PROCESS FOR TRANSITIONING A SYNTHETIC REFRIGERATION SYSTEM TO A CO2 REFRIGERATION SYSTEM

Description

BACKGROUND

The present invention relates to a refrigeration system, and more particularly to a process of transitioning a refrigeration system from a synthetic refrigerant to a CO2 refrigerant.

Many different facilities (e.g., a retail store, a supermarket, a warehouse, etc.) may include one or more refrigeration systems that condition a space based on predetermined conditions. Some refrigeration systems include one or more refrigerated display cases or evaporators for storing and/or preserving product (e.g., food product, etc.) at the proper storage temperature. Each refrigeration system typically includes, among other components, a condenser, a compressor, and a heat exchanger that absorbs heat from a space and transfers it to a refrigerant flowing through the refrigeration system (e.g., ambient, or another refrigeration circuit). Some facilities include one or more medium temperature merchandisers that maintain product within a first refrigerated temperature range (e.g., between 34° Fahrenheit and 41° degrees Fahrenheit) and one or more low temperature merchandisers that maintain food at a lower temperature range (e.g., approximately or below 0° Fahrenheit).

Some refrigeration systems use synthetic refrigerants that include hydrofluorocarbons (HFC), perfluorocarbons (PFC), other hydrocarbon (HC) based refrigerants, or blends. Replacing a refrigeration system that uses synthetic refrigerants with a refrigeration system that uses CO2 refrigerant is not simply a matter of removing the synthetic refrigerant and replacing with CO2. A CO2 refrigeration system, often arranged as a transcritical CO2 refrigeration system, requires different components relative to a synthetic refrigeration system due to the properties of CO2 at different temperature and pressure conditions.

In view of this, retailers and facility owners or managers (e.g., operators) are confronted with a decision about how to most cost-effectively transition from a synthetic refrigerant to a CO2 refrigerant because medium temperature equipment and low temperature equipment may have a different end-of-life timeframe. Currently, operators must change the entire system to CO2 even when just one of the circuits (e.g., the medium temperature circuit) still has viable usage.

Current solutions for transitioning to CO2 refrigeration systems (e.g., e.g., pumped systems and cascade systems) often have undesirably high energy losses in part due to the inclusion of heat transfer devices such as heat exchangers to transfer heat from (e.g., the low temperature circuit to the medium temperature circuit), in addition to other losses (e.g., parasitic pump losses), which increase as the number of pumps in the refrigeration system increase.

SUMMARY

In some aspects, the techniques described herein relate to a process for conversion of a first refrigeration system including a first medium temperature circuit and a first low temperature circuit configured to circulate a synthetic refrigerant to a second refrigeration system, the process including: replacing the first low temperature circuit with a second low temperature circuit by adding a heat exchanger to the first refrigeration system such that the second low temperature circuit is in heat exchange relationship with the first medium temperature circuit, the second low temperature circuit including a low temperature compressor, the heat exchanger configured to transfer heat between a CO2 refrigerant in the second low temperature circuit to the synthetic refrigerant in the first medium temperature circuit, and the second low temperature circuit including pipe connections; replacing a condenser of the first medium temperature circuit with a gas cooler; and connecting the second low temperature circuit to the first medium temperature circuit via the pipe connections such that the low temperature compressor is fluidly connected to a medium temperature compressor of the first medium temperature circuit.

In some aspects, the techniques described herein relate to a refrigeration system configured for staged conversion from a synthetic refrigeration system to a CO2 refrigeration system, the refrigeration system including: a first low temperature circuit including a first low temperature compressor configured to circulate a synthetic refrigerant; a first medium temperature circuit including a condenser and a first medium temperature compressor configured to circulate the synthetic refrigerant through the condenser; a second low temperature circuit configured to replace the first low temperature circuit, the second low temperature circuit including a CO2 receiver and configured to circulate a CO2 refrigerant; a second medium temperature circuit configured to replace the first medium temperature circuit, the second medium temperature circuit including a gas cooler and a flash tank, and the second medium temperature circuit configured to circulate the CO2 refrigerant; a heat exchanger configured to transfer heat between the CO2 refrigerant in the second low temperature circuit and the synthetic refrigerant in the first medium temperature circuit after a first conversion stage of the refrigeration system; and a bypass arrangement configured to fluidly couple the second low temperature circuit to the second medium temperature circuit after conversion of the refrigeration system, wherein the bypass arrangement is configured to redirect CO2 refrigerant flow to bypass the heat exchanger.

