Refrigerant system with multi-speed pulse width modulated compressor

Abstract

A refrigerant system is provided with a compressor having a motor that is operable at least at two distinct speeds. The pulse width modulation control is provided to cycle a compressor motor operation between its at least two speeds at a specific rate to exactly match thermal load demands in a conditioned space. The present invention reduces cycling and other efficiency losses as have been experienced in the prior art, as well as minimizes cost and may improve reliability. Also, the present invention can be utilized in conjunction with other known unloading techniques.

Description

BACKGROUND OF THE INVENTION[0001]This application relates to a refrigerant system wherein a compressor motor may operate at least at two speeds, and wherein a pulse width modulation control is provided to allow cycling the motor between the distinctive speeds at a specified adjustable rate to vary the refrigerant system capacity.[0002]Refrigerant systems are utilized to condition a secondary fluid, such as air. Compressors and refrigerant systems are typically sized to meet a maximum capacity demand. However, for the most part, a cooling or heating capacity demand is relatively low, and therefore, the refrigerant system needs to be unloaded by some means. In a single-circuit refrigerant system, a motor for a compressor is typically cycled between on and off operational stages. Alternatively, a suction modulation valve, or a variable speed compressor may be utilized. All of these methods of unloading have various drawbacks. When the unit is cycled on and off, the temperature and humi...

AI Technical Summary

Benefits of technology

The invention is about a compressor in a refrigerant system that has a multi-speed motor. This motor can change speeds by adding or removing windings. The compressor can switch between these speeds using solid state contactors, which are more expensive but offer higher reliability. The compressor motor can be controlled using pulse width modulation, which allows for precise tailoring of the refrigerant system's capacity. This modulation can be used in conjunction with other techniques such as switching on and off an economizer circuit, employing a compressor bypass valve, and using a suction modulation valve. The compressor motor is cycled quickly enough that the temperature of the air supplied to the environment is not significantly affected when the compressor switches between operating speeds.

Problems solved by technology

However, for the most part, a cooling or heating capacity demand is relatively low, and therefore, the refrigerant system needs to be unloaded by some means.

When the unit is cycled on and off, the temperature and humidity of the environment to be conditioned cannot be precisely controlled.

In the air conditioning case, this insufficient temperature control creates discomfort to the occupant of the indoor environment.

In the refrigeration case, the inadequate temperature control can lead to spoilage of goods that need to be refrigerated and kept within a specified temperature range.

Also, cycling losses occurring during compressor start-stop operation are detrimental to the efficiency of the refrigerant system.

Similarly, the use of a suction modulation valve has undesirable consequences, since an increased pressure ratio across the compressor reduces the refrigerant system efficiency and increases compressor discharge temperature.

Also, a suction modulation valve adds cost to the unit and becomes an additional reliability risk.

In the case of a variable speed compressor, a variable speed drive is also a significant cost adder.

Furthermore, a compressor speed, while controlled by a variable speed drive, often cannot be reduced below a certain value to meet tight temperature control requirements.

The variable speed drive systems introduce extra losses due to inefficiencies of the variable speed drives themselves.

Also, additional expensive means to cool the variable speed drive are often required.

Lastly, the use of a variable speed compressor and associated components introduce extra complexity into the system design, potentially leading to reliability problems.

Though this method is highly advantageous, it is often not as efficient as a variable speed option, and in some cases may lead to excessively high discharge temperatures.

Rapid cycling or pulse width modulation techniques have not yet been utilized to control the speed of a multi-speed compressor motor.

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