A refrigeration system comprising a compressor for compressing a
refrigerant, a condenser for condensing refrigerant to a liquid, an
evaporator for evaporating liquid refrigerant from the condenser to a
gas, an inner control loop for optimizing a supply of liquid refrigerant
to the evaporator, and an outer control loop for optimizing a level of
refrigerant in the evaporator, said outer control loop defining a supply
rate for said inner control loop based on an optimization including
measurement of evaporator performance, and said inner control loop
optimizing liquid refrigerant supply based on said defined supply rate.
Independent variables, such as proportion of oil in refrigerant, amount
of refrigerant, contaminants, non-condensibles, scale and other deposits
on heat transfer surfaces, may be estimated or measured. A model of the
system and/or a thermodynamic model approximating the system, for example
derived from temperature and pressure gages, as well as power
computations or measurements, is employed to determine or estimate the
effect on efficiency of deviance from an optimal state. Various methods
are provided for returning the system to an optimal state, and for
calculating a cost-effectiveness of employing such processes.