Patent Description:
Ice making machines are employed in commercial and residential applications around the world. In domestic applications, ice makers are typically located in a freezer compartment. The resulting ice is usually of poor quality due to the trapping of air and impurities during the freezing process. In commercial applications, the ice makers typically freeze the ice upright, or vertically, in a manner that removes the impurities and creates pure, clear ice cubes. Among other references, <CIT> and Patent Publication No. <CIT> are known and explain the embodiments of this process in detail. Commercial ice makers traditionally consist of a single ice making unit placed above an ice storage bin or automatic dispenser for accessing the ice. An ice level sensor signals when the bin or dispenser level is full, at which point, the ice making unit shuts down until the demand returns. As ice is dispensed or drawn from the bin, the ice falls away from the sensor and production resumes. <CIT> is known and further explains this process in detail. Such machines have received wide acceptance and are particularly desirable for commercial installations such as restaurants, bars, motels and various beverage retailers having a high and continuous demand for fresh ice.

The refrigerant selection is a key element in the design of the ice maker. Ice machine evaporators operate at a medium to low temperature, having an optimum temperature ranging from -<NUM> to -<NUM>. In September <NUM>, the Montreal Protocol banned the use of CFCs and began the phase-out of R-<NUM>. In its place, non-ozone depleting HFC refrigerants became the standard for the ice making application. In particular, R-404a, the pseudo-azeotropic blend of HFC-<NUM>, HFC-143a, and HFC-134a, provides a nearly stable temperature throughout the evaporation process, which is critical to producing a consistent ice slab across an evaporator. It is also non-flammable and, therefore, has no charge limitation placed on its use in commercial ice making machines. Higher ice capacities are possible by simply increasing the size of evaporator, compressor, and condensing unit, and in turn, increasing the amount refrigerant necessary to provide the proper charge for the system. Larger ice makers with self-contained condensing units could contain as much as <NUM> pounds (<NUM>,<NUM> grams) of R-404a, and systems with remote condensing units could have over <NUM> pounds (<NUM>,<NUM> grams) of R-404a, depending on the length of the connecting line sets.

Despite its optimum fit for the application, R-404a is receiving increasingly negative attention about its effect on the environment. GWP is the measure of given mass of greenhouse gas that is estimated to contribute global warming. Its relative scale is compared to that of Carbon Dioxide (CO<NUM>) gas, which by convention has a GWP of one. R-404A is estimated to have a GWP of <NUM>,<NUM>. Its direct release to the atmosphere is prohibited, however, the indirect release of refrigerant over the life of the equipment due to infinitesimal leakage can be nearly impossible to ascertain. An even greater impact exists with the indirect effect of the increased energy consumption required of equipment running on a reduced charge. In this case, - the impact is manifested with increase in carbon emissions released to the atmosphere during the creation of that additional energy. As such, the phase-out of HFC refrigerants has gained worldwide momentum. The European Union has taken measures to cut two-thirds of the emissions from fluorinated greenhouse gasses by <NUM> by passing "F-gas Regulations," which took effect January <NUM>. The United States has followed suit by passing similar phase-out schedules to take effect as early as January <NUM>. Individual states have taken up the challenge as well. Specifically, the state of California proposed a rule in June, <NUM>, to ban all refrigerants with a GWP greater than <NUM> by January, <NUM>. To date, there are several alternative refrigerants which offer a potential drop-in replacement, such as R-407A or HFO blends like R-<NUM>, but none are below California's <NUM> GWP limit. Also, in particular for ice making machines, it is a requirement that any alternative working fluid have a negligible temperature glide in order to make ice evenly over the evaporating surface. The aforementioned HFO blends have a comparatively high temperature glide which make them unsuitable for the application. Ice maker manufactures will have no choice but to comply with the new laws taking shape, and ultimately, there will be an end to the use of HFCs and the proposed HFO alternative blends, and the ice making equipment will need to be completely redesigned.

