Refrigerant Lubricated Bearings

FIELD

The present invention relates to cooling systems and to methods for operating such a cooling system.

BACKGROUND

Cooling systems, such as a chiller or air conditioning system, generally include a compressor, a condenser, an expansion device and an evaporator, which are connected into a so-called cooling cycle or refrigerant cycle. In the cooling cycle refrigerant is cycled from at least the compressor for compressing gaseous refrigerant to the condenser for condensing gaseous refrigerant to liquid refrigerant, from the condenser to the expansion for expanding the liquid refrigerant, from the expansion to an evaporator for evaporating the liquid refrigerant to gaseous refrigerant, and from the evaporating back to the compressor. Usually, such a cooling system removes heat from a liquid via the vapor-compression refrigerant cycle. The cooled liquid may then be used to cool air (e.g., air conditioning) or in an industrial process. A compressor of a cooling system typically employs bearings that require lubrication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic drawing of aspects of an exemplary cooling system in accordance with this disclosure, and

FIG. 2 illustrates a schematic drawing of aspects of an exemplary cooling system in accordance with this disclosure.

FIG. 3 illustrates a schematic drawing of aspects of an exemplary cooling system in accordance with this disclosure, and

FIG. 4 illustrates a schematic drawing of aspects of an exemplary cooling system in accordance with this disclosure.

DETAILED DESCRIPTION

Disclosed are one or more preferred embodiments that incorporate features of this invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiments. Rather, the invention is defined by the claims hereto.

FIGS. 1-4 illustrates interrelated aspects of an exemplary cooling system 100 having a cooling cycle 10 (indicated by thick arrows) and a lubrication cycle 20 (indicated by hollow arrows), wherein the lubrication cycle 20 also comprises refrigerant as lubricant.

An exemplary cooling system 100, such as a chiller or air conditioning system, generally includes in a cooling cycle 10 a compressor 12, a condenser 14 and an evaporator 16. Optionally there is also an expansion (not particularly illustrated), e.g., an expansion valve upstream of evaporator 16, which may be used for reducing pressure of the refrigerant in the cooling cycle 10.

As can be seen in the cooling cycle 10, compressor 12 compresses gaseous refrigerant which may be directed to condenser 14 to condense gaseous refrigerant into liquid refrigerant. Liquid refrigerant is then guided to evaporator 16 for evaporating liquid refrigerant to gaseous refrigerant, which is then transported back to compressor 12 for providing compressed gaseous refrigerant in a continuous cycle.

Compressor 12 itself comprises bearing assembly 2 with one or more rolling bearings. Bearing assembly 2 is schematically illustrated in FIGS. 1-4. Bearing assembly 2 may require lubrication during operation. In accordance with this disclosure, a cooling system, e.g., 100, uses refrigerant not only in cooling cycle 10, but also in lubrication cycle 20 for lubricating bearing assembly 2 using refrigerant as lubricant for bearing assembly 2.

As illustrated in FIG. 1, a portion of refrigerant is branched off from condenser 14 by a lubricating refrigerant supply line 22 and transported to bearing assembly 2 in compressor 12 thereby providing lubricating refrigerant to bearing assembly 2. Lubricating refrigerant is introduced into bearing assembly 2, usually under relatively high-pressure through a nozzle or injection device (not particularly illustrated), and exits compressor 12 via lubricating refrigerant feedback line 30 for feeding back lubricating refrigerant to the evaporator 16.

Since a first pressure level of condenser 14 is much higher than a second pressure level of evaporator 16, there is no need for an additional lubricating refrigerant propelling, such as a pump, for transporting lubricating refrigerant through lubrication cycle 20. In order to prevent reflux of lubricating refrigerant to condenser 12, a check valve 25 is disposed within lubricating refrigerant supply line 22 upstream of compressor 12, as illustrated in FIG. 1.

Bearings, e.g., 2, in compressors of cooling systems, e.g., in chillers or air condition systems, are often lubricated by the refrigerant used in the cooling system itself, as in exemplary embodiments illustrated in FIGS. 1 and 2. However, refrigerant may contain harmful products which may lead to corrosion or cause other damages to bearing, e.g., 2. Refrigerants used in air conditioning chillers are often not stable under all conditions. Molecules can break down and produce by-product compounds which are harmful to chillers and bearings, e.g., 2, used in the chiller compressor. Breakdown can be caused by heat, pressure or the presence of liquid contaminants that functions as catalysts or by inherent chemical instability of such refrigerant. Particularly damaging by-products are acids, in particular hydrofluoric acid (HF) and hydrochloric acid (HCl), which are very corrosive. HF and HCl are formed by fluorine and chlorine atoms contained in the refrigerant molecules. Of special concern are recently developed refrigerants such as R1234ze, R1233zd and R1234yf, which are formulated to break down easily in case they are leaked into atmosphere where they can potentially cause environmental problems.

