EP3417218A1

EP3417218A1 - Compressor capacity modulation system for multiple compressors

Info

Publication number: EP3417218A1
Application number: EP17753972.3A
Authority: EP
Inventors: Jacob A. Groshek
Original assignee: Emerson Climate Technologies Inc
Current assignee: Copeland LP
Priority date: 2016-02-19
Filing date: 2017-02-17
Publication date: 2018-12-26
Also published as: CN108700359A; WO2017143261A1; US20170241690A1; EP3417218A4; CN108700359B

Abstract

A system includes a plurality of compressors, an evaporator, an expansion device, and a system controller. The compressors may be linked in parallel. The system controller may: determine a saturated evaporator temperature, a saturated condensing temperature, and a target capacity demand; determine an estimated system capacity and an estimated power consumption for each compressor operating configuration; compare the estimated system capacity with the target capacity demand and an error tolerance value; select an optimum operating mode based on the comparisons and based on the estimated power consumption; and command activation and deactivation of the plurality of compressors to achieve the selected optimum operating mode. The optimum operating mode may be selected after the normal system logic achieves a steady state and may be selected from a group having the estimated system capacity within the error tolerance of the target capacity demand and a lowest associated power consumption value.

Description

COMPRESSOR CAPACITY MODULATION SYSTEM

FOR MULTIPLE COMPRESSORS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Utility Application No. 15/424,352, filed on February 3, 2017 and also claims the benefit of U.S. Provisional Application No. 62/297,680, filed on February 19, 2016. The entire disclosures of the above applications are incorporated herein by reference.

FIELD

[0002] The present disclosure relates to a compressor capacity modulation system and, more particularly, to a compressor capacity modulation system for multiple compressors that optimizes overall system efficiency.

BACKGROUND

[0003] This section provides background information related to the present disclosure which is not necessarily prior art.

[0004] Compressors are used in a wide variety of industrial and residential applications to circulate refrigerant within a refrigeration, heat pump, HVAC, or chiller system (generically referred to as "refrigeration systems") to provide a desired heating and/or cooling effect. In any of the foregoing systems, the compressor should provide consistent and efficient operation to ensure that the particular refrigeration system functions properly.

[0005] Compressor systems may include multiple fixed compressors connected together for increased efficiency and capacity modulation. The compressors have the capability to operate together or individually, delivering several discrete capacity steps as needed. System capacity can be modulated by using multiple refrigeration circuits or by using multiple compressors in a single- circuit. For example, in a four compressor system, frequently used in packaged rooftops, individual compressors can be turned on and off to achieve a specific output. In other examples, such as for chillers, two to eight compressors is the typical number per unit, which means, depending on the even or uneven combinations, up to 12 capacity steps are available to match the load by cycling the compressors on and off. [0006] The multiple fixed compressors are started and shut down in the order in which they are connected to meet capacity demands for the system. The multiple fixed compressors may also be started in the order of least to most run time. The compressors run until a temperature (or other) threshold is met. Based on the temperature's position relative to the threshold, the last compressor is turned on and off to modulate system capacity. Current multiple compressor systems are focused on meeting capacity needs and can tend to cycle unnecessarily, often overlooking more efficient operating modes.

SUMMARY

[0007] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0008] An example system includes a plurality of compressors, an evaporator, a condenser, and a system controller. The plurality of compressors may be linked in parallel by a common discharge line and a common suction line. The system controller may determine a saturated evaporator temperature of the evaporator, a saturated condensing temperature of the condenser, and a target capacity demand for the plurality of compressors. The system controller may determine an estimated system capacity and an estimated power consumption for each operating configuration of the plurality of compressors based on the saturated evaporator temperature and the saturated condensing temperature. The system controller may compare the estimated system capacity for each operating configuration with the target capacity demand and an error tolerance value. The system controller may select an optimum operating mode of the plurality of compressors based on the comparisons and based on the estimated power consumption for each operating configuration. The optimum operating mode may be selected from a group of operating configurations having the estimated system capacity within the error tolerance of the target capacity demand and the optimum operating mode having a lowest associated power consumption value in the group. The system controller may command activation and deactivation of the plurality of compressors to achieve the selected optimum operating mode. [0009] The compressor system may further include a plurality of compressors having at least one fixed capacity compressor and at least one two- stage compressor.

[0010] The compressor system may further include at least one two- stage compressor having a compressor with a delayed suction system.

[0011] The compressor system may further include at least one two- stage compressor having a compressor with a variable speed motor.

[0012] The compressor system may further include a plurality of compressors having a variable volume ratio compressor.

[0013] The compressor system may further include at least one two- stage compressor having a compressor with another capacity modulation scheme or a scroll separation system.

[0014] The compressor system may further include an estimated system capacity that is calculated based on characteristics of each of the plurality of compressors.

[0015] The compressor system may further include an operating configuration for the plurality of compressors having a location of each of the plurality of compressors and a coefficient performance curve for each of the plurality of compressors.

[0016] The compressor system may further include a system controller that determines the estimated power consumption for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration.

[0017] The compressor system may further include a system controller that determines the estimated system capacity for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration.

[0018] The compressor system may further include a system controller that determines whether the plurality of compressors have stabilized before selecting the optimum operating mode. The determination of whether the plurality of compressors have stabilized may be based on an output of at least one of a current sensor, a common suction line temperature sensor, a common discharge line temperature sensor, a common suction line pressure sensor, and a common discharge line pressure sensor. [0019] The compressor system may further include a plurality of compressors having two fixed capacity compressors with different capacities and one two-stage compressor, and having eleven associated operating configurations.

[0020] The compressor system may further include a plurality of compressors having two fixed capacity compressors and one two-stage compressor with different capacities, and having seven associated operating configurations.

