Method for controlling a supply of refrigerant to an evaporator

Abstract

A method for controlling a supply of refrigerant to an evaporator () of a vapor compression system (), such as a refrigeration system, an air condition system or a heat pump, is disclosed. The vapor compression system () comprises an evaporator (), a compressor (), a condenser () and an expansion device () arranged in a refrigerant circuit. The method comprises the steps of: Actuating a component, such as an expansion valve (), a fan or a compressor (), of the vapor compression system () in such a manner that a dry zone in the evaporator () is changed; measuring a temperature signal representing a temperature of refrigerant leaving the evaporator (); analyzing the measured temperature signal, e.g. including deriving a rate of change signal; determining a temperature value where a gain of a transfer function between the actuated component and the measured temperature drops from a maximum value to a minimum value, in a decreasing temperature direction; defining the determined temperature value as corresponding to a zero superheat (SH=0) value of refrigerant leaving the evaporator (), and controlling a supply of refrigerant to the evaporator () in accordance with the defined SH=0 temperature value, and on the basis of the measured temperature signal. The method steps may be repeated at certain time intervals in order to provide updated determinations of the SH=0 temperature value. The method allows the SH=0 point to be determined purely on the basis of the measured temperature signal. Subsequently, the supply of refrigerant to the evaporator () can be controlled purely on the basis of the measured temperature signal.