Patent Description:
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 <NUM>. 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>. <FIG> shows a refrigeration system <NUM> which is commonly used for commercial refrigeration in supermarkets. The system <NUM> is a direct expansion system which provides both medium and low temperature refrigeration via medium temperature refrigeration circuit <NUM> and low temperature refrigeration circuit <NUM>.

In a typical prior configuration labelled as <NUM> in <FIG>, the medium temperature refrigeration circuit <NUM> has R134a as its refrigerant. The medium temperature refrigeration circuit <NUM> provides both the medium temperature cooling and removes the rejected heat from the lower temperature refrigeration circuit <NUM> via a heat exchanger <NUM>. The medium temperature refrigeration circuit <NUM> extends between a roof <NUM>, a machine room <NUM> and a sales floor <NUM>. The low temperature refrigeration circuit <NUM> on the other hand has R744 as its refrigerant. The low temperature refrigeration circuit <NUM> extends between the machine room <NUM> and the sales floor <NUM>. Usefully, as discussed above, R744 has a low GWP.

However, while refrigeration systems of the type disclosed in <FIG> 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 <NUM>); 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.

<CIT> discloses a cascade cycle system comprising HFO1438mzz as the high temperature working fluid and HFO1234yf or HFO1234ze as the low temperature working fluid; wherein flooded evaporators and small compressors of about 5hp may be used.

The present invention includes a cascaded refrigeration system, as defined in the appended claims.

As used herein, the term "flammable" with respect to a refrigerant means that the refrigerant is not classified as A1 under ASHRAE <NUM>-<NUM> test protocol defining conditions and apparatus and using the current method ASTM E681-<NUM> annex A1). Accordingly, a refrigerant which is classified as A2L under ASHRAE <NUM>-<NUM> test protocol defining conditions and apparatus and using the current method ASTM E681-<NUM> 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 <NUM>-<NUM> test protocol defining conditions and apparatus and using the current method ASTM E681-<NUM> 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 -<NUM> to about -<NUM>, and preferably at temperature of about -<NUM>. As used herein with respect to temperatures, the term "about" is understood to mean variations in the identified temperature of +/- <NUM>. The refrigerant circulating in the medium temperature circuit can evaporate at a temperature of -<NUM> +/- <NUM>, or at - <NUM> +/- <NUM>.

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 -<NUM>. 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 -<NUM> to about -<NUM>, and preferably at temperature of about -<NUM>. The refrigerant circulating in the low temperature circuit can evaporate at a temperature of -<NUM> +/- <NUM>, or at - <NUM> +/- <NUM>.

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.

Optionally, each of said low temperature refrigeration circuits is contained in a separate low temperature refrigeration unit.

Optionally, said heat exchanger is a flooded heat exchanger in which said medium temperature refrigerant evaporates in said heat exchanger by absorbing heat from said low temperature refrigerant.

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 <NUM> above the boiling temperature of the liquid refrigerant in the heat exchanger.

Optionally, the flammable low temperature refrigerant comprises at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these.

Optionally, the flammable low temperature refrigerant comprises at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of HFO-1234yf, transHFO-1234ze, or combinations of these and the heat exchanger is a flooded heat exchanger in which said medium temperature refrigerant evaporates in said heat exchanger by absorbing heat from said low temperature refrigerant.

In preferred embodiments, the second circuit, preferably a medium temperature circuit, may be located substantially completely outside of said plurality of first refrigeration units, preferably outside of said plurality of low temperature circuits. As used herein, the term "substantially completely outside" means that the components of the second refrigeration circuit are not within said first refrigeration units except that transport piping and the like which may be considered part of the second refrigeration circuit can pass into the first refrigeration units in order to provide heat exchange between the refrigerant of the first and second refrigeration circuits.

As used herein, the term "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 second refrigeration circuit in its entirety. According to and consistent with such meanings, the preferred first refrigeration circuits and low temperature refrigeration circuits of the present invention are sometimes referred to herein as "self-contained" when contained within such first (preferably low temperature) refrigeration units, in accordance with the meanings described herein.

The second refrigeration circuit may further comprise a fluid receiver.

Each first 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 (preferably low temperature refrigeration circuit) may also be located within a first area, such as a shop floor.

Each refrigeration unit may comprise a space and/or objects contained within a space to be chilled, and preferably that space is within the refrigeration unit. Each evaporator may be located to chill its respective space/objects, preferably by cooling air within the space to be chilled.

As mentioned above, the second refrigeration circuit, and preferably medium temperature refrigeration circuit, may have components thereof that extend between the first refrigeration unit (preferably low temperature 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 second refrigeration circuit (preferably medium temperature refrigeration unit) 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.

Unless otherwise indicated herein for a particular embodiment, the refrigerant in each of the first refrigeration circuits may be different from or the same as the other refrigerants in the first refrigeration circuits, and each may also be the same or different to the refrigerant in the second refrigeration circuit.

Unless otherwise indicated herein for a particular embodiment, the refrigerant in the first refrigeration circuits and/or the refrigerant in the second refrigeration circuit may have low Global Warming Potential (GWP).

Unless otherwise indicated herein for a particular embodiment, the refrigerant in the first refrigeration circuits and/or the refrigerant in the second refrigeration circuit may have a GWP which is less than <NUM>. This is enabled by each first refrigeration circuit being provided in a respective refrigeration unit.

Unless otherwise indicated herein for a particular embodiment, the refrigerant in the second refrigeration circuit may be non-flammable, that is, classified as A1 under ASHRAE <NUM> (as measured by ASTM E681) or classified as A2L under ASHRAE <NUM> (as measured by ASTM E681). This may be desirable since the second refrigeration circuit may be quite long and may extend between different areas of a building: for example, between a shop floor (where refrigeration units might be deployed) to a machine room. Consequently, it may be unsafe to have a flammable refrigerant in the second refrigeration circuit since both the risk of leaks and the severity of potential leaks is increased as the second refrigeration circuit spans a greater area and therefore exposes more people and/or structures to risk of fire.