[0021] An example system includes a first circuit, a second circuit, and a system controller. The first circuit has a first plurality of compressors linked in parallel by a first common discharge line and a first common suction line. The second circuit has a second plurality of compressors linked in parallel by a second common discharge line and a second common suction line. The system controller determines an estimated system capacity and an estimated power consumption for each operating configuration of the plurality of compressors in the first circuit and the plurality of compressors in the second circuit based on a saturated evaporator temperature and a saturated condensing temperature. The system controller selects an optimum operating mode of the plurality of compressors in the first circuit and the plurality of compressors in the second circuit based on a comparison of the estimated system capacity for each operating configuration with a target capacity demand and an error tolerance value and based on the estimated power consumption for each operating configuration. The optimum operating mode is selected from a group of operating configurations that have the estimated system capacity within the error tolerance of the target capacity demand and the optimum operating mode has a lowest associated power consumption value in the group. The system controller commands activation and deactivation of the plurality of compressors in the first circuit and the plurality of compressors in the second circuit to achieve the selected optimum operating mode. It should be understood that the system is not limited to two circuits but can control and optimize the compressor operating modes in any number of circuits.

[0022] An example method for operating a system may include determining a saturated evaporator temperature of the evaporator, a saturated condensing temperature of the condenser, and a target capacity demand for a plurality of compressors; determining an estimated system capacity and an estimated power consumption for each operating configuration of the plurality of compressors based on the saturated evaporator temperature and the saturated condensing temperature; comparing the estimated system capacity for each operating configuration with the target capacity demand and an error tolerance value; selecting an optimum operating mode of the plurality of compressors based on the comparisons and based on the estimated power consumption for each operating configuration, the optimum operating mode being selected from a group of operating configurations having the estimated system capacity within the error tolerance of the target capacity demand and the optimum operating mode having a lowest associated power consumption value in the group; and commanding activation and deactivation of the plurality of compressors to achieve the selected optimum operating mode.

[0023] The method may further include a plurality of compressors including at least one of a fixed capacity compressor, a two-stage compressor, and a variable volume ratio compressor, wherein if the plurality of compressors includes the two-stage compressor, the two-stage compressor includes at least one of a compressor having a delayed suction system, a compressor having a variable speed motor, and a compressor having a scroll separation system.

[0024] The method may further include calculating the estimated system capacity based on the operating configuration for the plurality of compressors.

[0025] The method may further include an operating configuration for the plurality of compressors having a location of each of the plurality of compressors and a ten coefficient performance curve for each of the plurality of compressors.

[0026] The method may further include determining the estimated power consumption for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration.

[0027] The method may further include determining the estimated system capacity for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration.

[0028] The method may further include determining whether the plurality of compressors have stabilized before selecting the optimum operating mode, the determination of whether the plurality of compressors have stabilized being based on an output of at least one of a current sensor, a common suction line temperature sensor, a common discharge line temperature sensor, a common suction line pressure sensor, and a common discharge line pressure sensor.

[0029] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

[0030] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0031] Figure 1 is a schematic of a compressor system according to the present disclosure;

[0032] Figure 2 is a perspective view of multiple compressors of the compressor system of Figure 1 ;

[0033] Figure 3 is a chart illustrating a number of operating modes for a variety of compressor systems;

[0034] Figure 4 is a table illustrating the possible operating modes for an uneven trio compressor system;

[0035] Figure 5 is a schematic of a control system for the compressor system of Figure 1 ;

[0036] Figure 6 is an example pressure-temperature chart for a compressor;

[0037] Figure 7 is a flow chart illustrating the steps for operating the compressor system of Figure 1 ; and

[0038] Figure 8 is a graph illustrating the efficiency impact of an optimized fixed pressure ratio versus a traditional fixed pressure ratio versus a variable valve ratio compressor system.

[0039] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0040] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0041] With reference to FIG. 1 , a compressor capacity modulation system 10 is provided. The compressor capacity modulation system 10 may be used in conjunction with a heating, ventilation, and air conditioning (HVAC) system or refrigeration system 12 including at least multi-linked, or multi-connected, compressors 14, a condenser 18, and an evaporator 22. While the refrigeration system 12 is described and shown as including multi-linked compressors 14, the condenser 18, and the evaporator 22, the refrigeration system 12 may include additional and/or alternative components (for example only, an expansion valve). Further, the present disclosure is applicable to various types of refrigeration systems including, but not limited to, heating, ventilating, air conditioning (HVAC), heat pump, refrigeration, and chiller systems.

[0042] During operation of the refrigeration system 12, the multi-linked compressors 14 circulate refrigerant generally between the condenser 18 and the evaporator 22 to produce a desired heating and/or cooling effect. Specifically, the multi-linked compressors 14 receive refrigerant in vapor form and compress the refrigerant. The multi-linked compressors 14 provide pressurized refrigerant in vapor form to the condenser 18.

[0043] All or a portion of the pressurized refrigerant received from the multi-linked compressors 14 may be converted into a liquid state within the condenser 18. Specifically, the condenser 18 transfers heat from the refrigerant to the surrounding air, thereby cooling the refrigerant. When the refrigerant vapor is cooled to a temperature that is less than a saturation temperature, the refrigerant changes state from a vapor to a liquid. The condenser 18 may include a condenser fan (not illustrated) that increases the rate of heat transfer away from the refrigerant by forcing air across a heat-exchanger coil associated with the condenser 18.

[0044] The refrigerant may pass through an expansion valve (not illustrated) that expands the refrigerant prior to reaching the evaporator 22. The evaporator 22 may receive a mixture of vapor refrigerant and liquid refrigerant or purely liquid refrigerant from the condenser 18. The refrigerant absorbs heat in the evaporator 22. Accordingly, liquid refrigerant disposed within the evaporator 22 changes state from a liquid to a vapor when warmed to a temperature that is greater than or equal to the saturation temperature of the refrigerant. The evaporator 22 may include an evaporator fan (not illustrated) that increases the rate of heat transfer to the refrigerant by forcing air across a heat-exchanger coil associated with the evaporator 22.

