US20190264957A1

US20190264957A1 - Refrigeration systems and methods

Info

Publication number: US20190264957A1
Application number: US16/015,145
Authority: US
Inventors: Michael Petersen; Gustavo Pottker; Samuel F. Yana Motta; Ronald Peter Vogl; Ankit Sethi
Original assignee: Honeywell International Inc
Current assignee: Honeywell International Inc
Priority date: 2017-06-21
Filing date: 2018-06-21
Publication date: 2019-08-29

Abstract

Disclosed are distributed refrigeration systems, comprising: a plurality of first refrigeration circuits, with each first refrigeration circuit being provided in a respective refrigeration unit; a second refrigeration circuit, the second refrigeration circuit comprising a second circuit heat exchanger; and a third refrigeration circuit, wherein each first circuit heat exchanger is arranged to transfer heat energy between its respective first refrigeration circuit and the second refrigeration circuit; and a third circuit heat exchanger arranged to transfer heat energy between the second refrigeration circuit and the third refrigeration circuit.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to and claims the priority benefit of each of U.S. Provisional applications 62/522,851, filed Jun. 21, 2017 and 62/522,860, filed Jun. 21, 2017, each of which is incorporated herein by reference.

FIELD

This invention relates to refrigeration systems and methods, particularly, but not exclusively, to refrigeration systems suited for use with low GWP refrigerants.

BACKGROUND

The refrigeration industry is under increasing pressure—through regulatory changes and otherwise—to replace high global warming potential (GWP) refrigerants, such as R404A, with low GWP refrigerants, such as refrigerants with GWP below 150. This is of particularly importance in the commercial refrigeration system, where high volumes of refrigerant are used.
One approach has been to use low GWP refrigerants, such as carbon dioxide (R744) and hydrocarbon refrigerants. However, such an approach as has been heretofore used can suffer from significant safety and financial drawbacks, such as: poor system energy efficiency, leading to increased operating costs; high system complexity, leading to high initial system costs; low system serviceability and reliability, leading to high maintenance costs; and high system flammability. Systems which include highly flammable refrigerants according to prior arrangements have been particularly disadvantageous as they can lead to poor levels of safety; can conflict with regulatory code restrictions; and can increase liability on refrigeration system operators and manufacturers. Safety is a particular concern given that many commercial refrigeration applications, such as supermarket fridges, freezers and cold display cases are publically accessible and often operate in densely populated spaces.
Applicants have come to appreciate, therefore, that the refrigeration industry continues to need safe, robust and sustainable approaches for reducing the use of high GWP refrigerants which can be used with existing technologies.
One such approach that has been previously used is shown in FIG. 1A. FIG. 1 shows a refrigeration system 100 which is commonly used for commercial refrigeration in supermarkets. The system 100 is a direct expansion system which provides both medium and low temperature refrigeration via medium temperature refrigeration circuit 110 and low temperature refrigeration circuit 120.
In a typical prior configuration labelled as 100 in FIG. 1A, the medium temperature refrigeration circuit 110 has R134a as its refrigerant. The medium temperature refrigeration circuit 110 provides both the medium temperature cooling and removes the rejected heat from the lower temperature refrigeration circuit 120 via a heat exchanger 130. The medium temperature refrigeration circuit 110 extends between a roof 140, a machine room 141 and a sales floor 142. The low temperature refrigeration circuit 120 on the other hand has R744 as its refrigerant. The low temperature refrigeration circuit 120 extends between the machine room 141 and the sales floor 142. Usefully, as discussed above, R744 has a low GWP.
However, while refrigeration systems of the type disclosed in FIG. 1A may be able to provide good efficiency levels, applicants have come to appreciate that systems of this type have at least two major drawbacks: first, such systems use the high GWP refrigerant R134a (R134a having a GWP of around 1300); and second, even though the low temperature portions of such systems uses the low GWP refrigerant R744, this refrigerant exhibits the many drawbacks discussed above, including significant safety and financial drawbacks.

SUMMARY

The present invention includes a refrigeration system for providing cooling at a low temperature cooling level and at a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) low temperature flammable refrigerant;
- (ii) a compressor for compressing said low temperature flammable refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature flammable refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature flammable refrigerant;

(b) a medium temperature refrigeration unit comprising at least one medium temperature refrigeration circuit, said medium temperature refrigeration circuit comprising:

- (i) medium temperature flammable refrigerant;
- (ii) a compressor for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant; and

(c) a third refrigeration circuit (also sometimes referred to for convenience herein as a “common refrigeration circuit”) comprising a non-flammable refrigerant (also sometimes referred to for convenience herein as a “common refrigerant”), preferably comprising, or preferably comprising at least about 50% by weight, or preferably comprising at least 50% by weight of, or consisting essentially of, or consisting of transR1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F.
As used herein, the term “flammable” with respect to a refrigerant means that the refrigerant is not classified as A1 under ASHRAE 34-2016 test protocol defining conditions and apparatus and using the current method ASTM E681-09 annex A1). Accordingly, a refrigerant which is classified as A2L under ASHRAE 34-2016 test protocol defining conditions and apparatus and using the current method ASTM E681-09 annex A1 or is more flammable than the A2L classification, would be considered flammable.
Conversely, the term “non-flammable” with respect to a refrigerant means that the refrigerant is classified as A1 under ASHRAE 34-2016 test protocol defining conditions and apparatus and using the current method ASTM E681-09 annex A1).
As used herein, the term “medium temperature refrigeration” refers to refrigeration circuits in which the refrigerant circulating in the circuit is evaporating at a temperature of from about −5° C. to about −15° C., and preferably at temperature of about −10° C. As used herein with respect to temperatures, the term “about” is understood to mean variations in the identified temperature of +/−3° C. The refrigerant circulating in the medium temperature circuit can evaporate at a temperature of −10° C.+/−2° C., or at −10° C.+/−1° C.
Medium temperature refrigeration of the present invention can be used, for example, to cool products such as dairy, deli meats and fresh food. The individual temperature level for the different products is adjusted based on the product requirements.
Low temperature refrigeration is typically provided at an evaporation level of about −25° C. As used herein, the term “low temperature refrigeration” refers to refrigeration circuits in which the refrigerant circulating in the circuit is evaporating at a temperature of from about −20° C. to about −30° C., and preferably at temperature of about −25° C. The refrigerant circulating in the low temperature circuit can evaporate at a temperature of −25° C.+/−2° C., or at −25° C.+/−1° C.
Low temperature refrigeration of the present invention can be used, for example, to cool products such as ice cream and frozen goods, and again, the individual temperature level for the different products is adjusted based on the product requirements.
The present invention also includes a refrigeration system for providing cooling at a low temperature cooling level and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) low temperature flammable refrigerant in said system;
- (ii) a compressor having a power rating of about 2 horse power or less for compressing said low temperature flammable refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature flammable refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature flammable refrigerant;

- (i) medium temperature flammable refrigerant;
- (ii) a compressor having a power rating of about 2 horse power or less for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant; and

(c) a common refrigeration circuit comprising a common non-flammable refrigerant, preferably comprising, or preferably comprising at least about 50% by weight, or preferably consisting essentially of, or preferably consisting of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F.
The present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) medium temperature flammable refrigerant;
- (ii) a compressor having a power rating of about 2 horse power or less for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant, wherein at least said first refrigerant or at least said second refrigerant, and preferably where each of said first and second refrigerants, is an A2L flammable refrigerant comprising, or comprising at least about 50% by weight, or consisting essentially of, or consisting of HFO-1234fy; and

(c) a common refrigeration circuit comprising a non-flammable refrigerant comprising, or comprising at least about 50% by weight, or consisting essentially of, or consisting of transHFO-1233zd arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F.
As used herein, the term “consisting essentially of HFO-1234yf” refers to refrigerants which have at least about 75% by weight of HFO-1234yf and are permitted to include co-refrigerants provided such co-refrigerants do not negate the A2L flammability of the refrigerant and do not result in a refrigerant with a GWP greater than about 150. Accordingly, the refrigerant R455A as defined hereinafter consists essentially of R1234yf for the purposes of the present description.
The present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) low temperature flammable refrigerant in said system, said low temperature flammable refrigerant comprising at least about 50% by weight, or at least about 75% by weight, or at least 95% by weight, or at least 99% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these, preferably consisting essentially of or consisting of HFO-1234yf;
- (ii) a compressor having a horse power rating of about 2 horse power or less for compressing said low temperature flammable refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature flammable refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature flammable refrigerant;

- (i) medium temperature flammable refrigerant, said medium temperature flammable refrigerant comprising at least about 50% by weight, or at least about 75% by weight, or at least 95% by weight, or at least 99% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these, preferably consisting essentially of or consisting of HFO-1234yf;
- (ii) a compressor having a horse power rating of about 2 horse power or less for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant; and

- (i) low temperature flammable refrigerant in said system, said low temperature flammable refrigerant comprising at least about 50% by weight, or at least about 75% by weight, or at least 95% by weight, or at least 99% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these, preferably consisting essentially of or consisting of HFO-1234yf;
- (ii) a compressor for compressing said low temperature flammable refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature flammable refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature flammable refrigerant;

- (i) medium temperature flammable refrigerant, said medium temperature flammable refrigerant comprising at least about 50% by weight, or at least about 75% by weight, or at least 95% by weight, or at least 99% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these, preferably consisting essentially of or consisting of HFO-1234yf;
- (ii) a compressor for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant; and

(c) a common refrigeration circuit comprising a common non-flammable refrigerant, preferably comprising, or preferably comprising at least about 50% by weight, or preferably consisting essentially of, or preferably consisting of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F.
The present invention includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) low temperature refrigerant consisting essentially of HFO-1234yf in said system;
- (ii) a compressor for compressing said low temperature refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature refrigerant;

- (i) medium temperature refrigerant consisting essentially of HFO-1234yf in said system;
- (ii) a compressor for compressing said medium temperature refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit in which it is included by evaporating said medium temperature refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature refrigerant; and

(c) a third refrigeration circuit (also sometimes referred to for convenience herein as a “common refrigeration”) comprising a third refrigerant (also sometimes referred to for convenience herein as a “common refrigerant”) consisting essentially of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F.
The present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) low temperature flammable refrigerant in said system;
- (ii) a compressor for compressing said low temperature flammable refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature flammable refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature flammable refrigerant;

(c) a third refrigeration circuit (also sometimes referred to for convenience herein as a “common refrigeration”) comprising a third non-flammable refrigerant (also sometimes referred to for convenience herein as a “common refrigerant”) consisting essentially of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 60 F.
The first circuit heat exchangers (preferably low temperature circuit heat exchangers) and/or the second circuit heat exchangers (preferably medium temperature circuit heat exchangers) may be flooded heat exchangers.
As the term is used herein, “flooded heat exchanger” refers to a heat exchanger is which a liquid refrigerant is evaporated to produce refrigerant vapour with no substantial super heat. As the term is used herein, “no substantial super heat” means that the vapour exiting the evaporator is at a temperature that is not more than 1° C. above the boiling temperature of the liquid refrigerant in the heat exchanger.
Accordingly, the present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

(c) a common refrigeration circuit comprising a third non-flammable refrigerant, preferably comprising, or preferably comprising at least about 50% by weight, or preferably consisting essentially of, or preferably consisting of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 60 F, wherein each of said low temperature and said medium temperature heat exchangers comprises a common evaporator in which said common refrigerant evaporates at a temperature below said low temperature refrigerant condensing temperature and said medium temperature refrigerant condensing temperature, wherein said common evaporator is a flooded heat exchanger in which said common refrigerant evaporates by absorbing heat from said low temperature refrigerant or said medium temperature refrigerant.
The present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