With the aforementioned phase-out facing ice making manufacturers, the case for natural refrigerants has never been so prevalent. Propane (R-<NUM>) is a highly efficient and very environmentally friendly alternative having a GWP of only <NUM>. It can essentially be dropped into existing systems without major modification; however, R-<NUM> poses its own set of design challenges due to its flammability. The IEC has imposed a refrigerant charge limit of <NUM> grams in an effort to mitigate that risk. To take advantage of the benefits of R-<NUM>, manufacturers must develop techniques to limit the refrigerant charge of the system. One such technique is explained in <CIT>, where a traditional fin and tube condenser has been replaced with an equivalent microchannel condenser with an internal volume from <NUM> to <NUM> milliliters. However, microchannel condensers are traditionally more expensive than fin and tube condensers, and with a volume of only <NUM>, there still remains a limit on the maximum ice capacity that can be obtained with such a condenser. Ice manufacturers have successfully made <NUM> pounds (<NUM>) of ice per day with <NUM> grams of propane, , but no solution exists for icemakers requiring greater capacity in a single system. Logically, to achieve the higher ice capacities, those skilled in the art would then be lead to employ multiple systems into one machine. <CIT> discloses a multiple compressor system that includes a plurality of evaporators and expansion devices that responds advantageously to increasing demand by cycling the systems according to that demand. Although not directly related to ice making machines, one could imagine a similar system for a commercial ice maker that would respond similarly to ice demand. However, the cost of multiple systems would make the product unprofitable. The evaporator, being made of a high thermal conductive material such as copper, is in some cases the most expensive component of an ice making machine. Outside of material cost, the fabrication, overhead costs, and any additional cost of performance coatings, such as Electroless Nickel, can sum to as much as a third of the entire ice making machine material cost. There could also be some significant performance-related drawbacks. A dual-evaporator system with cycling control would scale or corrode one evaporator more rapidly than the other resulting in more frequent failures of one side, effectively reducing the ice making capacity in half. The increased warranty costs for a hydrocarbon dual evaporator system drastically effect the business case and consume any potential profits as compared with the single HFC system evaporator standard of the day. Therefore, the current solutions presented for R-<NUM> unfortunately offer little solution for larger ice making machines in a competitive market driven to reduce overall costs, especially with emerging manufacturers from around the world offering new competition.

A single R-<NUM> system ice maker still offers the best solution, as it reduces the number of required components and conserves cost, but there must be a means to increase the ice capacity without significantly adding refrigerant charge. Although not specifically intended, one method that could be incorporated is the one described in <CIT>, which uses two evaporator freeze plates with one refrigeration circuit. A rectangular cross-sectioned conduit is used between the two evaporator plates, increasing the efficiency of the system by recovering the heat traditionally lost on the opposite side of the refrigerant tubing. However, this method is unproven in the market and there is little evidence that flat conduit would last the duration of the icemakers service life due to the high probability of plate-tube separation. Surface imperfections in the flatness would cause pockets of air between the plate and tube, and ultimately lead to the build-up of ice between the two surfaces. Over repeated thermal cycling, the ice would expand to propagate behind the freeze plate, which lead to a reduced ice capacity and ultimately complete failure. On the contrary, ice making evaporators with round tubing attached to the freeze plate surface has been proven superior to the flat conduit by withstanding <NUM> or more years of thermal cycling without separation.

In <CIT>, an ice make is disclosed comprising a cylindrical auger-type ice making mechanism cooled by two hydrocarbon refrigeration circuits.

Thus, need remains for a single, commercial ice making machine capable of making more than <NUM> pounds of ice per day and that uses R-<NUM> as its refrigerant. The solution demands that (<NUM>) the individual systems adhere to limitations set in place for hydrocarbons, (<NUM>) manufacturing costs be limited by reducing the number of expensive components and systems, and (<NUM>) a proven and reliable method to produce an evaporator can be repeated with good adhesion to the freeze plate. The present disclosure allows higher ice capacities in the event the charge limitations increase for R-<NUM> single systems beyond <NUM> grams. Nonetheless, there will always be a charge limitation for use of flammable refrigerants for commercial equipment located and installed indoors. Those skilled in the art will have determined the maximum allowable ice capacity given the refrigerant limit, and in this case, the essence of the present disclosure in allowing still higher ice capacities would still apply.