[0045] As the liquid refrigerant absorbs heat, the ambient air disposed proximate to the evaporator 22 is cooled. The evaporator 22 may be disposed within a space to be cooled such as a building or refrigerated case where the cooling effect produced by the refrigerant absorbing heat is used to cool the space. The evaporator 22 may also be associated with a heat-pump refrigeration system where the evaporator 22 may be located remotely from the building such that the cooling effect is lost to the atmosphere and the rejected heat generated by the condenser 18 is directed to the interior of a space to be heated.

[0046] Referring additionally to Figure 2, the multi-linked compressors 14 may further include two or more compressors 26, 30, 34 connected in parallel. Each of the compressors 26, 30, 34 of the multi-linked compressors 14 includes a plurality of solenoids 36 and contactors 38 that can be activated to control the compressor. For example only, the solenoids 36 and contactors 38 may be activated to run the compressor at full capacity or load or at a part capacity or load, where applicable. For example only, three compressors 26, 30, 34 are illustrated in Figures 1 and 2. While three compressors are illustrated and described, it is understood that any number of compressors may be included in the multi-linked compressors 14, including two compressors and more than three compressors. The compressors 26, 30, 34 share a single suction header or common suction line 40 and a single discharge header or common discharge line 42.

[0047] While a single circuit of multi-linked compressors is discussed and illustrated, it is understood that there may be multiple circuits in a single system. Each circuit in the system includes its own multi-linked compressors linked in tandem, trio, quad, or any other number. The circuits in a multi circuit system are independent but may run through a common evaporator and a common condenser. The output may be modulated by turning on the individual circuits separately or in combination with other circuits. Thus, the present disclosure is not limited to a single circuit of multi-linked compressors, but may be applied across any number of multiple circuits, each having multi-linked compressors. [0048] The multi-linked compressors 14 may include one or more multi-stage compressors that are operable at multiple different capacity levels. For example, a two-stage compressor operable at full capacity or load (or full scroll volume ratio) and at modulated capacity or load (with a lower scroll volume ratio) can be used. The multi-stage compressor may utilize any manner of capacity modulation, including, but not limited to two-step capacity modulation or continuous capacity modulation. Two-step capacity modulation is where the compressor runs at either a full capacity or load (for example, 100% capacity) or a part capacity or load (for example, 67% capacity), depending on cooling and/or heating demand. For example, two-step capacity modulation may be accomplished with a delayed suction system that modulates compressor capacity by venting an intermediate pressurized chamber to the suction chamber, as described in U.S. Pat. No. 6,821 ,092, the disclosure of which is incorporated herein by reference. With continuous capacity modulation, or variable valve modulation, the capacity of the compressor can be modulated from 10-100 percent so that the output precisely matches the changing cooling requirements of the space. For example, a bypass valve and passage can be used to continuously modulate compressor capacity, without changing the speed of the motor. For further example, continuous capacity modulation can be accomplished with a variable speed capacity modulation system that varies the speed of the compressor motor. The compressor motor speed determines the rate of refrigerant flow; thus, by varying the motor frequency, capacity can be modulated. Therefore, with a variable speed capacity modulation system, capacity output increases and decreases with motor speed. For further example, continuous capacity modulation can be accomplished with a scroll separation capacity modulation system. In a scroll separation capacity modulation system, capacity control is achieved by separating the scroll sets axially over a small period of time. For example, a scroll separation capacity modulation system is described in U.S. Pat. No. 6,213,731 , which is incorporated herein by reference. In addition, any of the continuous capacity modulated systems can also be operated in two discrete capacity steps to accomplish two-step capacity modulation. A two- stage compressor, because of its capacity modulation, has three different operating, or power, modes: off, full capacity or load, and modulated, or reduced, capacity or load. [0049] The multi-linked compressors 14 may include fixed capacity compressors. A fixed capacity compressor is a compressor having a traditional scroll design with a single, standard built-in volume ration (BIVR). The fixed capacity compressor has two different operating, or power, modes: off and full capacity or load.

[0050] The multi-linked compressors 14 may include variable volume ratio compressors. A variable volume ratio compressor incorporates a bypass passage to eliminate over compression losses by porting compressed fluid though a bypass valve in a fixed scroll of the compressor. The variable volume ratio compressor has three different operating, or power, modes: off, full BIVR and capacity, and reduced scroll volume ratio. The variable volume ratio compressor may be a passive scheme or any other scheme. While the variable volume ratio compressor may be a passive scheme in terms of control, the variable volume ratio compressor adds additional complexity by adapting scroll volume ratio to meet needs. In multi-linked compressors, knowing which compressors have variable volume ratio designs and selectively turning them on and off can influence the overall system efficiency (see Figure 8, discussed in further detail below). Variable volume ratio compressors may offer higher efficiency over a larger range of system pressures, as compared with a compressor having an optimized fixed pressure ratio or a traditional fixed pressure ratio. The pressure ratio, as seen in Figure 8, is calculated as discharge pressure over suction pressure.

[0051] The multi-linked compressors 14 may be compressors linked in parallel in even multiples or uneven multiples. Even multiples are parallel compressors of the same BIVR and capacity; whereas uneven multiples are parallel compressors of different BIVR and/or capacities. The multi-linked compressors 14 may also incorporate one or more of the types of two-stage compressors, the fixed capacity compressors, and variable volume ratio compressors.

[0052] Now referring to Figure 3, in some embodiments, the multi-linked compressors 14 may be an even tandem of fixed capacity compressors, meaning that the multi-linked compressors 14 may include two fixed capacity compressors having the same BIVR and capacity being linked in parallel. Because of the two operating modes for each of the two fixed capacity compressors, and the fact that the two fixed capacity compressors have the same BIVR and capacity, the even tandem of fixed capacity compressors has two total possible operating, or power, modes, excluding the operating mode where all compressors are off, i.e., the two operating, or power, modes being: (1 ) one compressor on; and (2) two compressors on.