The refrigerant in the first refrigeration circuits may be flammable. This may be allowable in practice, at least in part, as a result of each first refrigeration circuit being provided in a respective refrigeration unit have a relatively low power compressor(s) contained therein.

Each first 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 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 refrigeration circuits.

The average temperature of each of the first refrigeration circuits may be lower than the average temperature of the second refrigeration circuit. This is because the second refrigeration circuit may be used to provide cooling, that is, remove heat from, the first refrigeration circuits; and each first refrigeration circuit may cool a space to be chilled in its respective refrigeration unit.

The second refrigeration circuit may cool, that is, remove heat from, each of the first refrigeration circuits.

Each heat exchanger may be arranged to transfer heat energy between its respective first refrigeration circuit and the second refrigeration circuit at a respective circuit interface location.

The second refrigeration circuit may comprise a second evaporator. The second evaporator may be coupled in parallel with the circuit interface locations.

Each of the circuit interface locations may be coupled in series-parallel combination with each other of the circuit interface locations. 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 by the second refrigeration circuit so that faults do not propagate through the system.

Each of the circuit interface locations may be coupled in series with at least one other circuit interface location.

Each of the circuit interface locations may be coupled in series with each other of the circuit interface locations.

Each of the circuit interface locations may be coupled in parallel with at least one other circuit interface location.

Each of the circuit interface locations may be coupled in parallel with each other of the circuit interface locations.

The second refrigerant, preferably the medium temperature refrigerant, may comprise a blended refrigerant. The blended refrigerant may comprise R515A.

R515A refrigerant is non-flammable. This is useful since the second refrigerant circuit (preferably medium temperature refrigerant) may span numerous areas, and so having a non-flammable refrigerant is important for reducing the severity of potential leaks.

In other embodiments the non-flammable refrigerant may comprise, or comprise at least about <NUM>%, or comprise at least <NUM>%, or consist essentially of or consist of HFO-1233zd(E).

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 second refrigeration circuit may further comprise a compressor.

The second refrigeration circuit may comprise an ambient cooling branch and a compressor branch comprising the compressor. This means that the compressor branch may be bypassed. The benefit of bypassing the compressor branch is that, if the ambient conditions are sufficiently cool relative to the second refrigerant, the compressor stage can be bypassed as sufficient cooling is provided by the ambient air.

The ambient cooling branch may be coupled in parallel with the compressor branch. The parallel arrangement allows for the compressor branch to be bypassed by the second refrigerant.

The ambient cooling branch may be exposed to outside ambient temperatures. This is for cooling the second refrigerant in the place of the compressor stage.

The ambient cooling branch may extend to the outside of the building or buildings comprising the first 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.

The ambient cooling branch may be coupled in series with the pump.

A valve may be provided at one of both of the junctions between the ambient cooling branch and the compressor branch to control the flow of refrigerant in each of the ambient cooling branch and the compressor branch. This allows control of whether or not and how much the compressor branch and/or ambient cooling branch are utilised.

The pump, the further evaporator and the circuit interface locations may be located between the valve or valves.

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

Throughout this specification, like reference numerals refer to like parts.

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 <FIG> and <FIG>.

<FIG> shows an example of a refrigeration system <NUM> for comparison with the further systems described below. The system <NUM> comprises a medium temperature refrigeration circuit <NUM> and a low temperature refrigeration circuit <NUM>.

The low temperature refrigeration circuit <NUM> has a compressor <NUM>, an interface with a heat exchanger <NUM> for rejecting heat to ambient conditions, an expansion valve <NUM> and an evaporator <NUM>. The low temperature refrigeration circuit <NUM> interfaces with the medium temperature refrigeration circuit <NUM> through the inter-circuit heat exchanger <NUM>, 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 <NUM> 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 <NUM>, compressor <NUM>, heat exchanger <NUM>, inter-circuit heat exchanger <NUM>, and expansion valve <NUM>. The components are connected together via pipes <NUM> containing a low temperature refrigerant.

The medium temperature refrigeration circuit <NUM> has a compressor <NUM>, a condenser <NUM> for rejecting heat to ambient conditions and a fluid receiver <NUM>. The liquid medium temperature refrigerant from receiver <NUM> is manifolded to flow to each of expansion valves <NUM> and <NUM>, thus providing two parallel connected branches: a low temperature sub-cooling cooling branch <NUM> downstream of expansion device <NUM> and a medium temperature cooling branch <NUM> downstream of expansion device <NUM>. 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 <NUM> includes medium temperature evaporator <NUM>, which is interfaced with a space to be chilled, such as the inside of a refrigerated compartment.

The medium temperature refrigerant is a high GWP refrigerant such as R134a. R134A is a hydro fluorocarbon (HFC). R134a is non-flammable and provides a good coefficient of performance.

The system <NUM> spans three areas of a building: a roof where the condensers <NUM> and <NUM> are located; a machine room where the compressors <NUM>, <NUM>, heat exchanger <NUM>, receiving tank <NUM> and expansion device <NUM> are located; and a sales floor <NUM> where the LT case, the MT case, and each of their expansion devices are located. The low temperature refrigeration circuit <NUM> and the medium temperature refrigeration circuit <NUM> thus each extend between the sales floor, the machine room and the roof. In use, the medium temperature circuit <NUM> provides medium temperature chilling to spaces to be chilled via the evaporator <NUM> and the low temperature circuit <NUM> provides low temperature chilling to spaces to be chilled via the evaporator <NUM>. The medium temperature circuit <NUM> also removes heat from the liquid condensate from the low temperature condenser <NUM>, thus providing subcooling to the liquid entering the evaporator <NUM>.

