Speed Control in Industrial Refrigeration: Theory, Application & Case Studies

Abstract

It is often standard practice in the field of industrial refrigeration to design and operate systems with little regard toward part-load performance. This approach is understandable, whether viewed from the standpoint of the design engineer, plant manager or chief operator. As long a space temperature and production rates are maintained during peak periods, the refrigeration system is viewed as operating "correctly". The truth is, most refrigeration systems spend some, if not most operating hours at reduced capacity. Screw compressors back off slide valves, evaporator coils utilize back-pressure regulators (BPRs) or liquid solenoids, and condensers cycle fans. Unfortunately, these control methods do not provide the maximum attainable reduction in brake horsepower (BHP) as refrigeration capacity is reduced. This paper will discuss the application of variable speed drive (VSD, also called "variable frequency drive", "adjustable speed drive", "inverter", or simply "freq. drive") technology to capacity control of screw compressors, evaporator fans, and condenser fans. As shown through theory and case study, speed control of these components provides maximum flexibility, control and energy efficiency.