Briefly, therefore, one embodiment of the invention is directed to an ice making assembly for forming ice using refrigerant capable of transitioning between liquid and gaseous states in which the assembly includes two refrigeration circuits with a single evaporator assembly, as defined in claim <NUM>. Preferably, the first and second refrigerant tubing are interleaved with one another as part of the evaporator assembly. Preferably, the water system of the ice making assembly has a water pump, a water distributor above the freeze plate, a purge valve, a water inlet valve, and a water reservoir located below the freeze plate adapted to hold water. The water pump is in fluid communication with the reservoir and the water distributor in order to cycle water over the freeze plate.

The present invention provides higher ice capacities while operating safely within the design limitations of hydrocarbon refrigerants. Solving this and the other aforementioned problems, the present invention comprises a unique evaporator assembly, wherein a single freeze plate is attached to dual, independent hydrocarbon refrigeration systems. The disclosed invention conserves material cost as compared to a traditional dual system ice maker by employing a single evaporator, single water circulation system, and single microprocessor to monitor and control the efficient production of ice.

These and other features, aspects and advantages of the invention will become more fully apparent from the following detailed description, appended claims, and accompanying drawings, wherein the drawings illustrate features in accordance with exemplary embodiments of the invention, and wherein:.

Before any embodiments of the invention are explained in detail, it will be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. Also, it will be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. All numbers expressing measurements and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about. " It should also be noted that any references herein to front and back, right and left, top and bottom and upper and lower are intended for convenience of description, not to limit an invention disclosed herein or its components to any one positional or spatial orientation.

<FIG> illustrates a conventional commercial ice maker <NUM> having an ice making assembly disposed inside of a cabinet <NUM> that may be mounted on top of an ice storage bin <NUM>. The ice storage bin <NUM> may include a door <NUM> that can be opened to provide access to the ice stored therein. The ice maker <NUM> may have other convention components not described herein without departing from the scope of the invention.

<FIG> illustrates certain principal components of one embodiment of an ice making assembly <NUM> having a water circuit <NUM> and two refrigeration circuits, <NUM> and <NUM>. The refrigeration circuits may be formed with identical components and, therefore, such components will be described using like reference numbers. The water circuit <NUM> may include a water reservoir <NUM>, water pump <NUM> circulating water to a water distribution manifold or tube <NUM> for distribution across an evaporator assembly <NUM>. During operation of the ice making assembly <NUM>, as water is pumped from water reservoir <NUM> by water pump <NUM> through a water line and out of distributor manifold or tube <NUM>, the water impinges on the evaporator assembly <NUM>, flows over the pockets of the freeze plate <NUM> and freezes into ice. The water reservoir <NUM> may be positioned below the evaporator assembly <NUM> to catch the water coming off of assembly <NUM> such that the water may be recirculated by water pump <NUM>.

The water circuit <NUM> may further include water supply line <NUM>, water filter <NUM> and water inlet valve <NUM> disposed thereon for filling the water reservoir <NUM> with water from a water supply, wherein some or all of the supplied water may be frozen into ice. The water reservoir <NUM> may include some form of a water level sensor, such as a float or conductivity meter, as is known in the art. The water circuit <NUM> may further include a water purge line <NUM> and purge valve <NUM> disposed thereon. Water and/or any contaminants remaining in reservoir <NUM> after ice has been formed may be purged via purge valve <NUM> through the purge line <NUM>.