In some aspects, the techniques described herein relate to a refrigeration system configured for staged conversion from a synthetic refrigeration system to a CO2 refrigeration system, the refrigeration system including: a first low temperature circuit and a first medium temperature circuit cooperatively configured to circulate a synthetic refrigerant; a second low temperature circuit including a CO2 receiver and a low temperature compressor configured to circulate a CO2 refrigerant; a second medium temperature circuit including a flash tank and configured to circulate the CO2 refrigerant; a heat exchanger configured to transfer heat between the synthetic refrigerant and the CO2 refrigerant during a first conversion stage; a first valve positioned between the flash tank and the CO2 receiver, the first valve configured to direct the CO2 refrigerant from the heat exchanger to the CO2 receiver after the first conversion stage and to bypass the heat exchanger after a second conversion stage; and a second valve positioned between the low temperature compressor and the second medium temperature circuit, the second valve configured to direct the CO2 refrigerant through the heat exchanger after the first conversion stage and to bypass the heat exchanger and to direct the CO2 refrigerant to the second medium temperature circuit after the second conversion stage.

Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustrating a refrigeration system.

FIG. 2 is a chart illustrating the process of transitioning a refrigeration system to a CO2 refrigerant.

FIG. 3 is a schematic illustrating a first step in a process of transitioning a refrigeration system.

FIG. 4 is a schematic illustrating a second step in a process of transitioning a refrigeration system.

FIG. 5 is a schematic illustrating a third step in a process of transitioning a refrigeration system.

FIG. 6 is a schematic illustrating the refrigeration system following completion of the process.

DETAILED DESCRIPTION

The term “synthetic refrigerant” refers to a refrigerant that has hydrofluorocarbons (HFC), perfluorocarbons (PFC), or other hydrocarbon (HC) based refrigerants or blends.

The term “synthetic refrigeration system” refers to a refrigeration system that circulates a synthetic refrigerant throughout the refrigeration system.

The term “hybrid refrigeration system” refers to a refrigeration system that circulates synthetic refrigerant through at least one circuit of the refrigeration system, and a CO2 refrigerant through at least another circuit of the refrigeration system.

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. Terms of degree, such as “substantially” or “approximately” are understood by those of ordinary skill to refer to reasonable ranges outside of the given value, for example, general tolerances associated with manufacturing, assembly, and use of the described embodiments.

It will be appreciated that the systems described and illustrated herein may include additional components (valves such as expansion valves or other control valves, controls, pressure regulators, etc.) that are not explicitly described and that one of ordinary skill in the art would appreciate to be part of the systems.

FIG. 1 illustrates an embodiment of a first or synthetic refrigeration system 10 including a first medium temperature circuit 14 and a first low temperature circuit 18. The illustrated first refrigeration system 10 is a synthetic refrigeration system in which a synthetic refrigerant is circulated to condition one or more spaces associated with the medium temperature circuit 14 and one or more spaces associated with the low temperature circuit 18. In the illustrated example, the first refrigeration system 10 includes a receiver 22 that stores synthetic refrigerant in a liquid and gaseous state, a medium temperature evaporator 26 (e.g., associated with a medium temperature merchandiser 28 or another medium temperature space), a medium temperature compressor 30, a low temperature evaporator 34 (e.g., associated with a low temperature merchandiser 36 or another low temperature space), a low temperature compressor 38, and a condenser 42.

The first medium temperature circuit 14 includes the medium temperature evaporator 26 and the medium temperature compressor 30. The first low temperature circuit 18 includes the low temperature evaporator 34 and the low temperature compressor 38. While the illustrated example shows that the refrigeration system 10 includes one medium temperature evaporator 26, one medium temperature compressor 30, one low temperature evaporator 34, and one low temperature compressor 38, it should be appreciated and understood that the first refrigeration system 10 may include any quantity of any one or more of these components. When more than one of any of these components is included in the first refrigeration system 10, the components may be arranged in a parallel arrangement (e.g., three medium temperature evaporators 26 arranged in parallel to each other) or a serial arrangement based on the desired parameters of the first refrigeration system 10. Each of the medium and low temperature compressors 30, 38 may include any type of compressor suitable for the application of the first refrigeration system (e.g., a rotary compressor, a scroll compressor, a screw compressor, a reciprocating compressor, a centrifugal compressor, or any combination thereof).

