JP7476398B2 - Low GWP cascade cooling system - Google Patents

Description

This application claims priority to provisional application 62/313,177, filed March 25, 2016, which is incorporated herein by reference in its entirety.
This application is also a continuation of and claims the benefit of priority to U.S. Application Serial No. 15/468,292, filed March 24, 2017, which is incorporated herein by reference in its entirety.

This application is also a continuation-in-part of currently pending U.S. application 15/400,891, filed January 6, 2017, which claims the benefit of priority to provisional application 62/275,382, filed January 6, 2016, each of which is incorporated herein by reference in its entirety.

This application is also a continuation-in-part of currently pending U.S. application 15/434,400, filed February 16, 2017, which claims the benefit of priority to 62/295,731, filed February 16, 2016, the entire contents of each of which are incorporated herein by reference.

The present invention relates to highly efficient, low global warming potential (low GWP) air conditioning and/or cooling systems and methods for providing safe and effective cooling.

In a typical air conditioning and refrigeration system, a compressor is used to compress a heat transfer vapor from a lower pressure to a higher pressure, thereby adding heat to the vapor. This added heat is typically rejected into a heat exchanger, usually called a condenser. The heat transfer vapor introduced into the condenser is condensed to produce a relatively high pressure liquid heat transfer fluid. Typically, the condenser uses a fluid available in large quantities in the surrounding environment, such as ambient air, as a heat sink. Once condensed, the high pressure heat transfer fluid is subjected to a substantially isenthalpic expansion, which occurs by passing the fluid through an expansion device or valve, where it expands to a lower pressure, thereby causing the fluid to undergo a temperature drop. The lower pressure and lower temperature heat transfer fluid from the expansion operation is typically then sent to an evaporator, where it absorbs heat and is thereby evaporated. This evaporation process provides cooling for the fluid or object that is intended to be cooled. In many typical air conditioning and refrigeration applications, the fluid to be cooled is the air in the conditioned living space or the air contained within the area to be cooled, such as the air inside a walk-in cooler or supermarket cooler or freezer. After the heat transfer fluid is evaporated at low pressure in the evaporator, it is returned to the compressor where the cycle begins again.

Creating an efficient, effective and safe air conditioning system that is simultaneously environmentally friendly, i.e., has both low GWP and low ozone depletion (ODP) effects, involves a complex and interrelated combination of factors and requirements. With regard to efficiency and effectiveness, it is important that the heat transfer fluid operates in an air conditioning and cooling system with a high level of efficiency and high relative capacity. At the same time, because the heat transfer fluid may leak into the atmosphere over time, it is important that the fluid has low values for both GWP and ODP.

Applicants have come to recognize that while some fluids can achieve both high levels of efficiency and effectiveness, and simultaneously achieve low levels of GWP and ODP, many fluids that meet this combination of requirements suffer from safety deficiencies. For example, fluids that may otherwise be acceptable may be undesirable due to flammability characteristics and/or toxicity issues. Applicants have come to recognize that the use of fluids with such characteristics is particularly undesirable in conventional air conditioning systems and many refrigeration systems, since such flammable and/or toxic fluids may be inadvertently released into the living space being cooled, walk-in cooler, cold storage container, chiller, freezer, or transport cooling container, thereby exposing or exposing the occupants thereof to dangerous conditions. Applicants have also come to recognize that this problem is even more significant for relatively small systems, e.g., systems having a capacity of less than 30 kW, for which the cost of an effective safety protection system, such as a fire protection system, is often not economically feasible.

According to one aspect of the invention, there is provided a cascade refrigeration system for providing cooling, either directly or indirectly, but preferably directly, to air located within an enclosure occupied or exposed to humans or other animals during normal use. As used herein, the term "enclosure" means a space that is at least partially defined (e.g., the enclosure may be open or closed on one or more sides) and contains the air to be cooled.

A preferred embodiment of the system includes at least a first evaporator disposed within the enclosure and part of a first relatively low temperature heat transfer circuit. The low temperature heat transfer circuit preferably includes a first heat transfer fluid in a vapor compression circulation loop including at least a compressor for increasing the pressure of the first heat transfer composition; a heat exchanger for condensing at least a portion of the first heat transfer composition from the relatively high pressure compressor; an expansion device for decreasing the pressure of the heat transfer composition from the condenser; and an evaporator for absorbing heat from the enclosure to be cooled into the heat transfer composition. Preferably, one or more of the compressor, condenser, and expansion valve, most preferably all of these, are disposed outside the enclosure, and the evaporator is disposed within the enclosure.

