1. Field of the Invention
The present disclosure is related to refrigerant systems and methods of their control. More particularly, the present disclosure is related to refrigerant systems having pulse width modulated refrigeration components.
2. Description of Related Art
Refrigerant systems are commonly used to provide conditioned air or other secondary loop fluid (such as water or glycol) to, for example, a refrigerator, a freezer, a building, a car, and other spaces with climate controlled environment.
The efficiency of refrigerant systems is directly related to the use of the system's refrigerant moving devices such as a compressor and secondary fluid moving devices such as fans or pumps. One method of increasing the efficiency of the refrigerant system is to efficiently unload these components during part-load operation to adequately reduce the capacity provided by a refrigerant system to more closely match the thermal demands in the conditioned environment.
One method of achieving capacity control is to continuously cycle the compressor motor between an “on” position and an “off” position. Typically, the compressor motor, when it is in the “on” position, operates at a constant speed. In this manner, a desired duty cycle for the compressor, and consequently capacity provided by the refrigerant system, can be achieved. However, the “on” and “off” cycling of the compressor motor is known to cause various undesired effects on the reliability of the refrigerant system. Additionally, quite often, a desired precise temperature and humidity control in the conditioned environment may not be achieved, causing discomfort to the occupant of the environment. Furthermore, there are irreversible losses associated with the compressor cycling between “on” and “off” positions that cannot be neglected.
Another prior art method proposed to achieve capacity control is to operate the compressor (and/or other refrigerant system components such as fans and pumps) in a pulse width modulated mode. Compressors operating in a pulse width modulated mode can circulate a time-averaged desired amount of refrigerant throughout the refrigerant system, and provide the desired capacity to satisfy thermal load demands in the climate conditioned environment, without the need to start and stop a compressor motor, which operates at a relatively constant speed.
For example, compressors can be operated in a pulse width modulated mode by employing two or more mechanical elements, such as orbiting and non-orbiting scroll members, that can move in and out of contact with one another at a predetermined rate to selectively compress the refrigerant during the time intervals when the scroll members are in contact with one another. The control can selectively engage and disengage the mechanical compression elements, thereby periodically providing the compressed refrigerant flow by the compressor and throughout the refrigerant system, while allowing the motor to run at a relatively constant speed.
Another known method to provide a lower refrigerant flow is to operate a refrigerant flow control device such as a solenoid valve, preferably at the compressor suction, in a pulse width modulated mode. The operation of the valve in the pulse width modulated mode is achieved by rapidly opening and closing the valve (with a cycle time normally varying from 2 to 20 seconds), while allowing the motor to operate at a relatively constant speed.
However, there is a continuing need for refrigerant systems and methods of controlling such systems that further improve upon the efficiency of prior art refrigerant systems.