(c) a common refrigeration circuit comprising a common non-flammable refrigerant, preferably comprising, or preferably comprising at least about 50% by weight, or preferably consisting essentially of, or preferably consisting of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F, wherein each of said low temperature and said medium temperature heat exchangers comprises a common evaporator in which said common refrigerant evaporates at a temperature below said low temperature refrigerant condensing temperature and said medium temperature refrigerant condensing temperature, wherein said common evaporator is a flooded heat exchanger in which said common refrigerant evaporates by absorbing heat from said low temperature refrigerant or said medium temperature refrigerant.
The present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) low temperature flammable refrigerant in said system, said low temperature flammable refrigerant comprising at least about 50% by weight, or at least about 75% by weight, or at least 95% by weight, or at least 99% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these, preferably consisting essentially of or consisting of HFO-1234yf;
- (ii) a compressor having a horse power rating of about 2 horse power or less for compressing said low temperature flammable refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature flammable refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature flammable refrigerant;
  - (b) a medium temperature refrigeration unit comprising at least one medium temperature refrigeration circuit, said medium temperature refrigeration circuit comprising:
- (i) medium temperature flammable refrigerant, said medium temperature flammable refrigerant comprising at least about 50% by weight, or at least about 75% by weight, or at least 95% by weight, or at least 99% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these, preferably consisting essentially of or consisting of HFO-1234yf;
- (ii) a compressor having a horse power rating of about 2 horse power or less for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant; and

(c) a third common refrigeration circuit comprising a common refrigerant consisting essentially of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F, wherein each of said low temperature and said medium temperature heat exchangers comprises a common evaporator in which said common refrigerant evaporates at a temperature below said low temperature refrigerant condensing temperature and said medium temperature refrigerant condensing temperature, wherein said common evaporator is a flooded heat exchanger in which said common refrigerant evaporates by absorbing heat from said low temperature refrigerant or said medium temperature refrigerant.
The present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

(c) a common refrigeration circuit comprising a common refrigerant consisting essentially of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F, wherein each of said low temperature and said medium temperature heat exchangers comprises a common evaporator in which said common refrigerant evaporates at a temperature below said low temperature refrigerant condensing temperature and said medium temperature refrigerant condensing temperature, wherein said common evaporator is a flooded heat exchanger in which said common refrigerant evaporates by absorbing heat from said low temperature refrigerant or said medium temperature refrigerant.
Applicants have found that the provision of flooded heat exchangers as described herein results in unexpected and highly improved heat transfer performance, for example between the first and second and/or second and third circuits. Accordingly, the efficiency of the overall refrigeration system is greatly and unexpectedly improved in the preferred systems as described herein.
The second circuit (preferably medium temperature circuit), and third circuit (the common circuit), may be located substantially completely outside of said first refrigeration units (preferably low temperature refrigeration units). As used herein, the term “substantially completely outside” means that the components of the second refrigeration circuit (and/or the third circuit when present) are not within said first refrigeration units except that transport piping and the like which may be considered part of the second refrigeration circuit (or third circuit if present) can pass into the first refrigeration units in order to provide heat exchange between the refrigerant of the first and second refrigeration circuits (or third circuit if present and appropriate according to the disclosure herein).
As used herein, the terms “first refrigeration unit” and “low temperature refrigeration unit” means an at least partially closed or closable structure that is capable of providing cooling within at least a portion of that structure and which is structurally distinct from any structure enclosing or containing said said common refrigeration circuit in its entirety. According to and consistent with such meanings, the preferred first refrigeration circuits (including the preferred low temperature refrigeration units) of the present invention are sometimes referred to herein as “self-contained” when contained within such first refrigeration units in accordance with the meanings described herein.
As used herein, the terms “second refrigeration unit” and “medium temperature refrigeration unit” means an at least partially closed or closable structure that is capable of providing cooling within at least a portion of that structure and which is structurally distinct from any structure enclosing or containing said common refrigeration circuit in its entirety. According to and consistent with such meanings, the preferred second refrigeration circuits (including preferably medium temperature refrigeration units) of the present invention are sometimes referred to herein as “self-contained” when contained within such first refrigeration units in accordance with the meanings described herein.
Each first refrigeration circuit (preferably low temperature refrigeration circuit) may be self-contained within its respective refrigeration unit.
Each first refrigeration circuit (preferably medium temperature refrigeration circuit) may be self-contained within its respective refrigeration unit.
Each refrigeration unit may be located within a first area. The first area may be a shop floor. This means that each first refrigeration circuit and each second refrigeration unit may also be arranged within a first area, such as a shop floor. This means that the first refrigeration circuit and the second refrigeration unit may not be required to extend across a large distance and so enables the use of flammable refrigerants that are also preferably low GWP refrigerants because the risk of and potential severity of refrigerant leaks is greatly reduced.
Each refrigeration unit may comprise a space and/or object to be chilled, and preferably that space and/or object are within the refrigeration unit.
Each first circuit and second circuit evaporator may be located to chill its respective space/objects, preferably by cooling air within the space to be chilled.
As mentioned above, the common refrigeration circuit may have components thereof that extend between the first refrigeration unit and/or the second refrigeration unit and a second area. The second area may be, for example, a machine room which houses a substantial portion of the components of the second refrigeration circuit.
The common refrigeration circuit may extend to a second and a third area.
The third area may be an area outside of the building or buildings in which the first refrigeration units and the second area(s) are located. This allows for ambient cooling to be exploited.
The third refrigeration circuit may extend between the second area and a third area. The third area may be an outside of the building or buildings comprising the first and second areas.
Any of the refrigerants in the first, second or third refrigeration circuits may have low Global Warming Potential (GWP).
Any of the refrigerants in the first, second or third refrigeration circuits may have a GWP which is less than 150.
The common refrigerant is preferably non-flammable. This may be desirable since the common refrigeration circuit can be quite long and may extend between different areas a great distance apart in the building which contains the low and medium temperature refrigeration units. For example, the common refrigerant circuit may extend between a shop floor (where the medium and low temperature refrigeration units might be deployed) to a machine room. Consequently, it may be relatively less safe to have a flammable refrigerant in the common refrigeration circuit in such a case since both the risk of leaks and the severity of potential leaks is increased as the common refrigeration circuit spans a greater area and therefore exposes more people and/or structures to risk of fire.
In preferred embodiments, the common refrigerant can act as a flame suppressant, and the common refrigeration circuit can be arranged to cause released of the common refrigerant into or in the vicinity of the first refrigeration circuit (preferably the low temperature refrigeration unit) and/or the second refrigeration circuit (preferably the low temperature refrigeration unit) to act as a flame suppressant in the event of a low temperature or medium temperature refrigerant leak since those refrigerants are preferably flammable.
Each first and second refrigeration circuit may comprise at least one fluid expansion device. The at least one fluid expansion device may be a capillary tube or an orifice tube. This is enabled by the conditions imposed on each first and second refrigeration circuit by its respective refrigeration unit being relatively constant. This means that simpler flow control devices, such as capillary and orifice tubes, can be and preferably are used to advantage in the first and second refrigeration circuits.
The average temperature of each of the first refrigeration circuits may be lower than the average temperature of the second refrigeration circuit and the third refrigeration circuit. The average temperature of the second refrigeration circuit may be lower than the average temperature of the third refrigeration circuit. This is because the third refrigeration circuit may cool the first and/or second refrigeration circuits.
At least one circuit interface location may be coupled in series-parallel combination with at least one other circuit interface location. Usefully, this means that if one of the circuit interface locations, first refrigeration circuits, or first refrigeration units has a fault or blockage detected, the location, circuit or unit at fault can be isolated and/or bypassed so that faults do not propagate through the system.
At least one circuit interface location may be coupled in parallel with at least one other circuit interface location.
Each circuit interface location may be coupled in parallel with each other circuit interface location.
The second refrigeration circuit may comprise a plurality of parallel connected cooling branches. Each cooling branch may comprise one or more circuit interface locations. The plurality of cooling branches may be connected in series with the pump and/or the further heat exchanger.
Each cooling branch may comprise a plurality of circuit interface locations.
The common refrigerant may comprise R1233zd(E) and/or R1234ze(Z).
The first refrigerant (preferably low temperature refrigerant), which is used in the first refrigerant circuits (preferably low temperature refrigeration circuits), may comprise any of R744, C3-C4 hydrocarbons, R1234yf, R1234ze(E), R455A and combinations of these. Hydrocarbons may comprise any of R290, R600a or R1270. These refrigerants are low GWP. The first refrigerant may be one of R744, hydrocarbons, R1234yf, R1234ze(E) or R455A. Hydrocarbons may be any of R290, R600a or R1270.
The second refrigerant (preferably medium temperature refrigerant), which is used in the second refrigerant circuits (preferably medium temperature refrigeration circuits), may comprise any of R744, C3-C4 hydrocarbons, R1234yf, R1234ze(E), R455A and combinations of these. Hydrocarbons may comprise any of R290, R600a or R1270. These refrigerants are low GWP.
The first refrigerant and second refrigerant may be one of R744, hydrocarbons, R1234yf, R1234ze(E) or R455A. Hydrocarbons may be any of R290, R600a or R1270.
The first and second refrigerants may comprise a blended refrigerant. The blended refrigerant may comprise a blend of A2L refrigerants. A2L refrigerants may comprise a blend of at least two of R1234ze(Z), R1234yf and/or R455A.
The first and second refrigerants may be a blend of HC refrigerants. HC refrigerants may comprise R290 and R1270.
The third or common refrigeration circuit may comprise a heat exchanger branch comprising the further heat exchanger.
The common refrigeration circuit may comprise an ambient cooling branch. This means that the heat exchanger branch may be bypassed. The benefit of bypassing the heat exchanger branch may be that, by doing so, heat is not exchanged with the third refrigeration circuit. Instead, heat is exchanged with the ambient air. This reduces use of the third refrigeration circuit as the load put upon it is reduced.
The ambient cooling branch of the common circuit may be coupled in parallel with the heat exchanger branch. The parallel arrangement allows for the heat exchanger branch to be bypassed by the common refrigerant and to flow in whole or in part through the ambient cooling branch.
The ambient cooling branch is preferably exposed to outside ambient temperatures. The ambient cooling branch may extend to the outside of the building or buildings comprising the first area and/or the second area.
Refrigerant entering the ambient cooling branch may be cooled by the ambient air temperature when the ambient air temperature is less than the temperature of the refrigerant entering the ambient cooling branch.
A valve may be provided at one of both of the junctions between the ambient cooling branch and the heat exchanger branch to control the flow of refrigerant in each of the ambient cooling branch and the heat exchanger branch. This allows control of whether or not and how much the third heat exchanger branch and/or the ambient cooling branch are utilised.
A valve may be used to prevent the flow of refrigerant to and from the heat exchanger branch.
The pump and the circuit interface locations may be arranged between the valve or valves.
The ambient cooling branch and the heat exchanger branch may be coupled in series with the pump.
The ambient cooling branch may be arranged to avoid operation of the third refrigeration circuit when the ambient air temperature is less than the temperature of the refrigerant entering the ambient cooling branch.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary arrangements of the disclosure shall now be described with reference to the drawings in which:

FIG. 1A shows an example of a previously used refrigeration system;
FIG. 1B shows an example of a refrigeration system that is the basis for the comparative examples described herein.
FIG. 2 shows a four circuit distributed refrigeration system which uses a flooded evaporator;
FIG. 3 shows a three circuit distributed refrigeration system which uses a flooded evaporator;
FIG. 3A shows an alternative three circuit distributed refrigeration system which uses a flooded evaporator;
FIGS. 4A and 4B show distributed refrigeration system with and without suction line heat exchangers, respectively;
FIG. 5 shows a graph of global warming potential for a refrigeration system having R515A and R744 refrigerants;
FIGS. 6A and 6B show graphs of coefficient of performance (COP) and relative COP, respectively, for an R1233zd three circuit flooded distributed refrigeration system without SLHX;
FIGS. 7A and 7B show graphs of COP and relative COP, respectively, for an R1233zd three circuit flooded distributed refrigeration system with SLHX;
FIGS. 8A and 8B show graphs of COP and relative COP respectively for an R1233zd two circuit flooded distributed refrigeration system without SLHX;
FIGS. 9A and 9B show graphs of COP and relative COP respectively for an R1233zd two circuit flooded distributed refrigeration system with SLHX;
FIGS. 10A and 10B respectively show graphs of the pressure levels and leak rates of a number of different refrigerants; and
FIG. 11 shows a graph of isentropic efficiency with pressure ratio for R290 and R124a refrigerants.
Throughout this specification, like reference numerals refer to like parts.

