HK1127518A - Refrigerant system with variable speed drive - Google Patents

Description

Refrigerant system with variable speed drive

Technical Field

The present invention relates generally to machines driven by variable speed drives, and more particularly to systems for heating, ventilation, air conditioning and refrigeration applications having variable speed components.

Background

In machines driven by variable speed drives, the loss in power and efficiency due to losses associated with the operation of the variable speed drive is about 5% to 10%. This loss of efficiency or additional power draw is one of the drawbacks that limit the application of variable speed drives in industrial or other devices. This limitation is particularly pronounced where the need to decelerate or accelerate the machine from its normal operating speed is not common.

In addition, variable speed drive electronics generate heat and often require cooling with an external source and/or by diverting a portion of the refrigerant circulating through the refrigerant system. Thus, operating a variable speed drive within certain temperature limits comes at the expense of additional efficiency and power draw losses. Moreover, variable speed drives are often a source of unreliability that reduces overall system maintenance and uninterrupted operating intervals.

Thus, there is a need for heating, ventilation, air conditioning and refrigeration systems having components (or incorporating variable speed drives) that are driven at variable speeds with increased operating efficiency and improved reliability. The method and apparatus of the present invention reduces losses associated with operation of a variable speed drive.

It is an object of the present invention to provide a system for heating, ventilation, air conditioning and refrigeration applications with improved operating efficiency and improved reliability.

It is a further object of the present invention to provide a system having increased service life and maintenance intervals for components of a variable speed drive system.

It is a further object of the present invention to provide a configuration that allows selective operation of a variable speed drive system.

Disclosure of Invention

In one aspect, a power control system for a refrigerant system having an AC motor with a normal operating speed is provided. The power control system includes a variable frequency drive connected to an ac motor, and a bypass device connected to the ac motor and connectable to a power source. The bypass device is selectively switchable between first and second positions. The first position provides a connection from the power source to the variable frequency drive, thereby causing the ac motor to run at a lower or higher speed than normal operating speed. The second position provides a connection from the power source to the ac motor by bypassing the variable frequency drive, thereby causing the ac motor to operate at a normal operating speed.

In another aspect, a refrigerant system is provided that includes a vapor compression system and a power control system. The vapor compression system includes a compressor having a compressor motor. The power control system includes a variable speed drive device and a bypass device. The bypass device is connected to the compressor motor and is connectable to a power source. The bypass device is selectively switchable between first and second positions. The first position provides a connection from the power source to the variable speed drive device, thereby causing the compressor motor to run at a lower or higher speed than normal operating speed. The second position provides a connection from the power source to the compressor motor by bypassing the variable speed drive device, thereby causing the compressor motor to operate at a normal operating speed.

In yet another aspect, a method of operating a refrigerant system to meet space heat load requirements is provided. The method includes providing a vapor compression system having a compressor including an AC motor, determining whether the AC motor needs to be operated at a speed below or above a normal operating speed to meet a space heat load demand, correspondingly reducing or increasing the speed of the AC motor to a speed below or above the normal operating speed to meet the space heat load demand, wherein the speed is varied by adjusting a frequency and/or voltage of power supplied to the AC motor via a variable frequency drive, and, if the space heat load demand is met by operating the AC motor at the normal operating speed, providing power to the AC motor by bypassing the variable frequency drive.

The variable speed drive device may be a variable frequency drive and the motor may be an alternating current motor. The variable speed drive device may be a voltage control module and the motor may be a dc motor. The bypass device can include a two-position switch and a bypass loop. A bypass loop may be connected between the variable speed drive device and the power source to provide a direct connection to the motor. Vapor compression systems typically have at least a condenser, an expansion device, and an evaporator, wherein the condenser and the evaporator have a fan that includes a fan motor. The fan motor may be connected to a bypass device, wherein a first position of the bypass device provides a connection from the power source to the variable speed drive device, thereby causing the fan motor to run at a lower or higher speed than normal operating speed, and wherein a second position of the bypass device provides a connection from the power source to the fan motor by bypassing the variable speed drive device, thereby allowing the fan motor to run at normal operating speed. The method can also include monitoring a parameter of the refrigerant system to determine a space heat load applied to the refrigerant system. Also, each fan may have a separate power control system to increase operational flexibility, as desired. Further, a variable speed liquid pump may be used in a similar manner in place of the fan, but circulating liquid (instead of air) through the condenser and evaporator.

The above-described and other features and advantages of the present disclosure will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.

