LOW GWP CASCADE REFRIGERATION SYSTEM

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No. 15/468,292, filed Mar. 24, 2017, which claims priority to Provisional Application 62/313,177, filed Mar. 25, 2016, which is incorporated herein by reference in its entirety.

U.S. application Ser. No. 15/468,292 is also a continuation-in-part of U.S. application Ser. No. 15/400,891, filed Jan. 6, 2017, now pending, which in turn claims the priority benefit of Provisional application 62/275,382, filed Jan. 6, 2016, each of which is incorporated herein by reference in its entirety.

U.S. application Ser. No. 15/468,292 is also a continuation-in-part of U.S. application Ser. No. 15/434,400, filed Feb. 16, 2017, now pending, which in turn claims the priority benefit of 62/295,731, filed Feb. 16, 2016, the entire contents of each of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to high efficiency, low-global warming potential (“low GWP”) air conditioning and/or refrigeration systems and methods for providing cooling that are safe and effective.

BACKGROUND

In typical air conditioning and refrigerant systems, a compressor is used to compress a heat transfer vapor from a lower to a higher pressure, which in turn adds heat to the vapor. This added heat is typically rejected in a heat exchanger, commonly referred to as a condenser. The heat transfer vapor that enters the condenser is condensed to produce a liquid heat transfer fluid at a relatively high pressure. Typically the condenser uses a fluid available in large quantities in the ambient environment, such as ambient outside air, as the heat sink. Once it has been condensed, the high-pressure heat transfer fluid undergoes a substantially isoenthalpic expansion, such would occur by passing the fluid through an expansion device or valve, where it is expanded to a lower pressure, which in turn results in the fluid undergoing a decrease in temperature. The lower pressure, lower temperature heat transfer fluid from the expansion operation then is typically routed to an evaporator, where it absorbs heat and in so doing evaporates. This evaporation process in turn results in cooling of the fluid or body to that it is intended to cool. In many typical air conditioning and refrigeration applications, the cooled fluid is the air which is contained in the region to be cooled, such as the air in the dwelling being air conditioned or the air inside a walk-in cooler or a 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 once again.

A complex and interrelated combination of factors and requirements is associated with forming efficient, effective and safe air conditioning systems that are at the same time environmentally friendly, that is, have both low GWP impact and low ozone depletion (“ODP” impact. With respect to efficiency and effectiveness, it is important for the heat transfer fluid to operate in air conditioning and refrigeration systems with high levels of efficiency and high relative capacity. At the same time, since it is possible that the heat transfer fluid may escape over time into the atmosphere, it is important for the fluid to have low values for both GWP and ODP.

Applicants have come to appreciate that while certain fluids are able to achieve high levels of both efficiency and effectiveness, and at the same time low levels of both GWP and ODP, many fluids which satisfy this combination of requirements nevertheless suffer from the disadvantage of having deficiencies in connection with safety. For example, fluids which might otherwise be acceptable may be disfavored because of flammability properties and/or toxicity concerns. Applicants have come to appreciate that the use of fluids having such properties is especially undesirable in typical air conditioning and in many refrigeration systems since such flammable and/or toxic fluids may inadvertently be released into the dwelling, walk-in, cold-box, chiller, freezer or transport refrigeration box which is being cooled, thus exposing or potentially exposing the occupants thereof to dangerous conditions. Applicants have also come to appreciate that this problem is even of a more intense concern for relatively small systems, e.g., systems with a capacity of less than 30 kw since for such systems the cost of effective safety protection systems, such as fire protections systems, are frequently not economically viable.

SUMMARY

According to one aspect of the invention, a cascade refrigerant system is provided for providing cooling of air, directly or indirectly but preferably directly, located in an enclosure that is occupied by or which will be exposed to humans or other animals during normal use. As used herein, the term “enclosure” means a space that is at least partially confined (e.g., the enclosure can be opened on one or more sides, or closed) and includes air that has been cooled.

Preferred embodiments of the present systems include at least a first evaporator which is located within the enclosure and is part of a first, relatively low temperature heat transfer circuit. The low temperature heat transfer circuit preferably comprises a first heat transfer fluid in a vapor compression circulation loop comprising at least: a compressor for raising 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 compressor at a relatively high pressure; an expansion device for lowering 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 said compressor, condenser and said expansion valve, and most preferably all of these, are located outside the enclosure and the evaporator is located within the enclosure.

The systems of the present invention also preferably include a second heat transfer circuit located substantially outside the enclosure, which is sometimes referred to herein by way of convenience as the “high temperature” loop. The high temperature loop preferably comprises a second heat transfer fluid in a vapor compression circulation loop comprising at least a compressor, a heat exchanger which serves to condense the heat transfer fluid in the high temperature loop, preferably by heat exchange with ambient air outside of the enclosure, and an expansion device for reducing the pressure of the second heat transfer fluid from the compressor.

An important aspect of preferred embodiments of the present invention is that the heat exchanger which serves as the condenser in the low temperature circuit is thermally coupled with the high temperature circuit by virtue of rejecting heat into the second heat transfer fluid, preferably by causing at least a substantial portion of said second heat transfer fluid to evaporate. In this way, the condenser of the low temperature circuit and the evaporator of the high temperature circuit are thermally coupled in this heat exchanger, which is sometimes referred to for convenience as “a cascade heat exchanger” in the systems and methods of the present invention.

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

Another important aspect of the preferred systems is that the first heat transfer fluid which is circulating in the low temperature loop comprises a refrigerant which has a GWP of not greater than about 500, more preferably not greater than about 400, and even more preferably not greater than about 150 and furthermore that the first heat transfer fluid has a flammability that is substantially less than the flammability of the second heat transfer fluid. Preferably, the second heat transfer fluid which is circulating in the high temperature loop also comprises a refrigerant which has a GWP of not greater than about 500, more preferably not greater than about 400, and even more preferably not greater than about 150, but since in normal operation this heat transfer fluid will never enter the enclosure, applicants have found that is advantageous to use a fluid in this high temperature loop that has one or properties that would be considered disadvantageous if it circulated within the enclosure, for example, flammability, toxicity and the like. In this way, the present systems allow additional possible unexpected advantages over systems that would rely only of the first heat transfer composition or only the second heat transfer composition, as explained in detail below.

In certain preferred embodiments the second refrigerant comprises, more preferably comprises at least about 50% by weight and even more preferably at least about 75% by weight, of trans-1,3,3,3-trifluoropropene (HFO-1234ze(E) and/or HFO-1234yf, and the second refrigerant has a flammability greater than, and preferably substantially greater than about, the flammability of CO2. In another embodiment the second refrigerant comprises, more preferably comprises at least about 75% by weight and even more preferably at least about 80% by weight, of trans-1,3,3,3-trifluoropropene (HFO-1234ze(E) and/or HFO-1234yf.

