Improvement in Starting Characteristics of a Hermetic Reciprocating Compressor by Offset Cylinder Arrangement

Abstract

Better starting performance of hermetic compressor has become one of the primary development targets due to variations in operating pressures of refrigerants. At starting reciprocating mechanism is subjected to critical conditions which impose greater forces on piston this causes the starting process difficult. In this work, an Excel program is developed to calculate the torque requirement of hermetic compressor by considering gas force, inertia of components, and frictional resistance. This saves time and cost associated with testing and performing iterations for motor selection. It is observed that 90% of total torque is required to overcome gas force, 9% for inertia, and 1% is loosed in friction. For reducing torque demand and improving starting ability, various methods were studied but offset cylinder method is implemented. Compressor prototype was built with cylinder offset by 0.6 mm which causes reduction in torque demand by 27% as compared to inline cylinder compressor. Prototype is tested on calorimeter for startability and results show that compressor has better starting ability than inline cylinder compressor and it can start satisfactorily in specified voltage range. Also, effect of various refrigerants on torque demand is discussed.