Drawings

Figure 1 is a schematic diagram of a refrigerant system having an exemplary embodiment of the power control system of the present invention,

FIG. 2 is a schematic diagram of a refrigerant system having an alternate exemplary embodiment of the power control system of the present invention, an

FIG. 3 is a schematic diagram of a refrigerant system having another alternative exemplary embodiment of the power control system of the present invention.

Detailed Description

Referring to FIG. 1, an exemplary embodiment of a system having a machine driven by a variable speed drive is shown and generally indicated by reference numeral 10. The exemplary embodiment of system 10 is a refrigerant system. It will be appreciated by those of ordinary skill in the art that the particular type of refrigerant system 10 can vary, including but not limited to heating, ventilation, air conditioning and refrigeration systems, and that the particular components of the system can vary to achieve particular space conditioning objectives. Such refrigerant system components are known to those of ordinary skill in the art. For example, a fan that moves air across a condenser and an evaporator can be replaced by a pump that circulates a liquid such as, for example, water or brine, for heat transfer purposes.

The refrigerant system 10 has a vapor compression system 20 and a power/control system 30. The vapor compression system 20 includes typical components for achieving desired characteristics within a conditioned space, including a refrigerant circuit 25 having various valves and interconnected tubes. The vapor compression system 20 includes a compressor 40, a condenser 50, and an evaporator 60 interconnected within a circuit 25. In the exemplary embodiment, fans 55 and 65 are in fluid communication with condenser 50 and evaporator 60, respectively, and an expansion device 70 is positioned in circuit 25 between the condenser and the evaporator. However, the particular configuration and components of the vapor compression system 20 (including the configuration of the refrigerant circuit 25) can vary depending on the particular requirements imposed on the system 10.

The power/control system 30 provides electrical power to drive components, such as the compressor 40 and/or fans 55 and 65, and to control one or more of the components of the vapor compression system 20. The power/control system 30 has a variable frequency drive 75 ("VFD") connected to an ac motor of the compressor 40 via the circuit 35 and also connected to a power source 80. A power bypass device 90 is provided between the VFD75 and the power source 80. In the exemplary embodiment of system 10, power bypass device 90 is a two-position switch 92 and a bypass loop 94. However, the present disclosure contemplates the use of other structures, devices, circuits, and/or methods to selectively provide power to the VFD75 or alternatively bypass the VFD75 and provide power directly to the motor of the compressor 40.

The VFD75 regulates the speed of the motor of the compressor 40 by varying the frequency and/or voltage of the power supplied to the motor. Power electronics for regulating or controlling frequency and voltage via the VFD75 are known in the art, such as, for example, rectifiers and inverter bridges, and can vary according to the particular needs of the system 10. This adjustment allows the motor of the compressor 40 to run at a lower or higher speed than normal operating speed. Such speed adjustments will improve system performance, for example, in the case when the thermal load within the conditioned space or ambient conditions for the refrigerant system changes or the user changes the conditioned space setting. However, when the compressor 40 needs to operate at its normal speed to meet sensible and latent capacity demands, then the use of the VFD75 incurs efficiency losses and additional power draw, such as the losses associated with the operation of the VFD power electronics and losses associated with the cooling of the VFD to operate within certain temperature limits mentioned above. To use the compressor 40 at normal operating speeds, the power bypass device 90 provides power directly to the compressor motor, thereby eliminating the VFD75 from the circuit and improving the operating efficiency and reliability of the refrigerant system.

Selective control or switching of the bypass device 90 can be accomplished by various methods and/or devices, including automatic and manual bypass. In the exemplary embodiment, bypass device 90 is operated by control system 95, and control system 95 determines whether the motor of compressor 40 is or will be operating at its normal operating speed to meet space heat load demands and opens or closes two-position switch 92 or other bypass device based on the determination. The opening or closing of the two-position switch 92 or other bypass device can be accomplished by various actuators, devices and methods known in the art, and the control system 95 can be a subsystem or subroutine of the overall control system for the refrigerant system 10. Alternatively, the opening or closing of the two-position switch 92 can be accomplished manually, and the control system 95 can provide a readable indication that the compressor 40 will be operating at normal operating speeds to meet space heat load demands.

