Compressor capacity modulation

Abstract

A pulsed modulated capacity modulation system for refrigeration, air conditioning or other types of compressors is disclosed in which suitable valving is provided which operates to cyclically block flow of suction gas to a compressor. A control system is provided which is adapted to control both the frequency of cycling as well as the relative duration of the on and off time periods of each cycle in accordance with sensed system operating conditions so as to maximize the efficiency of the system. Preferably the cycle time will be substantially less than the time constant of the load and will enable substantially continuously variable capacity modulation from substantially zero capacity to the full capacity of the compressor. Additional controls may be incorporated to modify one or more of the motor operating parameters to improve the efficiency of the motor during periods of reduced load.

Description

[0001]More than one reissue application has been filed for the reissue of U.S. Pat. No. 6,206,652. The reissue applications are application Ser. No. 11 / 152,834 (now U.S. Pat. No. RE40,830) and Ser. No. 11 / 152,836 (the present application), all of which are reissue applications of U.S. Pat. No. 6,206,652.[0002]The present application is a continuation-in-part of U.S. application Ser. No. 08 / 939,779 filed Sep. 29, 1997, which is now U.S. Pat. No. 6,047,557 issued Apr. 11, 2000.BACKGROUND AND SUMMARY OF THE INVENTION[0003]The present invention is directed to a system for modulating the capacity of a positive displacement compressor such as a refrigeration and / or air conditioning compressor and more specifically to a system incorporating a valving arrangement for cyclically blocking suction gas flow to the compressor while the compressor is continuously driven.[0004]Capacity modulation is often a desirable feature to incorporate in refrigeration and air conditioning compressors as well ...

AI Technical Summary

Benefits of technology

Enables precise control of compressor capacity, reducing energy consumption, minimizing temperature fluctuations, and extending defrost cycles, while improving oil return and reducing motor stress, leading to enhanced efficiency and tighter temperature control in refrigeration and air conditioning systems.

Problems solved by technology

While such arrangements do provide varying degrees of capacity modulation, the degree of modulation that can be achieved is available only in relatively large discrete steps.

This discrete step form of modulation does not allow the system capacity to be matched to the load requirement conditions at all but rather only to very roughly approach the desired capacity resulting in either an excess capacity or deficient capacity.

As system conditions will rarely if ever match these gross steps of modulation, the overall operating system efficiency will not be able to be maximized.

However, when discharge gas is recirculated back to suction, the work of compression is lost for that fraction of the gas recirculated thus resulting in reduced system efficiency.

Combinations of the aforementioned methods enables substantially quasi-infinite capacity modulation at slightly better efficiency but still fails to provide the ability to closely match the compressor capacity to the load being served.

Other approaches, which can result in selectively disabling the compression process of one or more of the cylinders of a multi-cylinder compressor, such as cylinder porting, stroke altering or clearance volume varying methods result in similar step modulation with a resulting mismatch between load and capacity and additionally suffer from dynamic load unbalance and hence vibration.

Operating at higher evaporator temperatures reduces the defrost energy required because the system develops frost more slowly at higher temperatures.

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