REFRIGERANT SYSTEM WITH VARIABLE SPEED DRIVE BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] This invention generally relates to machinery driven by variable speed drives and, more particularly, to systems for heating, ventilation, air-conditioning and refrigeration applications with variable speed components. 2. Description of the Related Art [0002] In machinery that is driven by variable speed drives, there is approximately a five to ten percent penalty in power and efficiency due to losses associated with the operation of the variable speed drive. This efficiency loss or additional power draw is one of the drawbacks that has limited the application of variable speed drives in industrial or other installations. This limitation is especially significant where the need to slow down or speed up the machinery from its normal operating speed is infrequent. [0003] Further, variable speed drive electronics generate heat and are frequently required to be cooled with an external source and/or by diverting a portion of refrigerant circulating through the refrigerant system. Therefore, additional efficiency and power draw penalties are paid to operate variable speed drives within the specified temperature limits. Also, variable speed drives often present a source of unreliability reducing overall system maintenance and uninterrupted service intervals. [0004] Accordingly, there is a need for heating, ventilation, air-conditioning and refrigeration systems with the components driven at variable speeds (or incorporating variable speed drives) with enhanced efficiency of the operation and improved reliability. The method and apparatus of the present invention reduces losses associated with the operation of variable speed drives. [0005] It is an object of the present invention to provide a system for heating, ventilation, air-conditioning and refrigeration applications with an enhanced operational efficiency and improved reliability. [0006] It is a further object of the present invention to provide such a system with an increased service life and maintenance intervals for the components of the variable speed drive system. [0007] It is yet a further object of the present invention to provide a configuration that allows for selective operation of the variable speed drive system. SUMMARY OF THE INVENTION [0008] 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 comprises a variable frequency drive connected to the AC motor; and a bypass device connected to the AC motor and conneetable to a power source. The bypass device is selectively switchable between first and second positions. The first position provides connection from the power source to the variable frequency drive thereby causing the AC motor to run at lower or higher than the normal operating speed. The second position provides connection from the power source to the AC motor by bypassing the variable frequency drive thereby causing the AC motor to run at the normal operating speed; [0009] In another aspect, a refrigerant system is provided, which comprises a vapor compression system and a power control system. The vapor compression system includes a compressor with 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 connection from the power source to the variable speed drive device thereby causing the compressor motor to run at lower or higher than a normal operating speed. The second position provides connection from the power source to the compressor motor by bypassing the variable speed drive device thereby causing the compressor motor to run at the normal operating speed. [0010] In yet another aspect, a method of operating a refrigerant system to meet space thermal load demands is provided. The method comprises: providing a vapor compression system haying a compressor with an AC motor; determining if the AC motor need to run at below or above a normal operating speed to satisfy the space thermal load demands; reducing or increasing a speed of the AC motor accordingly below or above the normal operating speed to satisfy the space thermal load demands, wherein the speed is varied by adjusting the frequency and/or voltage of power supplied to the AC motor via a variable frequency drive; and providing power to the AC motor by bypassing the variable frequency drive if the space thermal load demands are to be satisfied by running the AC motor at the normal operating speed. [0011] The variable speed drive device can be a variable frequency drive and the motor may be an AC motor. The variable speed drive device can be a voltage control module and the motor may be a DC motor. The bypass device can comprise a two-position switch and a bypass circuit. The bypass circuit may be connected between the variable speed drive device and the power source for providing the connection directly to the motor. The vapor compression system typically has at least a condenser, an expansion device, and evaporator, where a condenser and evaporator have fans with fan motors. The fan motors may be connected to the bypass device, wherein the first position of the bypass device provides connection from the power source to the variable speed drive device thereby causing the fan motor to run at lower or higher than a normal operating speed, and wherein the second position of the bypass device provides connection from the power source to the fan motor by bypassing the variable speed drive device thereby allowing the fan motor to run at the normal operating speed. The method can further comprise monitoring parameters of the refrigerant system to determine the space thermal load imposed upon the refrigerant system. Also, each of the fans may have a separate power control system increasing operational flexibility, if desired. Further, variable speed liquid pumps may be used in place of fans in a similar manner but to circulate liquid (instead of air) through condensers and evaporators. [0012] 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. BRIEF DESCRIPTION OF THE DRAWINGS [0013] Figure 1 is a schematic illustration of a refrigerant system with an exemplary embodiment of a power control system of the present invention; [0014] Figure 2 is a schematic illustration of a refrigerant system with an alternative exemplary embodiment of a power control system of the present invention; and [0015] Figure 3 is a schematic illustration of a refrigerant system with another alternative exemplary embodiment of a power control system of the present invention. DETAILED DESCRIPTION OF THE INVENTION [0016] Referring to FIG. 1, an exemplary embodiment of a system having machinery driven by variable speed drives is illustrated and generally referred to by reference numeral 10. The exemplary embodiment of system 10 is a refrigerant system. It should be understood by a person of ordinary skill in the art that the particular type of the refrigerant system 10 can be varied including (but not limited