In operation of the first refrigeration system 10, synthetic refrigerant is cooled in the condenser 42 by heat transfer with another environment (e.g., an ambient environment). The cooled synthetic refrigerant then enters the receiver 22 through a receiver inlet line 46. It will be appreciated that one or more refrigerant lines may be connected to the receiver 22 to direct refrigerant (e.g., gaseous refrigerant) from the receiver 22 to other portions of the first refrigeration system (e.g., the medium temperature compressor 30), re-directed through the condenser 42, etc.). Cooled synthetic refrigerant flow from the receiver 22 is split (e.g., by a three-way valve or other flow control) such that a portion of the synthetic refrigerant flows to the medium temperature evaporator 26 through a first liquid line 50 and another portion of the synthetic refrigerant flows to the low temperature evaporator 34 through a second liquid line 54 that branches from the first liquid line 50. In some examples, the second liquid line 54 may be coupled to the receiver 22 separate from the first liquid line 50. Refrigerant flowing through the medium temperature evaporator 26 exchanges heat with air that conditions the space associated with the medium temperature evaporator 26 (e.g., a product display area in the merchandiser 28). Refrigerant flowing through the low temperature evaporator 34 exchanges heat with air that conditions the space associated with the medium temperature evaporator 34 (e.g., a product display area in the merchandiser 36).

The synthetic refrigerant in the medium temperature evaporator 26 is heated due to the heat transfer, and the synthetic refrigerant flows through a medium temperature suction line 58 and enters the medium temperature compressor 30 in which the refrigerant is compressed to a high pressure, heated refrigerant. The synthetic refrigerant flows via a medium temperature discharge line 62 to the condenser 42 via a condenser inlet line 74. Heated synthetic refrigerant from the low temperature evaporator 34 flows through a low temperature suction line 66 into the low temperature compressor 38. The refrigerant is compressed in the low temperature compressor 38 and flows through a low temperature discharge line 70 to the condenser 42 via the condenser inlet line 74.

Synthetic refrigerant in the medium temperature discharge line 62 and synthetic refrigerant in the low temperature discharge line 70 are combined in the condenser inlet line 74 before entering the condenser 42. In an example, the medium temperature discharge line 62 and the condenser inlet line 74 may be configured as one pipe with a junction (e.g., a T-coupling) to which the low temperature discharge line 70 is coupled. In examples, the synthetic refrigerant may flow from the low temperature compressor 38 to the medium temperature compressor 30 in a two-stage compression process. The synthetic refrigeration system 10 may include valves or other fluid control structures to control the flow of refrigerant through the synthetic refrigeration system 10.

FIGS. 2-6 illustrate a staged conversion process for transitioning or converting a synthetic refrigeration system 10 to a CO2-based refrigeration system 110. The conversion may occur over one or more stages consistent with the disclosure herein. Similar structures of the CO2 refrigeration system 110 will be given the same numbers as their counterparts of the synthetic refrigeration system 10, plus the number “100.”

With reference to FIG. 2, in a first step S1, the synthetic low temperature circuit 18 is replaced with a CO2 low temperature circuit 118. Rather than a parallel flow medium temperature and low temperature refrigeration system 10, the replacement refrigeration system 110 exchanges heat between the CO2 low temperature circuit 118 and the first medium temperature circuit 14 via a heat exchanger 112, which removes heat from the CO2 low temperature circuit 118 to the synthetic medium temperature circuit 14. In a second step S2 (e.g., weeks, months, or years after the low temperature circuit 18 is replaced by the CO2 low temperature circuit 118), the synthetic medium temperature circuit 14 is replaced with a CO2 medium temperature circuit 114. In a third step S3, which is substantially contemporaneous with replacement of the medium temperature circuit 14, the CO2 low temperature circuit 118 and a CO2 medium temperature circuit 114 are connected to provide a transcritical CO2 refrigeration system 110.

FIG. 3 illustrates a first transitional refrigeration system 10a (e.g., a cascade refrigeration system) in which the synthetic refrigeration system 10 is transitioned or converted to a CO2 refrigeration system 110. In the first step (e.g., a first conversion stage), the synthetic low temperature circuit 18 is replaced with a CO2 low temperature circuit 118 that is configured to circulate a CO2 refrigerant, and the heat exchanger 112 is added to the system 10a to enable heat transfer between the CO2 low temperature circuit 118 and the synthetic medium temperature circuit 14. The first transitional refrigeration system 10a includes the synthetic medium temperature circuit 14, which has the receiver 22, the medium temperature evaporator 26 and the medium temperature compressor 30, and the condenser 42. The condenser 42 and the receiver 22 remain fluidly coupled by the receiver inlet line 46. Cooled synthetic refrigerant exits the receiver 22 and flows to the medium temperature evaporator 26 via the first liquid line 50. Heat is exchanged between the synthetic refrigerant in the medium temperature evaporator 26 and an airflow over the evaporator 26, and the heated refrigerant flows to the medium temperature compressor 30 via the medium temperature suction line 58.