The system of the present invention also preferably includes a second heat transfer circuit (sometimes referred to herein for convenience as a "hot" loop) disposed substantially outside the enclosure. The hot loop preferably includes a second heat transfer fluid in a vapor compression circulation loop including at least a compressor, a heat exchanger that serves to condense the heat transfer fluid in the hot loop, preferably by heat exchange with ambient air outside the enclosure, and an expansion device for reducing the pressure of the second heat transfer fluid from the compressor.

An important feature of the preferred embodiment of the present invention is that a heat exchanger acting as a condenser in the low temperature circuit is thermally coupled to the high temperature circuit for rejecting heat into a second heat transfer fluid, preferably by evaporating at least a substantial portion of the second heat transfer fluid. Thus, the low temperature circuit condenser and the high temperature circuit evaporator are thermally coupled in this heat exchanger, which is sometimes referred to for convenience in the systems and methods of the present invention as a "cascade heat exchanger."

Another important feature of the present invention in preferred embodiments includes the presence of a heat exchanger in the high temperature loop which has been found to advantageously and unexpectedly improve system performance by transferring heat from the second heat transfer fluid exiting the high temperature condenser to the portion of the second heat transfer fluid delivered to the suction side of the compressor. This heat exchanger is sometimes referred to herein for convenience as the "suction line heat exchanger."

Another important feature of the preferred system is that the first heat transfer fluid circulating in the low temperature loop comprises a refrigerant having a GWP of about 500 or less, more preferably about 400 or less, even more preferably about 150 or less, and further that the first heat transfer fluid has a flammability that is significantly lower than that of the second heat transfer fluid. Preferably, the second heat transfer fluid circulating in the high temperature loop also comprises a refrigerant having a GWP of about 500 or less, more preferably about 400 or less, even more preferably about 150 or less, but since in normal operation this heat transfer fluid is never introduced into the enclosure, applicants have found that it is advantageous to use in this high temperature loop a fluid that has one or more properties that would be considered disadvantageous if circulated in the enclosure, such as flammability, toxicity, etc. Thus, as will be explained in more detail below, the present system allows further possible unexpected advantages over systems that rely only on the first heat transfer composition or only on the second heat transfer composition.

In some preferred embodiments, the second refrigerant comprises, and more preferably comprises, at least about 50% by weight, and even more preferably at least about 75% by weight, trans-1,3,3,3-trifluoropropene (HFO-1234ze(E)) and/or HFO-1234yf, and the second refrigerant has a flammability that is about greater than, and preferably significantly greater than, the flammability of _CO2 . In other embodiments, the second refrigerant comprises, and more preferably comprises, at least about 75% by weight, and even more preferably at least about 80% by weight, trans-1,3,3,3-trifluoropropene (HFO-1234ze(E)) and/or HFO-1234yf.

FIG. 1 is a generalized process flow diagram of one preferred embodiment of an air conditioning system according to the present invention.

Preferred heat transfer compositions:
In each of the preferred aspects described herein, the system comprises:
(a) a relatively low temperature vapor compression loop including a compressor, an expander, and an evaporator in fluid communication within the loop, and a first heat transfer composition within the loop including a first refrigerant and preferably a lubricant for the compressor, the evaporator being disposed within an enclosure containing air to be cooled and capable of absorbing heat from the air at about such relatively low temperature;
(b) a relatively high temperature vapor compression loop including a compressor, a condenser, an expander, and a suction line heat exchanger in fluid communication within the loop, and a second heat transfer composition within the loop including a second refrigerant and preferably a lubricant for the compressor (the condenser is capable of transferring heat to a heat sink located outside the enclosure); and (c) a cascade heat exchanger for condensing the first refrigerant and evaporating the second refrigerant by heat exchange between the first and second refrigerants;
Including;
The suction line heat exchanger is in fluid communication with the cascade heat exchanger for receiving at least a portion of the second heat transfer composition discharged from the cascade heat exchanger and increases its temperature by absorbing heat from the first heat transfer composition discharged from the condenser, thereby reducing the temperature of the first heat transfer composition before it is introduced into the first loop expander.

As used herein, the terms "relatively low temperature" and "relatively high temperature," when used together with respect to the first and second heat transfer loops, are used in a relative sense to indicate the relative temperatures of the indicated heat transfer compositions, where the difference between them is at least about 5° C., unless otherwise indicated.

Preferably, the first refrigerant has a flammability substantially lower than that of the second refrigerant. In a preferred embodiment, the first refrigerant has a flammability classified as A1 according to ASHRAE standard 34 (which defines a method of measurement according to ASTM-E681) and the second refrigerant has a flammability classified as A2L according to ASHRAE standard 34 or a flammability higher than A2L, with an A2L classification being preferred for the second refrigerant. It is also preferred that the first and second refrigerants each have a Global Warming Potential (GWP) of less than about 150.