[0053] In other embodiments, the multi-linked compressors 14 may be an even trio of fixed capacity compressors meaning that the multi-linked compressors 14 may include three fixed capacity compressors having the same BIVR and capacity being linked in parallel. Because of the two operating modes for each of the three fixed capacity compressors, and the fact that the three fixed capacity compressors have the same BIVR and capacity, the even trio of fixed capacity compressors has three total possible operating, or power, modes, excluding the operating mode where all compressors are off, i.e., the three operating, or power modes, being: (1 ) one compressor on; (2) two compressors on; and (3) three compressors on.

[0054] In other embodiments, the multi-linked compressors 14 may be an uneven tandem of fixed capacity compressors meaning that the multi-linked compressors 14 may include two fixed capacity compressors having different BIVR and capacities being linked in parallel. Because of the two operating modes for each of the two fixed capacity compressors, and the fact that the two fixed capacity compressors have different BIVR and capacities, the uneven tandem of fixed capacity compressors has three total possible operating, or power, modes, excluding the operating mode where all compressors are off, i.e., the three operating, or power, modes being: (1 ) lower capacity compressor on; (2) higher capacity compressor on; and (3) both compressors on.

[0055] In other embodiments, the multi-linked compressors 14 may be an uneven trio of fixed capacity compressors meaning that the multi-linked compressors 14 may include three fixed capacity compressors having different BIVR and capacities being linked in parallel. Because of the two operating modes for each of the three fixed capacity compressors, and the fact that the three fixed capacity compressors have different BIVR and capacities, the uneven trio of fixed capacity compressors has seven total possible operating, or power, modes, excluding the operating mode where all compressors are off, i.e., the seven operating, or power, modes being: (1 ) lowest capacity compressor on; (2) middle capacity compressor on; (3) highest capacity compressor on; (4) lowest and middle capacity compressors on; (5) lowest and highest capacity compressors on; (6) middle and highest capacity compressors on; and (7) all three compressors on.

[0056] In other embodiments, the multi-linked compressors 14 may be an even tandem of two-stage compressors, meaning that the multi-linked compressors 14 may include one two-stage compressor and one fixed capacity compressor, with both compressors having the same BIVR and capacity being linked in parallel. Because of the three operating modes for the two-stage compressor and the two operating modes for the fixed capacity compressor, and the fact that the two-stage and the fixed capacity compressors have the same BIVR and capacities, the even tandem of two-stage compressors has four total possible operating, or power, modes, excluding the operating mode where all compressors are off, i.e., the four operating, or power, modes being: (1 ) fixed capacity compressor on (or two-stage compressor on at high capacity); (2) two-stage compressor on at low capacity; (3) fixed capacity compressor on and two stage compressor on at low capacity; and (4) fixed capacity compressor on and two stage compressor on at high capacity.

[0057] In other embodiments, the multi-linked compressors 14 may be an even trio of two-stage compressors meaning that the multi-linked compressors 14 may include one two-stage compressor and two fixed capacity compressors having the same BIVR and capacity being linked in parallel. Because of the three operating modes for the two-stage compressor and the two operating modes for each of the fixed capacity compressors, and the fact that the two-stage and fixed capacity compressors have the same BIVR and capacity, the even trio of two-stage compressors has six total possible operating, or power, modes, excluding the operating mode where all compressors are off, i.e., the six operating, or power, modes being: (1 ) either fixed capacity compressor on (or two-stage compressor on at high capacity); (2) two-stage compressor on at low capacity; (3) one fixed capacity compressor on and two-stage compressor on at low capacity; (4) two fixed capacity compressors on (or one fixed capacity compressor and two-stage compressor on at high capacity); (5) two fixed capacity compressors on and two- stage compressor on at low capacity; and (6) two fixed capacity compressors on and two-stage compressor on at high capacity.

[0058] In other embodiments, the multi-linked compressors 14 may be an uneven tandem of two-stage compressors, meaning that the multi-linked compressors 14 may include one two-stage compressor and one fixed capacity compressor having different BIVR and capacities being linked in parallel. Because of the three operating modes for the two-stage compressor and the two operating modes for the fixed capacity compressor, and the fact that the two-stage and fixed capacity compressors have different BIVR and capacities, the uneven tandem of two-stage compressors has five total possible operating, or power, modes, excluding the operating mode where all compressors are off, the five operating, or power, modes being: (1 ) two-stage compressor on at low capacity; (2) fixed capacity compressor on (3) two-stage compressor on at high capacity; (4) fixed capacity compressor on and two-stage compressor on at low capacity; and (5) fixed capacity compressor on and two-stage compressor on at high capacity.

[0059] In other embodiments, the multi-linked compressors 14 may be an uneven trio of two-stage compressors, meaning that the multi-linked compressors 14 may include one two-stage compressor and two fixed capacity compressors having different BIVR and capacities being linked in parallel. Because of the three operating modes for the two-stage compressor and the two operating modes for each of the fixed capacity compressors, and the fact that the two-stage and fixed capacity tech compressors have different BIVR and capacities, the uneven trio of two-stage compressors has eleven total possible operating, or power, modes, excluding the operating mode where all compressors are off, the eleven operating, or power, modes being: (1 ) lower capacity fixed compressor on; (2) higher capacity fixed compressor on; (3) two-stage compressor on at low capacity; (4) two-stage compressor on at high capacity; (5) lower capacity fixed compressor on and higher capacity fixed compressor on; (6) lower capacity fixed compressor on and two- stage compressor on at low capacity; (7) lower capacity fixed compressor on and two-stage compressor on at high capacity; (8) higher capacity fixed compressor on and two-stage compressor on at low capacity; (9) higher capacity fixed compressor on and two-stage compressor on at high capacity; (1 0) lower capacity fixed compressor on, higher capacity fixed compressor on, and two-stage compressor on at low capacity; and (1 1 ) lower capacity fixed compressor on, higher capacity fixed compressor on, and two-stage compressor on at high capacity.

