Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B1/00—Compression machines, plants or systems with non-reversible cycle
  • F25B1/04—Compression machines, plants or systems with non-reversible cycle with compressor of rotary type
  • F25B1/053—Compression machines, plants or systems with non-reversible cycle with compressor of rotary type of turbine type
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D17/00—Radial-flow pumps, e.g. centrifugal pumps; Helico-centrifugal pumps
  • F04D17/08—Centrifugal pumps
  • F04D17/10—Centrifugal pumps for compressing or evacuating
  • F04D17/12—Multi-stage pumps
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D23/00—Other rotary non-positive-displacement pumps
  • F04D23/001—Pumps adapted for conveying materials or for handling specific elastic fluids
  • F04D23/003—Pumps adapted for conveying materials or for handling specific elastic fluids of radial-flow type
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D25/00—Pumping installations or systems
  • F04D25/02—Units comprising pumps and their driving means
  • F04D25/06—Units comprising pumps and their driving means the pump being electrically driven
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D25/00—Pumping installations or systems
  • F04D25/16—Combinations of two or more pumps ; Producing two or more separate gas flows
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D27/00—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
  • F04D27/004—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids by varying driving speed
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/05—Shafts or bearings, or assemblies thereof, specially adapted for elastic fluid pumps
  • F04D29/051—Axial thrust balancing
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/05—Shafts or bearings, or assemblies thereof, specially adapted for elastic fluid pumps
  • F04D29/056—Bearings
  • F04D29/058—Bearings magnetic; electromagnetic
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/26—Rotors specially for elastic fluids
  • F04D29/28—Rotors specially for elastic fluids for centrifugal or helico-centrifugal pumps for radial-flow or helico-centrifugal pumps
  • F04D29/284—Rotors specially for elastic fluids for centrifugal or helico-centrifugal pumps for radial-flow or helico-centrifugal pumps for compressors
  • F04D29/286—Rotors specially for elastic fluids for centrifugal or helico-centrifugal pumps for radial-flow or helico-centrifugal pumps for compressors multi-stage rotors
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/40—Casings; Connections of working fluid
  • F04D29/42—Casings; Connections of working fluid for radial or helico-centrifugal pumps
  • F04D29/44—Fluid-guiding means, e.g. diffusers
  • F04D29/441—Fluid-guiding means, e.g. diffusers especially adapted for elastic fluid pumps
  • F04D29/444—Bladed diffusers

Definitions

• the present invention generally relates to a centrifugal compressor. More specifically, the present invention relates to a centrifugal compressor with a pair of compressors and a pair of motors.
• a chiller system is a refrigerating machine or apparatus that removes heat from a medium.
• a liquid such as water is used as the medium and the chiller system operates in a vapor-compression refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.
• refrigeration creates waste heat that must be exhausted to ambient or, for greater efficiency, recovered for heating purposes.
• a conventional chiller system often utilizes a centrifugal compressor, which is often referred to as a turbo compressor.
• turbo chiller systems can be referred to as turbo chillers.
• other types of compressors e.g. a screw compressor, can be utilized.
• a conventional centrifugal compressor basically includes a casing, an inlet guide vane, an impeller, a diffuser, a motor, various sensors and a controller. Refrigerant flows in order through the inlet guide vane, the impeller and the diffuser.
• the inlet guide vane is coupled to a gas intake port of the centrifugal compressor while the diffuser is coupled to a gas outlet port of the impeller.
• the inlet guide vane controls the flow rate of refrigerant gas into the impeller.
• the impeller increases the velocity of refrigerant gas.
• the diffuser works to transform the velocity of refrigerant gas (dynamic pressure), given by the impeller, into (static) pressure.
• the motor rotates the impeller.
• the controller controls the motor, the inlet guide vane and the expansion valve. In this manner, the refrigerant is compressed in a conventional centrifugal compressor.
• a conventional centrifugal compressor may have one or two stages.
• a motor drives the one or more impellers.