DETAILED DESCRIPTION OF THE DRAWINGS

Comparative Example

To aid the person skilled in the art's understanding of the refrigeration circuits of this disclosure and their respective advantages, a brief explanation of the functioning of a refrigeration system will be given in reference to the comparative refrigeration systems shown in FIGS. 1A and 1B.
FIG. 1B shows an example of a refrigeration system 100 for comparison with the further systems described below. The system 100 comprises a medium temperature refrigeration circuit 110 and a low temperature refrigeration circuit 120.
The low temperature refrigeration circuit 120 has a compressor 121, an interface with a heat exchanger 130 for rejecting heat to ambient conditions, an expansion valve 122 and an evaporator 123. The low temperature refrigeration circuit 120 interfaces with the medium temperature refrigeration circuit 110 through the inter-circuit heat exchanger 150, which serves to reject heat to from the low temperature refrigerant to the medium temperature refrigerant and thereby produce a subcooled refrigerant liquid in the low temperature refrigerant cycle. The evaporator 123 is interfaced with a space to be chilled, such as the inside of a freezer compartment. The components of the low temperature refrigeration circuit are connected in the order: evaporator 123, compressor 121, heat exchanger 130, inter-circuit heat exchanger 150, and expansion valve 122. The components are connected together via pipes 124 filled with a low temperature refrigerant.
The medium temperature refrigeration circuit 110 has a compressor 111, a condenser 113 for rejecting heat to ambient conditions and a fluid receiver 114. The liquid from receiver 114 is manifolded to flow to each of expansion valves 112 and 118, thus providing two parallel connected branches: a low temperature sub-cooling cooling branch 117 downstream of expansion device 118 and a medium temperature cooling branch 116 downstream of expansion device 112. The low temperature sub-cooling branch includes the inter-circuit heat exchanger which provides sub-cooling to the low temperature circuit as described above. The medium temperature cooling branch 116 includes medium temperature evaporator 119, which is interfaced with a space to be chilled, such as the inside of a fridge compartment.
The medium refrigerant is a high GWP refrigerant such as R134a. R134A is a hydro fluorocarbon (HFC). R134a is non-flammable and has a good coefficient of performance.
The system 100 spans three areas of a building: a roof where the condensers 113 and 130 are located; a machine room where the compressors 111, 112, heat exchanger 150, receiving tank 114 and expansion device 118 are located; and a sales floor 142 where the LT case, the MT case, and each of their expansion devices are located. The low temperature refrigeration circuit 120 and the medium temperature refrigeration circuit thus each extend between the sales floor, the machine room and the roof. In use, the medium temperature circuit 110 provides medium temperature chilling to spaces to be chilled via the evaporator 119 and the low temperature circuit 120 provides low temperature chilling to spaces to be chilled via the evaporator 123. The medium temperature circuit 110 also removes heat from the liquid condensate from the low temperature condenser 120, thus providing subcooling to the liquid entering the evaporator 123.
The individual and overall functionality of the various components of the low temperature refrigeration circuit 120 will now be described. Starting with heat exchanger 150, heat exchanger 130 is a device suitable for transferring heat between the low and medium temperature refrigerants. In one example, the heat exchanger 150 is a shell and tube heat exchanger. Other types of heat exchangers, such as plate heat exchangers and other designs, may also be used. In use, the medium temperature refrigerant absorbs heat from the low temperature refrigerant such that the low temperature refrigerant is chilled. This removal of heat via the heat exchanger 150 results in the liquid low temperature refrigerant from condenser 130 being subcooled, after which the subcooled, low temperature refrigerant flows to the expansion valve 122 via a liquid line of the pipes 124. The role of the expansion valve 122 is to reduce the pressure of the low temperature refrigerant. By doing so, the temperature of the low temperature refrigerant is correspondingly reduced since pressure and temperature are proportional. The low temperature, low pressure refrigerant then flows or is pumped to the evaporator 123. The evaporator 123 is used to transfer heat from the space to be cooled, e.g., low temperature refrigeration cases in a super market, to the low temperature refrigerant. That is, at the evaporator 123, the liquid refrigerant accepts heat from the space to be chilled and, in doing so, is evaporated to a gas. After the evaporator 123, the gas is drawn by the compressor 121, through a suction line of the pipes 124, to the compressor 121. On reaching the compressor 121, the low pressure and low temperature gaseous refrigerant is compressed. This causes the refrigerant temperature to increase. Consequently, the refrigerant is converted from a low temperature and low pressure gas to a high temperature and high pressure gas. The high temperature and high pressure gas is released into a discharge pipe of the pipes 124 to travel to the heat exchanger (condenser) 130, where the gas is condensed to a liquid in the manner previously described. This describes the operation of the low temperature refrigeration circuit 120 specifically, however the principles explained here can be applied to refrigeration cycles, generally.
The individual and overall functionality of the various components of the medium temperature refrigeration circuit 110 will now be described. Starting with heat exchanger 150, as described above the medium temperature refrigerant absorbs heat from the low temperature refrigerant via the heat exchanger 150. This absorption of heat causes the refrigerant in the medium temperature circuit 150, which is a low temperature gas and/or a mixture of gas and liquid on entering the heat exchanger 150, to be change liquid to the gas phase and/or to increase the temperature of the gas in the case where superheating will be produced. On leaving the heat exchanger 150, the gaseous refrigerant is sucked into the compressor 111 (along with the refrigerant from the evaporator 119) and is compressed by the compressor 111 to a high temperature and high pressure gas. This gas is released into the pipes 115 and travels to the condenser 113 which, in this example, is located on a roof of a building. In the condenser 113, the gaseous medium temperature refrigerant releases heat to the outside ambient air and so is cooled and condenses to a liquid. After the condenser 113, the liquid refrigerant collects in a fluid receiver 114. In this example, the fluid receiver 114 is a tank. On leaving the fluid receiver 114, the liquid refrigerant is manifolded to parallel connected medium temperature branch 116 and subcooling cooling branch 117. In the medium temperature branch 116, the liquid refrigerant flows to the expansion valve 112 which is used to lower the pressure and therefore temperature of the liquid refrigerant. The relatively cold liquid refrigerant then enters the heat exchanger 119 where it absorbs heat from the space to be chilled which is interfaced with the evaporator 119 f. In the subcooling branch 117, the liquid refrigerant similarly flows first to an expansion valve 118 where the pressure and temperature of the refrigerant is lowered. After the valve 118, the refrigerant flows to the inter-circuit heat exchanger 150, as described above. From there, the gaseous refrigerant from the heat exchanger is sucked by the compressor 111 to the compressor 111 where it re-joins the refrigerant from the medium temperature cooling branch 116.
Although not mentioned above, it will be clear that to function as intended, the temperature of the refrigerant in the medium temperature circuit 110 as it enters the heat exchanger 150 must be less than the temperature of the refrigerant in the low temperature circuit 120 as it enters the heat exchanger 150. If this were not the case, the medium temperature circuit 110 would not provide the desired subcooling to the low temperature refrigerant in circuit 120.
The above describes the operation of the comparative example of a refrigeration system 100 as illustrated in FIG. 1B. The principles of refrigeration described in reference to FIG. 1B can be applied equally well to the other refrigeration systems of this disclosure.

Inventive Systems

A number of refrigeration systems are described below. Each system has a number of refrigeration units and each of the refrigeration units has at least one dedicated refrigeration circuit located within it. That is, each refrigeration unit contains at least one refrigeration circuit.
The refrigeration circuit contained within a refrigeration unit may comprise at least a heat exchanger that removes heat to the refrigerant in the circuit, and an evaporator that adds heat to the refrigerant.
The refrigeration circuit contained within a refrigeration unit may comprise a compressor, at least a heat exchanger that removes heat from the refrigerant in the circuit (preferably by removing heat from the refrigerant vapor exiting the compressor), and an evaporator that adds heat to the refrigerant (preferably by cooling the area of the refrigeration unit being chilled). Applicants have found that the size of the compressor used in the preferred first refrigeration circuits (and preferably low temperature refrigeration circuits) of the present invention are important for achieving at least some of the highly advantageous and unexpected results of preferred embodiments of the present invention, and in particular, each compressor in in the circuit is preferably a small size compressor. As used herein, the term “small size compressor” means the compressor has a power rating of about 2 horsepower or less. As used herein with respect to compressor power rating, this value is determined by the input power rating for the compressor. As used with respect to compressor horse power rating, “about” means the indicated horse power+/−0.5 horse power. The compressor size in preferred embodiments may be from 0.1 horse power to about 2 horsepower, or from 0.1 horsepower to about 1 horse power. The compressor size may be from 0.1 horsepower up to 0.75 horsepower, or from 0.1 horsepower up to 0.5 horsepower.
A refrigeration unit may be an integrated physical entity, i.e. an entity which is not designed to be dismantled into component parts. A refrigeration unit might be a fridge or a freezer, for example. It will be understood that more than one refrigeration circuit (including particularly more than one low temperature refrigeration circuit) may be included within each refrigeration unit (including preferably each low temperature refrigeration unit).
The refrigeration circuits provided within each refrigeration unit may themselves be cooled by a common refrigeration circuit at least partially external to the refrigeration units. In contrast to the dedicated refrigeration circuits contained within each refrigeration unit, common refrigeration circuits (which are generally referred to herein as second and third refrigeration circuits) may be extended circuits which extend between multiple areas of the building housing the units: such as between a sales floor (where the refrigeration units are located) and a machine room and/or a roof or outside area.
Each refrigeration unit may comprise at least one compartment for storing goods, such as perishable goods. The compartments may define a space to be chilled by a refrigeration circuit contained within the refrigeration unit.
The present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) low temperature flammable refrigerant having a GWP of about 150 or less;
- (ii) a compressor having a power rating of about 2 horse power or less for compressing said low temperature flammable refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature flammable refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature flammable refrigerant;

- (i) medium temperature flammable refrigerant having a GWP of about 150 or less;
- (ii) a compressor having a power rating of about 2 horse power or less for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant; and

(c) a common refrigeration circuit comprising a common non-flammable refrigerant, preferably comprising, or preferably comprising at least about 50% by weight, or preferably consisting essentially of, or preferably consisting of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F.
The present invention also a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising: includes
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) medium temperature flammable refrigerant having a GWP of about 150 or less;
- (ii) a compressor having a power rating of about 2 horse power or less for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant, wherein at least said low temperature refrigerant or said medium temperature refrigerant, and preferably where each of said low and medium temperature refrigerants, is an A2L flammable refrigerant comprising, or comprising at least about 50% by weight, or consisting essentially of, or consisting of HFO-1234fy; and

(c) a common refrigeration circuit comprising a non-flammable refrigerant comprising, or comprising at least about 50% by weight, or consisting essentially of, or consisting of transHFO-1233zd arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F.
The present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) low temperature flammable refrigerant having a GWP of about 150 or less in said system, said low temperature flammable refrigerant comprising at least about 50% by weight, or at least about 75% by weight, or at least 95% by weight, or at least 99% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these, preferably consisting essentially of or consisting of HFO-1234yf;
- (ii) a compressor having a horse power rating of about 2 horse power or less for compressing said low temperature flammable refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature flammable refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature flammable refrigerant;

- (i) medium temperature flammable refrigerant having a GWP of about 150 or less, said medium temperature flammable refrigerant comprising at least about 50% by weight, or at least about 75% by weight, or at least 95% by weight, or at least 99% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these, preferably consisting essentially of or consisting of HFO-1234yf;
- (ii) a compressor having a horse power rating of about 2 horse power or less for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant; and