BRIEF DESCRIPTION OF THE DRAWINGS

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

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred Heat Transfer Compositions

In each of the preferred embodiments described herein the system includes:

(a) a relatively low temperature vapor compression loop comprising a compressor, an expander and an evaporator in fluid communication in said loop, and a first heat transfer composition in said loop comprising a first refrigerant and preferably lubricant for the compressor, said evaporator being located in an enclosure containing air to be cooled and being capable of absorbing heat from said air at about said relatively low temperature;

(b) a relatively high temperature vapor compression loop comprising a compressor, a condenser, an expander, and a suction line heat exchanger in fluid communication in said loop, and a second heat transfer composition in said loop comprising a second refrigerant and preferably lubricant for the compressor, said condenser being capable of transferring heat to a heat sink located outside said enclosure; and

(c) a cascade heat exchanger for condensing said first refrigerant and evaporating said second refrigerant by heat exchange between said first and second refrigerant,

wherein said suction line heat exchanger is in fluid communication with said cascade heat exchanger for receiving at least a portion of said second heat transfer composition exiting said cascade heat exchanger and increases the temperature thereof by absorbing heat from said first heat transfer composition exiting said condenser and thereby reducing the temperature of said first heat transfer composition prior to said first heat transfer composition entering said 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, and unless otherwise indicated, are used in a relative sense to designate the relative temperature of the indicated heat transfer compositions, where those differences are least about 5° C.

Preferably the first refrigerant has a flammability that is substantially less than the flammability of the second refrigerant. In preferred embodiments, the first refrigerant has a flammability according to ASHRAE Standard 34 (which specifies measurement according to ASTM E681) that is classified as A1 and the second refrigerant has a flammability according to ASHRAE Standard 34 that is classified as A2L or a higher flammability than A2L, although A2L classification for the second refrigerant is preferred. It is also preferred that the first and the second refrigerant each have a Global Warming Potential (GWP) that is less than about 150.

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

It is preferred that the second refrigerant comprises one or more of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)), 2,3,3,3-tetrafluoropropene (HFO-1234yf), R-227ea, and R-32 and combinations of two or more of these. In preferred embodiments, the second refrigerant comprises at least about 50%, more preferably at least about 80% by weight of 2, 3,3,3-tetrafluoropropene (HFO-1234yf). In other preferred embodiments, the second refrigerant comprises at least about 50%, more preferably at least about 80% by weight of or at least about 75% by weight, more preferably at least about 80% by weight of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)). In highly preferred embodiments, the second refrigerant comprises at least about 95% by weight, and in some embodiments consists essentially of or consists of HFO-1234ze(E), HFO-1234yf or combinations of two or more of these.

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

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

In other highly preferred embodiments, the second refrigerant comprises from about 85% to about 90% by weight of by weight of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) and from about 10% by weight 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% of trans1,3,3,3-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 will appreciate in view of the disclosures contained herein that the preferred embodiments of the present invention provide the advantage of utilizing only the safe (relatively low toxicity and low flammability) low GWP refrigerants within the enclosure to be cooled and a relatively less safe, but preferably low GWP refrigerant in the high temperature loop which is located entirely outside of 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, and unless otherwise indicated, are used in a relative sense to designate the relative safety of the indicated heat transfer compositions. Such configuration, especially when the high temperature system includes the preferred suction line heat exchanger, makes the systems and methods of the invention highly preferred for use in a location proximate to the humans or other animals occupying or using the enclosure, as is commonly encountered in walk-in freezers, supermarket coolers and the like.

Preferred embodiments of the second refrigerant are disclosed in the following table:

	Component

Second Refrigerant	R-1234yf,	R-1234ze(E),
Designation	wt %	wt %	R-32	R227ea

SR1	5	95	0	0
SR2	10	90	0	0
SR3	15	85	0	0
SR4	20	80	0	0
SR4	25	75	0	0
SR5	30	70	0	0
SR6	35	65	0	0
SR7	40	95	0	0
SR8	45	50	0	0
SR9	50	50	0	0
SR10	55	45	0	0
SR11	60	40	0	0
SR12	65	35	0	0
SR13	70	30	0	0
SR14	75	25	0	0
SR15	80	20	0	0
SR16	85	15	0	0
SR17	90	10	0	0
SR18	95	5	0	0
SR19	70	0	30	0
SR20	75	0	25	0
SR21	80	0	20	0
SR22	85	0	15	0
SR23	90	0	10	0
SR24	0	70	30	0
SR25	0	75	25	0
SR26	0	80	20	0
SR27	0	85	15	0
SR28	0	90	10	0
SR29	0	80	0	20
SR30	0	85	0	15
SR31	0	88	0	12
SR32	0	90	0	10
SR33	0	95	0	5

The first heat transfer composition and the second heat transfer compositions also each generally include a lubricant, generally in amounts of from about 30 to about 50 percent by weight of the heat transfer composition, with the balance comprising refrigerant and other optional components that may be present. Combinations of surfactants and solubilizing agents may also be added to the present compositions to aid oil solubility, as disclosed by U.S. Pat. No. 6,516,837, the disclosure of which is incorporated by reference. Commonly used refrigeration lubricants such as Polyol Esters (POEs) and Poly Alkylene Glycols (PAGs), silicone oil, mineral oil, alkyl benzenes (ABs) and poly(alpha-olefin) (PAO) that are used in refrigeration machinery with hydrofluorocarbon (HFC) refrigerants may be used with the refrigerant compositions of the present invention. The preferred lubricants are POEs.

Preferred combinations of first refrigerant, second refrigerant and lubricant according to one aspect of the invention are provided below.