Sensors are placed at various locations throughout the vapor compression system 20 to monitor operating parameters of the system. The data or information collected by the sensors can be used to control or switch the bypass device 90, such as by the control system 95, to open or close the two position switch 92. The sensors include, but are not limited to, a temperature sensor T (e.g., a temperature transducer), a pressure sensor P (e.g., a pressure transducer), a current sensor I, a power sensor W, a torque sensor TR, a slip sensor S, a transducer for each of these operating parameters, and the like. For refrigerant system 10, the use of pressure sensors and saturation temperature sensors is generally interchangeable, as there is a direct relationship between pressure and corresponding saturation temperature. Furthermore, the discharge of the compressor may have a temperature sensor for more accurate measurement. The corresponding operating parameters monitored by the sensors can include, but are not limited to, outdoor and indoor fan motor current, power, torque or slip, compressor motor current, power, torque or slip, condenser saturated discharge temperature, evaporator saturated suction temperature, compressor suction and discharge pressure, and compressor discharge temperature. The connection or communication method between the sensor and the bypass device 90, such as the control system 95, is not shown, but is known to those of ordinary skill in the art. The decision as to when to switch from variable frequency drive to constant speed operation is based on information gathered from these sensors. The transmission can be bypassed based at least in part on efficiency operating at the commercial frequency compared to operating at a speed different than that provided by the commercial frequency where there is additional inverter loss. Other considerations such as power limitations, safety considerations, and operational reliability may be included in the control logic of the control system 95 for forming the switching decisions. The control system 95 can include other sensors for determining whether the motor of the compressor 40 needs to run at normal operating speeds to meet space heat loads. Such sensors are capable of monitoring various parameters of the system 10, including the ambient temperature and the temperature of the conditioned space.

In the exemplary embodiment of system 10, fans 55 and 65 are also connected to bypass device 90 and controlled via bypass device 90. This allows selective variable speed control of the fan motor in the same manner as the speed of the motor of the compressor 40 is regulated by the VFD 75. When the fans 55 and 65 are or will be operating at normal operating speeds, the fans 55 and 65 can also be directly powered via the bypass device 90 to avoid the efficiency losses associated with the VFD 75.

The vapor compression system 20 is also capable of providing cooling to the VFD via refrigerant line 27 (as shown by the dashed lines) due to the heat generated by the power electronics of the VFD 75. A refrigerant line 26 draws a portion of the refrigerant from the main refrigerant circuit 25 downstream of the condenser 50 and returns it downstream of the evaporator 60 through a line 27, and may include valves 27A and 27B, each of which may be of an adjustable type. The refrigerant lines 26 and 27 supply a portion of the refrigerant from the primary refrigerant circuit 25 to the VFD75 to remove heat from the electronics of the VFD and then return the refrigerant to the primary refrigerant circuit 25. Other positions of the lines 26 and 27 relative to the main refrigerant circuit 25 are also possible. Additionally, the particular configuration and components of power control system 30 (including the configuration of circuit 35) may vary depending on the particular needs of refrigerant system 10. Similarly, similar design and control methods can be applied if a liquid pump 55 'or 65' (shown in phantom) is used in place of fan 55 or fan 65, respectively, for heat transfer interaction within vapor compression system 20. Each of the liquid pumps 55 'and 65' and the VFDs of the fans 55 and 65 may also be bypassed independently.

Referring to fig. 2, an alternative exemplary embodiment of a refrigerant system is shown, generally indicated by reference numeral 100. Likewise, it will be appreciated by those of ordinary skill in the art that the particular type of refrigerant system 100 can be varied, including (but not limited to) heating, ventilation, air conditioning, and refrigeration, and that the particular components of the system can be varied to achieve particular objectives.

Refrigerant system 100 has components and systems similar to and similarly identified as components and systems of refrigerant system 10 shown in fig. 1, such as vapor compression system 20 and components thereof. Refrigerant system 100 also has a power/control system 130 that includes components similar to and similarly identified as components of power/control system 30 shown in fig. 1. The power/control system 130 provides electrical power to drive components, such as the compressor 40 and fans 55 and 65, and to control one or more of the components of the vapor compression system 20. Similarly, if a fluid pump is used in place of fan 55 or fan 65, the same design and control method can be applied.

The power/control system 130 has a voltage control module 175 ("VCM") connected to the dc motor of the compressor 40 via circuitry 35 and also to the power source 80. A power bypass device 90, which in this alternative exemplary embodiment of system 100 is a two-position switch 92 and a bypass loop 94, is provided between VCM175 and power source 80. However, the present disclosure contemplates the use of other structures, devices, and/or methods to selectively power VCM175 or alternatively bypass the VCM and provide power directly to the motor of compressor 40.