- (i) low temperature flammable refrigerant having a GWP of about 150 or less, said low temperature flammable refrigerant comprising at least about 50% by weight, or at least about 75% by weight, or at least 95% by weight, or at least 99% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these, preferably consisting essentially of or consisting of HFO-1234yf;
- (ii) a compressor for compressing said low temperature flammable refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature flammable refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature flammable refrigerant;

- (i) medium temperature flammable refrigerant having a GWP of about 150 or less, said medium temperature flammable refrigerant comprising at least about 50% by weight, or at least about 75% by weight, or at least 95% by weight, or at least 99% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these, preferably consisting essentially of or consisting of HFO-1234yf;
- (ii) a compressor for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant; and

- (i) low temperature flammable refrigerant having a GWP of about 150 or less;
- (ii) a compressor for compressing said low temperature flammable refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature flammable refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature flammable refrigerant;

- (i) medium temperature flammable refrigerant having a GWP of about 150 or less;
- (ii) a compressor for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant; and

(c) a common refrigeration circuit comprising a common non-flammable refrigerant consisting essentially of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F.
The present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

(c) a common refrigeration circuit comprising a third non-flammable refrigerant, preferably comprising, or preferably comprising at least about 50% by weight, or preferably consisting essentially of, or preferably consisting of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 80 F, wherein each of said low temperature and said medium temperature heat exchangers comprises a common evaporator in which said common refrigerant evaporates at a temperature below said low temperature refrigerant condensing temperature and said medium temperature refrigerant condensing temperature, wherein said common evaporator is a flooded heat exchanger in which said common refrigerant evaporates by absorbing heat from said low temperature refrigerant or said medium temperature refrigerant.
The present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) low temperature flammable refrigerant having a GWP of about 150 or less, said low temperature flammable refrigerant comprising at least about 50% by weight, or at least about 75% by weight, or at least 95% by weight, or at least 99% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these, preferably consisting essentially of or consisting of HFO-1234yf;
- (ii) a compressor having a horse power rating of about 2 horse power or less for compressing said low temperature flammable refrigerant;
- (iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature flammable refrigerant, and
- (iv) a low temperature heat exchanger for rejecting heat from said low temperature flammable refrigerant;

(c) a common refrigeration circuit comprising a common non-flammable refrigerant consisting essentially of transHFO-1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 60 F, wherein each of said low temperature and said medium temperature heat exchangers comprises a common evaporator in which said common refrigerant evaporates at a temperature below said low temperature refrigerant condensing temperature and said medium temperature refrigerant condensing temperature, wherein said common evaporator is a flooded heat exchanger in which said common refrigerant evaporates by absorbing heat from said low temperature refrigerant or said medium temperature refrigerant.
In preferred embodiments, the flammable low temperature refrigerant and/or the flammable medium temperature refrigerant comprises at least 75% by weight, or at least about 95% by weight, or consists essentially of, or consists of a combination of R1234yf, difluormethane (R-32) and CO2. In preferred embodiments, the flammable low temperature refrigerant and/or the flammable medium temperature refrigerant comprises at least 75% by weight of a combination of R1234yf, difluormethane (R-32) and CO2, wherein the combination consists of, based on the total weight of R1234yf, R-32 and CO2, about 75.5% by weight of R-1234yf, about 21.5% by weight of R32 and about 3% by weight of CO2, and such a combination is sometimes referred to herein for convenience as R455A. As used herein in connection with percentages by weight of components in a refrigerant, the term “about” refers to the indicated amount+/−1% of the indicated amount.
The present invention also includes a refrigeration system for providing cooling at a low temperature and a medium temperature cooling level, said system comprising:
(a) a low temperature refrigeration unit comprising at least one low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

- (i) medium temperature flammable refrigerant having a GWP of about 150 or less;
- (ii) a compressor for compressing said medium temperature flammable refrigerant;
- (iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature flammable refrigerant; and
- (iv) a medium temperature heat exchanger for rejecting heat from said medium temperature flammable refrigerant, wherein one or both of said low temperature flammable refrigerant and said medium temperature flammable refrigerant is A2L flammable and consists essentially of R1234yf; and (c) a common refrigeration circuit comprising a non-flammable refrigerant comprising, or preferably comprising at least about 50% by weight, or preferably comprising at least 75% by weight of, or consisting essentially of, or consisting of transR1233zd and arranged to accept heat rejected from each of said low temperature and medium temperature heat exchangers at a temperature of from about 40 F to about 60 F.

Four Circuit Flooded Distributed Refrigeration System

A preferred distributed refrigeration system comprising four circuits according to the present invention will now be described in reference to FIG. 5.
FIG. 5 shows a distributed refrigeration system 500 with four circuits comprising low temperature refrigeration circuits 510 a and 510 b (which for the purposes of referred to together as one of four depicted circuits), medium temperature refrigeration circuits 510 c and 510 d (which for the purposes of convenience are referred to together as one of four depicted circuits), a flooded common refrigeration circuit 530 and fourth refrigeration circuit 550. The common refrigeration circuit is arranged to chill, that is, remove heat from, the low and medium temperature refrigeration circuits 510 a-510 d. The fourth refrigeration circuit 550 is arranged to chill that is, remove heat from, the common refrigeration circuit 530. Each of refrigeration circuits 510 is self-contained and provides dedicated cooling to a respective refrigeration unit (not shown).
More specifically, FIG. 5 shows a refrigeration system 500 which has refrigeration circuits 510 a, 510 b, 510 c, 510 d, each of which has an evaporator 511, a compressor 512, a heat exchanger 513 and an expansion valve 514. In each circuit 510 a, 510 b, 510 c, 510 d, the evaporators 511 a, 511 b, 511 c and 511 d, compressors 512 a, 512 b, 512 c and 512 d, the heat exchangers 513 a, 513 b, 513 c and 513 d, and the expansion valves 514 a, 514 b, 514 c and 514 d, respectively, are connected in series with one another in the order listed. Each of the circuits 510 a, 510 b, 510 c, 510 d is provided in, and preferably self-contained in, a respective refrigeration unit (not shown).
In this example, circuits 510 a and 510 b are housed in freezer—that is, low temperature—units and the circuits 510 c and 510 b are housed in fridge—that is, medium temperature—units. Fridges and freezers are examples of refrigeration units. In this way, a self-contained and dedicated refrigeration circuit is provided to each refrigeration unit. The refrigeration units (not shown), and therefore the refrigeration circuits 510 a, 510 b, 510 c, 510 b are located on or near a sales floor 501 of a supermarket.
The refrigerant in the refrigeration circuits 510 a, 510 b, 510 c, 510 d is a low GWP refrigerant such as R744, hydrocarbons (R290, R600a, R1270), R1234yf, R1234ze(E) or R455A. As the skilled person will appreciate, the refrigerants in each of the refrigeration circuits 510 may be the same or different to the refrigerants in the other of the first refrigeration circuits 510.
The refrigeration system 500 also has a common refrigeration circuit 530. The common refrigeration circuit 530 has two parallel connected branches: a heat exchanger branch and an ambient cooling branch. The heat exchanger branch has a heat exchanger 531 and a fluid receiver 532. The heat exchanger 531 and the fluid receiver are connected in series and in the order listed. The ambient cooling branch has a chiller 533. The heat exchanger branch and the ambient cooling branch are coupled in parallel by a first controllable valve 534 and a second controllable valve 535. The controllable valves 534, 535 are controllable such that the amount of refrigerant flowing in each of the heat exchanger branch and the ambient cooling branch is controllable. The heat exchanger branch and the ambient cooling branch are both coupled in series with a pump 536. The pump 536 is coupled in series with and immediately downstream from the first control valve 534.
The refrigeration circuit 530 connects to refrigeration circuits 510 a-510 d using two further branches which are connected in parallel with one another: a first cooling branch 538 and a second cooling branch 537. The first 538 and second 537 cooling branches are connected between the pump 536 and the second controllable valve 535.
The cooling branch 537 interfaces with two of the heat exchangers 513 a, 513 b of the refrigeration circuits 510 a, 510 b. The second cooling branch 538 interfaces with the other two of the heat exchangers 513 c, 513 d of the refrigeration circuits 510 c, 510 d.
In this example, the first cooling branch 538 is a low temperature branch and therefore interfaces with low temperature first refrigeration circuits—that is, the freezer circuits; whereas the second cooling branch 537 is a medium temperature branch and therefore interfaces with medium temperature refrigeration circuits—that is, the fridge circuits. The references to medium and low temperature cooling relate the temperatures at which energy is transferred in each system, as described above.
The first cooling branch 538 interfaces with each of the heat exchangers 513 a, 513 b of its respective refrigeration circuits 510 a, 510 b at respective circuit interface locations 539 a, 539 b. Each of the circuit interface locations 539 a, 539 b on the first cooling branch 538 is in combination with the other of the circuits interface locations 539 a, 539 b on the cooling branch 538.
The second cooling branch 537 interfaces with each of the heat exchangers 513 c, 513 d of its respective refrigeration circuits 510 c, 510 d at respective circuit interface locations 539 c, 539 d. Each of the circuit interface locations 539 c, 539 d on the second cooling branch 537 is in combination with the other of the circuits interface locations 539 c, 539 d on the second cooling branch 537.
The refrigeration system 500, in accordance with optional aspects of the invention, also has an optional air conditioning loop 560. Usefully, provision of the loop 560 in such preferred embodiments allows for an air conditioning circuit 561 to be added on to the system 500. Usefully, this takes advantage of the existing chilling infrastructure in the system 500 and so results in a more efficient and far simplified air conditioning circuit 561. This is largely because no additional working fluid is required in the air conditioning circuit 561 since the working fluid—that is, the refrigerant—in the system 500 is utilised instead.
The optional air conditioning loop 560 is coupled with the second refrigeration circuit 530. More specifically, the air conditioning loop 560 is coupled with the second cooling branch 537 and is connected downstream from the circuit interface locations 539 c, 539 d of the second branch 537. The air conditioning loop 560 has a circuit interface location 562 with the air conditioning circuit 561. More specifically, at the circuit interface location 562, the second cooling branch 537 interfaces an air conditioning heat exchanger 563. The air conditioning circuit 561 additionally comprises a fan 564. In use, the second cooling branch 537 removes heat from the air conditioning circuit 561 via the heat exchanger 563 in much the same way as it removes heat from its respective first refrigeration circuits 510 c, 5510 d. This results in the temperature of the refrigerant in the second cooling branch 537 increasing; and the temperature of the air in proximity to the air conditioning heat exchanger 563 decreasing. The fan 564 is used to circulate the cool air in proximity to the air conditioning heat exchanger 563 to where it is required. In this example, the circuit interface location 562 with the air conditioning unit 561 is connected with the circuit interface locations 539 c, 539 d of the second cooling branch 537 with the first cooling branch 538; however, as the person skilled in the art will appreciate based on the teachings and disclosures contained herein, many other arrangements are possible, such as simple parallel connections and simple series connections. As the person skilled in the art will also appreciate, the air conditioning loop 560 and unit 561 might equally well be removed from the system 500.
The common refrigeration circuit 530 includes portions that extend the circuit between the sales floor 501, a machine room 502 and a roof 503. The first cooling branch 538 and the second cooling branch 537 are primarily located on the sales floor 501. By primarily located on the sales floor 501, it is meant that the circuit interface locations 539, 562 are located on or near the sales floor 501. The junction between the first 538 and second 537 cooling branches and some of the first (low temperature refrigeration) circuit 538 are however located in the machine room 501. The heat exchanger branch is also located in the machine room 501, along with the pump 536 and first 534 and second 535 controllable valves. The ambient cooling branch includes portions that extend the branch between the machine room 501 and the roof 503. The chiller 533 is located on the roof.
In this example, the refrigerant in the common refrigeration circuit comprises, at least 75% by weight of R1233zd(E). Such refrigerants are non-flammable, low GWP refrigerants, that is, refrigerants that have a GWP of 500 or less, more preferably about 150 or less.
With reference again to FIG. 2, the refrigeration system 500 also has a refrigeration circuit 550, which cools the common refrigerant in the circuit 530. The refrigeration circuit 550 has a compressor 551, a chiller 552, an expansion valve 553 and an interface with the heat exchanger 531 of the common refrigeration circuit 530. The compressor 551, the chiller 552, the expansion valve 553 and the interface with the heat exchanger 531 of the refrigeration circuit 530 are connected in series and in the order listed.
The refrigeration circuit 550 includes portions that extend the circuit between the machine room 502 and the roof 503. The interface with the heat exchanger 531 of the refrigeration circuit 530, the compressor 551 and the expansion valve 553 are in the machine room 502. The chiller 552 is on the roof.
In this example, the refrigerant in the refrigeration circuit 550 can be an individual A2L refrigerant or HC refrigerant, or a blend of A2L refrigerants or HC refrigerants. A2L refrigerants can include R1234ze, R1234yf and R455A, for example. HC refrigerants can include R290 and R1270, for example.
The refrigeration system 500 is preferably a system that includes a receiver in refrigeration circuit 530 and/or on circuit 550. Accordingly the heat exchangers 513 are flooded.
In operation, the refrigeration circuit 550 extracts heat from the common refrigeration circuit 530 and the common circuit 530 extracts heat from at least the low and medium temperature circuits. The advantage of this approach is that because the circuit 550 is preferably located in a location remote from the areas in which members of the public have unrestricted access, such as a machine room and the roof, the refrigerant in that circuit can be a flammable, but low GWP refrigerant. Accordingly, the present systems can be unexpectedly effective since the common refrigeration circuit can be operated with a higher GWP (preferably up to about 500) and non-flammable refrigerant because this is the only circuit in which portions extend between the sales floor 501 and the machine room 502.
The potential advantages described in reference to the flooded and non-flooded cascaded refrigeration systems may apply equally well to the systems of the type described in this section wherein the heat exchangers are flooded or not flooded.
For the purposes of convenience, the term “flooded system,” “flooded cascade system,” and the like refer to systems of the present disclosure in which at least one and preferably all of the heat exchangers in the first refrigeration circuit (preferably low temperature circuit) and the second refrigeration circuit (preferably medium temperature circuit) for condensing said low and medium temperature refrigerants are flooded evaporators for the common refrigerant.
A further potential advantage of the flooded distributed refrigeration system hereof is that the system may further reduce GWP of the require refrigerants. This occurs in part for those embodiments which include a fourth third refrigeration such as 550 that replaces a part of the common refrigeration circuit as described herein. This can have the effect of shortening the common refrigeration circuit, therefore reducing the volume of non-flammable, but higher GWP refrigerant required in the common circuit. Instead, the fourth refrigeration circuit, which replaces some of the common refrigeration circuit, uses a low GWP, but flammable, refrigerant. Consequently, the system can operate with a further reduced GWP.
A yet further potential advantage of the four circuit flooded distributed refrigeration system is that it may have an air conditioning loop and complementary air conditioning circuit. The advantages of this are as discussed in the description above and include that a more efficient and simplified air condition circuit may be provided which takes advantage of the existing system.

