Variable-speed capacity control in refrigeration systems

This paper presents a review of the application of variable-speed capacity control to refrigeration systems. The aim is to put together diversified information in a single source and to appraise recent advances in variable-speed technology. The review reveals that although variable-speed drives based on inverters have been applied successfully to control the capacity of rotodynamic machines, such as pumps and fans, their application to positive displacement machines, such as compressors, has so far been restricted to small-capacity air-conditioning units. There has been only a very small uptake of the technology in the medium-range capacity units, due to a number of problems, such as insufficient development and integration of components, poor reliability, high capital cost and the failure of demonstration installations to produce the expected energy savings. Although inverter-based variable-speed compressor technology offers the potential for energy savings, considerable research work is still required for the development of optimised and cost-effective systems.