[0060] In other embodiments, the multi-linked compressors 14 may be a trio of uneven two-stage compressors comprising three two-stage compressors having different BIVR and capacities linked in parallel. Because of the three operating modes for each of the three two-stage compressors, and the fact that the two-stage compressors have different BIVR and capacities, the trio of two-stage compressors have twenty-six total possible operating, or power, modes, excluding the operating mode where all compressors are off, the twenty-six operating, or power, modes being: (1 ) lower capacity two-stage compressor on at high capacity; (2) lower capacity two-stage compressor on at low capacity; (3) middle capacity two-stage compressor on at high capacity; (4) middle capacity two-stage compressor on at low capacity; (5) higher capacity two-stage compressor on at high capacity; (6) higher capacity two-stage compressor on at low capacity; (7) lower and middle capacity two-stage compressors on at high capacity; (8) lower and middle capacity two-stage compressors on at low capacity; (9) lower capacity two- stage compressor on at high capacity and middle capacity two-stage compressors on at low capacity; (10) lower capacity two-stage compressor on at low capacity and middle capacity two-stage compressors on at high capacity; (1 1 ) lower and higher capacity two-stage compressors on at high capacity; (12) lower and higher capacity two-stage compressors on at low capacity; (13) lower capacity two-stage compressor on at high capacity and high capacity two-stage compressors on at low capacity; (14) lower capacity two-stage compressor on at low capacity and high capacity two-stage compressors on at high capacity (15) middle and higher capacity two-stage compressors on at high capacity; (16) middle and higher capacity two-stage compressors on at low capacity; (17) middle capacity two-stage compressor on at high capacity and high capacity two-stage compressors on at low capacity; (18) middle capacity two-stage compressor on at low capacity and high capacity two-stage compressors on at high capacity (19) lower, middle, and higher capacity two-stage compressors on at high capacity; (20) lower, middle, and higher capacity two-stage compressors on at low capacity; (21 ) lower and middle capacity two-stage compressors on at high capacity and higher capacity two-stage compressor on at low capacity; (22) lower and higher capacity two-stage compressors on at high capacity and middle capacity two-stage compressor on at low capacity; (23) middle and higher capacity two-stage compressors on at high capacity and lower capacity two-stage compressor on at low capacity; (24) lower and middle capacity two-stage compressors on at low capacity and higher capacity two-stage compressor on at high capacity; (25) lower and higher capacity two-stage compressors on at low capacity and middle capacity two-stage compressor on at high capacity; and (26) middle and higher capacity two-stage compressors on at low capacity and lower capacity two-stage compressor on a high capacity.

[0061] Now referring to Figure 4, the total possible operating modes is determined based on the number of possible operating modes for each of the compressors and whether the compressors have the same or different BIVR and capacities. For example, the uneven trio of two-stage compressors shown in Figure 4 has one two-stage compressor (for example, a two-stage compressor with a 83,000 BTU/hr capacity) and two fixed capacity compressors with different BIVR and capacities (for example, a fixed capacity compressor with a 76,000 BTU/hr capacity and a fixed capacity compressor with a 91 ,000 BTU/hr capacity) being linked in parallel. With this combination of compressors, there are eleven total possible operating modes, depicted by the eleven rows in Figure 4. Each possible operating mode is identified in Figure 4. With reference to the Key, the two-stage compressor has the possibility of being off (0), at a full BIVR and capacity or load (1 ), or at a lower or modulated capacity or load (-1 ). Each of the fixed capacity compressors has the possibility of being off (0) or at full BIVR and capacity or load (1 ). Thus, the different combinations of compressor on/off/modulated modes are combined to make the total eleven possible operating modes, excluding the operating mode where all compressors are off.

[0062] While the fixed capacity even tandem, fixed capacity even trio, fixed capacity uneven tandem, fixed capacity uneven trio, two-stage even tandem, two-stage even trio, two-stage uneven tandem, and two-stage uneven trio are discussed above, it is understood that any combination of two-stage, multi-stage, fixed capacity, and variable valve compressors may be combined in parallel for the multi-linked compressors 14. The total number of possible operating modes for the multi-linked compressor 14 is determined based on the number of possible operating modes for each of the compressors and whether the compressors have the same or different full BIVR and capacities.

[0063] Referring to Figures 1 , 2, and 5, a system controller 46 may be associated with the compressor capacity modulation system 10 and/or the multi- linked compressors 14 and may command start up, stabilization, shut down, more capacity, and less capacity for each of the multi-linked compressors 14 and/or the refrigeration system 12. The system controller 46 may utilize a series of sensors to determine both measured and non-measured operating parameters of the compressor 14 and/or the refrigeration system 12. While the system controller 46 is shown as being associated with the multi-linked compressors 14, the system controller 46 could be located anywhere within or outside of the refrigeration system 12. The system controller 46 may use the non-measured operating parameters in conjunction with the measured operating parameters to command start up, stabilization, shut down, more capacity, and less capacity for each of the multi- linked compressors 14 and/or the refrigeration system 12.

[0064] The system controller 46 may receive a common discharge line temperature to determine stabilization of the compressors in the multi-linked compressors 14, as further described below. The system controller 46 may also communicate with various sensors to determine a stabilization of the multi-linked compressors. For example, stabilization may be determined from a current sensor 50 measuring motor current of each of the compressors in the multi-linked compressors 14. Stabilization may also be determined from a suction line temperature. A suction line temperature sensor 54 may be placed in the suction line into the multi-linked compressors 14. The common discharge line temperature may be directly sensed by a discharge line temperature sensor 58 from the discharge line out of the multi-linked compressors 14 and the system controller may look for the discharge line temperature signal to steady out and/or a derivative of the signal to go to zero. Similarly, when the stabilization of the multi-linked compressors is determined from an output of the current sensor 50 or a suction line temperature sensor 54, the system controller 46 will look for the signal(s) to steady out and/or a derivative of the signal(s) to go to zero.