• each compressor's operating range will be dominated by impeller's operating range.
• a two stage compressor can have more limited operating range capability due to the fact that each stage can have its own boundary limits (choke flow limits, stall and surge limit, minimum unloading limit). Therefore, the compressor cannot or should not be operated when either impeller operates outside of the range.
• compressor efficiency will decline if either impeller does not operate at its designed point. The reason for this is due to the change of head coefficient and flow coefficient. Once these values are changed, the compressor cannot operate at its designed (Highest efficiency) point.
• one object of the present invention is to provide a centrifugal compressor that can maintain operation within the operating range.
• Another object of the present invention is to provide a centrifugal compressor that can improve efficiency.
• Yet another object of the present invention is to provide a centrifugal compressor that addresses one or more of the other discovered problems mentioned above or already known to those skilled in the art.
• a centrifugal compressor including a casing, a first compression mechanism and a second compression mechanism.
• the casing has a first inlet portion, a first outlet portion, a second inlet portion and a second outlet portion.
• the first compression mechanism includes a first inlet guide vane disposed in the first inlet portion, a first impeller disposed downstream of the first inlet guide vane, a first diffuser disposed in the first outlet portion downstream from the first impeller, and a first motor.
• the first impeller is attached to a first shaft rotatable about a first rotation axis.
• the first motor is arranged to rotate the first shaft in order to rotate the first impeller.
• the second compression mechanism includes a second inlet guide vane disposed in the second inlet portion, a second impeller disposed downstream of the second inlet guide vane, a second diffuser disposed in the second outlet portion downstream from the second impeller, and a second motor.
• the second impeller is attached to a second shaft rotatable about a second rotation axis.
• the second motor is arranged to rotate the second shaft in order to rotate the second impeller.
• Figure 1 is a schematic diagram illustrating a two stage chiller system (with an economizer) having a centrifugal compressor in accordance with an embodiment of the present invention
• Figure 2 is a perspective view of the centrifugal compressor of the chiller system illustrated in Figure 1, with portions broken away and shown in cross-section for the purpose of illustration;
• Figure 3 is a perspective view of internal parts (e.g., shafts, impellers, magnetic bearings and motors) of the centrifugal compressor illustrated in Figures 1-2;
• Figure 4 is an elevational view of the internal parts (e.g., shafts, impellers, magnetic bearings and motors) of the centrifugal compressor illustrated in Figure 3;
• Figure 5 is a schematic longitudinal partial cross-sectional view of the internal parts (e.g., shafts, impellers, magnetic bearings and motors) of the centrifugal compressor illustrated in Figures 3-4, with additional parts such as sensors, back-up bearings, coils, etc. schematically illustrated in more detail;
• internal parts e.g., shafts, impellers, magnetic bearings and motors
• Figure 6 is a flow chart illustrating a normal control of the centrifugal compressor illustrated in Figures 1-5;
• Figure 7A is a graph illustrating operating range of a two stage compressor (overall compressor operation), with A representing an overall operating point outside the overall operating range;
• Figure 7B is a graph illustrating operating range of a first stage impeller of the two stage compressor illustrated in Figure 7 A, with Al representing a fist stage operating point outside the first stage operating range;
• Figure 7C is a graph illustrating operating range of a second stage impeller of the two stage compressor illustrated in Figure 7A, with A2 representing a second stage operating point inside the second stage operating range;
• Figure 8A is a graph illustrating operating range of a two stage compressor (overall compressor operation), with A representing an overall operating point outside the overall operating range (like Figure 7A) and with B representing a shifted operating point within the overall operating range in accordance with the present invention;
• Figure 8B is a graph illustrating operating range of a first stage impeller of the two stage compressor illustrated in Figure 8 A, with Al representing a fist stage operating point outside the first stage operating range (like Figure 7B) and with Bl representing a shifted first operating point by decreasing the rotation speed of the first stage impeller in accordance with the present invention;