In preferred embodiments, the first refrigerant circulating in the cryogenic loop comprises carbon dioxide, preferably consists essentially of carbon dioxide, and more preferably consists of carbon dioxide in some embodiments.

The second refrigerant preferably comprises one or more of trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)), 2,3,3,3-tetrafluoropropene (HFO-1234yf), R-227ea, and R-32, and combinations of two or more thereof. In a preferred embodiment, the second refrigerant comprises at least about 50% by weight, more preferably at least about 80% by weight of 2,3,3,3-tetrafluoropropene (HFO-1234yf). In another preferred embodiment, the second refrigerant comprises at least about 50% by weight, more preferably at least about 80% by weight or at least about 75% by weight, more preferably at least about 80% by weight of trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)). In highly preferred embodiments, the second refrigerant comprises, and in some embodiments consists essentially of, or consists of, at least about 95% by weight of HFO-1234ze(E), HFO-1234yf, or a combination of two or more thereof.

In another highly preferred embodiment, the second refrigerant comprises about 70% to about 90% by weight HFO-1234yf, preferably about 80% by weight HFO-1234yf, and about 10% to about 30% by weight R32, preferably about 20% by weight R-32.

In another highly preferred embodiment, the second refrigerant comprises about 70% to about 90% by weight HFO-1234ze(E), preferably about 80% by weight HFO-1234ze(E), and about 10% to about 30% by weight R32, preferably about 20% by weight R-32.

In other highly preferred embodiments, the second refrigerant comprises about 85% to about 90% by weight of trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) and about 10% to about 15% by weight of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), and even more preferably in some embodiments, about 88% by weight of trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) and about 12% by weight of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea).

Those skilled in the art, in view of the disclosure contained herein, will recognize that preferred embodiments of the present invention provide the advantage of using only safe (relatively low toxicity and low flammability), low GWP refrigerants within the enclosure to be cooled, and relatively less safe, but preferably low GWP, refrigerants in the high temperature loop located entirely outside the enclosure.

As used herein, the terms "safe" and "relatively less safe," when used together with respect to the first and second heat transfer loops, are used in a relative sense to indicate the relative safety of the indicated heat transfer composition, unless otherwise indicated. Such configurations, particularly when the high temperature system includes the preferred suction line heat exchanger, make the systems and methods of the present invention highly suitable for use in locations in close proximity to humans or other animals occupying or using enclosures commonly encountered in walk-in freezers, supermarket coolers, and the like.

Preferred embodiments of the second refrigerant are disclosed in the table below.

The first and second heat transfer compositions also each typically include a lubricant, typically in an amount of about 30 to about 50% by weight of the heat transfer composition, with the remainder being the refrigerant and other optional ingredients that may be present. A combination of surfactants and solubilizers may also be added to the composition to promote oil solubility, as disclosed by U.S. Pat. No. 6,516,837, the disclosure of which is incorporated herein by reference. Commonly used refrigeration lubricants such as polyol esters (POE) and polyalkylene glycols (PAG), silicone oils, mineral oils, alkylbenzenes (AB), and poly(alpha-olefins) (PAO) used in chillers with hydrofluorocarbon (HFC) refrigerants may be used with the refrigerant compositions of the present invention. The preferred lubricant is POE.

Preferred combinations of a first refrigerant, a second refrigerant, and a lubricant according to one embodiment of the present invention are given below.

System operating conditions:
In general, it is contemplated that the operating conditions used in the present systems and methods can vary widely depending on the particular application in light of the disclosure contained herein. However, many preferred applications will advantageously employ operating parameters within the ranges shown in the table below. It is understood that all of these amounts are modified by "about."

When operated within the process conditions of the present invention, the use of the suction line heat exchanger described herein preferably provides at least a 2% improvement in COP, more preferably at least about a 3% improvement in COP, and even more preferably a 4% improvement in COP, compared to a similar system but without the suction line heat exchanger of the present invention.

In the following description, components or parts of the system that are or may be generally the same or similar in different embodiments are designated with the same numerals or symbols.
One preferred cooling system is shown in FIG. 1. The cooling system is generally designated as 10. The boundary generally designated as 100 diagrammatically represents an enclosure. The cold loop includes a compressor 11, a condensing side 12A of a cascade heat exchanger 12, an expansion valve 14, and an evaporator 15. As shown, the evaporator 15 is disposed within the enclosure 100 along with any associated conduits and other connections and associated equipment that transport the first heat transfer composition to and from the enclosure boundary. The evaporator 14 is preferably disposed inside the enclosure, and while in the illustrated drawings it is disclosed as being disposed inside the enclosure 100, it is recognized that in some embodiments it may be desirable and/or necessary to provide the expander 14 outside the enclosure. The hot loop includes a compressor 21, an evaporating side 12B of the cascade heat exchanger 12, an expansion valve 24, and a condenser 25, all of which are disposed outside the enclosure 100 along with any associated conduits and other connections and associated equipment. The high temperature circuit also includes a suction line heat exchanger 50 that enables the exchange of heat between the second heat transfer composition stream 30 discharged from the condenser 25 and the second heat transfer composition stream 31 discharged from the evaporative side 12B of the cascade heat exchanger 12.

