Method for controlling a defrost operation of a refrigeration system

Abstract

A method is for controlling a defrost operation of a refrigeration system (1) that has a condenser (5), an evaporator (7) and at least one heat exchanger (9) fluidly couplable with each other so as to form a first circuit (10) and a second circuit (11). The heat exchanger exchanges heat with an external environment. The first and second circuits have respective operative fluids and respective compressor means (12, 13). The refrigeration system can work in a first mode wherein one of the first or the second circuit has the heat exchanger fluidly interposed between the condenser and the respective compressor means, and wherein the heat exchanger operates as an evaporator. The method comprises defrosting the heat exchanger during the first mode by: monitoring if a temperature of the evaporator satisfies a defrost condition; and, if the temperature of the evaporator satisfies the defrost condition, fluidly coupling the evaporator in series to the heat exchanger.

Description

[0001] "METHOD FOR CONTROLLING A DEFROST OPERATION OF A

[0002] REFRIGERATION SYSTEM"

[0003] CROSS-REFERENCE TO RELATED APPLICATIONS

[0004] This Patent Application claims priority from Italian Patent Application No . 102024000003250 filed on February 15 , 2024 , the entire disclosure of which is incorporated herein by reference .

[0005] TECHNICAL FIELD

[0006] The present invention concerns a method for controlling a defrost operation of a refrigeration system, in particular a multi-purpose conditioning system for simultaneous heating and cooling .

[0007] BACKGROUND OF THE INVENTION

[0008] Refrigeration systems are known that are able to provide cold water and hot water simultaneously to a user .

[0009] For example , a multi-purpose conditioning system has two independent fluidic circuits that comprise each a respective operative fluid and a respective compressor for the circulation of the respective operative fluid within the circuit .

[0010] Such multi-purpose systems comprise also two heat exchangers on the user side of the system, shared by the two fluidic circuits ; and two heat exchangers on the source side , one per each fluidic circuit .

[0011] One of the two heat exchangers on the user side works as evaporator for production of cold water, the other of the two heat exchangers on the user side works as condenser for production of hot water .

[0012] The heat exchangers on the source side are configured to exchange heat with an external environment and may be used as condenser or evaporator , depending on the loads of the system .

[0013] When one of the two fluidic circuits uses the heat exchanger on the source side as evaporator and the temperature of the external environment is low, for example during winter, frost or ice may form on the heat exchanger on the source side .

[0014] Formation of frost or ice reduces the performance of the heat exchanger .

[0015] To defrost the heat exchanger on the source side , it is known to use the hot water at the condenser as a heat source .

[0016] However, using the condenser for defrosting operations reduces the ef ficiency of the overall system .

[0017] Therefore , the need is felt to provide a refrigeration system adapted to perform a defrosting operation while maintaining a high ef ficiency .

[0018] SUMMARY OF THE INVENTION

[0019] An aim of the present invention is to satis fy the above mentioned needs .

[0020] The aforementioned aim is reached by a method for controlling a defrost operation of a refrigeration system, a refrigeration system and a computer program, as claimed in the appended set of claims .

[0021] BRIEF DESCRIPTION OF DRAWINGS

[0022] For a better understanding of the present invention, a preferred embodiment is described in the following, by way of a non-limiting example , with reference to the attached drawings wherein :

[0023] • Figure 1 is a schematic diagram of a refrigeration system according to an embodiment of the present invention, during a first operating mode ;

[0024] • Figure 2 is a flow chart of a method for controlling a defrosting operation of the refrigeration system of Figure 1 , according to an embodiment of the present invention;

[0025] • Figure 3 is a schematic diagram o f the refrigeration system of Figure 1 , during a defrost operation of the method of Figure 2 ; and

[0026] • Figure 4 is a flow chart of additional steps of the method of Figure 2 , according to an embodiment of the present invention .

[0027] DETAILED DESCRIPTION OF THE INVENTION

[0028] Figure 1 schematically shows a refrigeration system 1 , hereinafter referred to as system 1 .

