Refrigeration Circuit

The present invention is related to the field of refrigeration circuits, more particularly, to refrigeration circuits using COas refrigerant (R-744).

An object of the present invention is to provide a R-744 refrigerant circuit able to reduce the power consumption by increasing the energy efficiency.

At present, there are different improvements introduced to the circuits with R-744 to increase their efficiency, which are mainly aimed to increase the efficiency of the facility in climates with high ambient temperatures.

The main problem in refrigeration circuits using R-744 is the high reduction in efficiency at medium-high ambient temperatures. This efficiency reduction is mainly despite to high power consumption of the medium-temperature compression rack (MTC).

A solution proposed consists of introducing in a circuit several ejectors (Multi-Ejector racks, MEJ). This circuit compresses part of the refrigerant of medium-temperature services to intermediate pressure (liquid receiver pressure). To do that, the multi-ejector uses R-744 with high pressure as motive flow, which reduces its pressure through a nozzle below the medium-temperature services pressure and, consequently, increases its velocity. Thus, the motive flow suctions part of the refrigerant of the medium-temperature services and is compressed to intermediate pressure. This circuit is used with different types of ejectors, the most used is the high-pressure multi-ejector.

The use of high-pressure multi-ejector reduces the refrigerant in the medium-temperature compression rack and consequently its power consumption. Additionally, the medium-temperature compression rack compresses part of the medium-temperature services refrigerant without a mechanical compressor taking the potential energy of the motive flow.

Nevertheless, this circuit needs an additional compression denoted as parallel compression rack to compress the refrigerant in vapor state generated by the multi-ejector. The vapor quality in the liquid receiver is higher and the capacity requirements in parallel compression rack is greater than the circuits without ejectors, having a similar cooling load.

The temperature at suction port of the medium-temperature compression rack is higher than the circuits without ejectors and, in consequence, the discharge temperature too, producing temperatures greater than 140° C. for ambient temperatures above 35° C.

The main problem of the high-pressure multi-ejector racks is that they do not operate efficiently for ambient temperatures below 30° C. in R-744 circuits. Also, the cost of using high-pressure multi-ejector racks is high. In addition, it has problems with the high oil transfer rate at the parallel compression rack due to the reduced superheat in suction port. Also, the suction pressure of the parallel compression rack is fixed by a liquid receiver, storing the refrigerant, and this compressor rack does not work at its optimal operating point (maximum compressor efficiency).

A lot of solutions have been proposed to improve the efficiency of a refrigeration circuit using R-744 at medium-high ambient temperatures. Nevertheless, few improvements are used at the present time. The most used improvements to R-744 circuits are the parallel compression, mechanical subcooling and ejectors, but these circuits have several limitations. Therefore, a circuit with lower limitations using R-744 for increasing the efficiency of the refrigeration process at medium-high ambient temperatures is needed.

As an example, document EP3872418 refers to a refrigerant circuit for increasing energy efficiency comprising a tank, storing liquid and vapor R-744; a first R-744 liquid line, connecting the tank to a medium-temperature line, and comprising a medium-temperature expansion valve connected to a medium-temperature evaporator connected to a suction line, which connects with a medium-temperature compressor; a low-temperature line, connected to the first R-744 liquid line, and comprising a low-temperature expansion valve connected to a low-temperature evaporator connected to a low-temperature compressor connected to the suction line; an adiabatic gas-cooler, connected to the medium-temperature compressor; a first back-pressure valve, connected to the tank and to a first heat exchanger, connected to the adiabatic gas-cooler; and a R-744 vapor line, connecting the tank with the first heat exchanger and with the suction line.

The present invention is directed to a R-744 refrigerant circuit able to increase the efficiency of the refrigeration process, thus, reducing the power consumption in a large variety of locations having different ambient conditions and increasing the operation temperature range.