VCM175 regulates the speed of the motor of compressor 40 by varying the voltage of the power supplied to the motor. Power electronics for regulating or controlling voltage via VCM175 are known in the art and can vary according to the particular needs of system 100. Regulating the voltage by VCM175 allows the motor of compressor 40 to run at a different speed than its normal operating speed and improves system performance during out-of-design conditions. When the compressor 40 is operating at normal speed, VCM175 is bypassed and electrical power is provided directly to the compressor's motor. This selective control or switching via bypass device 90 can be accomplished as described above with respect to the exemplary embodiment of system 10, including but not limited to using control system 95.

The present disclosure contemplates the use of other variable speed driver devices and/or power electronic circuits in place of VFD75 or VCM175 that can regulate the speed of the ac or dc motor for compressor 40 and/or other components of vapor compression system 20, but that can also bypass via bypass device 90 to provide power directly to the motor when normal operating speeds are anticipated, and avoid efficiency losses. Similarly, similar design and control methods can be applied if a liquid pump 55 'or 65' (shown in phantom) is used in place of the fan 55 or 65 with the heat exchanger in the vapor compression system 20. Each of the liquid pumps 55 'and 65' and the VCM of the fans 55 and 65 can be independently bypassed.

Referring to fig. 3, another alternative exemplary embodiment of a refrigerant system is shown, generally indicated by reference numeral 200. Likewise, it will be appreciated by those of ordinary skill in the art that the particular type of refrigerant system 200 can vary, including but not limited to heating, ventilation, air conditioning, and refrigeration, and that the particular components of the system can vary to achieve particular objectives.

Refrigerant system 200 has components and systems similar to and similarly identified as components and systems of refrigerant system 10 described above, such as vapor compression system 20 and its components. Refrigerant system 200 also has a power/control system 230 that includes components similar and similarly identified as components of power/control system 30. The power/control system 230 provides electrical power to drive components, such as the compressor 40 and fans 55 and 65, and to control one or more of the components of the vapor compression system 20.

The power/control system 230 has a plurality of variable frequency drives 275 operated by a system controller. Each of the VFDs is connected to different components of the refrigerant system 20, such as, for example, a motor of the compressor 40 and a motor of each of the fans 55 and 65. A power bypass device 90 is provided between the VFD275 and the power source 80, in this alternative exemplary embodiment of the system 200 a two-position switch 92 and a bypass loop 94. However, the present disclosure contemplates the use of other structures, devices, and/or methods to selectively provide power to the VFD275 or alternatively to bypass the VFD and provide power directly to the motor of the compressor 40 and the motors of the fans 55 and 65.

The power/control system 230 can utilize a voltage control module ("VCM") similar to that described with respect to the power/control system 130 coupled to the dc motor of the compressor 40. As mentioned above, system flexibility is increased by independently controlling each of the VFD or VCM for the different components of the refrigerant system 20. The VFD or VCM (or a combination of both) of each of the components can independently bypass or directly provide power to increase system operating efficiency and flexibility. Similarly, if a liquid pump 55 'or 65' (shown in phantom) is used in place of the fan 55 or 65 with the heat exchanger within the vapor compression system 20, similar design and control methods can be applied. The VFD or VCM of each of the liquid pumps 55 'and 65' may also be bypassed independently.

While the disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims (17)

1. A power control system (30) for a system (10, 100, 200) including an electric motor having a normal operating speed, the power control system (30) comprising:

a variable speed drive (75, 175, 275) connected to the electric motor, an

A bypass device (90) connected to the electric motor and connectable to the power source (80), wherein the bypass device (90) is selectively switchable between a first and a second position, wherein the first position provides electrical power from the power source (80) to the variable speed drive (75, 175, 275), thereby causing the electric motor to operate at a speed different from a normal operating speed, and wherein the second position provides electrical power from the power source (80) to the electric motor by bypassing the variable speed drive (75, 175, 275), thereby causing the electric motor to operate at the normal operating speed.

2. The system (10, 100, 200) of claim 1, wherein the bypass device (90) includes a two-position switch (92) and a bypass loop (94), and wherein the bypass loop (94) is connected between the variable speed drive (75, 175, 275) and a power source (80).

3. The system (10, 100, 200) of claim 1, wherein the variable speed device (75, 175, 275) is a variable frequency drive (75, 275), and wherein the electric motor is an alternating current motor.

4. The system (10, 100, 200) of claim 1, wherein the transmission (75, 175, 275) is a voltage control module (175, 275), and wherein the motor is a dc motor.