	SECOND HEAT TRANSFER	FIRST HEAT TRANSFER
	COMPOSITION	COMPOSITION

		Regrig.,		Lub,		Regrig.,		Lub,
EMBODIMENT	Refrig.	wt %	Lub	wt %	Refrig.	wt %	Lub	wt %
1	1234yf	90-99	PAG	1-10	CO2	90-99	POE	1-10
2	1234yf	80-89	PAG	11-20	CO2	80-90	POE	11-20
4	1234yf	90-99	POE	1-10	CO2	90-99	POE	1-10
5	1234yf	80-89	POE	11-20	CO2	80-90	POE	11-20
6	1234ze(E)	90-99	PAG	1-10	CO2	90-99	POE	1-10
7	1234ze(E)	80-89	PAG	11-20	CO2	80-90	POE	11-20
8	1234ze(E)	90-99	POE	1-10	CO2	90-99	POE	1-10
9	1234ze(E)	80-89	POE	11-20	CO2	80-90	POE	11-20
10	SR1	90-99	PAG	1-10	CO2	90-99	POE	1-10
11	SR1	80-89	PAG	11-20	CO2	80-90	POE	11-20
12	SR1	90-99	POE	1-10	CO2	90-99	POE	1-10
13	SR1	80-89	POE	11-20	CO2	80-90	POE	11-20
14	SR2	90-99	PAG	1-10	CO2	90-99	POE	1-10
15	SR2	80-89	PAG	11-20	CO2	80-90	POE	11-20
16	SR2	90-99	POE	1-10	CO2	90-99	POE	1-10
17	SR2	80-89	POE	11-20	CO2	80-90	POE	11-20
18	SR3	90-99	PAG	1-10	CO2	90-99	POE	1-10
19	SR3	80-89	PAG	11-20	CO2	80-90	POE	11-20
20	SR3	90-99	POE	1-10	CO2	90-99	POE	1-10
21	SR3	80-89	POE	11-20	CO2	80-90	POE	11-20
22	SR4	90-99	PAG	1-10	CO2	90-99	POE	1-10
23	SR4	80-89	PAG	11-20	CO2	80-90	POE	11-20
24	SR4	90-99	POE	1-10	CO2	90-99	POE	1-10
25	SR4	80-89	POE	11-20	CO2	80-90	POE	11-20
26	SR5	90-99	PAG	1-10	CO2	90-99	POE	1-10
27	SR5	80-89	PAG	11-20	CO2	80-90	POE	11-20
28	SR5	90-99	POE	1-10	CO2	90-99	POE	1-10
29	SR5	80-89	POE	11-20	CO2	80-90	POE	11-20
30	SR6	90-99	PAG	1-10	CO2	90-99	POE	1-10
31	SR6	80-89	PAG	11-20	CO2	80-90	POE	11-20
32	SR6	90-99	POE	1-10	CO2	90-99	POE	1-10
33	SR6	80-89	POE	11-20	CO2	80-90	POE	11-20
34	SR7	90-99	PAG	1-10	CO2	90-99	POE	1-10
35	SR7	80-89	PAG	11-20	CO2	80-90	POE	11-20
36	SR7	90-99	POE	1-10	CO2	90-99	POE	1-10
37	SR7	80-89	POE	11-20	CO2	80-90	POE	11-20
38	SR8	90-99	PAG	1-10	CO2	90-99	POE	1-10
39	SR8	80-89	PAG	11-20	CO2	80-90	POE	11-20
40	SR8	90-99	POE	1-10	CO2	90-99	POE	1-10
41	SR8	80-89	POE	11-20	CO2	80-90	POE	11-20
41	SR9	90-99	PAG	1-10	CO2	90-99	POE	1-10
42	SR9	80-89	PAG	11-20	CO2	80-90	POE	11-20
43	SR9	90-99	POE	1-10	CO2	90-99	POE	1-10
44	SR10	90-99	PAG	1-10	CO2	90-99	POE	1-10
45	SR10	80-89	PAG	11-20	CO2	80-90	POE	11-20
46	SR10	90-99	POE	1-10	CO2	90-99	POE	1-10
47	SR10	80-89	POE	11-20	CO2	80-90	POE	11-20
48	SR11	90-99	PAG	1-10	CO2	90-99	POE	1-10
49	SR11	80-89	PAG	11-20	CO2	80-90	POE	11-20
50	SR11	90-99	POE	1-10	CO2	90-99	POE	1-10
51	SR11	80-89	POE	11-20	CO2	80-90	POE	11-20
52	SR12	90-99	PAG	1-10	CO2	90-99	POE	1-10
53	SR12	80-89	PAG	11-20	CO2	80-90	POE	11-20
54	SR12	90-99	POE	1-10	CO2	90-99	POE	1-10
55	SR12	80-89	POE	11-20	CO2	80-90	POE	11-20
56	SR13	90-99	PAG	1-10	CO2	90-99	POE	1-10
57	SR13	80-89	PAG	11-20	CO2	80-90	POE	11-20
58	SR13	90-99	POE	1-10	CO2	90-99	POE	1-10
59	SR13	80-89	POE	11-20	CO2	80-90	POE	11-20
60	SR14	90-99	PAG	1-10	CO2	90-99	POE	1-10
61	SR14	80-89	PAG	11-20	CO2	80-90	POE	11-20
62	SR14	90-99	POE	1-10	CO2	90-99	POE	1-10
63	SR14	80-89	POE	11-20	CO2	80-90	POE	11-20
64	SR15	90-99	PAG	1-10	CO2	90-99	POE	1-10
65	SR15	80-89	PAG	11-20	CO2	80-90	POE	11-20
66	SR15	90-99	POE	1-10	CO2	90-99	POE	1-10
67	SR15	80-89	POE	11-20	CO2	80-90	POE	11-20
68	SR16	90-99	PAG	1-10	CO2	90-99	POE	1-10
69	SR16	80-89	PAG	11-20	CO2	80-90	POE	11-20
70	SR16	90-99	POE	1-10	CO2	90-99	POE	1-10
71	SR16	80-89	POE	11-20	CO2	80-90	POE	11-20
72	SR17	90-99	PAG	1-10	CO2	90-99	POE	1-10
73	SR17	80-89	PAG	11-20	CO2	80-90	POE	11-20
74	SR17	90-99	POE	1-10	CO2	90-99	POE	1-10
75	SR17	80-89	POE	11-20	CO2	80-90	POE	11-20
76	SR18	90-99	PAG	1-10	CO2	90-99	POE	1-10
77	SR18	80-89	PAG	11-20	CO2	80-90	POE	11-20
78	SR18	90-99	POE	1-10	CO2	90-99	POE	1-10
79	SR18	80-89	POE	11-20	CO2	80-90	POE	11-20
80	SR19	90-99	PAG	1-10	CO2	90-99	POE	1-10
81	SR19	80-89	PAG	11-20	CO2	80-90	POE	11-20
82	SR19	90-99	POE	1-10	CO2	90-99	POE	1-10
83	SR19	80-89	POE	11-20	CO2	80-90	POE	11-20
84	SR20	90-99	PAG	1-10	CO2	90-99	POE	1-10
85	SR20	80-89	PAG	11-20	CO2	80-90	POE	11-20
86	SR20	90-99	POE	1-10	CO2	90-99	POE	1-10
87	SR20	80-89	POE	11-20	CO2	80-90	POE	11-20
88	SR21	90-99	PAG	1-10	CO2	90-99	POE	1-10
89	SR21	80-89	PAG	11-20	CO2	80-90	POE	11-20
90	SR21	90-99	POE	1-10	CO2	90-99	POE	1-10
91	SR21	80-89	POE	11-20	CO2	80-90	POE	11-20
92	SR22	90-99	PAG	1-10	CO2	90-99	POE	1-10
93	SR22	80-89	PAG	11-20	CO2	80-90	POE	11-20
94	SR22	90-99	POE	1-10	CO2	90-99	POE	1-10
95	SR22	80-89	POE	11-20	CO2	80-90	POE	11-20
96	SR23	90-99	PAG	1-10	CO2	90-99	POE	1-10
97	SR23	80-89	PAG	11-20	CO2	80-90	POE	11-20
98	SR23	90-99	POE	1-10	CO2	90-99	POE	1-10
99	SR23	80-89	POE	11-20	CO2	80-90	POE	11-20
100	SR24	90-99	PAG	1-10	CO2	90-99	POE	1-10
101	SR24	80-89	PAG	11-20	CO2	80-90	POE	11-20
102	SR24	90-99	POE	1-10	CO2	90-99	POE	1-10
103	SR24	80-89	POE	11-20	CO2	80-90	POE	11-20
104	SR25	90-99	PAG	1-10	CO2	90-99	POE	1-10
105	SR25	80-89	PAG	11-20	CO2	80-90	POE	11-20
106	SR25	90-99	POE	1-10	CO2	90-99	POE	1-10
107	SR25	80-89	POE	11-20	CO2	80-90	POE	11-20
108	SR26	90-99	PAG	1-10	CO2	90-99	POE	1-10
109	SR26	80-89	PAG	11-20	CO2	80-90	POE	11-20
110	SR26	90-99	POE	1-10	CO2	90-99	POE	1-10
111	SR26	80-89	POE	11-20	CO2	80-90	POE	11-20
112	SR27	90-99	PAG	1-10	CO2	90-99	POE	1-10
113	SR27	80-89	PAG	11-20	CO2	80-90	POE	11-20
114	SR27	90-99	POE	1-10	CO2	90-99	POE	1-10
115	SR27	80-89	POE	11-20	CO2	80-90	POE	11-20
116	SR28	90-99	PAG	1-10	CO2	90-99	POE	1-10
117	SR28	80-89	PAG	11-20	CO2	80-90	POE	11-20
118	SR28	90-99	POE	1-10	CO2	90-99	POE	1-10
119	SR28	80-89	POE	11-20	CO2	80-90	POE	11-20
120	SR29	90-99	PAG	1-10	CO2	90-99	POE	1-10
121	SR29	80-89	PAG	11-20	CO2	80-90	POE	11-20
122	SR29	90-99	POE	1-10	CO2	90-99	POE	1-10
123	SR29	80-89	POE	11-20	CO2	80-90	POE	11-20
124	SR30	90-99	PAG	1-10	CO2	90-99	POE	1-10
125	SR30	80-89	PAG	11-20	CO2	80-90	POE	11-20
126	SR30	90-99	POE	1-10	CO2	90-99	POE	1-10
127	SR30	80-89	POE	11-20	CO2	80-90	POE	11-20
128	SR31	90-99	PAG	1-10	CO2	90-99	POE	1-10
129	SR31	80-89	PAG	11-20	CO2	80-90	POE	11-20
130	SR31	90-99	POE	1-10	CO2	90-99	POE	1-10
131	SR31	80-89	POE	11-20	CO2	80-90	POE	11-20
132	SR32	90-99	PAG	1-10	CO2	90-99	POE	1-10
133	SR32	80-89	PAG	11-20	CO2	80-90	POE	11-20
134	SR32	90-99	POE	1-10	CO2	90-99	POE	1-10
135	SR32	80-89	POE	11-20	CO2	80-90	POE	11-20
136	SR33	90-99	PAG	1-10	CO2	90-99	POE	1-10
137	SR33	80-89	PAG	11-20	CO2	80-90	POE	11-20
138	SR33	90-99	POE	1-10	CO2	90-99	POE	1-10
139	SR33	80-89	POE	11-20	CO2	80-90	POE	11-20

