charge	23,4 kg

Output:

Subcooling T_sub

4,7 K

2. Loss of charge of 5% (= 1,17 kg)

Input:

Ambient temperature T_amb 25°C

Refrigerant Charge

22,21 kg

Output:

Subcooling T_sub 3,6 K
Thus, there occurs a difference of ΔT_sub = 1,1 K between the expected subcooling temperature of 4,7 K and the actually measured subcooling temperature of 3,6 K, which indicates that there is a loss of refrigerant in the system.
Performing a number of test calculations may even allow to determine the amount of refrigerant lost by comparing the expected (calculated) and the actually measured subcooling temperatures T_sub.
Fig. 2 shows a schematic view of a refrigeration circuit 1b according to a second exemplary embodiment of the invention.
The refrigeration circuit 1b according to the second embodiment comprises basically the same components as the refrigeration circuit 1a of the first embodiment, namely in the direction of flow of a circulating refrigerant, as indicated by arrow A, a compressor unit comprising at least one compressor 2 for compressing the refrigerant; a condenser 4 and at least one evaporator 10a, 10b having a corresponding expansion device 8a, 8b connected upstream thereof. The components of the refrigeration circuit 1b according to the second embodiment, which are identical to the corresponding components of the refrigeration circuit 1a according to the first embodiment shown in Figure 1 are denoted by the same reference signs and will not be discussed in detail again.
The refrigeration circuit 1b according to a second exemplary embodiment of the invention comprises two or more evaporators 10a, 10b having a respective expansion device 8a, 8b connected upstream of each of the evaporators 10a, 10b, wherein the outlet of the condenser 4, in particular the outlet of the subcooling portion 4b, is connected to the respective expansion devices 8a, 8b of the two or more evaporators 10a, 10b by a receiver-free connection line 7 branching into receiver-free branch lines 9a, 9b connecting with the respective expansion devices 8a, 8b.
Refrigerant temperature sensors 22, 23 may be arranged at each of the conduits connecting the expansion devices 8a, 8b to the respectively associated evaporator 10a, 10b.
Each of the expansion devices 8a, 8b may be provided as a switchable expansion device 8a, 8b, which is switchable between an open state, in which it expands the refrigerant circulating within the refrigeration circuit 1b, and a closed state, in which it blocks the flow of refrigerant through the associated evaporator 10a, 10b allowing to selectively activate and deactivate the operation of each of the evaporators 10a, 10b.
As a further option the degree of expansion provided by the expansion devices 8a, 8b may be adjustable.
It is also possible to use a single, common expansion device 8 for delivering expanded refrigerant to two or more evaporators 10a, 10b.
Fig. 3 shows a schematic view of a refrigeration circuit 1c according to a third exemplary embodiment of the invention.
The refrigeration circuit 1c according to the third embodiment comprises basically the same components as the refrigeration circuit 1a of the first embodiment, namely in the direction of flow of a circulating refrigerant, as indicated by arrow A, a compressor unit comprising a compressor 2 for compressing the refrigerant; a condenser 40 and an evaporator 10 having a corresponding expansion device 8 connected upstream thereof. The components of the refrigeration circuit 1c according to the third embodiment, which are identical to the corresponding components of the refrigeration circuit 1a according to the first embodiment shown in Figure 1 are denoted by the same reference signs and will not be discussed in detail again.
The condenser 40 according to the third embodiment differs from the condenser 4 of the first embodiment in that a gas-liquid separator 42 is provided between the liquefying portion 40a and the subsequent subcooling portion 40b of the condenser 40.
The gas-liquid separator 42 is configured for separating a gas portion from a liquid portion of a gas-liquid-mixture, which leaves the liquefying portion 40a of the condenser 40 in case the condensing capacity of the liquefying portion 40a is not sufficient for condensing all gaseous refrigerant delivered from the compressor 2 to the liquefying portion 40a of the condenser 40. In the third embodiment the liquid portion of the gas-liquid-mixture is delivered to the subcooling portion 40b of the condenser 40 for subcooling and storage, as in the first embodiment shown in Figure 1, and the separated gas portion of the gas-liquid-mixture is delivered by means of a gas-return-line 44 back to the entry of the liquefying portion 40a in order to pass the liquefying portion 40a again for being liquefied as well.
As a result, in a refrigeration circuit 1c according to the third embodiment only liquefied refrigerant is delivered to the subcooling portion 40b of the condenser 40 which increases the efficiency of the subcooling portion 40b. This enhances the efficiency of the refrigeration circuit 1c, as in a refrigeration circuit 1b according to the third embodiment no gaseous refrigerant exits the condenser 40 and enters into the at least one expansion device 8.
A refrigeration circuit according to an exemplary embodiment of the invention comprises in the direction of flow of a circulating refrigerant a compressor unit for compressing the refrigerant, at least one condenser, and at least one evaporator having an expansion device connected upstream thereof. The condenser comprises a liquefying portion configured for at least partially liquefying the refrigerant and a subsequent subcooling portion, which is configured for subcooling and storing the liquefied refrigerant. The outlet of the liquefying portion is connected to the the subcooling portion by means of a receiver-free connection line, so that the liquefied refrigerant flows directly, i.e. without passing a receiver, from the liquefying portion into the subcooling portion. The outlet of the condenser, in particular the outlet of the subcooling portion, is connected to the expansion device of the at least one evaporator by means of a direct, in particular receiver-free, connection line so that the liquefied and subcooled refrigerant exiting the condenser flows from the subcooling portion into the expansion device without passing another device, in particular without passing a receiver.