While it is contemplated that the relative dimensions of the first and second cooling loops according to the present invention may vary widely within their ranges, applicants have found that highly advantageous results can be achieved in some embodiments by careful selection of the relative dimensions of the cooling loops. More specifically, it is contemplated and understood that under normal operating conditions the heat transfer compositions contained in the first and second cooling loops never mix or intermingle. However, applicants have come to recognize that the possibility of such intermingling of the first and second refrigerants may arise, for example in the event of a leak in the cascade heat exchanger. This mixed refrigerant stream may then become exposed to humans or other animals in or near the enclosure in the event of a leak in the enclosure being cooled. Thus, to ensure continued safe operation in the event of such a leak, applicants have come to recognize that by careful and judicious selection of the relative cooling loop dimensions, a safe system can be obtained in the event of such a leak.

Applicants believe that the systems and compositions of the present invention will be useful in many cooling applications, but preferred applications include cooling systems and methods for use in applications such as air treatment, such as cooling and/or heating, in enclosures such as residential living spaces, office spaces, warehouses, and the like, and in applications such as air treatment, such as cooling and/or heating, in association with enclosures used to keep items cool by cooling the air within the enclosure, such as walk-in containers, ice containers, transport coolers, and the like. As used herein, the term "transport cooler" is used to refer to a cryogenic/insulated container located on or constituting a portion or substantially all of a cargo trailer. Additionally, in preferred applications, the capacity of the system of the present invention is less than about 30 kW. In preferred applications, the capacity of the system of the present invention is less than about 15 kW, and in further applications, the capacity of the system of the present invention is less than about 10 kW.

Some preferred system, method and composition examples are described below.
A. The first refrigerant is _CO2 and the second refrigerant is R-1234ze(E):
As an example, the applicants considered a cascade cooling system according to the invention in which the first refrigerant is composed of _CO2 and the second refrigerant is composed of R01234ze(E). In order to achieve a cooling system according to the invention that is safe even in the event of intermixing between the first and second refrigerants, the applicants determined the flammability of various mixtures of these components (including vapors and liquids) as follows:

Based on the above discussion and analysis, and on the preferred embodiment of the present invention in which the first refrigerant consists essentially of _CO2 and the second refrigerant consists essentially of R-1234ze(E), it is preferred that the weight ratio of the loading of the first refrigerant (e.g., _CO2 ) to the second refrigerant (e.g., R-1234ze(E)) in the cryogenic loop is about 1.2 or greater. In such an embodiment, the system of the present invention remains safe, i.e., contains only non-flammable refrigerants, even in the event of complete intermixing between the first and second refrigerant compositions.

B. The first refrigerant is _CO2 and the second refrigerant is SR26:
As a further example, applicants have considered a cascade cooling system according to the invention in which a first refrigerant is composed of _CO2 and a second refrigerant is composed of SR26 (a 80:20 weight ratio combination of R-1234ze(E):R-32). To achieve a cooling system according to the invention that is safe even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures of these components (including vapors and liquids) as follows:

Based on the above discussion and analysis, and on the preferred embodiment of the present invention in which the first refrigerant consists essentially of _CO2 and the second refrigerant consists essentially of SR26, it is preferred that the weight ratio of the charge of the first refrigerant (e.g., _CO2 ) to the second refrigerant (e.g., SR26) in the cryogenic loop is about 1.0 or greater. In such an embodiment, the system of the present invention remains safe, i.e., contains only non-flammable refrigerants, even in the event of complete intermixing between the first and second refrigerant compositions.

C. The first refrigerant is _CO2 and the second refrigerant is R-32:
As a further example, applicants considered a cascade cooling system according to the present invention in which a first refrigerant was comprised of _CO2 and a second refrigerant was comprised of R-32. To achieve a cooling system according to the present invention that is safe even in the event of intermixing between the first and second refrigerants, applicants determined the flammability of various mixtures of these components (including vapors and liquids) as follows:

Based on the above discussion and analysis, and on the preferred embodiment of the present invention in which the first refrigerant consists essentially of _CO2 and the second refrigerant consists essentially of SR26, it is preferred that the weight ratio of the charge of the first refrigerant (e.g., _CO2 ) to the second refrigerant (e.g., SR26) in the cryogenic loop is about 0.9 or greater. In such an embodiment, the system of the present invention remains safe, i.e., contains only non-flammable refrigerants, even in the event of complete intermixing between the first and second refrigerant compositions.