• Figure 8C is a graph illustrating operating range of a second stage impeller of the two stage compressor illustrated in Figure 7A, with A2 representing a second stage operating point inside the second stage operating range (like Figure 7C);
• Figure 9A is a graph illustrating efficiency of a two stage compressor (overall compressor efficiency), with E representing a designed highest efficiency point and with D and E representing shifted lower efficiency operating points;
• Figure 9B is a graph illustrating efficiency of a first stage impeller of the two stage compressor illustrated in Figure 9A, with El representing a designed highest efficiency point of the first stage and with Dl and El representing shifted lower efficiency operating points of the first stage;
• Figure 9C is a graph illustrating efficiency of a second stage impeller of the two stage compressor illustrated in Figure 9A, with E2 representing a designed highest efficiency point of the second stage and with D2 and E2 representing shifted lower efficiency operating points of the second stage;
• Figure 1 OA is a graph illustrating efficiency of a two stage compressor (overall compressor efficiency) like Figure 9A, with E representing a designed highest efficiency point and with D and E representing shifted lower efficiency operating points;
• Figure 10B is a graph illustrating efficiency of a first stage impeller of the two stage compressor illustrated in Figure 9 A, with El representing a designed highest efficiency point of the first stage and with Dl and Fl representing shifted lower efficiency operating points of the first stage, and with arrows illustrating how the efficiency can be increased from points Dl or Fl by reducing or increasing the first impeller speed, respectively; and
• Figure 10C is a graph illustrating efficiency of a second stage impeller of the two stage compressor illustrated in Figure 9 A, with E2 representing a designed highest efficiency point of the second stage and with D2 and F2 representing shifted lower efficiency operating points of the second stage, and with arrows illustrating how the efficiency can be increased from points D2 or F2 by reducing or increasing the second impeller speed, respectively.
• FIG. 1 a chiller system 10 having a centrifugal compressor 22 in accordance with an embodiment of the present invention is illustrated.
• the centrifugal compressor 22 of Figure 1 is a two stage compressor, and thus, the chiller system 10 of Figure 1 is a two stage chiller system.
• the two stage chiller system of Figure 1 also includes an economizer.
• Figure 1 merely illustrates one example of a chiller system in which the centrifugal compressor 22 in accordance with the present invention can be used.
• the economizer of the chiller system 10 can be eliminated.
• the economizer is present for the reasons discussed below.
• the chiller system 10 is conventional, except for the centrifugal compressor 22 and the manner in which the centrifugal compressor 22 is controlled.
• the centrifugal compressor 22 includes a structure and is controlled to maintain operation within its operating range and to improve efficiency, as explained in more detail below. Therefore the chiller system 10 will not be discussed and/or illustrated in detail herein except as related to the centrifugal compressor 22 the manner in which the centrifugal compressor 22 is controlled.
• the conventional parts of the chiller system 10 can be constructed in variety of ways without departing the scope of the present invention.
• the chiller system 10 is preferably a water chiller that utilizes cooling water and chiller water in a conventional manner.
• the chiller system 10 basically includes a chiller controller 20, the centrifugal compressor 22, a condenser 24, an expansion valve or orifice 25, an economizer 26, an expansion valve or orifice 27, and an evaporator 28 connected together in series to form a loop refrigeration cycle.
• the economizer 26 is connected between the first compression mechanism and the second compression mechanism in the refrigerant circuit (e.g., to the intermediate stage).
• Various sensors are disposed throughout the circuit of the chiller system 10.
• the compressor 22 is a two-stage centrifugal compressor in the illustrated embodiment.
• the compressor 22 illustrated herein includes two impellers.
• the compressor 22 may include three or more impellers (not shown).
• the two-stage centrifugal compressor 22 of the illustrated embodiment is conventional except that the compressor 22 includes separate motors used to drive the two impellers.
• the motors are controlled in accordance with the present invention.
• the centrifugal compressor 22 includes first and second stages fiddly connected in series so that refrigerant compressed in the first stage is subsequently compressed in the second stage.
