Refrigerant System with Pulse Width Modulated Components and Variable Speed Compressor

Abstract

A variable speed drive is provided for operating a compressor motor in a refrigerant system. When a low load situation has been determined by the refrigerant system controls, the variable speed drive operates the compressor motor at lower speed mode of operation. Further, the operation of the variable speed drive is combined with a pulse width modulation control of different system components. In particular, at least one valve or compressor can be can be rapidly cycled by the control to regulate amount of refrigerant passing through the valve or compressor. Example valves would include a shut-off valve for an economizer cycle, an unloader valve, or a suction modulation valve.

Description

BACKGROUND OF THE INVENTION[0001]This application relates to a control for a refrigerant system having a variable speed compressor, and wherein pulse width modulation technologies are utilized to provide further control over the system.[0002]Refrigerant systems are utilized in many applications to condition an environment. In particular, air conditioners and heat pumps are employed to cool and / or heat air entering the environment. The cooling or heating load of the environment may vary with ambient conditions, occupancy level, other changes in sensible and latent load demands, and as the temperature and / or humidity set points are adjusted by an occupant of the environment.[0003]A feature that is known for improving the efficiency of refrigerant systems is the use of a variable speed drive for the compressor motor. Often, the compressor need not be operated at full speed, such as when the cooling load on the refrigerant system is relatively low. Under such circumstances, it might be ...

AI Technical Summary

Benefits of technology

[0007]In the disclosed embodiment of this invention, a compressor is provided with a variable speed drive. When a need for a low capacity is detected, the compressor is moved to a low speed to maintain adequate conditions in the environment without switching to a start-stop mode of operation. The compressor is incorporated into a refrigerant system, which has a pulse width modulation control for cycling some component in the system, other than cycling on and off the compressor motor. In disclosed embodiments, the cycled component is a valve, and may be a suction valve, and / or an economizer cycle shut-off valve and / or an unloader valve and / or cycled component is one of the scroll compressor pumping elements. By cycling these components on and off, the amount of refrigerant delivered to various locations in the refrigerant cycle is lowered, and thus the capacity can be lowered without lowering the compressor motor speed beyond the safe regime.

Problems solved by technology

However, compelling reliability concerns set a lower limit to the desirable compressor speed reduction.

As an example, inadequate lubrication of the compressor elements may present a problem at low operating speeds.

As an example, a scroll compressor could have a dramatic loss in performance due to a loss of radial compliance should it operate below a minimum speed.

These pulse width modulation techniques for control of a valve or internal scroll compression elements have not been utilized, however, in refrigerant systems having a variable speed drive compressor.

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