The individual and overall functionality of the various components of the low temperature refrigeration circuit <NUM> will now be described. Starting with heat exchanger <NUM>, heat exchanger <NUM> is a device suitable for transferring heat between the low and medium temperature refrigerants. In one example, the heat exchanger <NUM> 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 <NUM> results in the liquid low temperature refrigerant from condenser <NUM> being subcooled, after which the subcooled, low temperature refrigerant flows to the expansion valve <NUM> via a liquid line of the pipes <NUM>. The role of the expansion valve <NUM> 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 <NUM>. The evaporator <NUM> 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 <NUM>, the liquid refrigerant accepts heat from the space to be chilled and, in doing so, is evaporated to a gas. After the evaporator <NUM>, the gas is drawn by the compressor <NUM>, through a suction line of the pipes <NUM>, to the compressor <NUM>. On reaching the compressor <NUM>, 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 <NUM> to travel to the heat exchanger (condenser) <NUM>, where the gas is condensed to a liquid in the manner previously described. This describes the operation of the low temperature refrigeration circuit <NUM> 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 <NUM> will now be described. Starting with heat exchanger <NUM>, as described above the medium temperature refrigerant absorbs heat from the low temperature refrigerant via the heat exchanger <NUM>. This absorption of heat causes the refrigerant in the medium temperature circuit <NUM>, which is a low temperature gas and/or a mixture of gas and liquid on entering the heat exchanger <NUM>, 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 <NUM>, the gaseous refrigerant is sucked into the compressor <NUM> (along with the refrigerant from the evaporator <NUM>) and is compressed by the compressor <NUM> to a high temperature and high pressure gas. This gas is released into the pipes <NUM> and travels to the condenser <NUM> which, in this example, is located on a roof of a building. In the condenser <NUM>, the gaseous medium temperature refrigerant releases heat to the outside ambient air and so is cooled and condenses to a liquid. After the condenser <NUM>, the liquid refrigerant collects in a fluid receiver <NUM>. In this example, the fluid receiver <NUM> is a tank. On leaving the fluid receiver <NUM>, the liquid refrigerant is manifolded to parallel connected medium temperature branch <NUM> and subcooling cooling branch <NUM>. In the medium temperature branch <NUM>, the liquid refrigerant flows to the expansion valve <NUM> which is used to lower the pressure and therefore temperature of the liquid refrigerant. The relatively cold liquid refrigerant then enters the heat exchanger <NUM> where it absorbs heat from the space to be chilled which is interfaced with the evaporator 119f. In the subcooling branch <NUM>, the liquid refrigerant similarly flows first to an expansion valve <NUM> where the pressure and temperature of the refrigerant is lowered. After the valve <NUM>, the refrigerant flows to the inter-circuit heat exchanger <NUM>, as described above. From there, the gaseous refrigerant from the heat exchanger is sucked by the compressor <NUM> to the compressor <NUM> where it re-joins the refrigerant from the medium temperature cooling branch <NUM>.

Although not mentioned above, it will be clear that to function as intended, the temperature of the refrigerant in the medium temperature circuit <NUM> as it enters the heat exchanger <NUM> must be less than the temperature of the refrigerant in the low temperature circuit <NUM> as it enters the heat exchanger <NUM>. If this were not the case, the medium temperature circuit <NUM> would not provide the desired subcooling to the low temperature refrigerant in circuit <NUM>.

The above describes the operation of the comparative example of a refrigeration system <NUM> as illustrated in <FIG>. The principles of refrigeration described in reference to <FIG> can be applied equally well to the other refrigeration systems of this disclosure.

A number of refrigeration systems according to preferred embodiments of the present invention 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 <NUM> kilowatts (about <NUM> horse power) 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 kilowatts +/- <NUM> kilowatts (about <NUM> horse power) The compressor size in preferred embodiments may be from about <NUM> kilowatts (<NUM> horse power) to about <NUM> kilowatts (<NUM> horse power), or from about <NUM> kilowatts (<NUM> horse power) to about <NUM> kilowatts (<NUM> horse power). The compressor size may be from about <NUM> kilowatts (<NUM> horse power) to about <NUM> kilowatts (<NUM> horse power), or from about <NUM> kilowatts (<NUM> horse power) up to <NUM> kilowatts (<NUM> horse power).

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.

One embodiment of a refrigeration system according to the present invention is illustrated schematically in <FIG> and described in detail below.

<FIG> shows a cascaded refrigeration system <NUM>. More specifically, <FIG> shows a refrigeration system <NUM> which has three first refrigeration circuits 220a, 220b and 220c. Each of the first refrigeration circuits 220a, 220b, 220c has an evaporator <NUM>, a compressor <NUM>, a heat exchanger <NUM> and an expansion valve <NUM>. While each of the compressors, evaporators and heat exchangers in the circuit are illustrated by a single icon, it will be appreciated that the compressor, the evaporator, the heat exchanger, expansion valve, etc can each comprise a plurality of such units. In each circuit 220a, 220b and 220c, the evaporator <NUM>, the compressor <NUM>, the heat exchanger <NUM> and the expansion valve <NUM> are connected in series with one another in the order listed. Each of the first refrigeration circuits 220a, 220b and 220c is included within a separate respective refrigeration unit (not shown). In this example, each of the three refrigeration units is a freezer unit and the freezer unit houses its respective first refrigeration circuit. In this way, each refrigeration unit comprises a self-contained and dedicated refrigeration circuit. The refrigeration units (not shown), and therefore the first refrigeration circuits 220a, 220b, 220c, are arranged on a sales floor <NUM> of a supermarket.

In this example, the refrigerant in each of the first refrigeration circuits 220a, 220b, 220c is a low GWP refrigerant such as R744, C3 - C4 hydrocarbons (R290, R600a, R1270), R1234yf, R1234ze(E) or R455A. As the skilled person will appreciate, the refrigerants in each of the first refrigeration circuits 220a, 220b,220c may the same or different to the refrigerants in each other of the first refrigeration circuits 220a, 220b, 220c.