Water is another liquid contaminant that can break down and produce by-products that can corrode or diffuse into bearing components. A combination of water, HF, HCl and oxygen from entrapped air is a harmful mixture that causes severe damage to bearings. However, water itself is also problematic since it provides for poor lubrication and can cause corrosion and hydrogen embrittlement of steel components of bearings, e.g., 2.

It is therefore object of this disclosure, to provide a possibility for protecting a refrigerant lubricated bearing from harmful influence of by-products that cause corrosion or other damages.

For protecting bearing, e.g., 2, from harmful substances in refrigerant, upstream of the bearing assembly, a refrigerant supply line, e.g., 22, further comprises at least one filter, e.g., 24, 25, 26, 28, for filtering lubricating refrigerant. Such a filter contains material which absorbs, adsorbs and/or reacts with contaminants and/or by-products, so that refrigerant used for lubricating bearing, e.g., 2, is substantially free of harmful substances.

Because refrigerant is used as refrigerant in cooling cycle 10 (as well as lubricant in lubricating cycle 20), refrigerant is exposed to several mechanical components (e.g., compressor, condenser, evaporator, connecting lines) and thus exposed to heat and pressure, as well as to liquid and/or gaseous contaminants (e.g., air and moisture), which may cause molecules in a refrigerant to break down and produce byproduct compounds that are harmful to bearing assembly 2 used in compressor 12. Additionally, the breakdown of molecules may even be caused by an inherent chemical instability of a refrigerant itself, depending on the refrigerant chosen. Furthermore, particles, e.g., originating from wear or abrasion of mechanical components, may be present in refrigerant and which may be harmful for bearing assembly 2 when such refrigerant is used as lubricant. Such byproducts and/or particles may be very harmful to a refrigerant lubricated bearing assembly as they may lead to corrosion, increased wear, insufficient lubrication conditions, or otherwise cause damage in a bearing assembly, e.g., bearing assembly 2.

Consequently, there may be an arrangement of filter s 24, 26, and 28 (as in FIGS. 1 and 3), or an arrangement of individual and combined filter s 25, 28 (as shown in FIGS. 2 and 4) arranged in the lubricating refrigerant supply line 22 upstream of the bearing assembly 2. The filter (s) 24, 25, 26, 28 contain materials that may absorb or react with the byproducts, contaminants and/or particles, thereby removing particles, acids, or water and the like from refrigerant within cooling system 100.

Filter s, e.g., 24, 25, 26, 38, may adsorb, catch, or trap certain molecules from refrigerant by mechanical, chemical, and/or physical adsorption, depending on filter material type, surrounding environment composition, or an expected type of contaminant.

Highly damaging byproducts are acids, in particular hydrofluoric acid (HF) and hydrochloric acid (HCl), which are highly corrosive. Hydrofluoric acid and hydrochloric acid are formed by fluorine and chlorine atoms contained in the refrigerant itself. Of particular concern are recently developed refrigerants such as R1234ze, R1233zd and R1234yf, which are formulated to break down easily in case they are leaked into the atmosphere where they can potentially cause environmental problems. Such breakdown ensures that an environment is not harmfully contaminated by the refrigerant. Consequently, one of the filter units, e.g., filter unit 24 illustrated in the exemplary embodiments of FIG. 1, is an acid filter for filtering hydrofluoric acids and/or hydrochloric acids from refrigerant, wherein a filtering material of an acid filter, e.g., 24, may include Alumina (Al₂O₃), Silica (SiO2), Graphite Oxide, Graphene Oxide, Manganese Oxide (MgO), Aluminosilicate (Al2SiO5) and/or combinations thereof. Such filter materials have proven successful for filtering hydrofluoric and/or hydrochloric acids. Aluminum or aluminum compounds are preferably used for the hydrofluoric acids, as products of a reaction of aluminum and hydrofluoric acid is aluminum fluoride, a solid crystalline material, which may easily be removed. For adsorbing hydrochloric acids, a filter containing magnesium oxide is preferred, as reaction products of a reaction of HCl and magnesium oxide are magnesium chloride and water. Upon reading this disclosure in its entirety, one will appreciate that other suitable filter materials may be used.

In FIGS. 1 and 3, a second filter unit 26 is a desiccant filter for removing water (dissolved and/or free water) and/or moisture from the refrigerant. A filtering material of a desiccant filter, e.g., 26, is usually hygroscopic and may include Zeolite Scavenger sorbents, such as calcium zeolites, sodium zeolites, potassium zeolites, magnesium zeolites and combinations thereof, with all sizes and shapes, and graphene oxide, and combinations thereof for filtering dissolved water, and polymers, such as water absorbing filter, for filtering free water. Water or rather moisture and humidity has been identified as another liquid contaminant which react with the refrigerant so that the refrigerant may break down and produce byproducts that may corrode or diffuse into bearing components. Therefore, a combination of water, hydrofluoric acid, hydrochloric acids and/or oxygen from entrapped air, is a very harmful mixture that can cause severe damage to the bearing assembly.

