A method for controlling a supply of refrigerant to an evaporator including calculating a reference temperature

Abstract

A method for controlling a supply of refrigerant to an evaporator ( 2 ) of a vapour compression system ( 1 ) is disclosed. During a system identification phase an opening degree ( 12 ) of the expansion valve ( 3 ) is alternatingly increased and decreased, and a maximum temperature difference, (S 4 −S 2 ) max , between temperature, S 4 , of air flowing away from the evaporator ( 2 ) and temperature, S 2 , of refrigerant leaving the evaporator ( 2 ) is determined. During normal operation, the supply of refrigerant to the evaporator ( 2 ) is controlled by calculating a reference temperature, S 2,ref , based on the monitored temperature, S 4 , and the maximum temperature difference, (S 4 −S 2 ) max , determined during the system identification phase. The supply of refrigerant to the evaporator ( 2 ) is controlled in order to obtain a temperature, S 2 , of refrigerant leaving the evaporator ( 2 ) which is substantially equal to the calculated reference temperature, S 2,ref .

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 path, the method comprising the steps of:
 initiating a system identification phase, in which an opening degree of the expansion valve is alternatingly increased and decreased,   during the system identification phase, monitoring a temperature, S 2 , of refrigerant leaving the evaporator, and a temperature, S 4 , of air flowing across the evaporator, at a position where the air is flowing away from the evaporator, and determining a maximum temperature difference, (S 4 −S 2 ) max , between the monitored temperatures,   upon completion of the system identification phase, controlling a supply of refrigerant to the evaporator by:
 monitoring the temperature, S 2 , of refrigerant leaving the evaporator, and the temperature, S 4 , of air flowing away from the evaporator, 
 calculating a reference temperature, S 2,ref , based on the monitored temperature, S 4 , of air flowing away from the evaporator and the maximum temperature difference, (S 4 −S 2 ) max , determined during the system identification phase, and 
 controlling the supply of refrigerant to the evaporator, based on the calculated reference temperature, S 2,ref , and in order to obtain a temperature, S 2 , of refrigerant leaving the evaporator which is substantially equal to the calculated reference temperature, S 2,ref . 
   
     
     
         2 . The method according to  claim 1 , wherein the step of calculating a reference temperature, S 2,ref , comprises calculating a mean temperature,  S 4   , of the temperature, S 4 , of air flowing away from the evaporator, during a predefined previous time interval. 
     
     
         3 . The method according to  claim 2 , wherein the reference temperature, S 2,ref , is calculated as:
     S   2,ref =   S   4   −( S   4   −S   2 ) max +Δ,
   
       wherein Δ is a constant safety value. 
     
     
         4 . The method according to  claim 1 , wherein the step of controlling the supply of refrigerant to the evaporator is performed using a proportional integral (PI) regulator. 
     
     
         5 . The method according to  claim 4 , further comprising the steps of, during the system identification phase, determining one or more system dynamic parameters, supplying the system dynamic parameters to the proportional integral (PI) regulator, and designing the proportional integral (PI) regulator in accordance with the system dynamic parameters. 
     
     
         6 . The method according to  claim 1 , wherein the step of controlling the supply of refrigerant to the evaporator further comprises the steps of:
 obtaining an air temperature, T air , of an air flow across the evaporator,   comparing the obtained air temperature, T air , to a reference value, T air,ref , and   controlling the supply of refrigerant to the evaporator on the basis of the comparing step, as well as on the basis of the calculated reference temperature, S 2,ref .   
     
     
         7 . The method according to  claim 2 , wherein the step of controlling the supply of refrigerant to the evaporator is performed using a proportional integral (PI) regulator. 
     
     
         8 . The method according to  claim 3  wherein the step of controlling the supply of refrigerant to the evaporator is performed using a proportional integral (PI) regulator. 
     
     
         9 . The method according to  claim 2 , wherein the step of controlling the supply of refrigerant to the evaporator further comprises the steps of:
 obtaining an air temperature, T air , of an air flow across the evaporator,   comparing the obtained air temperature, T air , to a reference value, T air,ref , and   controlling the supply of refrigerant to the evaporator on the basis of the comparing step, as well as on the basis of the calculated reference temperature, S 2,ref .   
     
     
         10 . The method according to  claim 3 , wherein the step of controlling the supply of refrigerant to the evaporator further comprises the steps of:
 obtaining an air temperature, T air , of an air flow across the evaporator,   comparing the obtained air temperature, T air , to a reference value, T air,ref , and   controlling the supply of refrigerant to the evaporator on the basis of the comparing step, as well as on the basis of the calculated reference temperature, S 2,ref .   
     
     
         11 . The method according to  claim 4 , wherein the step of controlling the supply of refrigerant to the evaporator further comprises the steps of:
 obtaining an air temperature, T air , of an air flow across the evaporator,   comparing the obtained airs, T air , to a reference value, T air,ref , and   controlling the supply of refrigerant to the evaporator on the basis of the comparing step, as well as on the basis of the calculated reference temperature, S 2,ref .   
     
     
         12 . The method according to  claim 5 , wherein the step of controlling the supply of refrigerant to the evaporator further comprises the steps of:
 obtaining an air temperature, T air , of an air flow across the evaporator,   comparing the obtained air temperature, T air , to a reference value, T air,ref , and   controlling the supply of refrigerant to the evaporator on the basis of the comparing step, as well as on the basis of the calculated reference temperature, S 2,ref .