Refrigeration system with reduced compressor thrust load

Abstract

Example embodiments include a refrigeration system comprising: a compressor having a rotor separating a low pressure side from a high pressure side; a sump having a first fluid connection to the low pressure side of the compressor and a second fluid connection to the high pressure side of the compressor; a vent pipe fluidly connecting the first fluid connection and the second fluid connection; an intermediate reservoir located within the second fluid connection between the high pressure side of the compressor and the sump, where the intermediate reservoir is configured to collect oil from the compressor; and a valve located within the second fluid connection between the intermediate reservoir and the sump, where the valve is configured to release at least a portion of the oil from the intermediate reservoir in response to an oil level in the intermediate reservoir exceeding a liquid level setpoint.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 414,228, filed on October 7, 2023, entitled “REFRIGERATION SYSTEM WITH REDUCED COMPRESSOR THRUST LOAD,” which is expressly incorporated herein by reference in its entirety. Background Art

[0003] The described aspects relate to a refrigeration system, such as a chiller or a heat pump, using a lubricated compressor.

[0004] A refrigeration system, such as a chiller or heat pump, includes a compressor for compressing a refrigerant gas to a higher pressure, and a sump to collect lubricating oil used during operation of the compressor. Some refrigeration systems include at least a second compressor or auxiliary system in communication with the compressor and the sump, which provides an intermediate pressure stage between the compressor and the sump to further depressurize the sump to obtain better oil characteristics for operation with the compressor. In such a configuration, the pressure differential on opposite sides of the impeller / rotor of the compressor can result in increased thrust loads on the rotor support and / or bearings, which can result in a fault condition under some operating conditions.

[0005] Therefore, there is a need to improve refrigeration systems. Summary of the invention

[0006] A simplified summary of one or more aspects is presented below in order to provide a basic understanding of such aspects. The present invention content is not an extensive overview of all contemplated aspects, and is neither intended to identify the key or important elements of all aspects, nor to delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to a more detailed description presented later.

[0007] In one aspect, a refrigeration system includes: a compressor having a rotor separating a low-pressure side from a high-pressure side; a storage tank having a first fluid connection to the low-pressure side of the compressor and a second fluid connection to the high-pressure side of the compressor; a vent pipe fluidly connecting the first fluid connection and the second fluid connection; an intermediate reservoir located in the second fluid connection between the high-pressure side of the compressor and the storage tank, wherein the intermediate reservoir is configured to collect oil from the compressor; and a valve located in the second fluid connection between the intermediate reservoir and the storage tank, wherein the valve is configured to release at least a portion of the oil from the intermediate reservoir in response to the oil level in the intermediate reservoir exceeding a liquid level set point.

[0008] On the other hand, a compressor lubrication system includes: a first fluid connection between a tank and a low-pressure side of a compressor; a second fluid connection between the high-pressure side of the compressor and the tank; oil contained in the tank and configured to circulate from the tank via the first fluid connection to the low-pressure side of the compressor, through the compressor, and from the high-pressure side of the compressor to the tank via the second fluid connection during operation of the lubrication system; a vent pipe fluidly connecting the first fluid connection and the second fluid connection; an intermediate reservoir located in the second fluid connection between the high-pressure side of the compressor and the tank, wherein the intermediate reservoir is configured to collect oil from the compressor; and a valve located in the second fluid connection between the intermediate reservoir and the tank, wherein the valve is configured to release at least a portion of the oil from the intermediate reservoir in response to the oil level in the intermediate reservoir exceeding a liquid level set point. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The disclosed aspects will be described hereinafter in conjunction with the accompanying drawings, which are provided to illustrate and not to limit the disclosed aspects, wherein like reference numerals represent like elements, wherein dashed lines may represent optional elements, and wherein:

[0010] FIG. 1 is a schematic diagram of a prior art refrigeration system including an oil sump.

[0011] 2 is a cross-sectional view of a compressor lubrication circuit and oil sump of a prior art refrigeration system.

[0012] 3 is a simplified schematic diagram of the compressor lubrication circuit and oil sump of FIG. 2 .

[0013] 4 is a simplified schematic diagram of the compressor lubrication circuit and oil sump of FIG. 2 , but additionally including a pressure relief device positioned between the sump and the compressor inlet.

[0014] 5 is a simplified schematic diagram of the compressor lubrication circuit and oil sump of FIG. 2 similar to FIG. 4 , but additionally including a pressure relief device located between the sump and a low pressure point in the refrigeration system.

[0015] 6 is a simplified schematic diagram of the compressor lubrication circuit and oil sump of FIG. 2 , including an ejector pump, also referred to as a jet pump, implemented as a pressure relief device associated with the sump.

[0016] 7 is a simplified schematic diagram of the compressor lubrication circuit and oil sump of FIG. 2 , additionally including an auxiliary condenser implemented as a pressure reducing device associated with the sump.

[0017] Figure 8 is a partial cross-sectional side view of an example of an impeller / rotor and corresponding support structure for a compressor according to some aspects of the present invention.

[0018] Fig. 9is a simplified schematic diagram of a compressor lubrication circuit and oil sump of FIG. 2 similar to FIG. 5 , but incorporating an additional valve to control the pressure drop between the high pressure side of the compressor and the sump in accordance with aspects of the present invention.