The third filter unit 28 in turn is in the illustrated embodiment of FIGS. 1-4 a particle filter, which removes particles, e.g. particles originating form wear or abrasion of mechanical components, from the lubricating refrigerant. These particles are harmful to the surfaces of the bearing assembly, e.g., to races of bearing rings or rolling elements, and may lead to increased wear and insufficient lubrication conditions in the bearing assembly 2.

Besides the arrangement of filter units as illustrated in FIGS. 1 & 3, it is also possible to combine some or all filter units for reducing the overall required space or to use synergistic effects. Such embodiments are illustrated in FIGS. 2, 4, where the filter unit 25 is a combination of an acid filter and a desiccant filter. This is particularly preferably, as some of the adoption reaction of acids are competitive to the adsorption of water/moisture, or as mentioned above the reaction product of the chemical reaction may be water, which also needs to be removed from the refrigerant.

In summary, by using a filter arrangement for filtering harmful substances from the lubricating refrigerant, before the refrigerant is used for lubricating the bearing assembly, a lubricating refrigerant may be provided which is substantially free of harmful components. Thereby, the service life of the bearing assembly and the cooling system may be increased, as the lubricating conditions of the bearing assembly are improved.

As discussed above, it is possible to combine some or all filters for reducing overall component size and according a required space, or to use synergistic effects. For example, as illustrated in FIGS. 2 & 4, exemplary filter 25 is a combination of an acid filter and a desiccant filter. This is particularly useful as some reaction products of acids are competitive to adsorption of water/moisture, or as mentioned above a reaction product of a chemical reaction may be water, which should be removed from cooling system, e.g., 100, refrigerant.

As illustrated in FIGS. 3 and 4, an accumulator 40 may be arranged in lubricating refrigerant supply line 22, 23. Accumulator 40 is configured to ensure that a constant lubricating refrigerant supply is provided at compressor 12 even if pressure in supply line 22, 23 fluctuates. Consequently, accumulator 40 works as auxiliary reservoir for pressurized refrigerant, which may be fed to bearing assembly 2 if insufficient lubricating refrigerant supply is present in lubricating refrigerant supply line 22, 23.

Accumulator 40 usually has two compartments 42, 44, wherein top compartment 42 is filled with a gas or may contain a spring, which is adapted to provide a preload/load 46 onto a piston or bladder 48, which separates compartments 42, 44. Second compartment 44 is used for storing pressurize refrigerant. Such an accumulator 40 works as follows: at a start of a lubrication cycle, second compartment 44 of accumulator 40 is empty. As pressure builds up, second compartment 44 starts to fill up with liquid refrigerant. Pressure is balanced by pressure 46 of a compressed gas in first compartment 42 or by compression of a spring, if used. At steady state operation compartments 42, 44 each have approximately a same volume. This is controlled by selection of gas pressure or spring force 46 in first compartment 42.

A volume of pressurized liquid refrigerant in second compartment 44 serves as reserve lubricant in case of malfunction of a system, e.g., 100, for any reason, e.g., in a case of an unexpected pressure drop.

Lubricating refrigerant supply branch 22 may be branched off of a condenser, e.g., 14, as explained above, or may alternatively or in addition be branched off from an optional economizer. In case an economizer is present in the cooling cycle, it may be preferred to use refrigerant from an economizer with a lower pressure differential to an evaporator pressure level in order to lubricate a bearing assembly, e.g., 2. Thus, a choice of refrigerant type, low or medium pressure, the number of compressor stages and using or not using an economizer are economic considerations. The use of an economizer is particularly advantageous in case compressor 10 is a high-speed compressor which provides very high pressure to refrigerant which might be too high for lubricating bearing assembly 2. In such a case a pressure difference between an economizer and an evaporator can be configured to remain high enough for transporting refrigerant through lubricating cycle 20 and provide sufficient refrigerant at bearing assembly 2 for lubricating.

FIG. 4 illustrates exemplary embodiments in accordance with this disclosure. In addition to a cooling system as illustrated in FIG. 1, a cooling system 100 as in FIG. 2 has a first lubricating refrigerant supply branch 22-1, which branches off from condenser 14 or an economizer (not particularly illustrated, but downstream from condenser 14 and upstream from evaporator 16), and a second lubricating refrigerant supply branch 22-2 which branches off from evaporator 16. First and second lubricating refrigerant branches 22-1, 22-2 merge into a main lubricating refrigerant supply line 23. Second lubricating refrigerant supply branch 22-2 may be used at startup for providing a liquid refrigerant to compressor 12 even before compressor 12 starts operating. A pump 50 may be arranged in second refrigerant supply line 22-2 which transports liquid refrigerant from evaporator 16 to compressor 12. Since pump 50 is only operated during startup, energy consumption of cooling system 100 is not unduly increased relative to known systems with a constantly operating pump. Additionally, pump size may be reduced as only a small amount of refrigerant needs to be transported to compressor 12 in a pre-lubrication cycle. In order to avoid any reflux of refrigerant to evaporator 16, particularly during ordinary operation of a cooling system, e.g., 100, a further check valve 27 is arranged in second lubricating refrigerant supply line 22-2.