[0029] In this embodiment , the system 1 is a multi-purpose conditioning unit for simultaneous heating of a first user fluid and cooling of a second user fluid . The first and second user fluids may be for example water or air, in particular here water, depending on the speci fic application of the system 1 .

[0030] In particular, the system 1 is for a four-tube implant and is configured to provide refrigerated water and heated water on two independent hydronic circuits (not shown in Figure 1 ) .

[0031] The system 1 comprises a refrigeration cycle unit 2 for heating and refrigerating the user fluid via refrigeration cycle of an operative fluid and an electronic control unit 3 that is coupled to the refrigeration cycle unit 2 for controlling the functioning of the refrigeration cycle unit 2 .

[0032] The refrigeration cycle unit 2 comprises , inter alia, a condenser 5 , an evaporator 7 , and at least one additional heat exchanger . In particular, in this embodiment , the refrigeration cycle unit 2 comprises two additional heat exchangers 8 , 9 .

[0033] The condenser 5 , the evaporator 7 and the additional heat exchangers 8 , 9 are fluidly couplable with each other so as to form a f irst fluidic circuit 10 and a second fluidic circuit 11 .

[0034] The first fluidic circuit 10 and the second fluidic circuit 11 are fluidly independent from each other .

[0035] Accordingly, each of the first fluidic circuit 10 and the second fluidic circuit 11 comprises a respective operative fluid that may be the same or a di f ferent one between the two fluidic circuits 10 , 11 .

[0036] In detail , each circuit 10 , 11 comprises a respective compressor 12 , 13 each provided with inlets / outlets 12A, 12B and 13A, 13B and are configured each to allow flowing of the respective operative fluid through the respective fluidic circuit 10 , 11 by increasing the pressure between the inlets 12A, 12B and the outlets 13A, 13B .

[0037] The first and the second fluidic circuits 10 , 11 further comprise each respective valve means , inter alia the lamination valves , that are controllable by the control unit 3 for setting a speci fic fluidic configuration of the first and second fluidic circuits 10 , 11 , based on the operating mode of the system 1 and not further described for sake of brevity .

[0038] For simplicity, only some of the valves are shown in the embodiment of figure 1 .

[0039] In particular, for the first fluidic circuit 10 , only two lamination valves 12 , 13 are shown .

[0040] For the second f luidic circuit 11 , there are shown two lamination valves 15 , 16 and three valve means 18 , 19 , 20 configured to regulate the fluid passage between the related conduits .

[0041] The condenser 5 and the evaporator 7 are heat exchangers that are arranged on a user side of the system 1 . In practice , the condenser 5 and the evaporator 7 are configured to exchange heat each with a respective user fluid (e.g., water) .

[0042] In detail, the condenser 5 has a user inlet 22A and a user outlet 22B, fluidly coupled with each other. The condenser 5 is configured to receive a first user fluid (e.g., water) at the user inlet 22A and provide the first user fluid at the user outlet 22B (as schematically indicated by arrows in figure 1) .

[0043] The condenser 5 further has two first openings 23, 24 fluidly couplable to the second fluidic circuit 11 for allowing flowing of the respective operative fluid within the condenser 5, and two second openings 25, 26 fluidly couplable to the first fluidic circuit 10 for allowing flowing of the respective operative fluid within the condenser 5.

[0044] In use, the first and the second openings 23, 24, 25, 26 may operate as inlets or outlets according to the operative fluid flowing direction.

[0045] Clearly, the condenser 5 may be shared by both the first and the second fluidic circuit 10, 11 for heating the first user fluid.

[0046] The evaporator 7 has a user inlet 30A and a user outlet 30B, fluidly coupled with each other. The evaporator 7 is configured to receive a second user fluid (e.g., water) at the user inlet 30A and provide the second user fluid at the user outlet 30B (as schematically indicated by arrows in figure 1 ) .