• the first stage includes a first stage inlet guide vane 32a, a first impeller 34a, a first diffuser/volute 36a, a first stage compressor motor 38a and a first stage magnetic bearing 40a.
• the second stage includes a second stage inlet guide vane 32b, a second impeller 34b, a second diffuser/volute 36b, a second stage compressor motor 8b and a second stage magnetic bearing 40b.
• the centrifugal compressor 22 includes various conventional sensors (only some shown).
• a casing 30 covers the other parts of the centrifugal compressor 22.
• the casing 30 includes an inlet portion 31a and an outlet portion 33 a for the first stage of the compressor 22.
• the casing 30 also includes an inlet portion 31b and an outlet portion 33b for the second stage of the compressor 22.
• the casing 30 has a first inlet portion 3 la, a first outlet portion 33a, a second inlet portion 3 lb and a second outlet portion 33 b.
• the centrifugal compressor 22 includes the casing 30, a first compression mechanism (first stage) 23a and a second compression mechanism (second stage) 23 b.
• the first compression mechanism 23a includes the first inlet guide vane 32a disposed in the first inlet portion 31a, the first impeller 34a disposed downstream of the first inlet guide vane 32a, a first diffuser 36a disposed in the first outlet portion 33a downstream from the first impeller 34a, and the first motor 38a arranged to rotate the first shaft 42a in order to rotate the first impeller 34a.
• the first impeller 34a is attached to a first shaft 42a rotatable about a first rotation axis Xi.
• compression mechanism 23b includes the second inlet guide vane 32b disposed in the second inlet portion 31b, the second impeller 34b disposed downstream of the second inlet guide vane 32b, the second diffuser 36b disposed in the second outlet portion 33b downstream from the second impeller 34b, and the second motor 38b arranged to rotate the second shaft 42b in order to rotate the second impeller 34b.
• the second impeller 34b is attached to a second shaft 42b rotatable about a second rotation axis X 2 .
• the chiller controller 20 receives signals from the various sensors and controls the inlet guide vanes 32a and 32b, the compressor motors 38a and 38b, and the magnetic bearings 40a and 40b, as explained in more detail below.
• Refrigerant flows in order through the first stage inlet guide vane 32a, the first stage impeller 34a, the second stage inlet guide vane 32b, and the second stage impeller 34b.
• the inlet guide vanes 32a and 32b control the flow rate of refrigerant gas into the impellers 34a and 34b, respectively, in a conventional manner.
• the impellers 34a and 34b increase the velocity of refrigerant gas, generally without changing pressure.
• the motor speeds determine the amount of increase of the velocity of refrigerant gas.
• the diffusers/volutes 36a and 36b increase the refrigerant pressure.
• the diffusers/volutes 36a and 36b are non-movably fixed relative to the casing 30.
• the compressor motors 38a and 38b rotate the impellers 34a and 34b via first and second shafts 42a and 42b, respectively.
• the first diffuser 36a is connected to the second impeller 34b such that refrigerant compressed in the first compression mechanism 23a is further compressed in the second compression mechanism 23b, as best understood from Figure 1.
• the first and second magnetic bearings 40a and 40b magnetically rotatable support the shafts 42a and 42b, respectively.
• the bearing system may include a roller element, a hydrodynamic bearing, a hydrostatic bearing, and/or a magnetic bearing, or any combination of these. In this manner, the refrigerant is compressed in the centrifugal compressor 22.
• the first stage impeller 34a and the second stage impeller 34b of the compressor 22 are rotated, and the refrigerant of low pressure in the chiller system 10 is sucked by the first stage impeller 34a.
• the flow rate of the refrigerant is adjusted by the inlet guide vane 32a.
• the refrigerant sucked by the first stage impeller 34a is compressed to intermediate pressure, the refrigerant pressure is increased by the first diffuser/volute 36a, and the refrigerant is then introduced to the second stage impeller 34b.
• the flow rate of the refrigerant is adjusted by the inlet guide vane 32b.