[0065] The system controller 46 may also receive operating conditions of the compressor, such as a saturated evaporator temperature (Ts) and a saturated condensing temperature (Tc). The saturated evaporator temperature and saturated condensing temperature may be directly sensed from a temperature sensor 62 in the evaporator 22 and a temperature sensor 66 in the condenser 18, respectively. The saturated evaporator temperature and saturated condensing temperature may also be determined from pressures sensed from a pressure sensor 70 at the evaporator 22 and a pressure sensor 74 at the condenser 18, respectively. The condensing pressure sensed from the pressure sensor 74 is the pressure at which the refrigerant is phase changing from a vapor to a liquid. The evaporating pressure sensed from the pressure sensor 70 is the pressure at which the refrigerant is phase changing from a liquid to a vapor.

[0066] For example only, the saturated evaporator temperature may be directly correlated to the saturated evaporator pressure and the saturated condensing temperature may be directly correlated to the saturated condensing pressure. An example chart correlating the pressures with the temperatures for various refrigerant types is provided at Figure 6. Thus, the system controller 46 can determine the saturated evaporator temperature and saturated condensing temperature from looking up the sensed values in a table stored in a memory 78 within the system controller 46.

[0067] The system controller 46 may further store in memory 78 a ten- coefficient performance model for each of the multi-linked compressors 14. The ten-coefficient performance model is determined by the manufacturer or installer and describes the operating characteristics for the compressor. The ten-coefficient performance model may be entered into the memory 78 through a user interface 82 during installation or inspection or at the completion of manufacture. The ten- coefficient performance model is compressor model and size specific and is published by compressor manufacturers. Compressor capacity can be calculated from the ARI (Air-Conditioning and Refrigeration Institute, now the Air-Conditioning, Heating, & Refrigeration Institute) ten coefficient performance curve formula:

X = CO + (CI * 5) + (C2 * D) + (C3 * S²) + (C4 * S * D) + (C5 * D²) + (C6 * S³)

+ (C7 * D * S²) + (C8 * S * D²) + (C9 * D³)

where X is capacity (BTU/HR) or Power (watts or amps), S is saturated evaporating temperature, and D is saturated condensing temperature.

[0068] While a ten-coefficient performance model is discussed, it is understood that different coefficient characterizations may be implemented. For example, the compressor may be modeled based on a twenty-coefficient system. The present disclosure is not limited to a ten-coefficient performance model, but may implement any compressor characterization scheme such as a ten-coefficient scheme, a twenty-coefficient scheme, or any other number of coefficient schemes.

[0069] A position, or configuration, of each compressor in the multi-linked compressors 14 is also stored in the memory 78. For example, referring additionally to Figures 1 , 2, and 4, if the multi-linked compressors 14 are aligned in the order of two-stage compressor, fixed capacity compressor 1 , and fixed capacity compressor 2, the two-stage compressor may be assigned the A position, fixed capacity compressor 1 may be assigned the B position, and fixed capacity compressor 2 may be assigned the C position. Thus, the memory 78 stores the identity and location, or configuration, of each compressor in the multi-liked compressors 14.

[0070] The system controller 46 receives inputs for, or calculates from sensor data, common discharge line temperature, saturated evaporator temperature, saturated condensing temperature, the ten coefficient performance models or curves, and the identity and position of each compressor in the multi- linked compressors 14. From this data, the system controller 46 commands start up, stabilization, shut down, more capacity, and less capacity for the multi-linked compressors 14.

[0071] The system controller 46 may include processing circuitry 86 for carrying out the functions of a method 100 for modulating compressor capacity. Now referring to Figures 5 and 7, the system controller 46 receives a request for a target system capacity (or a capacity demand) at step 104. For example, the target system capacity may be calculated or determined based on a comparison of a current temperature within an air-conditioned or refrigerated space with a target temperature within the air-conditioned or refrigerated space. For further example, the target system capacity may be calculated or determined based on a current refrigerant temperature or pressure as compared with a target refrigerant temperature or pressure. The processing circuitry 86 may command a startup of one or more of the compressors 26, 30, 34 in the multi-linked compressors 14 at step 108 based on the capacity demand or request for a target system capacity. Once the compressors in the multi-linked compressors 14 are running, the processing circuitry 86 may wait for and determine a stabilization state of the activated compressor(s) 26, 30, 34 in the multi-linked compressors 14 at step 1 12.

[0072] The stabilization / start state follows a prescribed starting process which brings each of the compressors 26, 30, 34 in the multi-linked compressors 14 on one at a time to limit inrush current. For example, the largest capacity single compressor may be started first. The remaining compressors may be started in order of largest capacity to smallest capacity until the target system capacity is met. The stabilization/start state of the multi-linked compressors 14 starts with the first demand signal from the system controller 46 and ends with steady state operation of the activated compressors in the multi-linked compressors 14. Steady state operation is determined by monitoring a derivative value of discharge line temperature over time and watching for the derivative value to approach a low value or threshold value for a set period of time. For example only, a stability or steady state operation may be determined where the derivative value (a discharge line temperature change) is less than three degrees Fahrenheit (^QF) of discharge line temperature over a time frame of two minutes. Thus the target threshold value may be three degrees Fahrenheit (^QF). However, it is understood that the target threshold value threshold may change with each different system or application type. Some systems may stabilize faster than others. For example, if the system uses an electronic expansion valve rather than a traditional thermal expansion valve (TXV), the electronic expansion valve system will stabilize faster than the traditional system having the TXV. Thus, while an example of three degrees Fahrenheit (^QF) is provided, different target threshold values may be utilized to determine stability or steady state operation for different systems and application types.

[0073] As stated above, the system controller 46 may determine stabilization of the compressors 26, 30, 34 in the multi-linked compressors 14 through monitoring a common discharge line temperature. The system controller 46 may communicate with discharge line temperature sensor 58 to receive the common discharge line temperature. Alternatively, stabilization may be determined from the signal output of the current sensor 50 or the signal output of the suction line temperature sensor 54. The system controller 46 may determine that the multi- linked compressors 14 have stabilized when the discharge line temperature, the signal from the current sensor 50, or the suction line temperature sensor 54 becomes steady and/or a derivative of the temperatures or the current signal goes to zero.