Pump 50 may be a positive displacement pump and may also be used to control flow during ordinary operation, e.g., in case a pressure difference is fluctuating or a pressure difference is too low or too high. Positive displacement pumps have a close correlation between rotational speed and flow rate and are less affected by a pressure difference than ordinary dynamic pumps. It is further possible that the pump is a so-called rotary vane pump, which has advantages over known pumps as a they may also be used for pumping a mixture of gaseous and liquid fluids, which may be present in evaporator 16.

A cooling system 100 in accordance with FIG. 2 embodiments works as follows.

At startup of a cooling system, liquid refrigerant for lubrication is available in evaporator 16. As system pressure is building up, liquid refrigerant becomes available in condenser 14. Lubricating refrigerant pump 50 is first pumping refrigerant from evaporator 16, then after condenser 14 and evaporator 16 have reach a first pressure difference level, the source of liquid refrigerant is switched to condenser 14. Downstream from pump 50, refrigerant is supplied to bearing assembly 2 for lubrication through a nozzle, then drains from bearing assembly 2 to evaporator 16 by feedback line 30. In high speed compressors 12, a nozzle produces a jet that spays refrigerant into bearing assembly 2. Pressure drops through such a nozzle, which may be used to control refrigerant flow. In low speed compressors 12, jet injection may not be necessary, and refrigerant can flow into and through bearing assembly 2 without pressure drop. In such a case pump 50 may also function as a metering device.

In summary cooling systems in accordance with this disclosure have the following advantages:

Lubricating refrigerant flow is provided by a pressure difference between condenser, e.g., 12, and an evaporator, e.g., 16, instead of a pump. This reduces overall costs of a cooling system and increases overall reliability of the system.

Lubricating refrigerant flow has minimal variations due to use of an accumulator which ensures that lubrication of a bearing assembly, e.g., 2, is continuously provided. Additionally, interruptions of lubricating refrigerant flow are minimized and controlled. Since a pump is only used at startup (if at all) or if for any reason a pressure differential becomes too low, pump wear is minimized and additional power consumption is reduced. By using a rotary vane type pump internal leakage is minimized and pressure is created independently of speed. By using a variable speed drive for a pump, it is further possible to start such a pump at low speed for avoiding problems with cavitation, which usually occur when a mixture of liquid and gaseous fluids needs to be pumped. By not using the pump at steady-state conditions, overall energy consumption of the cooling system is reduced. By using a desiccant, acid and/or particle filter 25 in the lubricating refrigerant flow, a bearing assembly's exposure to harmful substances which may corrode the bearing components is also minimized.

A first exemplary cooling system: A cooling system includes a refrigerant cycle for cycling refrigerant from at a compressor in order to compress gaseous refrigerant to a condenser for condensing gaseous refrigerant to liquid refrigerant, from the condenser to an evaporator for evaporating the liquid refrigerant to gaseous refrigerant, and from the evaporating back to the compressor, and a lubrication cycle having at least one lubricating refrigerant supply line for providing refrigerant as lubricant to a bearing assembly, and the at least one lubricating refrigerant supply line branches off from the refrigerant cycle at the condenser for providing refrigerant to the bearing assembly, and rees with the refrigerant cycle at the evaporator, for feeding back refrigerant from the bearing assembly to the refrigerant cycle.

A second exemplary interrelated cooling system includes a refrigerant cycle for cycling refrigerant from at least a compressor for compressing gaseous refrigerant to a condenser for condensing gaseous refrigerant to liquid refrigerant, from the condenser to an economizer for lowering a pressure of the gaseous refrigerant, from the economizer to an evaporator for evaporating the liquid refrigerant to gaseous refrigerant, and from the evaporating back to the compressor, and a lubrication cycle having at least one lubricating refrigerant supply line for providing refrigerant as lubricant to a bearing assembly, and the at least one lubricating refrigerant supply line branches off from the refrigerant cycle at the economizer and/or at the compressor for providing refrigerant to the bearing assembly, and rees with the refrigerant cycle at the evaporator, for feeding back refrigerant from the bearing assembly to the refrigerant cycle.

A third interrelated exemplary cooling system includes the lubricating refrigerant supply line terminating in at least one nozzle or refrigerant injection device, which is adapted to provide and direct lubricating refrigerant to the bearings assembly in the compressor.

A fourth interrelated exemplary cooling system includes the lubrication cycle has a first lubricating refrigerant supply branch branching off from the condenser or from the economizer, and a second lubricating refrigerant supply branch branching off from the evaporator, which are both adapted to supply refrigerant to the bearing assembly.

A fifth interrelated exemplary cooling system includes the first and the second lubricating refrigerant supply line branches merge to a single main lubricating refrigerant supply line upstream of the bearing assembly.