A method for detecting a leak in a refrigeration circuit according to an exemplary embodiment of the invention comprises the steps of compressing the refrigerant; at least partially liquefying the refrigerant in a liquefying portion of a condenser; leading the at least partially liquefied refrigerant from the liquefying portion to an immediately subsequent subcooling portion of the condenser; subcooling the refrigerant in the subcooling portion of the condenser; leading the refrigerant from the outlet of the condenser, particularly the outlet of the subcooling portion, to an expansion device of at least one evaporator in a direct, i.e. receiver-free, manner, and evaporating the refrigerant. The method further comprises the steps of measuring the temperature of the liquid refrigerant leaving the subcooling portion of the condenser and detecting a leak in the refrigeration circuit based on the liquid temperature measured by the subcooling temperature sensor.
The refrigeration circuit according to an exemplary embodiment of the invention further comprises a subcooling temperature sensor, which is located at an outlet of the condenser and which is configured for measuring the temperature of refrigerant leaving the subcooling portion of the condenser, and a control unit, which is functionally connected to the temperature sensor and configured for detecting a leak in the refrigeration circuit based on the refrigerant temperature measured by the temperature sensor.
According to an exemplary embodiment of the invention, measuring and monitoring the temperature of the liquefied refrigerant leaving the condenser and in particular leaving the subcooling portion of the condenser allows to detect even a small loss of refrigerant from the refrigeration circuit with high reliability and accuracy. Thus any leakage of refrigerant may be reliably detected at an early stage of leakage even if a large amount of refrigerant is still present in the circuit, and the loss of a large amount of refrigerant can be avoided.
As the refrigeration circuit according to exemplary embodiments of the invention does not comprise a receiver, the costs and the space for providing such a receiver are saved. Thus, the refrigeration circuit may be produced and operated at low costs and occupies only little space.
In an embodiment the control unit comprises a comparison unit which is configured for comparing the temperatures measured by the subcooling temperature sensor to at least one predetermined value. Comparing the temperatures measured by the subcooling temperature sensor to at least one predetermined value allows an easy and reliable leak detection, as in case a leakage occurs, the subcooling temperature will considerably change and deviate from the predetermined value(s).
In an embodiment the control unit comprises a calculation unit which is configured for calculating the predetermined value(s). Providing such a calculation unit allows to calculate the predetermined value(s) based on the actual ambient and operating conditions of the refrigeration circuit. It therefore allows to flexibly adjust the predetermined value to said ambient and operating conditions.
In an embodiment the control unit further comprises a storing unit, which is configured for storing at least one predetermined value, which has been calculated before and/or which has been entered from an external source into the storing unit. Using stored values as predetermined values allows to save the cost for providing the calculation unit and/or to use predetermined values calculated by means of simulations, which have been carried out on elaborated computer based external simulation system. Alternatively or additionally, predetermined values, which have been measured before, in particular during the operation of the actual system, may be stored and used.
In an embodiment the refrigeration circuit comprises at least one additional temperature sensor, which is functionally connected to the control unit, and the control unit is configured for calculating the predetermined value and/or selecting the predetermined value from a plurality of stored predetermined values by using the temperature value measured by the at least one of the additional temperature sensors. The at least one additional temperature sensors may be one of an ambient air temperature sensor or a temperature sensor which is configured for measuring the temperature of the circulating refrigerant at a different position of the refrigeration circuit. This allows to adjust the predetermined value to the actual ambient temperature and/or to the temperature(s) of the refrigerant circulating within the refrigeration circuit.
In an embodiment the control unit is configured to stop the operation of the at least one compressor and/or to set off an alarm signal after detecting a leakage of the refrigeration circuit in order to avoid a further loss of refrigerant.
In an embodiment a gas-liquid-separator is arranged between the liquefying portion and the subcooling portion of the condenser, an inlet of the gas-liquid-separator being fluidly connected to an outlet of the liquefying portion of the condenser, a gas outlet of the gas-liquid-separator being fluidly connected to an inlet of the liquefying portion of the condenser, and a liquid outlet of the gas-liquid-separator being fluidly connected to an inlet of the subcooling portion of the condenser for delivering the gas-phase to the inlet of the liquefying portion to be liquefied. Such a gas-liquid-separator allows to separate a gas portion and a liquid portion from a gas-liquid-mixture leaving the liquefying portion of the condenser. Delivering only liquid refrigerant to the subcooling portion enhances its efficiency and the efficiency of refrigeration circuit.
In an embodiment two or more evaporators having a respective expansion device connected upstream thereof are provided. In said embodiment the outlet of the condenser, particularly the outlet of the subcooling portion, is connected to the respective expansion devices of the two or more evaporators by a receiver-free connection line branching into receiver-free branch lines connecting to the respective expansion devices. Providing a plurality of evaporators allow to provide a plurality of heat sinks at different locations, e.g. in a number of refrigerated goods presentation furnitures provided in a supermarket, which are operated by a single refrigeration circuit.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention is not limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