[0019] Fig.10 is similar to Fig. 9 FIG. 2 is a simplified schematic diagram of a compressor lubrication circuit and oil sump, but with the gear chambers vented by an additional oil reservoir and an additional valve.

[0020] Figures 11A to 11HH is a cross-sectional view of a composite diagram of an example heat pump.

[0021] Fig.12 According to some aspects of the present invention Figures 11A to 11HH A simplified schematic diagram of a heat pump of FIG. 1 further including one or more valves to maintain high pressure refrigerant in the condenser when the heat pump is stopped. DETAILED DESCRIPTION

[0022] Various aspects are now described with reference to the accompanying drawings. In the following description, for the purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. However, it is apparent that such aspects may be practiced without these specific details.

[0023] The described aspects relate to a refrigeration system configured to increase the pressure in a gear cavity on one side of an impeller / rotor of a compressor, which results in a reduction in thrust loads on the impeller / rotor and corresponding support components during reverse thrust operation. Further, the described aspects are configured to maintain a tank connected to the compressor at a relatively low pressure compared to the pressure at the compressor, which allows the oil in the tank to have desired properties (e.g., viscosity, concentration, etc.). The described aspects include a valve, such as an expansion valve or any other valve in which internal pressure losses are controlled to produce a desired pressure drop, for controlling the pressure differential between the gear cavity and the tank. In addition, the described aspects include a vent pipe configured to connect the gear cavity to the compressor suction port, and an intermediate reservoir between the gear cavity and the tank, which collects oil and controllably releases the oil to the tank via operation of a valve based on the oil level in the intermediate reservoir.

[0024] In one example embodiment, which should not be construed as limiting, The CYK compound centrifugal chiller / heat pump system ("CYK system") may include a valve, such as an expansion valve, that controls a differential pressure set point between the gear chamber and the sump (on a CYK system, typically the saturation temperature in the gear chamber is 35°C and the saturation temperature in the sump is 20°C). Additionally, in this example embodiment, the gear chamber leads directly to the compressor suction port via a vent pipe, and oil from the gear chamber is collected in an intermediate reservoir equipped with a level probe that communicates with the valve. The valve monitors the oil level relative to the level set point in the intermediate reservoir, controllably releasing the collected oil back to the sump. It should be understood that the configuration may be varied and still be within the principles of the described aspects. For example, the gear chamber may alternatively be any low pressure area in the system, such as a vented evaporator, and the intermediate reservoir may be integrated into the gear chamber or other low pressure area, rather than as a separate component.

[0025] The described aspects allow reducing the loads on the compressor, and in particular the loads on the impeller / rotor and the corresponding support structure, during reverse thrust, which increases the efficiency and reliability of the refrigeration system.

[0026] Various aspects discussed in detail below may be implemented in any of the systems described in FIGS. 1-12 .

[0027] Referring to FIG. 1 , a typical refrigeration system 21 includes a motor / compressor 23 in fluid communication with a condenser 25, which is in fluid communication with an evaporator 27. The refrigerant gas is compressed to a higher pressure in the compressor 23. The high-pressure refrigerant gas is condensed into a high-pressure liquid via heat exchange (not shown) after flowing to the condenser 25. The high-pressure refrigerant liquid is then sent to the evaporator 27. The expansion valve 31 between the condenser 25 and the evaporator 27 expands the high-pressure refrigerant liquid into a mist, which is a mixture of gas and liquid at a lower temperature. In the evaporator 27, as the liquid refrigerant mist changes from a liquid phase to a gas phase, the liquid refrigerant is evaporated, absorbing heat from the heat exchange fluid. The cooled heat exchange fluid can be sent directly to the building environment or indirectly to an intermediate medium, such as a chiller for storing cooling water until it is needed. The refrigerant gas from the evaporator 27 is at a low pressure after the phase change and is used as a refrigerant gas source for the compressor 23. A storage tank 10 is also depicted in FIG. 1 , which collects oil from the operation of the compressor 23 and is essential for the normal operation of the compressor 23. As shown, the sump 10 is located below the compressor so that the lubricating oil flows to the sump 10 by gravity.

[0028] Referring to FIG. 2 , a prior art centrifugal compressor 23 includes an associated sump system 10 in which some lubricating oil is retained in an auxiliary oil reserve 32 intended to maintain some oil supply during coasting in the event of a power outage. The compressor 23 includes an inlet 34 that receives refrigerant gas from a low pressure source, typically an evaporator (as shown in FIG. 1 ). The refrigerant gas is compressed by an impeller 36 before being delivered to a volute 38. Lubrication is provided to lubricate the shaft seal 40, the main journal and thrust bearing 42, the thrust ring 44, the double bellows shaft seal 46, the low speed gear rear bearing 48, the pinion shaft bearing 50, the thrust ring bearing 52, and the low speed gear 54. Since a small amount of pressurized refrigerant gas always leaks from the impeller 36 into the various lubricated components mentioned above, the lubricant and the refrigerant come into contact with each other. After lubricating the compressor components, the lubricant / refrigerant mixture is discharged into the sump 10 by gravity through a conduit 56. As the refrigerant gas settles in the oil sump 10 before recirculation, refrigerant gas in excess of the steady-state solubility is released from the mixture, depending on the pressure and temperature conditions in the sump. Although the exact amount of refrigerant that may be collected in the sump 10 at any one time is difficult to measure, it is estimated that the refrigerant absorbed by the oil and that should be separated in the sump 10 is about 1-3% of the total flow of the compressor. In order to avoid undesirable oil viscosity when the oil cools once the compressor is stopped, an oil heater 57 is provided to heat or maintain the lubricant within a predetermined temperature range so that the lubricant has an appropriate viscosity as soon as the compressor 23 is started. The fluid is pumped from the sump 10 by a submersible pump 60 and sent to an oil cooler 62, which is only started when the oil is above its predetermined operating temperature. The refrigerant gas separated from the oil in the sump is sent to the compressor inlet 34 through a vent line 102 (see FIG. 3 ), while the oil that may still include miscible refrigerant gas is sent to the oil reserve 32, where the oil is metered to the compressor for lubrication purposes, after which the lubrication cycle is repeated.