System Operating Conditions

It is generally contemplated that operating conditions used in the present systems and methods can be varied widely in view of the disclosure contained herein depending upon the specific applications. However, many preferred applications will advantageously use operating parameters within the ranges indicated in the table below, with all amounts understood to be modified by “about”:

	BROAD	INTERMEDIATE	NARROW

Evaporating	−45 to −25	−40 to −30	−35
temperature of the low
stage evaporator, ° C.
Condensing temperature	−10 to 10	−5 to 5	0
of the low-stage, ° C.
Evaporating	−15 to 5	−10 to 0	−5
temperature of the high-
stage, ° C.
Condensing	35 to 55	40 to 50	45 C.
Temperature of the
high-stage, ° C.
Evaporator Superheat	0 to 15	0 to 10	5
(each stage) , ° C.
Temperature rise in the	5 to 25	10 to 20	15
suction line of the low-
stage, ° C.
Temperature rise in the	0 to 15	0 to 10	5
suction line of the high-
stage, ° C.
Subcooling at both	0 to 10	0 to 5	0
expansion devices of
high and low stages, ° C.
Compressor discharge	from about	from about	not greater
temperature (low and	120 to about	125 to about	than 125
high stage), ° C.	130	130

When operating within the process conditions according to the present invention, the use of the suction line heat exchanger as described herein preferably produces at least a 2% COP improvement, more preferably at least about 3% COP improvement, and even more preferably a 4% COP improvement compared to the same system but without a suction-line heat exchanger according to the present invention.

In the following descriptions, components or elements of the system which are or can be generally the same or similar in different embodiments are designated with the same number or symbol.

One preferred refrigeration system is illustrated in FIG. 1. The refrigeration system is designated generally as 10. The boundaries designates generally as 100 represent schematically the enclosure. The low temperature loop comprises compressor 11, condensing side 12A of the cascade exchange 12, expansion valve 14 and evaporator 15. As illustrated, evaporator 15 is located within enclosure 100, together with any of the associated conduits and other connecting and related equipment to transport the first heat transfer composition to and from the enclosure boundary. Although the evaporator 14 is preferably located inside the enclosure, and is disclosed in the illustrated FIGURE as being located inside of the enclosure 100, it will be appreciated that in certain embodiments it may be desirable and/or necessary to provide the expander 14 outside of the enclosure. The high temperature loop comprises compressor 21, evaporating side 12B of the cascade exchange 12, expansion valve 24 and condenser 25, all located outside of enclosure 100, together with any of the associated conduits and other connecting and related equipment. The high temperature circuit also includes suction line heat exchanger 50 which enables the exchange of heat between the second heat transfer composition stream 30 exiting condenser 25 and the second heat transfer composition stream 31 exiting the evaporating side 12B of the cascade heat exchanger 12.

