Capacity control/modulation of a refrigeration compressor

• Main Author: Sng, Han Yang.
• Other Authors: Ooi Kim Tiow
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering::Control engineering
• Online Access: http://hdl.handle.net/10356/53779
• Institution: Nanyang Technological University

Refrigeration and air-conditioning are widely-used applications in modern day society to cool products and ventilate buildings. Many air-conditioning and refrigeration systems are designed to maintain a fixed amount of cooling capacity. In practice, loads exhibit wide ranges of variation depending on operating conditions such as weather and amount of insulation. To reduce the energy consumption, it is desirable to incorporate capacity control modules into these cooling systems. Over the past few decades, developments in capacity control methods have given rise to solutions such as gas bypass, unloaders, variable speed drives, multi-stage compressors or variable cylinder volume. A thorough evaluation of the effectiveness of these modulation technologies drew the conclusion that current capacity control methods are either costly to implement, too complex in design, fairly unreliable, or are unable to achieve optimal efficiencies. In particular, the review identified that capacity control methods for rolling piston compressors had only picked up in recent years, and there is potential for further improvements. Based on the findings of the review, a novel capacity control method was developed. The new method works on the principle of holding the vane of a rolling piston compressor in the retracted position to prevent any compression of refrigerant gas from occurring. Control of the vane is achieved via a piston design. A CAD model of the new design was built, and finite element analysis was carried out on the model to investigate the robustness of the design. Based on the operating parameters of the new design, a mathematical model was also derived to assess the response of the piston-vane system when it is activated. The results of the model are promising, and reflect that the piston-vane control system is able to respond to a switch from full load to no load almost instantaneously.