Each of the refrigeration circuits <NUM> and <NUM> may include a compressor <NUM>, condenser <NUM> for condensing compressed refrigerant vapor discharged from the compressor <NUM>, a condensing fan <NUM> positioned to blow a gaseous cooling medium across condenser <NUM>, a drier <NUM>, a heat exchanger <NUM>, thermal expansion device <NUM> for lowering the temperature and pressure of the refrigerant, a strainer <NUM>, and hot gas bypass valve <NUM>. As described more fully elsewhere herein, a form of refrigerant cycles through these components.

Thermal expansion device <NUM> may include, but is not limited to, a capillary tube, a thermostatic expansion valve or an electronic expansion valve. In certain embodiments, where thermal expansion device <NUM> is a thermostatic expansion valve or an electronic expansion valve, water circuit <NUM> may also include a temperature sensing bulb placed at the outlet of the evaporator assembly <NUM> to control thermal expansion device <NUM>. In other embodiments, where thermal expansion device <NUM> is an electronic expansion valve, water circuit <NUM> may also include a pressure sensor (not shown) placed at the outlet of the evaporator assembly <NUM> to control thermal expansion device <NUM> as is known in the art.

The refrigeration circuits <NUM> and <NUM>, as well as the water circuit <NUM> may be controlled by controller <NUM> for the startup, freezing, and harvesting cycles through a series of relays. The controller <NUM> may include a processor along with processor-readable medium storing code representing instructions to cause processor to perform a process. The processor may be, for example, a commercially available microprocessor, an application-specific integrated circuit (ASIC) or a combination of ASICs, which are designed to achieve one or more specific functions, or enable one or more specific devices or applications. In yet another embodiment, controller <NUM> may be an analog or digital circuit, or a combination of multiple circuits. Controller <NUM> may also include one or more memory components (not shown) for storing data in a form retrievable by controller <NUM>. Controller <NUM> can store data in or retrieve data from the one or more memory components. Controller <NUM> may also include a timer for measuring elapsed time. The timer may be implemented via hardware and/or software on or in controller <NUM> and/or in the processor in any manner known in the art without departing from the scope of the invention.

Having described each of the individual components of one embodiment of refrigeration circuits <NUM> and <NUM>, the manner in which the components interact and operate in various embodiments may now be described in reference again to <FIG>. Initially, each of the refrigeration circuits is charged with a hydrocarbon refrigerant, such as propane R290, to a certain charging limit, between <NUM> and <NUM> grams, or preferably up to about <NUM> grams. During operation of the refrigeration circuits, each compressor <NUM> receives low-pressure, substantially gaseous refrigerant from evaporator assembly <NUM> through an associated line (line <NUM> for the first refrigeration circuit <NUM> and line <NUM> for the second refrigeration circuit <NUM>). The compressor <NUM> pressurizes the refrigerant, and discharges high-pressure, substantially gaseous refrigerant to condenser <NUM>. The difference in pressure between suction side of the compressor <NUM> and the discharge side of the compressor <NUM> may be determined using two pressure sensors located on the suction and discharge lines, Ps <NUM> and Pd <NUM>. In condenser <NUM>, heat is removed from the refrigerant, causing the substantially gaseous refrigerant to condense into a substantially liquid refrigerant.

After exiting condenser <NUM>, the high-pressure, substantially liquid refrigerant is routed through the drier <NUM> to remove moisture and, if the drier <NUM> includes a form of filter such as a mesh screen, to remove certain particulates in the liquid refrigerant. The refrigerant then passes through a heat exchanger <NUM>, which uses the warm liquid refrigerant leaving the condenser <NUM> to heat the cold refrigerant vapor leaving the evaporator assembly <NUM>, and into the thermal expansion device <NUM>, which reduces the pressure of the substantially liquid refrigerant for introduction into evaporator assembly <NUM> through tee <NUM> via lines <NUM> and <NUM>. As the low-pressure expanded refrigerant is passed through the tubing of evaporator assembly <NUM>, the refrigerant absorbs heat from the tubes contained within evaporator assembly <NUM> and vaporizes as the refrigerant passes through the tubes, thus cooling evaporator <NUM>. Low-pressure, substantially gaseous refrigerant is discharged from the outlet of evaporator assembly <NUM> through a suction line (line <NUM> for the first refrigeration circuit <NUM> and line <NUM> for the second refrigeration circuit <NUM>), and is reintroduced into the inlet of each compressor <NUM>.