The refrigeration system <NUM> also has a second refrigeration circuit <NUM>. The second refrigeration circuit <NUM> has a compressor <NUM>, a condenser <NUM> and a fluid receiver <NUM>. The compressor <NUM>, the condenser <NUM> and the fluid receiver <NUM> are connected in series and in the order given. While each of the compressors, condensers, fluid receivers, etc. in the second circuit are illustrated by a single icon, it will be appreciated that the compressor, the evaporator, the heat exchanger, expansion valve, etc can each comprise a plurality of such units. The second refrigeration circuit <NUM> also has four parallel connected branches: three medium temperature cooling branches 217a, 217b and 217c; and one low temperature cooling branch <NUM>. The four parallel connected branches 217a, 217b, 217c and <NUM> are connected between the fluid receiver <NUM> and the compressor <NUM>. Each of the medium temperature cooling branches 217a, 217b and 217c has an expansion valve 218a, 218b and 218c and an evaporator 219a, 219b and 219c, respectively. The expansion valve <NUM> and evaporator <NUM> are connected in series and in the order given between the fluid receiver <NUM> and the condenser <NUM>. The low temperature cooling branch <NUM> has an expansion valve <NUM> and an interface, in the form of inlet and outlet piping, conduits, valves and the like (represented collectively as 260a, 260b and 260c, respectively) which bring the second refrigerant to and from each of the heat exchangers 230a, 230b, 230c of the first refrigeration circuits 220a, 220b, 220c. The low temperature cooling branch <NUM> interfaces each of the heat exchangers 230a, 230b, 230c of the first refrigeration circuits 220a, 220b, 220c at a respective circuit interface location 231a, 231b, 231c. Each circuit interface location 231a, 231b, 231c is arranged in series-parallel combination with each other of the circuit interface locations 231a, 231b, 231c.

The medium temperature refrigeration circuit <NUM> has components which extend between the sales floor <NUM>, a machine room <NUM> and a roof <NUM>. The low temperature cooling branch <NUM> and the medium temperature cooling branches 217a, 217b, 217c of the medium temperature refrigeration circuit <NUM> are located on the sales floor <NUM>. The compressor <NUM> and the fluid receiver <NUM> are located in the machine room <NUM>. The condenser <NUM> is located where it can be readily exposed to ambient conditions, such as on the roof <NUM>.

In this example, the refrigerant in the medium temperature refrigeration circuit <NUM> is a blend comprising R515A. R515A is a refrigerant which consists essentially of, and preferably consists of, about <NUM>% by weight of the hydrofluoroolefin (HFO) 1234ze(E) and about <NUM>% of HFC227ea (heptafluoropropane). Usefully, the blend results in a non-flammable refrigerant, which improves safety. Further advantageously, the blend has a low GWP, making it an environmentally friendly solution.

Use of the preferred embodiments as illustrated in <FIG> can be summarized as follows:.

A number of beneficial results can be achieved using arrangements of the present invention of the type shown in <FIG>, particularly from each first refrigeration circuit <NUM> being self-contained in a respective refrigeration unit.

For example, installation and uninstallation of the refrigeration units and the overall cascaded refrigeration system <NUM> is simplified. This is because the refrigeration units, with their built-in, self-contained first refrigeration circuits 220a, 220b, 220c, can be easily connected or disconnected with the second refrigeration circuit <NUM>, with no modification to the first refrigeration circuit <NUM>, 220b, 220c required. In other words, the refrigeration units may simply be 'plugged' in to, or out of, the second refrigeration circuit <NUM>.

Another advantage is that each refrigeration unit, including its respective first refrigeration circuit 220a, 220b, 220c, can be factory tested for defaults before being installed into a live refrigeration system <NUM>. This mitigates the likelihood of faults, which can include leaks of potentially harmful refrigerants. Accordingly, reduced leak rate can be achieved.

Another advantage is that the lengths of the first refrigeration circuits 220a, 220b, 220c can be reduced since each circuit 220a, 220b, 220c is arranged in its respective refrigeration unit, and does not extend between a series of units. The reduced circuit length can result in improved efficiency as there is reduced heat infiltration in shorter lines due to reduced surface area. Further, reduced circuit length can also result in reduced pressure drop, which improves the system <NUM> efficiency.

The reduced circuit length, and the provision of the circuits self-contained within respective refrigeration units, also provides the ability to use more flammable refrigerants, such as R744, hydrocarbons (R290, R600a, R1270), R1234yf, R1234ze(E) or R455A, which applicants have come to appreciate is a highly beneficial result. This is because both the likelihood of the refrigerant leaking is reduced (as discussed above) and because, even if the refrigerant were to leak, the leak would be contained to the relatively small area and containable area of the respective refrigeration unit, and because of the small size of the units, only a relatively small amount of refrigerant charge is used. In addition, this arrangement would permit the use of relatively low cost flame mitigation contingency procedures and/or devices since the area containing potentially flammable materials is much smaller, confined and uniform. Such more flammable refrigerants can have lower global warming potential (GWP). Advantageously therefore, governmental and societal targets for the use of low GWP refrigerants may be met and potentially even exceeded without compromising on safety of the system.

Another advantage is that each first refrigeration circuit 220a, 220b, 220c may only cool their respective refrigeration unit. This means that the load on each first refrigeration circuit 220a, 220b, 220c may remain relatively constant. That is, constant conditions are applied to the condensing <NUM> and evaporating <NUM> stages of the first refrigeration circuit <NUM>. This allows for the simplification of the design of the first refrigeration circuit <NUM> in that passive expansion devices <NUM>, such as capillary tubes or orifice tubes, can be used. This is in contrast to more complex circuits where electronic expansion devices and thermostatic expansion valves need to be used. Since the use of such complex devices is avoided, costs can be reduced and reliability can be increased.

Furthermore, importantly, the provision of a flooded heat exchanger in the second refrigeration circuit according to such embodiments results in improved heat transfer between the first and second circuits. Accordingly, the efficiency of the overall refrigeration system is improved.

There are several advantages that may arise from circuit interface locations being coupled in parallel with other circuit interface locations. One advantage may be that resilience is provided in the system since a fault associated with or suffered at one circuit interface location will not impact other circuit interface locations. This is because each circuit interface location is serviced by a respective branch of the second refrigeration circuit. Another advantage may be that heat transfer efficiency between first and second refrigeration circuits is improved because the temperature of the second refrigerant before each circuit interface location can be kept relatively constant. In contrast, if two circuit interface locations were coupled in series, the temperature of the refrigerant in the second refrigeration circuit may be higher before the downstream circuit interface location, than before the upstream circuit interface location.