[0047] The evaporator 7 further has two first openings 32, 33 fluidly couplable to the second fluidic circuit 11 for allowing flowing of the respective operative fluid within the evaporator 7, and two second openings 34, 35 fluidly couplable to the first fluidic circuit 10 for allowing flowing of the respective operative fluid within the evaporator 7 .

[0048] In use , the first and the second openings 32 , 33 , 34 , 35 may operate as inlets or outlets according to the operative fluid flowing direction .

[0049] Clearly, the evaporator 7 may be shared by both the first and the second fluidic circuits 10 , 11 for refrigerating the second user fluid .

[0050] The additional heat exchangers 8 , 9 are arranged on a source side of the system 1 so as to exchange heat with an external environment of the system 1 .

[0051] The additional heat exchangers 8 , 9 may comprise each a respective ventilation means 40 for allowing the heat exchange with the external environment .

[0052] The additional heat exchanger 8 is fluidly couplable to the first fluidic circuit 10 . The additional heat exchanger 9 is fluidly couplable to the second fluidic circuit 11 .

[0053] In detail , the additional heat exchanger 8 has two operative openings 42 , 43 fluidly couplable to the first fluidic circuit 10 for allowing flowing of the respective operative fluid within the additional heat exchanger 8 .

[0054] In use , openings 42 , 43 may operate as inlet or outlet according to the operative fluid flowing direction .

[0055] In detail , the additional heat exchanger 9 has two operative openings 47 , 48 fluidly couplable to the second fluidic circuit 11 for allowing flowing of the respective operative fluid within the additional heat exchanger 9 .

[0056] In use , openings 47 , 48 may operate as inlet or outlet according to the operative fluid flowing direction .

[0057] The control unit 3 is further configured to monitor one or more parameters of the refrigeration cycle unit 2 , for controlling the functioning of the system 1 . For example , the system 1 may comprise one or more sens ing means , such as temperature sensors , flowmeters , etc . , coupled to the electronic control unit 3 and configured to measure said parameters of the refrigeration cycle unit 2 .

[0058] In detail , the control unit 3 is configured to monitor a temperature of the evaporator 7 ; in particular, a temperature of the second user fluid that is refrigerated by the evaporator 7 .

[0059] According to an embodiment , the control unit 3 may be configured to monitor a temperature Tin of the second user fluid at entrance of the evaporator 7 or, in other words , at the user inlet 30A of the evaporator 7 .

[0060] For example , the system 1 may comprise temperature sensing means 50 for measuring the temperature Tin and electronically coupled to the control unit 3 . For example , the temperature sensing means 50 may measure the temperature Tin of the second user fluid while passing through the user inlet 30A, before passing through the user inlet 30A and / or after passing through the user inlet 30A.

[0061] According to an embodiment , the control unit 3 may be configured to monitor a temperature Tout of the second user fluid at exit of the evaporator 7 or, in other words , at the user outlet 30B of the evaporator 7 .

[0062] For example , the system 1 may comprise temperature sensing means 51 for measuring the temperature Tout and electronically coupled to the control unit 3 . For example , the temperature sensing means 51 may measure the temperature Tout of the second user fluid while passing through the user outlet 30B, before passing through the user outlet 30B and / or after passing through the user outlet 30B . Moreover, according to an embodiment , the control unit 3 may be further configured to monitor a temperature Text of the external environment coupled to the additional heat exchanger 9 , for example by means of speci fic temperature sensing means here not shown .

[0063] In use , the control unit 3 may set a speci fic fluidic configuration ( topology) of the first and the second fluidic circuits 10 , 11 , and control a flowing direction of the respective operative fluid, depending on the speci fic operating mode of the system 1 .

[0064] In the configuration of Figure 1 , the system 1 is in a first operating mode wherein the second fluidic circuit 11 has the compressor 13 fluidly interposed between the additional heat exchanger 9 and the condenser 5 and wherein the additional heat exchanger 9 is used as an evaporator of the operative fluid of the second fluidic circuit 11 .