<FIG> illustrate the first tubing <NUM> and second tubing <NUM> of evaporator assembly <NUM>. The first tubing <NUM> has an inlet <NUM> connected to line suction <NUM> and an outlet <NUM> connected to suction line <NUM>. Similarly, the second tubing <NUM> has an inlet <NUM> connected to line suction <NUM> and an outlet <NUM> connected to suction line <NUM>. Thus, in each refrigeration circuit, the refrigerant cycles from the condenser to the compressor to the evaporator tubing <NUM> and <NUM>.

<FIG> illustrates the first tubing <NUM> and the second tubing <NUM> thermally coupled to rear side of freeze plate <NUM> of the evaporator assembly <NUM>. <FIG> shows the front view of the freeze plate <NUM> of evaporator assembly <NUM>. The first tubing <NUM> and the second tubing <NUM> are preferably serpentine-shaped such that they may be interleaved with one another as illustrated in <FIG>. Such an arrangement assists in ensuring a consistent temperature across the freeze plate <NUM>, and thus, maximizing ice production by allowing for an even bridge thickness during ice making, while simultaneously minimizing the percentage of ice melt required to release the full batch during harvest. Using this arrangement, the refrigeration circuits <NUM> and <NUM> may each be charged at a level acceptable to meet the limitations of the IEC, while still providing a sufficiently high cooling capability to meet the needs of the commercial ice maker industry. The first and second tubing <NUM> and <NUM> depicted in <FIG> have a circular cross section and are arranged in a serpentine-like shape, such that the combination of the two tubings are distributed over the freeze plate to provide substantially uniform cooling over the freeze plate.

<FIG> illustrates the principal inputs and outputs to the controller <NUM> that may be included in one or more embodiments of the ice maker assembly <NUM>. The inputs may include some combination of a water level sensor <NUM> measuring the level of the water the reservoir <NUM>, a temperature probe <NUM> measuring the temperature near the evaporator assembly <NUM>, a harvest relay switch <NUM> that is activated based on a certain amount of ice formed on the freeze plate, a bin control switch <NUM> that detects the fullness of the ice storage bin <NUM>, and a pressure sensor <NUM> that may be used to detect the water pressure proximate the bottom of the reservoir <NUM>, which can be correlated to the water level in reservoir <NUM>.

The controller <NUM> issues signals to control the hot gas valve <NUM>, condenser fan <NUM>, and compressor <NUM> of each refrigeration circuit <NUM> and <NUM>, and the circulation pump <NUM>, water valve <NUM> and purge valve <NUM> of the water circuit <NUM>. The controller <NUM> receives operating power through a conventional power supply <NUM>.

Having described each of the individual components of embodiments of ice maker <NUM>, including the ice making assembly <NUM>, the manner in which the components interact and operate may now be described. Ice is produced by simultaneously running the refrigeration and water circulation systems. During a startup phase, it may be desirable not to start up both of the the compressors and condensers at the same time. During operation of ice making assembly <NUM> in a cooling cycle, comprising both a sensible cycle and a latent cycle, each compressor <NUM> receives low-pressure, substantially gaseous refrigerant from evaporator assembly <NUM> through suction lines <NUM> and <NUM>, pressurizes the refrigerant, and discharges high-pressure, substantially gaseous refrigerant to condenser <NUM>. In condenser <NUM>, heat is removed from the refrigerant, causing the substantially gaseous refrigerant to condense into a substantially liquid refrigerant.