Overall, the provision of a plurality of first refrigeration circuits according to the present invention , with each one arranged in a respective refrigeration unit, preferably being arranged as a self-contained refrigeration circuit, 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 improved system efficiency.

Particularly in view of the advantages described herein, the present invention includes a cascaded refrigeration system, comprising: a plurality of first refrigeration circuits, with each first refrigeration circuit comprising a first refrigerant which is flammable and which has a GWP of about <NUM> or less, a compressor having a horse power rating of about about <NUM> kilowatts (about <NUM> horse power) or less, and a heat exchanger in which said first refrigerant condenses; and a second refrigeration circuit containing a second refrigerant which is non-flammable, and an evaporator in which said second refrigerant evaporates at a temperature below said first refrigerant condensing temperature wherein said second refrigerant evaporates in said heat exchanger by absorbing heat from said first refrigerant.

Particularly in view of the advantages described herein, the present invention also includes a cascaded refrigeration system, comprising: a plurality of first refrigeration circuits, with each first refrigeration circuit comprising a first refrigerant which is flammable and which has a GWP of about <NUM> or less, a compressor having a horse power rating of about <NUM> kilowatts (about <NUM> horse power) or less, and a heat exchanger in which said first refrigerant condenses; and a second refrigeration circuit containing a second refrigerant which is non-flammable and which has a GWP of up to about <NUM>, and an evaporator in which said second refrigerant evaporates at a temperature below said first refrigerant condensing temperature wherein said second refrigerant evaporates in said heat exchanger by absorbing heat from said first refrigerant.

The present invention includes a cascaded refrigeration system,.

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and combinations of these.

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and combinations of these and the medium temperature refrigeration circuit contains a medium temperature refrigerant, wherein said medium temperature refrigerant is non-flammable and has a GWP of up to about <NUM>.

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and combinations of these and the medium temperature refrigeration circuit contains a medium temperature refrigerant, wherein said medium temperature refrigerant is non-flammable having a GWP of up to about <NUM> and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight of R1234ze(E).

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and combinations of these the medium temperature refrigeration circuit contains a medium temperature refrigerant, wherein said medium temperature refrigerant is non-flammable having a GWP of up to about <NUM> and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight of R1234ze(E) and from about <NUM>% by weight to about <NUM>% by weight of R227ea.

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and combinations of these and the medium temperature refrigeration circuit contains a medium temperature refrigerant, wherein said medium temperature refrigerant is non-flammable having a GWP of up to about <NUM> and comprising about <NUM>% by weight of R1234ze(E) and about <NUM>% by weight of R227ea.

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and combinations of these and the medium temperature refrigeration circuit contains a medium temperature refrigerant, wherein said medium temperature refrigerant is non-flammable having a GWP of up to about <NUM> and comprising at least about <NUM>% by weight of R1234ze(E), R1234yf or combinations of these.

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and combinations of these and the medium temperature refrigeration circuit contains a medium temperature refrigerant, wherein said medium temperature refrigerant is non-flammable having a GWP of up to about <NUM> and comprising at least about <NUM>% by weight of R1234ze(E), R1234yf or combinations of these and further comprising one or more of R1233zd(E) and CF3I.

As the person skilled in the art will appreciate in view of the teachings contained here, there may be any number of first refrigeration circuits <NUM>. In particular, there may be as many first refrigeration circuits <NUM> as there are refrigeration units to be cooled. Accordingly, the second refrigeration circuit <NUM> may be interfaced with any number of first refrigeration circuits <NUM>.

As will be clear to the skilled person in view of the teachings contained here, there may be any number and arrangement of medium temperature cooling branches <NUM> and evaporators <NUM>.

In alternative arrangements, each first refrigeration circuit <NUM> may be arranged fully in parallel with each other first refrigeration circuit <NUM>. An example of such an arrangement is shown in <FIG> shows a system <NUM> where each circuit interface location 231a, 231b, 231c is arranged fully in parallel with each other circuit interface location 231a, 231b, 231c. The components of the system <NUM> are otherwise the same as in system <NUM> (described in reference to <FIG>), and components of the system <NUM> function in substantially the same way as the system <NUM>, although it will be appreciated that the performance of the overall system and other important features of the overall system can be significantly impacted by this change in the arrangement.

Usefully, this means that a given portion of refrigerant from the second refrigeration circuit <NUM> only passes through one heat exchanger <NUM> before it is returned to the compressor <NUM>. This arrangement thus ensures that each of the heat exchangers <NUM> will receive second refrigerant at about the same temperature, since the arrangement prevents any of the heat exchanger from receiving a portion of the refrigerant that is pre-warmed as a result of passing through an upstream heat exchanger, as would be the case in a series arrangement.

As will be clear to the person skilled in the art in view of the teachings contained here, many other arrangements of the circuit interface locations 231a, 231b, 231c with respect to one and the second refrigeration circuit <NUM> can be achieved and indeed are envisaged.

As will be clear to the person skilled in the art in view of the teachings contained here, by virtue of the preferred modular first refrigeration circuit design the refrigeration system of the preferred embodiments of the present invention allows use of non-flammable, low-pressure refrigerants with relatively low GWP in the second refrigeration circuit <NUM>. Further, the preferred systems of the present invention produce the unexpected result of relatively safe and efficient se of flammable, low-pressure refrigerants with low GWP in the first refrigeration circuits, thereby providing a refrigeration system of reduced environmental impact and have excellent environmental properties, excellent safety features and improved system efficiency.

A preferred refrigeration system of the present invention is exemplified and will be now be described with reference to <FIG>.