[0074] The processing circuitry 86 communicates with the memory 78 and may receive the ten coefficient performance models and the identity and position of each compressor 26, 30, 34 in the multi-linked compressors 14 from the memory 78. From the inputs, the processing circuitry 86 may determine a current estimated system capacity (ESC) for the activated compressors in the multi-linked compressors 14 at step 1 16 based on the current saturated evaporator temperature, saturated condensing temperature, and the applicable ten coefficient performance model for the current group of activated compressors in the multi- linked compressors 14. The estimated system capacity may be the same as or close to the target capacity or the capacity demand from step 104. For example only, the estimated system capacity or target capacity may be determined from the ten coefficient performance models and the compressor efficiency formula previously described.

[0075] The processing circuitry 86 may receive the common discharge line temperature, saturated evaporator temperature, and saturated condensing temperature from various sensors or may calculate the common discharge line temperature, saturated evaporator temperature, and saturated condensing temperature from other received sensor data, as previously described. The processing circuitry 86 may then determine estimated compressor capacity and associated estimated power consumption values for all applicable operating modes for the multi-linked compressors 14 from the various inputs at step 120. For example only, compressor capacity may be calculated using the ten coefficient performance models for estimating compressor capacity and power consumption. As described above with reference to Figure 3, each discrete operating mode includes a combination of activated compressors, with any two-stage compressors operating at a particular operating level. The processing circuitry 86 uses the ten coefficient performance models for capacity and power to calculate the estimated capacity and the estimated power consumption for each discrete operating mode associated with the multi-linked compressors 14. For example, as shown in Figure 3, an uneven trio of compressors has eleven associated operating modes. In such case, the processing circuitry will calculate an estimated capacity and an estimated power consumption for each of the eleven operating modes using the ten coefficient performance models for the uneven trio of compressors.

[0076] At step 124, the processing circuitry 86 receives a capacity error tolerance (ET) from the memory 78. The ET may be saved in the memory and initially set by an installer or manufacturer. The ET may also be modified by a user of the system. The processing circuitry 86 then compares the estimated capacity values for each discrete operating mode to the target capacity and eliminates from consideration all modes with an estimated capacity value that is outside of the target system capacity plus or minus the error tolerance (ET) at step 128. In other words, any operating modes with an estimated capacity value that is not within the error tolerance (ET) of the target system capacity are eliminated from consideration.

[0077] At step 132, the processing circuitry 86 analyzes the power values for the remaining operating modes in consideration and selects the operating mode with the lowest estimated power consumption value from the operating modes that were not eliminated in step 128. The lowest power mode of the modes meeting the estimated system capacity is the optimum mode because the lowest power mode meets target capacity, plus or minus the error tolerance (ET) while using the least amount of power. In other words, the optimum operating mode corresponds to the configuration of the multi-linked compressors 14 that can meet the target capacity while consuming the least amount of power.

[0078] At step 136, the processing circuitry 86 activates contactors 38 and solenoids 36 of the multi-linked compressors 14 as needed to achieve the optimum mode or an optimized state. As discussed above, the optimized state will meet the capacity needs at the lowest power mode. In some cases, the current operating mode of the multi-linked compressors 14 may already correspond to the optimum operating mode. In such case, the processing circuitry 86 will not need to activate or deactivate any compressors or change the capacity level of any two-stage compressors to achieve the optimum operating mode. In other cases, the current operating mode may be different from the optimum operating mode. In such case, the processing circuitry 86 activates and deactivates compressors and commands any two-stage compressors to operate at the appropriate capacity level, as necessary, to accomplish the optimum operating mode.

[0079] At step 140, the processing circuitry 86 waits for and determines stabilization of the multi-linked compressors. For example, the processing circuitry waits until a derivative of the discharge line temperature out of the multi-linked compressor 14 approaches stability. For example only, the derivative of the discharge line temperature reaches stability when the derivative value to approaches a low value or threshold value for a set period of time (for example only, where the derivative value is less than three degrees Fahrenheit (^QF) over a time frame of two minutes). When the derivative of the discharge line temperature approaches stability, the multi-linked compressors 14 are operating in the optimized state. The optimized state, or optimization state, optimizes compressor modulation to both meet the capacity demand from the refrigerant system 12 and optimizes the performance of the multi-linked compressors 14 by minimizing power consumption.

[0080] At step 144, the system controller 46 may command the processing circuitry 86 to shut down compressors in the multi-linked compressors 14 once the demand for capacity has been removed. For example, once the target temperature within a cooled or refrigerated space has been reached, the system may remove the demand for cooling. The processing circuitry 86 then follows a pre-programmed powered shut down routine. The processing circuitry 86 will shut down the compressors of the multi-linked compressors 14 one at a time. For example only, the compressors may be shut down in the order of highest capacity compressor to lowest capacity compressor. In another example, the compressors may be shut down in order of position, shutting off C first, then B, then A.

[0081] Based on cooling requirements, instead of proceeding to step 144, the system controller 46 may command a new capacity. In such case, the processing circuitry will then return to step 104 and start the optimization algorithm over again.

[0082] Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0083] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having," are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0084] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0085] Spatially relative terms, such as "inner," "outer," "beneath," "below," "lower," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the example term "below" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0086] In this application, including the definitions below, the terms controller or module may be replaced with the term circuit. The terms controller or module may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; memory (shared, dedicated, or group) that stores code executed by a processor; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on- chip. [0087] The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared processor encompasses a single processor that executes some or all code from multiple modules. The term group processor encompasses a processor that, in combination with additional processors, executes some or all code from one or more modules. The term shared memory encompasses a single memory that stores some or all code from multiple modules. The term group memory encompasses a memory that, in combination with additional memories, stores some or all code from one or more modules. The term memory may be a subset of the term computer-readable medium. The term computer-readable medium does not encompass transitory electrical and electromagnetic signals propagating through a medium, and may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory tangible computer readable medium include nonvolatile memory, volatile memory, magnetic storage, and optical storage.