Four Circuit Flooded Distributed Refrigeration System—Alternatives

An alteration of the system 500 which is envisaged is that the refrigerant in the common refrigeration circuit 530 (preferably R1233zd(E)) is arranged to be released as a flame/fire suppression agent in the case of a leak of the flammable refrigerants in either or both of the low and medium temperature circuits (510 in the example) or the fourth refrigeration circuit (550 in the example). In one arrangement, an extra exit port is added to the first 536 and/or second 536 controllable values such that the refrigerant in the refrigeration circuit 530 is controllably releasable from the common refrigeration circuit 530. In another arrangement, an exit port is provided immediately downstream from the pump 536 so that the pump can actively pump the refrigerant from the refrigeration circuit 530 to act as a flame/fire suppression agent.
A further alteration of the system 500 which is envisaged is that the air conditioning loop 560 and circuit 561 might be either removed completely; or coupled or arranged elsewhere on the refrigeration circuit 530, or indeed on one of the refrigeration circuits 510 or on the fourth refrigeration circuit 550.
By virtue of its preferred modular design for the low and medium temperature refrigeration circuits, the present refrigeration systems allows use of flammable, low-pressure refrigerants with low GWP in the low and medium temperature refrigeration circuits. Further still, by virtue of its ambient cooling branch, the system provides reduced energy usage. Yet further still, by virtue of its preferred receiver in the common circuit and flooded design of evaporators in the low and medium temperature refrigeration circuits, the system provides unexpected improvement in system efficiencies. Also, by virtue of its optional but preferred additional air conditioning loop, the system additionally enables a simplified complementary air conditioning circuit.

Three Circuit Flooded Distributed Refrigeration System

Another refrigeration system forming part of this disclosure will now be described in reference to FIG. 6.
FIG. 6 shows a distributed refrigeration system 600 with two medium temperature refrigeration circuits 610 a, 610 b (which for the purposes of convenience are referred to together as one of the three depicted circuits), two low temperature refrigeration circuits 630 a, 630 b (which for the purposes of convenience are referred to together as one of three depicted circuits) and a common refrigeration circuit 650.
The common refrigeration circuit 650 is arranged to chill, that is, remove heat from, both the medium 610 and low 630 temperature refrigeration circuits. Each of the medium 610 a, 610 b and low 630 a, 630 b temperature refrigeration circuits is self-contained and provides dedicated cooling to a respective refrigeration unit (not shown).
More specifically, each of the two medium temperature refrigeration circuits 610 a, 610 b has an evaporator 611 a, 611 b, a compressor 612 a, 612 b, a heat exchanger 613 a, 613 b and an expansion valve 614 a, 614 b. In each medium temperature refrigeration circuit 610 a, 610 b, the evaporators (611 a and 611 b), the compressors (612 a and 612 b), the heat exchangers (613 a and 613 b) and the expansion valves (614 a and 614 b) are connected respectively in series with one another in the order listed. Each of the medium temperature refrigeration circuits 610 a, 610 b is provided in a respective refrigeration unit (not shown). In this example, the medium temperature refrigeration circuits 610 a, 610 b are housed in fridge—that is, medium temperature—units. A fridge is an example of a refrigeration unit. In this way, a self-contained and dedicated medium temperature refrigeration circuit 610 is provided to each refrigeration unit. The refrigeration units (not shown) and therefore the medium temperature refrigeration circuits 610 a, 610 b are located on or near a sales floor 601 of a supermarket.
The refrigerant in the medium temperature refrigeration circuits 610 a, 610 b is a flammable, low GWP refrigerant such as R744, hydrocarbons (R290, R600a, R1270), R1234yf, R1234ze(E) or R455A. As the skilled person will appreciate, the refrigerants in each of the medium temperature refrigeration circuits 610 a, 610 b may be the same or different to the refrigerants in the other of the medium temperature refrigeration circuits 610 a, 610 b.
Like the medium temperature refrigeration circuits 610 a, 610 b, each of the two low temperature refrigeration circuits 630 a, 630 b has an evaporator 631 a and 631 b, a compressor 632 a, 632 b, a heat exchanger 633 a, 633 b and an expansion valve 634 a, 634 b. In each low temperature refrigeration circuit 630 a, 630 b, the evaporators (631 a and 631 b), the compressors (632 a and 632 b), the heat exchangers (633 a and 633 b) and the expansion valves (634 a and 634 b) are connected, respectively, in series with one another in the order listed. Each of the medium temperature refrigeration circuits 630 a, 630 b is provided in a respective refrigeration unit (not shown). In this example, the low temperature refrigeration circuits 630 a, 630 b are housed in freezer—that is, medium temperature—units. A freezer is an example of a refrigeration unit. In this way, a self-contained and dedicated low temperature refrigeration circuit 630 is provided to each refrigeration unit. The refrigeration units (not shown) and therefore the low temperature refrigeration circuits 630 a, 630 b are located on the sales floor 601 of a supermarket.
Like the medium temperature refrigeration circuits 610 a, 610 b, the refrigerant in the low temperature refrigeration circuits 630 a, 630 b is a flammable, low GWP refrigerant such as R744, Hydrocarbons (R290, R600a, R1270), R1234yf, R1234ze(E) or R455A. As the skilled person will appreciate, the refrigerants in each of the low temperature refrigeration circuits 6130 a, 630 b may be the same or different to the refrigerants in the other of the low temperature refrigeration circuits 630 a, 630 b.
The refrigeration system 600 also has a common refrigeration circuit 650. The common refrigeration circuit 650 has a compressor branch 660 and an ambient cooling branch 670. The compressor branch 660 is connected in parallel with the ambient cooling branch 670.
The compressor branch 660 has a compressor 661, a chiller 662, an expansion valve 663 and a receiver 664. The compressor 661, the condenser 662 and the expansion valve 663 are connected in series and in the order given. The receiver 664 is connected between the compressor 661 inlet and the expansion valve 663 outlet. The ambient cooling branch 670 has a chiller 671.
The compressor branch 660 and the ambient cooling branch 670 are connected in parallel by first 665 and second 666 controllable valves. The controllable valves 665, 666 are controllable such that the amount of refrigerant flowing in each of the compressor branch 660 and the ambient cooling branch 670 is controllable. The first control valve 665 is connected in series with a pump 667.
The common refrigeration circuit 650 also has two further branches which are connected in parallel with one another: a medium temperature cooling branch 680 and a low temperature cooling branch 685. The medium temperature cooling branch 680 and the low temperature cooling branch 685 are connected between the pump 667 and the second controllable valve 666.
In this example, the low temperature cooling branch 685 interfaces with the low temperature refrigeration circuits 630—that is, the freezer circuits; whereas the medium temperature cooling branch 680 interfaces with the medium temperature refrigeration circuits 610—that is, the fridge circuits. The references to medium and low temperature cooling relate to relative temperature that heat is rejected to area being cooled by the refrigeration circuit, as per the description of such systems above.
The medium temperature cooling branch 680 interfaces each of the heat exchangers 613 a, 613 b of the medium temperature refrigeration circuits 610 a, 610 b at respective circuit interface locations 681 a, 681 b. Each of the circuit interface locations 681 a, 681 b is in series-parallel combination with the other circuit interface location 681 a, 681 b.
The low temperature cooling branch 685 interfaces each of the heat exchangers 633 a, 633 b of the low temperature refrigeration circuits 630 a, 630 b at respective circuit interface locations 686 a, 686 b. Each of the circuit interface locations 686 a, 686 b is in combination with the other circuit interface location 686 a, 686 b.
The refrigeration system 600 also has in preferred embodiments an air conditioning loop 690. Usefully, provision of the loop 690 allows for an air conditioning circuit 691 to be added on to the system 600. Usefully, this takes advantage of the existing chilling infrastructure in the system 600 and so results in a more efficient and far simplified air conditioning circuit 691. This is largely because no additional working fluid is required in the air conditioning circuit 691 since the working fluid—that is, the refrigerant—in the system 600 is utilised instead.
The optional air conditioning loop 690 is coupled with the second refrigeration circuit 650. More specifically, the air conditioning loop 690 may be coupled in one or more of several locations to the system. In one embodiment, the optional air conditioning loop 690 is coupled with the low temperature cooling branch 685 and is connected downstream from the circuit interface locations 633 a, 633 b of the low temperature cooling branch 685 with the low temperature refrigeration circuits 630 a, 630 b. The air conditioning loop 690 has a circuit interface location 692 with the air conditioning circuit 691. More specifically, at the circuit interface location 692, the low temperature cooling branch 685 interfaces an air conditioning heat exchanger 693. The air conditioning circuit 691 additionally comprises a fan 694. In use, the low temperature cooling branch 685 removes heat from the air conditioning circuit 691 via the heat exchanger 693 in much the same way as it removes heat from its respective low temperature refrigeration circuits 630 a, 630 b. This results in the temperature of the refrigerant in the low temperature cooling branch 685 increasing; and the temperature of the air in proximity to the air conditioning heat exchanger 693 decreasing. The fan 694 is used to circulate the cool air in proximity to the air conditioning heat exchanger 693 to where it's required. In this example, the circuit interface location 692 with the air conditioning unit 694 is connected in series-parallel with the circuit interface locations 633 a, 633 b of the second cooling branch 537 with the low temperature cooling branch 685; however, as the person skilled in the art will appreciate based on the disclosure and teachings contained herein, many other arrangements are possible, such as simple parallel connections and simple series connections. As the person skilled in the art will also appreciate based on the disclosure and teachings contained herein, the air conditioning loop 690 and unit 691 might equally well be removed from the system 600.
The common refrigeration circuit 650 includes portions that extend the circuit between the sales floor 601, a machine room 602 and a roof 603. The low temperature cooling branch 680 and the medium temperature cooling branch 685 are primarily located on or near the sales floor 601. By primarily located on or near the sales floor 601, it is meant that the circuit locations 681 a, 681 b, 686 a, 686 b are located on or near the sales floor 601. The junction between the low 680 and medium 686 temperature cooling branches and some of the pipes of the low 680 and medium 686 branches are however located far from the sales floor, for example, in the machine room 602.
The compressor branch 660 includes portions that extend the branch between the machine room 602 and the roof 603. More specifically, the compressor 661, the expansion valve 663 and the receiver 664 are located in the machine room 602. The condenser 662 is located remote from areas in which members of the public have unrestricted access, such as on the roof 603 and which provide ready access to ambient conditions.
The ambient cooling branch 670 includes portions that extend the branch between the machine room 602 and the roof 603. The chiller 671 is located on the roof 603.
The first and second controllable valves 665, 666 are located in the machine room 602. The pump 667 is located in the machine room 602.
In this example, the refrigerant in the common refrigeration circuit 650 is R1233zd(E). This is a non-flammable refrigerant.
Though structurally different, in use, the refrigeration system 600 operates in a similar manner to refrigeration system 500.
The potential advantages described in reference to the four circuit distributed system above for both the flooded and non-flooded cases apply equally well to the two three circuit flooded and non-flooded distributed refrigeration system described in this section.
The terms used to describe the flooded and non-flooded cascaded refrigeration systems and the four circuit flooded distributed refrigeration system are generally comparable to those used to describe the three circuit flooded distributed system.
A yet further potential advantage of the three circuit flooded distributed refrigeration system is that it may have an air conditioning loop and complementary air conditioning circuit. The advantages of this are as discussed in the description of the loop and include that a more efficient and simplified air condition circuit is provided which takes advantage of the existing system.
Overall, the provision of a plurality of low and medium temperature refrigeration circuits, each one located in a respective refrigeration unit, has such benefits as: reducing leak rates; simplifying the overall refrigeration system; enabling the use of otherwise unsafe low GWP refrigerants; improving maintenance and installation; and reducing pressure drop, leading to an improved system efficiency.