[0029] In heat pump systems where evaporation pressure and temperature tend to be significantly higher than the evaporation pressure and temperature in water coolers, the oil temperature should also be set to a higher value to keep the oil dilution at an acceptable value. Due to this higher temperature, if the oil of the same grade as in the water cooler system is used, the viscosity of the oil will decrease. Oil grades with higher viscosity can be used to compensate for the higher temperatures experienced in heat pump systems. However, even if this compensation is performed for viscosity, the temperature increase of the oil in such heat pump systems can also cause other problems. One of them is the risk of failure of shaft seals and bearings if the oil temperature is too high. Aspects described herein provide a system that compensates for some differences between the operation of standard coolers and higher temperature heat pumps, which are due to the temperature difference that also affects the operation of the oil temperature. These aspects should expand the scope of application of the current standard compressor system used in cooler applications to heat pump applications, with only minor, inexpensive modifications.

[0030] 3, a simplified lubrication cycle schematic includes a compressor 23 and a sump 10, from which lubricant and miscible refrigerant are discharged through conduit 56 to the sump 10. The refrigerant gas at the sump pressure then returns to the compressor inlet along gas conduit 102, while the lubricant with miscible refrigerant returns to the compressor 23 along conduit 104.

[0031] Referring to FIG. 4 , a simplified lubrication cycle schematic includes the compressor 23 and the sump 10 and additionally includes a pressure reducing device 409 positioned between the sump 10 and the compressor inlet 34 to extract refrigerant gas from the sump while reducing the pressure of the refrigerant gas in the sump. Although the pressure reducing device 409 is shown as being connected to the inlet of the compressor 34 via a connector 411 , it is not limited thereto, and as will be appreciated by those skilled in the art, the pressure reducing device 409 can be connected to any low-pressure point of the refrigeration circuit. Most commonly, the low-pressure point is the evaporator 27 , but it can also be connected to the evaporator 27 or the system between the evaporator inlet and the compressor inlet 34 , including the compressor inlet 34 , via any connector. The pressure reducing device 409 is capable of reducing the pressure (and temperature) of the refrigerant gas in the oil sump. As previously described, the reduction in the pressure of the refrigerant gas in the oil sump 10 has the beneficial effect of reducing the dilution of the refrigerant in the oil, thereby mitigating the reduction in oil viscosity while providing proper lubrication of the shaft seals and bearings. Reducing the refrigerant pressure in the oil sump initiates a "virtuous cycle" that combines several combined benefits, one of which is the ability of the refrigeration system 21 to operate at higher evaporating temperatures and pressures, such as those encountered under heat pump conditions. When operating under such heat pump conditions, the goal of the pressure reduction is to set the oil sump gas pressure to a value consistent with the validation range for the same compressor when operating as a water chiller. Thus, if a given type of compressor is validated, for example, for an evaporating temperature of 20°C (68°F) for a given refrigerant, the goal would be to set a sump pressure corresponding to a saturation temperature of 20°C in heat pump operation so as to set all lubrication parameters to the same standard values ​​as for the chiller. Although all of the details of the system as shown in FIG. 2 are not shown in the simplified version of FIG. 4 , it should be understood that all of the details of the system shown in FIG. 2 may also be in the simplified system of FIG. 4 , except that the pressure reducing device 409 is included between the sump and the low pressure point of the refrigeration system 21 .

[0032] The pressure reduction in the oil sump can be achieved in different ways.

[0033] Referring to FIG5 , for example, a simplified lubrication cycle schematic includes the compressor 23 and the sump 10, and additionally includes a pressure reducing device 509 located between the sump and the low pressure point of the refrigeration system 21. Although all details of the system as shown in FIG2 are not shown in the simplified version of FIG5 , it should be understood that all details of the system shown in FIG2 can also be in the simplified system of FIG5 , except that the pressure reducing device 509 is included between the sump and the low pressure point of the refrigeration system 21. In one aspect, the pressure reducing device 509 is a small additional "auxiliary" compressor 509 positioned between the sump 10 and the compressor inlet 34 to extract refrigerant gas from the sump 10 while reducing the pressure of the refrigerant gas in the sump. The suction side of the auxiliary compressor 509 is connected to the gas volume of the oil sump 10, and its discharge side is connected to the compressor inlet 34 of the main compressor 23, for example. In this embodiment, the capacity of the auxiliary compressor 509 is controlled in such a way that it maintains the refrigerant pressure in the oil sump 10 at a preselected value as described above (e.g., corresponding to the saturation pressure of the refrigerant fluid at 20° C. in the above example). As described above, the discharge of the auxiliary compressor 509 may also be connected to any lower pressure point in the refrigeration system 21, such as the evaporator 27 or any point between the evaporator 27 and the compressor inlet 34, as shown in FIG.