• the second stage impeller 34b compresses the refrigerant of intermediate pressure to high pressure, and the refrigerant pressure is increased by the second diffuser/volute 36b. The high pressure gas refrigerant is then discharged to the chiller system 10.
• the impellers 34a and 34b are driven by separate motors 38a or 38b, the rotation speeds of the first and second impellers 34a and 34b are independently variable.
• the first and second magnetic bearings 40a and 40b are conventional, except as explained herein. Thus, the first and second magnetic bearings 40a and 40b will not be discussed and/or illustrated in detail herein, except as related to the present invention. Rather, it will be apparent to those skilled in the art that any suitable magnetic bearing can be used without departing from the present invention.
• the first magnetic bearing 40a preferably includes a first impeller side radial magnetic bearing 44a, a first remote side radial magnetic bearing 46a and a first axial (thrust) magnetic bearing 48a.
• the second magnetic bearing 40b preferably includes a second impeller side radial magnetic bearing 44b, a second remote side radial magnetic bearing 46b and a second axial (thrust) magnetic bearing 48b.
• At least one radial magnetic bearing 44a or 46a rotatably supports the first shaft 42a, and at least one radial magnetic bearing 44b or 46b rotatably supports the second shaft 42b.
• the thrust magnetic bearing 48a axially supports the first shaft 42a along a first rotational axis Xt by acting on a first thrust disk 45a.
• the thrust magnetic bearing 48a includes the thrust disk 45a which is attached to the first shaft 42a.
• the thrust magnetic bearing 48b axially supports the second shaft 42b along a second rotational axis X2 by acting on a second thrust disk 45b.
• the thrust magnetic bearing 48b includes the thrust disk 45b which is attached to the second shaft 42b.
• the first thrust disk 45a extends radially from the first shaft 42a in a direction perpendicular to the first rotational axis Xi, and is fixed relative to the first shaft 42a.
• the second thrust disk 45b extends radially from the second shaft 42b in a direction
• first shaft 42a along the first rotational axis Xi is controlled by an axial position of the first thrust disk 45a
• a position of the second shaft 42b along the first rotational axis X2 is controlled by an axial position of the second thrust disk 45b.
• the first radial magnetic bearings 44a and 46a are disposed on opposite axial ends of the first compressor motor 38a
• the second radial magnetic bearings 44b and 46b are disposed on opposite axial ends of the second compressor motor 38b.
• the first and second rotation axes Xi and X2 are coincident with each other.
• the first and second rotation axes Xi and X2 are parallel.
• various sensors detect radial and axial positions of the shafts 42a and 42b relative to the magnetic bearings 44a, 44b, 46a, 46b, 48a and 48b, and send signals to the chiller controller 20 in a conventional manner.
• the chiller controller 20 controls the electrical current sent to the magnetic bearings the magnetic bearings 44a, 44b, 46a, 46b, 48a and 48b in a conventional manner to maintain the shafts 42a and 42 in the correct positions.
• the magnetic bearing 40a is preferably a combination of active magnetic bearings 44a, 46a, and 48a, which utilizes gap sensors 54a, 56a and 58a ( Figure 5) to monitor shaft position and send signals indicative of shaft position to the chiller controller 20.
• each of the magnetic bearings 44a, 46a and 48a are preferably active magnetic bearings.
• the magnetic bearing 40b is preferably a combination of active magnetic bearings 44b, 46b, and 48b, which utilizes gap sensors 54b, 56b and 58b ( Figure 5) to monitor shaft position and send signals indicative of shaft position to the chiller controller 20.
• each of the magnetic bearings 44b, 46b and 48b are preferably active magnetic bearings.
• the centrifugal compressor 22 includes a first magnetic bearing 40a rotatably supporting the first shaft 42a, and a second magnetic bearing 40b rotatably supporting the second shaft 42b.