<FIG> schematically shows a cascaded refrigeration system <NUM> with a second refrigeration circuit <NUM> that has a receiver that delivers liquid second refrigerant, which results in flooded evaporator operation in the first refrigeration circuit. More specifically, <FIG> shows a refrigeration system <NUM> which has two first refrigeration circuits 420a, 420b. Each of the first refrigeration circuits 420a, 420b has an evaporator <NUM>, a compressor <NUM>, a heat exchanger <NUM> and an expansion valve <NUM>. In each circuit 420a, 420b, the evaporator <NUM>, the compressor <NUM>, the heat exchanger <NUM> and the expansion valve <NUM> are connected in series with one another in the order listed. Each of the first refrigeration circuits 420a, 420b is provided in a respective refrigeration unit (not shown). In this example, each refrigeration unit is a freezer unit and the freezer unit houses its respective first refrigeration circuit. In this way, a self-contained and dedicated refrigeration circuit is provided to each refrigeration unit. The refrigeration units (not shown), and therefore the first refrigeration circuits 420a, 420b are located on a sales floor <NUM> of a supermarket.

In this example, the refrigerant in the first refrigeration circuits 420a, 420b, 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 first refrigeration circuits 420a, 420b may the same or different to the refrigerants in the other of the first refrigeration circuits 420a, 420b.

The refrigeration system <NUM> also has a second refrigeration circuit <NUM>. The second refrigeration circuit <NUM> has a compressor branch <NUM> and an ambient cooling branch <NUM>. The compressor branch <NUM> is connected in parallel with the ambient cooling branch <NUM>.

The compressor branch <NUM> has a compressor <NUM>, a condenser <NUM>, an expansion valve <NUM> and a receiver <NUM>. The compressor <NUM>, the condenser <NUM> and the expansion valve <NUM> are connected in series and in the order given. The receiver <NUM> is connected between the compressor <NUM> inlet and the expansion valve <NUM> outlet. The ambient cooling branch <NUM> has a chiller <NUM>.

The compressor branch <NUM> and the ambient cooling branch <NUM> are connected in parallel by first <NUM> and second <NUM> controllable valves. The controllable valves <NUM>, <NUM> are controllable such that the amount of refrigerant flowing in each of the compressor branch <NUM> and the ambient cooling branch <NUM> is controllable. The first control valve <NUM> is connected in series with a pump <NUM>.

The second refrigeration circuit <NUM> also has two further branches which are connected in parallel with one another: a medium temperature cooling branch <NUM> and a low temperature cooling branch <NUM>. The medium temperature cooling branch <NUM> and the low temperature cooling branch <NUM> are connected between the pump <NUM> and the second controllable valve <NUM>.

The medium temperature cooling branch <NUM> has an evaporator <NUM>. The low temperature cooling branch <NUM> interfaces each of the heat exchangers 430a, 430b of the first refrigeration circuits 420a, 420b at a respective circuit interface location 431a, 431b. Each of the circuit interface locations 431a, 431b is in series-parallel combination with the other circuit interface location 431a, 431b.

The second refrigeration circuit <NUM> includes components that extend the circuit between the sales floor <NUM>, a machine room <NUM> and a roof <NUM>. The low temperature cooling branch <NUM> and the medium temperature cooling branch <NUM> of the medium temperature refrigeration circuit <NUM> are preferably located primarily on the sales floor <NUM>. By primarily arranged on the sales floor <NUM>, it is meant that the circuit locations 431a, 431b and the evaporator <NUM> are arranged on or very near the sales floor <NUM>. The junction between the low <NUM> and medium <NUM> temperature cooling branches and some of the pipes of the low <NUM> and medium <NUM> branches are however located in the machine room <NUM>.

The compressor branch <NUM> includes components that extend the branch between the machine room <NUM> and the roof <NUM>. More specifically, the compressor <NUM>, the expansion valve <NUM> and the flooded receiver <NUM> are located in the machine room <NUM>. The condenser <NUM> is located where ready access to ambient air is possible, such as on the roof <NUM>.

The ambient cooling branch <NUM> includes components that extend the branch between the machine room <NUM> and the roof <NUM>. The chiller <NUM> is also located where ready access to ambient air is possible, such as on the roof <NUM>.

The first and second controllable valves <NUM>, <NUM> are located in the machine room <NUM>. The pump <NUM> is located in the machine room <NUM>.

In this example, the refrigerant in the second refrigeration circuit <NUM> is a R515A, as described above.

Though structurally different, in use, the refrigeration system <NUM> operates in a similar manner to refrigeration system <NUM> with the following key differences.

Firstly, the receiver in the second refrigeration circuit <NUM> in the refrigeration system <NUM> results in evaporators <NUM>430a and 430b being flooded evaporator, that is, the refrigerant enters the evaporator as a liquid, and some portion of the liquid refrigerant is not fully vaporised to a gas, which means that essentially no superheating occurs in the evaporator. How much of the refrigerant remains liquid is dependent on the working conditions of the system <NUM>. One feature of the refrigeration system <NUM> is the receiver <NUM>. The receiver <NUM> is arranged to separate the gaseous and liquid refrigerant after it has passed through the expansion valve <NUM> such that the refrigerant allowed through to the medium <NUM> and low <NUM> temperature cooling branches - and therefore through to the evaporator <NUM> and heat exchangers 430a, 430b - is essentially <NUM>% liquid. Another key feature of the refrigeration system <NUM> is the pump <NUM>. The pump <NUM> drives the refrigerant to the medium <NUM> and low <NUM> temperature branches. In alternative system arrangements, the density difference between the liquid and gaseous phases of the refrigerant drives the system and no pump or fan is required.

As the skilled person will appreciate based on the disclosure and teaching contained herein, there are several advantages associated with using a refrigeration arrangement which uses a flooded evaporator according to the present invention, as disclosed for example in system <NUM>. Applicants have found that one such advantage is and unexpected improvement in the coefficient of performance (COP). Without necessarily being bound to any particular theory, it is believed that this advantage, which is unexpected, arises in part because less compressor <NUM> work is required and the cooling capacity of the second refrigeration circuit <NUM> is improved because the system allows operation with superheating the refrigerant before it enters the compressor.