[0034] Referring to FIG6, in another example, a simplified lubrication cycle schematic includes the compressor 23 and the sump 10, and additionally includes an ejector pump 609, also referred to as an ejector pump, which is implemented as a pressure reducing device associated with the sump 10. Likewise, all details of the system as shown in FIG2 are not shown in the simplified version of FIG6, and it should be understood that all details of the system shown in FIG2 can also be in the simplified system of FIG6, except that the ejector pump 609 is positioned between the sump 10 and the low pressure point of the refrigeration system. In FIG6, high pressure gas from a conduit 615 in fluid communication with the condenser 25 is used to provide energy to operate the ejector pump 609 after passing through an expansion valve (not shown), if necessary. At the ejector outlet, a mixture of this high pressure refrigerant fluid from the condenser 25 and the low pressure gas pumped out from the oil sump 10 is sent to a low pressure point in the refrigeration system, preferably to the evaporator. Although shown in FIG6 as being in direct fluid communication with the compressor inlet 34 via conduit 611 (for consistency with FIGS. 4 and 5), the low pressure point may be located at any intermediate location between the compressor 23 and the evaporator 27 at low pressure, as previously discussed. An advantage of this embodiment using an ejector pump is that it avoids moving parts such as found when using the auxiliary compressor 509 of FIG5.

[0035] Referring to FIG. 7 , in another example, a simplified lubrication cycle schematic includes a compressor 23 and a sump 10, and further includes an auxiliary condenser 709 implemented as a pressure reducing device associated with the sump 10. Likewise, all details of the system as shown in FIG. 2 are not shown in the simplified version of FIG. 7 , and it should be understood that all details of the system shown in FIG. 2 may also be included in the simplified system of FIG. 7 , except that the auxiliary condenser 709 is included between the sump 10 and the low pressure point of the refrigeration system. In FIG. 7 , the refrigerant gas from the sump 10 is in fluid communication with the auxiliary condenser 709 via a conduit 713. The gas from the sump 10 enters the auxiliary condenser 709, where the gas is in heat exchange relationship with the cooling fluid flowing through the cooling circuit 715. The cooling fluid in the cooling circuit 715 cools the refrigerant gas, condensing it from a gas into a liquid, and the liquid refrigerant is sent to the liquid storage space 717 via a conduit 730.

[0036] The auxiliary condenser 709 is selected to provide a condensing pressure equal to the required refrigerant pressure in the oil storage tank 10. In one aspect, the refrigerant gas in the auxiliary condenser 709 is cooled by a cooling fluid having a temperature lower than that of the cold source of the heat pump. For example, if the desired condensing pressure in the auxiliary condenser 709 corresponds to a saturation temperature of 20°C (68°F), the auxiliary condenser 709 is preferably cooled with water having an inlet temperature of about 12°C (about 54°F) and a leaving temperature of about 18°C ​​(about 64°F). The cooling water can be provided by any available chilled water source and by groundwater within the required temperature range. The condensing pressure in the auxiliary condenser 709 can be controlled by changing the flow rate and / or temperature of the cooling fluid of the cooling circuit 715 of the auxiliary condenser 709 to maintain the desired gas pressure in the oil storage tank 10. As described in Figure 7, the liquid storage space 717 for condensing the refrigerant can be a separate container as shown in the figure, or can be a separate storage space integral with the auxiliary condenser 709.

[0037] According to the principle of the system, the liquid storage space 717 is at a lower pressure than the compressor inlet and the evaporator in the main refrigerant circuit. In order to avoid the accumulation of liquid refrigerant in the liquid storage space 717, the refrigerant is pumped back from the storage space 717 to the refrigerant system 21 by a pump 719 controlled by a liquid level sensor 721. The suction side of the pump 719 is connected to the fluid storage space 717, and its discharge side is in fluid communication with the refrigerant system 21. In order to reduce the head and absorption power of the pump, it is preferred to set the pump discharge port to the low-pressure part of the main refrigerant circuit 21. Although this low-pressure area can be the compressor inlet 34, as previously discussed with respect to Figures 3 to 6, Figure 7 depicts the low-pressure area as a conduit between the expansion valve 31 and the evaporator 27, although the refrigerant can be sent to the low-pressure area at any convenient point (such as between the expansion valve 31 and the compressor suction port 34). It is also generally desirable to avoid sending the refrigerant liquid directly from the liquid storage space 717 into the compressor suction port 34 (inlet) to avoid liquid overflow of the compressor 23. Therefore, a location along the conduit between the expansion valve 31 and the evaporator 27 is a desired and preferred refrigerant input, as is supplying the liquid refrigerant to the evaporator 27, such as at the liquid inlet of the evaporator 27. More specifically, if the evaporator 27 employs dry expansion technology (shell and tube or plate heat exchanger), it is desirable to discharge the liquid refrigerant into the main liquid line at the evaporator inlet. If the evaporator 27 is a flooded, falling film, or hybrid falling film type, an alternative is to discharge the liquid directly into the evaporator shell at a location away from the suction line to avoid liquid carryover to the compressor inlet 34.