According to a first aspect, the refrigeration circuit of the invention comprises at least one first compressor, a first gas-cooler, a first heat exchanger, a first pressure reduction valve, a medium temperature heat exchanger, a medium temperature expansion valve and a liquid receiver for storing the R-744, which is in a mixed physical state, thus, storing a liquid R-744 and a vapor R-744.

The liquid R-744 is extracted from the liquid receiver by means of an outlet liquid line that is split in a first liquid line and a second liquid line.

The second liquid line is directed to a first heat exchanger after passing through a first expansion valve.

The first liquid line is directed to the first heat exchanger and then to a medium temperature heat exchanger after passing through a medium temperature expansion valve to return to the second liquid line downstream the first expansion valve so that the mixture enters the first heat exchanger to exchange heat with the refrigerant in the first liquid line and then flow to the at least one first compressor through a suction line.

The outlet of the at least one compressor is connected through a discharge line to the inlet of the first gas-cooler, and the outlet of the first gas-cooler is connected to a gas-cooler outlet line which is directed to the liquid receiver after passing through a first pressure reduction valve.

According to a second aspect of the invention, the refrigeration circuit may also comprise an outlet vapor line connected to the liquid receiver and a third heat exchanger.

The outlet vapor line comprises a second pressure reduction valve and is directed to the suction line at the outlet of the first heat exchanger.

The third heat exchanger is located in the suction line, between the first heat exchanger after mixing with the outlet vapor line and the at least one first compressor. The refrigerant in the suction line exchanges heat with the refrigerant flowing through the gas-cooler outlet line upstream the first pressure reduction valve and the refrigerant flowing through the suction line.

According to a third aspect, the refrigeration circuit may also comprise a first motorised multi way valve () located in the suction line () either at the inlet or at the outlet of the third heat exchanger (), and a first pipe () connected to the first motorised multi way valve () and bypassing the third heat exchanger, creating a ring so that the refrigerant flows from the first heat exchanger mixed with the refrigerant from the outlet vapor line to the at least one first compressor either through the third heat exchanger, along the suction line, directly through the first pipe, bypassing the third heat exchanger, or as a mixture through both ways.

According to a fourth aspect, the refrigeration circuit may also comprise a second compressor connected to the at least one first compressor in parallel to the common discharge line, a second heat exchanger that exchanges heat between the refrigerant leaving the first gas-cooler and the refrigerant flowing through a first fluid line that branches from the gas-cooler outlet line, either at the inlet or at the outlet of the third heat exchanger, depressurized by a third expansion valve, and a second pipe that connects the inlet of the second compressor with the first fluid line leaving the second heat exchanger.

According to a fifth aspect, the refrigeration circuit may also comprise a first vapor line with a first motorised valve, connecting the outlet vapor line to the first fluid line at the inlet of the second heat exchanger.

According to a sixth aspect, the refrigeration circuit may also comprise a cooling line that connects the first liquid line at the inlet of the first heat exchanger with the first vapor line, and further comprises a cooling coil located within the liquid receiver and a fourth expansion valve.

According to a seventh aspect, the refrigeration circuit may also comprise a second motorised multi way valve located in the discharge line that is connected to the inlet of a fourth heat exchanger through a first branch. The outlet of the fourth heat exchanger is connected to the inlet of the first gas-cooler.

According to an eighth aspect, the refrigeration circuit may also comprise a third motorised multi way valve, located in the discharge line, that is connected to the outlet gas-cooler line through a second branch, bypassing the first gas-cooler.

According to a ninth aspect, the refrigeration circuit may also comprise a first check valve, located in the gas-cooler outlet line upstream the connection to the second branch, a third branch, comprising a third motorised valve that connects the inlet to the first gas-cooler with the outlet vapor line, and a fourth branch comprising a second expansion valve and a second check valve that connects the first liquid line with the gas-cooler outlet line upstream the first check valve.

The circuit may present several alternative configurations.