Although it is contemplated that the relative size of the first and second refrigeration loops according to the present invention maybe vary widely within the scope hereof, applicants have found that highly advantageous results can be achieved in certain embodiments by judicious selection of the relative sizes of the refrigeration loops. More specifically, it is contemplated and understood that under normal operating conditions the heat transfer composition contained in the first refrigeration loop and in the second refrigeration loop will never mix or intermingle. However, applicants have come to appreciate that the possibility of such intermixing of first and second refrigerants might occur for example, in the case of leakage in the cascade heat exchanger. This mixed refrigerant stream may then, in the event of a leak within the enclosure being cold, become exposed to humans or other animals located in or near the enclosure. Accordingly, in order to ensure continued safe operation even in the case of such leakage, applicants have come to appreciate that careful and judicious selection of the relative refrigeration loop sizes can result in a safe system even in the event of such a leakage.

While applicants contemplate that the systems and compositions of the present invention will be useful in many refrigeration applications, preferred applications include refrigeration systems and methods used in applications such as treating the air, including cooling and/or heating, in enclosures such as residential dwellings, office space, warehouses and the like, and in connection with enclosures used to keep items cool by cooling the air in the enclosure, such as walk-in boxes, cold-boxes, transport refrigeration boxes and the like. As used herein, the term “transport refrigeration box” is used to designate cold/insulated boxes which are located on or comprise a portion or substantially all of a truck trailer. Furthermore, in preferred applications the capacity of the system according to the present invention is less than about 30 kW. In preferred applications the capacity of the system according to the present invention is less than about 15 kW, and in yet further applications the capacity of the system according to the present invention is less than about 10 kW.

Examples of several preferred systems, methods and compositions are described below:

A. First Refrigerant is CO2 and Second Refrigerant is R-1234ze(E)

By way of example, applicants have considered a cascade refrigeration system according to the present invention in which the first refrigerant consists of CO2 in the second refrigerant consists of R01234ze(E). In order to arrive at a refrigeration system according to the present invention which is safe, even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures (including vapor and liquid) of these components as follows:

		Ratio
	Composition	CO2 to

Number	R1234ze	CO2	R1234ze	Flammability

1	99%	1%	0.01	Vapor and liquid flammable
2	90%	10%	0.11	Liquid flammable
3	70%	30%	0.43	Liquid flammable
4	50%	50%	1.00	Liquid flammable
5	46%	54%	1.17	Non-Flammable
6	40%	60%	1.50	Non-Flammable
7	30%	70%	2.33	Non-Flammable
8	5%	95%	19.00	Non-Flammable

Based upon the above considerations and analysis, and preferred aspects of the present invention in which the first refrigerant consists essentially of CO2 and a 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) in the low temperature loop to the second refrigerant (e.g. R-1234ze(E)) is not less than about 1.2. In such embodiments, the system of the present invention will remain safe, i.e., contain only nonflammable refrigerant, even in the event of complete intermixing between the first and the second refrigerant compositions.

B. First Refrigerant is CO2 and Second Refrigerant is SR26

By way of further example, applicants have considered a cascade refrigeration system according to the present invention in which the first refrigerant consists of CO2 and the second refrigerant consists of a SR26 (80:20 weight ratio combination of R-1234ze(E); R-32). In order to arrive at a refrigeration system according to the present invention which is safe, even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures (including vapor and liquid) of these components as follows:

	Composition	Ratio

	R1234ze +		CO2 to
	R32		R1234ze +
Number	(0.8/0.2)	CO2	R32	Flammability

1	100%	0%	0	Vapor and liquid flammable
2	99%	1%	0.01	Vapor and liquid flammable
3	90%	10%	0.11	Liquid flammable
5	70%	30%	0.43	Liquid flammable
6	50%	50%	1.00	Liquid flammable
7	49%	51%	1.04	Non-Flammable
8	40%	60%	1.50	Non-Flammable
9	30%	70%	2.33	Non-Flammable
10	5%	95%	19.00	Non-Flammable

Based upon the above considerations and analysis, and preferred aspects of the present invention in which the first refrigerant consists essentially of CO2 and a second refrigerant consists essentially of SR26, it is preferred that the weight ratio of the loading of the first refrigerant (e.g. CO2) in the low temperature loop to the second refrigerant (e.g. SR26) is not less than about 1.0. In such embodiments, the system of the present invention will remain safe, i.e., contain only nonflammable refrigerant, even in the event of complete intermixing between the first and the second refrigerant compositions.

C. First Refrigerant is CO2 and Second Refrigerant is R-32

By way of additional example, applicants have considered a cascade refrigeration system according to the present invention in which the first refrigerant consists of CO2 and the second refrigerant consists of a R-32. In order to arrive at a refrigeration system according to the present invention which is safe, even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures (including vapor and liquid) of these components as follows:

	Composition	Ratio

Number	R32	CO2	CO2 to R32	Flammability

1	100%	0%	0	Vapor and liquid flammable
2	99%	1%	0.01	Vapor and liquid flammable
3	90%	10%	0.11	Vapor and liquid flammable
4	80%	20%	0.25	Liquid flammable
5	70%	30%	0.43	Liquid flammable
6	60%	40%	0.67	Liquid flammable
7	53%	47%	0.89	Non-Flammable
8	50%	50%	1.00	Non-Flammable
9	40%	60%	1.50	Non-Flammable
10	10%	90%	9.00	Non-Flammable
11	5%	95%	19.00	Non-Flammable

Based upon the above considerations and analysis, and preferred aspects of the present invention in which the first refrigerant consists essentially of CO2 and a second refrigerant consists essentially of SR26, it is preferred that the weight ratio of the loading of the first refrigerant (e.g. CO2) in the low temperature loop to the second refrigerant (e.g. SR26) is not less than about 0.9. In such embodiments, the system of the present invention will remain safe, i.e., contain only nonflammable refrigerant, even in the event of complete intermixing between the first and the second refrigerant compositions.