to) heating, ventilation, air-conditioning and refrigeration systems, and the particular components of the system can be changed to accomplish the specific space conditioning objective. Such refrigerant system components are known by a person of ordinary skill in the art. For instance, fans moving air across the condenser and evaporator could be replaced by pumps circulating liquid, such as, for example, water or brine, for heat transfer purposes. [0017] 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 in the conditioned space including a refrigerant circuit 25 with various valves and interconnected pipes . The vapor compression system 20 includes a compressor 40, a condenser 50, and an evaporator 60 interconnected in the circuit 25. In the exemplary embodiment, fans 55 and 65 are in fluid communication with the condenser 50 and the evaporator 60, respectively, and an expansion device 70 is positioned between the condenser and evaporator within the circuit 25. However, the particular configuration and components of the vapor compression system 20 (including the configuration of refrigerant circuit 25) can be varied according to particular requirements imposed on system 10. [0018] The power/control system 30 provides electric power for driving the components, e.g., compressor 40 and/or fans 55 and 65, as well as control over one or more of the components of vapor compression system 20. Power/control system 30 has a variable frequency drive 75 ("VFD") that is connected to the AC motor of compressor 40 and which is also connected to a power source 80 via electric circuit 35. A power bypass device 90 is provided between VFD 75 and power source 80. In the exemplary embodiment of system 10, the power bypass device 90 is a two-position switch 92 and a bypass circuit 94. However, the present disclosure contemplates the use of other structures, devices, circuits and/or methods for selectively providing power to VFD 75 or alternatively bypassing the VFD 75 and providing the power directly to the motor of compressor 40. [0019] VFD 75 adjusts the speed of the motor of compressor 40 by varying the frequency and/or voltage of the power provided to the motor. The power electronics used to adjust or control the frequency and voltage via VFD 75 are known in the art, such as, for example, rectifiers and inverter bridges, and can be varied according to the particular needs of system 10. This adjustment allows the motor of compressor 40 to run at lower or higher than normal operating speed. For instance, such a speed adjustment will improve system performance under circumstances when thermal load in the conditioned space or environmental conditions for the refrigerant system change or a user alters the conditioned space setpoint. However, when compressor 40 is required to operate at its normal speed to meet sensible and latent capacity demands, then the use of VFD 75 incurs efficiency losses and additional power draw, e.g., the above-mentioned losses associated with operation of the VFD power electronics and losses associated with cooling of VFD to operate within specified temperature limits. For use of compressor 40 at the normal operating speed, power bypass device 90 provides the power directly to the compressor motor, thus excluding VFD 75 from an electric circuit and improving operational efficiency and reliability of the refrigerant system. [0020] The selective control or switching of the bypass device 90 can be accomplished by various methods and/or devices including both automatic and manual bypassing. In an exemplary embodiment, bypass device 90 is operated by a control system 95 that determines whether the motor of compressor 40 is, or will be, operating at its normal operating speed to satisfy the space thermal load demands, and opens or closes the two-position switch 92 or other bypass device based upon that determination. The opening or closing of the two-position switch 92 or other bypass device can be done by various actuators, devices and methods known in the art, and control system 95 can be a subsystem or subroutine of the overall control system for refrigerant system 10. Alternatively, the opening or closing of the two-position switch 92 can be done manually, and control system 95 can provide a readable indication that compressor 40 will be operating at a normal operating speed to satisfy the space thermal load demands. [0021] Sensors are disposed in various positions throughout the vapor compression system 20 to monitor operational parameters of the system. The data or information gathered by the sensors can be utilized for the control or switching of the bypass device 90, e.g., by control system 95 for the opening or closing of the two-position switch 92. The sensors include, but are not limited to, temperature sensors T (e.g., temperature transducers), pressure sensors P (e.g., pressure transducers), electric current sensors I, power sensors W, torque sensors TR, slip sensors S, transducers for each of these operational parameters, and the like. The use of pressure sensors and saturation temperature sensors are generally interchangeable for refrigerant system 10, since there is a direct relationship between pressure and corresponding saturation temperature. Further, the discharge of the compressor may have a temperature sensor for more refined measurements. The corresponding operational parameters monitored by the sensors can include, but are not limited to, the outdoor and indoor fan motor current, power, torque or slip; the compressor motor current, power, torque or slip; the condenser saturation discharge temperature; evaporator saturation suction temperature; the compressor suction and discharge pressure; and the compressor discharge temperature. The connection or method of communication between the sensors and the bypass device 90, e.g., control system 95, is not shown but is known to a person of ordinary skill in the art. The decision when to switch from variable frequency drive to constant speed operation would depend on the information gathered from these sensors. Bypassing of the variable speed device can be based, at least in part, on the efficiency of running at a line frequency as compared to operating at a speed other than provided by the line frequency where there are additional inverter losses. Other considerations such as power limitations, safety concerns and operational reliability may be included into the control logic of control system 95 for making a switching decision. Control system 95 can include other sensors for determining whether the motor of compressor 40 will need to run at normal operating speed to satisfy a space thermal load. Such sensors can monitor various parameters of the system 10, including the ambient temperature and the temperature of the conditioned space. [0022] In the exemplary embodiment of system 10, fans 55 and 65 are also connected to, and controlled via,