[0065] For the sake of clarity, in Figure 1 , the fluidic connections that are active during the first operating mode are identi fied by darker and wider lines , while the fluidic connections that are inactive during the first operating mode are identi fied by lighter and thinner lines .

[0066] In practice , during the first operating mode , the second fluidic circuit 11 has the compressor 13 arranged upstream of the condenser 5 and downstream of the additional heat exchanger 9 , and the condenser 5 upstream of the additional heat exchanger 9 .

[0067] In detail , during the first operating mode , the operative fluid of the second fluidic circuit 11 flows , in sequence ( as indicated by respective arrows in Figure 1 ) :

[0068] - through the compressor 13 , in particular into the respective inlet 13A and out of the respective outlet 13B ; through the condenser 5 , in particular from the operative inlet 23 and out of the operative outlet 24 ; - through the lamination valve 15 ;

[0069] - through the additional heat exchanger 9 , in particular into the operative inlet 48 and out of the operative outlet 47 ; and

[0070] - then returns to the compressor 13 .

[0071] In other words , during the first operating mode , the evaporator 7 is fluidly decoupled from the second fluidic circuit 11 .

[0072] During the first operating mode , the first fluidic circuit 10 may be set in one of many di f ferent topologies , depending on the speci fic operating conditions of the system 1 .

[0073] According to the embodiment of Figure 1 , during the first operating mode , the first fluidic circuit 10 may have the compressor 12 fluidly interposed between the evaporator 7 and the condenser 5 . The additional heat exchanger 8 is fluidly decoupled from the first fluidic circuit 10 .

[0074] In practice , during the first operating mode , the first fluidic circuit 10 may have the compressor 12 arranged upstream of the condenser 5 and downstream of the evaporator 7 , and the condenser 5 upstream of the evaporator 7 .

[0075] In detail , during the first operating mode of Figure 1 , the operative fluid of the first fluidic circuit 10 flows , in sequence :

[0076] - through the compressor 12 , in particular into the respective inlet 12A and out of the respective outlet 12B ; through the condenser 5 , in particular from the operative inlet 25 and out of the operative outlet 26 ;

[0077] - through the lamination valve 13 ; through the evaporator 7 , in particular into the operative inlet 35 and out of the operative outlet 34 ; and

[0078] - then returns to the compressor 12 . Figure 2 shows the flowchart of a method 70 for controlling defrosting of the additional heat exchanger 9, when the system 1 is in the first operating mode.

[0079] The method 70 may be performed by the control unit 3.

[0080] The method 70 may start (step S10) in response to the reception of a defrost request.

[0081] The control unit 3 may be configured to automatically detect when defrosting of the additional heat exchanger 9 is needed. For example, the system 1 may comprise sensing means for detecting formation of frost or ice on the additional heat exchanger 9. For example, the control unit 3 may be configured to perform a known algorithm for detecting when defrosting is needed.

[0082] Then, step Sil, the control unit 3 checks whether the system 1 is on and is set on an automatic control mode. For example, at step Sil the control unit 3 may check whether the system 1 is currently performing both heating of the first user fluid through the condenser 5 and refrigeration of the second user fluid through the evaporator 7.

[0083] In the negative case (branch N from step Sil) , the method 70 may proceed to a step S17.

[0084] In the affirmative case (branch Y from step Sil) , the control unit 3 checks (step S12) whether an eco-defrost mode of the system 1 is enabled. For example, the control unit 3 may check whether the system 1 is configured to perform the eco-defrost mode. The eco-defrost mode may be the defrost mode described in detail hereinafter with respect to step S15.

[0085] In the affirmative case (branch Y from step S12) , the control unit 3 proceeds to step S14.

[0086] In the negative case (branch N from step S12) , the method 70 may proceed to step S17. Steps Sil and S12 may be optional.

[0087] At step S14, the control unit 3 checks a first temperature condition, that is whether a temperature of the evaporator 7, in particular a temperature of the second user fluid at the evaporator 7, is higher than a cool setpoint of the system 1.