In a first configuration, the refrigeration circuit may additionally comprise:

In a second configuration, the refrigeration circuit may additionally comprise:

In a third configuration, the refrigeration circuit may additionally comprise:

These three configurations may also comprise:

With this configuration, the refrigerant flowing through the second pipe can be switched between the inlet of the second compressor and the inlet of the rest of compressors.

According to a tenth aspect of the invention, the refrigeration circuit may also comprise a low temperature liquid line connecting the first liquid line with the suction line, the low temperature liquid line comprising a low temperature expansion valve, a low temperature heat exchanger, a low temperature compressor, and a desuperheater.

According to an eleventh aspect of the invention, the refrigeration circuit may be configured so that the low temperature liquid line, at the outlet of the low temperature heat exchanger, is connected to the first heat exchanger upstream the low temperature compressor. In this situation, the first heat exchanger is configured to exchange heat between the refrigerant in the low temperature liquid line and the refrigerant flowing through the first liquid line.

According to a twelfth aspect of the invention, the refrigeration circuit may also comprise:

In this situation, the refrigerant may either flow to the first heat exchanger or directly flow the low temperature compressor, bypassing the first heat exchanger. The seventh motorised multi-way valve is configured to be controlled based on the superheat in the suction of the low temperature compressor.

According to a thirteenth aspect, the refrigeration circuit may also comprise a sixth motorised multi way valve located at the outlet of the desuperheater.

In this case, the refrigerant flowing from the desuperheater may be switched either to the suction line at the inlet of the at least one first compressor or to the sixth fluid line at the inlet of the pressure exchanger.

The present invention is directed to a refrigerant circuit with the capacity to increase the energy efficiency, particularly, when operating in changing-temperature environments in order to reduce the overall power consumption.

Further advantages of the refrigerant circuit are described in relation to the figures, which represent particular embodiments of the invention non-limiting the scope of the invention defined by the claims.

shows a first embodiment of the refrigerant circuit of the present invention.

It comprises a liquid receiver () connected to an outlet liquid line (), in order to provide the circuit with liquid, and to an inlet line to receive liquid from the circuit.

The outlet liquid line () is split in a first liquid line () and a second liquid line () that comprises a first expansion valve ().

The first liquid line () is directed to a first heat exchanger () and then to a medium temperature heat exchanger () after passing through a medium temperature expansion valve () which is then returned to the second liquid line () downstream the first expansion valve ().

The second liquid line () is directed to the first heat exchanger () after passing through the first expansion valve () and mix with the refrigerant of the first liquid line () leaving the medium temperature heat exchanger () to exchange heat with the refrigerant of the first liquid line (). The outlet of the first heat exchanger () is connected to the inlet of at least one first compressor () through a suction line ().

The outlet of the at least one compressor () is connected through a discharge line () to the inlet of a first gas-cooler (), and the outlet of the first gas-cooler () is connected to a gas-cooler outlet line () which is directed to the inlet line of the liquid receiver () after passing through a first pressure reduction valve ().

In this embodiment, the first heat exchanger () introduces a superheat in the suction line () to operate with low superheating in the medium temperature heat exchanger () and with higher evaporation temperature to reduce the energy consumption in the at least one first compressor (). Additionally, a subcooling in the first liquid line () is introduced in order to reduce the flash-gas in the expansion valves of the medium temperature expansion valve (), increasing the cooling capacity of the first compressors (). With the first expansion valve (), the superheat in the suction line () of the first compressors () is controlled.

shows an amendment to the circuit shown inwhere an outlet vapor line () and a third heat exchanger () have been introduced.

The outlet vapor line () comprises a second pressure reduction valve () and connects the liquid receiver () with the suction line () at the outlet of the first heat exchanger (), where the suction line (), before heading to the at least one first compressor (), is directed to a third heat exchanger () to exchange heat with the refrigerant flowing through the gas-cooler outlet line () upstream the first pressure reduction valve ().