A method for controlling a supply of refrigerant to an evaporator based on temperature measurements

Abstract

A method for controlling a supply of refrigerant to an evaporator ( 2 ) of a vapour compression system ( 1 ), such as a refrigeration system, an air condition system or a heat pump. The opening degree of the expansion valve ( 3 ) is controlled on the basis of an air temperature, T air , of air flowing across the evaporator ( 2 ), and in order to reach a reference air temperature, T air, ref . The opening degree is set to the calculated opening degree, overlaid with a perturbation signal. A temperature signal, S 2 , representing a temperature of refrigerant leaving the evaporator ( 2 ) is monitored and analysed. In the case that the analysis reveals that a dry zone of the evaporator ( 2 ) is approaching a minimum length, the opening degree of the expansion valve ( 3 ) is decreased. This provides a safety mechanism which ensures that liquid refrigerant is prevented from passing through the evaporator ( 2 ).

What is claimed is: 
     
         1 . A method for controlling a supply of refrigerant to an evaporator of a vapour compression system, the vapour compression system comprising at least one evaporator, at least one compressor, at least one condenser and at least one expansion valve arranged in a refrigerant circuit, the method comprising the steps of:
 obtaining a temperature, T air , of air flowing across the evaporator,   controlling an opening degree of the expansion valve, on the basis of the obtained temperature, T air , and in order to reach a reference air temperature, T air, ref , of the air flowing across the evaporator,   providing a perturbation signal, and setting the opening degree of the expansion valve to the controlled opening degree, overlaid with the perturbation signal,   monitoring a temperature signal, S 2 , representing a temperature of refrigerant leaving the evaporator,   analysing the temperature signal, S 2 , and   decreasing the opening degree of the expansion valve in the case that said analysis reveals that a dry zone of the evaporator is approaching a minimum length.   
     
     
         2 . The method according to  claim 1 , wherein the step of analysing the temperature signal, S 2 , comprises obtaining a rate of change of the temperature signal, S 2 , and wherein the step of decreasing the opening degree comprises decreasing the opening degree of the expansion valve in the case that an absolute value of the rate of change of the temperature signal, S 2 , reaches a maximum value. 
     
     
         3 . The method according to  claim 1 , wherein the step of analysing the temperature signal, S 2 , comprises the steps of:
 identifying a component of the temperature signal, S 2 , corresponding to the perturbation signal,   comparing the identified component of the temperature signal, S 2 , to the original perturbation signal, and   determining whether or not the dry zone of the evaporator is approaching a minimum length, based on said comparison.   
     
     
         4 . The method according to  claim 3 , wherein the step of comparing comprises determining a distortion of the identified component of the temperature signal, S 2 . 
     
     
         5 . The method according to  claim 1 , wherein the step of analysing the temperature signal, S 2 , comprises identifying one or more statistical components of the temperature signal, S 2 . 
     
     
         6 . The method according to  claim 1 , wherein the perturbation signal is a sinusoidal type signal. 
     
     
         7 . The method according to  claim 1 , wherein the perturbation signal is a relay type signal. 
     
     
         8 . The method according to  claim 1 , wherein the temperature, T air , is a temperature of air flowing towards the evaporator. 
     
     
         9 . The method according to  claim 1 , wherein the temperature, T air , is a temperature of air flowing away from the evaporator. 
     
     
         10 . The method according to  claim 1 , wherein the temperature, T air , represents a weighted value of a temperature of air flowing towards the evaporator and a temperature of air flowing away from the evaporator. 
     
     
         11 . The method according to  claim 1 , further comprising the step of performing a pull down process in the case that the temperature, T air , of air flowing across the evaporator is above a predefined upper threshold value. 
     
     
         12 . The method according to  claim 11 , wherein the step of performing a pull down process comprises the steps of:
 opening the expansion valve to a maximum opening degree,   monitoring a temperature signal, S 2 , representing a temperature of refrigerant leaving the evaporator,   analysing the temperature signal, S 2 , and   decreasing the opening degree of the expansion valve in the case that said analysis reveals that an absolute value of a rate of change of the temperature signal, S 2 , has reached a maximum value.   
     
     
         13 . A method for controlling a supply of refrigerant to an evaporator of a vapour compression system during a pull down process, the vapour compression system comprising at least one evaporator, at least one compressor, at least one condenser and at least one expansion valve arranged in a refrigerant circuit, the method comprising the steps of:
 opening the expansion valve to a maximum opening degree,   monitoring a temperature signal, S 2 , representing a temperature of refrigerant leaving the evaporator,   analysing the temperature signal, S 2 , and   decreasing the opening degree of the expansion valve in the case that said analysis reveals that an absolute value of a rate of change of the temperature signal, S 2 , reaches a maximum value.   
     
     
         14 . The method according to  claim 2 , wherein the perturbation signal is a sinusoidal type signal. 
     
     
         15 . The method according to  claim 3 , wherein the perturbation signal is a sinusoidal type signal. 
     
     
         16 . The method according to  claim 4 , wherein the perturbation signal is a sinusoidal type signal. 
     
     
         17 . The method according to  claim 5 , wherein the perturbation signal is a sinusoidal type signal. 
     
     
         18 . The method according to  claim 2 , wherein the perturbation signal is a relay type signal. 
     
     
         19 . The method according to  claim 3 , wherein the perturbation signal is a relay type signal. 
     
     
         20 . The method according to  claim 4 , wherein the perturbation signal is a relay type signal.