[0038] In one aspect, the system includes a mechanism to control the operation of the liquid pump 719, where an example of such a mechanism is depicted in FIG7 as a liquid level sensor 721. A desired arrangement is to have the fluid storage volume 717 located at the outlet of the auxiliary condenser 709, thereby allowing liquid refrigerant to flow from the auxiliary condenser 709 into the storage volume 717 by gravity. This volume can be contained in the same housing as the auxiliary condenser 709, or as a separate container. The liquid level in this storage volume is sensed by a liquid level sensor, which includes a control loop, simply depicted as liquid level sensor 721. This control loop portion of the liquid level sensor 721 manages the operation of the liquid pump 719 so as to maintain the liquid level in the fluid storage volume 717 within predetermined, preset acceptable limits. The liquid pump 719 can have a variable speed drive, the speed of which is controlled by the control loop of the liquid level sensor 721, or it can simply have an on / off sequence of operation, also under the control of the same control loop.

[0039] In another embodiment, the conventional mechanical pump 719 can be replaced by a purely static pumping system. In a variation of this aspect, the static pumping system can utilize an ejector pump 609 powered by high pressure gas from the main condenser 25. A mixture of pumped liquid from the fluid storage space 717 and high pressure gas from the main condenser 25 is returned to the evaporator 27. In another variation of this aspect, two fluid storage containers 717 can be located below the auxiliary condenser 715, each having an inlet (A) connected to the discharge port of the auxiliary condenser 709 to receive condensed refrigerant liquid, an inlet (B) connected to receive gas from the evaporator or main condenser 25, and each fluid storage container having an outlet (C) connected to the evaporator 27. Each of these connections has an automatic valve that can be opened or closed. The system is activated by a control circuit and operates in a "batch" manner.

[0040] Any of these described aspects can remove refrigerant from the oil in the lubricated compressor, and the present disclosure is not limited to use with centrifugal compressors. These aspects can also be used for reciprocating compressors, scroll compressors and turbines used in ORC systems, each of which requires lubrication. Auxiliary compressor 509 or ejector pump 609 can be advantageously used to remove refrigerant from the oil in these units, as described above. Assuming that water at the desired temperature is available, auxiliary condenser 709 has the further advantage of not requiring electricity to operate, although it is achieved using liquid pump 719.

[0041] The basic pressure reducing devices described above with reference to Figures 4 to 7 for separating the refrigerant from the lubrication system can also be applied to the refrigeration circuit to extend the operating limits of the refrigerant fluid used to cool the semi-hermetic motor. These pressure reducing devices 409 can be advantageously used in heat pump systems, which are usually operated at higher temperatures than chiller systems. These pressure reducing devices 409 extend the motor cooling capacity of the refrigerant, allowing the chiller system equipment to be used for heat pump applications. In these systems, the refrigerant is used to cool the motor and the motor cavity to prevent the heat generated when the motor is in operation. In the absence of such pressure reducing devices, the pressure in the motor housing and in the coils surrounding the motor stator is almost equal to or slightly higher than the pressure in the evaporator. However, the pressure reducing device is controlled to maintain the pressure in the motor cavity at a preset value below the pressure at the compressor inlet and preferably below the pressure of the evaporator, so that the refrigerant gas can be drawn through the housing. For systems operating in heat pump applications, it is necessary to maintain the pressure in the motor cavity at a preset value below the pressure at the compressor inlet, for example, at a saturation temperature of 20°C corresponding to the required pressure of a given refrigerant. These values ​​usually correspond to the temperature at which the compressor is verified when the system is operated as a water chiller system.

[0042] refer to Figure 8In the operation of any of the above examples described in Figures 1 to 7, the load on the impeller / rotor of the compressor 23 and the corresponding support structure may increase to or exceed a fault condition, such as during reverse thrust operation. For example, in a refrigeration system with a single compressor, the tank pressure is close to the suction pressure of the compressor, while the discharge pressure is typically much higher. Forward thrust and reverse thrust are designed for safe operation under design conditions. When a refrigeration system such as a YORK CYK-R134a system is used at a maximum pressure where the reverse thrust margin is not so high, the described aspects can reduce the reverse thrust load. In addition, on a heat pump using a low-pressure refrigerant (e.g., R1234ze, R1233zd), it is allowed to use a standard YK compressor at the HP level of CYK (these compressors typically have a lower reverse thrust maximum load compared to high-pressure compressors). Further, for example, in a refrigeration / heat pump system with an auxiliary system, the load on the high-speed reverse thrust increases. For example, when the pressure is reduced by the compressor 509 (or by the ejector 609, or otherwise by the heat exchanger 709), this increased thrust load may occur because the force exerted by the internal pressure of the gear on the rotor support area is reduced, and then the load on the reverse thrust increases. Under certain extreme conditions, the maximum available load of the reverse thrust may be exceeded and the system can no longer operate.