A sixth interrelated exemplary cooling system include a pump, which is arranged either in the second lubricating refrigerant supply line branch or in the main lubricating refrigerant supply line.

A seventh interrelated exemplary cooling system includes at least one filter 25 is arranged in the lubricating refrigerant supply line upstream of the bearing assembly.

An eighth interrelated exemplary cooling system includes an accumulator is arranged in the lubricating refrigerant supply line upstream of the bearing assembly.

A ninth interrelated exemplary cooling system includes a method of operating a cooling system, wherein the refrigerant being used as lubricant is driven through the lubrication cycle line by a pressure difference between the condenser or economizer and the evaporator.

A tenth interrelated exemplary cooling system includes a refrigerant lubricated bearing arrangement comprising a bearing assembly, which is lubricated by refrigerant, a refrigerant supply line for supplying refrigerant to the bearing assembly as lubricant, wherein upstream of the bearing assembly the refrigerant supply line further comprises at least one filter unit for filtering the refrigerant.

An eleventh interrelated exemplary cooling system includes the at least one filter unit comprises at least one of an acid filter, a desiccant filter and a particle filter.

A twelfth interrelated exemplary cooling system includes the at least one filter unit is a combined filter unit of at least an acid filter and a desiccant filter for filtering acid and moisture from the refrigerant.

A thirteenth interrelated exemplary cooling system includes the at least one filter unit is an filter arrangement of a plurality of filter elements comprising an acid filter, a desiccant filter or a combination of acid filter and desiccant filter, and a particle filter, wherein the acid filter is arranged upstream of the desiccant filter and the particle filter, and the desiccant filter or the combined filter of acid filter and desiccant filter is arranged upstream of the particle filter.

A fourteenth interrelated exemplary cooling system includes the filter unit is adapted to adsorb, catch or trap certain molecules from the refrigerant by chemical and/or physical adsorption.

A fifteenth interrelated exemplary cooling system includes the filter unit comprises an acid filter for filtering hydrofluoric acids and/or hydrochloric acids from the refrigerant, wherein a filtering material of the acid filter is selected from the group of Alumina (Al₂O₃), Silica (SiO₂), Graphite Oxide, Graphene Oxide, Manganese Oxide (MgO), Aluminosilicate (A1₂SiO₅) and combinations thereof.

A sixteenth interrelated exemplary cooling system includes the filter unit comprises a desiccant filter for filtering dissolved water and/or free water from the refrigerant, wherein a filtering material of the desiccant filter is selected from the group of Zeolite Scavenger sorbents, such as calcium zeolites, sodium zeolites, potassium zeolites, magnesium zeolites and combinations thereof, with all sizes and shapes, and graphene oxide, and combinations thereof for filtering dissolved water, and polymers, such as water absorbing filter, for filtering free water.

A seventeenth interrelated exemplary cooling system includes the filter unit comprises a particle filter for filtering particles from the refrigerant, wherein preferably the particle filter is a stainless steel mesh, a magnet for metallic particle and/or a combination thereof.

An eighteenth interrelated exemplary cooling system includes a refrigerant cycle line for cycling refrigerant from at least a compressor unit for compressing gaseous refrigerant to a condenser unit for condensing gaseous refrigerant to liquid refrigerant, from the condenser unit to an expansion unit for expanding the liquid refrigerant, form the expansion unit to an evaporator unit for evaporating the liquid refrigerant to gaseous refrigerant, and from the evaporating unit back to the compressor unit, wherein at least the compressor unit comprises a bearing arrangement according to any cooling systems in accordance with this disclosure.

A nineteenth interrelated exemplary cooling system includes the refrigerant supply line branches off from the refrigerant cycle line.

It will be appreciated that the interrelated exemplary embodiments above are non-limiting and only provided by way of example to ease a readers understanding of a variety of embodiments in accordance with this disclosure.

According to a preferred embodiment the cooling system operates as follows:

At startup of the cooling system, liquid refrigerant for lubrication is available in the evaporator. As the system pressure is building up, liquid refrigerant becomes available in the condenser. The lubricant pump is first pumping refrigerant from the evaporator, then after having reach a certain pressure difference level, the source of liquid refrigerant is switched to the condenser. Downstream from the pump, the refrigerant is supplied to the compressor bearings for lubrication through a nozzle, then drains from the bearing assembly to the evaporator. In high speed compressors, the nozzle produces a jet that spays refrigerant into the bearings. The pressure drops through the nozzle and the nozzle controls the flow. In low speed compressors, jet injection may not be necessary. The refrigerant can flow into the bearing housing without pressure drop, then through the bearings. In that case, it is also possible that the pump functions as a metering device.

The optional pump may be engaged at all times, but it is preferred to engage the pump only to pump refrigerant from the evaporator at startup, then to turn it off and to only use the pressure differential between the condenser (or economizer) and the evaporator to drive the lubricating refrigerant flow.