[0088] The apparatuses and methods described in this application may be partially or fully implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on at least one non-transitory tangible computer readable medium. The computer programs may also include and/or rely on stored data.

[0089] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

CLAIMS What is claimed is:

1 . A system comprising:

a plurality of compressors linked in parallel by a common discharge line and a common suction line;

an evaporator;

a condenser; and

a system controller that determines a saturated evaporator temperature of the evaporator, a saturated condensing temperature of the condenser, a target capacity demand for the plurality of compressors, and an estimated system capacity and an estimated power consumption for each operating configuration of the plurality of compressors based on the saturated evaporator temperature and the saturated condensing temperature;

wherein the system controller compares the estimated system capacity for each operating configuration with the target capacity demand and an error tolerance value and selects an optimum operating mode of the plurality of compressors based on the comparisons and the estimated power consumption for each operating configuration, the optimum operating mode being selected from a group of operating configurations having the estimated system capacity within the error tolerance of the target capacity demand and the optimum operating mode having a lowest associated power consumption value in the group; and

wherein the system controller commands activation and deactivation of the plurality of compressors to achieve the selected optimum operating mode.

2. The system of Claim 1 , wherein the plurality of compressors includes at least one fixed capacity compressor and at least one two-stage compressor.

3. The system of Claim 2, wherein the at least one two-stage compressor includes a compressor having a delayed suction system.

4. The system of Claim 2, wherein the at least one two-stage compressor includes a compressor having a variable speed motor.

5. The system of Claim 2, wherein the at least one two-stage compressor includes a compressor having a scroll separation system.

6. The system of Claim 1 , wherein the plurality of compressors includes a variable volume ratio compressor.

7. The system of Claim 1 , wherein the estimated system capacity is calculated based on characteristics of each of the plurality of compressors.

8. The system of Claim 1 , wherein the operating configuration for the plurality of compressors includes a location of each of the plurality of compressors and a coefficient performance curve for each of the plurality of compressors.

9. The system of Claim 1 , wherein the system controller determines the estimated power consumption for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration.

10. The system of Claim 1 , wherein the system controller determines the estimated system capacity for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration.

1 1 . The system of Claim 1 , wherein the system controller determines whether the plurality of compressors have stabilized before selecting the optimum operating mode, the determination of whether the plurality of compressors have stabilized being based on an output of at least one of a current sensor, a common suction line temperature sensor, a common discharge line temperature sensor, a common suction line pressure sensor, and a common discharge line pressure sensor.

12. The system of Claim 1 , wherein the plurality of compressors includes two fixed capacity compressors having different capacities and one two-stage compressor, and has eleven associated operating configurations.

13. The system of Claim 1 , wherein the plurality of compressors includes two fixed capacity compressors and one two-stage compressor with different capacities, and has seven associated operating configurations.

14. A system comprising:

a first circuit having a first plurality of compressors linked in parallel by a first common discharge line and a first common suction line;

a second circuit having a second plurality of compressors linked in parallel by a second common discharge line and a second common suction line; and

a system controller that determines an estimated system capacity and an estimated power consumption for each operating configuration of the plurality of compressors in the first circuit and the plurality of compressors in the second circuit based on a saturated evaporator temperature and a saturated condensing temperature;

wherein the system controller selects an optimum operating mode of the plurality of compressors in the first circuit and the plurality of compressors in the second circuit based on a comparison of the estimated system capacity for each operating configuration with a target capacity demand and an error tolerance value and based on the estimated power consumption for each operating configuration, the optimum operating mode being selected from a group of operating configurations having the estimated system capacity within the error tolerance of the target capacity demand and the optimum operating mode having a lowest associated power consumption value in the group; and

wherein the system controller commands activation and deactivation of the plurality of compressors in the first circuit and the plurality of compressors in the second circuit to achieve the selected optimum operating mode.

15. A method for operating a system comprising: determining a saturated evaporator temperature of the evaporator, a saturated condensing temperature of the condenser, and a target capacity demand for a plurality of compressors;

determining an estimated system capacity and an estimated power consumption for each operating configuration of the plurality of compressors based on the saturated evaporator temperature and the saturated condensing temperature;

comparing the estimated system capacity for each operating configuration with the target capacity demand and an error tolerance value;

selecting an optimum operating mode of the plurality of compressors based on the comparisons and based on the estimated power consumption for each operating configuration, the optimum operating mode being selected from a group of operating configurations having the estimated system capacity within the error tolerance of the target capacity demand and the optimum operating mode having a lowest associated power consumption value in the group; and

commanding activation and deactivation of the plurality of compressors to achieve the selected optimum operating mode.

16. The method of Claim 15, wherein the plurality of compressors includes at least one of a fixed capacity compressor, a two-stage compressor, and a variable volume ratio compressor, wherein if the plurality of compressors includes the two-stage compressor, the two-stage compressor includes at least one of a compressor having a delayed suction system, a compressor having a variable speed motor, and a compressor having a scroll separation system.

17. The method of Claim 15, further comprising calculating the estimated system capacity based on the operating configuration for the plurality of compressors.

18. The method of Claim 17, wherein the operating configuration for the plurality of compressors includes a location of each of the plurality of compressors and a ten coefficient performance curve for each of the plurality of compressors.

19. The method of Claim 15, further comprising determining the estimated power consumption for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration.

20. The method of Claim 15, further comprising determining the estimated system capacity for each operating configuration based on a ten coefficient performance curve for each of the plurality of compressors in the associated operating configuration.

21 . The method of Claim 15, further comprising determining whether the plurality of compressors have stabilized before selecting the optimum operating mode, the determination of whether the plurality of compressors have stabilized being based on an output of at least one of a current sensor, a common suction line temperature sensor, a common discharge line temperature sensor, a common suction line pressure sensor, and a common discharge line pressure sensor.