• the first shaft 42a has a first inlet end with the first impeller 34a mounted thereon and a first remote end with the first motor 38a mounted on the first shaft 42a between the first impeller 34a and the first remote end
• the second shaft 42b has a second inlet end with the second impeller 34b mounted thereon and a second remote end with the second motor 38b mounted on the second shaft 42b between the second impeller 34b and the second remote end.
• the first and second magnetic bearings 40a and 40b include a combination of radial and axial magnetic bearings.
• the magnetic bearing 44a is the first impeller side radial magnetic bearing axially disposed between the first impeller 34a and the first motor 38
• the magnetic bearing 44b is the second impeller side radial magnetic bearing axially disposed between the second impeller 34b and the second motor 38 b.
• the magnetic bearing 46a is the first remote side radial magnetic bearing axially disposed on a side of the first motor 38a that is remote from a side where the first impeller 34a is mounted
• the magnetic bearing 46b is the second remote side radial magnetic bearing axially disposed on a side of the second motor 38b that is remote from a side where the second impeller 34b is mounted.
• the first magnetic bearing 40a includes at least one first radial magnetic bearing 44a or 44b and at least one first axial thrust magnetic bearing 48a
• the second magnetic bearing 40b includes at least one second radial magnetic bearing 44b or 46b and at least one second axial thrust magnetic bearing 48b.
• the first axial thrust magnetic bearing 48a is axially disposed adjacent to the first remote side radial bearing 46a
• the second axial thrust magnetic bearing 48b is axially disposed adjacent to the second remote side radial bearing 46b.
• the first axial thrust magnetic bearing 48a is axially disposed at the first remote end of the first shaft 42a
• the second axial thrust magnetic bearing 48b is axially disposed at the second remote end of the second shaft 42b.
• the first and second remote ends (of the shafts 42a and 42b) and the first and second axial thrust magnetic bearings 48a and 48b are axially spaced from each other to form a gap therebetween.
• the gap sensors 54a, 54b, 56a, 56b, 58a and 58b are only shown schematically in Figure 5.
• back-up bearings (unnumbered), which are located at each end of each shaft 42a and 42b are provided in the illustrated embodiment as only shown in Figure 5. It will be apparent to those skilled in the art from this disclosure that the back-up bearings (unnumbered) could be eliminated.
• one or more of the gap sensors could be eliminated in order to simplify the magnetic bearings 40a and 40b.
• the magnetic bearings could be controlled passively by the chiller controller 20.
• the first motor 38a includes a first stator 60a and a first rotor 62a.
• the second motor 38b includes a second stator 60b and a second rotor 62b.
• the stator 60a is fixed to an interior surface of the casing 30, while the rotor 62a is fixed to the shaft 42a.
• the stator 60b is fixed to an interior surface of the casing 30, while the rotor 62b is fixed to the shaft 42b.
• the stators 60a and 60b and the rotors 62a and 62b are conventional.
• the rotor 62a when electricity is sent to the stator 60a, the rotor 62a is caused to rotate at a speed according to the supplied electricity. Moreover, when electricity is sent to the stator 60b, the rotor 62b is caused to rotate at a speed according to the supplied electricity. Since the rotors are fixed to the shafts, the shafts are also caused to rotate, and thus, the impellers 34a and 34b are also cause to rotate.
• the motors 38a and 38b preferably receive electricity from separate Variable Frequency Drives (VFDs) 64a and 64b, respectively.
• VFDs Variable Frequency Drives
• the Variable Frequency Drives (VFDs) 64a and 64b receive control signals from the chiller controller 20 to independently control the speeds of rotation of the first and second impellers 34a and 34b, respectively.
• VFDs 64a and 64b are controlled.
• VFDs Variable Frequency Drives
• independent control of the motors 38a and 38b to independently control the rotations speeds of the first and second impellers 34a and 34b will now be explained in more detail.
• rotation speeds of the first and second motors 38a and 38b are independently controllable.
• the controller 20 is programmed to independently control the rotation speeds of the first and second motors 38a and 38b in accordance with the flow chart of Figure 6.