In order to keep a supply of pressurized refrigerant in reserve, in case of a pump malfunction, a hydraulic accumulator is be filled by refrigerant, when the pump is started, which should be in a pre-lubrication cycle, before the compressor is started.

A compressor may be a centrifugal compressor which includes one or more impellers that compress the refrigerant. The impellers are mounted on a rotating shaft which is supported by a plurality of bearings. The bearing assembly requires a steady supply of lubricant, which is often oil.

A pump can be used to drive the refrigerant flow to the bearings. However, a pump may cavitate making it more difficult to supply the refrigerant to the bearings. There can also be operating conditions under which a supply of refrigerant provided by a pump is insufficient or a state of refrigerant is a mixture of liquid and vapor so that bearings may not be lubricated, properly. Additionally, there is a general reliability problem as a flow of bearing lubricant stops, if a pump for some reason stops working. A common reason why a pump stops working is a loss of electric power. Moreover, a pump that is constantly engaged also wears and consumes power.

It is therefore an object of the present disclosure to provide a cooling system with refrigerant lubricated bearings, which is operating reliably, and is cost-efficient.

In accordance with this disclosure some embodiments include a cooling system includes a refrigerant cycle for cycling refrigerant from at least a compressor for compressing gaseous refrigerant to a condenser for condensing gaseous refrigerant to liquid refrigerant, from the condenser to an evaporator for evaporating liquid refrigerant to gaseous refrigerant, and from an evaporating back to a compressor. Such a cooling system further comprises a lubrication cycle having at least one lubricating refrigerant supply line for providing refrigerant as lubricant to a bearing assembly, which may be part of a compressor.

For providing a stable supply of lubricating refrigerant to a bearing assembly, in some embodiments at least one lubricating refrigerant supply line branches off from a refrigerant cycle at a condenser for providing refrigerant to a bearing assembly, and rees with a refrigerant cycle at an evaporator, for feeding back refrigerant from a bearing assembly to a refrigerant cycle. Thereby, a pressure difference between a condenser and an evaporator may be used for transporting lubricating refrigerant in a lubricating cycle. A pressure difference results from a difference between a high pressure level of a compressor and a low pressure level of an evaporator. This transports refrigerant through a refrigerant cycle and also through a lubrication cycle.

According to a further aspect and/or a preferred embodiment, a refrigerant cycle may also comprise an economizer.

An economizer may be used in a cooling system in accordance with this disclosure in a two stage (or more generally multi stage) compressor. Thereby an expansion process is separated into two (or more) steps with an economizer in-between. Hence, liquid refrigerant from a condenser enters a first expansion device, which reduces a pressure of the refrigerant. This pressure drop causes a portion of liquid refrigerant to evaporate, and a resulting mixture of liquid and gaseous refrigerant enters an economizer. Consequently, a pressure in an economizer is between that of a condenser and an evaporator. An economizer itself is connected to a second expansion device and to an inlet to a second stage of a two stage compressor. In an economizer, a gaseous refrigerant is separated from a liquid refrigerant, and only remaining liquid refrigerant is fed to a second expansion device and further to an evaporator. A gaseous part of refrigerant in turn is recompressed by a second stage of such a compressor, and fed back from an outlet of a second stage compressor to a condenser. Since part of such refrigerant is already vaporized upstream of an evaporator, an amount of required compressor power is reduced as a gaseous part of such refrigerant generated in an economizer only needs to be compressed by the second stage impeller. In a system without an economizer, more gaseous refrigerant would be released and more gaseous refrigerant would be recompressed in-stead of being in liquid form and evaporate before going back to a first stage of a compressor. Thus, by using an economizer, a system efficiency is increased (by 4% to 6%), as recompression of gaseous refrigerant is waste of energy.

In embodiments, where an economizer is present, there is an additional or alternative possibility to branch off a lubricating supply line from a compressor or from an economizer. Using an economizer as branch off for a lubricating refrigerant supply line allows for a slower movement of refrigerant in a lubrication cycle and thereby for a more controlled distribution of refrigerant to a bearing assembly. It also reduces a speed with which refrigerant is introduced or sprayed into a bearing assembly.

A lubricating refrigerant supply line may terminate in a nozzle or injection device for directing and introducing refrigerant to a bearing assembly. A nozzle or injection device allows for an optimized and guided provision of lubricating refrigerant to a bearing assembly, and thereby for an improved lubrication. Further, it is preferred that a supply line itself is designed such that pressure drops across a nozzle rather than throughout a supply line.