D. The first refrigerant is _CO2 and the second refrigerant is ethane:
As a further example, applicants have considered a cascade cooling system according to the invention in which a first refrigerant is composed of _CO2 and a second refrigerant is composed of ethane. To achieve a cooling system according to the invention that is safe even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures of these components (including vapors and liquids) as follows:

Based on the above discussion and analysis, and on the preferred embodiment of the present invention in which the first refrigerant consists essentially of _CO2 and the second refrigerant consists essentially of ethane, it is preferred that the weight ratio of the charge of the first refrigerant (e.g., _CO2 ) to the second refrigerant (e.g., SR26) in the cryogenic loop is about 1.7 or greater. In such an embodiment, the system of the present invention remains safe, i.e., contains only non-flammable refrigerants, even in the event of complete intermixing between the first and second refrigerant compositions.

E. First refrigerant is _CO2 and second refrigerant is propane:
As a further example, applicants have considered a cascade cooling system according to the invention in which a first refrigerant is composed of _CO2 and a second refrigerant is composed of propane. To achieve a cooling system according to the invention that is safe even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures of these components (including vapors and liquids) as follows:

Based on the above discussion and analysis, and on the preferred embodiment of the present invention in which the first refrigerant consists essentially of _CO2 and the second refrigerant consists essentially of propane, it is preferred that the weight ratio of the loading of the first refrigerant (e.g., _CO2 ) to the second refrigerant (e.g., propane) in the cryogenic loop is greater than 4. In such an embodiment, the system of the present invention remains safe, i.e., contains only non-flammable refrigerants, even in the event of complete intermixing between the first and second refrigerant compositions.

Comparative Example C1:
Comparative Example C1 described below is based on a conventional walk-in cooler refrigeration system as shown in the following drawing.

In said drawing, the boundary of the cooler is shown diagrammatically by a rectangle 100. Housed within the cooler vessel are an evaporator 15 and an expander 14. The compressor 11 and condenser 20 are located outside the cooler vessel 100. The refrigerant circulating within this cooling loop is refrigerant R-404A (52% by weight R-143a, 44% by weight R-125, and 4% by weight R-134a).

The following operating parameters were used:
Evaporation temperature of evaporator 15 = -35°C;
Condensation temperature of the condenser 200 = 45°C;
- isentropic efficiency of expander 14 = 63%;
Evaporator superheat = 5°C;
Temperature rise in compressor suction line = 20°C;
- Expansion device subcooling = 0°C.

This normal system operation produced a compressor discharge temperature of 108.3°C.
Composite Examples H1A-H1D:
Based on the conventional refrigeration system shown in Example 1, a suction line heat exchanger was inserted to form a composite system that absorbs heat in the R-404A exiting the evaporator, thereby increasing the temperature of the R-404A entering the compressor by absorbing heat from the R-404A exiting the condenser before the stream is introduced to the expander. Operation with suction line heat exchangers having effectiveness values varying from 35% to 85% was evaluated. The results are reported in Table H1 below, along with those of Comparative Example C1, for comparison.

As can be seen from the results reported above, modifying conventional systems to include a suction line heat exchanger is not feasible in all cases as operation of such a combined system would result in a significant, unnecessary and undesirable increase in compressor discharge temperature.

Examples 1A-1E, 2A-2E, 3A-3E, 4A-4E, and 5A-5E:
A cascade cooling system having a suction line heat exchanger as shown in FIG. 1 was operated with each of the following refrigerants in the low temperature loop (second refrigerant): HFO-1234ze(E); HFO-1234yf; SR21 (80 wt. % HFO-1234yf and 20 wt. % R-32); SR26 (80 wt. % HFO-1234ze(E) and 20 wt. % R-32); and SR31 (88 wt. % HFO-1234ze(E) and 12 wt. % R-32). The refrigerant in the high temperature loop was _CO2 . With these refrigerants, the cascade system of the present invention was operated according to the following parameters:

Low temperature stage evaporation temperature (evaporator 15) = -35°C;
Low temperature stage condensation temperature = (cascade condenser 12A) = 0°C;
Evaporation temperature of the hot stage (evaporator 25) = -5°C;
Hot stage condensation temperature (cascade condenser 12B) = 45°C;
- Isentropic efficiency of the cold stage expander (expander 14) = 65%;
Isentropic efficiency of the hot stage expander (expander 24) = 63%;
Evaporator superheat (both evaporators) = 5°C;
Temperature rise in the suction line of the cold stage = 15°C;
Temperature rise in the suction line of the hot stage = 5°C;
Subcooling in both hot and cold stage expansion devices = 0°C;
- Suction line liquid line heat exchanger efficiency = Varies from 0% to 85%.