A second difference in the way the refrigeration system <NUM> operates compared to the refrigeration system <NUM> lies in the provision of the ambient cooling branch <NUM> and controllable valves <NUM>, <NUM>. The ambient cooling branch <NUM> allows the compressor branch <NUM> to be bypassed when the ambient temperature is sufficiently low to chill the refrigerant. This is achieved by routing the ambient cooling branch <NUM> to the roof <NUM> to provide maximum exposure of the refrigerant to the ambient air temperature. This is sometimes called winter operation. Usefully, this provides essentially free chilling of the refrigerant in the second refrigeration circuit <NUM>. Clearly this is advantageous both from a cost and environmental perspective as energy consumption is greatly reduced as compared to running the compressor branch <NUM>.

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) for condensing said first refrigerant (preferably low temperature refrigerant) are flooded evaporators for the second refrigerant (preferably the medium temperature refrigerant). In preferred embodiments, the medium temperature evaporator is also a flooded evaporator. The potential advantages described in reference to the cascaded refrigeration system apply equally well to the flooded cascaded refrigeration system: the terms used to describe the flooded and non-flooded cascaded refrigeration system being comparable.

Further advantages of the flooded cascaded refrigeration system can include: reduced energy consumption due to exploitation of the ambient cooling branch (winter operation); improved heat transfer performance in the heat exchangers and evaporators due to their flooded operation; no thermostatic expansion valves are required due to the provision of a pump in the circuit; and low cost materials can be used to manufacture the second refrigeration circuit due to it being suitable for low pressure refrigerant.

Particularly in view of the advantages described herein, the present invention includes a cascaded refrigeration system, comprising: a plurality of first refrigeration circuits, with each first refrigeration circuit comprising a first refrigerant which is flammable and which has a GWP of about <NUM> or less, a compressor having a horse power rating of about <NUM> kilowatts (about <NUM> horse power) or less, and a heat exchanger in which said first refrigerant condenses; and a second refrigeration circuit containing a second refrigerant which is non-flammable, and a flooded evaporator in which said second refrigerant evaporates at a temperature below said first refrigerant condensing temperature wherein said second refrigerant evaporates in said heat exchanger by absorbing heat from said first refrigerant.

Particularly in view of the advantages described herein, the present invention also includes a cascaded refrigeration system, comprising: a plurality of first refrigeration circuits, with each first refrigeration circuit comprising a first refrigerant which is flammable and which has a GWP of about <NUM> or less, a compressor having a horse power rating of about <NUM> kilowatts (about <NUM> horse power) or less, and a heat exchanger in which said first refrigerant condenses; and a second refrigeration circuit containing a second refrigerant which is non-flammable and which has a GWP of up to about <NUM>, and a flooded evaporator in which said second refrigerant evaporates at a temperature below said first refrigerant condensing temperature wherein said second refrigerant evaporates in said heat exchanger by absorbing heat from said first refrigerant.

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and combinations of these and the medium temperature refrigeration circuit contains a flooded evaporator.

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and the medium temperature refrigeration circuit contains a medium temperature refrigerant, wherein said medium temperature refrigerant is non-flammable and has a GWP of up to about <NUM>, and a flooded evaporator.

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and combinations of these and the medium temperature refrigeration circuit contains a medium temperature refrigerant, wherein said medium temperature refrigerant is non-flammable having a GWP of up to about <NUM> and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight of R1234ze(E), and a flooded evaporator.

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and combinations of these and the medium temperature refrigeration circuit contains a medium temperature refrigerant, wherein said medium temperature refrigerant is non-flammable having a GWP of up to about <NUM> and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight of R1234ze(E) and from about <NUM>% by weight to about <NUM>% by weight of R227ea, and a flooded evaporator.

In preferred embodiments, each low temperature refrigeration circuit comprises a flammable low temperature refrigerant having a GWP of about <NUM> or less and comprising at least about <NUM>% by weight, or at least about <NUM>% by weight, or at least <NUM>% by weight, or at least <NUM>% by weight of R744, R290, R600a, R1270, R1234yf, R1234ze(E), R455A and combinations of these and the medium temperature refrigeration circuit contains a medium temperature refrigerant, wherein said medium temperature refrigerant is non-flammable having a GWP of up to about <NUM> and comprising about <NUM>% by weight of R1234ze(E) and about <NUM>% by weight of R227ea, and a flooded evaporator.

The alternatives described above in reference to the cascaded refrigeration system apply equally well to the flooded cascaded refrigeration system: the terms first and second refrigeration circuit, circuit interface location and heat exchanger being comparable. Other alternatives include removal of the ambient cooling branch <NUM> and/or reversion of the flooded system to a direct expansion system.

A yet further alteration of the system <NUM> which is envisaged is that the ambient cooling branch <NUM> may be shortened and simplified such that it only bypasses the compressor <NUM>, rather than the entire compressor branch. This arrangement is shown in <FIG>.

<FIG> shows a refrigeration system <NUM> which is the largely the same as that described in reference to <FIG> with the following exceptions:.

Advantageously, the use of a shortened ambient chilling branch, that is, one in which the branch routes liquid refrigerant from receiver outlet to the condenser inlet results in: first, a simplified circuit as the chiller and first controllable valve at the inlet of the receiver pump are no longer required; and second, a lower cost circuit, since the amount of extra piping for the ambient chilling branch and the number of components is reduced, therefore reducing material costs.

As will be clear to the person skilled in the art in view of the teachings contained here, by virtue of the preferred modular first refrigeration circuit design the refrigeration system of the preferred embodiments of the present invention allows use of non-flammable, low-pressure refrigerants with relatively low GWP in the second refrigeration circuit. Further, the system <NUM> allows use of flammable, low-pressure refrigerants with low GWP in the first refrigeration circuits. Further still, by virtue of the use of an 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.

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 first refrigeration circuits 220a, 220b, 220c in system <NUM> may include an SLHX; and any of the first refrigeration circuits 420a, 420b may include an SLHX. For comparison, Figure7A shows a refrigeration circuit <NUM> without a SLHX; while Figure 7B shows a refrigeration circuit <NUM> with a SLHX <NUM>.