According to a further preferred embodiment, the lubrication cycle has a first lubricating refrigerant supply line branch branching off from the condenser and/or from an economizer, and a second lubricating refrigerant supply line branch branching off from an evaporator, wherein both branches are adapted to supply refrigerant to a bearing assembly. The use of refrigerant from an evaporator is preferred at startup of a cooling system. At a startup phase, refrigerant in an evaporator is liquid and can be used for lubricating bearings before a compressor is started, while there is no liquid refrigerant in a condenser, which could be used for lubricating the bearing assembly. Using refrigerant from an evaporator allows for a so-called pre-lubrication cycle during which refrigerant is provided to the bearing assembly before the compressor start operating. This in turn ensures a sufficient lubrication of a bearing assembly at all times. Thereby, a service life of a compressor may be prolonged. On will appreciate that more than two branches may be provided.

A second branch-off from an evaporator a pump is arranged, which may be operated at start up and provides liquid refrigerant to a bearing assembly of a compressor before operating a compressor. Use of a pump ensures that sufficient refrigerant is provided at a bearing assembly at start up and also in case a pressure difference has not been built up or drops during ordinary operation. Preferably, a pump is controlled such that it starts if a pressure differential between a condenser and/or economizer becomes less than a predetermined value. To avoid or minimize the risk of cavitation in a pump suction line, a pump speed may be controlled for slow start and/or variable speed.

A pump may be disposed in a main lubrication supply line, which is provided by a merging of a first and second branch supply lines upstream of a bearing assembly. A pump is preferably operated at start up only, or in order to drive a lubricating refrigerant in case of an unexpected drop in pressure difference. However, arranging a pump in a main supply line might increase a flow resistance in a lubrication supply line, as refrigerant has also to pass a pump.

According to a further preferred embodiment, the cooling system further comprises a filter 25 which is arranged in the lubricating refrigerant supply line upstream of the bearing assembly. Thereby, a filter 25 may be arranged in a main supply line and/or in one or both branches depending design considerations. This filter ensures that harmful substances, e.g., water and/or other substances, which may occur due to a breakdown of molecules of a refrigerant due to heat, pressure and/or mechanical abrasion, are filtered out of refrigerant so that refrigerant which is used for lubricating a bearing assembly is not contaminated. Advantageously, a filter comprises at least one for filtering out liquids, such as water and acids, and a second for filtering out contaminate particles.

An accumulator may be arranged in a lubrication cycle line upstream of a bearing assembly. An accumulator is preferably filled up with refrigerant at start-up and ensures that a continuous lubrication is provided at a bearing assembly even during pressure difference variations between a pressure level of a compressor/economizer and an evaporator. An accumulator may also serve as pressurized lubrication refrigerant reservoir at start-up instead of a pump or in case the pump is not working. Consequently, an accumulator is preferably adapted to operate in a pre-lubrication cycle, before a compressor is started.

Preferably, an accumulator has two compartments, one on top that is filled with a gas or may contain a spring, a second that is used for storing pressurize refrigerant. Two compartments are separated by a piston or a rubber bladder.

An exemplary accumulator works as follows: at start of a relubrication cycle, a second compartment of an accumulator is empty. As pressure builds up, a second compartment starts to fill up with liquid refrigerant. A pressure is balanced by a pressure of a compressed gas in a first compartment or by a compression of the spring, if used. At steady state operation two compartments have approximately a same volume. This is controlled by selection of gas pressure or spring force in a first compartment.

As mentioned above, a volume of pressurized liquid refrigerant in a second compartments serves as reserve lubricant in case of malfunction of a system for any reason.

In an exemplary method for operating a cooling system, a refrigerant being used as lubricant is driven through a lubrication cycle line by a pressure difference between a condenser or economizer and the evaporator.

For protecting the bearing from harmful substances in the refrigerant, it has been proposed that upstream of the bearing assembly, the refrigerant supply line further comprises at least one filter unit for filtering the lubricating refrigerant. Such a filter contains material which absorbs, adsorbs and/or reacts with contaminants and/or by-products, so that the refrigerant, which is used for lubricating the bearing, is substantially free of harmful substances.

According to a preferred embodiment, the at least one filter unit comprises at least one of an acid filter, a desiccant filter and a particle filter. Thereby, particles, acids and/or water may be removed from the refrigerant, which are the most harmful substances for the bearing, so that the bearing is protected from corrosion and other defects. Commercially available desiccant filters can also be used, for example to remove water. It is further preferred to arrange the filter(s) as kidney filter(s) that continuously filter the refrigerant in the cooling system. However, for refrigerant lubrication of the bearing assembly it is preferred to arrange the filters in line upstream of the bearing assembly.

Preferably, the at least one filter unit is a combined filter unit of at least an acid filter and a desiccant filter for filtering acid and moisture from the refrigerant. The combination of filters into e.g. one housing reduces the required space for the additional filters. Further synergistic effects may be exploit by combining the filter units and for increasing the filter's efficiency. Often, water and acid are competitive substances for the adsorption to the filter material. By providing a combined filter both, water and acid, may be equally and reliably removed. Additionally or alternatively, the filter elements may be designed to have the same dimensions as an oil or other filter element and may be placed in a filter housing that is already present in the flow path of the refrigerant used for the bearing lubrication.