Table 1/5-DT below shows the results in terms of discharge temperature for each example, with results from Comparative Example 1 shown for comparison.

As shown by the above table, all of the embodiments of the present invention met the preferred compressor discharge temperatures of the present invention, and in all cases the discharge temperatures were substantially better than the performance of the conventional system and even the combined system.

Table 1/5-COP below shows the results in terms of COP for each example, with results from Comparative Example 1 shown for comparison.

As shown by the above table, all of the examples of the present invention provided an improved COP of at least 121% compared to the system of Comparative Example 1. Additionally, all of the systems of the present invention that included an inlet line heat exchanger provided at least an additional 2% improvement over the systems of the present invention that did not have a heat exchanger, and the systems with a heat exchanger efficiency of 55% or greater for the inlet line heat exchanger provided at least an additional 3% improvement over the systems that did not have a heat exchanger.

Examples 6A-6E, 7A-7E, 8A-8E, 9A-9E:
The cascade cooling system without and with a suction line heat exchanger shown in FIG. 1 was operated using each of the following refrigerants (second refrigerant) in the cold loop and _CO2 in the hot loop (GWP of each refrigerant is shown):

The system of Figure 1 was operated using each of the refrigerants EX6-EX9 using the same operating conditions as shown in Examples 1-5 - Table 6/9-DT below shows the results in terms of discharge temperature for each Example, with results from Comparative Example 1 shown for comparison.

As shown by the above table, refrigerants EX6-EX9 produced acceptable discharge temperatures (within the preferred discharge temperature range) for a cascade system without a suction line heat exchanger (efficiency = 0). However, none of the refrigerants produced acceptable discharge temperatures (within the preferred discharge temperature range) for a cascade system for any efficiency value between 35% and 85%.

Examples 10A-10E, 11A-11E, 12A-12E, 13A-13E, 14A-14E, 15A-15E:
The cascade cooling system without and with a suction line heat exchanger shown in FIG. 1 was operated using each of the following refrigerants (second refrigerants) in the cold loop and _CO2 in the hot loop:

The system of Figure 1 was operated using each of the refrigerants EX10-EX15 using the same operating conditions as shown in Examples 1-5 - Table 10/15-DT below shows the results in terms of discharge temperature for each Example, with results from Comparative Example 1 shown for comparison.

As shown by the above table, refrigerants EX10-EX15 resulted in a second refrigerant having a GWP value below 500, but each refrigerant did not produce an acceptable discharge temperature (i.e., within the preferred discharge temperature range). For a cascade system without a suction line heat exchanger (efficiency = 0), the discharge temperatures were acceptable. However, for a system with a suction line heat exchanger, each of the EX10-EX13 refrigerants produced unacceptable discharge temperatures for the desired efficiency values of 85% or greater. Only the EX14 and EX15 refrigerants provided acceptable discharge temperatures for suction line heat exchangers with any of the efficiency values tested. These findings are summarized below.

At 35% efficiency, 30% more R1234ze(E) was required.
At 55% efficiency: 50% more R1234ze(E) was required.
At 75% efficiency: 60% more R1234ze(E) was required.

At 85% efficiency: 70% more R1234ze(E) was required.
Compositions containing at least about 78% R-1234ze(E) were acceptable for all efficiency values of the suction line heat exchanger and produced GWP values of about 150 or less.

Table 11/15-COP below shows the results in terms of COP for each example, with results from Comparative Example 1 shown for comparison.

As shown by the above table, all of the examples of the present invention provided a COP of at least 121% compared to the system of Comparative Example 1. Furthermore, in all of the tested systems of the present invention including a suction line heat exchanger, the use of the refrigerant of Example 15 showed at least an additional 2% improvement over the system of the present invention without a suction line heat exchanger. The use of the refrigerant of Example 14 in the tested systems of the present invention including a suction line heat exchanger with an efficiency of at least 55% showed at least an additional 2% improvement over the system of the present invention without a suction line heat exchanger (as shown in Table 11/15-DT) and had acceptable discharge temperatures. The use of the refrigerant of Example 13 in the tested systems of the present invention including a suction line heat exchanger with an efficiency of at least 55% but less than about 85% showed at least an additional 2% improvement over the system of the present invention without a suction line heat exchanger (as shown in Table 11/15-DT) and had acceptable discharge temperatures.

In contrast, using the refrigerant of Example 12 in a tested system of the present invention that includes a suction line heat exchanger having an efficiency of at least 75%, as shown in Table 11/15-DT, showed at least an additional 2% improvement over a system of the present invention that does not have a suction line heat exchanger, but this refrigerant did not provide an acceptable discharge temperature for this condition.

