Continuous and Discontinuous Capacity Control for High Speed Refrigeration Compressors

Abstract

The objective of this theoretical investigation was to find a capable and economical way of controlling high speed refrigeration compressors with a low number of cylinders. Compressors with 4 cylinders or more allow control by cutting-off one or two cylinder blocks because the remaining blocks maintain a sufficient smoothness of low speed fluctuation. The type of regulation to be found in this work should therefore apply primarily to twoand three-cylinder-compressors. Up to now the control of such compressors was performed only by externa 1 contra 1devices . These types of control do not affect the smoothness of low speed fluctuations, because they engage either before or after the compression. Application of external control affects all cylinders or only some of themwith respect to an application before or after the compression. External controls are characterized by a high energy input. Therefore they are economically not reasonab 1 e . Examples for those are throttling of the gas in the suction line and a discharge ill suction by-pass. To be economically efficient an internal controller action affecting the process of compression is preferred. Such an i nterna 1 contra 11 er action for 1 ow numbers of cylinders issupposedtoaffectall cylinderssimultaneously in order to achieve a sufficient smoothness of low speed fluctuations.