A method for generating early temperature warning in a vapour compression system

Abstract

A method for operating a vapour compression system ( 1 ) is disclosed. A cut-in temperature, a high temperature alarm limit and a high temperature alarm delay time are set. A maximum acceptable relative decay value is derived, based on the high temperature alarm limit and the high temperature alarm delay time. The vapour compression system ( 1 ) is operated while monitoring a temperature inside a refrigerated volume and continuously deriving a weighted mean temperature prevailing inside the refrigerated volume, during a moving time window of a predefined length. In the case that the weighted mean temperature inside the refrigerated volume exceeds the cut-in temperature, a timer is started, and a delay time is derived, based on the weighted mean temperature and the maximum acceptable relative decay value. A warning is generated when the timer reaches the derived delay time.

What is claimed is: 
     
         1 . A method for operating a vapour compression system, the vapour compression system comprising a compressor unit, a heat rejecting heat exchanger, at least one expansion device and at least one evaporator arranged in a refrigerant path, each evaporator being arranged in thermal contact with a refrigerated volume for storing goods, the method comprising the steps of, for at least one of the refrigerated volumes:
 setting control parameters related to the refrigerated volume, including setting a cut-in temperature, a high temperature alarm limit and a high temperature alarm delay time,   deriving a maximum acceptable relative decay value, based on the high temperature alarm limit and the high temperature alarm delay time,   operating the vapour compression system while monitoring a temperature inside the refrigerated volume and continuously deriving a weighted mean temperature prevailing inside the refrigerated volume, during a moving time window of a predefined length,   in the case that the weighted mean temperature inside the refrigerated volume exceeds the cut-in temperature, starting a timer and continuing to derive the weighted mean temperature prevailing inside the refrigerated volume, during a moving time window of a predefined length,   deriving a delay time, based on the weighted mean temperature and the maximum acceptable relative decay value, and   generating a warning when the timer reaches the derived delay time.   
     
     
         2 . The method according to  claim 1 , wherein the step of deriving a maximum acceptable relative decay value is performed using a mathematical model. 
     
     
         3 . The method according to  claim 1 , further comprising the step of deriving combinations of mean storage temperature and storage time resulting in a relative decay value corresponding to the derived maximum acceptable relative decay value, and wherein the step of deriving a delay time is based on the weighted mean temperature and the combinations of mean storage temperature and storage time. 
     
     
         4 . The method according to  claim 3 , wherein the step of deriving combinations of mean storage temperature and storage time resulting in a relative decay value corresponding to the derived maximum acceptable relative decay value is performed using a mathematical model. 
     
     
         5 . The method according to  claim 3 , wherein the step of deriving combinations of mean storage temperature and storage time resulting in a relative decay value corresponding to the derived maximum acceptable relative decay value comprises generating a look-up table and/or a graph. 
     
     
         6 . The method according to  claim 1 , wherein the step of deriving a delay time is performed continuously, based on the continuously derived weighted mean temperature, thereby obtaining a dynamically updated delay time. 
     
     
         7 . The method according to  claim 1 , further comprising the step of, in the case that the weighted mean temperature inside the refrigerated volume decreases below the cut-in temperature, stopping and resetting the timer. 
     
     
         8 . The method according to  claim 1 , wherein the weighted mean temperature is a mean kinetic temperature (MKT). 
     
     
         9 . The method according to  claim 1 , further comprising the step of scheduling inspection or maintenance of the vapour compression system in response to a generated warning. 
     
     
         10 . The method according to  claim 9 , further comprising the step of resetting the moving time window upon completion of the scheduled inspection or maintenance. 
     
     
         11 . The method according to  claim 1 , wherein the step of setting control parameters related to the refrigerated volume further comprises setting a cut-out temperature. 
     
     
         12 . The method according to  claim 1 , wherein the vapour compression system comprises at least two expansion devices and at least two evaporators, each expansion device controlling a refrigerant supply to one of the evaporators, wherein the method further comprises the step of performing diagnosis of the vapour compression system based on one or more warnings originating from the refrigerated volumes being arranged in thermal contact with the evaporators. 
     
     
         13 . The method according to  claim 12 , wherein the step of performing diagnosis of the vapour compression system comprises determining that a system related fault is occurring in the case that warnings originating from two or more refrigerated volumes occur within a predefined time interval.