[0043] refer to Fig. 9 , a simplified lubrication cycle schematic includes a compressor 23 and a sump 10, and further includes a pressure reducing device 509 located between the sump and a low pressure point of the refrigeration system 21, and a valve 902 that controls the pressure drop between the gearbox or high pressure side of the compressor 23 and the sump 10 to reduce the thrust load on the compressor 23. Although all details of the system shown in FIG. 2 are not included in the drawings, Fig. 9 2 is shown in a simplified version, but it should be understood that all details of the system shown in FIG. 2 can also be Fig. 9 In the simplified system of , except that the pressure reducing device 509 is included between the storage tank and the low pressure point of the refrigeration system 21, and the valve 902 (such as an expansion valve) is included between the gear box of the compressor 23 and the storage tank 10. Fig. 9 In the embodiment, valve 902, such as an expansion valve or any valve in which internal pressure loss is controlled to produce a desired pressure drop, can control the differential pressure set point between the gear chamber on the high pressure side of the compressor 23 and the sump 10. For example, in a YK-R1234ze or CYK-R1234ze heat pump system, a saturation temperature of 35° C. may exist in the gear chamber, while a saturation temperature of 20° C. may exist in the sump. Valve 902 can be controlled to allow an acceptable load on the reverse thrust.

[0044] Example 1

[0045] The above aspects were tested in an exemplary CYK assistance system for the R1234ze model.

[0046] The table below shows the thrust loads calculated from this test, comparing the effect of the expansion valve on the thrust loads.

[0047]

[0048] Results from Example 1

[0049] -100% load:

[0050] Without the expansion valve 902, the saturation temperature in the gear chamber is 18°C ​​and the total thrust load is 839 kg.

[0051] oWith the expansion valve 902, the saturation temperature in the gear chamber increases to 35°C, and the total thrust load is 147kg.

[0052] -25% load:

[0053] Without the expansion valve 902, the saturation temperature in the gear chamber is 18°C ​​and the total thrust load is 1282 kg.

[0054] oWith the expansion valve 902, the saturation temperature in the gear chamber increases to 35°C, and the total thrust load is 590kg.

[0055] - In some operation modes, using the CYK system without the expansion valve 902 may result in thrust failure, as the thrust load should be kept below 600 kg for reliable operation. Therefore, the use of the expansion valve 902 helps to reduce the thrust load and improve the operation of the system.

[0056] refer to Fig.10 , on the other hand, a simplified lubrication cycle schematic similar to that of FIGS. 5 to 7 includes the addition of an expansion valve 902 and a vent line 1005 through an intermediate reservoir 1010, which operate in conjunction to reduce the thrust load on the compressor 23. The addition of a valve 902 (such as an expansion valve) and a vent line 1005 through an intermediate reservoir 1010 acting as an additional oil receiver can similarly control the differential pressure set point between the gear cavity on the high pressure side of the compressor 23 and the sump 10, thereby allowing an acceptable load on reverse thrust.

[0057] In this regard, the gear chamber on the high pressure side of the compressor 23 is directly connected to the compression suction port through the vent pipe 1005. The vent pipe 1005 is connected to the intermediate reservoir 1010, which collects the oil from the gear chamber. Further, the liquid level set point 1015 is maintained in the intermediate reservoir 1010 by the valve 902. For example, a sensor such as a liquid level probe can monitor the oil level relative to the liquid level set point 1015 and provide a signal to the control circuit, and when the oil level exceeds the liquid level set point 1015, the control circuit operates to open the valve 902. Therefore, the oil exceeding the liquid level set point 1015 in the intermediate reservoir 1010 is sent back to the storage tank 10. The storage tank 10 is stabilized by the compressor 509, wherein the configuration allows the compressed refrigerant gas to pass through the vent pipe 511 to stabilize the pressure difference between the gear chamber on the high pressure side of the compressor 23 and the storage tank 10.

[0058] in other words, Fig.10 The system can be implemented in a refrigeration system such as that described in Figure 1, and can include: a compressor 23 having a rotor separating a low-pressure side from a high-pressure side; a storage tank 10 having a first fluid connection to the low-pressure side of the compressor 23 and a second fluid connection to the high-pressure side of the compressor 23; a vent pipe 1005, which fluidly connects the first fluid connection and the second fluid connection; an intermediate storage 1010, which is located in the second fluid connection between the high-pressure side of the compressor 23 and the storage tank 10, wherein the intermediate storage 1010 is configured to collect oil from the compressor 23; and a valve 902, which is located in the second fluid connection between the intermediate storage 1010 and the storage tank 10, wherein the valve 902 is configured to release at least a portion of the oil from the intermediate storage 1010 in response to the oil level in the intermediate storage 1010 exceeding a liquid level set point; and a compressor 509, which allows the pressure in the storage tank to be reduced by returning a mass of refrigerant gas to the compressor 34.

[0059] In another embodiment, Fig.10 The system can be implemented in a compressor lubrication system, which includes: a first fluid connection between a reservoir and a low-pressure side of a compressor; a second fluid connection between the high-pressure side of the compressor and the reservoir; oil contained in the reservoir and configured to circulate from the reservoir to the compressor, through the compressor, and from the high-pressure side of the compressor to the reservoir via the second fluid connection during operation of the lubrication system due to an oil pump (not shown); a vent pipe fluidly connecting the first fluid connection and the second fluid connection; an intermediate reservoir located in the second fluid connection between the high-pressure side of the compressor and the reservoir, wherein the intermediate reservoir is configured to collect oil from the compressor; and a valve located in the second fluid connection between the intermediate reservoir and the reservoir, wherein the valve is configured to release at least a portion of the oil from the intermediate reservoir in response to the oil level in the intermediate reservoir exceeding a liquid level set point.