The second liquid line 54 is disconnected from the low temperature evaporator 34 and is instead coupled to a first heat exchanger inlet 116 of the heat exchanger 112. The synthetic refrigerant flows from the receiver 22 through the second liquid line 54, enters the heat exchanger 112 and flows through the heat exchanger 112 in a first direction. Heat from the low temperature circuit 118 is transferred to the synthetic refrigerant, and the heated synthetic refrigerant exits through a first heat exchanger outlet 120. The heated synthetic refrigerant flows through a first heat exchanger outlet line 124 and is coupled to the medium temperature suction line 58. The synthetic refrigerant flowing from the first heat exchanger outlet line 124 combines with the synthetic refrigerant that flows directly from the evaporator 26 to the medium temperature compressor 30. The compressed refrigerant then flows to the condenser 42 via the line 62.

The CO2 low temperature circuit 118, which replaces the synthetic low temperature circuit 18, includes the low temperature evaporator 34, a CO2 receiver 122, and a CO2 low temperature compressor 138. The CO2 low temperature compressor 138 may be any suitable compressor that accommodates CO2 refrigerant (e.g., a rotary compressor, scroll compressor, screw compressor, reciprocating compressor, centrifugal compressor, etc.) and, in some examples, may be the same as the compressor 38. The CO2 receiver 122 may store a portion of the CO2 refrigerant (e.g., cooled refrigerant) in the CO2 low temperature circuit 118. The cooled CO2 refrigerant flows from the CO2 receiver 122 through a liquid line 154 to the CO2 low temperature evaporator 34. The CO2 refrigerant is in heat transfer with and removes heat from ambient air within the CO2 low temperature evaporator 34. The heated CO2 exits the CO2 low temperature evaporator 34 and travels through a low temperature suction line 166 to the CO2 low temperature compressor 138 in which the CO2 refrigerant is compressed. The heated and compressed CO2 refrigerant travels from the CO2 low temperature compressor 138 through a low temperature discharge line 170 to the second heat exchanger inlet 128. The CO2 refrigerant flows through the heat exchanger 112 in a second direction (e.g., opposite the direction of flow of the synthetic refrigerant in a counterflow arrangement, or in the same direction in a parallel flow arrangement), and exchanges heat with the cooled synthetic refrigerant flowing through the heat exchanger 112 in the first direction. The cooled CO2 refrigerant exits a second heat exchanger outlet 132 and flows through a CO2 receiver inlet line 146 and returns to the CO2 receiver 122.

The CO2 low temperature circuit 118 includes one or more valves 136 (e.g., three-way valves) that are configured to be coupled in the following steps of the process (FIG. 2). In the illustrated example, the valves 136 are positioned in the receiver inlet line 146 and the low temperature discharge line 170 and are configured to be connected to other lines at future steps to facilitate connection of the low temperature circuit 118 to the medium temperature circuit 14. The low temperature circuit 118 may include other fluid coupling structures to facilitate refrigerant flow and conditioning of the one or more spaces.

FIG. 4 illustrates a second transitional refrigeration system 10b that is consistent with the second step S2 in the process of transitioning the synthetic refrigeration system 10 of FIG. 1 to a CO2 refrigeration system 110. In the second step S2, the synthetic medium temperature circuit 14 is disconnected from the first heat exchanger inlet 116 and the first heat exchanger outlet 120 of the heat exchanger 112, and the circuit 14 is replaced with a CO2 medium temperature circuit 114 configured to operate with CO2 refrigerant. The second transitional refrigeration system 10b includes the CO2 low temperature circuit 118 described above with regard to the first step S1.

The CO2 medium temperature circuit 114 includes the medium temperature evaporator 26, a CO2 medium temperature compressor 130 that replaces the synthetic medium temperature compressor 30, a flash tank 140 that replaces the synthetic receiver 22, and a gas cooler 142 that replaces the condenser 42. The CO2 medium temperature compressor 130 may be any suitable compressor (e.g., a rotary compressor, scroll compressor, screw compressor, reciprocating compressor, centrifugal compressor, etc.).