Three Circuit Flooded Distributed Refrigeration System—Alternatives

The alternatives described above in reference to the flooded and non-flooded distributed refrigeration system, including the four circuit flooded distributed refrigeration system, apply equally well to the three circuit flooded distributed refrigeration system described herein.
A further alteration of the system 600 which is envisaged is that the refrigerant in the common refrigeration circuit 650 (R1233zd(E) in the example given) is arranged to be released as a flammability suppressant in the case of a leak of the flammable refrigerants in one or more of the medium 610 or low 630 temperature refrigeration circuits. In one arrangement, an extra exit port is added to the first 665 and/or second 666 controllable values such that the refrigerant in the common refrigeration circuit 650 is controllably releasable from the common refrigeration circuit 650. In another arrangement, an exit port is provided immediately downstream from the pump 667 so that the pump can actively pump the refrigerant from the common refrigeration circuit 650 to act as a flame or fire suppressing agent.
A further alteration of the system 600 which is envisaged is that the air conditioning loop 690 and circuit 691 might be either removed completely; or coupled or arranged elsewhere on the common refrigeration circuit 650, or indeed on one or more of the low 630 and medium 610 temperature refrigeration circuits.
A yet further alteration of the system 600 which is envisaged is that the ambient cooling branch 670 may be shortened and simplified such that it only bypasses the compressor 611, rather than the entire compressor branch. This arrangement is shown in FIG. 6A.
FIG. 6A shows a refrigeration system 600 which is the largely the same as that described in reference to FIG. 6 with the following exceptions:

- The chiller 671 of FIG. 6 is not present as it is no longer required.

This is because the ambient cooling branch 670 no longer bypasses the chiller 662 and so it does not require its own dedicated chiller.

- The first controllable valve 665 is not present as it is no longer required. This is because the refrigerant from the ambient cooling branch 670 simply feeds into the chiller 662 line, rather than meeting a junction of branches.
- The ambient cooling branch 670 is connected in parallel with the compressor 661 between the second controllable valve 666 and the line between the compressor 661 and the chiller 662.

Advantageously, the shortened ambient chilling branch 670 results in: first, a simplified circuit as the chiller 671 and first controllable valve 665 are no longer required; and second, a lower cost circuit, since the amount of extra piping for the ambient chilling branch 670 and the number of components is reduced, therefore reducing material costs.
In summary, by virtue of its modular low and medium temperature refrigeration circuit design, the refrigeration system allows use of flammable, low-pressure refrigerants with low GWP in the low and medium temperature refrigeration circuits. Further, by virtue of its ambient cooling branch, the system provides reduced energy usage. Yet further still, by virtue of its flooded design, the system delivers improved system efficiencies. Accordingly, a refrigeration system of reduced environmental impact is provided through use of reduced GWP refrigerants, reduced energy usage and improved system efficiency.

Suction Line Heat Exchanger

A further possible alteration of any of the systems forming part of this disclosure is that any number of the self-contained refrigeration circuits may include a suction line heat exchanger (SLHX).
More specifically, any of the refrigeration circuits 510 a, 510 b, 510 c, 510 d may include an SLHX; and any of the refrigeration circuits 630 a, 630 b and/or 10 a, 610 b temperature refrigeration circuits may include an SLHX.
For comparison, FIG. 7A shows a refrigeration circuit 700 without a SLHX; while FIG. 7B shows a refrigeration circuit 750 with a SLHX 760.
The circuit 700 in FIG. 7A has a compressor 710, a heat exchanger 720, an expansion valve 730 and an evaporator 740. The compressor 710, the heat exchanger 720, the expansion valve 730 and the evaporator 740 are connected in series and in the order listed. In use, the refrigeration circuit 700 functions as previously described.
The circuit 750 in FIG. 7B has the same components as the circuit 700, plus an additional SLHX 760. The SLHX provides a heat exchanging interface between the line connecting the evaporator 740 and the compressor 710, and the line connecting the heat exchanger 720 and the expansion valve 730. In other words, the SLHX 760 is positioned between the line connecting the evaporator 740 and the compressor 710 (herein referred to as the vapour line), and the line connecting the heat exchanger 720 and the expansion valve 730 (herein referred to as the liquid line).
In use, the SLHX transfers heat from the liquid line, after the heat exchanger 720, to the vapour line, after the evaporator 740. This results in two effects taking place: a first which improves the efficiency of the circuit 700; and a second which reduces the efficiency of the circuit 700.
Firstly, advantageously, on the liquid line side—that is, the high pressure side—the sub-cooling of the liquid refrigerant is increased. This is because extra heat is rejected to the liquid expansion side, which reduces the temperature of the refrigerant entering the expansion valve 730. This additional sub-cooling leads to lower inlet quality in the evaporator 740 after the expansion valve 730 process. This increases the enthalpy difference and so the capacity of the refrigerant to absorb heat in the evaporator 740 stage is increased. Accordingly, the performance of the evaporator 740 is improved.
Secondly, disadvantageously, on the vapour line side—that is, the low pressure side—the refrigerant exiting the evaporator 740 receives extra heat from the liquid line, which effectively increases the superheating. This results in a higher suction line temperature. As a result of the higher suction line temperature to the compressor 710, the enthalpy difference of the compression process increases. This increases the compressor power required to compress the refrigerant. Accordingly, this has a detrimental effect on the system performance.
In summary both the first and second effects of improved evaporator capacity and improved compressor power requirements need to be considered in order to determine whether or not introducing a SLHX results in an overall beneficial effect. For certain refrigerants, such as R717, the use of a SLHX leads to an overall reduction of the system efficiency. However, in contrast, use of a SLHX leads to an overall positive effect in the systems of the present invention.

Supporting Data

Data intended to demonstrate the technical effects of the various arrangements of this disclosed and to aid the person skilled in the art in putting the various arrangements in to practice will now be presented.
Table 1 shows the overall GWP for varying proportions of R515A and R744 refrigerants in the refrigeration system: 1 being the maximum combined value i.e. 100%. According to the 5th Intergovernmental Panel on Climate Change, R515A has a GWP of 403 and R755 a GWP of 1. Consequently, the overall GWP for 0 proportion R515A and 1 proportion R744 is 1 as [(1×1)=1]. Conversely, the overall GWP for 0.05 proportion R515A and 0.95 proportion R755 is 21.1 since [(0.05×403)+(0.95×1)=21.1]. In this way Table 1 shows the charge ratio restrictions considering GWP criteria.

TABLE 1

R515A	R744	Overall GWP

0	1	1
0.05	0.95	21.1
0.1	0.9	41.2
0.15	0.85	61.3
0.2	0.8	81.4
0.25	0.75	101.5
0.3	0.7	121.6
0.31	0.69	125.62
0.32	0.68	129.64
0.33	0.67	133.66
0.34	0.66	137.68
0.35	0.65	141.7
0.36	0.64	145.72
0.37	0.63	149.74
0.38	0.62	153.76
0.39	0.61	157.78
0.4	0.6	161.8
0.5	0.5	202
0.6	0.4	242.2
0.7	0.3	282.4
0.8	0.2	322.6
0.9	0.1	362.8
1	0	403

FIG. 5 shows the data in Table 1 in graphical form. The proportion of R515A is shown on the x-axis, and the overall GWP is shown on the y-axis. It is clear from this graph that there is a direct proportional relationship between the relative proportions of R515A and R744 and GWP: as the proportion of R515A increases, as does the GWP for the system. This is because R515A has a much higher GWP than R744, The directly proportional relationship is shown by the straight line on the graph which goes from 1 GWP at 0 proportion R515A to around 400 GWP at 1 proportion R515A. It is clear from this graph that the maximum allowed system GWP of 150 in preferred embodiments is found at around 0.35 weight proportion R515A.
Table 2 shows the boiling pressures at varying boiling temperatures for: R1233zd(E) refrigerant; a blend of 50 wt % proportion R1233zd(E) and 50 wt % proportion R1234ze; and a blend of 33 wt % R1233zd(E) and 67 wt % R1234ze.
TABLE 2

Evaporator Temperature Evaporator Pressure

Refrigerant (° C.) (bar)

R1233zd −1 0.46

5 0.60

10 0.73

R1233zd/R1234ze −1 1.02

(50%/50%) 5 1.29

10 1.55

R1233zd/R1234ze −12 1.00

(33%/67%) −1 1.27

5 1.60

10 1.92

The test refrigeration system is operated with an indoor refrigerant. The R1233zd(E) transHCFO-1233zd and the R1234ze is transHFO-1234ze.
The results in Table 2 show that the compositions in which the amount of transHFO-1234ze is at least 50% by weight permit the indoor circuit to operate under pressures greater than one atmosphere. Such a low pressure system is advantageous as it avoids the need for a purge system—aiding system complexity, while at the same time providing a system pressure sufficiently low to allow the use of relatively low-cost vessels and conduits. Further still, the low pressure avoids refrigerant leaks that might otherwise occur in high pressure systems.
Another characteristic which varies with the proportions of R1233zd(E) and R1234ze in the blend is the flammability of the refrigerant in the event of a leak from the refrigeration system. Table 3 shows various compositions by weight of the R1233zd(E) and R1234ze blend and the respective flammability of each composition. As is made clear in Table 3, blends having in excess of 67% by weight of transHFO-1234ze are flammable as measured according to American Society for Testing and Materials (ASTM) 681.
TABLE 3