D. First Refrigerant is CO2 and Second Refrigerant is Ethane

By way of additional example, applicants have considered a cascade refrigeration system according to the present invention in which the first refrigerant consists of CO2 and the second refrigerant consists of ethane. In order to arrive at a refrigeration system according to the present invention which is safe, even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures (including vapor and liquid) of these components as follows:

	Composition	Ratio

Number	Ethane	CO2	CO2 to Ethane	Flammability

1	100%	0%	0	Vapor and liquid flammable
2	90%	10%	0.11	Vapor and liquid flammable
3	80%	20%	0.25	Vapor and liquid flammable
4	70%	30%	0.43	Liquid flammable
5	60%	40%	0.67	Liquid flammable
6	50%	50%	1.00	Liquid flammable
7	40%	60%	1.50	Liquid flammable
8	37%	63%	1.70	Non-Flammable
9	30%	70%	2.33	Non-Flammable
10	20%	80%	4.00	Non-Flammable
11	10%	90%	9.00	Non-Flammable
12	5%	95%	19.00	Non-Flammable

Based upon the above considerations and analysis, and preferred aspects of the present invention in which the first refrigerant consists essentially of CO2 and a second refrigerant consists essentially of ethane, it is preferred that the weight ratio of the loading of the first refrigerant (e.g. CO2) in the low temperature loop to the second refrigerant (e.g. SR26) is not less than about 1.7. In such embodiments, the system of the present invention will remain safe, i.e., contain only nonflammable refrigerant, even in the event of complete intermixing between the first and the second refrigerant compositions.

E. First Refrigerant is CO2 and Second Refrigerant is Propane

By way of additional example, applicants have considered a cascade refrigeration system according to the present invention in which the first refrigerant consists of CO2 and the second refrigerant consists of propone. In order to arrive at a refrigeration system according to the present invention which is safe, even in the event of intermixing between the first and second refrigerants, applicants have determined the flammability of various mixtures (including vapor and liquid) of these components as follows:

	Composition	Ratio

Number	Propane	CO2	CO2 to Propane	Flammability

1	100%	0%	0	Vapor and liquid flammable
2	90%	10%	0.11	Liquid flammable
3	80%	20%	0.25	Liquid flammable
4	70%	30%	0.43	Liquid flammable
5	60%	40%	0.67	Liquid flammable
6	50%	50%	1.00	Liquid flammable
7	40%	60%	1.50	Liquid flammable
8	30%	70%	1.70	Liquid flammable
9	20%	80%	1.50	Liquid flammable
10	10%	90%	9.00	Non-Flammable
11	5%	95%	19.00	Non-Flammable

Based upon the above considerations and analysis, and preferred aspects of the present invention in which the first refrigerant consists essentially of CO2 and a second refrigerant consists essentially of propane, it is preferred that the weight ratio of the loading of the first refrigerant (e.g. CO2) in the low temperature loop to the second refrigerant (e.g. propane) is greater than 4. In such embodiments, the system of the present invention will remain safe, i.e., contain only nonflammable refrigerant, even in the event of complete intermixing between the first and the second refrigerant compositions.

EXAMPLES

Comparative Example C1

Comparative Example C1 as described below is based on a typical walk-in cooler refrigeration system as illustrated in FIG. 1.

In FIG. 1, the boundaries of the cooler are represented schematically by the box 100. Enclosed within the cooler box is the evaporator 15 and expander 14. Compressor 11 and condenser 20 are located outside the cooler box 100. The refrigerant circulating within this refrigeration loop is refrigerant R-404A (52 wt. % R-143a, 44 wt. % R-125 and 4 wt. % R-134a).

The following operating parameters are used:

• • Evaporating temperature of evaporator 15=−35° C.
  • Condensing temperature of condenser 200=45° C.
  • Isentropic efficiency of expander 14=63%
  • Evaporator Superheat=5° C.
  • Temperature rise in the compressor suction line=20° C.
  • Expansion device subcooling=0° C.
    The operation of this typical system produces a compressor discharge temperature of 108.3° C.

Hybrid Examples H1A-H1D

A hybrid system based on the typical refrigeration system as illustrated in Example 1 is formed but a suction line heat exchanger is inserted so as to absorb heat into the R-404A exiting the evaporator and thereby increasing the temperature of R-404A entering the compressor by absorbing heat from R-404A exiting the condenser prior to that stream entering expander. Operation using a suction line heat exchanger with Effectiveness values varying from 35% to 85% are evaluated. The results are reported in the following Table H1, together with the result of comparative Example C1 for comparison:

	TABLE H1
		C1	H1A	H1B	H1C	H1D

	Effectiveness,	0 (no heat	35	55	75	85
	%*	exchanger)
	Compressor	108.3	133.1	150.0	166.5	174.7
	Discharge
	Temperature,
	° C.
	*Effectiveness % of the suction line heat exchanger as used herein refers to the percentage of ideal operation with no heat loss

As can be seen from the results reported above, modifying a typical system to include a suction line heat exchanger is not viable since in every case there is a substantial, and unwanted and undesirable, increase in the compressor discharge temperature as a result of operating such a hybrid system.

Examples 1A-1E, 2A-2E, 3A-3E, 4A-4E and 5A-5E

A cascade refrigeration system having a suction line heat exchanger as illustrated in FIG. 1 is operated using each of the following refrigerants in the low temperature loop (the 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 is CO₂. Using these refrigerants, the cascade system of the present invention is operated according to the following parameters:

• • Evaporating temperature of the low stage (evaporator 15)=−35° C.
  • Condensing temperature of the low-stage=(cascade condenser 12A)=0° C.
  • Evaporating temperature of the high-stage (evaporator 25)=−5° C.
  • Condensing Temperature of the high-stage (cascade condenser 12B)=45° C.
  • Isentropic efficiency of the low-stage expander (expander 14)=65%
  • Isentropic efficiency of the high-stage expander (expander 24)=63%
  • Evaporator Superheat (both evaporators)=5° C.
  • Temperature rise in the suction line of the low-stage=15° C.
  • Temperature rise in the suction line of the high-stage=5° C.
  • Subcooling at both expansion devices of high and low stages=0° C.
  • Suction-line Liquid-line heat exchanger Effectiveness=vary from 0% to 85%.
    Table 1/5—DT below shows the results in terms of discharge temperature for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 1/5
DT

	C1 and
	1A-5A	1B-5B	1C-5C	1D-5D	1E-5E

Effectiveness, %*

	0 (no heat
	exchanger)	35	55	75	85

Refrigerant	Compressor Discharge Temperature, ° C.

R-404A	108.3	133.1	150.0	166.5	174.7
HFO-1234ze(E)	70	87	97	106	111
(Examples 1A-1E)
HFO-1234yf	65	81	91	100	105
(Examples 2A-2E)
SR21	68	85	95	104	109
(Examples 3A-3E)
SR26	88	102	110	117	121
(Examples 4A-4E)
SR31	81	96	104	112	116
(Examples 5A-5E)

As revealed by the table above, all Examples of the present invention satisfy the preferred compressor discharge temperatures of the present invention, and in all cases the discharge temperature is substantially superior to the performance of the typical system and even the hybrid system.

