الفهرس 
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Abstract
In a traditional refrigeration system, fixed speed motors are used;
this limits the use of the refrigeration system to a single application. In this experimental study a refrigeration system is used in cooling and freezing applications with the aid of an inverter driven scroll compressor, an inverter driven evaporator fan motors and an inverter driven condenser water pump using the environment friendly refrigerant R-507.
Operating the refrigeration system at variable speed operation enables part load operation, in cooling and freezing mode, without the need of any additional component. The flexibility obtained from the use of variable speed motors is constrained when using the thermostatic expansion valve due to its sluggish performance at part load. Using an electronic expansion valve overcomes the weak response of the thermostatic expansion valve at part load and increases the coefficient of performance of the refrigeration system.
Using variable speed motors with electronic expansion valve in medium temperature operation allows the refrigeration system to operate at 60 Hz compressor driving frequency resulting in an increase in the refrigeration capacity by 21.4% over the traditional fixed speed system with thermostatic expansion valve. It also improves the system coefficient of performance by 20% compared to the traditional fixed speed system with thermostatic expansion valve.