According to a further preferred embodiment, the at least one filter unit is an filter arrangement of a plurality of filter elements comprising a desiccant filter, an acid filter or a combination of acid filter and desiccant filter, and a particle filter, wherein the desiccant filter is arranged upstream of the acid filter and the particle filter, and the desiccant filter or the combined filter of acid filter and desiccant filter is arranged upstream of the particle filter. The indicated filter arrangement allows for an optimized filtering of the refrigerant. There are for examples filters which provide a very good adsorption of acids. However, in the presence of water their adsorption properties deteriorate as there is a competitive bonding of water and acid to the filter material, wherein the affinity of the filter material for hydrogen bonding is higher. Consequently, the removal of water or moisture from the refrigerant upstream of the acid filter allows for both an improved water/moisture and acid filtering. Of course it is also possible to arrange the particle filter upstream of desiccant filter and acid filter or a combination of both, or to arrange the filters in a still different order.

The filter unit itself is preferably adapted to adsorb, catch or trap certain molecules from the refrigerant by chemical and/or physical adsorption, wherein the kind of adsorption is depending on the material type and the surrounding environment composition. That means, when the adsorption is physical (Physisorption), the trapped molecules stay in the same chemical structure and are adsorbed via hydrogen bonds or van der Waals bonds. In this case the interaction between the filter material and the surrounding environment is reversable. Consequently, desorption, i.e. cleaning the filter, can occur, e.g. by heating the filter material or when two molecules are in competition. On the other hand, when the adsorption is chemical (Chemisorption), a chemical reaction occurs between the filter material and the surrounding environment molecules which may generate (in some cases) new products. In this case the adsorption is strong and occurs via covalent, metallic or ionic bonding.

According to a further preferred embodiment, the filter unit comprises an acid filter for filtering hydrofluoric acids and/or hydrochloric acids from the refrigerant, wherein a filtering material of the acid filter is selected from the group of Alumina (Al₂O₃), Silica (SiO2), Graphite Oxide, Graphene Oxide, Manganese Oxide (MgO), Aluminosilicate (Al2SiO5) and combinations thereof. These filter materials have proofed to be efficient in filtering hydrofluoric and/or hydrochloric acids.

For removing water and/or moisture from the refrigerant it is advantageous to use a filter unit which comprises a desiccant filter for filtering dissolved water and/or free water from the refrigerant. The filtering material of the desiccant filter is preferably selected from the group of Zeolite scavenger sorbents, such as calcium zeolites, sodium zeolites, potassium zeolites, magnesium zeolites and combinations thereof, with all sizes and shapes, and graphene oxide, and combinations thereof for filtering dissolved water, and polymers, such as water absorbing filter, for filtering free water. These kinds of filters are cost effective, commercially available and easy to handle.

According to a further preferred embodiment, the filter unit comprises a particle filter for filtering particles from the refrigerant, wherein a filtering material of the particle filter preferably is a stainless steel mesh, magnet for metallic particle and/or a combination thereof.

A further aspect of the present invention relates to a cooling system comprising a refrigerant cycle line for cycling refrigerant from at least a compressor unit for compressing gaseous refrigerant to a condenser unit for condensing gaseous refrigerant to liquid refrigerant, from the condenser unit to an optional expansion unit for expanding the liquid refrigerant, form the condenser or the optional expansion unit to an evaporator unit for evaporating the liquid refrigerant to gaseous refrigerant, and from the evaporating unit back to the compressor unit, wherein at least the compressor unit comprises a bearing arrangement as mentioned above.

Thereby it is preferred that the refrigerant supply line branches off from the refrigerant cycle line. This allows for a simplified design of the compressor and there is no need for an additional lubrication reservoir.

Further preferred embodiments are defined in the dependent claims as well as in the description and the figures. Thereby, elements described or shown in combi-nation with other elements may be present alone or in combination with other elements without departing from the scope of protection.

In the following, preferred embodiments of the invention are described in relation to the drawings, wherein the drawings are exemplarily only, and are not intended to limit the scope of protection. The scope of protection is defined by the accompanied claims, only.

Further preferred embodiments are defined in the dependent claims as well as in the description and the figures. Thereby, elements described or shown in combination with other elements may be present alone or in combination with other elements without departing from the scope of protection.

REFERENCE NUMERALS

- 100 Cooling system
- 10 Cooling cycle
- 12 compressor
- 14 condenser
- 16 evaporator
- 20 lubrication cycle
- 22 lubricating refrigerant supply line
- 22-1 first lubricating refrigerant supply line
- 22-2 second lubricating refrigerant supply line
- 23 main lubricating refrigerant supply line
- 30 lubricating refrigerant feedback line
- 32 check valve
- 60 check valve
- 24 first filter
- 26 second filter
- 25 combined filter
- 28 third filter
- 40 accumulator
- 42 first compartment
- 44 second compartment
- 46 spring force/gas pressure
- 48 piston/bladder
- 50 pump.

Refrigerant Lubricated Bearings

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