Nominal Composition Initial Vapor

(wt %) Composition (wt %)

R1233zd R1234ze R1233zd R1234ze Flammability

50.0 50.0 19.6 80.4 Non-flammable

40.0 60.0 13.4 86.6 Non-flammable

34.0 66.0 10.4 89.6 Non-flammable

33.0 67.0 9.9 90.1 Non-flammable

32.0 68.0 9.5 90.5 Flammable

Table 4 shows a comparison of a comparative example R404A direct expansion refrigeration system with the four circuit distributed refrigeration system described in reference to FIG. 2 without SLHX. In this case, the distributed refrigeration system has R1234ze(E) in the fourth refrigeration circuit and R1233zd(E) in the third (common) refrigeration circuit to remove the rejected heat from the first and second refrigeration circuits which provide low and medium temperature cooling. For this example the evaporation temperature of the R1234ze(E) refrigerant is varied to achieve a R1233zd(E) temperature of 80 F, 70 F, 60 F, 50 F and 40 F. The resulting system performance is compared to the comparative example R404A system without mechanical subcooling having an overall power of 54.8 kW and a resulting COP of 1.82, and a R404A system with mechanical subcooling to 50 F having an overall power of 49.6 kW and a COP of 2.02. The cooling capacity for each case is 100 kW with 67 kW MT and 33 kW LT load distribution.

TABLE 4

R1233zd(E)	Power

temperature

R744

R290

R1234yf

R455A

COP (% of R404Awo SC/w SC)

[F.]	[kW]	[kW]	[kW]	[kW]	R744	R290	R1234yf	R455A

80	74.9	60.1	54.1	53.3	1.34	1.66	1.85	1.87
					(73%/	(91%/	(101%/	(103%/
					66%)	82%)	92%)	93%)
70	64.1	57.2	50.0	49.4	1.56	1.75	2.00	2.02
					(86%/	(96%/	(110%/	(111%/
					77%)	87%)	99%)	100%)
60	58.0	55.0	47.1	46.4	1.72	1.82	2.12	2.16
					(95%/	(100%/	(116%/	(118%/
					86%)	90%)	105%)	107%)
50	54.8	53.5	45.8	45.4	1.83	1.87	2.18	2.20
					(100%/	(103%/	(120%/	(121%/
					91%)	93%)	108%)	109%)
40	53.7	53.2	46.4	46.7	1.86	1.88	2.16	2.14
					(102%/	(103%/	(118%/	(117%/
					92%)	93%)	107%)	106%)

As demonstrated by the results in Table 4, an unexpected maximum in performance is seen for a system with: R1233zd(E) at a temperature in the range of from about 40 F to about 80 F, more preferably at a temperature in the range of from about 40 F to about 60 F, and more preferably at a temperature of from about 45 F to about 55 F (preferably about 50 F) with both R1234yf and R455A in the low and medium temperature refrigeration circuits. It has been shown that these combination of refrigerants provide highly advantageous and unexpected performance, and the largest improvement over the comparative example R404A system.
The results in Table 4 are shown graphically in FIGS. 6A and 6B. FIG. 6A shows a graph of the COP of the R1233zd(E) system across a range of different cooling temperatures and with different refrigerants in the low and medium temperature refrigeration circuits. It is clear from this graph that the highest COP is achieved when the R1233zd(E) system has R1234yf and/or R455A in the low/medium temperature refrigeration circuits and at R1233zd(E) evaporating temperatures of around in the range of from about 40 F to about 80 F, more preferably at a temperature in the range of from about 40 F to about 60 F, and more preferably at a temperature of from about 45 F to about 55 F (preferably about 50 F).
Table 5 shows a comparison of a comparative example R404A DX refrigeration system with the distributed refrigeration system described in reference to FIG. 2 with SLHX. In this case, the distributed refrigeration system has R1234ze(E) in the fourth refrigeration circuit and R1233zd(E) in the common refrigeration circuit to remove the rejected heat from the low and medium refrigeration circuits to provide low and medium temperature cooling. In this case, the provide low and medium temperature refrigeration circuits also have SLHXs. For this example the evaporation temperature of the R1234ze(E) is varied to achieve a R1233zd(E) temperature of 80 F, 70 F, 60 F, 50 F and 40 F. The resulting system performance is compared to the comparative example R404A system without mechanical subcooling having an overall power of 54.8 kW and a resulting COP of 1.82, and a R404A system with mechanical subcooling to 50 F having an overall power of 49.6 kW and a COP of 2.02. The cooling capacity for each case is 100 kW with 67 kW MT and 33 kW LT load distribution.

TABLE 5

R1233zd(E)	Power

temperature

R744

R290

R1234yf

R455A

COP (% of R404Awo SC/w SC)

[F.]	[kW]	[kW]	[kW]	[kW]	R744	R290	R1234yf	R455A

80	69.1	56.8	49.7	50.2	1.45	1.76	2.01	1.99
					(79%/	(97%/	(110%/	(109%/
					72%)	87%)	100%)	99%)
70	60.0	54.3	46.4	46.6	1.67	1.84	2.16	2.14
					(91%/	(101%/	(118%/	(118%/
					83%)	91%)	107%)	106%)
60	54.6	52.2	44.0	43.9	1.83	1.91	2.27	2.28
					(101%/	(105%/	(125%/	(125%/
					91%)	95%)	113%)	113%)
50	51.6	50.8	43.0	42.9	1.94	1.97	2.33	2.33
					(106%/	(108%/	(128%/	(128%/
					96%)	98%)	116%)	116%)
40	50.5	50.4	43.5	43.8	1.98	1.98	2.30	2.28
					(109%/	(109%/	(126%/	(125%/
					98%)	98%)	114%)	113%)

As demonstrated by the results in Table 5, it is clear that the highest COP is achieved when the R1233zd(E) system has R1234yf and/or R455A in the low/medium temperature refrigeration circuits and at R1233zd(E) evaporating temperatures in the range of from about 40 F to about 80 F, more preferably at a temperature in the range of from about 40 F to about 60 F (which shows an unexpected maximum at a 1233zd(E) evaporating temperature of from about 45 F to about 55 F (preferably about 50 F). It has been shown that this combination at these temperatures provides the best performance and the largest improvement over the comparative example R404A system.
The results in Table 5 are shown graphically in FIGS. 7A and 7B. FIG. 7A sows a graph of the COP of the R1233zd(E) system across a range of different cooling temperatures and with different refrigerants in the first refrigeration circuits. It is clear from this graph that the highest COP is achieved when the R1233zd(E) system has R1234yf or R455A in the low and medium temperature refrigeration circuits and at R1233zd(E) cooing temperatures in the range of from about 40 F to about 80 F, more preferably at a temperature in the range of from about 40 F to about 60 F (which shows an unexpected maximum at a 1233zd(E) evaporating temperature of from about 45 F to about 55 F (preferably about 50 F)),
Table 6 below shows a comparison of a comparative example R404A DX refrigeration system with the three circuit flooded distributed refrigeration circuit described in reference to FIG. 3 without SLHX. In this case, the two circuit distributed refrigeration circuit has R1233zd(E) in the common refrigeration circuit to remove the rejected heat from the low and medium temperature refrigeration circuits to provide low and medium temperature cooling. For this example the evaporation temperature of the R1233zd(E) is varied to achieve a temperature of 80 F, 70 F, 60 F, 50 F and 40 F. The resulting system performance is compared to the comparative example R404A system without mechanical subcooling having an overall power of 54.8 kW and a resulting COP of 1.82, and a R404A system with mechanical subcooling to 50 F having an overall power of 49.6 kW and a COP of 2.02. The cooling capacity for each case is 100 kW with 67 kW MT and 33 kW LT load distribution.

TABLE 6

R1233zd(E)	Power

temperature

R744

R290

R1234yf

R455A

COP (% of R404Awo SC/w SC)

[F.]	[kW]	[kW]	[kW]	[kW]	R744	R290	R1234yf	R455A

80	69.9	55.6	49.7	49.0	1.43	1.80	2.01	2.04
					(78%/	(99%/	(110%/	(112%/
					71%)	89%)	100%)	101%)
70	57.8	51.2	44.1	43.6	1.73	1.95	2.27	2.29
					(95%/	(107%/	(124%/	(126%/
					86%)	97%)	112%)	114%)
60	51.6	48.8	41.1	40.5	1.94	2.05	2.43	2.47
					(106%/	(112%/	(133%/	(135%/
					96%)	102%)	121%)	122%)
50	57.0	55.7	47.9	47.5	1.75	1.80	2.09	2.11
					(96%/	(98%/	(114%/	(115%/
					87%)	89%)	104%)	104%)
40	83.2	82.4	74.5	74.8	1.20	1.21	1.34	1.34
					(66%/	(67%/	(74%/	(74%/
					60%)	60%)	67%)	67%)

As demonstrated by the results in Table 6, it is clear that the highest COP is achieved when the R1233zd(E) system has R1234yf and/or R455A in the low/medium temperature refrigeration circuits and particularly at R1233zd(E) evaporating temperatures in the range of from about 50 F to about 70 F, more preferably at a temperature in the range of from about 55 F to about 65 F (which shows an unexpected maximum at a 1233zd(E) evaporating temperature of from about 55 F to about 65 F (preferably about 50 F). It has been shown that this combination at these temperatures provides the best performance and the largest improvement over the comparative example R404A.
The results in Table 6 are shown graphically in FIGS. 8A and 8B. FIG. 8A shows a graph of the COP of the R1233zd(E) system across a range of different cooling temperatures and with different refrigerants in the low and medium temperature refrigeration circuits.
Table 7 shows a comparison of a comparative example R404A DX refrigeration system with the flooded distributed refrigeration circuit described in reference to FIG. 3 with SLHX. In this case, the low and medium temperature flooded distributed refrigeration circuit has R1233zd(E) in the common refrigeration circuit with SLHX removing the rejected heat from the low and medium temperature refrigeration circuits to provide medium and low temperature cooling. The medium and low temperature refrigeration circuits also use SLHX. For this example the evaporation temperature of the R1233zd(E) is varied to achieve a temperature of 80 F. 70 F, 60 F, 50 F and 40 F. The resulting system performance is compared to the comparative example R404A system without mechanical subcooling having an overall power of 54.8 kW and a resulting COP of 1.82, and a R404A system with mechanical subcooling to 50 F having an overall power of 49.6 kW and a COP of 2.02. The cooling capacity for each case is 100 kW with 67 kW MT and 33 kW LT load distribution.