• This loop illustrated in Figure 6 starts and repeats with following triggers: (1.) Compressor discharge pressure changes more than 10%/min; and/or (2.) Compressor suction pressure changes more than 10%/min.
• the first Variable Frequency Drive (VFD) 64a is connected to the first motor 38a and the controller 20 to variably control the rotation speed of the first motor 38a in accordance with Figure 6, and the second Variable Frequency Drive (VFD) 64b is connected to the second motor 38b and the controller 20 to variably control the rotation speed of the second motor 38b in accordance with Figure 6.
• Step S2-S4 are steps used to calculate current efficiency and determine if the first stage compression mechanism 23a is operating at a most efficient point (See for Example Figure 9B). If it is determined that the first stage compression mechanism 23a is operating at a most efficient point at step S4, the controller 20 proceeds to step S5. If not, the controller 20 proceeds to step S8. In steps S8-S10, the controller 20 adjusts the inlet guide vane 32a and the first VFD speed to improve the efficiency of the first compression mechanism 23a (See for example Figure 10B). If it is determined that the first stage compression mechanism 23a is operating at a most efficient point after these changes at step S 10, the controller 20 proceeds to step S5. If not, the controller 20 returns to *A to repeat the above determinations and controls.
• Step S5- S7 are steps used to calculate current efficiency and determine if the second stage compression mechanism 23b is operating at a most efficient point (See for Example Figure 9C). If it is determined that the second stage compression mechanism 23b is operating at a most efficient point at step S7, the controller 20 proceeds to step S14. If not, the controller 20 proceeds to step SI 1. In steps SI 1-S13, the controller 20 adjusts the inlet guide vane 32b and the second VFD speed to improve the efficiency of the second compression mechanism 23b (See for example Figure IOC). If it is determined that the second stage compression mechanism 23b is operating at a most efficient point after these changes at step SI 3, the controller 20 proceeds to step SI 4. If not, the controller 20 returns to *B to repeat the above determinations and controls.
• each stage operates by independent speed control.
• speed of each impeller By separately varying the speed of each impeller the operation range of each impeller can be maintained within its boundary limits as mentioned in the preceding paragraph.
• varying economizer flow over wide range of operating conditions can be possible when speeds of the impellers are independently variable as disclosed herein.
• each stage is operable by independent speed control; by separately varying the speed of each impeller the boundary limits can be adjusted for better matching of the each of the stages, and an increase in the operating range of the two stage compressor; independent speed control allows for better balancing of mass flow and work input between the each stages, especially when considering varying economizer flow over wide range of operating conditions.
• the illustrated embodiment technology can improve compressor's operating range and efficiency because new structure allows each compressor to rotate in different speed. Specifically, by rotating each impeller in different rotational speed, impellers would not be operated at outside of the operating range. Also, efficiency of 1 st and 2 nd stage impeller's rotational speed will be adjusted to increase their efficiency, and it will improve overall compressor efficiency.
• Figure 7A is a graph illustrating operating range of a two stage compressor (overall compressor operation), with A representing an overall operating point outside the overall operating range.
• Figure 7B is a graph illustrating operating range of the first stage impeller, with Al representing a fist stage operating point outside the first stage operating range.
• Figure 7C is a graph illustrating operating range of the second stage impeller, with A2 representing a second stage operating point inside the second stage operating range;
• Figure 8A is a graph illustrating operating range of a two stage compressor (overall compressor operation), with A representing an overall operating point outside the overall operating range (like Figure 7A) and with B representing a shifted operating point within the overall operating range in accordance with the present invention.
• Al represents a fist stage operating point outside the first stage operating range (like Figure 7B) and Bl represents a shifted first operating point by decreasing the rotation speed of the first stage impeller in accordance with the present invention.
• Figure 8C is like Figure 7C where A2 represents a second stage operating point inside the second stage operating range.
• Figure 9 A is a graph illustrating efficiency of a two stage compressor (overall compressor efficiency), with E representing a designed highest efficiency point and with D and E representing shifted lower efficiency operating points.