Examples 16A-16E, 17A-17E, 18A-18E, 19A-19E:
The cascade cooling system without and with a suction line heat exchanger shown in FIG. 1 was operated using each of the following refrigerants (second refrigerant) in the hot loop and _CO2 in the cold loop (GWP of each refrigerant is shown):

Using the same operating conditions as given in Examples 1-5, the system of Figure 1 was operated with each of the refrigerants EX16-EX19 - Table 16/19-DT below shows the results in terms of discharge temperature for each Example, with results from Comparative Example 1 shown for comparison.

As shown by the above table, refrigerants EX16-EX19 produced acceptable discharge temperatures (within the preferred discharge temperature range) for a cascade system without a suction line heat exchanger (efficiency = 0). However, none of the refrigerants produced acceptable discharge temperatures (within the preferred discharge temperature range) for a cascade system for any efficiency value between 35% and 85%.

Examples 20A-20E, 21A-21E, 22A-22E, 23A-23E, 24A-24E, 25A-25E:
The cascade cooling system without and with a suction line heat exchanger shown in FIG. 1 was operated using each of the following refrigerants (second refrigerants) in the cold loop and _CO2 in the hot loop:

Using the same operating conditions as shown in Examples 1-5, the system of Figure 1 was operated with each of the refrigerants EX20-EX25 - Table 20/25-DT below shows the results in terms of discharge temperature for each Example, with results from Comparative Example 1 shown for comparison.

As shown by the above table, refrigerants EX21-EX25 resulted in a second refrigerant having a GWP value below 500, but each refrigerant did not produce an acceptable discharge temperature (i.e., within the preferred discharge temperature range). For the cascade system without a suction line heat exchanger (efficiency = 0), the discharge temperatures were acceptable. However, for the system with a suction line heat exchanger, each of refrigerants EX20-EX22 produced unacceptable discharge temperatures for the desired efficiency values of 85% or greater. Only EX23, EX24, and EX25 provided acceptable discharge temperatures for the suction line heat exchanger for all of the efficiency values tested. These findings are summarized below.

At 35% efficiency, 30% more R1234yf was needed.
At 55% efficiency: 40% more R1234yf was needed.
At 75% and 85% efficiency: 60% more R1234yf was needed.

Table 20/25-COP below shows the results in terms of COP for each Example, with results from Comparative Example 1 shown for comparison.

As shown by the above table, all of the examples of the present invention provided a COP of at least 121% compared to the system of Comparative Example 1. Furthermore, in all of the tested systems of the present invention including a suction line heat exchanger, the use of the refrigerants of Examples 24 and 25 showed at least an additional 2% improvement over the system of the present invention without a suction line heat exchanger, and the refrigerants of Examples 22 and 23 showed at least an additional 2% improvement over the system of the present invention without a suction line heat exchanger for heat exchangers having an efficiency of 55% or more. The use of the refrigerant of Example 22 in the tested systems of the present invention including a suction line heat exchanger having an efficiency of at least 75% showed at least an additional 2% improvement over the system of the present invention without a suction line heat exchanger.

Importantly, the use of the refrigerants of Examples 24 and 25 in all of the tested systems of the present invention including a suction line heat exchanger not only provided an additional 2% improvement over the systems of the present invention not having a suction line heat exchanger, but also provided acceptable discharge temperatures (as shown in Table 21/25-DT) for all levels of suction line heat exchanger efficiency tested. The use of the refrigerants of Examples 22 and 23 in the tested systems of the present invention including a suction line heat exchanger having an efficiency of 55% not only provided an additional 2% improvement over the systems of the present invention not having a suction line heat exchanger, but also provided acceptable discharge temperatures (as shown in Table 21/25-DT).