[0088] In this embodiment, the control unit 3 checks whether the temperature Tin of the second user fluid is higher than the cool setpoint of the system 1. However, in addition or in alternative, the control unit 3 may check a different temperature of the second user fluid at the evaporator 7, such as the temperature Tout.

[0089] The cool setpoint of the system 1 is the setpoint temperature Tcof the second user fluid at exit of the evaporator 7 (e.g., at the user outlet 30B) . In other words, the cool setpoint is the temperature at which it is desired to provide the second user fluid at exit of the evaporator 7. For example, the cool setpoint may be set by the user of the system 1 depending on the specific application.

[0090] In detail, in this embodiment, the control unit 3 verifies if a difference between the temperature Tin at entrance of the evaporator 7 and the cool setpoint Tcis equal to or higher than a threshold, wherein the threshold may be higher than zero, for example of few degrees such as 2°C; this may improve the efficiency of the defrosting without compromising the functionality of the system 1 in refrigerating the second user fluid at the evaporator 7.

[0091] For example, the threshold may be chosen based on the compressor 13, for example based on one or more functional parameters of the compressor 13, so that the compressor 13 may keep compressing the respective operative fluid between inlet 13A and outlet 13B.If the first temperature condition is satisfied (branch Y from step S14) , then the control unit 3 proceeds to step S15. If the first temperature condition is not satisfied (branch N from step S14) , the method 70 may proceed to step S17.

[0092] At step S15, the control unit 3 modifies the topology of the second fluidic circuit 11 so that the evaporator 7 becomes fluidly coupled to the additional heat exchanger 9, in series to the additional heat exchanger 9.

[0093] In detail, as shown in Figure 3, the topology of the second fluidic circuit 11 is modified so that the respective operative fluid passes, after the compressor 13, through the additional heat exchanger 9, and, after the additional heat exchanger 9, through the evaporator 7.

[0094] In particular, the second fluidic circuit 11 may be modified so that the condenser 5 becomes fluidly decoupled from the second fluidic circuit 11; i.e., so that the operative fluid of the second fluidic circuit 11 does not flow through the condenser 5.

[0095] For the sake of clarity, in Figure 3, the fluidic connections that are active during the eco-defrost operation of step S15 are identified by darker and wider lines, while the fluidic connections that are inactive during the defrost operation of step S15 are identified by lighter and thinner.

[0096] In detail, the operative fluid of the second fluidic circuit 11 flows from the compressor 13 into the operative inlet 47 of the additional heat exchanger 9 and out of the operative outlet 48 of the additional heat exchanger 9; from the operative outlet 48 of the additional heat exchanger 9 into the operative inlet 33 of the evaporator 7 and out of the operative outlet 32 of the evaporator 7; and from the operative outlet 32 of the evaporator 7 back to the compressor 13. The topology of the second fluidic circuit 11 may be modified, by the control unit 3, by actuating the valves 18- 20 and other valves here not shown.

[0097] In practice, at step S15, defrosting of the additional heat exchanger 9 is performed by using the evaporator 7 as heat source, and not the condenser 5.

[0098] The control unit 3 may maintain the defrosting configuration described with reference to step S15, based on a second temperature condition.

[0099] In detail, at a step S16, the control unit 3 checks whether a temperature of the evaporator 7, in particular a temperature of the second user fluid at the evaporator 7, is equal to or lower than a forced-rest temperature.

[0100] In this embodiment, the control unit 3 checks whether the temperature Tout of the second user fluid is equal to or lower than the forced-rest temperature of the system 1. However, in addition or in alternative, the control unit 3 may check the temperature Tin of the second user fluid.

[0101] The forced-rest temperature may be a function of an antifreeze setpoint of the system 1. The antifreeze setpoint may be the freezing temperature TAF of the second user fluid.

[0102] For example, the forced-rest temperature may be equal to the freezing temperature TAF plus a threshold, wherein the threshold may be small, for example of few degrees, for example of 0,5°C. The Applicant has verified that the condition of step S16 may be particularly useful for optimizing the defrosting performance and, at the same time, safely operating the system 1.