After exiting condenser <NUM>, the high-pressure, substantially liquid refrigerant is routed through the drier <NUM>, across the heat exchanger <NUM> and to the thermal expansion device <NUM>, which reduces the pressure of the substantially liquid refrigerant for introduction into the first and second tubing <NUM> and <NUM> of the evaporator assembly <NUM> via lines <NUM> and <NUM> respectfully. As the low-pressure expanded refrigerant is passed through the first tubing <NUM> and the second tubing <NUM> of the evaporator assembly <NUM>, the refrigerant absorbs heat from the tubes contained within evaporator assembly <NUM> and vaporizes as the refrigerant passes through the tubes thus cooling the freeze plate. Low-pressure, substantially gaseous refrigerant is discharged from the outlet of evaporator assembly <NUM> through line <NUM> and <NUM>, passes across the heat exchanger <NUM>, and is reintroduced into the inlet of compressor <NUM>.

In certain embodiments, assuming that all of the components are working properly, at the start of the cooling cycle, water inlet valve <NUM> may be turned on to supply water to reservoir <NUM>. After the desired level of water is supplied to reservoir <NUM>, the water inlet valve <NUM> may be closed. Water pump <NUM> circulates the water from reservoir <NUM> to freeze plate <NUM> via distributor manifold or tube <NUM>. Compressor <NUM> causes refrigerant to flow through the refrigeration system. The water that is supplied by water pump <NUM> then, during the sensible cooling cycle, begins to cool as it contacts freeze plate <NUM>, returns to water reservoir <NUM> below freeze plate <NUM> and is recirculated by water pump <NUM> to freeze plate <NUM>. Once the cooling cycle enters the latent cooling cycle, water flowing across freeze plate <NUM> starts forming ice cubes. As the volume of ice increases on the freeze plate <NUM>, simultaneously the volume of water in the reservoir <NUM> decreases. The controller <NUM> may monitor either the amount of ice forming as measured by an ice thickness sensor, the decrease in the water in the reservoir <NUM> as measured by the water level sensor, or some other refrigeration system parameter to determine the desirable batch weight. Thus, the state of the freeze cycle may be calibrated to the water level in reservoir <NUM>. Controller <NUM> can thus monitor the water level in reservoir <NUM> and can control the various components accordingly.

At that point, the harvesting portion of the cycle begins. The controller <NUM> opens the purge valve <NUM> to remove the remaining water and impurities from the reservoir <NUM>. The water circuit <NUM> and the refrigeration circuits <NUM> and <NUM> are disabled. After the ice cubes are formed, hot gas valve <NUM> is opened allowing warm, high-pressure gas from compressor <NUM> to flow through a hot gas bypass line, through strainer <NUM> capable of removing particulates from the gas, check valve <NUM>, and tee <NUM> to enter the tubing of the evaporator assembly <NUM>, thereby harvesting the ice by warming freeze plate <NUM> to melt the formed ice to a degree such that the ice may be released from freeze plate <NUM> and fall into ice storage bin <NUM> where the ice can be temporarily stored and later retrieved. The hot gas valve <NUM> is then closed and the cooling cycle can repeat.

Several methods may be used to terminate the harvest cycle, each with the goal of improving the yield of ice produced and preventing the build-up of unharvested ice from cycle to cycle. One method is to monitor the evaporator outlet temperature, wait for it to reach some minimum value, and then incorporate time delay for safety. This indirect method of terminating harvest can prove unreliable over the life of the ice maker due to evaporator scaling from heavy sediment and minerals in the potable water supply. A more efficient method is to use a mechanical relay to trigger the end of a harvest, thereby eliminating wasted time. In one such case, the relay is attached to a horizontal flap beneath the evaporator assembly <NUM> and placed directly in the path of the sliding ice. As the ice slides away from the freeze plate <NUM>, the relay is triggered and sends a signal to the controller <NUM> to immediately terminate the harvest. Upon harvest termination, the water supply valve <NUM> opens for a short time to refill the reservoir <NUM> with fresh water. The ice maker continues alternating freeze and harvest cycles until either the ice bin sensor is satisfied, the ice maker satisfies some programmed, preset schedule stored in the controller's memory, or the unit is shutdown either manually or automatically from some safety device or feature embedded within the controller.

