Patent ID: 7631508

Claim:
A method of non-invasively determining a charge level (m total ) of a refrigerant in a vapor-compression cycle system comprising a compressor, a condenser, an expansion device, an evaporator, a discharge line fluidically connecting the compressor to the condenser, a liquid line fluidically connecting the condenser to the expansion device, a distribution line fluidically connecting the expansion device to the evaporator, and a suction line fluidically connecting the evaporator to the compressor, the method comprising: monitoring the system while operating the system to ascertain that the system is operating at approximately steady-state; determining the superheat (T sh ) and the subcooling (T sc ) of the system at the suction line and at the liquid line, respectively; and calculating the refrigerant charge level (m total ) based on the determined subcooling (T sc ), the determined superheat (T sh ), and rated operating conditions of the system including rated refrigerant charge level (m total,rated ), rated liquid line subcooling (T sc,rated ), and rated suction line superheat (T sh,rated ) using the equation ( m total −m total,rated )/ m total,rated =(1 /k ch ){( T sc −T sc,rated )− k sh/sc ( T sh −T sh,rated )} wherein k ch is and empirical constant and k sh/sc is the slope of a straight line plot of (T sc −T sc,rated ) versus (T sh −T sh,rated ) for the rated rrefrigerant charge for the system; and then adjusting the charge level of the refrigerant in the system in response to the calculated refrigerant charge level of the system.