[0103] While the temperature of the evaporator 7 is not lower than the forced-rest temperature, branch N from step S16, the method 70 returns to step S15; in other words, the defrosting configuration described with reference to step S15 is maintained.

[0104] In practice, according to the present invention, for defrosting the additional heat exchanger 9, the evaporator 7 is coupled in series to the additional heat exchanger 9, if the temperature of the evaporator 7 satisfies at least one defrost condition (e.g., based on the first and / or the second temperature condition) .

[0105] If the temperature of the evaporator 7 becomes equal to or lower than the forced-rest temperature (branch Y from step S16) , then method 70 may proceed to step S17. For example, at branch Y from step S16, the control unit 3 may verify if defrosting of the additional heat exchanger 9 is still needed and, in response, proceed to step S17.

[0106] At step S17, a configuration of the second fluidic circuit 11 that is different from the one discussed with reference to step S15 may be used for defrosting the additional heat exchanger 9. For example, at step S17, a conventional defrosting configuration may be employed.

[0107] For example, at step S17, the control unit 3, starting from the configuration of Figure 1, may reverse the flowing direction of the operative fluid in the second fluidic circuit 11, so that the condenser 3 is used as heat source for defrosting the additional heat exchanger 9.

[0108] According to an embodiment (Figure 4) , the method 70 for defrosting the additional heat exchanger 9 may further comprise monitoring, by the control unit 3, if the temperature Text of the external environment falls below a threshold (step S20) and, in response, increasing the cool setpoint Tcof the system 1 (step S21) .

[0109] For example, the control unit 3 may check whether the temperature Text of the external environment is equal to or lower than 10°C, in particular lower than 10°C. At step S21 , the cool setpoint Tcmay be increased by a value of few degrees , for example of 3 ° C . The Applicant has veri fied that increasing the cool setpoint Tc when the temperature Text is low ( falls below a threshold) may help defrosting the additional heat exchanger 8 without compromising the overall ef ficiency of the system 1 .

[0110] For example , the increase of the cool setpoint Tcmay be chosen based on the compressor 13 , for example based on one or more functional parameters of the compressor 13 , so that the compressor 13 may keep compressing the respective operative fluid between inlet 13A and outlet 13B .

[0111] Steps S20 and S21 may be performed only i f the conditions of steps S i l and S 12 are satis fied (branches Y from steps S i l and S 12 ) .

[0112] The method of defrosting the additional heat exchanger 9 according to the present invention allows to avoid using the condenser 5 to defrost the additional heat exchanger 9 . Therefore , the temperature of the first user fluid flowing in / out of the condenser 5 is not reduced because of the defrosting operation of the additional heat exchanger 9 .

[0113] Accordingly, the present invention allows to reduce the loss of energy occurred during the defrost operation of the additional heat exchanger 9 . Consequently, the seasonal ef ficiency of the system 1 may be increased .

[0114] Moreover, the fact of using the evaporator 7 for defrosting the additional heat exchanger 9 allows to ef fectively obtain a " storage of cold energy" and thus anticipate user requests at the evaporator 7 .

[0115] It is clear that modifications can be made to the present invention, without extending beyond the scope of protection defined by the claims .

[0116] For example, the first and second fluidic circuits 10, 11 may be configured to have, in use, different configurations with respect to the ones illustrated and described above, depending on the specific application and operating conditions of the system 1 . In the first operating mode, the first fluidic circuit 10 may be controlled so as to have a different configuration than the one described with reference to Figure 1 , depending on the specific application and operating conditions of the system 1 .

[0117] What has been described for the second fluidic circuit 11 may be applied also to the first fluidic circuit 10. For example, the defrosting method 70 may be used for defrosting the additional heat exchanger 8 of the first fluidic circuit 10, when the additional heat exchanger 8 is used as evaporator in the first fluidic circuit 10. The electronic control unit 3 may comprise electronic computing resources, centralized or distributed, such as one or more processing unit and one or more memories mutually coupled with each other .