In contrast, the refrigerant of Example 20 did not show an improvement of at least 2% in any of the heat exchanger efficiency values, and although Examples 21 and 22 showed an improvement of at least 2% in the 75% and 85% heat exchanger efficiency values, these heat exchanger efficiency values did not provide acceptable discharge as shown in Table 20/25-DT, and this refrigerant was not satisfactory for this condition.
The present invention includes the following embodiments.
(1)(a) a relatively low temperature vapor compression loop including a compressor, an expander, and an evaporator in fluid communication within the loop, and a first heat transfer composition within the loop including a first refrigerant and a lubricant for the compressor, the evaporator being disposed within an enclosure and capable of absorbing heat from a fluid within the enclosure at about such relatively low temperature;
(b) a relatively high temperature vapor compression loop including a compressor, a condenser, an expander, and a suction line heat exchanger in fluid communication within the loop, and a second heat transfer composition within the loop including a second refrigerant and preferably a lubricant for the compressor (the condenser can transfer heat to a heat sink located outside the enclosure); and
(c) a cascade heat exchanger for exchanging heat between the first and second refrigerants to condense the first refrigerant and evaporate the second refrigerant;
Including;
A heat transfer system for cooling the contents of an enclosure, wherein the suction line heat exchanger is in fluid communication with the cascade heat exchanger for receiving at least a portion of the second heat transfer composition discharged from the cascade heat exchanger and absorbs heat from the first heat transfer composition discharged from the condenser to increase its temperature, thereby reducing the temperature of the first heat transfer composition before it is introduced into the first loop expander.
(2) The system of (1), wherein the first refrigerant has a flammability classified as A1 under ASHRAE-34 (as measured by ASTM-E681) and the second refrigerant has a flammability classified as A2L under ASHRAE-34 (as measured by ASTM-E681) or a flammability higher than A2L.
(3) The system described in (1), wherein the compressor, the expander, and the condenser are not disposed within an enclosure.
(4) The system described in (5), wherein the suction line heat exchanger is not located within the enclosure.
(5) The system of (1), wherein the second refrigerant comprises one or more of trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)), 2,3,3,3-tetrafluoropropene (HFO-1234yf), R-227ea, R-32, and combinations of two or more thereof.
(6) The system of (1), wherein the second refrigerant comprises at least about 80% by weight of 2,3,3,3-tetrafluoropropene (HFO-12304yf).
(7) The system of (1), wherein the second refrigerant consists essentially of HFO-1234ze(E), HFO-1234yf, or a combination thereof.
(8) The system of (1), wherein the second refrigerant comprises about 70% to about 90% by weight HFO-1234yf, and about 10% to about 30% by weight R32.
(9) The system of (1), wherein the second refrigerant comprises about 70% to about 90% by weight of HFO-1234yze(E), and about 10% to about 30% by weight of R32.
(10) The system of (1), wherein the second refrigerant comprises about 85% to about 90% by weight of trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)), and about 10% to about 15% by weight of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea).

Claims (10)

1. A heat transfer system for cooling a content of the enclosure, the system further comprising:
(a) a relatively low temperature vapor compression loop including a compressor, an expander, and an evaporator in fluid communication within the loop, and a first heat transfer composition within the loop including a first refrigerant and a lubricant for the compressor , where the evaporator is disposed within an enclosure and capable of absorbing heat from a fluid within the enclosure at about such relatively low temperature , and where the first refrigerant consists essentially of carbon dioxide;
(b) a relatively high temperature vapor compression loop including a compressor, a condenser, an expander, and a suction line heat exchanger in fluid communication within the loop, and a second heat transfer composition within the loop including a second refrigerant , where the condenser is capable of transferring heat to a heat sink located outside the enclosure , the second refrigerant having a flammability greater than that of _CO2 ; and (c) a cascade heat exchanger for condensing the first refrigerant and evaporating the second refrigerant by heat exchange between the first and second refrigerants;
Including;
a suction line heat exchanger in fluid communication with the cascade heat exchanger for receiving at least a portion of the second heat transfer composition discharged from the cascade heat exchanger and for absorbing heat from the first heat transfer composition discharged from the condenser to increase its temperature, thereby reducing the temperature of the first heat transfer composition before it is introduced into the first loop expander ;
The system has a capacity of less than 30 kW; and
A heat transfer system, wherein the second refrigerant comprises at least 50% by weight HFO-1234yf . The system of claim 1, wherein the first refrigerant has a flammability classified as A1 under ASHRAE-34 (as measured by ASTM-E681) and the second refrigerant has a flammability classified as A2L under ASHRAE-34 (as measured by ASTM-E681) or a flammability higher than A2L. The system of claim 1, wherein the compressor, expander, and condenser are not disposed within an enclosure. The system of claim 1 , wherein the suction line heat exchanger is not located within the enclosure. 10. The system of claim 1, wherein the enclosure is used to keep the item cool by cooling the air within the enclosure, the enclosure being selected from a walk-in container, a cold storage container, and a transport cooling container. A system according to any one of claims 1 to 5, wherein the capacity of the system is less than 15 kW. A system according to any one of claims 1 to 6, wherein the capacity of the system is less than 10 kW. 10. The system of claim 1, wherein the second refrigerant comprises at least about 80% by weight 2,3,3,3-tetrafluoropropene (HFO-12 34 yf). The system of claim 1, wherein the second refrigerant comprises about 70% to about 90% by weight HFO-1234yf and about 10% to about 30% by weight R32. The system of any of claims 1 to 9, wherein the second heat transfer composition further comprises a lubricant for the compressor.