Table 1/5—COP below shows the results in terms of COP for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 1/5
COP

C1 and 1A-5A

1B-5B

1C-5C

1D-5D

1E-5E

Effectiveness, %*

0 (no heat exchanger)

35

55

75

85

Refrigerant	COP (COP/% COP compared to Comparative Example 1)

R-404A	0.89/100
HFO-1234ze(E)	1.12/125	1.14/128	1.16/130	1.17/131	1.18/132
(Examples 1A-1E)
HFO-1234yf	1.07/121	1.11/125	1.13/127	1.15/129	1.16/130
(Examples 2A-2E)
SR21	1.11/125	1.39/128	1.15/130	1.17/131	1.18/132
(Examples 3A-3E)
SR26	1.11/125	1.13/127	1.14/128	1.15/129	1.16/130
(Examples 4A-4E)
SR31	1.08/121	1.1/123	1.11/125	1.12/126	1.13/127
(Examples 5A-5E)

As revealed by the table above, all Examples of the present invention result in improved COP of at least 121% compared to the system of Comparative Example 1. In addition all systems of the present invention which include a suction-line heat exchanger show at least an additional 2% improvement versus the system of the present invention without heat exchanger, and a systems with 55% or higher heat exchanger effectiveness for the suction line heat exchanger show at least an additional 3% improvement versus the system without heat exchanger.

Examples 6A-6E, 7A-7E, 8A-8E, 9A-9E

A cascade refrigeration system having no suction line heat exchanger and a suction line heat exchanger as illustrated in FIG. 1 is operated using each of the following refrigerants in the low temperature loop (the second refrigerant) and CO₂ in the high temperature loop (showing the GWP of each refrigerant):

	Component

	Second Refrigerant	R-1234ze(E),	R-32,
	Designation	wt %	wt %	GWP

	EX6	0	100	677
	EX7	10	90	609
	EX8	20	80	542
	EX9	30	70	474

Using the same operating conditions identified in Examples 1-5, the system of FIG. 1 is operated with each of the refrigerants EX6-EX9, and Table 6/9—DT below shows the results in terms of discharge temperature for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 6/9
DT

	C1 and
	6A-9A	6B-9B	6C-9C	6D-9D	6E-9E

Effectiveness, %*

	0 (no heat
	exchanger)	35	55	75	85

Refrigerant	Compressor Discharge Temperature, ° C.

R-404A	108	133	150	167.5	175
Examples 6A-6E)	125	145	157	168	174
Examples7A-7E)	121	140	151	162	167
Examples 7A-7E	117	136	146	156	161
Examples 7A-7E	113	130	140	150	154

As revealed by the table above, using the refrigerants EX6-EX9 produce acceptable discharge temperatures (within the scope of preferred discharge temperature range) for cascade systems without a suction line heat exchanger (effectiveness=0). However, none of the refrigerants produce acceptable discharge temperatures (within the scope of preferred discharge temperature range) for cascade systems for any of the values of effectiveness from 35% to 85%.

Examples 10A-10E, 11A-11E, 12A-12E, 13A-13E, 14A-14E, 15A-15E

A cascade refrigeration system having no suction line heat exchanger and a suction line heat exchanger as illustrated in FIG. 1 is operated using each of the following refrigerants in the low temperature loop (the second refrigerant) and CO2 in the high temperature loop:

	Component

	Second Refrigerant	R-1234ze(E),	R-32,
	Designation	wt %	wt %	GWP

	EX10	40	60	407
	EX11	50	50	339
	EX12	60	40	271
	EX13	70	30	204
	EX14	80	20	136
	EX15	90	10	69

Using the same operating conditions identified in Examples 1-5, the system of FIG. 1 is operated with each of the refrigerants EX10-EX15, and Table 10/15—DT below shows the results in terms of discharge temperature for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 10/15
DT

	C1 and	10B-	10C-	10D-	10E-
	10A-15	15B	15C	15D	15E

Effectiveness, %*

	0 (no heat
	exchanger)	35	55	75	85

Refrigerant	Compressor Discharge Temperature, ° C.

R-404A	108	133	150	167.5	175
Examples 10A-10E	109	125	134	143	148
Examples 11-11E	104	120	128	137	141
Examples 12A-12E	100	114	122	130	134
Examples 13A-13E	94	108	116	124	128
Examples 14A-14E	88	102	110	117	121
Examples 15A-15E	81	95	103	111	115

As revealed by the table above, using the refrigerants EX10-EX15 results in a second refrigerant with a GWP value below 500, but not each refrigerant produces an acceptable discharge temperature (i.e., within the scope of preferred discharge temperature range). For cascade systems without a suction line heat exchanger (effectiveness=0), the discharge temperature is acceptable. However, for systems with a suction line heat exchanger, each of EX10-EX13 refrigerants produce unacceptable discharge temperatures for the desired effectiveness values of 85% or above. Only EX 14 and EX 15 provide acceptable discharge temperatures for suction line heat exchangers having any of the tested effectiveness values. These finding are summarized below:

• • At 35% effectiveness, greater than 30% of R1234ze(E) is required
  • At 55% effectiveness: greater than 50% of R1234ze(E) is required
  • At 75% effectiveness: greater than 60% of R1234ze(E) is required
  • At 85% effectiveness: greater than 70% of R1234ze(E) is required
  • Compositions containing at least about 78% of R-1234ze(E) are acceptable for all effectiveness values of the suction line heat exchanger and produce a GWP value of about 150 or less.

Table 10/15—COP below shows the results in terms of COP for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 10/15
COP

C1 and 10A-15A

10B-15B

10C-15C

10D-15D

10E-15E

Effectiveness, %*

0 (no heat exchanger)

35

55

75

85

Refrigerant	COP (COP/% COP compared to Comparative Example 1)

R-404A	0.89/100
Examples 10A-10E	1.1/123	1.11/124	1.1/124	1.1/124	1.1/124
Examples 11-11E	1.1/124	1.1/124	1.1/125	1.1/125	1.1/125
Examples 12A-12E	1.1/124	1.1/125	1.1/125	1.1/126	1.1/126
Examples 13A-13E	1.1/125	1.1/127	1.1/128	1.2/129	1.2/130
Examples 14A-14E	1.1/125	1.1/127	1.1/129	1.2/130	1.2/131
Examples 15A-15E	1.1/125	1.1/128	1.2/130	1.2/131	1.2/132

As revealed by the table above, all Examples of the present invention result a COP of at least 121% compared to the system of Comparative Example 1. In addition the use of the refrigerant of Example 15 in all tested systems of the present invention which include a suction-line heat exchanger show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger, The use of the refrigerant of Example 14 in tested systems of the present invention which include a suction-line heat exchanger with and effectiveness of at least 55% show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger and (as shown in Table 11/15—DT) have an acceptable discharge temperature. The use of the refrigerant of Example 13 in tested systems of the present invention which include a suction-line heat exchanger with and effectiveness of at least 55% but less than about 85% show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger and (as shown in Table 11/15—DT) have an acceptable discharge temperature.