[0060] In some embodiments, the vent line 511 may be connected to the evaporator or any low pressure area in the refrigeration or heat pump unit.

[0061] Additionally, in some embodiments, the intermediate reservoir 1010 may be integrated into the gear cavity rather than being a separate component.

[0062] Furthermore, it should be understood that although described with reference to FIGS. 5 and 9, Fig.10 The aspects of may be similarly applied to the aspects of FIGS. 6 and 7 , and / or to a multi-stage compressor system.

[0063] refer to Figures 11A to 11HH and 12, on the other hand, the heat pump 1100 is configured to allow high-pressure refrigerant to be maintained in the condenser 1120 even when the heat pump is stopped.

[0064] In one example, the heat pump 1100 includes a first compressor 1102 and a second compressor 1105, wherein the first compressor 1102 represents a relatively high pressure stage and the second compressor 1105 represents a relatively low pressure stage. Each compressor has a pressure regulation system with a sump (or oil reservoir), such as a sump 1110 for the compressor 1102 and a sump 1115 for the compressor 1105. The compressor 1102 outputs to a condenser 1120, which in turn outputs to an economizer 1130. The evaporator 1125 outputs to the compressor 1105. The economizer 1130 also has outputs to both the compressor 1102 and the evaporator 1125.

[0065] exist Fig.12 In the aspects described, ( Figures 11A to 11HH The example heat pump 1100 has been modified to have a check valve 1240 located at the discharge port of the compressor 1102, and a fast-acting valve 1235 and a fast-acting valve 1199 located at the outlet of the condenser 1120.

[0066] Adding these valves 1235, 1240, 1199 allows the refrigerant to be isolated in the condenser 1120 when the heat pump 1100 is stopped (including during a normal stop or a safety stop). After stopping, the heat in the condenser 1120 (e.g., high pressure / high temperature refrigerant) is then retained in the condenser 1120, and the pressure in the evaporator 1125 is then reduced. This configuration greatly reduces the risk of a pressure relief valve discharge.

[0067] In some aspects, a solenoid valve may be located on the primary side of the injector to further prevent the pressure relief valve from discharging.

[0068] For example, Figures 11A to 11HHThe aspects of 12 can be implemented in a YORK YK or CYK heat pump system. In a CYK system, the first stage compressor is typically a standard air conditioning compressor with a design working pressure (DWP) of 235 psig, and the second stage compressor is a high pressure compressor with a DWP that can be 415 psig. The intermediate pressure under nominal conditions is usually selected so that each compressor has a similar compression ratio; this allows the system to maximize the benefits of the economizer in the thermodynamic cycle. When the heat pump stops, the refrigerant in the high pressure / high temperature part of the heat pump (mainly concentrated at the condenser) is mixed with the refrigerant in the low pressure part of the heat pump (economizer, evaporator, etc.), and then the pressure inside the heat pump reaches equilibrium. Under certain extreme conditions before stopping, the equilibrium pressure may be higher than the DWP of the first stage compressor. In this case, the pressure relief valve will open to protect some heat pump components. Recently, there has been an increase in demand for such heat pumps operating at higher evaporation temperatures. For example, in the case of geothermal heat source applications, the evaporation temperature may be about 20°C under nominal conditions and 60°C under partial load. Considering a condenser outlet temperature of 90°C (e.g. for district heating discharge), the pressure may equilibrate at a saturation temperature close to 75°C. In these cases, the risk of the pressure relief valve opening is high. Therefore, the CYK system may be modified to include a check valve 1240 at the discharge of the compressor 1105, and fast acting valves 1235 and 1199 at the outlet of the condenser 1120, which allows the system to keep high pressure refrigerant in the condenser when the heat pump is stopped.

[0069] In addition, it should be understood that the above Fig. 9 or 10 described aspects for reducing the thrust load on the compressor may be Figures 11A to 11HH and 12 are implemented in the heat pump system described.

[0070] Other aspects of the disclosure are described in the following clauses:

[0071] Item 1. A compressor lubrication system comprising: a first fluid connection between a tank and a low-pressure side of a compressor; a second fluid connection between the high-pressure side of the compressor and the tank, wherein the lubrication system is configured to circulate oil contained in the tank from the tank, through the compressor, and from the high-pressure side of the compressor to the tank via the second fluid connection during operation; a vent pipe fluidly connecting the first fluid connection and the second fluid connection; an intermediate reservoir located in the second fluid connection between the high-pressure side of the compressor and the tank, wherein the intermediate reservoir is configured to collect oil from the compressor; and a valve located in the second fluid connection between the intermediate reservoir and the tank, wherein the valve is configured to release at least a portion of the oil from the intermediate reservoir.

[0072] Clause 2. The compressor lubrication system of Clause 1, wherein the valve releases the at least a portion of the oil from the intermediate reservoir in response to the oil level in the intermediate reservoir exceeding a level set point.

