Abstract: A refrigeration system includes a pump to deliver oil to the scroll compressor collected from the condenser and the evaporator. The refrigeration system also includes a heat exchanger in thermal communication with the oil at high temperature in the oil separator. Oil collected from the condenser and the evaporator is passed through the heat exchanger to gain a heat energy. The refrigeration system further includes a controller to control an oil return solenoid valve to adjust flow of heated oil from the pump into the scroll compressor based on a suction super heat at inlet of the scroll compressor. The heated oil evaporates the low-pressure liquid refrigerant particles in a low-pressure vapor refrigerant to avoid a flood-back in the refrigeration system.

Abstract: A method controls the level of liquid within an evaporator of a flooded-type chiller without level sensors. The flooded-type chiller includes at least one compressor, a condenser, an expansion valve and an evaporator. A number of sensors positioned in the system measures a number of first parameter information values. A controller calculates a number of second parameter information values based on the measured first parameter information values and further determines a virtual refrigerant level as a control signal based on the second parameter information values. Based on the determined virtual refrigerant level, the controller opens, closes or holds the expansion valve with respect to a dead zone for maintaining a pre-defined target refrigerant level so as to provide the desired refrigerant level and oil in the evaporator.