The circuit <NUM> in Figure 7A has a compressor <NUM>, a heat exchanger <NUM>, an expansion valve <NUM> and an evaporator <NUM>. The compressor <NUM>, the heat exchanger <NUM>, the expansion valve <NUM> and the evaporator <NUM> are connected in series and in the order listed. In use, the refrigeration circuit <NUM> functions as previously described.

The circuit <NUM> in Figure 7B has the same components as the circuit <NUM>, plus an additional SLHX <NUM>. The SLHX provides a heat exchanging interface between the line connecting the evaporator <NUM> and the compressor <NUM>, and the line connecting the heat exchanger <NUM> and the expansion valve <NUM>. In other words, the SLHX <NUM> is positioned between the line connecting the evaporator <NUM> and the compressor <NUM> (herein referred to as the vapour line), and the line connecting the heat exchanger <NUM> and the expansion valve <NUM> (herein referred to as the liquid line).

In use, the SLHX transfers heat from the liquid line, after the heat exchanger <NUM>, to the vapour line, after the evaporator <NUM>. This results in two effects taking place: a first which improves the efficiency of the circuit <NUM>; and a second which reduces the efficiency of the circuit <NUM>.

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 <NUM>. This additional sub-cooling leads to lower inlet quality in the evaporator <NUM> after the expansion valve <NUM> process. This increases the enthalpy difference and so the capacity of the refrigerant to absorb heat in the evaporator <NUM> stage is increased. Accordingly, the performance of the evaporator <NUM> is improved.

Secondly, disadvantageously, on the vapour line side - that is, the low pressure side - the refrigerant exiting the evaporator <NUM> 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 <NUM>, 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 type illustrated in the Figures as systems <NUM> and <NUM> herein.

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 <NUM> shows the overall GWP for varying proportions of R515A and R744 refrigerants in the refrigeration system: <NUM> being the maximum combined value i.e. <NUM>%. According to the 5th Intergovernmental Panel on Climate Change, R515A has a GWP of <NUM> and R755 a GWP of <NUM>. Consequently, the overall GWP for <NUM> proportion R515A and <NUM> proportion R744 is <NUM> as [(<NUM> x <NUM>) = <NUM>]. Conversely, the overall GWP for <NUM> proportion R515A and <NUM> proportion R755 is <NUM> since [(<NUM> x <NUM>) + (<NUM> x <NUM>) = <NUM>]. In this way Table <NUM> shows the charge ratio restrictions considering GWP criteria.

<FIG> shows the data in Table <NUM> 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 <NUM> GWP at <NUM> proportion R515A to around <NUM> GWP at <NUM> proportion R515A. It is clear from this graph that the maximum allowed system GWP of <NUM> in preferred embodiments is found at around <NUM> weight proportion R515A.

Table <NUM> shows the boiling pressures at varying boiling temperatures for: R1233zd(E) refrigerant; a blend of <NUM> wt% proportion R1233zd(E) and 50wt% proportion R1234ze; and a blend of 33wt% R1233zd(E) and 67wt% R1234ze.

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 <NUM> show that the compositions in which the amount of transHFO-1234ze is at least <NUM>% 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 <NUM> 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 <NUM>, blends having in excess of <NUM>% by weight of transHFO-1234ze are flammable as measured according to American Society for Testing and Materials (ASTM) <NUM>.

Table 4a shows blends not previously mentioned in this disclosure but which are be considered in Table 4b.

Table 4b shows a comparison of characteristics of the comparative refrigeration system described in reference to <FIG> but without a mechanical subcooler ('Comparative Example'); the comparative refrigeration system described in reference to <FIG> with the mechanical subcooler ('Comparative example with mechanical subcooler'); the cascaded refrigeration system described in reference to <FIG> ('Option <NUM>'); and the flooded cascaded refrigeration circuit described in reference to <FIG> ('Option <NUM>'), for different combinations of refrigerants.

Table 4b includes information on the coefficient of performance (COP) of each system. The COP is the ratio of useful cooling output from the system to work input to the system. Higher COPs equate to lower operating costs. The relative COP is the COP relative to the comparative example refrigeration system.

It is clear from Table 4b that the flooded cascaded refrigeration circuit achieves the best COP as its values for COP are in all cases higher than for the other systems.

The results shown in Table 4b are based on the below assumptions, where MT means medium temperature (second refrigeration circuit) and LT means low temperature (first refrigeration circuit) and units are as given.

It will be appreciated that the LT load of this example (<NUM>,<NUM> watts) will be provided according to the preferred aspects of the present invention by cumulative power rating of numerous small compressors. For example, if the LT portion of the refrigeration systems uses compressors rated at about <NUM> watts (about <NUM> horsepower) numerous (e.g., <NUM>) of such small compressors will be used according to the present invention. In contrast, it would be contemplated that the compressor load carried by the medium temperature system could be handled by a series of larger compressors (having a power rating of <NUM> horse power or greater) to provide the <NUM>,<NUM> watts (about <NUM> horse power) of cooling.

Table <NUM> shows a comparison of characteristics of the comparative example refrigeration system described in reference to <FIG> and the cascaded refrigeration system described in reference to <FIG> for different combinations of refrigerants in the cascaded refrigeration system and with suction line liquid line (SLHX) in the second refrigeration circuits (the medium temperature stage). Like Table 4b, Table <NUM> includes information on the actual and relative COPs of each system.

Claim 1:
A cascaded refrigeration system comprising:
(a) a plurality of low temperature refrigeration circuits, with each low temperature refrigeration circuit comprising:
(i) a flammable low temperature refrigerant having a GWP of about <NUM> or less;
(ii) a compressor having a horse power rating of about <NUM> horse power (about <NUM> kilowatts) or less; and
(iii) a heat exchanger in which said flammable low temperature refrigerant condenses; and
(b) a medium temperature refrigeration circuit comprising a non-flammable medium temperature refrigerant evaporating at a temperature below said low temperature refrigerant condensing temperature, wherein said medium temperature refrigerant evaporates in said heat exchanger by absorbing heat from said flammable refrigerant in said low temperature refrigeration circuit.