List of Reference Numerals

1a, 1b, 1c: refrigeration circuit
2: compressor unit
4,40: condenser
4a, 40a: liquefying portion
4b, 40b: subcooling portion
6: subcooling temperature sensor
7: receiver-free connection line
8, 8a, 8b: expansion device
9a, 9b: branch lines
10, 10a, 10b: evaporator
12: control unit
14: calculation and/or storage unit
16: acoustical alarm means
18: optical alarm means
20: ambient air temperature sensor
22, 23, 24, 26: refrigerant temperature sensors
28: input device
42: gas-liquid-separator
44: gas-return-line

Claims

Refrigeration circuit (1a; 1b; 1c) comprising in the direction of flow of a circulating refrigerant:
a compressor unit (2) for compressing the refrigerant;

a condenser (4, 40); and

at least one evaporator (10; 10a, 10b) having an expansion device (6) connected upstream thereof;

the refrigeration circuit (1a; 1b; 1c) further comprising

a subcooling temperature sensor (6) located at an outlet of the condenser (4, 40) for measuring the temperature of refrigerant leaving the condenser (4, 40);

a control unit (12) functionally connected to the subcooling temperature sensor (6) and configured for detecting a leak in the refrigeration circuit (1a; 1b; 1c) based on a comparison of the refrigerant temperature measured by the subcooling temperature sensor (6) with a predetermined temperature, the predetermined temperature being calculated from at least one temperature measured outside the condenser or from an external value, in particular the desired cooling capacity;

wherein the condenser (4, 40) comprises a liquefying portion (4a, 40a) configured for at least partially liquefying the refrigerant and a subsequent subcooling portion (4b, 40b) configured for subcooling and storing liquefied refrigerant; and