TABLE 7

R1233zd(E)	Power

temperature

R744

R290

R1234yf

COP (% of R404Awo SC/w SC)

[F.]	[kW]	[kW]	[kW]	R455A	R744	R290	R1234yf	R455A

80	64.4	52.5	45.6	46.0	1.55	1.90	2.19	2.17
					(85%/	(104%/	(120%/	(119%/
					77%)	94%)	109%)	108%)
70	54.1	48.5	40.9	41.2	1.85	2.06	2.44	2.43
					(101%/	(113%/	(134%/	(133%/
					92%)	102%)	121%)	120%)
60	48.6	46.3	38.5	38.3	2.06	2.16	2.60	2.61
					(113%/	(118%/	(143%/	(143%/
					102%)	107%)	129%)	129%)
50	53.7	53.0	45.0	45.0	1.86	1.89	2.22	2.22
					(102%/	(104%/	(122%/	(122%/
					92%)	94%)	110%)	110%)
40	78.4	78.3	70.1	72.2	1.28	1.28	1.43	1.38
					(70%/	(70%/	(78%/	(76%/
					63%)	63%)	71%)	69%)

As demonstrated by the results in Table 7, it is clear that the highest COP is achieved when the R1233zd(E) system has R1234yf and/or R455A in the low/medium temperature refrigeration circuits and particularly at R1233zd(E) evaporating temperatures in the range of from about 50 F to about 70 F, more preferably at a temperature in the range of from about 55 F to about 65 F (which shows an unexpected maximum at a 1233zd(E) evaporating temperature of from about 55 F to about 65 F (preferably about 50 F). It has been shown that this combination provides the best performance and the largest improvement over the comparative example R404A system.
The results in Table 7 are shown graphically in FIGS. 9A and 9B. FIG. 9A shows a graph of the COP of the R1233zd(E) system across a range of different cooling temperatures and with different refrigerants in the low and medium temperature refrigeration circuits.
Table 8 shows the benefits of using a three circuit flooded distributed refrigeration system, as described in reference to FIG. 2, with an additional heat exchanger to provide air conditioning (AC) needs (Option 3′). Different options for the refrigerants in the first refrigeration units for the Option 3 case are given. The results for Option 3 are compared with a comparative example R404A DX refrigeration system with a R410A AC system. The assumptions for this example are set out below:

- MT load: 67,000 W
- LT load: 33,000 W
- AC load: 100,000 W
- R1233zd temperature 50 F

TABLE 8

	Overall power	Relative power
Description	[kW]	[% of R404A]

R404A (Refrigeration) +	76.1	100%
R410A (AC)
Option 3 with R744 for first	72.5	95%
refrigeration circuits
Option
3 with R290 for first	71.7	94%
refrigeration circuits
Option
3 with R1234yf for first	63.9	84%
refrigeration circuits

The results in Table 10 show that all three variations of the four circuit flooded distributed refrigeration systems with additional heat exchanger for AC needs exhibit lower power than the comparative example R404A DX refrigeration system with a R410A AC system, Advantageously this means that the three circuit flooded distributed refrigeration systems with additional heat exchangers for AC needs use less power (for the same cooling capacity). Advantageously, this leads to reduced energy usage and an overall increase in system efficiency.

As previously described, the connected lines for the flooded R1233zd system can be constructed using PVC or other low cost plastics since the pressure of R1233zd is very low. Table 9 shows the material compatibility information of R1233zd with common types of plastics. The samples were submerged in R1233zd for two weeks at room temperature of between 24′C and 25° C. After the exposure of the samples to R1233zd, the samples were allowed to outgas for 24 hours. The weights and volumes of the samples were taken before being submerged in R1233zd and after the outgas stage: the results in the table show the average percent weight and volume change for each plastic sample. It can be seen from the results shown in Table 11 that the average percentage volume change is less than 5% for all of the plastic types tested. Since all these plastics are common low cost plastics, it can therefore be concluded from the results shown in Table 9 that R1233zd(E) is compatible with a large number of common, low cost plastic materials. Usefully, the ability to use low cost plastics for connecting lines, brings the system costs down.

TABLE 9

	AVE %	AVE %
SUBSTRATE (Plastics)	WT. Δ	VOL. Δ

ABS	3.35%	3.55%
DELRIN ®	0.54%	0.61%
HDPE	1.70%	1.19%
NYLON 66	−0.09%	−0.09%
POLYDARBONATE	3.55%	2.98%
ULTEM ® Polyetherimide	0.035%	−0.52%
KYNAR ® PVDF	0.13%	−0.27%
TEFLON ®	2.13%	3.93%
POLYPROPYLENE	4.96%	3.68%
PVD-TYPE 1	0.10%	0.04%
PET	0.08%	0.015%

The pressure level inside the refrigeration system and the effective pressure difference between the inside of the system and the outside (ambient) of the system have a direct impact on the potential leak rate in the event of a leak. Leaks can occur for a variety of reasons, including: corrosion; accidental puncture of lines and components; and improper connection of lines. The use of lower pressure refrigerants reduces the operational pressure levels inside the refrigeration system, thereby reducing the effective pressure difference between the inside and outside of the system. Consequently, the leak rate is lower in the event of a leak, as compared to when higher pressure refrigerants are used.

FIG. 10A shows a bar graph of the pressures in kPa of various different refrigerants. It is clear from FIG. 10A that R32 exhibits the highest pressure level.
FIG. 10B shows a bar graph of the leak rates in g/year for various different refrigerants. As expected from the results shown in FIG. 10A, R32 exhibits the highest leak rate (as it has the highest pressure level).
Table 10 shows the vapour pressure, leak rate and relative leak rate for the refrigerants shown in FIGS. 13A and 13B. Relative leak rate is the leak rates of the various different refrigerants compared to the refrigerant with the highest leak rate: R32.

TABLE 10

	Vapor pressure at 20D	Leak rate	Relative
Fluid	[kPa]	[g/year]	leak rate

R32	1474.6	278.4	100%
R1234yf	591.7	114.5	41%
R134a	571.7	104.0	37%
A1	453.7	69.3	25%
A2	430.7	66.8	24%
R1234ze(E)	427.3	68.9	25%

Refrigerants have different safety classes based on their toxicity and flammability characteristics. Flammable refrigerants with a classification of three have higher flammability and therefore have to follow certain charge restrictions. The charge of refrigerant means the amount of refrigerant in the system. Lower flammability classes, such as A2L, allow for larger refrigerant charges and offer more design opportunities for increased charges. The relationship between flammability and charge also has an effect on the potential compressor size to be used in the system and thus the isentropic efficiency of the compressor to be used in the system. FIG. 11 shows a graph of isentropic efficiencies over varying pressure ratios for an R290 compressor and an R134a compressor. R290 is a higher flammability class refrigerant than R134a, and so lower charges of R290 are used. Consequently, the R290 compressor is smaller than the R134a compressor.
Table 11 demonstrates that greater isentropic efficiencies are achieved with the larger R134a compressor than with the smaller R290 compressor. Finally, Table 13 shows the isentropic efficiencies and pressure ratios for R290 and R134a in tabular form and for varying condensing temperatures.

TABLE 11

Condensing	R290	R134a

temperature	Isentropic	Pressure	Isentropic	Pressure
[F.]	efficiency [%]	ratio	efficiency [%]	ratio

70	35.8	2.24	46.3	2.59
75	37.5	2.40	49.5	2.82
80	38.8	2.58	52.5	3.06
85	40	2.76	55.2	3.32
90	41	2.96	57.6	3.59
95	41.8	3.16	59.7	3.88
100	42.5	3.38	61.3	4.19
105	43	3.60	62.5	4.52
110	43.3	3.84	63.3	4.86
115	43.5	4.09	63.7	5.23
120	43.5	4.34	63.7	5.61
125	43.5	4.61	63.2	6.02
130	43.3	4.90	62.4	6.44
135	42.9	5.19	61.2	6.89
140	42.4	5.50	59.8	7.36

Where it is possible without apparent technical incompatibility, features of different arrangements, embodiments or aspects disclosed herein may be combined with some features optionally being omitted.

Claims

1. A refrigeration system for providing cooling at at least a low temperature cooling level and a medium temperature cooling level, said system comprising:

(a) a low temperature refrigeration unit comprising a low temperature refrigeration circuit, said low temperature refrigeration circuit comprising:

(i) a low temperature refrigerant consisting essentially of HFO-1234yf;

(ii) a compressor for compressing said low temperature refrigerant;

(iii) a low temperature evaporator for absorbing heat from a space in the low temperature refrigeration unit by evaporating said low temperature refrigerant, and

(iv) a low temperature heat exchanger for rejecting heat from said low temperature refrigerant;

(b) a medium temperature refrigeration unit comprising a medium temperature refrigeration circuit, said medium temperature refrigeration circuit comprising:

(i) medium temperature refrigerant consisting essentially of HFO-1234yf circulating in said system;

(ii) a compressor for compressing said medium temperature refrigerant;

(iii) a medium temperature evaporator for absorbing heat from a space in the medium temperature refrigeration unit by evaporating said medium temperature refrigerant; and

(iv) a medium temperature heat exchanger for rejecting heat from said medium temperature refrigerant; and

(c) a third refrigeration circuit arranged to accept heat rejected from each of said low temperature heat exchanger and medium temperature heat exchanger at a temperature of from about 40 F to about 80 F and wherein the refrigerant in said third refrigeration circuit consists essentially of transHFO-1233zd.

2. The refrigeration system of claim 1, wherein at least one of said low temperature heat exchanger and said medium temperature heat exchanger is a flooded heat exchanger and wherein said third refrigeration circuit comprises a pump for circulating said third refrigerant.

3. The refrigeration system of claim 2, wherein said third refrigeration circuit does not include a compressor.

4. The refrigeration system of claim 2, wherein said third refrigeration circuit includes a compressor and a fluid receiver.

5. The refrigeration system of claim 1, wherein each of the low temperature and medium temperature refrigeration units comprises a space to be chilled.

6. The refrigeration system of claim 1, wherein each of the low temperature and medium temperature refrigeration units is located within a first area.

7. The refrigeration system of claim 1, wherein each of said low temperature refrigerant and said medium temperature refrigerants is flammable and wherein said third refrigerant is non-flammable.

8. The refrigeration system of claim 7, wherein the third refrigeration circuit is arranged to release said third refrigerant in or in the vicinity of said low temperature or said medium temperature refrigerant unit in the event of a leak of said low temperature or said medium temperature refrigerant.

9. A refrigeration system for providing cooling at at least a low temperature and a medium temperature cooling level, said system comprising:

(i) low temperature refrigerant circulating in said system;

(ii) a compressor for compressing said low temperature refrigerant;

(i) medium temperature refrigerant circulating in said system;

(ii) a compressor for compressing said medium temperature refrigerant;

(c) a third refrigeration circuit comprising:

(i) a third refrigerant consisting essentially of transHFO-1233zd;

(ii) a compressor for compressing said third refrigerant;

(iii) a flooded evaporator arranged to accept heat rejected from each of said low temperature refrigerant and said medium temperature refrigerant in said low and medium temperature heat exchangers by evaporating said common refrigerant at a temperature of from about 50° F. to about 70° F.

10. The refrigeration system of claim 1, wherein each of said low temperature and medium temperature refrigerants is selected from the group consisting of R744, one or more C2-C4 hydrocarbons, R1234yf, and combinations of these.

11. The refrigeration system of claim 10, wherein at least one of the low temperature and medium temperature refrigerants comprises at least one hydrocarbon.

12. The refrigeration system of claim 11, wherein said at least one hydrocarbon comprises R290.

13. The refrigeration system of claim 10, wherein said wherein at least one of the low temperature and medium temperature refrigerants comprises HFO-1234yf.

14. The refrigeration system of claim 9, wherein the common refrigeration circuit comprises at least a first branch that when in operation rejects heat by heat exchange with ambient air and a compressor branch that when in operation rejects heat to a compression refrigeration system.

15. The refrigeration system of claim 14, wherein refrigerant entering the ambient cooling branch is cooled by ambient air.

16. The refrigeration system of claim 9 wherein said compressor in said low temperature refrigeration unit has a power rating of less than about 1 horsepower.

17. The refrigeration system of claim 9 wherein said compressor in said medium temperature refrigeration unit has a power rating of less than about 1 horsepower.

18. The refrigeration system of claim 9 wherein said compressor in said medium temperature refrigeration unit has a power rating of less than about 1 horsepower and wherein said compressor in said medium temperature refrigeration unit has a power rating of less than about 1 horsepower.

19. The refrigeration system of 18 wherein said third refrigeration system is located substantially completely outside of said low temperature refrigeration unit and substantially completely outside of said medium temperature refrigeration unit.

20. The refrigeration system of 9 wherein said third refrigeration system is located substantially completely outside of said low temperature refrigeration unit and substantially completely outside of said medium temperature refrigeration unit.