The flash tank 140 is configured to hold CO2 refrigerant, a portion of which is in a cooled liquid stage and another portion of which is in a cooled gas state. A main liquid line 150 fluidly couples the flash tank 140 and the medium temperature evaporator 26 so that liquid CO2 refrigerant flows through the medium temperature evaporator 26. The main liquid line 150 may include a stub 144 that branches from the main liquid line 150. In some examples, the stub 144 may be coupled to the flash tank 140. In other examples, the main liquid line 150 may include a valve that selectively permits a flow of refrigerant to another liquid line coupled to the valve. A medium temperature suction line 158 couples the outlet of the medium temperature evaporator 26 and the CO2 medium temperature compressor 130. The medium temperature suction line 158 includes a stub 148 that can be coupled to the low temperature circuit 118 in Step S3. A CO2 flash gas bypass line 152 is coupled to the flash tank 140 through which cooled CO2, in gas form, bypasses the main liquid line 150 and the medium temperature evaporator 26, and flows into the medium temperature suction line 158. The medium temperature compressor 130 is coupled to the gas cooler 142 by a CO2 medium temperature discharge line 162, through which CO2 refrigerant flows to the gas cooler 142. The CO2 refrigerant is cooled in the gas cooler 142 and returns to the flash tank 140 via a flash tank inlet line 156. A valve 160 (e.g., a throttle valve) is positioned in the flash tank inlet line 156 upstream of the flash tank 140 to control the flow of CO2 refrigerant into the flash tank 140, for instance, to reduce the pressure of the CO2 refrigerant as it flows through the valve. This results in a low pressure, cooled CO2 refrigerant. Another valve 164 is positioned in the suction bypass line 152 downstream of the flash tank 140 to control the flow of CO2 refrigerant from the flash tank 140 to the CO2 medium temperature compressor 130.

FIG. 5 illustrates the refrigeration system 110 following completion of the third step S3 in the process of transitioning the synthetic refrigeration system 10 of FIG. 1 to the CO2 refrigeration system 110. In the third step, the CO2 medium temperature circuit 114 and CO2 low temperature circuit 118 are coupled. The stub 144 of the main liquid line 150 is coupled to the CO2 receiver 122 by a medium temperature evaporator bypass line 174, which is coupled to the valve 136 in the receiver inlet line 146. This permits liquid CO2 refrigerant to flow from the flash tank 140 to the CO2 receiver 122. The stub 148 branching from the medium temperature suction line 158 is coupled to the one or more valves 136 in the low temperature discharge line 170 by a heat exchanger bypass line 178, which is positioned downstream of the CO2 low temperature compressor 138. With the valves 136 closed to off the heat exchanger 112, CO2 refrigerant can flow from the flash tank 140 to the receiver 122 and from the low temperature compressor 138 to the join the CO2 refrigerant in the medium temperature suction line 158 prior to being compressed in the medium temperature compressor 130. It will be appreciated that by bypassing the heat exchanger 112, the heat exchanger 112 can be removed from the refrigeration system 110, illustrated in FIG. 6.

It will be appreciated that the CO2 refrigeration system 110 in place at the completion of the process is more efficient than the transitional synthetic/CO2 refrigeration system 10a because refrigerant is not directed through the heat exchanger 112, which is only approximately 70% efficient in transferring heat from the CO2 refrigerant to the synthetic refrigerant.

The process embodied by the examples described and illustrated herein removes a synthetic refrigerant low temperature circuit and installs a cascade system with a CO2 low temperature circuit and a synthetic medium temperature circuit. The initial conversion includes transition or conversion of the low temperature side to CO2 refrigerant, and optionally later merging the converted low temperature side with a newly implemented medium temperature CO2 circuit. It will be appreciated that conversion of the low temperature side to CO2 may only stay in the cascade setup in some examples.

The examples described herein implement a cascade heat exchanger to facilitate transition from a synthetic refrigerant-based refrigeration system to a CO2 refrigerant-based refrigeration system, and the cascade heat exchanger may be bypassed or removed at a later time (e.g., in a second conversion stage that is different from the first conversion stage). That is, the heat exchanger may be implemented as a transitory solution (i.e. the heat exchanger is meant to be bypassed intentionally for full conversion to CO2 refrigerant) to convert the refrigeration system 10 to a CO2 refrigeration system 110. Bypass stubs and three-way valving on the low temperature side facilitates the conversion. The three-way valve(s) allow refrigerant to circulate through the cascade heat exchanger after initial conversion, and then allows redirection of the CO2 refrigerant directly to the medium temperature compressor after the medium temperature side is converted. This is facilitated by changing the three-way valve so that the CO2 refrigerant flows through the bypass line to the medium temperature compressor. As such, when the medium temperature circuit and the low temperature circuit are tied together, the bypass is opened to allow flow of CO2 refrigerant via the new-normal configuration rather than through the cascade heat exchanger. Thereafter, the cascade heat exchanger 112 can be removed.

In any of the previously described refrigeration systems, other expansion valves, throttle valves, or other fluid flow control fittings or structures may be used to optimize flow of refrigerant through the refrigeration systems 10, 10a, 10b, 110 to efficiently remove heat from the evaporators 26, 34.

Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.