Claims

CLAIMS1. A method for controlling a defrost operation of a refrigeration system (1) comprising a condenser (5) , an evaporator (7) and at least one heat exchanger (8, 9) fluidly couplable with each other so as to form a first circuit (10) and a second circuit (11) , the at least one heat exchanger being configured to exchange heat with an external environment, each of the first and the second circuit comprising a respective operative fluid and respective compressor means (12, 13) for compressing the respective operative fluid through the respective circuit, wherein the refrigeration system (1) is configured to work in a first operating mode wherein one of the first or the second circuit has the heat exchanger (9) fluidly interposed between the condenser (5) and the respective compressor means (13) , and wherein the heat exchanger (9) operates as an evaporator, the method comprising defrosting the heat exchanger (9) during the first operating mode, wherein defrosting the heat exchanger comprises: monitoring if a temperature (Tin, Tout) of the evaporator (7) satisfies a defrost condition; and in response to the temperature of the evaporator satisfying the defrost condition, fluidly coupling the evaporator (7) in series to the heat exchanger (9) .

2. The method according to the preceding claim, wherein defrosting the heat exchanger further comprises, in response to the temperature of the evaporator satisfying the defrost condition, fluidly decoupling the condenser (5) from the heat exchanger (9) .

3. The method according to the claim 1 or 2, wherein the defrost condition is satisfied if the temperature (Tin)of the evaporator is higher than a cool setpoint (Tc) of the refrigeration system.

4. The method according to the preceding claim, wherein the defrost condition is satisfied if a difference between the temperature of the evaporator and the cool setpoint is equal to or higher than a first threshold, the first threshold being different than zero.

5. The method according to any of the preceding claims, wherein the defrost condition is satisfied if the temperature of the evaporator is not lower than a forced-rest temperature of the refrigeration system, the forced-rest temperature being a function of an antifreeze setpoint (TAF) of the refrigeration system.

6. The method according to the preceding claim, wherein the forced-rest temperature is a function of the antifreeze setpoint plus a second threshold.

7. The method according to any of the preceding claims, wherein defrosting the heat exchanger (9) further comprises: monitoring a temperature (Text) of the external environment; and increasing a cool setpoint (Tc) of the refrigeration system, if the temperature of the external environment is lower than a third threshold.

8. The method according to any of the preceding claims, wherein the evaporator (7) is configured to refrigerate a user fluid, the temperature of the evaporator being a temperature (T±n, Tout) of the user fluid at the evaporator.

9. The method according to the preceding claim, wherein the temperature of the user fluid at the evaporator comprises a temperature (Tin) of the user fluid at entrance (30A) of the evaporator (7) and / or a temperature (Tout) of the user fluid at exit (30B) of the evaporator (7) .

10. A refrigeration system (1) comprising a condenser (5) , an evaporator (7) , and at least one heat exchanger (8, 9) fluidly couplable with each other so as to form a first circuit (10) and a second circuit (11) , the at least one heat exchanger being configured to exchange heat with an external environment, each of the first and the second circuit comprising a respective operative fluid and respective compressor means (12, 13) for compressing the respective operative fluid through the respective circuit, wherein the refrigeration system is configured to work in a first operating mode wherein one of the first or the second circuit has the heat exchanger (9) fluidly interposed between the condenser (5) and the respective compressor means (13) , and wherein the heat exchanger (9) operates as an evaporator, the refrigeration system further comprising an electronic control unit (3) that is configured to, for defrosting the heat exchanger (9) when the refrigeration system is in the first operating mode: monitor if a temperature (Tin, Tout) of the evaporator (7) satisfies a defrost condition; and in response to the temperature of the evaporator satisfying the defrost condition, fluidly couple the evaporator (7) in series to the heat exchanger (9) .

11. A computer program comprising instructions that, when executed by an electronic control unit (3) of a refrigeration system (1) , cause the electronic control unit to perform the method according to any of claims 1-9.

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