• E represents a designed highest efficiency point of the first stage and Dl and El represent shifted lower efficiency operating points of the first stage.
• Figure 9C with E2 represents a designed highest efficiency point of the second stage and D2 and E2 represent shifted lower efficiency operating points of the second stage.
• FIG. 9A-9C Figure 1 OA is a graph illustrating efficiency of a two stage compressor (overall compressor efficiency) like Figure 9A, with E representing a designed highest efficiency point and with D and E representing shifted lower efficiency operating points.
• E represents a designed highest efficiency point of the first stage
• Dl and Fl represent shifted lower efficiency operating points of the first stage.
• the arrows illustrate how the efficiency can be increased from points Dl or Fl by reducing or increasing the first impeller speed, respectively.
• Figure IOC is the same as Figure 10b but for the second stage.
• each impeller By rotating each impeller in different speed, each impeller can be operated at the point close to the designed point.
• flow coefficient is low (point like Dl or D2)
• the impeller speed will be decreased to get higher efficiency.
• flow coefficient is high (point like Fl and F2)
• the impeller speed will be increased to get higher efficiency.
• the overall compressor efficiency will be close to the highest efficiency.
• the change of rotation speed will require the change of IGV position as well. This is because the flow coefficient and head coefficient has been changed due to the rotational speed change. Specifically, if RPM of an impeller increases then the IGV should close to reduce inlet flow. On the other hand, if RPM of an impeller decreases then the IGV should open to increase inlet flow.
• the chiller controller 20 may include numerous control sections programmed to control the conventional parts in a conventional manner.
• conventional magnetic bearing control sections for example, conventional magnetic bearing control sections, conventional compressor variable frequency drives, a conventional compressor motor control sections, conventional inlet guide vane control sections, and conventional expansion valve control sections. These sections can be separate or combined sections.
• control sections are sections of the chiller controller 20 programmed to execute the control of the parts of the chiller 10 in accordance with Figure 6 and as described and illustrated herein.
• the precise number, location and/or structure of the control sections, portions and/or chiller controller 20 can be changed without departing from the present invention so long as the one or more controllers are programed to execute control of the parts of the chiller system 10 as explained herein.
• the chiller controller 20 is conventional, and thus, includes at least one microprocessor or CPU, an Input/output (I/O) interface, Random Access Memory (RAM), Read Only Memory (ROM), a storage device (either temporary or permanent) forming a computer readable medium programmed to execute one or more control programs to control the chiller system 10 as disclosed herein.
• the chiller controller 20 may optionally include an input interface such as a keypad to receive inputs from a user and a display device used to display various parameters to a user.
• the parts and programming are conventional, except as explained herein, and thus, will not be discussed in further detail herein, except as needed to understand the embodiments).
• section when used in the singular can have the dual meaning of a single part or a plurality of parts.
• detect as used herein to describe an operation or function carried out by a component, a section, a device or the like includes a component, a section, a device or the like that does not require physical detection, but rather includes determining, measuring, modeling, predicting or computing or the like to carry out the operation or function.
• the term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function. [0080]
• the terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Thermal Sciences (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)
• Control Of Positive-Displacement Air Blowers (AREA)
• Control Of Positive-Displacement Pumps (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=59969245

Family Applications (1)

Country Status (5)

Families Citing this family (4)

Family Cites Families (16)

• 2016
  • 2016-09-15 US US15/266,403 patent/US20180073779A1/en not_active Abandoned
• 2017
  • 2017-09-14 WO PCT/US2017/051455 patent/WO2018053067A1/en unknown
  • 2017-09-14 JP JP2019514826A patent/JP2019529777A/ja not_active Withdrawn
  • 2017-09-14 CN CN201780056596.9A patent/CN109715955A/zh active Pending
  • 2017-09-14 EP EP17772817.7A patent/EP3513078A1/de not_active Withdrawn

Also Published As

Similar Documents

Legal Events