In contrast, while the use of the refrigerant of Example 12 in tested systems of the present invention which include a suction-line heat exchanger with an effectiveness of at least 75% show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger, as shown in Table 11/15—DT, this refrigerant does not provide an acceptable discharge temperature for this conditions.

Examples 16A-16E, 17A-17E, 18A-18E, 19A-19E

A cascade refrigeration system having no suction line heat exchanger and a suction line heat exchanger as illustrated in FIG. 1 is operated using each of the following refrigerants in the high temperature loop (the second refrigerant) and CO₂ in the low temperature loop (showing the GWP of each refrigerant):

	Component

	Second Refrigerant	R-1234yf,	R-32,
	Designation	wt %	wt %	GWP

	EX16	0	100	677
	EX17	10	90	609
	EX18	20	80	542
	EX19	30	70	474

Using the same operating conditions identified in Examples 1-5, the system of FIG. 1 is operated with each of the refrigerants EX16-EX19, and Table 16/19—DT below shows the results in terms of discharge temperature for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 16/19
DT

	C1 and	16B-	16C-	16D-	16E-
	16A-19A	19B	19C	19D	19E

Effectiveness, %*

	0 (no heat
	exchanger)	35	55	75	85

Refrigerant	Compressor Discharge Temperature, ° C.

R-404A	108	133	150	167.5	175
Examples16A-16E)	125	145	157	168	174
Examples17A-17E)	119	138	149	160	166
Examples 18A-18E	113	132	142	153	158
Examples 19A-19E	107	125	136	146	151

As revealed by the table above, using the refrigerants EX16-EX19 produce acceptable discharge temperatures (within the scope of preferred discharge temperature range) for cascade systems without a suction line heat exchanger (effectiveness=0). However, none of the refrigerants produce acceptable discharge temperatures (within the scope of preferred discharge temperature range) for cascade systems for any of the values of effectiveness from 35% to 85%.

Examples 20A-20E, 21A-21E, 22A-22E, 23A-23E, 24A-24E, 25A-25E

A cascade refrigeration system having no suction line heat exchanger and a suction line heat exchanger as illustrated in FIG. 1 is operated using each of the following refrigerants in the low temperature loop (the second refrigerant) and CO2 in the high temperature loop:

	Component

	Second Refrigerant	R-1234ze(E),	R-32,
	Designation	wt %	wt %	GWP

	EX20	40	60	407
	EX21	50	50	339
	EX22	60	40	271
	EX23	70	30	204
	EX24	80	20	136
	EX25	90	10	69

Using the same operating conditions identified in Examples 1-5, the system of FIG. 1 is operated with each of the refrigerants EX20-EX25, and Tables 20/25—DT below shows the results in terms of discharge temperature for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 20/25
DT

	C1 and	20B-	20C-	20D-	20E-
	20A-25	25B	25C	25D	25E

Effectiveness, %*

	0 (no heat
	exchanger)	35	55	75	85

Refrigerant	Compressor Discharge Temperature, ° C.

R-404A	108	133	150	167.5	175
Examples 20A-20E	102	125	134	143	148
Examples 21-21E	97	113	123	132	137
Examples 22A-22E	92	107	116	125	130
Examples 23A-23E	86	102	110	119	123
Examples 24A-24E	81	96	109	112	116
Examples 25A-25E	74	89	97	105	110

As revealed by the table above, using the refrigerants EX21-EX25 results in a second refrigerant with a GWP value below 500, but not each refrigerant produces an acceptable discharge temperature (i.e., within the scope of preferred discharge temperature range). For cascade systems without a suction line heat exchanger (effectiveness=0), the discharge temperature is acceptable. However, for systems with a suction line heat exchanger, each of refrigerants EX20-EX22 produces unacceptable discharge temperatures for the desired effectiveness values of 85% or above. Only EX 23, EX24 and EX 25 provide acceptable discharge temperatures for suction line heat exchangers for all tested effectiveness values. These findings are summarized below:

• • At 35% effectiveness, greater than 30% of R1234yf is required
  • At 55% effectiveness: greater than 40% of R1234yf is required
  • At 75% and 85% effectiveness: greater than 60% of R1234yf is required

Table 20/25—COP below shows the results in terms of COP for each example, with result from Comparative Example 1 being shown for comparison:

TABLE 20/25
COP

C1 and 20A-25A

20B-25B

20C-25C

20D-25D

20E-25E

Effectiveness, %*

0 (no heat exchanger)

35

55

75

85

Refrigerant	COP (COP/% COP compared to Comparative Example 1)

R-404A	0.89/100
Examples 20A-20E	1.1/122	1.11/122	1.1/122	1.1/122	1.1/122
Examples21-21E	1.1/121	1.1/122	1.1/123	1.1/123	1.1/123
Examples 22A-22E	1.1/121	1.1/122	1.1/123	1.1/124	1.1/124
Examples 23A-23E	1.1/121	1.1/123	1.1/124	1.2/125	1.2/125
Examples 24A-24E	1.1/121	1.1/123	1.1/124	1.1/126	1.1/127
Examples 25A-25E	1.1/121	1.1/124	1.1/126	1.1/128	1.2/129

As revealed by the table above, all Examples of the present invention result a COP of at least 121% compared to the system of Comparative Example 1. In addition the use of the refrigerant of Examples 24 and 25 in all tested systems of the present invention which include a suction-line heat exchanger show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger, and the refrigerant of Examples 22 and 23 shows at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger for heat exchangers with effectiveness of 55% or greater. The use of the refrigerant of Examples 22 in tested systems of the present invention which include a suction-line heat exchanger with an effectiveness of at least 75% show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger.

Importantly, the use of the refrigerant of Examples 24 and 25 in all tested systems of the present invention which include a suction-line heat exchanger not only show at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger, such refrigerants (as shown in Table 21/25—DT) have an acceptable discharge temperature for all levels of suction line heat exchanger effectiveness tested. The use of the refrigerant of Examples 22 and 23 in tested systems of the present invention which include a suction-line heat exchanger with an effectiveness of 55% show not only at least an additional 2% improvement versus the system of the present invention without the suction-line heat exchanger but (as shown in Table 21/25—DT) also have an acceptable discharge temperature.

In contrast, while the use of the refrigerant of Example 20 does not demonstrate at least a 2% improvement for any values of heat exchanger effectiveness, and while Examples 21 and 22 show at least a 2% improvement for heat exchanger effectiveness values of 75% and 85%, these values of heat exchanger effectively do not does not provide an acceptable discharge, as shown in Table 20/25—DT, this refrigerant does not for this conditions.