[0073] Clause 3. A compressor lubrication system according to any of the preceding clauses, further comprising a sensor for monitoring the oil level relative to the liquid level set point and providing a signal to a control circuit, wherein when the oil level exceeds the liquid level set point, the control circuit operates to open the valve to release at least a portion of the oil.

[0074] Clause 4. The compressor lubrication system of the preceding clause, wherein the sensor is a fluid level probe.

[0075] Clause 5. The compressor lubrication system of any preceding clause, further comprising an oil pump for circulating oil from the sump to the compressor.

[0076] Clause 6. The compressor lubrication system of any preceding clause, wherein the vent line is in fluid communication with an evaporator of a refrigeration system.

[0077] Clause 7. Compressor lubrication system according to any of the preceding clauses, wherein the intermediate reservoir is integrated into a gear cavity of the compressor.

[0078] Clause 8. The compressor lubrication system of any preceding clause, further comprising the compressor and the sump to define a refrigeration system.

[0079] Clause 9. The compressor lubrication system of any preceding clause, wherein the refrigeration system is a heat pump refrigeration system.

[0080] Clause 10. The compressor lubrication system of any preceding clause, wherein the refrigeration system further comprises an economizer.

[0081] Clause 11. The compressor lubrication system of any of the preceding clauses, wherein the compressor comprises a first stage compressor and a second stage compressor, the first stage compressor having the first and second fluid connections connected thereto.

[0082] Clause 12. The compressor lubrication system of any preceding clause, further comprising one or more isolation valves for isolating the refrigerant when the heat pump is stopped.

[0083] Clause 13. The compressor lubrication system of any preceding clause, wherein the one or more isolation valves are fast acting valves.

[0084] Clause 14. The compressor lubrication system of any of the preceding clauses, further comprising a condenser, wherein the system is configured to allow high pressure refrigerant to be maintained in the condenser when the heat pump is stopped.

[0085] Clause 15. A compressor lubrication system according to any of the preceding clauses, wherein the compressor comprises a first stage compressor and a second stage compressor, wherein a first compressor lubrication system according to any of the preceding clauses provides lubricant to the first stage and a second compressor lubrication system provides lubricant to the second stage.

[0086] Although the foregoing disclosure discusses illustrative aspects and / or embodiments, it should be noted that various changes and modifications may be made herein without departing from the scope of the described aspects and / or embodiments as defined by the appended claims. Furthermore, although elements of the described aspects and / or embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is expressly provided. Additionally, all or part of any aspect and / or embodiment may be used together with all or part of any other aspect and / or embodiment, unless otherwise indicated.

Claims

1. A compressor lubrication system, comprising: a first fluid connection between the sump and the low pressure side of the compressor; a second fluid connection between the high pressure side of the compressor and the sump, wherein the lubrication system is configured to circulate oil contained in the sump from the sump, through the compressor, and from the high pressure side of the compressor to the sump via the second fluid connection during operation; a vent pipe fluidly connecting the first fluid connection member and the second fluid connection member; an intermediate reservoir located within the second fluid connection between the high pressure side of the compressor and the sump, wherein the intermediate reservoir is configured to collect oil from the compressor; as well as A valve is located in the second fluid connection between the intermediate reservoir and the sump, wherein the valve is configured to release at least a portion of the oil from the intermediate reservoir. 2 . The compressor lubrication system of claim 1 , wherein the valve releases the at least a portion of the oil from the intermediate reservoir in response to the oil level in the intermediate reservoir exceeding a level set point.

3. The compressor lubrication system of claim 2, further comprising a sensor for monitoring the oil level relative to the level set point and providing a signal to a control circuit, wherein when the oil level exceeds the level set point, the control circuit operates to open the valve to release the at least a portion of the oil.

4. The compressor lubrication system of claim 3, wherein the sensor is a fluid level probe.

5. A compressor lubrication system according to any one of the preceding claims, further comprising an oil pump for circulating oil from the sump to the compressor.

6. A compressor lubrication system according to any one of the preceding claims, wherein the vent line is in fluid communication with an evaporator of a refrigeration system.

7. Compressor lubrication system according to any of the preceding claims, wherein the intermediate reservoir is integrated into a gear chamber of the compressor.

8. A compressor lubrication system according to any one of the preceding claims, further comprising the compressor and the sump to define a refrigeration system.

9. The compressor lubrication system of claim 8, wherein the refrigeration system is a heat pump refrigeration system.

10. The compressor lubrication system of claim 8 or 9, wherein the refrigeration system further comprises an economizer.

11. The compressor lubrication system of claim 9 or 10, wherein the compressor comprises a first stage compressor and a second stage compressor, the first stage compressor having the first fluid connection and the second fluid connection connected thereto.

12. The compressor lubrication system according to claims 9 to 11, further comprising one or more isolation valves for isolating the refrigerant when the heat pump is stopped.

13. A compressor lubrication system according to claims 9 to 12, wherein the one or more isolation valves are fast acting valves.

14. The compressor lubrication system of any one of claims 9 to 13, further comprising a condenser, wherein the system is configured to allow high pressure refrigerant to be maintained in the condenser when the heat pump is stopped.

15. The compressor lubrication system of claim 8, wherein the compressor comprises a first stage compressor and a second stage compressor, wherein a first compressor lubrication system according to any one of claims 1 to 7 provides lubricant to the first stage and a second compressor lubrication system provides lubricant to the second stage.

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