Certain variations of the system described above are available. For example, the refrigeration circuits <NUM> and <NUM> may include single speed compressors <NUM> along with two thermostatic expansion valves <NUM> to maintain a superheat setting at the outlet of each individual circuit. Traditionally known methods for maintaining a balanced system by ensuring the proper charge of R-<NUM> (or other hydrocarbon refrigerant) for each individual circuit may be used to by ensuring a consistent installation of the thermostatic element. Alternatively, the refrigeration circuits <NUM> and <NUM> may include two variable speed compressors <NUM> along with two electronic expansion valves <NUM> for maintaining a superheat setting at the outlet of each individual circuit. Still further, the refrigeration circuits may include sensing devices, such as Piezo-resistive Micro-Electro-Mechanical Systems (MEMS) technology, to determine the operating characteristics of each circuit and apply a frequency generating function to alter the speed of the compressors in an effort to balance the suction temperatures of the cooling loop, thereby, maintaining an even, more stable differential across the freeze plate. This same control according to the current embodiment could also modify other variable speed components, similar to those listed in <CIT>, incorporated herein by reference, to achieve the same stabilizing function.

The ice making assembly <NUM> may further include means for operation in the event of a failure of one of the two refrigeration circuits. With only one system operational, it is presumed that the ice making capacity would reduce in half, as would be the case for a traditional, dual ice making system. However, the cycle time may be extended in the event of a failure, thus providing a "fail-safe" by allowing ice making to continue until the system failure was addressed. The evaporator would continue to operate and scale proportionately to the actual run time of the system, and no additional or alternate cleaning schedule would need to be employed. The controller could further notify the end user through means of an external display that the ice maker was operating in said "fail-safe" mode. The ice making assembly may also include the ability to operate in a reduced capacity mode, wherein only one of the refrigeration circuits would be operational, and therefore, half of the ice capacity could be used during periods of low ice demands or in an effort to save energy consumption.

In yet another embodiment of the invention, the refrigeration circuits may use spiral tubed, water-cooled condensers in place of the traditional fin and tube air cooled condensers. Other alternatives include the use of brazed plate heat exchangers as the condensing apparatus. For all cases, the condensers could be employed either in tandem on separate circuits, or employed as a single heat exchanger with dual ports to further minimize the number of required components for the ice making assembly.

Claim 1:
An ice making assembly (<NUM>) for forming ice using refrigerant capable of transitioning between liquid and gaseous states, the ice maker comprising:
a first refrigeration circuit (<NUM>) comprising a compressor (<NUM>), a condenser (<NUM>), a hot gas valve (<NUM>), an expansion device (<NUM>) and interconnecting lines (<NUM>) therefore wherein the refrigerant is approximately <NUM> to <NUM> grams of hydrocarbon refrigerant;
a second refrigeration circuit (<NUM>) comprising a compressor, a condenser, a hot gas valve, an expansion device and interconnecting lines therefore wherein the refrigerant is also approximately <NUM> to <NUM> grams of hydrocarbon refrigerant;
a single, shared evaporator assembly (<NUM>) comprising:
a first refrigerant tubing in fluid communication with the first refrigeration circuit such that the refrigerant may cycle through the first refrigerant tubing and the first refrigeration circuit;
a second refrigerant tubing in fluid communication with the second refrigeration circuit such that the refrigerant may cycle through the second refrigerant tubing and the second refrigeration circuit; and
a freeze plate (<NUM>) thermally coupled to the first and second refrigerant tubing; and
a water system for supplying water to the freeze plate;
wherein the first and second refrigerant tubings are each formed in a serpentine shape and the two serpentine-shaped tubing sections during harvest provide an even distribution of heat load.