wherein the outlet of the condenser (4, 40), particularly the outlet of the subcooling portion (4b, 40b), is connected to the expansion device (8; 8a, 8b) of the at least one evaporator (10; 10a, 10b) through a receiver-free connection line (7).
Refrigeration circuit (1a; 1b; 1c) of claim 1, wherein, the subcooling portion (4b, 40b) is connected to the liquefying portion (4a, 40a) without a further device arranged in between, or only by means of a gas-liquid-separator (42).
Refrigeration circuit (1a; 1b; 1c) of claim 1 or 2, wherein the control unit (12) comprises a comparison unit (14) which is configured for comparing the temperature measured by the subcooling temperature sensor (6) to a predetermined value.
Refrigeration circuit (1a; 1b; 1c) of claim 3, wherein the control unit (12) further comprises a calculation unit (14) which is configured for calculating the predetermined value.
Refrigeration circuit (1a; 1b; 1c) of claim 3 or 4, wherein the control unit (12) further comprises a storing unit (14) which is configured for storing at least one predetermined value.
Refrigeration circuit (1a; 1b; 1c) of claim 4 or 5, further comprising at least one additional temperature sensor (20, 22, 23, 24, 26) functionally connected to the control unit (12), wherein the control unit (12) is configured for calculating and/or selecting the predetermined value using the temperature value measured by the at least one of the additional temperature sensors (20, 22, 23, 24, 26).
Refrigeration circuit (1a; 1b; 1c) of claim 6, wherein the at least one additional temperature sensor (20, 22, 23, 24, 26) is at least one of an ambient air temperature sensor (20) and a temperature sensor (22, 23, 24, 26) configured for measuring the temperature of the refrigerant circulating within the refrigeration circuit (1a; 1b; 1c).
Refrigeration circuit (1a; 1b; 1c) of any of claims 4 to 7, wherein the control unit (12) is configured to reduce or even stop the operation of the at least one compressor (2) and/or to set off an alarm signal after detecting a leakage of the refrigeration circuit (1c).
Refrigeration circuit (1c) of any of the preceding claims, wherein a gas-liquid-separator (42) is arranged between the liquefying portion (4a, 40a) and the subcooling portion (4b, 40b) of the condenser (4, 40), an inlet of the gas-liquid-separator (42) being fluidly connected to an outlet of the liquefying portion (4a, 40a) of the condenser (4, 40).
Refrigeration circuit (1c) of claim 9, wherein a gas outlet of the gas-liquid-separator (42) is fluidly connected to an inlet of the condenser (4, 40), and wherein a liquid outlet of the gas-liquid-separator (42) is fluidly connected to an inlet of the subcooling portion (4b, 40b) of the condenser (4, 40).
Refrigeration circuit (1b) of any of the preceding claims, wherein two or more evaporators (10a, 10b) having a respective expansion device (8a, 8b) connected upstream thereof are provided, and wherein the outlet of the condenser (4, 40), particularly the outlet of the subcooling portion (4b, 40b), is connected to the respective expansion devices (8a, 8b) of the two or more evaporators (10; 10a, 10b) by a receiver-free connection line (7) branching into receiver-free branch lines (9a, 9b) connecting to the respective expansion devices (8a, 8b).
Method for detecting a leak in a refrigeration circuit (1a; 1b; 1c) comprising the steps of
compressing the refrigerant;
at least partially liquefying the refrigerant in a liquefying portion (4a, 40a) of a condenser (4, 40);
flowing the at least partially liquefied refrigerant from the liquefying portion (4a, 40a) to a subsequent subcooling portion (4b, 40b) of the condenser (4, 40);
subcooling the refrigerant in the subcooling portion (4b, 40b) of the condenser (4, 40);
leading the refrigerant from the outlet of the condenser (4, 40), particularly the outlet of the subcooling portion (4b, 40b), to an expansion device (8; 8a, 8b) of at least one evaporator (10; 10a, 10b) in a receiver-free manner, and evaporating the refrigerant; characterised in that the method further comprising the steps of
calculating a predetermined temperature from at least one temperature measured outside the condenser or from an external value, in particular the desired cooling capacity;

measuring the temperature of the liquid refrigerant leaving the subcooling portion (4b, 40b) of the condenser (4, 40); and

detecting a leak in the refrigeration circuit (1a; 1b; 1c) based on a comparison of the liquid refrigerant temperature measured by the subcooling temperature sensor (6) with the predetermined temperature.
Method of claim 12, wherein the at least partially liquefied refrigerant is led from the liquefying portion (4a,40a) to the subcooling portion (4b, 40b) without passing a further device except for an optional gas-liquid-separator (42).
Method of claim 12 or 13, wherein the refrigerant is led from the outlet of the condenser (4), particularly the outlet of the subcooling portion (4b), to two or more evaporators (10a, 10b) having a respective expansion device (8a, 8b) connected upstream thereof, through a direct, receiver-free connection line (7) branching into receiver-free branch lines (9a, 9b) connecting to the respective expansion devices (8a, 8b).
Method of any of claims 12 to 14, further comprising the steps of separating the gas phase from the liquid phase of at least partially liquefied refrigerant, delivering the liquid phase to the subcooling portion (40b) of the condenser (40) and delivering the gas phase to the liquefying portion (40a) of the condenser (40).