The most common refrigeration system in use for refrigerated food transport applications today is the vapour compression system. Mechanical refrigeration with the vapour compression cycle offers a wide range of options for compressor drive methods. The choice may be based on duty required, weight, noise requirements, maintenance requirements, installation cost, environmental considerations and fuel taxation. The performance and power requirements of these systems are normally assessed at full load. In reality however, transport refrigeration systems operate over a wide range of loads. To match the load the refrigeration system may be switched on and off or its capacity modulated to maintain the set temperature with a consequent reduction in efficiency. Depending on the system design envelope and the setup expected Coefficient of Performance (COP) is generally between 0.5 and 1.5.