5. Refrigerant system (10, 100, 200) comprising:

a vapor compression system (20) having a compressor (40) including a compressor motor, and

a power control system (30, 130, 230) having a speed change device (75, 175, 275) and a bypass device (90), wherein the bypass device (90) is connected to the compressor motor and connectable to a power source (80), wherein the bypass device (90) is selectively switchable between first and second positions, wherein the first position provides electrical power from the power source (80) to the speed change device (75, 175, 275), thereby causing the compressor motor to operate at a speed different from a normal operating speed, and wherein the second position provides electrical power from the power source (80) to the compressor motor by bypassing the speed change device (75, 175, 275), thereby causing the compressor motor to operate at the normal operating speed.

6. The system (10, 100, 200) of claim 5, wherein the variable speed device (75, 175, 275) is a variable frequency drive (75, 275), and wherein the compressor motor is an AC motor.

7. The system (10, 100, 200) of claim 5, wherein the variable speed device (75, 175, 275) is a voltage control module (175, 275), and wherein the compressor motor is a DC motor.

8. The system (10, 100, 200) of claim 5, wherein the bypass device (90) includes a two-position switch (92) and a bypass loop (94), and wherein the bypass loop (94) is connected between the transmission device (75, 175, 275) and a power source (80).

9. The system (10, 100, 200) of claim 5, wherein the vapor compression system (20) further comprises a condenser (50) and an evaporator (60), wherein the condenser (50) has a condenser fan (55) comprising a first fan motor or a condenser pump (55 ') comprising a first pump motor, wherein the evaporator (60) has an evaporator fan (65) comprising a second fan motor or an evaporator pump (65') comprising a second pump motor, wherein at least one of the first fan motor, the second fan motor, the first pump motor, or the second pump motor is connected to the bypass device (90), wherein the first position of the bypass device (90) provides electrical power from a power source (80) to the speed change device (75, 175, 275), thereby causing the first fan motor, the speed change device (75, 175, 275), and the evaporator (60) to operate in a first operating mode, The at least one of the second fan motor, the first pump motor, or the second pump motor operates at a speed different from a normal operating speed, and wherein the second position of the bypass device (90) provides electrical power from a power source (80) to the at least one of the first fan motor, the second fan motor, the first pump motor, or the second pump motor by bypassing the variable speed device (75, 175, 275), thereby allowing the at least one of the first fan motor, the second fan motor, the first pump motor, or the second pump motor to operate at the normal operating speed.

10. The system (10, 100, 200) of claim 9, wherein the variable speed device (75, 175, 275) is a variable frequency drive (75, 275), and wherein the at least one of the first fan motor, the second fan motor, the first pump motor, or the second pump motor is an alternating current motor.

11. The system (10, 100, 200) of claim 9, wherein the variable speed device (75, 175, 275) is a voltage control module (175, 275), and wherein the at least one of the first fan motor, the second fan motor, the first pump motor, or the second pump motor is a direct current motor.

12. The system (10, 100, 200) of claim 9, wherein the bypass device (90) includes a two-position switch (92) and a bypass loop (94), and wherein the bypass loop (94) is connected between the transmission device (75, 175, 275) and a power source (80).

13. A method of operating a refrigerant system (10, 100, 200) to meet a regulated space heat load, comprising:

providing a vapor compression system (20) having an electric motor,

determining whether the electric motor is to be operated at a speed different from a normal operating speed to meet a regulated space heat load,

adjusting the speed of the electric motor to meet the adjusted space heat load, wherein the speed is adjusted by a speed change device (75, 175, 275), an

If a space conditioning load can be met by operating the electric motor at the normal operating speed, power is provided to the electric motor by bypassing the transmission (75, 275, 275).

14. The method of claim 13, further comprising:

operating parameters of a refrigerant system (10, 100, 200) are monitored and the transmission (75, 275, 275) is bypassed based at least in part on an efficiency of operation at the industrial frequency where there is additional inverter loss compared to operation at a speed different from a speed provided by the industrial frequency.

15. The method of claim 14, further comprising:

monitoring the operating parameter of the refrigerant system (10, 100, 200) via at least one transducer selected from the group consisting of a temperature transducer, a pressure transducer, a current transducer, a power transducer, a torque transducer, a slip transducer, or any combination thereof.

16. The method of claim 13, further comprising:

adjusting a frequency or voltage of power supplied to the electric motor to adjust the speed, wherein the electric motor is a plurality of electric motors, and wherein each of the plurality of electric motors drives a refrigeration component selected from the group consisting essentially of a compressor, a condenser fan, a condenser pump, an evaporator fan, an evaporator pump, and any combination thereof, an

Independently and selectively bypassing the transmission (75, 275, 275) of at least one of the plurality of electric motors.

17. An apparatus, system or method for controlling one or more motors within a refrigerant system (10, 100, 200) as described above with respect to any of fig. 1 to 3.